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Thomas DN, Wills JW, Tracey H, Baldwin SJ, Burman M, Williams AN, Harte DSG, Buckley RA, Lynch AM. Ames test study designs for nitrosamine mutagenicity testing: qualitative and quantitative analysis of key assay parameters. Mutagenesis 2024; 39:78-95. [PMID: 38112628 DOI: 10.1093/mutage/gead033] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2023] [Accepted: 12/15/2023] [Indexed: 12/21/2023] Open
Abstract
The robust control of genotoxic N-nitrosamine (NA) impurities is an important safety consideration for the pharmaceutical industry, especially considering recent drug product withdrawals. NAs belong to the 'cohort of concern' list of genotoxic impurities (ICH M7) because of the mutagenic and carcinogenic potency of this chemical class. In addition, regulatory concerns exist regarding the capacity of the Ames test to predict the carcinogenic potential of NAs because of historically discordant results. The reasons postulated to explain these discordant data generally point to aspects of Ames test study design. These include vehicle solvent choice, liver S9 species, bacterial strain, compound concentration, and use of pre-incubation versus plate incorporation methods. Many of these concerns have their roots in historical data generated prior to the harmonization of Ames test guidelines. Therefore, we investigated various Ames test assay parameters and used qualitative analysis and quantitative benchmark dose modelling to identify which combinations provided the most sensitive conditions in terms of mutagenic potency. Two alkyl-nitrosamines, N-nitrosodimethylamine (NDMA) and N-nitrosodiethylamine (NDEA) were studied. NDMA and NDEA mutagenicity was readily detected in the Ames test and key assay parameters were identified that contributed to assay sensitivity rankings. The pre-incubation method (30-min incubation), appropriate vehicle (water or methanol), and hamster-induced liver S9, alongside Salmonella typhimurium strains TA100 and TA1535 and Escherichia coli strain WP2uvrA(pKM101) provide the most sensitive combination of assay parameters in terms of NDMA and NDEA mutagenic potency in the Ames test. Using these parameters and further quantitative benchmark dose modelling, we show that N-nitrosomethylethylamine (NMEA) is positive in Ames test and therefore should no longer be considered a historically discordant NA. The results presented herein define a sensitive Ames test design that can be deployed for the assessment of NAs to support robust impurity qualifications.
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Affiliation(s)
- Dean N Thomas
- GSK Research & Development, Genetic Toxicology and Photosafety, Stevenage SG1 2NY, United Kingdom
| | - John W Wills
- GSK Research & Development, Genetic Toxicology and Photosafety, Stevenage SG1 2NY, United Kingdom
| | - Helen Tracey
- GSK Research & Development, Genetic Toxicology and Photosafety, Stevenage SG1 2NY, United Kingdom
| | - Sandy J Baldwin
- GSK Research & Development, Genetic Toxicology and Photosafety, Stevenage SG1 2NY, United Kingdom
| | - Mark Burman
- GSK Research & Development, Genetic Toxicology and Photosafety, Stevenage SG1 2NY, United Kingdom
| | - Abbie N Williams
- GSK Research & Development, Genetic Toxicology and Photosafety, Stevenage SG1 2NY, United Kingdom
| | - Danielle S G Harte
- GSK Research & Development, Genetic Toxicology and Photosafety, Stevenage SG1 2NY, United Kingdom
| | - Ruby A Buckley
- GSK Research & Development, Genetic Toxicology and Photosafety, Stevenage SG1 2NY, United Kingdom
| | - Anthony M Lynch
- GSK Research & Development, Genetic Toxicology and Photosafety, Stevenage SG1 2NY, United Kingdom
- School of Medicine, Swansea University, Singleton Park, Swansea SA2 8PP, United Kingdom
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Paustenbach DJ, Brown SE, Heywood JJ, Donnell MT, Eaton DL. Risk characterization of N-nitrosodimethylamine in pharmaceuticals. Food Chem Toxicol 2024; 186:114498. [PMID: 38341171 DOI: 10.1016/j.fct.2024.114498] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2023] [Revised: 01/23/2024] [Accepted: 01/31/2024] [Indexed: 02/12/2024]
Abstract
Since 2018, N-nitrosodimethylamine (NDMA) has been a reported contaminant in numerous pharmaceutical products. To guide the pharmaceutical industry, FDA identified an acceptable intake (AI) of 96 ng/day NDMA. The approach assumed a linear extrapolation from the Carcinogenic Potency Database (CPDB) harmonic-mean TD50 identified in chronic studies in rats. Although NDMA has been thought to act as a mutagenic carcinogen in experimental animals, it has not been classified as a known human carcinogen by any regulatory agency. Humans are exposed to high daily exogenous and endogenous doses of NDMA. Due to the likelihood of a threshold dose for NDMA-related tumors in animals, we believe that there is ample scientific basis to utilize the threshold-based benchmark dose or point-of-departure (POD) approach when estimating a Permissible Daily Exposure limit (PDE) for NDMA. We estimated that 29,000 ng/kg/day was an appropriate POD for calculating a PDE. Assuming an average bodyweight of 50 kg, we expect that human exposures to NDMA at doses below 5800 ng/day in pharmaceuticals would not result in an increased risk of liver cancer, and that there is little, if any, risk for any other type of cancer, when accounting for the mode-of-action in humans.
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Affiliation(s)
- D J Paustenbach
- Paustenbach and Associates, 970 West Broadway, Suite E, Jackson, WY, USA
| | - S E Brown
- Paustenbach and Associates, 207 Canyon Blvd, Boulder, CO, USA.
| | - J J Heywood
- Paustenbach and Associates, 207 Canyon Blvd, Boulder, CO, USA
| | - M T Donnell
- Valeo Sciences LLC, 333 Corporate Drive, Suite 130, Ladera Ranch, CA, USA
| | - D L Eaton
- Professor Emeritus, Department of Environmental & Occupational Health Sciences, University of Washington, Seattle, WA, USA
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3
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Omori T, Hayashi M. The assessment and communication of genotoxicity test results: moving beyond binary. MUTATION RESEARCH. GENETIC TOXICOLOGY AND ENVIRONMENTAL MUTAGENESIS 2024; 893:503722. [PMID: 38272631 DOI: 10.1016/j.mrgentox.2023.503722] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2023] [Revised: 12/22/2023] [Accepted: 12/22/2023] [Indexed: 01/27/2024]
Abstract
Potential genotoxicity is one of the essential considerations in the safety assessment of chemicals to which humans may be exposed. Several endpoints are used to evaluate genotoxicity, but, in each case, a binary assessment (negative/positive) is demanded by regulators. The use of binary assessment has rarely been questioned, although we have pointed out some questions and difficulties with regard to the statistical methods used and the evaluation of biological significance, both of which inform the calls of negative/ positive. Here, we discuss these issues further, focusing on ambiguity and uncertainty in the binary paradigm, and we seek a new direction for genotoxicity assessment. To this end, we need to understand, acknowledge, and accept these ambiguities and study-related uncertainties and then to consider new strategies for safety assessment. We also discuss the communication of ambiguity and uncertainty in risk communication.
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Affiliation(s)
- Takashi Omori
- Department of Clinical Biostatistics, Graduate School of Medicine, Kyoto University, Japan
| | - Makoto Hayashi
- Representative, Makoto International Consulting, 4-23-3-1, Kami-imaizumi, Ebina 243-0431, Japan.
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Kobets T, Hickey C, Johnson G, Duan JD, Etter S, Smith B, Williams GM. Assessment of no-observed-effect-levels for DNA adducts formation by genotoxic carcinogens in fetal turkey livers. Toxicology 2024; 501:153714. [PMID: 38141718 DOI: 10.1016/j.tox.2023.153714] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2023] [Revised: 12/08/2023] [Accepted: 12/18/2023] [Indexed: 12/25/2023]
Abstract
For genotoxic carcinogens, covalent binding to DNA is a critical initiating event in tumorigenesis. The present research investigated dose-effect relationships of three genotoxic carcinogens representing different structural classes, 2-acetylaminofluorene (2-AAF), benzo[a]pyrene (B[a]P) and quinoline (QUI), to assess the existence of no-observed-effect-levels (NOELs) for the formation of DNA adducts. Carcinogens were administered into the air sac of fertilized turkey eggs over wide dose ranges in three daily injections on days 22 to 24 of incubation. DNA adducts were measured in the fetal turkey livers by the 32P-nucleotide postlabeling (NPL) assay. B[a]P and QUI produced DNA adducts in a dosage-related manner and exhibited NOELs at 0.65 and 0.35 mg/kg bw/day, respectively. In contrast, 2-AAF formed DNA adducts at all tested dosages down to 0.005 mg/kg bw/day. Benchmark dose (BMD) analysis identified the potencies of 2-AAF and QUI to be similar, while B[a]P was the least potent compound. Overall, findings in fetal turkey livers demonstrated that exposure levels to genotoxic compounds that do not result in DNA adducts can exist but are not evident with all carcinogens of this type. The use of mechanistic dose-effect studies for genotoxic endpoints can provide critical information for prioritization of concerns for risk assessment.
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Affiliation(s)
- Tetyana Kobets
- Department of Pathology, Microbiology and Immunology, New York Medical College, Valhalla, NY 10595, USA.
| | | | | | - Jian-Dong Duan
- Department of Pathology, Microbiology and Immunology, New York Medical College, Valhalla, NY 10595, USA
| | | | - Benjamin Smith
- Monell Chemical Senses Center, Philadelphia, PA 19104, USA
| | - Gary M Williams
- Department of Pathology, Microbiology and Immunology, New York Medical College, Valhalla, NY 10595, USA
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Bates CA, Haber LT, Moore MM, Schoeny R, Maier A. Development of a framework for risk assessment of dietary carcinogens. Food Chem Toxicol 2023; 180:114022. [PMID: 37716495 DOI: 10.1016/j.fct.2023.114022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2022] [Revised: 08/09/2023] [Accepted: 09/01/2023] [Indexed: 09/18/2023]
Abstract
Although there are a number of guidance documents and frameworks for evaluation of carcinogenicity, none of the current methods fully reflects the state of the science. Common limitations include the absence of dose-response assessment and not considering the impact of differing exposure patterns (e.g., intermittent, high peaks vs. lower, continuous exposures). To address these issues, we have developed a framework for risk assessment of dietary carcinogens. This framework includes an enhanced approach for weight of evidence (WOE) evaluation for genetic toxicology data, with a focus on evaluating studies based on the most recent testing guidance to determine whether a chemical is a mutagen. Included alongside our framework is a discussion of resources for evaluating tissue dose and the temporal pattern of internal dose, taking into account the chemical's toxicokinetics. The framework then integrates the mode of action (MOA) and associated dose metric category with the exposure data to identify the appropriate approach(es) to low-dose extrapolation and level of concern associated with the exposure scenario. This framework provides risk managers with additional flexibility in risk management and risk communication options, beyond the binary choice of linear low-dose extrapolation vs. application of uncertainty factors.
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Affiliation(s)
| | - Lynne T Haber
- Risk Science Center, University of Cincinnati College of Medicine, USA
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Menz J, Götz ME, Gündel U, Gürtler R, Herrmann K, Hessel-Pras S, Kneuer C, Kolrep F, Nitzsche D, Pabel U, Sachse B, Schmeisser S, Schumacher DM, Schwerdtle T, Tralau T, Zellmer S, Schäfer B. Genotoxicity assessment: opportunities, challenges and perspectives for quantitative evaluations of dose-response data. Arch Toxicol 2023; 97:2303-2328. [PMID: 37402810 PMCID: PMC10404208 DOI: 10.1007/s00204-023-03553-w] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2023] [Accepted: 06/21/2023] [Indexed: 07/06/2023]
Abstract
Genotoxicity data are mainly interpreted in a qualitative way, which typically results in a binary classification of chemical entities. For more than a decade, there has been a discussion about the need for a paradigm shift in this regard. Here, we review current opportunities, challenges and perspectives for a more quantitative approach to genotoxicity assessment. Currently discussed opportunities mainly include the determination of a reference point (e.g., a benchmark dose) from genetic toxicity dose-response data, followed by calculation of a margin of exposure (MOE) or derivation of a health-based guidance value (HBGV). In addition to new opportunities, major challenges emerge with the quantitative interpretation of genotoxicity data. These are mainly rooted in the limited capability of standard in vivo genotoxicity testing methods to detect different types of genetic damage in multiple target tissues and the unknown quantitative relationships between measurable genotoxic effects and the probability of experiencing an adverse health outcome. In addition, with respect to DNA-reactive mutagens, the question arises whether the widely accepted assumption of a non-threshold dose-response relationship is at all compatible with the derivation of a HBGV. Therefore, at present, any quantitative genotoxicity assessment approach remains to be evaluated case-by-case. The quantitative interpretation of in vivo genotoxicity data for prioritization purposes, e.g., in connection with the MOE approach, could be seen as a promising opportunity for routine application. However, additional research is needed to assess whether it is possible to define a genotoxicity-derived MOE that can be considered indicative of a low level of concern. To further advance quantitative genotoxicity assessment, priority should be given to the development of new experimental methods to provide a deeper mechanistic understanding and a more comprehensive basis for the analysis of dose-response relationships.
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Affiliation(s)
- Jakob Menz
- Department of Food Safety, German Federal Institute for Risk Assessment (BfR), Max-Dohrn-Str. 8-10, 10589, Berlin, Germany.
| | - Mario E Götz
- Department of Food Safety, German Federal Institute for Risk Assessment (BfR), Max-Dohrn-Str. 8-10, 10589, Berlin, Germany
| | - Ulrike Gündel
- Department of Chemical and Product Safety, German Federal Institute for Risk Assessment (BfR), Max-Dohrn-Str. 8-10, 10589, Berlin, Germany
| | - Rainer Gürtler
- Department of Food Safety, German Federal Institute for Risk Assessment (BfR), Max-Dohrn-Str. 8-10, 10589, Berlin, Germany
| | - Kristin Herrmann
- Department of Pesticides Safety, German Federal Institute for Risk Assessment (BfR), Max-Dohrn-Str. 8-10, 10589, Berlin, Germany
| | - Stefanie Hessel-Pras
- Department of Food Safety, German Federal Institute for Risk Assessment (BfR), Max-Dohrn-Str. 8-10, 10589, Berlin, Germany
| | - Carsten Kneuer
- Department of Pesticides Safety, German Federal Institute for Risk Assessment (BfR), Max-Dohrn-Str. 8-10, 10589, Berlin, Germany
| | - Franziska Kolrep
- Department of Safety in the Food Chain, German Federal Institute for Risk Assessment (BfR), Max-Dohrn-Str. 8-10, 10589, Berlin, Germany
| | - Dana Nitzsche
- Department of Chemical and Product Safety, German Federal Institute for Risk Assessment (BfR), Max-Dohrn-Str. 8-10, 10589, Berlin, Germany
| | - Ulrike Pabel
- Department of Safety in the Food Chain, German Federal Institute for Risk Assessment (BfR), Max-Dohrn-Str. 8-10, 10589, Berlin, Germany
| | - Benjamin Sachse
- Department of Food Safety, German Federal Institute for Risk Assessment (BfR), Max-Dohrn-Str. 8-10, 10589, Berlin, Germany
| | - Sebastian Schmeisser
- Department of Chemical and Product Safety, German Federal Institute for Risk Assessment (BfR), Max-Dohrn-Str. 8-10, 10589, Berlin, Germany
| | - David M Schumacher
- Department of Safety in the Food Chain, German Federal Institute for Risk Assessment (BfR), Max-Dohrn-Str. 8-10, 10589, Berlin, Germany
| | - Tanja Schwerdtle
- German Federal Institute for Risk Assessment (BfR), Max-Dohrn-Str. 8-10, 10589, Berlin, Germany
| | - Tewes Tralau
- Department of Pesticides Safety, German Federal Institute for Risk Assessment (BfR), Max-Dohrn-Str. 8-10, 10589, Berlin, Germany
| | - Sebastian Zellmer
- Department of Chemical and Product Safety, German Federal Institute for Risk Assessment (BfR), Max-Dohrn-Str. 8-10, 10589, Berlin, Germany
| | - Bernd Schäfer
- Department of Food Safety, German Federal Institute for Risk Assessment (BfR), Max-Dohrn-Str. 8-10, 10589, Berlin, Germany
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Kozal JS, Lynch HN, Klapacz J, Schoeny RS, Jean PA, Maier A. Mode of action assessment for propylene dichloride as a human carcinogen. Chem Biol Interact 2023; 382:110382. [PMID: 36754223 DOI: 10.1016/j.cbi.2023.110382] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2022] [Revised: 01/16/2023] [Accepted: 02/04/2023] [Indexed: 02/09/2023]
Abstract
As part of a systematic review of the non-cancer and cancer hazards of propylene dichloride (PDC), with a focus on potential carcinogenicity in workers following inhalation exposures, we determined that a mode of action (MOA)-centric framing of cancer effects was warranted. In our MOA analysis, we systematically reviewed the available mechanistic evidence for PDC-induced carcinogenesis, and we mapped biologically plausible MOA pathways and key events (KEs), as guided by the International Programme on Chemical Safety (IPCS)-MOA framework. For the identified pathways and KEs, biological concordance, essentiality of KEs, concordance of empirical observations among KEs, consistency, and analogy were evaluated. The results of this analysis indicate that multiple biologically plausible pathways may contribute to the cancer MOA for PDC, but that the relevant pathways vary by exposure route and level, tissue type, and species; further, more than one pathway may occur concurrently at high exposure levels. While several important data gaps exist, evidence from in vitro mechanistic studies, in vivo experimental animal studies, and ex vivo human tumor tissue analyses indicates that the predominant MOA pathway likely involves saturation of cytochrome p450 2E1 (CYP2E1)-glutathione (GSH) detoxification (molecular initiating event; MIE), accumulation of CYP2E1-oxidative metabolites, cytotoxicity, chronic tissue damage and inflammation, and ultimately tumor formation. Tumors may occur through several subsets of inflammatory KEs, including inflammation-induced aberrant expression of activation-induced cytidine deaminase (AID), which causes DNA strand breaks and mutations and can lead to tumors with a characteristic mutational signature found in occupational cholangiocarcinoma. Dose concordance analysis showed that low-dose mutagenicity (from any pathway) is not a driving MOA, and that prevention of target tissue damage and inflammation (associated with saturation of CYP2E1-GSH detoxification) is expected to also prevent the cascade of processes responsible for tumor formation.
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Affiliation(s)
| | | | - Joanna Klapacz
- Toxicology and Environmental Research and Consulting, The Dow Chemical Company, Midland, MI, 48674, USA
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Martus HJ, Zeller A, Kirkland D. International Workshops on Genotoxicity Testing (IWGT): Origins, achievements and ambitions. MUTATION RESEARCH. REVIEWS IN MUTATION RESEARCH 2023; 792:108469. [PMID: 37777464 DOI: 10.1016/j.mrrev.2023.108469] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 08/26/2023] [Indexed: 10/02/2023]
Abstract
Over the past thirty years, the International Workshops on Genotoxicity Testing (IWGT) became one of the leading groups in the field of regulatory genotoxicology, not only due to the diversity of participants with respect to geography and professional affiliation, but also due to the unique setup of recurring IWGT meetings every four years. The hallmarks of the IWGT process have been diligent initial planning approaches of the working groups, collection of data so as to stimulate data-driven discussions and debate, and striving to reach consensus recommendations. The scientific quality of the Working Groups (WGs) has been exceptional due to the selection of highly regarded experts on each topic. As a result, the IWGT working group reports have become important documents. The deliberations and publications have provided guidance on test systems and testing protocols that have influenced the development or revision of test guidelines of the Organisation for Economic Co-operation and Development (OECD), guidance by the International Council for Harmonisation (ICH), and strategic testing or data analysis approaches in general. This article summarizes the history of the IWGT, identifies some of its major achievements, and provides an outlook for the future.
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Affiliation(s)
| | - Andreas Zeller
- Pharmaceutical Sciences, pRED Innovation Center Basel, F. Hoffmann-La Roche Ltd, Grenzacherstrasse 124, CH-4070 Basel, Switzerland
| | - David Kirkland
- Kirkland Consulting, P O Box 79, Tadcaster LS24 0AS, United Kingdom
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9
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Hayashi M. “Statistical significance” and other important considerations in genotoxicity safety testing. MUTATION RESEARCH/GENETIC TOXICOLOGY AND ENVIRONMENTAL MUTAGENESIS 2023; 888:503627. [PMID: 37188432 DOI: 10.1016/j.mrgentox.2023.503627] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2023] [Revised: 03/28/2023] [Accepted: 03/29/2023] [Indexed: 04/03/2023]
Abstract
Toxicity assays, including genotoxicity assays, are important components of human safety assessments. The interpretation of the results of such assays depends on several factors, including validation of test performance, statistical analysis of the results, and, most importantly, scientific judgment concerning the relevance of the findings to human health risk under anticipated exposure conditions. Ideally, decisions should be made on the basis of studies that allow consideration of the exposure-response relationship of any observed genotoxic outcome and an estimate of the risks associated with expected human exposures. However, in practice, the available data are often limited; it may be necessary to make judgements on the basis of assays that provide only hazard information that is not related to human exposure levels; also, sometimes, decisions are based on studies with non-human (or even non-mammalian) cells that may respond differently than human systems. Too often, in such situations, decisions are based only on whether "statistical significance" has been achieved in a particular assay, rather than on an overall judgement about the weight of scientific evidence with regard to human risk. Among regulators and toxicologists, the concept of "statistical significance" has played an important role in decision-making. Toxicologists often rely on statistical evaluations based on nominal fixed thresholds (P-value = 0.05 or 0.01), but these are arbitrary values. Such "statistical significance" is merely one of many factors that should be taken into account before drawing final conclusions for risk assessment. Other factors are also very important, including adherence to test guidelines and Good Laboratory Practices (GLPs).
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Fortin AMV, Long AS, Williams A, Meier MJ, Cox J, Pinsonnault C, Yauk CL, White PA. Application of a new approach methodology (NAM)-based strategy for genotoxicity assessment of data-poor compounds. FRONTIERS IN TOXICOLOGY 2023; 5:1098432. [PMID: 36756349 PMCID: PMC9899896 DOI: 10.3389/ftox.2023.1098432] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Accepted: 01/02/2023] [Indexed: 01/24/2023] Open
Abstract
The conventional battery for genotoxicity testing is not well suited to assessing the large number of chemicals needing evaluation. Traditional in vitro tests lack throughput, provide little mechanistic information, and have poor specificity in predicting in vivo genotoxicity. New Approach Methodologies (NAMs) aim to accelerate the pace of hazard assessment and reduce reliance on in vivo tests that are time-consuming and resource-intensive. As such, high-throughput transcriptomic and flow cytometry-based assays have been developed for modernized in vitro genotoxicity assessment. This includes: the TGx-DDI transcriptomic biomarker (i.e., 64-gene expression signature to identify DNA damage-inducing (DDI) substances), the MicroFlow® assay (i.e., a flow cytometry-based micronucleus (MN) test), and the MultiFlow® assay (i.e., a multiplexed flow cytometry-based reporter assay that yields mode of action (MoA) information). The objective of this study was to investigate the utility of the TGx-DDI transcriptomic biomarker, multiplexed with the MicroFlow® and MultiFlow® assays, as an integrated NAM-based testing strategy for screening data-poor compounds prioritized by Health Canada's New Substances Assessment and Control Bureau. Human lymphoblastoid TK6 cells were exposed to 3 control and 10 data-poor substances, using a 6-point concentration range. Gene expression profiling was conducted using the targeted TempO-Seq™ assay, and the TGx-DDI classifier was applied to the dataset. Classifications were compared with those based on the MicroFlow® and MultiFlow® assays. Benchmark Concentration (BMC) modeling was used for potency ranking. The results of the integrated hazard calls indicate that five of the data-poor compounds were genotoxic in vitro, causing DNA damage via a clastogenic MoA, and one via a pan-genotoxic MoA. Two compounds were likely irrelevant positives in the MN test; two are considered possibly genotoxic causing DNA damage via an ambiguous MoA. BMC modeling revealed nearly identical potency rankings for each assay. This ranking was maintained when all endpoint BMCs were converted into a single score using the Toxicological Prioritization (ToxPi) approach. Overall, this study contributes to the establishment of a modernized approach for effective genotoxicity assessment and chemical prioritization for further regulatory scrutiny. We conclude that the integration of TGx-DDI, MicroFlow®, and MultiFlow® endpoints is an effective NAM-based strategy for genotoxicity assessment of data-poor compounds.
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Affiliation(s)
- Anne-Marie V. Fortin
- Department of Biology, University of Ottawa, Ottawa, ON, Canada,Environmental Health Science and Research Bureau, Health Canada, Ottawa, ON, Canada
| | - Alexandra S. Long
- Existing Substances Risk Assessment Bureau, Health Canada, Ottawa, ON, Canada
| | - Andrew Williams
- Environmental Health Science and Research Bureau, Health Canada, Ottawa, ON, Canada
| | - Matthew J. Meier
- Environmental Health Science and Research Bureau, Health Canada, Ottawa, ON, Canada
| | - Julie Cox
- Bureau of Gastroenterology, Infection and Viral Diseases, Health Canada, Ottawa, ON, Canada
| | - Claire Pinsonnault
- New Substances Assessment and Control Bureau, Health Canada, Ottawa, ON, Canada
| | - Carole L. Yauk
- Department of Biology, University of Ottawa, Ottawa, ON, Canada,*Correspondence: Carole L. Yauk, ; Paul A. White,
| | - Paul A. White
- Department of Biology, University of Ottawa, Ottawa, ON, Canada,Environmental Health Science and Research Bureau, Health Canada, Ottawa, ON, Canada,*Correspondence: Carole L. Yauk, ; Paul A. White,
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11
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Zhu X, Huo J, Zeng Z, Liu Y, Li R, Chen Y, Zhang L, Chen J. Determination of potential thresholds for N-ethyl-N-nitrosourea and ethyl methanesulfonate based on a multi-endpoint genotoxicity assessment platform in rats. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2022; 29:85128-85142. [PMID: 35793016 PMCID: PMC9646607 DOI: 10.1007/s11356-022-21605-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/26/2022] [Accepted: 06/17/2022] [Indexed: 06/15/2023]
Abstract
The main goal of the study was to investigate the genotoxic response of N-ethyl-N-nitrosourea (ENU) and ethyl methanesulfonate (EMS) at low doses in a multi-endpoint genotoxicity assessment platform in rats and to derive potential thresholds and related metrics. Male Sprague-Dawley rats were treated by daily oral gavage for 28 consecutive days with ENU (0.25 ~ 8 mg/kg bw) and EMS (5 ~ 160 mg/kg bw), both with six closely spaced dose levels. Pig-a gene mutation assay, micronucleus test, and comet assay were performed in several timepoints. Then, the dose-response relationships were analyzed for possible points of departure (PoD) using the no observed genotoxic effect level and benchmark dose (BMD) protocols with different critical effect sizes (CES, 0.05, 0.1, 0.5, and 1SD). Overall, dose-dependent increases in all investigated endpoints were found for ENU and EMS. PoDs varied across genetic endpoints, timepoints, and statistical methods, and selecting an appropriate lower 95% confidence limit of BMD needs a comprehensive consideration of the mode of action of chemicals, the characteristics of tests, and the model fitting methods. Under the experimental conditions, the PoDs of ENU and EMS were 0.0036 mg/kg bw and 1.7 mg/kg bw, respectively.
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Affiliation(s)
- Xuejiao Zhu
- Department of Nutrition, Food Safety and Toxicology, West China School of Public Health, Sichuan University, Chengdu, Sichuan, China
- West China School of Basic Medical Sciences and Forensic Medicine, Sichuan University, Chengdu, Sichuan, China
| | - Jiao Huo
- Department of Nutrition and Food Safety, Chongqing Center for Disease Control and Prevention, Chongqing, China
- Department of Nutrition, Food Safety and Toxicology, West China School of Public Health, Sichuan University, Chengdu, Sichuan, China
| | - Zhu Zeng
- Department of Nutrition, Food Safety and Toxicology, West China School of Public Health, Sichuan University, Chengdu, Sichuan, China
- Chengdu Fifth People's Hospital, Chengdu, Sichuan, China
| | - Yunjie Liu
- Department of Nutrition, Food Safety and Toxicology, West China School of Public Health, Sichuan University, Chengdu, Sichuan, China
- Food Safety Monitoring and Risk Assessment Key Laboratory of Sichuan Province, Chengdu, Sichuan, China
| | - Ruirui Li
- Department of Nutrition, Food Safety and Toxicology, West China School of Public Health, Sichuan University, Chengdu, Sichuan, China
- Food Safety Monitoring and Risk Assessment Key Laboratory of Sichuan Province, Chengdu, Sichuan, China
| | - Yiyi Chen
- Department of Nutrition, Food Safety and Toxicology, West China School of Public Health, Sichuan University, Chengdu, Sichuan, China
- Food Safety Monitoring and Risk Assessment Key Laboratory of Sichuan Province, Chengdu, Sichuan, China
| | - Lishi Zhang
- Department of Nutrition, Food Safety and Toxicology, West China School of Public Health, Sichuan University, Chengdu, Sichuan, China
- Food Safety Monitoring and Risk Assessment Key Laboratory of Sichuan Province, Chengdu, Sichuan, China
| | - Jinyao Chen
- Department of Nutrition, Food Safety and Toxicology, West China School of Public Health, Sichuan University, Chengdu, Sichuan, China.
- Food Safety Monitoring and Risk Assessment Key Laboratory of Sichuan Province, Chengdu, Sichuan, China.
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12
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Crosby ME, Ciurlionis R, Brayman TG, Kondratiuk A, Nicolette JJ. Exploring the molecular and functional cellular response to hydrazine via transcriptomics and DNA repair mutant cell lines. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2022; 63:336-350. [PMID: 36176055 PMCID: PMC9828720 DOI: 10.1002/em.22508] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2022] [Accepted: 09/23/2022] [Indexed: 05/04/2023]
Abstract
Hydrazine is a rodent carcinogen and is classified as a probable human carcinogen by IARC. Though hydrazine is positive in both in vitro and in vivo DNA strand break (comet) assays, hydrazine was reported to be negative in an in vitro mutation Muta Mouse lung epithelial cell (FE1) test, as well as in a regulatory-compliant, in vivo Big Blue mouse mutation test. In this article, mechanistic studies explored the cellular response to hydrazine. When tested in a regulatory-compliant mouse lymphoma assay, hydrazine yielded unusual, weakly positive results. This prompted an investigation into the transcriptional response to hydrazine in FE1 cells via RNA sequencing. Amongst the changes identified was a dose-dependent increase in G2/M DNA damage checkpoint activation associated genes. Flow cytometric experiments in FE1 cells revealed that hydrazine exposure led to S-phase cell cycle arrest. Clonogenic assays in a variety of cell lines harboring key DNA repair protein deficiencies indicated that hydrazine could sensitize cells lacking homology dependent repair proteins (Brca2 and Fancg). Lastly, hprt assays with hydrazine were conducted to determine whether a lack of DNA repair could lead to mutagenicity. However, no robust, dose-dependent induction of mutations was noted. The transcriptional and cell cycle response to hydrazine, coupled with functional investigations of DNA repair-deficient cell lines support the inconsistencies noted in the genetic toxicology regulatory battery. In summary, while hydrazine may be genotoxic, transcriptional and functional processes involved in cell cycle regulation and DNA repair appear to play a nuanced role in mediating the mutagenic potential.
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Affiliation(s)
- Meredith E. Crosby
- Pre‐Clinical Safety, AbbVie Inc.North ChicagoIllinoisUnited States
- Drug Safety and PharmacometricsRegeneron Pharmaceuticals Inc.TarrytownNew YorkUnited States
| | - Rita Ciurlionis
- Pre‐Clinical Safety, AbbVie Inc.North ChicagoIllinoisUnited States
| | | | | | - John J. Nicolette
- Pre‐Clinical Safety, AbbVie Inc.North ChicagoIllinoisUnited States
- Preclinical Sciences and Translational SafetyJanssen Research and DevelopmentRaritanNew JerseyUnited States
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13
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Hayashi M. Opinion: regulatory genotoxicity: past, present and future. Genes Environ 2022; 44:13. [PMID: 35449081 PMCID: PMC9026627 DOI: 10.1186/s41021-022-00242-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2022] [Accepted: 04/10/2022] [Indexed: 11/10/2022] Open
Abstract
I will reflect on the role of genotoxicity in the regulation of chemical safety, summarizing the past and current situation, and giving personal views for the future. This includes how genotoxicity information has been, and is being, used in the evaluation of the safety of chemical substances including pharmaceuticals, pesticides, food additives and industrial chemicals before they are introduced into the market for sale. In Japan, the Industrial Safety and Health Act, enacted in 1972, assures workers’ safety by including safety assessment of chemicals to which workers may be exposed in the workplace. The law firstly included the bacterial gene mutation assay with rat liver microsome fraction (Ames test) for the evaluation of chemical mutagenicity to predict carcinogenic potential, which was the forerunner of requiring a genotoxicity test by law. Since then, genotoxicity, especially the Ames test and the in vitro chromosomal aberration test using cultured mammalian cells (especially Chinese hamster cells) have been incorporated into several laws to assess the safety of various chemicals. Many test systems for different endpoints have been developed, improved, and used in practice. The battery strategy, combining several test systems to detect as many genotoxic chemicals as possible, was implemented because no one test system can detect all genotoxic agents with different mechanisms of genetic damage. In general, the standard battery consists of the Ames test, in vitro chromosomal aberration test and the in vivo rodent erythrocyte micronucleus test as a representative in vivo assay. Many other test systems have been used for supplementary testing as well as for research studies. Important keywords for regulatory science include 1) guidelines, 2) Good Laboratory Practice, 3) evaluation and interpretation of test results. Here, I discuss on these key points, and give personal opinions for the future.
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Affiliation(s)
- Makoto Hayashi
- makoto international consulting, 4-23-3-1, Ebina, Kanagawa, 243-0431, Japan.
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14
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Comprehensive interpretation of in vitro micronucleus test results for 292 chemicals: from hazard identification to risk assessment application. Arch Toxicol 2022; 96:2067-2085. [PMID: 35445829 PMCID: PMC9151546 DOI: 10.1007/s00204-022-03286-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2021] [Accepted: 02/23/2022] [Indexed: 11/08/2022]
Abstract
Risk assessments are increasingly reliant on information from in vitro assays. The in vitro micronucleus test (MNvit) is a genotoxicity test that detects chromosomal abnormalities, including chromosome breakage (clastogenicity) and/or whole chromosome loss (aneugenicity). In this study, MNvit datasets for 292 chemicals, generated by the US EPA’s ToxCast program, were evaluated using a decision tree-based pipeline for hazard identification. Chemicals were tested with 19 concentrations (n = 1) up to 200 µM, in the presence and absence of Aroclor 1254-induced rat liver S9. To identify clastogenic chemicals, %MN values at each concentration were compared to a distribution of batch-specific solvent controls; this was followed by cytotoxicity assessment and benchmark concentration (BMC) analyses. The approach classified 157 substances as positives, 25 as negatives, and 110 as inconclusive. Using the approach described in Bryce et al. (Environ Mol Mutagen 52:280–286, 2011), we identified 15 (5%) aneugens. IVIVE (in vitro to in vivo extrapolation) was employed to convert BMCs into administered equivalent doses (AEDs). Where possible, AEDs were compared to points of departure (PODs) for traditional genotoxicity endpoints; AEDs were generally lower than PODs based on in vivo endpoints. To facilitate interpretation of in vitro MN assay concentration–response data for risk assessment, exposure estimates were utilized to calculate bioactivity exposure ratio (BER) values. BERs for 50 clastogens and two aneugens had AEDs that approached exposure estimates (i.e., BER < 100); these chemicals might be considered priorities for additional testing. This work provides a framework for the use of high-throughput in vitro genotoxicity testing for priority setting and chemical risk assessment.
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15
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Thompson CM, Aardema MJ, Heintz MM, MacGregor JT, Young RR. A review of mammalian in vivo genotoxicity of hexavalent chromium: implications for oral carcinogenicity risk assessment. Crit Rev Toxicol 2022; 51:820-849. [DOI: 10.1080/10408444.2021.2000934] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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16
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Kumaravel TS, Sathya TN, Balaje R, Pradeepa P, Yogaraj D, Murali MR, Navaneethakrishnan KR, Murugan S, Jha AN. Genotoxicity evaluation of medical devices: A regulatory perspective. MUTATION RESEARCH. REVIEWS IN MUTATION RESEARCH 2022; 789:108407. [PMID: 35690410 DOI: 10.1016/j.mrrev.2021.108407] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2021] [Revised: 11/22/2021] [Accepted: 11/29/2021] [Indexed: 06/15/2023]
Abstract
This review critically evaluates our current regulatory understanding of genotoxicity testing and risk assessment of medical devices. Genotoxicity risk assessment of these devices begins with the evaluation of materials of construction, manufacturing additives and all residual materials for potential to induce DNA damage. This is followed by extractable and/or leachable (E&L) studies to understand the worst case and/or clinical exposures, coupled with risk assessment of extractables or leachables. The TTC (Threshold of Toxicological Concern) approach is used to define acceptable levels of genotoxic chemicals, when identified. Where appropriate, in silico predictions may be used to evaluate the genotoxic potentials of identifiable chemicals with limited toxicological data and above the levels defined by TTC. Devices that could not be supported by E&L studies are evaluated by in vitro genotoxicity studies conducted in accordance with ISO10993-3 and 33. Certain endpoints such as 'site of contact genotoxicity' that are specific for certain classes of medical devices are currently not addressed in the current standards. The review also illustrates the potential uses of recent advances to achieve the goal of robust genotoxicity assessment of medical devices which are being increasingly used for health benefits. The review also highlights the gaps for genotoxicity risk assessment of medical devices and suggests possible approaches to address them taking into consideration the recent advances in genotoxicity testing including their potential uses in biocompatibility assessment.
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Affiliation(s)
- Tirukalikundram S Kumaravel
- GLR Laboratories (Europe) Pvt. Ltd., Sharnbrook, MK44 1LZ, United Kingdom; GLR Laboratories Pvt Ltd, Chennai, 600068, India.
| | | | | | | | | | | | | | - Sivasubramanian Murugan
- GLR Laboratories (Europe) Pvt. Ltd., Sharnbrook, MK44 1LZ, United Kingdom; GLR Laboratories Pvt Ltd, Chennai, 600068, India
| | - Awadhesh N Jha
- School of Biological and Marine Sciences, University of Plymouth, Plymouth, PL4 8AA, United Kingdom
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17
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Doe JE, Boobis AR, Cohen SM, Dellarco VL, Fenner-Crisp PA, Moretto A, Pastoor TP, Schoeny RS, Seed JG, Wolf DC. The codification of hazard and its impact on the hazard versus risk controversy. Arch Toxicol 2021; 95:3611-3621. [PMID: 34559250 PMCID: PMC8492552 DOI: 10.1007/s00204-021-03145-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2021] [Accepted: 08/19/2021] [Indexed: 12/15/2022]
Abstract
The long running controversy about the relative merits of hazard-based versus risk-based approaches has been investigated. There are three levels of hazard codification: level 1 divides chemicals into dichotomous bands of hazardous and non-hazardous; level 2 divides chemicals into bands of hazard based on severity and/or potency; and level 3 places each chemical on a continuum of hazard based on severity and/or potency. Any system which imposes compartments onto a continuum will give rise to issues at the boundaries, especially with only two compartments. Level 1 schemes are only justifiable if there is no variation in severity, or potency or if there is no threshold. This is the assumption implicit in GHS/EU classification for carcinogenicity, reproductive toxicity and mutagenicity. However, this assumption has been challenged. Codification level 2 hazard assessments offer a range of choices and reduce the built-in conflict inherent in the level 1 process. Level 3 assessments allow a full range of choices between the extremes and reduce the built-in conflict even more. The underlying reason for the controversy between hazard and risk is the use of level 1 hazard codification schemes in situations where there are ranges of severity and potency which require the use of level 2 or level 3 hazard codification. There is not a major difference between level 2 and level 3 codification, and they can both be used to select appropriate risk management options. Existing level 1 codification schemes should be reviewed and developed into level 2 schemes where appropriate.
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Affiliation(s)
- John E Doe
- School of Pharmacy and Biomolecular Sciences, Liverpool John Moores University, Byrom Street, Liverpool, L3 3AF, UK.
| | - Alan R Boobis
- National Heart & Lung Institute, Hammersmith Campus, Imperial College London, London, W12 0NN, UK
| | - Samuel M Cohen
- Department of Pathology and Microbiology, Havlik-Wall Professor of Oncology, University of Nebraska Medical Center, Omaha, NE, 68198-3135, USA
| | | | | | - Angelo Moretto
- Dipartimento di Scienze Cardio-Toraco-Vascolari e Sanità Pubblica, (Department of Cardio-Thoraco-Vascular and Public Health Sciences), Università degli Studi di Padova, Padua, Italy
| | | | | | | | - Douglas C Wolf
- Syngenta Crop Protection LLC, Greensboro, NC, 27419, USA
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18
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Qu M, Xu H, Li W, Chen J, Zhang Y, Xu B, Li Z, Liu T, Guo L, Xie J. Dynamically monitoring cellular γ-H2AX reveals the potential of carcinogenicity evaluation for genotoxic compounds. Arch Toxicol 2021; 95:3559-3573. [PMID: 34510228 DOI: 10.1007/s00204-021-03156-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2021] [Accepted: 09/02/2021] [Indexed: 02/07/2023]
Abstract
Amongst all toxicological endpoints, carcinogenicity might pose the greatest concern. Genetic damage has been considered an important underlying mechanism for the carcinogenicity of chemical substances. The demand for in vitro genotoxic tests as alternative approaches is growing rapidly with the implementation of new regulations for compounds. However, currently available in vitro genotoxicity tests are often limited by relatively high false positive rates. Moreover, few studies have explored carcinogenicity potential by in vitro genotoxicity testing due to the shortage of suitable toxicological biomarkers to link gene damage with cancer risk. γ-H2AX is a recently acknowledged attractive endpoint (biomarker) for evaluating DNA damage and can simultaneously reflect the DNA damage response and repair of cells. We previously reported an ultrasensitive and reliable method, namely stable-isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS), for detecting cellular γ-H2AX and evaluating genotoxic chemicals. More importantly, our method can dynamically monitor the specific processes of genotoxic compounds affecting DNA damage and repair reflected by the amount of γ-H2AX. To clarify the possibility of using this method to assess the potential carcinogenicity of genotoxic chemicals, we applied it to a set of 69 model compounds recommended by the European Center for the Validation of Alternative Methods (ECVAM), with already-characterized genotoxic potential. Compared to conventional in vitro genotoxicity assays, including the Ames test, the γ-H2AX assay by MS has high accuracy (94-96%) due to high sensitivity and specificity (88% and 100%, respectively). The dynamic profiles of model compounds after exposure in HepG2 cells were explored, and a mathematical approach was employed to simulate and quantitatively model the DNA repair kinetics of genotoxic carcinogens (GCs) based on γ-H2AX time-effect curves up to 8 h. Two crucial parameters, i.e., k (rate of γ-H2AX decay) and t50 (time required for γ-H2AX from maximum decrease to half) estimated by the least squares method, were achieved. An open web server to help researchers calculate these two key parameters and profile simulated curves of the tested compound is available online ( http://ccb1.bmi.ac.cn:81/shiny-server/sample-apps/prediction1/ ). We detected a positive association between carcinogenic levels and k and t50 values of γ-H2AX in tested GCs, validating the potential of using this MS-based γ-H2AX in vitro assay to help preliminarily evaluate carcinogenicity and assess genotoxicity. This approach may be used alone or integrated into an existing battery of in vitro genetic toxicity tests.
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Affiliation(s)
- Minmin Qu
- State Key Laboratory of Toxicology and Medical Countermeasures, and Laboratory of Toxicant Analysis, Institute of Pharmacology and Toxicology, Academy of Military Medical Sciences, 27 Taiping Road, Haidian District, Beijing, 100850, China
| | - Hua Xu
- State Key Laboratory of Toxicology and Medical Countermeasures, and Laboratory of Toxicant Analysis, Institute of Pharmacology and Toxicology, Academy of Military Medical Sciences, 27 Taiping Road, Haidian District, Beijing, 100850, China.
| | - Wuju Li
- Beijing Institute of Basic Medical Sciences, 27 Taiping Road, Haidian District, Beijing, 100850, China
| | - Jia Chen
- State Key Laboratory of Toxicology and Medical Countermeasures, and Laboratory of Toxicant Analysis, Institute of Pharmacology and Toxicology, Academy of Military Medical Sciences, 27 Taiping Road, Haidian District, Beijing, 100850, China
| | - Yajiao Zhang
- State Key Laboratory of Toxicology and Medical Countermeasures, and Laboratory of Toxicant Analysis, Institute of Pharmacology and Toxicology, Academy of Military Medical Sciences, 27 Taiping Road, Haidian District, Beijing, 100850, China
| | - Bin Xu
- State Key Laboratory of Toxicology and Medical Countermeasures, and Laboratory of Toxicant Analysis, Institute of Pharmacology and Toxicology, Academy of Military Medical Sciences, 27 Taiping Road, Haidian District, Beijing, 100850, China
| | - Zhi Li
- State Key Laboratory of Toxicology and Medical Countermeasures, and Laboratory of Toxicant Analysis, Institute of Pharmacology and Toxicology, Academy of Military Medical Sciences, 27 Taiping Road, Haidian District, Beijing, 100850, China
| | - Tao Liu
- Beijing Institute of Basic Medical Sciences, 27 Taiping Road, Haidian District, Beijing, 100850, China
| | - Lei Guo
- State Key Laboratory of Toxicology and Medical Countermeasures, and Laboratory of Toxicant Analysis, Institute of Pharmacology and Toxicology, Academy of Military Medical Sciences, 27 Taiping Road, Haidian District, Beijing, 100850, China
| | - Jianwei Xie
- State Key Laboratory of Toxicology and Medical Countermeasures, and Laboratory of Toxicant Analysis, Institute of Pharmacology and Toxicology, Academy of Military Medical Sciences, 27 Taiping Road, Haidian District, Beijing, 100850, China.
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19
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Wills JW, Halkes-Wellstead E, Summers HD, Rees P, Johnson GE. Empirical Comparison of Genotoxic Potency Estimations: The In Vitro DNA-Damage ToxTracker Endpoints versus the In Vivo Micronucleus Assay. Mutagenesis 2021; 36:311-320. [PMID: 34111295 PMCID: PMC8391785 DOI: 10.1093/mutage/geab020] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2020] [Accepted: 06/09/2021] [Indexed: 11/30/2022] Open
Abstract
Genetic toxicology is an essential component of compound safety assessment. In the face of a barrage of new compounds, higher throughput, less ethically divisive in vitro approaches capable of effective, human-relevant hazard identification and prioritisation are increasingly important. One such approach is the ToxTracker assay, which utilises murine stem cell lines equipped with green fluorescent protein (GFP)-reporter gene constructs that each inform on distinct aspects of cellular perturbation. Encouragingly, ToxTracker has shown improved sensitivity and specificity for the detection of known in vivo genotoxicants when compared to existing ‘standard battery’ in vitro tests. At the current time however, quantitative genotoxic potency correlations between ToxTracker and well-recognised in vivo tests are not yet available. Here we use dose–response data from the three DNA-damage-focused ToxTracker endpoints and from the in vivo micronucleus assay to carry out quantitative, genotoxic potency estimations for a range of aromatic amine and alkylating agents using the benchmark dose (BMD) approach. This strategy, using both the exponential and the Hill BMD model families, was found to produce robust, visually intuitive and similarly ordered genotoxic potency rankings for 17 compounds across the BSCL2-GFP, RTKN-GFP and BTG2-GFP ToxTracker endpoints. Eleven compounds were similarly assessed using data from the in vivo micronucleus assay. Cross-systems genotoxic potency correlations for the eight matched compounds demonstrated in vitro–in vivo correlation, albeit with marked scatter across compounds. No evidence for distinct differences in the sensitivity of the three ToxTracker endpoints was found. The presented analyses show that quantitative potency determinations from in vitro data enable more than just qualitative screening and hazard identification in genetic toxicology.
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Affiliation(s)
- John W Wills
- Biominerals Research, Cambridge University Department of Veterinary Medicine, Cambridge, UK.,Centre for Nanohealth, Swansea University College of Engineering, Swansea, UK
| | | | - Huw D Summers
- Centre for Nanohealth, Swansea University College of Engineering, Swansea, UK
| | - Paul Rees
- Centre for Nanohealth, Swansea University College of Engineering, Swansea, UK.,Broad Institute of MIT & Harvard, Cambridge, MA, USA
| | - George E Johnson
- Institute of Life Science, Swansea University Medical School, Swansea, UK
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20
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Proctor DM, Bhat V, Suh M, Reichert H, Jiang X, Thompson CM. Inhalation cancer risk assessment for environmental exposure to hexavalent chromium: Comparison of margin-of-exposure and linear extrapolation approaches. Regul Toxicol Pharmacol 2021; 124:104969. [PMID: 34089813 DOI: 10.1016/j.yrtph.2021.104969] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2020] [Revised: 05/24/2021] [Accepted: 05/26/2021] [Indexed: 10/21/2022]
Abstract
Hexavalent chromium [Cr(VI)] exists in the ambient air at low concentrations (average upperbound ~0.1 ng/m3) yet airborne concentrations typically exceed EPA's Regional Screening Level for residential exposure (0.012 ng/m3) and other similar benchmarks, which assume a mutagenic mode of action (MOA) and use low-dose linear risk assessment models. We reviewed Cr(VI) inhalation unit risk estimates developed by researchers and regulatory agencies for environmental and occupational exposures and the underlying epidemiologic data, updated a previously published MOA analysis, and conducted dose-response modeling of rodent carcinogenicity data to evaluate the need for alternative exposure-response data and risk assessment approaches. Current research supports the role of non-mutagenic key events in the MOA, with growing evidence for epigenetic modifiers. Animal data show a weak carcinogenic response, even at cytotoxic exposures, and highlight the uncertainties associated with the current epidemiological data used in risk assessment. Points of departure from occupational and animal studies were used to determine margins of exposure (MOEs). MOEs range from 1.5 E+3 to 3.3 E+6 with a median of 5 E+5, indicating that current environmental exposures to Cr(VI) in ambient air should be considered of low concern. In this comprehensive review, the divergent results from default linear and MOE assessments support the need for more relevant and robust epidemiologic data, additional mechanistic studies, and refined risk assessment strategies.
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Affiliation(s)
- Deborah M Proctor
- ToxStrategies, Inc, 27001 La Paz Rd, Suite 260, Mission Viejo, CA, 92691, USA.
| | | | - Mina Suh
- ToxStrategies, Inc, 27001 La Paz Rd, Suite 260, Mission Viejo, CA, 92691, USA
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21
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Johnson GE, Dobo K, Gollapudi B, Harvey J, Kenny J, Kenyon M, Lynch A, Minocherhomji S, Nicolette J, Thybaud V, Wheeldon R, Zeller A. Permitted daily exposure limits for noteworthy N-nitrosamines. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2021; 62:293-305. [PMID: 34089278 DOI: 10.1002/em.22446] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2021] [Revised: 05/07/2021] [Accepted: 05/11/2021] [Indexed: 06/12/2023]
Abstract
A genotoxic carcinogen, N-nitrosodimethylamine (NDMA), was detected as a synthesis impurity in some valsartan drugs in 2018, and other N-nitrosamines, such as N-nitrosodiethylamine (NDEA), were later detected in other sartan products. N-nitrosamines are pro-mutagens that can react with DNA following metabolism to produce DNA adducts, such as O6 -alkyl-guanine. The adducts can result in DNA replication miscoding errors leading to GC>AT mutations and increased risk of genomic instability and carcinogenesis. Both NDMA and NDEA are known rodent carcinogens in male and female rats. The DNA repair enzyme, methylguanine DNA-methyltransferase can restore DNA integrity via the removal of alkyl groups from guanine in an error-free fashion and this can result in nonlinear dose responses and a point of departure or "practical threshold" for mutation at low doses of exposure. Following International recommendations (ICHM7; ICHQ3C and ICHQ3D), we calculated permissible daily exposures (PDE) for NDMA and NDEA using published rodent cancer bioassay and in vivo mutagenicity data to determine benchmark dose values and define points of departure and adjusted with appropriate uncertainty factors (UFs). PDEs for NDMA were 6.2 and 0.6 μg/person/day for cancer and mutation, respectively, and for NDEA, 2.2 and 0.04 μg/person/day. Both PDEs are higher than the acceptable daily intake values (96 ng for NDMA and 26.5 ng for NDEA) calculated by regulatory authorities using simple linear extrapolation from carcinogenicity data. These PDE calculations using a bench-mark approach provide a more robust assessment of exposure limits compared with simple linear extrapolations and can better inform risk to patients exposed to the contaminated sartans.
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Affiliation(s)
- George E Johnson
- Swansea University Medical School, Swansea University, Swansea, Wales, UK
| | - Krista Dobo
- Genetic Toxicology, Drug Safety Research and Development, Pfizer, Groton, Connecticut, USA
| | - Bhaskar Gollapudi
- Center for Toxicology and Mechanistic Biology, Exponent Consulting, Midland, Michigan, USA
| | | | | | - Michelle Kenyon
- Genetic Toxicology, Drug Safety Research and Development, Pfizer, Groton, Connecticut, USA
| | | | | | - John Nicolette
- Genetic, Environmental and Occupational Toxicology, AbbVie, Chicago, Illinois, USA
| | | | - Ryan Wheeldon
- Swansea University Medical School, Swansea University, Swansea, Wales, UK
| | - Andreas Zeller
- Pharmaceutical Sciences, pRED Innovation Center Basel, Hoffmann-La Roche Ltd, Basel, Switzerland
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22
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Thompson CM, Gentry R, Fitch S, Lu K, Clewell HJ. An updated mode of action and human relevance framework evaluation for Formaldehyde-Related nasal tumors. Crit Rev Toxicol 2021; 50:919-952. [PMID: 33599198 DOI: 10.1080/10408444.2020.1854679] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Formaldehyde is a reactive aldehyde naturally present in all plant and animal tissues and a critical component of the one-carbon metabolism pathway. It is also a high production volume chemical used in the manufacture of numerous products. Formaldehyde is also one of the most well-studied chemicals with respect to environmental fate, biology, and toxicology-including carcinogenic potential, and mode of action (MOA). In 2006, a published MOA for formaldehyde-induced nasal tumors in rats concluded that nasal tumors were most likely driven by cytotoxicity and regenerative cell proliferation, with possible contributions from direct genotoxicity. In the past 15 years, new research has better informed the MOA with the publication of in vivo genotoxicity assays, toxicogenomic analyses, and development of ultra-sensitive methods to measure endogenous and exogenous formaldehyde-induced DNA adducts. Herein, we review and update the MOA for nasal tumors, with particular emphasis on the numerous studies published since 2006. These new studies further underscore the involvement of cytotoxicity and regenerative cell proliferation, and further inform the genotoxic potential of inhaled formaldehyde. The data lend additional support for the use of mechanistic data for the derivation of toxicity criteria and/or scientifically supported approaches for low-dose extrapolation for the risk assessment of formaldehyde.
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Affiliation(s)
| | | | | | - Kun Lu
- Department of Environmental Sciences and Engineering, University of North Carolina at Chapel Hill, NC, USA
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23
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Bercu JP, Masuda-Herrera M, Johnson G, Czich A, Glowienke S, Kenyon M, Thomas R, Ponting DJ, White A, Cross K, Waechter F, Rodrigues MAC. Use of less-than-lifetime (LTL) durational limits for nitrosamines: Case study of N-Nitrosodiethylamine (NDEA). Regul Toxicol Pharmacol 2021; 123:104926. [PMID: 33862169 DOI: 10.1016/j.yrtph.2021.104926] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2020] [Revised: 04/02/2021] [Accepted: 04/06/2021] [Indexed: 11/30/2022]
Abstract
The ICH M7(R1) guideline describes a framework to assess the carcinogenic risk of mutagenic and carcinogenic pharmaceutical impurities following less-than-lifetime (LTL) exposures. This LTL framework is important as many pharmaceuticals are not administered for a patient's lifetime and as clinical trials typically involve LTL exposures. While there has been regulatory caution about applying LTL concepts to cohort of concern (COC) impurities such as N-nitrosamines, ICH M7 does not preclude this and indeed literature data suggests that the LTL framework will be protective of patient safety for N-nitrosamines. The goal was to investigate if applying the LTL framework in ICH M7 would control exposure to an acceptable excess cancer risk in humans. Using N-nitrosodiethylamine as a case study, empirical data correlating exposure duration (as a percentage of lifespan) and cancer incidence in rodent bioassays indicate that the LTL acceptable intake (AI) as derived using the ICH M7 framework would not exceed a negligible additional risk of cancer. Therefore, controlling N-nitrosamines to an LTL AI based on the ICH M7 framework is thus demonstrated to be protective for potential carcinogenic risk to patients over the exposure durations typical of clinical trials and many prescribed medicines.
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Affiliation(s)
- Joel P Bercu
- Gilead Sciences, Nonclinical Safety and Pathobiology (NSP), Foster City, CA, USA.
| | | | - George Johnson
- Institute of Life Science, Swansea University Medical School, Singleton Park, Swansea, SA3 5DE, UK
| | - Andreas Czich
- Sanofi, R&D Preclinical Safety, D-65926, Frankfurt, Germany
| | | | - Michelle Kenyon
- Pfizer Worldwide Research and Development, Genetic Toxicology, Eastern Point Road, Groton, CT, USA
| | - Rob Thomas
- Lhasa Limited, Granary Wharf House, 2 Canal Wharf, Leeds, LS11 5PS, UK
| | - David J Ponting
- Lhasa Limited, Granary Wharf House, 2 Canal Wharf, Leeds, LS11 5PS, UK
| | - Angela White
- GlaxoSmithKline R&D, Park Road, Ware, Hertfordshire, SG12 0DP, UK
| | - Kevin Cross
- Leadscope Inc. an Instem Company, Columbus, OH, 43215, USA
| | - Fernanda Waechter
- Aché Laboratórios Farmacêuticos S.A., Rodovia Presidente Dutra, km 222,2, Porto da Igreja, 07034-904, Guarulhos, SP, Brazil
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Elder DP, Johnson GE, Snodin DJ. Tolerability of risk: A commentary on the nitrosamine contamination issue. J Pharm Sci 2021; 110:2311-2328. [PMID: 33705731 DOI: 10.1016/j.xphs.2021.02.028] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2020] [Revised: 02/23/2021] [Accepted: 02/23/2021] [Indexed: 11/16/2022]
Abstract
For decades, regulators have grappled with different approaches to address the issue of control of impurities. Safety-based limits, such as permissible daily exposure (PDE), acceptable intake (AI), threshold of toxicological concern (TTC) and less than lifetime limits (LTL) have all been used. For many years these safety-based limits have been recognized as virtually safe doses (VSDs). Recently, however, many regulatory agencies are seeking to impose limits for N-nitrosamine impurities, which are significantly below the VSD. This commentary will discuss the evolution of safety-based limits for impurities, provide an overview of the valsartan N-nitrosamine contamination issue and review the toxicology of N-nitrosamines. The outcome of a lessons-learned exercise on sartan medications undertaken by the European Medicines Agency (EMA) will also be discussed. The review will also highlight the many analytical challenges inherent with controlling impurities to ppb-based limits. The use of highly sensitive, low ppb limits, methods may lead to future issues of batch rejection, based on false positives. Regulators initially viewed the N-nitrosamine risk as being insufficient to prompt immediate product discontinuation and patients were specifically advised to continue using their affected medication. Patients were also informed that exposure to N-nitrosamines is extremely common via food and drinking water.
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25
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Bhat VS, Cohen SM, Gordon EB, Wood CE, Cullen JM, Harris MA, Proctor DM, Thompson CM. An adverse outcome pathway for small intestinal tumors in mice involving chronic cytotoxicity and regenerative hyperplasia: a case study with hexavalent chromium, captan, and folpet. Crit Rev Toxicol 2020; 50:685-706. [PMID: 33146058 DOI: 10.1080/10408444.2020.1823934] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Small intestinal (SI) tumors are relatively uncommon outcomes in rodent cancer bioassays, and limited information regarding chemical-induced SI tumorigenesis has been reported in the published literature. Herein, we propose a cytotoxicity-mediated adverse outcome pathway (AOP) for SI tumors by leveraging extensive target species- and site-specific molecular, cellular, and histological mode of action (MOA) research for three reference chemicals, the fungicides captan and folpet and the transition metal hexavalent chromium (Cr(VI)). The gut barrier functions through highly efficient homeostatic regulation of SI epithelial cell sloughing, regenerative proliferation, and repair, which involves the replacement of up to 1011 cells per day. This dynamic turnover in the SI provides a unique local environment for a cytotoxicity mediated AOP/MOA. Upon entering the duodenum, cytotoxicity to the villous epithelium is the molecular initiating event, as indicated by crypt elongation, villous atrophy/blunting, and other morphologic changes. Over time, the regenerative capacity of the gut epithelium to compensate declines as epithelial loss accelerates, especially at higher exposures. The first key event (KE), sustained regenerative crypt proliferation/hyperplasia, requires sufficient durations, likely exceeding 6 or 12 months, due to extensive repair capacity, to create more opportunities for the second KE, spontaneous mutation/transformation, ultimately leading to proximal SI tumors. Per OECD guidance, biological plausibility, essentiality, and empirical support were assessed using modified Bradford Hill considerations. The weight-of-evidence also included a lack of induced mutations in the duodenum after up to 90 days of Cr(VI) or captan exposure. The extensive evidence for this AOP, along with the knowledge that human exposures are orders of magnitude below those associated with KEs in this AOP, supports its use for regulatory applications, including hazard identification and risk assessment.
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Affiliation(s)
| | - Samuel M Cohen
- Havlik-Wall Professor of Oncology, Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, NE, USA
| | | | - Charles E Wood
- Boehringer Ingelheim Pharmaceuticals, Inc., Ridgefield, CT, USA
| | - John M Cullen
- North Carolina State University, Raleigh, NC, USA.,EPL, Inc., Sterling, VA, USA
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26
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Gollapudi BB, Su S, Li AA, Johnson GE, Reiss R, Albertini RJ. Genotoxicity as a toxicologically relevant endpoint to inform risk assessment: A case study with ethylene oxide. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2020; 61:852-871. [PMID: 32926486 PMCID: PMC7756744 DOI: 10.1002/em.22408] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Revised: 09/03/2020] [Accepted: 09/04/2020] [Indexed: 05/05/2023]
Abstract
The purpose of the present investigation is to analyze the in vivo genotoxicity dose-response data of ethylene oxide (EO) and the applicability of the derived point-of-departure (PoD) values when estimating permitted daily exposure (PDE) values. A total of 40 data sets were identified from the literature, and benchmark dose analyses were conducted using PROAST software to identify a PoD value. Studies employing the inhalation route of exposure and assessing gene or chromosomal mutations and chromosomal damage in various tissues were considered the most relevant for assessing risk from EO, since these effects are likely to contribute to adverse health consequences in exposed individuals. The PoD estimates were screened for precision and the values were divided by data-derived adjustment factors. For gene mutations, the lowest PDE was 285 parts per trillion (ppt) based on the induction of lacI mutations in the testes of mice following 48 weeks of exposure to EO. The corresponding lowest PDE value for chromosomal mutations was 1,175 ppt for heritable translocations in mice following 8.5 weeks of EO exposure. The lowest PDE for chromosomal aberrations was 238 ppt in the mouse peripheral blood lymphocytes following 48 weeks of inhalation exposure. The diverse dose-response data for EO-induced genotoxicity enabled the derivation of PoDs for various endpoints, tissues, and species and identified 238 ppt as the lowest PDE in this retrospective analysis.
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Affiliation(s)
| | - Steave Su
- Exponent, Inc., Center for Health SciencesNew YorkNew YorkUSA
| | - Abby A. Li
- Exponent, Inc., Center for Health SciencesOaklandCaliforniaUSA
| | | | - Richard Reiss
- Exponent, Inc., Center for Health SciencesAlexandriaVirginiaUSA
| | - Richard J. Albertini
- Department of PathologyUniversity of Vermont College of MedicineBurlingtonVermontUSA
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27
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Boreiko CJ, Rossman TG. Antimony and its compounds: Health impacts related to pulmonary toxicity, cancer, and genotoxicity. Toxicol Appl Pharmacol 2020; 403:115156. [PMID: 32710957 DOI: 10.1016/j.taap.2020.115156] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Revised: 07/04/2020] [Accepted: 07/20/2020] [Indexed: 12/31/2022]
Abstract
Although occupational exposure to antimony and its compounds can produce pulmonary toxicity, human carcinogenic impacts have not been observed. Inhalation studies with respirable antimony trioxide particles administered to rats and mice have, however, induced carcinogenic responses in the lungs and related tissue sites. Genotoxicity studies conducted to elucidate mechanism(s) for tumor induction have produced mixed results. Antimony compounds do not induce gene mutations in bacteria or cultured mammalian cells, but chromosome aberrations and micronuclei have been observed, usually at highly cytotoxic concentrations. Indirect mechanisms of genotoxicity have been proposed to mediate these responses. In vivo genotoxicity tests have generally yielded negative results although several positive studies of marginal quality have been reported. Genotoxic effects may be related to indirect modes of action such as the generation of excessive reactive oxygen species (ROS), altered gene expression or interference with DNA repair processes. Such indirect mechanisms may exhibit dose-response thresholds. For example, interaction of ROS with in vivo antioxidant systems could yield a threshold for genotoxicity (and cancer) only at concentrations above the capacity of antioxidant defense mechanisms to control and/or eliminate damage from ROS.
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Affiliation(s)
| | - Toby G Rossman
- Environmental Medicine, NYU Grossman School of Medicine, New York, USA
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Nicolaidou V, Koufaris C. Application of transcriptomic and microRNA profiling in the evaluation of potential liver carcinogens. Toxicol Ind Health 2020; 36:386-397. [PMID: 32419640 DOI: 10.1177/0748233720922710] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Hepatocarcinogens are agents that increase the incidence of liver cancer in exposed animals or humans. It is now established that carcinogenic exposures have a widespread impact on the transcriptome, inducing both adaptive and adverse changes in the activities of genes and pathways. Chemical hepatocarcinogens have also been shown to affect expression of microRNA (miRNA), the evolutionarily conserved noncoding RNA that regulates gene expression posttranscriptionally. Considerable effort has been invested into examining the involvement of mRNA in chemical hepatocarcinogenesis and their potential usage for the classification and prediction of new chemical entities. For miRNA, there has been an increasing number of studies reported over the past decade, although not to the same degree as for transcriptomic studies. Current data suggest that it is unlikely that any gene or miRNA signature associated with short-term carcinogen exposure can replace the rodent bioassay. In this review, we discuss the application of transcriptomic and miRNA profiles to increase mechanistic understanding of chemical carcinogens and to aid in their classification.
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Affiliation(s)
- Vicky Nicolaidou
- Department of Life and Health Sciences, University of Nicosia, Nicosia, Cyprus
| | - Costas Koufaris
- Department of Biological Sciences, University of Cyprus, Nicosia, Cyprus
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29
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Gi M, Fujioka M, Totsuka Y, Matsumoto M, Masumura K, Kakehashi A, Yamaguchi T, Fukushima S, Wanibuchi H. Quantitative analysis of mutagenicity and carcinogenicity of 2-amino-3-methylimidazo[4,5-f]quinoline in F344 gpt delta transgenic rats. Mutagenesis 2020; 34:279-287. [PMID: 31233596 DOI: 10.1093/mutage/gez015] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2018] [Accepted: 06/09/2019] [Indexed: 11/13/2022] Open
Abstract
Quantitative analysis of the mutagenicity and carcinogenicity of the low doses of genotoxic carcinogens present in food is of pressing concern. The purpose of the present study was to determine the mutagenicity and carcinogenicity of low doses of the dietary genotoxic carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ). Male F344 gpt delta transgenic rats were fed diets supplemented with 0, 0.1, 1, 10 or 100 ppm IQ for 4 weeks. The frequencies of gpt transgene mutations in the liver were significantly increased in the 10 and 100 ppm groups. In addition, the mutation spectra was altered in the 1, 10 and 100 ppm groups: frequencies of G:C to T:A transversion were significantly increased in groups administered 1, 10 and 100 ppm IQ in a dose-dependent manner, and the frequencies of G:C to A:T transitions, A:T to T:A transversions and A:T to C:G transversions were significantly increased in the 100 ppm group. Increased frequencies of single base pair deletions and Spi- mutants in the liver, and an increase in glutathione S-transferase placental form (GST-P)-positive foci, a preneoplastic lesion of the liver in rats, was also observed in the 100 ppm group. In contrast, neither mutations nor mutation spectra or GST-P-positive foci were statistically altered by administration of IQ at 0.1 ppm. We estimated the point of departure for the mutagenicity and carcinogenicity of IQ using the no-observed-effect level approach and the Benchmark dose approach to characterise the dose-response relationship of low doses of IQ. Our findings demonstrate the existence of no effect levels of IQ for both in vivo mutagenicity and hepatocarcinogenicity. The findings of the present study will facilitate an understanding of the carcinogenic effects of low doses of IQ and help to determine a margin of exposure that may be useful for practical human risk assessment.
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Affiliation(s)
- Min Gi
- Department of Molecular Pathology, Osaka City University Graduate School of Medicine, Abeno-ku, Osaka, Japan
| | - Masaki Fujioka
- Department of Molecular Pathology, Osaka City University Graduate School of Medicine, Abeno-ku, Osaka, Japan
| | - Yukari Totsuka
- Division of Carcinogenesis and Cancer Prevention, National Cancer Center Research Institute, Chuo-ku, Tokyo, Japan
| | - Michiharu Matsumoto
- Japan Bioassay Research Center, Japan Organization of Occupational Health and Safety, Hadano, Kanagawa, Japan
| | - Kenichi Masumura
- Division of Genetics and Mutagenesis, National Institute of Health Sciences, Kawasaki-ku, Kawasaki, Kanagawa, Japan
| | - Anna Kakehashi
- Department of Molecular Pathology, Osaka City University Graduate School of Medicine, Abeno-ku, Osaka, Japan
| | - Takashi Yamaguchi
- Department of Molecular Pathology, Osaka City University Graduate School of Medicine, Abeno-ku, Osaka, Japan
| | - Shoji Fukushima
- Japan Bioassay Research Center, Japan Organization of Occupational Health and Safety, Hadano, Kanagawa, Japan.,Association for Promotion of Research on Risk Assessment, Nakagawa-ku, Nagoya, Japan
| | - Hideki Wanibuchi
- Department of Molecular Pathology, Osaka City University Graduate School of Medicine, Abeno-ku, Osaka, Japan
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30
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Wheeldon RP, Bernacki DT, Dertinger SD, Bryce SM, Bemis JC, Johnson GE. Benchmark Dose Analysis of DNA Damage Biomarker Responses Provides Compound Potency and Adverse Outcome Pathway Information for the Topoisomerase II Inhibitor Class of Compounds. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2020; 61:396-407. [PMID: 31983063 DOI: 10.1002/em.22360] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2019] [Revised: 01/11/2020] [Accepted: 01/21/2020] [Indexed: 06/10/2023]
Abstract
Genetic toxicology data have traditionally been utilized for hazard identification to provide a binary call for a compound's risk. Recent advances in the scientific field, especially with the development of high-throughput methods to quantify DNA damage, have influenced a change of approach in genotoxicity assessment. The in vitro MultiFlow® DNA Damage Assay is one such method which multiplexes γH2AX, p53, phospho-histone H3 biomarkers into a single-flow cytometric analysis (Bryce et al., [2016]: Environ Mol Mutagen 57:546-558). This assay was used to study human TK6 cells exposed to each of eight topoisomerase II poisons for 4 and 24 hr. Using PROAST v65.5, the Benchmark Dose approach was applied to the resulting flow cytometric datasets. With "compound" serving as covariate, all eight compounds were combined into a single analysis, per time point and endpoint. The resulting 90% confidence intervals, plotted in Log scale, were considered as the potency rank for the eight compounds. The in vitro MultiFlow data showed a maximum confidence interval span of 1Log, which indicates data of good quality. Patterns observed in the compound potency rank were scrutinized by using the expert rule-based software program Derek Nexus, developed by Lhasa Limited. Compound sub-classification and structural alerts were considered contributory to the potencies observed for the topoisomerase II poisons studied herein. The Topo II poison Adverse Outcome Pathway was evaluated with MultiFlow endpoints serving as Key Events. The step-wise approach described herein can be considered as a foundation for risk assessment of compounds within a specific mode of action of interest. Environ. Mol. Mutagen. 2020. © 2020 Wiley Periodicals, Inc.
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Affiliation(s)
- Ryan P Wheeldon
- Institute of Life Science, Swansea University Medical School, Swansea University, Wales, United Kingdom
| | | | | | | | | | - George E Johnson
- Institute of Life Science, Swansea University Medical School, Swansea University, Wales, United Kingdom
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31
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Schrenk D, Gao L, Lin G, Mahony C, Mulder PP, Peijnenburg A, Pfuhler S, Rietjens IM, Rutz L, Steinhoff B, These A. Pyrrolizidine alkaloids in food and phytomedicine: Occurrence, exposure, toxicity, mechanisms, and risk assessment - A review. Food Chem Toxicol 2020; 136:111107. [DOI: 10.1016/j.fct.2019.111107] [Citation(s) in RCA: 39] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2019] [Revised: 12/26/2019] [Accepted: 12/29/2019] [Indexed: 02/03/2023]
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32
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White PA, Long AS, Johnson GE. Quantitative Interpretation of Genetic Toxicity Dose-Response Data for Risk Assessment and Regulatory Decision-Making: Current Status and Emerging Priorities. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2020; 61:66-83. [PMID: 31794061 DOI: 10.1002/em.22351] [Citation(s) in RCA: 44] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2019] [Revised: 11/27/2019] [Accepted: 11/30/2019] [Indexed: 06/10/2023]
Abstract
The screen-and-bin approach for interpretation of genotoxicity data is predicated on three false assumptions: that genotoxicants are rare, that genotoxicity dose-response functions do not contain a low-dose region mechanistically characterized by zero-order kinetics, and that genotoxicity is not a bona fide toxicological endpoint. Consequently, there is a need to develop and implement quantitative methods to interpret genotoxicity dose-response data for risk assessment and regulatory decision-making. Standardized methods to analyze dose-response data, and determine point-of-departure (PoD) metrics, have been established; the most robust PoD is the benchmark dose (BMD). However, there are no standards for regulatory interpretation of mutagenicity BMDs. Although 5-10% is often used as a critical effect size (CES) for BMD determination, values for genotoxicity endpoints have not been established. The use of BMDs to determine health-based guidance values (HBGVs) requires assessment factors (AFs) to account for interspecies differences and variability in human sensitivity. Default AFs used for other endpoints may not be appropriate for interpretation of in vivo mutagenicity BMDs. Analyses of published dose-response data showing the effects of compensatory pathway deficiency indicate that AFs for sensitivity differences should be in the range of 2-20. Additional analyses indicate that the AF to compensate for short treatment durations should be in the range of 5-15. Future work should use available data to empirically determine endpoint-specific CES values; similarly, to determine AF values for BMD adjustment. Future work should also evaluate the ability to use in vitro dose-response data for risk assessment, and the utility of probabilistic methods for determination of mutagenicity HBGVs. Environ. Mol. Mutagen. 61:66-83, 2020. © 2019 Her Majesty the Queen in Right of Canada.
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Affiliation(s)
- Paul A White
- Environmental Health Science and Research Bureau, Health Canada, Ottawa, Ontario, Canada
| | - Alexandra S Long
- Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario, Canada
| | - George E Johnson
- Swansea University Medical School, Swansea, Wales, United Kingdom
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33
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Harris KL, Myers MB, McKim KL, Elespuru RK, Parsons BL. Rationale and Roadmap for Developing Panels of Hotspot Cancer Driver Gene Mutations as Biomarkers of Cancer Risk. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2020; 61:152-175. [PMID: 31469467 PMCID: PMC6973253 DOI: 10.1002/em.22326] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2019] [Revised: 08/23/2019] [Accepted: 08/26/2019] [Indexed: 05/24/2023]
Abstract
Cancer driver mutations (CDMs) are necessary and causal for carcinogenesis and have advantages as reporters of carcinogenic risk. However, little progress has been made toward developing measurements of CDMs as biomarkers for use in cancer risk assessment. Impediments for using a CDM-based metric to inform cancer risk include the complexity and stochastic nature of carcinogenesis, technical difficulty in quantifying low-frequency CDMs, and lack of established relationships between cancer driver mutant fractions and tumor incidence. Through literature review and database analyses, this review identifies the most promising targets to investigate as biomarkers of cancer risk. Mutational hotspots were discerned within the 20 most mutated genes across the 10 deadliest cancers. Forty genes were identified that encompass 108 mutational hotspot codons overrepresented in the COSMIC database; 424 different mutations within these hotspot codons account for approximately 63,000 tumors and their prevalence across tumor types is described. The review summarizes literature on the prevalence of CDMs in normal tissues and suggests such mutations are direct and indirect substrates for chemical carcinogenesis, which occurs in a spatially stochastic manner. Evidence that hotspot CDMs (hCDMs) frequently occur as tumor subpopulations is presented, indicating COSMIC data may underestimate mutation prevalence. Analyses of online databases show that genes containing hCDMs are enriched in functions related to intercellular communication. In its totality, the review provides a roadmap for the development of tissue-specific, CDM-based biomarkers of carcinogenic potential, comprised of batteries of hCDMs and can be measured by error-correct next-generation sequencing. Environ. Mol. Mutagen. 61:152-175, 2020. Published 2019. This article is a U.S. Government work and is in the public domain in the USA. Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society.
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Affiliation(s)
- Kelly L. Harris
- Division of Genetic and Molecular ToxicologyNational Center for Toxicological Research, US Food and Drug AdministrationJeffersonArkansas
| | - Meagan B. Myers
- Division of Genetic and Molecular ToxicologyNational Center for Toxicological Research, US Food and Drug AdministrationJeffersonArkansas
| | - Karen L. McKim
- Division of Genetic and Molecular ToxicologyNational Center for Toxicological Research, US Food and Drug AdministrationJeffersonArkansas
| | - Rosalie K. Elespuru
- Division of Biology, Chemistry and Materials ScienceCDRH/OSEL, US Food and Drug AdministrationSilver SpringMaryland
| | - Barbara L. Parsons
- Division of Genetic and Molecular ToxicologyNational Center for Toxicological Research, US Food and Drug AdministrationJeffersonArkansas
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Klapacz J, Gollapudi BB. Considerations for the Use of Mutation as a Regulatory Endpoint in Risk Assessment. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2020; 61:84-93. [PMID: 31301246 DOI: 10.1002/em.22318] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2019] [Revised: 07/08/2019] [Accepted: 07/10/2019] [Indexed: 06/10/2023]
Abstract
Assessment of a chemical's potential to cause permanent changes in the genetic code has been a common practice in the industry and regulatory settings for decades. Furthermore, the genetic toxicity battery of tests has typically been employed during the earliest stages of the research and development programs of new product development. A positive outcome from such battery has a major impact on the chemical's utility, industrial hygiene, product stewardship practices, and product life cycle analysis, among many other decisions that need to be taken by the industry, even before the registration of a chemical is undertaken. Under the prevailing regulatory paradigm, the dichotomous (yes/no) evaluation of the chemical's genotoxic potential leads to a conservative, linear no-threshold (LNT) risk assessment, unless compelling and undeniable data to the contrary can be provided to satisfy regulators, typically in a number of different global jurisdictions. With the current advent of predictive methods, new testing paradigms, mode-of-action/adverse outcome pathways, and quantitative risk assessment approaches, various stakeholders are starting to employ these state-of-the-science methodologies to further the conversation on decision making and advance the regulatory paradigm beyond the dominant LNT status quo. This commentary describes these novel methodologies, relevant biological responses, and how these can affect internal and regulatory risk assessment approaches. Environ. Mol. Mutagen. 61:84-93, 2020. © 2019 Wiley Periodicals, Inc.
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Affiliation(s)
- Joanna Klapacz
- Toxicology and Environmental Research and Consulting, The Dow Chemical Company, Midland, Michigan
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35
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Heflich RH, Johnson GE, Zeller A, Marchetti F, Douglas GR, Witt KL, Gollapudi BB, White PA. Mutation as a Toxicological Endpoint for Regulatory Decision-Making. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2020; 61:34-41. [PMID: 31600846 DOI: 10.1002/em.22338] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2019] [Revised: 09/09/2019] [Accepted: 09/14/2019] [Indexed: 05/23/2023]
Abstract
Mutations induced in somatic cells and germ cells are responsible for a variety of human diseases, and mutation per se has been considered an adverse health concern since the early part of the 20th Century. Although in vitro and in vivo somatic cell mutation data are most commonly used by regulatory agencies for hazard identification, that is, determining whether or not a substance is a potential mutagen and carcinogen, quantitative mutagenicity dose-response data are being used increasingly for risk assessments. Efforts are currently underway to both improve the measurement of mutations and to refine the computational methods used for evaluating mutation data. We recommend continuing the development of these approaches with the objective of establishing consensus regarding the value of including the quantitative analysis of mutation per se as a required endpoint for comprehensive assessments of toxicological risk. Environ. Mol. Mutagen. 61:34-41, 2020. © 2019 Wiley Periodicals, Inc.
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Affiliation(s)
- Robert H Heflich
- U.S. Food and Drug Administration, National Center for Toxicological Research, Jefferson, Arkansas
| | | | - Andreas Zeller
- Roche Pharma Research and Early Development, Roche Innovation Center Basel, F. Hoffmann-La Roche Ltd, Basel, Switzerland
| | - Francesco Marchetti
- Environmental Health Science and Research Bureau, Health Canada, Ottawa, Canada
| | - George R Douglas
- Environmental Health Science and Research Bureau, Health Canada, Ottawa, Canada
| | - Kristine L Witt
- National Institutes of Health, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina
| | | | - Paul A White
- Environmental Health Science and Research Bureau, Health Canada, Ottawa, Canada
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36
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Luijten M, Ball NS, Dearfield KL, Gollapudi BB, Johnson GE, Madia F, Peel L, Pfuhler S, Settivari RS, ter Burg W, White PA, van Benthem J. Utility of a next generation framework for assessment of genomic damage: A case study using the industrial chemical benzene. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2020; 61:94-113. [PMID: 31709603 PMCID: PMC6972600 DOI: 10.1002/em.22346] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2019] [Revised: 10/31/2019] [Accepted: 11/06/2019] [Indexed: 05/22/2023]
Abstract
We recently published a next generation framework for assessing the risk of genomic damage via exposure to chemical substances. The framework entails a systematic approach with the aim to quantify risk levels for substances that induce genomic damage contributing to human adverse health outcomes. Here, we evaluated the utility of the framework for assessing the risk for industrial chemicals, using the case of benzene. Benzene is a well-studied substance that is generally considered a genotoxic carcinogen and is known to cause leukemia. The case study limits its focus on occupational and general population health as it relates to benzene exposure. Using the framework as guidance, available data on benzene considered relevant for assessment of genetic damage were collected. Based on these data, we were able to conduct quantitative analyses for relevant data sets to estimate acceptable exposure levels and to characterize the risk of genetic damage. Key observations include the need for robust exposure assessments, the importance of information on toxicokinetic properties, and the benefits of cheminformatics. The framework points to the need for further improvement on understanding of the mechanism(s) of action involved, which would also provide support for the use of targeted tests rather than a prescribed set of assays. Overall, this case study demonstrates the utility of the next generation framework to quantitatively model human risk on the basis of genetic damage, thereby enabling a new, innovative risk assessment concept. Environ. Mol. Mutagen. 61:94-113, 2020. © 2019 The Authors. Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society.
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Affiliation(s)
- Mirjam Luijten
- Centre for Health ProtectionNational Institute for Public Health and the Environment (RIVM)BilthovenThe Netherlands
| | | | | | | | - George E. Johnson
- Swansea University Medical School, Swansea UniversitySwanseaUnited Kingdom
| | - Federica Madia
- European Commission, Joint Research Centre (JRC)IspraItaly
| | - Lauren Peel
- Health and Environmental Sciences InstituteWashingtonDistrict of Columbia
| | | | | | - Wouter ter Burg
- Centre for Safety of Substances and ProductsNational Institute for Public Health and the Environment (RIVM)BilthovenThe Netherlands
| | - Paul A. White
- Department of BiologyUniversity of OttawaOttawaOntarioCanada
| | - Jan van Benthem
- Centre for Health ProtectionNational Institute for Public Health and the Environment (RIVM)BilthovenThe Netherlands
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Sasaki JC, Allemang A, Bryce SM, Custer L, Dearfield KL, Dietz Y, Elhajouji A, Escobar PA, Fornace AJ, Froetschl R, Galloway S, Hemmann U, Hendriks G, Li HH, Luijten M, Ouedraogo G, Peel L, Pfuhler S, Roberts DJ, Thybaud V, van Benthem J, Yauk CL, Schuler M. Application of the adverse outcome pathway framework to genotoxic modes of action. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2020; 61:114-134. [PMID: 31603995 DOI: 10.1002/em.22339] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2019] [Revised: 09/17/2019] [Accepted: 09/23/2019] [Indexed: 05/22/2023]
Abstract
In May 2017, the Health and Environmental Sciences Institute's Genetic Toxicology Technical Committee hosted a workshop to discuss whether mode of action (MOA) investigation is enhanced through the application of the adverse outcome pathway (AOP) framework. As AOPs are a relatively new approach in genetic toxicology, this report describes how AOPs could be harnessed to advance MOA analysis of genotoxicity pathways using five example case studies. Each of these genetic toxicology AOPs proposed for further development includes the relevant molecular initiating events, key events, and adverse outcomes (AOs), identification and/or further development of the appropriate assays to link an agent to these events, and discussion regarding the biological plausibility of the proposed AOP. A key difference between these proposed genetic toxicology AOPs versus traditional AOPs is that the AO is a genetic toxicology endpoint of potential significance in risk characterization, in contrast to an adverse state of an organism or a population. The first two detailed case studies describe provisional AOPs for aurora kinase inhibition and tubulin binding, leading to the common AO of aneuploidy. The remaining three case studies highlight provisional AOPs that lead to chromosome breakage or mutation via indirect DNA interaction (inhibition of topoisomerase II, production of cellular reactive oxygen species, and inhibition of DNA synthesis). These case studies serve as starting points for genotoxicity AOPs that could ultimately be published and utilized by the broader toxicology community and illustrate the practical considerations and evidence required to formalize such AOPs so that they may be applied to genetic toxicity evaluation schemes. Environ. Mol. Mutagen. 61:114-134, 2020. © 2019 Wiley Periodicals, Inc.
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Affiliation(s)
| | | | | | - Laura Custer
- Bristol-Myers Squibb Company, Drug Safety Evaluation, New Brunswick, New Jersey
| | | | - Yasmin Dietz
- Sanofi-Aventis Deutschland GmbH, Frankfurt, Germany
| | | | | | | | | | | | | | | | - Heng-Hong Li
- Georgetown University, Washington, District of Columbia
| | - Mirjam Luijten
- National Institute for Public Health and the Environment, Bilthoven, The Netherlands
| | | | - Lauren Peel
- Health and Environmental Sciences Institute, Washington, District of Columbia
| | | | | | - Véronique Thybaud
- Sanofi, Research and Development, Preclinical Safety, Vitry-sur-Seine, France
| | - Jan van Benthem
- National Institute for Public Health and the Environment, Bilthoven, The Netherlands
| | - Carole L Yauk
- Environmental Health Science and Research Bureau, Health Canada, Ottawa, Ontario, Canada
| | - Maik Schuler
- Pfizer Inc, World Wide Research and Development, Groton, Connecticut
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Nohmi T, Matsumoto K. Effects of DNA polymerase kappa and mismatch repair on dose-responses of chromosome aberrations induced by three oxidative genotoxins in human cells. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2020; 61:193-199. [PMID: 31294882 DOI: 10.1002/em.22315] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2019] [Revised: 06/25/2019] [Accepted: 06/27/2019] [Indexed: 06/09/2023]
Abstract
Genotoxic carcinogens are regulated under the policy that there is no threshold or safe dose. It has been pointed out, however, that self-defense mechanisms, such as detoxification, DNA repair, and error-free translesion synthesis, may protect chromosome DNA from genotoxic insults, thereby constituting practical threshold. In this study, we examined dose responses of chromosome aberrations induced by three oxidative genotoxins, that is, hydrogen peroxide (H2 O2 ), menadione and paraquat, with or without DNA polymerase kappa (Polκ) activities and mismatch repair capacities in human cells. Polκ is involved in translesion synthesis across DNA damage and mismatch repair is responsible for correction of base-base mismatch in DNA. Polκ activity of the cells was inactivated either by point mutations in the catalytically essential amino acids (catalytically dead or CD) or by deletion of the POLK gene (knockout or KO). In the absence of mismatch repair, frequencies of chromosome aberrations induced by H2 O2 and menadione were not significantly different among CD, KO, and the wild type (WT) cells. In the presence of mismatch repair, however, cytotoxicity and clastogenicity were enhanced and Polκ modulated the sensitivity of the cells. No-observed-genotoxic-effect-levels (NOGELs) for H2 O2 and menadione were CD = KO < WT cells. In contrast, the sensitivities of the cells to paraquat were not significantly affected by the status of mismatch repair or Polκ activity. The results suggest that mismatch repair and Polκ coordinately modulate NOGELs for the clastogenicity of H2 O2 and menadione and also that DNA lesion(s) responsible for paraquat-induced chromosome aberrations are different from those induced by H2 O2 and menadione. Environ. Mol. Mutagen. 61:193-199, 2020. © 2019 Wiley Periodicals, Inc.
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Affiliation(s)
- Takehiko Nohmi
- Biological Safety Research Center, National Institute of Health Sciences, Kawasaki-shi, Kanagawa, Japan
| | - Kyomu Matsumoto
- Toxicology Division, The Institute of Environmental Toxicology, Joso-shi, Ibaraki, Japan
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Bernacki DT, Bryce SM, Bemis JC, Dertinger SD, Witt KL, Smith‐Roe SL. Evidence for an Aneugenic Mechanism of Action for Micronucleus Induction by Black Cohosh Extract. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2019; 60:845-856. [PMID: 31569270 PMCID: PMC6900087 DOI: 10.1002/em.22334] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/31/2019] [Revised: 09/03/2019] [Accepted: 09/07/2019] [Indexed: 06/10/2023]
Abstract
Black cohosh extract (BCE) is a popular botanical dietary supplement marketed to relieve symptoms of various gynecological ailments. Studies conducted by the National Toxicology Program (NTP) showed that BCE induces micronucleated erythrocytes in female rats and mice. Subsequently, the NTP showed that a variety of BCEs, including the sample that induced micronuclei (MN) in vivo ("NTP BCE") had a similar effect in human TK6 cells. Further testing with the MultiFlow® DNA Damage Assay revealed that TK6 cells exposed to NTP BCE, as well as a BCE reference material (BC XRM), exhibited a signature consistent with aneugenic activity in TK6 cells. Results from experiments reported herein confirmed these in vitro observations with NTP BCE and BC XRM. We extended these studies to include a novel test system, the MultiFlow Aneugen Molecular Mechanism Assay. For these experiments, TK6 cells were exposed to NTP BCE and BC XRM over a range of concentrations in the presence of fluorescent Taxol (488 Taxol). After 4 h, nuclei from lysed cells were stained with a nucleic acid dye and labeled with fluorescent antibodies against phospho-histone H3 (p-H3) and Ki-67. Whereas BCEs did not affect p-H3:Ki-67 ratios (a signature of aneugenic mitotic kinase inhibitors), 488 Taxol-associated fluorescence (a tubulin binder-sensitive endpoint) was affected. More specifically, 488 Taxol-associated fluorescence was reduced over the same concentration range that was previously observed to induce MN. These results provide direct evidence that BCEs destabilize microtubules in vitro, and this is the molecular mechanism responsible for the aneugenicity findings. Environ. Mol. Mutagen. 2019. © 2019 The Authors. Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society.
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Affiliation(s)
| | | | | | | | - Kristine L. Witt
- Division of the National Toxicology ProgramNIEHSResearch Triangle ParkNorth Carolina
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Nonanimal toxicology testing approaches for traditional and deemed tobacco products in a complex regulatory environment: Limitations, possibilities, and future directions. Toxicol In Vitro 2019; 62:104684. [PMID: 31618670 DOI: 10.1016/j.tiv.2019.104684] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Revised: 10/09/2019] [Accepted: 10/10/2019] [Indexed: 11/20/2022]
Abstract
The evaluation of tobacco products is complex due to a multitude of factors including product diversity, limited testing standards, and variability in user behavior. Alternative approaches in current testing paradigms have limitations that generally truncate their applicability beyond screening for hazard identification; this is also true for toxicological evaluations of tobacco products. In a regulatory context, results from tobacco product toxicity assessments are extrapolated to the in vivo condition to assess human health relevance at the individual and population level. A key limitation of alternative approaches is the difficulty and uncertainty in extrapolating results to adverse outcomes relevant to chronic tobacco exposures in humans. This difficulty and uncertainty are increased when comparing toxicological outcomes between tobacco products. Given that the interpretation and quantification of differences in assay results (e.g., mutagenicity) for tobacco product comparison may be inconclusive, the predictive value of these approaches for human risk of relevant downstream pathologies (e.g., carcinogenesis) can be limited. Development and validation of fit-for-purpose alternative approaches that are predictive of human toxicity and dose response assays with adequate sensitivity and specificity for product comparisons would help advance the field of predictive toxicology.
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Ito Y, Nakajima K, Masubuchi Y, Kikuchi S, Saito F, Akahori Y, Jin M, Yoshida T, Shibutani M. Differential responses on energy metabolic pathway reprogramming between genotoxic and non-genotoxic hepatocarcinogens in rat liver cells. J Toxicol Pathol 2019; 32:261-274. [PMID: 31719753 PMCID: PMC6831489 DOI: 10.1293/tox.2019-0048] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2019] [Accepted: 06/25/2019] [Indexed: 12/12/2022] Open
Abstract
To clarify difference in the responses on the reprogramming of metabolism toward carcinogenesis between genotoxic and non-genotoxic hepatocarcinogens in the liver, rats were repeatedly administered genotoxic hepatocarcinogens (N-nitrosodiethylamine, aflatoxin B1, N-nitrosopyrrolidine, or carbadox) or non-genotoxic hepatocarcinogens (carbon tetrachloride, thioacetamide, or methapyrilene hydrochloride) for 28, 84, or 90 days. Non-genotoxic hepatocarcinogens revealed transcript expression changes suggestive of suppressed mitochondrial oxidative phosphorylation (OXPHOS) after 28 days and increased glutathione S-transferase placental form-positive (GST-P+) foci downregulating adenosine triphosphate (ATP) synthase subunit beta, mitochondrial precursor (ATPB), compared with genotoxic hepatocarcinogens after 84 or 90 days, suggesting that non-genotoxic hepatocarcinogens are prone to suppress OXPHOS from the early stage of treatment, which is in contrast to genotoxic hepatocarcinogens. Both genotoxic and non-genotoxic hepatocarcinogens upregulated glycolytic enzyme genes and increased cellular membrane solute carrier family 2, facilitated glucose transporter member 1 (GLUT1) expression in GST-P+ foci for up to 90 days, suggesting induction of a metabolic shift from OXPHOS to glycolysis at early hepatocarcinogenesis by hepatocarcinogens unrelated to genotoxic potential. Non-genotoxic hepatocarcinogens increased c-MYC+ cells after 28 days and downregulated Tp53 after 84 or 90 days, suggesting a commitment to enhanced metabolic shift and cell proliferation. Genotoxic hepatocarcinogens also enhanced c-MYC activation-related metabolic shift until 84 or 90 days. In addition, both genotoxic and non-genotoxic hepatocarcinogens upregulated glutaminolysis-related Slc1a5 or Gls, or both, after 28 days and induced liver cell foci immunoreactive for neutral amino acid transporter B(0) (SLC1A5) in the subpopulation of GST-P+ foci after 84 or 90 days, suggesting glutaminolysis-mediated facilitation of cell proliferation toward hepatocarcinogenesis. These results suggest differential responses between genotoxic and non-genotoxic hepatocarcinogens on reprogramming of energy metabolic pathways toward carcinogenesis in liver cells from the early stage of hepatocarcinogen treatment.
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Affiliation(s)
- Yuko Ito
- Laboratory of Veterinary Pathology, Division of Animal Life Science, Institute of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan.,Pathogenetic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, 1-1 Yanagido, Gifu-shi, Gifu 501-1193, Japan
| | - Kota Nakajima
- Laboratory of Veterinary Pathology, Division of Animal Life Science, Institute of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan.,Pathogenetic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, 1-1 Yanagido, Gifu-shi, Gifu 501-1193, Japan
| | - Yasunori Masubuchi
- Laboratory of Veterinary Pathology, Division of Animal Life Science, Institute of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan.,Pathogenetic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, 1-1 Yanagido, Gifu-shi, Gifu 501-1193, Japan
| | - Satomi Kikuchi
- Laboratory of Veterinary Pathology, Division of Animal Life Science, Institute of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan.,Cooperative Division of Veterinary Sciences, Graduate School of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan
| | - Fumiyo Saito
- Chemicals Evaluation and Research Institute, Japan, 1-4-25 Kouraku, Bunkyo-ku, Tokyo 112-0004, Japan
| | - Yumi Akahori
- Chemicals Evaluation and Research Institute, Japan, 1-4-25 Kouraku, Bunkyo-ku, Tokyo 112-0004, Japan
| | - Meilan Jin
- Laboratory of Veterinary Pathology, College of Animal Science and Technology Veterinary Medicine, Southwest University, No.2 Tiansheng Road, BeiBei District, Chongqing 400715, P.R. China
| | - Toshinori Yoshida
- Laboratory of Veterinary Pathology, Division of Animal Life Science, Institute of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan.,Cooperative Division of Veterinary Sciences, Graduate School of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan
| | - Makoto Shibutani
- Laboratory of Veterinary Pathology, Division of Animal Life Science, Institute of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan.,Cooperative Division of Veterinary Sciences, Graduate School of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan.,Institute of Global Innovation Research, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan
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Takeshita T, Kanaly RA. In vitro DNA/RNA Adductomics to Confirm DNA Damage Caused by Benzo[ a]pyrene in the Hep G2 Cell Line. Front Chem 2019; 7:491. [PMID: 31338364 PMCID: PMC6629907 DOI: 10.3389/fchem.2019.00491] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Accepted: 06/25/2019] [Indexed: 11/13/2022] Open
Abstract
In the development of new chemical substances, genetic toxicity evaluations are a high priority for safety risk management. Evaluation of the possibility of compound carcinogenicity with accuracy and at reasonable cost in the early stages of development by in vitro techniques is preferred. Currently, DNA damage-related in vitro genotoxicity tests are widely-used screening tools after which next generation toxicity testing may be applied to confirm DNA damage. DNA adductomics may be used to evaluate DNA damage in vitro, however confirmation of DNA adduct identities through comparison to authentic standards may be time-consuming and expensive processes. Considering this, a streamlined method for confirming putative DNA adducts that are detected by DNA adductomics may be useful. With this aim, in vitro DNA adductome methods in conjunction with in vitro RNA adductome methods may be proposed as a DNA adductome verification approach by which to eliminate false positive annotations. Such an approach was evaluated by conducting in vitro assays whereby Hep G2 cell lines that were exposed to or not exposed to benzo[a]pyrene were digested to their respective 2'-deoxynucleosides or ribonucleosides and analyzed by liquid chromatography electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) by comparative DNA and RNA adductomics through neutral loss targeting of the [M + H]+ > [M + H - 116]+ or [M + H]+ > [M + H -132]+ transitions over predetermined ranges. Comparisons of DNA adductome maps revealed putative DNA adducts that were detected in exposed cells but not in unexposed cells. Similarly, comparisons of RNA adductome maps revealed putative RNA adducts in exposed cells but not in unexposed cells. Taken together these experiments revealed that analogous forms of putative damage had occurred in both DNA and RNA which supported that putative DNA adducts detected by DNA adductomics were DNA adducts. High resolution mass spectrometry (HRMS) was utilized to confirm that putative nucleic acid adducts detected in both DNA and RNA were derived from benzo[a]pyrene exposure and these putative adducts were identified as 7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene- (B[a]PDE)-type adducts. Overall, this study demonstrates the usefulness of utilizing DNA/RNA adductomics to screen for nucleic acid damage.
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Affiliation(s)
| | - Robert A. Kanaly
- Department of Life and Environmental System Science, Graduate School of Nanobiosciences, Yokohama City University, Yokohama, Japan
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Dertinger SD, Kraynak AR, Wheeldon RP, Bernacki DT, Bryce SM, Hall N, Bemis JC, Galloway SM, Escobar PA, Johnson GE. Predictions of genotoxic potential, mode of action, molecular targets, and potency via a tiered multiflow® assay data analysis strategy. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2019; 60:513-533. [PMID: 30702769 PMCID: PMC6880310 DOI: 10.1002/em.22274] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2018] [Revised: 01/14/2019] [Accepted: 01/23/2019] [Indexed: 05/08/2023]
Abstract
The in vitro MultiFlow® DNA Damage Assay multiplexes γH2AX, p53, phospho-histone H3, and polyploidization biomarkers into a single flow cytometric analysis. The current report describes a tiered sequential data analysis strategy based on data generated from exposure of human TK6 cells to a previously described 85 chemical training set and a new pharmaceutical-centric test set (n = 40). In each case, exposure was continuous over a range of closely spaced concentrations, and cell aliquots were removed for analysis following 4 and 24 hr of treatment. The first data analysis step focused on chemicals' genotoxic potential, and for this purpose, we evaluated the performance of a machine learning (ML) ensemble, a rubric that considered fold increases in biomarkers against global evaluation factors (GEFs), and a hybrid strategy that considered ML and GEFs. This first tier further used ML output and/or GEFs to classify genotoxic activity as clastogenic and/or aneugenic. Test set results demonstrated the generalizability of the first tier, with particularly good performance from the ML ensemble: 35/40 (88%) concordance with a priori genotoxicity expectations and 21/24 (88%) agreement with expected mode of action (MoA). A second tier applied unsupervised hierarchical clustering to the biomarker response data, and these analyses were found to group certain chemicals, especially aneugens, according to their molecular targets. Finally, a third tier utilized benchmark dose analyses and MultiFlow biomarker responses to rank genotoxic potency. The relevance of these rankings is supported by the strong agreement found between benchmark dose values derived from MultiFlow biomarkers compared to those generated from parallel in vitro micronucleus analyses. Collectively, the results suggest that a tiered MultiFlow data analysis pipeline is capable of rapidly and effectively identifying genotoxic hazards while providing additional information that is useful for modern risk assessments-MoA, molecular targets, and potency. Environ. Mol. Mutagen. 60:513-533, 2019. © 2019 Wiley Periodicals, Inc.
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Affiliation(s)
- Stephen D. Dertinger
- Litron Laboratories, Rochester, New York
- Correspondence to: Stephen D. Dertinger, Litron Laboratories, 3500 Winton Place, Rochester, NY 14623.
| | | | - Ryan P. Wheeldon
- Institute of Life Science, Swansea University Medical School, Swansea University, Swansea, Wales, United Kingdom
| | | | | | - Nikki Hall
- Litron Laboratories, Rochester, New York
| | | | | | | | - George E. Johnson
- Institute of Life Science, Swansea University Medical School, Swansea University, Swansea, Wales, United Kingdom
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Von Trompowsky ACM, Conde TR, Lemos RC, Quaresma BMC, Pitombeira MCS, de Carvalho AS, Boechat N, Salomão K, de Castro SL, Zamith HPDS. In vitro genotoxicity of nitroimidazoles as a tool in the search of new trypanocidal agents. Mem Inst Oswaldo Cruz 2019; 114:e190017. [PMID: 31271593 PMCID: PMC6598759 DOI: 10.1590/0074-02760190017] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2019] [Accepted: 05/28/2019] [Indexed: 11/21/2022] Open
Abstract
BACKGROUND Only benznidazole (Bnz) (1) and nifurtimox (Nfx) (2) are licensed for the
treatment of Chagas disease although their safety and efficacy profile are
far from ideal. Farmanguinhos from Fiocruz has developed seven
nitroimidazole compounds (4-10) analogs of megazol (3). OBJECTIVES To evaluate whether the genotoxic effect of 3 was abolished in the seven
nitroimidazoles (4-10) analogs using the in vitro alkaline
comet assay (CA) and the in vitro cytokinesis-block
micronucleus assay (CBMN) in whole human blood cells (WHBC) and correlate
this effect with their trypanocidal activity using bloodstream
trypomastigote forms of Trypanosoma cruzi. METHODS The toxicity of 3-10 to WHBC in the in vitro CA was
determined using the fluorescein diacetate/ethidium bromide assay. DNA
damage in the in vitro CA was evaluated according to tail
size in four classes (0-3) and methyl methane-sulfonate (MMS) was used as a
positive control. The cytotoxicity of 3-10 to WHBC in the CBMN was measured
using the cytokinesis-block proliferation index and the replication index.
The number of the micronucleate cells in 2,000 binucleate cells by
experimental group was determined. Mitomycin C and
N-deacetyl-N-methylcolchicine were used as positive controls. FINDINGS Compound 3 showed a significant DNA strand break effect through the
in vitro CA and highly significant clastogenic and/or
aneugenic effect in the CBMN. Compounds 5, 6, 8, 9 and 10 showed negative
results in the CBMN and positive results in the in vitro
CA, while the inverse effect was observed for 4 and 7. MAIN CONCLUSIONS Compound 10 was the most promising to proceed with the development as a drug
candidate in the treatment of Chagas disease showing absence of chromosomal
cytogenetic damage and high activity against T. cruzi,
about two times higher than 3 and the clinical drug 1.
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Affiliation(s)
- Ana Claudia Manoel Von Trompowsky
- Fundação Oswaldo Cruz-Fiocruz, Instituto Nacional de Controle de Qualidade em Saúde, Departamento de Farmacologia e Toxicologia, Rio de Janeiro, RJ, Brasil.,Fundação Oswaldo Cruz-Fiocruz, Instituto Nacional de Controle de Qualidade em Saúde, Programa de Pós-Graduação em Vigilância Sanitária, Rio de Janeiro, RJ, Brasil
| | - Taline Ramos Conde
- Fundação Oswaldo Cruz-Fiocruz, Instituto Nacional de Controle de Qualidade em Saúde, Departamento de Farmacologia e Toxicologia, Rio de Janeiro, RJ, Brasil
| | - Renata Calil Lemos
- Fundação Oswaldo Cruz-Fiocruz, Instituto Nacional de Controle de Qualidade em Saúde, Departamento de Farmacologia e Toxicologia, Rio de Janeiro, RJ, Brasil
| | - Bruna Maria Cs Quaresma
- Universidade Federal do Rio de Janeiro, Instituto de Ciências Biomédicas, Programa de Pós-Graduação em Farmacologia e Química Medicinal, Rio de Janeiro, RJ, Brasil
| | - Marcelly Cristina Sr Pitombeira
- Universidade Federal do Rio de Janeiro, Instituto de Ciências Biomédicas, Programa de Pós-Graduação em Farmacologia e Química Medicinal, Rio de Janeiro, RJ, Brasil.,Fundação Oswaldo Cruz-Fiocruz, Instituto de Tecnologia em Fármacos, Departamento de Síntese de Fármacos, Farmanguinhos, Rio de Janeiro, RJ, Brasil
| | - Alcione Silva de Carvalho
- Fundação Oswaldo Cruz-Fiocruz, Instituto de Tecnologia em Fármacos, Departamento de Síntese de Fármacos, Farmanguinhos, Rio de Janeiro, RJ, Brasil
| | - Núbia Boechat
- Fundação Oswaldo Cruz-Fiocruz, Instituto de Tecnologia em Fármacos, Departamento de Síntese de Fármacos, Farmanguinhos, Rio de Janeiro, RJ, Brasil
| | - Kelly Salomão
- Fundação Oswaldo Cruz-Fiocruz, Instituto Oswaldo Cruz, Laboratório de Biologia Celular, Rio de Janeiro, RJ, Brasil
| | - Solange Lisboa de Castro
- Fundação Oswaldo Cruz-Fiocruz, Instituto Oswaldo Cruz, Laboratório de Biologia Celular, Rio de Janeiro, RJ, Brasil
| | - Helena Pereira da Silva Zamith
- Fundação Oswaldo Cruz-Fiocruz, Instituto Nacional de Controle de Qualidade em Saúde, Departamento de Farmacologia e Toxicologia, Rio de Janeiro, RJ, Brasil.,Fundação Oswaldo Cruz-Fiocruz, Instituto Nacional de Controle de Qualidade em Saúde, Programa de Pós-Graduação em Vigilância Sanitária, Rio de Janeiro, RJ, Brasil
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Gollapudi P, Bhat VS, Eastmond DA. Concentration-response studies of the chromosome-damaging effects of topoisomerase II inhibitors determined in vitro using human TK6 cells. Mutat Res 2019; 841:49-56. [PMID: 31138411 DOI: 10.1016/j.mrgentox.2019.05.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Revised: 05/13/2019] [Accepted: 05/14/2019] [Indexed: 11/28/2022]
Abstract
Topoisomerase II (topo II) inhibitors are commonly used as chemotherapy to treat multiple types of cancer, though their use is also associated with the development of therapy related acute leukemias. While the chromosome-damaging effects of etoposide, a topo II poison, have been proposed to act through a threshold mechanism, little is known about the chromosome damaging effects and dose responses for the catalytic inhibitors of the enzyme. The current study was designed to further investigate the potencies and concentration-response relationships of several topoisomerase II inhibitors, including the topoisomerase II poison etoposide, as well as catalytic inhibitors aclarubicin, merbarone, ICRF-154 and ICRF-187 using both a traditional in vitro micronucleus assay as well as a flow-cytometry based version of the assay. Benchmark dose (BMD) analysis was used to identify models that best fit the data and estimate a BMD, in this case the concentration at which a one standard deviation increase above the control frequency would be expected. All of the agents tested were potent in inducing micronuclei in human lymphoblastoid TK6 cells, with significant increases seen at low micromolar, and in the cases of aclarubicin and etoposide, at low nanomolar concentrations. Use of the anti-kinetochore CREST antibody with the microscopy-based assay demonstrated that the vast majority of the micronuclei originated from chromosome breakage. In comparing the two versions of the micronucleus assay, significant increases in micronucleated cells were observed at similar or lower concentrations using the traditional microscopy-based assay. BMD modeling of the data exhibited several advantages and proved to be a valuable alternative for concentration-response analysis, producing points of departure comparable to those derived using traditional no-observed or lowest-observed genotoxic effect level (NOGEL or LOGEL) approaches.
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Affiliation(s)
- P Gollapudi
- Environmental Toxicology Graduate Program and Department of Molecular, Cell and Systems Biology, University of California, Riverside, CA, 92521, USA
| | - V S Bhat
- Environmental Toxicology Graduate Program and Department of Molecular, Cell and Systems Biology, University of California, Riverside, CA, 92521, USA
| | - D A Eastmond
- Environmental Toxicology Graduate Program and Department of Molecular, Cell and Systems Biology, University of California, Riverside, CA, 92521, USA.
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Doe JE, Boobis AR, Dellarco V, Fenner-Crisp PA, Moretto A, Pastoor TP, Schoeny RS, Seed JG, Wolf DC. Chemical carcinogenicity revisited 2: Current knowledge of carcinogenesis shows that categorization as a carcinogen or non-carcinogen is not scientifically credible. Regul Toxicol Pharmacol 2019; 103:124-129. [DOI: 10.1016/j.yrtph.2019.01.024] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2018] [Revised: 01/09/2019] [Accepted: 01/16/2019] [Indexed: 11/28/2022]
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Spassova MA. Statistical Approach to Identify Threshold and Point of Departure in Dose-Response Data. RISK ANALYSIS : AN OFFICIAL PUBLICATION OF THE SOCIETY FOR RISK ANALYSIS 2019; 39:940-956. [PMID: 30253453 DOI: 10.1111/risa.13191] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Revised: 08/09/2018] [Accepted: 08/18/2018] [Indexed: 06/08/2023]
Abstract
The study presents an integrated, rigorous statistical approach to define the likelihood of a threshold and point of departure (POD) based on dose-response data using nested family of bent-hyperbola models. The family includes four models: the full bent-hyperbola model, which allows for transition between two linear regiments with various levels of smoothness; a bent-hyperbola model reduced to a spline model, where the transition is fixed to a knot; a bent-hyperbola model with a restricted negative asymptote slope of zero, named hockey-stick with arc (HS-Arc); and spline model reduced further to a hockey-stick type model (HS), where the first linear segment has a slope of zero. A likelihood-ratio test is used to discriminate between the models and determine if the more flexible versions of the model provide better or significantly better fit than a hockey-stick type model. The full bent-hyperbola model can accommodate both threshold and nonthreshold behavior, can take on concave up and concave down shapes with various levels of curvature, can approximate the biochemically relevant Michaelis-Menten model, and even be reduced to a straight line. Therefore, with the use of this model, the presence or absence of a threshold may even become irrelevant and the best fit of the full bent-hyperbola model be used to characterize the dose-response behavior and risk levels, with no need for mode of action (MOA) information. Point of departure (POD), characterized by exposure level at which some predetermined response is reached, can be defined using the full model or one of the better fitting reduced models.
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Pottenger LH, Boysen G, Brown K, Cadet J, Fuchs RP, Johnson GE, Swenberg JA. Understanding the importance of low-molecular weight (ethylene oxide- and propylene oxide-induced) DNA adducts and mutations in risk assessment: Insights from 15 years of research and collaborative discussions. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2019; 60:100-121. [PMID: 30536466 PMCID: PMC6590209 DOI: 10.1002/em.22248] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2018] [Revised: 08/10/2018] [Accepted: 08/23/2018] [Indexed: 05/11/2023]
Abstract
The interpretation and significance of DNA adduct data, their causal relationship to mutations, and their role in risk assessment have been debated for many years. An extended effort to identify key questions and collect relevant data to address them was focused on the ubiquitous low MW N7-alkyl/hydroxyalkylguanine adducts. Several academic, governmental, and industrial laboratories collaborated to gather new data aimed at better understanding the role and potential impact of these adducts in quantifiable genotoxic events (gene mutations/micronucleus). This review summarizes and evaluates the status of dose-response data for DNA adducts and mutations from recent experimental work with standard mutagenic agents and ethylene oxide and propylene oxide, and the importance for risk assessment. This body of evidence demonstrates that small N7-alkyl/hydroxyalkylguanine adducts are not pro-mutagenic and, therefore, adduct formation alone is not adequate evidence to support a mutagenic mode of action. Quantitative methods for dose-response analysis and derivation of thresholds, benchmark dose (BMD), or other points-of-departure (POD) for genotoxic events are now available. Integration of such analyses of genetox data is necessary to properly assess any role for DNA adducts in risk assessment. Regulatory acceptance and application of these insights remain key challenges that only the regulatory community can address by applying the many learnings from recent research. The necessary tools, such as BMDs and PODs, and the example datasets, are now available and sufficiently mature for use by the regulatory community. Environ. Mol. Mutagen. 60: 100-121, 2019. © 2018 The Authors. Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society.
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Affiliation(s)
- L. H. Pottenger
- Olin Corporation/Blue Cube Operations, LLC, retired, LHP TOX CONSULT, LLCMidlandMIUSA
| | - G. Boysen
- Department of Environmental and Occupational Health and The Winthrop P Rockefeller Cancer Institute University of Arkansas for Medical SciencesLittle RockArkansasUSA
| | - K. Brown
- Leicester Cancer Research CentreUniversity of LeicesterLeicesterUnited Kingdom
| | - J. Cadet
- Institut Nanosciences et Cryogénie, CEA‐GrenobleGrenobleFrance
- Université de SherbrookeSherbrookeCanada
| | - R. P. Fuchs
- Centre de Recherche en Cancérologie de Marseille (CRCM), Inserm, U1068Marseille, 13009France
- CNRS, UMR7258Marseille, 13009France
- Institut Paoli‐CalmettesMarseille, 13009France
- Aix‐Marseille UniversityUM 105, 13284, MarseilleFrance
| | - G. E. Johnson
- Swansea University, Institute of Life SciencesSwanseaUnited Kingdom
| | - J. A. Swenberg
- University of North CarolinaChapel HillNorth CarolinaUSA
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Dose-dependence of chemical carcinogenicity: Biological mechanisms for thresholds and implications for risk assessment. Chem Biol Interact 2019; 301:112-127. [DOI: 10.1016/j.cbi.2019.01.025] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2018] [Revised: 01/11/2019] [Accepted: 01/25/2019] [Indexed: 12/19/2022]
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Huang C, Xu X, Wang D, Ma M, Rao K, Wang Z. The aryl hydrocarbon receptor (AhR) activity and DNA-damaging effects of chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs). CHEMOSPHERE 2018; 211:640-647. [PMID: 30098559 DOI: 10.1016/j.chemosphere.2018.07.087] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2018] [Revised: 06/29/2018] [Accepted: 07/16/2018] [Indexed: 06/08/2023]
Abstract
An increasing number of studies have indicated that environmental contamination with chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs) has been underestimated. However, insufficient available toxicological information on Cl-PAHs makes evaluating their risks to health challenging. Two in vitro bioassays were used in the present study to characterize the aryl hydrocarbon receptor (AhR) activity and DNA-damaging effects of 22 low-molecular-weight PAHs and their Cl-PAHs by using the EROD assay in rat hepatoma (H4IIE) cells and the SOS/umu test (S. typhimurium TA1535/pSK1002). Compared with their parent PAHs, most of the Cl-PAHs enhanced AhR-mediated activity in the EROD assay. 1,3,6,8-Tetrachloro-pyrene (1,3,6,8-Tetracl-Py) induced the greatest potency of EROD activity (83.1%-TCDD-max) and its single point ReP was 6.64 × 10-6. Compared with their parent PAHs, several Cl-PAHs showed significant DNA-damaging effects in the SOS/umu test with the addition of S9, and the toxic equivalency of benzo[a]pyrene (TEQBaP) was calculated for them. 9-Chloroanthracene (9-Ant) and 5,6-Dichloroacenaphthene (5,6-Dicl-Ace) had relatively high TEQBaP (0.62 and 0.54, respectively). However, only 1,3,6,8-Tetracl-Py elicited strong DNA-damaging effects in the absence of S9. The degree of chlorination, the position of chlorine substitutions, and the structure of parent PAHs influenced the potency of low-molecular-weight PAHs with regard to their AhR activity and DNA-damaging effects. More concern should be raised for these environmentally relevant pollutants.
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Affiliation(s)
- Chao Huang
- Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, 100085 Beijing, China; College of Resources and Environment, University of Chinese Academy of Sciences, 100049 Beijing, China
| | - Xiong Xu
- Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, 100085 Beijing, China; College of Resources and Environment, University of Chinese Academy of Sciences, 100049 Beijing, China
| | - Donghong Wang
- Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, 100085 Beijing, China; College of Resources and Environment, University of Chinese Academy of Sciences, 100049 Beijing, China.
| | - Mei Ma
- Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, 100085 Beijing, China; College of Resources and Environment, University of Chinese Academy of Sciences, 100049 Beijing, China.
| | - Kaifeng Rao
- State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, 100085 Beijing, China
| | - Zijian Wang
- State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, 100085 Beijing, China
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