1
|
Patlewicz G, Dean JL, Gibbons CF, Judson RS, Keshava N, Vegosen L, Martin TM, Pradeep P, Simha A, Warren SH, Gwinn MR, DeMarini DM. Integrating publicly available information to screen potential candidates for chemical prioritization under the Toxic Substances Control Act: A proof of concept case study using genotoxicity and carcinogenicity. Comput Toxicol 2021; 20:1-100185. [PMID: 35128218 PMCID: PMC8809402 DOI: 10.1016/j.comtox.2021.100185] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The Toxic Substances Control Act (TSCA) became law in the U.S. in 1976 and was amended in 2016. The amended law requires the U.S. EPA to perform risk-based evaluations of existing chemicals. Here, we developed a tiered approach to screen potential candidates based on their genotoxicity and carcinogenicity information to inform the selection of candidate chemicals for prioritization under TSCA. The approach was underpinned by a large database of carcinogenicity and genotoxicity information that had been compiled from various public sources. Carcinogenicity data included weight-of-evidence human carcinogenicity evaluations and animal cancer data. Genotoxicity data included bacterial gene mutation data from the Salmonella (Ames) and Escherichia coli WP2 assays and chromosomal mutation (clastogenicity) data. Additionally, Ames and clastogenicity outcomes were predicted using the alert schemes within the OECD QSAR Toolbox and the Toxicity Estimation Software Tool (TEST). The evaluation workflows for carcinogenicity and genotoxicity were developed along with associated scoring schemes to make an overall outcome determination. For this case study, two sets of chemicals, the TSCA Active Inventory non-confidential portion list available on the EPA CompTox Chemicals Dashboard (33,364 chemicals, 'TSCA Active List') and a representative proof-of-concept (POC) set of 238 chemicals were profiled through the two workflows to make determinations of carcinogenicity and genotoxicity potential. Of the 33,364 substances on the 'TSCA Active List', overall calls could be made for 20,371 substances. Here 46.67%% (9507) of substances were non-genotoxic, 0.5% (103) were scored as inconclusive, 43.93% (8949) were predicted genotoxic and 8.9% (1812) were genotoxic. Overall calls for genotoxicity could be made for 225 of the 238 POC chemicals. Of these, 40.44% (91) were non-genotoxic, 2.67% (6) were inconclusive, 6.22% (14) were predicted genotoxic, and 50.67% (114) genotoxic. The approach shows promise as a means to identify potential candidates for prioritization from a genotoxicity and carcinogenicity perspective.
Collapse
Affiliation(s)
- Grace Patlewicz
- Center for Computational Toxicology and Exposure, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA
| | - Jeffry L. Dean
- Center for Public Health and Environmental Assessment, U.S. Environmental Protection Agency, Cincinnati, Ohio, USA
| | - Catherine F. Gibbons
- Center for Public Health and Environmental Assessment, U.S. Environmental Protection Agency, Washington, District of Columbia, USA
| | - Richard S. Judson
- Center for Computational Toxicology and Exposure, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA
| | - Nagalakshmi Keshava
- Center for Public Health and Environmental Assessment, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA
| | - Leora Vegosen
- Center for Computational Toxicology and Exposure, U.S. Environmental Protection Agency, Cincinnati, Ohio, USA
- Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee, USA
| | - Todd M. Martin
- Center for Computational Toxicology and Exposure, U.S. Environmental Protection Agency, Cincinnati, Ohio, USA
| | - Prachi Pradeep
- Center for Computational Toxicology and Exposure, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA
- Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee, USA
| | - Anita Simha
- ORAU, contractor to U.S. Environmental Protection Agency through the National Student Services Contract, Research Triangle Park, North Carolina, USA
| | - Sarah H. Warren
- Center for Computational Toxicology and Exposure, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA
| | - Maureen R. Gwinn
- Center for Computational Toxicology and Exposure, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA
| | - David M. DeMarini
- Center for Computational Toxicology and Exposure, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA
| |
Collapse
|
2
|
Pradeep P, Judson R, DeMarini DM, Keshava N, Martin TM, Dean J, Gibbons CF, Simha A, Warren SH, Gwinn MR, Patlewicz G. Evaluation of Existing QSAR Models and Structural Alerts and Development of New Ensemble Models for Genotoxicity Using a Newly Compiled Experimental Dataset. ACTA ACUST UNITED AC 2021; 18. [PMID: 34504984 DOI: 10.1016/j.comtox.2021.100167] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Regulatory agencies world-wide face the challenge of performing risk-based prioritization of thousands of substances in commerce. In this study, a major effort was undertaken to compile a large genotoxicity dataset (54,805 records for 9299 substances) from several public sources (e.g., TOXNET, COSMOS, eChemPortal). The names and outcomes of the different assays were harmonized, and assays were annotated by type: gene mutation in Salmonella bacteria (Ames assay) and chromosome mutation (clastogenicity) in vitro or in vivo (chromosome aberration, micronucleus, and mouse lymphoma Tk +/- assays). This dataset was then evaluated to assess genotoxic potential using a categorization scheme, whereby a substance was considered genotoxic if it was positive in at least one Ames or clastogen study. The categorization dataset comprised 8442 chemicals, of which 2728 chemicals were genotoxic, 5585 were not and 129 were inconclusive. QSAR models (TEST and VEGA) and the OECD Toolbox structural alerts/profilers (e.g., OASIS DNA alerts for Ames and chromosomal aberrations) were used to make in silico predictions of genotoxicity potential. The performance of the individual QSAR tools and structural alerts resulted in balanced accuracies of 57-73%. A Naïve Bayes consensus model was developed using combinations of QSAR models and structural alert predictions. The 'best' consensus model selected had a balanced accuracy of 81.2%, a sensitivity of 87.24% and a specificity of 75.20%. This in silico scheme offers promise as a first step in ranking thousands of substances as part of a prioritization approach for genotoxicity.
Collapse
Affiliation(s)
- Prachi Pradeep
- Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee, USA
- Center for Computational Toxicology and Exposure, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA
| | - Richard Judson
- Center for Computational Toxicology and Exposure, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA
| | - David M DeMarini
- Center for Computational Toxicology and Exposure, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA
| | - Nagalakshmi Keshava
- Center for Computational Toxicology and Exposure, U.S. Environmental Protection Agency, Cincinnati, Ohio, USA
| | - Todd M Martin
- Center for Computational Toxicology and Exposure, U.S. Environmental Protection Agency, Cincinnati, Ohio, USA
| | - Jeffry Dean
- Center for Public Health and Environmental Assessment, U.S. Environmental Protection Agency, Cincinnati, Ohio, USA
| | - Catherine F Gibbons
- Center for Public Health and Environmental Assessment, U.S. Environmental Protection Agency, Washington, District of Columbia, USA
| | - Anita Simha
- ORAU, contractor to U.S. Environmental Protection Agency through the National Student Services Contract, Research Triangle Park, North Carolina, USA
| | - Sarah H Warren
- Center for Computational Toxicology and Exposure, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA
| | - Maureen R Gwinn
- Center for Computational Toxicology and Exposure, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA
| | - Grace Patlewicz
- Center for Computational Toxicology and Exposure, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA
| |
Collapse
|
3
|
Smith MT, Guyton KZ, Kleinstreuer N, Borrel A, Cardenas A, Chiu WA, Felsher DW, Gibbons CF, Goodson WH, Houck KA, Kane AB, La Merrill MA, Lebrec H, Lowe L, McHale CM, Minocherhomji S, Rieswijk L, Sandy MS, Sone H, Wang A, Zhang L, Zeise L, Fielden M. The Key Characteristics of Carcinogens: Relationship to the Hallmarks of Cancer, Relevant Biomarkers, and Assays to Measure Them. Cancer Epidemiol Biomarkers Prev 2020; 29:1887-1903. [PMID: 32152214 PMCID: PMC7483401 DOI: 10.1158/1055-9965.epi-19-1346] [Citation(s) in RCA: 45] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2019] [Revised: 01/15/2020] [Accepted: 03/04/2020] [Indexed: 12/21/2022] Open
Abstract
The key characteristics (KC) of human carcinogens provide a uniform approach to evaluating mechanistic evidence in cancer hazard identification. Refinements to the approach were requested by organizations and individuals applying the KCs. We assembled an expert committee with knowledge of carcinogenesis and experience in applying the KCs in cancer hazard identification. We leveraged this expertise and examined the literature to more clearly describe each KC, identify current and emerging assays and in vivo biomarkers that can be used to measure them, and make recommendations for future assay development. We found that the KCs are clearly distinct from the Hallmarks of Cancer, that interrelationships among the KCs can be leveraged to strengthen the KC approach (and an understanding of environmental carcinogenesis), and that the KC approach is applicable to the systematic evaluation of a broad range of potential cancer hazards in vivo and in vitro We identified gaps in coverage of the KCs by current assays. Future efforts should expand the breadth, specificity, and sensitivity of validated assays and biomarkers that can measure the 10 KCs. Refinement of the KC approach will enhance and accelerate carcinogen identification, a first step in cancer prevention.See all articles in this CEBP Focus section, "Environmental Carcinogenesis: Pathways to Prevention."
Collapse
Affiliation(s)
- Martyn T Smith
- Division of Environmental Health Sciences, School of Public Health, University of California Berkeley, Berkeley, California.
| | - Kathryn Z Guyton
- Monographs Programme, International Agency for Research on Cancer, Lyon, France
| | - Nicole Kleinstreuer
- Division of Intramural Research, Biostatistics and Computational Biology Branch, National Institute of Environmental Health Sciences (NIEHS), Research Triangle Park, North Carolina
- National Toxicology Program Interagency Center for the Evaluation of Alternative Toxicological Methods, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina
| | - Alexandre Borrel
- Division of Intramural Research, Biostatistics and Computational Biology Branch, National Institute of Environmental Health Sciences (NIEHS), Research Triangle Park, North Carolina
| | - Andres Cardenas
- Division of Environmental Health Sciences, School of Public Health, University of California Berkeley, Berkeley, California
| | - Weihsueh A Chiu
- Veterinary Integrative Biosciences, Texas A&M University, College Station, Texas
| | - Dean W Felsher
- Division of Oncology, Departments of Medicine and Pathology, Stanford University School of Medicine, Stanford, California
| | - Catherine F Gibbons
- Office of Research and Development, US Environmental Protection Agency, Washington, D.C
| | - William H Goodson
- California Pacific Medical Center Research Institute, San Francisco, California
| | - Keith A Houck
- Office of Research and Development, US Environmental Protection Agency, Research Triangle Park, North Carolina
| | - Agnes B Kane
- Department of Pathology and Laboratory Medicine, Alpert Medical School, Brown University, Providence, Rhode Island
| | - Michele A La Merrill
- Department of Environmental Toxicology, University of California, Davis, California
| | - Herve Lebrec
- Comparative Biology & Safety Sciences, Amgen Research, Amgen Inc., Thousand Oaks, California
| | - Leroy Lowe
- Getting to Know Cancer, Truro, Nova Scotia, Canada
| | - Cliona M McHale
- Division of Environmental Health Sciences, School of Public Health, University of California Berkeley, Berkeley, California
| | - Sheroy Minocherhomji
- Comparative Biology & Safety Sciences, Amgen Research, Amgen Inc., Thousand Oaks, California
| | - Linda Rieswijk
- Division of Environmental Health Sciences, School of Public Health, University of California Berkeley, Berkeley, California
- Institute of Data Science, Maastricht University, Maastricht, the Netherlands
| | - Martha S Sandy
- Office of Environmental Health Hazard Assessment, California Environmental Protection Agency, Oakland, California
| | - Hideko Sone
- Yokohama University of Pharmacy and National Institute for Environmental Studies, Tsukuba Ibaraki, Japan
| | - Amy Wang
- Office of the Report on Carcinogens, Division of National Toxicology Program, The National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina
| | - Luoping Zhang
- Division of Environmental Health Sciences, School of Public Health, University of California Berkeley, Berkeley, California
| | - Lauren Zeise
- Office of Environmental Health Hazard Assessment, California Environmental Protection Agency, Oakland, California
| | - Mark Fielden
- Expansion Therapeutics Inc, San Diego, California
| |
Collapse
|
4
|
Arzuaga X, Smith MT, Gibbons CF, Skakkebæk NE, Yost EE, Beverly BEJ, Hotchkiss AK, Hauser R, Pagani RL, Schrader SM, Zeise L, Prins GS. Proposed Key Characteristics of Male Reproductive Toxicants as an Approach for Organizing and Evaluating Mechanistic Evidence in Human Health Hazard Assessments. Environ Health Perspect 2019; 127:65001. [PMID: 31199676 PMCID: PMC6792367 DOI: 10.1289/ehp5045] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2019] [Revised: 05/22/2019] [Accepted: 05/30/2019] [Indexed: 05/20/2023]
Abstract
BACKGROUND Assessing chemicals for their potential to cause male reproductive toxicity involves the evaluation of evidence obtained from experimental, epidemiological, and mechanistic studies. Although mechanistic evidence plays an important role in hazard identification and evidence integration, the process of identifying, screening and analyzing mechanistic studies and outcomes is a challenging exercise due to the diversity of research models and methods and the variety of known and proposed pathways for chemical-induced toxicity. Ten key characteristics of carcinogens provide a valuable tool for organizing and assessing chemical-specific data by potential mechanisms for cancer-causing agents. However, such an approach has not yet been developed for noncancer adverse outcomes. OBJECTIVES The objective in this study was to identify a set of key characteristics that are frequently exhibited by exogenous agents that cause male reproductive toxicity and that could be applied for identifying, organizing, and summarizing mechanistic evidence related to this outcome. DISCUSSION The identification of eight key characteristics of male reproductive toxicants was based on a survey of known male reproductive toxicants and established mechanisms and pathways of toxicity. The eight key characteristics can provide a basis for the systematic, transparent, and objective organization of mechanistic evidence relevant to chemical-induced effects on the male reproductive system. https://doi.org/10.1289/EHP5045.
Collapse
Affiliation(s)
- Xabier Arzuaga
- National Center for Environmental Assessment, U.S. Environmental Protection Agency, Washington, DC, USA
| | - Martyn T. Smith
- University of California, Berkeley, School of Public Health, Berkeley, California, USA
| | - Catherine F. Gibbons
- National Center for Environmental Assessment, U.S. Environmental Protection Agency, Washington, DC, USA
| | - Niels E. Skakkebæk
- Department of Growth and Reproduction, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
| | - Erin E. Yost
- National Center for Environmental Assessment, U.S. Environmental Protection Agency, Research Triangle Park, NC, USA
| | - Brandiese E. J. Beverly
- Office of Health Assessment and Translation, National Toxicology Program, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, NC, USA
| | - Andrew K. Hotchkiss
- National Center for Environmental Assessment, U.S. Environmental Protection Agency, Research Triangle Park, NC, USA
| | - Russ Hauser
- Harvard T.H. Chan School of Public Health, Boston, Massachusetts, USA
| | - Rodrigo L. Pagani
- Department of Urology, University of Illinois at Chicago, Chicago, Illinois, USA
| | - Steven M. Schrader
- National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, Cincinnati, Ohio, USA (retired)
| | - Lauren Zeise
- Office of Environmental Health Hazard Assessment, California Environmental Protection Agency, Sacramento, California, USA
| | - Gail S. Prins
- Department of Urology, University of Illinois at Chicago, Chicago, Illinois, USA
- School of Public Health, University of Illinois at Chicago, Chicago, Illinois, USA
| |
Collapse
|
5
|
Gibbons CF, LeBaron MJ. Applied genetic toxicology: From principles to practice. Environ Mol Mutagen 2017. [PMID: 28621032 PMCID: PMC9523595 DOI: 10.1002/em.22106] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Affiliation(s)
- Catherine F Gibbons
- Office of Research and Development, US Environmental Protection Agency, Washington, District of Columbia
| | - Matthew J LeBaron
- Toxicology & Environmental Research & Consulting, The Dow Chemical Company, Midland, Michigan
| |
Collapse
|
6
|
Smith MT, Guyton KZ, Gibbons CF, Fritz JM, Portier CJ, Rusyn I, DeMarini DM, Caldwell JC, Kavlock RJ, Lambert PF, Hecht SS, Bucher JR, Stewart BW, Baan RA, Cogliano VJ, Straif K. Key Characteristics of Carcinogens as a Basis for Organizing Data on Mechanisms of Carcinogenesis. Environ Health Perspect 2016; 124:713-21. [PMID: 26600562 PMCID: PMC4892922 DOI: 10.1289/ehp.1509912] [Citation(s) in RCA: 364] [Impact Index Per Article: 45.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/05/2015] [Accepted: 11/13/2015] [Indexed: 05/10/2023]
Abstract
BACKGROUND A recent review by the International Agency for Research on Cancer (IARC) updated the assessments of the > 100 agents classified as Group 1, carcinogenic to humans (IARC Monographs Volume 100, parts A-F). This exercise was complicated by the absence of a broadly accepted, systematic method for evaluating mechanistic data to support conclusions regarding human hazard from exposure to carcinogens. OBJECTIVES AND METHODS IARC therefore convened two workshops in which an international Working Group of experts identified 10 key characteristics, one or more of which are commonly exhibited by established human carcinogens. DISCUSSION These characteristics provide the basis for an objective approach to identifying and organizing results from pertinent mechanistic studies. The 10 characteristics are the abilities of an agent to 1) act as an electrophile either directly or after metabolic activation; 2) be genotoxic; 3) alter DNA repair or cause genomic instability; 4) induce epigenetic alterations; 5) induce oxidative stress; 6) induce chronic inflammation; 7) be immunosuppressive; 8) modulate receptor-mediated effects; 9) cause immortalization; and 10) alter cell proliferation, cell death, or nutrient supply. CONCLUSION We describe the use of the 10 key characteristics to conduct a systematic literature search focused on relevant end points and construct a graphical representation of the identified mechanistic information. Next, we use benzene and polychlorinated biphenyls as examples to illustrate how this approach may work in practice. The approach described is similar in many respects to those currently being implemented by the U.S. EPA's Integrated Risk Information System Program and the U.S. National Toxicology Program. CITATION Smith MT, Guyton KZ, Gibbons CF, Fritz JM, Portier CJ, Rusyn I, DeMarini DM, Caldwell JC, Kavlock RJ, Lambert P, Hecht SS, Bucher JR, Stewart BW, Baan R, Cogliano VJ, Straif K. 2016. Key characteristics of carcinogens as a basis for organizing data on mechanisms of carcinogenesis. Environ Health Perspect 124:713-721; http://dx.doi.org/10.1289/ehp.1509912.
Collapse
Affiliation(s)
- Martyn T. Smith
- Division of Environmental Health Sciences, School of Public Health, University of California, Berkeley, Berkeley, California, USA
| | | | - Catherine F. Gibbons
- Office of Research and Development, U.S. Environmental Protection Agency, Washington, DC, USA, and Research Triangle Park, North Carolina, USA
| | - Jason M. Fritz
- Office of Research and Development, U.S. Environmental Protection Agency, Washington, DC, USA, and Research Triangle Park, North Carolina, USA
| | | | - Ivan Rusyn
- Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, Texas, USA
| | - David M. DeMarini
- Office of Research and Development, U.S. Environmental Protection Agency, Washington, DC, USA, and Research Triangle Park, North Carolina, USA
| | - Jane C. Caldwell
- Office of Research and Development, U.S. Environmental Protection Agency, Washington, DC, USA, and Research Triangle Park, North Carolina, USA
| | - Robert J. Kavlock
- Office of Research and Development, U.S. Environmental Protection Agency, Washington, DC, USA, and Research Triangle Park, North Carolina, USA
| | - Paul F. Lambert
- McArdle Laboratory for Cancer Research, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Stephen S. Hecht
- Masonic Cancer Center, University of Minnesota, Minneapolis, Minnesota, USA
| | - John R. Bucher
- National Toxicology Program, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, North Carolina, USA
| | - Bernard W. Stewart
- Faculty of Medicine, University of New South Wales, Sydney, New South Wales, Australia
| | - Robert A. Baan
- International Agency for Research on Cancer, Lyon, France
| | - Vincent J. Cogliano
- Office of Research and Development, U.S. Environmental Protection Agency, Washington, DC, USA, and Research Triangle Park, North Carolina, USA
| | - Kurt Straif
- International Agency for Research on Cancer, Lyon, France
| |
Collapse
|
7
|
Schlosser PM, Bale AS, Gibbons CF, Wilkins A, Cooper GS. Human health effects of dichloromethane: key findings and scientific issues. Environ Health Perspect 2015; 123:114-9. [PMID: 25325283 PMCID: PMC4314245 DOI: 10.1289/ehp.1308030] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2013] [Accepted: 10/16/2014] [Indexed: 05/19/2023]
Abstract
BACKGROUND The U.S. EPA's Integrated Risk Information System (IRIS) completed an updated toxicological review of dichloromethane in November 2011. OBJECTIVES In this commentary we summarize key results and issues of this review, including exposure sources, identification of potential health effects, and updated physiologically based pharmacokinetic (PBPK) modeling. METHODS We performed a comprehensive review of primary research studies and evaluation of PBPK models. DISCUSSION Hepatotoxicity was observed in oral and inhalation exposure studies in several studies in animals; neurological effects were also identified as a potential area of concern. Dichloromethane was classified as likely to be carcinogenic in humans based primarily on evidence of carcinogenicity at two sites (liver and lung) in male and female B6C3F1 mice (inhalation exposure) and at one site (liver) in male B6C3F1 mice (drinking-water exposure). Recent epidemiologic studies of dichloromethane (seven studies of hematopoietic cancers published since 2000) provide additional data raising concerns about associations with non-Hodgkin lymphoma and multiple myeloma. Although there are gaps in the database for dichloromethane genotoxicity (i.e., DNA adduct formation and gene mutations in target tissues in vivo), the positive DNA damage assays correlated with tissue and/or species availability of functional glutathione S-transferase (GST) metabolic activity, the key activation pathway for dichloromethane-induced cancer. Innovations in the IRIS assessment include estimation of cancer risk specifically for a presumed sensitive genotype (GST-theta-1+/+), and PBPK modeling accounting for human physiological distributions based on the expected distribution for all individuals 6 months to 80 years of age. CONCLUSION The 2011 IRIS assessment of dichloromethane provides insights into the toxicity of a commonly used solvent.
Collapse
Affiliation(s)
- Paul M Schlosser
- National Center for Environmental Assessment, U.S. Environmental Protection Agency, Washington, DC, USA
| | | | | | | | | |
Collapse
|
8
|
Natarajan M, Gibbons CF, Mohan S, Moore S, Kadhim MA. Oxidative stress signalling: a potential mediator of tumour necrosis factor alpha-induced genomic instability in primary vascular endothelial cells. Br J Radiol 2007; 80 Spec No 1:S13-22. [PMID: 17704321 DOI: 10.1259/bjr/15316848] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
Studying the potential role of tumour necrosis factor (TNF)alpha in the initiation of genomic instability is necessary to understand whether TNFalpha can serve as a signalling mediator of radiation-induced genomic instability in non-irradiated bystander cells. In this study, we examined whether TNFalpha could initiate processes through oxidative stress signalling that lead to DNA damage and genomic instability in primary vascular endothelium. In these cells, low linear energy transfer (LET) radiation (0.1-2 Gy) induced the secretion of TNFalpha into the culture medium. When added ectopically, TNFalpha at concentrations ranging from 0.1 ng ml(-1) to 10 ng ml(-1) increased (twofold to threefold) intracellular oxidative stress. Next, to examine whether TNFalpha induces genetic damage, cells were treated with TNFalpha for 5 h and analysed immediately using the single cell gel electrophoresis assay or after 3 days, 12 days and 20 days using solid stain chromosomal analysis. Cells exposed to 0.1 Gy, 1 Gy or 2 Gy or treated with 100 microM H2O2 were used as positive controls. The results showed that TNFalpha as low as 0.1 ng ml(-1) could initiate increased DNA damage compared with untreated controls. When examined in the progeny cells after several generations, the chromosomal instability appeared to be carried over even after day 12 and day 20. The increased genetic damage is inhibited in cells that are pre-incubated with the antioxidant enzyme catalase, the antioxidant N-acetyl-L-cysteine or the metal chelator pyrrolidine dithiocarbamate. These results clearly indicate that TNFalpha at concentrations at which no cytotoxicity is observed could induce genetic damage through free radical generation, which could, in turn, lead to the delayed events associated with genomic instability.
Collapse
Affiliation(s)
- M Natarajan
- Department of Radiation Oncology, University of Texas Health Science Center, San Antonio, TX 78229, USA.
| | | | | | | | | |
Collapse
|
9
|
Moore SR, Ritter LE, Gibbons CF, Grosovsky AJ. Spontaneous and radiation-induced genomic instability in human cell lines differing in cellular TP53 status. Radiat Res 2005; 164:357-68. [PMID: 16187738 DOI: 10.1667/rr3422.1] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Structural chromosomal rearrangements are commonly observed in tumor karyotypes and in radiation-induced genomic instability. Here we report the effects of TP53 deficiency on karyotypic stability before and after irradiation using related cells and clones differing in cellular TP53 status. The parental cell line, TK6, is a TP53 wild-type human B-lymphoblastoid line with a highly stable karyotype. In the two TK6 derivatives used here, TP53 has been inactivated by biochemical means (expression of HPV16 E6; TK6-5E) or genetic means (allelic inactivation; NH32). Biochemical inactivation of TP53 (TK6-5E) had little effect on the spontaneous karyotype, whereas allelic inactivation of TP53 (NH32) resulted in a modest increase in spontaneous karyotypic instability. After 2 Gy gamma irradiation, the number of unstable clones derived from TP53-deficient cells was significantly elevated compared to the TP53 wild-type counterpart. Extensively destabilized clones were common after irradiation in the set of clones derived from NH32 cells, and one was observed in the set of TK6-5E clones; however, they were never observed in TK6-derived clones. In two of the irradiated NH32 clones, whole chromosomes or chromosome bands were preferentially involved in alterations. These results suggest that genomic instability may differ both quantitatively and qualitatively as a consequence of altered TP53 expression. Some of the results showing repeated and preferential chromosome involvement in aberrations support a model in which instability may be driven by cis mechanisms.
Collapse
Affiliation(s)
- Stephen R Moore
- Department of Cell Biology and Neuroscience, and Environmental Toxicology Graduate Program, University of California, Riverside, California 92521, USA
| | | | | | | |
Collapse
|