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Möller C, Virzi J, Chang YJ, Keidel A, Chao MR, Hu CW, Cooke MS. DNA modifications: Biomarkers for the exposome? ENVIRONMENTAL TOXICOLOGY AND PHARMACOLOGY 2024; 108:104449. [PMID: 38636743 DOI: 10.1016/j.etap.2024.104449] [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: 02/12/2024] [Revised: 03/25/2024] [Accepted: 04/12/2024] [Indexed: 04/20/2024]
Abstract
The concept of the exposome is the encompassing of all the environmental exposures, both exogenous and endogenous, across the life course. Many, if not all, of these exposures can result in the generation of reactive species, and/or the modulation of cellular processes, that can lead to a breadth of modifications of DNA, the nature of which may be used to infer their origin. Because of their role in cell function, such modifications have been associated with various major human diseases, including cancer, and so their assessment is crucial. Historically, most methods have been able to only measure one or a few DNA modifications at a time, limiting the information available. With the development of DNA adductomics, which aims to determine the totality of DNA modifications, a far more comprehensive picture of the DNA adduct burden can be gained. Importantly, DNA adductomics can facilitate a "top-down" investigative approach whereby patterns of adducts may be used to trace and identify the originating exposure source. This, together with other 'omic approaches, represents a major tool for unraveling the complexities of the exposome and hence allow a better a understanding of the environmental origins of disease.
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Affiliation(s)
- Carolina Möller
- Oxidative Stress Group, Department of Molecular Biosciences, University of South Florida, Tampa, FL 33620, USA.
| | - Jazmine Virzi
- Oxidative Stress Group, Department of Molecular Biosciences, University of South Florida, Tampa, FL 33620, USA
| | - Yuan-Jhe Chang
- Department of Occupational Safety and Health, Chung Shan Medical University, Taichung 402, Taiwan
| | - Alexandra Keidel
- Oxidative Stress Group, Department of Molecular Biosciences, University of South Florida, Tampa, FL 33620, USA
| | - Mu-Rong Chao
- Department of Occupational Safety and Health, Chung Shan Medical University, Taichung 402, Taiwan; Department of Occupational Medicine, Chung Shan Medical University Hospital, Taichung 402, Taiwan
| | - Chiung-Wen Hu
- Department of Public Health, Chung Shan Medical University, Taichung 402, Taiwan
| | - Marcus S Cooke
- Oxidative Stress Group, Department of Molecular Biosciences, University of South Florida, Tampa, FL 33620, USA; College of Public Health, University of South Florida, Tampa, FL 33620, USA; Cancer Biology and Evolution Program, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL 33612, USA.
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Lynch HN, Kozal JS, Russell AJ, Thompson WJ, Divis HR, Freid RD, Calabrese EJ, Mundt KA. Systematic review of the scientific evidence on ethylene oxide as a human carcinogen. Chem Biol Interact 2022; 364:110031. [PMID: 35779612 DOI: 10.1016/j.cbi.2022.110031] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2022] [Revised: 06/16/2022] [Accepted: 06/24/2022] [Indexed: 11/25/2022]
Abstract
Ethylene oxide is a highly reactive chemical primarily used as an intermediate in chemical production and as a sterilant of medical equipment and food products; it also is produced endogenously as a result of physiological processes. We conducted a systematic review of the potential carcinogenicity of inhaled ethylene oxide in humans using methods that adhere to PRIMSA guidelines and that incorporate aspects from the Institute of Medicine (IOM) (now the National Academy of Medicine) as well as several US Environmental Protection Agency (EPA) frameworks for systematic reviews. After a comprehensive literature search and selection process, study quality was evaluated following a method adapted from the EPA Toxic Substances Control Act (TSCA) framework. The literature screening and selection process identified 24 primary studies in animals or humans and more than 50 mechanistic studies. Integrating epidemiological, animal, and mechanistic literature on ethylene oxide and cancer according to the IOM framework yielded classifications of suggestive evidence of no association between ethylene oxide and stomach cancer, breast cancer and lymphohematopoietic malignancies at human relevant exposures. However, we acknowledge that there is additional uncertainty in the classification for lymphohematopoietic malignancies owing to a paucity of evidence for specific types of these tumors, each of which is a distinct disease entity of possibly unique etiology.
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Affiliation(s)
| | | | | | | | | | | | | | - Kenneth A Mundt
- Cardno ChemRisk, Boston, MA, USA; University of Massachusetts, Amherst, MA, USA
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Vincent MJ, Kozal JS, Thompson WJ, Maier A, Dotson GS, Best EA, Mundt KA. Ethylene Oxide: Cancer Evidence Integration and Dose-Response Implications. Dose Response 2019; 17:1559325819888317. [PMID: 31853235 PMCID: PMC6906442 DOI: 10.1177/1559325819888317] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2019] [Revised: 10/11/2019] [Accepted: 10/15/2019] [Indexed: 11/16/2022] Open
Abstract
The International Agency for Research on Cancer (IARC) and the United States
Environmental Protection Agency (USEPA) classified ethylene oxide (EtO) as a
known human carcinogen. Critically, both noted that the epidemiological evidence
based on lymphoid and breast cancers was “limited,” but that the evidence in
animal studies was “sufficient” and “extensive” (respectively) and that EtO is
genotoxic. The USEPA derived one of the highest published inhalation unit risk
(IUR) values (3 × 10−3 per [µg/m3 EtO]), based on results
from 2 epidemiological studies. We performed focused reviews of the
epidemiological and toxicological evidence on the carcinogenicity of EtO and
considered the USEPA’s reliance on a genotoxic mode of action to establish EtO’s
carcinogenicity and to determine likely dose–response patterns. Higher quality
epidemiological studies demonstrated no increased risk of breast cancers or
lymphohematopoietic malignancies (LHM). Similarly, toxicological studies and
studies of early effect biomarkers in animals and humans provided no strong
indication that EtO causes LHM or mammary cancers. Ultimately, animal data are
inadequate to define the actual dose–response shape or predict tumor response at
very low doses with any confidence. We conclude that the IARC and USEPA
classification of EtO as a known human carcinogen overstates the underlying
evidence and that the IUR derived by USEPA grossly overestimates risk.
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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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Filser JG, Klein D. A physiologically based toxicokinetic model for inhaled ethylene and ethylene oxide in mouse, rat, and human. Toxicol Lett 2018; 286:54-79. [DOI: 10.1016/j.toxlet.2017.07.896] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2017] [Revised: 07/20/2017] [Accepted: 07/25/2017] [Indexed: 01/18/2023]
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Kirman C, Hays S. Derivation of endogenous equivalent values to support risk assessment and risk management decisions for an endogenous carcinogen: Ethylene oxide. Regul Toxicol Pharmacol 2017; 91:165-172. [DOI: 10.1016/j.yrtph.2017.10.032] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2016] [Revised: 09/08/2017] [Accepted: 10/26/2017] [Indexed: 01/26/2023]
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Liu S, Wang Y. Mass spectrometry for the assessment of the occurrence and biological consequences of DNA adducts. Chem Soc Rev 2015; 44:7829-54. [PMID: 26204249 PMCID: PMC4787602 DOI: 10.1039/c5cs00316d] [Citation(s) in RCA: 98] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Exogenous and endogenous sources of chemical species can react, directly or after metabolic activation, with DNA to yield DNA adducts. If not repaired, DNA adducts may compromise cellular functions by blocking DNA replication and/or inducing mutations. Unambiguous identification of the structures and accurate measurements of the levels of DNA adducts in cellular and tissue DNA constitute the first and important step towards understanding the biological consequences of these adducts. The advances in mass spectrometry (MS) instrumentation in the past 2-3 decades have rendered MS an important tool for structure elucidation, quantification, and revelation of the biological consequences of DNA adducts. In this review, we summarized the development of MS techniques on these fronts for DNA adduct analysis. We placed our emphasis of discussion on sample preparation, the combination of MS with gas chromatography- or liquid chromatography (LC)-based separation techniques for the quantitative measurement of DNA adducts, and the use of LC-MS along with molecular biology tools for understanding the human health consequences of DNA adducts. The applications of mass spectrometry-based DNA adduct analysis for predicting the therapeutic outcome of anti-cancer agents, for monitoring the human exposure to endogenous and environmental genotoxic agents, and for DNA repair studies were also discussed.
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Affiliation(s)
- Shuo Liu
- Environmental Toxicology Graduate Program, University of California, Riverside, California, USA
| | - Yinsheng Wang
- Environmental Toxicology Graduate Program, University of California, Riverside, California, USA and Department of Chemistry, University of California, Riverside, CA 92521-0403, USA.
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8
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Zhang F, Bartels MJ, LeBaron MJ, Schisler MR, Jeong YC, Gollapudi BB, Moore NP. LC–MS/MS simultaneous quantitation of 2-hydroxyethylated, oxidative, and unmodified DNA nucleosides in DNA isolated from tissues of mice after exposure to ethylene oxide. J Chromatogr B Analyt Technol Biomed Life Sci 2015; 976-977:33-48. [DOI: 10.1016/j.jchromb.2014.10.042] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2014] [Revised: 10/21/2014] [Accepted: 10/29/2014] [Indexed: 11/28/2022]
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Gavina JMA, Yao C, Feng YL. Recent developments in DNA adduct analysis by mass spectrometry: a tool for exposure biomonitoring and identification of hazard for environmental pollutants. Talanta 2014; 130:475-94. [PMID: 25159438 DOI: 10.1016/j.talanta.2014.06.050] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2014] [Revised: 06/19/2014] [Accepted: 06/22/2014] [Indexed: 02/08/2023]
Abstract
DNA adducts represent an important category of biomarkers for detection and exposure surveillance of potential carcinogenic and genotoxic chemicals in the environment. Sensitive and specific analytical methods are required to detect and differentiate low levels of adducts from native DNA from in vivo exposure. In addition to biomonitoring of environmental pollutants, analytical methods have been developed for structural identification of adducts which provides fundamental information for determining the toxic pathway of hazardous chemicals. In order to achieve the required sensitivity, mass spectrometry has been increasingly utilized to quantify adducts at low levels as well as to obtain structural information. Furthermore, separation techniques such as chromatography and capillary electrophoresis can be coupled to mass spectrometry to increase the selectivity. This review will provide an overview of advances in detection of adducted and modified DNA by mass spectrometry with a focus on the analysis of nucleosides since 2007. Instrument advances, sample and instrument considerations, and recent applications will be summarized in the context of hazard assessment. Finally, advances in biomonitoring applying mass spectrometry will be highlighted. Most importantly, the usefulness of DNA adducts measurement and detection will be comprehensively discussed as a tool for assessment of in vitro and in vivo exposure to environmental pollutants.
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Affiliation(s)
- Jennilee M A Gavina
- Exposure and Biomonitoring Division, Environmental Health Science and Research Bureau, Environmental and Radiation Health Sciences Directorate, Healthy Environments and Consumer Safety Branch, Health Canada, 50 Columbine Driveway, AL: 0800C, Ottawa, Ontario, Canada K1A 0K9
| | - Chunhe Yao
- Exposure and Biomonitoring Division, Environmental Health Science and Research Bureau, Environmental and Radiation Health Sciences Directorate, Healthy Environments and Consumer Safety Branch, Health Canada, 50 Columbine Driveway, AL: 0800C, Ottawa, Ontario, Canada K1A 0K9
| | - Yong-Lai Feng
- Exposure and Biomonitoring Division, Environmental Health Science and Research Bureau, Environmental and Radiation Health Sciences Directorate, Healthy Environments and Consumer Safety Branch, Health Canada, 50 Columbine Driveway, AL: 0800C, Ottawa, Ontario, Canada K1A 0K9.
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Nagy K, Ádány R, Szűcs S, Ádám B. Susceptibility of lung epithelial cells to alkylating genotoxic insult. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2013; 54:682-689. [PMID: 23907938 DOI: 10.1002/em.21800] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2012] [Revised: 06/04/2013] [Accepted: 06/04/2013] [Indexed: 06/02/2023]
Abstract
Alkylation is one of the most common types of DNA damage that can lead to mutations and cancer. Lung is the primary target organ of airborne alkylators such as ethylene oxide (EO). However, the ability of EO to cause lung cancer has not been clearly demonstrated yet. The aim of this study was to investigate the susceptibility of lung cells to alkylating DNA insult by detecting EO-mediated DNA damage with the alkaline comet assay in human lung epithelial cells, peripheral blood lymphocytes, and keratinocytes. The susceptibility of these cell types toward the alkylating insult induced by EO was compared against the oxidative DNA insult induced by hydrogen peroxide (H2 O2 ). Due to the volatility of EO, its active concentrations were monitored by gas chromatography during exposure and were found to decrease significantly in a time-dependent manner. EO induced a statistically significant genotoxic effect at the lowest concentration used (16.4 µM) in lung epithelial cells and in lymphocytes, while in keratinocytes, a genotoxic effect was not detected until 55.5 µM EO. However, lung epithelial cells demonstrated increased resistance to oxidative insult. In fact, oxidative DNA damage detectable by endonuclease treatment was minimal in lung cells compared with the other cell types. These results suggest an increased sensitivity of lung epithelial cells toward the alkylating effects of EO, which was not observed for oxidative DNA damage. Our findings point out the importance of DNA alkylation and the possible role of EO on the induction of lung cancer.
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Affiliation(s)
- Károly Nagy
- Department of Preventive Medicine, Faculty of Public Health, Medical and Health Science Center, University of Debrecen, Debrecen, Hungary
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11
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Affiliation(s)
- Natalia Tretyakova
- Department of Medicinal Chemistry, University of Minnesota, Minneapolis, Minnesota 55455, USA.
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Wu KY, Chiang SY, Shih WC, Huang CCJ, Chen MF, Swenberg JA. The application of mass spectrometry in molecular dosimetry: ethylene oxide as an example. MASS SPECTROMETRY REVIEWS 2011; 30:733-756. [PMID: 21328599 DOI: 10.1002/mas.20299] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Mass spectrometry plays an increasingly important role in the search for and quantification of novel chemically specific biomarkers. The revolutionary advances in mass spectrometry instrumentation and technology empower scientists to specifically analyze DNA and protein adducts, considered as molecular dosimeters, derived from reactions of a carcinogen or its active metabolites with DNA or protein. Analysis of the adducted DNA bases and proteins can elucidate the chemically reactive species of carcinogens in humans and can serve as risk-associated biomarkers for early prediction of cancer risk. In this article, we review and compare the specificity, sensitivity, resolution, and ease-of-use of mass spectrometry methods developed to analyze ethylene oxide (EO)-induced DNA and protein adducts, particularly N7-(2-hydroxyethyl)guanine (N7-HEG) and N-(2-hydroxyethyl)valine (HEV), in human samples and in animal tissues. GC/ECNCI-MS analysis after HPLC cleanup is the most sensitive method for quantification of N7-HEG, but limited by the tedious sample preparation procedures. Excellent sensitivity and specificity in analysis of N7-HEG can be achieved by LC/MS/MS analysis if the mobile phase, the inlet (split or splitless), and the collision energy are properly optimized. GC/ECNCI-HRMS and GC/ECNCI-MS/MS analysis of HEV achieves the best performance as compared with GC/ECNCI-MS and GC/EI-MS. In conclusion, future improvements in high-throughput capabilities, detection sensitivity, and resolution of mass spectrometry will attract more scientists to identify and/or quantify novel molecular dosimeters or profiles of these biomarkers in toxicological and/or epidemiological studies.
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Affiliation(s)
- Kuen-Yuh Wu
- Institute of Occupational Medicine and Industrial Hygiene, College of Public Health, National Taiwan University, Taipei, Taiwan.
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Cancer incidence and mortality in Swedish sterilant workers exposed to ethylene oxide: updated cohort study findings 1972-2006. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2011; 8:2009-19. [PMID: 21776215 PMCID: PMC3138010 DOI: 10.3390/ijerph8062009] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 05/04/2011] [Accepted: 05/28/2011] [Indexed: 11/26/2022]
Abstract
Objectives: To assess whether cancer incidence, mainly from lymphohaematopoietic tumours and breast cancer, and mortality were increased in a cohort of Swedish sterilant workers exposed to low levels of ethylene oxide (EtO), updated with 16 more years of follow up. Methods: The mortality and cancer incidence 1972–2006 experienced by a cohort of 2,171 male and female workers employed for at least one year in two plants producing medical equipment sterilised with EtO were investigated. Individual cumulative exposure to EtO was assessed by occupational hygienists. Cause-specific standardized rate ratios were calculated using the regional general population as a comparison for mortality (SMR) and cancer incidence (SIR). Internal Poisson-regression analyses were performed for selected causes. Results: The median cumulative exposure to EtO was 0.13 ppm-years. The overall cancer incidence was close to unity (SIR 0.94, 95% CI 0.82–1.08). Eighteen cases of lymphohaematopoietic cancer were observed (SIR 1.25, 95% CI 0.74–1.98). A healthy worker effect was indicated from a significantly decreased overall mortality and mortality from cardiovascular diseases. Internal analyses found significantly increased rate ratios for breast cancer for the two upper quartiles of cumulative exposure as compared to the lowest 50% of the cohort (IRR 2.76, 95% CI 1.20–6.33 and IRR 3.55, 95% CI 1.58–7.93). Conclusions: The findings from this updated study indicate limited or low risks for human cancer due to occupational exposure from ethylene oxide at the low cumulative exposure levels in this cohort. However a positive exposure-response relation with breast cancer was observed though.
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Comparative analysis of urinary N7-(2-hydroxyethyl)guanine for ethylene oxide- and non-exposed workers. Toxicol Lett 2011; 202:237-43. [DOI: 10.1016/j.toxlet.2011.02.009] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2010] [Revised: 02/17/2011] [Accepted: 02/17/2011] [Indexed: 11/19/2022]
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The formation and biological significance of N7-guanine adducts. Mutat Res 2009; 678:76-94. [PMID: 19465146 DOI: 10.1016/j.mrgentox.2009.05.006] [Citation(s) in RCA: 160] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2009] [Accepted: 05/13/2009] [Indexed: 11/24/2022]
Abstract
DNA alkylation or adduct formation occurs at nucleophilic sites in DNA, mainly the N7-position of guanine. Ever since identification of the first N7-guanine adduct, several hundred studies on DNA adducts have been reported. Major issues addressed include the relationships between N7-guanine adducts and exposure, mutagenesis, and other biological endpoints. It became quickly apparent that N7-guanine adducts are frequently formed, but may have minimal biological relevance, since they are chemically unstable and do not participate in Watson Crick base pairing. However, N7-guanine adducts have been shown to be excellent biomarkers for internal exposure to direct acting and metabolically activated carcinogens. Questions arise, however, regarding the biological significance of N7-guanine adducts that are readily formed, do not persist, and are not likely to be mutagenic. Thus, we set out to review the current literature to evaluate their formation and the mechanistic evidence for the involvement of N7-guanine adducts in mutagenesis or other biological processes. It was concluded that there is insufficient evidence that N7-guanine adducts can be used beyond confirmation of exposure to the target tissue and demonstration of the molecular dose. There is little to no evidence that N7-guanine adducts or their depurination product, apurinic sites, are the cause of mutations in cells and tissues, since increases in AP sites have not been shown unless toxicity is extant. However, more research is needed to define the extent of chemical depurination versus removal by DNA repair proteins. Interestingly, N7-guanine adducts are clearly present as endogenous background adducts and the endogenous background amounts appear to increase with age. Furthermore, the N7-guanine adducts have been shown to convert to ring opened lesions (FAPy), which are much more persistent and have higher mutagenic potency. Studies in humans are limited in sample size and differences between controls and study groups are small. Future investigations should involve human studies with larger numbers of individuals and analysis should include the corresponding ring opened FAPy derivatives.
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Marsden DA, Jones DJL, Britton RG, Ognibene T, Ubick E, Johnson GE, Farmer PB, Brown K. Dose-response relationships for N7-(2-hydroxyethyl)guanine induced by low-dose [14C]ethylene oxide: evidence for a novel mechanism of endogenous adduct formation. Cancer Res 2009; 69:3052-9. [PMID: 19276345 DOI: 10.1158/0008-5472.can-08-4233] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Ethylene oxide (EO) is widely used in the chemical industry and is also formed in humans through the metabolic oxidation of ethylene, generated during physiologic processes. EO is classified as a human carcinogen and is a direct acting alkylating agent, primarily forming N7-(2-hydroxyethyl)guanine (N7-HEG). To conduct accurate human risk assessments, it is vital to ascertain the relative contribution of endogenously versus exogenously derived DNA damage and identify the sources of background lesions. We have therefore defined in vivo dose-response relationships over a concentration range relevant to human EO exposures using a dual-isotope approach. By combining liquid chromatography-tandem mass spectrometry and high-performance liquid chromatography-accelerator mass spectrometry analysis, both the endogenous and exogenous N7-HEG adducts were quantified in tissues of [(14)C]EO-treated rats. Levels of [(14)C]N7-HEG induced in spleen, liver, and stomach DNA increased in a linear manner from 0.002 to 4 adducts/10(8) nucleotides. More importantly, the extent of damage arising through this route was insignificant compared with the background abundance of N7-HEG naturally present. However, at the two highest doses, [(14)C]EO exposure caused a significant increase in endogenous N7-HEG formation in liver and spleen, suggesting that EO can induce physiologic pathways responsible for ethylene generation in vivo and thereby indirectly promote N7-HEG production. We present evidence for a novel mechanism of adduct formation to explain this phenomenon, involving oxidative stress and 1-aminocyclopropane-1-carboxylic acid as a potential biosynthetic precursor to ethylene in mammalian cells. Based on the proposed pathway, N7-HEG may have potential as a biomarker of cellular oxidative stress.
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Affiliation(s)
- Debbie A Marsden
- Department of Cancer Studies and Molecular Medicine, University of Leicester, Leicester, United Kingdom
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