In vivo genotoxicity testing strategies: Report from the 7th International workshop on genotoxicity testing (IWGT)

Kirkland, David; Uno, Yoshifumi; Luijten, Mirjam; Beevers, Carol; Benthem, Jan van; Burlinson, Brian; Dertinger, Stephen D.; Douglas, George R.; Hamada, Shuichi; Horibata, Katsuyoshi; Lovell, David P.; Manjanatha, Mugimane G.; Martus, Hans-Joerg; Mei, Nan; Morita, Takeshi; Ohyama, Wakako; Williams, Andrew

doi:10.1016/j.mrgentox.2019.03.008

Cited by 39 publications

(33 citation statements)

References 109 publications

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“…The GIT MN assay appeared to be useful for the site‐specific analysis of micronuclei induction and some evaluation of the sensitivity and specificity was possible, based on a very limited number of substances. However, more substances would need to be tested to draw firm conclusions and the IWGT Working Group concluded that more work is required for an OECD guideline (Kirkland et al., 2019 ).…”

Section: In Vivo Follow‐up Of In Vitro Aneugensmentioning

confidence: 99%

“…The SC noted that at present further development and validation of the MN test in the GIT is required before it can be recommended as routine test in the follow‐up of substances that are aneugenic in vitro . However, data generated by applying the MN test in the GIT (stomach and colon) will be considered by EFSA and evaluated case by case as supporting evidence when obtained using appropriate dosing period and dose levels (Kirkland et al., 2019 ) in the comprehensive evaluation of all data to assess the in vivo aneugenic hazard.…”

Section: In Vivo Follow‐up Of In Vitro Aneugensmentioning

confidence: 99%

“…MN analysis has the potential to be integrated into repeat‐dose toxicity studies (Hayashi, 2016 ; Kirkland et al., 2019 ), providing that the highest dose applied be consistent with the requirements of the OECD TG for the mammalian erythrocyte MN assay (OECD TG 474) and/or ICH criteria. The major advantages of incorporating the MN analysis into conventional repeat‐dose toxicity studies are the reduction in the number of animals used, saving time and the possibility to use general toxicology observations for the interpretation of genotoxicity results.…”

Section: In Vivo Follow‐up Of In Vitro Aneugensmentioning

confidence: 99%

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Guidance on aneugenicity assessment

More¹,

Bampidis²,

Bragard³

et al. 2021

EFS2

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The EFSA Scientific Committee was asked to provide guidance on the most appropriate in vivo tests to follow up on positive in vitro results for aneugenicity, and on the approach to risk assessment for substances that are aneugenic but not clastogenic nor causing gene mutations. The Scientific Committee confirmed that the preferred approach is to perform an in vivo mammalian erythrocyte micronucleus test with a relevant route of administration. If this is positive, it demonstrates that the substance is aneugenic in vivo . A negative result with evidence that the bone marrow is exposed to the test substance supports a conclusion that aneugenic activity is not expressed in vivo . If there is no evidence of exposure to the bone marrow, a negative result is viewed as inconclusive and further studies are required. The liver micronucleus assay, even though not yet fully validated, can provide supporting information for substances that are aneugenic following metabolic activation. The gastrointestinal micronucleus test, conversely, to be further developed, may help to assess aneugenic potential at the initial site of contact for substances that are aneugenic in vitro without metabolic activation. Based on the evidence in relation to mechanisms of aneugenicity, the Scientific Committee concluded that, in principle, health‐based guidance values can be established for substances that are aneugenic but not clastogenic nor causing gene mutations, provided that a comprehensive toxicological database is available. For situations in which the toxicological database is not sufficient to establish health‐based guidance values, some approaches to risk assessment are proposed. The Scientific Committee recommends further development of the gastrointestinal micronucleus test, and research to improve the understanding of aneugenicity to support risk assessment.

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Section: In Vivo Follow‐up Of In Vitro Aneugensmentioning

confidence: 99%

Section: In Vivo Follow‐up Of In Vitro Aneugensmentioning

confidence: 99%

Section: In Vivo Follow‐up Of In Vitro Aneugensmentioning

confidence: 99%

See 1 more Smart Citation

Guidance on aneugenicity assessment

More¹,

Bampidis²,

Bragard³

et al. 2021

EFS2

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“…Although the Comet is only an indicator assay for DNA damage (i.e., identified alterations may be repaired) and is not definitive for characterizing mutagenicity, findings from recent publications (Kirkland, Levy, et al, 2019; Kirkland, Uno, et al, 2019) demonstrated a strong correlation of results for a given chemical in the Comet vs. transgenic rodent assay in the liver and gastrointestinal tract but not bone marrow, using an admittedly biased dataset of genotoxic and/or mutagenic chemicals.…”

Section: Discussionmentioning

confidence: 99%

Investigation of potential early key events and mode of action for 1,2‐dichloroethane‐induced mammary tumors in female rats

LeBaron

Hotchkiss

Zhang

et al. 2020

J of Applied Toxicology

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1,2‐dichloroethane (DCE or EDC) is a chlorinated hydrocarbon used as a chemical intermediate, including in the synthesis of polyvinyl chloride. Although DCE has induced tumors in both rats and mice, the overall weight‐of‐evidence suggests a lack of in vivo mutagenicity. The present study was conducted to explore a potential mode of action further for tumor formation in rat mammary tissue. Fischer 344 rats were exposed to target concentrations of 0 or 200 ppm of DCE vapors (6 hours/day, 7 days/week) for at least 28 days; 200 ppm represents a concentration of ~20% higher than that reported to induce mammary tumors. Endpoints examined included DNA damage (via Comet assay), glutathione (reduced, oxidized and conjugated), tissue DNA adducts, cell proliferation and serum prolactin levels. Exposure to DCE did not alter serum prolactin levels with consistent estrous stage, did not cause cell proliferation in mammary epithelial cells, nor result in histopathological alterations in the mammary gland. DNA adducts were identified, including the N7‐guanylethyl glutathione adduct, with higher adduct levels measured in liver (nontumorigenic target) compared with mammary tissue isolated from the same rats; no known mutagenic adducts were identified. DCE did not increase the Comet assay response in mammary epithelial cells, whereas DNA damage in the positive control (N‐nitroso‐N‐methylurea) was significantly increased. Although the result of this study did not identify a specific mode of action for DCE‐induced mammary tumors in rats, the lack of any exposure‐related genotoxic responses further contributes to the weight‐of‐evidence suggesting that DCE is a nongenotoxic carcinogen.

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“…In addition to the aforementioned duodenal MN assays, blood MN assays are generally negative for Cr(VI), captan, and folpet (Arce et al 2010, and. Recent recommendations by the International Working Group on Genotoxicity Testing concluded that the TGR and comet assays were essentially equivalent for detecting genotoxicity when one of these studies were coupled with an in vivo MN assay (Kirkland et al 2019). In addition, they noted that the TGR assay was preferable for MOA investigation, especially when conducted in target tissues.…”

Section: Efsa and Oecd)mentioning

confidence: 99%

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

Bhat

Cohen

Gordon³

et al. 2020

Critical Reviews in Toxicology

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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 10 11 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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In vivo genotoxicity testing strategies: Report from the 7th International workshop on genotoxicity testing (IWGT)

Cited by 39 publications

References 109 publications

Guidance on aneugenicity assessment

Guidance on aneugenicity assessment

Investigation of potential early key events and mode of action for 1,2‐dichloroethane‐induced mammary tumors in female rats

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

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