Michelle E Bishop, Audrey M Sims, Sharon K Guerrero, Kamela Mitchell, Nan Mei, Hannah Xu, Naomi L Kruhlak, Sruthi T King, Robert T Dorsam, Aisar H Atrakchi, Timothy J McGovern, Robert H Heflich
{"title":"Adjusting the Preincubation Conditions to Enhance the Ames Test for Detecting the Mutagenicity of N-Nitrosamines.","authors":"Michelle E Bishop, Audrey M Sims, Sharon K Guerrero, Kamela Mitchell, Nan Mei, Hannah Xu, Naomi L Kruhlak, Sruthi T King, Robert T Dorsam, Aisar H Atrakchi, Timothy J McGovern, Robert H Heflich","doi":"10.1002/em.70041","DOIUrl":"10.1002/em.70041","url":null,"abstract":"<p><p>Conducting S9-mediated preincubations at slightly acid pHs (e.g., pH 5.0 to pH 6.5) has been reported to enhance the mutagenicity of small-molecule nitrosamines in the Ames test. In this study, we have evaluated the effect of adjusting the preincubation mix used in the Enhanced Ames Test (EAT) from pH 7.4 to pH 6.0 and supplying the activation mix with preformed reducing equivalents (NADPH and NADH). Abbreviated EAT assays were conducted on five small-molecule N-nitrosamines and 10 nitrosamine drug substance-related impurities (NDSRIs) with tester strains TA1535 and WP2 uvrA (pKM101) and using S9 mixes containing 30% hamster liver S9. Testing on small-molecule nitrosamines found that the pH 6.0 preincubation mix enhanced the mutagenicity of N-nitroso-dimethylamine and N-nitroso-diethylamine but not N-nitroso-diphenylamine, N-nitroso-methyl-4-aminobutyric acid or N-(2,2-diethoxyethyl)-2,2-diethoxy-N-nitrosoethanamine. Of the 10 NDSRIs that were tested, N-nitroso-phenylephrine was consistently positive with the pH 6.0 preincubation mix, while it was generally negative with pH 7.4 preincubation mixes. The mutagenicity of the nine other NDSRIs that were tested was not changed by the slightly acid preincubation mix. The results indicate that performing preincubation reactions under slightly acid conditions increases the mutagenicity of some small-molecule nitrosamines, and in one case, produced a positive mutagenic response with an NDSRI that was otherwise negative in the EAT.</p>","PeriodicalId":11791,"journal":{"name":"Environmental and Molecular Mutagenesis","volume":"67 3","pages":"e70041"},"PeriodicalIF":2.7,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13102042/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147766180","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Vitamin C Regulates Redox Homeostasis and Mitigates Potassium Bromate-Induced Oxidative Injury to Rat Intestine.","authors":"Saima Nazir, Mir Kaisar Ahmad, Zubair-Ul-Nazir","doi":"10.1002/em.70045","DOIUrl":"10.1002/em.70045","url":null,"abstract":"<p><p>Potassium bromate (KBrO<sub>3</sub>), a probable human carcinogen, is generated as a disinfection by-product during ozonation of water and is also used as a flour maturing agent. It has been shown to induce oxidative damage and subsequent tissue-toxicity in individuals who get exposed to it. Previously, we have reported that KBrO<sub>3</sub> induces oxidative stress and subsequent intestinal toxicity, as is evident from DNA damage and the histological studies. In the present study, the protective efficacy of dietary antioxidant vitamin C on KBrO<sub>3</sub>-induced intestinal toxicity has been explored. Administration of KBrO<sub>3</sub> led to a decrease (almost 1.5 fold) in the brush border membrane enzymatic activities. The oxidative reductive homeostasis of the intestine was greatly affected, as reflected by the severe alterations in the antioxidant enzymatic system, besides altering the carbohydrate metabolism too. There was also an increase in DNA damage (+1.5 fold) and DNA-protein cross-linking (+2 fold). However, pretreatment with vitamin C resulted in significant attenuation/modulation in all these parameters. The biochemical studies were supported by the histological studies showing extensive intestinal damage in KBrO<sub>3</sub>-treated animals and greatly reduced tissue injury in the vitamin C + KBrO<sub>3</sub> group. These results show that vitamin C mitigates bromate-induced intestinal toxic insult and oxidative damage by improving antioxidant defense, tissue integrity, and energy metabolism and thus can be used as a therapeutic/protective agent against bromate and its related compounds.</p>","PeriodicalId":11791,"journal":{"name":"Environmental and Molecular Mutagenesis","volume":"67 3","pages":"e70045"},"PeriodicalIF":2.7,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147766195","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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