Safety Assessment, AstraZeneca R&D, Alderley Park, Macclesfield, Cheshire SK10 4TG, UK.
Toxicology. 2011 Dec 18;290(2-3):249-57. doi: 10.1016/j.tox.2011.10.002. Epub 2011 Oct 12.
The genotoxicity of methapyrilne (MP) has been evaluated in a number of assays since it was found to be a rat hepatocarcinogen with subsequent withdrawal as an over-the-counter antihistamine. Whilst it has not been classified as a genotoxin, there are reports of positive findings from mammalian cell gene mutation and transformation assays. To investigate further the genotoxic potential of MP, the alkaline Comet assay was used to evaluate DNA damage both in primary hepatocytes in culture and in vivo in the rat. To confirm bioactivation was required to induce the hepatotoxic mechanism, aminobenzotriazole, a broad spectrum cytochrome P450 enzyme inhibitor was used as a pre-treatment. The levels of glutathione and glutathione disulfide were determined in both hepatocytes in culture and in the liver following in vivo exposure. MP showed significant increases in DNA damage in freshly isolated male rat hepatocyte suspensions that could be significantly reduced by pre-incubation of aminobenzotriazole (ABT). DNA damage showed a marked sex difference, with male hepatocytes being more susceptible, and showing a concurrent depletion of glutathione (GSH) compared with female hepatocytes. Modulation of the GSH levels by diethylmaleate and γ-glutamylcysteinylethyl ester, elevated and reduced the levels of DNA damage, respectively. In the in vivo Comet assay, there was no evidence of DNA damage following MP (150mg/kg p.o) treatment for three consecutive days, although histological and liver enzyme changes were seen. Total protein GSH content was elevated in MP-treated animals and superoxide dismutase levels were increased specifically in periportal regions. Taken together, these data support the potential for MP to induce oxidative stress. The differences in DNA damage detected by the Comet assay in vitro, and in rat liver in vivo, could be attributed to differences in metabolism and response to oxidant insult or the inability of the assay to discriminate damage in a small number of individual cells in the whole liver.
甲吡戊胺的遗传毒性已在多项检测中进行了评估，因为它被发现是一种大鼠肝癌致癌物，随后被撤出非处方抗组胺药。虽然它没有被归类为遗传毒物，但有报道称哺乳动物细胞基因突变和转化检测呈阳性结果。为了进一步研究甲吡戊胺的遗传毒性潜力，使用碱性彗星试验评估了培养的原代肝细胞和大鼠体内的 DNA 损伤。为了确认生物激活是诱导肝毒性机制所必需的，使用了氨基苯并三唑，一种广泛的细胞色素 P450 酶抑制剂作为预处理。在体内暴露后，分别在培养的肝细胞和肝脏中测定了谷胱甘肽和谷胱甘肽二硫化物的水平。甲吡戊胺在新鲜分离的雄性大鼠肝细胞悬浮液中显示出明显的 DNA 损伤增加，这种增加可以通过氨基苯并三唑（ABT）的预孵育显著降低。DNA 损伤显示出明显的性别差异，雄性肝细胞更敏感，与雌性肝细胞相比，谷胱甘肽（GSH）同时耗竭。二乙基马来酸酯和γ-谷氨酰半胱氨酸乙酯对 GSH 水平的调节分别升高和降低了 DNA 损伤的水平。在体内彗星试验中，连续 3 天给予甲吡戊胺（150mg/kg，po）治疗后，没有证据表明 DNA 损伤，尽管观察到组织学和肝酶变化。给予甲吡戊胺的动物总蛋白 GSH 含量升高，过氧化物歧化酶水平特异性在门脉周围区域升高。综合这些数据，支持甲吡戊胺诱导氧化应激的潜力。在体外彗星试验和大鼠肝脏体内检测到的 DNA 损伤差异可能归因于代谢和对氧化剂损伤的反应差异，或者该试验无法区分整个肝脏中少数个别细胞的损伤。
