Micronucleus induction by metronidazole in rat vaginal mucosa

Micronucleus assays in rodent tissues other than bone marrow

This report updates previous reviews that were conducted as part of the third and fourth International Workshops on Genetic Toxicology Testing of micronucleus (MN) assays in rodent tissues other than bone marrow. Tissues discussed here are liver, lung, skin, colon, spleen, testes and foetal/neonatal tissues with transplacental exposure. Previous reviews have been updated to include literature published after 2000. In addition to the previously described tissues, MN assays in bladder, buccal mucosal cells, stomach and vagina are also included. MN assays using tissues other than bone marrow are critical for risk assessments, for in situ evaluation and for studies of systemic genotoxic effects and modes of action. Protocols for the majority of assays in tissues other than bone marrow have not yet been well standardised and validated for regulatory application, and further development is needed to support regulatory studies.

Genotoxicity revaluation of three commercial nitroheterocyclic drugs: nifurtimox, benznidazole, and metronidazole

Nitroheterocyclic compounds are widely used as therapeutic agents against a variety of protozoan and bacterial infections. However, the literature on these compounds, suspected of being carcinogens, is widely controversial. In this study, cytotoxic and genotoxic potential of three drugs, Nifurtimox (NFX), Benznidazole (BNZ), and Metronidazole (MTZ) was re-evaluated by different assays. Only NFX reduces survival rate in actively proliferating cells. The compounds are more active for base-pair substitution than frameshift induction in Salmonella; NFX and BNZ are more mutagenic than MTZ; they are widely dependent from nitroreduction whereas microsomal fraction S9 weakly affects the mutagenic potential. Comet assay detects BNZ- and NFX-induced DNA damage at doses in the range of therapeutically treated patient plasma concentration; BNZ seems to mainly act through ROS generation whereas a dose-dependent mechanism of DNA damaging is suggested for NFX. The lack of effects on mammalian cells for MTZ is confirmed also in MN assay whereas MN induction is observed for NFX and BNZ. The effects of MTZ, that shows comparatively low reduction potential, seem to be strictly dependent on anaerobic/hypoxic conditions. Both NFX and BNZ may not only lead to cellular damage of the infective agent but also interact with the DNA of mammalian cells.