Cytogenetic effects of benzimidazoles in mouse bone marrow

The cytogenetic effects of three benzimidazoles, i.e., benomyl, methyl thiophanate and methyl 2-benzimidazolecarbamate (MBC), were studied in mouse bone marrow cells by analyzing three genetic endpoints: micronuclei, structural chromosome aberrations plus or minus gaps, and aneugenic effects (hyperdiploidy or polyploidy). In general, the effects were small, but it was observed that benomyl and MBC significantly induced micronuclei as well as aneugenic effects, hyperdiploidy (no metaphases with more than one or two extra chromosomes, 2n + 1 or 2n + 2, were observed) and polyploidy (4n). The induction of chromosome gaps and breaks was less evident. Methyl thiophanate significantly induced micronuclei, but it was less effective than benomyl and MBC. Our results showed that micronuclei are a good indicator of aneugenic effects in mouse bone marrow cells. A curvilinear trend test has been devised to fit the curves originating from the time-dependent responses.