Genetic toxicity of N-methylcarbamate insecticides and their N-nitroso derivatives.

N-Methylcarbamate esters are an important group of insecticides. They have lower acute toxicity to vertebrates than organophosphates, although their genotoxicity has not been adequately studied. Here we investigate the cytotoxicity and genotoxicity of N-methylcarbamate insecticides and their N-nitroso derivatives in Chinese hamster V79 cells, using the hprt locus as a marker, and also assess inhibition of gap junctional intercellular communication. N-Methylcarbamate insecticides were chemically N-nitrosated to obtain the N-nitroso derivatives. N-Nitrosation greatly increased the cytotoxicity and mutagenicity of N-methylcarbamates at the hprt locus in Chinese hamster V79 cells. The mutagenic potential of N-nitroso-N-methylcarbamates was much higher than those of many other known mutagenic nitroso compounds, as well as some non-nitroso mutagenic alkylating agents. Parental N-methylcarbamates themselves were not mutagenic, however, they inhibited gap junctional intercellular communication half as effectively as the well-studied tumor promoter 12-O-tetradecanoylphorbol-13-acetate. The findings show that N-methylcarbamate insecticides and their N-nitroso derivatives have the potential to act through mediation of epigenetic and genotoxic mechanisms respectively in the multiple stages of chemical carcinogenesis.