The aromatic amine carcinogens o-toluidine and o-anisidine induce free radicals and intrachromosomal recombination in Saccharomyces cerevisiae

Aniline-based aromatic amine carcinogens are poorly detected in short-term mutagenicity assays such as the Salmonella reverse mutation (Ames) assay. More information on the mechanism of toxicity of such Salmonella-negative carcinogens is needed. Aniline and o-toluidine are negative in the Ames assay, but induce deletions (DEL) due to intrachromosomal recombination in Saccharomyces cerevisiae with an apparent threshold. We show here that the DEL assay also detects the genotoxic activity of another aromatic amine carcinogen, o-anisidine, which is also negative in the Salmonella assay. We also show that the DEL assay distinguishes between o-anisidine and its non-carcinogenic structural analog 2, 4-dimethoxyaniline. We have investigated whether the ability of the DEL assay to detect the carcinogens and to distinguish between the carcinogen/non-carcinogen pair is linked to rises in intracellular free radical species following exposure to the carcinogens. Toxicity induced by all three compounds was reduced in the presence of the free radical scavenger and antioxidant N-acetyl cysteine, recombination induced by o-anisidine and o-toluidine was also reduced by N-acetyl cysteine. All three compounds induced oxidation of the free radical-sensitive reporter compound dichlorofluorescin diacetate. Superoxide dismutase-deficient strains, however, were hypersensitive to cytotoxicity induced by o-toluidine and o-anisidine but not by the non-carcinogen 2,4-dimethoxyaniline, indicating a different potential for generating superoxide radical between the carcinogens and the non-carcinogen analog. The results indicate that the yeast DEL assay is a useful tool for investigating the genotoxic activity of aromatic amine carcinogens.