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. M ore information on the mechanism of toxicity of such Salmonella-negative ca rcinogens is needed. Aniline and o-toluidine are negative in the Ames assay , but induce deletions (DEL) due to intrachromosomal recombination in Sacch aromyces cerevisiae with an apparent threshold. We show here that the DEL a ssay also detects the genotoxic activity of another aromatic amine carcinog en, o-anisidine, which is also negative in the Salmonella assay. We also sh ow that the DEL assay distinguishes between o-anisidine and its non-carcino genic structural analog 2,4-dimethoxyaniline. We have investigated whether the ability of the DEL assay to detect the carcinogens and to distinguish b etween the carcinogen/non-carcinogen pair is linked to rises in intracellul ar free radical species following exposure to the carcinogens. Toxicity ind uced by all three compounds was reduced in the presence of the free radical scavenger and antioxidant N-acetyl cysteine, recombination induced by o-an isidine and o-toluidine was also reduced by N-acetyl cysteine. All three co mpounds induced oxidation of the free radical-sensitive reporter compound d ichlorofluorescin diacetate. Superoxide dismutase-deficient strains, howeve r, were hypersensitive to cytotoxicity induced by o-toluidine and o-anisidi ne but not by the non-carcinogen 2,4-dimethoxyaniline, indicating a differe nt 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 c arcinogens. (C) 1999 Elsevier Science B.V. All rights reserved.