Possible mechanisms of antimutagens by various teas as judged by their effects on mutagenesis by 2-amino-3-methylimidazo[4,5-f]quinoline and benzo[a]pyrene.

Possible mechanisms of antimutagenicity of various tea extracts (green, pouchong, oolong and black tea) toward 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and benzo[a]pyrene (B[a]P) were investigated using a Salmonella/microsome assay. Tea extracts exhibited no inhibitory effects toward IQ and B[a]P in bio-antimutagenic assays, indicating that their antimutagenic activity is desmutagenic in nature. The mutagenicities of IQ and B[a]P decreased as the reaction periods of tea extracts with promutagens, S9 mix, or mutagen metabolites increased. The antimutagenicity of tea extracts toward IQ could be attributed (primarily) to an interaction between tea extracts and S9 mix. Apart from their interaction with S9 mix, tea extracts also exhibited antimutagenicity by markedly decreasing the mutagenicity of B[a]P metabolites. These results suggest that tea extracts: (1) inhibit the cytochrome P-450-mediated metabolism of IQ and B[a]P to their ultimate mutagenic metabolite form; and (2) interact with both promutagens and their metabolites in such a way as to reduce their mutagenic potentials. Therefore, the antimutagenic actions of tea extracts are due to a combination of the above distinctive mechanisms, and can vary with the type of mutagen under test.