A. Bu-Abbas, X. Nunez, M.N. Clifford, R. Walker, C. Ioannides

The present study was undertaken to compare the antimutagenic activity of aqueous extracts, at the concentrations used for human consumption, from green, black and decaffeinated black tea. Antimutagenic potential was evaluated against three indirect-acting dietary carcinogens, Glu-P-1, benzo(a)pyrene and nitrosopyrrolidine. All three types of tea gave rise to strong and concentration-dependent suppression of the mutagenicity of the three premutagens in the presence of an activation system. No major difference in the antimutagenic potential of the three types of tea could be discerned. Black tea, decaffeinated black tea and, to a lesser extent, green tea also antagonized the mutagenicity of the direct-acting mutagen 9-aminoacridine. All three types of tea inhibited markedly the NADPH-dependent reduction of cytochrome c and the O-dealkylations of ethoxy-, methoxy- and, to a much lesser extent, pentoxy-resorufin. When the microsomal metabolism was terminated, after the metabolic activation of the premutagens, incorporation of the aqueous tea extracts into the activation system caused a concentration-dependent suppression of mutagenic response. No significant difference in the antimutagenic activity of the three types of tea in this system was evident. Bearing in mind the much higher concentration of flavanols in green tea compared with the black teas, it may be concluded either that these compounds are unlikely to be the major tea components responsible for the antimutagenic, and possibly anticarcinogenic, properties of tea or that their fermentation products are similarly active.