thearubigin and 2-amino-1-methyl-6-phenylimidazo(4-5-b)pyridine

Theafulvins were isolated from black tea aqueous infusions and their antimutagenic activity was evaluated against a number of food carcinogens. Theafulvins gave rise to a concentration-dependent inhibition of the mutagenicity of 2-amino-3-methylimidazo-[4,5-f]quinoline, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, benzo[a]pyrene, 7,12-dimethylbenz[a]anthracene, nitrosopyrrolidine and nitrosopiperidine, but, in contrast, the mutagenicity of aflatoxin B1 was enhanced. The mutagenicity exhibited by N'-methyl-N'-nitro-N-nitrosoguanidine and 9-aminoacridine was not influenced and weakly inhibited by theafulvins, respectively. The p-hydroxylation of aniline and the O-dealkylations of methoxy-, ethoxy- and, to a lesser extent, pentoxyresorufin were inhibited by theafulvins in a concentration-dependent manner. When microsomal metabolism was terminated after metabolic activation of the promutagens, incorporation of the theafulvins into the activation system did not modulate the mutagenic response. It is concluded that theafulvins play an important role in the antimutagenic activity of black tea by inhibiting cytochrome P450-dependent bioactivation of the carcinogens.

Topics: 9,10-Dimethyl-1,2-benzanthracene; Animals; Antimutagenic Agents; Benzo(a)pyrene; Carcinogens; Catechin; Chlorodiphenyl (54% Chlorine); Dose-Response Relationship, Drug; Imidazoles; Male; Microsomes, Liver; N-Nitrosopyrrolidine; Nitrosamines; Oxazines; Phenols; Polyphenols; Quinolines; Rats; Rats, Wistar; Tea; Vitamin K

Standard black and green tea extracts have been known to inhibit mutagenicity caused by PhIP, in the Salmonella typhimurium TA98 assay containing S9 fraction from the liver of rats induced with alpha-naphthoflavone and phenobarbital. Breeding and selection programs for high yielding tea clones have successfully increased yields in many tea producing areas. Six clonal teas and three seedling teas were obtained from a tea producing area in Southern Africa. Standard black and green teas were used as controls. Dose-dependent inhibition of the bacterial mutagenicity elicited by two concentrations of PhIP was found in the extracts of all the teas tested. This indicates that the clonal teas have not lost their anti-mutagenic properties. Small differences were found amongst the clonal teas in their ability to inhibit mutagenicity. This indicates that it may be possible to enhance this trait in future breeding and selection programs.

Topics: Anticarcinogenic Agents; Antimutagenic Agents; Antioxidants; Biflavonoids; Biotransformation; Breeding; Catechin; Imidazoles; Mutagenicity Tests; Mutagens; Phenols; Plant Extracts; Polyphenols; Salmonella typhimurium; Tea