Evaluation of the in vitro antimutagenic effect of Doash tea aqueous extracts.

Human carcinogens are formed mainly due to the lifestyle and diet that is followed. It is well known that dietary factors play a crucial role in the aetiology of human cancer. The new attractions of drug discovery using natural products remain an important issue in the current herbal medicine research. The present study aimed to evaluate the antimutagenic activity of the water extracts of Doash leaves against several known mutagens, both direct- and indirect-acting, belonging to different chemical classes. These classes are heterocyclic amines (HAs), polycyclic aromatic hydrocarbons and nitrosamines. The antimutagenic activity will be determined in Salmonella/microsomal system (Ames) using strains of Salmonella Typhimurium. Four Salmonella bacterial strains (TA98, TA97, TA100 and TA1530) were used in the present study. Results obtained showed that Doash extract possesses powerful antimutagenic properties, which impair the deleterious effects of various chemicals used in this study. One possible mechanism involved in this protection is the inhibition of the metabolic activation of chemical carcinogens to their reactive metabolites. We also suggest that the health benefits of Doash could be derived from the additive and synergistic combinations of the various phytochemicals present in Doash leaves. Other studies should also be conducted to determine the active components of Doash leaves, including macronutrients, micronutrients and other phytochemicals. Clinical studies should be performed before any claims that Doash consumption offers chemoprotection against cancer can be made.

Contribution of theafulvins to the antimutagenicity of black tea: their mechanism of action.

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.