INHIBITION OF LUNG CARCINOGENESIS BY BLACK TEA IN FISCHER RATS TREATED WITH A TOBACCO-SPECIFIC CARCINOGEN - CAFFEINE AS AN IMPORTANT CONSTITUENT

Here, we examined the effect of black tea and caffeine on lung tumorig enesis in F344 rats induced by the nicotine-derived carcinogen 4-(meth ylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in a 2-year bioassay, NN K was administered s.c. at a dose of 1.5 mg/kg body weight three times weekly for 20 weeks. Animals were given either black tea as drinking water at concentrations of 2%, 1%, or 0.5%, or caffeine in drinking wa ter at concentrations identical to those in 2% and 0.5% tea infusions for 22 weeks, The treatment period began 1 week before and ended 1 wee k after the NNK administration. The animals were sacrificed on week 10 1 for the examination of tumors in target organs, including lung, live r, nasal cavity, and other major organs. The NNK-treated group, given 2% black tea, showed a significant reduction of the total lung tumor ( adenomas, adenocarcinomas, and adenosquamous carcinomas) incidence fro m 47% to 19%, whereas the group given 1% and 0.5% black tea showed no change. The 2% tea also reduced liver tumor incidence induced by NNK f rom 34% in the group given only deionized water to 12%, The tumor inci dence in the nasal cavity, however, was not affected by either black t ea or caffeine at any of the concentrations tested. The most unexpecte d finding was the remarkable reduction of the lung tumor incidence, fr om 47% to 10%, in the group treated with 680 ppm caffeine, a concentra tion equivalent to that found in the 2% tea. This incidence is compara ble to background levels seen in the control group. This study demonst rated for the first time in a 2-year lifetime bioassay that black tea protects against lung tumorigenesis in F344 rats, and this effect appe ars to be attributed, to a significant extent, to caffeine as an activ e ingredient of tea.