Effects of tea on preneoplastic lesions and cell cycle regulators in rat liver

The effects of tea polyphenols and tea pigments on rat liver precancerous lesions and some cell cycle regulators were studied. A modified Solt-Farber model in rats was established by multiple low-dosage of N-nitrosodiethylamine (NDEA) i.p. injections, followed by i.p. CCl(4) injection and partial hepatectomy. Sixty male Wistar rats were randomly divided into four groups: positive control group, two tea-treated groups, and negative control group. Rats in tea-treated groups were given tea polyphenols (0.1%) and tea pigments (0.1%) in drinking fluid during the whole experiment. The number and area of glutathione S-transferase P (GST-P)-positive foci in the rat liver were used as biomarkers of precancerous liver lesions. Western blotting assay was carried out to detect the expression of cyclin D1, CDK4, and P21(WAF1/CIP1) on whole liver extract. At the end of the experiment (56 days), the number and area of GST-P-positive foci in liver increased significantly in carcinogen-administered positive control group, whereas no GST-P-positive foci were found in the negative control group in which animals did not receive carcinogen exposure. The number and area of GST-P-positive foci in tea-treated, carcinogen-exposed groups were significantly reduced as compared with the positive control group. It was also found that the expression of P21(WAF1/CIP1) was significantly induced and the expression of cyclin D1 and CDK4 was significantly inhibited in tea-treated groups. These results suggest that tea polyphenols and tea pigments are effective in preventing the precancerous liver lesions in rats, and modulation of cell cycle by regulating cell cycle regulators may be a possible mechanism.