Inhibition by Green Tea Extract of Diethylnitrosamine–initiated but Not Cholinedeficient L–Amino Acid–defined Diet–associated Development of Putative Preneo–plastic Glutathione S–Transferase Placental Form–positive Lesions in Rat Liver

摘要

The effects of green tea extract (GTE) on exogenous and endogenous models of rat liver carcinogenesis using diethylnitrosamine (DEN) and a choline–deficient, L–amino acid–defined (CDAA) diet were studied. For the exogenous carcinogenesis study, male Fischer 344 rats, 6 weeks old, were given a single intraperitoneal dose of 200 mg/Kg body weight of DEN, partially hepatectomized at week 3, and administered GTE at doses of 0, 0.01 and 0.1% in the drinking water from week 2 for 10 weeks. For the endogenous carcinogenesis study, rate were fed the CDAA diet and simultaneously given GTE for 12 weeks. All rats were killed at the end of week 12. After DEN–initiation, the apparent numbers of glutathione S–transferase placental form–positive foci, assayed as putative preneoplastic lesions, were decreased by the administration of GTE, though their sizes were not altered. In contrast, GTE did not significantly reduce the numbers of the lesions induced by the CDAA diet or affect their sizes. While the levels of 8–hydroxyguanine, a parameter of oxidative DNA damage, were reduced by the GTE administration in both experimental models, GTE did not protect against the CDAA–diet–associated liver tissue damage in terms of either histology or plasma marker enzyme levels. We conclude that, while GTE may be a possible chemopreventive agent for nitrosamine–initiated hepato–carcinogenesis in the absence of chronic hepatocyte damage, it does not significantly inhibit lesion development in hepatocarcinogenesis associated with the CDAA diet, a cirrhosis–associated model.