Laboratory studies on cancer chemoprevention by tea

Summarv TeJ pigments, the oxidative products of tea polyphenols. mainly contain [eJ theJt1a\'ins. thearubigins and other components. In short-renn screening studies. tea pigments \vas found to have significant inhibitory efffects in Gene mutation test. Micronuclei fonnation test. rvletabolic cooperation test. \ilice ear edema test. Viability and growth ability of Hela cells in soft agar and S-180 solid tumor test. In addition, in vitro studies showed that tea pigments induced quinone reductase (QR) activity· and glutathione Stransferase (GST) activity in Hep G2 cells. The pigments \vas found to be effective in preventing formation of liver, colorectal and oral cancers in animal models. It \vas also found that oral administration of 0.1~!Q tea pigments increased GST activity in rat liver by 18~/o, \vhich \vas accompanied by significant increase of GST 1-1, 1-2, and 3-3 protein expression. Tea pigments inhibited the proliferating cell nuclear antigen labeling index (PCNA-LI), the expression of Bcl-1 protein and ras-p21 protein, and induced the expression of Bax protein in rat colorectal cancer model induced by dimethylhydrazir.e (DMH). PCN~-\-LI, silver stained nucleolar organizer regi'ons (AgNOR) and epidennal growth factor receptor (EGFR) expression were also inhibited by tea pigments in the hamster oral cancer induced by dimethylbenzanthracene (DMBA). Our results suggest that tea pigments have significant chemopreventive effects on various animal cancer models, and the anti-cancer properties may be due to the activation of detoxifying enzymes such as QR and GST, the inhibition of cell proliferation and the induction of apoptosis.