CONTRIBUTION OF CAFFEINE AND FLAVANOLS IN THE INDUCTION OF HEPATIC PHASE-II ACTIVITIES BY GREEN TEA

Aqueous extracts of green tea, at concentrations of 2.5, 5.0 and 7.5%, were administered to rats as the sole drinking fluid for 4 weeks. Hep atic glutathione S-transferase (GST) activity, determined using 1-chlo ro-2,4-dinitrobenzene (CDNB) and 3,4-dichloronitrobenzene (DCNB) as su bstrates, and UDP-glucuronosyl transferase activity, determined using 2-aminophenol as substrate, were induced but the effect was not always dose dependent. At the two highest doses, hepatic catalase activity w as inhibited. In a second study, animals were exposed for 4 weeks to a queous extracts (2.5%, v/v) of green tea, black tea (which has a much lower content of flavanols compared with green tea) and decaffeinated black tea. Treatment with the black tea enhanced GST activity, whether monitored using CDNB or DCNB, and the glucuronidation of 2-aminopheno l. Treatment with decaffeinated black tea failed to modulate any of th ese activities, whereas treatment with green tea only enhanced the glu curonidation of 2-aminophenol. Finally, at this concentration of tea e xtract administration, black and decaffeinated black tea, but not gree n tea, suppressed catalase activity. It is concluded that neither flav anols nor caffeine are responsible for the induction of hepatic Phase II activities and inhibition of catalase activity in the rat. (C) 1998 Elsevier Science Ltd. All rights reserved