Effects of green tea catechins in a rat multi-organ carcinogenesis model

Abstract

The effects of dietary administration of green tea catechins (GTC) were examined using a multi-organ carcinogenesis model. Groups of 15 F344 male rats were initially treated with a single i.p. administration of 100 mg/kg body wt N-diethyl-nitrosamine, 4 i.p. administrations of 20 mg/kg body wt N-methylnitrosourea, 4 s.c. doses of 40 mg/kg body wt 1,2-dimethylhydrazine, together with 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine for 2 weeks and then 0.1% 2,2'-dihydroxy-di-n-propylnitrosamine for 2 weeks, both in the drinking water, for a total initiation period of 4 weeks. GTC in the diet, at doses of 1.0 or 0.1%, was administered from 1 day before and during carcinogen exposure, after carcinogen exposure or both during and after carcinogen exposure. Further groups of animals were treated with carcinogen, 1% GTC or basal diet alone as controls. All animals were killed at the end of week 36, and all major organs examined histopathologically. The numbers of small intestinal tumors (adenomas and carcinomas) per rat were significantly reduced in the groups treated with 1% GTC during (0.13 +/- 0.35) and after carcinogen exposure (0.31 +/- 0.48) and in those receiving 1% and 0.1% GTC both during and after carcinogen exposure (0.14 +/- 0.36, 0.46 +/- 0.97 respectively) as compared with the carcinogen alone group (1.07 +/- 1.21). On the other hand, numbers of glutathione S-transferase placental form positive liver foci per cm2 were slightly but significantly increased in the groups treated with 1 and 0.1% GTC during carcinogen exposure, 1% GTC after carcinogen exposure and 1% GTC both during and after carcinogen exposure. The results indicated that while GTC inhibits small intestinal carcinogenesis it slightly enhances hepatocarcinogenesis in a dose dependent manner when applied both during and after carcinogen exposure.

Chemoprotection: A review of the potential therapeutic antioxidant properties of green tea (Camellia sinensis) and certain of its constituents

“…Thus, green tea catechins exerted a significant protective effect against small intestinal cancer but slightly enhanced hepatocarcinogenesis in a dose dependent manner. 107 …”

Review Article: A Medium-Term Rat Liver Bioassay as a Rapid In Vivo Test for Carcinogenic Potential: A Historical Review of Model Development and Summary of Results from 291 Tests

“…For detecting carcinogenic agents active in other tissues within a relatively short period, we have developed whole-body system models using wide-spectrum initiation by sequential treatment with 3-5 potent carcinogens having different organ spectra of carcinogenicity. Using multiple organ initiator models (medium-term multi-organ models), preliminary results have indicated that most carcinogens can be detected because of increased development of lesions in target organs within 24 or 36 wk (9,14,(22)(23)(24)39). This approach is also receiving international recognition (29).…”

A Frequent Drinking of Green Tea Lowers the Levels of Endogenous Oxidative Stress in Small Intestines, Erythrocytes and Kidneys in Rats

“…1). Green tea catechins were also reported to inhibit small intestinal carcinogenesis but not hepatocarcinogenesis [38]. Such interesting differences probably result from the different distributions of catechins among the organs.…”