INHIBITION OF N-NITROSOMETHYLBENZYLAMINE-INDUCED ESOPHAGEAL TUMORIGENESIS IN RATS BY GREEN AND BLACK TEA

In this study, we investigated the effects of green tea and black tea, when given either during or after carcinogen treatment, on esophageal tumorigenesis in male Sprague-Dawley rats. Rats were treated with N-n itrosomethylbenzyl-amine (NMBzA) (2.5 mg/kg, s.c., twice weekly) for 5 weeks; 39 weeks after the initial dose of NMBzA, 65% of the rats had esophageal tumors with an average of 1.4 +/- 0.3 tumors per rat. In th e groups of rats receiving 0.6% of decaffeinated green tea (DGT) or de caffeinated black tea (DBT) (6 mg tea solids/ml) as the sole source of drinking fluid during the NMBzA-treatment period, esophageal tumor in cidence and multiplicity were reduced by similar to 70%. When the tea preparations were given after the NMBzA treatment period, the esophage al papilloma incidence and multiplicity were reduced by similar to 50% . The volume per tumor was much smaller in rats that received black te a after the carcinogen treatment period, In a second experiment, NMBzA was given to rats at a dose of 3.5 mg/kg (s.c., twice weekly) for 5 w eeks; after 16 weeks, the tumor incidence was 82% and tumor multiplici ty was 6.7 +/- 1.2 tumors per rat, In the groups of rats receiving 0.9 % regular green tea (RGT) or DGT after the NMBzA treatment period, tum or multiplicity was decreased by >55%. The volume per tumor was reduce d by similar to 60% in the rats receiving 0.9% RGT. Histological analy sis indicated that both the incidence and multiplicity of esophageal c arcinoma was decreased by either RGT or DGT. The blood and urine level s of green tea polyphenols levels were comparable to those in humans a fter tea ingestion. The above results indicate that both green tea and black tea can inhibit the tumorigenic action of NMBzA during the peri od of carcinogen treatment and the subsequent molecular events importa nt for esophageal tumorigenesis.