抄録
We are daily exposed to many kinds of chemicals through air, drinking water and foodstuffs. Some of these chemicals show mutagenic and carcinogenic activities. N-nitrosamines are potential candidates to induce human carcinogenesis, as these compounds are carcinogenic in animal studies and because they are formed by reaction of secondary amines with nitrite in the stomach environment. In Japan, stomach cancer is the most common malignancy. Therefore it is an important task to know how to inhibit carcinogenesis induced by N-nitrosamines. In this study, we examined if green tea acts as an inhibitor of the formation of N-nitrosamines. Furthermore, we determined the catechin concentration in a cup of green tea prepared from tea found in 13 countries, and examined the relationship between such concentrations and the incidence of cancer in several organs. Green tea leaves were brewed 8 times in hot water. Sodium nitrite and morpholine were added to each extract and adjusted to pH 3.0. After incubation at 37°C for 30 min, the concentration of formed N-nitrosomorpholine was determined by HPLC with a UV detector. The first and second green tea extracts inhibited the formation of N-nitrosomorpholine, while subsequent extracts accelerated its formation. These results suggested that the formation of nitrosamines in stomach may be reduced by green tea brews and that repeated brewing results in diminished inhibition of nitrosamine formation. We also demonstrated that the intake of catechins in tea producing areas is higher than that in non-producing areas. We observed a significant inverse correlation between standardized mortality ratio (SMR) of stomach cancer in males and the catechin concentration in green tea extracts. From these data, it is evident that green tea might be a potential chemopreventive agent to inhibit the formation of N-nitrosamine.
