Biol. Pharm. Bull. 28(9) 1702—1706 (2005)

umami (the fifth taste sensation)-component of tea and is contained 2—3% in tea leaves. Theanine is a glutamate derivative and is used extensively as supplements and beverages, because it has a brain nerve function such as a relaxing effect due to inducing alpha waves. But there are few reports about pharmacological action of theanine in comparison with catechin or caffeine, major tea components, and its effects on living individuals have not revealed closely. In recent studies, we showed that theanine enhanced doxorubicin (DOX), an anthracycline derivative, induced antitumor activity, and confirmed that this action contributed to the increase in the concentration of DOX in tumor with inhibition of the efflux of DOX from tumor cells. Besides, theanine induced the elevation of glutathione (GSH) level attributable to the increase of glutamate in the liver of mice, namely, theanine would reduce the adverse reaction of DOX. Although GSH in tissues are kept constant by homeostasis, whereas was decreased by disease or medicine or age. The usefulness of theanine was shown when the GSH level in liver decreased by the hepatic load of DOX. Furthermore, it was suggested that GSH level would increase by the metabolism of theanine. Thus, theanine was thought to be effective against tissue changes with GSH level reduction. On the other hand, it is suggested excessive uptake of alcohol causes a production of free radicals, a decrease of GSH level, and an increase in the amount of lipid peroxide (LPO) in liver, and shifting to an alcoholic liver injury. In the liver, theanine is metabolized, converted glutamate, and induced to increase GSH level. Namely, theanine may be expected to affect on to an alcoholic liver injury. Then, aiming at the prevention and medical treatment of a hepatic toxicity by the food components with little toxicity, we have studied the effect of theanine on ethanol metabolism and hepatic toxicity using ethanol single-administrated mice. To evaluate the effect of theanine on ethanol metabolism and its toxicity, theanine was intraperitoneally injected and ethanol was orally administered.