Yoshino K, Suzuki M, Sasaki K, Miyase T, Sano M
Laboratory of Health Science, School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan.
J Nutr Biochem. 1999 Apr;10(4):223-9. doi: 10.1016/s0955-2863(98)00103-x.
The oxidative dimerization of (-)-epigallocatechin gallate (EGCG), the major catechin of tea leaves (Camellia sinensis L.), in authentic intestinal juice (pH 8.5) and mouse plasma (pH 7.8) was investigated. EGCG was unstable in the alkaline solutions over pH 7.4. The content of EGCG was decreased to 19.4% and 60.7% at 5 minutes in the intestinal juice and plasma, respectively. Three products-P-1 (theasinensin A), P-2 (a new dimerized product reported in a previous paper), and P-3 (theasinensin D, a rotational isomer of P-1)-were detected in these fluids. The sum of the molar contents of the three products formed after 5 minutes of incubation at 37 degrees C corresponded to 35.1% and 21.9% of the degraded molar content of EGCG, respectively. These dimerization products of EGCG would be formed by the dehydrogenation and decarboxylation of EGCG under oxidative conditions in alkaline solutions. The formation of P-2 was greater than that of P-1 and of P-3 at 30 minutes of incubation in the intestinal juice and mouse plasma. Fe(2+)-chelating activities of the three products were much higher than that of EGCG, and superoxide anion radical-scavenging activity of P-2 was also significantly higher than that of EGCG. The absorbance of P-2 administered to male ddY mice was studied. The content of P-2 in mouse plasma was less than that of administration of EGCG, but P-2 was absorbed quickly within 30 minutes and metabolized slowly. These dimerization products of EGCG are expected to contribute to in vivo antioxidative activities enhanced by tea drinking.
对茶叶（茶树）的主要儿茶素（-）-表没食子儿茶素没食子酸酯（EGCG）在真实肠液（pH 8.5）和小鼠血浆（pH 7.8）中的氧化二聚反应进行了研究。EGCG在pH值高于7.4的碱性溶液中不稳定。在肠液和血浆中，5分钟时EGCG的含量分别降至19.4%和60.7%。在这些液体中检测到三种产物——P-1（茶黄素A）、P-2（前文报道的一种新的二聚产物）和P-3（茶黄素D，P-1的旋转异构体）。在37℃孵育5分钟后形成的这三种产物的摩尔含量总和分别相当于EGCG降解摩尔含量的35.1%和21.9%。EGCG的这些二聚产物将通过EGCG在碱性溶液中的氧化条件下脱氢和脱羧形成。在肠液和小鼠血浆中孵育30分钟时，P-2的形成量大于P-1和P-3。这三种产物的铁（2+）螯合活性远高于EGCG，P-2的超氧阴离子自由基清除活性也显著高于EGCG。研究了给雄性ddY小鼠施用P-2后的吸光度。小鼠血浆中P-2的含量低于施用EGCG后的含量，但P-2在30分钟内迅速吸收且代谢缓慢。EGCG的这些二聚产物有望对饮茶增强的体内抗氧化活性有所贡献。
