Aucamp J, Gaspar A, Hara Y, Apostolides Z
Department of biochemistry, University of Pretoria, South Africa.
Anticancer Res. 1997 Nov-Dec;17(6D):4381-5.
Some epidemiological studies have associated tea drinking with several health benefits, while other such studies have been inconclusive. The liver enzyme, xanthine oxidase (XO) produces uric acid and reactive oxygen species (ROS) during the catabolism of purines. Excess of the former can lead to gout and of the latter to increased oxidative stress, mutagenesis and possibly cancer. Polyphenols are antioxidants, and it has been suggested that they can reduce oxidative stress by their antioxidant properties. We report here on the inhibition of XO by five tea catechins and two flavones. The Ki values (microM) and types of inhibition were catechin (C) (Ki = 303.95, uncompetitive), epicatechin (EC) (Ki = 20.48, mixed), epigallocatechin (EGC) (Ki = 10.66, mixed), epicatechin gallate (ECg) (Ki = 2.86, mixed) and epigallocatechin gallate (EGCg) (Ki = 0.76, competitive). The Ki of EGCg was similar to that of allopurinol (Ki = 0.30, mixed), the drug of choice for inhibition of XO in gout patients. Thus, tea catechins may act at.an earlier stage than has previously been suspected, by inhibiting ROS production, rather than only neutralizing the already formed ROS. This suggests a new mechanism whereby tea drinking may prevent oxidative stress related diseases, e.g. atherosclerosis and cancer.
一些流行病学研究表明饮茶对健康有诸多益处，而其他此类研究尚无定论。肝脏酶黄嘌呤氧化酶（XO）在嘌呤分解代谢过程中产生尿酸和活性氧（ROS）。前者过量会导致痛风，后者过量会增加氧化应激、诱变作用并可能引发癌症。多酚是抗氧化剂，有人认为它们可凭借抗氧化特性减轻氧化应激。我们在此报告了五种茶儿茶素和两种黄酮对XO的抑制作用。其Ki值（微摩尔）及抑制类型分别为：儿茶素（C）（Ki = 303.95，非竞争性）、表儿茶素（EC）（Ki = 20.48，混合型）、表没食子儿茶素（EGC）（Ki = 10.66，混合型）、表儿茶素没食子酸酯（ECg）（Ki = 2.86，混合型）和表没食子儿茶素没食子酸酯（EGCg）（Ki = 0.76，竞争性）。EGCg的Ki值与别嘌呤醇（Ki = 0.30，混合型）相近，别嘌呤醇是痛风患者抑制XO的首选药物。因此，茶儿茶素可能比之前所怀疑的作用更早，通过抑制ROS的产生，而非仅仅中和已形成的ROS。这提示了一种新机制，据此饮茶可能预防与氧化应激相关的疾病，如动脉粥样硬化和癌症。
