PLOS ONE2014-01-20 1:52 AM

Green Tea and One of Its Constituents, Epigallocatechine-3-gallate, Are Potent Inhibitors of Human 11β-hydroxysteroid Dehydrogenase Type 1 绿茶和它成分中的3型茶多酚(EGCG-3- gallate)是人类11β-羟基类固醇脱氢酶1型(11β-HSD1)中的强效抑制剂

Abstract The microsomal enzyme 11β-hydroxysteroid deydrogenase type 1 (11β-HSD1) catalyzes the interconversion of glucocorticoid receptor-inert cortisone to receptor- active cortisol, thereby acting as an intracellular switch for regulating the access of glucocorticoid hormones to the glucocorticoid receptor. There is strong evidence for an important aetiological role of 11β-HSD1 in various metabolic disorders including insulin resistance, diabetes type 2, hypertension, dyslipidemia and obesity. Hence, modulation of 11β-HSD1 activity with selective inhibitors is being pursued as a new therapeutic approach for the treatment of the metabolic syndrome. Since tea has been associated with health benefits for thousands of years, we sought to elucidate the active principle in tea with regard to diabetes type 2 prevention. Several teas and tea specific polyphenolic compounds were tested for their possible inhibition of cortisone reduction with human liver microsomes and purified human 11β-HSD1. Indeed we found that tea extracts inhibited 11β-HSD1 mediated cortisone reduction, where green tea exhibited the highest inhibitory potency with an IC50 value of 3.749 mg dried tea leaves per ml. Consequently, major polyphenolic compounds from green tea, in particular catechins were tested with the same systems. (−)-Epigallocatechin gallate (EGCG) revealed the highest inhibition of 11β-HSD1 activity (reduction: IC50 = 57.99 µM; oxidation: IC50 = 131.2 µM). Detailed kinetic studies indicate a direct competition mode of EGCG, with substrate and/or cofactor binding. Inhibition constants of EGCG on cortisone reduction were Ki = 22.68 µM for microsomes and Ki = 18.74 µM for purified 11β-HSD1. In silicio docking studies support the view that EGCG binds directly to the active site of 11β-HSD1 by forming a hydrogen bond with Lys187 of the catalytic triade. Our study is the first to provide evidence that the health benefits of green tea and its polyphenolic compounds may be attributed to an inhibition of the cortisol producing enzyme 11β-HSD1. 论文摘要: 微粒体酶11β-羟类固醇脱氢酶1型(11β-HSD1)能催化糖皮质激素受体惰性皮质醇与受体活性皮质醇间的互变,从而如同细胞内开关一般能调控糖皮质激素对糖皮质激素受体的刺激。我们有确凿证据证明11β-HSD1在包括胰岛素抗药性,2型糖尿病,高血压,血脂异常和肥胖在内的各种代谢紊乱中起着重要病因作用。因此运用选择性抑制剂来调控11β-HSD1活性成为我们尝试治疗代谢综合征的新方法。千百年来喝茶对健康益处颇多,因而我们试图阐明茶叶中有助预防2型糖尿病的有效成分。我们检测了几类茶种和特定茶种内多酚化合物使人体肝微粒体和纯化人体11β-HSD1中皮质醇降低的抑制可能性。事实上,我们发现茶叶提取物抑制了11β-HSD1调节的皮质醇的降低,其中绿茶表现出最高的抑制能力,每毫升干茶叶中半抑制浓度(IC50值)达到3.749毫克。 因此,我们对绿茶中的主要多酚化合物,特别是儿茶素,使用相同系统进行了测试。茶多酚(EGCG)基揭示了11β-HSD1活性的高抑制性(降低:IC50 = 57.99微米,抗氧化:IC50 = 131.2微米)。结合基质和/或辅助因子,详细的动力学研究揭示了EGCG的直接竞争模式。皮质醇降低的EGCG抑制常数对于微粒体为KI = 22.68微米,对于纯化11β-HSD1为Ki = 18.74微米。在硅酸质对接研究中普遍支持这样的观点,即通过与Lys187的催化三分子形成氢键来将EGCG直接绑定到11β-HSD1的活性位点。我们的研究首次为绿茶有益健康提供确凿证据,且茶中的多酚类化合物可归因于11β-HSD1皮质醇产酶的抑制性。

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