Synthesis and Structure Identification of Thiol Conjugates of (-)-Epigallocatechin Gallate and Their Urinary Levels in Mice

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• 作者：Shengmin Sang ; Joshua D. Lambert ; Jungil Hong ; Shiying Tian ; Mao-Jung Lee ; Ruth E. Stark ; Chi-Tang Ho ; and Chung S. Yang
• 刊名：Chemical Research in Toxicology
• 出版年：2005
• 出版时间：November 2005
• 年：2005
• 卷：18
• 期：11
• 页码：1762 - 1769
• 全文大小：171K
• 年卷期：v.18,no.11(November 2005)
• ISSN：1520-5010

文摘

(-)-Epigallocatechin gallate (EGCG), the most abundant and most biologically activecompound in tea, has been proposed to have many beneficial health effects. The metabolicfate of EGCG, however, is not well understood. In the present study, we found that EGCG canbe oxidized by peroxidase and hydrogen peroxide and then reacted with cysteine or glutathioneto form conjugates. The structures of the cysteine and glutathione conjugates of EGCG wereidentified using 2D NMR and MS. Two thiol conjugates of EGCG (2'-cysteinyl EGCG and 2' '-cysteinyl EGCG) were identified by ESI-LC-MS/MS analysis from the urine samples of miceadministered 200 or 400 mg/kg EGCG, i.p. These conjugates were not found in urine samplesof mice after receiving EGCG at 50 mg/kg i.p., or 2000 mg/kg i.g., or in human urine followingconsumption of 3 g of decaffeinated green tea solids (containing 333 mg EGCG). At high doses,EGCG is believed to be oxidized to form EGCG quinone, which can react with glutathione toform the thiol conjugates. These results suggest that detectable amounts of thiol conjugates ofEGCG are formed only after rather high doses of EGCG are given to the mice.