Analysis of Plasma and Urinary Tea Polyphenols in Human Subjects

Tea has been shown to inhibit chemically induced tumorigenesis in many animal models, but the effects of tea consumption on human carcinogenesis are not conclusive. In order to develop biomarkers for tea consumption, we developed methods for the analysis of tea polyphenols in human plasma and urine samples using HPLC with the coulochem electrode array detection system. (-)-Epigallocatechin-3-gallate (EGCG), (—)-epigallocatechin (EGC), (—)-epicatechin-3-gallate (ECG), and (—)-epicatechin (EC) are the major polyphenols in green tea. Most of the tea polyphenols were in their conjugated forms in the plasma and urine. The samples were incubated with a mixture of /3-glucuronidase and sulfatase to generate the free form of tea polyphenols. After extraction into ethyl acetate and separation by reversed-phase chromatography, EGCG, EGC, and EC were identified on the basis of their retention times and electrochemical characteristics. Due to the high selectivity of the detection mode, interference was minimized. Good quantitative relationships were established for a large concentration range of tea polyphenols. The limits of detection for EGCG, EGC, ECG, and EC were from 0.5 to 1.5 ng/ml of plasma or urine sample. After ingestion of 1.2 g of decaffeinated green tea in warm water, the plasma samples collected at 1 h from 4 human volunteers contained 46-268 ng/ml of EGCG, 82-206 ng/ml of EGC, and 48-80 ng/ml of EC. ECG was not detected in plasma samples. The maximum urinary excretion of EGC and EC occurred at 3-6 h. Most of the EGC and EC were excreted in the first 9 h, and the cumulative urinary excretions in the first 24 h were 2.8-3.2 mg of EGC and 1.6-2.3 mg of EC. EGCG and ECG were not detected in the urine samples. Plasma and urinary levels of EGC, EC, and EGCG may be useful markers for quantifying human ingestion of tea and exposure to tea polyphenols. This information is important for studying the effects of tea consumption on human cancers.