Structural identification of two metabolites of catechins and their kinetics in human urine and blood after tea ingestion

Tea is a popular beverage consumed worldwide. The metabolic fate of its maj or constituents, catechins, however, is not well-known. In this study, two catechin metabolites were detected in the urine and plasma of human volunte ers after ingestion of green tea. These metabolites were identified by LC/E SI-MS and NMR as (-)-5-(3',4',5'-trihydroxyphenyl)-gamma-valerolactone (M4) and (-)-5-(3',4'-dihydroxyphenyl)-gamma-valerolactone (M6). The renal excr etion of M4 and M6 had a 3 h lag time and peaked 7.5-13.5 h after ingestion of a single dose of green tea, while (-)-epigallocatechin (EGC) and (-)-ep icatechin peaked at 2 h. M4 and M6 were two major tea metabolites with urin ary cumulative excretions as high as 8-25 times the levels of EGC and (-)-e picatechin in some of our subjects, and accounted for 6-39% of the amounts of ingested EGC and (-)-epicatechin. Both the metabolites appeared to be pr oduced by intestinal microorganisms, with EGC and (-)-epicatechin as the pr ecursors of M4 and M6, respectively. Repeated ingestion of green tea produc ed a slight accumulative effect of the metabolites. They were also detected in the plasma, exhibiting kinetics similar to those of the urinary metabol ites, and in the feces. Study on these metabolites may help us further unde rstand the cancer chemopreventive actions and other beneficial effects of t ea.