Identification of the major antioxidative metabolites in biological fluidsof the rat with ingested (+)-catechin and (-)-epicatechin

(+)-Catechin and (-)-epicatechin are known to be biologically effective ant ioxidants present in the human diet, particularly in wine and tea. We studi ed the metabolism of these compounds to elucidate the truly active structur es in biological fluids by their oral administration to rats. Without any t reatment with beta-glucuronidase and sulfatase, a pair of metabolites were detected at much higher concentrations in the plasma, bile, and urine than the originally ingested compounds. Each major metabolite found in the plasm a at the highest concentration was excreted in both the bile and urine, and was purified from urine. Their chemical structures were established to be (+)-catechin 5-O-beta-glucuronide and (-)-epicatechin 5-O-beta-glucuronide by MS and NMR analyses. These glucuronide conjugates exhibited high antioxi dative activities as superoxide anion radical scavengers like their parent compounds, It is concluded that (+)-catechin 5-O-beta-glucuronide and (-)-e picatechin 5-O-beta-glucuronide are the biologically active in vivo structu res of the ingested polyphenolic antioxidants.