The quantitative disposition of 3-O-methyl-(+)-[U-14C]catechin in man following oral administration

Three young male volunteers excreted 51.5, 33.6 and 55.9% of a single 2 g oral dose of radiolabelled 3-O-methyl-(+)-catechin in urine within 120 h of administration. Excretion of the unchanged compound, however, accounted for only 0.7, 0.1 and 0.2% of the dose. The major urinary metabolites were glucuronides of 3,3'-O-dimethyl-(+)-catechin (15.8% dose) and a glucuronide and a sulphate of 3-O-methyl-(+)-catechin (11.4% and 10.6% dose, respectively). No evidence for demethylation was obtained. 3-O-Methyl-(+)-catechin was detected and measured in plasma by h.p.l.c. 0.5-12 h after administration. Peak levels (11-18 micrograms/ml) were attained within two hours of administration and the half-life of removal from plasma was approx. 140 min. Metabolism of 3-O-methyl-(+)-catechin in man was found to vary significantly from other species, as methylated metabolites (3'-O-methyl ethers) in man represented only about 53% of the urinary metabolites, whereas in the mouse, rat and marmoset, 3'-O-methylation was almost quantitative (Hackett and Griffiths 1981). The glucuronic acid conjugates of 3-O-methyl-(+)-catechin detected in man also differed from those previously reported in the rat. Additionally, sulphate conjugation of 3-O-methyl-(+)-catechin was observed in man although not in other species. 3-O-Methyl-(+)-catechin, unlike (+)-catechin, did not undergo ring fission.