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

1. 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. 2. 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. 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 μg/ml) were attained within two hours of administration and the half-life of removal from plasma was approx. 140 min. 4. 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.