Enhancement of Antioxidative Ability of Rat Plasma by Oral Administration of (−)-Epicatechin

To check whether ingestion of (−)-epicatechin (EC) affects the antioxidative defense in blood plasma, we studied the oxidizability of plasma from Wistar rats after intragastrical EC administration at 10 or 50 mg/rat. The plasma pool obtained from control or EC-administered rats was oxidized with copper sulfate or 2,2′-azobis(2-amidinopropane)dihydrochloride (AAPH). EC metabolites in plasma 1 h after EC administration contained glucuronide and glucuronide-sulfate conjugates in both the free and O-methylated form. After 6 h, the plasma concentration of total EC metabolites decreased and the remaining conjugates were mostly present as the O-methylated form. Compared to the control group, the plasma obtained from rats 1 and 6 h after EC administration was more resistant against copper sulfate-induced oxidation on the basis of cholesteryl ester hydroperoxide (CE-OOH) accumulation. Also, the consumption of α-tocopherol during oxidation was suppressed in the plasma obtained from EC-treated rats. The content of CE-OOH and consumption of α-tocopherol in the plasma from EC-administered animals was much lower than those expected from the amount of nonmetabolized EC present in the plasma. Similar results were obtained from AAPH-induced oxidation of rat plasma after EC administration, except for the fact that CE-OOH accumulation was less suppressed in the plasma 6 h following administration. The O-methylated form was found to be more stable than the free form when EC-administered rat plasma was auto-oxidized at 37°. These results suggest that EC metabolites, particularly conjugates in the free form, possess an effective antioxidative activity in blood plasma.