Inhibitory Effects of Conjugated Epicatechin Metabolites on Peroxynitrite-mediated Nitrotyrosine Formation

Abstract

Previously, we identified four metabolites of (-)-epicatechin in blood and urine: (-)-epicatechin-3'-O-glucuronide (E3'G), 4'-O-methyl-(-)-epicatechin-3'-O-glucuronide (4'ME3'G), (-)-epicatechin-7-O-glucuronide (E7G), and 3'-O-methyl-(-)-epicatechin-7-O-glucuronide (3'ME7G) (Natsume et al. Free Radical Biol. Med. 34, 840-849, 2003). The aim of the current study was to compare the antioxidative activities of these metabolites with that of their parent compound. After oral administration of (-)-epicatechin, E3'G and 4'ME3'G were isolated from human urine, and E7G and 3'ME7G isolated from rat urine. We found that these compounds inhibited peroxynitrite-mediated tyrosine nitration, in the following order of potency: E3'G > (-)-epicatechin > E7G = 3'ME7G. = 4'ME3'G. These results demonstrate that the metabolites of (-)-epicatechin retain antioxidative activity on peroxynitrite-induced oxidative damages to some extent.

Keywords: (−)-epicatechin; glucuronide; metabolites; nitrotyrosine; peroxynitrite.

Fig. 1

Structures of (−)-epicatechin and its glucuronide metabolites isolated from human and rat urine. (a) (−)-epicatechin. (b) (−)-epicatechin-3'-O-glucuronide (E3'G). (c) 4'-O-mehyl-(−)-epicatechin-3'-O-glucuronide (4'ME3'G). (d) (−)-epicatechin-7-O-glucuornide (E7G), and (e) 3'-O-methyl-(−)-epicatechin-7-O-glucuonide (3'ME7G).

Fig. 2

Protective effect by (−)-epicatechin and its metabolites against nitration of tyrosine residues by peroxynitrite (−)-epicatechin (closed circles), E3'G (open triangles), 4'ME3'G (open squares), E7G (closed triangles) and 3'ME7G (closed squares). Each analysis was performed in duplicate.