(-)-Epicatechin elevates nitric oxide in endothelial cells via inhibition of NADPH oxidase

Dietary (-)-epicatechin is known to improve bioactivity of (NO)-N-. in arterial endothelium of humans, but the mode of action is unclear. We used the fluorophore 4,5-diaminofluorescein diacetate to visualize the (NO)-N-. level in living human umbilical vein endothelial cells (HUVEC). Untreated cells showed only a weak signal, whereas pretreatment with (-)-epicatechin (10 mu M) or apocynin (100 mu M) elevated the (NO)-N-. level. The effects were more pronounced when the cells were treated with angiotensin II with or without preloading of the cells with 'NO via PAPA-NONOate. While (-)-epicatechin scavenged O-2(-), its O-methylated metabolites prevented O-2(-) generation through inhibition of endothelial NADPH oxidase activity, even more strongly than apocynin. From the effect of 3,5-dinitrocatechol, an inhibitor of catechol-O-methyltransferase (COMT), on HUVEC it is concluded that (-)-epicatechin serves as 'prodrug' for conversion to apocynin-like NADPH oxidase inhibitors. These data indicate an (NO)-N-.-preserving effect of (-)-epicatechin via suppression of O-2(-)-mediated loss of (NO)-N-.. (c) 2007 Elsevier Inc. All rights reserved.