Mono-O-methylated flavanols and other flavonoids as inhibitors of endothelial NADPH oxidase

doi:10.1016/j.abb.2007.10.012

Archives of Biochemistry and Biophysics

Volume 469, Issue 2, 15 January 2008, Pages 209-219

https://doi.org/10.1016/j.abb.2007.10.012 Get rights and content

Abstract

The dietary flavan-3-ol (−)-epicatechin improves the bioactivity of nitric oxide in arterial vessels in vivo. Moreover, it effectively protects cultured vascular endothelial cells from signs of oxidative stress and elevates intracellular nitric oxide in vitro. We addressed the effects of (−)-epicatechin, its metabolic conversion products and structurally related compounds on NADPH oxidase activity in intact human umbilical vein endothelial cells (HUVEC) and in cell lysates. (−)-Epicatechin proved to be an O₂⁻-scavenger but did not inhibit NADPH oxidase activity, whereas the converse pattern was observed for the metabolites 3′- and 4′-O-methyl epicatechin. The dimer procyanidin B2 and (−)-epicatechin glucuronide were O₂⁻-scavengers and inhibited NADPH oxidase. Analysis of structure–activity relations with 45 compounds suggests an apocynin-like mode of NADPH oxidase inhibition. Notably, HUVEC converted (−)-epicatechin to NADPH oxidase-inhibitory methyl ethers. These data identify endothelial NADPH oxidase as candidate target of dietary flavonoids and particularly of their metabolites.

Section snippets

Enzymes and substrates

Catechol-O-methyltransferase (COMT), S-adenosyl-l-methionine (SAM), uridine 5′-diphosphoglucuronic acid (UDP-GA) and recombinant human UDP-glucuronyl transferases (UGT) 1A7 and 1A10 were obtained from Sigma–Aldrich (St. Louis, MO), and human leukocyte myeloperoxidase and human liver microsomes from Calbiochem (Schwalbach, Germany).

Chemicals

Flavonoids and other phenolics were obtained from following sources: Isorhamnetin, procyanidin B2, propylgallate and vanilline from Fluka (Deisenhofen, Germany),

HUVEC convert (−)-epicatechin to monomethyl ethers via catechol-O-methyltransferase

Incubation of HUVEC with (−)-epicatechin for 24 h led to conversion of this flavanol to a metabolite fraction, which co-migrated with authentic 3′-O-methyl epicatechin in thin-layer chromatography (Fig. 1). Presence of 3,5-dinitrocatechol (DNC), an inhibitor of catechol-O-methyltransferase (COMT) [20], prevented this conversion. In subsequent experiments applying HPLC, the methylated metabolite fraction was identified as a mixture of 3′- and 4′-O-methyl epicatechin (Steffen et al., unpublished

Endothelial NADPH oxidase activity as a possible target of dietary polyphenols or their metabolites

In this study we provide evidence that a large variety of flavonoids and their metabolites are capable of protecting vascular endothelial cells against O₂⁻ through inhibition of endothelial NADPH oxidase activity. For methodological reason, this action was directly demonstrated using cell lysates, in which the artificial activator SDS was employed to stimulate the NADPH oxidase [17], [18]. We adduce evidence, however, that inhibition of NADPH oxidase by these polyphenols also occurs in intact

Acknowledgment

H.S. is a Fellow of the National Foundation for Cancer Research (NFCR), Bethesda, MD.

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Mono-O-methylated flavanols and other flavonoids as inhibitors of endothelial NADPH oxidase

Abstract

Section snippets

Enzymes and substrates

Chemicals

HUVEC convert (−)-epicatechin to monomethyl ethers via catechol-O-methyltransferase

Endothelial NADPH oxidase activity as a possible target of dietary polyphenols or their metabolites

Acknowledgment

J. Am. Coll. Cardiol.

Am. J. Clin. Nutr.

Biochem. Biophys. Res. Commun.

Free Radic. Biol. Med.

Arch. Biochem. Biophys.

J. Biol. Chem.

Arch. Biochem. Biophys.

Arch. Biochem. Biophys.

Eur. J. Pharmacol.

Free Radic. Biol. Med.

Free Radic. Biol. Med.

Acta Histochem.

Life Sci.

Am J. Clin. Nutr.

Biochem. Biophys. Res. Commun.

Free Radic. Biol. Med.

Free Radic. Biol. Med.

Toxicol. Lett.

J. Biol. Chem.

JAMA

J. Cardiovasc. Pharmacol.

J. Am. Coll. Nutr.