Inhibition of NADPH oxidase activation in endothelial cells by ortho-methoxy-substituted catechols

David K. Johnson, Kurt J. Schillinger, David M. Kwait, Chambers V. Hughes, Erin J. McNamara, Fauod Ishmael, Robert W. O'Donnell, Ming Mei Chang, Michael G. Hogg, Jonathan S. Dordick, Lakshmi Santhanam, Linda M. Ziegler, James A. Holland

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177 Scopus citations


NADPH oxidase is a major enzymatic source of oxygen free radicals in stimulated endothelial cells (ECs). The ortho-methoxy-substituted catechol, apocynin (4-hydroxy-3-methoxyacetophenone), isolated from the traditional medicinal plant Picrorhiza kurroa, inhibits the release of superoxide anion (O2.-) by this enzyme. The compound acts by blocking the assembly of a functional NADPH oxidase complex. The underlying chemistry of this inhibitory activity, and its physiological significance to EC proliferation, have been investigated. A critical event is the reaction of ortho-methoxy-substituted catechols with reactive oxygen species (ROS) and peroxidase. Analysis of this reaction reveals that apocynin is converted to a symmetrical dimer through the formation of a 5,5′ carbon-carbon bond. Both reduced glutathione and L-cysteine inhibit this dimerization process. Catechols without the ortho-methoxy-substituted group do not undergo this chemical reaction. Superoxide production by an endothelial cell-free system incubated with apocynin was nearly completely inhibited after a lagtime for inhibition of ca. 2 min. Conversely, O2.- production was nearly completely inhibited, without a lagtime, by incubation with the dimeric form of apocynin. The apocynin dimer undergoes a two-electron transfer reaction with standard redox potentials of -0.75 and -1.34 V as determined by cyclic voltammetry. Inhibition of endothelial NADPH oxidase by apocynin caused a dose-dependent inhibition of cell proliferation. These findings identify a metabolite of an ortho-methoxy-substituted catechol, which may be the active compound formed within stimulated ECs that prevents NADPH oxidase complex assembly and activation.

Original languageEnglish (US)
Pages (from-to)191-203
Number of pages13
JournalEndothelium: Journal of Endothelial Cell Research
Issue number3
StatePublished - 2002

All Science Journal Classification (ASJC) codes

  • Physiology
  • Cell Biology


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