title: Inhibition of NADPH oxidase activation in endothelial cells by ortho-methoxy-substituted catechols.
abstract: 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.
authors.affiliation: Department of Chemistry, State University of New York College at Geneseo, USA.
authors.forename: David K
authors.initials: DK
authors.lastname: Johnson
authors.forename: Kurt J
authors.initials: KJ
authors.lastname: Schillinger
authors.forename: David M
authors.initials: DM
authors.lastname: Kwait
authors.forename: Chambers V
authors.initials: CV
authors.lastname: Hughes
authors.forename: Erin J
authors.initials: EJ
authors.lastname: McNamara
authors.forename: Fauod
authors.initials: F
authors.lastname: Ishmael
authors.forename: Robert W
authors.initials: RW
authors.lastname: O'Donnell
authors.forename: Ming-Mei
authors.initials: MM
authors.lastname: Chang
authors.forename: Michael G
authors.initials: MG
authors.lastname: Hogg
authors.forename: Jonathan S
authors.initials: JS
authors.lastname: Dordick
authors.forename: Lakshmi
authors.initials: L
authors.lastname: Santhanam
authors.forename: Linda M
authors.initials: LM
authors.lastname: Ziegler
authors.forename: James A
authors.initials: JA
authors.lastname: Holland
mesh_terms: D000098:Acetophenones / Q000737:chemistry / Q000494:pharmacology*; D002396:Catechols / Q000737:chemistry / Q000494:pharmacology*; D003545:Cysteine / Q000494:pharmacology; D019281:Dimerization; D004730:Endothelium, Vascular / Q000187:drug effects / Q000201:enzymology* / Q000254:growth & development; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005978:Glutathione / Q000494:pharmacology; D006861:Hydrogen Peroxide / Q000378:metabolism; D008956:Models, Chemical; D009247:NADH, NADPH Oxidoreductases / Q000037:antagonists & inhibitors / Q000097:blood; D019255:NADPH Oxidases / Q000378:metabolism*; D010084:Oxidation-Reduction; D009195:Peroxidase / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000032:analysis; D013481:Superoxides / Q000378:metabolism; D014451:Ubiquinone / Q000378:metabolism
chemical_list: D000098:Acetophenones; D002396:Catechols; D004791:Enzyme Inhibitors; D017382:Reactive Oxygen Species; D013481:Superoxides; D014451:Ubiquinone; C056165:acetovanillone; D006861:Hydrogen Peroxide; D009195:Peroxidase; D009247:NADH, NADPH Oxidoreductases; D019255:NADPH Oxidases; D005978:Glutathione; D003545:Cysteine