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.
Original language | English (US) |
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Pages (from-to) | 191-203 |
Number of pages | 13 |
Journal | Endothelium: Journal of Endothelial Cell Research |
Volume | 9 |
Issue number | 3 |
DOIs | |
State | Published - 2002 |
Externally published | Yes |
Keywords
- Catechols
- Endothelial cells
- NADPH oxidase
- Reactive oxygen species
ASJC Scopus subject areas
- Physiology
- Cell Biology