FIGURE 3.

Reactive oxygen species-producing systems in cardiovascular diseases. O₂ ^●− can be generated in extracellular myocardium by NAD(P)H, uncoupled eNOS, xanthine oxidase, and mitochondrial respiration chains. H₂O₂ can be spontaneously converted into OH^●− by Fe reaction and SOD. H₂O₂ can be detoxified by GSH peroxidase, Trx peroxidase, and catalase to H₂O and O₂. The myeloperoxidase enzyme can employ H₂O₂ to oxygenize chloride to the strong oxidizer HOCl. In addition, the decoupling of eNOS reduces the production of NO^● in endothelial cells, and the decrease in the expression and activity of eNOS further aggravates the production of NO^●. NAD(P)H, nicotinamide adenine dinucleotide (phosphate); eNOS, endothelial nitric oxide synthase; NO^●, nitric oxide; O₂ ^●−, superoxide; HOCl, hypochlorite; SOD, superoxide dismutase activity; H₂O₂, hydrogen peroxide; ONOO⁻, peroxynitrite; OH^●, hydroxyl radicals; GSH, glutathione; GSSG, oxidized glutathione; GPx, glutathione peroxidase; Trx, thioredoxin.