Apparent hydroxyl radical production by peroxynitrite: implications for endothelial injury from nitric oxide and superoxide.

Abstract

Superoxide dismutase reduces injury in many disease processes, implicating superoxide anion radical (02 ) as a toxic species in vivo. A critical target of superoxide may be nitric oxide (NO-) produced by endothelium, macrophages, neutrophils, and brain synaptosomes. Superoxide and NO-are known to rapidly react to form the stable peroxynitrite anion (ONOO-). We have shown that peroxynitrite has a pKa of 7.49 ± 0.06 at 3TC and rapidly decomposes once protonated with a half-life of 1.9 sec at pH 7.4. Peroxynitrite decomposition generates a strong oxidant with reactivity similar to hydroxyl radical, as assessed by the oxidation of deoxyribose or dimethyl sulfoxide. Product yields indicative of hydroxyl radical were 5.1 ± 0.1% and 24.3 + 1.0%, respectively, of added peroxynitrite. Product formation was not affected by the metal chelator diethyltriaminepentaacetic acid, suggesting that iron was not required to catalyze oxidation. In contrast, desferrioxamine was a potent, competitive inhibitor of peroxynitriteinitiated oxidation because of a direct reaction between desferrioxamine and peroxynitrite rather than by iron chelation. We propose that superoxide dismutase may protect vascular tissue stimulated to produce superoxide and NON under pathological conditions by preventing the formation of peroxynitrite.Vascular injury secondary to ischemia/reperfusion, inflammation, xenobiotic metabolism, hyperoxic exposure, and other diseases results in loss of endothelial barrier function, adhesion of platelets, and abnormal vasoregulation. The ability of superoxide dismutase (SOD) to often reduce endothelial injury indirectly implicates the participation of superoxide anion radical (Oj-) with many pathological processes (1). While O-' can be directly toxic (2), it has a limited reactivity with most biological molecules, raising questions about its toxicity per se (3). To account for the apparent toxicity of O-j in vivo, the secondary production of the far-more-reactive hydroxyl radical (HO-) is frequently proposed to occur by the iron-catalyzed Haber Recently, endothelium, macrophages, and brain synaptosome preparations have been shown to produce NOR by oxidizing arginine by a calcium-activated NADPH-dependent enzyme (6-9). NOR appears to be a major form of the endothelium-derived relaxing factor (EDRF) (10). Vasodilatory agents such as acetylcholine, ATP, and bradykinin initiate a receptor-mediated influx of Ca2 , triggering the production and extracellular release of NO-, which then activates soluble heme-containing guanylate cyclases to produce cGMP in vascular smooth muscle and platelets. Increased cGMP promotes relaxation in vascular smooth muscle and inhibits platelet aggregation as well as adhesion of platelets to endothelium (11). Macrophages produce NOR as part of their cytotoxic armamentarium (6).The half-life of EDRF and NON ranges from 4 to 50 sec (12), which is approximately doubled by SOD (13,14). NOR does not bind directly to the copper of SOD (15), suggesting that stabilization involves the scavenging of...

Improved functional outcome after spinal cord injury in iNOS-deficient mice

“…13 Normal movements, ability to walk on a 5 mm wide bar. with the body of work describing a destructive role of iNOS in cerebral ischaemia and traumatic brain injury.…”

“…with the body of work describing a destructive role of iNOS in cerebral ischaemia and traumatic brain injury. NO derived from iNOS catalytic activity may react with the superoxide anion to form peroxynitrite, 9 a molecule that is associated with oxidative tissue damage 13 and apoptotic neuronal death. 14 In contrast to this, other investigators have shown that functional end points after controlled cortical impact brain trauma were significantly worsened if iNOS was pharmacologically inhibited or genetically deficient in experimental rats and mice, respectively.…”

NADH oxidase activity of rat and human liver xanthine oxidoreductase: potential role in superoxide production

“…•- [21], can be produced solely by the action of XOR [19]. The XORderived ONOO -has been proposed as a bactericidal agent in milk and the digestive tract [19].…”

Temporal and Spatial Dynamics of Peroxynitrite-Induced Oxidative Damage After Spinal Cord Contusion Injury

“…Additional work has demonstrated that the infusion of PN at levels that mimic the estimated concentration produced in the contused spinal cord produces nitrative immunostaining and neuronal damage similar to that produced by contusion injury (Liu et al, 2005). The increase in 3-NT is paralleled by increases in LP products (Xiong et al, 2007) and the activation of the DNA repair enzyme poly-ADP ribose polymerase (Scott et al, 1999; Scott et al, 2004); both of these pathochemical events are known to be capable of being produced by PN (Beckman et al, 1990; Beckman, 1991; Beckman, 2002; Pacher et al, 2007; Radi et al, 1991). A recent report from our laboratory has shown that the coincident increase in the levels of 3-NT and the LP product 4-HNE during the first hour after injury persists at least until 7 days post-injury (Xiong et al, 2007).…”