Ascorbate Prevents the Interaction of Superoxide and Nitric Oxide Only at Very High Physiological Concentrations

• Published in: Circulation research Vol. 83; no. 9; pp. 916 - 922
• Main Authors: Jackson, Terence S, Xu, Aiming, Vita, Joseph A, Keaney, John F
• Format: Journal Article
• Language: English
• Published: Hagerstown, MD American Heart Association, Inc 02.11.1998; Lippincott; Lippincott Williams & Wilkins Ovid Technologies
• Subjects: Animals; Ascorbic Acid - pharmacology; Biological and medical sciences; Blood vessels and receptors; Endothelium, Vascular - drug effects; Endothelium, Vascular - physiology; Female; Fundamental and applied biological sciences. Psychology; Male; Nitric Oxide - physiology; Pyrogallol - pharmacology; Rabbits; Superoxides - metabolism; Vasodilation - drug effects; Vertebrates: cardiovascular system; Physiological condition; Ascorbic acid; Vitamin; Rabbit; Molecular interaction; Concentration; Oxidant; Lagomorpha; Antioxidant; Thoracic aorta; Prevention; Vertebrata; Mammalia; Blood vessel; Animal; Nitric oxide; Circulatory system
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/01.res.83.9.916

The bioactivity of nitric oxide (sup [round bullet, filled] NO) depends, in part, on its interaction with superoxide. Usually, superoxide dismutase (SOD) preserves sup [round bullet, filled] NO bioactivity by limiting the availability of superoxide. Ascorbic acid also effectively scavenges superoxide, but the extent to which this interaction is necessary for intact sup [round bullet, filled] NO bioactivity is not known. Therefore, the present study examined the effect of ascorbic acid on sup [round bullet, filled] NO bioactivity with isolated rabbit arterial segments. A steady flux of superoxide (1.15 to 2.3 [micro sign]mol [middle dot] L [center dot] min) produced either by pyrogallol autoxidation or a hypoxanthine/xanthine oxidase system inhibited endothelium-derived sup [round bullet, filled] NO-mediated arterial relaxation elicited by acetylcholine. This effect of superoxide was completely blocked by SOD (300 IU/mL) and the manganese SOD mimic EUK-8 (300 [micro sign]mol/L) and partially inhibited by ascorbic acid (10 mmol/L). Lower concentrations of ascorbic acid were ineffective despite scavenging >90% of superoxide. We increased the endogenous flux of superoxide (3.2 +/- 0.3-fold) by inhibiting vascular copper-zinc SOD with diethyldithiocarbamate. This increased endogenous flux of superoxide produced an impairment of sup [round bullet, filled] NO-mediated arterial relaxation that was reversed by EUK-8 (300 [micro sign]mol/L) but not ascorbic acid (10 mmol/L) despite equivalent scavenging of the endogenous superoxide flux. We used 3-nitrotyrosine formation (from peroxynitrite) as an indicator of sup [round bullet, filled] NO interaction with superoxide and found that SOD and EUK-8 compete more effectively with sup [round bullet, filled] NO for superoxide than does ascorbic acid. These data indicate that preservation of sup [round bullet, filled] NO bioactivity by superoxide scavengers depends not only on superoxide scavenging activity, but also on the rate of superoxide scavenging. Normal extracellular concentrations of ascorbic acid (30 to 150 [micro sign]mol/L) are not likely to prevent the interaction of sup [round bullet, filled] NO with superoxide under physiological conditions. (Circ Res. 1998;83:916-922.)