Nitric oxide, an endothelial cell relaxation factor, inhibits neutrophil superoxide anion production via a direct action on the NADPH oxidase.
Nitric oxide provokes vasodilation and inhibits platelet aggregation. We examined the effect of nitric oxide on superoxide anion production by three sources: activated intact neutrophils, xanthine oxidase/hypoxanthine, and the NADPH oxidase. Nitric oxide significantly inhibited the generation of superoxide anion by neutrophils exposed to either FMLP (10(-7)M) or PMA (150 ng/ml) (IC50 = 30 microM). To determine whether the effect of nitric oxide on the respiratory burst was due to simple scavenging of O2+, kinetic studies that compared effects on neutrophils and the cell-free xanthine oxidase system were performed. Nitric oxide inhibited O2+ produced by xanthine oxidase only when added simultaneously with substrate, consistent with the short half-life of NO in oxygenated solution. In contrast, the addition of nitric oxide to neutrophils 20 min before FMLP resulted in the inhibition of O2+ production, which suggests formation of a stable intermediate. The effect of nitric oxide on the cell-free NADPH oxidase superoxide-generating system was also examined: The addition of NO before arachidonate activation (t = -6 min) significantly inhibited superoxide anion production. Nitric oxide did not inhibit O2+ when added at NADPH initiation (t = 0). Treatment of the membrane but not cytosolic component of the oxidase was sufficient to inhibit O2+ generation. The data suggest that nitric oxide inhibits neutrophil O2+ production via direct effects on membrane components of the NADPH oxidase. This action must occur before the assembly of the activated complex.
Clancy
R M
RM
Department of Medicine, New York University Medical Center, New York 10016.
Leszczynska-Piziak
J
J
Abramson
S B
SB
D002118:Calcium / Q000378:metabolism; D015550:Cell Degranulation / Q000187:drug effects; D002478:Cells, Cultured; D006801:Humans; D009247:NADH, NADPH Oxidoreductases / Q000037:antagonists & inhibitors*; D019255:NADPH Oxidases; D009504:Neutrophils / Q000187:drug effects* / Q000378:metabolism; D009569:Nitric Oxide / Q000494:pharmacology*; D013481:Superoxides / Q000378:metabolism*; D014969:Xanthine Oxidase / Q000494:pharmacology
D013481:Superoxides; D009569:Nitric Oxide; D014969:Xanthine Oxidase; D009247:NADH, NADPH Oxidoreductases; D019255:NADPH Oxidases; D002118:Calcium