Nitric oxide synthase generates superoxide and nitric oxide in arginine-depleted cells leading to peroxynitrite-mediated cellular injury.

To determine the role of cytosolic L-Arg concentrations in controlling nitric oxide synthase -mediated *°2 generation in these cells, we examined the relationship of NO and *°2 production to cytosolic L-Arg levels

Y. Xia; V. L. Dawson; T. M. Dawson; S. H. Snyder; J. L. Zweier

2002

Scholarcy highlights

  • Besides synthesizing nitric oxide, purified neuronal NO synthase can produce superoxide at lower L-Arg concentrations
  • Since purified neuronal NO synthase has been reported to generate *°2 at low concentrations of L-Arg, experiments were performed on nNOS-transfected 293 cells to determine whether depleting cytosolic L-Arg could trigger nNOS to produce *2
  • To determine the role of cytosolic L-Arg concentrations in controlling NO synthase-mediated *°2 generation in these cells, we examined the relationship of NO and *°2 production to cytosolic L-Arg levels
  • In L-Arg-depleted cells, stimulation with A23187 increased lactate dehydrogenase release 5-fold. This increased LDH release could be largely prevented by the pretreatment with superoxide dismutase or N-nitro-L-arginine methyl ester with values of 28.2 ± 3.6 and 30.6 ± 3.5 units/liter, respectively, confirming that these cytotoxic effects were elicited by the NO and *°2 derived from activated NOS
  • Recent studies have suggested that nNOS in the absence of L-Arg can generate reduced oxygen species including *°2 and H202
  • The observed *°2 generation was quenched more than 90% by the NOS blocker L-NAME but not by D-NAME
  • All prior evidence of NOS-mediated *°2 generation, was based on studies of the isolated enzyme in which *O° generation might stem from alterations in the properties or conformation of the enzyme after isolation
  • Nitrotyrosine formation was observed in L-Arg-depleted cells after activation and this process was blocked by inhibition of nitric oxide synthase

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