Ascorbate inhibits iNOS expression in endotoxin- and IFNγ-stimulated rat skeletal muscle endothelial cells

Lipopolysaccharide endotoxin and interferon-gamma induced inducible nitric oxide synthase (iNOS) protein expression and nitrite/nitrate formation in microvascular endothelial cell cultures (ECs) derived from rat skeletal muscle. Pretreatment of ECs with ascorbate accumulated a large amount of ascorbate inside the cells and consequently decreased both intracellular oxidant level and iNOS induction. These effects of ascorbate were abolished in the presence of exogenous superoxide generated by xanthine oxidase/xanthine plus catalase but were not altered when N-nitro-L-arginine methyl ester was applied to inhibit nitric oxide synthesis. Ascorbate also attenuated the activation of transcription factor IRF-1 but not NFkappaB. These results indicate that ascorbate inhibits NOS expression in ECs by an antioxidant mechanism independent of both NFkappaB activation and the reported negative feedback effect of nitric oxide. (C) 2002 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.