Ascorbate-dependent enhancement of nitric oxide formation in activated macrophages

Macrophages activated with bacterial lipopolysaccharide (LPS) and cytokines produce nitric oxide through the induction of iNOS gene expression. Ascorbate increased NOx (nitrite and nitrate) formation by approximately 40% in a mouse macrophage-like cell line, J774.1, activated with LPS and interferon-gamma. Ascorbate alone exhibited no inductive activity toward NO formation. N(G)-Monomethyl-L-arginine inhibited nitrite formation in cells activated in the presence or absence of ascorbate. Northern and Western blotting analyses showed that both iNOS mRNA and protein steady-state levels were increased approximately twofold in cells activated in the presence of ascorbate compared to in cells activated only with the inducers. These data suggest that ascorbate increased NO production by increasing the amount of iNOS in the activated macrophages.