Pyrrolidine dithiocarbamate inhibits induction of nitric oxide synthase activity in rat alveolar macrophages.

Since nuclear factor kappa B (NF-kappa B) is activated during many inflammatory conditions, we assessed its role in expression of the L-arginine-nitric oxide pathway by rat alveolar macrophages. Pyrrolidine dithiocarbamate (PDTC), an inhibitor of NF-kappa B activation, was added to cultured macrophages stimulated with lipopolysaccharide (LPS) and interferon-gamma (IFN gamma). Inducible nitric oxide synthase (iNOS) activity was determined by measuring the stable nitrogen oxide end products of L-arginine oxidation: nitrite (NO2-) and nitrate (NO3-). Ten, 25 and 50 microM PDTC progressively inhibited iNOS activity by macrophages. When 50 microM PDTC was added 2 h before LPS + IFN gamma, L-arginine oxidation by macrophages was inhibited by > 99%; L-arginine oxidation was reduced by 70% if 50 microM PDTC and the stimuli were introduced together; NO2- and NO3- were not decreased significantly if 50 microM PDTC was added 6 h after LPS + IFN gamma. Cycloheximide added along with LPS + IFN gamma totally inhibits iNOS activity, while cycloheximide added 6 h after LPS + IFN gamma did not reduce NO2- and NO3- in tissue culture supernatants. These findings suggest iNOS activity in macrophages treated with LPS + IFN gamma requires NF-kappa B activation.