Nitrotyrosine formation after activation of murine macrophages with mycobacteria and mycobacterial lipoarabinomannan

Murine peritoneal macrophages, elicited with thioglycollate, were stimulate d in vitro with lipopolysaccharide (LPS). The production of nitrite, supero xide anion (SOA), and the accumulation of nitrotyrosine in the cells increa sed after treatment, and all were inhibitable by the NO synthase inhibitor N-G-monomethyl-L-arginine monoacetate (L-NMMA). This effect suggests a dire ct correlation between the accumulation of those metabolites and NO synthas e activity. Lipoarabinomannan (LAM) purified from Mycobacterium tuberculosi s was added to peritoneal macrophages in the presence of interferon-gamma ( IFN-gamma); the cells produced nitrite and SOA, both inhibitable by L-NMMA. There was, as well, accumulation of nitrotyrosine in the macrophage protei ns. Strikingly, the amount of nitrotyrosine measured after LAM plus IFN-gam ma, or LAM plus the low molecular weight adjuvant glutamylmuramyl dipeptide (GMDP), increased significantly in the presence of L-NMMA. These results s uggest that murine macrophages, upon LAM stimulation, might generate reacti ve nitrogen metabolites by a route other than NO synthase. Nitrotyrosine ac cumulation after infection of macrophages in vitro, with either live bacill e Calmette-Guerin (BCG) or live M. tuberculosis, in the presence or absence of IFN-gamma, showed no correlation with nitrite production, suggesting a low superoxide production.