Oxidation of mitochondrial and nuclear proteins by endogenously produced peroxynitrite in immunostimulated macrophages

Endogenously produced peroxynitrite ia toxic oxidant produced from NO and superoxide) suppresses mitochondrial respiration and induces DNA strand breakage in immunostimulated macrophages. In the present study we investigated the role of endogenous and exogenous nitric oxide (NO) and peroxynitrite in the process of protein oxidation, as measured by the detection of 2,4 dinitrophenylhydrazine-reactive carbonyls. In J774 macrophages. Exogenously added hydrogen peroxide and peroxynitrite, but not NO, caused a marked increase in protein oxidation in the macrophages. Moreover, immunostimulation of the macrophages with bacterial lipopolysaccharide and gamma-interferon (LPS/IFN) resulted in a marked increase in the protein oxidation of these cells. Fractionation of nuclei and mitochondrial from these cells, followed by detection of 2.4 dinitrophenylhydrazine-reactive carbonyls revealed that immunostimulation causes protein oxidation of a large number of mitochondrial as well as nuclear proteins. The inhibitor of NO synthase, N^G-methyl-L-arginine (L-NMA, 3 mM) and the cell-permeable superoxide dismutase mimetic Mn(III)tetrakis (4-benzoic acid) porphyrin (MnTBAP, (300 μM) both inhibited the increase in protein oxidation in response to LPS/IFN. These data demonstrate that immunostimulation induced marked protein oxidation in cultured macrophages. The protective effect of L-NMA as well as MnTBAP suggest that endogenous peroxynitrite (formed from the reaction of superoxide with NO, the latter produced by inducible NO synthase) induces protein oxidation in the immunostimulated cells.