CONCURRENT GENERATION OF NITRIC-OXIDE AND SUPEROXIDE DAMAGES SURFACTANT PROTEIN-A

The conditions under which nitric oxide (.NO) may modulate or promote lung injury have not been identified. We hypothesized that .NO-induced injury results from peroxynitrite, formed by the reaction of .NO with superoxide. The simultaneous generation of .NO and superoxide by 3-mo rpholinosydnonimine (SIN-1, 0.1-2 mM) resulted in oxidation of dihydro rhodamine, a marker of peroxynitrite production, and a dose-dependent decrease in the ability of SP-A to enhance lipid aggregation. Western blot analysis of SIN-1 exposed SP-A samples, overlaid with a polyclona l antibody against nitrotyrosine, were consistent with nitration of SP -A tyrosine residues. Superoxide dismutase (100 U/ml), L-cysteine (5 m M), xanthine oxidase (10 mU/ml) and xanthine (500 mu M), or urate (100 mu M) prevented the SIN-1-induced dihydrorhodamine oxidation and inju ry to SP-A. .NO alone, generated by S-nitroso-N-acetylpenicillamine pl us 100 mu M L-cysteine, or superoxide and hydrogen peroxide, generated by pterin and xanthine oxidase in the absence of iron, did not damage SP-A or oxidize dihydrorhodamine. We concluded that peroxynitrite, bu t not .NO or superoxide and hydrogen peroxide, in concentrations likel y to be encountered in vivo, caused nitrotyrosine formation and decrea sed the ability of SP-A to aggregate lipids.