Quantitation of nitrotyrosine levels in lung sections of patients and animals with acute lung injury

Peroxynitrite-mediated oxidation of dihydrorhodamine 123 occurs in early stages of endotoxic and hemorrhagic shock and ischemia-reperfusion injury

To quantify peroxynitrite production during shock, we measured oxidation of dihydrorhodamine 123 in rats. In endotoxic and hemorrhagic shock and splanchic ischemia-reperfusion, dihydrorhodamine oxidation rapidly increased, which was prevented by inhibition of endothelial nitric oxide (.NO) synthase (ecNOS). Thus, peroxynitrite is already formed at early stages of shock from ecNOS-derived .NO. Overproduction of .NO by the inducible NOS at late shock was not associated with additional increases in dihydrorhodamine oxidation. ecNOS inhibition enhanced dihydrorhodamine oxidation in control rats. These latter findings may be explained by .NO-mediated inhibition of peroxynitrite-induced dihydrorhodamine oxidation, a phenomenon also observed in vitro.

Nitric oxide and oxygen radicals: a question of balance

The production of superoxide and nitric oxide individually has been associated with the development of several diseases but only recently has it been realised that interactions between them may also be important in disease pathology. The central hypothesis which is emerging is that the balance between nitric oxide and superoxide generation is a critical determinant in the aetiology of many human diseases including atherosclerosis, neurodegenerative disease, ischaemia-reperfusion and cancer. These ideas are discussed in this short overview and placed in the context of the current and future status of therapies which could modulate the balance between nitric oxide and superoxide.

Mice lacking extracellular superoxide dismutase are more sensitive to hyperoxia

Extracellular superoxide dismutase (EC-SOD; superoxide:superoxide oxidoreductase, EC 1.15.1.1) is a secreted Cu- and Zn-containing tetrameric glycoprotein, the bulk of which is bound to heparan sulfate proteoglycans in the interstitium of tissues. To test the function of EC-SOD in vivo, mice carrying a targeted disruption of the EC-SOD gene were generated. The EC-SOD null mutant mice develop normally and remain healthy until at least 14 months of age. No compensatory induction of other SOD isoenzymes or other antioxidant enzymes was observed. When stressed by exposure to > 99% oxygen, the EC-SOD null mutant mice display a considerable reduction in survival time compared to wild-type mice and an earlier onset of severe lung edema. These findings suggest that while under normal physiological conditions other antioxidant systems may substitute for the loss of EC-SOD; when the animal is stressed these systems are unable to provide adequate protection.

Genetic and redox determinants of nitric oxide cytotoxicity in a Salmonella typhimurium model

Paradoxically, nitric oxide (NO) has been found to exhibit cytotoxic, antiproliferative, or cytoprotective activity under different conditions. We have utilized Salmonella mutants deficient in antioxidant defenses or peptide transport to gain insights into NO actions. Comparison of three NO donor compounds reveals distinct and independent cellular responses associated with specific redox forms of NO. The peroxynitrite (OONO-) generator 3-morpholinosydnonimine hydrochloride mediates oxygen-dependent Salmonella killing, whereas S-nitrosoglutathione (GSNO) causes oxygen-independent cytostasis, and the NO. donor diethylenetriamine-nitric oxide adduct has no antibacterial activity. GSNO has the greatest activity for stationary cells, a characteristic relevant to latent or intracellular pathogens. Moreover, the cytostatic activity of GSNO may best correlate with antiproliferative or antimicrobial effects of NO, which are unassociated with overt cell injury. dpp mutants defective in active dipeptide transport are resistant to GSNO, implicating heterolytic NO+ transfer rather than homolytic NO. release in the mechanism of cytostasis. This transport system may provide a specific pathway for GSNO-mediated signaling in biological systems. The redox state and associated carrier molecules are critical determinants of NO activity.

Peroxynitrite-mediated oxidative protein modifications

Proteins are targets of reactive species and detection of oxidatively modified proteins is often used as an index of oxidative stress. Peroxynitrite is a strong oxidant formed by reaction of nitric oxide with superoxide. Using fatty acid-free bovine serum albumin as a model we examined peroxynitrite-mediated protein modifications. The reaction of protein with peroxynitrite resulted in the oxidation of tryptophan and cysteine, in the nitration of tyrosine, in the formation of dityrosine, in the production of 2,4 dinitrophenylhydrazine-reactive carbonyls and in protein fragmentation. The formation of 3-nitrotyrosine represents a specific peroxynitrite-mediated protein modification that is different from modifications mediated by reactive oxygen species.

Endotoxin triggers the expression of an inducible isoform of nitric oxide synthase and the formation of peroxynitrite in the rat aorta in vivo

The free radicals nitric oxide (.NO) and superoxide (O2-) are known to react to form peroxynitrite (ONOO-), a highly reactive species. Peroxynitrite has been suggested to play an important role in the cellular damage associated with the overproduction of .NO, but there are very limited data regarding its in vivo formation. Here we demonstrate that injection of endotoxin into rats leads to the expression of an inducible isoform of .NO synthase (iNOS) in the thoracic aorta at 6 h and an increase in the circulating levels of nitrite/nitrate. Moreover, at the same time point, there is a marked increase in the immunoreactivity of nitrotyrosine, a marker of peroxynitrite in the aorta. The formation of nitrotyrosine was prevented by inhibiting the activity of NOS by NG-methyl-L-arginine in vivo. Our data suggest that during endotoxin shock, part of .NO, produced following the induction of iNOS, is converted into peroxynitrite in the vicinity of large blood vessels. The demonstration of the in vivo formation of peroxynitrite at sites of .NO overproduction may necessitate the development of novel and additional approaches for limiting or preventing .NO-related cytotoxic or vasodilatory actions during circulatory shock.