S-Nitroglutathione, a product of the reaction between peroxynitrite and glutathione that generates nitric oxide

Resistance of endothelium-dependent relaxation to elevation of O(-)(2) levels in rabbit carotid artery

Endogenous superoxide anion (O(-)(2)) interferes with the bioactivity of nitric oxide (NO) in endothelium-dependent arterial relaxation (EDR). Using the lucigenin chemiluminescence assay, we measured O(-)(2) in the thoracic and abdominal aortas and the carotid artery of rabbits to determine whether ambient O(-)(2) varies among the three arteries and differentially diminishes the effect of NO. Basal levels of O(-)(2) were significantly higher in carotid arteries than in the thoracic aorta [23 +/- 6.1 vs. 3.9 +/- 1.4 chemiluminescence units (CU); P < 0.05], whereas EDR in response to ACh (10(-8)-10(-5) M) was not significantly different on ANOVA. After treatment with the superoxide dismutase (SOD) inhibitor diethyldithiocarbamate (DDC; 10 mM), O(-)(2) levels were significantly elevated, becoming greater in the carotid artery and abdominal aorta than in the thoracic aorta (185 +/- 31.2 and 202 +/- 40.3 vs. 89 +/- 18 CU; P < 0.05). DDC significantly reversed EDR in the thoracic aorta but not in the carotid artery; at 10(-6) M ACh, the decrease seen with DDC was 48 +/- 6.2 vs. 6.8 +/- 8.0% of maximal relaxation in the thoracic aorta and carotid artery, respectively. In the thoracic aorta, exogenous SOD reversed the inhibition of EDR caused by DDC. Moreover, DDC/O(-)(2)-resistant EDR in the carotid artery was ablated by the addition of nitro-L-arginine methyl ester (300 microM; P < 0.05), an NO synthase inhibitor, consistent with peroxynitrite or an O(-)(2)-resistant NO donor being involved in carotid relaxation. Indeed, exogenous peroxynitrite caused similar relaxation of the carotid artery and thoracic aorta, which was unaffected by DDC. Our studies show a greater production of nitrite and O(-)(2) per unit area by the carotid artery, suggesting a greater amount of their product peroxynitrite. These findings support the hypothesis that peroxynitrite is the relaxing agent that resists high O(-)(2) in the carotid artery.

State-of-the-Art lecture. Role of angiotensin and oxidative stress in essential hypertension

In this review, we examine the possibility that small increments in angiotensin II are responsible for an increase in blood pressure and maintenance of hypertension through the stimulation of oxidative stress. A low dose of angiotensin II (2 to 10 ng x kg(-1) x min(-1), which does not elicit an immediate pressor response), when given for 7 to 30 days by continuous intravenous infusion, can increase mean arterial pressure by 30 to 40 mm Hg. This slow pressor response to angiotensin is accompanied by the stimulation of oxidative stress, as measured by a significant increase in levels of 8-iso-prostaglandin F(2alpha) (F(2)-isoprostane). Superoxide radicals and nitric oxide can combine chemically to form peroxynitrite, which can then oxidize arachidonic acid to form F(2)-isoprostanes. F(2)-isoprostanes exert potent vasoconstrictor and antinatriuretic effects. Furthermore, angiotensin II can stimulate endothelin production, which also has been shown to stimulate oxidative stress. In this way, a reduction in the concentration of nitric oxide (which is quenched by superoxide) along with the formation of F(2)-isoprostanes and endothelin could potentiate the vasoconstrictor effects of angiotensin II. We hypothesize that these mechanisms, which underlie the development of the slow pressor response to angiotensin II, also participate in the production of hypertension when circulating angiotensin II levels appear normal, as occurs in many cases of essential and renovascular hypertension.

Regulation of prostaglandin H2 synthase activity by nitrogen oxides

Nitric oxide and its derivatives have been shown to both activate and inhibit prostaglandin H(2) synthase 1 (PGHS-1). We set out to determine the mechanisms by which different nitrogen oxide derivatives modulate PGHS-1 activity. To this end, we show that 3-morpholinosydnonimine hydrochloride (SIN-1), a compound capable of generating peroxynitrite, activates purified PGHS-1 and also stimulates PGE(2) production in arterial smooth muscle cells in the presence of exogenous arachidonic acid. The effect of SIN-1 in smooth muscle cells was abrogated by superoxide and peroxynitrite inhibitors, which supports the hypothesis that peroxynitrite is an activating species of PGHS-1. Indeed, authentic peroxynitrite also induced PGE(2) production in arachidonic acid-stimulated cells. In contrast, when cells were exposed to the nitric oxide-releasing compound 1-hydroxy-2-oxo-3-[(methylamino)propyl]-3-methyl-1-triazene (NOC-7), PGHS-1 enzyme activity was inhibited in the presence of exogenous arachidonic acid. Finally, in lipid-loaded smooth muscle cells, we demonstrate that SIN-1 stimulates arachidonic acid-induced PGE(2) production; albeit, the extent of activation is reduced compared to that under normal conditions. These results indicate that formation of peroxynitrite is a key intermediary step in PGHS-1 activation. However, other forms of NO(x)() inhibit PGHS-1. These results may have implications in the regulation of vascular function and tone in normal and atherosclerotic arteries.

Peroxynitrite modification of protein thiols: oxidation, nitrosylation, and S-glutathiolation of functionally important cysteine residue(s) in the sarcoplasmic reticulum Ca-ATPase

Skeletal muscle contraction and relaxation is efficiently modulated through the reaction of reactive oxygen-nitrogen species with sarcoplasmic reticulum protein thiols in vivo. However, the exact locations of functionally important modifications are at present unknown. Here, we determine by HPLC-MS that the modification of one (out of 24) Cys residue of the sarcoplasmic reticulum (SR) Ca-ATPase isoform SERCA1, Cys(349), by peroxynitrite is sufficient for the modulation of enzyme activity. Despite the size and nature of the SR Ca-ATPase, a 110 kDa membrane protein, identification and quantitation of Cys modification was achieved through labeling with 4-(dimethylamino)phenylazophenyl-4'-maleimide (DABMI) and/or N-(2-iodoethyl)trifluoroacetamide (IE-TFA) followed by an exhaustive tryptic digestion and on-line HPLC-UV-electrospray MS analysis. The reaction with IE-TFA generates aminoethylcysteine, a new trypsin cleavage site, which allows the production of specific peptide fragments that are diagnostic for IE-TFA labeling, conveniently identified by mass spectrometry. Exposure of the SR Ca-ATPase to low concentrations (0.1 mM) of peroxynitrite resulted in the fully reversible chemical modification of Cys at positions 344, 349, 471, 498, 525, and 614 (nitrosylation of Cys(344) and Cys(349) was seen), whereas higher concentrations of peroxynitrite (0.45 mM) additionally affected Cys residues at positions 636, 670, and 674. When the SR Ca-ATPase was exposed to 0.45 mM peroxynitrite in the presence of 5.0 mM glutathione (GSH), thiol modification became partially reversible and S-glutathiolation was detected for Cys residues at positions 344, 349, 364, 498, 525, and 614. The extent of enzyme inactivation (determined previously) quantitatively correlated with the loss of labeling efficiency (i) of a single Cys residue and (ii) of the tryptic fragment containing both Cys(344) and Cys(349). Earlier results had shown that the independent selective modification of Cys(344) is functionally insignificant [Kawakita, M., and Yamashita, T. (1987) J. Biochem. (Tokyo) 102, 103-109]. Thus, we conclude that modification of only Cys(349) is responsible for the modulation of the SR Ca-ATPase activity by peroxynitrite.

Inhibition of guanylate cyclase stimulation by NO and bovine arterial relaxation to peroxynitrite and H2O2

The inhibitor of soluble guanylate cyclase (sGC) stimulation by nitric oxide (NO), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), was examined for its effects on the prolonged relaxation of endothelium-removed bovine coronary (BCA) and pulmonary (BPA) arteries to peroxynitrite (ONOO-) and on H2O2-elicited relaxation and sGC stimulation. Our previous studies suggest that ONOO- causes a prolonged relaxation of BPA by regenerating NO and that a 2-min exposure of BCA or BPA to 50 nM NO causes an ONOO--elicited relaxation. The relaxation of K+-precontracted BCA to 50 nM NO or 100 microM ONOO- was essentially eliminated by 10 microM ODQ. ODQ also eliminated relaxation to 0.1 nM-10 microM of NO donor S-nitroso-N-acetyl-penicillamine (SNAP), but it did not alter relaxation to 1-300 microM H2O2. Similar responses were also observed in BPA. ODQ did not increase lucigenin-detectable superoxide production in BCA, and it did not alter luminol-detectable endogenous ONOO- formation observed during a 2-min exposure of BCA to 50 nM NO. In addition, ODQ did not affect tissue release of NO after 2 min exposure of BCA to 50 nM NO. The activity of sGC in BPA homogenate that is stimulated by endogenous H2O2 was not altered by ODQ, whereas sGC activity in the presence of 10 microM SNAP (+fungal catalase) was reduced by ODQ. Thus relaxation of K+-precontracted BCA and BPA to ONOO- appears to be completely mediated by NO stimulation of sGC, whereas the actions of ODQ suggest that NO is not involved in H2O2-elicited relaxation and sGC stimulation. This study did not detect evidence for the participation of additional mechanisms potentially activated by ONOO- in the responses studied.

The inducible nitric oxide synthase in vascular and cardiac tissue

Expression of the inducible form of nitric oxide synthase (iNOS) has been reported in a variety of cardiovascular diseases. The resulting high output nitric oxide (NO) formation, besides the level of iNOS expression, depends also on the expression of the metabolic pathways providing the enzyme with substrate and cofactor. NO may trigger short and long term effects which are either beneficial or deleterious, depending on the molecular targets with which it interacts. These interactions are governed by local factors (like the redox state). In the cardiovascular system, the major targets involve not only guanylyl cyclase, but also other haem proteins, protein thiols, iron-non-haem complexes, and superoxide anion (forming peroxynitrite). The latter has several intracellular targets and may be cytotoxic, despite the existence of endogenous defence mechanisms. These interactions may either trigger NO effects or represent releasable NO stores, able to buffer NO and prolong its effects in blood vessels and in the heart. Besides selectively inhibiting iNOS, a number of other therapeutic strategies are conceivable to alleviate deleterious effects of excessive NO formation, including peroxynitrite (ONOO-) scavenging and inhibition of metabolic pathways triggered by ONOO-. When available, these approaches might have the advantage to preserve beneficial effects of iNOS induction. Counteracting vascular hyper-responsiveness to endogenous vasoconstrictor agonists in septic shock, or inducing cardiac protection against ischaemia-reperfusion injury are examples of such beneficial effects of iNOS induction.