thromboxane-a2 and peroxynitric-acid

Oxygen-derived free radicals have been implicated in the pathogenesis of myocardial injury. We therefore investigated the pathophysiology of myocardial injury induced in isolated rat hearts by perfusion with superoxide radical generated by reacting 2.5 mmol/l purine, 0.03 U/ml xanthine oxidase and 300 U/ml catalase. Perfusion with superoxide significantly (P<0.05) increased left ventricular end-diastolic pressure within 15 to 20 min. During the same time period, heart rate and left-ventricular developed pressure significantly declined to 44.6+/-8.2% and 31.0+/-4.9% of control, respectively. Superoxide perfusion also significantly increased production of prostaglandins, nitric oxide (detected as nitrites) and peroxynitrite (detected immunohistochemically as nitrotyrosine). N(G)-nitro-l-arginine (100 micromol/l), a nitric oxide synthase inhibitor, attenuated superoxide-induced generation of peroxynitrite, increased synthesis of prostacyclin, and partially blocked myocardial dysfunction, as did 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (30 micromol/l), a selective inhibitor of soluble guanylate cyclase, and ONO-3708 (10 micromol/l), a selective thromboxane A(2)receptor antagonist. In contrast, nitroglycerin (4 micromol/l) and sodium nitroprusside (1 micromol/l) each exacerbated the superoxide-induced myocardial dysfunction. These results suggest that nitric oxide and related reactive species contribute to myocardial injury induced by superoxide. Moreover, they suggest that oxidative stress can be delayed or inhibited by reducing levels of nitric oxide, by inhibiting soluble guanylate cyclase, and by blocking thromboxane/prostaglandin receptors.

Topics: 1-Methyl-3-isobutylxanthine; Animals; Aspartate Aminotransferases; Colforsin; Enzyme Inhibitors; Heart; Myocardial Contraction; Myocardium; Nitrates; Nitric Acid; Nitroarginine; Nitroglycerin; Nitroprusside; Oxadiazoles; Phosphodiesterase Inhibitors; Platelet Aggregation Inhibitors; Prostaglandins; Quinoxalines; Rats; Superoxides; Thromboxane A2; Vasodilator Agents

Peroxynitrite (ONOO(-)), a reactive oxidant produced by the reaction between nitric oxide and superoxide, was found to diffuse into the platelet cytosol and inhibit arachidonic acid-induced platelet aggregations with IC(50) value of 5.8 +/- 1.2 microM. A fluorescence assay established that ONOO(-) diffused into the platelet cytosol in a manner that was inhibited (50-70%) by 4, 4'-diisothiocyanatostilbene-2,2'-disulfonic acid, an inhibitor of HCO(3)(-)/Cl(-) anion exchanger. Treatment of platelets with (-)-epigallocatechin gallate (2 microM), a tea polyphenol and inhibitor of tyrosine nitration, abolished the inhibitory effect of ONOO(-) on arachidonate-induced aggregations by 88%. ONOO(-) (50-300 microM), added to platelets 1 min before arachidonic acid, inhibited (20-100%) formation of platelet cyclooxygenase (COX) products thromboxane A(2) and 12-hydroxyheptadecatrienoic acid. Interestingly, simultaneous addition of ONOO(-) and arachidonic acid stimulated eicosanoid production by 20 to 60%. The inhibition of thromboxane A(2) generation correlated with the 5- to 10-fold increase in the 3-nitrotyrosine levels of the platelet COX. Experiments with purified COX-1 and COX-2 also showed 9-fold increase of 3-nitrotyrosine levels, which correlated with decreased (93-98%) production of prostaglandin H(2) when ONOO(-) (50 microM) was added 1 min before arachidonic acid. However, the addition of ONOO(-) (50-100 microM) simultaneously with arachidonic acid increased prostaglandin H(2) formation by 30 to 60%. Thus, the inhibitory effect of ONOO(-) involved nitration of COX tyrosine residues, whereas the stimulatory effect was likely to be a result of ONOO(-) functioning as a peroxide activator of eicosanoid signaling. Increasing doses of ONOO(-) not only inhibited platelet COX but also induced formation of unique eicosanoids: iso-prostaglandin F(2alpha), epoxyhydroxyeicosatrienoic acid, and trans-arachidonic acids, suggesting that OH and NO(2) radicals were generated from ONOO(-) in platelets. Formation of ONOO(-) from NO and superoxide may function as a platelet hormone-like COX regulatory mechanism in inflammatory processes in which large amounts of these molecules are produced.

Topics: Blood Platelets; Cell Membrane; Cell Membrane Permeability; Chromatography, High Pressure Liquid; Cyclooxygenase 1; Cyclooxygenase 2; Cyclooxygenase 2 Inhibitors; Cyclooxygenase Inhibitors; Diffusion; Eicosanoids; Gas Chromatography-Mass Spectrometry; Humans; Immunoblotting; In Vitro Techniques; Indicators and Reagents; Isoenzymes; Membrane Proteins; Nitrates; Oxidants; Platelet Activation; Platelet Aggregation; Prostaglandin-Endoperoxide Synthases; Thromboxane A2; Tyrosine; Vasoconstriction

1. The pulmonary vasculature is constantly exposed to oxygen and reactive oxygen species such as nitric oxide (NO) and superoxide anions which can combine at a near diffusion limited rate, to form the powerful, oxidant, peroxynitrite (ONOO-). When formed in large amounts, ONOO- is thought to contribute to tissue injury and vascular dysfunction seen in diseases such as the acute respiratory distress syndrome (ARDS) and septic shock. Recent studies have shown that ONOO- can cause vasodilatation and at higher concentrations can activate poly (adenosine 5'-diphosphoribose) synthase (PARS) leading to consumption of nicotinamide adenine dinucleotide (NAD+) and adenosine 5'-triphosphate (ATP). As the lung represents a prime site for ONOO- formation, we characterized its effects on pulmonary vascular tone and on endothelial function. In addition, we have assessed the role of PARS in producing the vasoactive properties of ONOO- on pulmonary artery rings. 2. Isolated pulmonary artery rings from rats were mounted in organ baths containing warmed and gassed (95% O2: 5% CO2) Krebs buffer. Force was measured with isometric force transducers. After equilibration, ONOO- (10 nM-100 microM) was added in a cumulative manner. In separate experiments designed to assess any vasodilator properties of ONOO-, tissues were pre-contracted with the thromboxane mimetic U46619 (1 microM). Once a stable base-line was achieved, ONOO- was added in a cumulative fashion. ONOO- had no significant effect on resting pulmonary artery tone but caused concentration-dependent relaxations of pre-contracted vessels in the range 1 microM to 100 microM. In some experiments the effects of freshly prepared ONOO- solutions were compared with those allowed to decay at 4 degrees C for 2 days. 3. In some experiments either vehicle or ONOO- (1, 10 or 100 microM) was added for 15 min before U46619 (1 microM). Concentration-response curves to the endothelium-dependent vasodilator, acetylcholine (10 nM-100 microM) were then constructed. In these experiments, ONOO- (1 microM or 10 microM) had no effect on the actions of acetylcholine. However, at the highest concentration tested (100 microM), ONOO- increased acetylcholine-induced relaxations. 4. The vasodilator actions of ONOO- were unaffected by the NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME; 100 microM) or by removal of superoxide anions with superoxide dismutase (SOD) (30 units ml-1). However, the relaxations induced by ONOO- were signif

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Dose-Response Relationship, Drug; In Vitro Techniques; Male; NG-Nitroarginine Methyl Ester; Nitrates; Poly(ADP-ribose) Polymerases; Prostaglandin Endoperoxides, Synthetic; Pulmonary Artery; Rats; Rats, Wistar; Thromboxane A2; Vasodilation; Vasodilator Agents

The inhibition of platelet aggregation by peroxynitrite, a reactive oxygen species derived from the interaction of nitric oxide (NO) and superoxide, was examined in platelet-rich plasma. In this report, we have used a preparation of peroxynitrite that was free of H2O2 and MnO2. As such, peroxynitrite dose-dependently (50-200 microM) inhibited aggregation of human platelets stimulated by ADP (5 microM), collagen (0.5 microgram), thrombin (0.5U/microL) and U46619 (1 microM). In addition, peroxynitrite reversed platelet aggregation induced by collagen, ADP, and thrombin. Peroxynitrite, preincubated with platelet-poor plasma or albumin (7%) for 30 min, did not alter the inhibition of platelet aggregation. This suggested that the inhibitory action of peroxynitrite may be due to nitrosylation of proteins, which by themselves possess activity, rather than conversion to NO or NO donors. Furthermore, we show that peroxynitrite increased the cGMP level only at 200 microM concentrations, further suggesting that the action of peroxynitrite was not completely due to its conversion to NO or NO donors.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenosine Diphosphate; Adult; Blood Platelets; Collagen; Cyclic GMP; Humans; Nitrates; Platelet Aggregation; Platelet Aggregation Inhibitors; Prostaglandin Endoperoxides, Synthetic; Spectrophotometry; Thrombin; Thromboxane A2