Basilia Zingarelli

Endothelial dysfunction in a rat model of endotoxic shock. Importance of the activation of poly (ADP-ribose) synthetase by peroxynitrite.

DNA single strand breakage and activation of the nuclear enzyme poly (ADP-ribose) synthetase (PARS) contribute to peroxynitrite-induced cellular injury. We investigated the role of PARS activation in the pathogenesis of endothelial dysfunction. In human umbilical vein endothelial cells (HUVEC), DNA strand breakage (alkaline unwinding assay), PARS activation (incorporation or radiolabeled NAD+ into proteins), mitochondrial respiration [conversion of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide to formazan] and apoptotic index (cytoplasmatic release of histones) were measured. Endotoxin shock was induced in rats by bacterial lipopolysaccharide. Vascular reactivity of thoracic aortic rings were measured in organ chambers. In HUVEC, peroxynitrite caused a dose-dependent suppression of mitochondrial respiration, induced DNA strand breakage and caused an activation of PARS. Pharmacological inhibition of PARS reduced the acute and delayed suppression of mitochondrial respiration when cells were exposed to intermediate, but not high doses of peroxynitrite. Similarly, protection against the intermediate, but not high doses of peroxynitrite was seen in fibroblasts from the PARS-/- mice, when compared to wild-type controls. These data suggest that PARS plays a role in peroxynitrite-induced cytotoxicity, but at very high levels of oxidant exposure, PARS-independent cytotoxic mechanisms become predominant. Peroxynitrite-induced apoptosis was not affected by PARS inhibition. Vascular rings exposed to peroxynitrite and rings taken from rats subjected to endotoxic shock exhibited reduced endothelium-dependent relaxant responses in response to acetylcholine. The development of this endothelial dysfunction was ameliorated by the PARS inhibitor 3-aminobenzamide. Activation of PARS by peroxynitrite, therefore, may be involved in the development of endothelial dysfunction in endotoxemia.

Genetic Disruption of Poly (ADP-Ribose) Synthetase Inhibits the Expression of P-Selectin and Intercellular Adhesion Molecule-1 in Myocardial Ischemia/Reperfusion Injury

The nuclear enzyme poly (ADP-ribose) synthetase (PARS) has been shown to play an important role in the pathogenesis of ischemia/reperfusion injury and circulatory shock. The aim of this study was to investigate whether PARS activity may modulate endothelial-neutrophil interaction. We present evidence that genetic disruption of PARS provides protection against myocardial ischemia and reperfusion injury by inhibiting the expression of P-selectin and intercellular adhesion molecule-1 (ICAM-1) and, consequently, by inhibiting the recruitment of neutrophils into the jeopardized tissue. Furthermore, using in vitro studies, we demonstrate that in fibroblasts lacking a functional gene for PARS, cytokine-stimulated expression of ICAM-1 is significantly reduced compared with fibroblasts from animals with a normal genotype. Similarly, in cultured human endothelial cells, oxidative- or cytokine-dependent expression of P-selectin and ICAM-1 is reduced by pharmacological inhibition of PARS by 3-aminobenzamide. These findings provide the first direct evidence that PARS activation participates in neutrophil-mediated myocardial damage by regulating the expression of P-selectin and ICAM-1 in ischemic and reperfused myocardium, and they also provide the basis for a novel therapeutic approach for the treatment of reperfusion injury.

Melatonin is a scavenger of peroxynitrite

Peroxynitrite is a toxic oxidant formed from the reaction of superoxide and nitric oxide under conditions of inflammation and oxidant stress. Here we demonstrate that the pineal neurohormone melatonin inhibits peroxynitrite-mediated oxidant processes. Melatonin caused a dose-dependent inhibition of the oxidation of dihydrorhodamine 123 to rhodamine in vitro. Moreover, in cultured J774 macrophages, melatonin inhibited the development of DNA single strand breakage in response to peroxynitrite and reduced the suppression of mitochondrial respiration. Thus, melatonin appears to be a scavenger of peroxynitrite. This action may contribute to the antioxidant and antiinflammatory effects of melatonin in various pathophysiological conditions.

Role of Poly-ADP Ribosyltransferase Activation in the Vascular Contractile and Energetic Failure Elicited by Exogenous and Endogenous Nitric Oxide and Peroxynitrite

Stimulation of vascular smooth muscle with bacterial lipopolysaccharide (LPS) and proinflammatory cytokines induces the expression of a distinct isoform of NO synthase (inducible NOS [iNOS]) contributing to the suppression of vascular contractility. We have obtained evidence of the involvement of an indirect pathway triggered by NO and its reaction product peroxynitrite (ONOO-) through the activation of the nuclear enzyme poly-ADP ribosyltransferase (PARS) in the pathogenesis of cellular energetic and contractile failure in vascular smooth muscle. Exposure of vascular smooth muscle cells caused DNA strand breaks, activation of PARS, depletion of NAD+, and inhibition of mitochondrial respiration. The NAD+ depletion and inhibition of mitochondrial respiration were reduced by pharmacological inhibition of PARS. Stimulation of vascular smooth muscle cells with LPS and interferon gamma (IFN-gamma) triggered the production of superoxide anion over 3 to 48 hours and NO and ONOO- over 24 to 48 hours and resulted in significant DNA strand breakage. The decrease in mitochondrial respiration in response to LPS and IFN-gamma stimulation was inhibited by the ONOO- scavenger uric acid (100 mumol/L) and by inhibitors of iNOS. The PARS inhibitors 3-aminobenzamide (1 mmol/L), nicotinamide (1 mmol/L), and PD 128763 (100 mumol/L) inhibited the reduction in cellular NAD+ and ATP and the suppression of mitochondrial respiration in response to LPS and IFN-gamma stimulation. Administration of 3-aminobenzamide also reduced PARS activation and vascular hyporeactivity of rat thoracic aortas exposed to ONOO- (300 mumol/L to 1.5 mmol/L) in vitro. 3-Aminobenzamide (10 mg/kg IP) preserved the ex vivo contractility of aortas obtained from endotoxic rats and improved survival in lethal murine endotoxic shock. These data suggest that PARS activation due to iNOS induction (1) is involved in the energetic depletion of vascular smooth muscle cells that express iNOS and (2) contributes to the pathogenesis of vascular energetic and contractile failure in endotoxic shock. Inhibition of PARS may be a novel concept of therapeutic potential in shock.

Protective effect of melatonin in carrageenan-induced models of local inflammation: Relationship to its inhibitory effect on nitric oxide production and its peroxynitrite scavenging activity

Cuzzocrea S, Zingarelli B, Gilad E, Hake P, Salzman AL, Szabó C. Protective effect of melatonin in carrageenan‐induced models of local inflammation: Relationship to its inhibitory effect on nitric oxide production and its peroxynitrite scavenging activity. J. Pineal Res. 1997; 23:106–116.

Crucial Role of Endogenous Interleukin-10 Production in Myocardial Ischemia/Reperfusion Injury

BACKGROUND The anti-inflammatory cytokine interleukin-10 (IL-10) has been detected in the plasma of patients with myocardial ischemia/reperfusion. The aim of our study was to investigate the role of endogenously produced IL-10 in myocardial ischemia/reperfusion. METHODS AND RESULTS In the present study, we used wild-type and IL-10-deficient mice subjected to myocardial ischemia/reperfusion. Significant levels of IL-10 were produced in wild-type mice at 2 to 6 hours after myocardial reperfusion. The genetic deletion of IL-10 enhanced neutrophil infiltration into the reperfused tissues at 6 hours after reperfusion and increased infarct size and myocardial necrosis. Furthermore, in the absence of IL-10, an enhancement of the inflammatory response was seen, as demonstrated by increased plasma levels of tumor necrosis factor-alpha, nitrite/nitrate (breakdown products of NO), and increased tissue expression of intercellular adhesion molecule-1. Reperfusion for 24 hours was associated with a 75% mortality rate in IL-10-deficient mice, whereas no deaths occurred in the wild-type animals. CONCLUSIONS The present findings provide the first direct evidence that endogenous IL-10 inhibits the production of tumor necrosis factor-alpha and NO and serves to protect the ischemic and reperfused myocardium through the suppression of neutrophil recruitment.

Protection against myocardial ischemia and reperfusion injury by 3-aminobenzamide, an inhibitor of poly (ADP-ribose) synthetase

OBJECTIVE Peroxynitrite and hydroxyl radical, reactive oxidants produced during reperfusion, are potent triggers of DNA single strand breakage. DNA injury triggers the activation of the nuclear enzyme poly (ADP-ribose) synthetase (PARS), which contributes to cellular energetic depletion. Using 3-aminobenzamide, an inhibitor of PARS, we investigated the role of PARS in the pathogenesis of myocardial reperfusion injury in a rat model. METHODS AND RESULTS Occlusion of the left main coronary artery (one hour) followed by reperfusion (one hour) in the anesthetized rat caused severe cardiac necrosis, neutrophil infiltration, and increased plasma creatine phosphokinase activity. There was significant peroxynitrite production during reperfusion, as indicated by a massive increase in nitrotyrosine in the necrotic myocardium. Reperfusion was also associated with a significant loss of myocardial ATP. In vivo administration of the PARS inhibitor 3-aminobenzamide (10 mg/kg i.v.) to rats subjected to myocardial ischemia and reperfusion, reduced myocardial infarct size and blunted the increase in plasma creatine phosphokinase activity and myeloperoxidase activity in infarcted hearts. In addition, 3-aminobenzamide partially preserved the myocardial ATP levels. In vitro, pharmacological inhibition of PARS also ameliorated peroxynitrite-induced cytotoxicity in rat cardiac myocytes and human endothelial cells. CONCLUSION 3-aminobenzamide has significant protective effects in myocardial reperfusion injury. We hypothesize that activation of PARS activation plays a role in the pathophysiology of acute myocardial infarction.

The potential role of peroxynitrite in the vascular contractile and cellular energetic failure in endotoxic shock

Peroxynitrite is a toxic oxidant species produced from nitric oxide (NO) and superoxide. We have recently observed that the cell‐permeable superoxide dismutase mimetic Mn(III)tetrakis(4‐benzoic acid) porphyrin (MnTBAP) inhibits the suppression of mitochondrial respiration elicited by authentic peroxynitrite in vitro. Here we have investigated the relative potency of MnTBAP and a range of related compounds in terms of inhibition of peroxynitrite‐induced oxidation and cytotoxicity. In addition, we tested the effects of MnTBAP on the vascular and the cellular energetic failure in rodent models of endotoxic shock. We observed a dose‐related inhibition of the peroxynitrite‐induced oxidation of dihydrorhodamine 123 to rhodamine by MnTBAP, ZnTBAP and FeTBAP, but not by MnTMPyP [(5,10,15,20‐tetrakis(N‐methyl‐4′‐pirydyl)porphinato)‐manganese (III)]. In addition, MnTBAP, ZnTBAP and FeTBAP, but not MnTMPyP prevented the suppression of mitochondrial respiration by authentic peroxynitrite in cultured J774 macrophages. In rat cultured aortic smooth muscle cells, MnTBAP protected against the suppression of mitochondrial respiration in response to authentic peroxynitrite, immunostimulation and nitric oxide (NO) donor compounds. MnTBAP slightly reduced the amount of nitrite/nitrate produced in response to immunostimulation in these cells. Administration of MnTBAP, 15 mg kg−1 i.v., before the administration of endotoxin (15 mg kg−1, i.v.) to rats ameliorated the development of vascular hyporeactivity and the development of endothelial dysfunction in the thoracic aorta ex vivo. MnTBAP also prevented the endotoxin‐induced decrease in mitochondrial respiration, the development of DNA single strand breaks, and the depletion of intracellular NAD+ in peritoneal macrophages ex vivo. MnTBAP did not inhibit the expression by endotoxin of the inducible NO synthase in lung samples. MnTBAP did not alter survival rate in mice challenged with high dose endotoxin. Our findings, taken together with previous data demonstrating protective effects of NO synthase inhibitors against the endotoxin‐induced contractile and energetic failure in the models of shock used in the current study, and with the known ability of peroxynitrite to cause cellular energy depletion, suggest a role for peroxynitrite in the pathogenesis of cellular energetic failure and contractile dysfunction in endotoxin shock.

Antiinflammatory Effects of Mercaptoethylguanidine, a Combined Inhibitor of Nitric Oxide Synthase and Peroxynitrite Scavenger, in Carrageenan-induced Models of Inflammation

In vitro studies have demonstrated that mercaptoethylguanidine (MEG), a selective inhibitor of the inducible NO synthase (iNOS), is also effective as a scavenger of peroxynitrite (a potent cytotoxic oxidant produced by the reaction of NO and superoxide). In the present study, we evaluated the antiinflammatory potential of MEG treatment in two models of acute inflammation (carrageenan-induced paw edema and pleurisy), where oxyradicals, NO, and peroxynitrite play a crucial role in the inflammatory process. Our data show that MEG (given at 25 microg/paw in the paw edema model or 10 mg/kg in the pleurisy model) inhibits the inflammatory response (paw swelling, pleural exudate formation, mononuclear cell infiltration, histological injury) in both models. Furthermore, MEG reduced nitrite/nitrate concentrations in the exudate and reduced the activity of the inducible isoform of NO synthase in the lung ex vivo. MEG also reduced the appearance of nitrotyrosine immunoreactivity in the inflamed tissues. Taken together, the present results demonstrate that MEG exerts potent antiinflammatory effects. Part of these antiinflammatory effects may be related to an inhibition of the expression/activity of the inducible NO synthase, another part may be related to oxyradical and peroxynitrite scavenging.

Beneficial effects of 3-aminobenzamide, an inhibitor of poly (ADP-ribose) synthetase in a rat model of splanchnic artery occlusion and reperfusion

Peroxynitrite, a potent cytotoxic oxidant formed by the reaction of nitric oxide with superoxide anion, and hydroxyl radical, formed in the iron‐catalysed Fenton reaction, are important mediators of reperfusion injury. In in vitro studies, DNA single strand breakage, triggered by peroxynitrite or by hydroxyl radical, activates the nuclear enzyme poly (ADP‐ribose) synthetase (PARS), with consequent cytotoxic effects. Using 3‐aminobenzamide, an inhibitor of PARS, we investigated the role of PARS in the pathogenesis of splanchnic artery occlusion shock. Splanchnic artery occlusion and reperfusion shock (SAO/R) was induced in rats by clamping both the superior mesenteric artery and the coeliac trunk for 45min, followed by release of the clamp (reperfusion). At 60min after reperfusion, animals were killed for histological examination and biochemical studies. SAO/R rats developed a significant fall in mean arterial blood pressure, significant increase of tissue myeloperoxidase activity and marked histological injury to the distal ileum. SAO/R was also associated with a significant mortality (0% survival at 2h after reperfusion). There was a marked increase in the oxidation of dihydrorhodamine 123 to rhodamine (a marker of peroxynitrite‐induced oxidative processes) in the plasma of the SAO/R rats, starting early after reperfusion, but not during ischaemia alone. Immunohistochemical examination demonstrated a marked increase in the immunoreactivity to nitrotyrosine, a specific ‘footprint’ of peroxynitrite, in the necrotic ileum in shocked rats, as measured at 60min after the start of reperfusion. In addition, in ex vivo studies in aortic rings from shocked rats, we found reduced contractions to noradrenaline and reduced responsiveness to a relaxant effect to acetylcholine (vascular hyporeactivity and endothelial dysfunction, respectively). In a separate set of studies, using a 4000 Dalton fluorescent dextran tracer, we investigated the changes in epithelial permeability associated with SAO/R. Ten minutes of reperfusion, after 30min of splanchnic artery ischaemia, resulted in a marked increase in epithelial permeability. There was a significant increase in PARS activity in the intestinal epithelial cells, as measured 10min after reperfusion ex vivo. 3‐Aminobenzamide, a pharmacological inhibitor of PARS (applied at 10mg kg−1, i.v., 5min before reperfusion, followed by an infusion of 10mg kg−1 h−1), significantly reduced ischaemia/reperfusion injury in the bowel, as evaluated by histological examination. Also it significantly improved mean arterial blood pressure, improved contractile responsiveness to noradrenaline, enhanced the endothelium‐dependent relaxations and reduced the reperfusion‐induced increase in epithelial permeability. 3‐Aminobenzamide also prevented the infiltration of neutrophils into the reperfused intestine, as evidenced by reduced myeloperoxidase activity. It improved the histological status of the reperfused tissues, reduced the production of peroxynitrite in the late phase of reperfusion and improved survival. In conclusion, our study demonstrates that the PARS inhibitor 3‐aminobenzamide exerts multiple protective effects in splanchnic artery occlusion/reperfusion shock. We suggest that peroxynitrite and/or hydroxyl radical, produced during the reperfusion phase, trigger DNA strand breakage, PARS activation and subsequent cellular dysfunction. The vascular endothelium is likely to represent an important cellular site of protection by 3‐aminobenzamide in SAO shock.