Role of poly(ADP-ribose) synthetase activation in the development of experimental allergic encephalomyelitis

Peroxynitrite formation has been demonstrated during experimental allergic encephalomyelitis (EAE). Furthermore, peroxynitrite has been identified as an activator of poly(ADP-ribose) synthetase (PARS), an enzyme implicated in neurotoxicity. In the current study, we examined the role of PARS activation in the development of EAE. Administration of the PARS inhibitor 5-iodo-6-amino-1,2-benzopyrone (INH2BP) delayed the onset of EAE and reduced the incidence and severity of disease signs. Moreover, drug treatment lowered iNOS activity and decreased cell infiltration in cervical spinal tissues from EAE-sensitized animals. To conclude, the results of the present investigation suggest that PARS activity may contribute to the pathogenesis of EAE.

Effects of nicaraven on nitric oxide-related pathways and in shock and inflammation

Expression of the inducible isoform of nitric oxide (NO) synthase, and the formation of peroxynitrite from NO and superoxide are responsible for some of the pathophysiological alterations seen during reperfusion injury and in various inflammatory conditions. Some of the effects of peroxynitrite are related to DNA single-strand breakage, and activation of poly (ADP-ribose) synthetase. Here we investigated the effect of nicaraven (2(R,S)-1,2-bis(nicotinamido)propane), a known hydroxyl radical scavenger compound and neuroprotective agent, on several NO- and peroxynitrite related pathways in vitro, and in shock and inflammation in vivo. Nicaraven, at 10 microM-10 mM, failed to inhibit the peroxynitrite-induced oxidation of dihydrorhodamine 123, indicating that the agent does not act as a scavenger of peroxynitrite. In RAW murine macrophages stimulated with peroxynitrite, nicaraven caused a dose-dependent, slight inhibition of poly (ADP-ribose) synthetase activation, possibly due to a direct inhibitory effect on the catalytic activity of poly (ADP-ribose) synthetase. Nicaraven partially protected against the peroxynitrite-induced suppression of mitochondrial respiration in RAW macrophages and caused a slight, dose-dependent inhibition of nitrite production in RAW macrophages stimulated with bacterial lipopolysaccharide. We next investigated the effect of nicaraven treatment in a variety of models of inflammation and reperfusion injury. Nicaraven (at 10-100 microg/paw) exerted significant protective effects in the carrageenan-induced paw edema model and (at 100 mg/kg i.v.) reduced neutrophil infiltration and histological damage in splanchnic artery occlusion-reperfusion injury. However, nicaraven failed to alter the course of hemorrhagic and endotoxic shock and arthritis in rodent models. The current data indicate the limited role of hydroxyl radicals in the pathogenesis of the inflammatory conditions tested.

Beneficial effects of mercaptoethylguanidine, an inhibitor of the inducible isoform of nitric oxide synthase and a scavenger of peroxynitrite, in a porcine model of delayed hemorrhagic shock

OBJECTIVE

In rodent models, enhanced formation of nitric oxide and formation of peroxynitrite have been implicated in the pathogenesis of various forms of shock. Here we examined the effect of mercaptoethylguanidine (MEG), an inducible nitric oxide synthase inhibitor and peroxynitrite scavenger, in a severe hemorrhagic shock model.

DESIGN

Randomized, placebo-controlled trial.

SETTING

Animal laboratory.

SUBJECTS

Twenty-one anesthetized immature Yorkshire pigs.

INTERVENTIONS

Mechanical ventilation, sternotomy, continuous cardiac output (pulmonary artery flowmetry), and systemic and intracardial pressure measurements were taken. Pigs were bled to a cardiac index of 40 mL/kg/min for 2 hrs, which was followed by saline resuscitation (20 mL/kg). MEG was administered in the resuscitation fluid (15 mg/kg bolus plus 15 mg/kg/hr infusion).

MEASUREMENTS AND MAIN RESULTS

Hemodynamic variables, systemic and mixed venous blood gas tensions and oxygenation, arterial lactate concentration, myeloperoxidase activity, malondialdehyde content, and histologic injury in the lung and intestine were measured. Reduction of cardiac output to 40 mL/kg/min led to the following changes during hypovolemia: decreases in mean arterial blood pressure (to 30-35 mm Hg), both atrial pressures, systemic oxygen consumption (by 35%), mixed venous saturation (by 65%), and lactic acidosis (5.5-6.0 mM). Fluid replacement failed to restore blood pressure and cardiac output during resuscitation and was followed by gradual hemodynamic decompensation. Hemorrhagic shock induced lipid peroxidation, neutrophil deposition, and severe histologic alterations in the lung and intestine. MEG significantly ameliorated the decrease in blood pressure and cardiac output during resuscitation, improved survival rate, reduced lipid peroxidation in the intestine, and ameliorated neutrophil accumulation in the lung and intestine. MEG prevented the reduction in oxygen consumption during resuscitation.

CONCLUSIONS

When given during resuscitation, MEG exerted beneficial effects in a porcine model of severe hemorrhagic shock. We propose that the mode of MEG's action is related to improved cardiac contractility.

Protection against hypoxia-reoxygenation in the absence of poly (ADP-ribose) synthetase in isolated working hearts

Peroxynitrite and hydroxyl radical are reactive oxidants produced during myocardial reperfusion injury. They have been shown to induce dysfunction in cardiac myocytes, in part, via the activation of the nuclear enzyme poly (ADP-ribose) synthetase (PARS). These oxidants can trigger DNA single strand breakage, which triggers PARS activation, resulting in cellular NAD+ and ATP depletion and cytotoxicity. Recent work has demonstrated that hypoxia-reoxygenation of cardiac myocytes in vitro also causes peroxynitrite formation, PARS activation and cytotoxicity. In the present study, using hearts from genetically engineered mice lacking PARS, we have investigated whether the absence of PARS alters the functional response to hypoxia reoxygenation. Isolated work-performing mouse hearts were stabilized under the same loading condition (cardiac minute work of 250 mmHg x ml/min, an afterload of 50 mmHg aortic pressure and similar venous return of 5 ml/min, resulting in the same preload). After 30 min equilibration the hearts were subjected to 30 min hypoxia followed by 30 min of reoxygenation. At the end of the reoxygenation, in hearts from wild-type animals, there was a significant suppression in the rate of intraventricular pressure development (+dP/dt) from 3523 to 2907 mmHg. There was also a significant suppression in the rate of relaxation (-dP/dt) in the wild-type hearts from 3123 to 2168 mmHg. The time to peak pressure (TPP) increased from 0.48 to 0.59 ms/mmHg and the half-time of relaxation (RT1/2) increased from 0.59 to 0.74 ms/mmHg. In contrast, in the hearts from the PARS knockout animals, no significant suppression of +dP/dt (from 3654 to 3419 mmHg), and no significant increase in the TPP (from 0.462 to 0.448 ms/mmHg) were found, and the decrease in -dP/dt was partially ameliorated (from 3399 to 2687 mmHg) as well as the half-time of relaxation (from 0.507 to 0.55 ms/mmHg) when compared to the response to the wild-type hearts. The current data demonstrate that the reoxygenation induced suppression of the myocardial contractility is dependent on the functional integrity of PARS.

3-Aminobenzamide, an inhibitor of poly (ADP-ribose) synthetase, improves hemodynamics and prolongs survival in a porcine model of hemorrhagic shock

Hypoxia, energy deficit, and oxidative damage are principal mechanisms of injury in hemorrhagic shock (HS). Oxidant-induced cellular energetic failure and cell dysfunction is mediated, in part, via the activation of the nuclear enzyme poly (ADP-ribose) synthetase (PARS). Here we examine the effect of the PARS inhibitor 3-aminobenzamide (3AB) in a severe HS model. Pigs were bled to a cardiac index of 40 mL/kg/min for 2 h, which was followed by saline resuscitation (20 mL/kg). Hypovolemia induced decreases in mean arterial blood pressure (to 40-42 mmHg), in both atrial pressures, in systemic oxygen consumption (by 26-30%), and in mixed venous saturation (by 65%). HS also caused lactic acidosis (4.0-5.5 mM). Fluid replacement with saline caused only a partial and transient recovery of blood pressure and cardiac output, with no recovery of stroke work during resuscitation. Fluid replacement did not prevent the progressive hemodynamic decompensation. The PARS inhibitor 3AB (15 mg/kg) significantly ameliorated the fall in blood pressure, cardiac output, and stroke work; slightly increased left atrial pressure during resuscitation; and significantly prolonged survival. PARS inhibition also prevented the reduction in oxygen consumption and mixed venous saturation during resuscitation. Taking these data together, we conclude that pharmacological inhibition of PARS exerts beneficial effects in a porcine model of severe HS. We propose that favorable action of 3AB is related, at least in part, to an improved cardiac performance.

Protection against peroxynitrite-induced fibroblast injury and arthritis development by inhibition of poly(ADP-ribose) synthase

Peroxynitrite, a cytotoxic oxidant formed from nitric oxide (NO) and superoxide, induces DNA strand breakage, which activates the nuclear enzyme poly(ADP-ribose) synthase (PARS; EC 2.4.2.30). The cellular function of PARS was determined in fibroblast lines from PARS knockout animals (PARS-/-) and corresponding wild-type animals (PARS+/+), with the aid of the lipophilic PARS inhibitor 5-iodo-6-amino-1,2-benzopyrone (INH2BP). We investigated the role of PARS in peroxynitrite-induced fibroblast injury in vitro and also in the development of arthritis in vivo. Exposure of embryonic fibroblasts from the PARS+/+ animals to peroxynitrite caused DNA single-stand breakage and PARS activation and caused an acute suppression of mitochondrial respiration. INH2BP protected the PARS+/+ cells against the suppression of mitochondrial respiration in response to peroxynitrite (50-100 microM). Similarly to PARS inhibition with INH2BP, the PARS-/- cells were protected against peroxynitrite-induced injury. The protection against cellular injury by PARS-/- phenotype or INH2BP waned when cells were challenged with higher concentrations of the oxidant. Inhibition of PARS by INH2BP or by PARS-/- phenotype reduced inducible nitric-oxide synthase (iNOS; EC 1.14.13.39) mRNA levels and inhibited production of NO in immunostimulated cells. INH2BP had no peroxynitrite scavenging or hydroxyl radical scavenging effects, and it exerted no additional (nonspecific) effects in the PARS-/- cells. In collagen-induced arthritis, significant staining for nitrotyrosine, a marker of peroxynitrite formation, was found in the inflamed joints. Oral treatment with INH2BP (0.5 g/kg, daily), starting at the onset of arthritis (day 25), delayed the development of the clinical signs at days 26-35 and improved histological status in the knee and paw. Our data demonstrate that deletion of PARS by genetic manipulation or pharmacological inhibition of PARS protects against oxidant-induced cellular injury in vitro and exhibits anti-inflammatory effects in vivo.

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.

Protective effects of 3-aminobenzamide, an inhibitor of poly (ADP-ribose) synthase in a carrageenan-induced model of local inflammation

A cytotoxic cycle triggered by oxidant-induced DNA single strand breakage and subsequent activation of the nuclear enzyme poly (ADP-ribose) synthetase have been shown to contribute to the cellular injury during various forms of oxidant stress in vitro. The aim of the present study was to investigate the role of poly (ADP-ribose) synthetase in a model of acute local inflammation (carrageenan-induced pleurisy), where oxyradicals, nitric oxide and peroxynitrite are known to play a crucial role in the inflammatory process. The results show that the poly (ADP-ribose) synthetase inhibitor 3-aminobenzamide (given at 1-30 mg/kg) inhibits the inflammatory response (pleural exudate formation, mononuclear cell infiltration, histological injury). Moreover, 3-aminobenzamide reduces the formation of nitrotyrosine, an indicator of the formation of peroxynitrite, in the lung. The present results demonstrate that 3-aminobenzamide, presumably by inhibition of poly (ADP-ribose) synthetase, exerts potent anti-inflammatory effects. Part of the anti-inflammatory effects of 3-aminobenzamide may be related to a reduction of neutrophil recruitment into the inflammatory site.

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

In vitro studies have demonstrated that melatonin is a scavenger of oxyradicals and peroxynitrite and an inhibitor of nitric oxide (NO) production. In the present study, we evaluated the effect of melatonin 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 melatonin (given at 62.5 and 125 microg/paw in the paw edema model or 25 and 50 mg/kg in the pleurisy model) inhibits the inflammatory response (paw swelling, pleural exudate formation, mononuclear cell infiltration, and histological injury) in dose-dependent manner in both models. Furthermore, our data suggest that melatonin exerts an inhibitory effect on the expression of the inducible isoform of NO synthase. Melatonin also prevented the formation of nitrotyrosine, an indicator of peroxynitrite, in both models of inflammation. Taken together, the present results demonstrate that melatonin exerts potent antiinflammatory effects. Part of these antiinflammatory effects may be related to an inhibition of the expression of the inducible NO synthase, while another part may be related to oxyradical and peroxynitrite scavenging.