Effects of radiodetoxified endotoxin on nitric oxide production in J774 macrophages and in endotoxin shock

Radiodetoxified lipopolysaccharide (RD-LPS) is a 60Co-gamma-irradiated LPS with a modified structure, which decreases its toxic effects. To obtain a better understanding of the mechanism of the reduced toxicity of RD-LPS, here we studied the effect of RD-LPS on the regulation of nitric oxide (NO) production in vitro and in vivo. In control cells, stimulation by native LPS (10 μg/ml) induced the expression of the inducible NO synthase (iNOS) and production of NO, as measured by increase in the concentration of nitrite, breakdown product of NO. Pre-exposure of the cells for 24 h to a subthreshold concentration of RD-LPS (10 ng/ml) induced a complete desensitization to the LPS-induced NO production in comparison to control cells (P < 0.01). On the contrary, pre-exposure of the cells with native LPS (10 ng/ml) did not reduce LPS-induced NO synthesis. RD-LPS induced a smaller production of tumor necrosis factor (TNF) than native LPS, but did not induce a desensitization against subsequent LPS-induced TNF synthesis. ln in vivo studies, pretreatment of rats with repeated doses of sublethal RD-LPS (1 mg/kg/day i.p. for 4 days) inhibited increase of plasma nitrate/nitrite levels, NO production in peritoneal macrophages ex vivo and induction of lung iNOS activity, in response to a high-dose LPS challenge (15 mg/kg i.p.) given at the fifth day. Pretreatment with repeated sublethal doses of the native LPS (1 mg/kg/day i.p.) did not affect NO production in rats subjected to endotoxic shock. The results demonstrate that RD-LPS induces tolerance to the stimulatory effect of LPS on NO synthesis. Suppression of iNOS induction was only observed with RD-LPS, but not with native LPS in the models used herein. It remains to be further investigated whether suppression of iNOS induction by RD-LPS contributes to the protective effects of this compound in shock and inflammation.

Protective effects of isohelenin, an inhibitor of nuclear factor κB, in endotoxic shock in rats

Recent in vitro studies have shown that isohelenin, a sesquiterpene lactone, inhibits the NF-κB pathway. This study examines the effect of isoheleninin endotoxic shock induced by administration of Escherichia coli endotoxini n male Wistar rats. A group of rats received isohelenin (2 mg/kg intraperitoneally)15 min before endotoxin. In vehicle-treated rats, administration of endotoxin caused severe hypotension, which was associated with a marked hyporeactivity to norepinephrine and acetylcholine in ex vivo aortas. Elevated levels of plasma nitrate/nitrite, metabolites of nitric oxide (NO), were also found. These inflammatory events were preceded by cytosolic degradation of inhibitor-κBα (IκBα) and activation of nuclear factor-κB (NF-κB) in the lung within 15 min of endotoxin administration. Treatment with isohelenin resulted in hemodynamicimprovement and reduced plasma levels of NO metabolites. Nuclear translocation of NF-κB was inhibited by isohelenin treatment in the lung, whereas degradation of IκBα was unchanged. In a separate set of experiments, treatment with isohelenin significantly improved survival in mice challenged with endotoxin. We conclude that isohelenin exerts beneficial therapeutic effects during endotoxic shock through inhibition of NF-κB.

Altered macrophage function in tumor necrosis factor α- and endotoxin-induced tolerance

Pretreatment of rats with a sublethal dose of human recombinant tumor necrosis factor-α (hrTNFα, 10 μg/kg i.p.) or Salmonella enteritidis LPS (100 μg/kg, i.p.) prevented death when a lethal dose of S. enteritidis lipopolysaccharide (LPS, 15 mg/kg i.p.) was administered 24 h later. The resistance to the lethal effect of LPS was associated with similar alterations of the functional phenotype of peritoneal macrophages from both groups. In ex vivo studies, peritoneal macrophages were harvested 24 h after vehicle (control), hrTNFα or LPS injection and stimulated in vitro with LPS. In macrophages collected from control rats, LPS stimulated arachidonic acid (AA) metabolism, as assessed by 6-keto-prostaglandin F1α (6-keto-PGF1α) levels, nitric oxide (NO) production, as assessed by nitrite, and interleukin 6 (IL-6) production. In macrophages from hrTNFα-pretreated or LPS pretreated rats, basal and LPS-stimulated 6-keto-PGF1α production were significantly reduced compared to controls, while nitrite production was increased (P < 0.001). LPS induced IL-6 synthesis was not affected in macrophages from hrTNFα-pretreated rats but was significantly reduced in stimulated macrophages from LPS treated rats. Furthermore, the macrophage membrane content of guanine nucleotide binding regulatory (G) protein subunits was determined. Macrophages collected from hrTNFα-pretreated rats exhibited a marked reduction of the membrane content of the Giα3 subunit compared to control macrophages, whereas the Giα1,2 and Gβ subunits were not significantly affected. The decrease in Giα3 in hrTNFα treated rats is similar to that previously observed in macrophages from LPS tolerant rats. The results demonstrate that hrTNFα induces cross tolerance to the lethal effect of LPS, and that tolerance induced by TNF or LPS is associated with differential changes in peritoneal macrophage mediator production. These changes may, in part, be a consequence of altered signal transduction via specific G proteins.

mTOR regulates DNA damage response through NF-κB-mediated FANCD2 pathway in hematopoietic cells

Hematopoietic stem/progenitor cells (HSPCs) function to give rise to mature blood cells. Effective DNA damage response (DDR) and maintenance of genomic stability are crucial for normal functioning of HSPCs. Mammalian target of rapamycin (mTOR) integrates signals from nutrients and growth factors to control protein synthesis, cell growth, survival and metabolism, and has been shown to regulate DDR in yeast and human cancer cells through the p53/p21 signaling cascade. Here, we show that gene targeting of mTOR in HSPCs causes a defective DDR due to a variety of DNA damage agents, mimicking that caused by deficient FANCD2, a key component of the Fanconi anemia (FA) DDR machinery. Mechanistically, mTOR(-/-) HSPCs express drastically reduced FANCD2. Consistent with these genetic findings, inactivation of mTOR in human lymphoblast cells by pp242 or Torin 1, mTOR kinase inhibitors, suppresses FANCD2 expression and causes a defective DDR that can be rescued by reconstitution of exogenous FANCD2. Further mechanistic studies show that mTOR deficiency or inactivation increases phosphorylation and nuclear translocation of nuclear factor (NF)-κB, which results in an enhanced NF-κB binding to FANCD2 promoter to suppress FANCD2 expression. Thus, mTOR regulates DDR and genomic stability in hematopoietic cells through a noncanonical pathway involving NF-κB-mediated FANCD2 expression.

Protective effects of isohelenin, an inhibitor of nuclear factor kappaB, in endotoxic shock in rats

Recent in vitro studies have shown that isohelenin, a sesquiterpene lactone, inhibits the NF-kappaB pathway. This study examines the effect of isohelenin in endotoxic shock induced by administration of Escherichia coli endotoxin in male Wistar rats. A group of rats received isohelenin (2 mg/kg intraperitoneally) 15 min before endotoxin. In vehicle-treated rats, administration of endotoxin caused severe hypotension, which was associated with a marked hyporeactivity to norepinephrine and acetylcholine in ex vivo aortas. Elevated levels of plasma nitrate/nitrite, metabolites of nitric oxide (NO), were also found. These inflammatory events were preceded by cytosolic degradation of inhibitor-kappaBalpha (IkappaBalpha) and activation of nuclear factor-kappaB (NF-kappaB) in the lung within 15 min of endotoxin administration. Treatment with isohelenin resulted in hemodynamic improvement and reduced plasma levels of NO metabolites. Nuclear translocation of NF-kappaB was inhibited by isohelenin treatment in the lung, whereas degradation of IkappaBalpha was unchanged. In a separate set of experiments, treatment with isohelenin significantly improved survival in mice challenged with endotoxin. We conclude that isohelenin exerts beneficial therapeutic effects during endotoxic shock through inhibition of NF-kappaB.

Absence of endogenous interleukin 10 enhances early stress response during post-ischaemic injury in mice intestine

BACKGROUND

Interleukin 10 (IL-10) exerts a wide spectrum of regulatory activities in immune and inflammatory responses.

AIMS

The aim of this study was to investigate the role of endogenous IL-10 on modulation of the early inflammatory response after splanchnic ischaemia and reperfusion.

METHODS

Intestinal damage was induced by clamping the superior mesenteric artery and the coeliac trunk for 45 minutes followed by reperfusion in IL-10 deficient mice (IL-10(-/-)) and wild-type controls.

RESULTS

IL-10(-/-) mice experienced a higher rate of mortality and more severe tissue injury compared with wild-type mice subjected to ischaemia and reperfusion. Splanchnic injury was characterised by massive epithelial haemorrhagic necrosis, upregulation of P-selectin and intercellular adhesion molecule 1, and neutrophil infiltration. The degree of oxidative and nitrosative damage was significantly higher in IL-10(-/-) mice than in wild-type littermates, as indicated by elevated malondialdehyde levels and formation of nitrotyrosine. Plasma levels of the proinflammatory cytokines tumour necrosis factor alpha and interleukin 6 were also greatly enhanced in comparison with wild-type mice. These events were preceded by increased immunostaining and activity of the stress regulated c-Jun NH(2) terminal kinase and activation of the transcription factor activator protein 1 in the cellular nuclei of damaged tissue.

CONCLUSIONS

These data demonstrate that endogenous IL-10 exerts an anti-inflammatory role during reperfusion injury, possibly by regulating early stress related genetic response, adhesion molecule expression, neutrophil recruitment, and subsequent cytokine and oxidant generation.

Hypothermia as an adjunctive treatment for severe bacterial meningitis

Brain injury due to bacterial meningitis results in a high mortality rate and significant neurologic sequelae in survivors. The objective of this study was to determine if the application of moderate hypothermia shortly after the administration of antibiotics would attenuate the inflammatory response and increase in intracranial pressure that occurs in meningitis. For this study we used a rabbit model of severe Group B streptococcal meningitis. The first component of this study evaluated the effects of hypothermia on blood-brain barrier function and markers of inflammation in meningitic animals. The second part of the study evaluated the effects of hypothermia on intracranial pressure, cerebral perfusion pressure and brain edema. This study demonstrates that the use of hypothermia preserves CSF/serum glucose ratio, decreases CSF protein and nitric oxide and attenuates myeloperoxidase activity in brain tissue. In the second part of this study we show a decrease in intracranial pressure, an improvement in cerebral perfusion pressure and a decrease in cerebral edema in hypothermic meningitic animals. We conclude that in the treatment of severe bacterial meningitis, the application of moderate hypothermia initiated shortly after antibiotic therapy improves short-term physiologic measures associated with brain injury.

Soluble nitric oxide donor and surfactant improve oxygenation and pulmonary hypertension in porcine lung injury

Acute lung injury (ALI) is associated with diminished surfactant activity and pulmonary hypertension. NONOates are soluble NO donors which release NO in solution. Intratracheal NONOates reduce pulmonary hypertension and improve oxygenation in ALI. We hypothesized that the pharmacologic properties of NO donors would be unaltered after surfactant admixture in vitro and that aerosolized NONOate activity would be enhanced by surfactant pretreatment in vivo. NO donors were added to saline or surfactant and analyzed for nitrite/nitrate production and aortic ring vasodilation. Surfactant did not alter nitrate/nitrite production or aortic ring vasodilation. A porcine model of ALI with pulmonary hypertension was produced using intravenous oleic acid. Animals were assigned to Surfactant-Saline, Surfactant-NONOate, Saline-Saline, or Saline-NONOate groups. Saline or surfactant was instilled into the trachea, followed by gas exchange, pulmonary function, and hemodynamic measurements. NONOate or saline was then aerosolized, and additional data were collected. Oxygenation was improved in the Surfactant-NONOate group, while pulmonary hypertension was selectively reduced in both NONOate groups. Aerosolized NONOate following surfactant pretreatment improves oxygenation and reduces pulmonary hypertension in ALI.

Poly (ADP-ribose) synthetase mediates intestinal mucosal barrier dysfunction after mesenteric ischemia

Peroxynitrite-mediated DNA strand breaks trigger poly (ADP-ribose) synthetase (PARS) activation, resulting in intracellular energetic failure and organ dysfunction. We investigated the role of PARS activation on the inflammatory and functional response of the intestine to mesenteric ischemia-reperfusion injury. Anesthetized rats exposed to 15 min occlusion of the superior mesenteric artery showed an increased mucosal PARS activity (ex vivo incorporation of radiolabelled NAD+ in gut mucosal scrapings) as soon as 10 min after reperfusion. During the first 30 min of reperfusion, significant mucosal damage developed, as well as mucosal hyperpermeability to a 4000 MW fluorescent dextran (FD4). These alterations were significantly reduced by treatment with the NO synthase inhibitor L-NMA, which blocks the production of peroxynitrite, as well as with the PARS inhibitors 3-aminobenzamide and nicotinamide, whereas they were markedly enhanced by the glutathione depletor L-buthionine-(S,R)-sulfoximine. Also, PARS inhibition significantly reduced ileal neutrophil infiltration (myeloperoxidase activity) at 3 h reperfusion. In a second set of experiments, the effects of 15 or 30 min ischemia followed by 3 h reperfusion were evaluated in PARS knockout and wild-type mice. Significant protection against histological damage, neutrophil infiltration, and mucosal barrier failure (evaluated by the mucosal-to-serosal FD4 clearance of everted ileal sacs incubated ex vivo) was noted in PARS knockout mice, who also showed reduced alterations in remote organs, as shown by lesser lipid peroxidation (malondialdehyde formation) and neutrophil infiltration in the lung and liver. In conclusion, PARS plays a crucial role in mediating intestinal injury and dysfunction in the early and late phases of mesenteric reperfusion. Pharmacological inhibition of PARS may be a novel approach to protect tissues from reperfusion-related damage.

Mercaptoethylguanidine attenuates inflammation in bacterial meningitis in rabbits

Reactive oxygen and nitrogen species participate in the inflammatory process during meningitis. Among them, superoxide, nitric oxide (NO), and their reaction product peroxynitrite exert cytotoxic effects. Mercaptoethylguanidine (MEG) exerts beneficial effects in in vivo inflammatory conditions by scavenging peroxynitrite and inhibiting the inducible NO synthase. This study was designed to investigate whether MEG may attenuate inflammation and brain injury in experimental meningitis. Meningitis increased nitrite/nitrate, and protein content in the cerebrospinal fluid (CSF). In the brain tissue high levels of malondialdehyde and formation of nitrotyrosine indicated lipid peroxidation and nitrosative stress, respectively. Myeloperoxidase activity was increased indicating accumulation of neutrophils into the brain parenchyma. Treatment with MEG decreased nitrite/nitrate levels whereas it did not affect the bacterial clearance from the CSF. Furthermore, treatment with MEG markedly reduced brain tissue levels of myeloperoxidase and malondialdehyde. These data demonstrate that MEG could have a therapeutic role in meningitis.

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.

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.

Effect of genetic disruption of poly (ADP-ribose) synthetase on delayed production of inflammatory mediators and delayed necrosis during myocardial ischemia-reperfusion injury

The nuclear enzyme poly (ADP ribose) synthetase (PARS) has been shown to play an important role in the pathogenesis of various forms of ischemia or reperfusion injury and circulatory shock. Recent studies demonstrated that inhibition or genetic inactivation of PARS is beneficial in the early phase of myocardial reperfusion injury. The aim of the present study was to investigate whether inactivation of PARS influences the delayed myocardial necrosis and the production of the proinflammatory cytokine tumor necrosis factor alpha (TNFalpha), the anti-inflammatory cytokine interleukin-10 (IL-10), and the free radical nitric oxide in the late stage of myocardial reperfusion injury. The results demonstrate that genetic disruption of PARS provides marked protection against the delayed myocardial ischemia and reperfusion injury. In addition, in the absence of functional PARS, a suppression of TNFalpha, IL-10, and nitric oxide production was found. These findings provide direct evidence that PARS activation participates in the development of delayed cell injury and delayed mediator production in myocardial reperfusion injury.

Protective effect of 3-aminobenzamide, an inhibitor of poly (ADP-ribose) synthetase, against laryngeal injury in rats

The effect of 3-aminobenzamide, an inhibitor of poly (ADP-ribose) synthetase activity, was evaluated in a rat model of laryngeal injury induced by endotracheal intubation for 1 h. At 1 h after extubation, the laryngeal damage was characterized by areas of mucosal necrosis, submucosal edema, swelling of subglottic glands, and submucosal infiltration of inflammatory cells. Activity of myeloperoxidase, a marker of neutrophil infiltration, was also markedly increased into the damaged tissue. Immunohistochemistry for nitrotyrosine, an index of nitrosative stress, showed an intense staining in the inflamed larynx. Treatment with 3-aminobenzamide (10 mg/kg intraperitoneally) significantly reduced the appearance of mucosal damage and was associated with a significant reduction of tissue myeloperoxidase activity and nitrotyrosine immunoreactivity in the larynx. The results of this study suggest that poly (ADP-ribose) synthetase may play a role in the inflammatory process after laryngeal intubation and extubation, and administration of 3-aminobenzamide may be a beneficial therapeutic approach.

Effects of a novel guanylyl cyclase inhibitor on the vascular actions of nitric oxide and peroxynitrite in immunostimulated smooth muscle cells and in endotoxic shock

OBJECTIVE

Nitric oxide (NO), produced by the inducible isoform of NO synthase (NOS) in circulatory shock exerts cytotoxic and vasodilator effects. Part of these effects are mediated by formation of peroxynitrite, a toxic oxidant produced by the rapid reaction of NO and superoxide. Other parts of the vascular actions of NO in shock are thought to be mediated by the action of NO on the soluble guanylyl cyclase (GC) in the smooth muscle and subsequent decrease in the intracellular calcium levels. Using 1H-(1,2,4)oxadiazolo(4,3-alpha)quinoxalin-1 -one (ODQ), a potent inhibitor of GC, we studied the role of GC activation in the NO- and peroxynitrite-related vascular alterations.

DESIGN

In vitro: Controlled experiment using cultured rat aortic smooth muscle cells. In vivo: Prospective, randomized, controlled animal study.

SETTING

Experimental laboratory.

SUBJECTS

Male Wistar rats and male Swiss mice.

INTERVENTIONS

In vitro: a) Stimulation of rat aortic smooth muscle cells with bacterial lipopolysaccharide (LPS) and gamma-interferon, measurement of the production of nitrite and nitrate (breakdown products of NO), and suppression of mitochondrial respiration for 24 to 48 hrs, in the presence or absence of ODQ; and b) in norepinephrine-precontracted endothelium-denuded thoracic aortic rings, exposure to LPS (10 ng/mL) in the presence or absence of ODQ. In vivo: Rats treated in vivo with LPS (10 mg/kg iv for 3 hrs) and mice challenged with 60 mg/kg LPS ip, in the presence or absence of ODQ.

MEASUREMENTS AND MAIN RESULTS

Stimulation of rat aortic smooth muscle cells with bacterial LPS and gamma-interferon induced the production of nitrite and nitrate (breakdown products of NO) and suppression of mitochondrial respiration for 24 to 48 hrs. The amount of NO produced was slightly enhanced with ODQ (10-100 EM), whereas the suppression of mitochondrial respiration was not affected by ODQ (1-100 microM). ODQ did not affect the degree of suppression of mitochondrial respiration in response to NO donor agents or to peroxynitrite. Exposure to LPS (10 ng/mL) for 6 hrs caused a time-dependent relaxation of norepinephrine-precontracted endothelium-denuded thoracic aortic rings. This response was caused by the expression of inducible NOS and could be blocked by pharmacologic inhibitors of NOS such as N(G)-methylL-arginine. ODQ (1 microM) prevented the LPS-induced loss of vascular tone in this experimental system. Similar to the in vitro responses, there was a significant suppression of the norepinephrine-induced contractions in ex vivo experiments, in which rings were taken from animals treated in vivo with LPS (10 mg/kg for 3 hrs). ODQ treatment in vitro (1 microM) caused a complete restoration of the contractile responses. In mice challenged with 60 mg/kg LPS ip, ODQ (20 mg/kg), given either as a pretreatment or as a 4-hr posttreatment, improved survival at 24-144 hrs.

CONCLUSION

These studies indicate that GC activation does not contribute to NO- or peroxynitrite-induced cytotoxicity but does contribute to the vascular hyporeactivity induced by endotoxin in vitro and in vivo. GC inhibition alone is sufficient to influence survival in a murine model of severe sepsis.

Protective effects of poly (ADP-ribose) synthase inhibitors in zymosan-activated plasma induced paw edema

The aim of the present study was to investigate the role of poly (ADP-ribose) synthetase (PARS) in a model of acute local inflammation (zymosan-activated plasma (ZAP)-induced paw edema), in which the oxyradicals, nitric oxide and peroxynitrite, are known to play a crucial role. Injection of zymosan-activated plasma (ZAP) into the rat paw induced edema formation. The maximal increase in paw volume was observed at three hours after administration (maximal in paw volume: 1.29+/-0.09 ml). At this time point, there was a marked increase in neutrophil infiltration in the paw, as measured by an increase in myeloperoxidase (MPO) activity in the paw tissue (260+/-25 mU/100 mg wet tissue). However, ZAP-induced paw edema was significantly reduced in a dose-dependent manner by treatment with 3-aminobenzamide (3-AB) or nicotinamide (NIC), two inhibitors of PARS, at 1, 2, 3, 4 hours after ZAP injection. PARS inhibition also caused a significant reduction of MPO activity. The paw tissues were also examined immunohistochemically for the presence of nitrotyrosine (a footprint for peroxynitrite formation). At 3 h following ZAP injection, staining for nitrotyrosine were also found to be localised within discrete cells in the inflamed paw tissue. Treatment with PARS inhibitor prevented the appearance of nitrotyrosine in the tissues. Our results suggest that in paw edema induced by ZAP, inhibition of PARS exert potent anti-inflammatory effects.

Protective effect of poly(ADP-ribose) synthetase inhibition on multiple organ failure after zymosan-induced peritonitis in the rat

BACKGROUND AND METHODS

In the present study, we tested the hypothesis that peroxynitrite and subsequent activation of the nuclear enzyme poly(ADP-ribose) synthetase (PARS) play a role in the pathogenesis of multiple organ failure induced by peritoneal injection of zymosan in the rat. Animals were randomly divided into six groups (ten rats for each group). The first group was treated with ip administration of saline solution (0.9% NaCl) and served as the sham group. The second group was treated with ip administration of zymosan (500 mg/kg suspended in saline solution). In the third and fourth groups, rats received ip administration of 3-aminobenzamide (10 mg/kg) 1 and 6 hrs after zymosan or saline administration, respectively. In the fifth and sixth groups, rats received ip administration of nicotinamide (50 mg/kg) 1 and 6 hrs after zymosan or saline administration, respectively. After zymosan or saline injection, animals were monitored for 72 hrs to evaluate systemic toxicity (conjunctivitis, ruffled fur, diarrhea, and lethargy), loss of body weight, and mortality.

RESULTS

A severe inflammatory response, characterized by peritoneal exudation, high plasma and peritoneal levels of nitrate/nitrite (the breakdown products of nitric oxide), and leukocyte infiltration into peritoneal exudate, was induced by zymosan administration. This inflammatory process coincided with the damage of lung, small intestine, and liver as assessed by histologic examination and by an increase of myeloperoxidase activity, which is indicative of neutrophil infiltration. Zymosan-treated rats showed signs of systemic illness, significant loss of body weight, and high mortality rates. Peritoneal administration of zymosan in the rat also induced a significant increase in the plasma levels of peroxynitrite as measured by the oxidation of the fluorescent dihydrorhodamine 123. Immunohistochemical examination demonstrated a marked increase in the immunoreactivity to nitrotyrosine, a specific "footprint" of peroxynitrite, in the lung of zymosan-shocked rats. In vivo treatment with ip administration of 3-aminobenzamide (10 mg/kg, 1 and 6 hrs after zymosan injection) or nicotinamide (50 mg/kg, 1 and 6 hrs after zymosan injection) significantly decreased mortality, inhibited the development of peritonitis, and reduced peroxynitrite formation. In addition, PARS inhibitors were effective in preventing the development of organ failure because tissue injury and neutrophil infiltration, by myeloperoxidase evaluation, were reduced in the lung, small intestine, and liver.

CONCLUSIONS

In conclusion, the major findings of our study are that peroxynitrite and the consequent PARS activation exert a role in the development of multiple organ failure and that PARS inhibition is an effective anti-inflammatory therapeutic tool.

Reduced oxidative and nitrosative damage in murine experimental colitis in the absence of inducible nitric oxide synthase

BACKGROUND

Oxidative and nitrosative stress have been implicated in the pathogenesis of inflammatory bowel diseases.

AIMS

To study the role of nitric oxide (NO) derived from inducible NO synthase (iNOS) in an experimental model of murine enterocolitis.

METHODS

Trinitrobenzene sulphonic acid (TNBS) was instilled per rectum to induce a lethal colitis in iNOS deficient mice and in wild type controls. The distal colon was evaluated for histological evidence of inflammation, iNOS expression and activity, tyrosine nitration and malondialdehyde formation (as indexes of nitrosative and oxidative stress), myeloperoxidase activity (as index of neutrophil infiltration), and tissue localisation of intercellular adhesion molecule 1 (ICAM-1).

RESULTS

TNBS administration induced a high mortality and weight loss associated with a severe colonic mucosal erosion and ulceration, increased myeloperoxidase activity, increased concentrations of malondialdehyde, and an intense staining for nitrotyrosine and ICAM-1 in wild type mice. Genetic ablation of iNOS gene conferred to mice a significant resistance to TNBS induced lethality and colonic damage, and notably reduced nitrotyrosine formation and concentrations of malondialdehyde; it did not, however, affect neutrophil infiltration and intestinal ICAM-1 expression in the injured tissue.

CONCLUSION

Data show that activation of iNOS is required for nitrosative and oxidative damage in experimental colitis.

Protective effects of Mn(III)tetrakis (4-benzoic acid) porphyrin (MnTBAP), a superoxide dismutase mimetic, in paw oedema induced by carrageenan in the rat

In the present study we investigated the therapeutic efficacy of Mn(III)tetrakis (4-benzoic acid) porphyrin (MnTBAP), a superoxide dismutase mimetic which possesses peroxynitrite scavenging effects, in rats subjected to carrageenan-induced paw oedema. Local administration of MnTBAP (5, 25, and 50 microg/paw) significantly and dose dependently reduced carrageenan-induced paw oedema at all time points. MnTBAP also caused a significant dose-dependent reduction in paw myeloperoxidase activity and lipid peroxidation, as well as preventing histological injury. Immunohistochemical analysis for nitrotyrosine revealed a positive staining in paw from carrageenan-treated rats. No positive nitrotyrosine staining was found in the paws of the carrageenan-treated rats that received MnTBAP. Our study demonstrates that MnTBAP exerts protective effects in carrageenan-induced paw oedema. Part of these anti-inflammatory effects may be related to: 1) reduction of superoxide formation due to the superoxide dismutase-like activity of the compound; and 2) scavenging of peroxynitrite.

The protective role of endogenous glutathione in carrageenan-induced pleurisy in the rat

In the present study we investigated the protective role of endogenous glutathione, a known free radical scavenger, in rats subjected to carrageenan-induced pleurisy. In vivo depletion of endogenous glutathione pools with L-buthionine-(S,R)-sulfoximine (BSO, 1 g/kg for 24 h, intraperitoneally) enhances the carrageenan-induced degree of pleural exudation and polymorphonuclear leukocyte migration in rats subjected to carrageenan-induced pleurisy. Lung myeloperoxidase activity and lipid peroxidation were significantly increased in BSO pretreated rats. However, the inducible nitric oxide (NO) synthase in lung samples was unaffected by BSO pretreatment. Immunohistochemical analysis for nitrotyrosine revealed a positive staining in lungs from carrageenan-treated rats, which was massively enhanced by BSO pretreatment. Furthermore, in vivo BSO pretreatment significantly increased peroxynitrite formation as measured by the oxidation of the fluorescent dye dihydrorhodamine 123, enhanced the appearance of DNA damage, the decrease in mitochondrial respiration and partially decreased the cellular level of NAD+ in ex vivo macrophages harvested from the pleural cavity of rats subjected to carrageenan-induced pleurisy. In vivo treatment with exogenous glutathione (50 mg/kg i.p.) significantly reverts the effects of BSO and exerts anti-inflammatory effects. Thus, endogenous glutathione plays an important protective role against carrageenan-induced local inflammation.

Blockade of Poly(ADP-ribose) synthetase inhibits neutrophil recruitment, oxidant generation, and mucosal injury in murine colitis

BACKGROUND & AIMS

Inflammatory bowel disease is characterized by oxidative and nitrosative stress, leukocyte infiltration, and up-regulation of intercellular adhesion molecule 1 (ICAM-1) expression in the colon. Recent data show that oxidative and nitrosative stress in isolated enterocytes produces DNA single-strand breaks that activate the nuclear enzyme poly(ADP-ribose) synthetase (PARS), resulting in depletion of intracellular energetics and increased paracellular permeability. The aim of the present study was to examine the in vivo relevance of this injury pathway.

METHODS

Colitis was induced by rectal instillation of trinitrobenzenesulfonic acid (TNBS) in mice with a genetic deficiency of PARS (PARS-/-) and in wild-type littermates.

RESULTS

In wild-type mice, TNBS treatment resulted in colonic erosion and ulceration that was maintained up to 7 days. Neutrophil infiltration (indicated by myeloperoxidase activity in the mucosa) was associated with up-regulation of ICAM-1 and high levels of malondialdehyde and nitrotyrosine. TNBS-treated PARS-/- mice experienced a similar colonic injury that was, however, completely resolved by 6 days. Resolution of the damage was associated with absence of ICAM-1 up-regulation, reduction of neutrophil infiltration, lipid peroxidation, and nitrosative damage.

CONCLUSIONS

These data show that PARS plays a critical role in colonic inflammation possibly by regulating ICAM-1 expression, neutrophil recruitment, and the subsequent oxidant generation.

Beneficial effects of Mn(III)tetrakis (4-benzoic acid) porphyrin (MnTBAP), a superoxide dismutase mimetic, in carrageenan-induced pleurisy

Peroxynitrite, a potent cytotoxic oxidant formed by the reaction of NO with superoxide anion, has been proposed to have major pathogenetic role in inflammatory process. Here we have investigated the therapeutic efficacy of Mn(III)tetrakis (4-benzoic acid) porphyrin (MnTBAP), a novel superoxide dismutase mimetic that possesses peroxynitrite scavenging effect, in rats subjected to carrageenan-induced pleurisy. In vivo treatment with MnTBAP (3 and 10 mg/kg 5 min before carrageenan) prevented in a dose-dependent manner the carrageenan-induced the degree of pleural exudation, polymorphonuclear migration in rats subjected to carrageenan-induced pleurisy. Lung myeloperoxidase (MPO) activity and histological organ injury was significantly reduced by MnTBAP. However, MnTBAP did not inhibit the inducible NO synthase in lung samples. Immunohistochemical analysis for nitrotyrosine, a footprint of peroxynitrite, revealed a positive staining in lungs from carrageenan-treated rats. No positive nitrotyrosine staining was found in the lungs of the carrageenan-treated rats that received MnTBAP (10 mg/kg) treatment. In addition, in vivo MnTBAP treatment significantly reduced in a dose-dependent manner peroxynitrite formation as measured by the oxidation of the fluorescent dye dihydrorhodamine 123, prevented the appearance of DNA damage, the decrease in mitochondrial respiration and partially restored the cellular level of NAD+ in ex vivo macrophages harvested from the pleural cavity of rats subjected to carrageenan-induced pleurisy. Our study demonstrates that the MnTBAP exerts multiple protective effects in carrageenan-induced pleurisy. We suggest peroxynitrite produced during the inflammatory process trigger DNA strand breakage and subsequent cellular dysfunction. Part of these anti-inflammatory effects may be related to: (1) reduction of superoxide formation due to the superoxide dismutase-like activity of the compound and (2) scavenging of peroxynitrite.

Mercaptoethylguanidine, a combined inhibitor of nitric oxide synthase and peroxynitrite scavenger, reduces trinitrobenzene sulfonic acid-induced colonic damage in rats

The effect of mercaptoethylguanidine (MEG), a selective inhibitor of the inducible nitric oxide synthase and peroxynitrite scavenger, was evaluated in a rat model of colonic injury. A single intracolonic administration of trinitrobenzene sulfonic acid (TNBS, 20 mg/kg) dissolved in ethanol induced a severe colitis in male rats. Rats experienced bloody diarrhea and a significant loss of body weight. At 4 days after TNBS administration, the colon damage was characterized by areas of mucosal necrosis. Activity of myeloperoxidase, a marker of neutrophil infiltration, and levels of the 6-keto-prostaglandin F1alpha, were also markedly increased, whereas colonic ATP levels were reduced into the damaged tissue. Immunohistochemistry for the inducible nitric oxide synthase and nitrotyrosine, an index of nitrosative stress, showed an intense staining in the inflamed colon. Treatment with MEG (10 mg/kg i.v. b. i.d.) significantly reduced the appearance of diarrhea and the loss of body weight. This was associated with a remarkable amelioration of the disruption of the colonic architecture and suppression of the energetic failure, as well as a significant reduction of colonic myeloperoxidase activity and 6-keto-prostaglandin F1alpha levels. MEG also reduced the appearance of iNOS and nitrotyrosine immunoreactivity in the colon. The results of this study suggested that administration of MEG may be beneficial for the treatment of inflammatory bowel diseases.

Role of peroxynitrite and poly (ADP-ribosyl) synthetase activation in cardiovascular derangement induced by zymosan in the rat

Peritoneal administration of zymosan in the rat induced a severe inflammatory process characterised by an increase in the plasma levels of nitrite and nitrate, stable metabolites of nitric oxide (NO) and in the levels of peroxynitrite, as measured by the oxidation of the fluorescent dye dihydrorhodamine 123, at 18 hours zymosan challenge. Immunohistochemical examination demonstrated a marked increase in the immunoreactivity to nitrotyrosine, a specific "footprint" of peroxynitrite, in the aorta of zymosan-shocked rats. In ex vivo experiments, thoracic aorta rings of zymosan-treated rats showed a reduced contraction to noradrenaline and reduced responsiveness to the relaxant effect to acetylcholine (vascular hyporeactivity and endothelial dysfunction, respectively). Treatment of zymosan-shocked rats with 3-aminobenzamide or Nicotinamide, inhibitors of poly ADP-ribosil synthetase (PARS) activity reduced the production of peroxynitrite and significantly prevented the cardiovascular dysfunction. Our data suggest that peroxynitrite and PARS activation play a role in the zymosan-induced cardiovascular derangements in the rat.

Role of constitutive nitric oxide synthase and peroxynitrite production in a rat model of splanchnic artery occlusion shock

Peroxynitrite, a potent cytotoxic oxidant formed by the reaction of nitric oxide with superoxide anion, is an important mediator of reperfusion injury. In a rodent model of mesenteric ischemia and reperfusion injury we evaluated the contribution of the constitutive and/or inducible nitric oxide synthase (cNOS or iNOS) in the formation of peroxynitrite. Splanchnic artery occlusion (SAO) shock was induced in rats by clamping both the superior mesenteric artery and the celiac trunk for 45 min, followed by release of the clamps (reperfusion). A significant peroxynitrite production was found in the plasma of the splanchnic occlusion shocked rats at 60 minutes after reperfusion. Immunohistochemical examination demonstrated a marked increase in the immunoreactivity to nitrotyrosine, a specific "footprint" of peroxynitrite, in the necrotic ileum and the aorta of shocked rats. No change in plasma levels of nitrate/nitrite, tissue iNOS expression (by western blotting detection) or iNOS activity was found in the intestine at 60 minutes after reperfusion. On the contrary, activity of the cNOS was reduced (approximately 50%) in the reperfused ischemic intestinal tissue. Treatment with NG-nitro-L-arginine methyl ester, a non selective inhibitor of nitric oxide synthase (given at 3 mg/kg i.v., 5 min prior to reperfusion), significantly reduced plasma level of peroxynitrite and the immunohistochemical staining for nitrotyrosine in the ileum and aorta. Our results suggest that during splanchnic artery occlusion shock peroxynitrite formation is likely to be correlated with nitric oxide production from constitutive nitric oxide synthase activation rather than from the inducible isoform enzyme.

Protective effect of melatonin in a non-septic shock model induced by zymosan in the rat

In vitro studies have demonstrated that melatonin is a scavenger of oxyradicals and peroxynitrite and an inhibitor of nitric oxide (NO) production. Recently, it has been proposed that zymosan, a non-bacterial agent, causes inflammation by inducing the production of various cytokines and pro-inflammatory mediators. In the present study we evaluated the effect of melatonin treatment in a non-septic shock model induced by zymosan in the rat. Administration of zymosan (500 mg/kg intraperitoneally) in the rat induced acute peritonitis, as assessed by a marked increase in the leukocyte count in the exudate, as well as by an increase in the exudate nitrate/nitrite concentration. This inflammatory process coincided with the damage of lung, small intestine, and liver, as assessed by histological examination and by increase of myeloperoxidase activity, indicative of neutrophil infiltration. Peritoneal administration of zymosan in the rat induced also an significant increase in the plasma levels of nitrite and nitrate, stable metabolites of nitric oxide (NO), and in the levels of peroxynitrite, as measured by the oxidation of the fluorescent dye dihydrorhodamine 123, at 18 hr after zymosan challenge. Immunohistochemical examination demonstrated a marked increase in the immunoreactivity to nitrotyrosine, a specific "footprint" of peroxynitrite, in the lung of zymosan-shocked rats. Pretreatment of zymosan-shocked rats with melatonin (25 and 50 mg/kg, intraperitoneally, 5 min before zymosan) prevented in a dose dependent manner the development of peritonitis and reduced peroxynitrite formation. In addition, melatonin (50 mg/kg, intraperitoneally, 5 min before zymosan) was effective in preventing the development of organ failure since tissue injury and neutrophil infiltration, by myeloperoxidase evaluation, was reduced in lung, small intestine, and liver. Taken together, the present results demonstrate that melatonin exerts potent antiinflammatory effects.

Evidence for in vivo peroxynitrite production in human chronic hepatitis

During inflammation nitric oxide reacts at near diffusion limited rates with superoxide to form the strong oxidant peroxynitrite. Nitration on the ortho position is a major product of peroxynitrite attack on proteins. In the present study we investigated whether immunohistochemical detection of nitrotyrosine (footprint of peroxynitrite) can be associated with human hepatitis. Paraffin-embedded liver tissue biopsies from patients with chronic active hepatitis, chronic active hepatitis plus cirrhosis and chronic persistent hepatitis exhibit significant specific immunostaining with the antibody to nitrotyrosine. Positive staining was found in 57% and 72% of tissue specimens from patients with chronic hepatitis and cirrhosis, respectively. Immunohistochemical staining of nitrotyrosine residues was found in the hepatocytes and Kuppffer cells of the necrotic area. The presence of nitrotyrosine indicates that oxidants derived from nitric oxide such as peroxynitrite are generated in human hepatitis and may be involved in its pathogenesis.

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 inhibits expression of the inducible isoform of nitric oxide synthase in murine macrophages: role of inhibition of NFkappaB activation

The role of melatonin as an immunomodulator is well established. Recent reports showed that melatonin exerts protective effects in septic and hemorrhagic shock and in inflammation. The expression of the inducible isoform of nitric oxide synthase (iNOS) makes an important contribution to the pathophysiology of shock and inflammation. We studied, in cultured murine macrophages, the role of melatonin in the regulation of the expression of iNOS and defined the mode of melatonin's action. Our results show that melatonin, at 1 microM-1 mM, decreased the production of nitrite/nitrate (the breakdown products of NO) as well as the production of 6-keto-prostaglandin F1alpha (the major stable breakdown product of prostacyclin) in macrophages stimulated with bacterial lipopolysaccharide (10 microg/ml). We observed that melatonin reduces iNOS steady-state mRNA levels and iNOS protein expression in the same concentration range (1 microM-1 mM). Melatonin, up to 10 mM, exerted only a slight direct inhibitory effect on iNOS activity. Using iNOS promoter-luciferase constructs, we found that melatonin inhibits iNOS promoter activation. Inhibition of iNOS expression was associated with inhibition of activation of the transcription factor nuclear factor kappa B (NFkappaB). We conclude that melatonin inhibits NO production in immunostimulated macrophages mainly by inhibiting the expression of iNOS. This is due to inhibition of iNOS transcription, in part through inhibition of NFkappaB activation. Inhibition of iNOS-derived NO production by melatonin may contribute to the anti-inflammatory effects of this pineal secretory product.

Endotoxin tolerance alters macrophage membrane regulatory G proteins

Administration of sublethal doses of endotoxin (LPS) or tumor necrosis factor-alpha (TNF alpha) renders rats tolerant to supralethal doses of LPS. Peritoneal macrophages from tolerant rats are refractory to LPS induced arachidonic acid (AA) metabolism and cytokine production in vivo, and exhibit reduced membrane GTPase activity and GTP gamma S binding. Since LPS stimulated AA metabolism is mediated by Gi alpha proteins, we sought to determine whether Gi alpha and/or other G proteins are reduced in LPS tolerance. Rats were rendered tolerant by two daily sublethal doses of Salmonella enteritidis LPS, 100 micrograms/kg and 500 micrograms/kg administered intraperitoneally. Animals were allowed to rest for 72 hours. Alternatively, tolerance to LPS was induced by sublethal administration of human recombinant TNF alpha (10 micrograms/kg) intraperitoneally 24 hrs before the experiments. Macrophage membrane G protein content was determined by immunoblot analysis with specific antisera to Gi1,2 alpha, Gi3 alpha, Gs alpha and the G protein beta subunits (G beta). Membrane G proteins were differentially decreased in tolerant macrophages. In macrophages from rats rendered tolerant by sublethal doses of LPS, Gi3 alpha was reduced the most to 48 +/- 8% of control (n = 3, P < 0.05) and this reduction was significant compared to those of other G proteins. Gi1,2 alpha and G beta were reduced to 73 +/- 5% (n = 3, P < 0.05) and 65 +/- 4% (n = 3, P < 0.05) of control respectively. Gs alpha(L) and Gs alpha(H) were also reduced to 61 +/- 5% (n = 3, P < 0.05) and 68 +/- 3% (n = 3, P < 0.05) of control, respectively. In contrast, only Gi3 alpha was reduced in macrophage membranes from rats pretreated with TNF alpha. Gi3 alpha was reduced to 57 +/- 11% of control (n = 4, P < 0.05) whereas Gi1,2 alpha and G beta were not significantly affected. These results demonstrate selective changes in tolerant macrophage membrane G proteins and suggest a potential role for Gi3 alpha in mediating LPS tolerance. The molecular mechanisms underlying these changes and their significance in LPS tolerance merit further investigation.

Oxidation, tyrosine nitration and cytostasis induction in the absence of inducible nitric oxide synthase

In the present study, we evaluated the impact of the lack of the gene for inducible nitric oxide synthase (iNOS) on oxidation, tyrosine nitration and cytotoxicity reactions triggered by immunostimulation. In mice injected with E. coli endotoxin (bacterial lipopolysaccharide, LPS, 50 mg/kg i.p.), there was a significant increase in the degree of oxidation of dihydrorhodamine 123 to rhodamine 123. This response was attenuated by inhibition of NO biosynthesis with NG-methyl-L-arginine (L-NMA, 30 mg/kg i.p.). In mice lacking functional iNOS gene (iNOS knock-out mice), the degree of the LPS-induced, L-NMA inhibitable increase in dihydrorhodamine oxidation was decreased, but not completely abolished. LPS stimulation induced a marked increase in the immunoreactivity for nitrotyrosine (an indicator of peroxynitrite formation), as measured in the aorta and lung. An L-NMA inhibitable increase in nitrotyrosine staining induced by LPS was also observed in the tissues of the iNOS knockout animals. LPS treatment induced the appearance of DNA single strand breakage and a suppression of mitochondrial respiration in peritoneal macrophages ex vivo. A significant degree of LPS-induced DNA single strand breakage and suppression of mitochondrial respiration was still observed in the peritoneal macrophages obtained from the iNOS knockout animals. Macrophages from wild-type mice stimulated with LPS and interferon-gamma suppressed the proliferation of various target cells (P815 mastocytoma, L929 fibrosarcoma and embryonic lung fibroblast cell line): this effect was abolished by in vitro treatment with L-NMA (1 mM). Macrophages from the iNOS knockout animals exhibited a reduced degree of target cell cytostatic activity. The remainder of the cytostasis in iNOS knockout macrophages was abolished by preventing cell contact and neutralizing tumor necrosis factor á. The present results demonstrate that the lack of iNOS gene does not fully abolish oxidation, tyrosine nitration and cytostatic activity in response to immunostimulation. The current findings may have implications for the development of NO-based approaches for the experimental therapy of inflammation.

Peroxynitrate-mediated DNA strand breakage activates poly(ADP-ribose) synthetase and causes cellular energy depletion in a nonseptic shock model induced by zymosan in the rat

The aim of the present study was to investigate the role of poly(ADP-ribose) synthetase in a nonseptic shock model, wherein oxyradicals, nitric oxide, and peroxynitrite are known to play a crucial role in the inflammatory process. DNA single-strand breakage and activation of the nuclear enzyme poly(ADP-ribose) synthetase (PARS) triggers an energy-consuming, inefficient repair cycle, which contributes to peroxynitrite-induced cellular injury. Here we investigated whether peroxynitrite production and PARS activation are involved in cytotoxicity in macrophages collected from rats subjected to zymosan-induced shock. Macrophages harvested from the peritoneal cavity exhibited a significant production of peroxynitrite, as measured by the oxidation of the fluorescent dye dihydrorhodamine 123. Furthermore, zymosan-induced shock caused a suppression of macrophage mitochondrial respiration, DNA strand breakage, activation of PARS, and reduction of NAD+ cellular levels. In vivo treatment with 3-aminobenzamide (10 mg/kg intraperitoneally, 1 and 6 h after zymosan injection) or nicotinamide (50 mg/kg intraperitoneally, 1 and 6 h after zymosan injection) significantly inhibited the decrease in mitochondrial respiration and the activation of PARS, and partially restored the cellular level of NAD+. In a separate group of experiments, in vivo pretreatment with NG-nitro-L-arginine methyl ester, a nonselective inhibitor of nitric oxide synthesis (10 mg/kg intraperitoneally, 15 min before zymosan administration), reduced peroxynitrite formation and prevented the appearance of DNA damage, the decrease in mitochondrial respiration, and the loss of cellular levels of NAD+. Our study suggests that formation of peroxynitrite and subsequent activation of PARS may alter macrophage function in inflammatory processes and inhibition of nitric oxide, and that PARS may be a novel pharmacological approach to prevent cell injury in inflammation.

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.

Effect of L-buthionine-(S,R)-sulphoximine, an inhibitor of gamma-glutamylcysteine synthetase on peroxynitrite- and endotoxic shock-induced vascular failure

1. Peroxynitrite, a cytotoxic oxidant formed from the reaction of nitric oxide (NO) and superoxide is a mediator of cellular injury in ischaemia/reperfusion injury, shock and inflammation. Here we investigated whether L-buthionine-(S,R)-sulphoximine (BSO), an inhibitor of gamma-glutamylcysteine synthetase, alters endothelial and vascular smooth muscle injury in response to peroxynitrite in vitro and during endotoxic shock in vivo. 2. In human umbilical vein endothelial cells and in rat aortic smooth muscle cells, BSO (1 mM, for 24 h) enhanced, whereas glutathione (3 mM) or glutathione ethyl ester (3 mM) attenuated the peroxynitrite (100-1000 microM)-induced suppression of mitochondrial respiration (measured by the conversion of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) to formazan), formation of nitrotyrosine (detected by Western blotting), protein oxidation (measured by detection of 2,4 dinitrophenylhydrazine-reactive carbonyls), and DNA single strand breakage and activation of the nuclear enzyme poly (ADP-ribose) synthetase (PARS) (measured by the incorporation of radiolabelled NAD+ into nuclear proteins and by the alkaline unwinding assay, respectively). Glutathione ethyl ester treatment reduced the BSO-induced enhancement of peroxynitrite-induced cytotoxicity. 3. In rat isolated thoracic aortic rings, BSO treatment (in vivo, at 1 g kg(-1) intraperitoneally (i.p.) for 24 h) enhanced, whereas pretreatment with glutathione (in vitro, 3 mM) attenuated the peroxynitrite-induced reduction of the contractions to noradrenaline, and the peroxynitrite-induced impairment of the endothelium-dependent relaxations to acetylcholine. 4. In BSO-pretreated rats, treatment with bacterial lipopolysaccharide (LPS, 15 mg kg(-1), i.p., for 6 h) caused a more pronounced vascular hyporeactivity and endothelial dysfunction ex vivo. BSO pretreatment also increased the degree of nitrotyrosine staining (detected by imunohistochemistry) in the aorta after LPS treatment. 5. In conclusion, our results demonstrate that L-buthionine-(S,R)-sulphoximine, an inhibitor of gamma-glutamylcysteine synthetase enhances peroxynitrite- and endotoxic shock-induced vascular failure. Based on these findings, we suggest that endogenous glutathione plays an important protective role against peroxynitrite- and LPS-induced vascular injury.

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.

Peroxynitrite-mediated DNA strand breakage activates poly (ADP-ribose) synthetase and causes cellular energy depletion in carrageenan-induced pleurisy

The aim of the present study was to investigate the role of poly (ADP-ribose) synthetase in acute local inflammation (carrageenan-induced pleurisy), where oxyradicals, nitric oxide and peroxynitrite are known to play a crucial role in the inflammatory process. DNA single-strand breakage and activation of the nuclear enzyme poly (ADP-ribose) synthetase (PARS) triggers an energy-consuming, inefficient repair cycle, which contributes to peroxynitrite-induced cellular injury. Here we investigated whether peroxynitrite production and PARS activation are involved in cytotoxicity in macrophages collected from rats subjected to carrageenan-induced pleurisy. Macrophages harvested from the pleural cavity exhibited a significant production of peroxynitrite, as measured by the oxidation of the fluorescent dye dihydrorhodamine 123, and by nitrotyrosine Western blotting at 4 hr after carrageenan injection. Furthermore, carrageenan-induced pleurisy caused a suppression of macrophage mitochondrial respiration, DNA strand breakage, activation of PARS and reduction of NAD+ cellular levels. In vivo treatment with 3-aminobenzamide (10 mg/kg intraperitoneally, 1 hr after carrageenin injection) significantly inhibited the decrease in mitochondrial respiration and the activation of PARS and partially restored the cellular level of NAD+. In a separate group of experiments, in vivo pretreatment with NG-nitro-L-arginine methyl ester, a non-selective inhibitor of nitric oxide (NO) synthesis (10 mg/kg intraperitoneally, 15 min before carrageenan administration), reduced peroxynitrite formation and prevented the appearance of DNA damage, the decrease in mitochondrial respiration and the loss of cellular levels of NAD+. Our study suggests that formation of peroxynitrite and subsequent activation of PARS may alter macrophage function in inflammatory processes and inhibition of NO and PARS may be a novel pharmacological approach to prevent cell injury in inflammation.

Lipocortin 1 protects against splanchnic artery occlusion and reperfusion injury by affecting neutrophil migration

Splanchnic artery occlusion and reperfusion (SAO/R) shock was induced in rats by clamping both the superior mesenteric artery and the celiac trunk for 45 min, followed by release of the clamp (60-min reperfusion). Following this reperfusion period, rats developed a fall in mean arterial blood pressure, associated with a significant increase in tissue myeloperoxidase (MPO) activity in the intestine and a marked histologic injury to the distal ileum. Treatment of rats with a lipocortin-1 (LC1)-derived N-terminal peptide, peptide Ac(2-26), dose-dependently (0.125-0.5 mg/kg s.c.) reduced the progressive fall in blood pressure and prevented the infiltration of neutrophils into the reperfused intestine (reduced MPO activity). The LC1 peptide also reduced the degree of ischemia/reperfusion injury in the bowel as evaluated by histologic examination. The glucocorticoid dexamethasone (0.1 mg/kg s.c., -1 h) also produced a marked improvement in SAO/R shock (i.e., maintained mean arterial blood pressure and reduced tissue MPO activity), and this was reversed by pretreatment with two different antisera raised against the LC1 pharmacophore. Peptide Ac(2-26) (0.5 mg/kg s.c., -30 min) reduced (>60%) the extent of IL-1beta-induced cell emigration and significantly attenuated (approximately 45%) the number of adherent leukocytes in the rat mesenteric vascular bed, as assessed by video microscopy. These results suggest that LC1 inhibits neutrophil migration and accumulation into reperfused tissues, thereby ameliorating the outcome of SAO/R shock.

Lipocortin 1 protects against splanchnic artery occlusion and reperfusion injury by affecting neutrophil migration

Splanchnic artery occlusion and reperfusion (SAO/R) shock was induced in rats by clamping both the superior mesenteric artery and the celiac trunk for 45 min, followed by release of the clamp (60-min reperfusion). Following this reperfusion period, rats developed a fall in mean arterial blood pressure, associated with a significant increase in tissue myeloperoxidase (MPO) activity in the intestine and a marked histologic injury to the distal ileum. Treatment of rats with a lipocortin-1 (LC1)-derived N-terminal peptide, peptide Ac(2-26), dose-dependently (0.125-0.5 mg/kg s.c.) reduced the progressive fall in blood pressure and prevented the infiltration of neutrophils into the reperfused intestine (reduced MPO activity). The LC1 peptide also reduced the degree of ischemia/reperfusion injury in the bowel as evaluated by histologic examination. The glucocorticoid dexamethasone (0.1 mg/kg s.c., -1 h) also produced a marked improvement in SAO/R shock (i.e., maintained mean arterial blood pressure and reduced tissue MPO activity), and this was reversed by pretreatment with two different antisera raised against the LC1 pharmacophore. Peptide Ac(2-26) (0.5 mg/kg s.c., -30 min) reduced (&gt;60%) the extent of IL-1beta-induced cell emigration and significantly attenuated (approximately 45%) the number of adherent leukocytes in the rat mesenteric vascular bed, as assessed by video microscopy. These results suggest that LC1 inhibits neutrophil migration and accumulation into reperfused tissues, thereby ameliorating the outcome of SAO/R shock.

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.

Amelioration by mercaptoethylguanidine of the vascular and energetic failure in haemorrhagic shock in the anesthetised rat

The effects of mercaptoethylguanidine, a dual inhibitor of the inducible nitric oxide (NO) synthase and cyclooxygenase with scavenging effect on peroxynitrite, was studied on the delayed vascular decompensation and cellular energetic failure in a rat model of haemorrhagic shock. Shock was induced by bleeding of the animals to a mean arterial blood pressure of 50 mmHg. At 3 h, animals were resuscitated with Ringers-lactate and monitored for a subsequent 3 h period. In the treated group mercaptoethylguanidine (10 mg/kg/i.v. bolus, followed by 10 mg/kg/i.v. infusion) was administered from the beginning of the resuscitation. Haemorrhagic shock resulted in the upregulation of both the constitutive and the inducible NO synthase, as measured in the lung. In shocked rats mercaptoethylguanidine prevented the increase in plasma nitrite/nitrate and 6-keto-prostaglandin F1alpha levels, ameliorated the decrease in mean arterial blood pressure, and inhibited the development of vascular hyporeactivity of the thoracic aorta ex vivo. A significant nitrotyrosine staining, an indicator of peroxynitrite formation, was found in thoracic aortic rings from shocked animals, which was prevented by mercaptoethylguanidine treatment. In ex vivo experiments in peritoneal macrophages obtained from shocked rats, treatment with mercaptoethylguanidine prevented the reduction in the intracellular NAD+ content, ameliorated the suppression of mitochondrial respiration and reduced the development of DNA single strand breaks. Our data suggest that mercaptoethylguanidine may be an useful tool for the experimental therapy of haemorrhagic shock.

Inhibition of poly (ADP-ribose) synthetase attenuates neutrophil recruitment and exerts antiinflammatory effects

A cytotoxic cycle triggered by DNA single-strand breakage and poly (ADP-ribose) synthetase activation has been shown to contribute to the cellular injury during various forms of oxidant stress in vitro. The aim of this study was to investigate the role of poly (ADP-ribose) synthetase (PARS) in the process of neutrophil recruitment and in development of local and systemic inflammation. In pharmacological studies, PARS was inhibited by 3-aminobenzamide (10-20 mg/kg) in rats and mice. In other sets of studies, inflammatory responses in PARS-/- mice were compared with the responses in corresponding wild-type controls. Inhibition of PARS reduced neutrophil recruitment and reduced the extent of edema in zymosan- and carrageenan-triggered models of local inflammation. Moreover, inhibition of PARS prevented neutrophil recruitment, and reduced organ injury in rodent models of inflammation and multiple organ failure elicited by intraperitoneal injection of zymosan. Inhibition of PARS also reduced the extent of neutrophil emigration across murine mesenteric postcapillary venules. This reduction was due to an increased rate of adherent neutrophil detachment from the endothelium, promoting their reentry into the circulation. Taken together, our results demonstrate that PARS inhibition reduces local and systemic inflammation. Part of the antiinflammatory effects of PARS inhibition is due to reduced neutrophil recruitment, which may be related to maintained endothelial integrity.

Multiple organ failure following zymosan-induced peritonitis is mediated by nitric oxide

In the present study we tested the hypothesis that nitric oxide may play a role in the pathogenesis of multiple organ failure induced by peritoneal injection of zymosan in the rat. A severe inflammatory response characterized by peritoneal exudation, high plasma and peritoneal levels of nitrate/ nitrite (breakdown products of nitric oxide), prostaglandin E2 and leukocyte infiltration into peritoneal exudate was induced by zymosan administration. This inflammatory process started within 3 h of administration and onset occurred at 18 h, coinciding with damage of lung, small intestine and liver, as assessed by histological examination and by increase of myeloperoxidase activity, indicative of neutrophil infiltration. Furthermore, at 18 h after zymosan-induced peritonitis, expression of inducible nitric oxide synthase enzyme was found mainly in the macrophages of inflamed lungs. Subcutaneously administration of a nonisoform selective nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester, reduced formation of peritoneal exudate fluid, blocked plasma and peritoneal nitrate/nitrite accumulation, and attenuated the elevated release of peritoneal prostaglandin E2. In addition, nitric oxide synthase inhibition was effective in preventing the development of organ failure since tissue injury and neutrophil infiltration, by myeloperoxidase evaluation, was reduced in lung, small intestine, and liver. In conclusion, major findings of our study are that nitric oxide exerts a proinflammatory role in the development of multiple organ failure and nitric oxide synthase inhibition is an effective antiinflammatory therapeutic tool, since inhibits not only nitric oxide but also prostaglandin production and cellular infiltration in inflamed organs.

Role of peroxynitrite and activation of poly (ADP-ribose) synthase in the vascular failure induced by zymosan-activated plasma

1. Zymosan is a wall component of the yeast Saccharomyces Cerevisiae. Injection of zymosan into experimental animals is known to produce an intense inflammatory response. Recent studies demonstrated that the zymosan-induced inflammatory response in vivo can be ameliorated by inhibitors of nitric oxide (NO) biosynthesis. The cytotoxic effects of NO are, in part, mediated by the oxidant preoxynitrite and subsequent activation of the nuclear enzyme poly (ADP-ribose) synthetase (PARS). In the present in vitro study, we have investigated the cellular mechanisms of vascular failure elicited by zymosan-activated plasma and the contribution of peroxynitrite production and activation of PARS to the changes. 2. Incubation of rat aortic smooth muscle cells with zymosan-activated plasma (ZAP) induced the production of nitrite, the breakdown product of NO, due to the expression of the inducible isoform of NO synthase (iNOS) over 6 24 h. In addition, ZAP triggered the production of peroxynitrite in these cells, as measured by the oxidation of the fluorescent dye dihydrorhodamine 123 and by nitrotyrosine Western blotting. 3. Incubation of the smooth muscle cells with ZAP induced DNA single strand breakage and PARS activation. These effects were reduced by inhibition of NOS with NG-methyl-L-arginine (L-NMA, 3 mM), and by glutathione (3 mM), a scavenger of peroxynitrite. The PARS inhibitor 3-aminobenzamide (1 mM) inhibited the ZAP-induced activation of PARS. 4. Incubation of thoracic aortae with ZAP in vitro caused a reduction of the contractions of the blood vessels to noradrenaline (vascular hyporeactivity) and elicited a reduced responsiveness to the endothelium-dependent vasodilator acetylcholine (endothelial dysfunction). 5. Preincubation of the thoracic aortae with L-NMA (1 mM), glutathione (3 mM) or by the PARS inhibitor 3-aminobenzamide (1 mM) prevented the development of vascular hyporeactivity in response to ZAP. Moreover, glutathione and 3-aminobenzamide treatment protected against the ZAP-induced development of endothelial dysfunction. The PARS-related loss of the vascular contractility was evident at 30 min after incubation in endothelium-intact, but not in endothelium-denuded vessels and also manifested at 6 h after incubation with ZAP in endothelium-denuded rings. The acute response is probably related, therefore, to peroxynitrite formation (involving the endothelial NO synthase), whereas the delayed response may be related to the expression of iNOS in the smooth muscle. 6. The data obtained suggest that zymosan-activated plasma causes vascular dysfunction by inducing the simultaneous formation of superoxide and NO. These radicals combine to form peroxynitrite, which, in turn causes DNA injury and PARS activation. The protective effect of 3-aminobenzamide demonstrates that PARS activation contributes both to the development of vascular hyporeactivity and endothelial dysfunction during the vascular failure induced by ZAP.

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.

Protection by inhibition of poly (ADP-ribose) synthetase against oxidant injury in cardiac myoblasts In vitro

Peroxynitrite and hydroxyl radical are reactive oxidants produced during myocardial reperfusion injury. In various cell types, including macrophages and smooth muscle cells, peroxynitrite and hydrogen peroxide cause DNA single strand breakage, which triggers the activation of the nuclear enzyme poly (ADP-ribose) synthetase (PARS), resulting in cytotoxicity. Using 3-aminobenzamide and nicotinamide, inhibitors of PARS, we investigated the role of PARS in the pathogenesis of myocardial oxidant injury in H9c2 cardiac myoblasts in vitro. Peroxynitrite (100-1000 microM), hydrogen peroxide (0.3-10 microM) and the NO donor compounds S-nitroso-N-accetyl-DL-penicillamine (SNAP) and diethyltriamine NONOate all caused a dose-dependent reduction of the mitochondrial respiration of the cells, as measured by the mitochondrial-dependent conversion of MTT to formazan. Peroxynitrite and hydrogen peroxide, but not the NO donors caused activation of cellular PARS activity. The suppression of mitochondrial respiration by peroxynitrite and hydrogen peroxide, but not by the NO donors, was ameliorated by pharmacological inhibition of PARS. The protection by the PARS inhibitors diminished at extremely high concentrations of the oxidants. Hypoxia (1 h) followed by reoxygenation (1-24 h) also resulted in a significant activation of PARS, and caused a suppression of mitochondrial respiration, which was prevented by inhibition of PARS. Similar to the results obtained with the pharmacological inhibitors of PARS, a fibroblast cell line which derives from the PARS knockout mouse was protected against the suppression of mitochondrial respiration in response to peroxynitrite and reoxygenation, but not to NO donors, when compared to the result of cells derived from wild-type animals. Based on our data, we suggest that activation of PARS plays a role in the myocardial oxidant injury.

Inhibition of nitric oxide synthase with pyrazole-1-carboxamidine and related compounds

Guanidines, amidines, S-alkylisothioureas, and other compounds containing the amidine function (-C(=NH)NH2) have been described as inhibitors of the generation of nitric oxide (NO) by NO synthase (NOS). Here we report on the inhibition of the activity of NOS isoforms by compounds in which the amidine function is attached to a nitrogen of 1,2-diazo heterocycles to form N-carboxamidines and related compounds. 1H-Pyrazole-1-carboxamidine HCl (PCA) inhibited the activity of purified inducible NOS (iNOS), endothelial NOS (eNOS), and neuronal NOS (nNOS) isoforms to a similar extent (IC50 = 0.2 microM). 3-Methyl-PCA and 4-methyl-PCA showed reduced potencies, but a preference for iNOS [IC50 = 5 and 2.4 microM, respectively; cf. N(G)-methyl-L-arginine (NMA) IC50 = 6 microM]. Inhibition of purified iNOS by PCAs could be reversed completely by excess L-arginine, while their inhibition of NO production by stimulated RAW macrophages could be reversed by transfer to a drug-free medium. This suggests a competitive mode of inhibition. PCA caused potent concentration-dependent inhibition of the acetylcholine-induced, endothelium-dependent relaxations of precontracted rat thoracic aorta (IC50 = 30 microM). 4-Methyl-PCA inhibited the relaxations only at > or = 300 microM. In contrast, 4-methyl-PCA was more effective than both PCA and NMA in restoring the ex vivo contractility of aortic rings taken from lipopolysaccharide-treated rats. PCA and NMA, but not 4-methyl-PCA, caused marked increases in mean arterial pressure when administered i.v. to anesthetized rats. In conclusion, PCA and related compounds caused potent inhibition of NOS. Substitution of the pyrazole ring reduced potency, but improved selectivity towards iNOS as exemplified by 4-methyl-PCA.