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.     

The protective role of endogenous estrogens in carrageenan-induced lung injury in the rat.

BACKGROUND: We have recently demonstrated that 17beta-estradiol (E2) inhibits the increase of inducible nitric oxide synthetase (iNOS) activity in selected model systems such as macrophages, microglia, smooth muscle cells, and proposed that this effect might be associated with an anti-inflammatory activity of this hormone. Here we investigate the effects of endogenous estrogens in rats subjected to carrageenan-induced pleurisy. MATERIALS AND METHODS: Adult female rats were ovariectomized 3 weeks before the experiments to deplete circulating estrogens. Selected inflammatory markers, landmarks of the delayed phase of carrageenan-induced pleurisy, were measured in intact (N-OVX), and ovariectomized (OVX) female rats. In addition, the effect of hormone replacement was evaluated in ovariectomized rats with intraperitoneal injection of 17beta-estradiol (E2; 50 microg/kg) 1 hr before carrageenan treatment (OVX + E2). RESULTS: Ovariectomy enhanced the carrageenan-induced degree of pleural exudation and polymorphonuclear leukocyte migration in rats subjected to carrageenan-induced pleurisy. Lung myeloperoxidase (MPO) activity and lipid peroxidation were significantly increased in estrogens-deprived rats. The iNOS in lung samples was significantly increased by the surgery. The increase of iNOS activity was correlated with a marked enhancement in the production of TNF-alpha and IL-1beta. Immunohistochemical analysis for P-selectin and ICAM-I, as well as nitrotyrosine and poly (ADP-ribose) synthetase (PARS) revealed a positive staining in lungs from carrageenan-treated rats, which was markedly enhanced in ovariectomized rats when compared to cycling rats, particularly in the estrous phase of the cycle. Estrogen replacement counteracted the effect of surgery on all of the above indicators of lung inflammation, suggesting that in the cycling rat this hormone plays a key role in the increased sensitivity to inflammatory injury observed in the OVX rat. CONCLUSION: This study demonstrates that endogenous estrogens production plays an important protective role against carrageenan-induced acute inflammation by decreasing the expression of specific markers of the delayed phase of this well-known model of acute inflammation.     

Protective effects of n-acetylcysteine on lung injury and red blood cell modification induced by carrageenan in the rat.

Oxidative stress has been suggested as a potential mechanism in the pathogenesis of lung inflammation. The pharmacological profile of n-acetylcysteine (NAC), a free radical scavenger, was evaluated in an experimental model of lung injury (carrageenan-induced pleurisy). Injection of carrageenan into the pleural cavity of rats elicited an acute inflammatory response characterized by fluid accumulation in the pleural cavity that contained many neutrophils (PMNs), an infiltration of PMNs in lung tissues and subsequent lipid peroxidation, and increased production of nitrite/nitrate, tumor necrosis factor alpha, and interleukin 1beta. All parameters of inflammation were attenuated by NAC treatment. Furthermore, carrageenan induced an up-regulation of the adhesion molecules ICAM-1 and P-selectin, as well as nitrotyrosine and poly (ADP-ribose) synthetase (PARS), as determined by immunohistochemical analysis of lung tissues. The degree of staining for the ICAM-1, P-selectin, nitrotyrosine, and PARS was reduced by NAC. In vivo NAC treatment significantly reduced peroxynitrite formation as measured by the oxidation of the fluorescent dihydrorhodamine-123, prevented the appearance of DNA damage, an 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. A significant alteration in the morphology of red blood cells was observed 24 h after carrageenan administration. NAC treatment has the ability to significantly diminish the red blood cell alteration. Our results clearly demonstrate that NAC treatment exerts a protective effect and clearly indicate that NAC offers a novel therapeutic approach for the management of lung injury where radicals have been postulated to play a role.     

Regulation of prostaglandin generation in carrageenan-induced pleurisy by inducible nitric oxide synthase in knockout mice

In the present study, by comparing the responses in wild-type mice (iNOSWT) and mice lacking (iNOSKO) the inducible (or type 2) nitric oxide synthase (iNOS), we investigated the correlation between endogenous nitric oxide (NO) and prostaglandin (PG) generation in carrageenan-induced pleurisy. The inflammatory response in iNOSKO mice was significantly reduced in respect to iNOSWT animals, as demonstrated by the exudate volume (-63%) and numbers of infiltrating cells (-62%). The levels of NOx in the pleural exudate from carrageenan-treated mice were significantly (p < 0.01) decreased in iNOSKO mice (16 +/- 7.6 nmoles/mice) compared to iNOSWT animals (133 +/- 9 nmoles/mice). Similarly, the amounts of PGE2 in the pleural exudates of carrageenan-treated animals were significantly (p < 0.01) lower in iNOSKO compared to iNOSWT mice (120 +/- 20 pg/mice vs. 308 +/- 51 pg/mice). Also the amounts of 6-keto-PGF(1 alpha) produced by lungs from carrageenan-treated iNOSKO mice (1.01 +/- 0.10 ng/tissue mg) were significantly (p < 0.01) reduced compared to iNOSWT carrageenan-treated mice (2.1 +/- 0.09 ng/tissue mg). In conclusion our results confirm, by the use of iNOSKO mice that in carrageenan-induced pleurisy NO positively modulates PG biosynthesis.     

The protective role of localized nitric oxide production during inflammation may be mediated by the heme oxygenase-1/carbon monoxide pathway

Nitric oxide (NO) is an important part of the host defense mechanism; however, it displays both pro- and anti-inflammatory properties depending on its location and concentration. Importantly, excessive or inappropriate NO production can cause tissue damage. Systemic and local administration of NO synthase (NOS) inhibitors ameliorates and may exacerbate the inflammatory response, respectively. Here, we used a carrageenan-induced pleurisy model of acute inflammation in rats to confirm the location-dependent effects of NO and investigate the underlying mechanisms. As expected, localized suppression of NO production exacerbated inflammation, as evidenced by increased pleural exudate volumes and leukocyte counts and enhanced activity of enzymes related to oxidative stress. In contrast, local NO supplementation reduced leukocyte infiltration, vascular permeability, and the activity of oxidative stress-related enzymes. Interestingly, inhibition of heme oxygenase-1 (HO-1) reversed the anti-inflammatory effects of localized NO production, while the addition of hemin (HO-1 substrate) or carbon monoxide (CO; HO-1 metabolite) decreased leukocyte migration and exudation. Together, these findings confirm a protective role for NO at the inflammatory site, which appears to be mediated via NOS induction of the HO-1/CO pathway. Thus, NO supplementation may be a potential new treatment for oxidative stress-associated inflammatory diseases.     

Absence of endogenous interleukin-10 enhances the evolution of acute lung injury

Interleukin-10 (IL-10) exerts a wide spectrum of regulatory activities in the immune and inflammatory response. The aim of this study was to investigate the role of endogenous IL-10 on the modulation of the inflammatory response in mice subjected to carrageenan-induced lung injury. When compared to carrageenan-treated IL-10 wild-type (WT) mice, carrageenan-treated IL-10 knock-out mice (IL-10KO) mice experienced a higher rate of pleural exudation, and polymorphonuclear cell migration. Exudate levels of the pro-inflammatory cytokines tumour necrosis factor, interleukin-1beta and interleukin-6 were also greatly enhanced in IL-10KO mice in comparison to wild-type mice. Lung myeloperoxidase (MPO) activity was significantly reduced in IL-10WT mice when compared to IL-10KO mice-treated with carrageenan. The degree of oxidative and nitrosative damage was significantly higher in IL-10KO mice than in wild-type littermates, as indicated by elevated malondialdehyde levels and formation of nitrotyrosine and poly (ADP-ribose) synthetase (PARS). Staining of lung tissue sections obtained from carrageenan-treated IL-10WT with an anti-COX-2 antibody showed a positive staining of the inflamed tissue. Furthermore, expression of inducible nitric oxide synthase (iNOS) was found mainly in the macrophages of the inflamed lungs from carrageenan-treated IL-10WT mice. The intensity and degree of the staining for COX-2 and iNOS were markedly enhanced in tissue sections obtained from carrageenan-treated IL-10KO mice. Most notably, the degree of lung injury caused by carrageenan was also enhanced in IL-10KO mice. Taken together, our results clearly demonstrate that endogenous IL-10 exerts an anti-inflammatory role during acute inflammation and tissue damage associated with carrageenan-induced pleurisy, possibly by regulating neutrophil recruitment, and the subsequent cytokine and oxidant generation.     

Proinflammatory role of glucocorticoid-induced TNF receptor-related gene in acute lung inflammation

Glucocorticoid-induced TNFR-related gene (GITR) participates in the immune/inflammatory response. Because GITR expression has been described in cells other than T lymphocytes, we investigated whether it also modulates acute inflammatory response. Using GITR-deficient (GITR(-/-)) mice, we analyzed the role of GITR in the development of carrageenan-induced lung inflammation (pleurisy) by studying several proinflammatory markers 2-8 h after carrageenan injection. When compared with GITR(+/+), GITR(-/-) mice exhibited decreased production of turbid exudate containing a lower number of leukocytes. This was correlated with the reduction of inflammatory markers (including TNF-alpha, IL-1beta, myeloperoxidase, inducible NO synthase, and cyclooxygenase 2) in the pleural exudate and/or in the lung. Moreover, endothelial cells expressed lower levels of adhesion molecules. In lungs of GITR(+/+) mice, GITR ligand expression was not modulated during pleurisy, while that of GITR increased, as a consequence of increased infiltration by GITR-expressing cells and of GITR up-regulation in macrophages and endothelial cells. Finally, cotreatment of GITR(+/+) mice with carrageenan and Fc-GITR fusion protein decreased the number of inflammatory cells (pleural macrophages and lung neutrophils) as compared with carrageenan treatment alone, confirming that GITR plays a role in the modulation of pleurisy.     

Protective effect of melatonin on zymosan-induced cellular damage

We investigated whether in vivo melatonin treatment inhibits cellular injury induced by peroxynitrite production and PARS activation 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 suppressed macrophage mitochondrial respiration, DNA strand breakage, activation of the nuclear enzyme poly(ADP-ribose)synthetase (PARS) and reduction of cellular levels of NAD+. In vivo treatment with melatonin (25 and 50 mg/kg, i.p., 1 h after zymosan injection) significantly and dose-dependently reduced peroxynitrite formation and prevented the appearance of DNA damage, decrease in mitochondrial respiration, loss of cellular levels of NAD+ and PARS activation. Our study supports the view that the antioxidant and anti-inflammatoy effect of melatonin is also correlated with the inhibition of peroxynitrite production and PARS activation. In conclusion, melatonin may be a novel pharmacological approach to prevent cell injury in inflammation.     

Inhaled nitric oxide induced NOS inhibition and rebound pulmonary hypertension: a role for superoxide and peroxynitrite in the intact lamb

Previous in vivo studies indicate that inhaled nitric oxide (NO) decreases nitric oxide synthase (NOS) activity and that this decrease is associated with significant increases in pulmonary vascular resistance (PVR) upon the acute withdrawal of inhaled NO (rebound pulmonary hypertension). In vitro studies suggest that superoxide and peroxynitrite production during inhaled NO therapy may mediate these effects, but in vivo data are lacking. The objective of this study was to determine the role of superoxide in the decrease in NOS activity and rebound pulmonary hypertension associated with inhaled NO therapy in vivo. In control lambs, 24 h of inhaled NO (40 ppm) decreased NOS activity by 40% (P<0.05) and increased endothelin-1 levels by 64% (P<0.05). Withdrawal of NO resulted in an acute increase in PVR (60.7%, P<0.05). Associated with these changes, superoxide and peroxynitrite levels increased more than twofold (P<0.05) following 24 h of inhaled NO therapy. However, in lambs treated with polyethylene glycol-conjugated superoxide dismutase (PEG-SOD) during inhaled NO therapy, there was no change in NOS activity, no increase in superoxide or peroxynitrite levels, and no increase in PVR upon the withdrawal of inhaled NO. In addition, endothelial NOS nitration was 18-fold higher (P<0.05) in control lambs than in PEG-SOD-treated lambs following 24 h of inhaled NO. These data suggest that superoxide and peroxynitrite participate in the decrease in NOS activity and rebound pulmonary hypertension associated with inhaled NO therapy. Reactive oxygen species scavenging may be a useful therapeutic strategy to ameliorate alterations in endogenous NO signaling during inhaled NO therapy.     

The effect of peroxynitrite and some antioxidants on the rate of osmotic hemolysis of bovine erythrocytes

Bovine erythrocytes treated with peroxynitrite (ONOO(-)), a cytotoxic species formed in vivo via the reaction of nitric oxide (NO(.)) and the superoxide anion (O2(-.)), show an increased rate of hemolysis on sudden osmotic stress. The increase in the rate was peroxynitrite concentration dependent. In the presence of some antioxidants (uric acid, ascorbic acid, glutathione, melatonin and albumin), this effect was significantly lower, with ascorbic acid as the most efficient antioxidant.     

Part I: pathogenetic role of peroxynitrite in the development of diabetes and diabetic vascular complications: studies with FP15, a novel potent peroxynitrite decomposition catalyst

BACKGROUND: Peroxynitrite is a cytotoxic oxidant formed from nitric oxide (NO) and superoxide. Tyrosine nitration, a footprint of peroxynitrite, has been demonstrated in the pancreatic islets as well as in the cardiovascular system of diabetic subjects. Delineation of the pathogenetic role of peroxynitrite in disease conditions requires the use of potent, in vivo active peroxynitrite decomposition catalysts. The aim of the current work was to produce a potent peroxynitrite decomposition catalyst and to test its effects in rodent models of diabetes and its complications. METHODS: FP15 was synthesized and analyzed using standard chemical methods. Diabetes was triggered by the administration of streptozotocin. Tyrosine nitration was measured immunohistochemically. Cardiovascular and vascular measurements were conducted according to standard physiologic methods. RESULTS: FP15, a potent porphyrinic peroxynitrite decomposition catalyst, potently inhibited tyrosine nitration and peroxynitrite-induced cytotoxicity in vitro and in vivo. FP15 treatment (3-10 mg/kg/d) dose dependently and reduced the incidence and severity of diabetes mellitus in rats subjected to multiple low doses of streptozotocin, as well as in nonobese mice developing spontaneous autoimmune diabetes. Furthermore, treatment with FP15 protected against the development of vascular dysfunction (loss of endothelium-dependent relaxations) and the cardiac dysfunction (loss of myocardial contractility) in diabetic mice. FP15 treatment reduced tyrosine nitration in the diabetic pancreatic islets. CONCLUSIONS: The current results demonstrate the importance of endogenous peroxynitrite generation in the pathogenesis of autoimmune diabetes and diabetic cardiovascular complications. Peroxynitrite decomposition catalysts may be of therapeutic utility in diabetes and other pathophysiologic conditions.     

Role of nitric oxide in the oxidant stress during ischemia/reperfusion injury of the liver.

The potential role of nitric oxide (NO) and its reaction product with superoxide, peroxynitrite, was investigated in a model of hepatic ischemia-reperfusion injury in male Fischer rats in vivo. Pretreatment with the NO synthase inhibitor nitro-L-arginine (10 mg/kg) did neither affect the post-ischemic oxidant stress and liver injury during the initial reperfusion phase nor the subsequent infiltration of neutrophils into the liver and the later, neutrophil-induced injury phase. Furthermore, no evidence was found for a postischemic increase of the urinary excretion of nitrite, a stable oxidation metabolite of NO. In contrast, the administration of Salmonella enteritidis endotoxin (1 mg/kg) induced a significant diuresis in Fischer rats and an 800-fold enhancement of the urinary nitrite excretion. Nitro-L-arginine pretreatment inhibited the endotoxin-induced nitrite formation by 97%. Hepatic cGMP levels, as index of NO formation in the liver, were only increased significantly after endotoxin administration but not after ischemia and reperfusion. Our results provide no evidence for any enhanced generation of NO or peroxynitrite either systemically or locally during reperfusion and therefore it is unlikely that any of these metabolites are involved in the oxidant stress and liver injury during reperfusion after hepatic ischemia.     

Effect of Ocimum sanctum fixed oil on vascular permeability and leucocytes migration

Ocimum sanctum fixed oil significantly inhibited the rise in protein concentration and dye leakage in peritoneal fluid in experimentally induced peritoneal inflammation in mice. In carrageenan-induced pleurisy in rats, the fixed oil showed significant inhibition of leucocytes migration in the pleural exudate. The results suggest that the fixed oil can inhibit enhancement of the vascular/capillary permability and leucocyte migration following inflammatory stimulus.     

Effect of combination of nitric oxide synthase and cyclooxygenase inhibitors on carrageenan-induced pleurisy in rats

In the present study, we examined the effects of L-nitroarginine methylester (L-NAME), a non-selective nitric oxide synthase (NOS) inhibitor, indomethacin (IND), a non-selective COX inhibitor and a combination of these agents (L-NAME+IND) on carrageenan-induced pleurisy in rats. Exudate volume, albumin leakage, leukocyte influx, exudate and plasma nitrite/nitrate (NO(x)) levels and exudate PGE(2) levels increased markedly 6 h after an intrapleural injection of 2% carrageenan. First, the effects of L-NAME and IND alone were investigated. L-NAME non-significantly reduced exudate volume by 26% at 10 mg/kg (i.p.), and significantly by 45% at 30 mg/kg. IND dose-dependently decreased the exudate volume at 0.3-10 mg/kg (p.o.) and the effect reached the maximal level at 1 mg/kg (33%). Second, the effects of L-NAME (10 mg/kg, i.p.), IND (1 mg/kg, p.o.) and L-NAME+IND were examined. L-NAME and IND alone at the dose employed significantly reduced the exudate volume and albumin levels by 21-26%. L-NAME but not IND tended to reduce the increased exudate and plasma NO(x) by 18% and 19%, respectively. IND but not L-NAME significantly reduced leukocyte numbers and PGE(2) levels in the exudates by 25% and 77%, respectively. L-NAME+IND significantly reduced exudate volume, albumin leakage, leukocyte number, PGE(2) and NO(x) by 43%, 41%, 31%, 80% and 37%, respectively. The inhibitory effects of L-NAME+IND on exudate volume, albumin leakage and NO(x) levels were greater than those of L-NAME and IND alone. In conclusion, a non-selective NOS inhibitor and COX inhibitor showed anti-inflammatory effects at the early phase of carrageenan-induced pleurisy, and a combination of both inhibitors had a greater effect than each alone probably via the potentiation of NOS inhibition. The simultaneous inhibition of NOS and COX could be a useful approach in therapy for acute inflammation.     

Antioxidant and anti-inflammatory effects of products from Croton celtidifolius Bailon on carrageenan-induced pleurisy in rats

Croton celtidifolius Bailon, commonly known as Sangue-de-Adáve or Pau-Andrade, is a tree found in the Atlantic forest of southern Brazil. It has been popularly used for the treatment of inflammatory and ulcerative disorders. Phytochemical analysis demonstrated the presence of flavonoids and proanthocyanidins in an ethyl acetate fraction (EAF) from C. celtidifolius Bailon. In this study, we have evaluated the effects of EAF and its sub-fractions (35 and 63, catechin) on inflammatory (cell migration and plasma extravasation) and oxidative (lipid peroxidation, superoxide dismutase (SOD) activity and superoxide anion production) parameters in carrageenan-induced pleurisy in rats. NO production was also measured by nitrite/nitrate levels. EAF and sub-fraction 63 (63SF) showed anti-inflammatory activity, as indicated by a reduction in plasma extravasation and cell migration (mainly polymorphonuclear leukocytes) to the pleural cavity. Furthermore, EAF treatment decreased the production of superoxide radical anion by cells isolated from the pleural cavity, while it did not affect the nitrite/nitrate levels in exudates. The results show that C. celtidifolius contains substances with antioxidant and anti-inflammatory activity that, at least in part, act by a modulation of oxidative stress by phenolic compounds.     

Insulin renders diabetic rats resistant to acute ischemic stroke by arresting nitric oxide reaction with superoxide to form peroxynitrite

Background

The functions of free radicals on the effects of insulin that result in protection against cerebral ischemic insult in diabetes remain undefined. This present study aims to explain the contradiction among nitric oxide (NO)/superoxide/peroxynitrite of insulin in amelioration of focal cerebral ischemia–reperfusion (FC I/R) injury in streptozotocin (STZ)-diabetic rats and to delineate the underlying mechanisms. Long-Evans male rats were divided into three groups (age-matched controls, diabetic, and diabetic treated with insulin) with or without being subjected to FC I/R injury.

Results

Hyperglycemia exacerbated microvascular functions, increased cerebral NO production, and aggravated FC I/R-induced cerebral infarction and neurological deficits. Parallel with hypoglycemic effects, insulin improved microvascular functions and attenuated FC I/R injury in STZ-diabetic rats. Diabetes decreased the efficacy of NO and superoxide production, but NO and superoxide easily formed peroxynitrite in diabetic rats after FC I/R injury. Insulin treatment significantly rescued the phenomenon.

Conclusions

These results suggest that insulin renders diabetic rats resistant to acute ischemic stroke by arresting NO reaction with superoxide to form peroxynitrite.     

Green tea polyphenol extract attenuates lung injury in experimental model of carrageenan-induced pleurisy in mice

Here we investigate the effects of the green tea extract in an animal model of acute inflammation, carrageenan-induced pleurisy. We report here that green tea extract (given at 25 mg/kg i.p. bolus 1 h prior to carrageenan), exerts potent anti-inflammatory effects in an animal model of acute inflammation in vivo.Injection of carrageenan (2%) into the pleural cavity of mice elicited an acute inflammatory response characterized by fluid accumulation in the pleural cavity that contained many neutrophils (PMNs), an infiltration of PMNs in lung tissues and increased production of nitrite/nitrate, tumour necrosis factor alpha. All parameters of inflammation were attenuated by green tea extract treatment. Furthermore, carrageenan induced an up-regulation of the adhesion molecule ICAM-1, as well as nitrotyrosine and poly (ADP-ribose) synthetase (PARS) formation, as determined by immunohistochemical analysis of lung tissues. Staining for the ICAM-1, nitrotyrosine, and PARS was reduced by green tea extract.Our results clearly demonstrate that treatment with green tea extract exerts a protective effect and offers a novel therapeutic approach for the management of lung injury.     

Melatonin nitrosation promoted by NO*2; comparison with the peroxynitrite reaction

N-nitroso species have recently been detected in animal tissues. Protein N-nitrosotryptophan is the best candidate for this N-nitroso pool. N-nitrosation of N-blocked trytophan derivatives like melatonin (MelH) by N2O3 or peroxynitrite (ONOOH/ONOO- ) has been observed under conditions of pH and reagent concentrations similar to in vivo conditions. We studied the reaction of NO*2 with MelH. When NO*2 was synthesized by gamma-irradiation of aqueous neutral solutions of nitrate under anaerobic conditions, detected oxidation and nitration of MelH were negligible. In the presence of additional nitrite, when NO* was also generated, formation of 1-nitrosomelatonin increased with nitrite concentration. Nitrosation is not due to N2O3 but could proceed via successive additions of NO*2 and NO*. For comparison, peroxynitrite was infused into a solution of MelH under air leading to the same products as those detected in irradiated solutions but in different proportions. In the presence of additional nitrite, the formation of nitroderivatives increased significantly while N-formylkynuramine and 1-nitrosomelatonin were maintained at similar levels. Mechanistic implications are discussed.     

Androgen deprivation increases neuronal nitric oxide metabolism and its vasodilator effect in rat mesenteric arteries.

This study examines the effects of male sex hormones on the vasoconstrictor response to electrical field stimulation (EFS), as well as neuronal NO modulation of this response. For this purpose, denuded superior mesenteric artery from orchidectomized and control male Sprague-Dawley rats was used. EFS induced similar frequency-dependent contractions in segments from both groups. The NO synthase (NOS) inhibitor N(omega)-nitro-L-arginine methyl ester strengthened EFS-elicited contractions more in arteries from orchidectomized than from control male rats. The expression of nNOS was more pronounced in segments from control than from orchidectomized animals. Basal and EFS-induced NO release was similar in segments from both groups. In noradrenaline (NA)-precontracted segments, sodium nitroprusside (SNP) induced a concentration-dependent relaxation, that was greater in segments from orchidectomized than control male rats. 8-Bromo-cGMP induced a similar concentration-dependent relaxation in NA-precontracted segments from either group, and the cGMP levels induced by SNP were also similar in the two groups. Superoxide dismutase (SOD), a superoxide anion scavenger, did not modify the relaxation in segments from control male rats. In contrast, SOD enhanced the relaxation induced by SNP in segments from orchidectomized rats, and the effect was reversed by preincubation with SOD plus catalase. The generation of superoxide anion and of peroxynitrite was greater in segments from orchidectomized than control rats. In NA-precontracted segments from control or orchidectomized rats, exogenous peroxynitrite and H(2)O(2) induced a concentration-dependent relaxation. These results suggest that EFS induces a similar nNOS-derived NO release in segments from orchidectomized and control male rats, despite the decrease in nNOS expression in orchidectomized rats. The NO metabolism is higher in segments from orchidectomized male rats due to the increases in anion superoxide generation and peroxynitrite formation. The vasodilator effects of the peroxynitrite and H(2)O(2)0 generated from the NO metabolism are what enhance the functional role of the nNOS-derived NO release in the orchidectomized rats.     

Elevated serum leptin concentrations induced by experimental acute inflammation

Leptin is a pleiotropic hormone that regulates body weight and energy expenditure. Recent findings suggest that leptin may be involved in acute and/or chronic inflammation, however only limited results are available describing the effects of in vivo models of acute inflammation on leptin secretion. The aim of this study was to evaluate serum leptin levels in response to two well-established models of acute inflammation in rats: carrageenan rat paw induced oedema and carrageenan induced pleurisy. Our results clearly show that leptin levels rise in rats in which both oedema and pleurisy were induced. Serum leptin levels in carrageenan induced paw oedema were 3.86+/-0.16 microg/L in comparison to 1.83+/-0.17 microg/L of control animals (p<0.001). A similar result was observed in carrageenan induced pleurisy animals in which leptin levels were 4.87+/-0.27 microg/L in comparison to 2.19+/-0.16 microg/L of control animals (p<0.001). The increase in leptin levels induced following carrageenan-induced pleurisy appears to be dependent on adrenal function and it is markedly blunted in adrenalectomized rats. Leptin levels in carrageenan induced pleurisy, carried out on adrenalectomized rats, were lower than intact inflamed animals, suggesting a possible involvement of endogenous glucocorticoids. In summary the results here presented show that: a) an elevated plasma leptin concentration was induced during experimental models of inflammation b) this increase is mediated to a large extent by glucocorticoids. In conclusion, acute experimental models of inflammation are associated with changes in circulating leptin suggesting a possible involvement of this hormone in the anorexia/cachexia that is frequently associated with inflammatory processes. Furthermore, our data indicate the existence of a feedback loop among glucocorticoids and leptin which might contribute to the immune response to lace the inflammatory process.