The role of the L-arginine: nitric oxide pathway in circulatory shock

Nutraceuticals in the Treatment of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a severe disease characterized by the loss and obstructive remodeling of the pulmonary arterial wall, causing a rise in pulmonary arterial pressure and pulmonary vascular resistance, which is responsible for right heart failure, functional decline, and death. Although many drugs are available for the treatment of this condition, it continues to be life-threatening, and its long-term treatment is expensive. On the other hand, many natural compounds present in food have beneficial effects on several cardiovascular conditions. Several studies have explored many of the potential beneficial effects of natural plant products on PAH. However, the mechanisms by which natural products, such as nutraceuticals, exert protective and therapeutic effects on PAH are not fully understood. In this review, we analyze the current knowledge on nutraceuticals and their potential use in the protection and treatment of PAH, as well as whether nutraceuticals could enhance the effects of drugs used in PAH through similar mechanisms.

Torenia concolor Lindley var. formosana Yamazaki extracts improve inflammatory response and lipid accumulation via PPARs activation

Background/Introduction: At present, human diet is replete with sugar and fat. Abnormal metabolism and hyperglycemia or hyperlipidemia in the body induces the development of an overactive and continuous inflammatory response, resulting in obesity and metabolic syndromes, including hypertension, hyperlipidemia, and insulin resistance. Torenia concolor Lindley var. formosana Yamazaki (TC), a perennial creeping herbaceous plant, is a traditional Chinese medicinal herb widely used for the treatment of heat stroke, aching muscles and bones, cold, dysentery, and ambustion.

Purpose: This study evaluated the influence of TC on inflammation responses and lipid metabolism. Methods: In this study, ground TC powder was extracted with 95% ethanol. The ethanol was removed by vacuum concentration, and the resulting extract was further extracted with a number of solvents of different polarity to produce four final extracts: an ethanol extract (TCEE), an ethyl acetate extract (TCEAE), an n-butanol extract (TCBUE), and a water extract (TCWE). The anti-inflammatory efficacy of the extracts and their capability for lipid metabolism regulation was then explored.

Results: TCEE, TCEAE, and TCBUE exhibited good anti-inflammatory efficacy; TCEAE also simultaneously regulated lipid metabolism. In RAW264.7 cells, these three extracts suppressed the expression of iNOS and IL-6 via the signaling pathway activation of the transcription factor peroxisome proliferator activated receptor γ (PPARγ) and thereby showed anti-inflammatory efficacy. In 3T3-L1 cells, these three extracts promoted lipid metabolism and reduced lipid accumulation through the activation of PPARα and the increased expression of adiponectin, thus demonstrating regulation of lipid metabolism.

Conclusion: These results indicate that TC possesses anti-inflammatory efficacy and can regulate lipid metabolism through the activation of transcription factor PPARs. We speculate that these nutraceutical effects are attributable to betulin, an active ingredient in this herbal medicine.

Activation of mTOR/IκB-α/NF-κB pathway contributes to LPS-induced hypotension and inflammation in rats

Mammalian target of rapamycin (mTOR), a serine/threonine kinase plays an important role in various pathophysiological processes including cancer, metabolic diseases, and inflammation. Although mTOR participates in Toll-like receptor 4 signalling in different cell types, the role of this enzyme in sepsis pathogenesis and its effects on hypotension and inflammation in endotoxemic rats remains unclear. In this study we investigated the effects of mTOR inhibition on lipopolysaccharide (LPS)-induced changes on expressions and/or activities of ribosomal protein S6 (rpS6), an mTOR substrate, nuclear factor-κB (NF-κB) p65, inhibitor κB (IκB)-α, inducible nitric oxide synthase (iNOS), cyclooxygenase (COX)-2 with production of nitric oxide, peroxynitrite, prostacyclin, and tumor necrosis factor (TNF)-α and activity of myeloperoxidase (MPO), which results in hypotension and inflammation. Injection of LPS (10mg/kg, i.p.) to male Wistar rats decreased blood pressure and increased heart rate that were associated with elevated nitrotyrosine, 6-keto-PGF_1α, and TNF-α levels and MPO activity, and increased expressions and/or activities of rpS6, NF-κB p65, iNOS, and COX-2 and decreased expression of IκB-α in renal, cardiac, and vascular tissues. LPS also increased serum and tissue nitrite levels. Rapamycin (1mg/kg, i.p.) given one h after injection of LPS reversed these effects of LPS. These data suggest that the activation of mTOR/IκB-α/NF-κB pathway associated with vasodilator and proinflammatory mediator formation contributes to LPS-induced hypotension and inflammation.

Protective effect of suberoylanilide hydroxamic acid against lipopolysaccharide-induced liver damage in rodents

BACKGROUND

Lipopolysaccharide (LPS) has a deleterious effect on several organs, including the liver, and eventually leads to endotoxic shock and death. LPS-induced hepatotoxicity is characterized by disturbed intracellular redox balance and excessive reactive oxygen species (ROS) accumulation, leading to liver injury. We have shown that treatment with suberoylanilide hydroxamic acid (SAHA), a histone deacetylase inhibitor, improves survival in a murine model of LPS-induced shock, but the protective effect of SAHA against liver damage remains unknown. The goal of this study was to investigate the mechanism underlying SAHA action in murine livers.

METHOD

Male C57BL/6J mice (6-8 wk), weighing 20-25 g, were randomly divided into three groups: (A) a sham group was given isotonic sodium chloride solution (10 μL/g body weight, intraperitoneal, i.p.) with dimethyl sulfoxide (DMSO; 1 μL/g body weight, i.p.); (B) an LPS group was challenged with LPS (20 mg/kg, i.p.) dissolved in isotonic sodium chloride solution with DMSO; (C) and an LPS plus SAHA group was treated with SAHA (50 mg/kg, i.p.) dissolved in DMSO immediately after injection of LPS (20 mg/kg, i.p.). Mice were anesthetized, and their livers were harvested 6 or 24 h after injection to analyze whether SAHA affected production of ROS and activation of apoptotic proteins in the liver cells of challenged mice.

RESULTS

SAHA counteracted LPS-induced production of ROS (thiobarbituric acid reactive substances and nitrite) and reversed an LPS-induced decrease in antioxidant enzyme, glutathione. SAHA also attenuated LPS-induced hepatic apoptosis. Moreover, SAHA inhibited activation of the redox-sensitive kinase, apoptosis signal-regulating kinase-1, and the mitogen-activated protein kinases, p38 and Jun N-terminal kinase.

CONCLUSIONS

Our data indicate, for the first time, that SAHA is capable of alleviating LPS-induced hepatotoxicity and suggest that a blockade of the upstream events required for apoptosis signal-regulating kinase-1 action may serve as a new therapeutic option in the treatment of LPS-induced inflammatory conditions.

The uremic toxin indoxyl sulphate enhances macrophage response to LPS

Indoxyl sulphate (IS) is a protein-bound uremic toxin that results from the metabolism of dietary tryptophan normally excreted by kidney through the proximal tubules. Thus the toxin accumulates in the blood of patients with impaired renal function such as in chronic kidney disease (CKD). High IS serum levels in patients with CKD suggest its involvement in CKD progression and in the onset of complications. Its presence in plasma is also a powerful predictor of overall and cardiovascular morbidity/mortality. IS is a well known nephrovascular toxin but very little is known regarding its effects on the immune system and in particular during inflammation. In this study we examined the effect of IS on macrophage activation in response to lipopolysaccharide from E. coli (LPS), a gram negative bacterial endotoxin associated with inflammation and septic shock. To simulate the uremic condition, J774A.1 macrophages were incubated with IS at concentrations observed in uremic patients (1000-62.5 µM) both alone and during LPS challenge. IS alone induced release of reactive oxygen species (ROS), through a mechanism involving pro- and anti-oxidant systems, and alteration in intracellular calcium homeostasis. When added to J774A.1 macrophages in presence of LPS, IS significantly increased the nitric oxide (NO) release, inducible nitric oxide synthase (iNOS) and cycloxygenase-2 (COX-2) expression. IS pre-treatment was also associated with an increase in tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) production by macrophages stimulated with LPS. Mechanistic studies revealed that IS increased LPS-induced NF-kB nuclear translocation, ROS release and altered calcium concentrations, mainly because of mitochondrial calcium overloading. Moreover also in primary mouse peritoneal macrophages IS enhances the inflammatory response to LPS increasing ROS, NO, iNOS, COX-2, TNF-α, IL-6 and NF-kB levels. This study provides evidences that IS stimulates macrophage function and enhances inflammatory reasponse associated with LPS, thus contributing to altered immune response dysfunctions observed in CKD.

Neuroinflammatory processes in Alzheimer's disease

Generation of neurotoxic amyloid beta peptides and their deposition along with neurofibrillary tangle formation represent key pathological hallmarks in Alzheimer's disease (AD). Recent evidence suggests that inflammation may be a third important component which, once initiated in response to neurodegeneration or dysfunction, may actively contribute to disease progression and chronicity. Various neuroinflammatory mediators including complement activators and inhibitors, chemokines, cytokines, radical oxygen species and inflammatory enzyme systems are expressed and released by microglia, astrocytes and neurons in the AD brain. Degeneration of aminergic brain stem nuclei including the locus ceruleus and the nucleus basalis of Meynert may facilitate the occurrence of inflammation in their projection areas given the antiinflammatory and neuroprotective action of their key transmitters norepinephrine and acetylcholine. While inflammation has been thought to arise secondary to degeneration, recent experiments demonstrated that inflammatory mediators may stimulate amyloid precursor protein processing by various means and therefore can establish a vicious cycle. Despite the fact that some aspects of inflammation may even be protective for bystander neurons, antiinflammatory treatment strategies should therefore be considered. Non-steroidal anti-inflammatory drugs have been shown to reduce the risk and delay the onset to develop AD. While, the precise molecular mechanism underlying this effect is still unknown, a number of possible mechanisms including cyclooxygenase 2 or gamma-secretase inhibition and activation of the peroxisome proliferator activated receptor gamma may alone or, more likely, in concert account for the epidemiologically observed protection.

Role of nitroso radicals as drug targets in circulatory shock

A vast amount of circumstantial evidence implicates oxygen-derived free radicals (especially, superoxide and hydroxyl radical) and high-energy oxidants [such as peroxynitrite (OONO(-))] as mediators of shock and ischaemia/reperfusion injury. Reactive oxygen species can initiate a wide range of toxic oxidative reactions. These include initiation of lipid peroxidation, direct inhibition of mitochondrial respiratory chain enzymes, inactivation of glyceraldehyde-3 phosphate dehydrogenase, inhibition of membrane sodium/potassium adenosine 5'-triphosphate-ase activity, inactivation of membrane sodium channels and other oxidative modifications of proteins. All these toxicities are likely to play a role in the pathophysiology of shock and ischaemia and reperfusion. Moreover, various studies have clearly shown that treatment with either OONO(-) decomposition catalysts, which selectively inhibit OONO(-), or with superoxide dismutase (SOD) mimetics, which selectively mimic the catalytic activity of the human SOD enzymes, have been shown to prevent in vivo the delayed vascular decompensation and the cellular energetic failure associated with shock and ischaemia/reperfusion injury.

Abnormal activation of potassium channels in aortic smooth muscle of rats with peritonitis-induced septic shock

This study was conducted to examine the role of membrane hyperpolarization in mediating vascular hyporeactivity induced by cecal ligation and puncture (CLP) in endothelial-denuded strips of rat thoracic aorta ex vivo. The CLP for 18 h elicited a significant fall of blood pressure and a severe vascular hyporeactivity to norepinephrine as seen in severe sepsis. At the end of the in vivo experiments, thoracic aortas were removed from both CLP-treated and control rats. After removal of the endothelium, aortic segments were mounted in myographs for the recording of isometric tension and smooth muscle membrane potential. The membrane potential recording showed that a hyperpolarization was observed in the CLP-treated rats when compared with the control rats. This hyperpolarization was reversed by iberiotoxin (a large-conductance Ca2+-activated K+ channel blocker), 4-aminopyridine (a voltage-dependent K+ channel blocker), barium (an inward rectifier K+ channels blocker), N-(1-adamantyl)-N'-cyclohexyl-4-morpholinecarboxamidine hydrochloride (a pore-forming blocker of adenosine triphosphate (ATP)-sensitive K+ channels [KATP]), or methylene blue (a nonspecific guanylyl cyclase [GC] inhibitor). However, this hyperpolarization was not significantly affected by apamin (a small-conductance Ca2+-activated K+ channel blocker), glibenclamide (a sulfonylurea blocker of KATP), N(omega)-nitro-L-arginine methyl ester (a NOS inhibitor), or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (an NO-sensitive GC inhibitor). In addition, the basal tension of the tissues obtained from CLP rats was increased simultaneously, whereas membrane potential was reversed. In contrast, none of these inhibitors had significant effects on the membrane potential or the basal tension in control tissues. Thus, we provide electrophysiological and functional evidence demonstrating that an abnormal activation of K+ channels in vascular smooth muscle in animals with septic shock induced by CLP. Our observations suggest that the activation of large conductance Ca2+-activated K+ channels, voltage-dependent K+ channels, inward rectifier K+ channels, and KATP channels, but not small conductance Ca2+-activated K+ channels, contributes to CLP-induced vascular hyporeactivity. Furthermore, the hyperpolarization in septic shock induced by CLP is likely via non-NO-sensitive GC pathway.

Cardiovascular roles of nitric oxide: a review of insights from nitric oxide synthase gene disrupted mice

Nitric oxide (NO) is a gaseous molecule that plays many key roles in the cardiovascular system. Each of the enzymes that generate NO--neuronal, inducible and endothelial NO synthase-has been genetically disrupted in mice. This review discusses the cardiovascular phenotypes of each of the NO synthase (NOS) gene knockout mice, and the insights gained into the roles of NO in the cardiovascular system. Mice lacking the endothelial isoform are hypertensive, have endothelial dysfunction and show a more severe outcome in response to vascular injury, to stroke and cerebral ischaemia, and to diet-induced atherosclerosis. Mice lacking the neuronal isoform show a less severe outcome in response to stroke and cerebral ischaemia but have increased diet-induced atherosclerosis. Mice lacking the inducible isoform show reduced hypotension to septic shock. Together, NOS gene knockout mice have been useful tools that complement our other approaches to studying the multiple roles of NO in the cardiovascular system.

Increased induction of inducible nitric oxide synthase expression in aortae of type 2 diabetes rats

The aim of this study was to determine whether the pathway of inducible NO synthase (iNOS) in blood vessels is changed by type 2 diabetes. Lipopolysaccharide (LPS)-induced nitric oxide (NO) production and expression of iNOS and effects of LPS on phenylephrine-induced contractile force were compared in aortae isolated from Goto-Kakizaki (G-K) diabetes rats and aortae isolated from control Wistar rats. Both LPS-stimulated nitrite generation and iNOS expression levels were significantly higher in aortae from G-K rats than in those from control rats. Phenylephrine-induced contractile force in the presence of LPS was significantly lower in aortae from G-K rats than in those from control rats, while contractile force in the absence of LPS was comparable in the diabetic and control groups. On the other hand, incubation of aortae in high glucose-containing medium did not affect the LPS-stimulated nitrite accumulation and iNOS expression and the phenylephrine-induced contractile force, regardless of the presence of LPS. These results suggest that LPS-induced NO production through the iNOS pathway is increased and subsequent attenuation of contractile force by excess NO is enhanced in arteries of rats with type 2 diabetes.

Systematic evaluation of nitric oxide, tetrahydrobiopterin, and anandamide levels in a porcine model of endotoxemia

PURPOSE

Using a lipopolysaccharide (LPS)-treated porcine model, we examined: (1) whether nitric oxide (NO), anandamide, and tetrahydrobiopterin (BH4) increased or not in early endotoxic shock; and (2) the location of the major site of production of these molecules, by comparing their concentrations in arteries and the portal and hepatic veins.

METHODS

Ten pigs received an infusion of LPS at 1.7 microg x kg(-1)x h(-1) via the portal vein for 240 min. Consecutive changes in systemic hemodynamics, hepatosplanchnic circulation, and oxygen delivery were measured. Furthermore, the variable changes in the concentrations of nitrite and nitrate (NOx), anandamide, and BH4 were measured. To access the effects of surgery, anesthesia, and fluid management on BH4, an experiment without LPS infusion was performed in two other animals.

RESULTS

Mean arterial pressure and cardiac index started to decrease at 60 min after LPS infusion. However, systemic vascular resistance remained unchanged. Total hepatic blood flow and hepatic oxygen delivery also decreased significantly. NOx and anandamide did not change during LPS infusion. BH4 values did not change without LPS infusion. However, BH4 values increased significantly in the arterial, portal, and hepatic circulation during LPS infusion, especially in the hepatic vein (from 136.8 +/- 27.5 to 281.3 +/- 123.2 mol/ml; P < 0.01).

CONCLUSION

Our data suggest that the BH4 values were significantly increased in several organs, especially in the liver during endotoxic shock. Impaired cardiac output and decreased blood pressure appeared in the early phase of porcine endotoxemia. Longer-term observation of these parameters after LPS treatment should be performed as the next step in future studies.

Therapeutic effects of melatonin on peritonitis-induced septic shock with multiple organ dysfunction syndrome in rats

The pathogenesis of multiple organ dysfunction syndrome (MODS) in septic shock is complicated and not fully understood. Some studies show that an overproduction of nitric oxide (NO) leads to the refractory hypotension and multiple organ failure, while other studies suggest that free radicals, e.g. superoxide (O(2)(-)), contribute to the detrimental effect on vascular responsiveness and tissue/organ damage. Thus, this study was performed on the Wistar rat by using cecal ligation and puncture (CLP) to induce septic shock-associated MODS. We evaluated the effect of an antioxidant melatonin in CLP-induced septic rats and demonstrated that melatonin (3 mg/kg, i.v. at 3, 6, 12 hr after CLP) significantly (a) attenuated hyporeactivity to norepinephrine and delayed hypotension, (b) reduced plasma index of hepatic and renal dysfunction, (c) diminished plasma NO and interleukin-1beta (IL-1beta) concentrations as well as aortic O(2)(-) levels, (d) reduced marked infiltration of polymorphonuclear neutrophils (PMNs) in the lung and liver tissues, and (e) promoted the survival rate at 18 hr to twofold compared with the CLP alone group. The current study underlined the inhibition of plasma NO and IL-1beta as well as aortic O(2)(-) production and the reduction of PMN infiltration may lead to the amelioration of MODS, which may contribute to the beneficial effect of antioxidants (e.g. melatonin in this study) in conscious rats with peritonitis-induced lethality. Thus, the antioxidant could be a novel agent for the treatment of septic animals or patients in the early stage.

Therapeutic effects of hypertonic saline on peritonitis-induced septic shock with multiple organ dysfunction syndrome in rats

OBJECTIVE

Significant mortality in patients with sepsis results from the development of multiple organ dysfunction syndrome. Small-volume resuscitation with 7.5% NaCl hypertonic saline has been proposed to restore physiologic hemodynamics in hemorrhagic shock. Therefore, we hypothesized that hypertonic saline resuscitation could alleviate the development of multiple organ dysfunction syndrome in sepsis induced by cecal ligation and puncture.

DESIGN

Randomized, prospective animal experiment.

SETTING

Academic research laboratory.

SUBJECTS

Male Wistar rats.

INTERVENTIONS

The animals were randomly allocated to one of four groups: 1) sham operation (0.9% NaCl, 4 mL/kg intravenously, at 3 hrs after laparotomy); 2) sham operation plus hypertonic saline (7.5% NaCl, 4 mL/kg intravenously, at 3 hrs after laparotomy); 3) cecal ligation and puncture (0.9% NaCl, 4 mL/kg intravenously, at 3 hrs after cecal ligation and puncture); and 4) cecal ligation and puncture plus hypertonic saline (7.5% NaCl, 4 mL/kg intravenously, at 3 hrs after cecal ligation and puncture).

MEASUREMENTS AND MAIN RESULTS

Cecal ligation and puncture for 18 hrs was associated with circulatory failure (i.e., hypotension and vascular hyporeactivity to norepinephrine), multiple organ dysfunction syndrome (examined by biochemical variables and histologic studies), and 18-hr mortality. Hypertonic saline not only ameliorated the deterioration of hemodynamic changes but also attenuated neutrophil infiltration in the lung and the liver of septic animals. Hypertonic saline increased the survival rate at 9 and 18 hrs compared with the cecal ligation and puncture group. Moreover, hypertonic saline reduced plasma nitric oxide and interleukin-1beta and organ O2-* levels in rats that underwent cecal ligation and puncture.

CONCLUSIONS

Hypertonic saline prevented circulatory failure, alleviated multiple organ dysfunction syndrome, and decreased the mortality rate in animals receiving cecal ligation and puncture. These beneficial effects of hypertonic saline may be attributed to reducing the plasma concentration of nitric oxide and interleukin-1beta as well as the organ O2-* level and decreasing lung neutrophil infiltration and liver necrosis. Our study suggests that hypertonic saline could be a potential and inexpensive therapeutic agent in the early sepsis of animals or patients.

Combined effects of propofol and dexamethasone on rats with endotoxemia

OBJECTIVE

To clarify the effect of combined treatment with propofol and dexamethasone on hemodynamics, organ injury, and survival rate in rats with endotoxemia.

DESIGN

Randomized, prospective animal experiment.

SETTING

Academic research laboratory.

SUBJECTS

Male Wistar rats.

INTERVENTIONS

Rats were divided into five groups: a control group, a group of conscious rats infused with Escherichia coli lipopolysaccharide, two groups of lipopolysaccharide rats treated with either propofol or dexamethasone, and a group of lipopolysaccharide rats with combined treatment of propofol and dexamethasone.

MEASUREMENTS AND MAIN RESULTS

All hemodynamic and biochemical variables were measured during the 6-hr observation. Propofol plus dexamethasone attenuated hypotension and delayed hypoglycemia and metabolic acidosis caused by coadministration of E. coli lipopolysaccharide. In addition, propofol plus dexamethasone attenuated the lipopolysaccharide-induced multiple organ dysfunctions, such as lung, liver, and kidney. The increases in serum tumor necrosis factor-alpha, tissue nitric oxide, and superoxide anion levels were attenuated by propofol plus dexamethasone in lipopolysaccharide rats. Microscopic findings confirmed that propofol plus dexamethasone attenuated the substantial swelling and cell infiltration in lung and kidney caused by endotoxin. The 22-hr survival rate after endotoxin injection was markedly increased in lipopolysaccharide rats with combined treatment compared with the lipopolysaccharide rats (80% vs. 0%).

CONCLUSIONS

The combined treatment with propofol plus dexamethasone reduced mortality rate and attenuated organ injury in conscious rats treated with lipopolysaccharide. These protective effects may be associated with their anti-inflammatory capacity and antioxidant activity.

Glibenclamide dose response in patients with septic shock: effects on norepinephrine requirements, cardiopulmonary performance, and global oxygen transport

Adenosine triphosphate-sensitive potassium channels are important regulators of arterial vascular smooth muscle tone and are implicated in the pathophysiology of catecholamine tachyphylaxis in septic shock. The present study was designed as a prospective, randomized, double-blinded, clinical pilot study to determine whether different doses of glibenclamide have any effects on norepinephrine requirements, cardiopulmonary hemodynamics, and global oxygen transport in patients with septic shock. We enrolled 30 patients with septic shock requiring invasive hemodynamic monitoring and norepinephrine infusion of 0.5 microg.kg-1.min-1 or greater to maintain MAP between 65 and 75 mmHg. In addition to standard therapy, patients were randomized to receive either 10, 20, or 30 mg of enteral glibenclamide. Systemic hemodynamics, global oxygen transport including arterial lactate concentrations, gas exchange, plasma glucose concentrations, and electrolytes were determined at baseline and after 3, 6, and 12 h after administration of the study drug. Glibenclamide decreased plasma glucose concentrations in a dose-dependent manner but failed to reduce norepinephrine requirements. None of the doses had any effects on cardiopulmonary hemodynamics, global oxygen transport, gas exchange, or electrolytes. These data suggest that oral glibenclamide in doses from 10 to 30 mg fails to counteract arterial hypotension and thus to reduce norepinephrine requirements in catecholamine-dependent human septic shock.

Extracellular Signal-Regulated Kinase (ERK1/2) Contributes to Endotoxin-Induced Hyporeactivity via Nitric Oxide and Prostacyclin Production in Rat Aorta

This study was conducted to determine if mitogen-activated protein kinases (MAPKs) such as extracellular signal-regulated kinase (ERK1/2) contribute to endotoxin-induced vascular hyporeactivity via nitric oxide (NO) and/or prostacyclin (PGI(2)) production in the rat isolated thoracic aorta. Incubation of endothelium-intact rings with endotoxin (100 microg/ml) for 4 h decreased the E(max) value and increased the EC(50) value of norepinephrine. The endotoxin-induced increase in the EC(50) value of norepinephrine was decreased by phenylene-1,3-bis[ethane-2-isothiourea] dihydrobromide (1,3-PBIT), a selective inducible NO synthase inhibitor, and U0126, a selective inhibitor of ERK1/2 phosphorylation by MAPK kinase. The endotoxin-induced decrease in the E(max) value of norepinephrine was reversed by 1,3-PBIT and further decreased by U0126. 1,3-PBIT and U0126 decreased the endotoxin-induced increase in the tissue nitrite and 6-keto-PGF(1)(alpha) levels. These data suggest that events related to the activation of ERK1/2 contribute to the endotoxin-induced hyporeactivity by increasing NO and PGI(2) production.

A role for nitric oxide-mediated peroxynitrite formation in a model of endotoxin-induced shock

The aim of the present study was to assess the relative contributions of peroxynitrite formation following induction of nitric-oxide synthase (iNOS) in the pathophysiology of endotoxin-induced shock in the rat. To this end, we used a selective inhibitor of iNOS, N-(3-(aminomethyl)benzyl)acetamidine (1400W), and a peroxynitrite decomposition catalyst, 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato iron III chloride (FeTTPs). Intravenous (i.v.) administration of Escherichia coli lipopolysaccharide (LPS; 4 mg/kg) elicited a time-dependent fall in mean arterial pressure as well as liver, renal, and pancreatic tissue damage. 1400W (3-10 mg/kg i.v.) administered 30 min before LPS delayed the development of hypotension but did not improve survival. On the other hand, FeTTPs administered (10-100 mg/kg i.v.) inhibited in a dose-dependent manner LPS-induced hypotension, tissue injury, and improved mortality rate. In separate experiments, rats were treated with LPS (4 mg/kg) or saline for control, and their aortas were isolated and placed in organ baths 2 h later. Tissues from LPS-treated rats had significant inhibition of contractile activity to phenylephrine as well as a significantly impaired relaxation response to acetylcholine. FeTPPs, when administered (100 mg/kg i.v.) 1 h before LPS, prevented the LPS-induced aortic contractile and endothelial dysfunction. These results demonstrate that nitric oxide-derived peroxynitrite formation plays an important role in this model of endotoxemia. Our results also suggest that use of an iNOS inhibitor in this setting has little beneficial effect in part because, in the presence of a failing eNOS system, some NO is needed to maintain adequate organ function.

Lipoteichoic acid-induced nitric oxide synthase expression in RAW 264.7 macrophages is mediated by cyclooxygenase-2, prostaglandin E2, protein kinase A, p38 MAPK, and nuclear factor-kappaB pathways

We recently reported that lipoteichoic acid (LTA), a cell wall component of the gram-positive bacterium Staphylococcus aureus, stimulated inducible nitric oxide synthase (iNOS) expression, nitric oxide (NO) release, and cyclooxygenase-2 (COX-2) expression in RAW 264.7 macrophages. This study was carried out to further investigate the roles of COX-2 and prostaglandin E2 (PGE2) in LTA-induced iNOS expression and NO release in RAW 264.7 macrophages. Treatment of RAW 264.7 macrophages with LTA caused a time-dependent increase in PGE2 release. LTA-induced iNOS expression and NO release were inhibited by a non-selective COX inhibitor (indomethacin), a selective COX-2 inhibitor (NS-398), an adenylyl cyclase (AC) inhibitor (dideoxyadenosine, DDA), and a protein kinase A (PKA) inhibitor (KT-5720). Furthermore, both PGE2 and the direct PKA activator, dibutyryl-cAMP, also induced iNOS expression in a concentration-dependent manner. Stimulation of RAW 264.7 macrophages with LTA, PGE2, and dibutyryl-cAMP all caused p38 MAPK activation in a time-dependent manner. LTA-mediated p38 MAPK activation was inhibited by indomethacin, NS-398, and SB 203580, but not by PD 98059. The PGE2-mediated p38 MAPK activation was inhibited by DDA, KT-5720, and SB 203580, but not by PD 98059. LTA caused time-dependent activation of the nuclear factor-kappaB (NF-kappaB)-specific DNA-protein complex formation. The LTA-induced increase in kappaB-luciferase activity was inhibited by indomethacin, NS-398, KT-5720, and a dominant negative mutant of p38 alphaMAPK (p38 alphaMAPK DN). These results suggest that LTA-induced iNOS expression and NO release involve COX-2-generated PGE2 production, and AC, PKA, p38 MAPK, and NF-kappaB activation in RAW 264.7 macrophages.

Beneficial pleiotropic actions of melatonin in an experimental model of septic shock in mice: regulation of pro-/anti-inflammatory cytokine network, protection against oxidative damage and anti-apoptotic effects

Septic shock, the most severe problem of sepsis, is a lethal condition caused by the interaction of a pathogen-induced long chain of sequential intracellular events in immune cells, epithelium, endothelium, and the neuroendocrine system. The lethal effects of septic shock are associated with the production and release of numerous pro-inflammatory biochemical mediators including cytokines, nitric oxide and toxic oxygen and nitrogen radicals, together with development of massive apoptosis. As melatonin has remarkable properties as a cytokine modulator, antioxidant and anti-apoptotic agent, the present study was designed to evaluate the possible protective effect of melatonin against LPS-induced septic shock in Swiss mice. We observed that intraperitoneally (i.p.) administered-melatonin (10 mg/kg) 30 min prior, and 1 hr after i.p. LPS injection (0.75 mg/animal) markedly protected mice from the LPS lethal effects with 90% survival rates for melatonin and 20% for LPS-injected mice after 72 hr. The melatonin effect was mediated by modulating the release of pro-/anti-inflammatory cytokine levels, protection from oxidative damage and counteracting apoptotic cell death. Melatonin was able to partially counteract the increase in LPS-induced pro-inflammatory cytokine levels such as tumor necrosis factor-alpha, IL-12 and interferon-gamma at the local site of injection, while it increased the production of the anti-inflammatory cytokine IL-10 both locally and systemically. Furthermore, melatonin inhibited the LPS-induced nitrite/nitrate and lipid peroxidation levels in brain and liver and counteracted the sepsis-associated apoptotic process in spleen. In conclusion, we have demonstrated that melatonin improves the survival of mice with septic shock via its pleiotropic functions as an immunomodulator, antioxidant and anti-apoptotic mediator.

Comparison of effects of nitric oxide synthase (NOS) inhibitors on plasma nitrite/nitrate levels and tissue NOS activity in septic organs

An excessive production of nitric oxide (NO) by NO synthase (NOS) is considered to contribute to circulatory disturbance, tissue damage, and refractory hypotention, which are often observed in septic disorders. It is anticipated that a selective inducible NOS (iNOS) inhibitor with excellent pharmacokinetics may be potentially effective as a novel and potent therapeutic intervention in sepsis. We examined whether or not a selective iNOS inhibitor shows iNOS selectivity at the tissue level, when administered systemically. The effects of four NOS inhibitors on plasma nitrite/nitrate (NOx) and tissue NOS levels were compared in major organs (lungs, liver, heart, kidneys, and brain) 6 hr after the injection of E. coli lipopolysaccharide (LPS) into male Wistar-King rats. The rats treated with the three iNOS inhibitors (N-(3-(aminomethyl)benzyl)acetamidine (1400W), (1 S, 5 S, 6 R, 7 R )-2-aza-7-chloro-3-imino-5-methylbicyclo [4.1.0] heptane hydrochloride (ONO-1714), and aminoguanidine) administered 1 hr after LPS injection, showed dose-dependent decreases in plasma NOx levels and NOS activity in the lungs. The non-selective NOS inhibitor (N(G)-methyl-L-arginine (L-NMMA)) had an effect only at the maximum dose. The differences in in vitro iNOS selectivity among these drugs did not correlate with iNOS selectivity at the tissue level. The relationship between plasma NOx levels and NOS activity in the lungs showed a linear relationship with or without the NOS inhibitors. In conclusion, the iNOS selectivity of these drugs does not seem to differ at the tissue level. Plasma NOx levels may be a useful indicator of lung NOS activity.

Shock, inflammation and PARP

The activation of poly(ADP-ribose) polymerase (PARP) is well considered to play an important role in various patho-physiological conditions like inflammation and shock. A vast amount of circumstantial evidence implicates oxygen-derived free radicals (especially, superoxide and hydroxyl radical) and high-energy oxidants (such as peroxynitrite) as mediators of inflammation and shock. ROS (e.g., superoxide, peroxynitrite, hydroxyl radical and hydrogen peroxide) are all potential reactants capable of initiating DNA single strand breakage, with subsequent activation of the nuclear enzyme poly(ADP-ribose) synthetase (PARS), leading to eventual severe energy depletion of the cells, and necrotic-type cell death. During the last years, numerous experimental studies have clearly demonstrated the beneficial effects of PARP inhibition in cell cultures through rodent models and more recently in pre-clinical large animal models of acute and chronic inflammation. The aim of this review is to describe recent experimental evidence implicating PARP as a pathophysiological modulator of acute and chronic inflammation.

Role of poly(ADP-ribose) glycohydrolase (PARG) in shock, ischemia and reperfusion

Poly(ADP-ribosyl)ation is regulated by the synthesizing enzyme poly(ADP-ribose) polymerase-1 (PARP-1) and the degrading enzyme poly(ADP-ribose) glycohydrolase (PARG). Homeostasis of poly(ADP-ribosyl)ation has been proposed to be an important regulator for pathogenesis in multi-cellular organisms. Although the role of PARP-1 in tissue damage, inflammation and ischemia has been extensively studied, the function of PARG in various cellular processes is largely unknown. Recent studies using chemical inhibitors of PARG and genetically engineered Drosophila and mouse models that carry a disrupted PARG gene have started to shed new light on the biological function of PARG in vivo. These animal models and cells isolated from them will be useful for further validation of PARG as a potential pharmaceutical target to intervene the pathogenesis induced by acute tissue injury, ischemia and inflammation.

Lipoteichoic acid induces nuclear factor-kappaB activation and nitric oxide synthase expression via phosphatidylinositol 3-kinase, Akt, and p38 MAPK in RAW 264.7 macrophages

We previously demonstrated that lipoteichoic acid (LTA) might activate phosphatidylcholine-phospholipase C (PC-PLC) and phosphatidylinositol-phospholipase C (PI-PLC) to induce protein kinase C activation, which in turn initiates nuclear factor-kappaB (NF-kappaB) activation and finally induces inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) release in RAW 264.7 macrophages. In this study, we further investigated the roles of tyrosine kinase, phosphatidylinositiol 3-kinase (PI3K)/Akt, and p38 mitogen-activated protein kinase (MAPK) in LTA-induced iNOS expression and NO release in RAW 264.7 macrophages. Tyrosine kinase inhibitors (genistein and tyrphostin AG126), PI3K inhibitors (wortmannin and LY 294002), and a p38 MAPK inhibitor (SB 203580) attenuated LTA-induced iNOS expression and NO release in concentration-dependent manners. Treatment of RAW 264.7 macrophages with LTA caused time-dependent activations of Akt and p38 MAPK. The LTA-induced Akt activation was inhibited by wortmannin, LY 294002, genistein, and tyrphostin AG126. The LTA-induced p38 MAPK activation was inhibited by genistein, tyrphostin AG126, wortmannin, LY 294002, and SB 203580. The LTA-induced formation of an NF-kappaB-specific DNA-protein complex in the nucleus was inhibited by wortmannin, LY 294002, genistein, tyrphostin AG126, and SB 203580. Treatment of macrophages with LTA caused an increase in kappaB-luciferase activity, and this effect was inhibited by tyrphostin AG126, wortmannin, LY 294002, the Akt dominant negative mutant (AktDN), and SB 203580. Based on those findings, we suggest that LTA might activate the PI3K/Akt pathway through tyrosine kinase to induce p38 MAPK activation, which in turn initiates NF-kappaB activation, and ultimately induces iNOS expression and NO release in RAW 264.7 macrophages.

The pore-forming subunit of the K(ATP) channel is an important molecular target for LPS-induced vascular hyporeactivity in vitro

ATP-sensitive K(+) (K(ATP)) channel activation is implicated in the vascular hyporeactivity occurring in septic shock. However, channel inhibition with the sulphonylurea receptor (SUR) antagonist, glibenclamide (Glib) fails to reverse lipopolysaccharide (LPS)-induced vascular hyporeactivity in vitro. We investigated whether inhibitors that act by binding to the K(ATP) channel pore could be effective. Ring segments of endothelium-intact rat mesenteric artery were incubated with LPS in culture media for either 6 or 20 h before contractile responses to phenylephrine were assessed in the absence or presence of K(ATP) channel inhibitors. The pore-forming subunit inhibitors barium chloride (BaCl(2); 300 microM) and PNU-37883A (1 microM) significantly reversed hyporeactivity at both time points, although less so at 20 h. In contrast, the SUR inhibitors, Glib (10 microM), tolbutamide (Tolb) (1 mM) and PNU-99963 (1 microM) were ineffective. In LPS-incubated tissues, Glib and Tolb antagonised contractions to the thromboxane A2 mimetic, U46619 (9,11-dideoxy-9alpha, 11alpha-methanoepoxy prostaglandin F(2alpha)) (10(-7) M), whereas the pinacidil-derived inhibitor, PNU-99963, did not. Contractions to 60 mM KCl were unaffected by LPS at 6 h, but were significantly depressed by LPS at 20 h, suggesting that K(+)-channel-independent pathways contribute to hyporeactivity at the later time point. The inducible nitric oxide synthase (iNOS) inhibitor, 1400 W (10 microM) and Tolb inhibited the production of nitrite induced by LPS, whereas BaCl(2) and PNU-37883A had no effect. In conclusion, K(ATP) channels contribute to LPS-induced vascular hyporeactivity via the iNOS pathway in rat mesenteric artery. The effectiveness of pore inhibitors over SUR inhibitors of the K(ATP) channel suggests altered SUR function following LPS administration, which cannot be explained by thromboxane receptor inhibition.

Dextromethorphan prevents circulatory failure in rats with endotoxemia

Dextromethorphan (DM), an antitussive agent, has been claimed to have anti-inflammatory and immunomodulatory effects in vitro. Thus, the aim of this study was to evaluate the effects of DM on sepsis induced by intravenous (i.v.) administration of lipopolysaccharide (LPS) in anesthetized Wistar rats and by intraperitoneal administration in conscious ICR mice. Results demonstrated that pretreatment with DM (1, 5 and 10 mg/kg, i.v.) significantly attenuated the deleterious hemodynamic changes (e.g., hypotension and tachycardia) in rats treated with LPS. Meanwhile, DM (5 mg/kg) significantly inhibited the elevation of plasma tumor necrosis factor-alpha and interleukin-10 levels, as well as values of GOT and GPT (as an index of liver function), and BUN and creatinine (as an index of renal function) caused by LPS. The induction of inducible NO synthase and the overproduction of NO and superoxide anions by LPS were also reduced by DM. Moreover, infiltration of neutrophils into the lungs and liver of rats 6 h after treatment with LPS was also reduced by DM. In conclusion, the beneficial effects of DM on LPS-induced sepsis result from its anti-inflammatory and antioxidant effects. Thus, DM can possibly be used as a prophylactic agent for sepsis in the future.

Effect of methylguanidine in a model of septic shock induced by LPS

Septic shock, a severe form of sepsis, is characterized by cardiovascular collapse following microbial invasion of the body. The progressive hypotension, hyporeactivity to vasopressor agents and vascular leak leads to circulatory failure with multiple organ dysfunction and death. Many inflammatory mediators (e.g. TNF-alpha, IL-1 and IL-6) are involved in the pathogenesis of shock and, among them, nitric oxide (NO). The overproduction of NO during septic shock has been demonstrated to contribute to circulatory failure, myocardial dysfunction, organ injury and multiple organ failure. We have previously demonstrated with in vitro and in vivo studies that methylguanidine (MG), a guanidine compound deriving from protein catabolism, significantly inhibits iNOS activity, TNF-alpha release and carrageenan-induced acute inflammation in rats. The aim of the present study was to evaluate the possible anti-inflammatory activity of MG in a model of septic shock induced by lipopolysaccharide (LPS) in mice. MG was administered intraperitoneally (i.p.) at the dose of 30 mg/kg 1 h before and at 1 and 6 h after LPS-induced shock. LPS injection (10 mg/kg in 0.9% NaCl; 0.1 ml/mouse; i.p.) in mouse developed a shock syndrome with enhanced NO release and liver, kidney and pancreatic damage 18 h later. NOx levels, evaluated as nitrite/nitrate serum levels, was significantly reduced in MG-treated rats (78.6%, p < 0.0001; n = 10). Immunohistochemistry revealed, in the lung tissue of LPS-treated group, a positive staining for nitrotyrosine and poly(adenosine diphosphate [ADP] ribose) synthase, both of which were reduced in MG-treated mice. Furthermore, enzymatic evaluation revealed a significant reduction in liver, renal and pancreatic tissue damage and MG treatment also improved significantly the survival rate. This study provides evidence that MG attenuates the degree of inflammation and tissue damage associated with endotoxic shock in mice. The mechanisms of the anti-inflammatory effect of MG is, at least in part, dependent on the inhibition of NO formation.

Recent advances in the development of haemoglobin-based blood substitutes

The term 'blood substitute' is commonly used to describe products which can carry and deliver oxygen. These products are also referred to as 'oxygen carriers' or 'oxygen therapeutics'. Blood substitutes are a new generation of oxygen therapeutics and their introduction will redefine treatment approaches in a wide range of medical and surgical practices. There are two major classes of this new generation of oxygen therapeutics (1) modified haemoglobin solutions, referred to as haemoglobin-based blood substitutes (HBBS) and (2) perfluorocarbon emulsions. Tremendous progress has been made in the past four years with the development of HBBS. In comparison, not much progress has been made in the development of perfluorocarbons as oxygen carriers. In the present review we have limited our discussion to the development of HBBS. Several types of HBBS have been developed and are in different phases of clinical trials. Free haemoglobin has been crosslinked, conjugated, polymerised or encapsulated to prevent its dissociation into dimers. The stability and purity of HBBS are extremely important in overcoming most of the significant toxicities of these products. Commercial manufacturers have utilised better proprietary formulations and purification technologies, and HBBS developed by these organisations have demonstrated safety in both preclinical and clinical studies. Recent research activities suggest a broad range of therapeutic applications for these new generation of oxygen therapeutics, 'blood substitutes'. The introduction of HBBS in critical care medicine will introduce a new approach of not only improving perfusion, but delivering oxygen to tissues.

Benznidazole, a drug used in Chagas' disease, ameliorates LPS-induced inflammatory response in mice

Benznidazole (BZL) is a drug currently used for treating Chagas' disease. Given our earlier demonstration in which BZL downregulated cytokine and nitric oxide (NO) synthesis by LPS and/or IFN-gamma-stimulated murine macrophages, we have now analysed whether this compound could exert beneficial effects in a model of LPS-induced inflammation in C57BL/6 mice. The lethal model consisted of two LPS intraperitoneal injections, 200 microg each separated by 2 h, with BZL given orally at a dose of 200 mg/kg, 18 and 2 h before the first challenge and 20 and 44 hr following the second one. In this model, BZL treatment led to a significantly decreased mortality in comparison with untreated counterparts. Remaining experiments were carried out in mice given a unique LPS dose, pretreated with BZL or not, since those subjected to the lethal protocol were unsuitable for laboratory handling. Analysis of IL-1beta, IL-6, TNF-alpha, IL-12 and iNOS mRNA expression in liver samples taken at 90 min post-LPS showed a marked reduction of the two latter mRNAs in BZL-treated mice. These animals also displayed significantly decreased peaks levels of serum TNF-alpha and IL-6, accompanied by a diminished number of IL-6-producing peritoneal macrophages. Present effects may broaden the potential usefulness of BZL in situations accompanied by an excessive inflammatory response.

Thaliporphine increases survival rate and attenuates multiple organ injury in LPS-induced endotoxaemia

This study addressed the question of whether thaliporphine, a phenolic aporphine alkaloid obtained from Chinese herbs and possessing antioxidant and alpha-1 adrenoceptor antagonistic activity, has protective effects in endotoxaemic rats and we attempted to elucidate the mechanisms contributing to such protective effects. Injection of rats with endotoxin (E. coli lipopolysaccharide, LPS) induced severe hypotension and tachycardia as well as vascular hyporeactivity to noradrenaline. Pretreatment of LPS-treated rats with thaliporphine attenuated the delayed hypotension significantly whilst only a higher dose (1 mg/kg) of thaliporphine decreased LPS-induced tachycardia. LPS significantly increased nitric oxide (NO.) and superoxide anion (O(2).(-)) levels, a response that was reduced by pretreatment with 1 mg/kg thaliporphine. Endotoxaemia for 240 min resulted in a bell-shaped time course for the change of serum tumour necrosis factor-alpha (TNF-alpha) level with a peak at 60 min. Pretreatment of LPS-treated rats with 1 mg/kg thaliporphine significantly reduced the serum TNF-alpha level at 60 min. In addition, LPS caused a biphasic change in blood glucose and thaliporphine attenuated the late-phase decrease in blood glucose. Endotoxaemia induced multiple organ injury in the liver, kidney and heart, as indicated by increases of aspartate aminotransferase (GOT), alanine aminotransferase (GPT), creatinine (CRE), lactate dehydrogenase (LDH) and creatine phosphate kinase muscle-brain (CKMB) levels in serum. These increases of biochemical markers and inflammatory cell infiltration into injured tissues were reduced significantly by treatment with thaliporphine. In addition, thaliporphine increased the survival rate of LPS-treated mice dose-dependently. In conclusion, our results suggest that thaliporphine could be a novel agent for attenuating endotoxin-induced circulatory failure and multiple organ injury and may increase the survival rate. These beneficial effects of thaliporphine may be attributed to the suppression of TNF-alpha, NO. and O(2).(-) production.

Regulation of inflammatory responses by activated protein C: the molecular mechanism(s) and therapeutic implications

Activated protein C (APC), a natural anticoagulant, is formed from protein C by the action of the thrombin-thrombomodulin (TM) complex on the endothelial cell surface. Endothelial protein C receptor augments the activation of protein C by the thrombin/TM system. APC inactivates the activated form of coagulation factors V and VIII in the presence of protein S. Administration of APC reduced the pulmonary vascular injury and hypotension as well as the coagulation abnormalities by inhibiting production of the tumor necrosis factor-alpha (TNF-alpha) in rats given endotoxin (ET). These therapeutic effects of APC could not be attributed to its anticoagulant effects. APC inhibited ET-induced TNF-alpha production in human monocytes by inhibiting activation of nuclear factor K-B and activator protein-1 in vitro. Administration of the human plasma-derived APC ameliorated coagulation abnormalities without any adverse effects in patients with disseminated intravascular coagulation (DIC). Recombinant APC was reported to reduce the mortality of patients with severe sepsis, and the therapeutic effect was more marked in such patients with overt DIC than those without it. These observations strongly suggest that APC plays important roles in the regulation of inflammation as well as coagulation. Both anti-inflammatory and anticoagulant properties of APC might contribute to the therapeutic usefulness in patients with severe sepsis.

NO and KATP channels underlie endotoxin-induced smooth muscle hyperpolarization in rat mesenteric resistance arteries

1 Smooth muscle membrane potential and tension measurements were made in isolated mesenteric resistance arteries from rats exposed to bacterial endotoxin (lipopolysaccharide, LPS; 10 mg kg(-1), i.p.) for 3 h to mimic septic shock syndrome. 2 Over this period, rats developed an endotoxaemic response, assessed in vivo as a 41+/-4 mmHg drop in mean blood pressure, vascular hyporeactivity to noradrenaline (1 microg kg(-1), i.v.) and a significant increase in core body temperature. 3 In mesenteric small resistance arteries from these rats (o.d. 180 - 240 microm), phenylephrine (0.01-3 microm)-evoked contraction was not altered when compared with arteries from sham-operated animals, but the concentration-relaxation curve to acetylcholine (ACh; 0.01 - 3 microm) displayed a small, but significant, shift to the right. 4 The smooth muscle resting membrane potential (-70.3+/-1.6 mV) in arteries from LPS-treated rats was significantly greater than in control arteries (-55.4+/-1.2 mV), but in both cases the smooth muscle was depolarized to a similar potential by the application of N(omega)-nitro-L-arginine methyl ester (L-NAME; 0.3 mm; -54.1+/-2.3 vs -52.4+/-2.5 mV) or glibenclamide (10 microm; -55.0+/-2.1 vs -50.4+/-2.0 mV). 5 ACh (1 microm) elicited a maximal hyperpolarization, which ranged from -14.7+/-3.2 mV (in arteries from LPS-treated rats) to -20.6+/-2.4 mV (in arteries from sham-operated rats), and was not altered by the presence of L-NAME. Levcromakalim (1 microm) increased the smooth muscle membrane potential by around -24 mV in arteries from both sets of experimental animals. 6 These results indicate that at the level of the resistance vasculature, endotoxaemia is associated with pronounced smooth muscle hyperpolarization reflecting the action of NO on KATP channels. These changes were not associated with vascular hyporeactivity or depressed endothelial cell function in vitro, suggesting that mesenteric resistance arteries may not contribute to equivalent changes in vivo.

Abnormal activation of Na+-K+ pump in aortas from rats with endotoxaemia

A diminished reactivity to several vasoconstrictor agents is usually observed in blood vessels obtained from animals with endotoxic shock. The contractile state of vascular smooth muscle is influenced by the activity of the electrogenical sodium (Na(+)-K(+)) pump. Thus, we examined inhibitors and agonists of nitric oxide (NO)-guanosine 3':5'-cyclic monophosphate (cGMP) on contractions to phenylephrine (PE) and relaxations to potassium in isolated aortic segments from rats treated with bacterial endotoxin (lipopolysaccharide, LPS) for 6 h (i.e. to mimic a shock syndrome). Endotoxaemia for 6 h was associated with a severe hypotension and vascular hyporeactivity to noradrenaline and an increased plasma nitrate level in vivo. The PE-induced contraction was attenuated in aortic smooth muscle obtained from rats with endotoxic shock while the potassium-induced relaxation was greater in these preparations. Ouabain dose-dependently inhibited the potassium-induced relaxation in aortas from normal and endotoxaemic rats. 1 H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one enhanced the PE-induced contraction in endotoxaemic rats only, whereas it attenuated the difference of potassium-induced relaxation between normal and endotoxaemic rats. In contrast, in aortas obtained from normal rats, 8-bromo-cGMP reduced the PE-induced contraction and enhanced the potassium-induced relaxation to the level as seen in endotoxaemic animals. In aortas obtained from endotoxaemic rats, methylene blue further restored the PE-induced contraction to the normal and abolished the difference of potassium-induced relaxation between normal and endotoxaemic rats. These results suggest that the Na(+)-K(+) pump in the vascular bed of animals with endotoxic shock is abnormally activated and this augmented activation is modulated by cGMP.

GW274150, a potent and highly selective inhibitor of iNOS, reduces experimental renal ischemia/reperfusion injury

BACKGROUND

Generation of nitric oxide (NO) by inducible nitric oxide synthase (iNOS) may contribute to renal ischemia/reperfusion (I/R) injury. The aim of this study was to investigate the effects of GW274150, a novel, highly selective, potent and long-acting inhibitor of iNOS activity in rat and mouse models of renal I/R.

METHODS

Rats were administered GW274150 (5 mg/kg intravenous bolus administered 30 minutes prior to I/R) and subjected to bilateral renal ischemia (45 minutes) followed by reperfusion (6 hours). Serum and urinary indicators of renal dysfunction, tubular and reperfusion injury were measured, specifically, serum urea, creatinine, aspartate aminotransferase (AST) and N-acetyl-beta-d-glucosaminidase (NAG) enzymuria. In addition, renal sections were used for histologic scoring of renal injury and for immunologic evidence of nitrotyrosine formation and poly [adenosine diphosphate (ADP)-ribose] (PAR). Nitrate levels were measured in rat plasma using the Griess assay. Mice (wild-type, administered 5 mg/kg GW274150, and iNOS-/-) were subjected to bilateral renal ischemia (30 minutes) followed by reperfusion (24 hours) after which renal dysfunction (serum urea, creatinine), renal myeloperoxidase (MPO) activity and malondialdehyde (MDA) levels were measured.

RESULTS

GW274150, administered prior to I/R, significantly reduced serum urea, serum creatinine, AST, and NAG indicating reduction of renal dysfunction and injury caused by I/R. GW274150 reduced histologic evidence of tubular injury and markedly reduced immunohistochemical evidence of nitrotyrosine and PAR formation, indicating reduced peroxynitrite formation and poly (ADP-ribose) polymerase (PARP) activation, respectively. GW274150 abolished the rise in the plasma levels of nitrate (indicating reduced NO production). GW274150 also reduced the renal dysfunction in wild-type mice to levels similar to that observed in iNOS-/- mice subjected to I/R. Renal MPO activity and MDA levels were significantly reduced in wild-type mice administered GW274150 and iNOS-/- mice subjected to renal I/R, indicating reduced polymorphonuclear leukocyte (PMN) infiltration and lipid peroxidation.

CONCLUSIONS

These results suggest that (1). an enhanced formation of NO by iNOS contributes to the pathophysiology of renal I/R injury and (2). GW274150 reduces I/R injury of the kidney. We propose that selective inhibitors of iNOS activity may be useful against renal dysfunction and injury associated with I/R of the kidney.

Cardioprotective actions of an N-terminal fragment of annexin-1 in rat myocardium in vitro

We have previously shown that the glucocorticoid dexamethasone prevents the cardiodepressant actions of interferon-gamma plus lipopolysaccharide in cardiac tissue in vitro. We now demonstrate that an N-terminal fragment of annexin-1 (Ac2-26, 1 microM), a putative mediator of glucocorticoid actions, completely protects against interferon-gamma+lipopolysaccharide-induced depression of the inotropic response to isoprenaline in rat isolated papillary muscles. However, Ac2-26 does not preserve resting contractile function. Fifteen hours incubation with interferon-gamma+lipopolysaccharide also markedly induced mRNA expression (by real time polymerase chain reaction, PCR) of both the nitric oxide synthase 2 (NOS2) isoform of nitric oxide synthase (by 6.7 +/- 1.7-fold, P < 0.01) and cyclo-oxygenase-2 (by 3.4 +/- 0.6-fold, P < 0.05) in cardiomyocytes. Pretreatment with Ac2-26 (1 microM) prevented the induction of cyclo-oxygenase-2 mRNA, but not NOS2 mRNA, whereas dexamethasone (1 microM) suppressed the expression of both NOS2 mRNA and cyclo-oxygenase-2 mRNA. Co-incubation of dexamethasone with an anti-annexin-1 antibody did not attenuate the suppression of NOS2 mRNA. Thus, Ac2-26 reproduces some, but not all, of the cardioprotective effects of glucocorticoids in vitro in the absence of neutrophils. These protective actions are independent of changes in NOS2 expression.

Decreased modulation by lipopolysaccharide of aortic smooth muscle contractility in streptozotocin-induced hyperglycemic rats

Infection is a major complication of patients with diabetes, and endotoxemic shock is a serious complication during sepsis. The purpose of this study was to determine whether the action of bacterial lipopolysaccharide (LPS) on vasocontractility is altered in diabetic vessels. Diabetes was induced in 10-week-old Wistar rats by an intraperitoneal injection of streptozotocin. LPS-induced increase in cGMP (cyclic guanosine 3',5'-monophosphate) level was lower in aortae from streptozotocin-induced hyperglycemic (diabetic) rats than in those from vehicle-injected control rats, while LPS-induced nitric oxide production was not different in the diabetic and control aortae. Phenylephrine-induced contraction of diabetic aortae was lower than that of the control aortae. LPS treatment resulted in depression of contractile response to phenylephrine in both diabetic and control aortae, and the degree of depression was much lower in diabetic aortae. Treatment with N monomethyl l-arginine (l-NMMA) prevented diminution of phenylephrine-induced contraction of the aortae after LPS stimulation, and the degree of the preventive effect by l-NMMA was significantly lower in diabetic aortae than in the control aortae. Protein expression of inducible nitric oxide synthase detected by Western blot analysis was not different in the diabetic and control aortae. The decrease in cGMP production after LPS stimulation in diabetic aortae was not prevented by treatment of the aortae with superoxide dismutase but was partially prevented by that with Tiron (4,5-dihydroxy-1,3-benzene disulfonic acid), a cell-permeable scavenger of reactive oxygen species. These results suggest that LPS-induced depression of vasocontractility is attenuated in diabetic aortae due to a decrease in nitric oxide-stimulated cGMP production, probably resulting from increased inactivation of inducible nitric oxide by excessive intracellular oxidative stress. It is concluded that contractility of aortae from streptozotocin-induced hyperglycemic rats may be less affected by LPS during endotoxemia.

Induction of nitric oxide synthase in RAW 264.7 macrophages by lipoteichoic acid from Staphylococcus aureus: involvement of protein kinase C- and nuclear factor-kB-dependent mechanisms

This study investigates the signaling pathway involved in inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) release caused by Staphylococcus aureus lipoteichoic acid (LTA) in RAW 264.7 macrophages. A phosphatidylcholine-phospholipase C (PC-PLC) inhibitor (D-609) and a phosphatidylinositol-phospholipase C (PI-PLC) inhibitor (U-73122) attenuated LTA-induced iNOS expression and NO release. Two PKC inhibitors (Go 6976 and Ro 31-8220), an NF-kappaB inhibitor (pyrrolidine dithiocarbamate; PDTC), and long-term (24 h) 12-phorbol-13-myristate acetate (PMA) treatment each also inhibited LTA-induced iNOS expression and NO release. Treatment of cells with LTA caused an increase in PKC activity; this stimulatory effect was inhibited by D-609, U-73122, or Ro 31-8220. Stimulation of cells with LTA caused IkappaB-alpha phosphorylation and IkappaB-alpha degradation in the cytosol, and translocation of p65 and p50 NF-kappaB from the cytosol to the nucleus. Treatment of cells with LTA caused NF-kappaB activation by detecting the formation of NF-kappaB-specific DNA-protein complexes in the nucleus; this effect was inhibited by Go 6976, Ro 31-8220, long-term PMA treatment, PDTC, L-1-tosylamido-2-phenylethyl chloromethyl ketone (TPCK), and calpain inhibitor I. These results suggest that LTA might activate PC-PLC and PI-PLC to induce PKC activation, which in turn initiates NF-kappaB activation, and finally induces iNOS expression and NO release in RAW 264.7 macrophages.

Therapeutic potential of superoxide dismutase mimetics as therapeutic agents in critical care medicine

Oxidative stress results from an oxidant/antioxidant imbalance, an excess of oxidants, or a depletion of antioxidants. A considerable body of recent evidence suggests that oxidative stress and exaggerated production of reactive oxygen species play a major role in several aspects of septic shock and ischemia and reperfusion. Initiation of lipid peroxidation, direct inhibition of mitochondrial respiratory chain enzymes, inactivation of glyceraldehyde-3-phosphate dehydrogenase, inhibition of membrane Na /K adenosine triphosphatase activity, inactivation of membrane sodium channels, and other oxidative protein modifications contribute to the cytotoxic effect of reactive oxygen species. In addition, reactive oxygen species are potent triggers of DNA strand breakage, with subsequent activation of the nuclear enzyme poly-adenosine 5'-diphosphate ribosyl synthetase, and eventual severe energy depletion of the cells. Pharmacologic evidence suggests that the peroxynitrite-poly-adenosine 5'-diphosphate ribosyl polymerase pathway contributes to the cellular injury in shock and endothelial injury. Treatment with superoxide dismutase mimetics, which selectively mimic the catalytic activity of the human superoxide dismutase enzymes, has been shown to prevent the cellular energetic failure associated with shock and ischemia-reperfusion and to prevent tissue damage associated with these conditions. In this article, we will briefly review the role of superoxide in septic shock and ischemia-reperfusion injury. We hope to present evidence to support the potential development of superoxide dismutase mimetics as novel and effective agents in the area of critical care medicine.

Oxidative stress in septic shock and disseminated intravascular coagulation

Oxidative stress results from an oxidant/antioxidant imbalance, an excess of oxidants and/or a depletion of antioxidants. A considerable body of recent evidence suggests that oxidant stress plays a major role in several aspects of septic shock and disseminated intravascular coagulation (DIC), and it is the subject of this review. Immunohistochemical and biochemical evidence demonstrate the significant role of reactive oxygen species (ROS) in endotoxic and hemorrhagic shock, and in endothelial injury associated with DIC syndrome. Initiation of lipid peroxidation, direct inhibition of mitochondrial respiratory chain enzymes, inactivation of glyceraldehyde-3-phosphate dehydrogenase, inhibition of membrane Na+/K+ ATP-ase activity, inactivation of membrane sodium channels, and other oxidative protein modifications contribute to the cytotoxic effect of ROS. In addition, reactive oxygen species are potent triggers of DNA strand breakage, with subsequent activation of the nuclear enzyme poly-ADP ribosyl synthetase, with eventual severe energy depletion of the cells. Pharmacological evidence suggests that the peroxynitrite-poly-ADP ribosyl synthetase pathway contributes to the cellular injury in shock and endothelial injury. Treatment with superoxide dismutase mimetics (SODms), which selectively mimic the catalytic activity of the human superoxide dismutase enzymes, have been shown to prevent in vivo shock and the cellular energetic failure associated with shock.

The beneficial effects of protein tyrosine kinase inhibition on the circulatory failure induced by endotoxin in the rat

Implication of enhanced activity of tyrosine kinases has been established in the pathophysiology of many diseases associated with local (e.g., atherosclerosis) or systemic (e.g., septic shock) inflammation. The main objective of this study was to elucidate whether tyrosine kinase and nitric oxide were involved in endotoxin-induced impairment of vascular responses to sympathetic nerve stimulation (SNS) in rat isolated mesenteric bed. Therefore, the effects of genistein, an inhibitor of protein tyrosine kinase, and L-NAME (N-nitro-L-arginine methyl ester), an inhibitor of nitric oxide synthase, on endotoxin-induced shock were investigated in the thiopental-anesthetized rats. We also studied the effects of endotoxin on the vasoconstrictor responses to SNS in the rat isolated perfused mesenteric bed. Endotoxin injection (10 mg kg(-1), i.p.) produced a marked hypotension and a reduction of the pressor responses elicited by phenylephrine (0.1, 0.3, and 3 microg kg(-1), i.v.). Pretreatment of the rats with either genistein (10 mg kg(-1) i.p., 2 h before endotoxin injection), L-NAME (0.1 mg kg(-1), i.p., 30 min before endotoxin injection), or a combination of both attenuated the hypotension caused by endotoxin. SNS in the rat isolated perfused mesenteric bed caused a frequency-dependent vasoconstrictor response, which was abolished by tetrodotoxin (10(-7) M), prazoscin (10(-7) M), and guanethidine (10(-7)M). In mesenteric vascular beds removed from rats injected with endotoxin, the vasoconstrictor responses to SNS were markedly impaired. Although genistein and L-NAME pretreatment attenuated the vascular hyporeactivity to phenylephrine, they did not improve the impaired SNS response of the isolated vascular bed of endotoxin-treated animals. These results indicate that genistein and L-NAME pretreatment prevent the hypotension and the delayed hyporeactivity to phenylephrine induced by endotoxin, but they failed to restore the vascular hyporeactivity to SNS.

Carboxy-PTIO, a scavenger of nitric oxide, selectively inhibits the increase in medullary perfusion and improves renal function in endotoxemia

The acute renal failure associated with septic shock is associated with a high mortality despite dialytic therapies. Endotoxemia leads to marked changes in the distribution of intrarenal perfusion that may be independent of alterations in total renal blood flow or systemic hemodynamics. Modulation of this intrarenal redistribution may protect against acute renal failure. This study examines the effect of carboxy-2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (carboxy-PTIO), a scavenger of nitric oxide (NO), on systemic and intrarenal hemodynamics measured by laser Doppler flowmetry following the induction of endotoxemia in the anesthetized rat. Infusion of lipopolysaccharide (LPS) led to a prompt reduction in inulin clearance at 60 min, which remained reduced for 6 h in saline-treated rats. Administration of carboxy-PTIO led to a sustained increase in inulin clearance over 360 min post-LPS. During endotoxemia, cortical perfusion fell acutely by 29 +/- 8%, whereas medullary perfusion increased by 71 +/- 11%. The increase in medullary perfusion was potently and selectively inhibited by carboxy-PTIO. We propose that inhibition of medullary hyperemia maintains glomerular hydrostatic pressure, thus leading to the improved renal function during endotoxemia and that scavenging of NO may prove to be a useful therapeutic option in the acute renal failure associated with septic shock.

Interactions between lipoteichoic acid and peptidoglycan from Staphylococcus aureus: a structural and functional analysis

The cell wall of Gram-positive bacteria contains lipoteichoic acid (LTA) and peptidoglycan (PepG), which synergise to cause shock and organ failure in animals, and to activate human blood to release proinflammatory cytokines. The structural elements within LTA and PepG that are essential for the observed synergism are discussed.

Inhibition of inducible nitric oxide synthase reduces renal ischemia/reperfusion injury

BACKGROUND

Nitric oxide (NO), produced via inducible nitric oxide synthase (iNOS), is implicated in the pathophysiology of renal ischemia/reperfusion (I/R) injury. The aim of this study was to investigate the effects of the iNOS inhibitors L-N6-(1-iminoethyl)lysine (L-NIL) and aminoethyl-isothiourea (AE-ITU) on (a) renal dysfunction and injury mediated by bilateral I/R of rat kidneys in vivo and (b) cytokine-stimulated NO production by primary cultures of rat proximal tubule (PT) cells.

METHODS

Male Wistar rats subjected to bilateral renal ischemia (45 min) followed by reperfusion (6 h). Rats were administered either L-NIL (3 mg/kg IV bolus 15 min prior to I/R followed by 1 mg/kg/h throughout I/R) or AE-ITU (1 mg/kg IV bolus 15 min prior to I/R followed by 1 mg/kg/h throughout I/R). Serum and urinary biochemical indicators of renal dysfunction and injury were measured; serum creatinine (SCr, glomerular dysfunction), fractional excretion of Na+ (FENa, tubular dysfunction), serum aspartate aminotransferase (sAST, I/R injury) and urinary N-acetyl-beta-d-glucosaminidase (uNAG, tubular injury). Additionally, renal sections were used for histological grading of renal injury and for immunological evidence of nitrotyrosine formation. Nitrate/nitrate levels in plasma were measured using the Griess assay and used as an indicator of NO production. Primary cultures of rat PT cells were incubated with interferon-gamma(IFN-gamma, 100 IU/mL) and lipopolysaccharide (LPS, 10 microg/mL) for 24 h, either in the absence or presence of increasing concentrations of L-NIL or AE-ITU (0.001 to 1 mmol/L) after which nitrite/nitrate levels were measured using the Griess assay.

RESULTS

L-NIL and AE-ITU significantly reduced the I/R-mediated increases in SCr, FENa, sAST and uNAG, indicating attenuation of I/R-mediated renal dysfunction and injury. Specifically, L-NIL and AE-ITU reduced the I/R-mediated glomerular and tubular dysfunction and biochemical and histological evidence of tubular injury. Both L-NIL and AE-ITU attenuated the plasma levels of nitrate (indicating reduced NO production) and the immunohistochemical evidence of the formation of nitrotyrosine. In vitro, L-NIL and AE-ITU both significantly reduced cytokine-stimulated NO production by primary cultures of rat PT cells in a dose-dependent manner.

CONCLUSIONS

These results suggest that L-NIL and AE-ITU reduce the renal dysfunction and injury associated with I/R of the kidney, via inhibition of iNOS activity and subsequent reduction of NO (and peroxynitrite) generation. We propose that selective and specific inhibitors of iNOS activity may be useful against the NO-mediated renal dysfunction and injury associated with I/R of the kidney.