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

Soluble guanylate cyclase agonist, isoliquiritigenin attenuates renal damage and aortic calcification in a rat model of chronic kidney failure

AIMS

Chronic kidney disease (CKD) is a growing fatal health problem worldwide associated with vascular calcification. Therapeutic approaches are limited with higher costs and poor outcomes. Adenine supplementation is one of the most relevant CKD models to human. Insufficient Nitric Oxide (NO)/ cyclic Guanosine Monophosphate (cGMP) signaling plays a key role in rapid development of renal fibrosis. Natural products display proven protection against CKD. Current study therefore explored isoliquiritigenin, a bioflavonoid extracted from licorice roots, potential as a natural activator for soluble Guanylate Cyclase (sGC) in a CKD rat model.

MATERIALS AND METHODS

60 male Wistar rats were grouped into Control group (n = 10) and the remaining rats received adenine (200 mg/kg, p.o) for 2 wk to induce CKD. They were equally sub-grouped into: Adenine untreated group and 4 groups orally treated by isoliquiritigenin low or high dose (20 or 40 mg/kg) with/without a selective sGC inhibitor, ODQ (1-H(1,2,4)oxadiazolo(4,3-a)-quinoxalin-1-one, 2 mg/kg, i.p) for 8 wk.

KEY FINDINGS

Long-term treatment with isoliquiritigenin dose-dependently and effectively amended adenine-induced chronic renal and endothelial dysfunction. It not only alleviated renal fibrosis and apoptosis markers but also aortic calcification. Additionally, this chalcone neutralized renal inflammatory response and oxidative stress. Isoliquiritigenin beneficial effects were associated with up-regulation of serum NO, renal and aortic sGC, cGMP and its dependent protein kinase (PKG). However, co-treatment with ODQ antagonized isoliquiritigenin therapeutic impact.

SIGNIFICANCE

Isoliquiritigenin seems to exert protective effects against CKD and vascular calcification by activating sGC, increasing cGMP and its downstream PKG.

Aryl hydrocarbon receptor ligands enhance lung immunity through intestinal IKKβ pathways

BACKGROUND

Infection by antibiotic-resistant microorganisms is common in intensive care units and has become a global problem. Here, we determined the effect of aryl hydrocarbon receptor (AhR) stimulation on antibiotics-induced systemic defense impairment and its mechanisms.

METHODS

C57BL/6 wild-type (WT) mice received combined antibiotics with or without Ahr ligands (tryptophan and indole), or dead Lactobacillus plantarum supplementation. The defense mechanisms against Pseudomonas aeruginosa infection in the lung were examined.

RESULTS

Antibiotic treatments decreased the phagocytic activity, physiological activity, and the peroxynitrite production of alveolar macrophage (AMs). It also enhanced P. aeruginosa pneumonia-induced bacterial counts in the lung. Tryptophan and dead L. plantarum supplementation reversed antibiotic-induced intracellular adhesion molecule (ICAM) as well as IL-6 expression, and increased P. aeruginosa pneumonia-induced bacterial counts in the lung and increased phagocytic activity and peroxynitrite production of AMs. Moreover, these treatments reversed the antibiotics-induced reduction of Ahr expression, antibacterial proteins, reactive oxygen species (ROS) production, and NF-κB DNA binding activity of the intestinal mucosa and plasma IL-6 levels. P. aeruginosa counts increased and phagocytic activity of AMs and myeloperoxidase (MPO) activity decreased in intestinal IKKβ depleted mice. Antibiotics, antibiotic with tryptophan feeding, or antibiotic with dead L. plantarum feeding treatments did not change the phagocytic activity and peroxynitrite production of AMs, plasma IL-6 levels, and the expression of Ahr of intestine in intestinal IKKβ depleted mice.

CONCLUSION

Antibiotic treatment impairs lung immune defenses by decreasing Ahr expression in the intestine and peroyxnitrite production of the AMs. Ahr ligands reverses antibiotic-induced lung defense against bacterial infection through intestinal ROS production and NF-κB activation. The gut is critical in maintaining lung defense mechanism through the intestinal IKKβ pathways.

The role of endothelial mechanosensitive genes in atherosclerosis and omics approaches

Atherosclerosis is the leading cause of morbidity and mortality in the U.S., and is a multifactorial disease that preferentially occurs in regions of the arterial tree exposed to disturbed blood flow. The detailed mechanisms by which d-flow induces atherosclerosis involve changes in the expression of genes, epigenetic patterns, and metabolites of multiple vascular cells, especially endothelial cells. This review presents an overview of endothelial mechanobiology and its relation to the pathogenesis of atherosclerosis with special reference to the anatomy of the artery and the underlying fluid mechanics, followed by a discussion of a variety of experimental models to study the role of fluid mechanics and atherosclerosis. Various in vitro and in vivo models to study the role of flow in endothelial biology and pathobiology are discussed in this review. Furthermore, strategies used for the global profiling of the genome, transcriptome, miR-nome, DNA methylome, and metabolome, as they are important to define the biological and pathophysiological mechanisms of atherosclerosis. These "omics" approaches, especially those which derive data based on a single animal model, provide unprecedented opportunities to not only better understand the pathophysiology of atherosclerosis development in a holistic and integrative manner, but also to identify novel molecular and diagnostic targets.

Neuronal nitric oxide synthase and its interaction with soluble guanylate cyclase is a key factor for the vascular dysfunction of experimental sepsis

OBJECTIVE

Vascular dysfunction plays a central role in sepsis, and it is characterized by hypotension and hyporesponsiveness to vasoconstrictors. Nitric oxide is regarded as a central element of sepsis vascular dysfunction. The high amounts of nitric oxide produced during sepsis are mainly derived from the inducible isoform of nitric oxide synthase 2. We have previously shown that nitric oxide synthase 2 levels decrease in later stages of sepsis, whereas levels and activity of soluble guanylate cyclase increase. Therefore, we studied the putative role of other relevant nitric oxide sources, namely, the neuronal (nitric oxide synthase 1) isoform, in sepsis and its relationship with soluble guanylate cyclase. We also studied the consequences of nitric oxide synthase 1 blockade in the hyporesponsiveness to vasoconstrictors.

DESIGN

Randomized controlled prospective experimental study.

SETTING

Academic research laboratory.

SUBJECTS

Female Wistar rats submitted to cecal ligation and puncture method.

INTERVENTIONS

1) Six, 12, and 24 hours after cecal ligation and puncture, vascular reactivity to phenylephrine (3 and 30 nmol/kg) before and after 7-nitroindazole (45 μmol/kg, s.c.) or aminoguanidine (30 μmol/kg, s.c.) administration was evaluated. 2) Protein levels and interaction between nitric oxide synthase 1 and soluble guanylate cyclase were determined. 3) Six, 12, and 24 hours after cecal ligation and puncture, thoracic aorta segments were stimulated with phenylephrine in the presence or absence of 7-nitroindazole and cyclic guanosine monophosphate accumulation was determined. 4) After 24 hours of cecal ligation and puncture, norepinephrine was infused (10 μg/kg/min) in the presence or absence of 7-nitroindazole or S-methyl-L-thiocitrulline (1 μmol/kg, IV) and mean arterial pressure was registered.

MEASUREMENTS AND MAIN RESULTS

1) Both nitric oxide synthase 1 and soluble guanylate cyclase are expressed in higher levels in vascular tissues during sepsis; 2) both proteins physically interact and nitric oxide synthase 1 blockade inhibits cyclic guanosine monophosphate production; 3) pharmacological blockade of nitric oxide synthase 1 using 7-nitroindazole or S-methyl-L-thiocitrulline reverts the hyporesponsiveness to phenylephrine and increases the vasoconstrictor effect of norepinephrine and phenylephrine.

CONCLUSIONS

Sepsis induces increased expression and physical association of nitric oxide synthase 1/soluble guanylate cyclase and a higher production of cyclic guanosine monophosphate that together may help explain sepsis-induced vascular dysfunction. In addition, selective inhibition of nitric oxide synthase 1 restores the responsiveness to vasoconstrictors. Therefore, inhibition of nitric oxide synthase 1 (and possibly soluble guanylate cyclase) may represent a valuable alternative to restore the effectiveness of vasopressor agents during late sepsis.

Protective Effects of Quercetin on Rat Pial Microvascular Changes during Transient Bilateral Common Carotid Artery Occlusion and Reperfusion

The aim of this study was to assess the in vivo effects of quercetin on pial microvascular responses during transient bilateral common carotid artery occlusion (BCCAO) and reperfusion. Rat pial microcirculation was visualized by fluorescence microscopy through a closed cranial window. Pial arterioles were classified in five orders of branchings. Capillaries were assigned order 0, the smallest arterioles order 1, and the largest ones order 5. In ischemic rats, 30 min BCCAO and 60 min reperfusion caused arteriolar diameter decrease (by 14.5 ± 3.3% of baseline in order 2), microvascular leakage [0.47 ± 0.04, normalized gray levels (NGL)], leukocyte adhesion in venules (9 ± 2/100 μm venular length, v.l./30 s), and reduction of capillary perfusion (by 40 ± 7% of baseline). Moreover, at the end of BCCAO and reperfusion there was a significant increase in reactive oxygen species (ROS) formation when compared with baseline. Quercetin highest dose determined dilation in all arteriolar orders (by 40 ± 4% of baseline in order 2) and prevented microvascular permeability (0.15 ± 0.02 NGL), leukocyte adhesion (3 ± 1/100 μm v.l./30 s) as well as ROS formation, while capillary perfusion was protected. Inhibition of endothelial nitric oxide synthase (NOS) prior to quercetin reduced arteriolar dilation (order 2 diameter increase by 10.3 ± 2.5% of baseline) and caused permeability increase (0.29 ± 0.03 NGL); inhibition of neuronal NOS or inducible NOS did not affect quercetin-induced effects. Inhibition of guanylyl cyclase prior to quercetin reversed the quercetin’s effects on pial arteriolar diameter and leakage. In conclusion, quercetin was able to protect pial microcirculation from ischemia–reperfusion damage inducing arteriolar dilation likely by nitric oxide release. Moreover, quercetin scavenger activity blunted ROS formation preserving the blood–brain barrier integrity.

Role of central NO-cGMP pathway in vasopressin and oxytocin gene expression during sepsis

Sepsis induces massive production of inflammatory mediators, such as nitric oxide (NO), and causes neuroendocrine and cardiovascular alterations. This study investigates the involvement of the central NO-cGMP pathway in arginine vasopressin (AVP) and oxytocin (OXY) gene expression during sepsis induced by cecal ligation and puncture (CLP). Male Wistar rats received an i.c.v. injection of ODQ (0.25 μg/μL), a selective inhibitor of the heme site of soluble guanylate cyclase, or of 1% dymethilsulfoxide (DMSO), as vehicle. Thirty minutes after the injections, sepsis was induced by cecal ligation and puncture or the animals were sham operated. The ODQ pre-treatment did not alter the progressive NO increase observed after CLP. In the supraoptic nucleus (SON), this pretreatment increased the relative gene expression ratio of AVP and OXY in the initial phase of sepsis, but in the late phase, the gene expression of both hormones was reduced. In the paraventricular nucleus (PVN), soluble guanylate cyclase inhibition caused an even larger decrease in the relative gene expression ratio of AVP and OXY during sepsis. These results are indicative of a role of the NO-cGMP pathway in hormonal synthesis in the SON and PVN of the hypothalamus during polymicrobial sepsis.

Concomitant administration of nitric oxide and glucocorticoids improves protection against bronchoconstriction in a murine model of asthma

Glucocorticoids (GC) remain the first choice of treatment in asthma, but GC therapy is not always effective and is associated with side effects. In a porcine study in our laboratory, simultaneous administration of GC and nitric oxide (NO) attenuated the endotoxin-induced inflammatory response and made GC treatment more effective than inhaled NO or steroids alone. In the present study, we aimed to further investigate the interactions between NO and GC treatment in two murine models of asthma. Inflammation was induced by endotoxin, ovalbumin, or a combination of both. With an animal ventilator and a forced oscillation method (FlexiVent), lung mechanics and airway reactivity to methacholine in response to various treatments were assessed. We also describe histology and glucocorticoid receptor (GR) protein expression in response to inhaled NO treatment [40 ppm NO gas or NO donors sodium nitroprusside (SNP) or diethylamine NONOate (DEA/NO)]. SNP and GC provided protection against bronchoconstriction to a similar degree in the model of severe asthma. When GC-treated mice were given SNP, maximum airway reactivity was further reduced. Similar effects were seen after DEA/NO delivery to GC-treated animals. Using 1-H-[1,2,4]-oxadiazolo-[4,3-a]-quinoxalin-1-one (ODQ), a soluble guanylate cyclase inhibitor, we found this effect of NO donors to be mediated through a cGMP-independent mechanism. In the severe model, prolonged NO treatment restored or even increased the nuclear levels of GR. In conclusion, in our murine model of severe asthma GC treatment provided protection to only a limited degree against bronchoconstriction, while concomitant treatment with a NO donor was markedly more potent than the use of either NO or GC alone.

Prolonged NO treatment decreases alpha-adrenoreceptor agonist responsiveness in porcine pulmonary artery due to persistent soluble guanylyl cyclase activation

A cultured porcine pulmonary artery (PA) model was used to examine the effects of prolonged nitric oxide (NO) treatment on the response of this vessel to acutely applied NO and to the alpha-adrenoreceptor agonist phenylephrine. Two-hour treatment with the NO donor (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA-NO) decreased both NO and phenylephrine responsiveness. Twenty-four-hour treatment with DETA-NO resulted in a further reduction in NO responsiveness but no further reduction in phenylephrine responsiveness. Acute addition of soluble guanylyl cyclase (sGC) inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) had no effect on phenylephrine responsiveness in PA not treated with DETA-NO. ODQ treatment fully restored phenylephrine responsiveness in PA treated with DETA-NO. sGCbeta(1) subunit protein levels in PA tissue homogenate were 48.6 +/- 6.9, 51.6 +/- 3.5, and 41.3 +/- 2.8 ng/mg total protein for freshly prepared and 2-h and 24-h NO-treated PA, respectively. Steady-state tissue cGMP was not significantly different in control versus NO-treated PA. sGC specific activity in the absence of added NO was measured in PA homogenate and was 0.29 +/- 0.02, 1.38 +/- 0.12, and 0.53 +/- 0.08 micromol cGMP.min(-1).mg sGC(-1), in freshly prepared and 2-h and 24-h NO treated PA, respectively. Ten-minute Hb treatment completely normalized sGC basal activity in homogenates prepared from DETA-NO-treated PA, which was 0.23 +/- 0.02, 0.18 +/- 0.03, and 0.25 +/- 0.04 micromol cGMP.min(-1).mg sGC(-1), in freshly prepared and 2-h and 24-h NO-treated PA, respectively. The kinetics of the Hb reversal of NO-mediated sGC persistent activation do not support sGC covalent modification as the activation mechanism. We conclude that prolonged NO exposure results in a persistently increased sGC specific activity, which accounts for the observed alpha-adrenoreceptor agonist hyporesponsiveness.

Granulocyte-macrophage-colony-stimulating factor-dependent peritoneal macrophage responses determine survival in experimentally induced peritonitis and sepsis in mice

Granulocyte-macrophage-colony-stimulating factor (GM-CSF) plays a critical role in innate immunity by stimulating the differentiation of tissue macrophages via the transcription factor PU.1. Previous studies showed that GMCSF-deficient(GM-CSF-/-) mice had susceptibility to and impaired clearance of group B streptococcal bacteria by macrophages. For these studies, we hypothesized that GM-CSF-/- mice have increased susceptibility to peritonitis caused by immune dysfunction of peritoneal macrophages. We examined the role of peritoneal macrophages in pathogen clearance, cytokine responses, and survival in a murine cecal ligation and puncture (CLP) model of peritonitis/sepsis. Surprisingly, CLP minimally affected survival in GM-CSF-/- mice while markedly reducing survival in wild-type mice. This was not explained by differences in the composition of microbial flora, rates of bacterial peritonitis, or sepsis, all of which were similar in GM-CSF-/- and wild-type mice. However, survival correlated with peritoneal and serum TNF-alpha and IL-6 levels that were significantly lower in GM-CSF-/- than in control mice. After peritoneal LPS instillation, GM-CSF-/- mice also had improved survival and reduced TNF-alpha and IL-6 responses. In vitro studies demonstrated reduced secretion of TNF-alpha and IL-6 by peritoneal macrophages isolated from sham GM-CSF-/- mice as compared with macrophages from sham control mice. Peritoneal instillation of GM-CSF-/-/PU.1+ macrophages, but not GM-CSF-/-/PU.1+ macrophages into GM-CSF-/- mice conferred susceptibility to death after CLP or peritoneal LPS exposure. These results demonstrate that GM-CSFY/PU.1-dependent peritoneal macrophage responses are a critical determinant of survival after experimentally induced peritonitis/sepsis or exposure to LPS and have implications for therapies to treat such infections.

Desensitization of the soluble guanylyl cyclase/cGMP pathway by lipopolysaccharide in rat isolated pulmonary artery but not aorta

BACKGROUND AND PURPOSE

To investigate the function of soluble guanylyl cyclase (sGC)/3',5'-cyclic guanosine monophosphate (cGMP) pathway in lipopolysaccharide (LPS)-induced changes in vascular reactivity of rat isolated pulmonary artery and aorta.

EXPERIMENTAL APPROACH

Nitric oxide (NO) production, contraction responses to endothelin-1 (ET-1), relaxation responses to sodium nitroprusside (SNP), 8-pCPT-cGMP, BAY412272 and T-0156, SNP-induced cGMP production and expression of sGC(alpha1), sGC(beta1) and 3',5'-cyclic nucleotide phosphodiesterase-5 (PDE5) proteins were measured in LPS-treated pulmonary and aortic rings from male Wistar rats.

KEY RESULTS

In both vessels, LPS (10 microg mL(-1), 20 h) increased NO production, which was inhibited by the selective inducible NOS (iNOS) inhibitor 1400W (1 microM). In the aorta, LPS decreased ET-1-induced contractility and this decrease was inhibited by the selective sGC inhibitor ODQ (10 microM) but not by removal of endothelium, or inhibitors of cyclooxygenase (indomethacin, 10 microM) or iNOS (1400W, 1 microM). Furthermore, aortic relaxation responses to the direct sGC activator BAY412272 were enhanced. In the pulmonary artery, SNP (1 nM to 30 microM)-induced relaxation and cGMP production, BAY412272-induced relaxation and sGC(beta1) protein expression were decreased, whereas relaxation responses to the PDE5-specific inhibitor T-0156 (0.1-100 nM) were enhanced. Relaxation responses to the phosphodiesterase-resistant cGMP analogue, 8-pCPT-cGMP, and protein expression levels of sGC(alpha1) and PDE5 were not altered in either vessel.

CONCLUSION AND IMPLICATIONS

LPS caused a selective hypocontractility of rat aorta to ET-1 mediated mainly through NO-independent sGC activation, whereas in the pulmonary artery, the effect of sGC activation was reduced by a decreased protein expression of sGC(beta1) together with increased PDE5 activity.

Jejunal cholinergic, nitrergic, and soluble guanylate cyclase activity in postoperative ileus

BACKGROUND

In animal models of postoperative ileus (POI), inflammation of the intestine plays an important role in the pathogenesis of POI. Changes in alpha(2)-adrenoceptors and nitrergic regulation have been proposed to be implicated. The aim of our study was to investigate the presynaptic alpha(2)-receptor-mediated control of cholinergic nerve activity, the nitrergic nerve activity, and the possible role of soluble guanylate cyclase (sGC) during the inflammatory phase of POI.

METHODS

Ileus was induced by anesthesia and manipulation of the rat jejunum. Rats were treated with the sGC inhibitors methylene blue or ODQ; nonoperated animals served as controls. After 24 h, plasma and jejunal tissue were collected for biochemical assays, nitric oxide synthase-1 (NOS-1)-immunohistochemistry, acetylcholine (Ach)-release experiments, and muscle tension experiments.

RESULTS

In all operated animal groups, myeloperoxidase activity was significantly increased, which indicates initiation of an inflammatory response. The alpha(2)-adrenoceptor agonist UK14,304 reduced electrically induced Ach-release similarly in operated and nonoperated animals. In strips of operated animals, electrically induced nitrergic relaxations were decreased, whereas relaxations induced by exogenous nitric oxide (NO) remained unchanged compared with control. The number of myenteric neurons and the percentage of NOS-1-positive neurons were not influenced. Plasmatic cyclic guanosine monophosphate (cGMP) levels were decreased in all operated groups, whereas jejunal cGMP levels were unchanged compared with nonoperated controls; treatment with sGC inhibitors did not reduce plasmatic cGMP levels.

CONCLUSIONS

This study demonstrates that presynaptic alpha(2)-receptor mediated control of intestinal cholinergic nerve activity is unchanged during manipulation-induced inflammation. However, this inflammation induces impaired nitrergic neurotransmission related to decreased NOS-1 activity in the nitrergic nerves.

Influence of soluble guanylate cyclase inhibition on inflammation and motility disturbances in DSS-induced colitis

Nitric oxide (NO) has been associated with a spectrum of harmful to protective roles in inflammatory bowel disease. The involvement of soluble guanylate cyclase (sGC)--the downstream effector of NO--in the negative effect of NO in inflammatory models has been proposed but this has not been evaluated in inflammatory bowel diseases. The present study investigates therefore the influence of colonic inflammation on sGC activity, as well as the effect of in vivo sGC inhibition on colonic inflammation and on in vitro changes in colonic motility in the dextran sulfate sodium (DSS)-model of colitis in rat. Administration of 7% DSS in the drinking water for 6 days resulted in colonic inflammation as judged from histology and myeloperoxidase activity, accompanied by weight loss and bloody stools. Plasma and colonic tissue cyclic guanosine 3',5'-monophosphate (cGMP) levels were decreased in DSS-treated rats. Colonic levels of neuronal NO synthase (nNOS) mRNA and immunoreactivity were not influenced, while those of inducible NO synthase (iNOS) and colonic nitrite/nitrate levels were increased by DSS exposure. Circular muscle strips from inflamed distal colon showed decreased inhibitory responses towards electrical field stimulation and exogenous NO, while methacholine-induced phasic activity was suppressed. Inhibition of sGC by in vivo treatment with ODQ further reduced cGMP levels but did not prevent the inflammation and motility alterations. These results suggest that DSS-induced colitis in rats is accompanied by a reduced sensitivity of sGC, leading to reduced basal cGMP levels and decreased colonic responsiveness towards nitrergic stimuli, but pharmacological reduction of cGMP generation does not prevent the development of DSS-induced colitis.

THE GREEN TEA POLYPHENOL EPIGALLOCATECHIN-3-GALLATE IMPROVES SYSTEMIC HEMODYNAMICS AND SURVIVAL IN RODENT MODELS OF POLYMICROBIAL SEPSIS

Epigallocatechin-3-gallate (EGCG) is the main polyphenolic flavonoid found in green tea. Recent in vitro studies have suggested that EGCG inhibits activation of the nuclear factor-kappaB (NF-kappaB) pathway. The NF-kappaB is a transcriptional factor required for gene expression of many inflammatory mediators, including the inducible isoform of nitric oxide synthase (NOS2). Excessive NO production by NOS2 is directly linked to the vasoplegia, shock, and mortality associated with sepsis. Accordingly, we hypothesized that EGCG administration would inhibit NOS2 gene expression and thereby improve survival in a rodent model of polymicrobial sepsis. Polymicrobial sepsis was induced in male Sprague-Dawley rats (hemodynamic study) and C57BL6 mice (mortality study) via cecal ligation and double puncture (CL2P). Rodents were treated with either EGCG (10 mg/kg intraperitoneally) or vehicle at 1 and 6 h after CL2P and every 12 h thereafter. In the hemodynamic study, mean arterial blood pressure was monitored for 18 h, and rats were killed at 3, 6, and 18 h after CL2P. In the mortality study, survival was monitored for 72 h after CL2P in mice. In vehicle-treated rodents, CL2P was associated with profound hypotension and greater than 80% mortality rate. Epigallocatechin-3-gallate treatment significantly improved both the hypotension and survival. In vitro experiments further showed that EGCG inhibited activation of NF-kappaB and subsequent NOS2 gene expression in a primary culture of rat aortic smooth muscle cells. Epigallocatechin-3-gallate may therefore represent a potential nutritional supplement or pharmacologic agent in patients with sepsis.

Anaphylactic shock depends on PI3K and eNOS-derived NO

Anaphylactic shock is a sudden, life-threatening allergic reaction associated with severe hypotension. Platelet-activating factor (PAF) is implicated in the cardiovascular dysfunctions occurring in various shock syndromes, including anaphylaxis. Excessive production of the vasodilator NO causes inflammatory hypotension and shock, and it is generally accepted that transcriptionally regulated inducible iNOS is responsible for this. Nevertheless, the contribution of NO to PAF-induced shock or anaphylactic shock is still ambiguous. We studied PAF and anaphylactic shock in conscious mice. Surprisingly, hyperacute PAF shock depended entirely on NO, produced not by inducible iNOS, but by constitutive eNOS, rapidly activated via the PI3K pathway. Soluble guanylate cyclase (sGC) is generally regarded as the principal vasorelaxing mediator of NO. Nevertheless, although methylene blue partially prevented PAF shock, neither 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (ODQ) nor sGCalpha1 deficiency did. Also, in 2 different models of active systemic anaphylaxis, inhibition of NOS, PI3K, or Akt or eNOS deficiency provided complete protection. In contrast to the unsubstantiated paradigm that only excessive iNOS-derived NO underlies cardiovascular collapse in shock, our data strongly support the unexpected concept that eNOS-derived NO is the principal vasodilator in anaphylactic shock and define eNOS and/or PI3K or Akt as new potential targets for treating anaphylaxis.

Drugs modulating the biological effects of peroxynitrite and related nitrogen species

The term "reactive nitrogen species" includes nitrogen monoxide, commonly called nitric oxide, and some other remarkable chemical entities (peroxynitrite, nitrosoperoxycarbonate, etc.) formed mostly from nitrogen monoxide itself in biological environments. Regardless of the specific mechanisms implicated in their effects, however, it is clear that an integrated pharmacological approach to peroxynitrite and related species is only just beginning to take shape. The array of affected chemical and pathological processes is extremely broad. One of the most conspicuous mechanisms observed thus far has been the scavenging of the peroxynitrite anion by molecules endowed with antioxidant activity. This discovery has in turn lent great significance to several naturally occurring and synthetic antioxidants, which usually protect not only against oxidative reactions, but also from nitrating ones, both in vitro and in vivo. This has proven to be beneficial in different tissues, especially within the central nervous system. Taking these results and those of other biochemical investigations into account, many research lines are currently in progress to establish the true potential of reactive nitrogen species deactivators in the therapy of neurological diseases, ischemia-reperfusion damage, renal failure, and lung injury, among others.

Nitric oxide-dependent reduction in soluble guanylate cyclase functionality accounts for early lipopolysaccharide-induced changes in vascular reactivity

We investigated the role of soluble guanylate cyclase in lipopolysaccharide-induced hyporesponsiveness to phenylephrine. The effects of phenylephrine on the blood pressure of female Wistar rats were evaluated at 2, 8, and 24 h after lipopolysaccharide injection (12.5 mg/kg i.p.). Vasoconstrictive responses to phenylephrine were reduced 40 to 50% in all time periods. Methylene blue, a soluble guanylate cyclase inhibitor (15 micromol/kg i.v.) restored the reactivity to phenylephrine in animals injected with lipopolysaccharide 2 and 24 h earlier. However, it failed to do so in animals injected with lipopolysaccharide 8 h earlier. Incubation with sodium nitroprusside (SNP) increased lung and aorta cGMP levels in control animals and in tissues of rats treated with lipopolysaccharide 24 h earlier. However, SNP failed to increase tissue cGMP in rats injected 8 h earlier. Lipopolysaccharide reduced the vasodilatory response to NO donors 8 h after injection. This effect and the decreased lung cGMP accumulation in response to SNP were reversed by an NO synthase blocker. Guanylate cyclase protein levels were lower than controls in lungs harvested from rats injected 8 h earlier and were back to normal values in lungs of rats injected 24 h earlier with lipopolysaccharide. Thus, data indicate that there is a temporal window of 8 h after lipopolysaccharide injection in which soluble guanylate cyclase is not functional and that this loss of function is NO-dependent. Thus, the putative use of soluble guanylate cyclase inhibitors in the treatment of endotoxemia may be beneficial mainly at early stages of this condition.

Induction of oxidative stress and inhibition of plasminogen activator inhibitor-1 production in endothelial cells following exposure to organic extracts of diesel exhaust particles and urban fine particles

Endothelial cells play important roles in anticoagulant and fibrinolytic systems. Recent studies suggest that increases in ambient particulate matter (PM) levels have been associated with an increase in mortality rate from cardiovascular diseases. We examined the production of heme oxygenase-1 (HO-1) and factors related to the fibrinolytic function by rat heart microvessel endothelial cells exposed to organic extracts of diesel exhaust particles (OE-DEP) and urban fine particles (OE-UFP) to investigate the direct effects of these soluble organic fractions in these PM on the fibrinolytic function of endothelial cells. The cell monolayer exposed to 10 microg/ml OE-DEP produced a larger amount of HO-1 than cells exposed to 10 microg/ml OE-UFP. OE-DEP and OE-UFP exposure reduced plasminogen activator inhibitor-1 (PAI-1) production by the cells but did not affect the production of thrombomodulin, tissue-type plasminogen activator, or urokinase-type plasminogen activator. Increased PAI-1 synthesis in response to treatment with 1.0 ng/ml tumor necrosis factor-alpha or 0.5 ng/ml transforming growth factor-beta1 was reduced by OE-DEP exposure. Suppression of PAI-1 production by OE-DEP exposure was mediated through oxidative stress and was independent of HO-1 activity. These results suggest that exposure to the soluble organic fraction of PM and DEP induced oxidative stress and reduced the PAI-1 production of endothelial cells.

Decreased aortic smooth muscle contraction in a rat model of multibacterial sepsis

We investigated whether blockade of the smooth muscle cell (SMC) inducible nitric oxide synthase (iNOS)-soluble guanylyl cyclase (sGC) vasodilator pathway would restore the fall in vasoreactivity produced by sepsis following cecal ligation and perforation (CLP) in rats. Contraction of adjacent aortic rings paired for the presence or absence of endothelial cells (EC) was recorded following high [K(+)](e) (40 mm) or norepinephrine (NE, 10(-8) to 10(-5) m) in the presence of the nitric oxide synthase inhibitor (NOS), N(G)-nitro-l-arginine methyl ester (l-NAME, 0.3 mm) or the sGC inhibitor, 1H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one (ODQ, 5 mum). In EC-denuded rings, sepsis halved SMC contraction induced by high [K(+)](e) or NE; neither l-NAME nor ODQ produced an increase in NE E(max) or high [K(+)](e)-evoked contraction. In conclusion, SMC contractility is globally reduced in CLP; this reduction does not appear to be explained by induction of SMC NOS in this CLP model.

INDUCIBLE NITRIC OXIDE SYNTHASE INHIBITOR REVERSES EXACERBATING EFFECTS OF HYPERTONIC SALINE ON LUNG INJURY IN BURN

The use of hypertonic saline (HTS) resuscitation in major trauma patients is still controversial. The objective of this study is to determine if inhibition of inducible nitric oxide synthase (iNOS) to stabilize the endothelial permeability and to retain HTS in the vascular space will reverse its exacerbating effect on burn-induced lung damage. In Experiment 1, specific pathogen-free (SPF) rats underwent 35% total body surface area (TBSA) burn and were resuscitated with 7.5 mL/kg HTS (7.5% NaCl), 7.5 mL/kg saline, or 50 mL/kg saline (nearly equal sodium load as HTS) via femoral veins for 15 min immediately after the burn. In Experiment 2, S-methylisothiourea (SMT) (7.5 mg/kg, i.p.) was given immediately after the burn to rats from the different groups of Experiment 1. At 8 h after the burn, the permeability and myeloperoxidase (MPO) activity of lung tissues were determined, and plasma samples were assayed for peroxynitrite levels. Burn significantly induced lung MPO activity, lung permeability, and blood dihydrorhodamine 123 (DHR 123) oxidation in rats. HTS administration after burn significantly increased the blood DHR 123 oxidation level, lung MPO activity, lung permeability, and inflammatory cell infiltration in comparison with those of burn plus 7.5 mg/kg saline and burn plus 50 mL/kg saline rats. In contrast, burn plus SMT rats with HTS injection showed significant 54%, 11%, and 35% decreases in blood DHR 123 oxidation level, lung MPO activity, and lung permeability, respectively, in comparison with burn plus SMT plus 7.5 mg/kg saline rats. In conclusion, restoration of extracellular fluid in early burn shock with HTS supplementation significantly exacerbates burn-induced lung neutrophil deposition, lung hyperpermeability, and blood peroxynitrite production. Inhibition of iNOS before HTS supplementation reverses the deteriorating effects of HTS on thermal injury-induced lung damage to beneficial ones. Using HTS in thermal injury resuscitation without the inhibition of iNOS is dangerous.

Role of cyclic GMP in nitrous-oxide-induced anxiolytic-like behavior in the mouse light-dark exploration test

Nitric oxide (NO) has been implicated in the anxiolytic-like behavioral effects of nitrous oxide (N2O). This study was conducted to determine whether NO activates a soluble guanylyl cyclase (sGC)-cyclic guanosine monophosphate (cGMP) pathway in the behavioral response to N2O in the light-dark exploration test. In mice pretreated with an sGC inhibitor, the increased light-compartment activity normally induced by N2O was significantly attenuated. Pretreatment with a cGMP phosphodiesterase inhibitor antagonized the anxiogenic effect of 15% N2O and enhanced the anxiolytic effect of 25% N2O, implying that cGMP reduces anxiety. These preliminary findings suggest that a signaling pathway involving NO and cGMP may mediate the behavioral effects of N2O.

Differential effects of a selective inhibitor of soluble guanylyl cyclase on global and regional hemodynamics during canine endotoxic shock

Activation of soluble guanylyl cyclase (sGC) might occur early during septic shock and play a role in the regulation of vascular tone and the redistribution of blood flow. The aim of this study was to assess the effects of sGC inhibition with oxadiazoloquinoxalinone (ODQ) on global and regional hemodynamic parameters in a clinically relevant model of septic shock. Fifteen anesthetized adult mongrel dogs were equipped with femoral and pulmonary artery catheters and ultrasonic flow probes around the mesenteric, femoral and renal arteries. The animals were randomized to receive Escherichia coli endotoxin (2 mg/kg, i.v.) alone, endotoxin followed by ODQ (1 mg/kg i.v.), or ODQ alone. Endotoxin administration was followed by decreases in mean arterial pressure, cardiac index, mesenteric, renal and femoral blood flows (MBF, RBF and FBF), and increases in systemic and pulmonary vascular resistances. Fluid resuscitation restored cardiac index, systemic vascular resistance, pulmonary vascular resistance, MBF, RBF and FBF to pre-endotoxin levels. In the presence of endotoxin, ODQ administration increased MBF and prevented the restoration of FBF. Hence, selective inhibition of sGC may increase splanchnic blood flow in septic shock.

Peroxynitrite-induced relaxation in isolated canine cerebral arteries and mechanisms of action

The present study was undertaken to determine the vascular actions of peroxynitrite (ONOO(-)), the product of superoxide and nitric oxide (NO), in isolated canine cerebral arteries and to gain insight into its potential mechanisms of action. In the absence of any vasoactive agent, ONOO(-) (from 10(-7) to 10(-6) M) was able to reduce the basal tension. In prostaglandin F2alpha-precontracted canine basilar arterial rings, ONOO(-) elicited concentration-dependent relaxation at concentrations from 10(-8) to 10(-5) M. The effective concentrations producing approximately 50% maximal relaxation (EC(50)) to ONOO(-) were 4.06 x 10(-6) and 4.12 x 10(-6) M in intact and denuded rings, respectively (P > 0.05). No significant differences in relaxation responses were found in ring preparations with or without endothelium (P > 0.05). The presence of either 5 microM methylene blue (MB) or 5 microM 1H-[1,2,4]oxadiazolo-[4,3-alpha]quinoxalin-1-one (ODQ) significantly inhibited the relaxations induced by ONOO(-). Tetraethylammonium chloride (T-2265) significantly decreased the ONOO(-)-induced relaxations in a concentration-dependent manner. However, ONOO(-) had no effect on rings precontracted by high KCL (P > 0.05). Addition of low concentrations of calyculin A (50 nM) was able to abolish the ONOO(-)-induced relaxation. Furthermore, ONOO(-) significantly inhibited calcium-induced contractions of K(+)-depolarized canine cerebral rings in a concentration-related manner. Lastly, a variety of pharmacological agents and antagonists including L-NMMA, l-arginine, indomethacin, atropine, naloxone, diphenhydramine, cimetine, glibenclamide, haloperidol, etc., did not influence the relaxant effects of ONOO(-) on the rings. Our new results suggest that ONOO(-)-triggered relaxation, on canine cerebral arteries, is mediated by elevation of cyclic guanosine monophosphate (cGMP) levels, membrane hyperpolarization via K+ channel activation, activation of myosin light chain phosphatase activity, and interference with calcium movement and cellular membrane Ca(2+) entry.

Burn-induced lung damage in rat is mediated by a nitric oxide/cGMP system

This study was conducted to demonstrate the burn-induced lung neutrophil deposition and damage in rats is affected by the nitric oxide (NO)-dependent downstream cGMP signaling. In experiment 1, 1H-[1,2,4] oxadiazolo [4,3-alpha] quinoxalin-1-one (ODQ) was given (20 mg/kg i.p.) to specific pathogen-free Sprague-Dawley rats immediately postburn to suppress the guanylate cyclase (GC) activity. At 8 h after burn, blood was assayed for the peroxynitrite-mediated dihydrorhodamine 123 (DHR 123) oxidation and lung tissues were harvested for myeloperoxidase (MPO) determination and histological studies. Pulmonary microvascular dysfunction was quantified by measuring the extravasations of Evans blue dye. In experiment 2, Sodium nitroprusside (SNP) was given (2 mM, i.p.) to elevate cGMP levels and ODQ (20 mg/kg, i.p.) or methylene blue (100 microM, i.p.) or saline was given. The animals were sacrificed 4 h after injection and lung tissues were harvested for iNOS mRNA study. The MPO activity in lung, blood DHR 123 oxidation level, and lung permeability increased up to 2-fold, 4-fold, and 2.5-fold after burn. Inhibition of GC by ODQ administration significantly decreased MPO activity, blood DHR 123 oxidation, and lung permeability by 55%, 66%, and 53%, respectively, and markedly decreased the thermal injury-induced perivascular and interstitial inflammatory cell infiltration and septum edema. The protective effects of ODQ were comparable to the use of selective iNOS inhibitor as demonstrated previously. Furthermore, ODQ decreased the burn or SNP-induced iNOS mRNA levels at 4 h after burn. These findings suggest that burn-induced lung dysfunction is mediated by the NO/cGMP system because it is abolished by application of either iNOS inhibitor or GC inhibitor. Also, the beneficial effect of ODQ is partly due to the attenuation of burn-induced iNOS expression by GC inhibition.

Carbon monoxide inhalation protects rat intestinal grafts from ischemia/reperfusion injury

Carbon monoxide (CO), a byproduct of heme catalysis by heme oxygenases, has been shown to exert anti-inflammatory effects. This study examines the cytoprotective efficacy of inhaled CO during intestinal cold ischemia/reperfusion injury associated with small intestinal transplantation. Orthotopic syngenic intestinal transplantation was performed in Lewis rats after 6 hours of cold preservation in University of Wisconsin solution. Three groups were examined: normal untreated controls, control intestinal transplant recipients kept in room air, and recipients exposed to CO (250 ppm) for 1 hour before and 24 hours after surgery. In air grafts, mRNA levels for interleukin-6, cyclooxygenase-2, intracellular adhesion molecule (ICAM-1), and inducible nitric oxide synthase rapidly increased after intestinal transplant. Histopathological analysis revealed severe mucosal erosion, villous congestion, and inflammatory infiltrates. CO effectively blocked an early up-regulation of these mediators, showed less severe histopathological changes, and resulted in significantly improved animal survival of 92% from 58% in air-treated controls. CO also significantly reduced mRNA for proapoptotic Bax, while it up-regulated anti-apoptotic Bcl-2. These changes in CO-treated grafts correlated with well-preserved CD31(+) vascular endothelial cells, less frequent apoptosis/necrosis in intestinal epithelial and capillary endothelial cells, and improved graft tissue blood circulation. Protective effects of CO in this study were mediated via soluble guanylyl cyclase, because 1H-(1,2,4)oxadiazole (4,3-alpha) quinoxaline-1-one (soluble guanylyl cyclase inhibitor) completely reversed the beneficial effect conferred by CO. Perioperative CO inhalation at a low concentration resulted in protection against ischemia/reperfusion injury to intestinal grafts with prolonged cold preservation.

Cyclooxygenase-2 inhibition attenuates lipopolysaccharide-induced cardiovascular failure

The present study aimed to determine the relevance of cyclooxygenase-2 (COX-2)-derived prostanoids for the adverse effects of lipopolysaccharides (LPSs) on cardiovascular function. For this goal, male Sprague-Dawley rats received a single intravenous dose of LPS (10 mg/kg) and were treated with different cyclooxygenase inhibitors. Injection of LPS caused a marked decrease of systolic arterial pressure, from 128 to 79 mm Hg, and a concomitant increase of heart rate, from 380 to 530 minutes(-1). Both the decrease of systemic arterial pressure and the increase of heart rate induced by LPS were almost absent if the animals also received the COX-2 blocker rofecoxib (20 mg/kg), regardless whether the drug was given 1 hour before or 1 hour after LPS. Although plasma and organ levels of prostanoids were lowered by rofecoxib, the characteristic LPS-induced increases of NO synthase II and COX-2 gene expression, as well as of plasma and tissue nitrate/nitrite concentrations, were not affected by rofecoxib. Although rofecoxib treatment did also not change LPS-induced tissue cytokine concentrations, it markedly improved LPS-induced liver damage, as indicated by the decrease of transaminases. Moreover, the overall well-being of the LPS-injected animals improved on concomitant treatment with the COX-2 inhibitor. Taken together, our data suggest that COX-2-derived prostanoids are major mediators for the detrimental effects of LPS on cardiovascular and organ function.

Does methylene blue administration to septic shock patients affect vascular permeability and blood volume?

OBJECTIVE

To assess the effects of the inhibition of guanylate cyclase, an enzyme involved in sepsis-related vascular and myocardial dysfunctions, on hemodynamic variables including blood volume and pulmonary vascular permeability during septic shock.

DESIGN

Prospective, open study with repeated measurements.

SETTING

A medicosurgical intensive care unit of a university hospital.

PATIENTS

Fifteen patients with septic shock associated with persisting hypotension despite conventional treatment including fluid loading, vasopressors, and inotropes.

INTERVENTIONS

A fiberoptic catheter was inserted for the determination of blood and extravascular volumes by the thermal-dye double indicator technique, using indocyanine green (COLD system). A bolus dose of methylene blue (3 mg/kg) was infused intravenously over 10 mins. COLD-derived variables were recorded before methylene blue and 20 mins, 1 hr, and 2 hrs after the end of methylene blue infusion.

MEASUREMENTS AND MAIN RESULTS

Standard hemodynamic and oxygen-derived variables; total, intrathoracic, systolic, and diastolic cardiac blood volumes; extravascular lung water; plasma osmolarity; and lactate and protein concentrations were recorded. Mean arterial and pulmonary artery pressures, systemic and pulmonary vascular resistances, and left ventricular stroke work index increased, and blood lactate transiently decreased after methylene blue (p <.05). The other variables recorded were unchanged during the 2-hr period following methylene blue infusion.

CONCLUSIONS

This study confirmed the acute vasoconstrictive and positive inotropic effects of methylene blue during septic shock. These effects were not associated with changes in blood volume, myocardial diastolic function, or pulmonary vascular permeability assessed by extravascular lung water.

Effect of inhibition of inducible nitric oxide synthase and guanylyl cyclase on endotoxin-induced delay in gastric emptying and intestinal transit in mice

Nitric oxide (NO) is postulated to play a role in endotoxin-induced ileus. We investigated the effect of selective blockade of inducible NO synthase (iNOS) and guanylyl cyclase on endotoxin-induced ileus in mice. Thirty minutes before injection of lipopolysaccharides (LPS), mice were pretreated with L-NAME (N omega-nitro-L-arginine methyl ester, non-selective NOS inhibitor), 1400W (N-(3-(aminomethyl)benzyl)acetamide, selective iNOS inhibitor), ODQ (1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one, guanylyl cyclase inhibitor), dimethyl sulfoxide (DMSO, vehicle), or dexamethasone. After 18 h, general well being deteriorated and the mice developed hypothermia and a significant delay in gastric emptying and intestinal transit as measured by Evans blue. 1400W completely reversed the endotoxin-induced delay in gastric emptying, while L-NAME did not have these beneficial effects. On the contrary, even in control mice, L-NAME delayed gastric emptying. Dexamethasone, DMSO, and ODQ mimicked the effect of 1400W on endotoxin-induced delay in gastric emptying. The endotoxin-induced delay in transit was significantly improved only by 1400W. None of the drugs reversed the hypothermia. In LPS mice treated with L-NAME, the behavior scale increased even further, while it decreased after treatment with 1400W. In conclusion, selective inhibition of iNOS reverses the endotoxin-induced delay in gastric emptying and transit and improves general well being. The pathway used by NO, derived from iNOS, may involve inhibition of guanylyl cyclase or radical scavenging.

New approach to treatment of shock--restitution of vasoreactivity

Our objective was to observe the therapeutic effect of restituting vasoreactivity agent in severe shock. A hemorrhagic shock (HS) model was reproduced in rat and the response of arterioles of spinotrapezius muscle to norepinephrine (NE) in HS was tested. The diameter, blood velocity, and volumetric flow in arteriole, and the mean arterial pressure (MAP) were measured. The therapeutic effect was observed after the treatment of restituting vasoreactivity agent (glybenclamide--an inhibitor of ATP sensitive potassium channel, and tiron--an oxygen free radical scavenger). The arteriolar vasoreactivity was significantly reduced with 15 fold increase of NE threshold 2 h post HS. After treated with restituting agent (RA), the vascular hyporeactivity of rat was apparently recovered, and the increased level of MAP following injection of dopamine was 1.8 times and 1.9 times more than that in NS-treated and DMSO-treated group respectively. After reinfusion of shed blood, the value of systemic blood pressure maintained more than 100 mmHg and volumetric flow in arterioles in RA group were 2 times more than those in NS treated group within the 2 h observation periods. The average survival time in RA treated group was also 1.8 times and 1.6 times longer than that in NS-treated and DMSO-treated group respectively. The restituting vasoreactivity agent is able to recover the lower vasoreactivity with excellent anti-shock effect in severe hemorrhagic shock.

Biliverdin IX is an endogenous inhibitor of soluble guanylyl cyclase

Heme oxygenase (HO) converts heme to carbon monoxide (CO) and biliverdin IX. CO is a weak activator of soluble guanylyl cyclase (SGC), the enzyme that catalyzes the conversion of GTP to the second messenger cGMP. HO overexpression has recently been shown to inhibit production of cGMP by SGC in vivo. The aim of the present study was to investigate a possible influence of biliverdin IX on SGC activity. Using recombinant alpha(1)/beta(1) isoform of SGC, we show an inhibitory effect of biliverdin IX in the micromolar range both on basal and NO stimulated guanylyl cyclase activity. Bilirubin IX which differs from biliverdin IX in two hydrogen atoms had no effect. Biliverdin IX reduced maximal guanylyl cyclase activity (V(max) values) while it had no effect on the K(M) values indicating unchanged affinity towards the substrate GTP. Concentration response experiments using the NO donor, 2,2-diethyl-1-nitroso-oxyhydrazine (DEA/NO), showed that enzyme activities at maximal DEA/NO concentration were reduced by biliverdin IX. The affinity of the NO-donor, DEA/NO, towards SGC was significantly reduced in the presence of biliverdin IX. Biliverdin IX lowered enzyme activity at maximal activator concentrations of YC-1 and protoporphyrin IX (PPIX) while it had no significant effect on the EC(50) values of these two NO independent activators. The inhibitory effect of biliverdin IX on PPIX activated enzyme activity is not shared by ODQ, which indicates that the inhibitory mechanism of biliverdin IX is different from ODQ.

Is nitric oxide overproduction the target of choice for the management of septic shock?

Sepsis is a heterogeneous class of syndromes caused by a systemic inflammatory response to infection. Septic shock, a severe form of sepsis, is associated with the development of progressive damage in multiple organs, and is a leading cause of patient mortality in intensive care units. Despite important advances in understanding its pathophysiology, therapy remains largely symptomatic and supportive. A decade ago, the overproduction of nitric oxide (NO) had been discovered as a potentially important event in this condition. As a result, great hopes arose that the pharmacological inhibition of NO synthesis could be developed into an efficient, mechanism-based therapeutic approach. Since then, an extraordinary effort by the scientific community has brought a deeper insight regarding the feasibility of this goal. Here we present in summary form the present state of knowledge of the biological chemistry and physiology of NO. We then proceed to a systematic review of experimental and clinical data, indicating an up-regulation of NO production in septic shock; information on the role of NO in septic shock, as provided by experiments in transgenic mice that lack the ability to up-regulate NO production; effects of pharmacological inhibitors of NO production in various experimental models of septic shock; and relevant clinical experience. The accrued evidence suggests that the contribution of NO to the pathophysiology of septic shock is highly heterogeneous and, therefore, difficult to target therapeutically without appropriate monitoring tools, which do not exist at present.

Nitric oxide-dependent down-regulation of angiotensin II type 2 receptors during experimental sepsis

OBJECTIVE

The systemic renin-angiotensin system is highly activated during septic shock. This has focused interest in regulation of the adrenal angiotensin II type 2 receptor (AT2) as the target thought to mediate angiotensin II-induced adrenal catecholamine release during experimental sepsis in vivo. In addition, the influence of typical endogenous mediators of sepsis, such as proinflammatory cytokines and nitric oxide, on AT2 receptor expression should be investigated in vitro.

DESIGN

Prospective animal trial followed by a controlled cell culture study.

SETTING

Laboratory of the Department of Anesthesiology.

SUBJECTS

Male Sprague-Dawley rats weighing 200-250 g, PC12 cell line.

INTERVENTIONS

Rats were injected with lipopolysaccharide to stimulate Gram-negative sepsis or lipoteichoic acid to stimulate Gram-positive sepsis. AT2 receptor expression, abundance of the proinflammatory cytokines (interleukin-1beta, tumor necrosis factor-alpha, and interferon-gamma), and nitric oxide synthase II expression have been determined in the adrenal gland. Rat adrenal pheochromocytoma cells were incubated with these cytokines or with the nitric oxide donors sodium nitroprusside or S-nitroso-N-acetylpenicillamine to investigate the regulation of AT2 receptors during severe inflammation on a cellular level.

MEASUREMENTS AND MAIN RESULTS

In the adrenal gland, AT2 receptor expression was down-regulated in both models of sepsis, whereas tissue cytokine concentrations were elevated and nitric oxide synthase II expression was induced. Incubation of PC12 cells with proinflammatory cytokines resulted in a dose-dependent diminished expression of AT2 receptors, which was mimicked by incubation with nitric oxide donors. Blocking of cytokine-induced nitric oxide synthesis by co-incubation of PC12 cells with NG-nitro-l-arginine methyl ester prevented down-regulation of AT2 receptors.

CONCLUSIONS

These findings show that in our model of sepsis, the expression of AT2 receptors in the adrenal gland is down-regulated in a nitric oxide-dependent manner. Because AT2 receptors are thought to be involved in adrenal catecholamine secretion in a stimulatory fashion, the diminished expression of AT2 receptors could play an important role in the pathogenesis of septic shock via impaired angiotensin II-induced adrenal catecholamine release, despite a strong activation of the systemic renin-angiotensin system.

The selective guanylate cyclase inhibitor ODQ reduces multiple organ injury in rodent models of Gram-positive and Gram-negative shock

OBJECTIVE

An enhanced formation of endogenous nitric oxide contributes to the circulatory failure caused by endotoxin (lipopolysaccharide). Many of the biological actions of nitric oxide are mediated by the guanylate cyclase/cyclic guanosine 3prime;,5'-monophosphate system. We recently discovered that two cell wall components, namely lipoteichoic acid and peptidoglycan of the Gram-positive bacterium Staphylococcus aureus, synergize to cause shock and multiple organ dysfunction syndrome in the rat. Here we investigate the effects of a selective guanylate cyclase inhibitor, 1H-(1,2,4)oxadiazole(4,3-alpha)quinoxaline-1-one (ODQ), on the circulatory failure and multiple organ dysfunction syndrome (kidney, liver, lung) caused by a) coadministration of lipoteichoic acid and peptidoglycan (Gram-positive shock) or b) lipopolysaccharide (Gram-negative shock) in the anesthetized rat. Furthermore, we investigated whether ODQ scavenges superoxide anions and/or hydroxyl radicals.

DESIGN

The in vivo portion of the study was a prospective, randomized, controlled animal study. The in vitro portion included a) cultured ventricular myoblasts of the rat, H9c2(2-1) cells, and b) a cell free superoxide anion assay system.

SETTING

University-based research laboratory.

SUBJECTS

Seventy-five anesthetized, male Wistar rats were used for the in vivo study.

INTERVENTIONS

For the in vivo portion of the study, after surgical preparation, anesthetized rats were observed for 6 hrs. All rats were pretreated and received an intravenous infusion of saline (1.5 mL.kg-1.hr-1), which was maintained throughout the experiment. The rats were assigned to nine groups. Group 1 contained control rats (sham) subjected to 2 mL/kg saline intraperitoneally, 2 hrs before the experiment (n = 7). Group 2 contained control rats (sham) that received 2 mg/kg ODQ intraperitoneally, 2 hrs before the experiment (n = 9). Group 3 contained control rats (sham) that received 2 mL/kg dimethyl sulfoxide, 30% v/v in saline intraperitoneally, as a vehicle for ODQ, 2 hrs before the experiment (n = 6). In group 4 rats, Gram-positive shock was induced by coadministration of lipoteichoic acid (3 mg/kg intravenously) and peptidoglycan (10 mg/kg intravenously) (n = 10). In group 5, rats were pretreated with ODQ (as described previously) before lipoteichoic acid/peptidoglycan (n = 9). In group 6, rats were pretreated with dimethyl sulfoxide (as described previously) before lipoteichoic acid/peptidoglycan (n = 7). In group 7, Gram-negative shock was induced by lipopolysaccharide (6 mg/kg intravenously) (n = 11). In group 8, rats were pretreated with ODQ (as described previously) before lipopolysaccharide (n = 8). In group 9, rats were pretreated with dimethyl sulfoxide (as described previously) before lipopolysaccharide (n = 8). For the in vitro portion of the study, rat cells were preincubated with vehicle (saline and/or dimethyl sulfoxide) and ODQ (0.1 microM to 1 mM) for 2 hrs. The cells then were exposed to H2O2 (1 mM) for 4 hrs at 37 degrees C, after which time cell viability was determined by measuring the mitochondrial-dependent reduction of 3-(4,5-di-methyliazol-2-yl)-2,5-diphenyltetrazolium bromide to blue formazan. Next, an aqueous solution was incubated with ODQ (as described previously), and superoxide anions were produced by using a hypoxanthine/xanthine-oxidase assay. The chemiluminescence assay was used to evaluate any potential antioxidative effects of ODQ.

MEASUREMENTS AND MAIN RESULTS

In vivo, administration of lipoteichoic acid/peptidoglycan or lipopolysaccharide resulted within 6 hrs in hypotension, acute renal dysfunction, hepatocellular injury, and lung injury. Pretreatment of rats with ODQ attenuated the renal dysfunction, lung injury, and hepatocellular injury caused by lipoteichoic acid/peptidoglycan or lipopolysaccharide. In vitro, administration of H2O2 (for 4 hrs) to rat cardiomyoblasts decreased mitochondrial respiration attributable to generation of hydroxyl radicals. Pretreatment of cells with ODQ did not abolish this cell injury. In addition, ODQ did not scavenge superoxide anions.

CONCLUSIONS

These results imply that ODQ, an inhibitor of guanylate cyclase, reduces the multiple organ injury and dysfunction caused by wall fragments of Gram-positive or Gram-negative bacteria in the anesthetized rat. The observed protective effects of ODQ are not attributable to the ability of ODQ to reduce the formation or the effects of superoxide anions or hydroxyl radicals.

Endotoxin-induced vascular hyporesponsiveness in rat aorta: in vitro effect of aminoguanidine

The current study was designed to evaluate the endotoxin-induced alterations of the mechanisms involved in Ca(2+)handling within the rat thoracic aorta and further to examine whether in vitro inhibition of inducible nitric oxide synthase (iNOS) by aminoguanidine would account for this effect or not. Endothelium denuded aortic rings from rats injected with lipopolysaccharide (LPS) (5 mg kg(-1), i.p. 18 h prior to functional studies) or saline were mounted in isolated organ baths. Various experimental conditions were studied on paired rings of the same animal which were incubated in the presence or absence of aminoguanidine (100 microM). Phenylephrine contractility in Ca(2+)-containing buffer or in Ca(2+)-free buffer, contractions induced by K(+)depolarization and CaCl(2)in depolarized muscle and by caffeine exposure were significantly decreased in LPS-treated rings and were reversed by aminoguanidine exposure. Aminoguanidine also improved the contractions recorded while switching the Ca(2+)-free buffer to Ca(2+)-containing buffer. We conclude that endotoxin induces a generalized contractile defect in vascular smooth muscle including impairment in the influx of extracellular Ca(2+)and release of Ca(2+)from intracellular stores. An increase in iNOS activation leading to excessive nitric oxide synthesis, possibly non-endothelial in origin, may account for this defect.

Paradoxical rescue from ischemic lung injury by inhaled carbon monoxide driven by derepression of fibrinolysis

Carbon monoxide (CO) can arrest cellular respiration, but paradoxically, it is synthesized endogenously by heme oxygenase type 1 (Ho-1) in response to ischemic stress. Ho-1-deficient (Hmox1-/-) mice exhibited lethal ischemic lung injury, but were rescued from death by inhaled CO. CO drove ischemic protection by activating soluble guanylate cyclase and thereby suppressed hypoxic induction of the gene encoding plasminogen activator inhibitor-1 (PAI-1) in mononuclear phagocytes, which reduced accrual of microvascular fibrin. CO-mediated ischemic protection observed in wild-type mice was lost in mice null for the gene encoding PAI-1 (Serpine1). These data establish a fundamental link between CO and prevention of ischemic injury based on the ability of CO to derepress the fibrinolytic axis. These data also point to a potential therapeutic use for inhaled CO.

Hemodynamic and cardiovascular effects of nitric oxide modulation in the therapy of septic shock

Nitric oxide synthase (NOS) of the inducible subtype (iNOS) plays a pivotal role in vasodilation associated with sepsis. Various biochemical pathways are involved, revealing targets for inhibiting the consequence of iNOS activation. Interactions of transcription factors, inducers, cofactors, and regulators of iNOS are important in understanding the development of iNOS inhibitors. Inhibition through L-arginine analogs, depletion of arginine, inhibition of cofactors, modulating gene transcription, and scavenging nitric oxide have been studied. Human studies were conducted only with nonselective L-arginine analogs. Reduction of mortality from sepsis was not reported. It is anticipated that iNOS-specific compounds will be clinically useful. The focus of future human trials will be on these agents. Although ideal therapy for treating vasodilation from sepsis is not available, research into the pathophysiology of NOS in sepsis clarified the complexities surrounding this therapeutic dilemma.