Role of neuronal nitric oxide synthase in ovine sepsis model

7-nitroindazol-loaded nanoemulsions: Preparation, characterization and its improved inhibitory effect on nitric oxide synthase-1

Nitric oxide (NO) participates in several physiological processes such as maintenance of blood pressure, host defense, neurotransmission, inhibition of platelet aggregation and learning and memory. NO is also involved in several diseases or dysfunctions in the cardiovascular, central nervous and musculoskeletal systems. NO also has been shown to be a major player in sepsis. NOS-1-derived NO has been shown to be a relevant species in physiology but also is an important element in pathology. There exist some NOS-1 inhibitors and among of them, 7-nitroindazole has been used for its in vivo selectivity. However, 7-NI has a very short half-life (∼2 h) and a poor water solubility. In this study, we describe the preparation and characterization of 7-NI-loaded nanoemulsions (NE_7-NI). The chemical stability of 7-NI was greatly increased and the drug release rate could be controlled after nanoemulsification. NE_7-NI reduced NO production in a long-lasting manner in vascular smooth muscle cells and skeletal muscle, without cytotoxicity. Our results evidenced that nanoemulsification approach increases the effective action time of 7-NI, rendering a suitable dosage form, which may be an interesting tool to study the role of NOS-1 in physiology and disease.

Inhibition of neuronal nitric oxide synthase activity does not alter vasopressin secretion in septic rats

BACKGROUND/PURPOSE

During the early phase of sepsis, hypotension is accompanied by increase of plasma vasopressin hormone (AVP) levels, which decline during the late phase. This hypotension is due in part to increase of nitric oxide (NO) synthesis by nitric oxide synthase (NOS) enzyme. Neuronal isoform of this enzyme (nNOS) is present in vasopressinergics neurons of hypothalamus, but its role in vasopressin secretion during sepsis is unknown.

METHODS

We evaluated the role of nNOS in NO production and vasopressin secretion during sepsis. Wistar rats received 7-nitroindazole (50 mg/kg, i.p.), an inhibitor of nNOS activity, or vehicle and were submitted to septic stimulus by cecal ligation and puncture (CLP). At the time points 0, 4, 6, 18 and 24 h after sepsis induction the animals were decapitated and neurohypophysis and hypothalamus were removed for analysis of vasopressin content and NOS activity, respectively. Hematocrit, serum sodium, osmolality, proteins and plasmatic AVP were quantified.

RESULTS

Mortality was not affected by 7-nitroindazole (7-NI). Sodium and plasma proteins levels decreased after CLP and the treatment anticipated the protein loss, and delayed serum sodium decrease. Septic animals treated with 7-NI showed decrease of osmolality 4 h after CLP. Nitric oxide synthase activity in hypothalamus increased at 4 and 24 h after CLP and was reduced with 7-NI. Neurohypophysis content of AVP diminished after CLP and 7-NI did not alter this parameter. Plasma AVP levels increased at 6 h and decreased 18 and 24 h after CLP. Treatment with 7-NI did not alter plasma vasopressin levels.

CONCLUSION

We concluded that nNOS does not have a substantial role in vasopressin secretion during experimental sepsis.

C-Type Natriuretic Peptide Induces Anti-contractile Effect Dependent on Nitric Oxide, Oxidative Stress, and NPR-B Activation in Sepsis

AIMS

To evaluate the role of nitric oxide, reactive oxygen species (ROS), and natriuretic peptide receptor-B activation in C-type natriuretic peptide-anti-contractile effect on Phenylephrine-induced contraction in aorta isolated from septic rats.

METHODS AND RESULTS

Cecal ligation and puncture (CLP) surgery was used to induce sepsis in male rats. Vascular reactivity was conducted in rat aorta and resistance mesenteric artery (RMA). Measurement of survival rate, mean arterial pressure (MAP), plasma nitric oxide, specific protein expression, and localization were evaluated. Septic rats had a survival rate about 37% at 4 h after the surgery, and these rats presented hypotension compared to control-operated (Sham) rats. Phenylephrine-induced contraction was decreased in sepsis. C-type natriuretic peptide (CNP) induced anti-contractile effect in aortas. Plasma nitric oxide was increased in sepsis. Nitric oxide-synthase but not natriuretic peptide receptor-B expression was increased in septic rat aortas. C-type natriuretic peptide-anti-contractile effect was dependent on nitric oxide-synthase, ROS, and natriuretic peptide receptor-B activation. Natriuretic peptide receptor-C, protein kinase-Cα mRNA, and basal nicotinamide adenine dinucleotide phosphate (NADPH)-dependent ROS production were lower in septic rats. Phenylephrine and CNP enhanced ROS production. However, stimulated ROS production was low in sepsis.

CONCLUSION

CNP induced anti-contractile effect on Phenylephrine contraction in aortas from Sham and septic rats that was dependent on nitric oxide-synthase, ROS, and natriuretic peptide receptor-B activation.

Arginine and citrulline and the immune response in sepsis

Arginine, a semi-essential amino acid is an important initiator of the immune response. Arginine serves as a precursor in several metabolic pathways in different organs. In the immune response, arginine metabolism and availability is determined by the nitric oxide synthases and the arginase enzymes, which convert arginine into nitric oxide (NO) and ornithine, respectively. Limitations in arginine availability during inflammatory conditions regulate macrophages and T-lymfocyte activation. Furthermore, over the past years more evidence has been gathered which showed that arginine and citrulline deficiencies may underlie the detrimental outcome of inflammatory conditions, such as sepsis and endotoxemia. Not only does the immune response contribute to the arginine deficiency, also the impaired arginine de novo synthesis in the kidney has a key role in the eventual observed arginine deficiency. The complex interplay between the immune response and the arginine-NO metabolism is further underscored by recent data of our group. In this review we give an overview of physiological arginine and citrulline metabolism and we address the experimental and clinical studies in which the arginine-citrulline NO pathway plays an essential role in the immune response, as initiator and therapeutic target.

Protective role of peroxisome proliferator-activated receptor-β/δ against pulmonary oxygen toxicity mediated through changes in NOS expression levels

Recent studies have demonstrated that peroxisome proliferator-activated receptor-beta/delta (PPAR-β/δ) has a protective effect during lung injury induced by bleomycin and polymicrobial sepsis, but its function in pulmonary oxygen toxicity is unknown. In this study, we used GW0742, a PPAR-β/δ agonist, and GSK0660, a PPAR-β/δ antagonist, to test the role of PPAR-β/δ in lung injury due to hyperbaric oxygen (HBO2) exposure. Lung injury was induced in rats by HBO2 exposure (2.3 ATA, 100%O2, 8 hours). Sixty male Sprague-Dawley rats were randomly divided into 6 groups: air+vehicle, air+GW0742, air+GSK0660, HBO2+vehicle, HBO2+GW0742, and HBO2+GSK0660. Rats were injected with vehicle or GW0742 (0.3 mg/kg, i.p.) or GSK0660 (1 mg/kg, i.p.) at 1 hour, 6 hours, and 12 hours before either air or oxygen exposure. Administration of GW0742 to rats exposed to HBO2 significantly reduced the observed lung injury, extravascular lung water, total protein levels in bronchoalveolar lavage fluid, and the levels of iNOS and nNOS in the lungs when compared to untreated rats exposed to HBO2. Treatment of rats with GSK0660 exacerbated lung injury and elevated the levels of nNOS and eNOS in the lungs. In addition, nNOS and eNOS knock-out mice were examined. The results indicated that after HBO2 exposure, the lung injury was obviously decreased in the nNOS(-/-)+GSK0660 mice compared to the wild-type +GSK0660 mice; furthermore, administration of GSK0660 significantly elevated the lung injury in the eNOS(-/-) mice. Collectively, these data indicate that PPAR-β/δ activation can protect against pulmonary oxygen toxicity in the lungs of rats through changes in the expression of NOS.

Human mesenchymal stem cells reduce the severity of acute lung injury in a sheep model of bacterial pneumonia

BACKGROUND

Human bone marrow-derived mesenchymal stem (stromal) cells (hMSCs) improve survival in mouse models of acute respiratory distress syndrome (ARDS) and reduce pulmonary oedema in a perfused human lung preparation injured with Escherichia coli bacteria. We hypothesised that clinical grade hMSCs would reduce the severity of acute lung injury (ALI) and would be safe in a sheep model of ARDS.

METHODS

Adult sheep (30-40 kg) were surgically prepared. After 5 days of recovery, ALI was induced with cotton smoke insufflation, followed by instillation of live Pseudomonas aeruginosa (2.5×10(11) CFU) into both lungs under isoflurane anaesthesia. Following the injury, sheep were ventilated, resuscitated with lactated Ringer's solution and studied for 24 h. The sheep were randomly allocated to receive one of the following treatments intravenously over 1 h in one of the following groups: (1) control, PlasmaLyte A, n=8; (2) lower dose hMSCs, 5×10(6) hMSCs/kg, n=7; and (3) higher-dose hMSCs, 10×10(6) hMSCs/kg, n=4.

RESULTS

By 24 h, the PaO2/FiO2 ratio was significantly improved in both hMSC treatment groups compared with the control group (control group: PaO2/FiO2 of 97±15 mm Hg; lower dose: 288±55 mm Hg (p=0.003); higher dose: 327±2 mm Hg (p=0.003)). The median lung water content was lower in the higher-dose hMSC-treated group compared with the control group (higher dose: 5.0 g wet/g dry [IQR 4.9-5.8] vs control: 6.7 g wet/g dry [IQR 6.4-7.5] (p=0.01)). The hMSCs had no adverse effects.

CONCLUSIONS

Human MSCs were well tolerated and improved oxygenation and decreased pulmonary oedema in a sheep model of severe ARDS.

TRAIL REGISTRATION NUMBER

NCT01775774 for Phase 1. NCT02097641 for Phase 2.

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.

Heterogeneity of the effects of combined nitric oxide synthase inhibition on organ perfusion in ovine sepsis

INTRODUCTION

Previous studies demonstrated beneficial effects of early neuronal nitric oxide synthase (nNOS) and subsequent inducible NOS (iNOS) inhibition on the development of multiple organ dysfunctions in septic sheep. However, the effects of NOS inhibition on regional blood flow remained undetermined. The current study was conducted to assess the effects of combined NOS inhibition on blood flow to various organs in an ovine sepsis model.

METHODS

Eighteen adult, female sheep were randomly allocated to the following groups: (1) sham-injured, non-treated group, (2) injured (smoke inhalation and instillation of Pseudomonas aeruginosa into the lungs), non-treated group (control), and (3) injured, treated group (specific nNOS inhibition from 1 h to 12 h and iNOS inhibition from 12 h to 24 h post-injury). Fluorescent microspheres were injected at baseline and various time points post-injury. At the end of the 24-h experimental period, tissue from various organs was harvested.

RESULTS

Blood flow to the ileum was significantly increased in the control group from 12 h to 24 h versus sham (P < 0.05). This increase was attenuated in the treatment group (P < 0.05). In contrast, blood flow to the pancreas was significantly increased in the treatment group after 12 h and 24 h versus both sham and control (P < 0.05). Blood flow to the spleen was significantly lower after 24h in the control group versus sham and treatment (P < 0.05 both).

CONCLUSIONS

Combined NOS inhibition significantly influenced the pathologically altered organ perfusion during ovine sepsis. However, this treatment strategy showed heterogeneous effects on organ perfusion, perhaps dependent on the sepsis-related degree of NO production and ensuing changes in regional flow.

Effects of lipopolysaccharide on the neuronal control of mesenteric vascular tone in rats: mechanisms involved

The aim of the present study was to investigate the effects of lipopolysaccharide (LPS) on the contractile response induced by electrical field stimulation (EFS) in rat mesenteric segments, as well as the mechanisms involved. Effects of LPS incubation for 2 or 5 h were studied in mesenteric segments from male Wistar rats. Vasomotor responses to EFS, nitric oxide (NO) donor DEA-NO, and noradrenaline (NA) were studied. Phosphorylated neuronal NO synthase protein expression was analyzed, and NO, superoxide anion (O2·), and peroxynitrite releases were also determined. Lipopolysaccharide increased EFS-induced vasoconstriction at 2 h. This increase was lower after 5-h preincubation. N-nitro-L-arginine methyl ester increased vasoconstrictor response only in control segments. Vasodilator response to DEA-NO was increased by LPS after 5-h preincubation and was decreased by O2· scavenger tempol. Basal NO release was increased by LPS. Electrical field stimulation-induced NO release was reduced by LPS compared with control conditions. Lipopolysaccharide exposure increased both O2· and peroxynitrite release. Vasoconstriction to exogenous NA was markedly increased by LPS compared with control conditions after 2-h incubation and remained unchanged after 5-h incubation. Short-term exposure of rat mesenteric arteries to LPS produced a time-dependent enhanced contractile response to EFS. The early phase (2 h) was associated to a reduction in NO from neuronal NO synthase and an enhanced response to NA. After 5 h of LPS exposure, this enhancement was reduced, because of restoration of the adrenergic component and maintenance of the nitrergic reduction.

Mechanistic aspects of inducible nitric oxide synthase-induced lung injury in burn trauma

INTRODUCTION

Although the beneficial effects of inducible nitric oxide synthase (iNOS) inhibition in acute lung injury secondary to cutaneous burn and smoke inhalation were previously demonstrated, the mechanistic aspects are not completely understood. The objective of the present study is to describe the mechanism(s) underlying these favourable effects. We hypothesised that iNOS inhibition prevents formation of excessive reactive nitrogen species and attenuates the activation of poly(ADP) (poly(adenosine diphosphate)) ribose polymerase, thus mitigating the severity of acute lung injury in sheep subjected to combined burn and smoke inhalation.

METHODS

Adult ewes were chronically instrumented for a 24-h study and allocated to groups: sham: not injured, not treated, n = 6; control: injured, not treated, n = 6; and BBS-2: injured treated with iNOS dimerisation inhibitor BBS-2, n = 6. Control and BBS-2 groups received 40% total body surface area 3rd-degree cutaneous burn and cotton smoke insufflation into the lungs under isoflurane anaesthesia.

RESULTS

Treatment with iNOS inhibitor BBS-2 significantly improved pulmonary gas exchange (partial pressure of oxygen in the blood/fraction of inspired oxygen (PaO₂/FiO₂) 409 ± 43 mmHg vs. 233 ± 50 mmHg in controls, p < 0.05) and reduced airway pressures (peak pressure 20 ± 1 cm H₂O vs. 28 ± 2 cm H₂O in controls, p < 0.05) and lung water content (lung wet-to-dry ratio 4.1 ± 0.3 vs. 5.2 ± 0.2 in controls, p < 0.05) 24h after the burn and smoke injury. BBS-2 significantly reduced the increases in lung lymph nitrite/nitrate (10 ± 3 μM vs. 26 ± 6 μM in controls, p < 0.05) and 3-nitrotyrosine (109 ± 11 (densitometry value) vs. 151 ± 18 in controls, p < 0.05). Burn/smoke-induced increases in lung tissue nitrite/nitrate, poly(ADP)ribose polymerase, nuclear factor-κB (NF-κB) activity, myeloperoxidase activity and malondialdehyde formation and interleukin (IL)-8 expression were also attenuated with BBS-2.

CONCLUSIONS

The results provide strong evidence that BBS-2 ameliorated acute lung injury by inhibiting the inducible nitric oxide synthase/reactive nitrogen species/poly(ADP-ribose) polymerase (iNOS/RNS/PARP) pathway.

Right man, right time, right place?--on the time course of the mediator orchestra in septic shock

Appropriate timing of treatment assumes particular importance in critical care. Lange and colleagues recently reported on the time course of the different nitric oxide synthase (NOS) isoforms, nitrosative stress, and poly(ADP-ribosylation) during Pseudomonas aeruginosa pneumonia-induced ovine septic shock. Initially, endothelial NOS expression was increased together with markers of peroxynitrite formation, DNA damage, and nuclear factor-kappa-B activation. Later on, measurable NOS activity and nitric oxide production resulted mainly from inducible NOS activation. These results emphasize the need for long-term, large-animal studies investigated over days so that future therapeutic interventions can be better tailored and matched to the exact time course of the activation of the mediator orchestra.

Time course of nitric oxide synthases, nitrosative stress, and poly(ADP ribosylation) in an ovine sepsis model

Introduction

Different isoforms of nitric oxide synthases (NOS) and determinants of oxidative/nitrosative stress play important roles in the pathophysiology of pulmonary dysfunction induced by acute lung injury (ALI) and sepsis. However, the time changes of these pathogenic factors are largely undetermined.

Methods

Twenty-four chronically instrumented sheep were subjected to inhalation of 48 breaths of cotton smoke and instillation of live Pseudomonas aeruginosa into both lungs and were euthanized at 4, 8, 12, 18, and 24 hours post-injury. Additional sheep received sham injury and were euthanized after 24 hrs (control). All animals were mechanically ventilated and fluid resuscitated. Lung tissue was obtained at the respective time points for the measurement of neuronal, endothelial, and inducible NOS (nNOS, eNOS, iNOS) mRNA and their protein expression, calcium-dependent and -independent NOS activity, 3-nitrotyrosine (3-NT), and poly(ADP-ribose) (PAR) protein expression.

Results

The injury induced severe pulmonary dysfunction as indicated by a progressive decline in oxygenation index and concomitant increase in pulmonary shunt fraction. These changes were associated with an early and transient increase in eNOS and an early and profound increase in iNOS expression, while expression of nNOS remained unchanged. Both 3-NT, a marker of protein nitration, and PAR, an indicator of DNA damage, increased early but only transiently.

Conclusions

Identification of the time course of the described pathogenetic factors provides important additional information on the pulmonary response to ALI and sepsis in the ovine model. This information may be crucial for future studies, especially when considering the timing of novel treatment strategies including selective inhibition of NOS isoforms, modulation of peroxynitrite, and PARP.

Pulmonary vascular permeability changes in an ovine model of methicillin-resistant Staphylococcus aureus sepsis

Introduction

Endothelial dysfunction is a hallmark of sepsis, associated with lung transvascular fluid flux and pulmonary dysfunction in septic patients. We tested the hypothesis that methicillin-resistant Staphylococcus aureus (MRSA) sepsis following smoke inhalation increases pulmonary transvascular fluid flux via excessive nitric oxide (NO) production.

Methods

Ewes were chronically instrumented, and randomised into either a control or MRSA sepsis (MRSA and smoke inhalation) group.

Results

Pulmonary function remained stable in the control group, whereas the MRSA sepsis group developed impaired gas exchange and significantly increased lung lymph flow, permeability index and bloodless wet-to-dry weight-ratio (W/D ratio). The plasma nitrate/nitrite (NOx) levels, lung inducible nitric oxide synthases (iNOS) and endothelial nitric oxide synthases (eNOS), vascular endothelial growth factor (VEGF) protein expressions and poly-(ADP)-ribose (PAR) were significantly increased by MRSA challenge.

Conclusions

These results provide evidence that excessive NO production may mediate pulmonary vascular hyperpermeability in MRSA sepsis via up regulation of reactive radicals and VEGF.