Nitric oxide in shock

A novel antihypoglycemic role of inducible nitric oxide synthase in liver inflammatory response induced by dietary cholesterol and endotoxemia

AIMS

The current study aim was to elucidate the antihypoglycemic role and mechanism of inducible nitric oxide synthase (iNOS) under inflammatory stress.

METHODS

Liver inflammatory stress was induced in wild-type (WT) and iNOS-knockout (iNOS(-/-)) mice by lipopolysaccharide (LPS) (5 mg/kg) with and without the background of nonalcoholic steatohepatitis (NASH)-Induced by high cholesterol diet (HCD, 6 weeks).

RESULTS

HCD led to steatohepatitis in WT and iNOS(-/-) mice. LPS administration caused marked liver inflammatory damage only in cholesterol-fed mice, which was further exacerbated in the absence of iNOS. Glucose homeostasis was significantly impaired and included fatal hypoglycemia and inhibition of glycogen decomposition. In iNOS(-/-) hypoxia-inducible factor-1 (HIF1), signaling was impaired compared to control WT. Using hydrodynamic gene transfer method HIF1α was expressed in the livers of iNOS(-/-) mice, and significantly ameliorated cholesterol and LPS-induced liver damage. WT mice overexpressing HIF1α exhibited higher blood glucose levels and lower glycogen contents after LPS injection. Conversely, induction of HIF1α was not effective in preventing LPS-induced glucose lowering effect in iNOS(-/-) mice. The critical role of NO signaling in hepatocytes glucose output mediated by HIF1 pathway was also confirmed in vitro. Results also demonstrated increased oxidative stress and reduced heme oxygenase-1 mRNA in the livers of iNOS(-/-) mice. Furthermore, the amounts of plasma tumor necrosis factor-α (TNFα) and intrahepatic TNFα mRNA were significantly elevated in the absence of iNOS.

INNOVATION AND CONCLUSION

These data highlight the essential role of iNOS in the glycemic response to LPS in NASH conditions and argues for the beneficial effects of iNOS.

Nitric oxide production by endotoxin preparations in TLR4-deficient mice

Sepsis and septic shock result from an exacerbated systemic inflammatory reaction to infection. Their incidence is rising, and they have recently become the main cause of death in intensive care units. Septic shock is defined as sepsis accompanied by life-threatening refractory hypotension, for which excessive nitric oxide (NO), produced by inducible NO synthase iNOS, is thought responsible. LPS, a vital outer membrane component of Gram-negative bacteria, mimics most of the septic effects and is widely used as a model for septic shock. TLR4 is the signal-transducing receptor for LPS, evidenced by the resistance of TLR4-deficient C3H/HeJ and C57BL/10ScNJ mice. As expected, we found that TLR4 deficiency precludes LPS-induced cytokine production, independent of the purity of the LPS preparation. However, various conventional LPS preparations induced NO in TLR4-deficient mice to the same level as in control animals, while ultrapure LPS did not, indicating the presence of NO-producing contaminant(s). Nevertheless, despite identical iNOS induction pattern and systemic NO levels, the contaminant does not cause hypotension, hypothermia, or any other sign of morbidity. Using mice deficient for TLR2, TRL3, TLR4, TRL2x4, TLR9, MyD88 or TRIF, we found that the contaminant signals via TLR2 and MyD88. In conclusion, conventional LPS preparations generally used in endotoxic shock research contain TLR2 agonists that induce iNOS and high levels of systemic NO as such, and synergize with LPS towards the production of pro-inflammatory cytokines, morbidity and mortality. Surprisingly, the excessive iNOS-derived systemic NO production induced by impure LPS in TLR4⁻/⁻ is not accompanied by hypotension or morbidity.

TLR2 activation causes no morbidity or cardiovascular failure, despite excessive systemic nitric oxide production

AIMS

Septic shock is the leading cause of death in intensive care units worldwide, resulting from a progressive systemic inflammatory reaction causing cardiovascular and organ failure. Nitric oxide (NO) is a potent vasodilator and inhibition of NO synthases (NOS) can increase blood pressure in septic shock. However, NOS inhibition does not improve outcome, on the contrary, and certain NO donors may even provide protection. In addition, NOS produce superoxide in case of substrate or cofactor deficiency or oxidation. We hypothesized that excessive systemic iNOS-derived NO production is insufficient to trigger cardiovascular failure and shock.

METHODS AND RESULTS

We found that the systemic injection with various synthetic Toll-like receptor-2 (TLR2), TLR3, or TLR9 agonists triggered systemic NO production identical to that of lipopolysaccharide (LPS) or tumour necrosis factor. In contrast to the latter, however, these agonists did not cause hypothermia or any other signs of discomfort or morbidity, and inflammatory cytokine production was low. TLR2 stimulation with the triacylated lipopeptide Pam3CSK4 not only caused identical NO levels in circulation, but also identical iNOS expression patterns as LPS. Nevertheless, Pam3CSK4 did not cause hypotension, bradycardia, reduced blood flow, or inadequate tissue perfusion in the kidney or the liver.

CONCLUSION

We demonstrate that excessive iNOS-derived NO in circulation is not necessarily linked to concomitant cardiovascular collapse, morbidity, or mortality. As such, our data indicate that the central role of iNOS-derived NO in inflammation-associated cardiovascular failure may be overestimated.

Role of the venous return in critical illness and shock: part II-shock and mechanical ventilation

OBJECTIVE

To provide a conceptual and clinical review of the physiology of the venous system as it is related to cardiac function in health and disease.

DATA

An integration of venous and cardiac physiology under normal conditions, critical illness, and resuscitation.

SUMMARY

The usual clinical teaching of cardiac physiology focuses on left ventricular pathophysiology and pathology. Due to the wide array of shock states dealt with by intensivists, an integrated approach that takes into account the function of the venous system and its interaction with the right heart may be more useful. In part II of this two-part review, we describe the physiology of venous return and its interaction with the right heart function as it relates to mechanical ventilation and various shock states including hypovolemic, cardiogenic, obstructive, and septic shock. In particular, we demonstrate how these shock states perturb venous return/right heart interactions. We also show how compensatory mechanisms and therapeutic interventions can tend to return venous return and cardiac output to appropriate values.

CONCLUSION

An improved understanding of the role of the venous system in pathophysiologic conditions will allow intensivists to better appreciate the complex circulatory physiology of shock and related therapies. This should enable improved hemodynamic management of this disorder.

Evaluation of the effects of ozone therapy on Escherichia coli-induced cytitis in rat

OBJECTIVES

The aim of the study was to investigate the effect of ozone on oxidative/nitrosative stress and bladder injury caused by Escherichia coli in rat bladder.

METHODS

Twenty-one Wistar-Albino-type female rats included in the study were divided into three groups of equal number: (1) sham operation (control), (2) E. coli-only (EC), (3) EC + ozone. After ozone therapy for 3 days, urine and tissue samples were obtained for biochemical, microbiological, and histopathological analysis.

RESULTS

Tissue malondialdehyde (MDA), myeloperoxidase (MPO), and nitric oxide (NO) level were increased, whereas superoxide dismutase (SOD) and glutathione peroxidase (GPx) activity was decreased in the EC group. MDA, MPO, and NO levels were decreased, whereas SOD, GPx activity was increased in the ozone-treated group. Also, there was no bacterial translocation in this group.

CONCLUSION

The results of the present study suggest that ozone may be used as an agent to protect the bladder from oxidative/nitrosative stress occurring in cystitis.

Nitric oxide suppresses NLRP3 inflammasome activation and protects against LPS-induced septic shock

Inflammasomes are multi-protein complexes that trigger the activation of caspase-1 and the maturation of interleukin-1β (IL-1β), yet the regulation of these complexes remains poorly characterized. Here we show that nitric oxide (NO) inhibited the NLRP3-mediated ASC pyroptosome formation, caspase-1 activation and IL-1β secretion in myeloid cells from both mice and humans. Meanwhile, endogenous NO derived from iNOS (inducible form of NO synthase) also negatively regulated NLRP3 inflammasome activation. Depletion of iNOS resulted in increased accumulation of dysfunctional mitochondria in response to LPS and ATP, which was responsible for the increased IL-1β production and caspase-1 activation. iNOS deficiency or pharmacological inhibition of NO production enhanced NLRP3-dependent cytokine production in vivo, thus increasing mortality from LPS-induced sepsis in mice, which was prevented by NLRP3 deficiency. Our results thus identify NO as a critical negative regulator of the NLRP3 inflammasome via the stabilization of mitochondria. This study has important implications for the design of new strategies to control NLRP3-related diseases.

Generation of nitric oxide and reactive oxygen species by neutrophils and monocytes from septic patients and association with outcomes

In this study, our aims were to evaluate the reactive oxygen species (ROS) and nitric oxide (NO) generation by monocytes and neutrophils from septic patients and to correlate their levels with clinical outcomes. Forty-nine septic patients and 19 healthy volunteers were enrolled in the study. The ROS and NO production was quantified in monocytes and neutrophils in whole blood by flow cytometry, constitutively, and after stimulation with Staphylococcus aureus and Pseudomonas aeruginosa. Nitric oxide production by monocytes was higher in septic patients compared with healthy volunteers for all conditions and by neutrophils at baseline, and ROS generation in monocytes and neutrophils was higher in septic patients than in healthy volunteers for all conditions. Nitric oxide production by monocytes and neutrophils was decreased at day 7 compared with that at admission (day 0) in survivors at baseline and after stimulation with S. aureus. Reactive oxygen species production by the monocytes and neutrophils was decreased in survivors at day 7 compared with day 0 under all conditions, except by neutrophils at baseline. No difference was found in NO and ROS generation by monocytes and neutrophils between day 7 and day 0 in nonsurvivors. Generation of NO and ROS by neutrophils and monocytes is increased in septic patients, and their persistence is associated with poor outcome.

NS-398 reverses hypotension in endotoxemic rats: contribution of eicosanoids, NO, and peroxynitrite

We have previously demonstrated that inhibition of vasodilator prostanoids, PGI2 and PGE2, and nitric oxide (NO) synthesis by a selective cyclooxygenase-2 (COX-2) inhibitor, NS-398, restores blood pressure as a result of increased systemic and renal levels of 20-hydroxyeicosatetraenoic acid (20-HETE) in endotoxemic rats. The aim of this study was to further investigate the effects of NS-398 on the changes in expression and/or activity of COX-2, cytochrome P450 4A1 (CYP4A1), inducible NO synthase (iNOS), and peroxynitrite formation in serum, renal, cardiac, and/or vascular tissues of lipopolysaccharide (LPS)-treated rats. LPS (10mg/kg, i.p.)-induced decrease in blood pressure was associated with increased protein levels of COX-2, iNOS, and nitrotyrosine in kidney, heart, thoracic aorta, and superior mesenteric artery. The activities of COX-2 and iNOS as well as levels of PGI2, PGE2, and nitrotyrosine were also increased in the systemic circulation and renal, cardiac, and vascular tissues of LPS-treated rats. In contrast, renal, cardiac, and vascular CYP4A1 protein expression as well as systemic and tissue levels of 20-HETE were decreased in endotoxemic rats. These effects of LPS, except COX-2 protein expression, were prevented by NS-398 (10 mg/kg, i.p.), given 1h after injection of LPS. These data suggest that COX-2-derived vasodilator prostanoids, PGI2 and PGE2, produced during endotoxemia increase iNOS protein expression and activity as well as peroxynitrite formation resulting in decreased CYP4A1 protein expression and 20-HETE synthesis. Taken together, we concluded that an increase in 20-HETE levels associated with a decrease in the production of vasodilator prostanoids and NO participates in the effect of NS-398 to prevent hypotension in the rat model of septic shock.

Contribution of vasoactive eicosanoids and nitric oxide production to the effect of selective cyclooxygenase-2 inhibitor, NS-398, on endotoxin-induced hypotension in rats

Our previous studies with the use of non-selective cyclooxygenase (COX) inhibitor, indomethacin, demonstrated that prostanoids produced during endotoxaemia increase inducible nitric oxide synthase (iNOS) protein expression and nitric oxide synthesis, and decrease cyctochrome P450 (CYP) 4A1 protein expression and CYP 4A activity. The results suggest that dual inhibition of iNOS and COX by indomethacin restores blood pressure presumably due to increased production of 20-hydroxyeicosatetraenoic acid (20-HETE) derived from CYP 4A in endotoxaemic rats. The present study examined whether increased levels of vasoconstrictor eicosanoids, 20-HETE, prostaglandin F(2α) (PGF(2α) )and thromboxane A(2) (TxA(2) ), would contribute to the effect of selective COX-2 inhibition to prevent endotoxin (ET)-induced fall in blood pressure associated with an increase in the production of vasodilator prostanoids, prostaglandin I(2) (PGI(2) ) and prostaglandin E(2) (PGE(2) ) and nitric oxide synthesis. Mean arterial blood pressure fell by 31 mmHg and heart rate (HR) rose by 90 beats/min. in male Wistar rats treated with ET (10 mg/kg, i.p.). The fall in mean arterial pressure and increase in HR were associated with increased levels of 6-keto-prostaglandin F(1α) (6-keto-PGF(1α) ), PGE(2) , TxB(2) , and nitrite in the serum, kidney, heart, thoracic aorta and/or superior mesenteric artery. Systemic and renal 20-HETE and PGF(2α) levels were also decreased in endotoxaemic rats. These effects of ET were prevented by a selective COX-2 inhibitor, N-(2-cyclohexyloxy-4-nitrophenyl)methansulphonamide (10 mg/kg, i.p.), given 1 hr after injection of ET. These data suggest that an increase in 20-HETE and PGF(2α) levels associated with decreased production of PGI(2) , PGE(2) , and TxA(2) , and nitric oxide synthesis contributes to the effect of selective COX-2 inhibitor to prevent the hypotension during rat endotoxaemia.

Detailed mechanistic investigation into the S-nitrosation of cysteamine

The nitrosation of cysteamine (H₂NCH₂CH₂SH) to produce cysteamine-S-nitrosothiol (CANO) was studied in slightly acidic medium by using nitrous acid prepared in situ. The stoichiometry of the reaction was H₂NCH₂CH₂SH + HNO₂ → H₂NCH₂CH₂SNO + H₂O. On prolonged standing, the nitrosothiol decomposed quantitatively to yield the disulfide, cystamine: 2H₂NCH₂CH₂SNO → H₂NCH₂CH₂S-SCH₂CH₂NH₂ + 2NO. NO₂ and N₂O₃ are not the primary nitrosating agents, since their precursor (NO) was not detected during the nitrosation process. The reaction is first order in nitrous acid, thus implicating it as the major nitrosating agent in mildly acidic pH conditions. Acid catalyzes nitrosation after nitrous acid has saturated, implicating the protonated nitrous acid species, the nitrosonium cation (NO⁺) as a contributing nitrosating species in highly acidic environments. The acid catalysis at constant nitrous acid concentrations suggests that the nitrosonium cation nitrosates at a much higher rate than nitrous acid. Bimolecular rate constants for the nitrosation of cysteamine by nitrous acid and by the nitrosonium cation were deduced to be 17.9 ± 1.5 (mol/L)^-1 s^-1 and 6.7 × 10⁴ (mol/L)^-1 s^-1, respectively. Both Cu(I) and Cu(II) ions were effective catalysts for the formation and decomposition of the cysteamine nitrosothiol. Cu(II) ions could catalyze the nitrosation of cysteamine in neutral conditions, whereas Cu(I) could only catalyze in acidic conditions. Transnitrosation kinetics of CANO with glutathione showed the formation of cystamine and the mixed disulfide with no formation of oxidized glutathione (GSSG). The nitrosation reaction was satisfactorily simulated by a simple reaction scheme involving eight reactions.

Oxidative Stress in Critically Ill Children with Sepsis

Sepsis is one of the leading causes of death in critically ill patients in the intensive care unit. Sepsis accounts for significant morbidity and mortality in critically ill children as well. The pathophysiology of sepsis is characterized by a complex systemic inflammatory response, endothelial dysfunction, and alterations in the coagulation system, which lead to perturbations in the delivery of oxygen and metabolic substrates to the tissues, end-organ dysfunction, and ultimately death. Oxidative stress plays a crucial role as both a promoter and mediator of the systemic inflammatory response, suggesting potential targets for the treatment of critically ill children with the sepsis syndrome. Herein, we will provide a brief review of the role of oxidative and nitrosative stress in the pathophysiology of sepsis.

New concepts in the pathogenesis, diagnosis and treatment of bacteremia and sepsis

Bacteremia and sepsis are major health concerns. Despite intensive research, there are only a limited number of successful treatment options, and it is difficult to see the forest for the trees when considering the pathogenesis of this condition. Studies in the last decade have shown that a major pathophysiologic event in sepsis is the progression from proinflammation to an immunosuppressive state. However, recent genome-based data indicate that sepsis-related inflammatory responses are highly variable, which calls in question the classic two-phase model of sepsis. Adequate and timely antimicrobial treatment is a cornerstone for survival in patients with bacteremia and sepsis. However, microbial resistance has emerged as an increasing challenge for clinicians and with an increasing number of resistant pathogens causing infections, selection of empiric antimicrobial treatment has become difficult. Treatment options currently under way are targeted to enhance immune responses, rebalance the regulation of the dysregulated immune system, remove endotoxin and block/inhibit apoptosis.

Inorganic nitrite therapy: historical perspective and future directions

Over the past several years, investigators studying nitric oxide (NO) biology and metabolism have come to learn that the one-electron oxidation product of NO, nitrite anion, serves as a unique player in modulating tissue NO bioavailability. Numerous studies have examined how this oxidized metabolite of NO can act as a salvage pathway for maintaining NO equivalents through multiple reduction mechanisms in permissive tissue environments. Moreover, it is now clear that nitrite anion production and distribution throughout the body can act in an endocrine manner to augment NO bioavailability, which is important for physiological and pathological processes. These discoveries have led to renewed hope and efforts for an effective NO-based therapeutic agent through the unique action of sodium nitrite as an NO prodrug. More recent studies also indicate that sodium nitrate may also increase plasma nitrite levels via the enterosalivary circulatory system resulting in nitrate reduction to nitrite by microorganisms found within the oral cavity. In this review, we discuss the importance of nitrite anion in several disease models along with an appraisal of sodium nitrite therapy in the clinic, potential caveats of such clinical uses, and future possibilities for nitrite-based therapies.

Piroxicam reverses endotoxin-induced hypotension in rats: contribution of vasoactive eicosanoids and nitric oxide

Nitric oxide (NO) produced by inducible NO synthase (iNOS) is responsible for endotoxin-induced vascular hyporeactivity and hypotension resulting in multiple organ failure. Endotoxic shock is also characterized by decreased expression of constitutive cyclooxygenase (COX-1), cytochrome P450 (CYP) 4A and endothelial NOS (eNOS). Our previous studies demonstrated that dual inhibition of iNOS and COX with a selective COX-2 inhibitor, NS-398, or a non-selective COX inhibitor, indomethacin, restores blood pressure presumably because of increased production of 20-hydroxyeicosatetraenoic acid (20-HETE) derived from arachidonic acid (AA) by CYP4A in endotoxaemic rats. The aim of this study was to investigate the effects of piroxicam, a preferential COX-1 inhibitor, on the endotoxin-induced changes in blood pressure, expression of COX-1, inducible COX (COX-2), CYP4A1, eNOS, iNOS and heat shock protein 90 (hsp90), and production of PGI(2), PGE(2), 20-HETE and NO. Injection of endotoxin (10 mg/kg, i.p.) to male Wistar rats caused a fall in blood pressure and an increase in heart rate associated with elevated renal 6-keto-PGF(1α) and PGE(2) levels as well as an increase in COX-2 protein expression. Endotoxin also caused an elevation in systemic and renal nitrite levels associated with increased renal iNOS protein expression. In contrast, systemic and renal 20-HETE levels and renal expression of eNOS, COX-1 and CYP4A1 were decreased in endotoxaemic rats. The effects of endotoxin, except for renal COX-1 and eNOS protein expression, were prevented by piroxicam (10 mg/kg, i.p.), given 1 hr after injection of endotoxin. Endotoxin did not change renal hsp90 protein expression. These data suggest that a decrease in the expression and activity of COX-2 and iNOS associated with an increase in CYP4A1 expression and 20-HETE synthesis contributes to the effect of piroxicam to prevent the hypotension during rat endotoxaemia.

Effect of selective inhibitors of nitric oxide synthesis on the course of experimental hemorrhagic shock

Selective inhibitors of NO synthesis (derivatives of lysine, ornithine, and isothiourea) increased the efficiency of infusion therapy for experimental hemorrhagic shock in rats. These changes were related to improvement of cardiac function (increase in stroke volume, cardiac output, and left ventricular efficiency). Among the three inhibitors, N5-(1-iminoethyl)-L-ornithine dihydrochloride was most potent on this experimental model. This compound improved cardiac function and microcirculation and provided 100% survival of experimental animals.

Effect of NO inhibitors on hypovolemic shock-induced hypotension

In vivo effect of isothiourea derivatives on NO production was studied by the method of electron paramagnetic resonance spectroscopy with a spin trap. We evaluated the influence of these compounds on hemodynamic parameters in anesthetized rats with hypovolemic shock. A correlation was found between the size of S,N-substituents in isothiourea derivatives (methyl, ethyl, and isopropyl) and NO inhibitory activity of compounds. The antihypotensive effect was more pronounced in compounds with high NO inhibitory activity containing the isopropyl radical.

Importance of TLR2 on hepatic immune and non-immune cells to attenuate the strong inflammatory liver response during Trypanosoma cruzi acute infection

BACKGROUND

Toll-like receptors (TLR) and cytokines play a central role in the pathogen clearance as well as in pathological processes. Recently, we reported that TLR2, TLR4 and TLR9 are differentially modulated in injured livers from BALB/c and C57BL/6 (B6) mice during Trypanosoma cruzi infection. However, the molecular and cellular mechanisms involved in local immune response remain unclear.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we demonstrate that hepatic leukocytes from infected B6 mice produced higher amounts of pro-inflammatory cytokines than BALB/c mice, whereas IL10 and TGFβ were only released by hepatic leukocytes from BALB/c. Strikingly, a higher expression of TLR2 and TLR4 was observed in hepatocytes of infected BALB/c mice. However, in infected B6 mice, the strong pro-inflammatory response was associated with a high and sustained expression of TLR9 and iNOS in leukocytes and hepatic tissue respectively. Additionally, co-expression of gp91- and p47-phox NADPH oxidase subunits were detected in liver tissue of infected B6 mice. Notably, the pre-treatment previous to infection with Pam3CSK4, TLR2-agonist, induced a significant reduction of transaminase activity levels and inflammatory foci number in livers of infected B6 mice. Moreover, lower pro-inflammatory cytokines and increased TGFβ levels were detected in purified hepatic leukocytes from TLR2-agonist pre-treated B6 mice.

CONCLUSIONS/SIGNIFICANCE

Our results describe some of the main injurious signals involved in liver immune response during the T. cruzi acute infection. Additionally we show that the administration of Pam3CSk4, previous to infection, can attenuate the exacerbated inflammatory response of livers in B6 mice. These results could be useful to understand and design novel immune strategies in controlling liver pathologies.

Temporal trends of circulating nitric oxide and pro-inflammatory cytokine responses ex vivo in intra-abdominal sepsis: results from a cohort study

OBJECTIVE AND DESIGN

To evaluate the association of pro-inflammatory mediators with organ dysfunction and adverse outcome in intra-abdominal sepsis patients.

SUBJECTS

Twenty-one patients admitted to the Intensive Care Unit (ICU) were prospectively included in the study. Only patients with surgical diagnosis of intra-abdominal sepsis were enrolled.

RESULTS

Tumor necrosis factor-α (TNFα) and interleukin (IL)-6 produced ex vivo were significantly lower in non-survivors on admission (p = 0.021) and day 2 (p = 0.013), respectively. Nitric oxide (NO(x)) levels were significantly higher in non-survivors from the onset of sepsis and until day 4 after diagnosis (p < 0.05). Circulating lymphocyte counts were lower in non-survivors after admission over time, but there was no association with impaired cytokine production in this group of patients during the entire follow-up. All non-survivors developed nosocomial pneumonia concomitantly with multiple organ dysfunction and septic shock. There was a significant correlation between nitric oxide (NO(x)) concentrations and the sequential organ failure assessment (SOFA) score at day 2 (r = 0.598, p = 0.009), and ICU stay (r = 0.605, p = 0.006). Continuously high NO(x) levels correlated with organ failure. The pro-inflammatory mediators TNFα, IL-6 and NO(x), and also the Simplified Acute Physiology Score II (SAPS-II), discriminate survivors from non-survivors. According to logistic regression models, although these parameters are independently associated with the outcome, they do not improve the predictive power of the SAPS-II score for mortality risk.

CONCLUSIONS

Disturbances in inflammatory responses and increase in NO(x) generation seem to characterize early intra-abdominal sepsis, in which immune suppression is associated with an increased susceptibility to nosocomial infections. Sequential NO(x) determinations could be a useful approach for improving the management of patients with intra-abdominal sepsis.

Mitochondrial protein tyrosine nitration

Mitochondria are primary loci for the intracellular formation and reactions of reactive oxygen and nitrogen species including superoxide (O₂•⁻), hydrogen peroxide (H₂O₂) and peroxynitrite (ONOO⁻). Depending on formation rates and steady-state levels, the mitochondrial-derived short-lived reactive species contribute to signalling events and/or mitochondrial dysfunction through oxidation reactions. Among relevant oxidative modifications in mitochondria, the nitration of the amino acid tyrosine to 3-nitrotyrosine has been recognized in vitro and in vivo. This post-translational modification in mitochondria is promoted by peroxynitrite and other nitrating species and can disturb organelle homeostasis. This study assesses the biochemical mechanisms of protein tyrosine nitration within mitochondria, the main nitration protein targets and the impact of 3-nitrotyrosine formation in the structure, function and fate of modified mitochondrial proteins. Finally, the inhibition of mitochondrial protein tyrosine nitration by endogenous and mitochondrial-targeted antioxidants and their physiological or pharmacological relevance to preserve mitochondrial functions is analysed.

Vascular hyporesponsiveness to vasopressors in septic shock: from bench to bedside

PURPOSE

To delineate some of the characteristics of septic vascular hypotension, to assess the most commonly cited and reported underlying mechanisms of vascular hyporesponsiveness to vasoconstrictors in sepsis, and to briefly outline current therapeutic strategies and possible future approaches.

METHODS

Source data were obtained from a PubMed search of the medical literature with the following MeSH terms: Muscle, smooth, vascular/physiopathology; hypotension/etiology; shock/physiopathology; vasodilation/physiology; shock/therapy; vasoconstrictor agents.

RESULTS

Nitric oxide (NO) and peroxynitrite are crucial components implicated in vasoplegia and vascular hyporeactivity. Vascular ATP-sensitive and calcium-activated potassium channels are activated during shock and participate in hypotension. In addition, shock state is characterized by inappropriately low plasma glucocorticoid and vasopressin concentrations, a dysfunction and desensitization of alpha-receptors, and an inactivation of catecholamines by oxidation. Numerous other mechanisms have been individualized in animal models, the great majority of which involve NO: MEK1/2-ERK1/2 pathway, H(2)S, hyperglycemia, and cytoskeleton dysregulation associated with decreased actin expression.

CONCLUSIONS

Many therapeutic approaches have proven their efficiency in animal models, especially therapies directed against one particular compound, but have otherwise failed when used in human shock. Nevertheless, high doses of catecholamines, vasopressin and terlipressin, hydrocortisone, activated protein C, and non-specific shock treatment have demonstrated a partial efficiency in reversing sepsis-induced hypotension.

Impaired microvascular perfusion in sepsis requires activated coagulation and P-selectin-mediated platelet adhesion in capillaries

PURPOSE

Impaired microvascular perfusion in sepsis is not treated effectively because its mechanism is unknown. Since inflammatory and coagulation pathways cross-activate, we tested if stoppage of blood flow in septic capillaries is due to oxidant-dependent adhesion of platelets in these microvessels.

METHODS

Sepsis was induced in wild type, eNOS(-/-), iNOS(-/-), and gp91phox(-/-) mice (n = 14-199) by injection of feces into the peritoneum. Platelet adhesion, fibrin deposition, and blood flow stoppage in capillaries of hindlimb skeletal muscle were assessed by intravital microscopy. Prophylactic treatments at the onset of sepsis were intravenous injection of platelet-depleting antibody, P-selectin blocking antibody, ascorbate, or antithrombin. Therapeutic treatments (delayed until 6 h) were injection of ascorbate or the glycoprotein IIb/IIIa inhibitor eptifibatide, or local superfusion of the muscle with NOS cofactor tetrahydrobiopterin or NO donor S-nitroso-N-acetylpenicillamine (SNAP).

RESULTS

Sepsis at 6-7 h markedly increased the number of stopped-flow capillaries and the occurrence of platelet adhesion and fibrin deposition in these capillaries. Platelet depletion, iNOS and gp91phox deficiencies, P-selectin blockade, antithrombin, or prophylactic ascorbate prevented, whereas delayed ascorbate, eptifibatide, tetrahydrobiopterin, or SNAP reversed, septic platelet adhesion and/or flow stoppage. The reversals by ascorbate and tetrahydrobiopterin were absent in eNOS(-/-) mice. Platelet adhesion predicted 90% of capillary flow stoppage.

CONCLUSION

Impaired perfusion and/or platelet adhesion in septic capillaries requires NADPH oxidase, iNOS, P-selectin, and activated coagulation, and is inhibited by intravenous administration of ascorbate and by local superfusion of tetrahydrobiopterin and NO. Reversal of flow stoppage by ascorbate and tetrahydrobiopterin may depend on local eNOS-derived NO which dislodges platelets from the capillary wall.

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.

Time course of liver nitric oxide concentration in early septic shock by cecal ligation and puncture in rats

An overwhelming nitric oxide (NO) production is a crucial step in the circulatory events as well as in the cellular alterations taking place in septic shock. However, evidences of this role arise from studies assessing the NO production on an intermittent basis precluding any clear evaluation of temporal relationship between NO production and circulatory alterations. We evaluated this relationship by using a NO specific electrode allowing a continuous measurement of NO production. Septic shock was induced by a cecal ligation and puncture (CLP) in a first group of anesthetized rats. After the same CLP, a second group received a selective iNOS inhibitor (L-NIL). Control rats were sham operated or sham operated with L-NIL administration. While NO concentration was measured every 2 min by a NO-sensitive electrode over 7h following CLP, the liver microcirculation was recorded by a laser-Doppler flowmeter. CLP induced a severe septic shock with hypotension occurring at a mean time of 240 min after CLP. At the same time, an increase in liver NO concentration was observed, whereas a decrease in microvascular liver perfusion was noted. In the septic shock group, L-NIL administration induced an increase in arterial pressure whereas the liver NO concentration returned to baseline values. In addition, shock groups experienced an increase in iNOS mRNA. These data showed a close temporal relationship between the increase in liver NO concentration and the microvascular alteration taking place in the early period of septic shock induced by CLP. The iNOS isoform is involved in this NO increase.

Reactive oxygen species and small-conductance calcium-dependent potassium channels are key mediators of inflammation-induced hypotension and shock

Septic shock is associated with life-threatening vasodilation and hypotension. To cause vasodilation, vascular endothelium may release nitric oxide (NO), prostacyclin (PGI2), and the elusive endothelium-derived hyperpolarizing factor (EDHF). Although NO is critical in controlling vascular tone, inhibiting NO in septic shock does not improve outcome, on the contrary, precipitating the search for alternative therapeutic targets. Using a hyperacute tumor necrosis factor (TNF)-induced shock model in mice, we found that shock can develop independently of the known vasodilators NO, cGMP, PGI2, or epoxyeicosatrienoic acids. However, the antioxidant tempol efficiently prevented hypotension, bradycardia, hypothermia, and mortality, indicating the decisive involvement of reactive oxygen species (ROS) in these phenomena. Also, in classical TNF or lipopolysaccharide-induced shock models, tempol protected significantly. Experiments with (cell-permeable) superoxide dismutase or catalase, N-acetylcysteine and apocynin suggest that the ROS-dependent shock depends on intracellular (*)OH radicals. Potassium channels activated by ATP (K(ATP)) or calcium (K(Ca)) are important mediators of vascular relaxation. While NO and PGI2-induced vasodilation involves K(ATP) and large-conductance BK(Ca) channels, small-conductance SK(Ca) channels mediate vasodilation induced by EDHF. Interestingly, also SK(Ca) inhibition completely prevented the ROS-dependent shock. Our data thus indicate that intracellular (*)OH and SK(Ca) channels represent interesting new therapeutic targets for inflammatory shock. Moreover, they may also explain why antioxidants other than tempol fail to provide survival benefit during shock.

Crosstalk between TNF and glucocorticoid receptor signaling pathways

TNF is a Janus-faced protein. It possesses impressive anti-tumor activities, but it is also one of the strongest known pro-inflammatory cytokines, which hampers its use as a systemic anti-cancer agent. TNF has been shown to play a detrimental role in inflammatory diseases such as rheumatoid arthritis and inflammatory bowel disease. Glucocorticoids are strongly anti-inflammatory and exert their therapeutic effects through binding to their receptor, the glucocorticoid receptor. Therefore, glucocorticoids have been used for over half a century for the treatment of inflammatory diseases. However, many patients are or become resistant to the therapeutic effects of glucocorticoids. Inflammatory cytokines have been suggested to play an important role in this steroid insensitivity or glucocorticoid resistance. This review aims to highlight the mechanisms of mutual inhibition between TNF and GR signaling pathways.

Role of neuronal nitric oxide synthase in ovine sepsis model

Smoke inhalation injury is often complicated with pneumonia, which frequently leads to subsequent development of sepsis. Excessive NO has been shown to mediate many sepsis-related pathological responses. In the present study, we used our well-established ovine smoke inhalation and pneumonia/sepsis model to examine the hypothesis that neuronal NO synthase (NOS) may be primarily responsible for these pathological alterations. We report the beneficial effects of the specific neuronal NOS (nNOS) inhibitor ZK234238. Adult female sheep were surgically prepared for the study. After 5 to 7 days' recovery, sheep were anesthetized and given double injury: insufflation of 48 breaths of cotton smoke (<40 degrees C) into the airway of each animal and subsequent instillation of live Pseudomonas aeruginosa (5 x 10(11) colony-forming units) into each sheep's lung via tracheostomy tube. All sheep were mechanically ventilated and fluid resuscitated by lactated Ringer's solution. Sheep were randomly allocated into groups: control (injured not treated, n = 6) and treated (injured, but treated with ZK234238, n = 4). Continuous infusion of ZK234238 (100 microg x kg(-1) x h(-1)) was started 1 h after insult. ZK234238 attenuated the hypotension (at 18 and 24 h) and fall in systemic vascular resistance (at 24 h) seen in control animals. ZK234238 significantly inhibited increased fluid accumulation as well as increased plasma nitrate/nitrite 24 h after injury. Neuronal NOS inhibition significantly reduced lung water content and attenuated inflammatory indices such as lung tissue myeloperoxidase activity, IL-6 mRNA, and reactive nitrogen species. The above results suggest that the nNOS-derived NO may be involved in the pathophysiology of sepsis-related multiorgan dysfunction.

Modification of the hepatic hemodynamic response to acute changes in PaCO2 by nitric oxide synthase inhibition in rabbits

BACKGROUND

Hypercapnia has been reported to modify liver circulation. The vascular regulations implicated in this response remain partly unknown.

METHODS

Using anesthetized and ventilated rabbits, we designed this study to evaluate the hepatic artery and portal vein blood flow velocity adjustments (20 MHz pulsed Doppler) after changes in PaCO2 (by varying the inspiratory fraction of CO2 and to assess the proper role of pH, independent of PaCO2 changes, the role of portal vein CO2, and the effect of nitric oxide synthase inhibition on CO2-induced modifications of hepatic hemodynamics.

RESULTS

Increasing PaCO2 from 30.9 +/- 5 mm Hg to 77 +/- 11 mm Hg increased arterial blood pressure by 20% (P < 0.01) and hepatic artery blood flow velocity by 90% (P < 0.05) and decreased aortic blood flow velocity by 15% and portal vein blood flow velocity by 40% (both P < 0.05). Changes in pH (1 mL of 0.1 N hydrochloric acid infusion) or isolated changes in portal vein CO2 at constant PaCO2 induced by CO2 insufflation in an open abdomen had no effect on hepatic hemodynamics. Pretreatment with a nitric oxide synthase inhibitor, N(omega)-nitro-L-arginine (2.5 mg/kg), blunted the systemic response to hypercapnia, whereas the portal modifications persisted, with a largely attenuated hepatic artery blood flow increase.

CONCLUSIONS

CO2 per se acts on hepatic blood flow by its systemic effect, probably via chemoreflexes. Nitric oxide does not mediate hepatosplanchnic hemodynamic modifications to acute changes in PaCO2 but may play a permissive role by regulating the amplitude of hepatic vascular response.

A synthetic analogue of 20-HETE, 5,14-HEDGE, reverses endotoxin-induced hypotension via increased 20-HETE levels associated with decreased iNOS protein expression and vasodilator prostanoid production in rats

Nitric oxide (NO) produced by inducible NO synthase (iNOS) is responsible for endotoxin (ET)-induced hypotension and vascular hyporeactivity and plays a major contributory role in the multiorgan failure. Endotoxic shock is also associated with an increase in vasodilator prostanoids as well as a decrease in endothelial NO synthase (eNOS) and cytochrome P450 4A protein expression, and production of a vasoconstrictor arachidonic acid product, 20-hydroxyeicosatetraenoic acid (20-HETE). The aim of this study was to investigate the effects of a synthetic analogue of 20-HETE, N-[20-hydroxyeicosa-5(Z),14(Z)-dienoyl]glycine (5,14-HEDGE), on the ET-induced changes in eNOS, iNOS and heat shock protein 90 (hsp90) expression as well as 20-HETE and vasodilator prostanoid (6-keto-PGF(1alpha) and PGE(2)) production. ET-induced fall in blood pressure and rise in heart rate were associated with an increase in iNOS protein expression and a decrease in eNOS protein expression in heart, thoracic aorta, kidney and superior mesenteric artery. ET did not change hsp90 protein expression in the tissues. ET-induced changes in eNOS and iNOS protein expression were associated with increased 6-keto-PGF(1alpha) and PGE(2) levels and a decrease in 20-HETE levels, in the serum and kidney. These effects of ET on the iNOS protein expression and 6-keto-PGF(1alpha), PGE(2) and 20-HETE levels were prevented by 5,14-HEDGE. Furthermore, a competitive antagonist of vasoconstrictor effects of 20-HETE, 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid, prevented the effects of 5,14-HEDGE on the ET-induced changes in systemic and renal levels of these prostanoids and 20-HETE. These data are consistent with the view that an increase in systemic and renal 20-HETE levels associated with a decrease in iNOS protein expression and vasodilator prostanoid production contributes to the effect of 5,14-HEDGE to prevent the hypotension during rat endotoxemia.

Nitrite protects against morbidity and mortality associated with TNF- or LPS-induced shock in a soluble guanylate cyclase-dependent manner

Nitrite (NO₂⁻), previously viewed as a physiologically inert metabolite and biomarker of the endogenous vasodilator NO, was recently identified as an important biological NO reservoir in vasculature and tissues, where it contributes to hypoxic signaling, vasodilation, and cytoprotection after ischemia–reperfusion injury. Reduction of nitrite to NO may occur enzymatically at low pH and oxygen tension by deoxyhemoglobin, deoxymyoglobin, xanthine oxidase, mitochondrial complexes, or NO synthase (NOS). We show that nitrite treatment, in sharp contrast with the worsening effect of NOS inhibition, significantly attenuates hypothermia, mitochondrial damage, oxidative stress and dysfunction, tissue infarction, and mortality in a mouse shock model induced by a lethal tumor necrosis factor challenge. Mechanistically, nitrite-dependent protection was not associated with inhibition of mitochondrial complex I activity, as previously demonstrated for ischemia–reperfusion, but was largely abolished in mice deficient for the soluble guanylate cyclase (sGC) α1 subunit, one of the principal intracellular NO receptors and signal transducers in the cardiovasculature. Nitrite could also provide protection against toxicity induced by Gram-negative lipopolysaccharide, although higher doses were required. In conclusion, we show that nitrite can protect against toxicity in shock via sGC-dependent signaling, which may include hypoxic vasodilation necessary to maintain microcirculation and organ function, and cardioprotection.

Evaluation of efficacy, biodistribution, and inflammation for a potent siRNA nanoparticle: effect of dexamethasone co-treatment

Despite recent progress, systemic delivery remains the major hurdle for development of safe and effective small inhibitory RNA (siRNA)-based therapeutics. Encapsulation of siRNA into liposomes is a promising option to overcome obstacles such as low stability in serum and inefficient internalization by target cells. However, a major liability of liposomes is the potential to induce an acute inflammatory response, thereby increasing the risk of numerous adverse effects. In this study, we characterized a liposomal siRNA delivery vehicle, LNP201, which is capable of silencing an mRNA target in mouse liver by over 80%. The biodistribution profile, efficacy after single and multiple doses, mechanism of action, and inflammatory toxicity are characterized for LNP201. Furthermore, we demonstrate that the glucocorticoid receptor (GR) agonist dexamethasone (Dex) inhibits LNP201-induced cytokine release, inflammatory gene induction, and mitogen-activated protein kinase (MAPK) phosphorylation in multiple tissues. These data present a possible clinical strategy for increasing the safety profile of siRNA-based drugs while maintaining the potency of gene silencing.

sGC(alpha)1(beta)1 attenuates cardiac dysfunction and mortality in murine inflammatory shock models

Altered cGMP signaling has been implicated in myocardial depression, morbidity, and mortality associated with sepsis. Previous studies, using inhibitors of soluble guanylate cyclase (sGC), suggested that cGMP generated by sGC contributed to the cardiac dysfunction and mortality associated with sepsis. We used sGC(alpha)(1)-deficient (sGC(alpha)(1)(-/-)) mice to unequivocally determine the role of sGC(alpha)(1)beta(1) in the development of cardiac dysfunction and death associated with two models of inflammatory shock: endotoxin- and TNF-induced shock. At baseline, echocardiographic assessment and invasive hemodynamic measurements of left ventricular (LV) dimensions and function did not differ between wild-type (WT) mice and sGC(alpha)(1)(-/-) mice on the C57BL/6 background (sGC(alpha)(1)(-/-B6) mice). At 14 h after endotoxin challenge, cardiac dysfunction was more pronounced in sGC(alpha)(1)(-/-B6) than WT mice, as assessed using echocardiographic and hemodynamic indexes of LV function. Similarly, Ca(2+) handling and cell shortening were impaired to a greater extent in cardiomyocytes isolated from sGC(alpha)(1)(-/-B6) than WT mice after endotoxin challenge. Importantly, morbidity and mortality associated with inflammatory shock induced by endotoxin or TNF were increased in sGC(alpha)(1)(-/-B6) compared with WT mice. Together, these findings suggest that cGMP generated by sGC(alpha)(1)beta(1) protects against cardiac dysfunction and mortality in murine inflammatory shock models.

Arginine, citrulline and nitric oxide metabolism in sepsis

Arginine has vasodilatory effects, via its conversion by NO synthase into NO, and immunomodulatory actions which play important roles in sepsis. Protein breakdown affects arginine availability and the release of asymmetric dimethylarginine, an inhibitor of NO synthase, may therefore affect NO synthesis in patients with sepsis. The objective of the present study was to investigate whole-body in vivo arginine and citrulline metabolism and NO synthesis rates, and their relationship to protein breakdown in patients with sepsis or septic shock and in healthy volunteers. Endogenous leucine flux, an index of whole-body protein breakdown rate, was measured in 13 critically ill patients with sepsis or septic shock and seven healthy controls using an intravenous infusion of [1-13C]leucine. Arginine flux, citrulline flux and the rate of conversion of arginine into citrulline (an index of NO synthesis) were measured with intravenous infusions of [15N2]guanidino-arginine and [5,5-2H2]citrulline. Plasma concentrations of nitrite plus nitrate, arginine, citrulline and asymmetric dimethylarginine were measured. Compared with controls, patients had a higher leucine flux and higher NO metabolites, but arginine flux, plasma asymmetric dimethylarginine concentration and the rate of NO synthesis were not different. Citrulline flux and plasma arginine and citrulline were lower in patients than in controls. Arginine production was positively correlated with the protein breakdown rate. Whole-body arginine production and NO synthesis were similar in patients with sepsis and septic shock and healthy controls. Despite increased proteolysis in sepsis, there is a decreased arginine plasma concentration, suggesting inadequate de novo synthesis secondary to decreased citrulline production.

Reduced skin inflammatory response in mice lacking inducible nitric oxide synthase

The skin is the largest organ in the body and one of its main functions is to protect the body from environmental and endogenous noxious conditions, such as injury, infection and inflammation. The inducible nitric oxide synthase (iNOS) has been implicated as a key component in the inflammatory response. In the present study, we assessed the role of iNOS in the skin inflammation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA). Mice deficient in iNOS had reduced edema and cellular infiltration in the skin following topical TPA application. Moreover, the genetic blockage of iNOS signaling inhibited the TPA-induced ERK and p38 activation resulting in reduced COX-2 upregulation. Finally, immunohistochemical studies revealed that iNOS knockout mice exhibited marked inhibition of AP-1, CREB and NF-kappaB transcriptional factors activation. Together, these results indicate that TPA induces the activation of several iNOS-dependent intracellular signaling pathways that have a key role in the control of inflammatory response in the skin. Therefore, selective iNOS inhibitors may be potentially relevant tools for cutaneous skin disease drug development.