Biology of nitric oxide signaling

Potential pharmacokinetic interactions of therapeutic cytokines or cytokine modulators on small-molecule drugs: mechanistic understanding via studies using in vitro systems

The potential pharmacokinetic interactions between macromolecules and small-molecule drugs have received more and more attention with the increasing development of macromolecule therapeutics. Studies have shown that cytokines can differentially modulate drug-metabolizing enzymes and transporters, which raises concerns on the potential interactions of therapeutic cytokines and cytokine modulators on the disposition of small-molecule drugs. Although many in vitro studies have been conducted to characterize the effects of cytokines on drug-metabolizing enzymes and transporters, these studies were limited to only a handful of cytokines, such as interleukin-1 (IL-1), IL-6, tumor necrosis factor-α, and interferon. It is also challenging to translate these in vitro results to in vivo. In addition, information on the impact of cytokine modulators on drug-metabolizing enzymes and transporters is rather limited. More research is needed in this area. The present review is to provide a summary of the in vitro findings on the pharmacokinetic interactions of therapeutic cytokines and cytokine modulators on small-molecule drugs. Discussion on current challenges in assessing these interactions is also included.

The role of oxidative stress during inflammatory processes

Abstract The production of various reactive oxidant species in excess of endogenous antioxidant defense mechanisms promotes the development of a state of oxidative stress, with significant biological consequences. In recent years, evidence has emerged that oxidative stress plays a crucial role in the development and perpetuation of inflammation, and thus contributes to the pathophysiology of a number of debilitating illnesses, such as cardiovascular diseases, diabetes, cancer, or neurodegenerative processes. Oxidants affect all stages of the inflammatory response, including the release by damaged tissues of molecules acting as endogenous danger signals, their sensing by innate immune receptors from the Toll-like (TLRs) and the NOD-like (NLRs) families, and the activation of signaling pathways initiating the adaptive cellular response to such signals. In this article, after summarizing the basic aspects of redox biology and inflammation, we review in detail the current knowledge on the fundamental connections between oxidative stress and inflammatory processes, with a special emphasis on the danger molecule high-mobility group box-1, the TLRs, the NLRP-3 receptor, and the inflammasome, as well as the transcription factor nuclear factor-κB.

Inducible nitric oxide synthase inhibition reverses pulmonary arterial dysfunction in lung transplantation

BACKGROUND

Ischemia-reperfusion injury (IRI) after lung transplantation remains a significant cause of morbidity and mortality. Lung IRI induces nitric oxide synthesis (iNOS) and reactive nitrogen species, decreasing nitric oxide bioavailability. We hypothesized that ischemia-induced iNOS intensifies with reperfusion and contributes to IRI-induced pulmonary arterial regulatory dysfunction, which may lead to early graft failure and cause pulmonary edema. The aim of this study was to determine whether ischemia-reperfusion alters inducible and endothelial nitric oxide synthase expression, potentially affecting pulmonary perfusion. We further evaluated the role of iNOS in post-transplantation pulmonary arterial disorder.

METHODS

We randomized 32 Sprague-Dawley rats into two groups. The control group was given a sham operation whilst the experimental group received orthotropic lung transplants with a modified three-cuff technique. Changes in lung iNOS, and endothelial nitric oxide synthase expression were measured after lung transplantation by enzyme-linked immunosorbent assay (ELISA). Vasoconstriction in response to exogenous phenylephrine and vasodilation in response to exogenous acetylcholine of pulmonary arterial rings were measured in vitro as a measure of vascular dysfunction. To elucidate the roles of iNOS in regulating vascular function, an iNOS activity inhibitor (N6-(1-iminoethyl)-L-lysine, L-NIL) was used to treat isolated arterial rings. In order to test whether iNOS inhibition has a therapeutic effect, we further used L-NIL to pre-treat transplanted lungs and then measured post-transplantation arterial responses.

RESULTS

Lung transplantation caused upregulation of iNOS expression. This was also accompanied by suppression of both vasoconstriction and vasodilation of arterial rings from transplanted lungs. Removal of endothelium did not interfere with the contraction of pulmonary arterial rings from transplanted lungs. In contrast, iNOS inhibition rescued the vasoconstriction response to exogenous phenylephrine of pulmonary arterial rings from transplanted lungs. In addition, lung transplantation led to suppression of PaO2/FiO2 ratio, increased intrapulmonary shunt (Q s/Q t), and increase of lung wet to dry ratio (W/D), malondialdehyde and myeloperoxidase levels, all of which were reversed upon iNOS inhibition. Furthermore, inhibition of iNOS significantly rescued vascular function and alleviated edema and inflammatory cell infiltration in the transplanted lung.

CONCLUSIONS

Our data suggest that lung transplantation causes upregulation of iNOS expression, and pulmonary vascular dysfunction. iNOS inhibition reverses the post-transplantational pulmonary vascular dysfunction.

The effects of nitroglycerin during cardiopulmonary resuscitation

The outcome for both in-hospital and out-of hospital cardiac arrest remains dismal. Vasopressors are used to increase coronary perfusion pressure and thus facilitate return of spontaneous circulation during cardiopulmonary resuscitation. However, they are associated with a number of potential adverse effects and may decrease endocardial and cerebral organ blood flow. Nitroglycerin has a favourable haemodynamic profile which promotes forward blood flow. Several studies suggest that combined use of nitroglycerin with vasopressors during resuscitation, is associated with increased rates of resuscitation and improved post-resuscitation outcome. This article reviews the effects of nitroglycerin during cardiopulmonary resuscitation and postresuscitation period, as well as the beneficial outcomes of a combination regimen consisting of a vasopressor and a vasodilator, such as nitroglycerin.

Hippocampus and nitric oxide

Since it was first identified to play an important role in relaxation of blood vessels, nitric oxide has been demonstrated to regulate many biological processes, especially in the central nervous system. Of the three types of enzymes that produce nitric oxide in humans and rodents, neuronal type is found almost exclusively in the nervous system. This gaseous molecule is a nonclassical neurotransmitter, which maintains the activities of neural cells and regulates the normal functions of brain. It appears to play a role in promoting the transfer of nerve signals from one neuron to another, maintaining the synaptic strength. Meanwhile, nitric oxide is a unique regulator on neurogenesis and synaptogenesis, producing the positive or negative effects upon different signal pathways or cellular origins and locations. Based on its significant roles in neural plasticity, nitric oxide is involved in a number of central nervous diseases, such as ischemia, depression, anxiety, and Alzheimer's disease. Clarifying the profiles of nitric oxide in the brain tissues and its participation in pathophysiological processes opens a new avenue for development of new therapeutic strategies. Thus, this chapter specifies the effects of nitric oxide in the hippocampus, a key structure implicated in the modulation of mood and memories, exhibiting the trend of future research on nitric oxide.

Pathogenesis of chronic cardiorenal syndrome: is there a role for oxidative stress?

Cardiorenal syndrome is a frequently encountered clinical condition when the dysfunction of either the heart or kidneys amplifies the failure progression of the other organ. Complex biochemical, hormonal and hemodynamic mechanisms underlie the development of cardiorenal syndrome. Both in vitro and experimental studies have identified several dysregulated pathways in heart failure and in chronic kidney disease that lead to increased oxidative stress. A decrease in mitochondrial oxidative metabolism has been reported in cardiomyocytes during heart failure. This is balanced by a compensatory increase in glucose uptake and glycolysis with consequent decrease in myocardial ATP content. In the kidneys, both NADPH oxidase and mitochondrial metabolism are important sources of TGF-β1-induced cellular ROS. NOX-dependent oxidative activation of transcription factors such as NF-kB and c-jun leads to increased expression of renal target genes (phospholipaseA2, MCP-1 and CSF-1, COX-2), thus contributing to renal interstitial fibrosis and inflammation. In the present article, we postulate that, besides contributing to both cardiac and renal dysfunction, increased oxidative stress may also play a crucial role in cardiorenal syndrome development and progression. In particular, an imbalance between the renin-angiotensin-aldosterone system, the sympathetic nervous system, and inflammation may favour cardiorenal syndrome through an excessive oxidative stress production. This article also discusses novel therapeutic strategies for their potential use in the treatment of patients affected by cardiorenal syndrome.

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.

Oxidative state of the liver of rats with adjuvant-induced arthritis

Adjuvant-induced arthritis is an experimental immunopathology in rats that is often used as a model for studying autoimmune chronic inflammation and inflammatory cachexia. In these animals oxidative stress is quite pronounced in the articular inflammation sites. The purpose of this study was to evaluate oxidative stress in the liver of arthritic rats in which morphological and metabolic alterations have been reported to occur. Oxidative injury parameters, levels and production of reactive oxygen species (ROS), and antioxidant parameters were measured in the total liver homogenate and in subcellular fractions, namely cytosol, mitochondria, and peroxisomes. Arthritic rats presented higher levels of ROS than controls in the total homogenate (46% higher) and in all subcellular fractions (51, 38, and 55% higher for mitochondria, peroxisome, and cytosol, respectively). Arthritic rats also presented higher levels of protein carbonyl groups in the total homogenate (75%) and in all subcellular fractions (189, 227, and 260%, respectively, for mitochondria, peroxisomes, and cytosol). The TBARS levels of arthritic rats were more elevated in the total homogenate (36%), mitochondria (20%), and peroxisomes (16%). Arthritic rats also presented higher levels of NO markers in the peroxisomes (112%) and in the cytosol (35%). The catalase activity of all cell compartments was strongly diminished (between 77 and 87%) by arthritis, and glutathione peroxidase activities were diminished in the mitochondria (33.7%) and cytosol (41%). The cytosolic glucose-6-phosphate dehydrogenase activity, on the other hand, was increased (62.9%), the same happening with inducible peroxisomal NO synthase (119.3%). The superoxide dismutase and glutathione reductase activities were not affected. The GSH content was diminished by arthritis in all cellular compartments (50 to 59% diminution). The results reveal that the liver of rats with adjuvant-induced arthritis presents a pronounced oxidative stress and that, in consequence, injury to lipids and proteins is highly significant. The higher ROS content of the liver of arthritic rats seems to be the consequence of both a stimulated pro-oxidant system and a deficient antioxidant defense with a predominance of the latter as indicated by the strongly diminished activities of catalase and glutathione peroxidase.

Common polymorphisms in nitric oxide synthase (NOS) genes influence quality of aging and longevity in humans

Nitric oxide (NO) triggers multiple signal transduction pathways and contributes to the control of numerous cellular functions. Previous studies have shown in model organisms that the alteration of NO production has important effects on aging and lifespan. We studied in a large sample (763 subjects, age range 19-107 years) the variability of the three human genes (NOS1, -2, -3) coding for the three isoforms of the NADPH-dependent enzymes named NO synthases (NOS) which are responsible of NO synthesis. We have then verified if the variability of these genes is associated with longevity, and with a number of geriatric parameters. We found that gene variation of NOS1 and NOS2 was associated with longevity. In addition NOS1 rs1879417 was also found to be associated with a lower cognitive performance, while NOS2 rs2297518 polymorphism showed to be associated with physical performance. Moreover, SNPs in the NOS1 and NOS3 genes were respectively associated with the presence of depression symptoms and disability, two of the main factors affecting quality of life in older individuals. On the whole, our study shows that genetic variability of NOS genes has an effect on common age related phenotypes and longevity in humans as well as previously reported for model organisms.

Inhibiting inducible nitric oxide synthase with rutin reduces renal ischemia/reperfusion injury

BACKGROUND

Nitric oxide (NO) seems to play an important role during renal ischemia/reperfusion (I/R) injury. We investigated whether rutin inhibits inducible nitric oxide synthase (iNOS) and reduces 3-nitrotyrosine (3-NT) formation in the kidneys of rats during I/R.

METHODS

Wistar albino rats were nephrectomized unilaterally and, 2 weeks later, subjected to 45 minutes of left renal pedicle occlusion followed by 3 hours of reperfusion. We intraperitoneally administered L-N6-(1-iminoethyl)lysine (L-NIL; 3 mg/kg) for 30 minutes or rutin (1 g/kg) for 60 minutes before I/R. After reperfusion, kidney samples were taken for immunohistochemical analysis of iNOS and 3-NT. We measured plasma nitrite/nitrate and cyclic guanosine monophosphate (cGMP) to evaluate NO levels.

RESULTS

Ischemia/reperfusion caused plasma cGMP to increase significantly. Similarly, plasma nitrite/nitrate was elevated in the I/R group compared with the control group. Histochemical staining was positive for iNOS and 3-NT in the I/R group. Pretreatment with L-NIL or rutin significantly mitigated the elevation of plasma cGMP and nitrite/nitrate. These changes in biochemical parameters were also associated with changes in immunohistochemical appearance. Pretreatment with L-NIL or rutin significantly decreased the incidence and severity of iNOS and 3-NT formation in the kidney tissues.

CONCLUSION

Our findings suggest that high activity of iNOS causes renal I/R injury, and that rutin exerts protective effects, probably by inhibiting iNOS.

Time profile of oxidative stress and neutrophil activation in ovine acute lung injury and sepsis

The formation of oxidative stress in the lung and activation of neutrophils are major determinants in the development of respiratory failure after acute lung injury and sepsis. However, the time changes of these pathogenic factors have not been sufficiently described. Twenty-four chronically instrumented sheep were subjected to cotton smoke inhalation injury and instillation of live Pseudomonas aeruginosa into both lungs. The sheep were euthanized at 4, 8, 12, 18, and 24 h after injury. Additional sheep received sham injury and were euthanized after 24 h. Pulmonary function was assessed by determination of oxygenation index and pulmonary shunt fraction. In addition, lung tissue was harvested at the respective time points for the measurement of malondialdehyde, interleukin 6, poly(ADP ribose), myeloperoxidase, and alveolar polymorphonuclear neutrophil score. The injury induced severe respiratory failure that was associated with an early increase in lipid peroxidation and interleukin 6 expression. The injury further led to an increase in poly(ADP ribose) activity that reached its peak at 12 h after injury and declined afterward. In addition, progressive increases in markers of neutrophil accumulation in the lung were observed. The peak of neutrophil accumulation in the lung was associated with a severe depletion of circulating neutrophils. The results from our model may enhance the understanding of the pathophysiological alterations after acute lung injury and sepsis and thus be useful in exploring therapeutic interventions directed at modifying the expression or activation of inflammatory mediators.

Platonin mitigates lung injury in a two-hit model of hemorrhage/resuscitation and endotoxemia in rats

BACKGROUND

Traumatic hemorrhagic shock and subsequent resuscitation may promote bacteria translocation and cause endotoxemia, a two-hit process that will induce severe lung injury. The pathogenesis involves oxidative stress, neutrophil infiltration, and inflammatory response. Platonin, a potent antioxidant, possesses potent anti-inflammation capacity. We sought to elucidate whether platonin could mitigate acute lung injury in a two-hit model of traumatic hemorrhage/resuscitation and subsequent endotoxemia.

METHODS

Adult male rats were randomized to receive traumatic hemorrhage/resuscitation plus lipopolysaccharide (HS/L) alone or HS/L plus platonin (200 μg/kg; n = 12 in each group). Sham groups were used simultaneously. At 6 hours after resuscitation, rats were killed and the levels of lung injury were assayed.

RESULTS

Rats treated with HS/L alone had severe lung injury as evidenced by significant alterations in lung function (i.e., arterial blood gas and alveolar-arterial oxygen difference) and histology. Significant increases in polymorphonuclear leukocytes/alveoli ratio (neutrophil infiltration index) and significant increases in the concentrations of inflammatory molecules (including chemokine, cytokine, and prostaglandin E2) and malondialdehyde (lipid peroxidation index) revealed that HS/L caused significant oxidative stress, neutrophil infiltration, and inflammatory response in rat lungs. Moreover, our data revealed that the levels of functional and histologic alteration as well as polymorphonuclear leukocytes/alveoli ratio and the concentrations of inflammatory molecules and malondialdehyde in rats treated with HS/L plus platonin (200 μg/kg) were significantly lower than those treated with HR/L alone.

CONCLUSIONS

Platonin mitigates lung injury in a two-hit model of traumatic hemorrhage/resuscitation and endotoxemia in rats.

Thaliporphine preserves cardiac function of endotoxemic rabbits by both directly and indirectly attenuating NFκB signaling pathway

Cardiac depression in sepsis is associated with the increased morbidity and mortality. Although myofilaments damage, autonomic dysfunction, and apoptosis play roles in sepsis-induced myocardial dysfunction, the underlying mechanism is not clear. All of these possible factors are related to NFκB signaling, which plays the main role in sepsis signaling. Thaliporphine was determined to possess anti-inflammatory and cardioprotective activity by suppressing NFκB signaling in rodents. The purpose of this study is to further prove this protective effect in larger septic animals, and try to find the underlying mechanisms. The systolic and diastolic functions were evaluated in vivo by pressure-volume analysis at different preloads. Both preload-dependent and -independent hemodynamic parameters were performed. Inflammatory factors of whole blood and serum samples were analyzed. Several sepsis-related signaling pathways were also determined at protein level. Changes detected by conductance catheter showed Thaliporphine could recover impaired left ventricular systolic function after 4 hours LPS injection. It could also reverse the LPS induced steeper EDPVR and gentler ESPVR, thus improve Ees, Ea, and PRSW. Thaliporphine may exert this protective effect by decreasing TNFα and caspase3 dependent cell apoptosis, which was consistent with the decreased serum cTnI and LDH concentration. Thaliporphine could protect sepsis-associated myocardial dysfunction in both preload-dependent and -independent ways. It may exert these protective effects by both increase of "good"-PI3K/Akt/mTOR and decrease of "bad"-p38/NFκB pathways, which followed by diminishing TNFα and caspase3 dependent cell apoptosis.

Inhibitor of neuronal nitric oxide synthase improves gas exchange in ventilator-induced lung injury after pneumonectomy

BACKGROUND

Mechanical ventilation with high tidal volumes may cause ventilator-induced lung injury (VILI) and enhanced generation of nitric oxide (NO). We demonstrated in sheep that pneumonectomy followed by injurious ventilation promotes pulmonary edema. We wished both to test the hypothesis that neuronal NOS (nNOS), which is distributed in airway epithelial and neuronal tissues, could be involved in the pathogenesis of VILI and we also aimed at investigating the influence of an inhibitor of nNOS on the course of VILI after pneumonectomy.

METHODS

Anesthetized sheep underwent right pneumonectomy, mechanical ventilation with tidal volumes (VT) of 6 mL/kg and FiO2 0.5, and were subsequently randomized to a protectively ventilated group (PROTV; n = 8) keeping VT and FiO2 unchanged, respiratory rate (RR) 25 inflations/min and PEEP 4 cm H2O for the following 8 hrs; an injuriously ventilated group with VT of 12 mL/kg, zero end-expiratory pressure, and FiO2 and RR unchanged (INJV; n = 8) and a group, which additionally received the inhibitor of nNOS, 7-nitroindazole (NI) 1.0 mg/kg/h intravenously from 2 hours after the commencement of injurious ventilation (INJV + NI; n = 8). We assessed respiratory, hemodynamic and volumetric variables, including both the extravascular lung water index (EVLWI) and the pulmonary vascular permeability index (PVPI). We measured plasma nitrite/nitrate (NOx) levels and examined lung biopsies for lung injury score (LIS).

RESULTS

Both the injuriously ventilated groups demonstrated a 2-3-fold rise in EVLWI and PVPI, with no significant effects of NI. In the INJV group, gas exchange deteriorated in parallel with emerging respiratory acidosis, but administration of NI antagonized the derangement of oxygenation and the respiratory acidosis significantly. NOx displayed no significant changes and NI exerted no significant effect on LIS in the INJV group.

CONCLUSION

Inhibition of nNOS improved gas exchange, but did not reduce lung water extravasation following injurious ventilation after pneumonectomy in sheep.

Mitochondrial antioxidants alleviate oxidative and nitrosative stress in a cellular model of sepsis

PURPOSE

Mitochondrial dysfunction plays a key role in sepsis.

METHODS

We used a sepsis model of human endothelial cells (HUVEC) to study mitochondrial function during normoxic (21% O(2)) and hypoxic (1% O(2)) conditions.

RESULTS

When stimulated with a LPS cocktail, HUVEC displayed an increase of nitric oxide (NO) in normoxic and hipoxic conditions, being higher at 21% O(2). LPS-activation for 24 h at 1% O(2) increased ROS production, which was reversed with the mitochondrial antioxidant Mitoquinone (MQ) and Glutathione Ethyl Ester (GEE). Activated cells displayed diminished mitochondrial O(2) consumption with specific inhibition of Complex I, accompanied by increase in tyrosine nitration and Type II NOS protein expression, effects which were recovered by antioxidants and/or with L-NAME. These parameters varied with O(2) environment, namely inhibition of respiration observed in both O(2) environments at 24 h was very similar, whereas O(2) consumption rate fell earlier in 1% O(2)-exposed cells. While no significant differences were detected at earlier time points, at 24 h tyrosine nitration was higher in normoxic vs. hypoxic cells.

CONCLUSIONS

Mitochondria are heavily implicated in sepsis. Mitochondrial antioxidants provide a mechanistic model for the development of potential therapies.

S-allylmercaptocysteine reduces carbon tetrachloride-induced hepatic oxidative stress and necroinflammation via nuclear factor kappa B-dependent pathways in mice

Purpose

To study the protective effects and underlying molecular mechanisms of SAMC on carbon tetrachloride (CCl₄)-induced acute hepatotoxicity in the mouse model.

Methods

Mice were intraperitoneally injected with CCl₄ (50 μl/kg; single dose) to induce acute hepatotoxicity with or without a 2-h pre-treatment of SAMC intraperitoneal injection (200 mg/kg; single dose). After 8 h, the blood serum and liver samples of mice were collected and subjected to measurements of histological and molecular parameters of hepatotoxicity.

Results

SAMC reduced CCl₄-triggered cellular necrosis and inflammation in the liver under histological analysis. Since co-treatment of SAMC and CCl₄ enhanced the expressions of antioxidant enzymes, reduced the nitric oxide (NO)-dependent oxidative stress, and inhibited lipid peroxidation induced by CCl₄. SAMC played an essential antioxidative role during CCl₄-induced hepatotoxicity. Administration of SAMC also ameliorated hepatic inflammation induced by CCl₄ via inhibiting the activity of NF-κB subunits p50 and p65, thus reducing the expressions of pro-inflammatory cytokines, mediators, and chemokines, as well as promoting pro-regenerative factors at both transcriptional and translational levels.

Conclusions

Our results indicate that SAMC mitigates cellular damage, oxidative stress, and inflammation in CCl₄-induced acute hepatotoxicity mouse model through regulation of NF-κB. Garlic or garlic derivatives may therefore be a potential food supplement in the prevention of liver damage.

Genetic deletion of NOS3 increases lethal cardiac dysfunction following mouse cardiac arrest

STUDY AIMS

Cardiac arrest mortality is significantly affected by failure to obtain return of spontaneous circulation (ROSC) despite cardiopulmonary resuscitation (CPR). Severe myocardial dysfunction and cardiovascular collapse further affects mortality within hours of initial ROSC. Recent work suggests that enhancement of nitric oxide (NO) signaling within minutes of CPR can improve myocardial function and survival. We studied the role of NO signaling on cardiovascular outcomes following cardiac arrest and resuscitation using endothelial NO synthase knockout (NOS3(-/-)) mice.

METHODS

Adult female wild-type (WT) and NOS3(-/-) mice were anesthetized, intubated, and instrumented with left-ventricular pressure-volume catheters. Cardiac arrest was induced with intravenous potassium chloride. CPR was performed after 8min of untreated arrest. ROSC rate, cardiac function, whole-blood nitrosylhemoglobin (HbNO) concentrations, heart NOS3 content and phosphorylation (p-NOS3), cyclic guanosine monophosphate (cGMP), and phospho-troponin I (p-TnI) were measured.

RESULTS

Despite equal quality CPR, NOS3(-/-) mice displayed lower rates of ROSC compared to WT (47.6% [10/21] vs. 82.4% [14/17], p<0.005). Among ROSC animals, NOS3(-/-) vs. WT mice exhibited increased left-ventricular dysfunction and 120min mortality. Prior to ROSC, myocardial effectors of NO signaling including cGMP and p-TnI were decreased in NOS3(-/-) vs. WT mice (p<0.05). Following ROSC in WT mice, significant NOS3-dependent increases in circulating HbNO were seen by 120min. Significant increases in cardiac p-NOS3 occurred between end-arrest and 15min post-ROSC, while total NOS3 content was increased by 120min post-ROSC (p<0.05).

CONCLUSIONS

Genetic deletion of NOS3 decreases ROSC rate and worsens post-ROSC left-ventricular function. Poor cardiovascular outcomes are associated with differences in NOS3-dependent myocardial cGMP signaling and circulating NO metabolites.

The effects of methylene blue on ovine post-pneumonectomy pulmonary oedema

BACKGROUND

We recently reported that post-pneumonectomy pulmonary oedema (PPO) occurs after ventilating the remaining lung with excessive tidal volumes. Studies in small animals have indicated that nitric oxide (NO) release increases in hyper-inflated lungs, but confirmatory evidence from larger animals is still lacking. We hypothesized that PPO could be prevented by methylene blue (MB), an inhibitor of NO synthase.

METHODS

Sheep were subjected to a right-sided pneumonectomy (PE) and randomly assigned to a protectively ventilated group ((PROTV group, n=7) with tidal volumes of 6 ml/kg at 20 inflations/min and a positive end-expiratory pressure (PEEP) of 2 cmH(2)O, and two groups undergoing 'injurious ventilation' (INJV) with tidal volumes of 12 ml/kg and zero end-expiratory pressure (ZEEP), a control group (INJV group, n=7) and a treatment group subjected to MB 1 h after PE (INJV+MB group, n=7). Haemodynamic variables, lung mechanics, blood gases and plasma nitrites and nitrates (NOx) were determined.

RESULTS

PE reduced pulmonary blood volume, extravascular lung water (EVLWI) and quasistatic lung compliance in all groups, in parallel with a rise in peak airway pressure (P<0.05). In the INJV group, pulmonary arterial pressure, EVLWI and pulmonary vascular permeability index increased and arterial oxygenation decreased towards cessation of the experiments. These changes were not antagonized by MB. Plasma NOx increased in all the groups compared with baseline, but with no intergroup difference.

CONCLUSION

MB did not reduce PPO and accumulation of NOx in sheep subjected to ventilation with excessive tidal volumes and ZEEP.

Methaemoglobinaemia risk factors with inhaled nitric oxide therapy in newborn infants

BACKGROUND

Inhaled nitric oxide (iNO), commonly used for hypoxic neonates, may react with haemoglobin to form methaemoglobin (MetHb). MetHb monitoring during iNO therapy has been questioned since low doses of iNO are used.

AIM

To evaluate the incidence of and identify risk factors associated with elevated MetHb in neonates treated with iNO.

METHODS

Neonates who were treated with iNO and had at least one MetHb measurement were included. Demographic characteristics and methods of iNO administration (dosage, duration) at the time of each MetHb measurement were analysed.

RESULTS

Four hundred and fifty-two MetHb measurements from 81 premature and 82 term and near-term infants were analysed. MetHb was above 5% in one-term infant, and between 2.5-5% in 16 infants. A higher maximum dose of iNO (22.7 vs 17.7 p.p.m.), but not gestational age, was a significant risk factor for elevated MetHb. Significantly higher oxygen levels (75.5% vs 51.7%) were associated with higher MetHb in term infants. Preterm infants had no risk for high MetHb when iNO was kept below 8 p.p.m. These data suggest the possibility of limiting blood withdrawal when low doses iNO are used.

CONCLUSION

High MetHb is exceptional in neonates treated with low dose iNO. Associated risk factors are related to high iNO dose and the simultaneous use of high concentrations of oxygen.

Identification of KT-15073 as an inhibitor of lipopolysaccharide-induced microglial activation

Neuroinflammation has recently been implicated as an important mechanism responsible for the progression of neurodegenerative diseases. Activated microglia produce various proinflammatory cytokines and nitric oxide (NO) that are toxic to neurons. Thus, inhibition of microglial activation may alleviate neuroinflammatory and neurodegenerative processes. Among several fluorovinyloxyacetamide derivatives that were screened by microglia cell-based assay, a novel synthetic compound KT-15073 was identified to strongly attenuate the microglial production of NO and tumor necrosis factor-alpha (TNF-alpha). This compound also suppressed the gene expression of interleukin-1beta, inducible nitric oxide synthase, and TNF-alpha. KT-15073 inhibited the nuclear translocation and DNA binding of nuclear factor-kappaB as well as phosphorylation of p38 mitogen-activated protein kinase. In addition, KT-15073 reduced the cytotoxicity of lipopolysaccharide (LPS)-stimulated microglia toward B35 neuroblastoma cells in the microglia/neuroblastoma coculture, suggesting that the compound might exhibit the neuroprotective activity. Thus, KT-15073 has an anti-inflammatory activity in microglia, and may have a therapeutic potential for the treatment of neuroinflammatory or neurodegenerative diseases.

Hypercapnic acidosis in ventilator-induced lung injury

RATIONALE

Permissive hypercapnia is established in lung injury management. Therapeutic hypercapnia causes benefit or harm, depending on the context. Ventilator-associated lung injury has a wide spectrum of candidate mechanisms, affording multiple opportunities for intervention such as hypercapnia to exert benefit or harm.

OBJECTIVES

To confirm (1) that hypercapnia attenuates in vivo ventilator-induced lung injury (VILI); (2) biological plausibility of such protection (e.g., dose-response, time series, inflammatory profile); and (3) that the associated biochemical events are consistently beneficial.

METHODS

A mouse model of VILI was established in vivo. Injurious ventilation was established, hypercapnia applied and markers of inflammation measured.

MEASUREMENTS

Lung injury was quantified by gas exchange, elastance, microvascular leak, histology and levels of cytokines and eicosanoids, cyclooxygenase and tissue nitrotyrosine.

MAIN RESULTS

Injurious ventilation caused significant lung injury (mechanics, microvascular leak, histology) and release of inflammatory cytokines, chemokines and eicosanoids. Hypercapnia attenuated these responses, with dose-response and time-dependent effects. No adverse effects of hypercapnia were observed in controls. Hypercapnia suppressed the transcription (mRNA) and translation (protein) of the major inducible prostanoid-generating enzyme (COX-2), but the effects on the downstream eicosanoids were modest. However, hypercapnia significantly increased lung tissue nitrotyrosine-at PaCO(2) levels that were protective.

CONCLUSIONS

Hypercapnia provided consistent and biologically plausible in vivo protection against VILI, but elevated lung tissue levels of nitro-tyrosine as previously described in sepsis. Clinicians and those designing clinical trials need to be aware of the potential for detrimental effects when using hypercapnia in order to balance benefits versus harm with this approach.

Nitric oxide, derived from inducible nitric oxide synthase, decreases hypoxia inducible factor-1alpha in macrophages during aspirin-induced mesenteric inflammation

BACKGROUND AND PURPOSE

Nitric oxide (NO) modulates expression of hypoxia inducible factor-1 (HIF-1), a transcription factor regulating function of myeloid cells. Here, we have assessed the role played by NO, formed by inducible NOS (iNOS), in the inflammation induced by aspirin in the gut, by modulating HIF-1 activity.

EXPERIMENTAL APPROACH

The role of iNOS-derived NO on leucocyte-endothelial interactions induced by aspirin was evaluated by intravital microscopy in mesenteric venules of rats pretreated with selective iNOS inhibitors, 1400W or l-N6-(1-iminoethyl)-lysine. NO was localized by fluorescence microscopy, using DAF-FM. iNOS, HIF-1alpha and CD36 were localized by immunohistochemistry.

KEY RESULTS

Leucocyte-endothelial interactions increased at 6 h and returned to normal levels 24 h after aspirin administration. Numbers of migrated leucocytes were similar between 6 and 24 h after aspirin. iNOS expression and iNOS-derived NO synthesis were observed in leucocytes of the mesentery of aspirin-treated rats. Blockade of iNOS activity in aspirin-treated rats: (i) did not modify leucocyte infiltration at 6 h, but reduced the number of polymorphonuclear leucocyte and increased that of macrophages at 24 h; (ii) increased HIF-1alpha immunostaining in macrophages of the mesentery; and (iii) prevented the decrease in CD36 immunostaining induced by aspirin in these cells.

CONCLUSIONS AND IMPLICATIONS

NO, associated with acute gut inflammation induced by aspirin, diminished HIF-1alpha stabilization in macrophages. Early inhibition of iNOS-derived NO synthesis, by increasing the activity of HIF-1 in these cells, may accelerate the clearance of leucocytes.

MMP-2, MMP-9, and iNOS expression in human dental pulp subjected to orthodontic traction

OBJECTIVE

To test the hypothesis that some metalloproteinases (MMP-2, MMP-9) and inducible nitric oxide synthetase (iNOS) enzymes in dental pulp samples do not vary when subjected to orthodontic treatment.

MATERIALS AND METHODS

Human dental pulps were taken from male and female patients (N=10; age 10-14 years). A straight wire technique was used with nickel-titanium or steel archwires. The increase of pressure applied on teeth was gradual. Five patients were subjected to premolar extractions after 14 months of treatment and one after 24 months. Samples were Bouin-fixed, paraffin-embedded, and afterwards processed for immunohistochemistry using anti-MMP-2, anti-MMP-9, and anti-iNOS antibodies.

RESULTS

A reduction of MMP-2, MMP-9, and iNOS expression occurred in treated samples. This became more evident with increased treatment time.

CONCLUSION

The hypothesis is rejected. The reduction of expression of those proteins revealed a time-dependent relationship.

Potential role for lipopolysaccharide in congenital sensorineural hearing loss

Congenital sensorineural hearing loss (SNHL) is common. In the Western world, the incidence is 1-3 per 1000 live births. The aetiology encompasses genetic and non-genetic factors accounting for 55 % and 45 % of cases, respectively. Reports that describe the contribution of intrauterine infection to the occurrence of congenital SNHL are limited, and comparative analysis of the different pathogens is lacking. Lipopolysaccharide (LPS), a product of bacteriolysis, has been demonstrated to be associated with inner ear damage in experimental studies. To elucidate the potential role of this toxin in congenital SNHL and to identify the pathogenesis and transmission routes, we reviewed the literature. We speculate that different routes of exposure to LPS in utero may result in congenital inner ear damage.

Biochemical and cellular toxicology of peroxynitrite: implications in cell death and autoimmune phenomenon

Reactive nitrogen species include nitric oxide (.NO), peroxynitrite (ONOO(-)) and nitrogen dioxide radical (NO2*). Peroxynitrite is a reactive oxidant, produced from nitric oxide (*NO) and superoxide anion (O(2*-), that reacts with a variety of biological macromolecules. It is produced in the body in response to physiological stress and environmental toxins. It is a potent trigger of oxidative protein and DNA damage-including DNA strand breakage and base modification. It activates the nuclear enzyme poly-ADP ribose polymerase (PARP) resulting in energy depletion and apoptosis/necrosis of cells. Peroxynitrite generation is a crucial pathological mechanism in stroke, diabetes, inflammation, neurodegeneration, cancer, etc. Peroxynitrite modified DNA may also lead to the generation of autoantibodies in various autoimmune disorders such as systemic lupus erythematosus (SLE). In chronic inflammatory diseases, peroxynitrite formed by phagocytic cells may cause damage to DNA, generating neoepitopes leading to the production of autoantibodies. Hence, understanding the pathophysiology of peroxynitrite could lead to important therapeutic interventions.

Role of arginine guanidinium moiety in nitric-oxide synthase mechanism of oxygen activation

Nitric-oxide synthases (NOS) are highly regulated heme-thiolate enzymes that catalyze two oxidation reactions that sequentially convert the substrate L-Arg first to N(omega)-hydroxyl-L-arginine and then to L-citrulline and nitric oxide. Despite numerous investigations, the detailed molecular mechanism of NOS remains elusive and debatable. Much of the dispute in the various proposed mechanisms resides in the uncertainty concerning the number and sources of proton transfers. Although specific protonation events are key features in determining the specificity and efficiency of the two catalytic steps, little is known about the role and properties of protons from the substrate, cofactors, and H-bond network in the vicinity of the heme active site. In this study, we have investigated the role of the acidic proton from the L-Arg guanidinium moiety on the stability and reactivity of the ferrous heme-oxy complex intermediate by exploiting a series of L-Arg analogues exhibiting a wide range of guanidinium pK(a) values. Using electrochemical and vibrational spectroscopic techniques, we have analyzed the effects of the analogues on the heme, including characteristics of its proximal ligand, heme conformation, redox potential, and electrostatic properties of its distal environment. Our results indicate that the substrate guanidinium pK(a) value significantly affects the H-bond network near the heme distal pocket. Our results lead us to propose a new structural model where the properties of the guanidinium moiety finely control the proton transfer events in NOS and tune its oxidative chemistry. This model may account for the discrepancies found in previously proposed mechanisms of NOS oxidation processes.

PGC-1-related coactivator modulates mitochondrial-nuclear crosstalk through endogenous nitric oxide in a cellular model of oncocytic thyroid tumours

Background

The PGC-1 related coactivator (PRC), which shares structural and functional features with PGC-1α, is believed to regulate several metabolic pathways as well as mitochondrial biogenesis. Its involvement in the early programming of cell proliferation suggests the existence of finely regulated crosstalk between mitochondrial functions and the cell cycle status.

Methodology/Principal Findings

PRC-regulated pathways were explored in a cell-line model derived from mitochondrial-rich tumours with an essentially oxidative metabolism and specifically high PRC expression. The functional status of mitochondria was compared to the results of microarray analysis under conditions of temporal PRC inhibition. To specify the fine PRC regulation, the expression levels of the genes and proteins involved in the oxidative phosphorylation process were studied by real time quantitative PCR and western blotting. As in earlier studies on PGC-1α, we investigated the role of nitric oxide in PRC-regulated mitochondrial biogenesis and determined its action in the control of the phosphorylation status of the mitogen-activated protein kinase pathway.

Conclusion/Significance

We found that nitric oxide rapidly influences PRC expression at the transcriptional level. Focusing on mitochondrial energetic metabolism, we observed that PRC differentially controls respiratory chain complexes and coupling efficiency in a time-dependent manner to maintain mitochondrial homeostasis. Our results highlight the key role of PRC in the rapid modulation of metabolic functions in response to the status of the cell cycle.

Mechanisms of peroxynitrite-mediated nitration of tyrosine

The mechanisms of tyrosine nitration by peroxynitrous acid or nitrosoperoxycarbonate were investigated with the CBS-QB3 method. Either the protonation of peroxynitrite or a reaction with carbon dioxide gives a reactive peroxide intermediate. Peroxynitrous acid-mediated nitration of phenol occurs via unimolecular decomposition to give nitrogen dioxide and hydroxyl radicals. Nitrosoperoxycarbonate also undergoes unimolecular decomposition to give carbonate and nitrogen dioxide radicals. The reactions of tyrosine with the hydroxyl or carbonate radicals give a phenoxy radical intermediate. The reaction of the nitrogen dioxide with this radical intermediate followed by tautomerization gives nitrated tyrosine in both cases. According to CBS-QB3 calculations, the rate-limiting step for the nitration of phenol is the decomposition of peroxynitrous acid or nitrosoperoxycarbonate.

TNP-470 Inhibits Oxidative Stress, Nitric Oxide Production and Nuclear Factor Kappa B Activation in a Rat Model of Hepatocellular Carcinoma

The objective of this study is to determine if treatment with the angiogenesis inhibitor TNP-470 results in impairment of oxidative stress, inhibition of nuclear factor kappa B (NF-kappaB) activation and decrease of nitric oxide production in an experimental model of rat hepatocarcinogenesis. Tumour was induced by diethylnitrosamine and promoted by two-thirds hepatectomy plus acetaminofluorene administration. Experiments were carried out at 28 weeks after initiating the treatment. TNP-470 was administered at 30mg/kg, three times per week from 20 to 28 weeks. Carcinomatous tissue growing outside dysplastic nodules and a marked expression of placental glutathione S-transferase were detected in rats with induced carcinogenesis. Liver concentrations of thiobarbituric acid reactive substances, reduced glutathione (GSH) and glutathione disulfide (GSSG) were significantly higher than those of controls and there was a significant increase in the GSSG/GSH ratio. Tumour growth was accompanied by augmented expression of inducible nitric oxide synthase, activation of (NF-kappaB) and proteolysis of IkappaB. All these effects were absent in animals receiving TNP-470. Our results indicate that TNP-470 inhibits oxidative stress, nitric oxide production and NF-kappaB activation induced by experimental hepatocarcinogenesis. These changes would contribute to the beneficial effects of TNP-470 in cancer treatment.

Transcriptional profiling identifies the metabolic phenotype of gonococcal biofilms

Neisseria gonorrhoeae, the etiologic agent of gonorrhea, is frequently asymptomatic in women, often leading to chronic infections. One factor contributing to this may be biofilm formation. N. gonorrhoeae can form biofilms on glass and plastic surfaces. There is also evidence that biofilm formation may occur during natural cervical infection. To further study the mechanism of gonococcal biofilm formation, we compared transcriptional profiles of N. gonorrhoeae biofilms to planktonic profiles. Biofilm RNA was extracted from N. gonorrhoeae 1291 grown for 48 h in continuous-flow chambers over glass. Planktonic RNA was extracted from the biofilm runoff. In comparing biofilm with planktonic growth, 3.8% of the genome was differentially regulated. Genes that were highly upregulated in biofilms included aniA, norB, and ccp. These genes encode enzymes that are central to anaerobic respiratory metabolism and stress tolerance. Downregulated genes included members of the nuo gene cluster, which encodes the proton-translocating NADH dehydrogenase. Furthermore, it was observed that aniA, ccp, and norB insertional mutants were attenuated for biofilm formation on glass and transformed human cervical epithelial cells. These data suggest that biofilm formation by the gonococcus may represent a response that is linked to the control of nitric oxide steady-state levels during infection of cervical epithelial cells.

Detection of exhaled hydrogen sulphide gas in rats exposed to intravenous sodium sulphide

BACKGROUND AND PURPOSE

Sodium sulphide (Na(2)S) disassociates to sodium (Na(+)) hydrosulphide, anion (HS(-)) and hydrogen sulphide (H(2)S) in aqueous solutions. Here we have established and characterized a method to detect H(2)S gas in the exhaled breath of rats.

EXPERIMENTAL APPROACH

Male rats were anaesthetized with ketamine and xylazine, instrumented with intravenous (i.v.) jugular vein catheters, and a tube inserted into the trachea was connected to a pneumotach connected to a H(2)S gas detector. Sodium sulphide, cysteine or the natural polysulphide compound diallyl disulphide were infused intravenously while the airway was monitored for exhaled H(2)S real time.

KEY RESULTS

Exhaled sulphide concentration was calculated to be in the range of 0.4-11 ppm in response to i.v. infusion rates ranging between 0.3 and 1.1 mg x kg(-1) x min(-1). When nitric oxide synthesis was inhibited with N(omega)-nitro-L-arginine methyl ester the amount of H(2)S exhaled during i.v. infusions of sodium sulphide was significantly increased compared with that obtained with the vehicle control. An increase in circulating nitric oxide using DETA NONOate [3,3-bis(aminoethyl)-1-hydroxy-2-oxo-1-triazene] did not alter the levels of exhaled H(2)S during an i.v. infusion of sodium sulphide. An i.v. bolus of L-cysteine, 1 g.kg(-1), and an i.v. infusion of the garlic derived natural compound diallyl disulphide, 1.8 mg x kg(-1) x min(-1), also caused exhalation of H(2)S gas.

CONCLUSIONS AND IMPLICATIONS

This method has shown that significant amounts of H(2)S are exhaled in rats during sodium sulphide infusions, and the amount exhaled can be modulated by various pharmacological interventions.

Resistance to peroxynitrite in Neisseria gonorrhoeae

Neisseria gonorrhoeae encodes a number of important genes that aid in survival during times of oxidative stress. The same immune cells capable of oxygen-dependent killing mechanisms also have the capacity to generate reactive nitrogen species (RNS) that may function antimicrobially. F62 and eight additional gonococcal strains displayed a high level of resistance to peroxynitrite, while Neisseria meningitidis and Escherichia coli showed a four- to seven-log and a four-log decrease in viability, respectively. Mutation of gonococcal orthologues that are known or suspected to be involved in RNS defence in other bacteria (ahpC, dnrN and msrA) resulted in no loss of viability, suggesting that N. gonorrhoeae has a novel mechanism of resistance to peroxynitrite. Whole-cell extracts of F62 prevented the oxidation of dihydrorhodamine, and decomposition of peroxynitrite was not dependent on ahpC, dnrN or msrA. F62 grown in co-culture with E. coli strain DH10B was shown to protect E. coli viability 10-fold. Also, peroxynitrite treatment of F62 did not result in accumulation of nitrated proteins, suggesting that an active peroxynitrite reductase is responsible for peroxynitrite decomposition rather than a protein sink for amino acid modification.

Sulfaphenazole protects heart against ischemia-reperfusion injury and cardiac dysfunction by overexpression of iNOS, leading to enhancement of nitric oxide bioavailability and tissue oxygenation

The objective of this study was to establish the cardioprotective effect of sulfaphenazole (SPZ), a selective inhibitor of cytochrome P450 2C9 enzyme, in an in vivo rat model of acute myocardial infarction (MI). MI was induced by 30 min ligation of left anterior descending coronary artery, followed by 24 h reperfusion (I/R). The study used 6 groups: I/R (control); SPZ; L-NAME; L-NAME + SPZ; 1400W (an inhibitor of iNOS); 1400W + SPZ. The agents were administered orally through drinking water for 3 days prior to induction of I/R. Myocardial oxygenation (pO(2)) at the I/R site was measured using EPR oximetry. The preischemic pO(2) value was 18 +/- 2 mm Hg in all groups. At 1 h of reperfusion, the SPZ group showed a significantly higher hyperoxygenation when compared to control (45 +/- 1 vs. 34 +/- 2 mm Hg). The SPZ group showed a significant improvement in the contractile functions and reduction in infarct size. Histochemical staining of SPZ-treated hearts exhibited significantly lower levels of superoxide and peroxynitrite, and markedly increased levels of iNOS activity and nitric oxide. Western blot analysis indicated upregulation of Akt and attenuation of p38MAPK activities in the reperfused myocardium. The study established that SPZ attenuated myocardial I/R injury through overexpression of iNOS, leading to enhancement of nitric oxide bioavailability and tissue oxygenation.

Transcriptional regulation of metabolic pathways, alternative respiration and enterotoxin genes in anaerobic growth of Bacillus cereus ATCC 14579

AIMS

To assess genes specifically activated during anaerobic growth that are involved in metabolism and pathogenesis of the foodborne pathogen Bacillus cereus.

METHODS AND RESULTS

Growth under anaerobic conditions in Brain Heart Infusion (BHI) broth revealed a reduced growth rate and lower yield as compared to growth under aerobic conditions. Subsequently, comparative transcriptome analysis showed specific genes induced under anaerobic conditions. These included novel genes identified for anaerobic growth of B. cereus, encoding metabolic pathways, such as the arginine deiminase pathway (ArcABDC), formate dehydrogenase (FdhF) and pyruvate formate lyase (Pfl), and alternative respiratory proteins, such as arsenate reductases. Notably, haemolytic enzyme encoding genes were induced during anaerobic growth, and enterotoxin genes were induced in high cell density transition and stationary phases of aerobic cultures.

CONCLUSIONS

These data point to induction of stress adaptation and pathogenicity factors and rearrangements of expression of metabolic pathways in response to oxygen limitations in B. cereus.

SIGNIFICANCE AND IMPACT OF THE STUDY

The reported changes in gene expression show that the foodborne pathogen B. cereus can adjust to anaerobic conditions, such as encountered in the human GI-tract.

Differential effects of nitric oxide synthesis on pulmonary vascular function during lung ischemia-reperfusion injury

Lung ischemia-reperfusion (IR) injury causes alveolar, epithelial and endothelial cell dysfunction which often results in decreased alveolar perfusion, characteristic of an acute respiratory distress syndrome. Nitric oxide (NO) from endothelium-derived NO synthase (eNOS) helps maintain a low pulmonary vascular resistance. Paradoxically, during acute lung injury, overproduction of NO via inducible NO synthase (iNOS) and oxidative stress lead to reactive oxygen and nitrogen species (ROS and RNS) formation and vascular dysfunction. RNS potentiate vascular and cellular injury by oxidation, by decreasing NO bioavailability, and by regulating NOS isoforms. RNS potentiate their own production by uncoupling NO production through eNOS by oxidation and disruption of Akt-mediated phosphorylation of eNOS. This review focuses on effects of NO which cause vascular dysfunction in the unique environment of the lung and presents a hypothesis for interplay between eNOS and iNOS activation with implications for development of new strategies to treat vascular dysfunction associated with IR.

Nitric oxide and vascular reactivity in sepsis

Sepsis and septic shock are major causes of morbidity and mortality in critically ill patients. Sepsis and septic shock induce a profound fall in the peripheral vascular tone. NO has been implicated as a key player in vascular changes of sepsis and septic shock. In this brief review, two points are focused in greater detail: first, the involvement of guanylate cyclase and potassium channels in NO vascular effects in sepsis; second, the role played by NO and its two effectors in the long-lasting modifications of vascular reactivity in sepsis. Some recent developments in the area are reviewed.

Differences in nitric oxide steady states between arginine, hypoxanthine, uracil auxotrophs (AHU) and non-AHU strains of Neisseria gonorrhoeae during anaerobic respiration in the presence of nitrite

Neisseria gonorrhoeae can grow by anaerobic respiration using nitrite as an alternative electron acceptor. Under these growth conditions, N. gonorrhoeae produces and degrades nitric oxide (NO), an important host defense molecule. Laboratory strain F62 has been shown to establish and maintain a NO steady-state level that is a function of the nitrite reductase/NO reductase ratio and is independent of cell number. The nitrite reductase activities (122-197 nmol NO2 reduced x min(-1) x OD600(-1)) and NO reductase activities (88-155 nmol NO reduced x min(-1) x OD600(-1)) in a variety of gonococcal clinical isolates were similar to the specific activities seen in F62 (241 nmol NO2 reduced x min(-1) x OD600(-1) and 88 nmol NO reduced x min(-1) x OD600(-1), respectively). In seven gonococcal strains, the NO steady-state levels established in the presence of nitrite were similar to that of F62 (801-2121 nmol x L-1 NO), while six of the strains, identified as arginine, hypoxanthine, and uracil auxotrophs (AHU), that cause asymptomatic infection in men had either two- to threefold (373-579 nmol x L-1 NO) or about 100-fold (13-24 nmol x L-1 NO) lower NO steady-state concentrations. All tested strains in the presence of a NO donor, 2,2'-(hydroxynitrosohydrazono)bis-ethanimine/NO, quickly lowered and maintained NO levels in the noninflammatory range of NO (<300 nmol x L-1). The generation of a NO steady-state concentration was directly affected by alterations in respiratory control in both F62 and an AHU strain, although differences in membrane function are suspected to be responsible for NO steady-state level differences in AHU strains.

Methylene blue in the treatment of vasoplegia following severe burns

Vasoplegia resulting from severe burns may persist despite adequate fluid resuscitation and treatment with norepinephrine (NE), vasopressin (VP), and steroids. The adenylate cyclase inhibitor methylene blue (MB), currently used in the burn patient to treat methemoglobinemia, has been used to treat vasoplegia after cardiopulmonary bypass. We report the case of MB infusion in two burn patients refractory to NE. The patients had severe burns, 95 and 80% TBSA not responding to conventional treatment. Fluid requirements were estimated according to Parkland formula and then to maintain a urinary output of 30-50 ml/hr. Patient #1, 95% TBSA, was adrenally insufficient and was receiving steroids according to the Annane protocol, as well as VP at 0.2 U/min. His NE requirements were 55 mcg/kg/min. Patient #2, 80% TBSA, was receiving 20 mcg/kg/min of NE. Circulatory failure was defined as inability to maintain mean arterial pressure >70 mm Hg. Hemodynamic and physiologic parameters were measured before and after infusion of a single dose of 2 mg/kg of MB. Both patients showed dramatic improvements in their shock after MB. Patient #1 had an initial reaction within 30 minutes and reached peak effect at 1 hour. His NE requirements decreased to 0.2 mcg/kg/min and VP decreased to 0.04 U/min. Patient #2 showed effects within 15 minutes of the infusion and by 2 hours the NE was stopped. No adverse side effects were noted in either of the two patients. The fact that MB successfully reversed refractory vasoplegia after severe burns suggests a new tool for treating a small subgroup of patients who exhibit persistent vasoplegia from their burn injury. A controlled randomized trial is needed to test its effects on a large number of patients and graft survival.

Roles of nitric oxide in inflammatory downregulation of human cytochromes P450

The purpose of this study was to determine the role of nitric oxide (NO) in the downregulation of human cytochrome P450 (CYP) enzymes and mRNAs by an inflammatory stimulus in cultured human hepatocytes. We focused on CYP2B6 because previous studies showed that rat CYP2B proteins undergo an NO-dependent degradation in response to inflammatory stimuli. To ensure high-level expression of CYP2B6, the inducer phenytoin was present at all times. Stimulation of cells with a mixture of tumor necrosis factor-alpha, interleukin-1, and interferon-gamma (ILmix) downregulated CYP2B6 mRNA and protein to 9 and 19% of control levels. The NO donor NOC-18 downregulated CYP2B6 protein to 30% of control, with only a small effect on CYP2B6 mRNA. Nitric oxide synthase inhibitors attenuated the downregulation of CYP2B6 protein but not mRNA by ILmix. These findings demonstrate that the posttranscriptional NO-dependent downregulation of CYP2B enzymes, observed previously in rat hepatocytes, is conserved in human CYP2B6. This mechanism is specific for CYP2B6 among the enzymes tested. No evidence was found for regulation of CYP2E1 mRNA or protein by NO. NOC-18 treatment downregulated CYP3A4 mRNA to 50% of control. However, NOS inhibitors failed to block the effects of ILmix on CYP3A4 expression.

Nitrogen and oxygen molecules in meningitis-associated labyrinthitis and hearing impairment

Pneumococcal meningitis remains a serious disease with a case fatality rate of 15%-25%. Furthermore, long-term residues affect up to 50% of survivors. One of the most frequent sequelae is sensorineural hearing loss, which occurs in 26% of survivors of pneumococcal meningitis. Unfortunately, sufficient treatment regimens are still missing. New insights into the pathology and pathophysiology of meningitis-associated hearing loss have come from animal models of bacterial meningitis. Most likely, bacteria reach the cochlea through the cochlear aquaeduct. Once arrived in the perilymphatic spaces, they induce a severe suppurative labyrinthitis. The blood-labyrinth barrier breaks, hair cells are damaged, and neurons in the spiral ganglion undergo cell death, leading to meningitis-associated hearing loss. Reactive oxygen and nitrogen species, in particular peroxynitrite, seem to be among the crucial mediators of cochlear damage and hearing loss during meningitis. In our rat model of pneumococcal meningitis, adjunctive therapy with the antioxidants and peroxynitrite scavengers Mn(III)tetrakis(4-bencoic acid)-porphyrin (MnTBAP) and N-Acetyl-L-Cystein (NAC) significantly attenuated acute and long-term hearing loss. In several other animal studies of pneumococcal meningitis, adjunctive antioxidant therapy also protected infected animals from intracranial complications. Therefore, the use of antioxidants seems to be a promising future treatment option in pneumococcal meningitis.