Impact of inhaled nitric oxide on platelet aggregation and fibrinolysis in rats with endotoxic lung injury. Role of cyclic guanosine 5'-monophosphate

Inhaled nitric oxide: role in the pathophysiology of cardio-cerebrovascular and respiratory diseases

Nitric oxide (NO) is a key molecule in the biology of human life. NO is involved in the physiology of organ viability and in the pathophysiology of organ dysfunction, respectively. In this narrative review, we aimed at elucidating the mechanisms behind the role of NO in the respiratory and cardio-cerebrovascular systems, in the presence of a healthy or dysfunctional endothelium. NO is a key player in maintaining multiorgan viability with adequate organ blood perfusion. We report on its physiological endogenous production and effects in the circulation and within the lungs, as well as the pathophysiological implication of its disturbances related to NO depletion and excess. The review covers from preclinical information about endogenous NO produced by nitric oxide synthase (NOS) to the potential therapeutic role of exogenous NO (inhaled nitric oxide, iNO). Moreover, the importance of NO in several clinical conditions in critically ill patients such as hypoxemia, pulmonary hypertension, hemolysis, cerebrovascular events and ischemia-reperfusion syndrome is evaluated in preclinical and clinical settings. Accordingly, the mechanism behind the beneficial iNO treatment in hypoxemia and pulmonary hypertension is investigated. Furthermore, investigating the pathophysiology of brain injury, cardiopulmonary bypass, and red blood cell and artificial hemoglobin transfusion provides a focus on the potential role of NO as a protective molecule in multiorgan dysfunction. Finally, the preclinical toxicology of iNO and the antimicrobial role of NO-including its recent investigation on its role against the Sars-CoV2 infection during the COVID-19 pandemic-are described.

The effect of tadalafil therapy on kidney damage caused by sepsis in a polymicrobial septic model induced in rats: a biochemical and histopathological study

Introduction

Sepsis is an inflammatory reaction to bacteria involving the whole body and is a significant cause of mortality and economic costs. The purpose of this research was to determine whether tadalafil exhibits a preventive effect on sepsis in a septic model induced in rats with cecal ligation and puncture (CLP).

Materials and Methods

Rats were randomly separated into groups, 10 rats in each: (i) a sham (control) group, (ii) an untreated sepsis group, (iii) a sepsis group treated with 5mg/kg tadalafil and (iv) a sepsis group treated with 10mg/kg tadalafil. A polymicrobial sepsis model was induced in rats using CLP. Rats were sacrificed after 16h, and blood and kidney tissues were collected for biochemical and histopathological study.

Results

Levels of the inflammatory parameter IL-6 decreased significantly in the sepsis groups receiving tadalafil in comparison with the untreated sepsis group (p<0.05). In terms of histopathology, inflammation scores investigated in kidney tissues decreased significantly in the sepsis groups receiving tadalafil compared to the untreated sepsis group (p<0.05). In addition, levels of creatinine and cystatin C measured in septic rats receiving tadalafil were lower by a clear degree than in septic rats (p<0.05).

Conclusion

In this study, tadalafil exhibited a preventive effect for sepsis-related damage by suppressing inflammation in serum and kidney tissue of septic rats in a polymicrobial sepsis model induced with CLP.

Nitric oxide charged catheters as a potential strategy for prevention of hospital acquired infections

BACKGROUND

Catheter-Associated Hospital-Acquired Infections (HAI's) are caused by biofilm-forming bacteria. Using a novel approach, we generated anti-infective barrier on catheters by charging them with Nitric Oxide (NO), a naturally-produced gas molecule. NO is slowly released from the catheter upon contact with physiological fluids, and prevents bacterial colonization and biofilm formation onto catheter surfaces.

AIMS AND METHODS

The aim of the study was to assess the anti-infective properties of NO-charged catheters exposed to low concentration (up to 103 CFU/ml) of microbial cells in-vitro. We assessed NO-charged tracheal tubes using Pseudomonas aeruginosa, dialysis and biliary catheters using Escherichia coli, and urinary catheters using E. coli, Candida albicans or Enterococcus faecalis. Safety and tolerability of NO-charged urinary catheters were evaluated in a phase 1 clinical study in 12 patients. Six patients were catheterized with NO-charged catheters (NO-group), followed by 6 patients catheterized with regular control catheters (CT-group). Comparison of safety parameters between the study groups was performed.

RESULTS

NO-charged tracheal, dialysis biliary and urinary catheters prevented P. aeruginosa, E. coli and C. albicans attachment and colonization onto their surfaces and eradicated corresponding planktonic microbial cells in the surrounding media after 24-48 hours, while E. faecalis colonization onto urinary catheters was reduced by 1 log compared to controls. All patients catheterized with an NO-charged urinary catheter successfully completed the study without experiencing NO-related AE's or serious AE's (SAE's).

CONCLUSION

These data highlight the potential of NO-based technology as potential platform for preventing catheter-associated HAI's.

Prevention of hyperoxia-induced bronchial hyperreactivity by sildenafil and vasoactive intestinal peptide: impact of preserved lung function and structure

Objective

Hyperoxia exposure leads to the development of lung injury and bronchial hyperreactivity (BHR) via involvement of nitric oxide (NO) pathway. We aimed at characterizing whether the stimulation of the NO pathway by sildenafil or vasoactive intestinal peptide (VIP) is able to prevent the hyperoxia-induced development of BHR. The respective roles of the preserved lung volume and alveolar architecture, the anti-inflammatory and anti-apoptotic potentials of these treatments in the diminished lung responsiveness were also characterized.

Materials and methods

Immature (28-day-old) rats were exposed for 72 hours to room air (Group C), hyperoxia (>95%, Group HC), or hyperoxia with the concomitant administration of vasoactive intestinal peptide (VIP, Group HV) or sildenafil (Group HS). Following exposure, the end-expiratory lung volume (EELV) was assessed plethysmographically. Airway and respiratory tissue mechanics were measured under baseline conditions and following incremental doses of methacholine to assess BHR. Inflammation was assessed by analyzing the bronchoalveolar lavage fluid (BALF), while biochemical and histological analyses were used to characterize the apoptotic and structural changes in the lungs.

Results

The BHR, the increased EELV, the aberrant alveolarization, and the infiltration of inflammatory cells into the BALF that developed in Group HC were all suppressed significantly by VIP or sildenafil treatment. The number of apoptotic cells increased significantly in Group HC, with no evidence of statistically significant effects on this adverse change in Groups HS and HV.

Conclusions

These findings suggest that stimulating the NO pathway by sildenafil and VIP exert their beneficial effect against hyperoxia-induced BHR via preserving normal EELV, inhibiting airway inflammation and preserving the physiological lung structure, whereas the antiapoptotic potential of these treatments were not apparent in this process.

Role of the hemostatic system on sickle cell disease pathophysiology and potential therapeutics

Recent studies suggest that sickle cell disease (SCD) is a hypercoagulable state contributing to vaso-occlusive events in the microcirculation, resulting in acute and chronic sickle cell-related organ damage. In this article, we review the existing evidence for contribution of hemostatic system perturbation to SCD pathophysiology. We also review the data showing increased risk of thromboembolic events, particularly newer information on the incidence of venous thromboembolism. Finally, the potential role of platelet inhibitors and anticoagulants in SCD is briefly reviewed.

Propofol exerts anti-inflammatory effects in rats with lipopolysaccharide-induced acute lung injury by inhibition of CD14 and TLR4 expression

We investigated the effect of propofol (Prop) administration (10 mg kg-1 h-1, intravenously) on lipopolysaccharide (LPS)-induced acute lung injury and its effect on cluster of differentiation (CD) 14 and Toll-like receptor (TLR) 4 expression in lung tissue of anesthetized, ventilated rats. Twenty-four male Wistar rats were randomly divided into three groups of 8 rats each: control, LPS, and LPS+Prop. Lung injury was assayed via blood gas analysis and lung histology, and tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) levels were determined in bronchoalveolar lavage fluid using ELISA. Real-time polymerase chain reaction was used to detect CD14 and TLR4 mRNA levels, and CD14 and TLR4 protein expression was determined by Western blot. The pathological scores were 1.2 ± 0.9, 3.3 ± 1.1, and 1.9 ± 1.0 for the control, LPS, and LPS+Prop groups, respectively, with statistically significant differences between control and LPS groups (P < 0.05) and between LPS and LPS+Prop groups (P < 0.05). The administration of LPS resulted in a significant increase in TNF-α and IL-1β levels, 7- and 3.5-fold, respectively (P < 0.05), while treatment with propofol partially blunted the secretion of both cytokines (P < 0.05). CD14 and TLR4 mRNA levels were increased in the LPS group (1.48 ± 0.05 and 1.26 ± 0.03, respectively) compared to the control group (1.00 ± 0.20 and 1.00 ± 0.02, respectively; P < 0.05), while propofol treatment blunted this effect (1.16 ± 0.05 and 1.12 ± 0.05, respectively; P < 0.05). Both CD14 and TLR4 protein levels were elevated in the LPS group compared to the control group (P < 0.05), while propofol treatment partially decreased the expression of CD14 and TLR4 protein versus LPS alone (P < 0.05). Our study indicates that propofol prevents lung injury, most likely by inhibition of CD14 and TLR4 expression.

Inhaled nitric oxide reduces secondary brain damage after traumatic brain injury in mice

Ischemia, especially pericontusional ischemia, is one of the leading causes of secondary brain damage after traumatic brain injury (TBI). So far efforts to improve cerebral blood flow (CBF) after TBI were not successful because of various reasons. We previously showed that nitric oxide (NO) applied by inhalation after experimental ischemic stroke is transported to the brain and induces vasodilatation in hypoxic brain regions, thus improving regional ischemia, thereby improving brain damage and neurological outcome. As regional ischemia in the traumatic penumbra is a key mechanism determining secondary posttraumatic brain damage, the aim of the current study was to evaluate the effect of NO inhalation after experimental TBI. NO inhalation significantly improved CBF and reduced intracranial pressure after TBI in male C57 Bl/6 mice. Long-term application (24 hours NO inhalation) resulted in reduced lesion volume, reduced brain edema formation and less blood-brain barrier disruption, as well as improved neurological function. No adverse effects, e.g., on cerebral auto-regulation, systemic blood pressure, or oxidative damage were observed. NO inhalation might therefore be a safe and effective treatment option for TBI patients.

Anti-inflammatory and vasoprotective activity of a retroviral-derived peptide, homologous to human endogenous retroviruses: endothelial cell effects

Malignant and inflammatory tissues sometimes express endogenous retroviruses or their proteins. A highly-conserved sequence from retroviral transmembrane (TM) proteins, termed the “immunosuppressive domain (ID)”, is associated with inhibition of immune and inflammatory functions. An octadecapeptide (MN10021) from the ID of retroviral TM protein p15E inhibits in vitro release of pro-inflammatory cytokines and increases synthesis of anti-inflammatory IL-10. We sought to determine if MN10021 has significant in vivo effects. MN10021, prepared by solid-phase synthesis, was dimerized through a naturally-occurring, carboxy-terminal cysteine. In vivo anti-inflammatory activity was determined using a murine model of sodium periodate (NaIO₄)-induced peritonitis. In vivo vasoprotective effects were determined using: (1) a carrageenan-induced model of disseminated intravascular coagulation (DIC) in mice; (2) a reverse passive Arthus model in guinea pigs; and (3) vasoregulatory effects in spontaneously hypertensive rats (SHR). In vitro studies included: (1) binding/uptake of MN10021 using human monocytes, cultured fibroblasts, and vascular endothelial cells (VEC); (2) gene expression by RT-PCR of MN10021-treated VEC; and (3) apoptosis of MN10021-treated VEC exposed to staurosporine or TNF-α. One-tenth nmol MN10021 inhibits 50 percent of the inflammatory response in the mouse peritonitis model. Furthermore, 73 nmol MN10021 completely protects mice in a lethal model of carrageenan-induced DIC and inhibits vascular leak in both the mouse DIC model and a guinea pig reverse passive Arthus reaction. MN10021 binds to and is taken up in a specific manner by both human monocytes and VEC but not by cultured human fibroblasts. Surprisingly, orally-administered MN10021 lowers blood pressure in SHR rats by 10–15% within 1 h suggesting a direct or indirect effect on the vascular endothelium. MN10021 and derived octapeptides induce iNOS (inducible nitric oxide synthase) mRNA in VEC and nitrate in VEC cell culture supernatants and protect VEC from induced apoptosis or necrosis. However, pretreatment of VEC with nitro-L-arginine methyl ester (L-NAME), while inhibiting the release of nitrate, does not block the anti-apoptotic effect of MN10021 and derived octapeptides suggesting that their potent vasoprotective and anti-inflammatory activity is not nitric oxide dependent.

Inhaled Nitric Oxide Reduces Brain Damage by Collateral Recruitment in a Neonatal Stroke Model

Background and Purpose—

We recently demonstrated that endogenous nitric oxide (NO) modulates collateral blood flow in a neonatal stroke model in rats. The inhalation of NO (iNO) has been found to be neuroprotective after ischemic brain damage in adults. Our objective was to examine whether iNO could modify cerebral blood flow during ischemia–reperfusion and reduce lesions in the developing brain.

Methods—

In vivo variations in cortical NO concentrations occurring after 20-ppm iNO exposure were analyzed using the voltammetric method in P7 rat pups. Inhaled NO-mediated blood flow velocities were measured by ultrasound imaging with sequential Doppler recordings in both internal carotid arteries and the basilar trunk under basal conditions and in a neonatal model of ischemia–reperfusion. The hemodynamic effects of iNO (5 to 80 ppm) were correlated with brain injury 48 hours after reperfusion.

Results—

Inhaled NO (20 ppm) significantly increased NO concentrations in the P7 rat cortex and compensated for the blockade of endogenous NO synthesis under normal conditions. Inhaled NO (20 ppm) during ischemia increased blood flow velocities and significantly reduced lesion volumes by 43% and cellular damage. In contrast, both 80 ppm iNO given during ischemia and 5 or 20 ppm iNO given 30 minutes after reperfusion were detrimental.

Conclusions—

Our findings strongly indicate that, with the appropriate timing, 20 ppm iNO can be transported into the P7 rat brain and mediated blood flow redistribution during ischemia leading to reduced infarct volume and cell injury.

Nitrite- and nitroxyl-induced relaxation in porcine coronary (micro-) arteries: underlying mechanisms and role as endothelium-derived hyperpolarizing factor(s)

To investigate the vasorelaxant efficacy of nitrite and nitroxyl (HNO) in porcine coronary (micro)arteries (PC(M)As), evaluating their role as endothelium-derived hyperpolarizing factors (EDHFs), preconstricted PCAs and PCMAs were exposed to UV light (a well-known inductor of nitrite; wave-length: 350-370nm), nitrite, the HNO donor Angeli's salt, or bradykinin. UV light-induced relaxation of PCAs increased identically after endothelium removal and endothelial nitric oxide (NO) synthase (eNOS) blockade. UV light-induced relaxation diminished during Na(+)-K(+)-ATPase inhibition and S-nitrosothiol-depletion, and disappeared during NO scavenging with hydroxocobalamin or soluble guanylyl cyclase (sGC) inhibition with ODQ. Nitrite-induced relaxation of PCAs required millimolar levels, i.e., >1000 times endogenous vascular nitrite. Angeli's salt relaxed PCMAs more potently than PCAs, and this was due to the fact that HNO directly activated sGC in PCMAs, whereas in PCAs this occurred following its conversion to NO only. sGC activation by NO/HNO resulted in Na(+)-K(+)-ATPase stimulation and K(v) channel activation. The HNO scavenger l-cysteine blocked bradykinin-induced relaxation in PCAs, and potentiated it in PCMAs. The latter did not occur in the presence of hydroxocobalamin, suggesting that it depended on l-cysteine-induced generation of vasorelaxant S-nitrosothiols. In all experimental setups, incubation with red wine extract mimicked the effects of ODQ. In conclusion, nitrite, via its conversion to NO and S-nitrosothiols, and HNO, either directly, or via its conversion to NO, mediate relaxant effects involving the sGC-cGMP pathway, Na(+)-K(+)-ATPase and/or K(v) channels. Red wine extract counteracts these beneficial effects. NO blocks nitrite activation, and HNO, but not nitrite, may act as EDHF in the coronary vascular bed.

Effects of inhaled nitric oxide on hemostasis in healthy adults treated with heparin: a randomized, controlled, blinded crossover study

Background

Effects of nitric oxide (NO) on hemostasis have been studied in various investigational settings, but data regarding inhaled NO on bleeding and platelet function are conflicting. It is not known if inhaled NO has an effect when administered with drugs that influence hemostasis. This trial evaluated effects of inhaled NO on hemostasis in the presence of heparin using aspirin as a positive control.

Patients/Methods

Twelve healthy adult males were enrolled in a single-center, randomized, single-blind, four-way crossover trial. Subjects received 80 ppm NO or medical air (placebo) inhalation for 30 min with simultaneous injection of placebo or heparin. Aspirin capsules were used as a positive control. Parameters of hemostasis were measured before treatment and at post-treatment intervals.

Results

Activated clotting time (ACT), prothrombin time (PT) and activated partial thromboplastin time (aPTT) increased only in groups that received heparin. Areas under the curve for ACT in heparin groups receiving inhaled NO were judged to be equivalent to those receiving medical air for both 0- to 4-h (ratio: 1.00; 90% CI, 0.90-1.11) and 0- to 24-h time intervals (ratio: 1.01; 90% CI, 0.92-1.12). Changes in bleeding time and platelet aggregation were observed only in aspirin groups. No clinically significant changes in hemoglobin, red blood cell counts or haematocrit were observed in any group.

Conclusions

Inhaled NO, when administered with heparin, exhibited no significant additive effects on ACT, PT, aPTT, bleeding time or platelet aggregation.

Inhalation of nitric oxide prevents ischemic brain damage in experimental stroke by selective dilatation of collateral arterioles

RATIONALE

Stroke is the third most common cause of death in industrialized countries. The main therapeutic target is the ischemic penumbra, potentially salvageable brain tissue that dies within the first few hours after blood flow cessation. Hence, strategies to keep the penumbra alive until reperfusion occurs are needed.

OBJECTIVE

To study the effect of inhaled nitric oxide on cerebral vessels and cerebral perfusion under physiological conditions and in different models of cerebral ischemia.

METHODS AND RESULTS

This experimental study demonstrates that inhaled nitric oxide (applied in 30% oxygen/70% air mixture) leads to the formation of nitric oxide carriers in blood that distribute throughout the body. This was ascertained by in vivo microscopy in adult mice. Although under normal conditions inhaled nitric oxide does not affect cerebral blood flow, after experimental cerebral ischemia induced by transient middle cerebral artery occlusion it selectively dilates arterioles in the ischemic penumbra, thereby increasing collateral blood flow and significantly reducing ischemic brain damage. This translates into significantly improved neurological outcome. These findings were validated in independent laboratories using two different mouse models of cerebral ischemia and in a clinically relevant large animal model of stroke.

CONCLUSIONS

Inhaled nitric oxide thus may provide a completely novel strategy to improve penumbral blood flow and neuronal survival in stroke or other ischemic conditions.

Bench-to-bedside review: Inhaled nitric oxide therapy in adults

Nitric oxide (NO) is an endogenous mediator of vascular tone and host defence. Inhaled nitric oxide (iNO) results in preferential pulmonary vasodilatation and lowers pulmonary vascular resistance. The route of administration delivers NO selectively to ventilated lung units so that its effect augments that of hypoxic pulmonary vasoconstriction and improves oxygenation. This 'Bench-to-bedside' review focuses on the mechanisms of action of iNO and its clinical applications, with emphasis on acute lung injury and the acute respiratory distress syndrome. Developments in our understanding of the cellular and molecular actions of NO may help to explain the hitherto disappointing results of randomised controlled trials of iNO.

Effect of inhaled nitric oxide on cerebrospinal fluid and blood nitrite concentrations in newborn lambs

Inhaled nitric oxide (iNO) has many extrapulmonary effects. As the half-life of nitric oxide (NO) in blood is orders of magnitude less than the circulation time from lungs to the brain, the mediator of systemic effects of iNO is unknown. We hypothesized that concentrations of nitrite, a circulating byproduct of NO with demonstrated NO bioactivity, would increase in blood and cerebrospinal fluid (CSF) during iNO therapy. iNO (80 ppm) was given to six newborn lambs and results compared with six control lambs. Blood and CSF nitrite concentrations increased 2-fold in response to iNO. cGMP increased in blood but not CSF suggesting brain guanylate cyclase activity was not increased. When sodium nitrite was infused i.v. blood and CSF nitrite levels increased within 10 min and reached similar levels of 14.6 +/- 1.5 microM after 40 min. The reactivity of nitrite in Hb-free brain homogenates was investigated, with the findings that nitrite did not disappear nor did measurable amounts of s-nitroso, n-nitroso, or iron-nitrosyl-species appear. We conclude that although nitrite diffuses freely between blood and CSF, due to its lack of reactivity in the brain, nitrite's putative role as the mediator of the systemic effects of iNO is limited to intravascular reactions.

Nitrite infusion in humans and nonhuman primates: endocrine effects, pharmacokinetics, and tolerance formation

BACKGROUND

The recent discovery that nitrite is an intrinsic vasodilator and signaling molecule at near-physiological concentrations has raised the possibility that nitrite contributes to hypoxic vasodilation and to the bioactivity of nitroglycerin and mediates the cardiovascular protective effects of nitrate in the Mediterranean diet. However, important questions of potency, kinetics, mechanism of action, and possible induction of tolerance remain unanswered.

METHODS AND RESULTS

In the present study, we performed biochemical, physiological, and pharmacological studies using nitrite infusion protocols in 20 normal human volunteers and in nonhuman primates to answer these questions, and we specifically tested 3 proposed mechanisms of bioactivation: reduction to nitric oxide by xanthine oxidoreductase, nonenzymatic disproportionation, and reduction by deoxyhemoglobin. We found that (1) nitrite is a relatively potent and fast vasodilator at near-physiological concentrations; (2) nitrite functions as an endocrine reservoir of nitric oxide, producing remote vasodilation during first-pass perfusion of the opposite limb; (3) nitrite is reduced to nitric oxide by intravascular reactions with hemoglobin and with intravascular reductants (ie, ascorbate); (4) inhibition of xanthine oxidoreductase with oxypurinol does not inhibit nitrite-dependent vasodilation but potentiates it; and (5) nitrite does not induce tolerance as observed with the organic nitrates.

CONCLUSIONS

We propose that nitrite functions as a physiological regulator of vascular function and endocrine nitric oxide homeostasis and suggest that it is an active metabolite of the organic nitrates that can be used therapeutically to bypass enzymatic tolerance.

Inhaled nitric oxide attenuates pulmonary inflammation and fibrin deposition and prolongs survival in neonatal hyperoxic lung injury

Administration of inhaled nitric oxide (iNO) is a potential therapeutic strategy to prevent bronchopulmonary dysplasia (BPD) in premature newborns with respiratory distress syndrome. We evaluated this approach in a rat model, in which premature pups were exposed to room air, hyperoxia, or a combination of hyperoxia and NO (8.5 and 17 ppm). We investigated the anti-inflammatory effects of prolonged iNO therapy by studying survival, histopathology, fibrin deposition, and differential mRNA expression (real-time RT-PCR) of key genes involved in the development of BPD. iNO therapy prolonged median survival 1.5 days ( P = 0.0003), reduced fibrin deposition in a dosage-dependent way up to 4.3-fold ( P < 0.001), improved alveolar development by reducing septal thickness, and reduced the influx of leukocytes. Analysis of mRNA expression revealed an iNO-induced downregulation of genes involved in inflammation (IL-6, cytokine-induced neutrophilic chemoattractant-1, and amphiregulin), coagulation, fibrinolysis (plasminogen activator inhibitor 1 and urokinase-type plasminogen activator receptor), cell cycle regulation (p21), and an upregulation of fibroblast growth factor receptor-4 (alveolar formation). We conclude that iNO therapy improves lung pathology and prolongs survival by reducing septum thickness, inhibiting inflammation, and reducing alveolar fibrin deposition in premature rat pups with neonatal hyperoxic lung injury.

Inhaled nitric oxide increases endothelial permeability in Pseudomonas aeruginosa pneumonia

OBJECTIVE

Pneumonia is a frequent cause of acute respiratory distress syndrome (ARDS), and Pseudomonas aeruginosa is a leading pathogen in nosocomial pneumonia. The management of ARDS remains a major problem, and only a limited number of options can improve the oxygenation. Inhaled nitric oxide (iNO) has been widely used, although this molecule is a free radical potentially harmful through the generation of toxic radical derivatives. The goal of our study was to assess the consequences of iNO (10 ppm) in a rat model of P. aeruginosa-induced lung injury.

DESIGN

The animals were exposed for 24 h to iNO after instillation of the pathogen. Distal alveolar fluid clearance (DAFC) and epithelial and endothelial permeability were measured with a double flux of radio-labeled albumin.

RESULTS

DAFC and epithelial permeability were increased in pneumonia but not influenced by iNO. In contrast, endothelial permeability was statistically significantly higher in the pneumonic animals exposed to iNO than in the pneumonic group without iNO (0.24+/-0.03 vs 0.47+/-0.1, p<0.05). This increase was not related to the production of nitrate/nitrite, nor to the increase of the inflammatory response evaluated by cytokine levels in the bronchoalveolar lavage fluid (TNF-alpha, IL-6, IL-10). The alveolar recruitment of polymorphonuclear neutrophils was comparable in the pneumonic group exposed to iNO and the pneumonic group without iNO.

CONCLUSION

iNO increases the endothelial permeability in P. aeruginosa pneumonia. The mechanism is not related to the production of nitrate/nitrite or to a greater inflammatory response.

Pulmonary exposure to diesel exhaust particles enhances coagulatory disturbance with endothelial damage and systemic inflammation related to lung inflammation

Pulmonary exposure to diesel exhaust particles (DEP) enhances lung inflammation related to bacterial endotoxin (lipopolysaccharide [LPS]) in mice. Severe lung inflammation can reportedly induce coagulatory abnormalities and systemic inflammation. This study examined the effects of components of DEP on lung inflammation, pulmonary permeability, coagulatory changes, systemic inflammatory response, and lung-to-systemic translocation of LPS in a murine model of lung inflammation. ICR mice were divided into six experimental groups that intratracheally received vehicle, LPS (2.5 mg/kg), organic chemicals in DEP (DEP-OC; 4 mg/kg) extracted with dicloromethane), residual carbonaceous nuclei of DEP (washed DEP: 4 mg/kg), DEP-OC + LPS, or washed DEP + LPS. Both DEP components exacerbated lung inflammation, vascular permeability, and the increased fibrinogen and E-selectin levels induced by LPS. With overall trends, the exacerbation was more prominent with washed DEP than with DEP-OC. Washed DEP + LPS significantly decreased activated protein C and antithrombin-III and elevated circulatory levels of interleukin (IL)-6, keratinocyte chemoattractant (KC), and LPS as compared with LPS alone, whereas DEP-OC + LPS elevated IL-6, KC, and LPS without significance. These results show that DEP components, especially washed DEP, amplify the effects if LPS on the respiratory system and suggest that they contribute to the adverse health effects of particulate air pollution on the sensitive populations with predisposing vascular and/or pulmonary diseases, including ischemic vascular diseases and respiratory infection.

Circulating NO Pool in Humans

Nitric oxide (NO) generated from L-arginine by NO synthases in the endothelium and in other cells plays a central role in several aspects of vascular biology and has been linked to many regulatory functions in mammalian cells. Whereas for a long time the signaling actions of NO in the vasculature have been thought to be short-lived as a result of the rapid reaction of NO with hemoglobin, recent studies changed the biochemical thinking of NO. NO is not anymore the paracrine agent with only local effects, but, like a hormone, it disseminates throughout the body. Thus, a circulating pool of NO exists, opening new considerable pharmacological and therapeutical avenues in the diagnosis and therapy of cardiovascular diseases. In this review we briefly discuss the major routes of NO metabolism and transport in the mammalian circulation, considering plasma, red blood cell and tissue compartments separately, with a special focus on the implication of the circulating NO pool in clinical research.

Reciprocal regulation of airway rejection by the inducible gas-forming enzymes heme oxygenase and nitric oxide synthase

Obliterative bronchiolitis (OB) develops insidiously in nearly half of all lung transplant recipients. Although typically preceded by a CD8⁺ T cell–rich lymphocytic bronchitis, it remains unresponsive to conventional immunosuppression. Using an airflow permissive model to study the role of gases flowing over the transplanted airway, it is shown that prolonged inhalation of sublethal doses of carbon monoxide (CO), but not nitric oxide (NO), obliterate the appearance of the obstructive airway lesion. Induction of the enzyme responsible for the synthesis of CO, heme oxygenase (Hmox) 1, increased carboxyhemoglobin levels and suppressed lymphocytic bronchitis and airway luminal occlusion after transplantation. In contrast, zinc protoporphyrin IX, a competitive inhibitor of Hmox, increased airway luminal occlusion. Compared with wild-type allografts, expression of inducible NO synthase (iNOS), which promotes the influx of cytoeffector leukocytes and airway graft rejection, was strikingly reduced by either enhanced expression of Hmox-1 or exogenous CO. Hmox-1/CO decreased nuclear factor (NF)-κB binding activity to the iNOS promoter region and iNOS expression. Inhibition of soluble guanylate cyclase did not interfere with the ability of CO to suppress OB, implicating a cyclic guanosine 3′,5′-monophosphate–independent mechanism through which CO suppresses NF-κB, iNOS transcription, and OB. Prolonged CO inhalation represents a new immunosuppresive strategy to prevent OB.

Inhaled nitric oxide therapy in adults: European expert recommendations

BACKGROUND

Inhaled nitric oxide (iNO) has been used for treatment of acute respiratory failure and pulmonary hypertension since 1991 in adult patients in the perioperative setting and in critical care.

METHODS

This contribution assesses evidence for the use of iNO in this population as presented to a expert group jointly organised by the European Society of Intensive Care Medicine and the European Association of Cardiothoracic Anaesthesiologists.

CONCLUSIONS

Expert recommendations on the use of iNO in adults were agreed on following presentation of the evidence at the expert meeting held in June 2004.

Lack of alteration of endogenous nitric oxide pathway during prolonged nitric oxide inhalation in intensive care unit patients

OBJECTIVE

To compare hemodynamic and gasometric variables and the plasma concentrations of nitric oxide metabolites (cyclic guanosine monophosphate and nitrate and nitrite), endothelin-1, and renin-angiotensin metabolites before and after the start of nitric oxide inhalation, after prolonged nitric oxide inhalation, and before and after nitric oxide withdrawal.

DESIGN

Prospective study.

SETTING

Surgical intensive care unit, university hospital.

SUBJECTS

Patients with acute lung injury and right ventricular failure.

INTERVENTIONS

Nitric oxide inhalation (10-12 ppm) during a median of 2.9 days (12 hrs to 6.5 days).

MEASUREMENTS AND MAIN RESULTS

The pulmonary vasodilator effects of inhaled nitric oxide improved arterial oxygenation in patients with acute lung injury (p < .05) and reduced right atrial pressure in patients with right ventricular dysfunction (p < .01). These beneficial effects lasted the whole period of prolonged inhaled nitric oxide therapy up to 6.5 days. However, when inhaled nitric oxide was withdrawn, pulmonary vasodilator effects rapidly disappeared, and Pao2/Fio2 ratio markedly deteriorated in all studied patients to return to pre-inhaled nitric oxide levels. Changes in plasma cyclic guanosine monophosphate and nitrate and nitrite paralleled those of pulmonary vasodilatory effects. An immediate increase in plasma cyclic guanosine monophosphate with a slightly delayed increase in plasma nitrate and nitrite was observed at inhaled nitric oxide start with no attenuation during the prolonged inhaled nitric oxide therapy. A marked decrease toward pre-inhaled nitric oxide levels was seen within hours of inhaled nitric oxide withdrawal. In addition, no alteration of plasma endothelin-1 or renin-angiotensin mediators was observed during or after inhaled nitric oxide therapy.

CONCLUSIONS

Our study showed a lack of attenuation in the beneficial effects of inhaled nitric oxide and a lack of alteration of endogenous nitric oxide, endothelin-1, and renin-angiotensin pathways during prolonged nitric oxide inhalation.

The procoagulant potential of environmental particles (PM10)

BACKGROUND AND AIMS

Epidemiology studies have shown that cardiovascular (CV) disease is primarily responsible for the mortality associated with increased pulmonary environmental particle (PM10) exposure. The mechanisms involved in PM10 mediated CV effects are unknown although changes in plasma viscosity and in the homoeostasis of blood coagulation have been implicated. It was hypothesised that PM10 exposure would result in an inflammatory response and enhance the activation of the extrinsic coagulation mechanisms in pulmonary and vascular cells in culture.

METHODS

Primary human monocyte derived macrophages and human umbilical cord vein endothelial, human alveolar type II epithelial (A549), and human bronchial epithelial (16HBE) cells were tested for their inflammatory and procoagulant response to PM10 exposure. IL-8, tissue factor (TF), and tissue plasminogen activator (tPA) gene expression and protein release, and coagulation enhancing ability of culture media were determined 6 and 24 hours following exposure.

RESULTS

The culture media from macrophages and 16HBE bronchial epithelial cells, but not A549 cells, exposed to PM10 had an enhanced ability to cause clotting. Furthermore, H2O2 also increased the clotting activity. Apoptosis was significantly increased in macrophages exposed to PM10 and LPS as shown by annexin V binding. TF gene expression was enhanced in macrophages exposed to PM10, and HUVEC tissue factor and tPA gene and protein expression were inhibited.

CONCLUSIONS

These data indicate that PM10 has the ability to alter macrophage, epithelial, and endothelial cell function to favour blood coagulation via activation of the extrinsic pathway and inhibition of fibrinolysis pathways.

Inhaled NO improves early pulmonary function and modifies lung growth and elastin deposition in a baboon model of neonatal chronic lung disease

Nitric oxide (NO) serves multiple functions in the developing lung, and pulmonary NO production is decreased in a baboon model of chronic lung disease (CLD) after premature birth at 125 days (d) gestation (term = 185d). To determine whether postnatal NO administration alters the genesis of CLD, the effects of inhaled NO (iNO, 5 ppm) were assessed in the baboon model over 14d. iNO caused a decrease in pulmonary artery pressure in the first 2d and a greater rate of spontaneous closure of the ductus arteriosus, and lung compliance was greater and expiratory resistance was improved during the first week. With iNO, postmortem pressure-volume curves were shifted upward, lung DNA content and cell proliferation were increased, and lung growth was preserved to equal that which occurs during the same period in utero. In addition, the excessive elastin deposition characteristic of CLD was normalized by iNO, and there was evidence of stimulation of secondary crest development. Thus, in the baboon model of CLD, iNO improves early pulmonary function and alters lung growth and extracellular matrix deposition. As such, NO biosynthetic pathway dysfunction may contribute to the pathogenesis of CLD.

Direct demonstration of nitric oxide formation in organs of rabbits treated by transdermal glyceryl trinitrate using an in vivo spin trapping technique

Glyceryl trinitrate (GTN) is commonly delivered by a patch for the treatment of angina pectoris. The idea is now generally accepted that GTN requires a biotransformation process that activates the drug, in particular through nitric oxide (NO) generation. However, the pharmacokinetics of NO delivery from GTN still remains obscure. The objective of this study was to assess GTN-derived NO formation in vascular tissues and organs in rabbit given GTN patches. NO levels were evaluated in rabbits after 3 h of treatment with a 10 mg GTN patch (GTN group; n = 7) or a placebo patch (CTL; n = 7). Nitrosylhaemoglobin (HbNO) was evaluated by electron spin resonance (ESR) spectroscopy in red cell suspension. In vivo spin trapping technique using FeMGD as a spin trap, associated with ESR was used to quantify NO in tissues. The NO-spin trap complex, which is a relatively stable product, has been measured in several tissues. The ESR spectrum corresponding to HbNO was not found in red cell of GTN or CTL rabbits. The spectrum corresponding to the NO-spin trap complex was observed in all analysed tissues of CTL rabbits. The signal was significantly increased in liver, renal medulla, heart left ventricle and spleen of GTN-treated rabbits, and to a lesser extent in right ventricle and lung. No difference was shown between NO-spin trap levels measured in aorta or inferior vena cava from GTN or CTL rabbits. These data suggest that GTN patch treatment induced NO release, and that tissue-specific differences in transdermal GTN-derived NO exist. The GTN-NO pathway appears to be largely involved in organs such as the liver, kidney and heart.

Nitrosylhemoglobin formation after infusion of NO solutions: ESR studies in pigs

A saturated nitric oxide (NO) solution (1.88 mM) infused i.v. in the anesthetized pig at a dose of 68 nmol/kg/min for 24 min resulted in a time-dependent increase of nitrosylhemoglobin [HbFe(II)NO] as determined by electron spin resonance (ESR), reaching a C(max) of 7.99 +/- 0.42 microM at the end of the infusion, compared to 1.13 +/- 0.42 microM before (p < 0.01). This indicates that NO i.v. is efficiently bioconserved as HbFe(II)NO (approximately 34% of the NO dose) and to a greater extent than by the oxidative pathway (approximately 24% of the NO dose), as determined by measuring plasma nitrites/nitrates (chemiluminescence) and Met-Hb (ESR analysis). When the NO infusion was stopped, HbFe(II)NO declined with a t(1/2) of 15 min, indicating that it is a stable storage form of NO, able to deliver NO distally to the site of administration. No significant differences were observed in systemic and pulmonary vascular resistances during and after NO infusion, but PO(2) showed a significant decrease 15 and 30 min after the infusion. Thus, in normoxic/physiological conditions, HbFe(II)NO does not induce significant NO-dependent vasorelaxation.

Enhanced S -Nitroso-Albumin Formation From Inhaled NO During Ischemia/Reperfusion

In the present study, we investigated whether inhaled nitric oxide (NO) was transported by plasma proteins, such as S -nitroso-albumin (SNO-Alb), in the feline circulation and whether this molecule delivers NO to the periphery under conditions of stress, specifically ischemia/reperfusion (I/R). A flow probe was interposed between the femoral and superior mesenteric artery for blood flow measurements, and a branch of the superior mesenteric vein was cannulated for arterial-venous sampling. In animals breathing room air, SNO-Alb was below detection level in arterial or venous blood. NO inhalation resulted in a significant arterial-venous gradient for SNO-Alb. Concomitant with this loss of SNO-Alb across the intestinal vasculature was an increase in nitrite (NO 2 − ). However, this release of NO was not sufficient to alter intestinal blood flow. I/R during NO inhalation caused a very large increase in arterial SNO-Alb that permitted a 5-fold increase in SNO-Alb consumption and significant generation of NO 2 − within the postischemic intestinal vasculature. The increased SNO-Alb consumption was sufficient to dramatically improve intestinal blood flow. The very large burst of arterial SNO-Alb during I/R was completely blocked by the administration of superoxide dismutase, suggesting that oxidative stress contributed to the increased SNO-Alb formation. Our data suggest that inhaled NO can increase nitrosothiol production and these molecules may be a functional NO delivery system during cardiovascular disease.

Circulating NO pool: assessment of nitrite and nitroso species in blood and tissues

The formation of nitric oxide (NO) has been linked to many regulatory functions in mammalian cells. With the appreciation that NO-mediated nitrosation reactions are involved in cell signaling and pathology there is a need to elucidate and better characterize the different biochemical pathways of NO in vivo. Despite significant methodological advances over the years one major obstacle in assessing the significance of nitrosated species and other NO-related metabolites remains: their reliable measurement in complex biological matrices. In this review we briefly discuss the major routes of NO metabolism and transport in the mammalian circulation, considering plasma, red blood cell, and tissue compartments separately. In addition, we attempt to give a recommendation as to the most appropriate analytical technique and sample processing procedures for the reliable quantification of either species.

Evidence for the extrapulmonary localization of inhaled nitric oxide

Inhaled nitric oxide (NO) has emerged as a promising pulmonary vasodilator to treat pulmonary hypertension associated with heart disease and ventilation/perfusion mismatching. However, the pharmacokinetics of inhaled NO still remains obscure and its cardiopulmonary selectivity appears to be increasingly under debate. In the present study measured NO content and levels of cyclic guanosine 3',5'monophosphate (cGMP), a mediator of NO-induced vasodilation, in a variety of organs from rats subjected to NO inhalation. Electron spin resonance spectroscopy associated to a spin trapping technique using N-methyl D-glucamine dithiocarbamate (FeMGD) was used to directly quantify NO levels in the lung, kidney, liver, aorta, and heart from anesthetized Wistar rats subjected to various doses (0, 20, 50, 100, or 200 ppm) and various times (0, 30, 45, or 75 minutes) of inhaled NO. Inhaled NO at a dose of 100 and 200 ppm significantly increased the NO-FeMGD complex in all organs studied. An increase of cGMP was detected in the lung and the aorta after inhaled NO for 45 minutes at the dose of 50 ppm. No changes in NO levels and its metabolites were shown between 30 and 75 minutes of inhaled NO. The results show that inhaled NO at a dose of 100 ppm or more increases NO levels in other organs beside the lung, strongly suggesting that inhaled NO would be more than a pulmonary vasodilator and its selectivity remains to be reconsidered when used for therapeutic purposes.

Hypercapnic acidosis attenuates endotoxin-induced acute lung injury

Deliberate induction of prophylactic hypercapnic acidosis protects against lung injury after in vivo ischemia-reperfusion and ventilation-induced lung injury. However, the efficacy of hypercapnic acidosis in sepsis, the commonest cause of clinical acute respiratory distress syndrome, is not known. We investigated whether hypercapnic acidosis--induced by adding CO2 to inspired gas--would be protective against endotoxin-induced lung injury in an in vivo rat model. Prophylactic institution of hypercapnic acidosis (i.e., induction before endotoxin instillation) attenuated the decrement in arterial oxygenation, improved lung compliance, and attenuated alveolar neutrophil infiltration compared with control conditions. Therapeutic institution of hypercapnic acidosis, that is, induction after endotoxin instillation, attenuated the decrement in oxygenation, improved lung compliance, and reduced alveolar neutrophil infiltration and histologic indices of lung injury. Therapeutic hypercapnic acidosis attenuated the endotoxin-induced increase in the higher oxides of nitrogen and nitrosothiols in the lung tissue and epithelial lining fluid. Lung epithelial lining fluid nitrotyrosine concentrations were increased with hypercapnic acidosis. We conclude that hypercapnic acidosis attenuates acute endotoxin-induced lung injury, and is efficacious both prophylactically and therapeutically. The beneficial actions of hypercapnic acidosis were not mediated by inhibition of peroxynitrite-induced nitration within proteins.

Inhaled nitric oxide induces cerebrovascular effects in anesthetized pigs

Although inhaled nitric oxide (NO(i)) is considered to act selectively on pulmonary vessels, EEG abnormalities and even occasional neurotoxic effects of NO(i) have been proposed. Here, we investigated cerebrovascular effects of increasing concentrations of 5, 10 and 50 ppm NO(i) in seven anesthetized pigs. Cerebral hemodynamics were assessed non-invasively by use of near-infared spectroscopy and indicator dilution techniques. NO(i) increased cerebral blood volume significantly and reversibly. This effect was not attributable to changes of macrohemodynamic parameters or arterial blood gases. Simultaneously, cerebral transit time increased while cerebral blood flow remained unchanged. These data demonstrate a vasodilatory action of NO(i) in the cerebral vasculature, which may occur preferentially in the venous compartment.

Inhaled NO inhibits platelet aggregation and elevates plasma but not intraplatelet cGMP in healthy human volunteers

Effects of inhaled nitric oxide (NO) on human platelet function are controversial. It is uncertain whether intraplatelet cGMP mediates the effect of inhaled NO on platelet function. We investigated the effect of 30 ppm inhaled NO on platelet aggregation and plasma and intraplatelet cGMP in 12 subjects. We performed platelet aggregation studies by using a photooptical aggregometer and five agonists (ADP, collagen, epinephrine, arachidonic acid, and ristocetin). During inhalation, the maximal extent of platelet aggregation decreased by 75% with epinephrine (P < 0.005), 56% with collagen (P < 0.005), and 20% with arachidonic acid (P < 0.05). Responses to ADP (8% P > 0.05) and ristocetin (5% P > 0.05) were unaffected. Platelet aggregation velocity decreased by 64% with collagen (P < 0.005), 60% with epinephrine (P < 0.05), 33% with arachidonic acid (P < 0.05), and 14% with ADP (P > 0.05). Plasma cGMP levels increased from 2.58 +/- 0.43 to 9.99 +/- 5.57 pmol/ml (P < 0.005), intraplatelet cGMP levels were unchanged (means +/- SD: 1.96 +/- 0.58 vs. 2.71 +/- 1.67 pmol/109 platelets; P > 0.05). Inhaled NO inhibits platelet aggregation via a cGMP independent mechanism.

Platelets inhibit the lysis of pulmonary microemboli

Using tracings of (125)I-labeled fibrin(ogen) in rodents, we examined the hypothesis that platelets impede the lysis of pulmonary emboli. (125)I-Microemboli (ME, 3-10 micron diameter) lodged homogeneously throughout the lungs after intravenous injection in both rats and mice (60% of injected dose), caused no lethality, and underwent spontaneous dissolution (50 and 100% within 1 and 5 h, respectively). Although lung homogenates displayed the most intense fibrinolytic activity of all the major organs, dissolution of ME was much slower in isolated perfused lungs (IPL) than was observed in vivo. Addition of rat plasma to the perfusate facilitated ME dissolution in IPL to a greater extent than did addition of tissue-type plasminogen activator alone, suggesting that permeation of the clot by plasminogen is the rate-limited step in lysis. Platelet-containing ME injected in rats lysed much more slowly than did ME formed from fibrin alone. (125)I-Thrombi, formed in the pulmonary vasculature of mice in response to intravascular activation of platelets by injection of collagen and epinephrine, were essentially resistant to spontaneous dissolution. Moreover, injection of the antiplatelet glycoprotein IIb/IIIa antibody 7E3 F(ab')(2) facilitated spontaneous dissolution of pulmonary ME and augmented fibrinolysis by a marginally effective dose of Retavase (10 microg/kg) in rats. These studies show that platelets suppress pulmonary fibrinolysis. The mechanism(s) by which platelets stabilize ME and utility of platelet inhibitors to facilitate their dissolution deserves further study.

Effects of inhaled nitric oxide on regional blood flow are consistent with intravascular nitric oxide delivery

Nitric oxide (NO) may be stabilized by binding to hemoglobin, by nitrosating thiol-containing plasma molecules, or by conversion to nitrite, all reactions potentially preserving its bioactivity in blood. Here we examined the contribution of blood-transported NO to regional vascular tone in humans before and during NO inhalation. While breathing room air and then room air with NO at 80 parts per million, forearm blood flow was measured in 16 subjects at rest and after blockade of forearm NO synthesis with N(G)-monomethyl-L-arginine (L-NMMA) followed by forearm exercise stress. L-NMMA reduced blood flow by 25% and increased resistance by 50%, an effect that was blocked by NO inhalation. With NO inhalation, resistance was significantly lower during L-NMMA infusion, both at rest and during repetitive hand-grip exercise. S-nitrosohemoglobin and plasma S-nitrosothiols did not change with NO inhalation. Arterial nitrite levels increased by 11% and arterial nitrosyl(heme)hemoglobin levels increased tenfold to the micromolar range, and both measures were consistently higher in the arterial than in venous blood. S-nitrosohemoglobin levels were in the nanomolar range, with no significant artery-to-vein gradients. These results indicate that inhaled NO during blockade of regional NO synthesis can supply intravascular NO to maintain normal vascular function. This effect may have application for the treatment of diseases characterized by endothelial dysfunction.

Effects of inhaled nitric oxide on regional blood flow are consistent with intravascular nitric oxide delivery

Nitric oxide (NO) may be stabilized by binding to hemoglobin, by nitrosating thiol-containing plasma molecules, or by conversion to nitrite, all reactions potentially preserving its bioactivity in blood. Here we examined the contribution of blood-transported NO to regional vascular tone in humans before and during NO inhalation. While breathing room air and then room air with NO at 80 parts per million, forearm blood flow was measured in 16 subjects at rest and after blockade of forearm NO synthesis with N(G)-monomethyl-L-arginine (L-NMMA) followed by forearm exercise stress. L-NMMA reduced blood flow by 25% and increased resistance by 50%, an effect that was blocked by NO inhalation. With NO inhalation, resistance was significantly lower during L-NMMA infusion, both at rest and during repetitive hand-grip exercise. S-nitrosohemoglobin and plasma S-nitrosothiols did not change with NO inhalation. Arterial nitrite levels increased by 11% and arterial nitrosyl(heme)hemoglobin levels increased tenfold to the micromolar range, and both measures were consistently higher in the arterial than in venous blood. S-nitrosohemoglobin levels were in the nanomolar range, with no significant artery-to-vein gradients. These results indicate that inhaled NO during blockade of regional NO synthesis can supply intravascular NO to maintain normal vascular function. This effect may have application for the treatment of diseases characterized by endothelial dysfunction.

Inhaled nitric oxide down-regulates intrapulmonary nitric oxide production in lipopolysaccharide-induced acute lung injury

OBJECTIVE

To examine whether inhaled nitric oxide (NO) affected the intrapulmonary production of NO, reactive oxygen species, and nuclear factor-kappaB in a lipopolysaccharide (LPS)-induced model of acute lung injury.

DESIGN

Prospective, randomized, laboratory study.

SETTING

Experimental laboratory at a biomedical institute.

SUBJECTS

Twenty male rabbits weighing 2.5-3.5 kg.

INTERVENTIONS

Saline or LPS (5 mg/kg of body weight) was administered intravenously with or without NO inhalation (10 ppm) in each group of five rabbits.

MEASUREMENTS AND MAIN RESULTS

LPS increased the lung leak index, the neutrophils and NO levels in bronchoalveolar lavage fluid, and NO levels produced by resting and stimulated alveolar macrophages. Inhaled NO decreased the lung leak index, the neutrophils and NO levels as measured by nitrite levels in the lavage fluid, and NO produced by the resting and stimulated alveolar macrophages. Inhaled NO also blocked the activities of reactive oxygen species and nuclear factor-kappaB binding to DNA in lavage cells and in alveolar macrophages.

CONCLUSION

Inhaled NO attenuates LPS-induced acute lung injury, possibly by decreasing NO production in the lungs. The mechanism of reducing NO production resulting from inhaled NO may involve, in part, the activities of reactive oxygen species and/or nuclear factor-kappaB.

Inhaled nitric oxide and acute lung injury

The nitric oxide (NO) field has been one of the most exciting scientific ventures over the past 10 years. Among the researches developed, the use of inhalation of NO gas allowed us to propose this therapy in lung diseases with promising results. Because of its property as a "selective" pulmonary vasodilator and because of its apparent clinical safety, inhaled NO has been proposed in acute lung injury (ALI) to improve severe hypoxemia. In this situation, the abnormal ventilation-perfusion ratio is improved by inhaled NO, limiting arterial hypoxia. The major clinical trials performed in adults, however, have failed to show any benefit on mortality and on mechanical ventilation requirements. Inhaled NO has been shown as an efficient therapy in pediatric ALI, probably because of a lower comorbidity. Because of the inhaled NO uptake by the lung, the extra vascular lung effects might be in the future the most important development in relation with platelet anti-agregant and anti-inflammatory properties.

Relative role of heme nitrosylation and beta-cysteine 93 nitrosation in the transport and metabolism of nitric oxide by hemoglobin in the human circulation

To quantify the reactions of nitric oxide (NO) with hemoglobin under physiological conditions and to test models of NO transport on hemoglobin, we have developed an assay to measure NO-hemoglobin reaction products in normal volunteers, under basal conditions and during NO inhalation. NO inhalation markedly raised total nitrosylated hemoglobin levels, with a significant arterial-venous gradient, supporting a role for hemoglobin in the transport and delivery of NO. The predominant species accounting for this arterial-venous gradient is nitrosyl(heme)hemoglobin. NO breathing increases S-nitrosation of hemoglobin beta-chain cysteine 93, however only to a fraction of the level of nitrosyl(heme)hemoglobin and without a detectable arterial-venous gradient. A strong correlation between methemoglobin and plasma nitrate formation was observed, suggesting that NO metabolism is a primary physiological cause of hemoglobin oxidation. Our results demonstrate that NO-heme reaction pathways predominate in vivo, NO binding to heme groups is a rapidly reversible process, and S-nitrosohemoglobin formation is probably not a primary transport mechanism for NO but may facilitate NO release from heme.

Functional coupling of oxygen binding and vasoactivity in S-nitrosohemoglobin

S-Nitrosohemoglobin (SNO-Hb) is a vasodilator whose activity is allosterically modulated by oxygen ("thermodyamic linkage"). Blood vessel contractions are favored in the oxygenated structure, and vasorelaxant activity is "linked" to deoxygenation, as illustrated herein. We further show that transnitrosation reactions between SNO-Hb and ambient thiols transduce the NO-related bioactivity, whereas NO itself is inactive. One remaining problem is that the amounts of SNO-Hb present in vivo are so large as to be incompatible with life were all the S-nitrosothiols transformed into bioactive equivalents during each arterial-venous cycle. Experiments were therefore undertaken to address how SNO-Hb conserves its NO-related activity. Our studies show that 1) increased O(2) affinity of SNO-Hb (which otherwise retains allosteric responsivity) restricts the hypoxia-induced allosteric transition that exchanges NO groups with ambient thiols for vasorelaxation; 2) some NO groups released from Cys(beta93) upon transition to T structure are autocaptured by the hemes, even in the presence of glutathione; and 3) an O(2)-dependent equilibrium between SNO-Hb and iron nitrosylhemoglobin acts to conserve NO. Thus, by sequestering a significant fraction of NO liberated upon transition to T structure, Hb can conserve NO groups that would otherwise be released in an untimely or deleterious manner.

Inhaled nitric oxide does not influence bleeding time or platelet function in healthy volunteers

BACKGROUND

Bleeding time has been reported to increase during gaseous nitric oxide (NO) inhalation in healthy volunteers and patients, and it has been speculated that inhaled NO inhibits platelet function. However, results have not been unanimous, and we have been unable to document any effects of inhaled NO on circulating platelets.

MATERIALS AND METHODS

We performed a double-blind, placebo controlled cross-over study in which healthy volunteers (n = 15) inhaled NO (30 ppm, 30 min) or control gas. Aspirin (640 mg x 1 orally) was used as positive control on the third occasion (n = 14). Bleeding time was measured, and platelet function was determined flow cytometrically by measuring the expression of P-selectin on circulating platelets and locally activated platelets in wound blood. Skin perfusion close to the site for bleeding time incisions was assessed by laser Doppler flowmetry.

RESULTS

Bleeding time was unaffected by NO, as there were slight increases during both NO and control inhalation (+20% and +14% respectively, P = 0.9). Similarly, NO inhalation had no effect on platelet P-selectin expression in either systemic or wound blood, or on skin perfusion. Aspirin pretreatment, on the other hand, prolonged bleeding time (P < 0.001) and decreased P-selectin expression of platelets in wound blood (P = 0.03).

CONCLUSIONS

This first placebo-controlled study indicates that inhaled NO does not influence either bleeding time, platelet activity or skin perfusion. Thus, it is unlikely that treatment of critically ill patients with inhaled NO will aggravate haemostatic disturbances, which has previously been feared, by influencing platelet function.

The oxyhemoglobin reaction of nitric oxide

The oxidation of nitric oxide (NO) to nitrate by oxyhemoglobin is a fundamental reaction that shapes our understanding of NO biology. This reaction is considered to be the major pathway for NO elimination from the body; it is the basis for a prevalent NO assay; it is a critical feature in the modeling of NO diffusion in the circulatory system; and it informs a variety of therapeutic applications, including NO-inhalation therapy and blood substitute design. Here we show that, under physiological conditions, this reaction is of little significance. Instead, NO preferentially binds to the minor population of the hemoglobin's vacant hemes in a cooperative manner, nitrosylates hemoglobin thiols, or reacts with liberated superoxide in solution. In the red blood cell, superoxide dismutase eliminates superoxide, increasing the yield of S-nitrosohemoglobin and nitrosylated hemes. Hemoglobin thus serves to regulate the chemistry of NO and maintain it in a bioactive state. These results represent a reversal of the conventional view of hemoglobin in NO biology and motivate a reconsideration of fundamental issues in NO biochemistry and therapy.