Pretreatment with inhaled nitric oxide inhibits neutrophil migration and oxidative activity resulting in attenuated sepsis-induced acute lung injury

Stem-Cell Therapy for Bronchopulmonary Dysplasia (BPD) in Newborns

Premature newborns are at a higher risk for the development of respiratory distress syndrome (RDS), acute lung injury (ALI) associated with lung inflammation, disruption of alveolar structure, impaired alveolar growth, lung fibrosis, impaired lung angiogenesis, and development of bronchopulmonary dysplasia (BPD) with severe long-term developmental adverse effects. The current therapy for BPD is limited to supportive care including high-oxygen therapy and pharmacotherapy. Recognizing more feasible treatment options to improve lung health and reduce complications associated with BPD is essential for improving the overall quality of life of premature infants. There is a reduction in the resident stem cells in lungs of premature infants with BPD, which strongly suggests a critical role of stem cells in BPD pathogenesis; this warrants the exploration of the potential therapeutic use of stem-cell therapy. Stem-cell-based therapies have shown promise for the treatment of many pathological conditions including acute lung injury and BPD. Mesenchymal stem cells (MSCs) and MSC-derived extracellular vesicles (EVs) including exosomes are promising and effective therapeutic modalities for the treatment of BPD. Treatment with MSCs and EVs may help to reduce lung inflammation, improve pulmonary architecture, attenuate pulmonary fibrosis, and increase the survival rate.

A Comprehensive Summary of the Knowledge on COVID-19 Treatment

Currently, the world is challenged by the coronavirus disease 2019 (COVID-19) pandemic. Epidemiologists and researchers worldwide are invariably trying to understand and combat this precarious new disease. Scrutinizing available drug options and developing potential new drugs are urgent needs to subdue this pandemic. Several intervention strategies are being considered and handled worldwide with limited success, and many drug candidates are yet in the trial phase. Despite these limitations, the development of COVID-19 treatment strategies has been accelerated to improve the clinical outcome of patients with COVID-19, and some countries have efficiently kept it under control. Recently, the use of natural and traditional medicine has also set the trend in coronavirus treatment. This review aimed to discuss the prevailing COVID-19 treatment strategies available globally by examining their efficacy, potential mechanisms, limitations, and challenges in predicting a future potential treatment candidate and bridging them with the effective traditional Chinese medicine (TCM). The findings might enrich the knowledge on traditional alternative medication and its complementary role with Western medicine in managing the COVID-19 epidemic.

Oxidative Stress and Microvessel Barrier Dysfunction

Clinical and experimental evidence indicate that increased vascular permeability contributes to many disease-associated vascular complications. Oxidative stress with increased production of reactive oxygen species (ROS) has been implicated in a wide variety of pathological conditions, including inflammation and many cardiovascular diseases. It is thus important to identify the role of ROS and their mechanistic significance in microvessel barrier dysfunction under pathological conditions. The role of specific ROS and their cross talk in pathological processes is complex. The mechanisms of ROS-induced increases in vascular permeability remain poorly understood. The sources of ROS in diseases have been extensively reviewed at enzyme levels. This review will instead focus on the underlying mechanisms of ROS release by leukocytes, the differentiate effects and signaling mechanisms of individual ROS on endothelial cells, pericytes and microvessel barrier function, as well as the interplay of reactive oxygen species, nitric oxide, and nitrogen species in ROS-mediated vascular barrier dysfunction. As a counter balance of excessive ROS, nuclear factor erythroid 2 related factor 2 (Nrf2), a redox-sensitive cell-protective transcription factor, will be highlighted as a potential therapeutic target for antioxidant defenses. The advantages and limitations of different experimental approaches used for the study of ROS-induced endothelial barrier function are also discussed. This article will outline the advances emerged mainly from in vivo and ex vivo studies and attempt to consolidate some of the opposing views in the field, and hence provide a better understanding of ROS-mediated microvessel barrier dysfunction and benefit the development of therapeutic strategies.

The Pathophysiology of Nitrogen Dioxide During Inhaled Nitric Oxide Therapy

Administration of inhaled nitric oxide (NO) with the existing compressed gas delivery systems is associated with unavoidable codelivery of nitrogen dioxide (NO2), an unwanted toxic contaminant that forms when mixed with oxygen. The NO2 is generated when NO is diluted with O2-enriched air before delivery to the patient. When NO2 is inhaled by the patient, it oxidizes protective antioxidants within the epithelial lining fluid (ELF) and triggers extracellular damage in the airways. The reaction of NO2 within the ELF triggers oxidative stress (OS), possibly leading to edema, bronchoconstriction, and a reduced forced expiratory volume in 1 second. Nitrogen dioxide has been shown to have deleterious effects on the airways of high-risk patients including neonates, patients with respiratory and heart failure, and the elderly. Minimizing co-delivery of NO2 for the next generation delivery systems will be a necessity to fully optimize the pulmonary perfusion of NO because of vasodilation, whereas minimizing the negative ventilatory and histopathological effects of NO2 exposure during inhaled NO therapy.

Modulation of endotoxin-induced cardiopulmonary dysfunction by S-nitroso-albumin

Nitric oxide (NO) is an endogenous vasodilator and modulator of inflammation. During endotoxemia, the beneficial effects of NO are overwhelmed by the inflammatory cascade, resulting in a functional depletion of NO. S-nitroso-albumin ( S-NO-alb) exists as a novel and highly stable NO thiol complex that slowly releases NO into the vascular micro-environment. Using a porcine model, we examined the ability of intravenous S-NO-alb to modulate cardiopulmonary dysfunction characteristic of endotoxemia. Pigs were anesthetized, instrumented for standard cardiopulmonary function measurements, and randomly assigned to receive: (i) albumin + saline; (ii) albumin + LPS; or (iii) S-NO-alb + LPS. Cardiopulmonary parameters were evaluated every 30 min and ex vivo phorbol myristate acetate (PMA)-stimulated superoxide release was serially determined as a marker of in vivo neutrophil priming. Lung myeloperoxidase (MPO) activity was measured as a marker of neutrophil migration into the lung. LPS-induced cardiopulmonary dysfunction was characterized by a sustained elevation in mean pulmonary arterial pressure, pulmonary vascular resistance, and peak intratracheal pressure, as well as a reduction in cardiac index, stroke volume index and PaO2 over 6 h. Pretreatment with S-NO-alb attenuated LPS-induced cardiopulmonary dysfunction without adversely affecting systemic hemodynamics. Moreover, S-NO-alb blunted the LPS-induced hypoxemic response and reduced neutrophil activation. S-NO-alb did not, however, attenuate LPS-induced increases in lung MPO. Our results suggest that S-NO-alb can selectively modulate endotoxin-induced pulmonary dysfunction, attenuate neutrophil priming and block the early mortality (40%) in this model.

The effects of arginase inhibitor on lung oxidative stress and inflammation caused by pneumoperitoneum in rats

Background

Pneumoperitoneum-induced oxidative stress and organ injury are known to be associated with nitric oxide (NO) inactivation. Because arginase competes with NO synthase (NOS) for a common substrate, L-arginine, arginase inhibition may increase NO bioavailability. Therefore, we evaluated the ability of the arginase inhibitor, 2 (S)-amino-6-boronohexanoic acid (ABH), to attenuate pneumoperitoneum-induced decrease of NO bioavailability and lung injury.

Methods

Thirty rats were randomly divided into the following groups: 1) the PP-ABH group received a subcutaneous injection of ABH (5 mg/kg) 1 h before induction of pneumoperitoneum (insufflation to intraperitoneal pressure of 15 mmHg for 60 min); 2) the PP group received saline by subcutaneous injection 1 h before induction of pneumoperitoneum; and 3) the control group received saline by subcutaneous injection before a sham procedure with no gas insufflation. After desufflation, blood was collected to determine levels of plasma nitrite, NOS, inflammatory cytokines, and malondialdehyde, a marker of oxidative stress. Lung tissue was obtained for histological evaluation.

Results

We found that plasma nitrite levels were lower in the PP group and higher in the PP-ABH group, compared with controls (P <0.01 and P <0.05, respectively). In the PP group, endothelial NOS activity was decreased and inducible NOS activity was increased compared with the PP-ABH and control groups. Malondialdehyde levels increased 3-fold in the PP group and 2-fold in the PP-ABH group compared with controls. Tumor necrosis factor-α, interleukin-6, and interleukin-1ß levels were elevated in the PP group compared to the control group, but the increase in cytokine production was attenuated or blocked in the PP-ABH group. Lung injury scores were 4.8-fold higher in the PP group and 2-fold higher in the PP-ABH group compared with controls (P <0.001 and P <0.01, respectively).

Discussion

Pneumoperitoneum decreases NO bioavailability and increases the inflammation cytokines, resulting in organ injuries. Inhibition of arginase activity could maintain NO bioavailability by attenuating pneumoperitoneum-induced changes in NOS activity. In addition, arginase inhibition attenuated the oxidative stress and inflammation and decreased the severity of lung injury caused by pneumoperitoneum.

Conclusions

By increasing NO bioavailability and suppressing oxidative stress and inflammation, pretreatment with an arginase inhibitor may protect against lung injury caused by pneumoperitoneum.

Glycyrrhizic Acid Prevents Sepsis-Induced Acute Lung Injury and Mortality in Rats

Glycyrrhizic acid (GA), an active ingredient in licorice, has multiple pharmacological activities. However, the effects of GA on sepsis-induced acute lung injury (ALI) have not been determined. Tthe aim of this study was to investigate the molecular mechanism involved in the effects of GA against sepsis-induced ALI in rats. We found that GA alleviated sepsis-induced ALI through improvements in various pathological changes, as well as decreases in the lung wet/dry weight ratio and total protein content in bronchoalveolar lavage fluid, and a significant increase in the survival rate of treated rats. Additionally, GA markedly inhibited sepsis-induced pulmonary inflammatory responses. Moreover, we found that treatment with GA inhibited oxidative stress damage and apoptosis in lung tissue induced by ALI. Finally, GA treatment significantly inhibited NF-κ B, JNK and P38 MAPK activation. Our data indicate that GA has a protective effect against sepsis-induced ALI by inhibiting the inflammatory response, damage from oxidative stress, and apoptosis via inactivation of NF-κB and MAPK signaling pathways, providing a molecular basis for a new medical treatment for sepsis-induced ALI.

Combined iNO and endothelial progenitor cells improve lung alveolar and vascular structure in neonatal rats exposed to prolonged hyperoxia

BACKGROUND

Stem cells or inhaled nitric oxide (iNO) are reported to improve lung structures in bronchopulmonary dysplasia (BPD) models. We hypothesized that combined iNO and transplanted endothelial progenitor cells (EPCs) might restore lung structure in rats after neonatal hyperoxia.

METHODS

Litters were separated into eight groups: room air, hyperoxia, hyperoxia + iNO, hyperoxia + iNO + L-NAME, hyperoxia + EPCs, hyperoxia + EPCs + L-NAME, hyperoxia + EPCs + iNO, and hyperoxia + EPCs + iNO + L-NAME. Litters were exposed to hyperoxia from the 21st day, then, sacrificed. EPCs were injected on the 21st day. L-NAME was injected daily for 7 d from the 21st day. Serum vascular endothelial growth factor (VEGF), radial alveolar count (RAC), VIII factor, EPCs engraftment, lung VEGF, VEGFR2, endothelial nitric oxide (eNOS) and SDF-1 expression, and NO production were examined.

RESULTS

Hyperoxia exposure led to air space enlargement, loss of lung capillaries, and low expression of VEGF and eNOS. Transplanted EPCs, when combined with iNO, had significantly increased engraftment in lungs, compared to EPCs alone, upon hyperoxia exposure. There was improvement in alveolarization, microvessel density, and upregulation of VEGF and eNOS proteins in the hyperoxia-exposed EPCs with iNO group, compared to hyperoxia alone.

CONCLUSION

Combined EPCs and iNO improved lung structures after neonatal hyperoxia. This was associated with the upregulation of VEGF and eNOS expression.

Endothelial nitric oxide synthase deficient mice are protected from lipopolysaccharide induced acute lung injury

Lipopolysaccharide (LPS) derived from the outer membrane of gram-negative bacteria induces acute lung injury (ALI) in mice. This injury is associated with lung edema, inflammation, diffuse alveolar damage, and severe respiratory insufficiency. We have previously reported that LPS-mediated nitric oxide synthase (NOS) uncoupling, through increases in asymmetric dimethylarginine (ADMA), plays an important role in the development of ALI through the generation of reactive oxygen and nitrogen species. Therefore, the focus of this study was to determine whether mice deficient in endothelial NOS (eNOS^-/-) are protected against ALI. In both wild-type and eNOS^-/- mice, ALI was induced by the intratracheal instillation of LPS (2 mg/kg). After 24 hours, we found that eNOS^-/-mice were protected against the LPS mediated increase in inflammatory cell infiltration, inflammatory cytokine production, and lung injury. In addition, LPS exposed eNOS^-/- mice had increased oxygen saturation and improved lung mechanics. The protection in eNOS^-/- mice was associated with an attenuated production of NO, NOS derived superoxide, and peroxynitrite. Furthermore, we found that eNOS^-/- mice had less RhoA activation that correlated with a reduction in RhoA nitration at Tyr³⁴. Finally, we found that the reduction in NOS uncoupling in eNOS^-/- mice was due to a preservation of dimethylarginine dimethylaminohydrolase (DDAH) activity that prevented the LPS-mediated increase in ADMA. Together our data suggest that eNOS derived reactive species play an important role in the development of LPS-mediated lung injury.

Inhaled nitric oxide increases urinary nitric oxide metabolites and cyclic guanosine monophosphate in premature infants: relationship to pulmonary outcome

OBJECTIVE

Inhaled nitric oxide (iNO) has been tested to prevent bronchopulmonary dysplasia (BPD) in premature infants, however, the role of cyclic guanosine monophosphate (cGMP) is not known. We hypothesized that levels of NO metabolites (NOx) and cGMP in urine, as a noninvasive source for biospecimen collection, would reflect the dose of iNO and relate to pulmonary outcome.

STUDY DESIGN

Studies were performed on 125 infants who required mechanical ventilation at 7 to 14 days and received 24 days of iNO at 20-2 ppm. A control group of 19 infants did not receive iNO.

RESULTS

In NO-treated infants there was a dose-dependent increase of both NOx and cGMP per creatinine (maximal 3.1- and 2-fold, respectively, at 10-20 ppm iNO) compared with off iNO. NOx and cGMP concentrations at both 2 ppm and off iNO were inversely related to severity of lung disease during the 1st month, and the NOx levels were lower in infants who died or developed BPD at term. NOx was higher in Caucasian compared with other infants at all iNO doses.

CONCLUSION

Urinary NOx and cGMP are biomarkers of endogenous NO production and lung uptake of iNO, and some levels reflect the severity of lung disease. These results support a role of the NO-cGMP pathway in lung development.

Gaseous therapeutics in acute lung injury

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) remain major causes of morbidity and mortality in critical care medicine despite advances in therapeutic modalities. ALI can be associated with sepsis, trauma, pharmaceutical or xenobiotic exposures, high oxygen therapy (hyperoxia), and mechanical ventilation. Of the small gas molecules (NO, CO, H₂S) that arise in human beings from endogenous enzymatic activities, the physiological significance of NO is well established, whereas that of CO or H₂S remains controversial. Recent studies have explored the potential efficacy of inhalation therapies using these small gas molecules in animal models of ALI. NO has vasoregulatory and redox-active properties and can function as a selective pulmonary vasodilator. Inhaled NO (iNO) has shown promise as a therapy in animal models of ALI including endotoxin challenge, ischemia/reperfusion (I/R) injury, and lung transplantation. CO, another diatomic gas, can exert cellular tissue protection through antiapoptotic, anti-inflammatory, and antiproliferative effects. CO has shown therapeutic potential in animal models of endotoxin challenge, oxidative lung injury, I/R injury, pulmonary fibrosis, ventilator-induced lung injury, and lung transplantation. H₂S, a third potential therapeutic gas, can induce hypometabolic states in mice and can confer both pro- and anti-inflammatory effects in rodent models of ALI and sepsis. Clinical studies have shown variable results for the efficacy of iNO in lung transplantation and failure for this therapy to improve mortality in ARDS patients. No clinical studies have been conducted with H₂S. The clinical efficacy of CO remains unclear and awaits further controlled clinical studies in transplantation and sepsis.

The value of the lipopolysaccharide-induced acute lung injury model in respiratory medicine

Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is a syndrome characterized by pulmonary edema and acute inflammation. Lipopolysaccharide (LPS), a major component in Gram-negative bacteria, has been used to induce ALI/ARDS. LPS-induced animal models highlight ways to explore mechanisms of multiple diseases and provide useful information on the discovery of novel biomarkers and drug targets. However, each model has its own merits and drawbacks. The goal of this article is to summarize and evaluate the results of experimental findings in LPS-induced ALI/ARDS, and the possible mechanisms and treatments elucidated. Advantages and disadvantages of such models in pulmonary research and new directions for future investigations are also discussed.

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.

Resuscitating the microcirculation in sepsis: the central role of nitric oxide, emerging concepts for novel therapies, and challenges for clinical trials

Microcirculatory dysfunction is a critical element of the pathogenesis of severe sepsis and septic shock. In this Bench-to-Bedside review, we present: 1) the central role of the microcirculation in the pathophysiology of sepsis; 2) new translational research techniques of in vivo video microscopy for assessment of microcirculatory flow in human subjects; 3) clinical investigations that reported associations between microcirculatory dysfunction and outcome in septic patients; 4) the potential role of novel agents to "rescue" the microcirculation in sepsis; 5) current challenges facing this emerging field of clinical investigation; and 6) a framework for the design of future clinical trials aimed to determine the impact of novel agents on microcirculatory flow and organ failure in patients with sepsis. We specifically focus this review on the central role and vital importance of the nitric oxide (NO) molecule in maintaining microcirculatory homeostasis and patency, especially when the microcirculation sustains an insult (as with sepsis). We also present the scientific rationale for clinical trials of exogenous NO administration to treat microcirculatory dysfunction and augment microcirculatory blood flow in early sepsis therapy.

Sickle cell disease vasculopathy: a state of nitric oxide resistance

Sickle cell disease (SCD) is a hereditary hemoglobinopathy characterized by microvascular vaso-occlusion with erythrocytes containing polymerized sickle (S) hemoglobin, erythrocyte hemolysis, vasculopathy, and both acute and chronic multiorgan injury. It is associated with steady state increases in plasma cell-free hemoglobin and overproduction of reactive oxygen species (ROS). Hereditary and acquired hemolytic conditions release into plasma hemoglobin and other erythrocyte components that scavenge endothelium-derived NO and metabolize its precursor arginine, impairing NO homeostasis. Overproduction of ROS, such as superoxide, by enzymatic (xanthine oxidase, NADPH oxidase, uncoupled eNOS) and nonenzymatic pathways (Fenton chemistry), promotes intravascular oxidant stress that can likewise disrupt NO homeostasis. The synergistic bioinactivation of NO by dioxygenation and oxidation reactions with cell-free plasma hemoglobin and ROS, respectively, is discussed as a mechanism for NO resistance in SCD vasculopathy. Human physiological and transgenic animal studies provide experimental evidence of cardiovascular and pulmonary resistance to NO donors and reduced NO bioavailability that is associated with vasoconstriction, decreased blood flow, platelet activation, increased endothelin-1 expression, and end-organ injury. Emerging epidemiological data now suggest that chronic intravascular hemolysis is associated with certain clinical complications: pulmonary hypertension, cutaneous leg ulcerations, priapism, and possibly stroke. New therapeutic strategies to limit intravascular hemolysis and ROS generation and increase NO bioavailability are discussed.

Nitric oxide plays a key role in the platelet-activating factor-induced enhancement of resistance against systemic candidiasis

Platelet-activating factor (PAF) has been demonstrated to augment resistance against Candida albicans infection. In this study, the role of nitric oxide (NO) in PAF-induced resistance in the kidneys was investigated. Pretreatment of the C. albicans-infected mice with PAF resulted in strong expression of messenger RNA (mRNA) and the protein synthesis of inducible nitric oxide synthase (iNOS). These PAF effects were inhibited to a significant degree by pretreatment with the nuclear factor-kappaB inhibitor, pyrrolidinedithiocarbamate. Pretreatment with PAF protected the mice from death caused by C. albicans infection and reduced the growth of fungus in the kidneys. The protective activity of PAF was abrogated by pretreatment with the iNOS inhibitor, aminoguanidine, and in the iNOS(-/-) mice. The PAF markedly increased the infiltration of neutrophils, but not macrophages, and also enhanced the mRNA expression levels of the CXC chemokine, keratinocyte-derived chemokine, in C. albicans-infected kidneys. These effects of PAF were attenuated in the aminoguanidine-treated mice and the iNOS(-/-) mice. These data show that NO plays an important role in PAF-induced protection against C. albicans.

Role of the endothelium in pulmonary arterial hypertension

Pulmonary hypertension represents a significant disease burden in both the developed and developing worlds. Certain forms of pulmonary hypertension are more common in some countries than others but people of all races, all ages and both sexes are affected. Treatment options are limited and expensive. The development of new therapies will be determined by improved understanding of endothelial cell biology.

The Role of Endogenous Histamine on the Pathogenesis of the Lipopolysaccharide (LPS)-Induced, Acute Lung Injury: A Pilot Study

Histamine is widely distributed in the lungs and increases capillary permeability and P-selectin expression. To observe the role of histamine in acute lung injury (ALI), we measured the histamine and protein concentrations and cell numbers in the bronchoalveolar lavage (BAL) of LPS-induced ALI in rats. We instilled LPS (3 mg/kg) intratracheally, in conjunction with the intravenous histamine receptor antagonists (mepyramine, a H1-receptor antagonist, or ranitidine, a H2-receptor antagonist). LPS increased protein concentration and neutrophil numbers in the BAL as well as myeloperoxidase (MPO) activity in lungs after 6 h. LPS also increased histamine concentration in BAL after 2 h. Mepyramine and ranitidine attenuated the increased histamine concentrations. Total cell number in the BAL and MPO activity in the lungs were significantly decreased and neutrophil numbers and protein concentration in the BAL seemed to decrease with the administration of ranitidine at 6 h. In conclusion, endogenous histamine might be involved in the recruitment of neutrophils and protein leaks in LPS-induced ALI via the H2 receptors.

Pre-emptive and continuous inhaled NO counteracts the cardiopulmonary consequences of extracorporeal circulation in a pig model

Cardiopulmonary bypass (CPB) activates a systemic inflammatory response characterized clinically by alterations in cardiovascular and pulmonary function. The aim of this study was to measure the cardiopulmonary consequences in sham-operated pigs, and in animals subjected to CPB in the presence or absence of lipopolysaccharide (LPS). We also investigated, if the perioperative administration of inhaled NO exerts significant cardiopulmonary effects in an anaesthetized and mechanically ventilated pig model of extracorporeal circulation. Thirty pigs were randomized into six equal groups (sham; sham+INO; CPB; CPB+INO; CPB+LPS; CPB+LPS+INO) and subjected to anaesthesia with mechanical ventilation for up to 24h. We found that CPB+LPS group has the highest degree of lung injury. We also demonstrated that there was a significant difference on the cardiovascular parameters (heart rate, central venous pressure, stroke volume index, and mean systemic arterial blood pressure) between the CPB groups and the sham groups. The deteriorated lung mechanics was associated with a decrease in active subfraction of surfactant (LA) with time during the procedure (P=0.0003), on which inhaled NO had only an initial beneficial effect. In our model, inhaled NO had no long-term beneficial effect on lung mechanics and surfactant homeostasis despite improving lung haemodynamics, inflammation, and oxygenation. We conclude from this study that the use of pre-emptive and continuous inhaled NO therapy has protective and safe effects against lung ischemia/reperfusion associated with CPB.

Effects of Inhaled Nitric Oxide on Inflammation and Apoptosis After Cardiopulmonary Bypass

BACKGROUND

Cardiopulmonary bypass (CPB), a procedure often used during cardiac surgery, is associated with an inflammatory process that leads to lung injury. We hypothesized that inhaled nitric oxide (INO), which has anti-inflammatory properties, possesses the ability to modulate lung cell apoptosis and prevent CPB-induced inflammation.

METHODS

Twenty male pigs were randomly classified into four groups: sham, sham plus INO, CPB, and CPB plus INO. INO (20 ppm) was administered for 24 h after anesthesia. CPB was performed 90 min into INO treatment. BAL fluid and blood were collected at time 0 (before CPB), at 4 h after beginning CPB, and 24 h after beginning CPB (T24).

RESULTS

At T(24), BAL interleukin (IL)-8 levels and neutrophil percentages were elevated significantly in the CPB group. At T(24), INO reduced IL-8 concentrations and attenuated the increase of neutrophil percentage in the CPB-plus-INO group. Nitrite-plus-nitrate (NOx) concentrations were decreased significantly in groups without INO. Moreover, animals treated with INO showed higher rates of pulmonary apoptosis compared to their respective control groups except for the sham-plus-INO group, in which they were diminished.

CONCLUSION

These results demonstrate that NOx production is reduced after CPB, and that INO acts as an anti-inflammatory agent by decreasing neutrophil numbers and their major chemoattractant, IL-8. INO also increases cell apoptosis in the lungs during inflammatory conditions, which may explain, in part, how it resolves pulmonary inflammation.

Sequential exposures to ozone and lipopolysaccharide in postnatal lung enhance or inhibit cytokine responses

Sequential exposures to inhaled environmental pollutants may result in injuries/responses not predicted by evaluating exposures to an individual toxicant. This may indicate that the lung is damaged or primed by earlier events, so exposure to a nontoxic dose of an environmental pollutant may be sufficient to trigger adverse responses. The present study was designed to test the hypothesis that stimulating lung epithelial damage or inflammatory cell activation followed by a second stimulus leads to responses not seen after individual exposures in the postnatal lung. C57Bl/6 mice ages 4, 10, and 56 days were exposed to either a 10-minute inhalation of lipopolysaccharide (LPS), with an estimated deposited dose of 26 EU, followed immediately by 2.5 PPM ozone for 4 hours, or to 2.5 PPM ozone for 4 hours followed immediately by a 10-minute inhalation of LPS and examined 2 hours post exposure. Abundance of proinflammatory cytokine messages was measured by RNase protection assay. Exposure to LPS followed by ozone induced an inflammatory response in 4-day-old mice, which was not detected after LPS or ozone exposure alone. This exposure sequence also generated a synergistic increase in interleukin (IL)-6 mRNA abundance in 10- and 56-day-old mice but not in 4-day-old mice. Exposure to ozone followed by LPS inhibited IL-1alpha and IL-1beta responses in 4-, 10-, and 56-day-old mice; furthermore, this inhibitory effect was observed after 1.0 and 0.5 PPM ozone exposures. These results demonstrate that preexposure to LPS, which primarily activates inflammatory cell recruitment, can cause sensitization to a secondary stimulus. However, preexposure to ozone, which primarily damages the epithelium, inhibited proinflammatory responses. Thus it was concluded that sequential exposures to ozone and LPS resulted in responses not predicted by evaluating individual exposures during postnatal lung development.

Different effects of surfactant and inhaled nitric oxide in modulation of inflammatory injury in ventilated piglet lungs

Septic acute lung injury (ALI) causes high morbidity and mortality in intensive care service as a result of biotrauma and dysfunction in the lungs and other organ systems. We hypothesized that surfactant and/or inhaled nitric oxide (iNO) may have different effects in modulation of inflammatory injury in septic ALI. Twenty-four healthy, 6-9 kg piglets were anesthetized, and intraperitoneally injected with Escherichia coli, followed by a low tidal volume ventilation until sepsis and ALI developed within 4-6 h. They were then randomly treated in groups (n=6 each) as: control (C), inhaled NO at 10 ppm (NO), surfactant at 100mg/kg (Surf), or both surfactant and iNO (SNO). A normal control group (N) was sham-injected and similarly ventilated. Over the 24 h of treatment period, both Surf, and SNO groups had significantly improved PaO2/FiO2, dynamic compliance and resistance of respiratory system. At 24h, the best alveolar aeration and least protein leakage, the lowest wet-to-dry lung weight ratio and lung injury score were found in SNO. Activity of nuclear factor kappa B (NF-kappaB) and myeloperoxidase, interleukin 8 mRNA expression and melondialdehyde were significantly increased, and IL-10 mRNA decreased, in lung tissue of the C group, but were significantly altered in the SNO group, and moderately altered in either NO or Surf group. We conclude that the effects of lung protection by surfactant and/or iNO in this model may be different in modulation of inflammatory cytokine mRNA expression and activity of NF-kappaB, and iNO did not have adverse effects.

Inhaled nitric oxide improves the survival of the paraquat-injured rats

The purpose of this study was to evaluate the effects of inhaled nitric oxide (NO) on the paraquat-induced lung injury in rats. The rats were assigned to four groups: control; inhaled NO (5 ppm); paraquat (PQ, 30 mg/kg); and PQ+NO group. For first 18 h the inhalation of NO mixed with room air was performed. Total white blood cell (WBC), neutrophil, total protein, lactate dehydrogenase (LDH), transforming growth factor-beta1 (TGF-beta1) in serum and/or bronchoalveolar lavage (BAL) fluid, serum malonaldehyde (MDA), and myeloperoxidase (MPO) of lung were measured and lung histopathology were also reviewed. The 72-h survival rate of PQ group was 58%, but the survival rate of PQ+NO group, NO group and control group were 100%, respectively. The serum MDA and TGF-beta1 in BAL fluid and blood of PQ+NO group were significantly lower than those of PQ group. However, inhaled NO did not decrease the elevated total WBC and neutrophil counts, and total protein, LDH and MPO activity in the lung injured by PQ. The alveolar septal thickening and inflammatory cell infiltration were not different between PQ and PQ+NO groups. NO inhalation may be beneficial for the survival of paraquat-induced injured rats by attenuating lipid peroxidation and production of TGF-beta1.

Inhaled nitric oxide in 2003: a review of its mechanisms of action

PURPOSE

To review the pulmonary and systemic effects of endogenous nitric oxide and inhaled nitric oxide administered to patients.

SOURCE

A systematic search for experimental data, human case reports, and randomized clinical trials since 1980, the year of discovery of endothelium-derived relaxing factor.

PRINCIPAL FINDINGS

Nitric oxide has pulmonary and systemic effects. Inhaled nitric oxide not only causes selective pulmonary vasodilation but also results in pulmonary vasoconstriction of the vessels perfusing non-ventilated alveolae. The systemic effects of inhaled nitric oxide, which include modulation of the distribution of systemic blood flow, increase in renal output, interaction with coagulation, fibrinolysis and platelet functions, alteration of the inflammatory response, are described and the mechanisms of nitric oxide transport are explained. The possible toxicity of inhaled nitric oxide is also discussed.

CONCLUSION

The multiple effects of inhaled nitric oxide support its role as a pulmonary and extra-pulmonary medication.

Regulatory effects of iNOS on acute lung inflammatory responses in mice

The role of endogenous NO in the regulation of acute lung injury is not well defined. We investigated the effects of inducible nitric oxide synthase (iNOS) and endothelial NOS (eNOS) on the acute inflammatory response in mouse lungs. Acute lung injury was induced by intratracheal instillation of bacterial lipopolysaccharide (LPS) into wild-type (WT) mice and mice deficient in iNOS (iNOS(-/-)) or eNOS (eNOS(-/-)). Endpoints of inflammatory injury were myeloperoxidase (MPO) content and leak of albumin into lung. Inflammatory injury was similar in WT and eNOS(-/-) mice but was substantially increased in iNOS(-/-) mice. Bronchoalveolar lavage (BAL) fluids of iNOS(-/-) and WT mice showed similar levels of CXC chemokines (MIP-2, KC) but enhanced levels of CC chemokines (MCP-1, MCP-3). Increased lung content of MPO in iNOS(-/-) mice was reduced by anti-MCP-1 to values found in WT mice. In vitro stimulation of microvascular endothelial cells with LPS and IFN gamma revealed elevated production of CXC and CC chemokines in cells from iNOS(-/-) mice when compared to endothelial cells from iNOS(+/+) mice. Peritoneal macrophages from iNOS(-/-) donors also revealed increased production of CC chemokines after stimulation with LPS and interferon (IFN gamma). These data indicate that absence of iNOS causes enhanced lung inflammatory responses in mice which may be related to enhanced production of MCP-1 by endothelial cells and macrophages. It appears that iNOS affects the lung inflammatory response by regulating chemokine production.

Endotoxin-induced shock in the pig--limited effects of low and high concentrations of inhaled nitric oxide

AIM

This study was carried out to study the prophylactic effects of inhalation of nitric oxide (NO) before and during the induction of endotoxic shock.

METHODS

Eighteen anaesthetized pigs received an infusion of 10-20 microg kg(-1) endotoxin during 2 h after pre-treatment with the cortisol-synthesis inhibitor metyrapone. Three groups were tested (n = 6 each) and received 0, 0.2 or 20 ppm inhaled NO from 30 min before start of endotoxin infusion until 4 h after start of endotoxin. Both 0.2 and 20 ppm NO were able to improve blood gas values.

RESULTS

Area above curve values of arterial P2/FiO2 from 0 to 4 h were 0.83 +/- 0.09 kPa h (control), 0.78 +/- 0.22 (0.2 ppm NO, non-significant) and 0.31 +/- 0.06 (20 ppm NO, P < 0.01, Mann-Whitney U-test, compared to control). Area under curve values of PCO2 from 0 to 4 h were 3.96 +/- 0.66 kPa h (control), 1.20 +/- 0.46 (0.2 ppm NO, P < 0.05, Mann-Whitney U-test, compared to control) and 2.78 +/- 1.06 (20 ppm NO group, non-significant). The increase in pulmonary arterial pressure (PAP) was partly prevented by 20 ppm NO, but not by 0.2 ppm NO at 4 h. Inhaled NO did not affect the levels of BAL fluid total protein, tumour necrosis factor-alpha, interleukin-8 and neutrophil counts.

CONCLUSIONS

The addition of a high (20 ppm), but not a low (0.2 ppm), concentration of NO to the inhaled air during endotoxin shock improves arterial oxygen tension and reduces pulmonary artery pressure. Neither dose affects lung mechanics or inflammatory indices, in spite of being given prophylactically.

Acute respiratory distress syndrome in the septic surgical patient

The acute respiratory distress syndrome (ARDS) is a process of acute inflammatory lung injury that affects a diverse array of surgical and medical patients. The syndrome is mediated by a complex and interacting system of chemical mediators produced by several types of pulmonary cells. Regardless of the predisposing causes, activation of the nuclear factor kappa B seems to be, at the molecular level, a signature event of ARDS, leading to the rapid activation of intracellular signaling pathways, which coordinate the induction of multiple genes encoding inflammatory mediators. There are at least two compelling reasons for promoting an understanding of these interactions and their molecular mediators and second messengers: new therapies intended to modulate these factors continue to be developed, and the levels of some of these molecules, most notably cytokines, may serve as early indicators of the onset of ARDS.

Upregulation of reactive oxygen species generation and phagocytosis, and increased apoptosis in human neutrophils during severe sepsis and septic shock

We evaluated neutrophil activation by measuring its phagocytic ability and oxidative burst activity in 16 patients with sepsis and 16 healthy volunteers. We also focused on neutrophil apoptosis as a regulatory mechanism of the inflammatory response. Neutrophil phagocytosis was evaluated by the detection of propidium iodide (PI)-labeled Staphylococcus aureus added to whole blood. Reactive oxygen species (ROS) formation was quantified by measuring the oxidation of 2',7' dichlorofluorescein diacetate (DCFH-DA) at baseline and after cell stimulation with phorbol myristate acetate (PMA), and bacterial cells (killed S. aureus) or products (lipopolysaccharide [LPS] and N-formyl-methionyl-leucyl-phenylalanine [FMLP]). Apoptosis was assessed in neutrophils stained with annexin V and PI. Neutrophil phagocytic ability was increased in patients with sepsis compared with healthy controls (median geometric mean fluorescence intensity [GMFI] was 101.9 and 54.7, respectively; P = 0.05). ROS formation was enhanced in patients with sepsis compared with healthy volunteers at baseline (median GMFI 275.6 and 52.1, respectively; P < 0.001), and after stimulation with S. aureus (median GMFI 2395.8 and 454.9, respectively; P < 0.001), PMA (median GMFI 1120.6 and 307.5, respectively; P = 0.003), FMLP (median GMFI 792.4 and 123.2, respectively; P < 0.001), and LPS (median GMFI 624.8 and 144.8, respectively; P < 0.001). Early neutrophil apoptosis was increased in patients with sepsis compared with healthy volunteers (median 11.3% and 9.1%, respectively; P = 0.03). These data demonstrate that neutrophil function is enhanced in patients with sepsis. Additionally, circulating neutrophils from patients with sepsis presented with increased early apoptosis, which may be consequence of a regulatory mechanism of the inflammatory response.

Effects of acute hypoxia and lipopolysaccharide on nitric oxide synthase-2 expression in acute lung injury

The potential role of nitric oxide synthase-2 (NOS2) in acute lung injury (ALI) has gained increasing attention. This study evaluates the effects of hypoxia, an important feature of ALI, on NOS2 expression in a rat model of ALI caused by exposure to hypoxia and LPS. Exposure to hypoxia alone had no effect on the expression of NOS2 in rat lungs. LPS treatment resulted in a significant increase in NOS2 in the lungs, which was further enhanced by concomitant exposure to hypoxia. Immunohistochemical analysis and in situ hybridization showed no changes in the expression of NOS2 in lung resident cells under any conditions. The increase in NOS2 levels is mainly due to the influx of NOS2-expressing inflammatory cells. By morphologic analysis, these inflammatory cells were identified as neutrophils, lymphocytes, and monocytes. In vitro experiments of lung epithelial and endothelial cell lines showed no detectable expression of NOS2 with any of the treatments. In a macrophage cell line, LPS-induced NOS2 expression was not affected by the concomitant exposure to hypoxia. In conclusion, LPS increases NOS2 expression in rat lungs through the recruitment of NOS2-producing leukocytes. Simultaneous exposure to LPS and hypoxia results in a greater influx of inflammatory cells that further enhances NOS2 expression.

An emerging role for nitric oxide in sickle cell disease vascular homeostasis and therapy

Nitric oxide participates in the compensatory response to chronic vascular injury in patients with sickle cell disease. The authors have found reductions of basal and stimulated nitric oxide production and responses to exogenous nitric oxide in male patients with sickle cell disease. Gender differences in nitric oxide bioavailability are probably caused in part by the protective effects of ovarian estrogen on nitric oxide synthase expression and activity in women. Further, in men, and likely all patients during vaso-occlusive crisis and the acute chest syndrome, nitric oxide is destroyed by increased circulating plasma hemoglobin and superoxide. The combined effects of inhaled nitric oxide gas of improving pulmonary ventilation to perfusion matching and hemodynamics, reducing alveolar and systemic inflammation, and inhibiting circulating plasma hemoglobin (and thus restoring peripheral nitric oxide bioavailability) may modulate the course of the disease, including the frequency and severity of vaso-occlusive crises and acute chest syndrome episodes. Possible effects of chronic nitric oxide-based therapies on erythrocyte density, pulmonary artery pressures, and fetal hemoglobin induction deserve study.

Tratamientos complementarios: óxido nítrico, posición en prono y surfactante

The management of hypoxic respiratory failure is based on oxygen delivery and ventilatory support with lung-protective ventilation strategies. Better understanding of acute lung injury have led to new therapeutic approaches that can modify the outcome of these patients. These adjunctive oxygenation strategies include inhaled nitric oxide and surfactant delivery, and the use of prone positioning. Nitric oxide is a selective pulmonary vasodilator that when inhaled, improves oxygenation in clinical situations such as persistent pulmonary hypertension of the newborn, pulmonary hypertension associated with congenital heart disease, and acute respiratory distress syndrome (ARDS). When applied early in ARDS, prone positioning improves distribution of ventilation and reduces the intrapulmonary shunt. The surfactant has dramatically decreased mortality caused by hyaline membrane disease in premature newborns, although the results have been less successful in ARDS. Greater experience is required to determine whether the combination of these treatments will improve the prognosis of these patients.

The role of nitric oxide in treatment of acute lung injury after surgery with extracorporeal circulation

Postoperative acute lung injury (ALI) compromises oxygen transfer across alveolar-capillary membrane with consecutive hypoxia, one of its indicators being reduction of oxygenation index PaO2/FiO2 below 40 kPa (300 mm Hg). Management of ALI includes different procedures like mechanical lung ventilation (MLV), drugs and others. One of the new possibilities for treatment of ALI is nitric oxide (NO) inhalation. The aim of this prospective study was to examine the role of NO inhalation in treatment of ALI. 14 patients with ALI developed immediately after operation with extracorporeal circulation (ECC) were included in the study. Group A (n = 8) inhaled NO and group B (n = 6) did not inhale NO during treatment of ALI. All other therapeutic measures were the same in both groups. The groups were similar in relation to demographic data, type of surgery and duration of ECC. PaO2/FiO2 was calculated before operation (T1), immediately after surgery (T2) and after lung recovery, when the need for MLV stopped (T3). The duration of MLV was also registered. PaO2/FiO2 (kPa) in referent times was in group A 54,9 ? 1,6, 33,8 ? 1,2 and 46,2 ? 0,8 and in group B 52,2 ? 1,1, 33,5 ? 1,5 and 47,3 ? 0,9, respectively. There was a statistically significant decrease of PaO2/FiO2 in T2 and T3 vs T1 in both groups (p < 0,05), while the difference between the groups was not statistically significant. The duration of MLV (h) in group B (28,5 ? 1,6) was statistically significantly shorter than in group A (63,1 ? 8,7) (p < 0,01). According to the results of this study we conclude that NO inhalation during ALI after surgery with ECC significantly reduces the duration of MVL and improves pulmonary recovery .

Targets for pharmacological intervention of endothelial hyperpermeability and barrier function

Many diseases share the common feature of vascular leakage, and endothelial barrier dysfunction is often the underlying cause. The subsequent stages of endothelial barrier dysfunction contribute to endothelial hyperpermeability. Vasoactive agents induce loss of junctional integrity, a process that involves actin-myosin interaction. Subsequently, the interaction of leukocytes amplifies leakage by the leukocyte-derived mediators. The processes mainly occur at the postcapillary venules. The whole microvascular bed, including the capillaries, becomes involved in vascular leakage by the induction of angiogenesis. Plasma leakage results from gaps between endothelial cells as well as by the induction of transcellular transport pathways. Several mechanisms can improve endothelial barrier function, depending on the tissue affected and the cause of hyperpermeability. They include blockade of specific receptors and elevation of cyclic AMP (cAMP) by agents such as beta(2)-adrenergic agents. However, current therapies based on these principles often fail. Recent research has identified several new promising targets for pharmacological therapy. Endogenous compounds were also found with barrier-improving characteristics. Important insights were obtained in the different pathways involved in barrier dysfunction. Such insights regard the regulation of endothelial contraction and endothelial junction integrity: inhibitors of RhoA activation and Rho kinase represent a potentially valuable group of agents with endothelial hyperpermeability reducing properties, and strategies to target vascular endothelial growth factor (VEGF)-mediated edema are under current investigation. In clinical practice, not only tools to improve an impaired endothelial barrier function are necessary. Sometimes, a controlled, temporal, and local increase in permeability can also be desired, for example, with the aim to enhance drug delivery. Therefore, vessel leakiness is also being exploited to enable tissue access of liposomes, viral vectors, and other therapeutic agents that do not readily cross healthy endothelium. This review discusses strategies for targeting signaling molecules in therapies for diseases involving altered endothelial permeability.

Pharmacology of acute lung injury

The acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is a clinical syndrome that affects both medical and surgical patients. To date, despite improved understanding of the pathogenesis of ALI/ARDS, pharmacological modalities have been unsuccessful in decreasing mortality. However, several pharmacological agents for ARDS are in development and have shown great promise. In addition to the anti-inflammatory category including late corticosteroids, inhaled nitric oxide, alveolar surfactant, and vasodilators are being evaluated. Replacements of anticoagulation mediators have also suggested beneficial effects on the patient outcome. This article provides an overview of pharmacological treatments of ALI/ARDS.

Intracellular signalling involved in modulating human endothelial barrier function

The endothelium dynamically regulates the extravasation of hormones, macromolecules and other solutes. In pathological conditions, endothelial hyperpermeability can be induced by vasoactive agents, which induce tiny leakage sites between the cells, and by cytokines, in particular vascular endothelial growth factor, which increase the exchange of plasma proteins by vesicles and intracellular pores. It is generally believed that the interaction of actin and non-muscle myosin in the periphery of the endothelial cell, and the destabilization of endothelial junctions, are required for endothelial hyperpermeability induced by vasoactive agents. Transient short-term hyperpermeability induced by histamine involves Ca2+/calmodulin-dependent activation of the myosin light chain (MLC) kinase. Prolonged elevated permeability induced by thrombin in addition involves activation of the small GTPase RhoA and Rho kinase, which inhibits dephosphorylation of MLC. It also involves the action of other protein kinases. Several mechanisms can increase endothelial barrier function, depending on the tissue affected and the cause of hyperpermeability. They include blockage of specific receptors, and elevation of cyclic AMP by agents such as beta2-adrenergic agents. Depending on the vascular bed, nitric oxide and cyclic GMP can counteract or aggravate endothelial hyperpermeability. Finally, inhibitors of RhoA activation and Rho kinase represent a potentially valuable group of agents with endothelial hyperpermeability-reducing properties.

Effects of inhaled nitric oxide in a mouse model of sepsis-induced acute lung injury

OBJECTIVE

Although inhaled nitric oxide transiently improves oxygenation in patients with acute lung injury, it has not affected clinical outcomes. As well, the effects of inhaled nitric oxide on the pathophysiologic features of acute lung injury have not been well defined. Therefore, we assessed the effects of inhaled nitric oxide on the degree of pulmonary inflammation and injury in a mouse model of sepsis-induced acute lung injury.

DESIGN

Randomized, controlled animal study.

SETTING

Research laboratory of an academic institution.

SUBJECTS

Male C57Bl/6 mice.

INTERVENTIONS

Sepsis was induced by cecal ligation and perforation. At the time of surgery, septic and naïve mice were randomized to exposure to either 40 ppm inhaled nitric oxide or room air for 24 hrs before they were killed.

MEASUREMENTS AND MAIN RESULTS

Sepsis-induced acute lung injury was characterized by increased pulmonary myeloperoxidase (68 +/- 13 vs. 13 +/- 3 mU/mg protein in naïve mice, p <.01), pulmonary 8-isoprostane content (627 +/- 51 vs. 88 +/- 20 pg/mg protein in naïve mice, p <.01), and protein in bronchoalveolar lavage fluid (p <.05). Inhaled nitric oxide exposure in septic mice completely abrogated the septic increases in myeloperoxidase activity (p <.05) and pulmonary 8-isoprostane content (p <.05) but had no effect on bronchoalveolar lavage protein. The induction of sepsis also was associated with an increase in pulmonary inducible NO synthase activity (2.8 +/- 0.5 vs. 0.4 +/- 0.1 pmol small middle dotmin-1 small middle dotmg-1 protein in naïve mice, p <.05), and inhaled nitric oxide attenuated this increase in pulmonary inducible NO synthase activity (p <.05).

CONCLUSIONS

Exposure to inhaled nitric oxide early in the course of sepsis-induced acute lung injury is associated with reduced pulmonary leukocyte infiltration and less oxidative injury. Decreased lung inflammation and injury with inhaled nitric oxide is associated with decreased pulmonary inducible NO synthase activity. Therefore, inhaled NO may have greater clinical benefit if administered earlier in the natural history of acute lung injury in patients.

Nitric oxide-derived nitrate anion contributes to endotoxic shock and multiple organ injury/dysfunction

OBJECTIVE

Because nitrate represents the major end-product of nitric oxide in vivo and can affect enzyme activity, cell electrophysiological functions, and cell membrane integrity, we hypothesized that overaccumulated nitric oxide-derived nitrate anion in tissues or organs in vivo may contribute to endotoxic shock and multiple organ injury/dysfunction during endotoxemia.

DESIGN

Prospective, experimental animal study.

SETTING

Laboratory at a university hospital.

SUBJECTS

Sprague-Dawley rats.

INTERVENTIONS

Rats were injected intraperitoneally with 5, 10, or 20 mg/kg lipopolysaccharide or saline and were studied in groups at 0, 6, 12, and 24 hrs.

MEASUREMENTS AND MAIN RESULTS

Significant differences were seen between nitrate concentrations in the heart, lung, kidney, liver, brain, aorta, diaphragm, spleen, thymus, testis or ovary, hind limb muscle, intestine, adipose tissue, bone, bladder, urine and plasma, which imply a nitrate gradient between intracellular and extracellular compartments. Lipopolysaccharide significantly increased nitrate concentration at 12 hrs in most tissues and organs, except in the brain, adipose tissue, and muscle. It increased more in plasma than in tissues. The lipopolysaccharide dose-dependent nitrate concentration was observed only in the aorta and lungs. The nitrate concentration change was paralleled by the systemic inflammatory response syndrome, as indicated by alterations of myeloperoxidase activity and by impaired histologic and cellular membrane integrity in tissues and organs. Mean arterial pressure was negatively correlated with nitrate concentration modifications in the aorta during 24 hrs of endotoxemia.

CONCLUSIONS

These results collectively indicate that overaccumulated nitric oxide-derived nitrate anion in tissues or organs in vivo contributes to endotoxic shock and multiple organ injury/dysfunction during endotoxemia.

Inhaled nitric oxide attenuates acute lung injury via inhibition of nuclear factor-kappa B and inflammation

The effect of inhaled nitric oxide (NO) on inflammatory process in acute lung injury (ALI) is unclear. The aims of this study were to 1) examine whether inhaled NO affects the biochemical lung injury parameters and cellular inflammatory responses and 2) determine the effect of inhaled NO on the activation of nuclear factor-kappa B (NF-kappa B) in lipopolysaccharide (LPS)-induced ALI. Compared with saline controls, rabbits treated intravenously with LPS showed increases in total protein and lactate dehydrogenase in the bronchoalveolar lavage (BAL) fluid, indicating ALI. LPS-treated animals with NO inhalation (LPS-NO) showed significant decreases in these parameters. Neutrophil numbers in the BAL fluid, the activity of reactive oxygen species in BAL cells, and the levels of interleukin (IL)-1 beta and IL-8 in alveolar macrophages were increased in LPS-treated animals. In contrast, neutrophil numbers and these cellular activities were substantially decreased in LPS-NO animals, compared with LPS-treated animals. NF-kappa B activation in alveolar macrophages from LPS-treated animals was also markedly increased, whereas this activity was effectively blocked in LPS-NO animals. These results suggest that inhaled NO attenuates LPS-induced ALI and pulmonary inflammation. This attenuation may be associated with the inhibition of NF-kappa B activation.

Beneficial effects of nitric oxide inhalation on pulmonary bacterial clearance

OBJECTIVE

The beneficial effects of nitric oxide inhalation on oxygenation during acute respiratory distress syndrome are well described. In contrast, the effects of nitric oxide on pulmonary inflammatory response are much less known in vivo. The objectives of this study were to evaluate the effects of nitric oxide inhalation on bacterial clearance during bacterial pneumonia and on alveolar neutrophil functions.

DESIGN

Controlled animal study.

SETTING

Research laboratory of an academic institution.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Severe pneumonia was induced by alveolar instillation of live Pseudomonas aeruginosa (1.5 x 10(8) colony-forming units/kg) in rats. After instillation, rats were exposed to oxygen alone (FIO(2) 100%) or to oxygen (FIO(2) approximately 100%) plus nitric oxide (10 ppm) during 24 hrs.

MEASUREMENTS AND MAIN RESULTS

Oxygen plus nitric oxide inhalation compared with oxygen alone increased recruitment of alveolar neutrophils (32.5 +/- 4.6 x 10(6) cells/mL vs. 23.4 +/- 1.9 x 10(6) cells/mL, p <.05) and improved bacterial clearance in the bronchoalveolar lavage fluid (8.1 +/- 4.2 x 10(2) vs. 1.6 +/- 1.0 x 10(5) colony-forming units/mL, p <.05) and in the pulmonary parenchyma (1.7 +/- 1.14 x 10(7) vs. 3.4 +/- 1.5 x 10(8) colony-forming units/mL, p <.05). However, neither protein concentration in the bronchoalveolar lavage fluid nor mortality rates were modified by nitric oxide inhalation. The ex vivo alveolar neutrophil functions were similar regardless of whether rats previously inhaled nitric oxide. In vitro experiments demonstrated that nitric oxide donor had a direct bactericidal effect against P. aeruginosa and did not modify alveolar neutrophil functions.

CONCLUSIONS

These results suggest a beneficial effect of nitric oxide inhalation on bacterial clearance of P. aeruginosa attributable to both a direct bactericidal effect and an influx of alveolar neutrophils with preserved functions.

Selective protective effects of nitric oxide inhalation on allergen-induced acute airway reactions in the pig

BACKGROUND

Nitric oxide (NO) is thought to be an important mediator of inflammatory processes during allergic reactions in the respiratory tract.

OBJECTIVE

This study was undertaken to investigate the effects of inhalation of NO on the allergen-induced acute airway reactions in the pig.

METHODS

Specific pathogen-free pigs were sensitized with Ascaris suum antigen and challenged with an allergen aerosol during mechanical ventilation and anaesthesia. One group (n = 8) was treated with inhaled NO (20 ppm) which was given from 30 min before allergen challenge until the experiments were completed at 120 min after challenge. A control group (n = 8) did not receive NO (< 0.001 ppm).

RESULTS

Inhalation of 20 ppm NO prevented the fall in arterial pO2/FiO2 levels that was observed in the control group (areas under the curve between 0 and 120 min were 3.7 +/- 1.4 kPa/min in NO-treated pigs vs. 15.9 +/- 3.4 in controls, P < 0.01, Mann-Whitney U-test) and it decreased baseline pulmonary arterial pressure (change from time-point - 30-0 was 3.1 +/- 5.3% in the control and - 19.9 +/- 3.5% in the NO group, P < 0.01), which in turn resulted in a lower pulmonary arterial pressure during allergen challenge. NO also caused vasodilatation in the bronchial circulation, resulting in increased bronchial vascular conductance throughout the experiment. NO inhalation caused a small, but non-significant, reduction in the allergen-induced bronchoconstrictor response, whereas histamine release, as detected in urine, was not changed. Total protein levels in bronchoalveolar lavage (BAL) fluid were significantly decreased in the NO group at 120 min after challenge compared with 45 min (373 +/- 101 microg/mL vs. 631 +/- 184, respectively, P < 0.05, Wilcoxon matched pairs test), whereas levels in the control group did not change between these two time-points (513 +/- 282 vs. 599 +/- 354, not significant).

CONCLUSION

These findings indicate that NO inhalation improves ventilation/perfusion matching and causes some bronchodilatation during the allergen-induced acute airway reaction, whereas histamine release is not affected. Moreover, NO inhalation enhanced the clearance of extravasated protein in the airways, possibly through increased bronchial blood flow. Even though some protective effects were seen, this study does not support a therapeutic role for exogenous NO in acute allergic reactions.

Nitric oxide suppresses IL-8 transcription by inhibiting c-Jun N-terminal kinase-induced AP-1 activation

The role of activator protein-1 (AP-1) in tumor necrosis factor-alpha (TNF-alpha)-induced interleukin-8 (IL-8) gene expression was evaluated. We showed that TNF-alpha activates AP-1 in the transformed endothelial cell line ECV304 by transient transfections of IL-8 promoter construct pGL-3BF(2). Mutation of either the AP-1 site or the NF-IL-6 site on the IL-8 promoter suppressed the TNF-alpha-induced activation, suggesting cooperation between these transcription factors and transcription factor NF-kappaB. Overexpression of dominant negative mutants of c-Jun suppressed AP-1-driven transcription of the IL-8 promoter following stimulation by TNF-alpha, suggesting that cooperative interaction between AP-1 and NF-kappaB is essential for IL-8 transcription in the presence of TNF-alpha. We also showed that nitric oxide (NO), in the form of an exogenous NO donor, suppressed the level of activation of the AP-1 subunit, c-Jun, by down-regulation of c-Jun NH2 terminal kinase. This down-regulation could be the putative mechanism of action for NO-mediated inhibition of IL-8 secretion in activated endothelium. These observations suggest for the first time that NO has broad suppressive activities on various proinflammatory effectors in activated endothelium.

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.