Exhaled nitric oxide production by nitric oxide synthase-deficient mice

The Nitric Oxide Pathway in Pulmonary Arterial Hypertension: Pathomechanism, Biomarkers and Drug Targets

The altered Nitric Oxide (NO) pathway in the pulmonary endothelium leads to increased vascular smooth muscle tone and vascular remodelling, and thus contributes to the development and progression of pulmonary arterial hypertension (PAH). The pulmonary NO signalling is abrogated by the decreased expression and dysfunction of the endothelial NO synthase (eNOS) and the accumulation of factors blocking eNOS functionality. The NO deficiency of the pulmonary vasculature can be assessed by detecting nitric oxide in the exhaled breath or measuring the degradation products of NO (nitrite, nitrate, S-nitrosothiol) in blood or urine. These non-invasive biomarkers might show the potential to correlate with changes in pulmonary haemodynamics and predict response to therapies. Current pharmacological therapies aim to stimulate pulmonary NO signalling by suppressing the degradation of NO (phosphodiesterase- 5 inhibitors) or increasing the formation of the endothelial cyclic guanosine monophosphate, which mediates the downstream effects of the pathway (soluble guanylate cyclase sensitizers). Recent data support that nitrite compounds and dietary supplements rich in nitrate might increase pulmonary NO availability and lessen vascular resistance. This review summarizes current knowledge on the involvement of the NO pathway in the pathomechanism of PAH, explores novel and easy-to-detect biomarkers of the pulmonary NO.

Possible pathogenic roles of nitric oxide in asthma

Nitric oxide (NO) has broad physiologic functions, including vasodilation, bronchodilatation, neurotransmission, inflammation, and host defense. Fraction of exhaled NO (FeNO) is used as a biomarker of eosinophilic airway inflammation for asthma control. However, the role of NO in the pathogenesis and progression of asthma is not well understood. Additionally, the absence of bronchial eosinophilic inflammation, mucus hypersecretion, and increased Th2 cytokine levels in mice lacking NO synthase isoforms (n/i/eNOS^-/-), suggests that NO has an essential role in the promoting the pathogenesis of asthma. Recent clinical data investigating antibodies for interleukin (IL)-4 receptor α, which inhibits both IL-4 and IL-13 signaling, and anti-IL-13 antibody suggest a unique association between NO and the pathogenesis and progression of asthma. Antibody therapies targeting several cytokines may provide clues to elucidate the mechanisms underlying the pathogenesis and progression of asthma.

Increased exhaled nitric oxide precedes lung fibrosis in two murine models of systemic sclerosis

Exhaled nitric oxide (NO) is increased as a result of lung inflammation, which in turn causes subsequent interstitial lung disease in patients with systemic sclerosis (SSc). However, the exact time course of inflammatory and fibrotic changes in the SSc lung has not yet been described. Our objective was to assess the chronological evolution of lung inflammatory and fibrotic processes in mice pre-treated with hypochlorous acid (HOCl) or bleomycin. C57BL/6 mice were randomized into three groups receiving subcutaneous injections of HOCl, bleomycin, or PBS for 2, 4 or 6 weeks. Exhaled NO (eNO) was measured at the end of each injection period and after 2 resting weeks without injection (8 week group). Mice were then sacrificed to obtain skin and lung tissues to measure fibrotic changes and NO synthases (NOS) expression. Increased eNO, inducible NOS and nitrotyrosine expression in bronchial epithelium, lung neutrophils and macrophages were observed at early phases in both HOCl- and bleomycin-treated mice. Conversely, lung vascular endothelial NOS expression decreased significantly at 6th and 8th weeks. Skin fibrosis was significantly increased from the 4th week and lung fibrosis from 6th week. We conclude that lung inflammation occurs early after injury as reflected by increased exhaled NO and inducible NOS expression, and precedes fibrotic changes in skin and lungs of mice pre-treated with bleomycin and HOCl. Early detection and treatment of pulmonary inflammation might be useful in preventing subsequent occurrence of lung fibrosis in SSc patients.

Exhaled nitric oxide measurement to monitor pulmonary hypertension in a pneumonectomy-monocrotaline rat model

The use of fractional exhaled nitric oxide (FeNO) has been suggested as a quantitative marker for pulmonary arterial hypertension (PAH) in humans. To further characterize FeNO in PAH we investigated this marker in a rodent model. Since there is no standardized technique for FeNO measurement in animals, we intended to reduce measuring errors and confounders of an existing published method by mathematical modification and tested its applicability in an NO-regulating therapy concept of PAH. Thirty-three male Sprague-Dawley rats underwent unilateral pneumonectomy and monocrotaline (MCT) injection and were observed for 49 days. A telemetric catheter was introduced into the left pulmonary artery to continuously record mean pulmonary arterial pressure (mPAP), and FeNO was assessed. After 35 days, animals were randomized to receive either oral l-arginine (300 mg/kg) in combination with tetrahydrobiopterin (20 mg/kg) therapy (n = 12) or vehicle (n = 11) daily over a period of 14 days. mPAP at baseline was 17.19 ± 9.62 mmHg, which increased to 53.1 ± 10.63 mmHg 28 days after monocrotaline exposure (P < 0.001). Using the modified technique, we found an inverse correlation between exhaled NO and pulmonary pressures before (r = -0.366, P = 0.043) and after MCT (r = -0.363, P = 0.038) as well as after therapy administration (r = -0.657, P = 0.02). Our modified technique proved robust in a rodent model, since valid and reproducible data were gained and showed an inverse correlation between exhaled NO and mPAP, whereas the existing method did not.

Phosphatidylinositol 3-kinase inhibitor suppresses inducible nitric oxide synthase expression in bronchiole epithelial cells in asthmatic rats

Inducible nitric oxide synthase (iNOS) is known to produce nitric oxide (NO), which is a main contributor to asthmatic airway inflammation. Recent studies have shown that phosphatidylinositol 3-kinase (PI3K) is ubiquitously expressed in airway epithelial cells and its inhibition could relieve airway inflammation and hyperresponsiveness. This study aimed to explore the interaction of PI3K and NO signaling in allergic asthma. We investigated the effects of PI3K inhibitor wortmannin on iNOS expression in bronchiole epithelial cells and NO, IL-4 and IFN-γ levels in lung tissues of asthmatic rat model, which was prepared by 10% OVA solution sensitization and 1% OVA aerosol challenge. Our results showed that the ratio of eosinophils to total cells in BALF, PI3K activity, NO and IL-4 levels in lung tissues was increased after OVA sensitization and challenge, but then was attenuated by the administration of wortmannin. In contrast, IFN-γ level in lung tissues was decreased after OVA sensitization and challenge and increased after the administration of wortmannin. The expression of iNOS protein in bronchiole epithelial cells, iNOS mRNA level and iNOS activity in lung tissues was markedly upregulated after OVA sensitization and challenge, but the upregulation was significantly antagonized by wortmannin. Taken together, these data provide evidence that PI3K functions upstream to modulate iNOS/NO signaling, which then promotes the development of airway inflammation in asthmatic animal model. PI3K inhibitor wortmannin could lead to reduced iNOS expression and NO production, therefore inhibiting airway inflammatory responses.

Nitric oxide synthase enzymes in the airways of mice exposed to ovalbumin: NOS2 expression is NOS3 dependent

Objectives and Design. The function of the airway nitric oxide synthase (NOS) isoforms and the lung cell types responsible for its production are not fully understood. We hypothesized that NO homeostasis in the airway is important to control inflammation, which requires upregulation, of NOS2 protein expression by an NOS3-dependent mechanism. Materials or Subjects. Mice from a C57BL/6 wild-type, NOS1^−/−, NOS2^−/−, and NOS3^−/− genotypes were used. All mice strains were systemically sensitized and exposed to filtered air or ovalbumin (OVA) aerosol for two weeks to create a subchronic model of allergen-induced airway inflammation. Methods. We measured lung function, lung lavage inflammatory and airway epithelial goblet cell count, exhaled NO, nitrate and nitrite concentration, and airway NOS1, NOS2, and NOS3 protein content. Results. Deletion of NOS1 or NOS3 increases NOS2 protein present in the airway epithelium and smooth muscle of air-exposed animals. Exposure to allergen significantly reduced the expression of NOS2 protein in the airway epithelium and smooth muscle of the NOS3^−/− strain only. This reduction in NOS2 expression was not due to the replacement of epithelial cells with goblet cells as remaining epithelial cells did not express NOS2. NOS1^−/− animals had significantly reduced goblet cell metaplasia compared to C57Bl/6 wt, NOS2^−/−, and NOS3^−/− allergen-exposed mice. Conclusion. The airway epithelial and smooth muscle cells maintain a stable airway NO concentration under noninflammatory conditions. This “homeostatic” mechanism is unable to distinguish between NOS derived from the different constitutive NOS isoforms. NOS3 is essential for the expression of NOS2 under inflammatory conditions, while NOS1 expression contributes to allergen-induced goblet cell metaplasia.

Increased parasympathetic tone as the underlying cause of asthma: a hypothesis

Asthma is a chronic inflammatory disease of airways that is characterized by increased responsiveness of the tracheo-bronchial tree to multiple number of stimuli. Immunological theory does not explain all features in asthma, for example hyper-reactivity of the airways. Neurogenic theory also fails to explain the pathogenesis of asthma comprehensively. Higher parasympathetic tone has been reported in asthmatics but has never been suggested as a major underlying cause of asthma. This article attempts to explain the occurrence of hyper-responsiveness, inflammatory/allergic reactions and broncho-constriction in asthma on a common basis of inherent higher parasympathetic tone in asthmatics. The higher background parasympathetic firing leads to increased nitric oxide (NO) production owing to its co-localization with acetylcholine (ACh) in inhibitory non-adrenergic and non-cholinergic (i-NANC) nerves. NO is a neurotransmitter of i-NANC system and it mediates bronchodilation. Increased NO release has been found to be responsible for hyper-responsiveness and increased inflammation in the airways. The authors suggest that an inherently higher background parasympathetic tone in concert with inflammation or a specific genetic background could modify the effects of NO on lung homeostasis in humans leading to increased susceptibility to an asthmatic state.

Pathophysiology, management and treatment of smoke inhalation injury

Smoke inhalation injury continues to increase morbidity and mortality in burn patients in both the third world and industrialized countries. The lack of uniform criteria for the diagnosis and definition of smoke inhalation injury contributes to the fact that, despite extensive research, mortality rates have changed little in recent decades. The formation of reactive oxygen and nitrogen species, as well as the procoagulant and antifibrinolytic imbalance of alveolar homeostasis, all play a central role in the pathogenesis of smoke inhalation injury. Further hallmarks include massive airway obstruction owing to cast formation, bronchospasm, the increase in bronchial circulation and transvascular fluid flux. Therefore, anticoagulants, antioxidants and bronchodilators, especially when administered as an aerosol, represent the most promising treatment strategies. The purpose of this review article is to provide an overview of the pathophysiological changes, management and treatment options of smoke inhalation injury based on the current literature.

Neuronal nitric oxide synthase inhibition attenuates cardiopulmonary dysfunctions after combined burn and smoke inhalation injury in sheep

OBJECTIVE

We hypothesized that nitric oxide derived from the neuronal nitric oxide synthase (NOS) is responsible for much of the injury resulting from skin burn and smoke inhalation. Therefore, we aimed to examine the effects of selective neuronal NOS inhibition on cardiopulmonary functions and cellular injury in sheep with acute respiratory distress syndrome secondary to combined burn and smoke inhalation injury.

DESIGN

Prospective, randomized, controlled laboratory experiment.

SETTING

Investigational intensive care unit.

SUBJECTS

A total of 22 chronically instrumented adult ewes.

INTERVENTIONS

Sheep were randomly assigned to either healthy controls (sham), injured controls (40% third-degree flame burn; 48 breaths of cotton smoke), or an injury group treated with the specific neuronal NOS inhibitor 7-nitroindazole (1 mg x kg(-1) x hr(-1)) from 1 hr postinjury to the end of the 48-hr study period. Hypoxic pulmonary vasoconstriction was assessed as decrease in left pulmonary blood flow in response to single-lung hypoxic challenges (100% nitrogen) at baseline, 24 hrs, and 48 hrs.

MEASUREMENTS AND MAIN RESULTS

The combination injury contributed to a approximately 90% loss of hypoxic pulmonary vasoconstriction and was associated with significant pulmonary shunting and death of one animal. The increase in nitrate/nitrite plasma levels in injured controls (12 hrs: 17 +/- 2 vs. 6 +/- 1 microM in sham animals; p < .001) was linked to increases in inducible NOS messenger RNA and 3-nitrotyrosine formation in lung tissue (48 hrs: 22 +/- 1 vs. 0.8 +/- 0.3 nM in sham animals; p < .001). 7-Nitroindazole treatment prevented the injury-associated changes in inducible NOS messenger RNA, nitrate/nitrite, and 3-nitrotyrosine, thereby attenuating the loss of hypoxic pulmonary vasoconstriction and improving gas exchange. In addition, 7-nitroindazole decreased lung tissue concentrations of hemoxygenase-1 and ameliorated myocardial depression, airway obstruction, pulmonary edema, ventilatory pressures, and histopathologic changes seen in injured controls.

CONCLUSIONS

The present study provides evidence that neuronal NOS-derived nitric oxide plays a pivotal role in the pathogenesis of acute respiratory distress syndrome resulting from combined burn and smoke inhalation injury.

Nitric oxide metabolism and the acute chest syndrome of sickle cell anemia

OBJECTIVE

To review the role of endothelial dysfunction and nitric oxide metabolism in the pathogenesis of the acute chest syndrome.

DATA SOURCE

A thorough literature search of PubMed for publications relevant to acute chest syndrome and nitric oxide metabolism in sickle cell disease was performed using search terms that included acute chest syndrome, sickle cell disease, nitric oxide metabolism, arginine, nitrite, nitrate, exhaled nitric oxide, nitric oxide synthase, and oxidant injury. We identified randomized controlled trials, case reports, editorials, and review articles from English-language and non-English-language studies of adult, pediatric, animal, and human subjects that describe the pathophysiology of acute chest syndrome, the biology of nitric oxide relevant to the pathophysiology of sickle cell disease, and the evidence for the role of endothelial dysfunction and abnormal nitric oxide metabolism in acute chest syndrome. We identified and reviewed 350 publications by the initial search and subsequent bibliography review. The articles most pertinent to the topic of this article were selected to support the discussion.

RESULTS

Acute chest syndrome is the leading cause of acute respiratory system dysfunction and a leading cause of morbidity and mortality among patients with sickle cell disease. Evidence is available to support decreased nitric oxide production, increased nitric oxide consumption, and abnormal metabolism of nitric oxide in patients with acute chest syndrome. Moreover, substrate availability is disturbed, and alternate pathways for substrate and nitric oxide metabolism exist.

CONCLUSIONS

Abnormalities of nitric oxide metabolism are prevalent during acute illness and baseline health in patients with sickle cell disease. Further investigation is needed to understand the clinical significance of aberrant nitric oxide metabolism as well as the potential for therapeutic manipulation of the arginine-nitric oxide pathway in patients with sickle cell disease.

Nitric oxide as a noninvasive biomarker of lipopolysaccharide-induced airway inflammation: possible role in lung neutrophilia

Lipopolysaccharide (LPS) is known to generate nitric oxide (NO) in the airway through the activation of nitric-oxide synthase (NOS). The functional consequences of this on the inflammatory response are not clear, with conflicting data published. In the clinic, exhaled NO (ex-NO) is used as a noninvasive biomarker to assess the extent of airway inflammation. It is proposed that monitoring levels of ex-NO could be a useful guide to determining the effectiveness of disease modifying therapies. The aim was, using pharmacological tools, to determine the role of NO in an aerosolized LPS-driven animal model of airway inflammation by assessment of ex-NO, neutrophilia, and inflammatory biomarkers, using a nonselective NOS inhibitor, N(G)-nitro-l-arginine methyl ester (l-NAME), and a selective inducible NOS (iNOS) inhibitor, N-3 (aminomethyl)benzyl)acetamidine (1400W). Real-time mRNA analysis of the lung tissue indicated an increased gene expression of iNOS following LPS challenge with minimal impact on constitutive NOS isoforms. LPS induced an increase in ex-NO, which appeared to correlate with the increase in iNOS gene expression and airway neutrophilia. Treatment with l-NAME and 1400W resulted in comparable reductions in ex-NO, a reduction in airway neutrophilia, but had little impact on a range of inflammatory biomarkers. This study indicates that the LPS-induced rise in ex-NO is due to enhanced iNOS activity and that NO has a role in airway neutrophilia. Additionally, it appears using ex-NO as a guide to monitoring airway inflammation may have some use, but data should be interpreted with caution when assessing therapies that may directly impact on NO formation.

Expression of nitric oxide synthase-2 in the lungs decreases airway resistance and responsiveness

Individuals with asthma have increased levels of nitric oxide in their exhaled air. To explore its role, we have developed a regulatable transgenic mouse capable of overexpressing inducible nitric oxide synthase in a lung-specific fashion. The CC10-rtTA-NOS-2 mouse contains two transgenes, a reverse tetracycline transactivator under the control of the Clara cell protein promoter and the mouse nitric oxide synthase-2 (NOS-2) coding region under control of a tetracycline operator. Addition of doxycycline to the drinking water of CC10-rtTA-NOS-2 mice causes an increase in nitric oxide synthase-2 that is largely confined to the airway epithelium. The fraction of expired nitric oxide increases over the first 24 h from approximately 10 parts per billion to a plateau of approximately 20 parts per billion. There were no obvious differences between CC10-rtTA-NOS-2 mice, with or without doxycycline, and wild-type mice in lung histology, bronchoalveolar protein, total cell count, or count differentials. However, airway resistance was lower in CC10-rtTA-NOS-2 mice with doxycycline than in CC10-rtTA-NOS-2 mice without doxycycline or wild-type mice with doxycycline. Moreover, doxycycline-treated CC10-rtTA-NOS-2 mice were hyporesponsive to methacholine compared with other groups. These data suggest that increased nitric oxide in the airways has no proinflammatory effects per se and may have beneficial effects on pulmonary function.

Multiple contributing roles for NOS2 in LPS-induced acute airway inflammation in mice

Acute lung inflammation and injury were induced by intranasal instillation of lipopolysaccharide (LPS) in normal and type 2 nitric oxide synthase (NOS2)-deficient (NOS2-/-) C57BL/6 mice. LPS-induced increases in extravasated airway neutrophils and in lung lavage fluid of TNF-alpha and macrophage inflammatory protein-2 were markedly lower in NOS2-/- than in wild-type mice, indicating that NOS2-derived nitric oxide (NO.) participates in inflammatory cytokine production and neutrophil recruitment. Instillation of LPS also increased total lung lavage protein and induced matrix metalloproteinase-9 and mucin 5AC, as indexes of lung epithelial injury and/or mucus hyperplasia, and increased tyrosine nitration of lung lavage proteins, a marker of oxidative injury. All these responses were less pronounced in NOS2-/- than in wild-type mice. Inhibition of NOS activity also suppressed production of TNF-alpha and macrophage inflammatory protein-2 by LPS-stimulated mouse alveolar MH-S macrophages, and this was restored by NO. donors, illustrating involvement of NO. in macrophage cytokine signaling. Oligonucleotide microarray (GeneChip) analysis of global lung gene expression revealed that LPS inhalation induced a range of transcripts encoding proinflammatory cytokines and chemokines, stress-inducible factors, and other extracellular factors and suppressed mRNAs encoding certain cytoskeletal proteins and signaling proteins, responses that were generally attenuated in NOS2-/- mice. Comparison of both mouse strains revealed altered expression of several cytoskeletal proteins, cell surface proteins, and signaling proteins in NOS2-/- mice, changes that may partly explain the reduced responsiveness to LPS. Collectively, our results suggest that NOS2 participates in the acute inflammatory response to LPS by multiple mechanisms: involvement in proinflammatory cytokine signaling and alteration of the expression of various genes that affect inflammatory-immune responses to LPS.

Contributions of nitric oxide synthase isozymes to exhaled nitric oxide and hypoxic pulmonary vasoconstriction in rabbit lungs

We investigated the source(s) for exhaled nitric oxide (NO) in isolated, perfused rabbits lungs by using isozyme-specific nitric oxide synthase (NOS) inhibitors and antibodies. Each inhibitor was studied under normoxia and hypoxia. Only nitro-L-arginine methyl ester (L-NAME, a nonselective NOS inhibitor) reduced exhaled NO and increased hypoxic pulmonary vasoconstriction (HPV), in contrast to 1400W, an inhibitor of inducible NOS (iNOS), and 7-nitroindazole, an inhibitor of neuronal NOS (nNOS). Acetylcholine-mediated stimulation of vascular endothelial NOS (eNOS) increased exhaled NO and could only be inhibited by L-NAME. Selective inhibition of airway and alveolar epithelial NO production by nebulized L-NAME decreased exhaled NO and increased hypoxic pulmonary artery pressure. Immunohistochemistry demonstrated extensive staining for eNOS in the epithelia, vasculature, and lymphatic tissue. There was no staining for iNOS but moderate staining for nNOS in the ciliated cells of the epithelia, lymphoid tissue, and cartilage cells. Our findings show virtually all exhaled NO in the rabbit lung is produced by eNOS, which is present throughout the airways, alveoli, and vessels. Both vascular and epithelial-derived NO modulate HPV.

Effects of sex and of gene variants in constitutive nitric oxide synthases on exhaled nitric oxide

Genetic factors may contribute to the variability of exhaled nitric oxide in healthy individuals. We studied exhaled nitric oxide and genetic variants in both neuronal and endothelial nitric oxide synthases in 105 healthy nonsmoking and smoking subjects. Genomic DNA was screened for a repeat polymorphism in intron 20 of the neuronal nitric oxide synthase gene and for the 894G/T mutation of the endothelial nitric oxide synthase gene. Exhaled nitric oxide was significantly higher in males than females among both nonsmokers (p < 0.0001) and smokers (p = 0.003). No association was found between exhaled nitric oxide and the endothelial nitric oxide synthase gene variant. However, healthy nonsmoking females with greater numbers of repeats (i.e., both alleles with 12 or more repeats) in neuronal nitric oxide synthase had significantly lower nitric oxide levels than did females with fewer numbers of repeats (i.e., at least one allele with fewer than 12 repeats) (13.6 +/- 1.6 versus 19.4 +/- 1.6 ppb, p = 0.02). No association was found between exhaled nitric oxide and neuronal nitric oxide synthase genotype in males. These data suggest that variants in the neuronal nitric oxide synthase gene contribute to the variability of airway nitric oxide concentrations in healthy females.

Endothelial nitric oxide synthase variants in cystic fibrosis lung disease

Variants in the genes encoding for the nitric oxide synthases may act as disease modifier loci in cystic fibrosis, affecting both an individual's nitric oxide level and pulmonary function. In this study, the 894G/T variant in exon 7 of the endothelial nitric oxide synthase gene was related to exhaled nitric oxide and pulmonary function in 70 cystic fibrosis patients who were aged 14.8 +/- 6.9 years (mean +/- SD), with a FEV1 of 69.4 +/- 24.8% predicted. Although there was no association between endothelial nitric oxide synthase genotypes and exhaled nitric oxide in males, nitric oxide levels were significantly higher in female cystic fibrosis patients with an 894T mutant allele, compared with female patients homozygous for the 894G wild-type allele (7.0 +/- 4.4 versus 3.6 +/- 1.9 parts per billion, p = 0.02). Furthermore, in female patients, colonization of airways with Pseudomonas aeruginosa was significantly (p < 0.05) less frequent when carrying an 894T mutant allele as compared with wild type. These data suggest that the 894T variant in the endothelial nitric oxide synthase gene is associated with increased airway nitric oxide formation in female cystic fibrosis patients, possibly affecting colonization of airways with P. aeruginosa.

Nitric oxide and protein nitration in the cystic fibrosis airway

Cystic fibrosis (CF), characterized by chronic airway infection and inflammation, ultimately leads to respiratory failure. Exhaled nitric oxide (NO), elevated in most inflammatory airway diseases, is decreased in CF, suggesting either decreased production or accelerated metabolism of NO. The present studies performed on two groups of CF patients provide further support for a disordered NO airway metabolism in CF respiratory tract disease. Despite confirmation of subnormal NOS2 in the CF airway epithelium, alternative isoforms NOS1 and NOS3 were present, and inflammatory cells in the CF airway expressed abundant NOS2. Increased immunohistochemical staining for nitrotyrosine was demonstrated in lung tissues from patients with CF as compared to control. To our knowledge, this is the first report localizing nitrotyrosine in diseased CF lung tissue. While the relative NOS2 deficiency in CF respiratory tract epithelium may contribute to the lower expired NO levels, these results suggest that increased metabolism of NO is also present in advanced CF lung disease. The significance of altered NO metabolism and protein nitration in CF remains to be fully elucidated.

Inhaled diazeniumdiolates (NONOates) as selective pulmonary vasodilators

Selective pulmonary vasodilators cause vasodilatation limited to the pulmonary vasculature, within well-ventilated lung regions. Selective pulmonary vasodilators ideally cause only a minimal effect on the systemic circulation and improve ventilation/perfusion matching. NONOates are a novel group of chemical compounds that spontaneously and continuously release nitric oxide under physiological conditions, over periods of up to 24 h. Inhaled NONOates retain the benefits of gaseous nitric oxide without many of its therapeutic disadvantages. This review focuses on the therapeutic potential of inhaled NONOates in pulmonary hypertension, other lung conditions associated with right ventricular dysfunction and in asthma. The potential toxicity of NONOates is also discussed.

Exhaled and nasal nitric oxide as a marker of pneumonia in ventilated patients

Because inflammation stimulates the expression of inducible nitric oxide (NO) synthase (iNOS) with an associated increased local NO production, we hypothesized that patients with pneumonia would have increased excretion of NO into their airways. To test this hypothesis, NO was measured in the exhaled air and from the nasal cavities of 49 consecutively intubated and mechanically ventilated patients in our ICU. After excluding NO gas contamination in the inspiratory circuit, nasal NO and end-expiratory and mean exhaled tracheal NO levels and plasma nitrate concentrations were measured using a fast response chemiluminescence analyzer. Twenty-one patients (43%) presented with infectious pneumonia. End- expiratory exhaled NO concentrations were significantly higher in patients with pneumonia as compared with patients without pneumonia (5.9 +/- 1 ppb versus 3.2 +/- 0.5 ppb, p < 0.01). Similarly, mean nasal NO was higher in patients with pneumonia (1039 +/- 138 ppb versus 367 +/- 58 ppb, p = 0.003). Plasma nitrate levels did not differ between patient groups. Threshold values of tracheal or nasal NO were defined and subsequently validated in 60 other patients. Positive and negative values of a maximal tracheal level > 5 ppb for pneumonia were 74% and 89%, respectively. Thus tracheal and nasal NO levels may be of help in distinguishing patients with acute pneumonia from other causes. Furthermore, because these differences in airway NO levels were not paralleled in blood nitrite concentrations, we conclude that pneumonia per se is not associated with systemic NO production.