S-nitrosoglutathione breakdown prevents airway smooth muscle relaxation in the guinea pig

The Precision Interventions for Severe and/or Exacerbation-Prone (PrecISE) Asthma Network: An overview of Network organization, procedures, and interventions

Asthma is a heterogeneous disease, with multiple underlying inflammatory pathways and structural airway abnormalities that impact disease persistence and severity. Recent progress has been made in developing targeted asthma therapeutics, especially for subjects with eosinophilic asthma. However, there is an unmet need for new approaches to treat patients with severe and exacerbation-prone asthma, who contribute disproportionately to disease burden. Extensive deep phenotyping has revealed the heterogeneous nature of severe asthma and identified distinct disease subtypes. A current challenge in the field is to translate new and emerging knowledge about different pathobiologic mechanisms in asthma into patient-specific therapies, with the ultimate goal of modifying the natural history of disease. Here, we describe the Precision Interventions for Severe and/or Exacerbation-Prone Asthma (PrecISE) Network, a groundbreaking collaborative effort of asthma researchers and biostatisticians from around the United States. The PrecISE Network was designed to conduct phase II/proof-of-concept clinical trials of precision interventions in the population with severe asthma, and is supported by the National Heart, Lung, and Blood Institute of the National Institutes of Health. Using an innovative adaptive platform trial design, the PrecISE Network will evaluate up to 6 interventions simultaneously in biomarker-defined subgroups of subjects. We review the development and organizational structure of the PrecISE Network, and choice of interventions being studied. We hope that the PrecISE Network will enhance our understanding of asthma subtypes and accelerate the development of therapeutics for severe asthma.

An Update on Thiol Signaling: S-Nitrosothiols, Hydrogen Sulfide and a Putative Role for Thionitrous Acid

Long considered vital to antioxidant defenses, thiol chemistry has more recently been recognized to be of fundamental importance to cell signaling. S-nitrosothiols—such as S-nitrosoglutathione (GSNO)—and hydrogen sulfide (H₂S) are physiologic signaling thiols that are regulated enzymatically. Current evidence suggests that they modify target protein function primarily through post-translational modifications. GSNO is made by NOS and other metalloproteins; H₂S by metabolism of cysteine, homocysteine and cystathionine precursors. GSNO generally acts independently of NO generation and has a variety of gene regulatory, immune modulator, vascular, respiratory and neuronal effects. Some of this physiology is shared with H₂S, though the mechanisms differ. Recent evidence also suggests that molecules resulting from reactions between GSNO and H₂S, such as thionitrous acid (HSNO), could also have a role in physiology. Taken together, these data suggest important new potential targets for thiol-based drug development.

S-Nitrosoglutathione Attenuates Airway Hyperresponsiveness in Murine Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) is characterized by lifelong obstructive lung disease and profound, refractory bronchospasm. It is observed among survivors of premature birth who have been treated with prolonged supplemental oxygen. Therapeutic options are limited. Using a neonatal mouse model of BPD, we show that hyperoxia increases activity and expression of a mediator of endogenous bronchoconstriction, S-nitrosoglutathione (GSNO) reductase. MicroRNA-342-3p, predicted in silico and shown in this study in vitro to suppress expression of GSNO reductase, was decreased in hyperoxia-exposed pups. Both pretreatment with aerosolized GSNO and inhibition of GSNO reductase attenuated airway hyperresponsiveness in vivo among juvenile and adult mice exposed to neonatal hyperoxia. Our data suggest that neonatal hyperoxia exposure causes detrimental effects on airway hyperreactivity through microRNA-342-3p-mediated upregulation of GSNO reductase expression. Furthermore, our data demonstrate that this adverse effect can be overcome by supplementing its substrate, GSNO, or by inhibiting the enzyme itself. Rates of BPD have not improved over the past two decades; nor have new therapies been developed. GSNO-based therapies are a novel treatment of the respiratory problems that patients with BPD experience.

Augmentation of CFTR maturation by S-nitrosoglutathione reductase

S-nitrosoglutathione (GSNO) reductase regulates novel endogenous S-nitrosothiol signaling pathways, and mice deficient in GSNO reductase are protected from airways hyperreactivity. S-nitrosothiols are present in the airway, and patients with cystic fibrosis (CF) tend to have low S-nitrosothiol levels that may be attributed to upregulation of GSNO reductase activity. The present study demonstrates that 1) GSNO reductase activity is increased in the cystic fibrosis bronchial epithelial (CFBE41o(-)) cells expressing mutant F508del-cystic fibrosis transmembrane regulator (CFTR) compared with the wild-type CFBE41o(-) cells, 2) GSNO reductase expression level is increased in the primary human bronchial epithelial cells expressing mutant F508del-CFTR compared with the wild-type cells, 3) GSNO reductase colocalizes with cochaperone Hsp70/Hsp90 organizing protein (Hop; Stip1) in human airway epithelial cells, 4) GSNO reductase knockdown with siRNA increases the expression and maturation of CFTR and decreases Stip1 expression in human airway epithelial cells, 5) increased levels of GSNO reductase cause a decrease in maturation of CFTR, and 6) a GSNO reductase inhibitor effectively reverses the effects of GSNO reductase on CFTR maturation. These studies provide a novel approach to define the subcellular location of the interactions between Stip1 and GSNO reductase and the role of S-nitrosothiols in these interactions.

Nitrogen chemistry and lung physiology

The versatile chemistry of nitrogen is important to pulmonary physiology. Indeed, almost all redox forms of nitrogen are relevant to pulmonary physiology and to pathophysiology. Here we review the relevance to pulmonary biology of (a) elemental nitrogen; (b) reduced forms of nitrogen such as amines, ammonia, and hydroxylamine; and (c) oxidized forms of nitrogen such as the nitroxyl anion, the nitric oxide free radical, and S-nitrosothiols. Our focus is on oxidized nitrogen in the form of S-nitrosothiol bond-containing species, which are now appreciated to be important to every type of cell-signaling process in the lung. We also review potential clinical applications of nitrogen oxide biochemistry. These principles are being translated into clinical practice as diagnostic techniques and therapies for a range of pulmonary diseases including asthma, cystic fibrosis, adult respiratory distress syndrome, primary ciliary dyskinesia, and pulmonary hypertension.

Phenotype of asthmatics with increased airway S-nitrosoglutathione reductase activity

S-Nitrosoglutathione is an endogenous airway smooth muscle relaxant. Increased airway S-nitrosoglutathione breakdown occurs in some asthma patients. We asked whether patients with increased airway catabolism of this molecule had clinical features that distinguished them from other asthma patients. We measured S-nitrosoglutathione reductase expression and activity in bronchoscopy samples taken from 66 subjects in the Severe Asthma Research Program. We also analysed phenotype and genotype data taken from the program as a whole. Airway S-nitrosoglutathione reductase activity was increased in asthma patients (p=0.032). However, only a subpopulation was affected and this subpopulation was not defined by a "severe asthma" diagnosis. Subjects with increased activity were younger, had higher IgE and an earlier onset of symptoms. Consistent with a link between S-nitrosoglutathione biochemistry and atopy: 1) interleukin 13 increased S-nitrosoglutathione reductase expression and 2) subjects with an S-nitrosoglutathione reductase single nucleotide polymorphism previously associated with asthma had higher IgE than those without this single nucleotide polymorphism. Expression was higher in airway epithelium than in smooth muscle and was increased in regions of the asthmatic lung with decreased airflow. An early-onset, allergic phenotype characterises the asthma population with increased S-nitrosoglutathione reductase activity.

Airway gas exchange and exhaled biomarkers

During inspiration and expiration, gases traverse the conducting airways as they are transported between the environment and the alveolar region of the lungs. The term "conducting" airways is used broadly as the airway tree is thought largely to provide a conduit for the respiratory gases, oxygen and carbon dioxide. However, despite a significantly smaller surface area, and thicker barrier separating the gas phase from the blood when compared to the alveolar region, the airway tree can participate in gas exchange under special conditions such as high water solubility, high chemical reactivity, or production of the gas within the airway wall tissue. While these conditions do not apply to the respiratory gases, other gases demonstrate substantial exchange of the airways and are of particular importance to the inflammatory response of the lungs, the medical-legal field, occupational health, metabolic disorders, or protection of the delicate alveolar membrane. Given the significant structural differences between the airways and the alveolar region, the physical determinants that control airway gas exchange are unique and require different models (both experimental and mathematical) to explore. Our improved physiological understanding of airway gas exchange combined with improved analytical methods to detect trace compounds in the exhaled breath provides future opportunities to develop new exhaled biomarkers that are characteristic of pulmonary and systemic conditions.

γ-Glutamyltransferase catabolism of S-nitrosoglutathione modulates IL-8 expression in cystic fibrosis bronchial epithelial cells

S-nitrosoglutathione (GSNO) is an endogenous nitrosothiol involved in several pathophysiological processes. A role for GSNO has been envisaged in the expression of inflammatory cytokines such as IL-8; however, conflicting results have been reported. γ-Glutamyltransferase (GGT) enzyme activity can hydrolyze the γ-glutamyl bond present in the GSNO molecule thus greatly accelerating the release of bioactive nitric oxide. Expression of GGT is induced by oxidative stress, and activated neutrophils contribute to GGT increase in cystic fibrosis (CF) lung exudates by releasing GGT-containing microvesicles. This study was aimed at evaluating the effect of GSNO catabolism mediated by GGT on production of IL-8 in CF transmembrane regulation protein-mutated IB3-1 bronchial cells. The rapid, GGT-catalyzed catabolism of GSNO caused a decrease in both basal and lipopolysaccharide-stimulated IL-8 production in IB3-1 cells, by modulating both NF-κB and ERK1/2 pathways, along with a decrease in cell proliferation. In contrast, a slow decomposition of GSNO produced a significant increase in both cell proliferation and expression of IL-8, the latter possibly through p38-mediated stabilization of IL-8 mRNA. Our data suggest that the differential GSNO catabolism mediated by GGT enzyme activity can downregulate the production of IL-8 in CF cells. Hence, the role of GGT activity should be considered when evaluating GSNO for both in vitro and in vivo studies, the more so in the case of GSNO-based therapies for cystic fibrosis.

S-nitrosoglutathione reductase inhibition regulates allergen-induced lung inflammation and airway hyperreactivity

Allergic asthma is characterized by Th2 type inflammation, leading to airway hyperresponsivenes, mucus hypersecretion and tissue remodeling. S-Nitrosoglutathione reductase (GSNOR) is an alcohol dehydrogenase involved in the regulation of intracellular levels of S-nitrosothiols. GSNOR activity has been shown to be elevated in human asthmatic lungs, resulting in diminished S-nitrosothiols and thus contributing to increased airway hyperreactivity. Using a mouse model of allergic airway inflammation, we report that intranasal administration of a new selective inhibitor of GSNOR, SPL-334, caused a marked reduction in airway hyperreactivity, allergen-specific T cells and eosinophil accumulation, and mucus production in the lungs in response to allergen inhalation. Moreover, SPL-334 treatment resulted in a significant decrease in the production of the Th2 cytokines IL-5 and IL-13 and the level of the chemokine CCL11 (eotaxin-1) in the airways. Collectively, these observations reveal that GSNOR inhibitors are effective not only in reducing airway hyperresponsiveness but also in limiting lung inflammatory responses mediated by CD4(+) Th2 cells. These findings suggest that the inhibition of GSNOR may provide a novel therapeutic approach for the treatment of allergic airway inflammation.

S-nitrosoglutathione

BACKGROUND

S-Nitrosoglutathione (GSNO) is the S-nitrosated derivative of glutathione and is thought to be a critical mediator of the down stream signaling effects of nitric oxide (NO). GSNO has also been implicated as a contributor to various disease states.

SCOPE OF REVIEW

This review focuses on the chemical nature of GSNO, its biological activities, the evidence that it is an endogenous mediator of NO action, and implications for therapeutic use.

MAJOR CONCLUSIONS

GSNO clearly exerts its cellular actions through both NO- and S-nitrosation-dependent mechanisms; however, the chemical and biological aspects of this compound should be placed in the context of S-nitrosation as a whole.

GENERAL SIGNIFICANCE

GSNO is a central intermediate in formation and degradation of cellular S-nitrosothiols with potential therapeutic applications; thus, it remains an important molecule of study. This article is part of a Special Issue entitled Cellular functions of glutathione.

Biomarkers in asthma: a real hope to better manage asthma

Diagnosis and treatment of asthma are currently based on assessment of patient symptoms and physiologic tests of airway reactivity. Research over the past decade has identified an array of biochemical and cellular biomarkers, which reflect the heterogeneous and multiple mechanistic pathways that may lead to asthma. These mechanistic biomarkers offer hope for optimal design of therapies targeting the specific pathways that lead to inflammation. This article provides an overview of blood, urine, and airway biomarkers; summarizes the pathologic pathways that they signify; and begins to describe the utility of biomarkers in the future care of patients with asthma.

Glutathione redox control of asthma: from molecular mechanisms to therapeutic opportunities

Asthma is a chronic inflammatory disorder of the airways associated with airway hyper-responsiveness and airflow limitation in response to specific triggers. Whereas inflammation is important for tissue regeneration and wound healing, the profound and sustained inflammatory response associated with asthma may result in airway remodeling that involves smooth muscle hypertrophy, epithelial goblet-cell hyperplasia, and permanent deposition of airway extracellular matrix proteins. Although the specific mechanisms responsible for asthma are still being unraveled, free radicals such as reactive oxygen species and reactive nitrogen species are important mediators of airway tissue damage that are increased in subjects with asthma. There is also a growing body of literature implicating disturbances in oxidation/reduction (redox) reactions and impaired antioxidant defenses as a risk factor for asthma development and asthma severity. Ultimately, these redox-related perturbations result in a vicious cycle of airway inflammation and injury that is not always amenable to current asthma therapy, particularly in cases of severe asthma. This review will discuss disruptions of redox signaling and control in asthma with a focus on the thiol, glutathione, and reduced (thiol) form (GSH). First, GSH synthesis, GSH distribution, and GSH function and homeostasis are discussed. We then review the literature related to GSH redox balance in health and asthma, with an emphasis on human studies. Finally, therapeutic opportunities to restore the GSH redox balance in subjects with asthma are discussed.

S-nitrosoglutathione reductase in human lung cancer

S-Nitrosoglutathione (GSNO) reductase regulates cell signaling pathways relevant to asthma and protects cells from nitrosative stress. Recent evidence suggests that this enzyme may prevent human hepatocellular carcinoma arising in the setting of chronic hepatitis. We hypothesized that GSNO reductase may also protect the lung against potentially carcinogenic reactions associated with nitrosative stress. We report that wild-type Ras is S-nitrosylated and activated by nitrosative stress and that it is denitrosylated by GSNO reductase. In human lung cancer, the activity and expression of GSNO reductase are decreased. Further, the distribution of the enzyme (including its colocalization with wild-type Ras) is abnormal. We conclude that decreased activity of GSNO reductase could leave the human lung vulnerable to the oncogenic effects of nitrosative stress, as is the case in the liver. This potential should be considered when developing therapies that inhibit pulmonary GSNO reductase to treat asthma and other conditions.

Utility of two-compartment models of exhaled nitric oxide in patients with asthma

Two-compartment models provide more precise information about the contribution of the different portions of the airways to exhaled nitric oxide (NO). Airway wall concentration of NO (Caw,NO) and maximum flux of NO in the airways (J'aw,NO) reflect the tissue production rate of NO and they can be modified by corticosteroids. The airway wall diffusing capacity of NO (Daw,NO) depends on diverse physical and anatomical determinants of the airways, such as gas exchange surface area. Daw,NO can be modified by structural and physiological changes that are characteristic of airway remodeling, which take place over the long term. The alveolar concentration of NO (Calv,NO) represents the degree of small airway inflammation. The persistence of high Calv,NO in patients treated with inhaled corticosteroids could reflect the incapacity of these drugs to reach distal locations due to the heterogeneity of the acinar ventilation. In this review, we evaluate the parameters provided by the compartmentalized analysis of exhaled NO that could be useful in characterizing asthma patients.

S-nitrosoglutathione supplementation to ovalbumin-sensitized and -challenged mice ameliorates methacholine-induced bronchoconstriction

S-nitrosoglutathione (GSNO) is an endogenous bronchodilator present in micromolar concentrations in airway lining fluid. Airway GSNO levels decrease in severe respiratory failure and asthma, which is attributable to increased metabolism by GSNO reductase (GSNOR). Indeed, we have found that GSNOR expression and activity correlate inversely with lung S-nitrosothiol (SNO) content and airway hyperresponsiveness (AHR) to methacholine (MCh) challenge in humans with asthmatic phenotypes (Que LG, Yang Z, Stamler JS, Lugogo NL, Kraft M. Am J Respir Crit Care Med 180: 226-231, 2009). Accordingly, we hypothesized that local aerosol delivery of GSNO could ameliorate AHR and inflammation in the ovalbumin-sensitized and -challenged (OVA) mouse model of allergic asthma. Anesthetized, paralyzed, and tracheotomized 6-wk-old male control and OVA C57BL/6 mice were administered a single 15-s treatment of 0-100 mM GSNO. Five minutes later, airway resistance to MCh was measured and SNOs were quantified in bronchoalveolar lavage (BAL). Duration of protection was evaluated following nose-only exposure to 10 mM GSNO for 10 min followed by measurements of airway resistance, inflammatory cells, and cytokines and chemokines at up to 4 h later. Acute delivery of GSNO aerosol protected OVA mice from MCh-induced AHR, with no benefit seen above 20 mM GSNO. The antibronchoconstrictive effects of GSNO aerosol delivered via nose cone were sustained for at least 4 h. However, administration of GSNO did not alter total BAL cell counts or cell differentials and had modest effects on cytokine and chemokine levels. In conclusion, in the OVA mouse model of allergic asthma, aerosolized GSNO has rapid and sustained antibronchoconstrictive effects but does not substantially alter airway inflammation.

S-Nitrosylation signaling regulates cellular protein interactions

BACKGROUND

S-Nitrosothiols are made by nitric oxide synthases and other metalloproteins. Unlike nitric oxide, S-nitrosothiols are involved in localized, covalent signaling reactions in specific cellular compartments. These reactions are enzymatically regulated.

SCOPE

S-Nitrosylation affects interactions involved in virtually every aspect of normal cell biology. This article is part of a Special Issue entitled Regulation of Cellular Processes by S-nitrosylation.

MAJOR CONCLUSIONS AND SIGNIFICANCE

S-Nitrosylation is a regulated signaling reaction.

The biochemistry of asthma

BACKGROUND

Asthma is not one disease. Different patients have biochemically distinct phenotypes.

SCOPE OF REVIEW

Biomarker analysis was developed to identify inflammation in the asthmatic airway. It has led to a renewed interest in biochemical abnormalities in the asthmatic airway. The biochemical determinants of asthma heterogeneity are many. Examples include decreased activity of superoxide dismutases; increased activity of eosinophil peroxidase, S-nitrosoglutathione reductase, and arginases; decreased airway pH; and increased levels of asymmetric dimethyl arginine.

MAJOR CONCLUSIONS

New discoveries suggest that biomarkers such as exhaled nitric oxide reflect complex airway biochemistry. This biochemistry can be informative and therapeutically relevant.

GENERAL SIGNIFICANCE

Improved understanding of airway biochemistry will lead to new tests to identify biochemically unique subpopulations of patients with asthma. It will also likely lead to new, targeted treatments for these specific asthma subpopulations. This article is part of a Special Issue entitled Biochemistry of Asthma.

Breath formate is a marker of airway S-nitrosothiol depletion in severe asthma

BACKGROUND

Children with severe asthma have poor symptom control and elevated markers of airway oxidative and nitrosative stress. Paradoxically, they have decreased airway levels of S-nitrosothiols (SNOs), a class of endogenous airway smooth muscle relaxants. This deficiency results from increased activity of an enzyme that both reduces SNOs to ammonia and oxidizes formaldehyde to formic acid, a volatile carboxylic acid that is more easily detected in exhaled breath condensate (EBC) than SNOs. We therefore hypothesize that depletion of airway SNOs is related to asthma pathology, and breath formate concentration may be a proxy measure of SNO catabolism.

METHODS AND FINDINGS

We collected EBC samples from children and adolescents, including 38 with severe asthma, 46 with mild-to-moderate asthma and 16 healthy adolescent controls, and the concentration of ionic constituents was quantified using ion chromatography. The concentrations of EBC components with volatile conjugates were log-normally distributed. Formate was the principal ion that displayed a significant difference between asthma status classifications. The mean EBC formate concentration was 40% higher in samples collected from all asthmatics than from healthy controls (mean = 5.7 microM, mean+/-standard deviation = 3.1-10.3 microM vs. 4.0, 2.8-5.8 microM, p = 0.05). EBC formate was higher in severe asthmatics than in mild-to-moderate asthmatics (6.8, 3.7-12.3 microM vs. 4.9, 2.8-8.7 microM, p = 0.012). In addition, formate concentration was negatively correlated with methacholine PC(20) (r = -0.39, p = 0.002, asthmatics only), and positively correlated with the NO-derived ion nitrite (r = 0.46, p<0.0001) as well as with total serum IgE (r = 0.28, p = 0.016, asthmatics only). Furthermore, formate was not significantly correlated with other volatile organic acids nor with inhaled corticosteroid dose.

CONCLUSIONS

We conclude that EBC formate concentration is significantly higher in the breath of children with asthma than in those without asthma. In addition, amongst asthmatics, formate is elevated in the breath of those with severe asthma compared to those with mild-to-moderate asthma. We suggest that this difference is related to asthma pathology and may be a product of increased catabolism of endogenous S-nitrosothiols.

Increased nitrosoglutathione reductase activity in hypoxic pulmonary hypertension in mice

Altered S-nitrosothiols (RSNO) signaling is linked to pulmonary hypertension. Recent studies have shown that S-nitrosoglutathione (GSNO) reductase (GSNOR) catalyzes the degradation of GSNO and indirectly regulates the level of RSNO in vivo. Our present study tested the hypothesis that chronic hypoxia causes pulmonary hypertension, in part, by the change of GSNOR activity that contributes to the depletion of RSNO. Male mice were exposed to normobaric hypoxia in a ventilated chamber for 1 to 21 days or normoxia for 21 days. Right ventricular systolic pressure, right ventricle hypertrophy, and the number and media thickness of muscular pulmonary vessels increased significantly after 21 days of hypoxic exposure. Hypoxia induced the overexpression of endothelial nitric oxide synthase and inducible nitric oxide synthase. The mRNA expression of GSNOR decreased on day 1 of hypoxic exposure, but increased significantly on day 7 compared with the normoxic group. The protein expression of GSNOR increased significantly in the lung tissue after 7 days of hypoxic exposure and its enzymatic activities also increased. Both the ratios of glutathione to glutathione disulfide and nitrate to nitrite were significantly lower in the hypoxic groups than in the normoxic controls. The results suggest an increased GSNOR activity interfered with the metabolism of RSNO in mice with hypoxic pulmonary hypertension. An imbalanced of redox status is associated with the pathogenesis of hypoxic pulmonary hypertension.

Genetic variants of GSNOR and ADRB2 influence response to albuterol in African-American children with severe asthma

African Americans are disproportionately affected by asthma. Social and economic factors play a role in this disparity, but there is evidence that genetic factors may also influence the development of asthma and response to therapy in African American children. Our hypothesis is that variations in asthma related genes contribute to the observed asthma disparities by influencing the response to asthma-specific therapy. In order to test this hypothesis, we characterized the clinical response to asthma-specific therapy in 107 African American children who presented to the emergency room in status asthmaticus, with a primary outcome indicator of length of time on continuous albuterol. Single locus analysis indicated that genotype variation in glutathione-dependent S-nitrosoglutathione reductase (GSNOR) is associated with a decreased response to asthma treatment in African American children. A post hoc multi-locus analysis revealed that a combination of four single nucleotide polymorphisms (SNPs) within GSNOR, adrenergic receptor beta 2, and carbamoyl phosphate synthetase-1 give a 70% predictive value for lack of response to therapy. This predictive model needs replication in other cohorts of patients with asthma, but suggests gene-gene interactions may have greater significance than that identified with single variants. Our findings also suggest that genetic variants may contribute to the observed population disparities in asthma.

S-nitrosoglutathione reductase: an important regulator in human asthma

RATIONALE

Nitric oxide bioactivity, mediated through the formation of S-nitrosothiols (SNOs), has a significant effect on bronchomotor tone. S-Nitrosoglutathione is an endogenous bronchodilator that is decreased in children with asthmatic respiratory failure and in adults with asthma undergoing segmental airway challenge. Recently we showed that S-nitrosoglutathione reductase (GSNOR) regulates endogenous SNOs. Mice with genetic deletion of GSNOR are protected from airway hyperresponsivity in an allergic asthma model.

OBJECTIVES

We hypothesized that GSNOR is increased in human asthma and correlates with lung SNO content and airway reactivity.

METHODS

We recruited 36 subjects with mild asthma with FEV(1) 88.5 +/- 2.3% predicted and 34 healthy control subjects with FEV(1) 100.7 +/- 2.5% predicted. Bronchoalveolar lavage (BAL) was performed in all subjects. Cell counts, differentials, GSNOR activity, and SNO levels were determined in BAL.

MEASUREMENTS AND MAIN RESULTS

SNO content was decreased in asthmatic BAL compared with control BAL and correlated inversely with GSNOR expression in BAL cell lysates. Furthermore, GSNOR activity measured from BAL samples was significantly increased in subjects with asthma compared with control subjects and correlated inversely with the provocative concentration of methacholine causing a 20% decrease in FEV(1).

CONCLUSIONS

These findings suggest that GSNOR is an important regulator of airway SNO content and airways hyperresponsiveness in human asthma.

Human carbonyl reductase 1 is an S-nitrosoglutathione reductase

Human carbonyl reductase 1 (hCBR1) is an NADPH-dependent short chain dehydrogenase/reductase with broad substrate specificity and is thought to be responsible for the in vivo reduction of quinones, prostaglandins, and other carbonyl-containing compounds including xenobiotics. In addition, hCBR1 possesses a glutathione binding site that allows for increased affinity toward GSH-conjugated molecules. It has been suggested that the GSH-binding site is near the active site; however, no structures with GSH or GSH conjugates have been reported. We have solved the x-ray crystal structures of hCBR1 and a substrate mimic in complex with GSH and the catalytically inert GSH conjugate hydroxymethylglutathione (HMGSH). The structures reveal the GSH-binding site and provide insight into the affinity determinants for GSH-conjugated substrates. We further demonstrate that the structural isostere of HMGSH, S-nitrosoglutathione, is an ideal hCBR1 substrate (Km = 30 microm, kcat = 450 min(-1)) with kinetic constants comparable with the best known hCBR1 substrates. Furthermore, we demonstrate that hCBR1 dependent GSNO reduction occurs in A549 lung adenocarcinoma cell lysates and suggest that hCBR1 may be involved in regulation of tissue levels of GSNO.

Genetic variation in S-nitrosoglutathione reductase (GSNOR) and childhood asthma

BACKGROUND

S-nitrosothiols are potent endogenous bronchodilators depleted in asthmatic airway lining fluid. S-nitrosoglutathione reductase (GSNOR; also known as alcohol dehydrogenase 5 or formaldehyde dehydrogenase) catalyzes the metabolism of S-nitrosoglutathione (GSNO) and controls intracellular levels of S-nitrosothiols. GSNOR knockout mice have increased lung S-nitrosothiol levels and are therefore protected from airway hyperresponsiveness after methacholine or allergen challenge.

OBJECTIVE

We sought to investigate whether genetic variation in GSNOR is associated with childhood asthma and atopy.

METHODS

We genotyped 5 tagging and 2 additional single nucleotide polymorphisms (SNPs) in GSNOR in 532 nuclear families consisting of asthmatic children aged 4 to 17 years and both parents in Mexico City. Atopy was determined by means of skin prick testing.

RESULTS

Carrying 1 or 2 copies of the minor allele of SNP rs1,154,404 was associated with decreased risk of asthma (relative risk [RR], 0.77; 95% CI, 0.61-0.97; P = .028 for 1 copy and RR, 0.66; 95% CI, 0.44-0.99; P = .046 for 2 copies). Homozygosity for the minor allele of SNP rs28,730,619 was associated with increased risk of asthma (RR, 1.60; 95% CI, 1.13-2.26; P = .0077). Haplotype analyses supported the single SNP findings. GSNOR SNPs were not associated with the degree of atopy.

CONCLUSION

This is the first study of genetic polymorphisms in GSNOR and asthma. These data suggest that genetic variation in GSNOR might play a role in asthma susceptibility.

CLINICAL IMPLICATIONS

The association of GSNOR polymorphisms with asthma suggests a potential therapeutic target.

Inhaledl-Arginine Improves Exhaled Nitric Oxide and Pulmonary Function in Patients with Cystic Fibrosis

RATIONALE

Nitric oxide formation is deficient in airways of patients with cystic fibrosis (CF). Since nitric oxide has bronchodilatory effects, nitric oxide deficiency may contribute to airway obstruction in CF.

OBJECTIVES

We reasoned that inhalation of l-arginine, the precursor of enzymatic nitric oxide formation, could improve airway nitric oxide formation and pulmonary function in patients with CF.

MEASUREMENTS

Exhaled nitric oxide, pulmonary function, and peripheral oxygen saturation were measured before and after a single inhalation of nebulized l-arginine solution in patients with CF and in healthy subjects. A saline solution of similar osmolarity (1.7%) was used as control.

RESULTS

Nebulized l-arginine not only significantly increased exhaled nitric oxide concentrations but also resulted in a sustained improvement of FEV(1) in patients with CF. Oxygen saturation also increased significantly after the inhalation of l-arginine. Nebulized saline resulted in a small but significant increase in exhaled nitric oxide but a decrease in FEV(1) in patients with CF. In control subjects inhalation of l-arginine increased exhaled nitric oxide concentrations, but FEV(1) decreased. No effect of saline on exhaled nitric oxide, pulmonary function, or oxygen saturation was observed in healthy subjects.

CONCLUSIONS

These data suggest that a single inhalation of l-arginine acutely and transiently improves pulmonary function in CF through the formation of nitric oxide. Augmentation of airway nitric oxide formation by inhalation of l-arginine is a promising therapeutic approach in patients with CF.

Exercise-induced bronchoconstriction alters airway nitric oxide exchange in a pattern distinct from spirometry

Exhaled nitric oxide (NO) is altered in asthmatic subjects with exercise-induced bronchoconstriction (EIB). However, the physiological interpretation of exhaled NO is limited because of its dependence on exhalation flow and the inability to distinguish completely proximal (large airway) from peripheral (small airway and alveolar) contributions. We estimated flow-independent NO exchange parameters that partition exhaled NO into proximal and peripheral contributions at baseline, postexercise challenge, and postbronchodilator administration in steroid-naive mild-intermittent asthmatic subjects with EIB (24-43 yr old, n = 9) and healthy controls (20-31 yr old, n = 9). The mean +/- SD maximum airway wall flux and airway diffusing capacity were elevated and forced expiratory flow, midexpiratory phase (FEF(25-75)), forced expiratory volume in 1 s (FEV(1)), and FEV(1)/forced vital capacity (FVC) were reduced at baseline in subjects with EIB compared with healthy controls, whereas the steady-state alveolar concentration of NO and FVC were not different. Compared with the response of healthy controls, exercise challenge significantly reduced FEV(1) (-23 +/- 15%), FEF(25-75) (-37 +/- 18%), FVC (-12 +/- 12%), FEV(1)/FVC (-13 +/- 8%), and maximum airway wall flux (-35 +/- 11%) relative to baseline in subjects with EIB, whereas bronchodilator administration only increased FEV(1) (+20 +/- 21%), FEF(25-75) (+56 +/- 41%), and FEV(1)/FVC (+13 +/- 9%). We conclude that mild-intermittent steroid-naive asthmatic subjects with EIB have altered airway NO exchange dynamics at baseline and after exercise challenge but that these changes occur by distinct mechanisms and are not correlated with alterations in spirometry.

IgE sensitisation in relation to flow-independent nitric oxide exchange parameters

BACKGROUND

A positive association between IgE sensitisation and exhaled NO levels has been found in several studies, but there are no reports on the compartment of the lung that is responsible for the increase in exhaled NO levels seen in IgE-sensitised subjects.

METHODS

The present study comprised 288 adult subjects from the European Community Respiratory Health Survey II who were investigated in terms of lung function, IgE sensitisation (sum of specific IgE), smoking history and presence of rhinitis and asthma. Mean airway tissue concentration of NO (CawNO), airway transfer factor for NO (DawNO), mean alveolar concentration of NO (CalvNO) and fractional exhaled concentration of NO at a flow rate of 50 mL s(-1) (FENO 0.05) were determined using the extended NO analysis.

RESULTS

IgE-sensitised subjects had higher levels (geometric mean) of FENO 0.05 (24.9 vs. 17.3 ppb) (p < 0.001), DawNO (10.5 vs. 8 mL s(-1)) (p = 0.02) and CawNO (124 vs. 107 ppb) (p < 0.001) and positive correlations were found between the sum of specific IgE and FENO 0.05, CawNO and DawNO levels (p < 0.001 for all correlations). Sensitisation to cat allergen was the major determinant of exhaled NO when adjusting for type of sensitisation. Rhinitis and asthma were not associated with the increase in exhaled NO variables after adjusting for the degree of IgE sensitisation.

CONCLUSION

The presence of IgE sensitisation and the degree of allergic sensitisation were related to the increase in airway NO transfer factor and the increase in NO concentration in the airway wall. Sensitisation to cat allergen was related to the highest increases in exhaled NO parameters. Our data suggest that exhaled NO is more a specific marker of allergic inflammation than a marker of asthma or rhinitis.

Decreased systemic bioavailability of L-arginine in patients with cystic fibrosis

Background

L-arginine is the common substrate for nitric oxide synthases and arginases. Increased arginase levels in the blood of patients with cystic fibrosis may result in L-arginine deficiency and thereby contribute to low airway nitric oxide formation and impaired pulmonary function.

Methods

Plasma amino acid and arginase levels were studied in ten patients with cystic fibrosis before and after 14 days of antibiotic treatment for pulmonary exacerbation. Patients were compared to ten healthy non-smoking controls.

Results

Systemic arginase levels measured by ELISA were significantly increased in cystic fibrosis with exacerbation compared to controls (17.3 ± 12.0 vs. 4.3 ± 3.4 ng/ml, p < 0.02). Arginase levels normalized with antibiotic treatment. Plasma L-arginine was significantly reduced before (p < 0.05) but not after treatment. In contrast, L-ornithine, proline, and glutamic acid, all downstream products of arginase activity, were normal before, but significantly increased after antibiotic therapy. Bioavailability of L-arginine was significantly reduced in cystic fibrosis before and after exacerbation (p < 0.05, respectively).

Conclusion

These observations provide further evidence for a disturbed balance between the L-arginine metabolic pathways in cystic fibrosis.

Endogenous S-nitrosoglutathione modifies 5-lipoxygenase expression in airway epithelial cells

S-Nitrosoglutathione (GSNO) is an endogenous bronchodilator with several beneficial pulmonary effects. Levels are decreased in the asthmatic airway, and GSNO inhalation has been proposed as an asthma therapy. 5-lipoxygenase (5-LO) is the rate-limiting enzyme in the synthetic pathway for cysteinyl leukotrienes (CysLTs), bronchoconstricting agents that are overproduced in asthma. Here, we have studied the effect of GSNO on the expression of 5-LO in human airway A549 cell lines and in primary normal human tracheobronchial epithelial (NHBE) cells in vitro. GSNO at concentrations of 0.5-1 microM caused a 3- to 6-fold increase in 5-LO expression. However, GSNO at>5 microM significantly inhibited both 5-LO expression and LT production. We also found that airway epithelial cells had gamma-glutamyl transpeptidase (gamma-GT) activity. The effect of 1 microM GSNO on 5-LO expression was prevented by the gamma-GT inhibitor, acivicin, suggesting a convergence of GSNO and CysLT metabolic pathway that may be relevant to asthma. Our data demonstrate that GSNO levels<or=1 microM, likely recapitulating those in the asthmatic airway, increase 5-LO expression, an effect that may increase inflammation and bronchoconstriction. However, GSNO at concentrations>5microM suppresses 5-LO expression. These data suggest that GSNO might inhibit 5-LO expression in the clinical setting.

Nitric oxide and redox signaling in allergic airway inflammation

A number of diseases of the respiratory tract, as exemplified in this review by asthma, are associated with increased amounts of nitric oxide (NO) in the expired breath. Asthma is furthermore characterized by increased production of reactive oxygen species that scavenge NO to form more reactive nitrogen species as demonstrated by the enhanced presence of nitrated proteins in the lungs of these patients. This increased oxidative metabolism leaves less bioavailable NO and coincides with lower amounts of S-nitrosothiols. In this review, we speculate on mechanisms responsible for the increased amounts of NO in inflammatory airway disease and discuss the apparent paradox of higher levels of NO as opposed to decreased amounts of S-nitrosothiols. We will furthermore give an overview of the regulation of NO production and biochemical events by which NO transduces signals into cellular responses, with a particular focus on modulation of inflammation by NO. Lastly, difficulties in studying NO signaling and possible therapeutic uses for NO will be highlighted.

Nitric oxide in health and disease of the respiratory system

During the past decade a plethora of studies have unravelled the multiple roles of nitric oxide (NO) in airway physiology and pathophysiology. In the respiratory tract, NO is produced by a wide variety of cell types and is generated via oxidation of l-arginine that is catalyzed by the enzyme NO synthase (NOS). NOS exists in three distinct isoforms: neuronal NOS (nNOS), inducible NOS (iNOS), and endothelial NOS (eNOS). NO derived from the constitutive isoforms of NOS (nNOS and eNOS) and other NO-adduct molecules (nitrosothiols) have been shown to be modulators of bronchomotor tone. On the other hand, NO derived from iNOS seems to be a proinflammatory mediator with immunomodulatory effects. The concentration of this molecule in exhaled air is abnormal in activated states of different inflammatory airway diseases, and its monitoring is potentially a major advance in the management of, e.g., asthma. Finally, the production of NO under oxidative stress conditions secondarily generates strong oxidizing agents (reactive nitrogen species) that may modulate the development of chronic inflammatory airway diseases and/or amplify the inflammatory response. The fundamental mechanisms driving the altered NO bioactivity under pathological conditions still need to be fully clarified, because their regulation provides a novel target in the prevention and treatment of chronic inflammatory diseases of the airways.

Nitric oxide represses inhibitory kappaB kinase through S-nitrosylation

Nitric oxide (NO) possesses antiinflammatory effects, which may be exerted via its ability to inhibit the transcription factor, NF-kappaB. A commonly proposed mode of action for inhibition of NF-kappaBbyNO involves interference with NF-kappaB binding to DNA. Because activation of inhibitory kappaB kinase (IKK), the prerequisite enzyme complex necessary to induce NF-kappaB, is subject to redox regulation, we assessed whether IKK could present a more proximal target for NO to inhibit NF-kappaB activation. We demonstrate here that S-nitrosothiols (SNO) caused a dose-dependent inhibition of the enzymatic activity of IKK, in lung epithelial cells and in Jurkat T cells, which was associated with S-nitrosylation of the IKK complex. Using biotin derivatization of SNO, we revealed that IKKbeta, the catalytic subunit required for NF-kappaB activation, was a direct target for S-nitrosylation. A mutant version of IKKbeta containing a Cys-179-to-Ala mutation was refractory to inhibition by SNO or to increases in S-nitrosylation, in contrast to wild-type IKKbeta, demonstrating that Cys-179 is the main target for attack by SNO. Importantly, inhibition of NO synthase activity in Jurkat T cells resulted in activation of IKK, in association with its denitrosylation. Moreover, NO synthase inhibition enhanced the ability of tumor necrosis factor alpha to activate IKK, illustrating the importance of endogenous NO in regulating the extent of NF-kappaB activation by cytokines. Collectively, our findings demonstrate that IKKbeta is an important target for the redox regulation of NF-kappaB by endogenous or exogenous NO, providing an additional mechanism for its antiinflammatory properties.

Airway diffusing capacity of nitric oxide and steroid therapy in asthma

Exhaled nitric oxide (NO) concentration is a noninvasive index for monitoring lung inflammation in diseases such as asthma. The plateau concentration at constant flow is highly dependent on the exhalation flow rate and the use of corticosteroids and cannot distinguish airway and alveolar sources. In subjects with steroid-naive asthma (n = 8) or steroid-treated asthma (n = 12) and in healthy controls (n = 24), we measured flow-independent NO exchange parameters that partition exhaled NO into airway and alveolar regions and correlated these with symptoms and lung function. The mean (+/-SD) maximum airway flux (pl/s) and airway tissue concentration [parts/billion (ppb)] of NO were lower in steroid-treated asthmatic subjects compared with steroid-naive asthmatic subjects (1,195 +/- 836 pl/s and 143 +/- 66 ppb compared with 2,693 +/- 1,687 pl/s and 438 +/- 312 ppb, respectively). In contrast, the airway diffusing capacity for NO (pl.s-1.ppb-1) was elevated in both asthmatic groups compared with healthy controls, independent of steroid therapy (11.8 +/- 11.7, 8.71 +/- 5.74, and 3.13 +/- 1.57 pl.s-1.ppb-1 for steroid treated, steroid naive, and healthy controls, respectively). In addition, the airway diffusing capacity was inversely correlated with both forced expired volume in 1 s and forced vital capacity (%predicted), whereas the airway tissue concentration was positively correlated with forced vital capacity. Consistent with previously reported results from Silkoff et al. (Silkoff PE, Sylvester JT, Zamel N, and Permutt S, Am J Respir Crit Med 161: 1218-1228, 2000) that used an alternate technique, we conclude that the airway diffusing capacity for NO is elevated in asthma independent of steroid therapy and may reflect clinically relevant changes in airways.

S-nitrosylation in health and disease

S-nitrosylation is a ubiquitous redox-related modification of cysteine thiol by nitric oxide (NO), which transduces NO bioactivity. Accumulating evidence suggests that the products of S-nitrosylation, S-nitrosothiols (SNOs), play key roles in human health and disease. In this review, we focus on the reaction mechanisms underlying the biological responses mediated by SNOs. We emphasize reactions that can be identified with complex (patho)physiological responses, and that best rationalize the observed increase or decrease in specific classes of SNOs across a spectrum of disease states. Thus, changes in the levels of various SNOs depend on specific defects in both enzymatic and non-enzymatic mechanisms of nitrosothiol formation, processing and degradation. An understanding of these mechanisms is crucial for the development of an integrated model of NO biology, and for effective treatment of diseases associated with dysregulation of NO homeostasis.

S-Nitrosoglutathione induces functional DeltaF508-CFTR in airway epithelial cells

S-Nitrosoglutathione (GSNO) is an endogenous bronchodilator levels of which are reduced in the airways of cystic fibrosis (CF) patients. GSNO has recently been shown to increase maturation of CFTR in CF cell lines at physiological concentrations. The ability of S-nitrosoglutathione to direct the DeltaF508-CFTR to the plasma membrane and restore the function of the cAMP-dependent chloride transport in cultured human airway epithelial cells has been studied. Immunocytochemistry showed a time- and dose-dependent increase of apically located CFTR after GSNO treatment. Chloride transport studies with the fluorescent dye N-(ethoxycarbonylmethyl)-6-methoxyquinolinium bromide (MQAE) showed that GSNO was able to induce a fourfold increase of cAMP-dependent chloride transport. Our data and the fact that endogenous GSNO levels are lower in the airways of CF patients make GSNO an interesting candidate for pharmacological treatment of cystic fibrosis.

Oxidative stress in allergic respiratory diseases

There is ample evidence that allergic disorders, such as asthma, rhinitis, and atopic dermatitis, are mediated by oxidative stress. Excessive exposure to reactive oxygen and nitrogen species is the hallmark of oxidative stress and leads to damage of proteins, lipids, and DNA. Oxidative stress occurs not only as a result of inflammation but also from environmental exposure to air pollution and cigarette smoke. The specific localization of antioxidant enzymes in the lung and the rapid reaction of nitric oxide with reactive oxygen species, such as superoxide, suggest that antioxidant enzymes might also function as cell-signaling agents or regulators of cell signaling. Therapeutic interventions that decrease exposure to environmental reactive oxygen species or augment endogenous antioxidant defenses might be beneficial as adjunctive therapies for allergic respiratory disorders.

Acute effects of aerosolized S-nitrosoglutathione in cystic fibrosis

S-nitrosoglutathione (GSNO), a naturally occurring constituent of airway lining fluid, enhances ciliary motility, relaxes airway smooth muscle, inhibits airway epithelial amiloride-sensitive sodium transport, and prevents pathogen replication. Remarkably, airway levels of GSNO are low in patients with cystic fibrosis (CF). We hypothesized that replacement of airway GSNO would improve gas exchange in CF. In a double-blind, placebo controlled study, we administered 0.05 ml/kg of 10 mM GSNO or phosphate buffered saline by aerosol to patients with CF and followed oxygen saturation, spirometry, respiratory rate, blood pressure, heart rate, and expired nitric oxide (NO). Nine patients received GSNO and 11 placebo. GSNO inhalation was associated with a modest but sustained increase in oxygen saturation at all time points. Expired NO increased in the low ppb range with GSNO treatment, peaking at 5 minutes but remaining above baseline at 30 minutes. There were no adverse effects. We conclude that GSNO is well tolerated in patients with CF and improves oxygenation through a mechanism that may be independent of free NO. Further, GSNO breakdown increases expired NO. We suggest that therapy aimed at restoring endogenous GSNO levels in the CF airway may merit study.

Alterations in exhaled gas profile during allergen-induced asthmatic response

The source of exhaled carbon monoxide (CO) and the relationship to airway inflammation are not clear. If CO is produced by the inflamed airway, we hypothesized that inflammation induced by allergen challenge would increase exhaled CO of atopic asthmatics. Eight atopic asthmatics underwent whole lung allergen challenge. CO, nitric oxide (NO), oxygen, and carbon dioxide (CO(2)) were measured simultaneously in exhaled breath which was collected into Mylar balloons before (baseline), immediately after, and at subsequent times after allergen. NO was higher in asthmatics than control subjects at baseline, increased further in seven of the eight asthmatics after allergen, and was inversely correlated to specific conductance. In contrast, exhaled CO of asthmatics was not higher than that of control individuals at baseline, decreased immediately after allergen, and returned to baseline levels during the late asthmatic response. Thus, allergen-induced airway inflammation did not lead to increased exhaled CO in asthma.

S-Nitrosylation of mitochondrial caspases

Caspase-3 is a cysteine protease located in both the cytoplasm and mitochondrial intermembrane space that is a central effector of many apoptotic pathways. In resting cells, a subset of caspase-3 zymogens is S-nitrosylated at the active site cysteine, inhibiting enzyme activity. During Fas-induced apoptosis, caspases are denitrosylated, allowing the catalytic site to function. In the current studies, we sought to identify the subpopulation of caspases that is regulated by S-nitrosylation. We report that the majority of mitochondrial, but not cytoplasmic, caspase-3 zymogens contain this inhibitory modification. In addition, the majority of mitochondrial caspase-9 is S-nitrosylated. These studies suggest that S-nitrosylation plays an important role in regulating mitochondrial caspase function and that the S-nitrosylation state of a given protein depends on its subcellular localization.

NO chemical events in the human airway during the immediate and late antigen-induced asthmatic response

A wealth of evidence supports increased NO (NO.) in asthma, but its roles are unknown. To investigate how NO participates in inflammatory airway events in asthma, we measured NO. and NO. chemical reaction products [nitrite, nitrate, S-nitrosothiols (SNO), and nitrotyrosine] before, immediately and 48 h after bronchoscopic antigen (Ag) challenge of the peripheral airways in atopic asthmatic individuals and nonatopic healthy controls. Strikingly, NO(3)(-) was the only NO. derivative to increase during the immediate Ag-induced asthmatic response and continued to increase over 2-fold at 48 h after Ag challenge in contrast to controls [P < 0.05]. NO(2)(-) was not affected by Ag challenge at 10 min or 48 h after Ag challenge. Although SNO was not detectable in asthmatic airways at baseline or immediately after Ag, SNO increased during the late response to levels found in healthy controls. A model of NO. dynamics derived from the current findings predicts that NO. may have harmful effects through formation of peroxynitrite, but also subserves an antioxidant role by consuming reactive oxygen species during the immediate asthmatic response, whereas nitrosylation during the late asthmatic response generates SNO, safe reservoirs for removal of toxic NO. derivatives.