Bronchodilator S-nitrosothiol deficiency in asthmatic respiratory failure

GSNO reductase and beta2-adrenergic receptor gene-gene interaction: bronchodilator responsiveness to albuterol

BACKGROUND

Short-acting inhaled beta2-agonists such as albuterol are used for bronchodilation and are the mainstay of asthma treatment worldwide. There is significant variation in bronchodilator responsiveness to albuterol not only between individuals but also across racial/ethnic groups. The beta2-adrenergic receptor (beta2AR) is the target for beta2-agonist drugs. The enzyme, S-nitrosoglutathione reductase (GSNOR), which regulates levels of the endogenous bronchodilator S-nitrosoglutathione, has been shown to modulate the response to beta2-agonists.

OBJECTIVE

We hypothesized that there are pharmacogenetic interactions between GSNOR and beta2AR gene variants that are associated with variable response to albuterol.

METHODS

We performed family-based analyses to test for association between GSNOR gene variants and asthma and related phenotypes in 609 Puerto Rican and Mexican families with asthma. In addition, we tested these individuals for pharmacogenetic interaction between GSNOR and beta2AR gene variants and responsiveness to albuterol using linear regression. Cell transfection experiments were performed to test the potential effect of the GSNOR gene variants.

RESULTS

Among Puerto Ricans, several GSNOR SNPs and a haplotype in the 3'UTR were significantly associated with increased risk for asthma and lower bronchodilator responsiveness (P=0.04-0.007). The GSNOR risk haplotype affects expression of GSNOR mRNA and protein, suggesting a gain of function. Furthermore, gene-gene interaction analysis provided evidence of pharmacogenetic interaction between GSNOR and beta2AR gene variants and the response to albuterol in Puerto Rican (P=0.03), Mexican (P=0.15) and combined Puerto Rican and Mexican asthmatics (P=0.003). Specifically, GSNOR+17059*beta2AR+46 genotype combinations (TG+GG*AG and TG+GG*GG) were associated with lower bronchodilator response.

CONCLUSION

Genotyping of GSNOR and beta2AR genes may be useful in identifying Latino individuals, who might benefit from adjuvant therapy for refractory asthma.

Review: Chemical and structural modifications of pulmonary collectins and their functional consequences

The lung is continuously exposed to inhaled pathogens (toxic pollutants, micro-organisms, environmental antigens, allergens) from the external environment. In the broncho-alveolar space, the critical balance between a measured protective response against harmful pathogens and an inappropriate inflammatory response to harmless particles is discerned by the innate pulmonary immune system. Among its many components, the surfactant proteins and specifically the pulmonary collectins (surfactant proteins A [SP-A] and D [SP-D]) appear to provide important contributions to the modulation of host defense and inflammation in the lung. Many studies have shown that multimerization of SP-A and SP-D are important for efficient local host defense including neutralization and opsonization of influenza A virus, binding Pneumocystis murina and inhibition of LPS-induced inflammatory cell responses. These observations strongly imply that oligomerization of collectins is a critical feature of its function. However, during the inflammatory state, despite normal pool sizes, chemical modification of collectins can result in alteration of their structure and function. Both pulmonary collectins can be altered through proteolytic inactivation, nitration, S-nitrosylation, oxidation and/or crosslinking as a consequence of the inflammatory milieu facilitated by cytokines, nitric oxide, proteases, and other chemical mediators released by inflammatory cells. Thus, this review will summarize recent developments in our understanding of the relationship between post-translational assembly of collectins and their modification by inflammation as an important molecular switch for the regulation of local innate host defense.

Direct inhibition of arginase attenuated airway allergic reactions and inflammation in a Dermatophagoides farinae-induced NC/Nga mouse model

The expression of arginase I has been a focus of research into the pathogenesis of experimental asthma, because arginase deprives nitric oxide synthase (NOS) of arginine and therefore participates in the attenuation of bronchodilators such as nitric oxide (NO). The present study used an intranasal mite-induced NC/Nga mouse model of asthma to investigate the contribution of arginase to the asthma pathogenesis, using an arginase inhibitor, N(omega)-hydroxy-nor-l-arginine (nor-NOHA). The treatment with nor-NOHA inhibited the increase in airway hyperresponsiveness (AHR) and the number of eosinophils in bronchoalveolar lavage fluid. NOx levels in the lung were elevated despite suppressed NOS2 mRNA expression. Accompanied by the attenuated activity of arginase, the expression of arginase I at both the mRNA and protein level was downregulated. The levels of mRNA for T helper 2 cytokines such as IL-4, IL-5, and IL-13, and for chemotactants such as eotaxin-1 and eotaxin-2, were reduced. Moreover, the accumulation of inflammatory cells and the ratio of goblet cells in the bronchiole were decreased. The study concluded that the depletion of NO caused by arginase contributes to AHR and inflammation, and direct administration of an arginase inhibitor to the airway may be beneficial and could be of use in treating asthma due to its anti-inflammatory and airway-relaxing effects, although it is not clear whether the anti-inflammatory effect is direct or indirect.

Use of exhaled nitric oxide measurement to identify a reactive, at-risk phenotype among patients with asthma

RATIONALE

Exhaled nitric oxide (Fe(NO)) is a biomarker of airway inflammation in mild to moderate asthma. However, whether Fe(NO) levels are informative regarding airway inflammation in patients with severe asthma, who are refractory to conventional treatment, is unknown. Here, we hypothesized that classification of severe asthma based on airway inflammation as defined by Fe(NO) levels would identify a more reactive, at-risk asthma phenotype.

METHODS

Fe(NO) and major features of asthma, including airway inflammation, airflow limitation, hyperinflation, hyperresponsiveness, and atopy, were determined in 446 individuals with various degrees of asthma severity (175 severe, 271 non-severe) and 49 healthy subjects enrolled in the Severe Asthma Research Program.

MEASUREMENTS AND MAIN RESULTS

Fe(NO) levels were similar among patients with severe and non-severe asthma. The proportion of individuals with high Fe(NO) levels (>35 ppb) was the same (40%) among groups despite greater corticosteroid therapy in severe asthma. All patients with asthma and high Fe(NO) had more airway reactivity (maximal reversal in response to bronchodilator administration and by methacholine challenge), more evidence of allergic airway inflammation (sputum eosinophils), more evidence of atopy (positive skin tests, higher serum IgE and blood eosinophils), and more hyperinflation, but decreased awareness of their symptoms. High Fe(NO) identified those patients with severe asthma characterized by the greatest airflow obstruction and hyperinflation and most frequent use of emergency care.

CONCLUSIONS

Grouping of asthma by Fe(NO) provides an independent classification of asthma severity, and among patients with severe asthma identifies the most reactive and worrisome asthma phenotype.

Redox control of asthma: molecular mechanisms and therapeutic opportunities

An imbalance in reducing and oxidizing (redox) systems favoring a more oxidative environment is present in asthma and linked to the pathophysiology of the defining symptoms and signs including airflow limitation, hyper-reactivity, and airway remodeling. High levels of hydrogen peroxide, nitric oxide ((*)NO), and 15-F(2t)-isoprostane in exhaled breath, and excessive oxidative protein products in lung epithelial lining fluid, peripheral blood, and urine provide abundant evidence for pathologic oxidizing processes in asthma. Parallel studies document loss of reducing potential by nonenzymatic and enzymatic antioxidants. The essential first line antioxidant enzymes superoxide dismutases (SOD) and catalase are reduced in asthma as compared to healthy individuals, with lowest levels in those patients with the most severe asthma. Loss of SOD and catalase activity is related to oxidative modifications of the enzymes, while other antioxidant gene polymorphisms are linked to susceptibility to develop asthma. Monitoring of exhaled (*)NO has entered clinical practice because it is useful to optimize asthma care, and a wide array of other biochemical oxidative and nitrative biomarkers are currently being evaluated for asthma monitoring and phenotyping. Novel therapeutic strategies that target correction of redox abnormalities show promise for the treatment of asthma.

The ontogeny, distribution, and regulation of alcohol dehydrogenase 3: implications for pulmonary physiology

Class III alcohol dehydrogenase (ADH3), also termed formaldehyde dehydrogenase or S-nitrosoglutathione reductase, plays a critical role in the enzymatic oxidation of formaldehyde and reduction of nitrosothiols that regulate bronchial tone. Considering reported associations between formaldehyde vapor exposure and childhood asthma risk, and thus potential involvement of ADH3, we reviewed the ontogeny, distribution, and regulation of mammalian ADH3. Recent studies indicate that multiple biological and chemical stimuli influence expression and activity of ADH3, including the feedback regulation of nitrosothiol metabolism. The levels of ADH3 correlate with, and potentially influence, bronchial tone; however, data gaps remain with respect to the expression of ADH3 during postnatal and early childhood development. Consideration of ADH3 function relative to the respiratory effects of formaldehyde, as well as to other chemical and biological exposures that might act in an additive or synergistic manner with formaldehyde, might be critical to gain better insight into the association between formaldehyde exposure and childhood asthma.

Protection from lipopolysaccharide-induced lung injury by augmentation of airway S-nitrosothiols

RATIONALE

S-Nitrosothiols (SNO) inhibit immune activation of the respiratory epithelium and airway SNO levels are decreased in inflammatory lung disease. Ethyl nitrite (ENO) is a gas with chemical properties favoring SNO formation. Augmentation of airway SNO by inhaled ENO treatment may decrease lung inflammation and subsequent injury by inhibiting activation of the airway epithelium.

OBJECTIVES

To determine the effect of inhaled ENO on airway SNO levels and LPS-induced lung inflammation/injury.

METHODS

Mice were treated overnight with inhaled ENO (10 ppm) or air, followed immediately by exposure to aerosolized LPS or saline. Parameters of inflammation and lung injury were quantified 1 hour after completion of the aerosol exposure and correlated to lung airway and tissue SNO levels.

MEASUREMENTS AND MAIN RESULTS

Aerosolized LPS induced a decrease in airway and lung tissue SNO levels including S-nitrosylated NF-kappaB. The decrease in lung SNO was associated with an increase in lung NF-kappaB activity, cytokine/chemokine expression (keratinocyte-derived chemokine, tumor necrosis factor-alpha, and IL-6), airway neutrophil influx, and worsened lung compliance. Pretreatment with inhaled ENO restored airway SNO levels and reduced LPS-mediated NF-kappaB activation thereby inhibiting the downstream inflammatory response and preserving lung compliance.

CONCLUSIONS

Airway SNO serves an antiinflammatory role in the lung. Inhaled ENO can be used to augment airway SNO and protect from LPS-induced acute lung injury.

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.

Reactive nitrogen species: molecular mechanisms and potential significance in health and disease

Reactive nitrogen species (RNS) are various nitric oxide-derived compounds, including nitroxyl anion, nitrosonium cation, higher oxides of nitrogen, S-nitrosothiols, and dinitrosyl iron complexes. RNS have been recognized as playing a crucial role in the physiologic regulation of many, if not all, living cells, such as smooth muscle cells, cardiomyocytes, platelets, and nervous and juxtaglomerular cells. They possess pleiotropic properties on cellular targets after both posttranslational modifications and interactions with reactive oxygen species. Elevated levels of RNS have been implicated in cell injury and death by inducing nitrosative stress. The aim of this comprehensive review is to address the mechanisms of formation and removal of RNS, highlighting their potential cellular targets: lipids, DNA, and proteins. The specific importance of RNS and their paradoxic effects, depending on their local concentration under physiologic conditions, is underscored. An increasing number of compounds that modulate RNS processing or targets are being identified. Such compounds are now undergoing preclinical and clinical evaluations in the treatment of pathologies associated with RNS-induced cellular damage. Future research should help to elucidate the involvement of RNS in the therapeutic effect of drugs used to treat neurodegenerative, cardiovascular, metabolic, and inflammatory diseases and cancer.

Analysis of exhaled breath condensate in respiratory medicine: methodological aspects and potential clinical applications

Analysis of exhaled breath condensate (EBC) is a noninvasive method for studying the composition of airway lining fluid and has the potential for assessing lung inflammation. EBC is mainly formed by water vapor, but also contains aerosol particles in which several biomolecules including leukotrienes, 8-isoprostane, prostaglandins, hydrogen peroxide, nitric oxide-derived products, and hydrogen ions, have been detected in healthy subjects. Inflammatory mediators in EBC are detected in healthy subjects and some of them are elevated in patients with different lung diseases. Analysis of EBC is completely noninvasive, is particularly suitable for longitudinal studies, and is potentially useful for assessing the response to pharmacological therapy. Identification of selective profiles of biomarkers of lung diseases might also have a diagnostic value. However, EBC analysis currently has important limitations. The lack of standardized procedures for EBC analysis and validation of some analytical techniques makes it difficult comparison of results from different laboratories. Analysis of EBC is currently more useful for relative measures than for quantitative assessment of inflammatory mediators. Reference analytical techniques are required to provide definitive evidence for the presence of some inflammatory mediators in EBC and for their accurate quantitative assessment in this biological fluid. Several methodological issues need to be addressed before EBC analysis can be considered for clinical applications. However, further research in this area is warranted due to the relative lack of noninvasive methods for assessing lung inflammation.

S-nitrosylation of surfactant protein-D controls inflammatory function

The pulmonary collectins, surfactant proteins A and D (SP-A and SP-D) have been implicated in the regulation of the innate immune system within the lung. In particular, SP-D appears to have both pro- and anti-inflammatory signaling functions. At present, the molecular mechanisms involved in switching between these functions remain unclear. SP-D differs in its quaternary structure from SP-A and the other members of the collectin family, such as C1q, in that it forms large multimers held together by the N-terminal domain, rather than aligning the triple helix domains in the traditional "bunch of flowers" arrangement. There are two cysteine residues within the hydrophobic N terminus of SP-D that are critical for multimer assembly and have been proposed to be involved in stabilizing disulfide bonds. Here we show that these cysteines exist within the reduced state in dodecameric SP-D and form a specific target for S-nitrosylation both in vitro and by endogenous, pulmonary derived nitric oxide (NO) within a rodent acute lung injury model. S-nitrosylation is becoming increasingly recognized as an important post-translational modification with signaling consequences. The formation of S-nitrosothiol (SNO)-SP-D both in vivo and in vitro results in a disruption of SP-D multimers such that trimers become evident. SNO-SP-D but not SP-D, either dodecameric or trimeric, is chemoattractive for macrophages and induces p38 MAPK phosphorylation. The signaling capacity of SNO-SP-D appears to be mediated by binding to calreticulin/CD91. We propose that NO controls the dichotomous nature of this pulmonary collectin and that posttranslational modification by S-nitrosylation causes quaternary structural alterations in SP-D, causing it to switch its inflammatory signaling role. This represents new insight into both the regulation of protein function by S-nitrosylation and NO's role in innate immunity.

The Janus face of alcohol dehydrogenase 3

Many carbonyl metabolizing enzymes are equally involved in xenobiotic and endogenous metabolism, but few have been investigated in terms of substrate competition and interference between different cellular pathways. Mammalian alcohol dehydrogenase 3 (ADH3) represents the key enzyme in the formaldehyde detoxification pathway by oxidation of S-hydroxymethylglutathione [HMGSH; the glutathione (GSH) adduct of formaldehyde]. In addition, several studies have established ADH3 as S-nitrosoglutathione (GSNO) reductase in endogenous NO homeostasis during the last decade. GSNO depletion associates with various diseases including asthma, and evidence for a causal relationship between ADH3 and asthma pathology has been put forward. In a recent study, we showed that ADH3-mediated alcohol oxidation, including HMGSH oxidation, is accelerated in presence of GSNO which is concurrently reduced under immediate cofactor recycling [C.A. Staab, J. Alander, M. Brandt, J. Lengqvist, R. Morgenstern, R.C. Grafström, J.-O. Höög, Reduction of S-nitrosoglutathione by alcohol dehydrogenase 3 is facilitated by substrate alcohols via direct cofactor recycling and leads to GSH-controlled formation of glutathione transferase inhibitors, Biochem. J. 413 (2008) 493-504]. Thus, considering the usually low cytosolic free NADH/NAD(+) ratio, formaldehyde may trigger and promote GSNO reduction by enzyme-bound cofactor recycling. These findings provided evidence for formaldehyde-induced, ADH3-mediated GSNO depletion with potential direct implications for asthma. Furthermore, analysis of product formation as a function of GSH concentrations suggested that, under conditions of oxidative stress, GSNO reduction can lead to the formation of glutathione sulfinamide and its hydrolysis product glutathione sulfinic acid, both potent inhibitors of glutathione transferase activity.

S-nitrosylated S100A8: novel anti-inflammatory properties

S100A8 and S100A9, highly expressed by neutrophils, activated macrophages, and microvascular endothelial cells, are secreted during inflammatory processes. Our earlier studies showed S100A8 to be an avid scavenger of oxidants, and, together with its dependence on IL-10 for expression in macrophages, we postulated that this protein has a protective role. S-nitrosylation is an important posttranslational modification that regulates NO transport, cell signaling, and homeostasis. Relatively few proteins are targets of S-nitrosylation. To date, no inflammation-associated proteins with NO-shuttling capacity have been identified. We used HPLC and mass spectrometry to show that S100A8 and S100A9 were readily S-nitrosylated by NO donors. S-nitrosylated S100A8 (S100A8-SNO) was the preferred nitrosylated product. No S-nitrosylation occurred when the single Cys residue in S100A8 was mutated to Ala. S100A8-SNO in human neutrophils treated with NO donors was confirmed by the biotin switch assay. The stable adduct transnitrosylated hemoglobin, indicating a role in NO transport. S100A8-SNO suppressed mast cell activation by compound 48/80; intravital microscopy was used to demonstrate suppression of leukocyte adhesion and extravasation triggered by compound 48/80 in the rat mesenteric microcirculation. Although S100A8 is induced in macrophages by LPS or IFN-gamma, the combination, which activates inducible NO synthase, did not induce S100A8. Thus, the antimicrobial functions of NO generated under these circumstances would not be compromised by S100A8. Our results suggest that S100A8-SNO may regulate leukocyte-endothelial cell interactions in the microcirculation, and suppression of mast cell-mediated inflammation represents an additional anti-inflammatory property for S100A8.

Basic science review: nitric oxide--releasing prosthetic materials

Prosthetic devices that come into contact with blood ultimately fail secondary to thrombus formation. This limits the utility of a variety of materials used to surgically treat cardiovascular disease, including vascular grafts and stents, as well as sensors and catheters placed within the circulatory system. Moreover, systemic anticoagulation that is used to prevent malfunction of these devices has potential for serious complications. It is known that nitric oxide (NO) produced via the endothelium imparts thromboresistant properties to native blood vessels. Thus, if NO were delivered locally to the site of the prosthetic material, it has the potential to halt thrombus formation while limiting life-threatening side effects. This review serves to examine the variety of NO-releasing materials that have been created with the two different classes of NO donors, the diazeniumdiolates and S-nitrosothiols, and the clinical applications of these prosthetics for potential future use.

Inhibition of arginase activity enhances inflammation in mice with allergic airway disease, in association with increases in protein S-nitrosylation and tyrosine nitration

Pulmonary inflammation in asthma is orchestrated by the activity of NF-kappaB. NO and NO synthase (NOS) activity are important modulators of inflammation. The availability of the NOS substrate, l-arginine, is one of the mechanisms that controls the activity of NOS. Arginase also uses l-arginine as its substrate, and arginase-1 expression is highly induced in a murine model of asthma. Because we have previously described that arginase affects NOx content and interferes with the activation of NF-kappaB in lung epithelial cells, the goal of this study was to investigate the impact of arginase inhibition on the bioavailability of NO and the implications for NF-kappaB activation and inflammation in a mouse model of allergic airway disease. Administration of the arginase inhibitor BEC (S-(2-boronoethyl)-l-cysteine) decreased arginase activity and caused alterations in NO homeostasis, which were reflected by increases in S-nitrosylated and nitrated proteins in the lungs from inflamed mice. In contrast to our expectations, BEC enhanced perivascular and peribronchiolar lung inflammation, mucus metaplasia, NF-kappaB DNA binding, and mRNA expression of the NF-kappaB-driven chemokine genes CCL20 and KC, and lead to further increases in airways hyperresponsiveness. These results suggest that inhibition of arginase activity enhanced a variety of parameters relevant to allergic airways disease, possibly by altering NO homeostasis.

Selective inhibition of inducible NO synthase activity in vivo reverses inflammatory abnormalities in surfactant protein D-deficient mice

Surfactant protein D (SP-D)-deficient (SP-D-/-) mice exhibit early development of emphysema. Previously we have shown that SP-D deficiency results in increased production and activity of inducible NO synthase (iNOS). In this study, we examined whether treatment with the iNOS inhibitor 1400W could inhibit the inflammatory phenotype. Mice were treated with 1400W systemically for 7 wk from 3 wk of age. Treatment reduced total lung NO synthase activity to 14.7+/-6.1% of saline-treated 10-wk-old SP-D-/- littermates. Long-term administration of 1400W reduced lung inflammation and cellular infiltration; and significantly attenuated the increased levels of matrix metalloproteinases 2 and 9, chemokines (KC, TARC), and cytokines (IFN-gamma) seen in bronchoalveolar lavage (BAL) of SP-D-/- mice. Abrogation of these levels was associated with decreasing BAL chemotactic activity for RAW cells. Two weeks of treatment with 1400W reduced total lung NO synthase (NOS) activity to 12.7+/-6.3% of saline-treated SP-D-/- mice. Short-term iNOS inhibition resulted in attenuation of pulmonary inflammation within SP-D-/- mice as shown by decreases in total BAL cell count (63+/-6% of SP-D-/- control), macrophage size (>25 microm) within the BAL (62+/-10% of SP-D-/- control), and a percentage of BAL macrophages producing oxidants (76+/-9% of SP-D-/- control). These studies showed that s.c. delivery of 1400W can be achieved in vivo and can attenuate the inflammatory processes within SP-D deficiency. Our results represent the first report linking defects in the innate immune system in the lung with alterations in NO homeostasis.

DETANO and nitrated lipids increase chloride secretion across lung airway cells

We investigated the cellular mechanisms by which nitric oxide (NO) increases chloride (Cl-) secretion across lung epithelial cells in vitro and in vivo. Addition of (Z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl) amino] diazen-1-ium-1, 2-diolate (DETANONOate [DETANO];1-1,000 microM) into apical compartments of Ussing chambers containing Calu-3 cells increased short-circuit currents (I(sc)) from 5.2 +/- 0.8 to 15.0 +/- 2.1 microA/cm(2) (X +/- 1 SE; n = 7; P < 0.001). NO generated from two nitrated lipids (nitrolinoleic and nitrooleic acids; 1-10 microM) also increased I(sc) by about 100%. Similar effects were noted across basolaterally, but not apically, permeabilized Calu-3 cells. None of these NO donors increased I(sc) in Calu-3 cells pretreated with 10 microM 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (an inhibitor of soluble guanylyl cyclase). Scavenging of NO either prevented or reversed the increase of I(sc). These data indicate that NO stimulation of soluble guanylyl cyclase was sufficient and necessary for the increase of I(sc) via stimulation of the apical cystic fibrosis transmembrane regulator (CFTR). Both Calu-3 and alveolar type II (ATII) cells contained CFTR, as demonstrated by in vitro phosphorylation of immunoprecipitated CFTR by protein kinase (PK) A. PKGII (but not PKGI) phosphorylated CFTR immuniprecipitated from Calu-3 cells. Corresponding values in ATII cells were below the threshold of detection. Furthermore, DETANO, 8-Br-cGMP, or 8-(4-chlorophenylthio)-cGMP (up to 2 mM each) did not increase Cl- secretion across amiloride-treated ATII cells in vitro. Measurements of nasal potential differences in anesthetized mice showed that perfusion of the nares with DETANO activated glybenclamide-sensitive Cl- secretion. These findings suggest that small concentrations of NO donors may prove beneficial in stimulating Cl- secretion across airway cells without promoting alveolar edema.

Mechanistic considerations for formaldehyde-induced bronchoconstriction involving S-nitrosoglutathione reductase

Inhalation of formaldehyde vapor has long been suspected of producing airway pathophysiology such as asthma and hyperresponsivity, presumably via irritant mechanisms. Recent studies on asthma and airway biology implicate changes in nitric oxide (NO) disposition in the adverse effects of formaldehyde, principally because enzymatic reduction of the endogenous bronchodilator S-nitrosoglutathione (GSNO) is dependent upon GSNO reductase (formally designated as alcohol dehydrogenase-3, ADH3), which also serves as the primary enzyme for cellular detoxification of formaldehyde. Considering recent evidence that regulation of bronchodilators like GSNO might play a more important role in asthma than inflammation per se, formaldehyde also needs to be considered as influencing ADH3-mediated GSNO catabolism. This is due to changes in ADH3 cofactors and thiol redox state among several potential mechanisms. Data suggest that deregulation of GSNO turnover provides a plausible, enzymatically based mechanism by which formaldehyde might exacerbate asthma and induce bronchoconstriction.

Reductive gas-phase chemiluminescence and flow injection analysis for measurement of the nitric oxide pool in biological matrices

There is growing evidence for nitric oxide (NO.) being involved in cell signaling and pathology. Much effort has been made to elucidate and characterize the different biochemical reaction pathways of NO.in vivo. However, a major obstacle in assessing the significance of nitrosated species and oxidized metabolites often remains: a reliable analytical technique for the detection of NO. in complex biological matrices. This chapter presents refined methodologies, such as chemiluminescence detection and flow injection analysis, compared with adequate sample processing procedures to reliably quantify and assess the circulating and resident NO(.) pool, consisting of nitrite, nitrate, nitroso, and nitrosylated species.

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.

CAT-2 amplifies the agonist-evoked force of airway smooth muscle by enhancing spermine-mediated phosphatidylinositol-(4)-phosphate-5-kinase-gamma activity

We investigated the effect the loss of the CAT-2 gene (CAT-2-/-) has on lung resistance (R(L)) and tracheal isometric tension. The R(L) of CAT-2-/- mice at a maximal dose of acetylcholine (ACh) was decreased by 33.66% (P = 0.05, n = 8) compared with that of C57BL/6 (B6) mice. The isometric tension of tracheal rings from CAT-2-/- mice showed a significant decrease in carbachol (CCh)-induced force generation (33.01%, P < 0.05, n = 8) compared with controls. The isoproterenol- or the sodium nitroprusside-induced relaxation was not affected in tracheal rings from CAT-2-/- mice. The activity of iNOS and arginase in lung tissue lysates of CAT-2-/- mice was indistinguishable from that of B6 mice. Furthermore, the expression of phospholipase-Cbeta (PLC-beta) and phosphatidylinositol-(4)-phosphate-5-kinase-gamma (PIP-5K-gamma) was examined in the lung tissue of CAT-2-/- and B6 mice. The expression of PIP-5K-gamma but not PLC-beta was significantly reduced in CAT-2-/- compared with B6 mice. The reduced airway smooth muscle (ASM) contractility to CCh seen in the CAT-2-/- tracheal rings was completely reversed by pretreating the rings with 100 muM spermine. This increase in the CAT-2-/- tracheal ring contraction upon spermine pretreatment correlated with a recovery of the expression of PIP-5K-gamma. Our data indicates that CAT-2 exerts control over ASM force development through a spermine-dependent pathway that directly correlates with the expression level of PIP-5K-gamma in the lung.

Proteomic methods for analysis of S-nitrosation

This review discusses proteomic methods to detect and identify S-nitrosated proteins. Protein S-nitrosation, the post-translational modification of thiol residues to form S-nitrosothiols, has been suggested to be a mechanism of cellular redox signaling by which nitric oxide can alter cellular function through modification of protein thiol residues. It has become apparent that methods that will detect and identify low levels of S-nitrosated protein in complex protein mixtures are required in order to fully appreciate the range, extent and selectivity of this modification in both physiological and pathological conditions. While many advances have been made in the detection of either total cellular S-nitrosation or individual S-nitrosothiols, proteomic methods for the detection of S-nitrosation are in relative infancy. This review will discuss the major methods that have been used for the proteomic analysis of protein S-nitrosation and discuss the pros and cons of this methodology.

S-Nitrosothiol measurements in biological systems

S-Nitrosothiol (SNO) cysteine modifications are regulated signaling reactions that dramatically affect, and are affected by, protein conformation. The lability of the SNO bond can make SNO-modified proteins cumbersome to measure accurately. Here, we review methodologies for detecting SNO modifications in biology. There are three caveats. (1) Many assays for biological SNOs are used near the limit of detection: standard curves must be in the biologically relevant concentration range. (2) The assays that are most reliable are those that modify SNO protein or peptide chemistry the least. (3) Each result should be quantitatively validated using more than one assay. Improved assays are needed and are in development.

Thiols in nitric oxide synthase-containing Nocardia sp. strain NRRL 5646

Mycothiol (MSH) [1-D-myo-inosityl-2-(N-acetyl-l-cysteinyl)amido-2-deoxy-alpha-D-glucopyranoside], isolated as the bimane derivative, was established to be the major thiol in Nocardia sp. strain NRRL 5646, a species most closely related to Nocardia brasiliensis strain DSM 43758(T). Thiol formation and detection of MSH-dependent formaldehyde dehydrogenase activity in cell extracts are relevant to the possible modulation of nitric oxide toxicity generated by strain NRRL 5646.

S-nitrosylating agents: a novel class of compounds that increase cystic fibrosis transmembrane conductance regulator expression and maturation in epithelial cells

The endogenous bronchodilator, S-nitrosoglutathione (GSNO), increases expression, maturation, and function of both the wild-type and the DeltaF508 mutant of the cystic fibrosis transmembrane conductance regulatory protein (CFTR). Though transcriptional mechanisms of action have been identified, GSNO seems also to have post-transcriptional effects on CFTR maturation. Here, we report that 1) GSNO is only one of a class of S-nitrosylating agents that, at low micromolar concentrations, increase DeltaF508 and wild-type CFTR expression and maturation; 2) NO itself (at these concentrations) and 8-bromocyclic GMP are minimally active on CFTR; 3) a novel agent, S-nitrosoglutathione diethyl ester, bypasses the need for GSNO bioactivation by gamma-glutamyl transpeptidase to increase CFTR maturation; 4) surprisingly, expression-but not S-nitrosylation-of cysteine string proteins (Csp) 1 and 2 is increased by GSNO; 5) the effect of GSNO to increase full maturation of wild-type CFTR is inhibited by Csp silencing (si)RNA; 6) proteins relevant to CFTR trafficking are SNO-modified, and SNO proteins traffic through the endoplasmic reticulum (ER) and Golgi after GSNO exposure; and 7) GSNO alters the interactions of DeltaF508 CFTR with Csp and Hsc70 in the ER and Golgi. These data suggest that GSNO is one of a class of S-nitrosylating agents that act independently of the classic NO radical/cyclic GMP pathway to increase CFTR expression and maturation. They also suggest that the effect of GSNO is dependent on Csp and on intracellular SNO trafficking. We speculate that these data will be of relevance to the development of NO donor-based therapies for CF.

Specific detection of gaseous NO and 15NO in the headspace from liquid-phase reactions involving NO-generating organic, inorganic, and biochemical samples using a mid-infrared laser

Nitric oxide (NO) is an important biological signaling agent. The specific detection of NO represents a continuing challenge in the field of NO research. Many methods are currently employed for the detection of NO. Here, we report a qualitative but specific detection method for gaseous NO liberated in and from solution taking advantage of its low solubility. Importantly, our mid-infrared laser absorption method does not depend on any chemical derivatization of NO, and is applicable over a wide range of concentrations for both protein work and in organic-inorganic modeling work. We also apply this method to the specific detection of 15NO.

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.

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.

Reflex regulation of airway smooth muscle tone

Autonomic nerves in most mammalian species mediate both contractions and relaxations of airway smooth muscle. Cholinergic-parasympathetic nerves mediate contractions, whereas adrenergic-sympathetic and/or noncholinergic parasympathetic nerves mediate relaxations. Sympathetic-adrenergic innervation of human airway smooth muscle is sparse or nonexistent based on histological analyses and plays little or no role in regulating airway caliber. Rather, in humans and in many other species, postganglionic noncholinergic parasympathetic nerves provide the only relaxant innervation of airway smooth muscle. These noncholinergic nerves are anatomically and physiologically distinct from the postganglionic cholinergic parasympathetic nerves and differentially regulated by reflexes. Although bronchopulmonary vagal afferent nerves provide the primary afferent input regulating airway autonomic nerve activity, extrapulmonary afferent nerves, both vagal and nonvagal, can also reflexively regulate autonomic tone in airway smooth muscle. Reflexes result in either an enhanced activity in one or more of the autonomic efferent pathways, or a withdrawal of baseline cholinergic tone. These parallel excitatory and inhibitory afferent and efferent pathways add complexity to autonomic control of airway caliber. Dysfunction or dysregulation of these afferent and efferent nerves likely contributes to the pathogenesis of obstructive airways diseases and may account for the pulmonary symptoms associated with extrapulmonary disorders, including gastroesophageal reflux disease, cardiovascular disease, and rhinosinusitis.

Overexpression of endothelial nitric oxide synthase suppresses features of allergic asthma in mice

Background

Asthma is associated with airway hyperresponsiveness and enhanced T-cell number/activity on one hand and increased levels of exhaled nitric oxide (NO) with expression of inducible NO synthase (iNOS) on the other hand. These findings are in paradox, as NO also relaxes airway smooth muscle and has immunosuppressive properties. The exact role of the endothelial NOS (eNOS) isoform in asthma is still unknown. We hypothezised that a delicate regulation in the production of NO and its bioactive forms by eNOS might be the key to the pathogenesis of asthma.

Methods

The contribution of eNOS on the development of asthmatic features was examined. We used transgenic mice that overexpress eNOS and measured characteristic features of allergic asthma after sensitisation and challenge of these mice with the allergen ovalbumin.

Results

eNOS overexpression resulted in both increased eNOS activity and NO production in the lungs. Isolated thoracic lymph nodes cells from eNOS overexpressing mice that have been sensitized and challenged with ovalbumin produced significantly less of the cytokines IFN-γ, IL-5 and IL-10. No difference in serum IgE levels could be found. Further, there was a 50% reduction in the number of lymphocytes and eosinophils in the lung lavage fluid of these animals. Finally, airway hyperresponsiveness to methacholine was abolished in eNOS overexpressing mice.

Conclusion

These findings demonstrate that eNOS overexpression attenuates both airway inflammation and airway hyperresponsiveness in a model of allergic asthma. We suggest that a delicate balance in the production of bioactive forms of NO derived from eNOS might be essential in the pathophysiology of asthma.

Circulating NO Pool in Humans

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

S-nitrosothiol signaling in respiratory biology

Genetic and biochemical data demonstrate a pivotal role for S-nitrosothiols (SNOs) in mediating the actions of nitric oxide synthases (NOSs). SNOs serve to convey NO bioactivity and to regulate protein function. This understanding is of immediate interest to the pulmonary clinical and research communities. This article reviews the following: (1) biochemical and cellular evidence that SNOs in amino acids, peptides, and proteins elicit NOS-dependent signaling in the respiratory system and (2) studies that link SNO signaling to pulmonary medicine. SNO-mediated signaling is involved in the regulation of minute ventilation, ventilation-perfusion matching, pulmonary arterial pressure, basal airway tone, and respiratory and peripheral muscle function. Derangements in SNO signaling are implicated in many disorders relevant to pulmonary and critical care medicine, including apnea, hypoxemia, pulmonary hypertension, asthma, cystic fibrosis, pneumonia, and septic shock.

Reactive nitrogen species in the respiratory tract

Endogenous Nitric Oxide (NO) plays a key role in the physiological regulation of airway functions. In response to various stimuli activated inflammatory cells (e.g., eosinophils and neutrophils) generate oxidants ("oxidative stress") which in conjunction with exaggerated enzymatic release of NO and augmented NO metabolites produce the formation of strong oxidizing reactive nitrogen species, such as peroxynitrite, in various airway diseases including asthma, chronic obstructive pulmonary diseases (COPD), cystic fibrosis and acute respiratory distress syndrome (ARDS). Reactive nitrogen species provoke amplification of inflammatory processes in the airways and lung parenchyma causing DNA damage, inhibition of mitochondrial respiration, protein dysfunction and cell damage ("nitrosative stress"). These effects alter respiratory homeostasis (such as bronchomotor tone and pulmonary surfactant activity) and the long-term persistence of "nitrosative stress" may contribute to the progressive deterioration of pulmonary functions leading to respiratory failure. Recent studies showing that protein nitration can be dynamic and reversible ("denitration mechanisms") open new horizons in the treatment of chronic respiratory diseases affected by the deleterious actions of "nitrosative stress".

Modulation of nitric oxide pathways: therapeutic potential in asthma and chronic obstructive pulmonary disease

Nitric oxide (NO) is present in the exhaled breath of humans and other mammalian species. It is generated in the lower airways by enzymes of the nitric oxide synthase (NOS) family, although nonenzymatic synthesis and consumptive processes may also influence levels of NO in exhaled breath. The biological properties of NO in the airways are multiple, complex, and bidirectional. Under physiological conditions, NO appears to play a homeostatic bronchoprotective role. However, its proinflammatory properties could also potentially cause tissue injury and contribute to airway dysfunction in disease states such as asthma and chronic obstructive pulmonary disease (COPD). This article will review the physiological and pathophysiological roles of NO in the airways, discuss the rationale for the use of drugs that modulate NO pathways--nitric oxide synthase inhibitors and NO donors--to treat inflammatory airway diseases, and attempt to predict the likely therapeutic benefit of such agents.

Oxidative stress in asthma and COPD: antioxidants as a therapeutic strategy

Asthma and chronic obstructive pulmonary disease (COPD) are inflammatory lung diseases that are characterized by systemic and chronic localized inflammation and oxidative stress. Sources of oxidative stress arise from the increased burden of inhaled oxidants, as well as elevated amounts of reactive oxygen species (ROS) released from inflammatory cells. Increased levels of ROS, either directly or via the formation of lipid peroxidation products, may play a role in enhancing the inflammatory response in both asthma and COPD. Moreover, in COPD it is now recognized as the main pathogenic factor for driving disease progression and increasing severity. ROS and lipid peroxidation products can influence the inflammatory response at many levels through its impact on signal transduction mechanisms, activation of redox-sensitive transcriptions factors, and chromatin regulation resulting in pro-inflammatory gene expression. It is this impact of ROS on chromatin regulation by reducing the activity of the transcriptional co-repressor, histone deacetylase-2 (HDAC-2), that leads to the poor efficacy of corticosteroids in COPD, severe asthma, and smoking asthmatics. Thus, the presence of oxidative stress has important consequences for the pathogenesis, severity, and treatment of asthma and COPD. However, for ROS to have such an impact, it must first overcome a variety of antioxidant defenses. It is likely, therefore, that a combination of antioxidants may be effective in the treatment of asthma and COPD. Various approaches to enhance the lung antioxidant screen and clinical trials of antioxidant compounds are discussed.

Mechanisms of cystic fibrosis transmembrane conductance regulator activation by S-nitrosoglutathione

We investigated the mechanisms by which S-nitrosoglutathione (GSNO) alters cystic fibrosis transmembrane conductance regulator (CFTR) mediated chloride (Cl(-)) secretion across Calu-3 cells, an extensively used model of human airway gland serous cells. Confluent monolayers of Calu-3 cells, grown under an air-liquid interface, were mounted in Ussing chambers for the measurements of chloride short circuit current (I(sc)) and trans-epithelial resistance (R(t)). Addition of GSNO into the apical compartment of these chambers resulted in significant and sustained increase of I(sc) with an IC(50) of 3.2 +/- 1 mum (mean +/- 1 S.E.; n = 6). Addition of either glibenclamide or pre-treatment of Calu-3 cells with the soluble guanylate cyclase inhibitor 1H-(1,2,4)-oxadiazolo[4,3-a]quinoxalin-1-one totally prevented the GSNO-induced increase of I(sc). Conversely, BAY 41-2272, a sGC stimulator, increased I(sc) in a dose-response fashion. The GSNO increase of I(sc) was reversed by addition of two phosphatases (PP2A1, PP2A2) into the apical compartment of Ussing chambers containing Calu-3 monolayers. Oxy-myoglobin (oxy-Mb, 300 mum) added into the apical compartment of Ussing chambers either prior or after GSNO either completely prevented or immediately reversed the increase of I(sc). However, smaller concentrations of oxy-Mb (1-10 mum), sufficient to scavenge NO in the medium (as assessed by direct measurement of NO in the Ussing chamber using an ISO-NO meter) decreased I(sc) partially. Oxy-Mb did not reverse the increase of I(sc) following addition of GSNO and cysteine (50 mum). These findings indicate that GSNO stimulates Cl secretion via both cGMP-dependent and cGMP-independent mechanisms.

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.

Exhaled nitric oxide in paediatric asthma

Assessment of airway function is difficult in young children with asthma, and in addition, only reflects the status of the disease at the time of the measurement. Thus, there is increasing interest in monitoring airway inflammation in asthma, which may provide a longer term assessment of disease activity. Most methods of assessing asthmatic inflammation are invasive, and are not feasible in the paediatric population. This review discusses exhaled nitric oxide as a marker of asthmatic inflammation, and compares it with other recognized markers. Exhaled nitric oxide has the potential to become a noninvasive method of assessing asthma control in the paediatric population.

Assaying all of the nitrogen oxides in breath modifies the interpretation of exhaled nitric oxide

Exhaled nitric oxide (NO) assays measure the quantity of NO that emanates from the airway, not the amount of NO that is formed. Consumptive processes-including oxidation reactions-decrease the amount of gas phase NO available for exhalation. Higher oxides of nitrogen (HiNO(x)) are resulting reaction products, and are easily measured in exhaled breath condensate (EBC). We performed concurrent sampling of exhaled breath for gas phase NO and EBC HiNO(x) in controls and stable asthmatics. We identified that, mole for mole, asthma patients hourly exhale more HiNO(x) than they do NO, with a HiNO(x)/NO ratio of 1.21 (0.54-3.4). This is the reverse of the ratio found in controls, in whom the HiNO(x)/NO ratio was 0.75 (0.44-0.93), p=0.04. The sum of the hourly molar exhalation of NO and HiNO(x) was significantly higher in asthmatics (333 nmol/h (221-543) than controls (179 (138-231), p<0.001). We conclude that exhaled oxides of nitrogen are more informative when measured together as opposed to in isolation. We suggest that inflammation can be better evaluated with HiNO(x) and NO measured concurrently, and that the level of oxidation in the lung can be evaluated by comparing the easily measured ratios of HiNO(x) to NO in the exhaled breath.

SNOR and wheeze: the asthma enzyme?

Conventionally, asthma is defined as involving both airway inflammation and airway smooth muscle hyper-responsiveness. However, Que and coworkers have recently uncoupled these concepts, showing that mice lacking an S-nitrosothiol reductase have allergen-induced airway inflammation but do not have airway hyper-responsiveness. These data are consistent with recent clinical evidence that: (i) S-nitrosothiol signaling is abnormal in human asthma, (ii) nitric oxide in exhaled air might be only a biomarker for the metabolism of more physiologically relevant nitrogen oxides and (iii) the biochemical response to airway inflammation is central to asthma pathophysiology.

Influence of different therapeutic strategies on exhaled NO and lung inflammation in asthma and COPD

Nitric oxide (NO), a simple free radical gas, elicits a diverse range of physiological and pathophysiological effects, and plays an important role in pulmonary diseases. Nitrosative stress and nitration of proteins in airway epithelium maybe responsible for steroid resistance in asthma and their ineffectiveness in chronic obstructive pulmonary disease (COPD), supporting the potential role of future therapeutic strategies aimed at regulating NO synthesis in asthma and COPD. Here, we have reviewed the potential role of NO modulators (NO synthase inhibitors and NO donors), which if given on a regular basis may have clinical benefit in asthma and COPD.

Soluble guanylyl cyclase expression is reduced in allergic asthma

Soluble guanylyl cyclase (sGC) is an enzyme highly expressed in the lung that generates cGMP contributing to airway smooth muscle relaxation. To determine whether the bronchoconstriction observed in asthma is accompanied by changes in sGC expression, we used a well-established murine model of allergic asthma. Histological and biochemical analyses confirmed the presence of inflammation in the lungs of mice sensitized and challenged with ovalbumin (OVA). Moreover, mice sensitized and challenged with OVA exhibited airway hyperreactivity to methacholine inhalation. Steady-state mRNA levels for all sGC subunits (alpha1, alpha2, and beta1) were reduced in the lungs of mice with allergic asthma by 60-80%, as estimated by real-time PCR. These changes in mRNA were paralleled by changes at the protein level: alpha1, alpha2, and beta1 expression was reduced by 50-80% as determined by Western blotting. Reduced alpha1 and beta1 expression in bronchial smooth muscle cells was demonstrated by immunohistochemistry. To study if sGC inhibition mimics the airway hyperreactivity seen in asthma, we treated naïve mice with a selective sGC inhibitor. Indeed, in mice receiving ODQ the methacholine dose response was shifted to the left. We conclude that sGC expression is reduced in experimental asthma contributing to the observed airway hyperreactivity.

Protection from experimental asthma by an endogenous bronchodilator

Mechanisms that protect against asthma remain poorly understood. S-nitrosoglutathione (GSNO), an endogenous bronchodilator, is depleted from asthmatic airways, suggesting a protective role. We report that, following allergen challenge, wild-type mice exhibiting airway hyperresponsivity have increased airway levels of the enzyme GSNO reductase (GSNOR) and are depleted of lung S-nitrosothiols (SNOs). In contrast, mice with genetic deletion of GSNOR exhibit increases in lung SNOs and are protected from airway hyperresponsivity. Our results indicate that endogenous SNOs, governed by GSNOR, are critical regulators of airway responsivity and may provide new therapeutic approaches to asthma.