Multiple roles of nitric oxide in the airways

Asymmetric dimethylarginine potentiates lung inflammation in a mouse model of allergic asthma

Nitric oxide (NO), formed by nitric oxide synthase (NOS), is an important mediator of lung inflammation in allergic asthma. Asymmetric dimethylarginine (ADMA), a competitive endogenous inhibitor of NOS, is metabolized by the enzyme dimethylarginine dimethylaminohydrolase (DDAH). Elevated ADMA has been shown to affect lung function in mice, and by inhibiting NOS it alters NO and reactive oxygen species production in mouse lung epithelial cells. However, the effects of altered ADMA levels during lung inflammation have not been explored. A model of allergen-induced airway inflammation was utilized in combination with the modulation of endogenous circulating ADMA levels in mice. Airway inflammation was assessed by quantifying inflammatory cell infiltrates in lung lavage and by histology. Lung DDAH expression was assessed by quantitative PCR and immunohistochemistry. Nitrite levels were determined in lung lavage fluid as a measure of NO production. iNOS expression was determined by immunohistochemistry, immunofluorescence, Western blot, and quantitative PCR. NF-κB binding activity was assessed by a transcription factor binding assay. Allergen-induced lung inflammation was potentiated in mice with elevated circulating ADMA and was reduced in mice overexpressing DDAH. Elevated ADMA reduced nitrite levels in lung lavage fluid in both allergen-challenged and control animals. ADMA increased iNOS expression in airway epithelial cells in vivo following allergen challenge and in vitro in stimulated mouse lung epithelial cells. ADMA also increased NF-κB binding activity in airway epithelial cells in vitro. These data support that ADMA may play a role in inflammatory airway diseases such as asthma through modulation of iNOS expression in lung epithelial cells.

Exercise regulates heat shock proteins and nitric oxide

Heat shock proteins (HSP) produced during exercise have important roles in modulating the effects of oxidative stresses to preserve cellular function. The ability of HSP to regulate nitric oxide, which has both protective and detrimental effects on the airways and circulation, may have implications for exercise-induced asthma. Exercise regulates HSP and nitric oxide interactions and protects against organ dysfunction and oxidative stresses.

Patterned electrode-based amperometric gas sensor for direct nitric oxide detection within microfluidic devices

This article describes a thin amperometric nitric oxide (NO) sensor that can be microchannel embedded to enable direct real-time detection of NO produced by cells cultured within the microdevice. A key for achieving the thin ( approximately 1 mm) planar sensor configuration required for sensor-channel integration is the use of gold/indium-tin oxide patterned electrode directly on a porous polymer membrane (pAu/ITO) as the base working electrode. The electrochemically deposited Au-hexacyanoferrate layer on pAu/ITO is used to catalyze NO oxidation to nitrite at lower applied potentials (0.65-0.75 V vs Ag/AgCl) and stabilize current output. Furthermore, use of a gas-permeable membrane to separate internal sensor compartments from the sample phase imparts excellent NO selectivity over common interfering agents (e.g., nitrite, ascorbate, ammonia, etc.) present in culture media and biological fluids. The optimized sensor design reversibly detects NO down to the approximately 1 nM level in stirred buffer and <10 nM in flowing buffer when integrated within a polymeric microfluidic device. We demonstrate utility of the channel-embedded sensor by monitoring NO generation from macrophages cultured within non-gas-permeable microchannels, as they are stimulated with endotoxin.

Concomitant administration of nitric oxide and glucocorticoids improves protection against bronchoconstriction in a murine model of asthma

Glucocorticoids (GC) remain the first choice of treatment in asthma, but GC therapy is not always effective and is associated with side effects. In a porcine study in our laboratory, simultaneous administration of GC and nitric oxide (NO) attenuated the endotoxin-induced inflammatory response and made GC treatment more effective than inhaled NO or steroids alone. In the present study, we aimed to further investigate the interactions between NO and GC treatment in two murine models of asthma. Inflammation was induced by endotoxin, ovalbumin, or a combination of both. With an animal ventilator and a forced oscillation method (FlexiVent), lung mechanics and airway reactivity to methacholine in response to various treatments were assessed. We also describe histology and glucocorticoid receptor (GR) protein expression in response to inhaled NO treatment [40 ppm NO gas or NO donors sodium nitroprusside (SNP) or diethylamine NONOate (DEA/NO)]. SNP and GC provided protection against bronchoconstriction to a similar degree in the model of severe asthma. When GC-treated mice were given SNP, maximum airway reactivity was further reduced. Similar effects were seen after DEA/NO delivery to GC-treated animals. Using 1-H-[1,2,4]-oxadiazolo-[4,3-a]-quinoxalin-1-one (ODQ), a soluble guanylate cyclase inhibitor, we found this effect of NO donors to be mediated through a cGMP-independent mechanism. In the severe model, prolonged NO treatment restored or even increased the nuclear levels of GR. In conclusion, in our murine model of severe asthma GC treatment provided protection to only a limited degree against bronchoconstriction, while concomitant treatment with a NO donor was markedly more potent than the use of either NO or GC alone.

Induced sputum nitrites correlate with FEV1 in children with cystic fibrosis

AIM

To determine the difference in the levels of nitrites in induced sputum of children with cystic fibrosis (CF) and controls. Furthermore, to evaluate the association between induced sputum nitrites and lung function in children with CF.

METHODS

Nitrites, cell differentials, white blood cell count, were estimated in induced sputum of 20 children with CF and 10 age-matched healthy controls. Nitrites in induced sputum samples were measured using the Greiss assay. Lung function was ascertained by spirometry.

RESULTS

We observed high levels of nitrites in CF (184.8 +/- 11.07 microM/L) versus controls (56.4 +/- 5.7 microM/L) (p < 0.01). A positive correlation between neturophil percent and nitrites, white blood cell count and nitrites (p < 0.05) in children with CF was observed. Sputum nitrites correlated negatively with FEV(1) (p < 0.05) in children with CF.

CONCLUSION

Induced sputum nitrite could serve as a useful non invasive marker for assessing the degree of inflammation in the airways of children with CF.

Nitric oxide in both bronchoalveolar lavage fluid and serum is associated with pathogenesis and severity of antigen-induced pulmonary inflammation in rats

BACKGROUND

Nitric oxide (NO) is considered as a hallmark for allergic airway inflammation in asthmatics and animal models. But the correlation between NO and antigen-induced pulmonary inflammation (AIPI), a rat model for asthma, in varying genetic background population has not been completely understood.

OBJECTIVE

The objective in this study is to observe the different responsiveness to AIPI in two commonly used inbred rat strains and verify the correlation between NO from different sources and pathological parameters of AIPI by using Dark Agouti (DA), E3, F1 (E3 x DA), and F2 rat populations.

METHODS

AIPI was induced by systemically immunizing and intranasally challenging E3, DA, F1 (DA x E3), and F2 rats with ovalbumin (OVA). Pathological changes and mucus secretion in lungs were observed after hematoxylin and eosin (HE) and periodic acid Schiff (PAS) staining, whereas eosinophils in bronchoalveolar lavage fluid (BALF) were counted after Giemsa staining. Delayed-type hyperresponsiveness was determined by subcutaneous injection of OVA in ear. Total immunoglobulin E (IgE) and OVA-specific IgG1 were detected with enzyme-linked immunosorbent assay (ELISA). NO concentration was measured by the Griess method.

RESULTS

DA rats were unresponsive to OVA treatment, whereas E3 rats were susceptible to AIPI. F1 rats manifested the same responsiveness to OVA treatment as DA rats, and individual F2 rats showed the variable severity of AIPI. NO concentration in BALF and serum was significantly elevated in E3 rats but not in DA and F1 rats after OVA treatment. In F2 rats, NO concentration in serum was positively correlated with eosinophils in BALF, total IgE, and pathological scores, whereas NO concentration in BALF correlated only with eosinophils in BALF and total IgE.

CONCLUSION

DA and F1 rats are resistant, whereas E3 rats are sensitive, to AIPI. NO in serum can represent the severity of allergic inflammation and pathological changes in lungs in F2 population.

Exhaled nitric oxide in the diagnosis and management of childhood asthma

The management of asthma in children and adolescents is currently guided by assessment of clinical symptoms, exacerbation risk and spirometric measure of lung function. The use of biomarkers, an objective measure which indicates normal or pathophysiologic processes and/or the response to a treatment intervention, could greatly enhance the efficacy and safety of current algorithms. Measurement of the fraction of expired nitric oxide in exhaled air (FeNO) has been suggested as a readily determined biomarker that can aid in the diagnosis and management of asthma. FeNO has been used to identify steroid responsive patients, adjust the dose of controller medications, most notably inhaled corticosteroids, and predict relapse during medication taper. In spite of early enthusiasm for the utility of this measure, more recent data suggest a more limited role for FeNO. This review will focus on the use of FeNO in the diagnosis and management of asthma in children and adolescents.

Inhibitory effect of melatonin on lung oxidative stress induced by respiratory syncytial virus infection in mice

Previous research has shown that antioxidant (butylated hydroxyanisole) treatment ameliorates respiratory syncytial virus (RSV)-induced disease and lung inflammation. Melatonin has been reported to exhibit a wide varieties of biological effects, including antioxidant and anti-inflammation, and has no evident toxicity and side effect. But it is not known whether melatonin would modify RSV-induced lung disease and oxidative stress. The present study was to establish the involvement of oxidative stress in the pathogenesis of RSV-induced lung inflammation, and to investigate the protective effect of administration of melatonin in mice with RSV-induced oxidative pulmonary injury for 4 days. Malondialdehyde (MDA), an end product of lipid peroxidation, and glutathione (GSH) and superoxide dismutase (SOD) and nitric oxide (NO) levels were evaluated in lung tissue homogenates by spectrophotometry. Hydroxyl radical (.-OH), one of the indicators of free radical formation, was also detected in lung homogenates by Fenton reaction. Tumor necrosis factor-a (TNF-a) concentrations in mouse serum were measured with ELISA assay. The results demonstrated that the mice intranasally inoculated with RSV resulted in oxidative stress changes by increasing NO, MDA and .-OH levels, and decreasing GSH and SOD activities, whereas administration of melatonin significantly reversed all these effects. Furthermore, melatonin inhibited production of proinflammatory cytokines such as TNF-a in serum of RSV-infected mice. These results suggest that melatonin ameliorates RSV-induced lung inflammatory injury in mice via inhibition of oxidative stress and proinflammatory cytokine production and may be as a novel therapeutic agent in virus-induced pulmonary infection.

Red wine polyphenolic compounds inhibit tracheal smooth muscle contraction during allergen-induced hyperreactivity of the airways

The aims of the study were to investigate the short and long-term effects of Provinol (red wine polyphenolic compounds) on tracheal smooth muscle reactivity using an in-vitro model of ovalbumin-induced airway inflammation in guinea-pig trachea, and to evaluate the role of nitric oxide (NO) in the bronchodilatory effect of Provinol.

The amplitude of tracheal smooth muscle contraction in response to mediators of bronchoconstriction —histamine (10 nM-1 mM), acetylcholine (10 nM-1 mM) and to allergen (ovalbumin 10−5-10−3 g mL−1) was used as a parameter of tracheal smooth muscle reactivity. To test the short-term effects of Provinol, isolated tracheal strips were pre-treated for 30 min with Provinol (10−4mg mL−1) alone or in combination with Nω-nitro-L-arginine methyl ester (L-NAME; 10−6mol L−1). To test the long-term effects of Provinol, isolated tracheal strips were prepared from guinea pigs that had been treated for 14 days with Provinol (20mg kg−1 per day) alone or in combination with L-NAME (40 mg kg−1 per day).

Incubation of tracheal smooth muscle with Provinol decreased the amplitude of contraction in response to ovalbumin, histamine and acetylcholine. The non-selective NO synthase inhibitor L-NAME partially abolished the effect of Provinol on acetylcholine and ovalbumin-induced but not histamine-induced bronchoconstriction. A similar profile was observed after 14 days' oral administration of Provinol.

In conclusion, Provinol inhibited the allergen- and spasmogen-induced contraction of tracheal smooth muscle in ovalbumin-sensitized guinea pigs via a mechanism that was mediated at least partially through the metabolism of NO.

Inducible nitric oxide synthase inhibition attenuates lung tissue responsiveness and remodeling in a model of chronic pulmonary inflammation in guinea pigs

We evaluated the influence of iNOS-derived NO on the mechanics, inflammatory, and remodeling process in peripheral lung parenchyma of guinea pigs with chronic pulmonary allergic inflammation. Animals treated or not with 1400 W were submitted to seven exposures of ovalbumin in increasing doses. Seventy-two hours after the 7th inhalation, lung strips were suspended in a Krebs organ bath, and tissue resistance and elastance measured at baseline and after ovalbumin challenge. The strips were submitted to histopathological measurements. The ovalbumin-exposed animals showed increased maximal responses of resistance and elastance (p<0.05), eosinophils counting (p<0.001), iNOS-positive cells (p<0.001), collagen and elastic fiber deposition (p<0.05), actin density (p<0.05) and 8-iso-PGF2alpha expression (p<0.001) in alveolar septa compared to saline-exposed ones. Ovalbumin-exposed animals treated with 1400 W had a significant reduction in lung functional and histopathological findings (p<0.05). We showed that iNOS-specific inhibition attenuates lung parenchyma constriction, inflammation, and remodeling, suggesting NO-participation in the modulation of the oxidative stress pathway.

Alveolar and bronchial nitric oxide output in healthy children

Exhaled nitric oxide (NO) concentration is a marker of pulmonary inflammation. It is usually measured at a single exhalation flow rate. However, measuring exhaled NO at multiple flow rates allows assessment of the flow-independent NO parameters: alveolar NO concentration, bronchial NO flux, bronchial wall NO concentration, and bronchial diffusing capacity of NO. Our aim was to determine the flow-independent NO parameters in healthy schoolchildren and to compare two different mathematical approaches. Exhaled NO was measured at four flow rates (10, 50, 100, and 200 ml/sec) in 253 schoolchildren (7-13 years old). Flow-independent NO parameters were calculated with linear method (flows >or=50 ml/sec) and non-linear method (all flows). Sixty-six children (32 boys and 34 girls) with normal spirometry and no history or present symptoms of asthma, allergy, atopy or other diseases were included in the analysis. Median bronchial NO flux was 0.4 nl/sec (mean +/- SD: 0.5 +/- 0.3 nl/sec) and median alveolar NO concentration was 1.9 ppb (2.0 +/- 0.8 ppb) with the linear method. Bronchial NO flux correlated positively with height (r = 0.423; P < 0.001), FEV(1) (r = 0.358; P = 0.003), and FVC (r = 0.359; P = 0.003). With the non-linear method, median bronchial wall NO concentration was 49.6 ppb (68.0 +/- 53.3 ppb) and bronchial diffusing capacity of NO was 10.0 pl/sec/ppb (11.8 +/- 7.5 pl/sec/ppb). The non-linear method gave lower alveolar NO concentration (1.4 [1.5 +/- 0.7] ppb, P < 0.001) and higher bronchial NO flux (0.5 [0.6 +/- 0.3] nl/sec, P < 0.001) than the linear method, but the results were highly correlated between the two methods (r = 0.854 and r = 0.971, P < 0.001). In conclusion, the multiple flow rate method is feasible in children but different mathematical methods give slightly different results. Reference values in healthy children are of value when applying bronchial and alveolar NO parameters in the diagnostics and follow-up of inflammatory lung diseases.

Elevated asymmetric dimethylarginine alters lung function and induces collagen deposition in mice

Increasing evidence suggests that lung mechanics and structure are maintained in part by an intimate balance between the L-arginine-metabolizing enzymes nitric oxide synthase (NOS) and arginase. Asymmetric dimethylarginine (ADMA) is a competitive endogenous inhibitor of NOS. The role of ADMA in the regulation of NOS and arginase in the airways has not yet been explored. Our objective was to investigate the role of ADMA in lung physiology. A murine model of continuous subcutaneous ADMA infusion via osmotic minipump was used for assessment of elevated ADMA in vivo, and primary lung fibroblasts were used for in vitro assessments. Two weeks after minipump placement, animals were anesthetized and mechanically ventilated, and lung mechanical responses were evaluated. Lungs were assessed histologically and biochemically for collagen content, arginase activity, and arginase protein levels. Lung lavage fluid was assessed for cellularity, nitrite, urea, and cytokine concentrations. ADMA infusion resulted in significantly enhanced lung resistance and decreased dynamic compliance in response to methacholine. These physiologic changes were associated with significantly increased lung collagen content in the absence of inflammation. Significant decreases in lung fluid nitrite were accompanied by elevated lung fluid urea and arginase activity in lung homogenates. These changes were reversed in mice 4 weeks after completion of ADMA administration. In addition, treatment of primary mouse lung fibroblasts with ADMA stimulated arginase activity and collagen formation in vitro. These data support the idea that ADMA may play a role in airway diseases, including asthma and pulmonary fibrosis, through NOS inhibition and enhancement of arginase activity.

Partitioned exhaled nitric oxide to non-invasively assess asthma

Asthma is a chronic inflammatory disease of the lungs, characterized by airway hyperresponsiveness. Chronic repetitive bouts of acute inflammation lead to airway wall remodeling and possibly the sequelae of fixed airflow obstruction. Nitric oxide (NO) is a reactive molecule synthesized by NO synthases (NOS). NOS are expressed by cells within the airway wall and functionally, two NOS isoforms exist: constitutive and inducible. In asthma, the inducible isoform is over expressed, leading to increased production of NO, which diffuses into the airway lumen, where it can be detected in the exhaled breath. The exhaled NO signal can be partitioned into airway and alveolar components by measuring exhaled NO at multiple flows and applying mathematical models of pulmonary NO dynamics. The airway NO flux and alveolar NO concentration can be elevated in adults and children with asthma and have been correlated with markers of airway inflammation and airflow obstruction in cross-sectional studies. Longitudinal studies which specifically address the clinical potential of partitioning exhaled NO for diagnosis, managing therapy, and predicting exacerbation are needed.

Bordetella bronchiseptica responses to physiological reactive nitrogen and oxygen stresses

Bordetella bronchiseptica can establish prolonged airway infection consistent with a highly developed ability to evade mammalian host immune responses. Upon initial interaction with the host upper respiratory tract mucosa, B. bronchiseptica are subjected to antimicrobial reactive nitrogen species (RNS) and reactive oxygen species (ROS), effector molecules of the innate immune system. However, the responses of B. bronchiseptica to redox species at physiologically relevant concentrations (nM-microM) have not been investigated. Using predicted physiological concentrations of nitric oxide (NO), superoxide and hydrogen peroxide (H2O2) on low numbers of CFU of B. bronchiseptica, all redox active species displayed dose-dependent antimicrobial activity. Susceptibility to individual redox active species was significantly increased upon introduction of a second species at subantimicrobial concentrations. An increased bacteriostatic activity of NO was observed relative to H2O2. The understanding of Bordetella responses to physiologically relevant levels of exogenous RNS and ROS will aid in defining the role of endogenous production of these molecules in host innate immunity against Bordetella and other respiratory pathogens.

Exhaled nitric oxide monitoring in COPD using a portable analyzer

BACKGROUND

The exhaled nitric oxide (FeNO) is a non-invasive marker of airway inflammation in asthma. A very recent statement has suggested FeNO as potential outcome in chronic obstructive pulmonary disease (COPD). Recently, a new hand-held FeNO analyzer (NIOX MINO) has been developed.

PATIENTS AND METHODS

We have evaluated the NIOX MINO in COPD patients and monitored FeNO levels during 1-year assessment in the outpatient setting. Short-term variability in FeNO was compared using a NIOX MINO and a stationary chemiluminescence analyzer (NOA, Sensormedics) in healthy volunteers and COPD patients on two consecutive months. Long-term FeNO variability was assessed on a cohort of 70 COPD outpatients measuring FeNO for 1 year. The intra-individual FeNO coefficient of variation (eNOCoV) was taken as index FeNO long-term variability.

RESULTS

In COPD there were no significant differences between NIOX MINO and NOA FeNO values recorded at baseline and 1 month later. Ninety five percent limits of agreement between NIOX MINO and NOA were-2.7 and 1.9ppb with significant reliability (r=0.96, p<0.0001). Mean FeNO at baseline was 15.0+/-9.5ppb. Over the 1-year period the overall mean FeNO was 15.5+/-10.1ppb. The long-term eNOCoV was 33.9+/-16.4% (range 8.1-83.1%), and it was significantly associated with exacerbation rate (r=0.57, p<0.0001).

CONCLUSION

FeNO electrochemical hand-held analyzer is feasible in COPD showing good agreement with stationary chemiluminescence analyzer. COPD patients exhibit a wide range of FeNO levels and a high variability of FeNO over time, which was positively associated with the number of exacerbations.

Arginase and pulmonary diseases

Recent studies have indicated that arginase, which converts L-arginine into L-ornithine and urea, may play an important role in the pathogenesis of various pulmonary disorders. In asthma, chronic obstructive pulmonary disease (COPD) and cystic fibrosis, increased arginase activity in the airways may contribute to obstruction and hyperresponsiveness of the airways by inducing a reduction in the production of bronchodilatory nitric oxide (NO) that results from its competition with constitutive (cNOS) and inducible (iNOS) NO synthases for their common substrate. In addition, reduced L-arginine availability to iNOS induced by arginase may result in the synthesis of both NO and the superoxide anion by this enzyme, thereby enhancing the production of peroxynitrite, which has procontractile and pro-inflammatory actions. Increased synthesis of L-ornithine by arginase may also contribute to airway remodelling in these diseases. L-Ornithine is a precursor of polyamines and L-proline, and these metabolic products may promote cell proliferation and collagen production, respectively. Increased arginase activity may also be involved in other fibrotic disorders of the lung, including idiopathic pulmonary fibrosis. Finally, through its action of inducing reduced levels of vasodilating NO, increased arginase activity has been associated with primary and secondary forms of pulmonary hypertension. Drugs targeting the arginase pathway could have therapeutic potential in these diseases.

Arginine homeostasis in allergic asthma

Allergic asthma is a chronic disease characterized by early and late asthmatic reactions, airway hyperresponsiveness, airway inflammation and airway remodelling. Changes in l-arginine homeostasis may contribute to all these features of asthma by decreased nitric oxide (NO) production and increased formation of peroxynitrite, polyamines and l-proline. Intracellular l-arginine levels are regulated by at least three distinct mechanisms: (i) cellular uptake by cationic amino acid (CAT) transporters, (ii) metabolism by NO-synthase (NOS) and arginase, and (iii) recycling from l-citrulline. Ex vivo studies using animal models of allergic asthma have indicated that attenuated l-arginine bioavailability to NOS causes deficiency of bronchodilating NO and increased production of procontractile peroxynitrite, which importantly contribute to allergen-induced airway hyperresponsiveness after the early and late asthmatic reaction, respectively. Decreased cellular uptake of l-arginine, due to (eosinophil-derived) polycations inhibiting CATs, as well as increased consumption by increased arginase activity are major causes of substrate limitation to NOS. Increasing substrate availability to NOS by administration of l-arginine, l-citrulline, the polycation scavenger heparin, or an arginase inhibitor alleviates allergen-induced airway hyperresponsiveness by restoring the production of bronchodilating NO. In addition, reduced l-arginine levels may contribute to the airway inflammation associated with the development of airway hyperresponsiveness, which similarly may involve decreased NO synthesis and increased peroxynitrite formation. Increased arginase activity could also contribute to airway remodelling and persistent airway hyperresponsiveness in chronic asthma via increased synthesis of l-ornithine, the precursor of polyamines and l-proline. Drugs that increase the bioavailability of l-arginine in the airways - particularly arginase inhibitors - may have therapeutic potential in allergic asthma.

Racial differences in nitric oxide-dependent vasorelaxation

Along with the growing heterogeneity of the American population, ethnic/racial disparity is becoming a clear health issue in the United States. The awareness of ethnic/racial disparities has been growing because of considerable data gathered from recent clinical and epidemiological studies. These studies have highlighted the importance of addressing these differences in the diagnosis and treatment of various diseases potentially according to race. It is becoming particularly clear that there is a 2- to 3-fold racial difference in certain cardiovascular diseases (eg, preeclampsia) associated with dysfunctional nitric oxide-mediated vasodilation. In this review, the authors summarize the current literature on racial disparities in nitric oxide-mediated vasodilation in relation to cardiovascular health with an emphasis on vascular nitric oxide bioavailability as a balance between production via endothelial nitric oxide synthase and degradation through reactive oxygen species. The major hypotheses postulated on the biological basis of these differences are also highlighted.

Exhaled nitric oxide: a test for diagnosis and control of asthma?

The fractional concentration of nitric oxide (FE(NO)) in exhaled breath is a noninvasive marker of airway inflammation in asthma. The precise role of FE(NO) in the asthma management algorithm has not been defined. However, there are compelling data for use of FE(NO) for diagnosing asthma, assessing control and severity, titrating inhaled corticosteroids, and detecting ongoing airway inflammation. This article reviews the biology of nitric oxide in airway pathology and its role in asthma.

Exhaled nitric oxide in childhood asthma: a review

As an 'inflammometer', the fraction of nitric oxide in exhaled air (Fe(NO)) is increasingly used in the management of paediatric asthma. Fe(NO) provides us with valuable, additional information regarding the nature of underlying airway inflammation, and complements lung function testing and measurement of airway hyper-reactivity. This review focuses on clinical applications of Fe(NO) in paediatric asthma. First, Fe(NO) provides us with a practical tool to aid in the diagnosis of asthma and distinguish patients who will benefit from inhaled corticosteroids from those who will not. Second, Fe(NO) is helpful in predicting exacerbations, and predicting successful steroid reduction or withdrawal. In atopic asthmatic children Fe(NO) is beneficial in adjusting steroid doses, discerning those patients who require additional therapy from those whose medication dose could feasibly be reduced. In pre-school children Fe(NO) may be of help in the differential diagnosis of respiratory symptoms, and may potentially allow for better targeting and monitoring of anti-inflammatory treatment.

Functional role and species-specific contribution of arginases in pulmonary fibrosis

Lung fibrosis is characterized by increased deposition of ECM, especially collagens, and enhanced proliferation of fibroblasts. l-arginine is a key precursor of nitric oxide, asymmetric dimethylarginine, and proline, an amino acid enriched in collagen. We hypothesized that l-arginine metabolism is altered in pulmonary fibrosis, ultimately affecting collagen synthesis. Expression analysis of key enzymes in the arginine pathway, protein arginine methyltransferases (Prmt), arginine transporters, and arginases by quantitative (q) RT-PCR and Western blot revealed significant upregulation of arginase-1 and -2, but not Prmt or arginine transporters, during bleomycin-induced pulmonary fibrosis in mice. HPLC revealed a concomitant, time-dependent decrease in pulmonary l-arginine levels. Arginase-1 and -2 mRNA and protein expression was increased in primary fibroblasts isolated from bleomycin-treated mice, compared with controls, and assessed by qRT-PCR and Western blot analysis. TGF-beta1, a key profibrotic mediator, induced arginase-1 and -2 mRNA expression in primary and NIH/3T3 fibroblasts. Treatment of fibroblasts with the arginase inhibitor, NG-hydroxy-l-arginine, attenuated TGF-beta1-stimulated collagen deposition, but not collagen mRNA expression or Smad signaling, in fibroblasts. In human lungs derived from patients with idiopathic pulmonary fibrosis, arginase activity was unchanged, but arginase-1 expression significantly decreased when compared with donor lungs. Our results thus demonstrate that arginase-1 is expressed and functionally important for collagen deposition in lung fibroblasts. TGF-beta1-induced upregulation of arginase-1 suggests an interplay between profibrotic agents and l-arginine metabolism during the course of lung fibrosis in the mouse, whereas species-specific regulatory mechanisms may account for the differences observed in mouse and human.

Resting tension affects eNOS activity in a calcium-dependent way in airways

The alteration of resting tension (RT) from 0.5 g to 2.5 g increased significantly airway smooth muscle contractions induced by acetylcholine (ACh) in rabbit trachea. The decrease in extracellular calcium concentration [Ca²⁺]_o from 2 mM to 0.2 mM reduced ACh-induced contractions only at 2.5 g RT with no effect at 0.5 g RT. The nonselective inhibitor of nitric oxide synthase (NOS), N^G-nitro-L-arginine methyl ester (L-NAME) increased ACh-induced contractions at 2.5 g RT. The inhibitor of inducible NOS, S-methylsothiourea or neuronal NOS, 7-nitroindazole had no effect. At 2.5 g RT, the reduction of [Ca²⁺]_o from 2 mM to 0.2 mM abolished the effect of L-NAME on ACh-induced contractions. The NO precursor L-arginine or the tyrosine kinase inhibitors erbstatin A and genistein had no effect on ACh-induced contractions obtained at 2.5 g RT. Our results suggest that in airways, RT affects ACh-induced contractions by modulating the activity of epithelial NOS in a calcium-dependent, tyrosine-phosphorylation-independent way.

Anti-asthmatic potential of a D-galactose-binding lectin from Synadenium carinatum latex

Extracts from the plant Synadenium carinatum latex are widely and indiscriminately used in popular medicine to treat a great number of inflammatory disorders and although the mechanisms underlying these effects remain undefined, the lectin isolated from S. carinatum latex (ScLL) is thought to be in part responsible for these anti-inflammatory effects. In order to elucidate possible immunoregulatory activities of ScLL, we investigated the effects of ScLL administration in models of acute and chronic inflammation. Oral administration of ScLL significantly inhibited neutrophil and eosinophil extravasation in models of acute and chronic inflammation and reduced eosinophil and mononuclear blood counts during chronic inflammation. ScLL administration reduced IL(interleukin)-4 and IL-5 levels but increased interferon-gamma and IL-10 in an asthma inflammatory model, which suggested that it might induce a TH2 to TH1 shift in the adaptive immune response. ScLL also inhibited IkappaBalpha degradation, a negative regulator of proinflammatory NF-kappaB. Taken together, these results provide the first description of a single factor isolated from S. carinatum latex extract with immunoregulatory functions and suggest that ScLL may be useful in the treatment of allergic inflammatory disorders.

Effects of nebulized ketamine on allergen-induced airway hyperresponsiveness and inflammation in actively sensitized Brown-Norway rats

Since airway hyperresponsiveness (AHR) and allergic inflammatory changes are regarded as the primary manifestations of asthma, the main goals of asthma treatment are to decrease inflammation and maximize bronchodilation. These goals can be achieved with aerosol therapy. Intravenous administration of the anesthetic, ketamine, has been shown to trigger bronchial smooth muscle relaxation. Furthermore, increasing evidence suggests that the anti-inflammatory properties of ketamine may protect against lung injury. However, ketamine inhalation might yield the same or better results at higher airway and lower ketamine plasma concentrations for the treatment of asthma. Here, we studied the effect of ketamine inhalation on bronchial hyperresponsiveness and airway inflammation in a Brown-Norway rat model of ovalbumin(OVA)-induced allergic asthma. Animals were actively sensitized by subcutaneous injection of OVA and challenged by repeated intermittent (thrice weekly) exposure to aerosolized OVA for two weeks. Before challenge, the sensitizened rats received inhalation of aerosol of phosphate-buffered saline (PBS) or aerosol of ketamine or injection of ketamine respectivity. Airway reactivity to acetylcholine (Ach) was measured in vivo, and various inflammatory markers, including Th2 cytokines in bronchoalveolar lavage fluid (BALF), as well as induciable nitric oxide synthase (iNOS) and nitric oxide (NO) in lungs were examined. Our results revealed that delivery of aerosolized ketamine using an ultrasonic nebulizer markedly suppressed allergen-mediated airway hyperreactivity, airway inflammation and airway inflammatory cell infiltration into the BALF, and significantly decreased the levels of interleukin-4 (IL-4) in the BALF and expression of iNOS and the concentration of NO in the inflamed airways from OVA-treated rats. These findings collectively indicate that nebulized ketamine attenuated many of the central components of inflammatory changes and AHR in OVA-provoked experimental asthma, potentially providing a new therapeutic approach against asthma.

A potentiating effect of endogenous NO in the physiologic secretion from airway submucosal glands

It is known that several second messengers, such as Ca(2+) or cAMP, play important roles in the intracellular pathway of electrolyte secretion in tracheal submucosal gland. However, the participation of cGMP, and therefore nitric oxide (NO), is not well understood. To investigate the physiologic role of NO, we first examined whether tracheal glands can synthesize NO in response to acetylcholine (ACh), and then whether endogenous NO has some effects on the ACh-triggered ionic currents. From the experiments using the NO-specific fluorescent indicator 4,5-diaminofluorescein diacetate salt (DAF-2DA), we found that a physiologically relevant low dose of ACh (100 nM) stimulated the endogenous NO synthesis, and it was almost completely suppressed in the presence of the nonspecific NO synthase (NOS) inhibitor Nomega-Nitro-L-arginine Methyl Ester Hydrochloride (L-NAME) or the neuronal NOS (nNOS)-specific inhibitor 7-Nitroindazole (7-NI). Patch-clamp experiments revealed that both the NOS inhibitors (L-NAME or 7-NI) and cGK inhibitors (KT-5823 or Rp-8-Br-cGMP) partially decreased ionic currents induced by 30 nM of ACh, but not in the case of 300 nM of ACh. Our results indicate that NO can be synthesized through the activation of nNOS endogenously and has potentiating effects on the gland secretion, under a physiologically relevant ACh stimulation. When cells were stimulated by an inadequately potent dose of ACh, which caused an excess elevation in [Ca(2+)](i), the cells were desensitized. Therefore, due to NO, gland cells become more sensitive to calcium signaling and are able to maintain electrolyte secretion without desensitization.

Aspects of nitric oxide in health and disease: a focus on hypertension and cardiovascular disease

Nitric oxide (nitrogen monoxide) (NO) plays an important role in a wide range of physiologic processes. A major mediator of endothelial function, NO regulates vasodilatory and antithrombotic actions in the vasculature and plays a role in reproductive functions, bronchodilation, bone formation, memory, insulin sensitivity, and gastrointestinal relaxation. NO is formed from NO synthase. Impaired NO bioactivity is strongly associated with endothelial dysfunction and cardiovascular disease, but is also implicated in a broad range of other disorders, including pulmonary hypertension, insulin resistance, erectile dysfunction, and preeclampsia. Numerous therapies designed to target NO are being investigated and developed, including NO donors and stimulants. The recent African-American Heart Failure Trial (A-HeFT) showed that the NO donor isosorbide dinitrate, combined with the vasodilator hydralazine, significantly reduced morbidity and mortality in black patients with moderate-to-severe heart failure. Antihypertensive drugs, including angiotensin-converting enzyme inhibitors, calcium channel blockers, and third-generation beta-blockers, are NO stimulants that have demonstrated significant improvement of endothelial function and NO bioactivity. Other cardiovascular therapies that may improve NO bioactivity include statins, l-arginine, and nonpharmacologic approaches such as exercise and dietary changes.

Severe asthma in adults: what are the important questions?

The term severe refractory asthma (SRA) in adults applies to patients who remain difficult to control despite extensive re-evaluation of diagnosis and management following an observational period of at least 6 months by a specialist. Factors that influence asthma control should be recognized and adequately addressed prior to confirming the diagnosis of SRA. This report presents statements according to the literature defining SRA in order address the important questions. Phenotyping SRA will improve our understanding of mechanisms, natural history, and prognosis. Female gender, obesity, and smoking are associated with SRA. Atopy is less frequent in SRA, but occupational sensitizers are common inducers of new-onset SRA. Viruses contribute to severe exacerbations and can persist in the airways for long periods. Inflammatory cells are in the airways of the majority of patients with SRA and persist despite steroid therapy. The T(H)2 immune process alone is inadequate to explain SRA. Reduced responsiveness to corticosteroids is common, and epithelial cell and smooth muscle abnormalities are found, contributing to airway narrowing. Large and small airway wall thickening is observed, but parenchymal abnormalities may influence airway limitation. Inhaled corticosteroids and bronchodilators are the mainstay of treatment, but patients with SRA remain uncontrolled, indicating a need for new therapies.

Mechanism of relaxation induced by nicotine in normal and ovalbumin-sensitized guinea-pig trachea

Nicotine is an irritant molecule in the cigarette that contributes airway hyper-reactivity. The aim of this study was to investigate the mechanism of these effects and effects of nicotine on the isolated trachea preparations from control and ovalbumin-sensitized guinea-pigs. Nicotine (3x10(-5) to 3x10(-4) M) produced concentration-dependent relaxation on isolated trachea preparations precontracted by carbachol (10(-6) M) in both groups. We found that the relaxant effect of nicotine decreased in the presence of N(w)-nitro L-arginine methyl ester (L-NAME) (10(-6) M), and hexamethonium (10(-2) M) but not in the presence of alpha-bungarotoxin (10(-3) M), and tetrodotoxin (3.1x10(-6) M) in isolated trachea preparations in both groups. The relaxant effect of nicotine was less significant in isolated trachea preparations from ovalbumin-sensitized guinea-pigs than from control guinea-pigs (P<0.05). The contractions elicited by carbachol (10(-6) M) were not significantly different in the ovalbumin-sensitized group than in the control group. Nicotine (10(-4) M) significantly increased the cGMP levels in trachea preparations compared with the control preparations.(P<0.05). These results suggest that nicotine-induced relaxation response in normal and ovalbumin sensitized guinea-pigs trachea is at least in part mediated by nitric oxide (NO) since it was significantly reduced in the presence of L-NAME. The decreased relaxation response to nicotine in ovalbumin sensitized guinea-pigs trachea may be due to impaired production and/or liberation of NO.

Ambient and microenvironmental particles and exhaled nitric oxide before and after a group bus trip

OBJECTIVES

Airborne particles have been linked to pulmonary oxidative stress and inflammation. Because these effects may be particularly great for traffic-related particles, we examined associations between particle exposures and exhaled nitric oxide (FE(NO)) in a study of 44 senior citizens, which involved repeated trips aboard a diesel bus.

METHODS

Samples of FE(NO) collected before and after the trips were regressed against microenvironmental and ambient particle concentrations using mixed models controlling for subject, day, trip, vitamins, collection device, mold, pollen, room air nitric oxide, apparent temperature, and time to analysis. Although ambient concentrations were collected at a fixed location, continuous group-level personal samples characterized microenvironmental exposures throughout facility and trip periods.

RESULTS

In pre-trip samples, both microenvironmental and ambient exposures to fine particles were positively associated with FE(NO). For example, an interquartile increase of 4 microg/m(3) in the daily microenvironmental PM(2.5) concentration was associated with a 13% [95% confidence interval (CI), 2-24%) increase in FE(NO). After the trips, however, FE(NO) concentrations were associated pre-dominantly with microenvironmental exposures, with significant associations for concentrations measured throughout the whole day. Associations with exposures during the trip also were strong and statistically significant with a 24% (95% CI, 15-34%) increase in FE(NO) predicted per interquartile increase of 9 microg/m(3) in PM(2.5). Although pre-trip findings were generally robust, our post-trip findings were sensitive to several influential days.

CONCLUSIONS

Fine particle exposures resulted in increased levels of FE(NO) in elderly adults, suggestive of increased airway inflammation. These associations were best assessed by microenvironmental exposure measurements during periods of high personal particle exposures.

Therapeutic use of citrulline in cardiovascular disease

L-citrulline is the natural precursor of L-arginine, substrate for nitric oxide synthase (NOS) in the production of NO. Supplemental administration L-arginine has been shown to be effective in improving NO production and cardiovascular function in cardiovascular diseases associated with endothelial dysfunction, such as hypertension, heart failure, atherosclerosis, diabetic vascular disease and ischemia-reperfusion injury, but the beneficial actions do not endure with chronic therapy. Substantial intestinal and hepatic metabolism of L-arginine to ornithine and urea by arginase makes oral delivery very ineffective. Additionally, all of these disease states as well as supplemental L-arginine enhance arginase expression and activity, thus reducing the effectiveness of L-arginine therapy. In contrast, L-citrulline is not metabolized in the intestine or liver and does not induce tissue arginase, but rather inhibits its activity. L-citrulline entering the kidney, vascular endothelium and other tissues can be readily converted to L-arginine, thus raising plasma and tissue levels of L-arginine and enhancing NO production. Supplemental L-citrulline has promise as a therapeutic adjunct in disease states associated with L-arginine deficiencies.

Airway hyperresponsiveness in allergically inflamed mice: the role of airway closure

RATIONALE

Allergically inflamed mice exhibit airway hyperresponsiveness to inhaled methacholine, which computer simulations of lung impedance suggest is due to enhanced lung derecruitment and which we sought to verify in the present study.

METHODS

BALB/c mice were sensitized and challenged with ovalbumin to induce allergic inflammation; the control mice were sensitized but received no challenge. The mice were then challenged with inhaled methacholine and respiratory system impedance tracked for the following 10 minutes. Respiratory elastance (H) was estimated from each impedance measurement. One group of mice was ventilated with 100% O(2) during this procedure and another group was ventilated with air. After the procedure, the mice were killed and ventilated with pure N(2), after which the trachea was tied off and the lungs were imaged with micro-computed tomography (micro-CT).

RESULTS

H was significantly higher in allergic mice than in control animals after methacholine challenge. The ratio of H at the end of the measurement period between allergic and nonallergic mice ventilated with O(2) was 1.36, indicating substantial derecruitment in the allergic animals. The ratio between lung volumes determined by micro-CT in the control and the allergic mice was also 1.36, indicative of a corresponding volume loss due to absorption atelectasis. Micro-CT images and histograms of Hounsfield units from the lungs also showed increased volume loss in the allergic mice compared with control animals after methacholine challenge.

CONCLUSIONS

These results support the conclusion that airway closure is a major component of hyperresponsiveness in allergically inflamed mice.

Increased alveolar nitric oxide concentration and high levels of leukotriene B(4) and 8-isoprostane in exhaled breath condensate in patients with asbestosis

BACKGROUND

Inhaled asbestos fibres can cause inflammation and fibrosis in the lungs called asbestosis. However, there are no non-invasive means to assess and follow the severity of the inflammation. Exhaled nitric oxide (NO) measured at multiple exhalation flow rates can be used to assess the alveolar NO concentration and bronchial NO flux, which reflect inflammation in the lung parenchyma and airways, respectively. The aim of the present study was to investigate whether exhaled NO or markers in exhaled breath condensate could be used to assess inflammation in asbestosis.

METHODS

Exhaled NO and inflammatory markers (leukotriene B(4) and 8-isoprostane) in exhaled breath condensate were measured in 15 non-smoking patients with asbestosis and in 15 healthy controls. Exhaled NO concentrations were measured at four constant exhalation flow rates (50, 100, 200 and 300 ml/s) and alveolar NO concentration and bronchial NO flux were calculated according to the linear model of pulmonary NO dynamics.

RESULTS

The mean (SE) alveolar NO concentration was significantly higher in patients with asbestosis than in controls (3.2 (0.4) vs 2.0 (0.2) ppb, p = 0.008). There was no difference in bronchial NO flux (0.9 (0.1) vs 0.9 (0.1) nl/s, p = 0.93) or NO concentration measured at ATS standard flow rate of 50 ml/s (20.0 (2.0) vs 19.7 (1.8) ppb, p = 0.89). Patients with asbestosis had increased levels of leukotriene B4 (39.5 (6.0) vs 15.4 (2.9) pg/ml, p = 0.002) and 8-isoprostane (33.5 (9.6) vs 11.9 (2.8) pg/ml, p = 0.048) in exhaled breath condensate and raised serum levels of C-reactive protein (2.3 (0.3) vs 1.1 (0.2) mug/ml, p = 0.003), interleukin-6 (3.5 (0.5) vs 1.7 (0.4) pg/ml, p = 0.007) and myeloperoxidase (356 (48) vs 240 (20) ng/ml, p = 0.034) compared with healthy controls.

CONCLUSIONS

Patients with asbestosis have an increased alveolar NO concentration and high levels of leukotriene B4 and 8-isoprostane in exhaled breath. Measurement of exhaled NO at multiple exhalation flow rates and analysis of inflammatory markers in exhaled breath condensate are promising non-invasive means for assessing inflammation in patients with asbestosis.

Acute effect of cigarette smoke and nicotine on airway blood flow and airflow in healthy smokers

Cigarette smoke contains irritants and vasoactive substances. We wanted to determine the effect of smoking a cigarette and of nasally or orally inhaled nicotine on airway blood flow (Q(aw)) and airflow in smokers. In ten healthy current smokers, Q(aw), FEV(1), and FEF(25-75) were measured before and at 5, 30, and 180 min after smoking a cigarette. The effects of systemic nicotine using a nicotine nasal spray and local nicotine using a nicotine inhaler were also studied. Mean (+/- SE) Q(aw) increased by 81% +/- 16% (p = 0.03) 5 min after smoking a cigarette and was no longer different from baseline at 30 and 180 min. Nicotine nasal spray and nicotine oral inhaler had no effect on Q(aw.) FEV(1) and FEF(25-75) remained unchanged after smoking a cigarette and after local or systemic nicotine administration. Smoking a cigarette is followed by a transient increase in airway blood flow but no changes in airflow. Nicotine, at the rate and dose provided by the nasal spray (systemic action) and oral inhaler (local and systemic action), does not appear to be involved in the Q(aw) change, suggesting a pharmacologic or nonspecific irritant effect of other cigarette smoke constituents.

Involvement of Syk kinase in TNF-induced nitric oxide production by airway epithelial cells

We have recently found that Syk is widely expressed in lung epithelial cells (EC) and participates in beta1 integrin signaling. In this study, we assessed the role of Syk in regulation of NO production. Stimulation of human bronchial EC line HS-24 by TNF caused an increased expression of inducible nitric oxide synthase (iNOS). Inhibition of Syk using siRNA or piceatannol down-regulated the iNOS expression and reduced NO production. This effect occurred in EC simultaneously stimulated via beta1 integrins, suggesting that TNF and beta1 integrins provide co-stimulatory signals. Inhibition of Syk down-regulated TNF-induced p38 and p44/42 MAPK phosphorylation and nuclear translocation of p65 NF-kappaB. Thus, TNF-induced activation of pro-inflammatory signaling in EC leading to enhanced expression of iNOS and NO production was dependent on Syk. Syk-mediated signaling regulates NO production at least partly via activating the MAPK cascade. Understanding the role of Syk in airway EC may help in developing new therapeutic tools for inflammatory lung disorders.

Exhaled nitric oxide measurements: clinical application and interpretation

The use of exhaled nitric oxide measurements (F(E)NO) in clinical practice is now coming of age. There are a number of theoretical and practical factors which have brought this about. Firstly, F(E)NO is a good surrogate marker for eosinophilic airway inflammation. High F(E)NO levels may be used to distinguish eosinophilic from non-eosinophilic pathologies. This information complements conventional pulmonary function testing in the assessment of patients with non-specific respiratory symptoms. Secondly, eosinophilic airway inflammation is steroid responsive. There are now sufficient data to justify the claim that F(E)NO measurements may be used successfully to identify and monitor steroid response as well as steroid requirements in the diagnosis and management of airways disease. F(E)NO measurements are also helpful in identifying patients who do/do not require ongoing treatment with inhaled steroids. Thirdly, portable nitric oxide analysers are now available, making routine testing a practical possibility. However, a number of issues still need to be resolved, including the diagnostic role of F(E)NO in preschool children and the use of reference values versus individual F(E)NO profiles in managing patients with difficult or severe asthma.

Production of nitric oxide by airways neutrophils in the initial phase of murine asthma

In experimental models of asthma, nitric oxide (NO) is produced and contributes to the physiopathology of the disease. Neutrophil is the first cell to infiltrate the lung in response to antigen stimulation, it has the capacity to produce NO but a clear demonstration that neutrophils contribute to NO production in asthma is lacking. This was the aim of the present study. At weekly intervals C57Bl/6 mice were sensitized twice with ovalbumin-alumen and challenged twice with ovalbumin aerosol. The peak of neutrophil infiltration in the bronchoalveolar lavage fluid (BALF) was 12 h after challenge, when neutrophils constituted 70% of the cell population and eosinophils only 1.5%. BALF cell preparations were stained with a NO-sensitive fluorescent dye (DAF-2) and with a nucleus marker (DAPI). Most DAF-2 stained cells could be identified as polymorphonuclear leukocytes, by the co-localization of both DAF-2 and DAPI staining. Cells from animals treated with l-NAME, were not stained for DAF-2 confirming the specificity of DAF-2 staining for NO. Moreover, the peak expression of inducible nitric oxide synthase (NOS2), in BALF cells and lung homogenates, was coincident with the peak of BALF neutrophil influx. NOS2 protein expression (arbitrary units) was detected 6 h after challenge (17.8+/-9.1 in BALF cells; 47.5+/-7.7 in lung homogenates), peak expression was at 12 h (54.5+/-8.7 and 133.7+/-10), decreasing thereafter, being no longer detected after 24 h. Thus, the neutrophils infiltrating the lung in the initial phase of murine asthma are producing NO via NOS2.

Aspergillus fumigatus challenge increases cytokine levels in nasal lavage fluid

Several studies have shown an association between exposure in moisture-damaged buildings and adverse health effects. There are several indicator microbes of moisture damage, but Aspergillus fumigatus is one of the best-documented molds provoking health problems in different occupational conditions. We assessed whether inhalation of a commercial A. fumigatus solution would affect cytokine levels (tumor necrosis factor [TNF]-alpha, interleukin [IL]-1beta, IL-4, IL-6, interferon [IFN]-gamma) in nasal lavage fluid (NAL) compared with that evoked by placebo challenge. Twenty-seven subjects were studied: 13 had occupational exposure in a moisture-damaged building, 4 were atopic, and 10 were considered as controls. In all the subjects, the IL-1beta levels were increased significantly both at 6 (p = 0.013) and 24 h (p = .005) after the A. fumigatus challenge compared to placebo. In subjects with previous occupational exposure in a moisture-damaged building, IL-4 concentrations were increased significantly both at 6 (p =.046) and 24 h (p =.008) after the A. fumigatus challenge compared with placebo. Furthermore, in the control group, TNF-alpha levels were significantly increased at 6 h after the A. fumigatus challenge compared to placebo (p = .028). Thus, these data show a link between markers of inflammation in NAL and experimental A. fumigatus challenge.

Role of the l-citrulline/l-arginine cycle in iNANC nerve-mediated nitric oxide production and airway smooth muscle relaxation in allergic asthma

Nitric oxide synthase (NOS) converts L-arginine into nitric oxide (NO) and L-citrulline. In NO-producing cells, L-citrulline can be recycled to L-arginine in a two-step reaction involving argininosuccinate synthase (ASS) and -lyase (ASL). In guinea pig trachea, L-arginine is a limiting factor in neuronal nNOS-mediated airway smooth muscle relaxation upon inhibitory nonadrenergic noncholinergic (iNANC) nerve stimulation. Moreover, in a guinea pig model of asthma iNANC nerve-induced NO production and airway smooth muscle relaxation are impaired after the allergen-induced early asthmatic reaction, due to limitation of L-arginine. Using guinea pig tracheal preparations, we now investigated whether (i) the L-citrulline/L-arginine cycle is active in airway iNANC nerves and (ii) the NO deficiency after the early asthmatic reaction involves impaired L-citrulline recycling. Electrical field stimulation-induced relaxation was measured in tracheal open-rings precontracted with histamine. L-citrulline as well as the ASL inhibitor succinate did not affect electrical field stimulation-induced relaxation under basal conditions. However, reduced relaxation induced by a submaximal concentration of the NOS inhibitor N(omega)-nitro-L-arginine was restored by L-citrulline, which was prevented by the additional presence of succinate or the ASS inhibitor alpha-methyl-D,L-aspartate. Remarkably, the impaired iNANC relaxation after the early asthmatic reaction was restored by L-citrulline. In conclusion, the L-citrulline/L-arginine cycle is operative in guinea pig iNANC nerves in the airways and may be effective under conditions of low L-arginine utilization by nNOS (caused by NOS inhibitors), and during reduced L-arginine availability after allergen challenge. Enzymatic dysfunction in the L-citrulline/L-arginine cycle appears not to be involved in the L-arginine limitation and reduced iNANC activity after the early asthmatic reaction.

Role of spirometry and exhaled nitric oxide to predict exacerbations in treated asthmatics

OBJECTIVE

To evaluate the complementary roles of exhaled nitric oxide (NO) and spirometry to predict asthma exacerbations requiring one or more tapering courses of systemic corticosteroids.

METHODS

We prospectively studied 44 nonsmoking asthmatics (24 women) aged 51 +/- 21 years (mean +/- SD) who were clinically stable for 6 weeks and receiving 250 mug of fluticasone/50 mug of salmeterol or equivalent for 3 years. Total exhaled NO (FENO), small airway/alveolar NO (CANO), large airway NO flux (J'awNO), and spirometry were measured.

RESULTS

Baseline FEV(1) was 2.1 +/- 0.7 L, 70 +/- 20% of predicted after 180 mug of albuterol. Twenty-two of 44 asthmatics had one or more exacerbations over 18 months, 16 of 22 asthmatics had two exacerbations, and 6 of 22 asthmatics were hospitalized, including 1 asthmatic with near-fatal asthma. When baseline FEV(1) was </= 76% predicted, exacerbations occurred in 20 of 31 asthmatics (65%). If baseline FEV(1) was > 76% of predicted, exacerbations occurred only in 2 of 13 asthmatics (15%) [p = 0.003, chi(2)]. Using a receiver operating characteristic (ROC) curve for first exacerbation, the area under the curve was 0.67 with cutoff FEV(1) of 76% of predicted (sensitivity, 0.91; specificity, 0.50; positive predictive value, 0.65; negative predictive value, 0.85; positive likelihood ratio [LR(+)], 1.8; negative likelihood ratio [LR(-)], 0.18). When baseline FENO was >/= 28 parts per billion (ppb), exacerbations occurred in 13 of 17 asthmatics (76%); if baseline FENO was < 28 ppb, exacerbations occurred in only 9 of 27 asthmatics (33%) [p = 0.005, chi(2)]. Using the ROC curve for first exacerbation, the area under the curve was 0.71 with FENO cutoff point of 28 ppb (sensitivity, 0.59; specificity, 0.82; positive predictive value, 0.77; negative predictive value, 0.87; LR(+), 3.3; LR(-), 0.5). Independent of baseline FEV(1), FENO >/= 28 ppb increased the relative risk (RR) for exacerbation by 3.4 (95% confidence interval [CI], 1.3 to 9.1; Mantel-Haenszel, p = 0.007). An abnormal increase in CANO increased RR by 3.0 (95% CI, 0.9 to 9.9; p = 0.04), and abnormal J'awNO increased RR by 2.4 (95% CI, 1.0 to 5.6; p = 0.04). Independent of baseline FENO, FEV(1) </= 76% predicted increased RR by 1.7 (95% CI, 1.0 to 2.7; p = 0.02). Combined baseline FENO >/= 28 ppb and FEV(1) </= 76% of predicted identified 13 stable asthmatics with 85% probability for future exacerbation, whereas 9 asthmatics with FENO < 28 ppb and FEV(1) > 76% of predicted had a 0% probability of exacerbation.

CONCLUSION

Combining FENO and FEV(1) percentage of predicted can stratify risk for asthma exacerbation.

Association study of promoter polymorphisms within the NOS3 gene and allergic diseases

BACKGROUND

Nitric oxide (NO) is an important mediator of physiologic and pathologic processes in the airways. On this basis, we hypothesized that polymorphisms in the NOS3 gene could be associated with the disease process.

METHODS

Two promoter variants (-786C/T and -691C/T) were examined in a Caucasian Czech population of allergic patients [n = 671, with a subgroup of asthmatics (n = 305)] and healthy controls (n = 334) using PCR-RFLP analyses.

RESULTS

NOS3 -786C/T and -691C/T were not associated with allergic diseases or asthma. However, the -786 variant was significantly associated with asthma in men (p < 0.01, p(corr) < 0.05) but not in women. NOS3 -691C/T was found to be in strong linkage disequilibrium with -786C/T, and the distribution of combined genotypes was marginally different between the asthmatic and control men.

CONCLUSION

Our results suggest that NOS3 gene variants may be one of the factors that participate in the pathogenesis of asthma in men.

Exhaled nitric oxide in healthy nonatopic school-age children: determinants and height-adjusted reference values

Exhaled nitric oxide (FENO) was proposed as a marker of airway inflammation, but data about FENO in healthy children measured with standardized methods are so far limited. In order to assess the determinants of FENO in healthy children, we investigated a population-based sample of school-age children (n = 276) with a questionnaire, skin-prick tests, spirometry, and the measurement of FENO. The FENO of 114 nonatopic and nonsmoking children considered healthy were analyzed with stepwise multiple regression analysis, which showed significant associations with age, standing height, weight, and body surface area, but not with gender. Height was found to be the best independent variable for the regression equation for FENO, which on average showed an increase in the height range of 120-180 cm from 7 to 14 ppb. In the random sample of children, increased FENO was associated with atopy (odds ratio, 9.0; 95% confidence interval, 3.9-21.1; P < 0.0001), and significantly with allergic rhinitis and atopic dermatitis, but not with asthma. Respiratory symptom-free children with skin-prick test positivity had significantly higher FENO than healthy nonatopic subjects. We conclude that height is the best determinant of FENO in healthy children. Due to the strong effect of atopy, FENO data should not be interpreted without knowing the atopic status of the child. The present reference values of FENO may serve in clinical assessments for measuring airway inflammation in children.

Respiratory syncytial virus infection in a murine model of cystic fibrosis

Viral respiratory infections play an important role in the development and progression of pulmonary disease in cystic fibrosis (CF). The CF mouse model provides a tool to examine the relationship between the cystic fibrosis transmembrane conductance regulator (CFTR) defect and lung disease. This work investigates the cellular response to a common viral pathogen, respiratory syncytial virus (RSV) in the lung of CF mice. RSV was administered by intranasal inoculation of CFTR(tm1Unc)-Tg(FABPCFTR)1Jaw/J (CFTR-/-) and control mice. At day 5 post infection, viral titers, bronchoalveolar fluid nitrate levels (BALF) cell and differential counts, histology and studies on airway mechanics were performed. CFTR-/- mice had an impaired ability to clear RSV. This was associated with an exaggerated inflammatory response (increased lymphocytes and neutrophils) in BALF of RSV-infected CFTR-/- mice and a decreased ability to generate nitric oxide (NO) (measured as BAL nitrate). Lung histopathology of RSV-infected CFTR-/- mice demonstrated increased inflammation compared to RSV (-) CFTR-/- and control mice (regardless of RSV treatment). The airway response to methacholine was increased by RSV infection in CF mice when compared to controls. The CFTR-/- mouse exhibits an aberrant response to RSV infection. This model should be useful in providing further mechanistic information on the biology of respiratory viruses in mammalian models, and provide new insights into the pathogenesis of airway inflammation in patients with CF.

Nasal NO measurement by direct sampling from the nose during breathhold: aspiration flow, nasal resistance and reproducibility

The objective of this study was assessment of the effect of aspiration flow, the nasal cycle, and time on nasal nitric oxide (nNO) concentrations in air sampled from one nostril during breathhold. nNO was measured in 45 healthy subjects (19 males, aged 18-45 years) from one nostril during breathholding. We compared nNO values and time to plateau in both nostrils with 3 aspiration flows (280, 700, 1,200 ml/min) and assessed the short-term and long-term reproducibility. Mean nNO values at flows of 280, 700 and 1,200 ml/min differed significantly (P < 0.01): 854, 474, 380 ppb, respectively. The (median) plateau was reached after 6, 4 and 3 s for the different flows. The within-subject coefficient of variability was always < 5%. We found no difference in nNO between left-, right-, largest or smallest nostril (P > 0.10). nNO values after 6, 24 h and 7 days were not significantly different from baseline (P > 0.10) and showed fair reproducibility. The highest aspiration flow was experienced as unpleasant. nNO can be measured in either nostril and shows no diurnal variation. The measurement is quick, reproducible, feasible and best accepted with an aspiration flow of 700 ml/min during breathhold for 10 s.

Markers of lung disease in exhaled breath: nitric oxide

Management of airway inflammation requires proper monitoring and treatment to improve long-term outcomes. However, achieving this goal is difficult, as current methods have limitations. Although nitric oxide (NO) was first identified 200 years ago, its physiological importance was not recognized until the early 1980s. Many studies have established the role of NO as an essential messenger molecule in body systems. In addition, studies have demonstrated a significant relationship between changes in exhaled NO levels and other markers of airway inflammation. The technique used to measure NO in exhaled breath is noninvasive, reproducible, sensitive, and easy to perform. Consequently, there is growing interest in the use of exhaled NO in the management of asthma and other pulmonary conditions. The purpose of this review is to promote a basic understanding of the physiologic actions of NO, measurement techniques, and ways that research findings might translate to future application in clinical practice. Specifically, the article will review the role of exhaled NO in regard to its historical background, mechanisms of action, measurement techniques, and implications for clinical practice and research.

Increased oxidative stress in asymptomatic current chronic smokers and GOLD stage 0 COPD

Background

Chronic obstructive pulmonary disease (COPD) is associated with increased oxidative and nitrosative stress. The aim of our study was to assess the importance of these factors in the airways of healthy smokers and symptomatic smokers without airway obstruction, i.e. individuals with GOLD stage 0 COPD.

Methods

Exhaled NO (FENO) and induced sputum samples were collected from 22 current smokers (13 healthy smokers without any respiratory symptoms and 9 with symptoms i.e. stage 0 COPD) and 22 healthy age-matched non-smokers (11 never smokers and 11 ex-smokers). Sputum cell differential counts, and expressions of inducible nitric oxide synthase (iNOS), myeloperoxidase (MPO), nitrotyrosine and 4-hydroxy-2-nonenal (4-HNE) were analysed from cytospins by immunocytochemistry. Eosinophil cationic protein (ECP) and lactoferrin were measured from sputum supernatants by ELISA.

Results

FENO was significantly decreased in smokers, mean (SD) 11.0 (6.7) ppb, compared to non-smokers, 22.9 (10.0), p < 0.0001. Induced sputum showed increased levels of neutrophils (p = 0.01) and elevated numbers of iNOS (p = 0.004), MPO (p = 0.003), nitrotyrosine (p = 0.003), and 4-HNE (p = 0.03) positive cells in smokers when compared to non-smokers. Sputum lactoferrin levels were also higher in smokers than in non-smokers (p = 0.02). Furthermore, we noted four negative correlations between FENO and 1) total neutrophils (r = -0.367, p = 0.02), 2) positive cells for iNOS (r = -0.503, p = 0.005), 3) MPO (r = -0.547, p = 0.008), and 4) nitrotyrosine (r = -0.424, p = 0.03). However, no major differences were found between never smokers and ex-smokers or between healthy smokers and stage 0 COPD patients.

Conclusion

Our results clearly indicate that several markers of oxidative/nitrosative stress are increased in current cigarette smokers compared to non-smokers and no major differences can be observed in these biomarkers between non-symptomatic smokers and subjects with GOLD stage 0 COPD.

A critical appraisal of methods used in early clinical development of novel drugs for the treatment of asthma

Asthma is a heterogeneous disorder characterized by chronic airway inflammation, hyperresponsiveness and remodeling. Being the hallmark of asthma, airway inflammation has become the most important target for therapeutic agents. Consequently, during the past decade various semi-and non-invasive methods have been explored to sample the airway inflammation in asthma. In this review, we provide a practical overview of the current status of various sampling techniques including sputum induction, exhaled breath analysis, and bronchoprovocation tests (BPTs). We focus on their applicability for monitoring in clinical practice and in intervention trials in asthma.