Role of exhaled nitric oxide in asthma

Copper homeostasis dysregulation in respiratory diseases: a review of current knowledge

Cu is an essential micronutrient for various physiological processes in almost all human cell types. Given the critical role of Cu in a wide range of cellular processes, the local concentrations of Cu and the cellular distribution of Cu transporter proteins in the lung are essential for maintaining a steady-state internal environment. Dysfunctional Cu metabolism or regulatory pathways can lead to an imbalance in Cu homeostasis in the lungs, affecting both acute and chronic pathological processes. Recent studies have identified a new form of Cu-dependent cell death called cuproptosis, which has generated renewed interest in the role of Cu homeostasis in diseases. Cuproptosis differs from other known cell death pathways. This occurs through the direct binding of Cu ions to lipoylated components of the tricarboxylic acid cycle during mitochondrial respiration, leading to the aggregation of lipoylated proteins and the subsequent downregulation of Fe-S cluster proteins, which causes toxic stress to the proteins and ultimately leads to cell death. Here, we discuss the impact of dysregulated Cu homeostasis on the pathogenesis of various respiratory diseases, including asthma, chronic obstructive pulmonary disease, idiopathic interstitial fibrosis, and lung cancer. We also discuss the therapeutic potential of targeting Cu. This study highlights the intricate interplay between copper, cellular processes, and respiratory health. Copper, while essential, must be carefully regulated to maintain the delicate balance between necessity and toxicity in living organisms. This review highlights the need to further investigate the precise mechanisms of copper interactions with infections and immune inflammation in the context of respiratory diseases and explore the potential of therapeutic strategies for copper, cuproptosis, and other related effects.

Inflammatory and contractile profile in LPS-challenged equine isolated bronchi: Evidence for IL-6 as a potential target against AHR in equine asthma

BACKGROUND

Airway inflammation and airway hyperresponsiveness (AHR) are pivotal characteristics of equine asthma. Lipopolysaccharide (LPS) may have a central role in modulating airway inflammation and dysfunction. Therefore, the aim of this study was to match the inflammatory and contractile profile in LPS-challenged equine isolated bronchi to identify molecular targets potentially suitable to counteract AHR in asthmatic horses.

METHODS

Equine isolated bronchi were incubated overnight with LPS (0.1-100 ng/ml). The contractile response to electrical field stimulation (EFS) and the levels of cytokines, chemokines, and neurokinin A (NKA) were quantified. The role of capsaicin sensitive-sensory nerves, neurokinin-2 (NK₂) receptor, transient receptor potential vanilloid type 1 receptors (TRPV1), and epithelium were also investigated.

RESULTS

LPS 1 ng/ml elicited AHR to EFS (+238.17 ± 25.20% P < 0.001 vs. control). LPS significantly (P < 0.05 vs. control) increased the levels of IL-4 (+36.08 ± 1.62%), IL-5 (+38.60 ± 3.58%), IL-6 (+33.79 ± 2.59%), IL-13 (+40.91 ± 1.93%), IL-1β (+1650.16 ± 71.16%), IL-33 (+88.14 ± 8.93%), TGF-β (22.29 ± 1.03%), TNF-α (+56.13 ± 4.61%), CXCL-8 (+98.49 ± 17.70%), EOTAXIN (+32.26 ± 2.27%), MCP-1 (+49.63 ± 4.59%), RANTES (+36.38 ± 2.24%), and NKA (+112.81 ± 6.42%). Capsaicin sensitive-sensory nerves, NK₂ receptor, and TRPV1 were generally involved in the LPS-mediated inflammation. Epithelium removal modulated the release of IL-1β, IL-33, and TGF-β. Only the levels of IL-6 fitted with AHR to a wide range of EFS frequencies, an effect significantly (P < 0.05) inhibited by anti-IL-6 antibody; exogenous IL-6 induced significant (P < 0.05) AHR to EFS similar to that elicited by LPS.

CONCLUSION

Targeting IL-6 with specific antibody may represent an effective strategy to treat equine asthma, especially in those animals suffering from severe forms of this disease.

Biomarkers of asthma

Biomarkers may be diagnostic of asthma, they may predict or reflect response to therapy or they may identify patients at risk of asthma exacerbation. A biomarker is most often measured in biologic fluids that are sampled using relatively non-invasive sampling techniques such as blood, sputum, urine or exhaled breath. Biomarkers should be stable, readily quantifiable and their measurement should be reproducible and not confounded by other host factors, or the presence of comorbidities. However, asthma comprises multiple molecular endotypes and single, sensitive, specific, biomarkers reflecting these endotypes may not exist. Combining biomarkers may improve their predictive capability in asthma. The most well-established endotypes are those described as Type2 and non-Type2 asthma. Clinical trials established the fraction of exhaled nitric oxide (FeNO) and blood eosinophil counts as key biomarkers of response to corticosteroid or targeted anti-inflammatory therapy in Type2 asthma. However, these biomarkers may have limited value in the management of asthma in real-life settings or routine clinical practise. Biomarkers for Type2 asthma are not well described or validated and more research is needed. Breathomics has provided evidence to propose a number of exhaled volatile organic compounds (VOCs) as surrogate biomarkers for airway inflammatory phenotypes, disease activity and adherence to therapy. Analysis of urinary eicosanoids has identified eicosanoids related to Type2 and non-Type2 inflammation. Future clinical trials will be important in determining how exhaled VOCs or urinary eicosanoid profiles can be used to direct precision treatments. Their future clinical use will also depend on developing simplified instrumentation for biomarker analysis at the point-of-care.

Boosting nitric oxide in stress and respiratory infection: Potential relevance for asthma and COVID-19

Nitric oxide (NO) is a ubiquitous signaling molecule that is critical for supporting a plethora of processes in biological organisms. Among these, its role in the innate immune system as a first line of defense against pathogens has received less attention. In asthma, levels of exhaled NO have been utilized as a window into airway inflammation caused by allergic processes. However, respiratory infections count among the most important triggers of disease exacerbations. Among the multitude of factors that affect NO levels are psychological processes. In particular, longer lasting states of psychological stress and depression have been shown to attenuate NO production. The novel SARS-CoV-2 virus, which has caused a pandemic, and with that, sustained levels of psychological stress globally, also adversely affects NO signaling. We review evidence on the role of NO in respiratory infection, including COVID-19, and stress, and argue that boosting NO bioavailability may be beneficial in protection from infections, thus benefitting individuals who suffer from stress in asthma or SARS-CoV-2 infection.

Role and mechanisms of autophagy in lung metabolism and repair

Mammalian lungs are metabolically active organs that frequently encounter environmental insults. Stress responses elicit protective autophagy in epithelial barrier cells and the supportive niche. Autophagy promotes the recycling of damaged intracellular organelles, denatured proteins, and other biological macromolecules for reuse as components required for lung cell survival. Autophagy, usually induced by metabolic defects, regulates cellular metabolism. Autophagy is a major adaptive response that protects cells and organisms from injury. Endogenous region-specific stem/progenitor cell populations are found in lung tissue, which are responsible for epithelial repair after lung damage. Additionally, glucose and fatty acid metabolism is altered in lung stem/progenitor cells in response to injury-related lung fibrosis. Autophagy deregulation has been observed to be involved in the development and progression of other respiratory diseases. This review explores the role and mechanisms of autophagy in regulating lung metabolism and epithelial repair.

Nutritional immunity: the impact of metals on lung immune cells and the airway microbiome during chronic respiratory disease

Nutritional immunity is the sequestration of bioavailable trace metals such as iron, zinc and copper by the host to limit pathogenicity by invading microorganisms. As one of the most conserved activities of the innate immune system, limiting the availability of free trace metals by cells of the immune system serves not only to conceal these vital nutrients from invading bacteria but also operates to tightly regulate host immune cell responses and function. In the setting of chronic lung disease, the regulation of trace metals by the host is often disrupted, leading to the altered availability of these nutrients to commensal and invading opportunistic pathogenic microbes. Similarly, alterations in the uptake, secretion, turnover and redox activity of these vitally important metals has significant repercussions for immune cell function including the response to and resolution of infection. This review will discuss the intricate role of nutritional immunity in host immune cells of the lung and how changes in this fundamental process as a result of chronic lung disease may alter the airway microbiome, disease progression and the response to infection.

Could nasal nitric oxide help to mitigate the severity of COVID-19?

The nasal cavity and turbinates play important physiological functions by filtering, warming and humidifying inhaled air. Paranasal sinuses continually produce nitric oxide (NO), a reactive oxygen species that diffuses to the bronchi and lungs to produce bronchodilatory and vasodilatory effects. Studies indicate that NO may also help to reduce respiratory tract infection by inactivating viruses and inhibiting their replication in epithelial cells. In view of the pandemic caused by the novel coronavirus (SARS-CoV-2), clinical trials have been designed to examine the effects of inhaled nitric oxide in COVID-19 subjects. We discuss here additional lifestyle factors such as mouth breathing which may affect the antiviral response against SARS-CoV-2 by bypassing the filtering effect of the nose and by decreasing NO levels in the airways. Simple devices that promote nasal breathing during sleep may help prevent the common cold, suggesting potential benefits against coronavirus infection. In the absence of effective treatments against COVID-19, the alternative strategies proposed here should be considered and studied in more detail.

Bio-inspired nano-engineered strip for semiquantitative FeNO analysis

A point-of-care, non-invasive, low-cost and sensitive nano-biodiagnostic is needed in today's age for rapid and accurate self-diagnosis as well as for the management of asthma, which is advantageous for low resource areas where asthma is prevalent. The objective of this research work was to prepare the miniature, nanosponges coated paper strip to detect the asthma using certain biomarkers present in exhaled air. The asthma biomarker, nitric oxide present in exhaled air (FeNO) was chosen, which on reaction with nanosponges of diazotizing agent gave significant color change. The pyromellitic anhydride cross-linked β-cyclodextrin-based nanosponges of sulfanilamide and N-(1-naphthyl) ethylenediamine dihydrochloride were prepared using a polymer condensation method and coated on Whatman filter paper strip (1 × 5 cm2). The thickness of coating was found to be uniform (400 ± 50 μm) which was determined using SEM analysis. The Hue-Saturation-Value scale was used to detect the color change using a smartphone app. We also investigated the performance of a nano-engineered paper strip by comparing this with commercially available, FDA approved FeNO analyzer-NIOX MINO. Our findings demonstrated no significant difference in results obtained using both the techniques. Besides good repeatability, the paper strip showed increasing saturation with NO concentration and the capacity to detect the biomarker down to mean value of 20.33 ppb level. The successful validation and method comparison indicated that a bioinspired strip can provide on-site analysis and daily monitoring for diagnosis and management of asthma.

Assessment of breath volatile organic compounds in acute cardiorespiratory breathlessness: a protocol describing a prospective real-world observational study

INTRODUCTION

Patients presenting with acute undifferentiated breathlessness are commonly encountered in admissions units across the UK. Existing blood biomarkers have clinical utility in distinguishing patients with single organ pathologies but have poor discriminatory power in multifactorial presentations. Evaluation of volatile organic compounds (VOCs) in exhaled breath offers the potential to develop biomarkers of disease states that underpin acute cardiorespiratory breathlessness, owing to their proximity to the cardiorespiratory system. To date, there has been no systematic evaluation of VOC in acute cardiorespiratory breathlessness. The proposed study will seek to use both offline and online VOC technologies to evaluate the predictive value of VOC in identifying common conditions that present with acute cardiorespiratory breathlessness.

METHODS AND ANALYSIS

A prospective real-world observational study carried out across three acute admissions units within Leicestershire. Participants with self-reported acute breathlessness, with a confirmed primary diagnosis of either acute heart failure, community-acquired pneumonia and acute exacerbation of asthma or chronic obstructive pulmonary disease will be recruited within 24 hours of admission. Additionally, school-age children admitted with severe asthma will be evaluated. All participants will undergo breath sampling on admission and on recovery following discharge. A range of online technologies including: proton transfer reaction mass spectrometry, gas chromatography ion mobility spectrometry, atmospheric pressure chemical ionisation-mass spectrometry and offline technologies including gas chromatography mass spectroscopy and comprehensive two-dimensional gas chromatography-mass spectrometry will be used for VOC discovery and replication. For offline technologies, a standardised CE-marked breath sampling device (ReCIVA) will be used. All recruited participants will be characterised using existing blood biomarkers including C reactive protein, brain-derived natriuretic peptide, troponin-I and blood eosinophil levels and further evaluated using a range of standardised questionnaires, lung function testing, sputum cell counts and other diagnostic tests pertinent to acute disease.

ETHICS AND DISSEMINATION

The National Research Ethics Service Committee East Midlands has approved the study protocol (REC number: 16/LO/1747). Integrated Research Approval System (IRAS) 198921. Findings will be presented at academic conferences and published in peer-reviewed scientific journals. Dissemination will be facilitated via a partnership with the East Midlands Academic Health Sciences Network and via interaction with all UK-funded Medical Research Council and Engineering and Physical Sciences Research Council molecular pathology nodes.

TRIAL REGISTRATION NUMBER

NCT03672994.

Oxidative damage of SP-D abolishes control of eosinophil extracellular DNA trap formation

The asthmatic airways are highly susceptible to inflammatory injury by air pollutants such as ozone (O₃ ), characterized by enhanced activation of eosinophilic granulocytes and a failure of immune protective mechanisms. Eosinophil activation during asthma exacerbation contributes to the proinflammatory oxidative stress by high levels of nitric oxide (NO) production and extracellular DNA release. Surfactant protein-D (SP-D), an epithelial cell product of the airways, is a critical immune regulatory molecule with a multimeric structure susceptible to oxidative modifications. Using recombinant proteins and confocal imaging, we demonstrate here that SP-D directly bound to the membrane and inhibited extracellular DNA trap formation by human and murine eosinophils in a concentration and carbohydrate-dependent manner. Combined allergic airway sensitization and O₃ exposure heightened eosinophilia and nos2 mRNA (iNOS) activation in the lung tissue and S-nitrosylation related de-oligomerisation of SP-D in the airways. In vitro reproduction of the iNOS action led to similar effects on SP-D. Importantly, S-nitrosylation abolished the ability of SP-D to block extracellular DNA trap formation. Thus, the homeostatic negative regulatory feedback between SP-D and eosinophils is destroyed by the NO-rich oxidative lung tissue environment in asthma exacerbations.

The potential role of exhaled breath analysis in the diagnostic process of pneumonia-a systematic review

Diagnostic strategies currently used for pneumonia are time-consuming, lack accuracy and suffer from large inter-observer variability. Exhaled breath contains thousands of volatile organic compounds (VOCs), which include products of host and pathogen metabolism. In this systematic review we investigated the use of so-called 'breathomics' for diagnosing pneumonia. A Medline search yielded 18 manuscripts reporting on animal and human studies using organic and inorganic molecules in exhaled breath, that all could be used to answer whether analysis of VOC profiles could potentially improve the diagnostic process of pneumonia. Papers were categorised based on their specific aims; the exclusion of pneumonia; the detection of specific respiratory pathogens; and whether targeted or untargeted VOC analysis was used. Ten studies reported on the association between VOCs and presence of pneumonia. Eight studies demonstrated a difference in exhaled VOCs between pneumonia and controls; in the individual studies this discrimination was based on unique sets of VOCs. Eight studies reported on the accuracy of a breath test for a specific respiratory pathogen: five of these concerned pre-clinical studies in animals. All studies were valued as having a high risk of bias, except for one study that used an external validation cohort. The findings in the identified studies are promising. However, as yet no breath test has been shown to have sufficient diagnostic accuracy for pneumonia. We are in need of studies that further translate the knowledge from discovery studies to clinical practice.

The use of fractional exhaled nitric oxide is valuable in select asthmatic patients

PURPOSE OF REVIEW

Clinical management of asthma is challenging and measuring fractional exhaled nitric oxide (FeNO) can be another tool to assist in meeting this challenge.

RECENT FINDINGS

Asthma is a heterogeneous condition. There are many different phenotypes. FeNO can help the physician identify which patients have eosinophilic inflammation and would potentially respond to corticosteroid therapy.

SUMMARY

FeNO is a complement to standard asthma care. FeNO can be used in the initial diagnosis of asthma and aid in stratification of which patients would be steroid responsive but also for assessment of disease severity, response to treatment, and compliance.

Interleukin-13 stimulates production of nitric oxide in cultured human nasal epithelium

The diversity and extent of signaling functions of nitric oxide (NO) in cell physiology as well as its presence and influence as a common component of ambient air pollution and tobacco smoke are gaining increasing research attention relative to both health and disease. While cellular NO production is typically associated with inflammatory cells and processes, the airway epithelium particularly of the paranasal sinuses, has been documented to be a rich source of excreted NO. Inasmuch as excreted NO derives from both mucosal and inflammatory cell sources, distinguishing the individual contribution of these compartments to total excreted cellular NO is potentially problematic. We simulated an inflammatory mucosal environment by stimulating human nasal epithelial cultures with interleukin-13 (IL-13), a mediator produced by eosinophils in asthma, allergic rhinitis, and sinusitis. While a consistent baseline of NO excretion in control cultures was documented, widely variable individual responses to IL-13 exposure were observed in companion cultures maintained under identical conditions and tested at the same time. These studies suggest that cellular NO excretion by the healthy epithelial mucosa is subject to considerable individual variability and may be significantly elevated among some individuals in the presence of IL-13 stimulation.

Intravenous superoxide dismutase as a protective agent to prevent impairment of lung function induced by high tidal volume ventilation

Background

Positive-pressure mechanical ventilation is essential in assisting patients with respiratory failure in the intensive care unit and facilitating oxygenation in the operating room. However, it was also recognized as a primary factor leading to hospital-acquired pulmonary dysfunction, in which pulmonary oxidative stress and lung inflammation had been known to play important roles. Cu/Zn superoxide dismutase (SOD) is an important antioxidant, and possesses anti-inflammatory capacity. In this study, we aimed to study the efficacy of Cu/Zn SOD, administered intravenously during high tidal volume (HTV) ventilation, to prevent impairment of lung function.

Methods

Thirty-eight male Sprague-Dawley rats were divided into 3 groups: 5 h ventilation with (A) low tidal volume (LTV; 8 mL/kg; n = 10), (B) high tidal volume (HTV; 18 mL/kg; n = 14), or (C) HTV and intravenous treatment of Cu/Zn SOD at a dose of 1000 U/kg/h (HTV + SOD; n = 14). Lung function was evaluated both at baseline and after 5-h ventilation. Lung injury was assessed by histological examination, lung water and protein contents in the bronchoalveolar lavage fluid (BALF). Pulmonary oxidative stress was examined by concentrations of methylguanidine (MG) and malondialdehyde (MDA) in BALF, and antioxidative activity by protein expression of glutathione peroxidase-1 (GPx-1) in the lung. Severity of lung inflammation was evaluated by white blood cell and differential count in BALF, and protein expression of inducible nitric oxide synthase (iNOS), intercellular adhesion molecule-1 (ICAM-1), tumor necrosis factor-α (TNF-α), matrix metalloproteinase-9 (MMP-9), and mRNA expression of nuclear factor-κB (NF-κB) in the lung. We also examined protein expression of surfactant protein (SP)-A and D and we measured hourly changes in serum nitric oxide (NO) level.

Results

Five hours of LTV ventilation did not induce a major change in lung function, whereas 5 h of HTV ventilation induced apparent combined restrictive and obstructive lung disorder, together with increased pulmonary oxidative stress, decreased anti-oxidative activity and increased lung inflammation (P < 0.05). HTV ventilation also decreased SP-A and SP-D expression and suppressed serum NO level during the time course of ventilation. Cu/Zn SOD administered intravenously during HTV ventilation effectively reversed associated pulmonary oxidative stress and lung inflammation (P < 0.05); moreover, it preserved SP-A and SP-D expressions in the lung and increased serum nitric oxide (NO) level, enhancing vascular NO bioavailability.

Conclusions

HTV ventilation can induce combined restrictive and obstructive lung disorders. Intravenous administration of Cu/Zn SOD during HTV ventilation can prevent lung function impairment and lung injury via reducing pulmonary oxidative stress and lung inflammation, preserving pulmonary surfactant expression, and enhancing vascular NO bioavailability.

Applicability of biotechnologically produced insect silks

Silks are structural proteins produced by arthropods. Besides the well-known cocoon silk, which is produced by larvae of the silk moth Bombyx mori to undergo metamorphosis inside their silken shelter (and which is also used for textile production by men since millennia), numerous further less known silk-producing animals exist. The ability to produce silk evolved multiple independent times during evolution, and the fact that silk was subject to convergent evolution gave rise to an abundant natural diversity of silk proteins. Silks are used in air, under water, or like honey bee silk in the hydrophobic, waxen environment of the bee hive. The good mechanical properties of insect silk fibres together with their non-toxic, biocompatible, and biodegradable nature renders these materials appealing for both technical and biomedical applications. Although nature provides a great diversity of material properties, the variation in quality inherent in materials from natural sources together with low availability (except from silkworm silk) impeded the development of applications of silks. To overcome these two drawbacks, in recent years, recombinant silks gained more and more interest, as the biotechnological production of silk proteins allows for a scalable production at constant quality. This review summarises recent developments in recombinant silk production as well as technical procedures to process recombinant silk proteins into fibres, films, and hydrogels.

Changing Paradigms in the Treatment of Severe Asthma: The Role of Biologic Therapies

Cytokine antagonists are monoclonal antibodies that offer new treatment options for refractory asthma but will also increase complexity because they are effective only for patients with certain asthma subtypes that remain to be more clearly defined. The clinical and inflammatory heterogeneity within refractory asthma makes it difficult to manage the disease and to determine which, if any, biologic therapy is suitable for a specific patient. The purpose of this article is to provide a data-driven discussion to clarify the use of biologic therapies in patients with refractory asthma. We first discuss the epidemiology and pathophysiology of refractory asthma. We then interpret current evidence for biomarkers of eosinophilic or type 2-high asthma so that clinicians can determine potential treatments for patients based on knowledge of their effectiveness in specific asthma phenotypes. We then assess clinical data on the efficacy, safety, and mechanisms of action of approved and pipeline biologic therapies. We conclude by discussing the potential of phenotyping or endotyping refractory asthma and how biologic therapies can play a role in treating patients with refractory asthma.

Two inflammatory phenotypes of nasal polyps and comorbid asthma

BACKGROUND

Nasal polyps and comorbid asthma (NPCA) is a common united airway disease. However, the inflammatory phenotyes of NPCA are not clear.

OBJECTIVE

To identify inflammatory phenotypes of NPCA.

METHODS

A total of 106 patients diagnosed with NPCA were recruited from rhinologic clinics. A combined method of biopsies from nasal polyps and fractional exhaled nitric oxide (FeNO) was used to explore inflammatory phenotyes of NPCA. Patients were evaluated with respect to clinical, functional, and inflammatory parameters. Clinical outcomes after medical treatment were also assessed.

RESULTS

Two distinct inflammatory phenotypes (eosinophilic [64.15%] and noneosinophilic phenotypes [35.85%]) were identified. Inflammatory patterns of upper and lower airways were consistent in NPCA. Patients with eosinophilic NPCA had a higher nasal polyps recurrence rate than did patients with noneosinophilic NPCA, a more severe asthma phenotype (P < .001), higher exhaled nitric oxide levels (P < .001), higher IgE levels (P < .001), higher Lund-Mackay scores (P < .05), and more blood eosinophilia (P < .001). In addition, eosinophilic NPCA was associated with worse pulmonary function and responded well to an 8-week course of medical treatment based on computed tomographic findings and the ratio of forced expiratory volume in 1 second to forced vital capacity. The total IgE concentration was a marker for eosinophilic NPCA (optimal cutoff, >55.5 kU/L; sensitivity, 86.2%; specificity, 85.4%).

CONCLUSION

Patients with NPCA had 2 inflammatory phenotypes with distinct clinical profiles. Total IgE is a marker of eosinophilic NPCA.

Quantum cascade lasers (QCLs) in biomedical spectroscopy

This review focuses on the recent applications of QCLs in mid-IR spectroscopy of clinically relevant samples.

Statins in Asthma: Potential Beneficial Effects and Limitations

Asthma's sustenance as a global pandemic, across centuries, can be attributed to the lack of an understanding of its workings and the inability of the existing treatment modalities to provide a long lasting cure without major adverse effects. The discovery of statins boosted by a better comprehension of the pathophysiology of asthma in the past few decades has opened up a potentially alternative line of treatment that promises to be a big boon for the asthmatics globally. However, the initial excellent results from the preclinical and animal studies have not borne the results in clinical trials that the scientific world was hoping for. In light of this, this review analyzes the ways by which statins could benefit in asthma via their pleiotropic anti-inflammatory properties and explain some of the queries raised in the previous studies and provide recommendations for future studies in this field.

Shot-noise limited Faraday rotation spectroscopy for detection of nitric oxide isotopes in breath, urine, and blood

Measurement of NO and/or its metabolites in the various body compartments has transformed our understanding of biology. The inability of the current NO measurement methods to account for naturally occurring and experimental NO isotopes, however, has prevented the scientific community from fully understating NO metabolism in vivo. Here we present a mid-IR Faraday rotation spectrometer (FRS) for detection of NO isotopes. The instrument utilizes a novel dual modulation/demodulation (DM) FRS method which exhibits noise performance at only 2 times the fundamental quantum shot-noise level and provides the record sensitivity in its class. This is achieved with a system that is fully autonomous, robust, transportable, and does not require cryogenic cooling. The DM-FRS enables continuous monitoring of nitric oxide isotopes with the detection limits of 3.72 ppbv/Hz^1/2 to¹⁴NO and 0.53 ppbv/Hz^1/2 to¹⁵NO using only 45 cm active optical path. This DM-FRS measurement method can be used to improve the performance of conventional FRS sensors targeting other radical species. The feasibility of the instrument to perform measurements relevant to studies of NO metabolism in humans is demonstrated.

Suppressive effect of insulin on the gene expression and plasma concentrations of mediators of asthmatic inflammation

BACKGROUND AND HYPOTHESIS

Following our recent demonstration that the chronic inflammatory and insulin resistant state of obesity is associated with an increase in the expression of mediators known to contribute to the pathogenesis of asthma and that weight loss after gastric bypass surgery results in the reduction of these genes, we have now hypothesized that insulin suppresses the cellular expression and plasma concentrations of these mediators.

METHODS

The expression of IL-4, LIGHT, LTBR, ADAM-33, and TSLP in MNC and plasma concentrations of LIGHT, TGF-β1, MMP-9, MCP-1, TSLP, and NOM in obese patients with T2DM were measured before, during, and after the infusion of a low dose (2 U/h) infusion of insulin for 4 hours. The patients were also infused with dextrose or saline for 4 hours on two separate visits and served as controls. Results. Following insulin infusion, the mRNA expression of IL-4, ADAM-33, LIGHT, and LTBR mRNA expression fell significantly (P < 0.05 for all). There was also a concomitant reduction in plasma NOM, LIGHT, TGF-β1, MCP-1, and MMP-9 concentrations.

CONCLUSIONS

Insulin suppresses the expression of these genes and mediators related to asthma and may, therefore, have a potential role in the treatment of asthma.

Pharmacologic inhibition of S-nitrosoglutathione reductase protects against experimental asthma in BALB/c mice through attenuation of both bronchoconstriction and inflammation

Background

S-nitrosoglutathione (GSNO) serves as a reservoir for nitric oxide (NO) and thus is a key homeostatic regulator of airway smooth muscle tone and inflammation. Decreased levels of GSNO in the lungs of asthmatics have been attributed to increased GSNO catabolism via GSNO reductase (GSNOR) leading to loss of GSNO- and NO- mediated bronchodilatory and anti-inflammatory actions. GSNOR inhibition with the novel small molecule, N6022, was explored as a therapeutic approach in an experimental model of asthma.

Methods

Female BALB/c mice were sensitized and subsequently challenged with ovalbumin (OVA). Efficacy was determined by measuring both airway hyper-responsiveness (AHR) upon methacholine (MCh) challenge using whole body plethysmography and pulmonary eosinophilia by quantifying the numbers of these cells in the bronchoalveolar lavage fluid (BALF). Several other potential biomarkers of GSNOR inhibition were measured including levels of nitrite, cyclic guanosine monophosphate (cGMP), and inflammatory cytokines, as well as DNA binding activity of nuclear factor kappa B (NFκB). The dose response, onset of action, and duration of action of a single intravenous dose of N6022 given from 30 min to 48 h prior to MCh challenge were determined and compared to effects in mice not sensitized to OVA. The direct effect of N6022 on airway smooth muscle tone also was assessed in isolated rat tracheal rings.

Results

N6022 attenuated AHR (ED₅₀ of 0.015 ± 0.002 mg/kg; Mean ± SEM) and eosinophilia. Effects were observed from 30 min to 48 h after treatment and were comparable to those achieved with three inhaled doses of ipratropium plus albuterol used as the positive control. N6022 increased BALF nitrite and plasma cGMP, while restoring BALF and plasma inflammatory markers toward baseline values. N6022 treatment also attenuated the OVA-induced increase in NFκB activation. In rat tracheal rings, N6022 decreased contractile responses to MCh.

Conclusions

The significant bronchodilatory and anti-inflammatory actions of N6022 in the airways are consistent with restoration of GSNO levels through GSNOR inhibition. GSNOR inhibition may offer a therapeutic approach for the treatment of asthma and other inflammatory lung diseases. N6022 is currently being evaluated in clinical trials for the treatment of inflammatory lung disease.

Clinical utility of asthma biomarkers: from bench to bedside

Asthma is a chronic disease characterized by airway inflammation, bronchial hyperresponsiveness, and recurrent episodes of reversible airway obstruction. The disease is very heterogeneous in onset, course, and response to treatment, and seems to encompass a broad collection of heterogeneous disease subtypes with different underlying pathophysiological mechanisms. There is a strong need for easily interpreted clinical biomarkers to assess the nature and severity of the disease. Currently available biomarkers for clinical practice - for example markers in bronchial lavage, bronchial biopsies, sputum, or fraction of exhaled nitric oxide (FeNO) - are limited due to invasiveness or lack of specificity. The assessment of markers in peripheral blood might be a good alternative to study airway inflammation more specifically, compared to FeNO, and in a less invasive manner, compared to bronchoalveolar lavage, biopsies, or sputum induction. In addition, promising novel biomarkers are discovered in the field of breath metabolomics (eg, volatile organic compounds) and (pharmaco)genomics. Biomarker research in asthma is increasingly shifting from the assessment of the value of single biomarkers to multidimensional approaches in which the clinical value of a combination of various markers is studied. This could eventually lead to the development of a clinically applicable algorithm composed of various markers and clinical features to phenotype asthma and improve diagnosis and asthma management.

Asthma in pregnancy: a review

Asthma is one of the most common medical conditions in women of childbearing age. There are now data to show that asthma is not a benign condition with respect to maternal and fetal health. Despite this there are several problems encountered in the management of such women. There is a tendency to cease or reduce optimal asthma treatments because pregnant women and/or their clinicians may believe they pose a risk to the fetus. There is also a lack of clinician awareness of the complications of asthma in pregnancy.

Stress, asthma, and respiratory infections: pathways involving airway immunology and microbial endocrinology

Stress and infections have long been independently associated with asthma pathogenesis and exacerbation. Prior research has focused on the effect of psychological stress on Th cells with particular relevance to atopic asthma. In this review, we propose new perspectives that integrate the role of infection in the relationship between psychological stress and asthma. We highlight the essential role of the mucosal epithelia of the airways in understanding the interaction between infections and the stress-asthma relationship. In addition, we review findings suggesting that psychological stress not only modulates immune processes, but also the pathogenic qualities of bacteria, with implications for the pathogenesis and exacerbation asthma.

Academic exam stress and depressive mood are associated with reductions in exhaled nitric oxide in healthy individuals

Nitric oxide (NO) has beneficial effects on cardiovascular and immune health. Stress and depression have been linked to a reduction in serum NO. In this study, we examined the effect of academic exam stress on the fraction of NO in exhaled air (FeNO) and spirometric lung function in 41 healthy college students. Participants completed assessments at mid-semester as well as in the early and late phase of an academic exam period. Negative affect, depressive mood, and salivary cortisol were elevated during exams, whereas FeNO and lung function decreased. Higher depressive mood was associated with lower FeNO, whereas higher negative affect was associated higher FeNO across time. These findings provide initial evidence that depression and prolonged stress can alter FeNO and lung function in healthy individuals, which could have adverse consequences for cardiovascular, airway, and immune health.

Evidence of microglial activation in autism and its possible role in brain underconnectivity

Evidence indicates that children with autism spectrum disorder (ASD) suffer from an ongoing neuroinflammatory process in different regions of the brain involving microglial activation. When microglia remain activated for an extended period, the production of mediators is sustained longer than usual and this increase in mediators contributes to loss of synaptic connections and neuronal cell death. Microglial activation can then result in a loss of connections or underconnectivity. Underconnectivity is reported in many studies in autism. One way to control neuroinflammation is to reduce or inhibit microglial activation. It is plausible that by reducing brain inflammation and microglial activation, the neurodestructive effects of chronic inflammation could be reduced and allow for improved developmental outcomes. Future studies that examine treatments that may reduce microglial activation and neuroinflammation, and ultimately help to mitigate symptoms in ASD, are warranted.

Exhaled nitric oxide

Nitric oxide (NO) is now considered an important biomarker for respiratory disease. Studies have confirmed that the fractional concentration of exhaled nitric oxide (FENO) is elevated in the airways of patients who have asthma in comparison with controls. The level of FENO correlates well with the presence and level of inflammation, and decreases with glucocorticoid treatment. NO has potential to be used not only as a diagnostic aid but also as a management tool for assessing severity, monitoring response to therapy, and gaining control of asthma symptoms. This article reviews the biology of NO and its role in respiratory disease.

Environmental effects on fractional exhaled nitric oxide in allergic children

Fractional exhaled nitric oxide (FeNO) is a non-invasive marker of airway inflammation in asthma and respiratory allergy. Environmental factors, especially indoor and outdoor air quality, may play an important role in triggering acute exacerbations of respiratory symptoms. The authors have reviewed the literature reporting effects of outdoor and indoor pollutants on FeNO in children. Although the findings are not consistent, urban and industrial pollution-mainly particles (PM(2.5) and PM(10)), nitrogen dioxide (NO(2)), and sulfur dioxide (SO(2))-as well as formaldehyde and electric baseboard heating have been shown to increase FeNO, whilst ozone (O(3)) tends to decrease it. Among children exposed to Environmental Tobacco Smoke (ETS) with a genetic polymorphisms in nitric oxide synthase genes (NOS), a higher nicotine exposure was associated with lower FeNO levels. Finally, although more studies are needed in order to better investigate the effect of gene and environment interactions which may affect the interpretation of FeNO values in the management of children with asthma, clinicians are recommended to consider environmental exposures when taking medical histories for asthma and respiratory allergy. Further research is also needed to assess the effects of remedial interventions aimed at reducing/abating environmental exposures in asthmatic/allergic patients.

Effects of atopy and rhinitis on exhaled nitric oxide values - a systematic review

Background

Atopy and rhinitis are among the factors affecting exhaled nitric oxide (FeNO) values and may contribute to difficulties in the clinical interpretation of FeNO measurements. However, data assessing their effects on FeNO values had never been summarized. This review aims to evaluate the effect of atopy and rhinitis in FeNO values in otherwise healthy individuals.

Methods

A systematic review was performed in Pubmed, Scopus and ISI Web of Knowledge. A two-step selection process was completed, and from 2357 references 19 were included. The inclusion criteria were: participants without known diseases other than rhinitis; atopy assessement by SPT or Specific IgE; and FeNO measurements according to ATS/ERS recommendations.

Results

The 8 articles measuring FeNO in children showed higher values in both allergic rhinitis and atopic children when compared with healthy children. The 11 articles performed in adults observed higher FeNO in AR patients comparatively with either healthy or atopic individuals. However, adult healthy and atopic individuals had similar FeNO values.

Conclusions

FeNO values are higher in individuals with rhinitis and/or atopy without other health problems. These effects are small, seem to be independent and should be further studied using multivariate models. The effect of atopy was observed only in children. The combined effect of atopy and rhinitis produced higher FeNO values in adults. These results support that both atopy and rhinitis should be considered when interpreting or when defining FeNO reference values.

Nitric oxide metabolism in asthma pathophysiology

BACKGROUND

Asthma, a chronic inflammatory disease is typically characterized by bronchoconstriction and airway hyper-reactivity.

SCOPE OF REVIEW

A wealth of studies applying chemistry, molecular and cell biology to animal model systems and human asthma over the last decade has revealed that asthma is associated with increased synthesis of the gaseous molecule nitric oxide (NO).

MAJOR CONCLUSION

The high NO levels in the oxidative environment of the asthmatic airway lead to greater formation of reactive nitrogen species (RNS) and subsequent oxidation and nitration of proteins, which adversely affect protein functions that are biologically relevant to chronic inflammation. In contrast to the high levels of NO and nitrated products, there are lower levels of beneficial S-nitrosothiols (RSNO), which mediate bronchodilation, due to greater enzymatic catabolism of RSNO in the asthmatic airways.

GENERAL SIGNIFICANCE

This review discusses the rapidly accruing data linking metabolic products of NO as critical determinants in the chronic inflammation and airway reactivity of asthma. This article is part of a Special Issue entitled Biochemistry of Asthma.

Inflammatory markers in childhood asthma

The major characteristic of asthma is persistent airway inflammation that fails to resolve spontaneously. Dysregulation of pro- and anti-inflammatory mechanisms is responsible for the development of chronic inflammation. The inflammatory reaction is mediated by numerous cells and their mediators. Detection and quantification of airway inflammation in children are subject to many requirements, e.g., use of biologic samples obtained in a non-invasive way; use of standardized analytical methods to determine biomarkers that can identify inflammation processes (inflammation itself, oxidative stress, apoptosis and remodelling); determining the role of systemic inflammation; assessment of correlation of various biomarkers of inflammation with clinical parameters and their diagnostic efficacy; providing a tool(s) to monitor diseases, and to evaluate adequacy of therapy; and predicting the clinical course of inflammation and prognosis of asthma. Using standardized analyses, it is now possible to determine direct markers of local inflammation, i.e., fractional nitric oxide (marker of oxidative stress) in exhaled breath, pH (marker of acid stress) in breath condensate, and indirect markers in blood/serum, i.e., eosinophil granulocytes (indicating migration), eosinophil cationic protein (marker of activated eosinophil granulocytes) and C-reactive protein (marker of systemic inflammation). However, none of these biomarkers are specific for asthma. Further standardization of the known pulmonary biomarkers of local inflammation and identification of new ones will allow for longitudinal follow-up of inflammation in children with asthma.

Air pollution and increased levels of fractional exhaled nitric oxide in children with no history of airway damage

Air pollution is associated with a wide range of adverse respiratory events. In order to study the mechanism associated with these effects, the relationships between fractional exhaled nitric oxide (FeNO), a potential marker of airway inflammation, and exposure to air pollution were examined in schoolchildren. FeNO was measured in 104 children (34 asthmatics and 70 non-asthmatics) drawn from the general population simultaneously with air pollution assessments (fine particles with an aerodiameter under 2.5 microm, nitrogen dioxide, acetaldehyde, and formaldehyde, with pumps and passive samplers) in schoolyards and classrooms. Asthmatics exhaled more FeNO than non-asthmatics. FeNO levels were significantly elevated in both asthmatic and non-asthmatic children exposed to high concentrations of formaldehyde, acetaldehyde, and PM(2.5). Differences between high versus low exposure in non-asthmatics resulted in an FeNO increase ranging from 45% for indoor acetaldehyde to 62% for indoor PM(2.5). Stronger associations were found in non-asthmatic children who were atopic, suggesting that atopic children may be more sensitive to air pollution than non-atopic children. Exposure to air pollution may lead to airway inflammation, as measured by FeNO, in schoolchildren. These associations occur even in children with no history of airway damage and seem to be enhanced in atopic subjects.

Exhaled nitric oxide - circadian variations in healthy subjects

OBJECTIVE

Exhaled nitric oxide (eNO) has been suggested as a marker of airway inflammatory diseases. The level of eNO is influenced by many various factor including age, sex, menstrual cycle, exercise, food, drugs, etc. The aim of our study was to investigate a potential influence of circadian variation on eNO level in healthy subjects.

METHODS

Measurements were performed in 44 women and 10 men, non-smokers, without respiratory tract infection in last 2 weeks. The eNO was detected at 4-hour intervals from 6 a.m. to 10 p.m. using an NIOX analyzer. We followed the ATS/ERS guidelines for eNO measurement and analysis.

RESULTS

Peak of eNO levels were observed at 10 a.m. (11.1 +/- 7.2 ppb), the lowest value was detected at 10 p.m. (10.0 +/- 5.8 ppb). The difference was statistically significant (paired t-test, P<0.001).

CONCLUSIONS

The daily variations in eNO, with the peak in the morning hours, could be of importance in clinical practice regarding the choice of optimal time for monitoring eNO in patients with respiratory disease.

L-arginine reverses cigarette-induced reduction of fractional exhaled nitric oxide in asthmatic smokers

INTRODUCTION

Complex mechanisms regulate nitric oxide (NO) synthesis. Cigarette smoking decreases fractional exhaled NO (FE(NO)), while asthmatic inflammation increases FE(NO). To assess whether the smoking-induced decrease in FE(NO) levels was reversible, asthmatic and non-asthmatic smokers inhaled the NO synthase (NOS) substrate, L-arginine. Aminoguanidine, a relatively selective Type II NOS inhibitor, was used also to assess the role of NOS subtypes in these changes of FE(NO).

METHODS

The study was a single-blinded, placebo-controlled, cross-over design in two parts. Part I: smoking asthmatic and non-asthmatic smoking subjects smoked one cigarette and then inhaled nebulised L-arginine or L-alanine (control). Spirometry, FE(NO), nasal NO (FN(NO)), FE(CO), were measured for 4 h. Part II: subjects inhaled nebulised aminoguanidine prior to an identical protocol as in Part I. Change in FE(NO) was assessed as area under the curve (AUC).

RESULTS

Part I: In asthmatic smokers, cigarette smoking followed by L-arginine caused a significant median increase in AUC of 29.2(17)% FE(NO) change/hour (p = 0.04), which did not occur in non-asthmatic smokers (baseline FE(NO) 12.7(7.1-18) vs. 6.7(4-9.2) ppb, respectively). Part II: Aminoguanidine prior to smoking caused a significant fall in FE(NO) in both asthmatic and non-asthmatic smokers. L-arginine showed significant reversal of this effect in both asthmatic and non-asthmatic subjects.

CONCLUSIONS

In asthmatic smokers, L-arginine increases FE(NO) after cigarette smoking but not in non-asthmatic smokers. The decrease in FE(NO) after aminoguanidine and subsequent partial reversal by L-arginine in both groups, suggests that Type II NOS contributes to the FE(NO) in both.

Exhaled nitric oxide

Exhaled nitric oxide (FENO) is a noninvasive easily measurable biomarker that is proving to be an excellent surrogate for eosinophilic inflammation in the lungs of patients who have asthma. Although large-scale normative data are still awaited, preliminary studies have shown FENO to be helpful in diagnosing and assessing severity and control for asthma. FENO levels have also proven helpful in diagnosing and managing several other inflammatory lung diseases.

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.

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.

Exhaled nitric oxide is decreased by exposure to the hyperbaric oxygen therapy environment

Exhaled nitric oxide (eNO) detects airway inflammation. Hyperbaric oxygen therapy (HBOT) is used for tissue hypoxia, but can cause lung damage. We measured eNO following inhalation of oxygen at different tensions and pressures. Methods. Part 1, eNO was measured before and after HBOT. Part 2, normal subjects breathed 40% oxygen. Results. Baseline eNO levels in patients prior to HBOT exposure were significantly higher than in normal subjects (P < .05). After HBOT, eNO significantly decreased in patients (15.4 ± 2.0 versus 4.4 ± 0.5 ppb, P < .001), but not in normal subjects, after either 100% O₂ at increased pressure or 40% oxygen, 1 ATA. In an in vitro study, nitrate/nitrite release decreased after 90 minutes HBOT in airway epithelial (A549) cells. Conclusion. HBO exposure causes a fall in eNO. Inducible nitric oxide synthase (iNOS) may cause elevated eNO in patients secondary to inflammation, and inhibition of iNOS may be the mechanism of the reduction of eNO seen with HBOT.

Measurement of exhaled nitric oxide in beef cattle using tunable diode laser absorption spectroscopy

Measurement of nitric oxide (NO) in the expired breath of crossbred calves received at a research facility was performed using tunable diode laser absorption spectroscopy. Exhaled NO (eNO) concentrations were measured using NO absorption lines at 1912.07 cm(-1) and employing background subtraction. The lower detection limit and measurement precision were determined to be approximately 330 parts in 10(12) per unit volume. A custom breath collection system was designed to collect lower airway breath of spontaneously breathing calves while in a restraint chute. Breath was collected and analyzed from calves upon arrival and periodically during a 42 day receiving period. There was a statistically significant relationship between eNO, severity of bovine respiratory disease (BRD) in terms of number of times treated, and average daily weight gain over the first 15 days postarrival. In addition, breathing patterns and exhaled CO2 showed a statistically significant relationship with BRD morbidity.

AMP challenge induces a decrease in FE(NO) in asthmatic subjects modulated by nedocromil

BACKGROUND

Allergen challenge results in an immediate reduction in exhaled nitric oxide (FE(NO)) followed by a long-term increase. To study mast cell activation in relation to nitric oxide (NO), the study investigated the effect of inhaled adenosine monophosphate (AMP) as a mast cell activator and mast cell stabilizer - nedocromil sodium - on FE(NO). The NO synthase (NOS) iso-enzyme involved was studied by the NOS inhibitor aminoguanidine.

MATERIALS AND METHODS

A double-blind, placebo-controlled, cross-over study was performed in two parts. Part I: eight atopic asthmatic subjects inhaled nedocromil or placebo before the AMP challenge. Spirometry and FE(NO) were measured at intervals over a 24-h period. Part II: seven subjects inhaled aminoguanidine before an identical protocol was used, as in Part I.

RESULTS

Part I: AMP challenge caused a significant decrease from baseline FE(NO)[placebo, 28.9 (20.3-37.4)%, P < 0.002 and nedocromil, 20.9 (8.2-33.6)%, P < 0.01]. Nedocromil gave partial protection against this decrease in FE(NO). The time-FE(NO) curve (AUC(0-24)) differed significantly between nedocromil and placebo: 2.7% (-3.6 to -9) vs. -6.6% (-12 to -1.3) FE(NO) changes h(-1), P < 0.002, respectively. Nedocromil protected against AMP-induced bronchoconstriction (AMP PC(20)) [nedocromil 182 (72.5-291) mg mL(-1) vs. placebo 21.7 (10.7-33) mg mL(-1), P < 0.002]. Part II: nebulized aminoguanidine resulted in a significant reduction in FE(NO) from baseline and was greater than after AMP alone (P = 0.006). Nedocromil increased AMP PC(20), but no longer protected against the late decrease in FE(NO).

CONCLUSIONS

The AMP challenge caused a reduction in FE(NO) as a result of prior treatment with nedocromil. Aminoguanidine abolished the nedocromil-induced protection on the late reduction in FE(NO), but not on AMP PC(20). Inducible NOS was implicated in the late FE(NO) decrease after the AMP challenge.

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.