Relationship between exhaled nitric oxide and airway hyperresponsiveness following experimental rhinovirus infection in asthmatic subjects

ERS technical standard: Global Lung Function Initiative reference values for exhaled nitric oxide fraction (F ENO50 )

BACKGROUND

Elevated exhaled nitric oxide fraction at a flow rate of 50 mL·s-1 (F ENO50 ) is an important indicator of T-helper 2-driven airway inflammation and may aid clinicians in the diagnosis and monitoring of asthma. This study aimed to derive Global Lung Function Initiative reference equations and the upper limit of normal for F ENO50 .

METHODS

Available individual F ENO50 data were collated and harmonised using consensus-derived variables and definitions. Data collected from individuals who met the harmonised definition of "healthy" were analysed using the generalised additive models of location, scale and shape (GAMLSS) technique.

RESULTS

Data were retrospectively collated from 34 782 individuals from 34 sites in 15 countries, of whom 8022 met the definition of healthy (19 sites, 11 countries). Overall, height, age and sex only explained 12% of the between-subject variability of F ENO50 (R2=0.12). F ENO device was neccessary as a predictor of F ENO50 , such that the healthy range of values and the upper limit of normal varied depending on which device was used. The range of F ENO50 values observed in healthy individuals was also very wide, and the heterogeneity was partially explained by the device used. When analysing a subset of data in which F ENO50 was measured using the same device and a stricter definition of health (n=1027), between-site heterogeneity remained.

CONCLUSION

Available F ENO50 data collected from different sites using different protocols and devices were too variable to develop a single all-age reference equation. Further standardisation of F ENO devices and measurement are required before population reference values might be derived.

Clinical Characteristics of Post-COVID-19 Persistent Cough in the Omicron Era

Cough is one of the most common symptoms of acute coronavirus disease 2019, but cough may persist for weeks or months. This study aimed to examine the clinical characteristics of patients with post-coronavirus disease (COVID) persistent cough in the Omicron era. We conducted a pooled analysis comparing 3 different groups: 1) a prospective cohort of post-COVID cough (> 3 weeks; n = 55), 2) a retrospective cohort of post-COVID cough (> 3 weeks; n = 66), and 3) a prospective cohort of non-COVID chronic cough (CC) (> 8 weeks; n = 100). Cough and health status was assessed using patient-reported outcomes (PROs). Outcomes, including PROs and systemic symptoms, were longitudinally evaluated in the prospective post-COVID cough registry participants receiving usual care. A total of 121 patients with post-COVID cough and 100 with non-COVID CC were studied. Baseline cough-specific PRO scores did not significantly differ between post-COVID cough and non-COVID CC groups. There were no significant differences in chest imaging abnormality or lung function between groups. However, the proportions of patients with fractional exhaled nitric oxide (FeNO) ≥ 25 ppb were 44.7% in those with post-COVID cough and 22.7% in those with non-COVID CC, which were significantly different. In longitudinal assessment of the post-COVID registry (n = 43), cough-specific PROs, such as cough severity or Leicester Cough Questionnaire (LCQ) scores, significantly improved between visits 1 and 2 (visit interval: median 35 [interquartile range, IQR: 23-58] days). In the LCQ score, 83.3% of the patients showed improvement (change ≥ +1.3), but 7.1% had worsened (≤ -1.3). The number of systemic symptoms was median 4 (IQR: 2-7) at visit 1 but decreased to median 2 (IQR: 0-4) at visit 2. In summary, post-COVID persistent cough was similar in overall clinical characteristics to CC. Current cough guideline-based approaches may be effective in most patients with post-COVID cough. Measurement of FeNO levels may also be useful for cough management.

Variability of fractional exhaled nitric oxide is associated with the risk and aetiology of COPD exacerbations

BACKGROUND AND OBJECTIVE

Acute exacerbations of chronic obstructive pulmonary disease (AECOPD) are heterogeneous in aetiology and accelerate disease progression. Here, we aimed to investigate the association of fractional exhaled nitric oxide (FeNO) and its variability with AECOPD of different aetiology.

METHODS

FeNO was determined in 2157 visits (1697 stable, 133 AECOPD and 327 follow-up) of 421 COPD patients from the PREVENT study, an investigator-initiated, longitudinal and interventional study, who were on daily treatment with inhaled corticosteroids/long-acting β2-agonists.

RESULTS

Longitudinal measurements of FeNO revealed an intra-subject variability of FeNO that was significantly higher in exacerbators compared to non-exacerbators (p < 0.001) and positively associated with the number of AECOPD. As FeNO variability increased, the probability of patients to remain AECOPD-free decreased. In patients included in the highest FeNO variability quartile (≥15.0 ppb) the probability to remain free of AECOPD was only 35% as compared to 80% for patients included in the lowest FeNO variability quartile (0.50-4.39 ppb). The change of FeNO from the last stable visit to AECOPD was positively associated with the probability of viral infections and this association was stronger in current smokers than ex-smokers. In contrast, the change in FeNO from the last stable visit to an AECOPD visit was inversely associated with the probability of bacterial infections in ex-smokers but not in current smokers.

CONCLUSION

FeNO variability was associated with the risk and aetiology of AECOPD differentially in current and ex-smokers.

The role of exhaled nitric oxide (FeNO) in the evaluation of lung parenchymal involvement in COVID-19 patients

The inflammatory balance is an important factor in the clinical course of COVID-19 (SARS-CoV-2) infection, which has affected over 300 million people globally since its appearance in December 2019. This study aimed to evaluate the correlation between exhaled nitric oxide (FeNO) level and parenchymal involvement in COVID-19. The study included 106 patients with the delta variant of COVID-19 identified by real-time PCR as well as 40 healthy control groups between October 2021 and March 2022. The patients were analyzed in three groups: moderate COVID-19 (group 1), severe COVID-19 without macrophage activation syndrome (MAS) (group 2), and severe COVID-19 with MAS (group 3). FeNO and CT scores were significantly higher in groups 2 and 3 at admission and discharge compared to group 1 (p = 0.001 for all). In addition, CT score at admission and CT score and FeNO level at discharge were higher in group 3 than in group 2 (p = 0.001 for all). It was found that the FeNO levels were higher in Groups 2 and 3 than in the control group (p = 0.001) during the admission. FeNO and CT scores showed strong positive correlation at admission and discharge (r = 0.917, p = 0.001; r = 0.790, p = 0.001). In receiver operating characteristic curve analysis for prediction of MAS, FeNO at a cut-off of 10.5 ppb had 66% sensitivity and 71% specificity. COVID-19 causes more severe lung involvement than other viral lower respiratory tract infections, leading to the frequent use of chest CT in these patients. FeNO assessment is a practical and noninvasive method that may be useful in evaluating for parenchymal infiltration in the diagnosis and follow-up of COVID-19 patients.

Nasal nitric oxide is decreased in acute mild COVID-19 and related to viral load

Gaseous nitric oxide levels from the lungs (FeNO) and from the nose (nNO) have been demonstrated to react to acute infection or influenza vaccination. There are no published data on nNO levels during acute COVID-19, but normal levels of FeNO have been reported in one study. Our aim was to assess if acute mild COVID-19 alters nasal or bronchial NO output at the time of acute infection and at a 2-month follow up, and if this is related to symptoms or viral load. This study included 82 subjects with mild acute airway infection who did not need hospitalisation: 43 cases (RT-PCR-positive for SARS-CoV-2 in routine testing from nasopharynx) and 39 age- (+/- 5 years) and gender-matched controls (RT-PCR-negative for SARS-CoV-2). During acute infection, the cases had lower nNO compared to controls (526 [345-688] vs. 773 [677-929] ppb; p<0.001), but after two months, there was no significant difference between the groups (766 [597-965] vs. 893 [739-1066] ppb; p=0.162). There was no difference in FeNO between the groups at either of the visits. Nasal NO correlated with the cycle threshold (Ct) value of the nasopharyngeal RT-PCR test for SARS-CoV-2 (Spearman's rs=0.550; p<0.001), that is, nNO was lower with a higher viral load. Nasal NO output was decreased in acute COVID-19 in relation to higher viral load, suggesting that the type and intensity of inflammatory response affects the release of NO from airway mucosa. In these subjects without significant lower airway involvement, there were no clinically relevant findings regarding FeNO.

Experimental Antiviral Therapeutic Studies for Human Rhinovirus Infections

Rhinovirus infection is common and usually causes mild, self-limiting upper respiratory tract symptoms. Rhinoviruses can cause exacerbation of chronic respiratory diseases, such as asthma or chronic obstructive pulmonary disease, leading to a significant burden of morbidity and mortality. There has been a great deal of progress in efforts to understand the immunological basis of rhinovirus infection. However, despite a number of in vitro and in vivo attempts, there have been no effective treatments developed. This review article summarises the up to date virological and immunological understanding of these infections. We discuss the challenges researchers face, and key solutions, in their work to investigate potential therapies including in vivo rhinovirus challenge studies. Finally, we explore past and present experimental therapeutic strategies employed in the treatment of rhinovirus infections and highlight promising areas of future work.

Nitric oxide's physiologic effects and potential as a therapeutic agent against COVID-19

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for COVID-19 pneumonia, a pandemic that precipitates huge pressures on the world's social and economic systems. Disease severity varies among individuals. SARS-CoV-2 infection can be associated with e.g. flu-like symptoms, dyspnoea, severe interstitial pneumonia, acute respiratory distress syndrome, multiorgan dysfunction, and generalized coagulopathy. Nitric oxide (NO), is a small signal molecule that impacts pleiotropic functions in human physiology, which can be involved in the significant effects of COVID-19 infection. NO is a neurotransmitter involved in the neural olfactory processes in the central nervous system, and some infected patients have reported anosmia as a symptom. Additionally, NO is a well-known vasodilator, important coagulation mediator, anti-microbial effector and inhibitor of SARS-CoV replication. Exhaled NO is strongly related to the type-2 inflammatory response found in asthma, which has been suggested to be protective against SARS-CoV-2 infection. Several reports indicate that the use of inhaled NO has been an effective therapy during this pandemic since the ventilation-perfusion ratio in COVID-19 patients improved afterwards and they did not require mechanical ventilation. The aim of this mini-review is to summarize relevant actions of NO that could be beneficial in the treatment of COVID-19.

Evolution of Airway Inflammation in Preschoolers with Asthma-Results of a Two-Year Longitudinal Study

Fractional exhaled nitric oxide (FeNO) is a non-invasive marker for eosinophilic airway inflammation and has been used for monitoring asthma. Here, we assess the characteristics of FeNO from preschool to school age, in parallel with asthma activity. A total of 167 asthmatic children and 66 healthy, age-matched controls were included in the 2-year prospective PreDicta study evaluating wheeze/asthma persistence in preschool-aged children. Information on asthma/rhinitis activity, infections and atopy was recorded at baseline. Follow-up visits were performed at 6-month intervals, as well as upon exacerbation/cold and 4–6 weeks later in the asthmatic group. We obtained 539 FeNO measurements from asthmatics and 42 from controls. At baseline, FeNO values did not differ between the two groups (median: 3.0 ppb vs. 2.0 ppb, respectively). FeNO values at 6, 12, 18 and 24 months (4.0, CI: 0.0–8.6; 6.0, CI: 2.8–12.0; 8.0, CI: 4.0–14.0; 8.5, CI: 4.4–14.5 ppb, respectively) increased with age (correlation p ≤ 0.001) and atopy (p = 0.03). FeNO was non-significantly increased from baseline to the symptomatic visit, while it decreased after convalescence (p = 0.007). Markers of disease activity, such as wheezing episodes and days with asthma were associated with increased FeNO values during the study (p < 0.05 for all). Age, atopy and disease activity were found to be important FeNO determinants in preschool children. Longitudinal and individualized FeNO assessment may be valuable in monitoring asthmatic children with recurrent wheezing or mild asthma.

In vivo experimental models of infection and disease

Human and animal models continue to play a crucial role in research to understand host immunity to rhinovirus (RV) and identify disease mechanisms. Human models have provided direct evidence that RV infection is capable of exacerbating chronic respiratory diseases and identified immunological processes that correlate with clinical disease outcomes. Mice are the most commonly used nonhuman experimental RV infection model. Although semipermissive, under defined experimental conditions sufficient replication occurs to induce host immune responses that recapitulate immunity and disease during human infection. The capacity to use genetically modified mouse strains and drug interventions has shown the mouse model to be an invaluable research tool defining causal relationships between host immunity and disease and supporting development of new treatments. Used in combination the insights achieved from human and animal experimental infection models provide complementary insights into RV biology and yield novel therapeutic options to reduce the burden of RV-induced disease.

Exhaled nitric oxide in a middle-aged Icelandic population cohort

The prevalence of atopy and asthma is relatively low in Iceland. The purpose of this study was to describe exhaled nitric oxide (FeNO) levels in the general population in correlation with demographic characteristics, smoking status, asthma, rhinitis, atopic status and lung function tests. Altogether 403 subjects, from the European Community Respiratory Health Survey (ECRHS) III who answered the main questionnaire and were checked by FeNO measurements, lung function testing, skin prick testing and measurement of total IgE and specific IgE were included. The geometric mean (95% CI) of FeNO was 16.2 ppb (15.2-17.1) and the prevalence of higher FeNO (⩾25 ppb) was 19.5% in the random sample. Subjects with higher FeNO levels were less likely to be current smokers and more likely to have asthma and rhinitis. Having higher FeNO values was also associated with higher total IgE, having specific IgE to at least one allergen and being skin prick test positive. Current smokers had significantly lower levels of FeNO, geometric mean (95% CI) 9.6 ppb (8.4-11.0), than ex-smokers 18.2 ppb (16.6-20.0) and never smokers 17.3 ppb (16.1-18.5). In multivariable models, having asthma (OR (95% CI) 2.10 (1.20-3.67)), having a specific IgE (OR 2.30 (1.25-4.23)) and being skin prick test positive (OR 2.06 (1.18-3.60)) were independently positively associated with a higher FeNO (⩾25) whereas current smoking was independently negatively associated with a higher FeNO (OR 0.19 (0.06-0.63)). Higher levels of FeNO (⩾25 ppb) were found in one out of five Icelanders; FeNO was positively associated with asthma and allergy and negatively with smoking.

Presence of rhinovirus in the respiratory tract of adolescents and young adults with asthma without symptoms of infection

Background

Viral respiratory infections have been associated with up to 80% of wheezing episodes and asthma exacerbations. However, studies on the role of these viruses in asthmatic patients in the interval between exacerbations are sparse. This study aimed to determine the presence of respiratory viruses, without symptoms of infection, in the airways of young asthmatics as compared to healthy controls.

Material and Methods

Patients 10–35 years of age with stable asthma and a group of healthy controls were analyzed regarding the presence of RNA from common respiratory viruses in nasopharyngeal aspirates by PCR. Self-reported asthma control and quality of life, fraction of exhaled nitric oxide (FeNO), spirometry, and bronchial responsiveness to methacholine were recorded. Blood samples were collected to assess IgE sensitisation and eosinophil cationic protein (ECP) levels.

Results

In 354 patients with asthma and 108 healthy controls, human rhinovirus (HRV) was the only virus detected (4.5% of asthmatics vs. 0.9% of controls; p = 0.08). HRV⁺ asthma patients had a higher degree of aeroallergen IgE sensitisation (median 37.7 vs. 10.4 kU_A/L, p = 0.04), and a tendency for higher levels of serum ECP (median 17.2 vs. 12.6 μg/L, p = 0.07), as compared to their HRV⁻ counterparts.

Conclusions

Absence of symptoms of respiratory tract infection notwithstanding, HRV seems to be more prevalent in the airways of adolescents and young adults with asthma and a high degree of aeroallergen IgE sensitisation than in controls. The presence of HRV seems also to be related to systemic eosinophilic inflammation despite ongoing treatment with inhaled corticosteroids.

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Cross-sectional study on adolescents and young adults with asthma and healthy controls.

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Common respiratory viruses examined in nasopharyngeal aspirates by PCR.

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Only rhinovirus detected in subjects without symptoms of respiratory tract infection.

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Prevalence of rhinovirus tended to be higher in asthmatics compared to controls.

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Presence of rhinovirus associated with high degree of aeroallergen IgE sensitisation.

Setting reference values for exhaled nitric oxide: a systematic review

BACKGROUND

The values obtained when the fraction of exhaled nitric oxide (FeNO) is measured are affected by several factors that are specific to the individual patient, making interpretation difficult, especially in the initial assessment of patients with respiratory symptoms.

METHODS

Systematic review of studies on FeNO reference values and individual-specific factors that influence them.

RESULTS

From 3739 references, 15 studies were included. Four studies included children and adolescents. In nine studies, samples were selected from the general population. Most studies reported objective measures for atopy (nine studies), but not for smoking status (one). Significant determinants of FeNO values reported were age and height (seven studies), atopy (six), smoking (four), weight (four), sex (three) and race (three). Additional factors were included in eight studies. R2 was reported in only five studies. The logarithmic transformation of FeNO was inadequately described in seven studies.

CONCLUSION

There are several equations for FeNO reference values that may be used in clinical practice, although the factors they include and the statistical methods they use vary considerably. We recommend the development of standard methods for the evaluation of normal FeNO data and that reference equations should be formulated based on a predetermined physiological model.

Infection in severe asthma exacerbations and critical asthma syndrome

In chronic persistent asthma and severe acute exacerbations of bronchial asthma, infectious agents are the predominant triggers that drive disease and airway pathobiology. In acute exacerbations of bronchial asthma (AEBA) including near fatal and fatal asthma, viral agents, particularly human rhinovirus-C, respiratory syncytial virus and influenza A appear to be the more prevalent and recurring threats. Both viral, and to a lesser extent bacterial agents, can play a role, and co-infection may also be present and worsen prognosis in hospitalized patients, placing a portion at risk for critical asthma syndrome. During severe acute exacerbations, infectious agents must be treated empirically, but the initial treatment regimens can vary and viral coverage may also vary based on seasonality and patient age. Early treatment with ceftriaxone and azithromycin, along with oseltamivir in winter months, should be initiated with all cases of severe exacerbations where infection is suspected, and definitely in critical asthma syndrome until infection is excluded by appropriate diagnostic testing. In this manuscript we will outline the impact of the major viral agents on severe asthma including the data from the 2009 H1N1 influenza pandemic. The role of bacterial infections in acute exacerbations of asthma will also be reviewed as well as the benefit of empiric antibiotics and the role of macrolides in both acute and chronic asthma.

Application of nitric oxide measurements in clinical conditions beyond asthma

Fractional exhaled nitric oxide (FeNO) is a convenient, non-invasive method for the assessment of active, mainly Th2-driven, airway inflammation, which is sensitive to treatment with standard anti-inflammatory therapy. Consequently, FeNO serves as a valued tool to aid diagnosis and monitoring in several asthma phenotypes. More recently, FeNO has been evaluated in several other respiratory, infectious, and/or immunological conditions. In this short review, we provide an overview of several clinical studies and discuss the status of potential applications of NO measurements in clinical conditions beyond asthma.

The Effect of Viral Infection on Exhaled Nitric Oxide in Children with Acute Asthma Exacerbations

BACKGROUND

Fraction of exhaled nitric oxide (Feno) level is used as an aid in the diagnosis and management of chronic asthma. Its role in acute asthma remains to be studied.

OBJECTIVE

To determine whether Feno levels are elevated in children with asthma exacerbations compared with baseline, and whether there is a difference in Feno levels based on PCR positive (+) (respiratory virus isolated by PCR analysis) versus PCR negative (-) (respiratory virus not isolated by PCR analysis) status.

METHODS

Children with a previous Feno level measurement while stable and who presented to an urgent care facility with an asthma exacerbation were enrolled. Feno levels, spirometry, and nasal swabs for viral PCR were obtained at the time of the exacerbation and following a course of prednisone. Data were available on 66 children. Linear mixed models were used to regress the outcomes of interest (FEV1, FEV1/forced vital capacity, forced expiratory flow at 25% to 75% of forced vital capacity, and natural log Feno) on detected virus (yes/no), visit (baseline, exacerbation, follow-up), and the interaction between the detected virus and visit.

RESULTS

Compared with baseline, higher Feno values and lower lung function were found at the time of an exacerbation. A respiratory virus was detected in 59% of the exacerbations. The interaction between PCR (+) and PCR (-) groups and visit on log Feno was marginally significant (P = .07). There was no difference in log Feno between the PCR (+) and PCR (-) groups at baseline, while higher log Feno was found in the PCR (-) group at the time of exacerbation and following prednisone (P = .05 and .001, respectively).

CONCLUSIONS

Higher Feno concentration in PCR (-) exacerbations suggests an eosinophilic predominance in nonviral compared with viral exacerbations.

Exhaled nitric oxide and the management of childhood asthma--yet another promising biomarker "has been" or a misunderstood gem

Childhood asthma is a common chronic condition. Approximately five percent of all children in western countries are prescribed treatment with inhaled corticosteroids (ICS) to prevent asthma symptoms. Current guidelines advocate titrating ICS dose to symptoms but this approach is not without problem, e.g. how to discern asthmatic from non-asthmatic symptoms? And when to reduce ICS dose? This review describes the strengths and weaknesses of fractional exhaled nitric oxide (FENO) as an objective index for individualising asthma control in children. Epidemiological and mechanistic evidence suggest that FENO should be a promising biomarker for eosinophilic airway inflammation (a hall mark for asthma) but somewhat surprisingly, clinical trials in children have not consistently found benefit from adding FENO to a symptom-based approach to ICS treatment in children. There are a number of reasons why FENO has apparently failed to translate from promising biomarker to clinically useful tool, and one reason may be a lack of understanding of what merits a significant intrasubject change in FENO. This review describes the rise and apparent fall of FENO as biomarker for asthma and then focuses on more recent evidence which suggest that FENO may prove to have a role in the management of childhood asthma, and in particular preventing exacerbations.

Utility of animal and in vivo experimental infection of humans with rhinoviruses in the development of therapeutic agents for viral exacerbations of asthma and chronic obstructive pulmonary disease

There is an association with acute viral infection of the respiratory tract and exacerbations of asthma and chronic obstructive pulmonary disease (COPD). Although these exacerbations are associated with several types of viruses, human rhinoviruses (HRVs) are associated with the vast majority of disease exacerbations. Due to the lack of an animal species that is naturally permissive for HRVs to use as a facile model system, and the limitations associated with animal models of asthma and COPD, studies of controlled experimental infection of humans with HRVs have been used and conducted safely for decades. This review discusses how these experimental infection studies with HRVs have provided a means of understanding the pathophysiology underlying virus-induced exacerbations of asthma and COPD with the goal of developing agents for their prevention and treatment.

Viral infections and asthma: an inflammatory interface?

Asthma is a chronic inflammatory disease of the airways in which the majority of patients respond to treatment with corticosteroids and β₂-adrenoceptor agonists. Acute exacerbations of asthma substantially contribute to disease morbidity, mortality and healthcare costs, and are not restricted to patients who are not compliant with their treatment regimens. Given that respiratory viral infections are the principal cause of asthma exacerbations, this review article will explore the relationship between viral infections and asthma, and will put forward hypotheses as to why virus-induced exacerbations occur. Potential mechanisms that may explain why current therapeutics do not fully inhibit virus-induced exacerbations, for example, β₂-adrenergic desensitisation and corticosteroid insensitivity, are explored, as well as which aspects of virus-induced inflammation are likely to be attenuated by current therapy.

Intercellular adhesion molecule-1 as a drug target in asthma and rhinitis

Intercellular adhesion molecule-1 (ICAM-1) is a transmembrane glycoprotein receptor of the immunoglobulin superfamily. Endothelial cells, epithelial cells, leukocytes and neutrophils are the major cells expressing ICAM-1. Ligands of ICAM-1 are macrophage adhesion ligand-1, leukocyte function-associated antigen-1 and fibrinogen (extracellular matrix protein). In normal physiological conditions, engagement of ICAM-1 receptor with immunological cells surface ligands assists in homing and trafficking of inflammatory cells to distant tissues. ICAM-1 has also long been known to mediate cell-to-cell interaction during antigen presentation and outside-in cell signalling pathways. ICAM-1-mediated elevated inflammation is implicated in asthma. On respiratory epithelial cells surface, ICAM-1 acts as natural binding site for human rhinovirus (HRV), a common cold virus that ultimately causes exacerbation of asthma. This review presents the findings on the role of ICAM-1 in the complication of asthma and in particular asthma exacerbation by HRV.

Reference ranges and determinant factors for exhaled nitric oxide in a healthy korean elderly population

Purpose

Exhaled nitric oxide (NO) is a useful non-invasive biomarker for asthma diagnosis; however, the literature suggests that exhaled NO levels may be affected by demographic factors. The present analysis investigated determinant factors that present exhaled NO reference levels for Korean elderly adults.

Methods

For reference levels, we analyzed the baseline data of healthy adult participants in the Ansung cohort. The fraction of exhaled NO (FeNO) was measured by NIOX MINO®. The characterization of the subjects was performed through structured questionnaires, spirometry, and methacholine challenge tests. To validate the diagnostic utility of the determined reference levels, asthma patients were recruited from medical institutions for FeNO measurement.

Results

A total of 570 healthy subjects were analyzed (mean age, 59.9±12.3; male, 37.0%) for reference levels. FeNO levels significantly correlated with weight, height, body mass index, atopy, or forced expiratory volume in 1 second % predicted by simple linear regression analysis. Multiple linear regression analysis identified gender as an independent determinant for FeNO levels; subsequently, the reference values for FeNO were 18.2±10.6 ppb (5th to 95th percentile, 6.0 to 37.4 ppb) for males and 12.1±6.9 ppb (5th to 95th percentile, 2.5 to 27.0 ppb) for females. The diagnostic utility of FeNO reference levels was validated by receiver operating curve analysis (area under curve, 0.900 for males and 0.885 for females) for diagnosing asthma. The optimal cutoff values for the prediction of asthma were 30.5 ppb for males and 20.5 ppb for females.

Conclusions

The current analysis presented reference ranges and the diagnostic utility of FeNO levels for asthma in Korean elderly adults.

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.

Assessment of airflow limitation, airway inflammation, and symptoms during virus-induced wheezing episodes in 4- to 6-year-old children

Background

It is disputed whether recurrent episodes of wheeze in preschool-aged children comprise a distinct asthma phenotype.

Objective

We sought to prospectively assess airflow limitation and airway inflammation in children 4 to 6 years old with episodic virus-induced wheeze.

Methods

Ninety-three children 4 to 6 years old with a history of mild, virus-induced episodes of wheeze who were able to perform acceptable fraction of exhaled nitric oxide (Feno) maneuvers and spirometry (with forced expiratory time ≥0.5 seconds) were followed prospectively. Lung function and Feno values were measured every 6 weeks (baseline) within the first 48 hours of an acute wheezing episode (day 0) and 10 and 30 days later. Symptom scores and peak flow measurement were recorded daily.

Results

Forty-three children experienced a wheezing episode. At day 0, Feno values were significantly increased, whereas forced expiratory volume at 0.5 seconds (FEV_0.5) significantly decreased compared with baseline (16 ppb [interquartile range {IQR}, 13-20 ppb] vs 9 ppb IQR, 7-11 ppb] and 0.84 L [IQR, 0.75-0.99 L] vs 0.99 L [IQR, 0.9-1.07 L], respectively; both P < .001). Airflow limitation at day 0 was reversible after bronchodilation. FEV_0.5 and Feno values were significantly associated with each other and with lower and upper respiratory tract symptoms when assessed longitudinally but not cross-sectionally at all time points independently of atopy. Feno and FEV_0.5 values returned to baseline levels within 10 days.

Conclusions

Mild episodes of wheeze in preschoolers are characterized by enhanced airway inflammation, reversible airflow limitation, and asthma-related symptoms. Feno values increase significantly during the first 48 hours and return to personal baseline within 10 days from the initiation of the episode. Longitudinal follow-up suggests that symptoms, inflammation, and lung function correlate well in this phenotype of asthma.

Nitric oxide metabolites as biomarkers for influenza-like acute respiratory infections presenting to the emergency room

AIMS

Nitric oxide (NO) is increased in the respiratory tract in pulmonary infections. The aim was to determine whether nasal wash NO metabolites could serve as biomarkers of viral pathogen and disease severity in children with influenza-like illness (ILI) presenting to the emergency department (ED) during the 2009 influenza A H1N1 pandemic.

METHODS

Children ≤18 years old presenting to the ED with ILI were eligible. Nasal wash specimens were tested for NO metabolites, nitrate and nitrite, by HPLC and for respiratory viruses by real-time PCR.

RESULTS

Eighty-nine patients with ILI were prospectively enrolled during Oct-Dec, 2009. In the entire cohort, nasal wash nitrite was low to undetectable (interquartile range [IQR], 0 - 2 μM), while median nitrate was 3.4 μM (IQR 0-8.6). Rhinovirus (23%), respiratory syncytial virus (RSV) (20%), novel H1N1 (19%), and adenovirus (11%) were the most common viruses found. Children with RSV subtype B-associated ILI had higher nitrate compared to all other viruses combined (P=0.002).

CONCLUSION

Concentration of NO-derived nitrate in nasal secretions in children in the ED is suggestive of viral pathogen causative for ILI, and thus might be of clinical utility. Predictive potential of this putative biomarker for ILI needs further evaluation in sicker patients in a prospective manner.

Exhaled nitric oxide in asthma: progress since the introduction of standardized methodology

The measurement of nitric oxide (NO) in exhaled breath has given us the ability to learn about and monitor the inflammatory status of the airway through a non-invasive method that is easy to perform and repeat. This has been most useful in the diagnosis and management of asthma and has promised a seemingly unlimited potential for evaluating the airways and how clinical decisions are made (Grob N M and Dweik R A 2008 Chest133 837-9). The exhaled NO field was initially limited, however, due to the absence of standardized methodology. The ATS and ERS jointly released recommendations for standardized methods of measuring and reporting exhaled NO in 1999 that were revised in 2005 (1999 Am. J. Respir. Crit. Care. Med. 160 2104-17; 2005 Am. J. Respir. Crit. Care. Med. 171 912-30). In this paper, we summarize the literature that followed this standardization. We searched the literature for all papers that included the term 'exhaled nitric oxide' and selected those that followed ATS guidelines for online measurement for further review. We also reviewed cut-off values suggested by groups studying exhaled nitric oxide. We found a wide range of NO values reported for normal and asthma populations. The geometric mean for FE(NO) ranged from 10 ppb to 33 ppb in healthy adult control populations. For asthma, the FE(NO) geometric mean ranged from 6 ppb to 98 ppb. This considerable variation likely reflects the different clinical settings and purposes of measurement. Exhaled NO has been used for a multitude of reasons that range from screening, to diagnosis, to monitoring the effect of therapy. The field of exhaled NO has made undeniable progress since the standardization of the measurement methods. Our challenge now is to have guidelines to interpret exhaled NO levels in the appropriate context. As the utility of exhaled NO continues to evolve, it can serve as a good example of the crucial role of the standardization of collection and measurement methods to propel any new test in the right direction as it makes its way from a research tool to a clinically useful test.

Virus infection-induced bronchial asthma exacerbation

Infection with respiratory viruses, including rhinoviruses, influenza virus, and respiratory syncytial virus, exacerbates asthma, which is associated with processes such as airway inflammation, airway hyperresponsiveness, and mucus hypersecretion. In patients with viral infections and with infection-induced asthma exacerbation, inflammatory mediators and substances, including interleukins (ILs), leukotrienes and histamine, have been identified in the airway secretions, serum, plasma, and urine. Viral infections induce an accumulation of inflammatory cells in the airway mucosa and submucosa, including neutrophils, lymphocytes and eosinophils. Viral infections also enhance the production of inflammatory mediators and substances in airway epithelial cells, mast cells, and other inflammatory cells, such as IL-1, IL-6, IL-8, GM-CSF, RANTES, histamine, and intercellular adhesion molecule-1. Viral infections affect the barrier function of the airway epithelial cells and vascular endothelial cells. Recent reports have demonstrated augmented viral production mediated by an impaired interferon response in the airway epithelial cells of asthma patients. Several drugs used for the treatment of bronchial asthma reduce viral and pro-inflammatory cytokine release from airway epithelial cells infected with viruses. Here, I review the literature on the pathogenesis of the viral infection-induced exacerbation of asthma and on the modulation of viral infection-induced airway inflammation.

Lower respiratory tract infection induced by a genetically modified picornavirus in its natural murine host

Infections with the picornavirus, human rhinovirus (HRV), are a major cause of wheezing illnesses and asthma exacerbations. In developing a murine model of picornaviral airway infection, we noted the absence of murine rhinoviruses and that mice are not natural hosts for HRV. The picornavirus, mengovirus, induces lethal systemic infections in its natural murine hosts, but small genetic differences can profoundly affect picornaviral tropism and virulence. We demonstrate that inhalation of a genetically attenuated mengovirus, vMC₀, induces lower respiratory tract infections in mice. After intranasal vMC₀ inoculation, lung viral titers increased, peaking at 24 h postinoculation with viral shedding persisting for 5 days, whereas HRV-A01a lung viral titers decreased and were undetectable 24 h after intranasal inoculation. Inhalation of vMC₀, but not vehicle or UV-inactivated vMC₀, induced an acute respiratory illness, with body weight loss and lower airway inflammation, characterized by increased numbers of airway neutrophils and lymphocytes and elevated pulmonary expression of neutrophil chemoattractant CXCR2 ligands (CXCL1, CXCL2, CXCL5) and interleukin-17A. Mice inoculated with vMC₀, compared with those inoculated with vehicle or UV-inactivated vMC₀, exhibited increased pulmonary expression of interferon (IFN-α, IFN-β, IFN-λ), viral RNA sensors [toll-like receptor (TLR)3, TLR7, nucleotide-binding oligomerization domain containing 2 (NOD2)], and chemokines associated with HRV infection in humans (CXCL10, CCL2). Inhalation of vMC₀, but not vehicle or UV-inactivated vMC₀, was accompanied by increased airway fluid myeloperoxidase levels, an indicator of neutrophil activation, increased MUC5B gene expression, and lung edema, a sign of infection-related lung injury. Consistent with experimental HRV inoculations of nonallergic, nonasthmatic human subjects, there were no effects on airway hyperresponsiveness after inhalation of vMC₀ by healthy mice. This novel murine model of picornaviral airway infection and inflammation should be useful for defining mechanisms of HRV pathogenesis in humans.

Is FENO50 useful diagnostic tool in suspected asthma?

BACKGROUND

Asthma diagnosis is based on the presence of symptoms and the demonstration of airflow variability. Airway inflammation measured by fractional exhaled nitric oxide, measured at a flow rate of 50 ml/s (FE(NO50)) remains a controversial diagnostic tool.

AIM

To assess the ability of FE(NO50) to identify bronchial hyperresponsiveness (BHR) to methacholine (provocative concentration of methacholine causing a 20% fall in FEV(1); PC20M ≤ 16 mg/ml) and to establish whether or not symptoms relate to FE(NO50) and PC20M in patients with no demonstrated reversibility to β(2) -agonist.

METHODS

We conducted a prospective study on 174 steroid naive patients with respiratory symptoms, forced expiratory volume in 1 s (FEV(1) ) ≥ 70% predicted and no demonstrated reversibility to β(2) -agonist. Patients answered to a standardised symptom questionnaire and underwent FE(NO50) and methacholine challenge. Receiver-operating characteristic (ROC) curve and logistic regression analysis assessed the relationship between PC20M and FE(NO50) , taking into account covariates (smoking, atopy, age, gender and FEV(1)).

RESULTS

A total of 82 patients had a PC20M ≤ 16 mg/ml and had significantly higher FE(NO50) (19 ppb vs. 15 ppb; p < 0.05). By constructing ROC curve, we found that FE(NO50) cut-off value of 34 ppb was able to identify not only BHR with high specificity (95%) and positive predictive value (88%) but low sensitivity (35%) and negative predictive value (62%). When combining all variables into the logistic model, FE(NO50) (p = 0.0011) and FEV(1) (p < 0.0001) were independent predictors of BHR whereas age, gender, smoking and atopy had no influence. The presence of diurnal and nocturnal wheezing was associated with raised FE(NO50) (p < 0.001 and p < 0.05, respectively).

CONCLUSION

The value of FE(NO50) > 34 ppb has high predictive value of PC20M < 16 in patients with suspected asthma in whom bronchodilating test failed to demonstrate reversibility or was not indicated. However, FE(NO50) ≤ 34 ppb does not rule out BHR and should prompt the clinician to ask for a methacholine challenge.

Daily exhaled nitric oxide measurements and asthma exacerbations in children

BACKGROUND

Fractional exhaled Nitric Oxide (FeNO) is a biomarker for eosinophilic airway inflammation and can be measured at home on a daily basis. A short-term increase in FeNO may indicate a higher risk of future asthma exacerbations.

OBJECTIVE

To assess changes in FeNO before and after asthma exacerbations compared to a stable control period.

METHODS

A post hoc analysis was performed on daily FeNO measurements over 30 weeks in children with asthma (n = 77). Moderate exacerbations were defined by an increase in symptom scores and severe exacerbations by prescription of prednisone. Individual mean and maximum FeNO, the variability of FeNO assessed by the coefficient of variation (CV), and slopes of FeNO in time were all quantified in 3-week blocks. Cross-correlation of FeNO with symptoms and autocorrelation of FeNO were assessed in relation to exacerbations and examined as predictors for exacerbations compared to reference periods using logistic regression.

RESULTS

Fractional exhaled nitric oxide could be assessed in relation to 25 moderate and 12 severe exacerbations. The CV, slope, cross-correlation, and autocorrelation of daily FeNO increased before moderate exacerbations. Increases in slope were also randomly seen in 19% of 2-week blocks of children without exacerbations. At least 3-5 FeNO measurements in the 3 weeks before an exacerbation were needed to calculate a slope that could predict moderate exacerbations. No specific pattern of FeNO was seen before severe exacerbations.

CONCLUSION

Fractional exhaled nitric oxide monitoring revealed changes in FeNO prior to moderate exacerbations. Whether this can be used to prevent loss of asthma control should be further explored.

Effect of the influenza A (H1N1) live attenuated intranasal vaccine on nitric oxide (FE(NO)) and other volatiles in exhaled breath

For the 2009 influenza A (H1N1) pandemic, vaccination and infection control were the main modes of prevention. A live attenuated H1N1 vaccine mimics natural infection and works by evoking a host immune response, but currently there are no easy methods to measure such a response. To determine if an immune response could be measured in exhaled breath, exhaled nitric oxide (FE(NO)) and other exhaled breath volatiles using selected ion flow tube mass spectrometry (SIFT-MS) were measured before and daily for seven days after administering the H1N1 2009 monovalent live intranasal vaccine (FluMist®, MedImmune LLC) in nine healthy healthcare workers (age 35 ± 7 years; five females). On day 3 after H1N1 FluMist® administration there were increases in FE(NO) (MEAN±SEM: day 0 15 ± 3 ppb, day 3 19 ± 3 ppb; p < 0.001) and breath isoprene (MEAN±SEM: day 0 59 ± 15 ppb, day 3 99 ± 17 ppb; p = 0.02). MS analysis identified the greatest number of changes in exhaled breath on day 3 with 137 product ion masses that changed from baseline. The exhaled breath changes on day 3 after H1N1 vaccination may reflect the underlying host immune response. However, further work to elucidate the sources of the exhaled breath changes is necessary.

The airway epithelium: soldier in the fight against respiratory viruses

The airway epithelium acts as a frontline defense against respiratory viruses, not only as a physical barrier and through the mucociliary apparatus but also through its immunological functions. It initiates multiple innate and adaptive immune mechanisms which are crucial for efficient antiviral responses. The interaction between respiratory viruses and airway epithelial cells results in production of antiviral substances, including type I and III interferons, lactoferrin, β-defensins, and nitric oxide, and also in production of cytokines and chemokines, which recruit inflammatory cells and influence adaptive immunity. These defense mechanisms usually result in rapid virus clearance. However, respiratory viruses elaborate strategies to evade antiviral mechanisms and immune responses. They may disrupt epithelial integrity through cytotoxic effects, increasing paracellular permeability and damaging epithelial repair mechanisms. In addition, they can interfere with immune responses by blocking interferon pathways and by subverting protective inflammatory responses toward detrimental ones. Finally, by inducing overt mucus secretion and mucostasis and by paving the way for bacterial infections, they favor lung damage and further impair host antiviral mechanisms.

Determinants of exhaled nitric oxide levels (FeNO) in childhood atopic asthma: evidence for neonatal respiratory distress as a factor associated with low FeNO levels

BACKGROUND

In allergic asthmatic children exhaled nitric oxide (FeNO) levels are related to eosinophilic inflammation by correlation analysis. Whether FeNO can be modified by factors potentially influencing the natural history of asthma in early life is not known.

OBJECTIVE

To evaluate the frequency of anamnestic factors influencing the natural history of asthma and to identify potential determinants for elevated or low FeNO levels by multivariate analysis.

METHODS

One hundred seventy-one children with mild-moderate asthma were stratified according to their FeNO levels into three groups: low (<20 ppb), mid (20-40 ppb), and high (>40 ppb). The frequency of nine anamnestic factors together with indices of allergic sensitization (total and allergen-specific immunoglobulin E [IgE], blood eosinophil counts) and of airflow limitation (forced expiratory volume in one second [FEV(1)]% predicted) were evaluated. Results. Among factors related to the patient history, neonatal respiratory distress was reported only in children with low FeNO levels, whereas this factor was never reported in children with mid-to-high FeNO levels (p = .008). As compared with low FeNO group, mid and high FeNO groups showed higher eosinophil counts and a tendency to have lower FEV(1) values. By multivariate analysis, four factors (eosinophils >300 cells/mm(3), cat-specific IgE, house dust mites [HDM]-specific IgE, FEV(1) ≤ 86% predicted) turned out to be significantly associated with mid-high FeNO levels and two factors (eosinophils >600 cells/mm(3), total IgE >355 kU/L) with high FeNO levels.

CONCLUSIONS

Besides confirming the well-known tight association between blood eosinophilia and/or allergic sensitization and FeNO, these data provide new evidence for neonatal respiratory distress as potential factor associated with low FeNO levels in childhood atopic asthma.

Relationship between exhaled nitric oxide and IgE sensitisation in patients with asthma: influence of steroid treatment

INTRODUCTION

The influence of the degree of immunoglobulin E (IgE) sensitisation on the fraction of expired nitric oxide (FE(NO)) in asthma patients being treated with inhaled corticosteroids (ICS) is not well known.

OBJECTIVES

To investigate the relationship between IgE sensitisation and FE(NO), and the effect of a step-up in ICS treatment on this relationship, in patients with allergic asthma.

METHODS

A primary health care centre recruited 20 non-smoking patients with perennial allergic asthma (18 years-50 years, six male) outside the pollen season. At every visit (0, 2, 4, 8 weeks), FE(NO) was measured and an exposure questionnaire was completed. ICS dose was adjusted according to FE(NO) (>or=22 ppb prescribed increase in ICS). Quantitative analyses of serum IgE (eight common aeroallergens) confirmed allergy.

RESULTS

At baseline, FE(NO) and the sum of IgE antibody titres for perennial allergens correlated significantly (r = 0.47, P = 0.04). After a step-up in ICS treatment, this correlation had disappeared. Nine patients had persistently elevated FE(NO) at last visit (mean 35 ppb vs 16 ppb). This group was more frequently exposed to relevant allergens or colds (89% vs 27% of patients, P < 0.05) and had higher IgE antibody titres (perennial allergens) compared with the normalised group (mean 28.9 kU/L vs 10.7 kU/L, P < 0.05).

CONCLUSION

Serum IgE against perennial allergens and FE(NO) correlate in patients with allergic asthma. However, this relationship disappears after a high-dose ICS regimen, suggesting that FE(NO) relates to bronchial inflammation and not IgE levels per se. High degree of IgE sensitisation together with allergen exposure may lead to ICS-resistant airways inflammation.

Asthma tests in the assessment of military conscripts

BACKGROUND

Respiratory diseases such as asthma may affect individuals' fitness for military service. In order to assess fitness for military service in subjects with asthma symptoms at conscription, objective and reliable tests are needed.

OBJECTIVE

To prospectively determine the diagnostic value of the mannitol and methacholine bronchial provocation test (BPT) as well as exhaled nitric oxide in assessing physician-diagnosed asthma in a group of Swiss Armed Forces conscripts.

METHODS

Questionnaire, spirometry, BPT with methacholine and mannitol, exhaled nitric oxide (FeNO) and skin prick testing were conducted in 18-20-year-old male conscripts. Asthma was diagnosed by a military physician not involved in this study according to the medical record, results of BPT, current respiratory symptoms and use of asthma medication.

RESULTS

Two hundred and eighty four subjects participated in the study. Complete data for the BPT with methacholine, mannitol and measurement of FeNO were available on 235 subjects. Forty-two conscripts (17.9%) had physician-diagnosed asthma. The sensitivity/specificity of mannitol to identify physician-diagnosed asthma was 41%/93% and for methacholine it was 43%/92%. Using a cut-off point of 36.5 p.p.b., FeNO had a similar negative predictive value to rule out physician-diagnosed asthma as BPT with mannitol or methacholine.

CONCLUSION

BPT with mannitol has a sensitivity and specificity similar to methacholine for the diagnosis of physician-diagnosed asthma in military conscripts but is less costly to perform without the need to use and maintain a nebulizer.

Arginase: a key enzyme in the pathophysiology of allergic asthma opening novel therapeutic perspectives

Allergic asthma is a chronic inflammatory airways' disease, characterized by allergen-induced early and late bronchial obstructive reactions, airway hyperresponsiveness (AHR), airway inflammation and airway remodelling. Recent ex vivo and in vivo studies in animal models and asthmatic patients have indicated that arginase may play a central role in all these features. Thus, increased arginase activity in the airways induces reduced bioavailability of L-arginine to constitutive (cNOS) and inducible (iNOS) nitric oxide synthases, causing a deficiency of bronchodilating and anti-inflammatory NO, as well as increased formation of peroxynitrite, which may be involved in allergen-induced airways obstruction, AHR and inflammation. In addition, both via reduced NO production and enhanced synthesis of L-ornithine, increased arginase activity may be involved in airway remodelling by promoting cell proliferation and collagen deposition in the airway wall. Therefore, arginase inhibitors may have therapeutic potential in the treatment of acute and chronic asthma. This review focuses on the pathophysiological role of arginase in allergic asthma and the emerging effectiveness of arginase inhibitors in the treatment of this disease.

A rat model of picornavirus-induced airway infection and inflammation

Background

Infection of the lower airways by rhinovirus, a member of the picornavirus family, is an important cause of wheezing illnesses in infants, and plays an important role in the pathogenesis of rhinovirus-induced asthma exacerbations. Given the absence of natural rhinovirus infections in rodents, we investigated whether an attenuated form of mengovirus, a picornavirus whose wild-type form causes systemic rather than respiratory infections in its natural rodent hosts, could induce airway infections in rats with inflammatory responses similar to those in human rhinovirus infections.

Results

After inoculation with 10⁷ plaque-forming units of attenuated mengovirus through an inhalation route, infectious mengovirus was consistently recovered on days 1 and 3 postinoculation from left lung homogenates (median Log₁₀ plaque-forming units = 6.0 and 4.8, respectively) and right lung bronchoalveolar lavage fluid (median Log₁₀ plaque-forming units = 5.8 and 4.0, respectively). Insufflation of attenuated mengovirus, but not vehicle or UV-inactivated virus, into the lungs of BN rats caused significant increases (P < 0.05) in lower airway neutrophils and lymphocytes in the bronchoalveolar lavage fluid and patchy peribronchiolar, perivascular, and alveolar cellular infiltrates in lung tissue sections. In addition, infection with attenuated mengovirus significantly increased (P < 0.05) lower airway levels of neutrophil chemoattractant CXCR2 ligands [cytokine-induced neutrophil chemoattractant-1 (CINC-1; CXCL1) and macrophage inflammatory protein-2 (MIP-2; CXCL2)] and monocyte chemoattractant protein-1 (MCP-1; CCL2) in comparison to inoculation with vehicle or UV-inactivated virus.

Conclusion

Attenuated mengovirus caused a respiratory infection in rats with several days of viral shedding accompanied by a lower airway inflammatory response consisting of neutrophils and lymphocytes. These features suggest that mengovirus-induced airway infection in rodents could be a useful model to define mechanisms of rhinovirus-induced airway inflammation in humans.

Infections

This chapter reviews the epidemiological evidence implicating infectious pathogens as triggers and will discuss the mechanisms of interaction between the host–pathogen response and preexisting airway pathology that result in an exacerbation. Asthma is a multifaceted syndrome involving atopy, bronchial hyperreactivity, and IgE and non-IgE-mediated acute and chronic immune responses. The asthmatic airway is characterized by an infiltrate of eosinophils and of T-lymphocytes expressing the type 2 cytokines IL-4, IL-5, and IL-13. Trigger factors associated with acute exacerbations of asthma include exposure to environmental allergens, especially animals, molds, pollens and mites, cold, exercise, and drugs. The frequency of exacerbations is a major factor in the quality of life of patients with COPD. The typical clinical features of an exacerbation include increased dyspnea, wheezing, cough, sputum production, and worsened gas exchange. Although noninfectious causes of exacerbations such as allergy, air pollution, or inhaled irritants including cigarette smoke may be important, acute airway infections are the major precipitants. The infection and consequent host inflammatory response result in increased airway obstruction. The success of vaccination to prevent respiratory virus infections has been limited by significant variation within the major virus types causing disease. Currently much of the treatment of infective exacerbations of asthma and COPD is symptomatic, consisting of increased bronchodilators, either short-acting β 2—agonists in inhaled or intravenous form or anticholinergics or theophyllines, or supportive in the form of oxygen and in severe cases noninvasive or invasive ventilatory measures.

Nitric oxide inhibits human rhinovirus-induced transcriptional activation of CXCL10 in airway epithelial cells

BACKGROUND

Human rhinovirus (HRV) infections trigger exacerbations of asthma and chronic obstructive pulmonary disease. Nitric oxide (NO) inhibits HRV replication in human airway epithelial cells and suppresses HRV-induced epithelial production of several cytokines and chemokines.

OBJECTIVE

We sought to delineate the mechanisms by which NO inhibits HRV-induced epithelial production of CXCL10, a chemoattractant for type 1 T cells and natural killer cells.

METHODS

Primary human bronchial epithelial cells or cells of the BEAS-2B human bronchial epithelial cell line were exposed to HRV-16 in the presence or absence of the NO donor 3-(2-hydroxy-2-nitroso-1-propylhydrazino)-1-propanamine (PAPA NONOate). A cGMP analogue and an inhibitor of soluble guanylyl cyclase were used to examine the role of the cyclic guanosine monophosphate (cGMP) pathway in the actions of NO. BEAS-2B cells were transfected with CXCL10 promoter-luciferase constructs and the effects of PAPA NONOate were examined to study mechanisms of transcriptional regulation. Electrophoretic mobility shift assays were also used.

RESULTS

PAPA NONOate inhibited HRV-16-induced increases in CXCL10 mRNA and protein. Inhibition of CXCL10 production occurred through a cGMP-independent pathway. PAPA NONOate inhibited HRV-16-induced CXCL10 transcription by blocking nuclear translocation, binding, or both of both nuclear factor kappaB and IFN response factors (IRFs) to their respective recognition elements in the CXCL10 promoter.

CONCLUSIONS

NO inhibits HRV-16-induced production of CXCL10 by inhibiting viral activation of nuclear factor kappaB and of IRFs, including IRF-1, through a cGMP-independent pathway. The broad-ranging inhibition of HRV-induced epithelial cytokine and chemokine production by NO suggests a potential therapeutic utility of NO donors in viral exacerbations of asthma and chronic obstructive pulmonary disease.

Adjuvant Activity of Ambient Particulate Matter in Macrophage Activity-Suppressed,N-Acetylcysteine-Treated, iNOS- and IL-4-Deficient Mice

In previous studies, we have shown strong adjuvant activity for Ottawa dust (EHC-93) after coexposure of the BALB/c mouse to EHC-93 and ovalbumin. Mice were intranasally sensitized at days 0 and 14 with 200 microg ovalbumin and 150 microg EHC-93, and challenged with ovalbumin at days 35, 38, and 41 with 200 microg ovalbumin. Mice were autopsied at day 42. This adjuvant activity was shown for the antibody response to ovalbumin (immunoglobulins E, G1, and G2a), histopathological lesions in the lung, cytokines, and the numbers of eosinophils in lung lavages. To study the mechanisms of this adjuvant activity, mice (BALB/cC.D2-Vil6) with natural-resistance-associated macrophage protein (Nramp1s), BALB/c mice pretreated with the antioxidant N-acetylcysteine (NAC), mice (B6.129P2-Nos2tmLau) deficient in inducible nitric oxide synthase (iNOS), and mice with interleukin-4 (IL-4) deficiency (BALB/cIl4< tm2Nnt) were coexposed to ovalbumin and EHC-93. Our studies have shown that the adjuvant activity induced after such coexposure does not change if the macrophage activation of the mice is disturbed or if the mice have been pretreated with N-acetylcysteine. In addition, the adjuvant activity does not develop through the pathway in which inducible nitric oxide synthase is involved. Because the histopathological lesions are statistically significant less in the IL-4 knockout strain in comparison with the wild type, we conclude that interleukin-4 might play an important role in the adjuvant activity caused by EHC-93.

History, technical and regulatory aspects of exhaled nitric oxide

The history of nitric oxide (NO) in exhaled breath as a marker of inflammation is summarized, followed by measurement aspects of exhaled NO including NO excretion models of NO in the airway, the estimation of flow-independent NO exchange parameters and issues with the standardization of these methods. Regulatory considerations in the US are also presented. A brief summary of the state of the art for clinical application of exhaled NO is also included.

The use of fraction of exhaled nitric oxide in pulmonary practice

The measurement of the fractional concentration of exhaled nitric oxide (FeNO) is a convenient, noninvasive, point-of-service office test for airway inflammation. The first half of this practice management review presents the methodological, interpretative, and clinical applications of FeNO. The second half discusses practical management issues, including current and future technology, equipment specifications, US Food and Drug Administration regulations, cost, current procedural terminology coding, and reimbursement. The measurement of FeNO is helpful in the diagnosis of asthma. It is predictive of a response to inhaled corticosteroids (ICSs). Monitoring FeNO is useful in maintaining asthma control by allowing the assessment of adherence to medication and dose titration of ICSs. An elevated level of FeNO is predictive of asthma relapse following corticosteroid withdrawal especially in children. The advances in technology, ease of use, and clinical utility will lead to greater availability, acceptance, and routine application in the care of asthma.

Seasonal variation and environmental predictors of exhaled nitric oxide in children with asthma

The fraction of exhaled nitric oxide (FeNO), a measure of airway inflammation, shows promise as a noninvasive tool to guide asthma management, but there is a paucity of longitudinal data about seasonal variation and environmental predictors of FeNO in children. The objective of this project was to evaluate how environmental factors affect FeNO concentrations over a 12-month study period among children with doctor diagnosed asthma. We conducted a prospective cohort study of 225 tobacco-smoke exposed children age 6-12 years with doctor-diagnosed asthma including measures of FeNO, medication use, settled indoor allergens (dust mite, cat, dog, and cockroach), and tobacco smoke exposure. Baseline geometric mean FeNO was 12.4 ppb (range 1.9-60.9 ppb). In multivariable analyses, higher baseline FeNO levels, atopy, and fall season were associated with increased FeNO levels, measured 6 and 12 months after study initiation, whereas inhaled steroid use, summer season, and increasing nicotine exposure were associated with lower FeNO levels. In secondary analyses of allergen sensitization, only sensitization to dust mite and cat were associated with increased FeNO levels. Our data demonstrate that FeNO levels over a year long period reflected baseline FeNO levels, allergen sensitization, season, and inhaled steroid use in children with asthma. These results indicate that FeNO levels are responsive to common environmental triggers as well as therapy for asthma in children. Clinicians and researchers may need to consider an individual's baseline FeNO levels to manage children with asthma.

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.

Exhaled nitric oxide: independent effects of atopy, smoking, respiratory tract infection, gender and height

Measurement of exhaled nitric oxide is widely used in respiratory research and clinical practice, especially in patients with asthma. However, interpretation is often difficult, due to common interfering factors, and little is known about interactions between factors. We assessed the influences and interactions of factors such as smoking, respiratory tract infections and respiratory allergy concerning exhaled nitric oxide values, with the aim to derive a scheme for adjustment. We studied 897 subjects (514 females, 383 males; mean age+/-standard deviation 34.5+/-13.0 years) with and without respiratory allergy (allergic rhinitis and/or asthma), smoking and respiratory tract infection. Logarithmic nitric oxide levels were described by an additive model comprising respiratory allergy, smoking, respiratory tract infection, gender and height (p0.001 each), without significant interaction terms. Geometric mean was 17.5ppb in a healthy female non smoker of height 170cm, whereby respiratory allergy corresponded to a change by factor 1.50, smoking 0.63, infection 1.24, male gender 1.17, and each 10cm increase (decrease) in height to 1.11 (0.90). Factors were virtually identical when excluding asthma and using the category allergic rhinitis instead of respiratory allergy (n=863). Within each category formed by combinations of these different predictors, the range of residual variation was approximately constant. We conclude that the factors influencing exhaled nitric oxide, which we analyzed, act independently of each other. Thus, circumstances such as smoking and respiratory tract infection do not appear to affect the usefulness of exhaled nitric oxide, provided that appropriate factors for adjustment are applied.

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.

Determinants of exhaled nitric oxide levels in healthy, nonsmoking African American adults

BACKGROUND

Asthma is a significant cause of morbidity and mortality for African Americans. Fraction of exhaled nitric oxide (FeNO) levels are increased in patients with asthma, and airway levels of nitric oxide metabolites regulate airway inflammation and airway diameter. More needs to be known about the factors that regulate FeNO. There is a need for FeNO reference values for African Americans.

OBJECTIVE

We sought to establish reference values and identify factors associated with FeNO levels in healthy African American adults.

METHODS

FeNO levels were measured in 895 healthy, nonsmoking African Americans between the ages of 18 and 40 years. FeNO measurements were repeated in 84 subjects. Factors potentially associated with FeNO were measured, including blood pressure, height, weight, and serum total IgE, eosinophil cationic protein, C-reactive protein, and nitrate levels. Data on respiratory symptoms, including upper respiratory tract infection (URI) symptoms, were collected. Univariate and multivariate analyses of the relationship between these variables and FeNO levels were performed.

RESULTS

In healthy, nonsmoking African Americans FeNO levels were stable during repeated measurements (intraclass correlation coefficient, 0.81). Sex (P < .0001), serum total IgE levels (P < .0001), and current URI symptoms (P = .0002) contributed significantly to FeNO variability but together accounted for less than 50% of the variation in FeNO levels.

CONCLUSION

The high correlation between repeated measurements of FeNO and the low correlation coefficients of known factors associated with FeNO suggest that other factors might contribute substantially to variability of FeNO levels in African Americans.