NO in exhaled air is correlated with markers of eosinophilic airway inflammation in corticosteroid-dependent childhood asthma

The association of exhaled nitric oxide with air pollutants in young infants of asthmatic mothers

BACKGROUND

Exhaled nitric oxide is a marker of airway inflammation. Air pollution induces airway inflammation and oxidative stress. Little is known about the impact of air pollution on exhaled nitric oxide in young infants.

METHODS

The Breathing for Life Trial recruited pregnant women with asthma into a randomised controlled trial comparing usual clinical care versus inflammometry-guided asthma management in pregnancy. Four hundred fifty-seven infants from the Breathing for Life Trial birth cohort were assessed at six weeks of age. Exhaled nitric oxide was measured in unsedated, sleeping infants. Its association with local mean 24-h and mean seven-day concentrations of ozone, nitric oxide, nitrogen dioxide, carbon monoxide, sulfur dioxide, ammonia, particulate matter less than 10 μm (PM10) and less than 2.5 μm (PM2.5) in diameter was investigated. The air pollutant data were sourced from local monitoring sites of the New South Wales Air Quality Monitoring Network. The association was assessed using a 'least absolute shrinkage and selection operator' (LASSO) approach, multivariable regression and Spearman's rank correlation.

RESULTS

A seasonal variation was evident with higher median exhaled nitric oxide levels (13.6 ppb) in warmer months and lower median exhaled nitric oxide levels (11.0 ppb) in cooler months, P = 0.008. LASSO identified positive associations for exhaled nitric oxide with 24-h mean ammonia, seven-day mean ammonia, seven-day mean PM10, seven-day mean PM2.5, and seven-day mean ozone; and negative associations for eNO with seven-day mean carbon monoxide, 24-h mean nitric oxide and 24-h mean sulfur dioxide, with an R-square of 0.25 for the penalized coefficients. These coefficients selected by LASSO (and confounders) were entered in multivariable regression. The achieved R-square was 0.27.

CONCLUSION

In this cohort of young infants of asthmatic mothers, exhaled nitric oxide showed seasonal variation and an association with local air pollution concentrations.

Use of FeNO to predict anti-IL-5 and IL-5R biologics efficacy in a real-world cohort of adults with severe eosinophilic asthma

INTRODUCTION

Severe eosinophilic asthma (SEA) is associated with multiple exacerbations. Fractional exhaled nitric oxide (FeNO), a biomarker of airway T2 inflammation, is known to be correlated with the risk of exacerbations. While the use of FeNO is well established to predict the therapeutic response to dupilumab (anti-IL-4/IL-13), it remains uncertain for biologics targeting the IL-5 pathway.

METHODS

We conducted an observational, retrospective, monocentric analysis of adults with SEA who started mepolizumab (anti-IL-5) or benralizumab (anti-IL-5R) between January 1, 2016 and December 31, 2020.

RESULTS

Data were collected for 109 patients. All participants reported uncontrolled asthma with a median of 3 annual exacerbations and a median Asthma Control Test score of 12. They all had an initial blood eosinophilia >300/mm³, with a median at 610/mm³ (IQR 420-856). Patients with a baseline FeNO ≥50 ppb reported more exacerbations in the previous year than those with a FeNO <50 ppb (p = 0.02). After initiation of treatment, change in FeNO was not associated with therapeutic response. However, decrease in the annual number of exacerbations was significantly greater in patients with a baseline FeNO ≥50 ppb than in those with a baseline FeNO <50 ppb (-3.3 ± 2.7 vs -0.9 ± 2.4, respectively; p = 0.01). There was no association between baseline FeNO values and subsequent lung function, asthma control or reduction of oral corticosteroids use.

CONCLUSION

In this real-world cohort, adults with SEA who had a baseline FeNO ≥50 ppb experienced a greater decrease in exacerbations after 12 months of anti-IL-5 or IL-5R biologics than those with a FeNO <50 ppb.

Recent insights in the role of biomarkers in severe asthma management

Contemporary asthma management requires a proactive and individualized approach, combining precision diagnosis and personalized treatment. The introduction of biologic therapies for severe asthma to everyday clinical practice, increases the need for specific patient selection, prediction of outcomes and monitoring of these costly and long-lasting therapies. Several biomarkers have been used in asthma in disease identification, prediction of asthma severity and prognosis, and response to treatment. Novel advances in the area of personalized medicine regarding disease phenotyping and endotyping, encompass the development and application of reliable biomarkers, accurately quantified using robust and reproducible methods. The availability of powerful omics technologies, together with integrated and network-based genome data analysis, and microbiota changes quantified in serum, body fluids and exhaled air, will lead to a better classification of distinct phenotypes or endotypes. Herein, in this review we discuss on currently used and novel biomarkers for the diagnosis and treatment of asthma.

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

RATIONALE

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

METHODS

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

MEASUREMENTS AND MAIN RESULTS

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

CONCLUSIONS

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

Effect of heterogeneous ventilation and nitric oxide production on exhaled nitric oxide profiles

Elevated exhaled nitric oxide (NO) in the breath of asthmatic subjects is thought to be a noninvasive marker of lung inflammation. Asthma is also characterized by heterogeneous bronchoconstriction and inflammation, which impact the spatial distribution of ventilation in the lungs. Since exhaled NO arises from both airway and alveolar regions, and its level in exhaled breath depends strongly on flow, spatial heterogeneity in flow patterns and NO production may significantly affect the exhaled NO signal. To investigate the effect of these factors on exhaled NO profiles, we developed a multicompartment mathematical model of NO exchange using a trumpet-shaped central airway segment that bifurcates into two similarly shaped peripheral airway segments, each of which empties into an alveolar compartment. Heterogeneity in flow alone has only a minimal impact on the exhaled NO profile. In contrast, placing 70% of the total airway NO production in the central compartment or the distal poorly ventilated compartment can significantly increase (35%) or decrease (-10%) the plateau concentration, respectively. Reduced ventilation of the peripheral and acinar regions of the lungs with concomitant elevated NO production delays the rise of NO during exhalation, resulting in a positive phase III slope and reduced plateau concentration (-11%). These features compare favorably with experimentally observed profiles in exercise-induced asthma and cannot be simulated with single-path models. We conclude that variability in ventilation and NO production in asthmatic subjects impacts the shape of the exhaled NO profile and thus impacts the physiological interpretation.

Temporal association of nitric oxide levels and airflow in asthma after whole lung allergen challenge

Exhaled nitric oxide (NO) levels are high in asthmatic subjects and increase with exacerbations. We hypothesized that higher levels of NO observed during asthma exacerbations are due to increased synthesis of NO. Exhaled NO and peak flows were measured in 11 asthmatic and 9 healthy control subjects before and after experimental asthmatic response induced by whole lung allergen challenge. Baseline peak flows of asthmatics were significantly lower than controls and decreased significantly immediately after challenge (P = 0.004). NO was measured by collecting exhaled breaths without breath hold (NO0) and after a 15-s breath hold (NO15). The rate of NO accumulation over time [parts/billion per second (ppb/s)] was calculated by DeltaNO/Deltat = (NO15 - NO0)/15, where Delta denotes a change and t is time. The NO accumulation rates in asthmatic and control subjects were similar at baseline; however, NO accumulation at 24 h increased threefold from baseline in asthmatic compared with control subjects (asthmatic subjects, 0.6 +/- 0.2 ppb/s; control subjects, 0.2 +/- 0.1 ppb/s; P = 0.01). Our study suggests that increased NO during an asthma exacerbation is due to increased synthesis, perhaps by increased expression of NO synthases.