Increasing utility of FeNO as a biomarker of type-2 inflammation in severe asthma

Since the discovery that nitric oxide (NO) can be measured in the exhaled breath and that the fractional exhaled NO (FeNO) is increased in asthma, FeNO has been recognised as a biomarker of type 2 inflammation in the airways, reflecting the effect of type 2-associated cytokines, interleukin (IL)-4 and IL-13, that play an important role in bronchial hyperresponsiveness, mucus secretion and goblet cell hyperplasia, and T-helper type 2 polarisation, and also in allergic and eosinophilic inflammation. Since 2011, FeNO, which remains a convenient measurement for patients as young as 5 years, has been recommended for use in the diagnosis of eosinophilic airway inflammation as a supportive adjunct towards the diagnosis of asthma and in assessing corticosteroid responsiveness. 1 Dweik RA Sorkness RL Wenzel S et al. Use of exhaled nitric oxide measurement to identify a reactive, at-risk phenotype among patients with asthma. Am J Respir Crit Care Med. 2010; 181: 1033-1041 Crossref PubMed Scopus (220) Google Scholar Baseline FeNO as a prognostic biomarker for subsequent severe asthma exacerbations in patients with uncontrolled, moderate-to-severe asthma receiving placebo in the LIBERTY ASTHMA QUEST study: a post-hoc analysisIn uncontrolled, moderate-to-severe asthma, higher baseline FeNO levels were associated with greater risk of severe asthma exacerbations, particularly in combination with elevated eosinophil count and prior exacerbations, supporting the added value of FeNO as a prognostic biomarker. Further research is needed to confirm FeNO as an independent predictor for asthma exacerbations. Full-Text PDF The inflammatory profile of exacerbations in patients with severe refractory eosinophilic asthma receiving mepolizumab (the MEX study): a prospective observational studyExacerbations on mepolizumab are two distinct entities, which can largely be differentiated using FeNO: non-eosinophilic events are driven by infection with a low FeNO and high C-reactive protein concentration, whereas eosinophilic exacerbations are FeNO high. The results of the MEX study challenge the routine use of oral corticosteroids for the treatment of all asthma exacerbation events on mepolizumab, as well as the switching of biological therapies for treatment failure without profiling the inflammatory phenotype of ongoing asthma exacerbations. Full-Text PDF