Development and validation of a panel of volatile biomarkers of airway eosinophilia in severe asthma.

Type 2 inflammation and airway eosinophilia have an incidence in 40-60% of severe asthmatics. Therefore, a number of biological therapies have been developed to target the type 2 inflammatory pathways involved in eosinophil activation, such as anti-IL5 and anti-IL5 receptor-α monoclonal antibodies.

There is, therefore, the need to develop non-invasive biomarkers to assess airway eosinophilia, which seems to play an increasingly important role to improve severe asthmatics’ stratification for eosinophil targeted therapies

This study aimed to develop a panel of volatile biomarkers of airway eosinophilia identifying, by GC-MS analysis and statistical modelling, volatile organic compounds (VOCs) in severe asthmatics’ sputum headspace samples, which were able to discriminate with a moderate accuracy eosinophil-enriched and non-eosinophil-enriched sputum headspaces. In order to optimise the headspace sampling method, the headspace background signal, generated within the sampling system in absence of sputum sample, was characterised, and its daily abundance variations were evaluated.

Furthermore, the discovered panel of VOCs was validated in exhaled breath of severe asthmatics eligible for anti-IL5/Rα treatments by targeted GCxGC-FID/MS analysis. The statistical model developed showed a high accuracy to predict severe asthmatics’ one-year response to anti-IL5/Rα therapies. The in vitro selected VOCs were also validated in exhaled breath of exacerbating eosinophilic asthmatics and exacerbating non-eosinophilic asthmatics - whose classification was based on the blood eosinophil count threshold of 0.5x109/L - and healthy volunteers. The panel of VOCs revealed a high discriminatory accuracy among acute eosinophilic asthmatics, acute non-eosinophilic asthmatics and healthy volunteers, suggesting that the selected VOCs represent a promising, non-invasive clinical tool for asthma exacerbation prediction. A future challenge will be to identify the metabolic pathways, in activated eosinophil cultures, which may be involved in the origin of the selected VOCs, in order to confirm their inflammatory origin.