A novel non-invasive method allowing for discovery of pathologically relevant proteins from small airways

Abstract BackgroundBreath contains an aerosol of droplet particles, which are formed from the epithelial lining fluid when the small airways close and re-open during inhalation succeeding a full expiration. These particles can be collected by impaction using the PExA® method (Particles in Exhaled Air), and constitute a potential source of biomarkers reflecting pathological processes in the small airways.ObjectiveOur aim was to investigate if PExA method may be useful for discovery of biomarkers that reflect pathology of small airways.Methods10 healthy controls and 20 subjects with asthma, of whom 10 with small airway involvement as indicated by a high lung clearance index (LCI ≥2.9 z-score), were examined using the PExA instrument. The samples were analysed with the SOMAscan proteomics platform (SomaLogic Inc).ResultsTwo hundred-seven proteins were detected in up to 80% of the samples. Nine proteins showed differential abundance in subjects with asthma and high LCI as compared to healthy controls. Two of these were less abundant (ALDOA4, C4), and seven more abundant (FIGF, SERPINA1, CD93, CCL18, F10, IgM, IL1RAP). sRAGE levels were lower in ex-smokers (n=14) than in never smokers (n=16). Gene Ontology (GO) annotation database analyses revealed that the PEx proteome is enriched in extracellular proteins associated with extracellular exosome-vesicles and innate immunity.ConclusionThe applied analytical method was reproducible and allowed identification of pathologically interesting proteins in PEx samples from asthmatic subjects with high LCI. The results suggest that PEx based proteomics is an novel and promising approach to study respiratory diseases with small airway involvement.