Plasma proteins elevated in severe asthma despite oral steroid use and unrelated to Type-2 inflammation

Rationale: Asthma phenotyping requires novel biomarker discovery. Objectives: To identify plasma biomarkers associated with asthma phenotypes by application of a new proteomic panel to samples from two well-characterised cohorts of severe (SA) and mild-to-moderate (MMA) asthmatics, chronic obstructive pulmonary disease (COPD) subjects and healthy controls (HC). Methods: An antibody-based array targeting 177 proteins predominantly involved in pathways relevant to inflammation, lipid metabolism, signal transduction and extracellular matrix was applied to plasma from 525 asthmatics and HC in the U-BIOPRED cohort, and 142 subjects with asthma and COPD from the validation cohort BIOAIR. Effects of oral corticosteroids (OCS) were determined by a two-week, placebo-controlled OCS trial in BIOAIR, and confirmed by relation to objective OCS measures in U-BIOPRED. Results: In U-BIOPRED, 110 proteins were significantly different, mostly elevated, in SA compared to MMA and HC. Ten proteins were elevated in SA versus MMA in both U-BIOPRED and BIOAIR (alpha-1-antichymotrypsin, apolipoprotein-E, complement component 9, complement factor I, macrophage inflammatory protein-3, interleukin-6, sphingomyelin phosphodiesterase 3, RANK, TGF-β1, and glutathione S-transferase). OCS treatment decreased most proteins, yet differences between SA and MMA remained following correction for OCS use. Consensus clustering of U-BIOPRED protein data yielded six clusters associated with asthma control, quality of life, blood neutrophils, hsCRP, and BMI, but not Type-2 inflammatory biomarkers. The mast cell specific enzyme carboxypeptidase A3 was one major contributor to cluster differentiation. Conclusions: The plasma proteomic panel revealed previously unexplored yet potentially useful Type-2-independent biomarkers, and validated several proteins with established involvement in the pathophysiology of severe asthma.