Sputum YKL-40 is a potential biomarker of COPD-asthma overlap

Introduction : The clinical features and pathophysiology of COPD-asthma overlap remain poorly characterized. We have developed two panels of potential biomarkers for COPD-asthma overlap phenotype: neutrophil-derived biomarkers of COPD (Iwamoto H, etc. ERJ, 2013) and asthma markers of T helper 2 (Th2) type -driven inflammation (the chitinase-like protein YKL-40 and periostin). Aims : Our aim was to clarify the similarity and differences between asthma, COPD and their overlap, and to identify reliable, specific and sensitive biomarkers for the COPD-asthma overlap. Methods : Based on their medical history and self-reported questionnaire data, the 132 study subjects were categorized into 5 groups: non-smokers (n=24), smokers (n=23), asthma (n=32), COPD (n=39), and COPD-asthma overlap patients (n=14). Plasma and/ or sputum levels of YKL-40 and periostin were measured by EIA/ELISA. Results : Plasma periostin and sputum YKL-40 levels were significantly elevated in overlap compared with asthma patients. However, only sputum YKL-40 could differentiate patients with overlap from COPD (p=0.01, AUC=0.766) and asthma (p= 0.003, AUC=0.820). Sputum YKL-40 was significantly associated with neutrophil levels, eosinophil levels, ICS use%, and further independently (multivariate stepwise regression) with reduced lung function. Conclusion : Elevated levels of sputum YKL-40 indicate that amplified Th2-type driven airway inflammation could be an additional feature of COPD-asthma overlap. Sputum YKL-40 associates with obstructive disease severity, FEV 1 and FEV 1 /FVC. The data suggest that monitoring of sputum YKL-40 could be useful in clinical practice for identifying COPD-asthma overlap.