Serum Levels of Eosinophil-Derived Neurotoxin: A Biomarker for Asthma Severity in Adult Asthmatics

Eosinophilic inflammation is a key component of severe asthma (SA). However, there has been no reliable serum biomarker for the eosinophilic inflammation of SA. We hypothesized that serum eosinophil-derived neurotoxin (EDN) could predict the eosinophilic inflammation of SA in adult asthmatics. Severe asthmatics (n = 235), nonsevere asthmatics (n = 898), and healthy controls (n = 125) were enrolled from Ajou University Hospital, South Korea. The serum levels of EDN and periostin were measured by enzyme-linked immunosorbent assay and compared between severe and nonsevere asthmatics. Their associations with total eosinophil count (TEC) and clinical parameters were evaluated; clinical validation of the K-EDN kit for the measurement of serum EDN was evaluated. Severe asthmatics were older and had longer disease duration with significantly lower levels of forced expiratory volume in 1 second and methacholine PC20 than nonsevere asthmatics. Significant differences were found in TEC or sputum eosinophil count (%) between the groups. The serum levels of EDN and periostin were significantly higher in severe asthmatics than in nonsevere asthmatics and in healthy controls (all < 0.05). Although significant correlations were found between serum EDN levels measured by the 2 kits (ρ = 0.545, < 0.0001), higher correlation coefficients between serum EDN levels measured by the K-EDN kit and TEC were higher (ρ = 0.358, < 0.0001) than those between serum EDN levels measured by the MBL kit and TEC (ρ = 0.319, < 0.0001) or serum periostin level (ρ = 0.222, < 0.0001). Multivariate regression analysis demonstrated that serum EDN levels measured by the K-EDN kit predicted the phenotype of SA ( = 0.003), while 2 other biomarkers did not. The serum EDN level may be a useful biomarker for assessing asthma severity in adult asthmatics.