Sputum Neurturin Levels in Adult Asthmatic Subjects

BACKGROUND: Neurturin (NRTN) is a neurotrophic factor that was originally identified in the development and maintenance of neural cells. Recent studies involving NRTN knockout mice have reported its anti-inflammatory effects in allergic airway conditions. However, the role of NRTN in human asthma has not yet been identified. OBJECTIVE: The purposes of the present study were to confirm the presence of NRTN in the airways and to investigate the clinical and pathogenetic roles of NRTN in asthma. METHODS: The NRTN levels in the induced sputum were measured by enzyme-linked immunosorbent assay (ELISA). Relationships between NRTN and clinical characteristics, asthma control status, and airway inflammation were assessed. RESULTS: Sixty-four asthmatic subjects were enrolled in the study. All asthmatic subjects had detectable sputum NRTN levels, with a mean (SD) level of 2.03 (1.29) ng/mL. The sputum NRTN levels had significant positive correlations with sputum eosinophil and exhaled nitric oxide levels and were significantly higher in the atopic subjects than in the non-atopic subjects. No significant difference in sputum NRTN levels were observed for asthma control status and asthma exacerbation. In sputum inflammatory analyses, sputum NRTN level was positively correlated with interleukin (IL)-5 and IL-13 levels, and negatively correlated with matrix metalloproteinase (MMP)-9 level. CONCLUSION: It is plausible that sputum NRTN could serve as a new marker for Type 2 airway inflammation, implicating its role in the process of airway remodeling in asthma. Future studies should investigate the clinical relevance of sputum NRTN level in prospective analyses.