Release of sputum neutrophil granules is associated with pulmonary function and disease severity in childhood asthma

Myeloperoxidase (MPO) and human neutrophil lipocalin or neutrophil gelatinase-associated lipocalin (HNL/NGAL) are stored in neutrophil granulocytes and secreted upon activation of the cells. They have been proposed to reflect the degree of inflammation in the airways. However, their role as potential markers of disease severity in childhood asthma remains unknown. This study investigated the relationship between the expression of MPO and HNL/NGAL and childhood asthma.

A total of 83 pediatric patients with asthma and 59 controls were enrolled. Using enzyme-linked immunosorbent assays, the human MPO and HNL/NGAL levels were measured in sputum supernatants. Assessments including spirometry, methacholine challenge test, and atopy test were conducted.

No difference in sputum neutrophil counts was observed between pediatric patients with asthma and controls. However, sputum MPO and HNL/NGAL levels were significantly higher in patients with asthma than in controls (p = 0.021 and p < 0.001, respectively), especially in patients with moderate-to-severe persistent asthma. In patients with asthma, sputum MPO and HNL/NGAL levels showed a positive correlation with sputum neutrophil counts (MPO, r = 0.433, p < 0.001; HNL/NGAL, r = 0.584, p < 0.001) and with each other (r = 0.628, p < 0.001). Moreover, sputum HNL/NGAL level demonstrated better ability to accurately reflect current pulmonary function, airway inflammation, and limitations than MPO level in this study.

Sputum MPO and HNL/NGAL levels, which reflect neutrophil activation in airways, were increased in pediatric patients with asthma. Moreover, sputum MPO and HNL/NGAL may serve as appropriate assessment indicators of asthma severity in pediatric patients.