Nitric oxide production by pulmonary leukocytes from induced sputum in patients with asthma and its effect on epithelial cell viability

Introduction: Nitric oxide (NO) is one of many factors potentially involved in lung remodeling in asthma. The aim of the study was to assess the effect of pulmonary leukocytes from patients with bronchial asthma on alveolar epithelial cell damage in relation to NO production. Materials and Methods: Induced sputum samples were obtained from 25 patients with bronchial asthma and 10 healthy volunteers. Twelve asthmatics were on inhaled corticosteroid treatment and 13 were corticosteroid free. Type II-like alveolar epithelial (A549) cells were cultured for 48 h in the presence of cell-free media from a 24-h culture of leukocytes obtained from the induced sputa (IS-Su). The level of NO was measured in supernatants from the cell cultures and the viability of the A549 cells was established. Results: The levels of NO in IS-Su from corticosteroid-free asthmatics were significantly higher (p=0.001) than those in IS-Su from healthy controls. Furthermore, NO production by A549 cells exposed to IS-Su from steroid-free asthmatics (group A) was significantly higher than that from asthmatics on corticosteroid therapy (group cA) as well as from healthy controls (p=0.01 and p=0.001, respectively). Lower viability of the epithelial cells exposed to IS-Su was observed in group A compared with controls (median: 72% vs. 97.5%; p < 0.001). In addition, a negative correlation (R-S=-0.706, p < 0.001) was found between the levels of NO produced by pulmonary leukocytes and the viability of epithelial cells. Conclusions: The results suggest that in the course of asthma, pulmonary leukocytes may interact with alveolar epithelial cells by inducing an excessive production of NO which, in turn, may contribute to epithelium impairment.