Increased levels of osteopontin in sputum supernatant of smoking asthmatics.

Smoking may modify the inflammatory pattern of the asthmatic airways. Osteopontin (OPN) has been associated with inflammation and fibrosis. In asthma, sputum levels of OPN are elevated and have been related to the underlying severity and to mediators expressing remodeling and inflammation. To evaluate the levels of OPN in sputum supernatants of asthmatic patients and to investigate the possible role of smoking as well as associations with mediators and cells involved in the inflammatory and remodeling process. We studied 103 asthma patients (49 smokers) and 40 healthy subjects (20 smokers) who underwent lung function tests, bronchial hyperresponsiveness to methacholine, and sputum induction for cell count identification and measurement of OPN, TGF-β1, IL-8, IL-13 and ECP in sputum supernatants. The concentrations of all mediators were measured using enzyme immunoassays. OPN levels (pg/ml) were significantly higher in smoking asthmatics compared to non-smoking asthmatics, and both non-smoking and smoking controls [median (interquartile ranges) 1120 (651,1817) vs. 197 (118,341) vs. 50 (42,70) vs. 102 (77,110) pg/ml, respectively; p<0.001]. Regression analysis provided significant associations between OPN and sputum neutrophils, IL-8 and TGF-β1, the most significant being the one with TGF-β1. These associations were present only in smoking asthmatics. Smoking habit significantly affects sputum OPN levels in asthma. The associations of OPN with sputum neutrophils, TGF-β1 and IL-8 in smoking asthmatics suggest a possible role for OPN in the neutrophilic inflammation and remodeling process in this phenotype of asthma.