BACKGROUND - Osteopontin (OPN) is a phosphorylated acidic glycoprotein that can function as both an extracellular matrix molecule and a cytokine. Published data support that OPN is upregulated in surgical lung tissue samples of patients with COPD. The aim of this study was to determine the levels of OPN in sputum supernatants of patients with COPD and to investigate possible associations with mediators and cells involved in the inflammatory and remodeling process as well as with the extent of emphysema.
METHODS - Seventy-seven patients with COPD and 40 healthy subjects (20 smokers) were studied. All subjects underwent lung function tests, sputum induction for cell count identification, and OPN, transforming growth factor-β1, matrix metalloproteinase (MMP)-2, IL-8, and leukotriene-4 measurement in sputum supernatants. High-resolution CT (HRCT) scan of the chest was performed for quantification of emphysema.
RESULTS - OPN levels (pg/mL) were significantly higher in patients with COPD compared with healthy smokers and nonsmokers (median [interquartile range], 1,340 [601, 6,227] vs 101 [77, 110] vs 68 [50, 89], respectively; P < .001). Regression analysis showed a significant association between OPN and sputum neutrophils, IL-8, MMP-2, and the extent of emphysema. The associations previously listed were not observed in healthy subjects.
CONCLUSIONS - OPN levels are higher in patients with COPD compared with healthy subjects. OPN may play a role in the neutrophilic inflammation and in the pathogenesis of emphysema.