Decreased levels of irisin, a skeletal muscle cell-derived myokine, are related to emphysema associated with chronic obstructive pulmonary disease

Yukari Sugiyama, Kazuhisa Asai, Kazuhiro Yamada, Yuko Kureya, Naoki Ijiri, Tetsuya Watanabe, Hiroshi Kanazawa, Kazuto Hirata Department of Respiratory Medicine, Graduate School of Medicine, Osaka City University, Osaka, Japan Background: Cigarette smoking-induced oxidant–antioxidant imbalance is a factor that contributes to the pathogenesis of COPD through epithelial cell apoptosis. Irisin is a skeletal muscle cell-derived myokine associated with physical activity. Irisin is also known to decrease oxidant-induced apoptosis in patients with diabetes mellitus. However, the correlation between irisin and emphysema in COPD and its role in epithelial cell apoptosis remains unknown. Subjects and methods: Forty patients with COPD were enrolled in this study. Pulmonary function tests and measurements of the percentage of low-attenuation area on high-resolution computed tomography images were performed, and the results were evaluated for correlation with serum irisin levels. The effect of irisin on cigarette-smoke extract-induced A549 cell apoptosis and the expression of Nrf2, a transcription factor for antioxidants, was also examined in vitro. Results: Serum irisin levels were significantly correlated with lung diffusing capacity for carbon monoxide divided by alveolar volume (r=0.56, P