Background: The protein deacetylase sirtuin-1 (SIRT1) is an anti-aging molecule that is decreased in the lung from patients with chronic obstructive pulmonary disease (COPD). Recently, SIRT1 was reported to be detectable in serum, but serum SIRT1 levels have not yet been reported in patients with COPD.

Methods: Serum SIRT1 was measured by Western blotting, and relative ratio of band density in samples against that of a positive control were calculated.

Results: Several molecular sizes of SIRT1, including 120kDa (actual size) and fragments (102, 75kDa) were quantified by Western blotting. Among them, only the 120kDa serum SIRT1 (s120S) was significantly decreased in the patients with COPD compared to the control subjects without COPD (s120S ratio in healthy: 0.90±0.34, vs COPD: 0.68±0.24; p=0.014), and was positively correlated with airway obstruction (FEV1/ FVC; r=0.31; p=0.020) and its severity measured by FEV1 % predicted (r=0.29; p=0.029). Serum s120S also showed a positive correlation with body mass index (BMI; r=0.36; p=0.0077) and diffusing capacity of the lung per unit volume (KCO%; r=0.32; p=0.025). It was also significantly decreased with increasing severity of lung emphysema (r=-0.40, p=0.027) and with a clinical history of frequent COPD exacerbations (infrequent: 0.76±0.20 vs frequent: 0.56±0.26; p=0.027). SIRT1 was not detected in supernatant of A549 and primary epithelial cells in normal culture condition.

Conclusions: Serum SIRT1 (s120S) was decreased in the patients with COPD, potentially as reflected by the reduced SIRT1 within cells as a result of oxidative stress, and might be a potential biomarkers for certain disease characteristics of COPD.