SIRT1 and chronic obstructive pulmonary disease: The aim of this study is to analyze SIRT1 function in the peripheral blood mononuclear cells (PBMCs) of patients with COPD compared to nonsmokers and smokers with normal lung function, by quantifying its activity along with protein expression and investigating the relationship between SIRT1 activity and markers of oxidative stress as well as with parameters of lung function in the three groups.