Pulmonary Surfactant Protein A in Finnish Cigarette Smokers: from Proteomics to Cohort Studies

Surfactant protein A (SP-A), a large multimeric protein found in the airways and alveoli of the lungs, has been linked to the pathogenesis of COPD. Our recent non-hypothesis driven proteomic studies on lung tissues revealed a remarkable elevation of SP-A in the lung tissues of COPD patients, already in the earlier stages of the disease. SP-A could be detected in alveolar and bronchiolar epithelium of smokers and patients with COPD. SP-A release into the circulation was investigated in a large Finnish cohort including a population of 446 apparently healthy cigarette smokers and 35 non-smokers in a cross-sectional study and prospective 2-year follow-up. The levels of plasma SP-A were assayed using a validated EIA method. Plasma SP-A was detectable in all subjects and the SP-A levels were elevated in smokers compared to non-smokers. Altogether 111 smokers succeeded to quit smoking. After the follow-up the SP-A levels were higher in those who continued smoking compared to those who stopped. In conclusion, SP-A can be proposed to be a sensitive marker of early lung damage related to smoking. Whether SP-A can be used as a marker for COPD development, remains to be elucidated.