Circulating Endothelial Stem Cells in Age-Matched Smokers with or without Mild-to-Moderate Pulmonary Emphysema

Previous studies have suggested a role for an increased apoptosis of the endothelial cells in the pulmonary capillaries of the alveolar septa in the pathogenesis of pulmonary emphysema. In animal models, circulating endothelial stem cells may contribute to the repair of lung damage. It is unknown if a decrease in the blood of these cells may contribute to the pathogenesis of pulmonary emphysema in humans. The aim of our study was to investigate by flow cytometry the number of total (CD34+) and endothelial stem (triple positive for CD34+/CD133/VEGF-R2) cells in the peripheral venous blood of age-matched smokers with or without pulmonary emphysema. The presence and the severity of pulmonary emphysema was determined using HRCT of the chest with density mask and the NETT score (0 to 4; NEJM 2001). All the subjects were free from concomitant diseases or drugs able to interfere with the number of circulating stem cells. Venous blood samples from 37 subjects (mean age: 66.8±1.4, 25M/12F, mean 33.11±3.2 pack-years, 12 current and 25 ex-smokers) were obtained. Their mean HRCT NETT score is 1.7±0.4. Twenty-two subjects (59.5%) had chronic airflow obstruction (mean post-bronchodilator FEV1/FVC ratio=56.8%±2.7) whereas 39.5% (n=15) had normal lung function (FEV1/FVC ratio=77.1%±1.4). We found a significant correlation between the absolute number of circulating CD34+ cells and the absolute number of circulating endothelial stem cells (r=0.593, p<0.0001). Also there was a significant correlation between the percentage of circulating endothelial stem cells and the number of pack-years smoked (r=0.42, p<0.05). No correlation was found between total and endothelial stem cells number and HRCT score of pulmonary emphysema or lung function data. These data suggest that the number of circulating endothelial stem cells is not related to pulmonary emphysema severity.