Exercise capacity and circulating endothelial progenitor cells in hemodialysis patients

Mobilization of circulating endothelial progenitor cells (EPCs) is increased after acute exercise and training. This study aims to evaluate whether, in a low performance population, EPC levels may be related to exercise capacity in steady state conditions. Study population consisted of sixteen hemodialysis patients. The distance walked in the 6-minute walking test (6 MWD) and the maximal speed attained in an incremental treadmill test were used to assess the exercise capacity. Physical functioning was measured by the scale on the SF36 questionnaire. Quantification of peripheral blood CD34(+) cells and enumeration of EPCs, assessed as CD34(+) cells coexpressing AC 133 and vascular endothelial growth factor receptor-2, were performed. Hemoglobin concentration, white blood cells, high-sensitivity C-reactive protein, total cholesterol, and triglycerides were measured. Statistical analysis examined the relationship between blood progenitors cells versus performance parameters, laboratory parameters, age, body mass index, hemodialysis duration, and erythropoietin therapy. Univariate analysis revealed a significant association between percentage values of EPC and performance parameters only: 6 MWD (r=0.720; p=0.0017), maximal treadmill speed (r=0.721; p=0.0016), and physical functioning score (r=0.506; p=0.0453). A similar statistical association between EPC absolute values and performance parameters was found. No correlation between CD34 (+) and any parameter under study was observed. Multivariate analysis indicated 6 MWD as the most significant independent factor associated with EPC level. EPC percentage value was significantly lower (p=0.0087) in the worse (6 MWD < 300 m, n=8) than in the better performing group (6 MWD > 300 m, n=8). In a group of renal patients, mobilization of EPCs was related to the degree of exercise capacity, suggesting a possible connection with the cardiovascular risk in low performance populations limited by chronic diseases.