A quantitative assessment of circulating progenitor cells in competitive athletes and in sedentary subjects

Aim: Hematopoietic stem cells (HSCs)and endothelial progenitor cells (EPCs)are known to play a role in the vascular responses and adaptations to exercise. We performed a quantitative assessment of HSCs and EPCs in adolescents in order to investigate whether resting levels of circulating HSCs and EPCs are comparable between elite athletes and sedentary healthy subjects. Methods: HSCs and EPCs levels were measured in adolescent competitive football players and in age and sexmatched sedentary controls. A laboratory testing was also performed to determine the white blood cells count and the lipid profile. All athletes were evaluated at the same stage of their training program, after 6 months of training. Controls were not engaged in any kind of routine training program. Results: Twenty male competitive athletes (18.4±0.5 years)and 9 sedentary controls (18.7±0.4 years)participated in the study. As expected, HDL cholesterol was higher in athletes as compared with controls (P<0.05). No significant differences in the other laboratory parameters were observed among groups. Circulating levels of HSCs were significantly lower in athletes in comparison with sedentary controls (P<0.05). Conversely, EPCs and KDR+ cell subpopulations did not substantially differ between athletes and controls. Conclusio: Adolescent athletes exhibit lower levels of circulating HSCs but not of EPCs compared to sedentary controls. The process of tissue repair associated with intensive training can contribute to this difference, acting as a stimulus for mobilization and homing of HSCs in the site of injuries.