Enhancement of homing capability of endothelial progenitor cells to ischaemic myocardium through physiological ischaemia training

Abstract

To investigate the effects of physiological ischaemia training on the quantity and activity of endothelial progenitor cells in rabbits with intermittent myocardial ischaemia. A reversible coronary artery water balloon occluder (5.0 mm inner diameter) was placed around the proximal left ventricular branch and intermittent myocardial ischaemia was induced by deflation and inflation of the occluder. A wire electrode was inserted longitudinally into the epineurium of the sciatic nerve to generate physiological ischaemia training through isometric contraction induced by electrical stimulation. Rabbits were randomly divided into 3 groups: a sham operated group (SO), an intermittent myocardial ischaemia-only group (MI), and an MI plus physiological ischaemia training group (PT). Intermittent myocardial ischaemia was induced with 2-min ischaemia followed by 1-h reperfusion. Physiological ischaemia training was induced by electrical stimulation (40% maximum current strength, 1 ms, 40 Hz), 4-min per session, twice a day, 5 days per week for 4 weeks. At the end-points, endothelial progenitor cells were isolated and cultured for analysis of their migration ability. Endothelial progenitor cells were identified by dual-staining with Dil-labelled acetylated low-density lipoprotein and fluorescein isothiocyanate-labelled Ulex europaeus agglutinin-1. Circulating endothelial progenitor cells (CD34(+)/Flk-1(+)) were counted by fluorescence-activated cell sorter, and capillary density was evaluated by immunohistochemistry examination. Group PT showed the highest migration capacity of endothelial progenitor cells (151 cells, standard deviation 16/high power field) and the highest increase in circulating endothelial progenitor cells (p < 0.01) after 4 weeks' physiological ischaemia training. Capillary density in the myocardium was also significantly enhanced in group PT (p < 0.05). Pearson's analysis demonstrated a positive correlation between the number circulating endothelial progenitor cells and capillary density in the myocardium after 4 weeks' physiological ischaemia training (p < 0.05). Physiological ischaemia training may enhance the quantity and activity of endothelial progenitor cells in the blood, resulting in an increase in angiogenesis in the ischaemic heart region.