Bradykinin Preconditioning Improves Therapeutic Potential of Human Endothelial Progenitor Cells in Infarcted Myocardium

OBJECTIVES: Stem cell preconditioning (PC) is a powerful approach in reducing cell death after transplantation. We hypothesized that PC human endothelial progenitor cells (hEPCs) with bradykinin (BK) enhance cell survival, inhibit apoptosis and repair the infarcted myocardium. METHODS: The hEPCs were preconditioned with or without BK. The hEPCs apoptosis induced by hypoxia along with serum deprivation was determined by annexin V-fluorescein isothiocyanate/ propidium iodide staining. Cleaved caspase-3, Akt and eNOS expressions were determined by Western blots. Caspase-3 activity and vascular endothelial growth factor (VEGF) levels were assessed in hEPCs. For in vivo studies, the survival and cardiomyocytes apoptosis of transplanted hEPCs were assessed using 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindodi- carbocyanine,4-chlorobenzenesul-fonate salt labeled hEPCs and TUNEL staining. Infarct size and cardiac function were measured at 10 days after transplantation, and the survival of transplanted hEPCs were visualized using near-infrared optical imaging. RESULTS: In vitro data showed a marked suppression in cell apoptosis following BK PC. The PC reduced caspase-3 activation, increased the Akt, eNOS phosphorylation and VEGF levels. In vivo data in preconditioned group showed a robust cell anti-apoptosis, reduction in infarct size, and significant improvement in cardiac function. The effects of BK PC were abrogated by the B2 receptor antagonist HOE140, the Akt and eNOS antagonists LY294002 and L-NAME, respectively. CONCLUSIONS: The activation of B2 receptor-dependent PI3K/Akt/eNOS pathway by BK PC promotes VEGF secretion, hEPC survival and inhibits apoptosis, thereby improving cardiac function in vivo. The BK PC hEPC transplantation for stem cell-based therapies is a novel approach that has potential for clinical used.