Endothelial progenitor cells (EPCs) protect kidneys from acute ischemic damage. The aim of this study was to identify "treatment parameters" that optimize an EPC-based therapy of acute ischemic renal failure. Male C57BL/6N mice underwent unilateral nephrectomy with simultaneous contralateral renal artery clamping for 30, 35, and 40 min. Tagged murine EPCs were systemically injected at the time of reperfusion. In some experiments, EPCs were pretreated with the Epac (exchange protein directly activated by cAMP-1) activator 8-pCPT-2'-O-Me-cAMP (Epac-1 Ac) and the integrin binding antagonist cyclic Arg-Gly-Asp peptide (cRGD). Injections of 10(6) EPCs after 30 and 35 min of renal ischemia protected animals from acute renal failure. The same effect occurred with 0.5 x 10(6) EPCs after a 35-min period of ischemia. If ischemia lasted for 40 min, 0.5 x 10(6) cells mice did not prevent acute renal failure. To analyze whether EPC integrin receptor activation would modify the cells' renoprotective activity, EPCs were pretreated with Epac-1 Ac. Such animals did not develop acute renal failure, even if ischemia lasted for 40 min. This effect was negated if the cells were pretreated with both Epac-1 Ac and cRGD. In kidneys from those animals medullopapillary EPCs were significantly accumulated. In vitro Epac-1 Ac preactivation of EPCs did not increase the overall expression intensity but induced a redistribution of beta(1)-integrins toward the cell membranes. We conclude that EPC pretreatment with the integrin receptor activator 8-pCPT-2'-O-Me-cAMP augments the anti-ischemic potential of the cells.