Erythropoietin (EPO) and its non-erythrogenic derivative, carbarmylated EPO (CEPO), have been reported to activate different receptors (homomeric EPO receptor vs. heteromeric receptor consisting of EPO receptor monomer and common β-subunit). The aim of this study was to examine differences between EPO and CEPO in efficacy of cardioprotection against infarction and in activation of pro-survival kinases.

In isolated rat hearts, infarction was induced by global ischemia followed by reperfusion. Infarct size was determined 2 h after reperfusion, and ventricular tissues for immunoblotting were sampled at 5 min after reperfusion.

Pretreatment with EPO (10 units/ml) before ischemia reduced infarct size (% of risk area; %IS/AR) from 47.0 ± 2.1% of the control after 20-min ischemia to 24.7 ± 4.3% and from 62.0 ± 3.0% after 25-min ischemia to 45.5 ± 4.1%. Desialylated EPO (asialoEPO, 100 ng/ml) mimicked the protection by EPO. However, CEPO (100 ng/ml) failed to reduce infarct size after 20-min ischemia (%IS/AR = 47.5 ± 5.9%) and that after 25-min ischemia (%IS/AR = 56.1 ± 4.2%). The infarct size-limiting effect of CEPO was not shown either by increasing CEPO dose to 500 ng/ml or by shortening ischemia to 15 min. Both EPO and CEPO enhanced phosphorylation of cytosolic GSK-3β upon reperfusion. In contrast, phosphorylation of GSK-3β, Akt, and PKC-ε in mitochondria upon reperfusion was significantly enhanced by EPO but not by CEPO.

EPO affords more potent protection against infarction than does CEPO by distinct activation of signaling leading to phosphorylation of pro-survival protein kinases in mitochondria upon reperfusion.