A nonerythropoietic derivative of erythropoietin protects the myocardium from ischemia-reperfusion injury

Abstract

The cytokine erythropoietin (EPO) protects the heart from ischemic injury, in part by preventing apoptosis. However, EPO administration can also raise the hemoglobin concentration, which, by increasing oxygen delivery, confounds assignment of cause and effect. The availability of EPO analogs that do not bind to the dimeric EPO receptor and lack erythropoietic activity, e.g., carbamylated EPO (CEPO), provides an opportunity to determine whether EPO possesses direct cardioprotective activity. In vivo, cardiomyocyte loss after experimental myocardial infarction (MI) of rats (40 min of occlusion with reperfusion) was reduced from approximately 57% in MI-control to approximately 45% in animals that were administered CEPO daily for 1 week (50 microg/kg of body weight s.c.) with the first dose administered intravenously 5 min before reperfusion. CEPO did not increase the hematocrit, yet it prevented increases in left ventricular (LV) end-diastolic pressure, reduced LV wall stress in systole and diastole, and improved LV response to dobutamine infusion compared with vehicle-treated animals. In agreement with the cardioprotective effect observed in vivo, staurosporine-induced apoptosis of adult rat or mouse cardiomyocytes in vitro was also significantly attenuated ( approximately 35%) by CEPO, which is comparable with the effect of EPO. These data indicate that prevention of cardiomyocyte apoptosis, in the absence of an increase in hemoglobin concentration, explains EPO's cardioprotection. Nonerythropoietic derivatives such as CEPO, devoid of the undesirable effects of EPO, e.g., thrombogenesis, could represent safer and more effective alternatives for treatment of cardiovascular diseases, such as MI and heart failure. Furthermore, these findings expand the activity spectrum of CEPO to tissues outside the nervous system.

Fig. 1.

Mean percentage of myocytes positive for TdT assay counted on 450 cells in each dish obtained by isolation from different rat or mouse hearts. Shown are data for rat control (n = 9), S (Staurosporine, n = 10), rat S plus C (S plus CEPO, n = 10), mouse S plus C (n = 4), and mouse S plus E (S plus EPO; n = 4). *, P < 0.05; **, P < 0.01 versus staurosporine.

Fig. 2.

Histomorphometric evaluation of infarct size (A), number of cardiac myocyte nuclei in left ventricle (B), cardiac myocyte volume per nucleus (C), and cross-sectional area of cardiac myocytes in the spared left ventricle of Sham-operated rats and in coronary-ligated rats untreated or treated with CEPO (D). MI-control group; CEPO, MI-CEPO group. *, P < 0.01 versus vehicle.

Fig. 3.

CEPO administration prevents full increase in LV wall stress in diastole (A) and in systole (B). *, P < 0.05 or **, P < 0.01 versus MI-control (VEH).

Fig. 4.

Echo dobutamine stress test for the assessment of myocardial viability in lightly sedated rats. Inotropic reserve (A), Maximum (peak) SF (B), and maximum heart rate (C) on dobutamine in Sham-operated rats and in coronary ligated rats untreated or treated with CEPO are shown. VEH, MI-control group; CEPO, MI-CEPO group. *, P < 0.05; **, P < 0.01 versus VEH group.