Cardioprotective Effects of Erythropoietin in Rats Subjected to Ischemia–Reperfusion Injury: Assessment of Infarct Size with99mTc-Annexin V

Abstract

Administration of erythropoietin (EPO) during or immediately after myocardial ischemia can reduce subsequent myocardial apoptosis, a key phenomenon in myocardial ischemia-reperfusion injury. In this study, we assessed the effect of EPO on (99m)Tc-annexin V myocardial uptake and whether the accumulation of (99m)Tc-annexin V can predict cardiac remodeling and functional deterioration. Eighteen rats with left coronary artery (LCA) occlusion were randomized to receive either an intravenous injection of EPO (EPO group) or saline (nontherapy [nT] group) immediately after release of the occlusion. After 20 min of LCA occlusion and 30 min of reperfusion, the rats were injected with (99m)Tc-annexin V. One hour after (99m)Tc-annexin V injection, the LCA was reoccluded and (201)Tl was injected intravenously, and the rats were sacrificed 1 min later. The heart was removed and sectioned, and dual-tracer autoradiography was performed to evaluate the distribution of the area at risk (defined on the thallium autoradiograph) and the area of apoptosis (defined on the annexin autoradiograph). Adjacent histologic specimens had deoxyuridine triphosphate nick-end labeling (TUNEL) staining to confirm the presence of apoptosis and were compared with autoradiography. Another 16 rats were randomized to EPO and nT groups and underwent echocardiography immediately after release of the LCA occlusion and at 2 and 4 wk after surgery. The areas of (99m)Tc-annexin V accumulation in the EPO group were smaller than those in the nT group, though the (201)Tl defect areas of these 2 groups were comparable (area ratio, 0.318 +/- 0.038 vs. 0.843 +/- 0.051, P < 0.001, for annexin and 24.8 +/- 2.1 vs. 25.9 +/- 2.6 mm(2), P = NS, for thallium). (99m)Tc-annexin V accumulation correlated with the density of TUNEL-positive cells (r = 0.886, P < 0.001). In the nT group, left ventricular end-diastolic dimension (Dd) increased from baseline at 2 wk by 34.7% +/- 3.8% and remained stable at 34.9% +/- 5.0% at 4 wk after coronary occlusion. In the EPO group, Dd increased by 8.5% +/- 2.1% (P < 0.01 vs. nT at 2 wk) and 13.2% +/- 2.8% (P < 0.01 vs. nT at 4 wk). In the nT group, the left ventricular percentage of fractional shortening decreased by 42.2% +/- 3.4% and 52.9% +/- 3.4% at 2 and 4 wk, respectively, whereas in the EPO group it decreased 9.0% +/- 1.9% at 2 wk (P < 0.01 vs. nT at 2 wk) and 11.1% +/- 6.7% at 4 wk (P < 0.01 vs. nT at 4 wk). This study demonstrated that a single treatment with EPO immediately after release of coronary ligation suppressed cardiac remodeling and functional deterioration. (99m)Tc-annexin V autoradiographs and TUNEL staining confirm that this change is due to a decrease in the extent of myocardial apoptosis in the ischemic/reperfused region.