Abstract 950: Inhibition of Apoptosis with the Biotherapeutic Protein PTD-Bir3-RING Reduces Infarct Size when Administered within the First Hours of Reperfusion
Current investigated cardioprotective strategies against myocardial infarction are performed within the first minutes of reperfusion. In this study, we hypothesized that another window for cardioprotection exists when performed within the first hours of reperfusion. For this purpose, we used a biotherapeutic approach by mimicking the X-linked Inhibitor of Apoptosis Protein (X-IAP), which is presently the most effective endogenous inhibitor of apoptosis. We fused the C-terminal part of X-IAP (Bir3-Ring) to the protein transduction domain (PTD) of HIV1 transactivator of transcription domain which confers to the protein (PTD-Bir3-RING) the ability to cross any cell membrane. After anesthesia, 6 – 8 weeks old C57/BL6-J mice were subjected to 30min coronary artery occlusion followed by 24h coronary artery reperfusion (CAR). Intravenous injections of saline (control) or 0.8μg/g of PTD-Bir3-Ring were performed at 30min, 3h or 6h after the onset of CAR. In control mice, IS (TTC staining) reached 44±4% of the area at risk after 24h CAR. Administered at 30min and 3h during CAR, PTD-Bir3-RING significantly reduced IS (27±4% and 29±4%, respectively). This cardioprotection was lost when the protein was administered at 6h CAR. We verified with immunohistochemistry that the protein was present within the cardiomyocytes. Concomitantly, caspases 3, 8 and 9 activities were inhibited and TUNEL-positive cardiomyocytes were reduced by 50% vs control. Furthermore, Akt and Bad phosphorylation increased while Bax and truncated Bid expression decreased in PTD-Bir3-RING treated groups. Thus, these results demonstrate that potent inhibition of apoptosis with PTD-Bir3-RING, an original product of biotherapy, reduces myocardial infarct size even when administered late during reperfusion. These results also suggest that beyond the first minutes of reperfusion, an additional window of cardioprotection exists within the first hours of reperfusion.