Jiawen Liu

Reductions in cardiac infarct size can be achieved in ischaemic preconditioning, a procedure which subjects the heart to intermittent, non-lethal cycles of ischaemia and reperfusion. Similar cardioprotection can be induced upon preconditioning distal tissues such as the upper limb, and this procedure is called remote ischaemic preconditioning. Nano-sized, cell-derived vesicles known as exosomes have been shown previously to be capable of inducing cardioprotection when administered acutely, and we hypothesized that exosomes produced after remote ischaemic preconditioning (RIPC) enhances the observed cardioprotection. We also investigated whether exosomes can confer cardioprotection 24 h later. We isolated exosomes from the plasma of three healthy male volunteers before and after they underwent four cycles of 5 min upper limb ischaemia and 5 min reperfusion, and then administered the exosomes to primary rat ventricular cardiomyocytes isolated from male Sprague Dawley rats. Cardiomyocytes were subjected to 2.5 h of simulated ischaemia and 1 h simulated reperfusion. We assessed cardiomyocyte viability with propidium iodide staining and observed significant reductions in cardiomyocyte death when control exosomes were administered either 30 min or 24 h before hypoxia. Exosomes obtained after RIPC induced a similar degree of cardioprotection at both time points. As miRNA-144/451 have been proposed to mediate RIPC, we investigated whether introducing antagomiRs of miRNA-144/451 with the exosomes would attenuate cardioprotection after 24 h. No significant differences in cardioprotection were observed, suggesting that miRNA-144/451 may not be directly involved in this model. Our findings suggest that regardless of their origin from control or RIPC hearts, exosomes per se can be used to induce cardioprotection either acutely or after 24 h.