Rationale Preconditioning is widely known to protect cardiomyocytes from reperfusion-induced cell death by activation of several pro-survival transductional pathways. The fact that preconditioning can be achieved remotely (Remote Ischaemic Preconditioning, RIPC) means that humoral factors are released from ischaemic limbs into the circulation carrying a pro-survival message. Exosomes are circulating nano-sized vesicles that mediate inter-cellular communication by carrying diverse proteins and RNA molecules. Here we studied the role of exosomes in mediating RIPC.

Methods and Results We isolated exosomes from plasma of rats or humans subjected to RIPC. We characterised control or RIPC exosomes by electron microscopy, flow cytometry, western blot and nano-particle tracking analysis. Exosome concentration increased dramatically after RIPC in humans (from 3.5 ± 0.3x10⁸ to 1.1 ± 0.3x10⁹ exosomes/ml plasma; p < 0.01, n = 6), and administration of purified exosomes protected the heart from infarct in different settings including an in vivo rat model (vehicle: 47.4 ± 4.7; RIPC-Exosomes: 20.5 ± 3.9%Infarct/AAR; p < 0.01), ex vivo Langendorff (vehicle: 35.2 ± 3.3; RIPC-Exosomes: 21.2 ± 2.5% Infarct/AAR; p < 0.01), and in vitro hypoxia-reoxygenation of cardiomyocytes (43 ± 7% protection from death, p < 0.01). RIPC-Exosomes triggered rapid ERK phosphorylation (3.9 ± 0.1 fold over vehicle), and inhibition of upstream PI3K or MEK abolished ERK activation and inhibited cardioprotection.

Conclusions We demonstrate that RIPC dramatically increases the concentration of exosomes in the circulation. Exosomes acutely activate pro-survival kinases that rapidly prepare the heart against ischemia-reperfusion injury. Exosomes represent a novel agent with the potential to be an endogenous, non-immunogenic and multi-signalling tool for cardioprotection.