The 10th Biennial Hatter Cardiovascular Institute workshop: cellular protection-evaluating new directions in the setting of myocardial infarction, ischaemic stroke, and cardio-oncology.

Due to its poor capacity for regeneration, the heart is particularly sensitive to the loss of contractile cardiomyocytes. The onslaught of damage caused by ischaemia and reperfusion, occurring during an acute myocardial infarction and the subsequent reperfusion therapy, can wipe out upwards of a billion cardiomyocytes. A similar program of cell death can cause the irreversible loss of neurons in ischaemic stroke. Similar pathways of lethal cell injury can contribute to other pathologies such as left ventricular dysfunction and heart failure caused by cancer therapy. Consequently, strategies designed to protect the heart from lethal cell injury have the potential to be applicable across all three pathologies. The investigators meeting at the 10th Hatter Cardiovascular Institute workshop examined the parallels between ST-segment elevation myocardial infarction (STEMI), ischaemic stroke, and other pathologies that cause the loss of cardiomyocytes including cancer therapeutic cardiotoxicity. They examined the prospects for protection by remote ischaemic conditioning (RIC) in each scenario, and evaluated impasses and novel opportunities for cellular protection, with the future landscape for RIC in the clinical setting to be determined by the outcome of the large ERIC-PPCI/CONDI2 study. It was agreed that the way forward must include measures to improve experimental methodologies, such that they better reflect the clinical scenario and to judiciously select combinations of therapies targeting specific pathways of cellular death and injury.

The Caspase 1 Inhibitor VX-765 Protects the Isolated Rat Heart via the RISK Pathway.

PURPOSE: Protecting the heart from ischaemia-reperfusion (IR) injury is a major goal in patients presenting with an acute myocardial infarction. Pyroptosis is a novel form of cell death in which caspase 1 is activated and cleaves interleukin 1ß. VX-785 is a highly selective, prodrug caspase 1 inhibitor that is also clinically available. It has been shown to be protective against acute IR in vivo rat model, and therefore might be a promising possibility for future cardioprotective therapy. However, it is not known whether protection by VX-765 involves the reperfusion injury salvage kinase (RISK) pathway. We therefore investigated whether VX-765 protects the isolated, perfused rat heart via the PI3K/Akt pathway and whether protection was additive with ischaemic preconditioning (IPC). METHODS: Langendorff-perfused rat hearts were subject to ischaemia and reperfusion injury in the presence of 30 µM VX-765, with precedent IPC, or the combination of VX-765 and IPC. RESULTS: VX-765 reduced infarct size (28 vs 48% control; P < 0.05) to a similar extent as IPC (30%; P < 0.05). The PI3 kinase inhibitor, wortmannin, abolished the protective effect of VX-765. Importantly in the model used, we were unable to show additive protection with VX-765 + IPC. CONCLUSIONS: The caspase 1 inhibitor, VX-765, was able to reduce myocardial infarction in a model of IR injury. However, the addition of IPC did not demonstrate any further protection.

Plasma exosomes protect the myocardium from ischemia-reperfusion injury.

BACKGROUND: Exosomes are nanometer-sized vesicles released from cells into the blood, where they can transmit signals throughout the body. Shown to act on the heart, exosomes' composition and the signaling pathways they activate have not been explored. We hypothesized that endogenous plasma exosomes can communicate signals to the heart and provide protection against ischemia and reperfusion injury. OBJECTIVES: This study sought to isolate and characterize exosomes from rats and healthy volunteers, evaluate their cardioprotective actions, and identify the molecular mechanisms involved. METHODS: The exosome-rich fraction was isolated from the blood of adult rats and human volunteers and was analyzed by protein marker expression, transmission electron microscopy, and nanoparticle tracking analysis. This was then used in ex vivo, in vivo, and in vitro settings of ischemia-reperfusion, with the protective signaling pathways activated on cardiomyocytes identified using Western blot analyses and chemical inhibitors. RESULTS: Exosomes exhibited the expected size and expressed marker proteins CD63, CD81, and heat shock protein (HSP) 70. The exosome-rich fraction was powerfully cardioprotective in all tested models of cardiac ischemia-reperfusion injury. We identified a pro-survival signaling pathway activated in cardiomyocytes involving toll-like receptor (TLR) 4 and various kinases, leading to activation of the cardioprotective HSP27. Cardioprotection was prevented by a neutralizing antibody against a conserved HSP70 epitope expressed on the exosome surface and by blocking TLR4 in cardiomyocytes, identifying the HSP70/TLR4 communication axis as a critical component in exosome-mediated cardioprotection. CONCLUSIONS: Exosomes deliver endogenous protective signals to the myocardium by a pathway involving TLR4 and classic cardioprotective HSPs.

Mitochondrial cyclophilin-D as a potential therapeutic target for post-myocardial infarction heart failure.

The pharmacological inhibition or genetic ablation of cyclophilin-D (CypD), a critical regulator of the mitochondrial permeability transition pore (mPTP), confers myocardial resistance to acute ischemia-reperfusion injury, but its role in post-myocardial infarction (MI) heart failure is unknown. The aim of this study was to determine whether mitochondrial CypD is also a therapeutic target for the treatment of post-MI heart failure. Wild-type (WT) and CypD(-/-) mice were subjected to either sham surgery or permanent ligation of the left main coronary artery to induce MI, and were assessed at either 2 or 28 days to determine the long-term effects of CypD ablation. After 2 days, myocardial infarct size was smaller and left ventricular (LV) function was better preserved in CypD(-/-) mice compared to WT mice. After 28 days, when compared to WT mice, in the CypD(-/-) mice, mortality was halved, myocardial infarct size was reduced, LV systolic function was better preserved, LV dilatation was attenuated and in the remote non-infarcted myocardium, there was less cardiomyocyte hypertrophy and interstitial fibrosis. Finally, ex vivo fibroblast proliferation was found to be reduced in CypD(-/-) cardiac fibroblasts, and in WT cardiac fibroblasts treated with the known CypD inhibitors, cyclosporin-A and sanglifehrin-A. Following an MI, mice lacking CypD have less mortality, smaller infarct size, better preserved LV systolic function and undergo less adverse LV remodelling. These findings suggest that the inhibition of mitochondrial CypD may be a novel therapeutic treatment strategy for post-MI heart failure.