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Aims: Interleukin 11 (IL11) was initially thought important for platelet production, which led to recombinant IL11 being developed as a drug to treat thrombocytopenia. IL11 was later found to be redundant for haematopoiesis and its use in patients is associated with unexplained and severe cardiac side effects. Here we aim to identify, for the first time, direct cardiomyocyte toxicities associated with IL11, which was previously believed cardioprotective., Methods and Results: We injected recombinant mouse lL11 (rmIL11) into mice and studied its molecular effects in the heart using immunoblotting, qRT-PCR, bulk RNA-seq, single nuclei RNA-seq (snRNA-seq) and ATAC-seq. The physiological impact of IL11 was assessed by echocardiography in vivo and using cardiomyocyte contractility assays in vitro. To determine the activity of IL11 specifically in cardiomyocytes we made two cardiomyocyte-specific Il11ra1 knockout (CMKO) mouse models using either AAV9-mediated and Tnnt2-restricted (vCMKO) or Myh6 (m6CMKO) Cre expression and an Il11ra1 floxed mouse strain. In pharmacologic studies, we studied the effects of JAK/STAT inhibition on rmIL11-induced cardiac toxicities. Injection of rmIL11 caused acute and dose-dependent impairment of left ventricular ejection fraction (saline: 62.4% ± 1.9; rmIL11: 32.6% ± 2.9, p<0.001, n=5). Following rmIL11 injection, myocardial STAT3 and JNK phosphorylation were increased and bulk RNA-seq revealed upregulation of pro-inflammatory pathways (TNFα, NFκB and JAK/STAT) and perturbed calcium handling. snRNA-seq showed rmIL11-induced expression of stress factors (Ankrd1, Ankrd23, Xirp2), activator protein-1 (AP-1) transcription factor genes and Nppb in the cardiomyocyte compartment. Following rmIL11 injection, ATAC-seq identified the Ankrd1 and Nppb genes and loci enriched for stress-responsive, AP-1 transcription factor binding sites. Cardiomyocyte-specific effects were examined in vCMKO and m6CMKO mice, which were both protected from rmIL11-induced left ventricular impairment and molecular pathobiologies. In mechanistic studies, inhibition of JAK/STAT signalling with either ruxolitinib or tofacitinib prevented rmIL11-induced cardiac dysfunction., Conclusions: Injection of IL11 directly activates IL11RA/JAK/STAT3 in cardiomyocytes to cause acute heart failure. Our data overturn the earlier assumption that IL11 is cardioprotective and explain the serious cardiac side effects associated with IL11 therapy., (© The Author(s) 2024. Published by Oxford University Press on behalf of the European Society of Cardiology.)

Patients with Type 2 diabetes mellitus (T2DM) frequently exhibit a distinctive cardiac phenotype known as diabetic cardiomyopathy. Cardiac complications associated with T2DM include cardiac inflammation, hypertrophy, fibrosis, and diastolic dysfunction in the early stages of the disease, which can progress to systolic dysfunction and heart failure. Effective therapeutic options for diabetic cardiomyopathy are limited and often have conflicting results. The lack of effective treatments for diabetic cardiomyopathy is due in part, to our poor understanding of the disease development and progression, as well as a lack of robust and valid preclinical human models that can accurately recapitulate the pathophysiology of the human heart. In addition to cardiomyocytes, the heart contains a heterogeneous population of non-myocytes including fibroblasts, vascular cells, autonomic neurons, and immune cells. These cardiac non-myocytes play important roles in cardiac homeostasis and disease, yet the effect of hyperglycaemia and hyperlipidaemia on these cell types is often overlooked in preclinical models of diabetic cardiomyopathy. The advent of human-induced pluripotent stem cells provides a new paradigm in which to model diabetic cardiomyopathy as they can be differentiated into all cell types in the human heart. This review will discuss the roles of cardiac non-myocytes and their dynamic intercellular interactions in the pathogenesis of diabetic cardiomyopathy. We will also discuss the use of sodium-glucose cotransporter 2 inhibitors as a therapy for diabetic cardiomyopathy and their known impacts on non-myocytes. These developments will no doubt facilitate the discovery of novel treatment targets for preventing the onset and progression of diabetic cardiomyopathy., Competing Interests: Conflict of interest: none declared., (© The Author(s) 2022. Published by Oxford University Press on behalf of the European Society of Cardiology.)

Circadian rhythms are internal regulatory processes controlled by molecular clocks present in essentially every mammalian organ that temporally regulate major physiological functions. In the cardiovascular system, the circadian clock governs heart rate, blood pressure, cardiac metabolism, contractility, and coagulation. Recent experimental and clinical studies highlight the possible importance of circadian rhythms in the pathophysiology, outcome, or treatment success of cardiovascular disease, including ischaemic heart disease. Disturbances in circadian rhythms are associated with increased cardiovascular risk and worsen outcome. Therefore, it is important to consider circadian rhythms as a key research parameter to better understand cardiac physiology/pathology, and to improve the chances of translation and efficacy of cardiac therapies, including those for ischaemic heart disease. The aim of this Position Paper by the European Society of Cardiology Working Group Cellular Biology of the Heart is to highlight key aspects of circadian rhythms to consider for improvement of preclinical and translational studies related to ischaemic heart disease and cardioprotection. Applying these considerations to future studies may increase the potential for better translation of new treatments into successful clinical outcomes., Competing Interests: Conflict of interest: P.F. is the founder and CEO of Pharmahungary Group, a group of R&D companies. L.W.V.L. Outside the current work: consultancy fees to UMCU from Abbott, Medtronic, Vifor, and Novartis., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author(s) 2021. For permissions, please email: journals.permissions@oup.com.)

Aims: Hypertrophic cardiomyopathy (HCM) is characterized by cardiomyocyte hypertrophy and disarray, and myocardial stiffness due to interstitial fibrosis, which result in impaired left ventricular filling and diastolic dysfunction. The latter manifests as exercise intolerance, angina, and dyspnoea. There is currently no specific treatment for improving diastolic function in HCM. Here, we investigated whether myeloperoxidase (MPO) is expressed in cardiomyocytes and provides a novel therapeutic target for alleviating diastolic dysfunction in HCM., Methods and Results: Human cardiomyocytes derived from control-induced pluripotent stem cells (iPSC-CMs) were shown to express MPO, with MPO levels being increased in iPSC-CMs generated from two HCM patients harbouring sarcomeric mutations in the MYBPC3 and MYH7 genes. The presence of cardiomyocyte MPO was associated with higher chlorination and peroxidation activity, increased levels of 3-chlorotyrosine-modified cardiac myosin binding protein-C (MYBPC3), attenuated phosphorylation of MYBPC3 at Ser-282, perturbed calcium signalling, and impaired cardiomyocyte relaxation. Interestingly, treatment with the MPO inhibitor, AZD5904, reduced 3-chlorotyrosine-modified MYBPC3 levels, restored MYBPC3 phosphorylation, and alleviated the calcium signalling and relaxation defects. Finally, we found that MPO protein was expressed in healthy adult murine and human cardiomyocytes, and MPO levels were increased in diseased hearts with left ventricular hypertrophy., Conclusion: This study demonstrates that MPO inhibition alleviates the relaxation defect in hypertrophic iPSC-CMs through MYBPC3 phosphorylation. These findings highlight cardiomyocyte MPO as a novel therapeutic target for improving myocardial relaxation associated with HCM, a treatment strategy which can be readily investigated in the clinical setting, given that MPO inhibitors are already available for clinical testing., (© The Author(s) 2021. Published by Oxford University Press on behalf of the European Society of Cardiology.)

Aims: Genetic and pharmacological inhibition of mitochondrial fission induced by acute myocardial ischaemia/reperfusion injury (IRI) has been shown to reduce myocardial infarct size. The clinically used anti-hypertensive and heart failure medication, hydralazine, is known to have anti-oxidant and anti-apoptotic effects. Here, we investigated whether hydralazine confers acute cardioprotection by inhibiting Drp1-mediated mitochondrial fission., Methods and Results: Pre-treatment with hydralazine was shown to inhibit both mitochondrial fission and mitochondrial membrane depolarisation induced by oxidative stress in HeLa cells. In mouse embryonic fibroblasts (MEFs), pre-treatment with hydralazine attenuated mitochondrial fission and cell death induced by oxidative stress, but this effect was absent in MEFs deficient in the mitochondrial fission protein, Drp1. Molecular docking and surface plasmon resonance studies demonstrated binding of hydralazine to the GTPase domain of the mitochondrial fission protein, Drp1 (KD 8.6±1.0 µM), and inhibition of Drp1 GTPase activity in a dose-dependent manner. In isolated adult murine cardiomyocytes subjected to simulated IRI, hydralazine inhibited mitochondrial fission, preserved mitochondrial fusion events, and reduced cardiomyocyte death (hydralazine 24.7±2.5% vs. control 34.1±1.5%, P=0.0012). In ex vivo perfused murine hearts subjected to acute IRI, pre-treatment with hydralazine reduced myocardial infarct size (as % left ventricle: hydralazine 29.6±6.5% vs. vehicle control 54.1±4.9%, P=0.0083), and in the murine heart subjected to in vivo IRI, the administration of hydralazine at reperfusion, decreased myocardial infarct size (as % area-at-risk: hydralazine 28.9±3.0% vs. vehicle control 58.2±3.8%, P<0.001)., Conclusion: We show that, in addition to its antioxidant and anti-apoptotic effects, hydralazine, confers acute cardioprotection by inhibiting IRI-induced mitochondrial fission, raising the possibility of repurposing hydralazine as a novel cardioprotective therapy for improving post-infarction outcomes., (© The Author(s) 2021. Published by Oxford University Press on behalf of the European Society of Cardiology.)

Normal cardiac contractile and relaxation functions are critically dependent on a continuous energy supply. Accordingly, metabolic perturbations and impaired mitochondrial bioenergetics with subsequent disruption of ATP production underpin a wide variety of cardiac diseases, including diabetic cardiomyopathy, dilated cardiomyopathy, hypertrophic cardiomyopathy, anthracycline cardiomyopathy, peripartum cardiomyopathy, and mitochondrial cardiomyopathies. Crucially, there are no specific treatments for preventing the onset or progression of these cardiomyopathies to heart failure, one of the leading causes of death and disability worldwide. Therefore, new treatments are needed to target the metabolic disturbances and impaired mitochondrial bioenergetics underlying these cardiomyopathies in order to improve health outcomes in these patients. However, investigation of the underlying mechanisms and the identification of novel therapeutic targets have been hampered by the lack of appropriate animal disease models. Furthermore, interspecies variation precludes the use of animal models for studying certain disorders, whereas patient-derived primary cell lines have limited lifespan and availability. Fortunately, the discovery of human-induced pluripotent stem cells has provided a promising tool for modelling cardiomyopathies via human heart tissue in a dish. In this review article, we highlight the use of patient-derived iPSCs for studying the pathogenesis underlying cardiomyopathies associated with metabolic perturbations and impaired mitochondrial bioenergetics, as the ability of iPSCs for self-renewal and differentiation makes them an ideal platform for investigating disease pathogenesis in a controlled in vitro environment. Continuing progress will help elucidate novel mechanistic pathways, and discover novel therapies for preventing the onset and progression of heart failure, thereby advancing a new era of personalized therapeutics for improving health outcomes in patients with cardiomyopathy., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author(s) 2020. For permissions, please email: journals.permissions@oup.com.)

Aims: To establish pre-clinical proof of concept that sustained subcutaneous delivery of the secretome of human cardiac stem cells (CSCs) can be achieved in vivo to produce significant cardioreparative outcomes in the setting of myocardial infarction., Methods and Results: Rats were subjected to permanent ligation of left anterior descending coronary artery and randomized to receive subcutaneous implantation of TheraCyte devices containing either culture media as control or 1 × 106 human W8B2+ CSCs, immediately following myocardial ischaemia. At 4 weeks following myocardial infarction, rats treated with W8B2+ CSCs encapsulated within the TheraCyte device showed preserved left ventricular ejection fraction. The preservation of cardiac function was accompanied by reduced fibrotic scar tissue, interstitial fibrosis, cardiomyocyte hypertrophy, as well as increased myocardial vascular density. Histological analysis of the TheraCyte devices harvested at 4 weeks post-implantation demonstrated survival of human W8B2+ CSCs within the devices, and the outer membrane was highly vascularized by host blood vessels. Using CSCs expressing plasma membrane reporters, extracellular vesicles of W8B2+ CSCs were found to be transferred to the heart and other organs at 4 weeks post-implantation. Furthermore, mass spectrometry-based proteomic profiling of extracellular vesicles of W8B2+ CSCs identified proteins implicated in inflammation, immunoregulation, cell survival, angiogenesis, as well as tissue remodelling and fibrosis that could mediate the cardioreparative effects of secretome of human W8B2+ CSCs., Conclusions: Subcutaneous implantation of TheraCyte devices encapsulating human W8B2+ CSCs attenuated adverse cardiac remodelling and preserved cardiac function following myocardial infarction. The TheraCyte device can be employed to deliver stem cells in a minimally invasive manner for effective secretome-based cardiac therapy., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author(s) 2020. For permissions, please email: journals.permissions@oup.com.)

Aims: Remote ischaemic conditioning (RIC) has been shown to reduce myocardial infarct size in animal models of myocardial infarction. Platelet thrombus formation is a critical determinant of outcome in ST-segment elevation myocardial infarction (STEMI). Whether the beneficial effects of RIC are related to thrombotic parameters is unclear., Methods and Results: In a substudy of the Effect of Remote Ischaemic Conditioning on clinical outcomes in STEMI patients undergoing Primary Percutaneous Coronary Intervention (ERIC-PPCI) trial, we assessed the effect of RIC on thrombotic status. Patients presenting with STEMI were randomized to immediate RIC consisting of an automated autoRIC™ cuff on the upper arm inflated to 200 mmHg for 5 min and deflated for 5 min for four cycles (n = 53) or sham (n = 47). Venous blood was tested at presentation, discharge (48 h) and 6-8 weeks, to assess platelet reactivity, coagulation, and endogenous fibrinolysis using the Global Thrombosis Test and thromboelastography. Baseline thrombotic status was similar in the two groups. At discharge, there was some evidence that the time to in vitro thrombotic occlusion under high shear stress was longer with RIC compared to sham (454 ± 105 s vs. 403 ± 105 s; mean difference 50.1 s; 95% confidence interval 93.7-6.4, P = 0.025), but this was no longer apparent at 6-8 weeks. There was no difference in clot formation or endogenous fibrinolysis between the study arms at any time point., Conclusion: RIC may reduce platelet reactivity in the first 48 h post-STEMI. Further research is needed to delineate mechanisms through which RIC may reduce platelet reactivity, and whether it may improve outcomes in patients with persistent high on-treatment platelet reactivity., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author(s) 2020. For permissions, please email: journals.permissions@oup.com.)

Ischaemic heart disease (IHD) is a complex disorder and a leading cause of death and morbidity in both men and women. Sex, however, affects several aspects of IHD, including pathophysiology, incidence, clinical presentation, diagnosis as well as treatment and outcome. Several diseases or risk factors frequently associated with IHD can modify cellular signalling cascades, thus affecting ischaemia/reperfusion injury as well as responses to cardioprotective interventions. Importantly, the prevalence and impact of risk factors and several comorbidities differ between males and females, and their effects on IHD development and prognosis might differ according to sex. The cellular and molecular mechanisms underlying these differences are still poorly understood, and their identification might have important translational implications in the prediction or prevention of risk of IHD in men and women. Despite this, most experimental studies on IHD are still undertaken in animal models in the absence of risk factors and comorbidities, and assessment of potential sex-specific differences are largely missing. This ESC WG Position Paper will discuss: (i) the importance of sex as a biological variable in cardiovascular research, (ii) major biological mechanisms underlying sex-related differences relevant to IHD risk factors and comorbidities, (iii) prospects and pitfalls of preclinical models to investigate these associations, and finally (iv) will provide recommendations to guide future research. Although gender differences also affect IHD risk in the clinical setting, they will not be discussed in detail here., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author(s) 2020. For permissions, please email: journals.permissions@oup.com.)

The coronary circulation is both culprit and victim of acute myocardial infarction. The rupture of an epicardial atherosclerotic plaque with superimposed thrombosis causes coronary occlusion, and this occlusion must be removed to induce reperfusion. However, ischaemia and reperfusion cause damage not only in cardiomyocytes but also in the coronary circulation, including microembolization of debris and release of soluble factors from the culprit lesion, impairment of endothelial integrity with subsequently increased permeability and oedema formation, platelet activation and leucocyte adherence, erythrocyte stasis, a shift from vasodilation to vasoconstriction, and ultimately structural damage to the capillaries with eventual no-reflow, microvascular obstruction (MVO), and intramyocardial haemorrhage (IMH). Therefore, the coronary circulation is a valid target for cardioprotection, beyond protection of the cardiomyocyte. Virtually all of the above deleterious endpoints have been demonstrated to be favourably influenced by one or the other mechanical or pharmacological cardioprotective intervention. However, no-reflow is still a serious complication of reperfused myocardial infarction and carries, independently from infarct size, an unfavourable prognosis. MVO and IMH can be diagnosed by modern imaging technologies, but still await an effective therapy. The current review provides an overview of strategies to protect the coronary circulation from acute myocardial ischaemia/reperfusion injury. This article is part of a Cardiovascular Research Spotlight Issue entitled 'Cardioprotection Beyond the Cardiomyocyte', and emerged as part of the discussions of the European Union (EU)-CARDIOPROTECTION Cooperation in Science and Technology (COST) Action, CA16225., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author(s) 2018. For permissions, please email: journals.permissions@oup.com.)

Acute myocardial infarction (AMI) and the heart failure (HF) that often complicates this condition, are among the leading causes of death and disability worldwide. To reduce myocardial infarct (MI) size and prevent heart failure, novel therapies are required to protect the heart against the detrimental effects of acute ischaemia/reperfusion injury (IRI). In this regard, targeting cardiac innervation may provide a novel therapeutic strategy for cardioprotection. A number of cardiac neural pathways mediate the beneficial effects of cardioprotective strategies such as ischaemic preconditioning and remote ischaemic conditioning, and nerve stimulation may therefore provide a novel therapeutic strategy for cardioprotection. In this article, we provide an overview of cardiac innervation and its impact on acute myocardial IRI, the role of extrinsic and intrinsic cardiac neural pathways in cardioprotection, and highlight peripheral and central nerve stimulation as a cardioprotective strategy with therapeutic potential for reducing MI size and preventing HF following AMI. This article is part of a Cardiovascular Research Spotlight Issue entitled 'Cardioprotection Beyond the Cardiomyocyte', and emerged as part of the discussions of the European Union (EU)-CARDIOPROTECTION Cooperation in Science and Technology (COST) Action, CA16225., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author(s) 2019. For permissions, please email: journals.permissions@oup.com.)

New therapies are required to reduce myocardial infarct (MI) size and prevent the onset of heart failure in patients presenting with acute myocardial infarction (AMI), one of the leading causes of death and disability globally. In this regard, the immune cell response to AMI, which comprises an initial pro-inflammatory reaction followed by an anti-inflammatory phase, contributes to final MI size and post-AMI remodelling [changes in left ventricular (LV) size and function]. The transition between these two phases is critical in this regard, with a persistent and severe pro-inflammatory reaction leading to adverse LV remodelling and increased propensity for developing heart failure. In this review article, we provide an overview of the immune cells involved in orchestrating the complex and dynamic inflammatory response to AMI-these include neutrophils, monocytes/macrophages, and emerging players such as dendritic cells, lymphocytes, pericardial lymphoid cells, endothelial cells, and cardiac fibroblasts. We discuss potential reasons for past failures of anti-inflammatory cardioprotective therapies, and highlight new treatment targets for modulating the immune cell response to AMI, as a potential therapeutic strategy to improve clinical outcomes in AMI patients. This article is part of a Cardiovascular Research Spotlight Issue entitled 'Cardioprotection Beyond the Cardiomyocyte', and emerged as part of the discussions of the European Union (EU)-CARDIOPROTECTION Cooperation in Science and Technology (COST) Action, CA16225., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author(s) 2019. For permissions, please email: journals.permissions@oup.com.)

Aims: Nitroglycerine (NTG) given prior to an ischaemic insult exerts cardioprotective effects. However, whether administration of an acute low dose of NTG in a clinically relevant manner following an ischaemic episode limits infarct size, has not yet been explored., Methods and Results: Adult mice were subjected to acute myocardial infarction in vivo and then treated with vehicle or low-dose NTG prior to reperfusion. This treatment regimen minimized myocardial infarct size without affecting haemodynamic parameters but the protective effect was absent in mice rendered tolerant to the drug. Mechanistically, NTG was shown to nitrosate and inhibit cyclophilin D (CypD), and NTG administration failed to limit infarct size in CypD knockout mice. Additional experiments revealed lack of the NTG protective effect following genetic (knockout mice) or pharmacological inhibition (L-NAME treatment) of the endothelial nitric oxide synthase (eNOS). The protective effect of NTG was attributed to preservation of the eNOS dimer. Moreover, NTG retained its cardioprotective effects in a model of endothelial dysfunction (ApoE knockout) by preserving CypD nitrosation. Human ischaemic heart biopsies revealed reduced eNOS activity and exhibited reduced CypD nitrosation., Conclusion: Low-dose NTG given prior to reperfusion reduces myocardial infarct size by preserving eNOS function, and the subsequent eNOS-dependent S-nitrosation of CypD, inhibiting cardiomyocyte necrosis. This novel pharmacological action of NTG warrants confirmation in clinical studies, although our data in human biopsies provide promising preliminary results., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author(s) 2018. For permissions, please email: journals.permissions@oup.com.)

Morbidity and mortality from ischaemic heart disease (IHD) and heart failure (HF) remain significant in Europe and are increasing worldwide. Patients with IHD or HF might benefit from novel therapeutic strategies, such as cell-based therapies. We recently discussed the therapeutic potential of cell-based therapies and provided recommendations on how to improve the therapeutic translation of these novel strategies for effective cardiac regeneration and repair. Despite major advances in optimizing these strategies with respect to cell source and delivery method, the clinical outcome of cell-based therapy remains unsatisfactory. Major obstacles are the low engraftment and survival rate of transplanted cells in the harmful microenvironment of the host tissue, and the paucity or even lack of endogenous cells with repair capacity. Therefore, new ways of delivering cells and their derivatives are required in order to empower cell-based cardiac repair and regeneration in patients with IHD or HF. Strategies using tissue engineering (TE) combine cells with matrix materials to enhance cell retention or cell delivery in the transplanted area, and have recently received much attention for this purpose. Here, we summarize knowledge on novel approaches emerging from the TE scenario. In particular, we will discuss how combinations of cell/bio-materials (e.g. hydrogels, cell sheets, prefabricated matrices, microspheres, and injectable matrices) combinations might enhance cell retention or cell delivery in the transplantation areas, thereby increase the success rate of cell therapies for IHD and HF. We will not focus on the use of classical engineering approaches, employing fully synthetic materials, because of their unsatisfactory material properties which render them not clinically applicable. The overall aim of this Position Paper from the ESC Working Group Cellular Biology of the Heart is to provide recommendations on how to proceed in research with these novel TE strategies combined with cell-based therapies to boost cardiac repair in the clinical settings of IHD and HF., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author(s) 2019. For permissions, please email: journals.permissions@oup.com.)

Extracellular vesicles (EVs)-particularly exosomes and microvesicles (MVs)-are attracting considerable interest in the cardiovascular field as the wide range of their functions is recognized. These capabilities include transporting regulatory molecules including different RNA species, lipids, and proteins through the extracellular space including blood and delivering these cargos to recipient cells to modify cellular activity. EVs powerfully stimulate angiogenesis, and can protect the heart against myocardial infarction. They also appear to mediate some of the paracrine effects of cells, and have therefore been proposed as a potential alternative to cell-based regenerative therapies. Moreover, EVs of different sources may be useful biomarkers of cardiovascular disease identities. However, the methods used for the detection and isolation of EVs have several limitations and vary widely between studies, leading to uncertainties regarding the exact population of EVs studied and how to interpret the data. The number of publications in the exosome and MV field has been increasing exponentially in recent years and, therefore, in this ESC Working Group Position Paper, the overall objective is to provide a set of recommendations for the analysis and translational application of EVs focussing on the diagnosis and therapy of the ischaemic heart. This should help to ensure that the data from emerging studies are robust and repeatable, and optimize the pathway towards the diagnostic and therapeutic use of EVs in clinical studies for patient benefit., (© The Author 2017. Published by Oxford University Press on behalf of the European Society of Cardiology.)

Despite advances in myocardial reperfusion therapies, acute myocardial ischaemia/reperfusion injury and consequent ischaemic heart failure represent the number one cause of morbidity and mortality in industrialized societies. Although different therapeutic interventions have been shown beneficial in preclinical settings, an effective cardioprotective or regenerative therapy has yet to be successfully introduced in the clinical arena. Given the complex pathophysiology of the ischaemic heart, large scale, unbiased, global approaches capable of identifying multiple branches of the signalling networks activated in the ischaemic/reperfused heart might be more successful in the search for novel diagnostic or therapeutic targets. High-throughput techniques allow high-resolution, genome-wide investigation of genetic variants, epigenetic modifications, and associated gene expression profiles. Platforms such as proteomics and metabolomics (not described here in detail) also offer simultaneous readouts of hundreds of proteins and metabolites. Isolated omics analyses usually provide Big Data requiring large data storage, advanced computational resources and complex bioinformatics tools. The possibility of integrating different omics approaches gives new hope to better understand the molecular circuitry activated by myocardial ischaemia, putting it in the context of the human 'diseasome'. Since modifications of cardiac gene expression have been consistently linked to pathophysiology of the ischaemic heart, the integration of epigenomic and transcriptomic data seems a promising approach to identify crucial disease networks. Thus, the scope of this Position Paper will be to highlight potentials and limitations of these approaches, and to provide recommendations to optimize the search for novel diagnostic or therapeutic targets for acute ischaemia/reperfusion injury and ischaemic heart failure in the post-genomic era., (© The Author 2017. Published by Oxford University Press on behalf of the European Society of Cardiology.)

Ischaemic heart disease and the heart failure that often results, remain the leading causes of death and disability in Europe and worldwide. As such, in order to prevent heart failure and improve clinical outcomes in patients presenting with an acute ST-segment elevation myocardial infarction and patients undergoing coronary artery bypass graft surgery, novel therapies are required to protect the heart against the detrimental effects of acute ischaemia/reperfusion injury (IRI). During the last three decades, a wide variety of ischaemic conditioning strategies and pharmacological treatments have been tested in the clinic-however, their translation from experimental to clinical studies for improving patient outcomes has been both challenging and disappointing. Therefore, in this Position Paper of the European Society of Cardiology Working Group on Cellular Biology of the Heart, we critically analyse the current state of ischaemic conditioning in both the experimental and clinical settings, provide recommendations for improving its translation into the clinical setting, and highlight novel therapeutic targets and new treatment strategies for reducing acute myocardial IRI., (The last two authors contributed equally to the paper as joint senior authors. Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2017. For permissions, please email: journals.permissions@oup.com.)

Ischaemic heart disease (IHD) remains the leading cause of death and disability worldwide. As a result, novel therapies are still needed to protect the heart from the detrimental effects of acute ischaemia-reperfusion injury, in order to improve clinical outcomes in IHD patients. In this regard, although a large number of novel cardioprotective therapies discovered in the research laboratory have been investigated in the clinical setting, only a few of these have been demonstrated to improve clinical outcomes. One potential reason for this lack of success may have been the failure to thoroughly assess the cardioprotective efficacy of these novel therapies in suitably designed preclinical experimental animal models. Therefore, the aim of this Position Paper by the European Society of Cardiology Working Group Cellular Biology of the Heart is to provide recommendations for improving the preclinical assessment of novel cardioprotective therapies discovered in the research laboratory, with the aim of increasing the likelihood of success in translating these new treatments into improved clinical outcomes., (© The Author 2014. Published by Oxford University Press on behalf of the European Society of Cardiology.)

Aims: Hypoxia-inducible factor-1 (HIF-1) has been reported to promote tolerance against acute myocardial ischaemia-reperfusion injury (IRI). However, the mechanism through which HIF-1 stabilization actually confers this cardioprotection is not clear. We investigated whether HIF-1α stabilization protects the heart against acute IRI by preventing the opening of the mitochondrial permeability transition pore (MPTP) and the potential mechanisms involved., Methods and Results: Stabilization of myocardial HIF-1 was achieved by pharmacological inhibition of prolyl hydroxylase (PHD) domain-containing enzyme using GSK360A or using cardiac-specific ablation of von Hippel-Lindau protein (VHL(fl/fl)) in mice. Treatment of HL-1 cardiac cells with GSK360A stabilized HIF-1, increased the expression of HIF-1 target genes pyruvate dehydrogenase kinase-1 (PDK1) and hexokinase II (HKII), and reprogrammed cell metabolism to aerobic glycolysis, thereby resulting in the production of less mitochondrial oxidative stress during IRI, and less MPTP opening, effects which were shown to be dependent on HKII. These findings were further confirmed when HIF-1 stabilization in the rat and murine heart resulted in smaller myocardial infarct sizes (both in vivo and ex vivo), decreased mitochondrial oxidative stress, and inhibited MPTP opening following IRI, effects which were also found to be dependent on HKII., Conclusions: We have demonstrated that acute HIF-1α stabilization using either a pharmacological or genetic approach protected the heart against acute IRI by promoting aerobic glycolysis, decreasing mitochondrial oxidative stress, activating HKII, and inhibiting MPTP opening., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2014. For permissions please email: journals.permissions@oup.com.)

Aims: Old age and diabetes are risk factors that often coexist increasing the vulnerability of the heart to the lethal effects of ischaemia-reperfusion injury (IRI). However, to our knowledge, no investigations have examined IRI and cardioprotective signalling in animal models bearing these co-morbidities concomitantly. The ability of the heart to recover following IRI is greatly dependent on its innate cardioprotective potential, in which a central role is played by Akt. We aimed to investigate in an aging diabetic rat model, the susceptibility of the heart to IRI, the achievability of ischaemic preconditioning (IPC) against this lethal event, and the changes in Akt signalling, as the main prosurvival intracellular pathway., Methods and Results: Our data showed that the isolated hearts of aged, diabetic Goto-Kakizaki rats were more susceptible to sub-lethal injury and not amenable to cardioprotection via IPC, compared with younger diabetic rat hearts. Western blot analysis of the heart tissue suggested a chronic up-regulation of Akt phosphorylation, and reduced expression of the mitochondrial regulator PGC-1α and of the anti-oxidant enzyme catalase, potentially due to the Akt up-regulation. Moreover, no further activation of Akt could be achieved following IPC., Conclusion: An increased susceptibility to IRI in the aged, diabetic heart could be a consequence of impaired Akt signalling due to chronic Akt phosphorylation. Additional Akt phosphorylation required for IPC protection may therefore not be possible in the aged, diabetic rat heart and may explain why this cardioprotective manoeuvre cannot be achieved in these hearts.

Coronary heart disease (CHD) is the leading cause of death and disability worldwide. Despite current therapy, the morbidity and mortality for patients with CHD remains significant. The most important manifestations of CHD arise from acute myocardial ischaemia-reperfusion injury (IRI) in terms of cardiomyocyte death and its long-term consequences. As such, new therapeutic interventions are required to protect the heart against the detrimental effects of acute IRI and improve clinical outcomes. Although a large number of cardioprotective therapies discovered in pre-clinical studies have been investigated in CHD patients, few have been translated into the clinical setting, and a significant number of these have failed to show any benefit in terms of reduced myocardial infarction and improved clinical outcomes. Because of this, there is currently no effective therapy for protecting the heart against the detrimental effects of acute IRI in patients with CHD. One major factor for this lack of success in translating cardioprotective therapies into the clinical setting can be attributed to problems with the clinical study design. Many of these clinical studies have not taken into consideration the important data provided from previously published pre-clinical and clinical studies. The overall aim of this ESC Working Group Cellular Biology of the Heart Position Paper is to provide recommendations for optimizing the design of clinical cardioprotection studies, which should hopefully result in new and effective therapeutic interventions for the future benefit of CHD patients.

Coronary heart disease (CHD) is the leading cause of morbidity and mortality worldwide. For a large number of patients with CHD, coronary artery bypass graft (CABG) surgery remains the preferred strategy for coronary revascularization. Over the last 10 years, the number of high-risk patients undergoing CABG surgery has increased significantly, resulting in worse clinical outcomes in this patient group. This appears to be related to the ageing population, increased co-morbidities (such as diabetes, obesity, hypertension, stroke), concomitant valve disease, and advances in percutaneous coronary intervention which have resulted in patients with more complex coronary artery disease undergoing surgery. These high-risk patients are more susceptible to peri-operative myocardial injury and infarction (PMI), a major cause of which is acute global ischaemia/reperfusion injury arising from inadequate myocardial protection during CABG surgery. Therefore, novel therapeutic strategies are required to protect the heart in this high-risk patient group. In this article, we review the aetiology of PMI during CABG surgery, its diagnosis and clinical significance, and the endogenous and pharmacological therapeutic strategies available for preventing it. By improving cardioprotection during CABG surgery, we may be able to reduce PMI, preserve left ventricular systolic function, and reduce morbidity and mortality in these high-risk patients with CHD.

Aims: It has been suggested that mitochondrial reactive oxygen species (ROS), Akt and Erk1/2 and more recently the mitochondrial permeability transition pore (mPTP) may act as mediators of ischaemic preconditioning (IPC), although the actual interplay between these mediators is unclear. The aim of the present study is to determine whether the cyclophilin-D (CYPD) component of the mPTP is required by IPC to generate mitochondrial ROS and subsequently activate Akt and Erk1/2., Methods and Results: Mice lacking CYPD (CYPD-/-) and B6Sv129 wild-type (WT) mice were used throughout. We have demonstrated that under basal conditions, non-pathological mPTP opening occurs (indicated by the percent reduction in mitochondrial calcein fluorescence). This effect was greater in WT cardiomyocytes compared with CYPD-/- ones (53 ± 2% WT vs. 17 ± 3% CYPD-/-; P < 0.01) and was augmented by hypoxic preconditioning (HPC) (70 ± 9% WT vs. 56 ± 1% CYPD-/-; P < 0.01). HPC reduced cell death following simulated ischaemia-reperfusion injury in WT (23.2 ± 3.5% HPC vs. 43.7 ± 3.2% WT; P < 0.05) but not CYPD-/- cardiomyocytes (19.6 ± 1.4% HPC vs. 24.4 ± 2.6% control; P > 0.05). HPC generated mitochondrial ROS in WT (four-fold increase; P < 0.05) but not CYPD-/- cardiomyocytes. HPC induced significant Akt phosphorylation in WT cardiomyocytes (two-fold increase; P < 0.05), an effect which was abrogated by ciclosporin-A (a CYPD inhibitor) and N-2-mercaptopropionyl glycine (a ROS scavenger). Finally, in vivo IPC of adult murine hearts resulted in significant phosphorylation of Akt and Erk1/2 in WT but not CYPD-/- hearts., Conclusion: The CYPD component of the mPTP is required by IPC to generate mitochondrial ROS and phosphorylate Akt and Erk1/2, major steps in the IPC signalling pathway.

Mitochondria are dynamic and are able to interchange their morphology between elongated interconnected mitochondrial networks and a fragmented disconnected arrangement by the processes of mitochondrial fusion and fission, respectively. Changes in mitochondrial morphology are regulated by the mitochondrial fusion proteins (mitofusins 1 and 2, and optic atrophy 1) and the mitochondrial fission proteins (dynamin-related peptide 1 and mitochondrial fission protein 1) and have been implicated in a variety of biological processes including embryonic development, metabolism, apoptosis, and autophagy, although the majority of studies have been largely confined to non-cardiac cells. Despite the unique arrangement of mitochondria in the adult heart, emerging data suggest that changes in mitochondrial morphology may be relevant to various aspects of cardiovascular biology-these include cardiac development, the response to ischaemia-reperfusion injury, heart failure, diabetes mellitus, and apoptosis. Interestingly, the machinery required for altering mitochondrial shape in terms of the mitochondrial fusion and fission proteins are all present in the adult heart, but their physiological function remains unclear. In this article, we review the current developments in this exciting new field of mitochondrial biology, the implications for cardiovascular physiology, and the potential for discovering novel therapeutic strategies for treating cardiovascular disease.

Ischaemic postconditioning (brief periods of ischaemia alternating with brief periods of reflow applied at the onset of reperfusion following sustained ischaemia) effectively reduces myocardial infarct size in all species tested so far, including humans. Ischaemic postconditioning is a simple and safe manoeuvre, but because reperfusion injury is initiated within minutes of reflow, postconditioning must be applied at the onset of reperfusion. The mechanisms of protection by postconditioning include: formation and release of several autacoids and cytokines; maintained acidosis during early reperfusion; activation of protein kinases; preservation of mitochondrial function, most strikingly the attenuation of opening of the mitochondrial permeability transition pore (MPTP). Exogenous recruitment of some of the identified signalling steps can induce cardioprotection when applied at the time of reperfusion in animal experiments, but more recently cardioprotection was also observed in a proof-of-concept clinical trial. Indeed, studies in patients with an acute myocardial infarction showed a reduction of infarct size and improved left ventricular function when they underwent ischaemic postconditioning or pharmacological inhibition of MPTP opening during interventional reperfusion. Further animal studies and large-scale human studies are needed to determine whether patients with different co-morbidities and co-medications respond equally to protection by postconditioning. Also, our understanding of the underlying mechanisms must be improved to develop new therapeutic strategies to be applied at reperfusion with the ultimate aim of limiting the burden of ischaemic heart disease and potentially providing protection for other organs at risk of reperfusion injury, such as brain and kidney.

Many of the originally identified cardiovascular 'growth factors' have been demonstrated to exert a diverse variety of actions within the cardiovascular system, the majority of which are unrelated to their initially proposed mechanism of action. Interestingly, several of these growth factors have been demonstrated to protect the cardiomyocyte from the detrimental effects of acute ischaemia-reperfusion injury, through the activation of a variety of cell-surface receptors and the subsequent recruitment of a number of intracellular signal transduction pathways, which include components of the reperfusion injury salvage kinase pathway. This article will review several of these cardioprotective growth factors with respect to their ability to confer direct myocardial protection, focusing on the underlying signalling pathways involved and their potential for clinical application.

Remote ischaemic preconditioning (RIPC) represents a strategy for harnessing the body's endogenous protective capabilities against the injury incurred by ischaemia and reperfusion. It describes the intriguing phenomenon in which transient non-lethal ischaemia and reperfusion of one organ or tissue confers resistance to a subsequent episode of lethal ischaemia reperfusion injury in a remote organ or tissue. In its original conception, it described intramyocardial protection, which could be relayed from the myocardium served by one coronary artery to another. It soon became apparent that myocardial infarct size could be dramatically reduced by applying brief ischaemia and reperfusion to an organ or tissue remote from the heart before the onset of myocardial infarction. The concept of remote organ protection has now been extended beyond that of solely protecting the heart to providing a general form of inter-organ protection against ischaemia-reperfusion injury. This article reviews the history and evolution of the phenomenon that is RIPC, the potential mechanistic pathways underlying its cardioprotective effect, and its emerging application in the clinical setting.

Objective: The opening of the mitochondrial permeability transition pore (mPTP) at the time of myocardial reperfusion is a critical determinant of cell death. Emerging studies suggest that suppression of mPTP opening may underlie the cardioprotection elicited by both ischemic preconditioning (IPC) and postconditioning (IPost). To further evaluate the role of the mPTP in cardioprotection, we hypothesized that hearts deficient in cyclophilin-D (CYP-D-/-), a key component of the mPTP, will be resistant to cardioprotection conferred by ischemic and pharmacological preconditioning and postconditioning., Methods and Results: Male/female wild type or CYP-D-/- mice were subjected to 30 min of ischemia and 120 min of reperfusion. In wild type mice subjected to in vivo myocardial ischemia-reperfusion injury, a significant reduction in myocardial infarct size was observed with the following treatments (n>/=6/group; P<0.05): (1) IPC (28+/-4% vs. 46.2+/-4% in control); (2) Diazoxide (5 mg/kg) pre-treatment (26.4+/-3% vs. 54+/-10% in vehicle control); (3) IPost-1 or IPost-2, three or six 10-s cycles of ischemia-reperfusion (27.2+/-3% and 32+/-4%, respectively vs. 46.2+/-4% in control); (4) Bradykinin (40 mug/kg) (28.3+/-1% vs. 48+/-4% in vehicle control); (5) cyclosporin-A (10 mg/kg) (32.3+/-3% vs. 48+/-4% in vehicle control) (6) sanglifehrin-A (25 mg/kg) (29.3+/-3% vs. 48+/-4% in vehicle control). Interestingly, however, no infarct-limiting effects were demonstrated in CYP-D-/- mice with the same treatment protocols: (27.9+/-5% in control vs. 31.2+/-7% with IPC, 30.2+/-5% with IPost-1, 24.7+/-8% with IPost-2; 30.1+/-4% in vehicle control vs. 26.4+/-7% with diazoxide; 24.6+/-4% in vehicle control vs. 24.9+/-5% with bradykinin, 26.8+/-7% with cyclosporin-A, 32.5+/-6% with sanglifehrin-A: n>/=6/group: P>0.05)., Conclusion: This study demonstrates that the mPTP plays a critical role in the cardioprotection elicited by ischemic and pharmacological preconditioning and postconditioning.

Despite nearly twenty years of research into the field of ischemic preconditioning, the actual mechanism of protection remains unclear. However, much progress has been made in elucidating the signal transduction pathways that convey the extracellular signal initiated by the preconditioning stimulus to the intracellular targets of cardioprotection, with many of these pathways involving the activation of a diverse array of survival protein kinase cascades. The powerful protective benefits of ischemic preconditioning have not yet been realised in the clinical arena, not least because of the prerequisite for any preconditioning intervention to be applied prior to the onset of index ischemia, which in the case of an acute myocardial infarction is difficult to institute. In this regard, the newly described phenomenon of ischemic postconditioning, which comprises a cardioprotective intervention that can be applied at the time of myocardial reperfusion, offers a far more attractive and amenable approach to myocardial protection. Interestingly, certain survival protein kinase cascades recruited at the time of myocardial reperfusion appear to be shared by both ischemic preconditioning and postconditioning, thereby offering a potentially common target of cardioprotection. The often disputed roles these different protein kinases play in mediating the cardioprotective effects of ischemic preconditioning and postconditioning are reviewed in this article, and include protein kinases C, G, and A, members of the MAPK family (Erk1/2, p38, JNK and BMK1), the PI3K-Akt cascade, and the JAK-STAT pathway.

Objectives: Recruitment of the survival kinase cascades, PI3K-Akt and Raf-MEK1/2-Erk1/2, at the time of reperfusion, following a lethal ischemic insult, may mediate the protection associated with ischemic preconditioning (IPC). The exact interplay between these two kinase cascades in mediating this effect is not clear. We examine the 'cross-talk' between these kinase cascades in their contribution to IPC-induced protection., Methods and Results: In isolated perfused rat hearts subjected to 35 min of lethal ischemia +/- ischemic preconditioning, the phosphorylation states of Akt, Erk1/2, p70S6K were determined after 15 min of reperfusion, and infarct size was measured after 120 min of reperfusion. IPC induced a threefold increase in Akt, Erk1/2, and p70S6K phosphorylation, at reperfusion. We found that inhibiting the PI3K-Akt (using LY294008) at reperfusion induced the phosphorylation of Erk1/2-p70S6K, and conversely, that inhibiting the MEK1/2-Erk1/2 pathway (using PD 98059) at reperfusion, induced the phosphorylation of Akt, suggesting 'cross-talk' between the two kinase pathways. However, this effect was not accompanied by a reduction in infarct size (43.1 +/- 7.2% with LY 294008 and 57.7 +/- 7.0% with PD 98059 vs. 46.3 +/- 5.8% in control; P = NS), suggesting that both the kinase cascades may need to be activated to mediate IPC-induced protection. IPC reduced the infarct-risk volume ratio to 17.8 +/- 2.3% from 46.3 +/- 5.8% in control (P < 0.01). Inhibiting p70S6K, a kinase situated downstream of both PI3K and Erk1/2, using rapamycin, abolished IPC-induced protection (46.0 +/- 7.7% with IPC+RAPA vs. 17.8 +/- 2.3% with IPC; P < 0.01)., Conclusions: We report that, the survival kinase cascades PI3K-Akt and MEK1/2-Erk1/2, which are recruited at the time of reperfusion in response to ischemic preconditioning, exhibit 'cross-talk' such that inhibiting one cascade activates the other and vice versa. Furthermore, at the time of reperfusion, these kinase cascades mediate IPC-induced protection, by acting in concert via p70S6K., (Copyright 2004 European Society of Cardiology)

Reperfusion is a pre-requisite to salvaging viable myocardium, following an acute myocardial infarction. Reperfusion of ischaemic myocardium, however, is not without risk, as the act of reperfusion itself can paradoxically result in myocyte death: a phenomenon termed lethal reperfusion-induced injury. Therapeutic strategies that target and attenuate reperfusion-induced cell death may provide novel pharmacological agents, which can be used as an adjunct to current reperfusion therapy, to limit myocardial infarction. Recent evidence has implicated apoptotic cell death during the phase of reperfusion as an important contributor to lethal reperfusion-induced injury. Targeting anti-apoptotic mechanisms of cellular protection at the time of reperfusion may therefore offer a potential approach to attenuating reperfusion-induced cell death. In this regard, ischaemia-reperfusion has been shown to activate the anti-apoptotic pro-survival kinase signalling cascades, phosphatidylinositol-3-OH kinase (PI3K)-Akt and p42/p44 extra-cellular signal-regulated kinases (Erk 1/2), both of which have been implicated in cellular survival. Activating these pro-survival kinase cascades at the time of reperfusion has been demonstrated to confer protection against reperfusion-induced injury. We and others have shown that insulin, insulin-like growth factor-1 (IGF-1), transforming growth factor-beta1 (TGF-beta1), cardiotrophin-1 (CT-1), urocortin, atorvastatin and bradykinin protect the heart, by activating the PI3K-Akt and/or Erk 1/2 kinase cascades, when given at the commencement of reperfusion, following a lethal ischaemic insult. Pharmacological manipulation and up-regulation of these pro-survival kinase cascades, which we refer to as the Reperfusion Injury Salvage Kinase (RISK) pathway, as an adjunct to reperfusion may therefore protect the myocardium from lethal reperfusion-induced cell death and provide a novel strategy to salvaging viable myocardium and limiting infarct size.

Objective: The opening of the mitochondrial permeability transition pore (mPTP) in the first few minutes of post-ischaemic reperfusion is a critical determinant of reperfusion-induced cell death. We hypothesised that the novel immunosuppressant, sanglifehrin-A (SFA), given at the time of reperfusion, protects the myocardium from ischaemia-reperfusion injury, by suppressing mPTP opening., Methods: Isolated perfused rat hearts were subjected to 35 min ischaemia/120 min reperfusion, and were treated with (1) SFA (1.0 microM) or (2) DMSO vehicle for the first 15 min of reperfusion or (3) SFA (1.0 microM) after the first 15 min of reperfusion. We examined the effect of SFA on mPTP opening directly, using a myocyte model of oxidative stress. Laser illumination of adult rat myocytes loaded with the fluorophore, TMRM, generates oxidative stress, which induces mPTP opening (represented by mitochondrial membrane depolarisation) followed by rigour contracture., Results: In the isolated perfused heart model, SFA, given during the first 15 min of post-ischaemic reperfusion, reduced the infarct-risk volume ratio from 43.9+/-2.5% in the control group to 23.8+/-4.2% with SFA (p=0.001). However, when SFA was given after the first 15 min of reperfusion, there was no change in infarct size (43.8+/-5.7% with SFA vs. 43.9+/-2.5% in control; p=NS), suggesting that SFA has to be present during the first 15 min of reperfusion to induce protection. In the isolated adult myocyte model, SFA was shown to inhibit mPTP opening in the setting of oxidative stress, represented by an increase in the ROS threshold required to induce: mitochondrial membrane depolarisation (from 269+/-21 to 777+/-100 s; p<0.001) and rigour contracture (from 613+/-14 to 1329+/-129 s; p<0.001)., Conclusions: Inhibiting mPTP opening during the first few minutes of reperfusion, using sanglifehrin-A, limits infarct size and protects myocytes from oxidative stress.

Objective: We propose that ischemic preconditioning (IPC) and mitochondrial K(ATP) channel activation protect the myocardium by inhibiting mitochondrial permeability transition pore (MPTP) opening at reperfusion., Methods: Isolated rat hearts were subjected to 35 min ischemia/120 min reperfusion and assigned to the following groups: (1) control; (2) IPC of 2x5 min each of preceding global ischemia; (3,4,5) 0.2 micromol/l cyclosporin A (CsA, which inhibits MPTP opening), 5 micromol/l FK506 (which inhibits the phosphatase calcineurin without inhibiting MPTP opening), or 20 micromol/l atractyloside (Atr, a MPTP opener) given at reperfusion; (6,7) pre-treatment with 30 micromol/l diazoxide (Diaz, a mitochondrial K(ATP) channel opener) or 200 nmol/l 2 chloro-N(6)-cyclopentyl-adenosine (CCPA, an adenosine A1 receptor agonist); (8) IPC+Atr; (9) Diaz+Atr; (10) CCPA+Atr. The effect of mitochondrial K(ATP) channel activation on calcium-induced MPTP opening in isolated calcein-loaded mitochondria was also assessed., Results: IPC, CsA when given at reperfusion, and pre-treatment with diazoxide or CCPA all limited infarct size (19.9+/-2.6% in IPC; 24.6+/-1.9% in CsA, 18.0+/-1.7% in Diaz, 20.4+/-3.3% in CCPA vs. 44.7+/-2.0% in control, P<0.0001). Opening the MPTP with atractyloside at reperfusion abolished this cardio-protective effect (47.7+/-1.8% in IPC+Atr, 42.3+/-3.2% in Diaz+Atr, 51.2+/-1.6% in CCPA+Atr). Atractyloside and FK506, given at reperfusion, did not influence infarct size (45.7+/-2.1% in Atr and 43.1+/-3.6% in FK506 vs. 44.7+/-2.0% in control, P=NS). Diazoxide (30 micromol/l) was shown to reduce calcium-induced MPTP opening by 52.5+/-8.0% in calcein-loaded mitochondria. 5-Hydroxydecanoic acid (100 micromol/l) was able to abolish the cardio-protective effects of both diazoxide and IPC., Conclusion: One interpretation of these data is that IPC and mitochondrial K(ATP) channel activation may protect the myocardium by inhibiting MPTP opening at reperfusion.