Cardioprotection by remote ischemic preconditioning of the rat heart is mediated by extracellular vesicles

Exosomes and exosomal miRNAs in cardiovascular protection and repair

Cell-cell communication between cardiac and vascular cells and from stem and progenitor cells to differentiated cardiovascular cells is both an important and complex process, achieved through a diversity of mechanisms that have an impact on cardiovascular biology, disease and therapeutics. In recent years, evidence has accumulated suggesting that extracellular vesicles (EVs) are a new system of intercellular communication. EVs of different sizes are produced via different biogenesis pathways and have been shown to be released and taken up by most of known cell types, including heart and vascular cells, and stem and progenitor cells. This review will focus on exosomes, the smallest EVs (up to 100nm in diameter) identified so far. Cells can package cargoes consisting of selective lipids, proteins and RNA in exosomes and such cargoes can be shipped to recipient cells, inducing expressional and functional changes. This review focuses on exosomes and microRNAs in the context of cardiovascular disease and repair. We will describe exosome biogenesis and cargo formation and discuss the available information on in vitro and in vivo exosomes-based cell-to-cell communication relevant to cardiovascular science. The methods used in exosome research will be also described. Finally, we will address the promise of exosomes as clinical biomarkers and their impact as a biomedical tool in stem cell-based cardiovascular therapeutics.

Remote ischaemic conditioning: cardiac protection from afar

For patients with ischaemic heart disease, remote ischaemic conditioning may offer an innovative, non‐invasive and virtually cost‐free therapy for protecting the myocardium against the detrimental effects of acute ischaemia‐reperfusion injury, preserving cardiac function and improving clinical outcomes. The intriguing phenomenon of remote ischaemic conditioning was first discovered over 20 years ago, when it was shown that the heart could be rendered resistant to acute ischaemia‐reperfusion injury by applying one or more cycles of brief ischaemia and reperfusion to an organ or tissue away from the heart – initially termed ‘cardioprotection at a distance’. Subsequent pre‐clinical and then clinical studies made the important discovery that remote ischaemic conditioning could be elicited non‐invasively, by inducing brief ischaemia and reperfusion to the upper or lower limb using a cuff. The actual mechanism underlying remote ischaemic conditioning cardioprotection remains unclear, although a neuro‐hormonal pathway has been implicated. Since its initial discovery in 1993, the first proof‐of‐concept clinical studies of remote ischaemic conditioning followed in 2006, and now multicentre clinical outcome studies are underway. In this review article, we explore the potential mechanisms underlying this academic curiosity, and assess the success of its application in the clinical setting.

Plasma from human volunteers subjected to remote ischemic preconditioning protects human endothelial cells from hypoxia-induced cell damage

Short repeated cycles of peripheral ischemia/reperfusion (I/R) can protect distant organs from subsequent prolonged I/R injury; a phenomenon known as remote ischemic preconditioning (RIPC). A RIPC-mediated release of humoral factors might play a key role in this protection and vascular endothelial cells are potential targets for these secreted factors. In the present study, RIPC-plasma obtained from healthy male volunteers was tested for its ability to protect human umbilical endothelial cells (HUVEC) from hypoxia–induced cell damage. 10 healthy male volunteers were subjected to a RIPC-protocol consisting of 4 × 5 min inflation/deflation of a blood pressure cuff located at the upper arm. Plasma was collected before (T0; control), directly after (T1) and 1 h after (T2) the RIPC procedure. HUVEC were subjected to 24 h hypoxia damage and simultaneously incubated with 5 % of the respective RIPC-plasma. Cell damage was evaluated by lactate dehydrogenase (LDH)-measurements. Western blot experiments of hypoxia inducible factor 1 alpha (HIF1alpha), phosphorylated signal transducer and activator of transcription 5 (STAT5), protein kinase B (AKT) and extracellular signal-related kinase 1/2 (ERK-1/2) were performed. Furthermore, the concentrations of hVEGF were evaluated in the RIPC-plasma by sandwich ELISA. Hypoxia–induced cell damage was significantly reduced by plasma T1 (p = 0.02 vs T0). The protective effect of plasma T1 was accompanied by an augmentation of the intracellular HIF1alpha (p = 0.01 vs T0) and increased phosphorylation of ERK-1/2 (p = 0.03 vs T0). Phosphorylation of AKT and STAT5 remained unchanged. Analysis of the protective RIPC-plasma T1 showed significantly reduced levels of hVEGF (p = 0.01 vs T0). RIPC plasma protects endothelial cells from hypoxia–induced cell damage and humoral mediators as well as intracellular HIF1alpha may be involved.

Remote ischemic conditioning

In remote ischemic conditioning (RIC), brief, reversible episodes of ischemia with reperfusion in one vascular bed, tissue, or organ confer a global protective phenotype and render remote tissues and organs resistant to ischemia/reperfusion injury. The peripheral stimulus can be chemical, mechanical, or electrical and involves activation of peripheral sensory nerves. The signal transfer to the heart or other organs is through neuronal and humoral communications. Protection can be transferred, even across species, with plasma-derived dialysate and involves nitric oxide, stromal derived factor-1α, microribonucleic acid-144, but also other, not yet identified factors. Intracardiac signal transduction involves: adenosine, bradykinin, cytokines, and chemokines, which activate specific receptors; intracellular kinases; and mitochondrial function. RIC by repeated brief inflation/deflation of a blood pressure cuff protects against endothelial dysfunction and myocardial injury in percutaneous coronary interventions, coronary artery bypass grafting, and reperfused acute myocardial infarction. RIC is safe and effective, noninvasive, easily feasible, and inexpensive.

Remote ischemic preconditioning for myocardial protection: update on mechanisms and clinical relevance

Ischemic heart disease is the leading cause of death for both men and women worldwide, accruing 7.4 million deaths in 2012. There has been a continued search for better cardioprotective modalities that would reduce myocardial ischemia-reperfusion injury. Among these attempts, a more convenient model of ischemic preconditioning, known as remote ischemic preconditioning (RIPC) was first introduced in 1993 by Przyklenk and colleagues who reported that brief regional occlusion-reperfusion episodes in one vascular bed of the heart render protection to remote myocardial tissue. Subsequently, major advances in myocardial RIPC came with the use of skeletal muscle as the ischemic stimulus. To date, numerous studies have revealed that RIPC applied to the kidney, liver, mesentery, and skeletal muscle, have all exhibited cardioprotective effects. The main purpose of this review article is to summarize the new advances in understanding the molecular mechanisms of RIPC during the past 5 years, including those related to capsaicin-activated C sensory fibers, hypoxia-inducible factor 1α, connexin 43, extracellular vesicles, microRNA-144, microRNA-1, and nitrite. In addition, we have discussed results from several recent human clinical trials with RIPC. Taken together, the emerging clinical evidence supports the concept that the effectiveness of RIPC paired with its low-cost and non-invasive features makes it an ideal treatment before reperfusion after sustained ischemia. More carefully designed studies are warranted to fully exploit the clinical benefits of RIPC and its potential implications in patients with cardiovascular disease.

Remote conditioning the heart overview: translatability and mechanism

Conditioning the heart to resist predictable and unpredictable ischaemia-reperfusion (IR) injury is one of the fastest growing areas of bench to bedside research within cardiology. Basic science has provided important insights into signalling pathways and protective mechanisms in the heart, and a growing number of clinical studies have, with important exceptions, shown the potential applicability and beneficial effect of various mechanical conditioning strategies achieved by intermittent short-lasting-induced ischaemia of the heart itself or a remote tissue. Remote ischaemic conditioning (RIC) in particular has been utilized in a number of clinical settings with promising results. However, while many novel 'downstream' mechanisms of RIC have been discovered, translation to pharmacological conditioning has not yet been convincingly demonstrated in clinical studies. One explanation for this apparent failure may be that most pharmacological approaches mimic a single instrument in a complex orchestra activated by mechanical conditioning. Recent studies, however, provide important insights into upstream events occurring in RIC, which may allow for development of drugs activating more complex systems of biological organ protection. With this review, we will systematically examine the first generation of pharmacological cardioprotection studies and then provide a summary of the recent discoveries in basic science that could illuminate the path towards more advanced approaches in the next generation of pharmacological agents that may work by reproducing the diverse effects of RIC, thereby providing protection against IR injury.

Postconditioning signalling in the heart: mechanisms and translatability

The protective effect of ischaemic postconditioning (short cycles of reperfusion and reocclusion of a previously occluded vessel) was identified over a decade ago commanding intense interest as an approach for modifying reperfusion injury which contributes to infarct size in acute myocardial infarction. Elucidation of the major mechanisms of postconditioning has identified potential pharmacological targets for limitation of reperfusion injury. These include ligands for membrane-associated receptors, activators of phosphokinase survival signalling pathways and inhibitors of the mitochondrial permeability transition pore. In experimental models, numerous agents that target these mechanisms have shown promise as postconditioning mimetics. Nevertheless, clinical studies of ischaemic postconditioning and pharmacological postconditioning mimetics are equivocal. The majority of experimental research is conducted in animal models which do not fully portray the complexity of risk factors and comorbidities with which patients present and which we now know modify the signalling pathways recruited in postconditioning. Cohort size and power, patient selection, and deficiencies in clinical infarct size estimation may all represent major obstacles to assessing the therapeutic efficacy of postconditioning. Furthermore, chronic treatment of these patients with drugs like ACE inhibitors, statins and nitrates may modify signalling, inhibiting the protective effect of postconditioning mimetics, or conversely induce a maximally protected state wherein no further benefit can be demonstrated. Arguably, successful translation of postconditioning cannot occur until all of these issues are addressed, that is, experimental investigation requires more complex models that better reflect the clinical setting, while clinical investigation requires bigger trials with appropriate patient selection and standardization of clinical infarct size measurements.

Remote ischemic conditioning: from experimental observation to clinical application: report from the 8th Biennial Hatter Cardiovascular Institute Workshop

In 1993, Przyklenk and colleagues made the intriguing experimental observation that ‘brief ischemia in one vascular bed also protects remote, virgin myocardium from subsequent sustained coronary artery occlusion’ and that this effect ‘…. may be mediated by factor(s) activated, produced, or transported throughout the heart during brief ischemia/reperfusion’. This seminal study laid the foundation for the discovery of ‘remote ischemic conditioning’ (RIC), a phenomenon in which the heart is protected from the detrimental effects of acute ischemia/reperfusion injury (IRI), by applying cycles of brief ischemia and reperfusion to an organ or tissue remote from the heart. The concept of RIC quickly evolved to extend beyond the heart, encompassing inter-organ protection against acute IRI. The crucial discovery that the protective RIC stimulus could be applied non-invasively, by simply inflating and deflating a blood pressure cuff placed on the upper arm to induce cycles of brief ischemia and reperfusion, has facilitated the translation of RIC into the clinical setting. Despite intensive investigation over the last 20 years, the underlying mechanisms continue to elude researchers. In the 8th Biennial Hatter Cardiovascular Institute Workshop, recent developments in the field of RIC were discussed with a focus on new insights into the underlying mechanisms, the diversity of non-cardiac protection, new clinical applications, and large outcome studies. The scientific advances made in this field of research highlight the journey that RIC has made from being an intriguing experimental observation to a clinical application with patient benefit.

Differential expression of microRNAs in ischemic heart disease

Recent studies provide evidence that ischemic preconditioning (IP) and ischemia/reperfusion (IR) injury lead to altered expression of microRNAs (miRNAs) that affect the survival and recovery of cardiomyocytes. These endogenous ∼22-nucleotide noncoding RNAs negatively regulate gene expression via degradation and translational inhibition of their target mRNAs. miRNAs are involved in differentiation, proliferation, electrical conduction, angiogenesis and apoptosis. These pathways can lead to physiological and pathological adaptations. This review intends to explore several facets of miRNA expression and the underlying mechanisms involved in IR injury, as well as IP as a cardioprotective strategy. In addition, we will investigate miRNA interaction with the renin-angiotensin system and the potential use of miRNAs in developing sensitive biomarkers for cardiovascular disease.

Pathologic function and therapeutic potential of exosomes in cardiovascular disease

The heart is a very complex conglomeration of organized interactions between various different cell types that all aid in facilitating myocardial function through contractility, sufficient perfusion, and cell-to-cell reception. In order to make sure that all features of the heart work effectively, it is imperative to have a well-controlled communication system among the different types of cells. One of the most important ways that the heart regulates itself is by the use of extracellular vesicles, more specifically, exosomes. Exosomes are types of nano-vesicles, naturally released from living cells. They are believed to play a critical role in intercellular communication through the means of certain mechanisms including direct cell-to-cell contact, long-range signals as well as electrical and extracellular chemical molecules. Exosomes contain many unique features like surface proteins/receptors, lipids, mRNAs, microRNAs, transcription factors and other proteins. Recent studies indicate that the exosomal contents are highly regulated by various stress and disease conditions, in turn reflective of the parent cell status. At present, exosomes are well appreciated to be involved in the process of tumor and infection disease. However, the research on cardiac exosomes is just emerging. In this review, we summarize recent findings on the pathologic effects of exosomes on cardiac remodeling under stress and disease conditions, including cardiac hypertrophy, peripartum cardiomyopathy, diabetic cardiomyopathy and sepsis-induced cardiovascular dysfunction. In addition, the cardio-protective effects of stress-preconditioned exosomes and stem cell-derived exosomes are also summarized. Finally, we discuss how to epigenetically reprogram exosome contents in host cells which makes them beneficial for the heart.

Exosomes: a potential key target in cardio-renal syndrome

Exosomes have proven roles in regulating immune response, antigen presentation, RNA and protein transfer, and cell–cell (organ–organ) interaction/signaling. These microvesicles can be considered a mechanism of non-classical secretion of proteins, and they represent a subproteome, thus assisting in the difficult task of biomarker discovery in a biological fluid as urine, plasma, or serum. A potential role of exosomes in the cardio-renal syndrome is currently underexplored. Cardiovascular disease continues to be the leading cause of morbidity and mortality worldwide and, particularly, rates of cardiovascular events and death consistently increase as kidney function worsens. In other words, chronic kidney disease acts as a risk multiplier. Unfortunately, the relationship between markers of cardiovascular risk in kidney pathology often differs from that in the general population. Efforts in the search for novel action mechanisms simultaneously operating in both pathologies are thus of maximum interest. This article focuses to the role of exosomes in cardiovascular and renal diseases, in the search for novel key targets of interaction between heart and kidneys.

A randomized pilot trial of remote ischemic preconditioning in heart failure with reduced ejection fraction

Background

Remote ischemic preconditioning (RIPC) induced by transient limb ischemia confers multi-organ protection and improves exercise performance in the setting of tissue hypoxia. We aimed to evaluate the effect of RIPC on exercise capacity in heart failure patients.

Methods

We performed a randomized crossover trial of RIPC (4×5-minutes limb ischemia) compared to sham control in heart failure patients undergoing exercise testing. Patients were randomly allocated to either RIPC or sham prior to exercise, then crossed over and completed the alternate intervention with repeat testing. The primary outcome was peak VO2, RIPC versus sham. A mechanistic substudy was performed using dialysate from study patient blood samples obtained after sham and RIPC. This dialysate was used to test for a protective effect of RIPC in a mouse heart Langendorff model of infarction. Mouse heart infarct size with RIPC or sham dialysate exposure was also compared with historical control data.

Results

Twenty patients completed the study. RIPC was not associated with improvements in peak VO2 (15.6+/−4.2 vs 15.3+/−4.6 mL/kg/min; p = 0.53, sham and RIPC, respectively). In our Langendorff sub-study, infarct size was similar between RIPC and sham dialysate groups from our study patients, but was smaller than expected compared to healthy controls (29.0%, 27.9% [sham, RIPC] vs 51.2% [controls]. We observed less preconditioning among the subgroup of patients with increased exercise performance following RIPC (p<0.04).

Conclusion

In this pilot study of RIPC in heart failure patients, RIPC was not associated with improvements in exercise capacity overall. However, the degree of effect of RIPC may be inversely related to the degree of baseline preconditioning. These data provide the basis for a larger randomized trial to test the potential benefits of RIPC in patients with heart failure.

Trial Registration

ClinicalTrials.gov +++++NCT01128790

MicroRNA-144 is a circulating effector of remote ischemic preconditioning

Remote ischemic preconditioning (rIPC) induced by cycles of transient limb ischemia and reperfusion is a powerful cardioprotective strategy with additional pleiotropic effects. However, our understanding of its underlying mediators and mechanisms remains incomplete. We examined the role of miR-144 in the cardioprotection induced by rIPC. Microarray studies first established that rIPC increases, and IR injury decreases miR-144 levels in mouse myocardium, the latter being rescued by both rIPC and intravenous administration of miR-144. Going along with this systemic treatment with miR-144 increased P-Akt, P-GSK3β and P-p44/42 MAPK, decreased p-mTOR level and induced autophagy signaling, and induced early and delayed cardioprotection with improved functional recovery and reduction in infarct size similar to that achieved by rIPC. Conversely, systemic administration of a specific antisense oligonucleotide reduced myocardial levels of miR-144 and abrogated cardioprotection by rIPC. We then showed that rIPC increases plasma miR-144 levels in mice and humans, but there was no change in plasma microparticle (50-400 nM) numbers or their miR-144 content. However, there was an almost fourfold increase in miR-144 precursor in the exosome pellet, and a significant increase in miR-144 levels in exosome-poor serum which, in turn, was associated with increased levels of the miR carriage protein Argonaute-2. Systemic release of microRNA 144 plays a pivotal role in the cardioprotection induced by rIPC. Future studies should assess the potential for plasma miR-144 as a biomarker of the effectiveness of rIPC induced by limb ischemia, and whether miR-144 itself may represent a novel therapy to reduce clinical ischemia-reperfusion injury.

Novel therapeutic strategies for cardioprotection

The morbidity and mortality from ischemic heart disease (IHD) remain significant worldwide. The treatment for acute myocardial infarction has improved over the past decades, including early reperfusion of occluded coronary arteries. Although it is essential to re-open the artery as soon as possible, paradoxically this leads to additional myocardial injury, called acute ischemia-reperfusion injury (IRI), for which currently no effective therapy is available. Therefore, novel therapeutic strategies are required to protect the heart from acute IRI in order to reduce myocardial infarction size, preserve cardiac function and improve clinical outcomes in patients with IHD. In this review article, we will first outline the pathophysiology of acute IRI and review promising therapeutic strategies for cardioprotection. These include novel aspects of mitochondrial function, epigenetics, circadian clocks, the immune system, microvesicles, growth factors, stem cell therapy and gene therapy. We discuss the therapeutic potential of these novel cardioprotective strategies in terms of pharmacological targeting and clinical application.