Remote ischemic preconditioning preserves mitochondrial function and influences myocardial microRNA expression in atrial myocardium during coronary bypass surgery

Remote ischemic preconditioning differentially attenuates post-ischemic cardiac arrhythmia in streptozotocin-induced diabetic versus nondiabetic rats

Background

Sudden cardiac death (SCD), a leading cause of global mortality, most commonly arises from a substrate of cardiac ischemia, but requires an additional trigger. Diabetes mellitus (DM) predisposes to SCD even after adjusting for other DM-linked cardiovascular pathology such as coronary artery disease. We previously showed that remote liver ischemia preconditioning (RLIPC) is highly protective against cardiac ischemia reperfusion injury (IRI) linked ventricular arrhythmias and myocardial infarction, via induction of the cardioprotective RISK pathway, and specifically, inhibitory phosphorylation of GSK-3β (Ser 9).

Methods

We evaluated the impact of acute streptozotocin-induced DM on coronary artery ligation IRI-linked ventricular arrhythmogenesis and RLIPC therapy in rats.

Results

Post-IRI arrhythmia induction was similar in nondiabetic and DM rats, but, unexpectedly, DM rats exhibited lower incidence of SCD during reperfusion (41 vs. 100%), suggesting uncontrolled hyperglycemia does not acutely predispose to SCD. RLIPC was highly effective in both nondiabetic and DM rats at reducing incidence and duration of, and increasing latency to, all classes of ventricular tachyarrhythmias. In contrast, atrioventricular block (AVB) was highly responsive to RLIPC in nondiabetic rats (incidence reduced from 72 to 18%) but unresponsive in DM rats. RISK pathway induction was similar in nondiabetic and DM rats, thus not explaining the DM-specific resistance of AVB to therapy.

Conclusions

Our findings uncover important acute DM-specific differences in responsiveness to remote preconditioning for ventricular tachyarrhythmias versus AVB, which may have clinical significance given that AVB is a malignant arrhythmia twofold more common in human diabetics than nondiabetics, and correlated to plasma glucose levels >10 mmol/L.

Ischaemic preconditioning for the reduction of renal ischaemia reperfusion injury

BACKGROUND

Ischaemia reperfusion injury can lead to kidney dysfunction or failure. Ischaemic preconditioning is a short period of deprivation of blood supply to particular organs or tissue, followed by a period of reperfusion. It has the potential to protect kidneys from ischaemia reperfusion injury.

OBJECTIVES

This review aimed to look at the benefits and harms of local and remote ischaemic preconditioning to reduce ischaemia and reperfusion injury among people with renal ischaemia reperfusion injury.

SEARCH METHODS

We searched Cochrane Kidney and Transplant's Specialised Register to 5 August 2016 through contact with the Information Specialist using search terms relevant to this review.

SELECTION CRITERIA

We included all randomised controlled trials measuring kidney function and the role of ischaemic preconditioning in patients undergoing a surgical intervention that induces kidney injury. Kidney transplantation studies were excluded.

DATA COLLECTION AND ANALYSIS

Studies were assessed for eligibility and quality; data were extracted by two independent authors. We collected basic study characteristics: type of surgery, remote ischaemic preconditioning protocol, type of anaesthesia. We collected primary outcome measurements: serum creatinine and adverse effects to remote ischaemic preconditioning and secondary outcome measurements: acute kidney injury, need for dialysis, neutrophil gelatinase-associated lipocalin, hospital stay and mortality. Summary estimates of effect were obtained using a random-effects model, and results were expressed as risk ratios (RR) and their 95% confidence intervals (CI) for dichotomous outcomes, and mean difference (MD) and 95% CI for continuous outcomes.

MAIN RESULTS

We included 28 studies which randomised a total of 6851 patients. Risk of bias assessment indicated unclear to low risk of bias for most studies. For consistency regarding the direction of effects, continuous outcomes with negative values, and dichotomous outcomes with values less than one favour remote ischaemic preconditioning. Based on high quality evidence, remote ischaemic preconditioning made little or no difference to the reduction of serum creatinine levels at postoperative days one (14 studies, 1022 participants: MD -0.02 mg/dL, 95% CI -0.05 to 0.02; I2 = 21%), two (9 studies, 770 participants: MD -0.04 mg/dL, 95% CI -0.09 to 0.02; I2 = 31%), and three (6 studies, 417 participants: MD -0.05 mg/dL, 95% CI -0.19 to 0.10; I2 = 68%) compared to control.Serious adverse events occurred in four patients receiving remote ischaemic preconditioning by iliac clamping. It is uncertain whether remote ischaemic preconditioning by cuff inflation leads to increased adverse effects compared to control because the certainty of the evidence is low (15 studies, 3993 participants: RR 3.47, 95% CI 0.55 to 21.76; I2 = 0%); only two of 15 studies reported any adverse effects (6/1999 in the remote ischaemic preconditioning group and 1/1994 in the control group), the remaining 13 studies stated no adverse effects were observed in either group.Compared to control, remote ischaemic preconditioning made little or no difference to the need for dialysis (13 studies, 2417 participants: RR 0.85, 95% CI 0.37 to 1.94; I2 = 60%; moderate quality evidence), length of hospital stay (8 studies, 920 participants: MD 0.17 days, 95% CI -0.46 to 0.80; I2 = 49%, high quality evidence), or all-cause mortality (24 studies, 4931 participants: RR 0.86, 95% CI 0.54 to 1.37; I2 = 0%, high quality evidence).Remote ischaemic preconditioning may have slightly improved the incidence of acute kidney injury using either the AKIN (8 studies, 2364 participants: RR 0.76, 95% CI 0.57 to 1.00; I2 = 61%, high quality evidence) or RIFLE criteria (3 studies, 1586 participants: RR 0.91, 95% CI 0.75 to 1.12; I2 = 0%, moderate quality evidence).

AUTHORS' CONCLUSIONS

Remote ischaemic preconditioning by cuff inflation appears to be a safe method, and probably leads to little or no difference in serum creatinine, adverse effects, need for dialysis, length of hospital stay, death and in the incidence of acute kidney injury. Overall we had moderate-high certainty evidence however the available data does not confirm the efficacy of remote ischaemic preconditioning in reducing renal ischaemia reperfusion injury in patients undergoing major cardiac and vascular surgery in which renal ischaemia reperfusion injury may occur.

Cardiomyocyte mitochondria as targets of humoral factors released by remote ischemic preconditioning

INTRODUCTION

Remote ischemic preconditioning (RIPC) reduces myocardial infarct size, and protection can be transferred with plasma to other individuals, even across species. Mitochondria are the end-effectors of cardioprotection by local ischemic conditioning maneuvers. We have now analyzed mitochondrial function in response to RIPC.

MATERIAL AND METHODS

Plasma from pigs undergoing placebo or RIPC (infarct size reduction by 67% in RIPC pigs compared to placebo) was transferred to isolated perfused rat hearts subjected to 30 min global ischemia followed by 120 min reperfusion for infarct size measurement. Additional experiments were terminated at 10 min reperfusion to isolate mitochondria for functional measurements. Effects of RIPC pig plasma were compared to local ischemic preconditioning (IPC) or to infusion of tumor necrosis factor α (TNF-α).

RESULTS

Ischemia/reperfusion (I/R) induced an infarct of 41 ±2% of total ventricular mass. Placebo pig plasma did not affect infarct size (38 ±1, p = 0.13). The RIPC pig plasma reduced infarct size (27 ±2, p < 0.001), as did IPC (20 ±1, p < 0.001) and TNF-α (28 ±2, p < 0.001). Associated with cardioprotection, reductions of mitochondrial adenosine diphosphate (ADP)-stimulated respiration, adenosine triphosphate (ATP) production and calcium retention capacity (CRC) by I/R and placebo pig plasma were prevented by RIPC pig plasma, as they were by IPC and TNF-α. Mitochondrial reactive oxygen species production (nmol H₂O₂/100 µg protein) induced by I/R (272 ±34) was comparable in response to placebo pig plasma (234 ±28, p = 0.37) and was reduced by RIPC pig plasma (83 ±15, p < 0.001) as well as by IPC (78 ±21, p < 0.001) and TNF-α (125 ±42, p = 0.002).

CONCLUSIONS

In rat myocardium, mitochondria are an intracellular target of protection induced by humoral factors retrieved from pigs undergoing RIPC.

MiR-23a Regulates the Vasculogenesis of Coronary Artery Disease by Targeting Epidermal Growth Factor Receptor

OBJECTIVE

Circulating microRNAs (miRNAs) in patient body fluids have recently been considered to hold the potential of being novel disease biomarkers and drug targets. We aimed to investigate the correlation between the levels of circulating miR-23a and the expression of epidermal growth factor receptor (EGFR) in the pathogenesis of patients with coronary heart disease to further explore the mechanism involved in its vasculogenesis.

METHOD

Three different cohorts, including 13 acute myocardial infarction (AMI) patients, 176 angina pectoris patients, and 127 control subjects, were enrolled to investigate the expression levels of circulating miR-23a in patients with myocardial ischemia and also the relationship between plasma miR-23a and severity of coronary stenosis. Plasma miR-23a levels of participants were examined by real-time quantitative PCR. Simultaneously, plasma cardiac troponin I (cTnI) concentrations were measured by ELISAs. We further detected the correlation of miR-23a and EGFR by molecular and animal assays.

RESULT

MiR-23a was enriched in not only diseased endothelial progenitor cells (EPCs) but also in the plasma of patients with coronary artery disease (CAD). Besides, we found out miR-23a was able to suppress EGFR expression and EPC activities. Reporter assays confirmed the direct binding and repression of miR-23a to the 3'-UTR of EGFR mRNA. Knockdown of miR-23a not only restored EGFR levels and angiogenic activities of diseased EPCs in vitro, but further promoted blood flow recovery in ischemic limbs of mice.

CONCLUSION

Circulating miR-23a may be a new biomarker for CAD and as a potential diagnostic tool. And increased miR-23a level may be used to predict the presence and severity of coronary lesions in patients with CAD.

Modulating microRNAs in cardiac surgery patients: Novel therapeutic opportunities?

This review focuses on microRNAs (miRs) in cardiac surgery, where they are emerging as potential targets for therapeutic intervention as well as novel clinical biomarkers. Identification of the up/down-regulation of specific miRs in defined groups of cardiac surgery patients can lead to the development of novel strategies for targeted treatment in order to maximise therapeutic results and minimise acute, delayed or chronic complications. MiRs could also be involved in determining the outcome independently of complications, for example in relation to myocardial perfusion and fibrosis. Because of their relevance in disease, their known sequence and pharmacological properties, miRs are attractive candidates for therapeutic manipulation. Pharmacological inhibition of individual miRs can be achieved by modified antisense oligonucleotides, referred to as antimiRs, while miR replacement can be achieved by miR mimics to increase the level of a specific miR. MiR mimics can restore the function of a lost or down-regulated miR, while antimiRs can inhibit the levels of disease-driving or aberrantly expressed miRs, thus de-repressing the expression of mRNAs targeted by the miR. The main delivery methods for miR therapeutics involve lipid-based vehicles, viral systems, cationic polymers, and intravenous or local injection of an antagomiR. Local delivery is particularly desirable for miR therapeutics and options include the development of devices specific for local delivery, light-induced antimiR, and vesicle-encapsulated miRs serving as therapeutic delivery agents able to improve intracellular uptake. Here, we discuss the potential therapeutic use of miRNAs in the context of cardiac surgery.

Randomized controlled trial of remote ischemic preconditioning and atrial fibrillation in patients undergoing cardiac surgery

AIM

To study whether remote ischemic preconditioning (RIPC) has an impact on clinical outcomes, such as post-operative atrial fibrillation (POAF).

METHODS

This was a prospective, single-center, single-blinded, randomized controlled study. One hundred and two patients were randomized to receive RIPC (3 cycles of 5 min ischemia and 5 min reperfusion in the upper arm after induction of anesthesia) or no RIPC (control). Primary outcome was POAF lasting for five minutes or longer during the first seven days after surgery. Secondary outcomes included length of hospital stay, incidence of inpatient mortality, myocardial infarction, and stroke.

RESULTS

POAF occurred at a rate of 54% in the RIPC group and 41.2% in the control group (P = 0.23). No statistically significant differences were noted in secondary outcomes between the two groups.

CONCLUSION

This is the first study in the United States to suggest that RIPC does not reduce POAF in patients with elective or urgent cardiac surgery. There were no differences in adverse effects in either group. Further studies are required to assess the relationship between RIPC and POAF.

Effect of remote ischemic preconditioning on electrophysiological and biomolecular parameters in nonvalvular paroxysmal atrial fibrillation (RIPPAF study): Rationale and study design of a randomized, controlled clinical trial

Remote ischemic preconditioning (RIPC) has been studied in models of different cardiovascular entities. Recently, a beneficial effect of RIPC on incidence of atrial fibrillation (AF) in postsurgical patients has been suggested. However, the potential impact of RIPC on electrophysiological- and thrombogenesis-related parameters in the setting of paroxysmal nonvalvular AF has not been investigated. The aim of the study is to answer the following questions: (1) Does RIPC have impact on inducibility of AF in patients with known paroxysmal AF? If yes, what are the direct electrophysiological mechanisms of this phenomenon, and could RIPC be implemented to reduce AF burden? (2) Does RIPC have the potential to minimize thrombogenic effects of simulated episodes of AF? If so, what are inhibited components of thrombogenesis and can this be used to reduce thromboembolic risk related to paroxysmal AF? The presented study is a 2-arm, randomized, placebo-controlled, double-blinded, single-center trial in a cohort of 146 patients with paroxysmal AF referred for AF ablation in sinus rhythm. The study will collect electrophysiological data such as variability of P-wave morphology, atrial refractory period, conduction times, and inducibility/sustainability of AF. Furthermore, AF-induced prothrombotic processes will be analyzed by quantification of platelet aggregates, analysis of platelet function, and measurement of thrombogenesis-related plasma markers. Moreover, the study will provide a unique bio-database for further analysis of molecular and genetic mechanisms responsible for observed results.

Time to Give Up on Cardioprotection?

The mortality from acute myocardial infarction (AMI) remains significant, and the prevalence of post-myocardial infarction heart failure is increasing. Therefore, cardioprotection beyond timely reperfusion is needed. Conditioning procedures are the most powerful cardioprotective interventions in animal experiments. However, ischemic preconditioning cannot be used to reduce infarct size in patients with AMI because its occurrence is not predictable; several studies in patients undergoing surgical coronary revascularization report reduced release of creatine kinase and troponin. Ischemic postconditioning reduces infarct size in most, but not all, studies in patients undergoing interventional reperfusion of AMI, but may require direct stenting and exclusion of patients with >6 hours of symptom onset to protect. Remote ischemic conditioning reduces infarct size in patients undergoing interventional reperfusion of AMI, elective percutaneous or surgical coronary revascularization, and other cardiovascular surgery in many, but not in all, studies. Adequate dose-finding phase II studies do not exist. There are only 2 phase III trials, both on remote ischemic conditioning in patients undergoing cardiovascular surgery, both with neutral results in terms of infarct size and clinical outcome, but also both with major problems in trial design. We discuss the difficulties in translation of cardioprotection from animal experiments and proof-of-concept trials to clinical practice. Given that most studies on ischemic postconditioning and all studies on remote ischemic preconditioning in patients with AMI reported reduced infarct size, it would be premature to give up on cardioprotection.

Effect of remote ischemic preconditioning on myocardial injury and inflammatory response induced by ablation for atrial fibrillation: A randomized controlled trial

BACKGROUND

Remote ischemic preconditioning (RIPC) has been suggested to reduce postoperative release of cardiac and inflammatory markers in patients undergoing cardiac surgery. This study aimed to evaluate the effect of RIPC on nonischemic myocardial damage and inflammatory response in patients undergoing radiofrequency catheter ablation for paroxysmal atrial fibrillation (AF).

METHODS

Seventy-two patients with drug-refractory paroxysmal AF undergoing radiofrequency catheter ablation were randomized into RIPC or control groups. RIPC (intermittent arm ischemia through four cycles of 5-min inflation and 5-min deflation of a blood-pressure cuff) was performed once daily on 2 consecutive days before the ablation and immediately before ablation. Cardiac troponin-I (cTnI), high-sensitive C-reactive protein (hs-CRP), and interleukin (IL)-6 levels were measured before RIPC/sham RIPC, after the ablation, and 24 and 72h later. The early recurrence of atrial fibrillation (ERAF) in the two groups was observed over the subsequent 3months.

RESULTS

Radiofrequency ablation resulted in a significant rise in cTnI, hs-CRP, and IL-6 in both groups, which persisted for 72h. The RIPC group showed a lower increase in cTnI (P<0.001), hs-CRP (P=0.003), and IL-6 (P=0.008) than the control and tended to have a lower risk of ERAF (hazard ratio [HR]=0.77, 95% confidence interval [CI]: 0.32-1.88).

CONCLUSIONS

These results show that RIPC before ablation for paroxysmal AF significantly reduces the increase in cTnI, hs-CRP, and IL-6 associated with the procedure and results in a lower risk of ERAF. These findings suggest that RIPC could provide cardioprotection against nonischemic myocardial damage.

Cardiac-specific miRNA in cardiogenesis, heart function, and cardiac pathology (with focus on myocardial infarction)

Cardiac miRNAs (miR-1, miR133a, miR-208a/b, and miR-499) are abundantly expressed in the myocardium. They play a central role in cardiogenesis, heart function and pathology. While miR-1 and miR-133a predominantly control early stages of cardiogenesis supporting commitment of cardiac-specific muscle lineage from embryonic stem cells and mesodermal precursors, miR-208 and miR-499 are involved in the late cardiogenic stages mediating differentiation of cardioblasts to cardiomyocytes and fast/slow muscle fiber specification. In the heart, miR-1/133a control cardiac conductance and automaticity by regulating all phases of the cardiac action potential. miR-208/499 located in introns of the heavy chain myosin genes regulate expression of sarcomeric contractile proteins. In cardiac pathology including myocardial infarction (MI), expression of cardiac miRNAs is markedly altered that leads to deleterious effects associated with heart wounding, arrhythmia, increased apoptosis, fibrosis, hypertrophy, and tissue remodeling. In acute MI, circulating levels of cardiac miRNAs are significantly elevated making them to be a promising diagnostic marker for early diagnosis of acute MI. Great cardiospecific capacity of these miRNAs is very helpful for enhancing regenerative properties and survival of stem cell and cardiac progenitor transplants and for reprogramming of mature non-cardiac cells to cardiomyocytes.

Apoptosis-related microRNA changes in the right atrium induced by remote ischemic perconditioning during valve replacement surgery

We previously found that remote ischemic perconditioning (RIPerc) was effective in attenuating myocardial injury during cardiac surgery. Given that microRNAs (miRs) act as an important player in ischemic/reperfusion (I/R) injury and apoptosis, this study aimed to investigate whether RIPerc reduces apoptosis in atrial myocardium and which apoptosis-related miRs are involved during valve replacement surgery. Here, we demonstrated that RIPerc inhibited apoptosis in atrial myocardium during cardiac ischemia and that 17 miRs showed at least a 1.5-fold change in expression after ischemia. Of the 17 miRs, 9 miRs, including miR-1, miR-21, miR-24, and miR-195, which are related to apoptosis, exhibited different expression patterns in the RIPerc group compared with the control. Using qRT-PCR and Western blotting, we demonstrated that miR-1 and miR-195 were downregulated and that their common putative target gene Bcl-2 was upregulated in the RIPerc group. However, the differences in miR-21 and miR-24 expression, together with programmed cell death 4 (PDCD4), which is the target gene of miR-21, were not significant. These findings provide some insight into the role of miRs in the cardioprotective effects induced by RIPerc.

From Protecting the Heart to Improving Athletic Performance - the Benefits of Local and Remote Ischaemic Preconditioning

Remote Ischemic Preconditioning (RIPC) is a non-invasive cardioprotective intervention that involves brief cycles of limb ischemia and reperfusion. This is typically delivered by inflating and deflating a blood pressure cuff on one or more limb(s) for several cycles, each inflation-deflation being 3-5 min in duration. RIPC has shown potential for protecting the heart and other organs from injury due to lethal ischemia and reperfusion injury, in a variety of clinical settings. The mechanisms underlying RIPC are under intense investigation but are just beginning to be deciphered. Emerging evidence suggests that RIPC has the potential to improve exercise performance, via both local and remote mechanisms. This review discusses the clinical studies that have investigated the role of RIPC in cardioprotection as well as those studying its applicability in improving athletic performance, while examining the potential mechanisms involved.

Remote ischaemic preconditioning for coronary artery bypass grafting

This is the protocol for a review and there is no abstract. The objectives are as follows:

To assess the benefits and harms of remote ischaemic preconditioning in patients undergoing coronary artery bypass grafting, with or without valve surgery.

Epigenetic mechanisms in atrial fibrillation: New insights and future directions

Atrial fibrillation (AF) is the most common sustained arrhythmia. AF is a complex disease that results from genetic and environmental factors and their interactions. In recent years, numerous studies have shown that epigenetic mechanisms significantly participate in AF pathogenesis. Even though a poor understanding of the molecular and electrophysiologic mechanisms of AF, accumulated evidence has suggested that the relevance of epigenetic changes in the development of AF. The aim of this review is to describe the present knowledge about the epigenetic regulatory features significantly participates in AF, and look ahead on new perspectives of epigenetic mechanisms research. Epigenetic regulatory features such as DNA methylation, histone modification, and microRNA influence gene expression by epigenetic mechanisms and by directly binding to various factor response elements in the target gene promoters. Given the role of epigenetic alterations in regulating genes, there is potential for the integration of factors-induced epigenetic alterations as informative factors in the risk assessment process. In this review, new insight into the epigenetic mechanisms in AF pathogenesis is discussed, with special emphasis on DNA methylation, histone modification, and microRNA. Further studies are needed to reveal the potential targets of epigenetic mechanisms, and it can be developed as a therapeutic target for AF.

Cardiac over-expression of microRNA-1 induces impairment of cognition in mice

Large cohort studies have revealed a close relationship between cognitive impairment and cardiovascular diseases, although the mechanism underlying this relationship remains incompletely understood. In this study, using a transgenic (Tg) mouse model of cardiac-specific over-expression of microRNA-1-2 (miR-1-2), we observed that microRNA-1 (miR-1) levels were increased not only in the heart but also in the hippocampus and blood, whereas its levels did not change in the skeletal muscle of Tg mice compared with age-matched wild-type (WT) mice. Six-month-old Tg mice showed cognitive impairment compared with age-matched WT mice, as assessed using the Morris Water Maze test. The brain-derived neurotrophic factor (BDNF) level and cyclic AMP-responsive element-binding protein (CREB) phosphorylation were also significantly reduced in the hippocampi of the Tg mice, as evaluated by Western blot. Further examination showed that BDNF protein expression was down- or up-regulated by miR-1 over-expression or inhibition, respectively, and was unchanged by binding site mutations or miRNA-masks for the 3'UTR of Bdnf, indicating that this gene is a potential target of miR-1. Knockdown of miR-1 by hippocampal stereotaxic injection of an anti-miR-1 oligonucleotide fragment carried by a lentivirus vector (lenti-pre-AMO-miR-1) led to up-regulation of BDNF expression and prevented the reduction in cognitive performance in the Tg mice without affecting cardiac function. Our findings demonstrate that cardiac over-expression of miR-1 also induces behavioral abnormalities that may be associated, at least in part, with the down-regulation of BDNF expression in the hippocampus. This study definitely contributes to the understanding of the relationship between cardiovascular disease and cognitive impairment.

Molecular basis of cardioprotection: signal transduction in ischemic pre-, post-, and remote conditioning

Reperfusion is mandatory to salvage ischemic myocardium from infarction, but reperfusion per se contributes to injury and ultimate infarct size. Therefore, cardioprotection beyond that by timely reperfusion is needed to reduce infarct size and improve the prognosis of patients with acute myocardial infarction. The conditioning phenomena provide such cardioprotection, insofar as brief episodes of coronary occlusion/reperfusion preceding (ischemic preconditioning) or following (ischemic postconditioning) sustained myocardial ischemia with reperfusion reduce infarct size. Even ischemia/reperfusion in organs remote from the heart provides cardioprotection (remote ischemic conditioning). The present review characterizes the signal transduction underlying the conditioning phenomena, including their physical and chemical triggers, intracellular signal transduction, and effector mechanisms, notably in the mitochondria. Cardioprotective signal transduction appears as a highly concerted spatiotemporal program. Although the translation of ischemic postconditioning and remote ischemic conditioning protocols to patients with acute myocardial infarction has been fairly successful, the pharmacological recruitment of cardioprotective signaling has been largely disappointing to date.

Mitochondrial cardiomyopathy and related arrhythmias

Mitochondrial dysfunction has been shown to be involved in the pathophysiology of arrhythmia, not only in inherited cardiomyopathy due to specific mutations in the mitochondrial DNA but also in acquired cardiomyopathy such as ischemic or diabetic cardiomyopathy. This article briefly discusses the basics of mitochondrial physiology and details the mechanisms generating arrhythmias due to mitochondrial dysfunction. The clinical spectrum of inherited and acquired cardiomyopathies associated with mitochondrial dysfunction is discussed followed by general aspects of the management of mitochondrial cardiomyopathy and related arrhythmia.

Renal Nerve-Mediated Erythropoietin Release Confers Cardioprotection During Remote Ischemic Preconditioning

BACKGROUND

Remote ischemic preconditioning (RIPC) induced by transient limb ischemia is a powerful innate mechanism of cardioprotection against ischemia. Several described mechanisms explain how RIPC may act through neural pathways or humoral factors; however, the mechanistic pathway linking the remote organ to the heart has not yet been fully elucidated. This study aimed to investigate the mechanisms underlying the RIPC-induced production of Janus kinase (JAK)-signal transducer and activator of the transcription (STAT)-activating cytokines and cardioprotection by using mouse and human models of RIPC.

METHODS AND RESULTS

Screened circulating cardioprotective JAK-STAT-activating cytokines in mice unexpectedly revealed increased serum erythropoietin (EPO) levels after RIP induced by transient ischemia. In mice, RIPC rapidly upregulated EPO mRNA and its main transcriptional factor, hypoxia-inducible factor-1α (HIF1α), in the kidney. Laser Doppler blood flowmetry revealed a prompt reduction of renal blood flow (RBF) after RIPC. RIPC activated cardioprotective signaling pathways and the anti-apoptotic Bcl-xL pathway in the heart, and reduced infarct size. In mice, these effects were abolished by administration of an EPO-neutralizing antibody. Renal nerve denervation also abolished RIPC-induced RBF reduction, EPO production, and cardioprotection. In humans, transient limb ischemia of the upper arm reduced RBF and increased serum EPO levels.

CONCLUSIONS

Based on the present data, we propose a novel RIPC mechanism in which inhibition of infarct size by RIPC is produced through the renal nerve-mediated reduction of RBF associated with activation of the HIF1α-EPO pathway.

Remote ischemic preconditioning and incidence of postoperative atrial fibrillation

OBJECTIVES

Although remote ischemic preconditioning (RIPC) has shown favorable effects on ischemia-reperfusion injury, much remains unknown of its mechanisms and clinical significance. We hypothesized that RIPC would reduce the incidence of postoperative atrial fibrillation (POAF) following coronary artery bypass graft (CABG) surgery. In addition, we investigated whether RIPC could induce alterations of circulating microRNA in blood plasma.

DESIGN

This is a single-center, double-blind, randomized controlled trial. 92 adult patients referred for first-time isolated CABG surgery were randomly assigned to either RIPC (n = 45) or control (n = 47). The RIPC-stimulus comprised three 5-min cycles of upper arm ischemia, induced by inflating a blood pressure cuff to 200 mmHg, with an intervening 5 min reperfusion. Heart rhythm was assessed by telemetry. MicroRNA expression was assessed in plasma by real-time polymerase chain reaction.

RESULTS

Of the 92 patients included in the study, 27 patients developed POAF (29%). 17 of these patients belonged to the RIPC group (38%), and 10 to the control group (21%). There were no significant alterations of microRNA expression.

CONCLUSIONS

We did not observe a reduced incidence of POAF by RIPC before CABG surgery. Larger multi-center studies may be necessary to further clarify this issue.

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.

MiR-214 regulates the pathogenesis of patients with coronary artery disease by targeting VEGF

Circulating microRNAs (miRNAs) in patient body fluids have recently been considered to hold the potential of being novel disease biomarkers and drug targets. We aimed to investigate the correlation between the levels of circulating miR-214 and the expression of vascular endothelial growth factor (VEGF) in the pathogenesis of coronary heart disease patients to further explore the mechanism involved in the vasculogenesis. Three different cohorts, including 13 acute myocardial infarction patients, 176 angina pectoris patients, and 127 control subjects, were enrolled to investigate the expression levels of circulating miR-214 in patients with myocardial ischemia and also the relationship between plasma miR-214 and severity of coronary stenosis. Plasma miR-214 levels of participants were examined by real-time quantitative PCR. Simultaneously, plasma cardiac troponin I concentrations were measured by ELISA assays. We further detected the correlation of miR-214 and VEGF by molecular and animal assays. MiR-214 was enriched in not only diseased endothelial progenitor cells (EPCs) but also the plasma of coronary artery disease (CAD) patients. Besides, we found out miR-214 was able to suppress VEGF expression and EPC activities. Reporter assays confirmed the direct binding and repression of miR-214 to the 39-UTR of VEGF mRNA. Knockdown of miR-214 not only restored VEGF levels and angiogenic activities of diseased EPCs in vitro, but also further promoted blood flow recovery in ischemic limbs of mice. Circulating miR-214 may be a new biomarker for CAD and as a potential diagnostic tool. And increased miR-214 level may be used to predict the presence and severity of coronary lesions in CAD patients.

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 Ischemic Preconditioning of the Heart: Protective Responses in Functional and Biophysical Properties of Cardiac Mitochondria

Remote ischemic preconditioning (RIP)-induced protection of myocardial energetics was well documented on the level of tissue, but data concerning the involvement of mitochondria were missing. We aimed at the identification of changes in membrane properties and respiratory functions induced in rat heart mitochondria by RIP. Experiments were performed on 46 male Wistar rats divided into control and RIP-treated groups of 21 animals each. Blood flow in the occluded area was recorded by MRI angiography in four animals. RIP protocol comprised of three successive 5-min occlusions each followed by 5-min reperfusions of descending branches of the right hind limb femoral artery. The efficacy of RIP was evaluated as the extent of RIP-induced protection against damage to the functions of mitochondria isolated by differential centrifugation after 30-min global ischemia followed by 40-min reperfusion of the hearts in Langendorff mode. Assessments: mitochondrial membrane fluidity with a fluorescent probe DPH, CoQ9 and CoQ10 with HPLC, mitochondrial respiration with the Oxygraph-2k (Oroboros). Results revealed that RIP was affecting the mitochondria. The immediate protection conferred by RIP involves beneficial and prognostically significant effects: a total elimination of ischemia/reperfusion-induced depression of mitochondrial membrane fluidity and a trend for better preservation of mitochondrial state 3 respiration.

Protective role of Klotho on cardiomyocytes upon hypoxia/reoxygenation via downregulation of Akt and FOXO1 phosphorylation

Klotho is a novel anti-aging hormone involved in human coronary artery disease. The present study aimed to detect the effects and mechanism of Klotho on cardiomyocytes in a hypoxia/reoxygenation (H/R) model in vitro. Neonatal Sprague-Dawley rat cardiomyocytes were randomly distributed into experimental groups as follows: Control group; H/R group, 4‑h hypoxia followed by 3‑h reoxygenation; and H/R+Klotho group, incubated with 0.1, 0.2 or 0.4 µg/ml Klotho protein for 16 h and then subjected to 4‑h hypoxia/3‑h reoxygenation. In order to evaluate cardiomyocyte damage, cell viability and lactate dehydrogenase (LDH) levels were measured. Cell apoptosis was measured by flow cytometry. The 2',7'-dichlorofluorescein diacetate reagent was used to estimate the intracellular generation of reactive oxygen species (ROS). Immunofluorescence staining was used to test whether Klotho induced decreased nuclear translocation of forkhead box protein O1 (FOXO1). Western blot analysis was performed to detect protein levels of FOXO1, phospho-FOXO1, Akt, phospho-Akt and superoxide dismutase 2 (SOD2). Cell viability was significantly decreased, levels of LDH in the cardiomyocyte culture medium were significantly increased and the apoptotic rate was enhanced in the H/R group when compared with those of the control group. Compared with the H/R group, cell viability of the H/R+Klotho groups was significantly higher (P<0.05). Treatment with Klotho protein resulted in a significant resistance of cardiomyocytes to apoptosis and the release of LDH was decreased. Intracellular ROS levels in the H/R group were significantly elevated above those of the control group (P<0.05). Following treatment with Klotho, intracellular ROS levels were significantly decreased compared with those of the H/R group (P<0.05). Western blot analysis confirmed that Klotho protein treatment increased FOXO1 levels in the nucleus and decreased FOXO1 levels in the cytoplasm. Furthermore, exogenous Klotho protein promoted translocation of FOXO1 from cytoplasm to nucleus. In addition, the administration of Klotho protein suppressed phosphorylation of FOXO1 and Akt, and markedly increased the protein expression levels of SOD2. In conclusion, treatment with Klotho protein had beneficial effects on cardiomyocytes undergoing H/R injury. The mechanism of this effect may be associated with suppressed apoptosis of cardiomyocytes, inhibition of phosphorylation of FOXO1 and Akt as well as suppression of cytoplasm transfer of FOXO1.

Harnessing the Therapeutic Potential of MicroRNAs for Cardiovascular Disease

Cardiovascular diseases are one of the most common causes of death in humans and are responsible for billions of dollars in health care expenditures. As the molecular basis of cardiac diseases continues to be explored, there remains the hope for identification of more effective therapeutics. MicroRNAs (miRNAs) are recognized as important regulators of numerous biological pathways and stress responses, including those found in cardiovascular diseases. MicroRNA signatures of cardiovascular diseases can provide targets for miRNA adjustment and offer the possibility of changing gene and protein expression to treat certain pathologies. These adjustments can be conferred using advances in oligonucleotide delivery methods, which can target single miRNAs, families of miRNAs, and certain tissue types. In this review, we will discuss the use of miRNAs in vivo and recent advances in their use for cardiovascular disease in mammalian models.

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.

An Argonaute 2 switch regulates circulating miR-210 to coordinate hypoxic adaptation across cells

Complex organisms may coordinate molecular responses to hypoxia by specialized avenues of communication across multiple tissues, but these mechanisms are poorly understood. Plasma-based, extracellular microRNAs have been described, yet their regulation and biological functions in hypoxia remain enigmatic. We found a unique pattern of release of the hypoxia-inducible microRNA-210 (miR-210) from hypoxic and reoxygenated cells. This microRNA is also elevated in human plasma in physiologic and pathologic conditions of altered oxygen demand and delivery. Released miR-210 can be delivered to recipient cells, and the suppression of its direct target ISCU and mitochondrial metabolism is primarily evident in hypoxia. To regulate these hypoxia-specific actions, prolyl-hydroxylation of Argonaute 2 acts as a molecular switch that reciprocally modulates miR-210 release and intracellular activity in source cells as well as regulates intracellular activity in recipient cells after miR-210 delivery. Therefore, Argonaute 2-dependent control of released miR-210 represents a unique communication system that integrates the hypoxic response across anatomically distinct cells, preventing unnecessary activity of delivered miR-210 in normoxia while still preparing recipient tissues for incipient hypoxic stress and accelerating adaptation.

Atrial fibrillation and microRNAs

Atrial fibrillation (AF) is the most common sustained arrhythmia, especially in the elderly, and has a significant genetic component. Recently, several independent investigators have demonstrated a functional role for small non-coding RNAs (microRNAs) in the pathophysiology of this cardiac arrhythmia. This report represents a systematic and updated appraisal of the main studies that established a mechanistic association between specific microRNAs and AF, focusing both on the regulation of electrical and structural remodeling of cardiac tissue.