Cyclosporine A at reperfusion fails to reduce infarct size in the in vivo rat heart

Immediate Intracoronary Delivery of Human Umbilical Cord Mesenchymal Stem Cells Reduces Myocardial Injury by Regulating the Inflammatory Process Through Cell-Cell Contact with T Lymphocytes

Inflammatory response regulation is a mechanism through which human umbilical cord mesenchymal stem cells (HUCMSCs) improve myocardial ischemia reperfusion injury (IRI); however, the timing of HUCMSC delivery to achieve maximum effectiveness is controversial. To investigate the effects of HUCMSC delivery on the acute inflammatory stage of IRI, we transplanted HUCMSCs or HUCMSCs with cyclosporin A (CsA) through the coronary artery simultaneously during ischemia reperfusion in pigs. Ferumoxytol-labeled HUCMSCs (HUCMSC), HUCMSCs with cyclosporin A (HUCMSC+CsA), and PBS (control) groups were investigated to evaluate the homing of transplanted cells and changes in infarct features, cardiac activity, and inflammatory response at three time points post-transplantation. Animals were sacrificed 2 weeks later for histological analysis of the hearts. We detected Prussian blue-dyed granules distributed around T lymphocyte clusters in the infarct area in the HUCMSC group. Infarct size and collagen deposition in the infarct area were lower in the HUCMSC group than in the control and HUCMSC+CsA groups. Cardiac function was mildly impaired in both the control and HUCMSC groups, whereas added CsA had a more severe impact. The levels of proinflammatory markers were lower in the HUCMSC group than in the control group at 24-h follow-up, and the difference was more significant after adding CsA. There were more CD3⁺ T lymphocytes and Foxp3⁺ Tregs in the HUCMSC group infarct area than in the other two groups. Proliferation rate of T lymphocytes was higher in the HUCMSC group than in the other two groups. Indirect co-culture experiments in vitro showed that MSCs promoted the generation of CD4⁺CD25⁺ Foxp3⁺Tregs through a paracrine mechanism. These results indicate that immediate intracoronary delivery of HUCMSCs after ischemia reperfusion can reduce acute myocardial IRI and promote myocardial repair, mainly through T lymphocyte interactions to regulate the intense inflammatory response during the acute inflammatory stage.

Mitochondrial ion channels as targets for cardioprotection

Acute myocardial infarction (AMI) and the heart failure (HF) that often result remain the leading causes of death and disability worldwide. As such, new therapeutic targets need to be discovered to protect the myocardium against acute ischaemia/reperfusion (I/R) injury in order to reduce myocardial infarct (MI) size, preserve left ventricular function and prevent the onset of HF. Mitochondrial dysfunction during acute I/R injury is a critical determinant of cell death following AMI, and therefore, ion channels in the inner mitochondrial membrane, which are known to influence cell death and survival, provide potential therapeutic targets for cardioprotection. In this article, we review the role of mitochondrial ion channels, which are known to modulate susceptibility to acute myocardial I/R injury, and we explore their potential roles as therapeutic targets for reducing MI size and preventing HF following AMI.

Oxidative Stress in Cell Death and Cardiovascular Diseases

ROS functions as a second messenger and modulates multiple signaling pathways under the physiological conditions. However, excessive intracellular ROS causes damage to the molecular components of the cell, which promotes the pathogenesis of various human diseases. Cardiovascular diseases are serious threats to human health with extremely high rates of morbidity and mortality. Dysregulation of cell death promotes the pathogenesis of cardiovascular diseases and is the clinical target during the disease treatment. Numerous studies show that ROS production is closely linked to the cell death process and promotes the occurrence and development of the cardiovascular diseases. In this review, we summarize the regulation of intracellular ROS, the roles of ROS played in the development of cardiovascular diseases, and the programmed cell death induced by intracellular ROS. We also focus on anti-ROS system and the potential application of anti-ROS strategy in the treatment of cardiovascular diseases.

Critical appraisal of STAT3 pattern in adult cardiomyocytes

The signal transducer and activator of transcription 3, STAT3, transfers cellular signals from the plasma membrane to the nucleus, acting as a signaling molecule and a transcription factor. Reports proposed an additional non-canonical role of STAT3 that could regulate the activity of complexes I and II of the electron transport chain and the opening of the mitochondrial permeability transition pore (PTP) after ischemia-reperfusion in various cell types. The native expression of STAT3 in heart mitochondria, together with a direct versus an indirect transcriptional role in mitochondrial functions, have been recently questioned. The objective of the present study was to investigate the cellular distribution of STAT3 in mouse adult cardiomyocytes under basal and stress conditions, along with assessing its presence and activity in cardiac mitochondria using structural and functional approaches. The analysis of the spatial distribution of STAT3 signal in the cardiomyocytes interestingly showed that it is transversely distributed along the T-tubules and in the nucleus. This distribution was neither affected by hypoxia nor by hypoxia/re‑oxygenation conditions. Focusing on the mitochondrial STAT3 localization, our results suggest that serine-phosphorylated STAT3 (PS727-STAT3) and total STAT3 are detected in crude but not in pure mitochondria of mouse adult cardiomyocytes, under basal and ischemia-reperfusion conditions. The inhibition of STAT3, with a pre-validated non-toxic Stattic dose, had no significant effects on mitochondrial respiration, but a weak effect on the calcium retention capacity. Overall, our results exclusively reveal a unique cellular distribution of STAT3 in mouse adult cardiomyocytes, along the T-tubules and in nucleus, under different conditions. They also challenge the expression and activity of STAT3 in mitochondria of these cells under basal conditions and following ischemia-reperfusion. In addition, our results underline technical methods, complemental to cell fractionation, to evaluate STAT3 roles during hypoxia-reoxygenation and at the interface between nucleus and endoplasmic reticulum.

Cyclosporine-insensitive mode of cell death after prolonged myocardial ischemia: Evidence for sarcolemmal permeabilization as the pivotal step

A prominent theory of cell death in myocardial ischemia/reperfusion (I/R) posits that the primary and pivotal step of irreversible cell injury is the opening of the mitochondrial permeability transition (MPT) pore. However, the predominantly positive evidence of protection against infarct afforded by the MPT inhibitor, Cyclosporine A (CsA), in experimental studies is in stark contrast with the overall lack of benefit found in clinical trials of CsA. One reason for the discrepancy might be the fact that relatively short experimental ischemic episodes (<1 hour) do not represent clinically-realistic durations, usually exceeding one hour. Here we tested the hypothesis that MPT is not the primary event of cell death after prolonged (60–80 min) episodes of global ischemia. We used confocal microcopy in Langendorff-perfused rabbit hearts treated with the electromechanical uncoupler, 2,3-Butanedione monoxime (BDM, 20 mM) to allow tracking of MPT and sarcolemmal permeabilization (SP) in individual ventricular myocytes. The time of the steepest drop in fluorescence of mitochondrial membrane potential (ΔΨ_m)-sensitive dye, TMRM, was used as the time of MPT (T_MPT). The time of 20% uptake of the normally cell-impermeable dye, YO-PRO1, was used as the time of SP (T_SP). We found that during reperfusion MPT and SP were tightly coupled, with MPT trending slightly ahead of SP (T_SP-T_MPT = 0.76±1.31 min; p = 0.07). These coupled MPT/SP events occurred in discrete myocytes without crossing cell boundaries. CsA (0.2 μM) did not reduce the infarct size, but separated SP and MPT events, such that detectable SP was significantly ahead of MPT (T_SP -T_MPT = -1.75±1.28 min, p = 0.006). Mild permeabilization of cells with digitonin (2.5–20 μM) caused coupled MPT/SP events which occurred in discrete myocytes similar to those observed in Control and CsA groups. In contrast, deliberate induction of MPT by titration with H₂O₂ (200–800 μM), caused propagating waves of MPT which crossed cell boundaries and were uncoupled from SP. Taken together, these findings suggest that after prolonged episodes of ischemia, SP is the primary step in myocyte death, of which MPT is an immediate and unavoidable consequence.

Hypercholesterolemia Abrogates Remote Ischemic Preconditioning-Induced Cardioprotection: Role of Reperfusion Injury Salvage Kinase Signals

Remote ischemic preconditioning (RIPC) is one of the most powerful intrinsic cardioprotective strategies discovered so far and experimental data indicate that comorbidity may interfere with the protection by RIPC. Therefore, we investigate whether RIPC-induced cardioprotection was intact in hypercholesterolemic rat hearts exposed to ischemia reperfusion in vivo. Normal or hypercholesterolemic rat hearts were exposed to 30 min of ischemia and 2 h of reperfusion, with or without RIPC, PI3K inhibitor wortmannin, MEK-ERK1/2 inhibitor PD98059, GSK3β inhibitor SB216763. Infarct size, apoptosis, MG53, PI3K-p85, p-Akt, p-ERK1/2, p-GSK3β, and cleaved Caspase-3 were determined. RIPC reduced infarct size, limited cardiomyocyte apoptosis following IR that was blocked by wortmannin but not PD98059. RIPC triggered unique cardioprotective signaling including MG53, phosphorylation of Akt, and glycogen synthase kinase-3ß (GSK3β) in concert with reduced proapoptotic active caspase-3. In contrast, RIPC failed to reduce myocardial necrosis and apoptosis as well as to increase the phosphorylated Akt and GSK3β in hypercholestorolemic myocardium. Importantly, we found that inhibition of GSK with SB216763 reduced myocardial infarct size in healthy and hypercholesterolemic hearts, but no additional cardioprotective effect was achieved when combined with RIPC. Our results suggest that acute GSK3β inhibition may provide a novel therapeutic strategy for hypercholesterolemic patients during acute myocardial infarction, whereas RIPC is less effective due to signaling events that adversely affect GSK3β.

Critical Issues for the Translation of Cardioprotection

The translation from numerous successful animal experiments on cardioprotection beyond that by reperfusion to clinical practice has to date been disappointing. Animal experiments often use reductionist approaches and are mostly performed in young and healthy animals which lack the risk factors, comorbidities, and comedications which are characteristics of patients suffering an acute myocardial infarction or undergoing cardiovascular surgery. Conceptually, it is still unclear by how much the time window for successful reperfusion is extended by preconditioning, and how long the duration of ischemia can be so that adjunct cardioprotection by postconditioning at reperfusion still protects. Experimental studies addressing long-term effects of adjunct cardioprotection beyond infarct size reduction, that is, on repair, remodeling, and mortality, are lacking. Technically, reproducibility and robustness of experimental studies are often limited. Grave faults in design and conduct of clinical trials have also substantially contributed to the failure of translation of cardioprotection to clinical practice. Cardiovascular surgery with ischemic cardioplegic arrest is only a surrogate of acute myocardial infarction and confounded by the choice of anesthesia, hypothermia, cardioplegia, and traumatic myocardial injury. Trials in patients with acute myocardial infarction have been performed on agents/interventions with no or inconsistent previous animal data and in patients who had either some reperfusion already at admission or were reperfused too late to expect any myocardial salvage. Of greatest concern is the lack of adequate phase II dosing and timing studies when rushing from promising proof-of-concept trials with surrogate end points such as infarct size to larger clinical outcome trials. Future trials must focus on interventions/agents with robust preclinical evidence, have solid phase II dosing and timing data, and recruit patients who have truly a chance to benefit from adjunct cardioprotection.

Cyclophilin D Modulates the Cardiac Mitochondrial Target of Isoflurane, Sevoflurane, and Desflurane

BACKGROUND

Volatile anesthetics are known to limit myocardial ischemia-reperfusion injuries. Mitochondria were shown to be major contributors to cardioprotection. Cyclophilin D (CypD) is one of the main regulators of mitochondria-induced cell death. We compared the effect of isoflurane, sevoflurane, and desflurane in the presence or absence of CypD, to clarify its role in the mechanism of cardioprotection induced by these anesthetics.

METHODS

Oxidative phosphorylation, mitochondrial membrane potential, and H2O2 production were measured in isolated mitochondria from wild-type (WT) or CypD knockout mice in basal conditions and after hypoxia-reoxygenation in the presence or absence of volatile anesthetics.

RESULTS

All volatile anesthetics inhibited mitochondrial state 3 of complex I, decreased membrane potential, and increased adenosine diphosphate consumption duration in both WT and CypD knockout mice. However, they differently modified H2O2 production after stimulation by succinate: CypD ablation reduced H2O2 production, isoflurane decreased H2O2 level in WT but not in CypD knockout mice, sevoflurane affected both lines whereas desflurane increased H2O2 production in CypD knockout and had no effect on WT mice.

CONCLUSIONS

This study showed different effects of isoflurane, sevoflurane, and desflurane on mitochondrial functions and highlighted the implication of CypD in the regulation of adenosine diphosphate consumption and complex I-induced radical oxygen species production.

Mitochondrial Membrane Permeability Inhibitors in Acute Myocardial Infarction: Still Awaiting Translation

Despite therapeutic advances, acute myocardial infarction (AMI) remains a leading cause of morbidity and mortality worldwide. One potential limitation of the current treatment paradigm is the lack of effective therapies to optimize reperfusion after ischemia and prevent reperfusion-mediated injury. Experimental studies indicate that this process accounts for up to 50% of the final infarct size, lending it importance as a potential target for cardioprotection. However, multiple therapeutic approaches have shown potential in pre-clinical and early phase trials but a paucity of clear clinical benefit when expanded to larger studies. Here we explore this history of trials and errors of the studies of cyclosporine A and other mitochondrial membrane permeability inhibitors, agents that appeared to have a promising pre-clinical record yet provided disappointing results in phase III clinical trials.

Novel, selective EPO receptor ligands lacking erythropoietic activity reduce infarct size in acute myocardial infarction in rats

Erythropoietin (EPO) has been shown to protect the heart against acute myocardial infarction in pre-clinical studies, however, EPO failed to reduce infarct size in clinical trials and showed significant safety problems. Here, we investigated cardioprotective effects of two selective non-erythropoietic EPO receptor ligand dimeric peptides (AF41676 and AF43136) lacking erythropoietic activity, EPO, and the prolonged half-life EPO analogue, darbepoetin in acute myocardial infarction (AMI) in rats. In a pilot study, EPO at 100U/mL significantly decreased cell death compared to vehicle (33.8±2.3% vs. 40.3±1.5%, p<0.05) in rat neonatal cardiomyocytes subjected to simulated ischemia/reperfusion. In further studies (studies 1-4), in vivo AMI was induced by 30min coronary occlusion and 120min reperfusion in male Wistar rats. Test compounds and positive controls for model validation (B-type natriuretic peptide, BNP or cyclosporine A, CsA) were administered iv. before the onset of reperfusion. Infarct size (IS) was measured by standard TTC staining. In study 1, 5000U/kg EPO reduced infarct size significantly compared to vehicle (45.3±4.8% vs. 59.8±4.5%, p<0.05). In study 2, darbepoetin showed a U-shaped dose-response curve with maximal infarct size-reducing effect at 5μg/kg compared to the vehicle (44.4±5.7% vs. 65.9±2.7%, p<0.01). In study 3, AF41676 showed a U-shaped dose-response curve, where 3mg/kg was the most effective dose compared to the vehicle (24.1±3.9% vs. 44.3±2.5%, p<0.001). The positive control BNP significantly decreased infarct size in studies 1-3 by approximately 35%. In study 4, AF43136 at 10mg/kg decreased infarct size, similarly to the positive control CsA compared to the appropriate vehicle (39.4±5.9% vs. 58.1±5.4% and 45.9±2.4% vs. 63.8±4.1%, p<0.05, respectively). This is the first demonstration that selective, non-erythropoietic EPO receptor ligand dimeric peptides AF41676 and AF43136 administered before reperfusion are able to reduce infarct size in a rat model of AMI. Therefore, non-erythropoietic EPO receptor peptide ligands may be promising cardioprotective agents.

9th Hatter Biannual Meeting: position document on ischaemia/reperfusion injury, conditioning and the ten commandments of cardioprotection

In the 30 years since the original description of ischaemic preconditioning, understanding of the pathophysiology of ischaemia/reperfusion injury and concepts of cardioprotection have been revolutionised. In the same period of time, management of patients with coronary artery disease has also been transformed: coronary artery and valve surgery are now deemed routine with generally excellent outcomes, and the management of acute coronary syndromes has seen decade on decade reductions in cardiovascular mortality. Nonetheless, despite these improvements, cardiovascular disease and ischaemic heart disease in particular, remain the leading cause of death and a significant cause of long-term morbidity (with a concomitant increase in the incidence of heart failure) worldwide. The need for effective cardioprotective strategies has never been so pressing. However, despite unequivocal evidence of the existence of ischaemia/reperfusion in animal models providing a robust rationale for study in man, recent phase 3 clinical trials studying a variety of cardioprotective strategies in cardiac surgery and acute ST-elevation myocardial infarction have provided mixed results. The investigators meeting at the Hatter Cardiovascular Institute workshop describe the challenge of translating strong pre-clinical data into effective clinical intervention strategies in patients in whom effective medical therapy is already altering the pathophysiology of ischaemia/reperfusion injury-and lay out a clearly defined framework for future basic and clinical research to improve the chances of successful translation of strong pre-clinical interventions in man.

Skeletal muscle ischemia-reperfusion injury and cyclosporine A in the aging rat

Old patients exhibit muscle impairments and increased perioperative risk during vascular surgery procedures. Although aging generally impairs protective mechanisms, data are lacking concerning skeletal muscle in elderly. We tested whether cyclosporine A (CsA), which protects skeletal muscle from ischemia-reperfusion (IR) in young rats, might reduce skeletal muscle mitochondrial dysfunction and oxidative stress in aging rats submitted to hindlimb IR. Wistar rats aged 71-73 weeks were randomized to IR (3 h unilateral tourniquet application and 2 h reperfusion) or IR + CsA (10 mg/kg cyclosporine IV before reperfusion). Maximal oxidative capacity (VM ax ), acceptor control ratio (ACR), and relative contribution of the mitochondrial respiratory chain complexes II, III, IV (VS ucc ), and IV (VTMPD /Asc ), together with calcium retention capacity (CRC) a marker of apoptosis, and tissue reactive oxygen species (ROS) production were determined in gastrocnemius muscles from both hindlimbs. Compared to the nonischemic hindlimb, IR significantly reduced mitochondrial coupling, VMax (from 7.34 ± 1.50 to 2.87 ± 1.22 μMO2 /min/g; P < 0.05; -70%), and VS ucc (from 6.14 ± 1.07 to 3.82 ± 0.83 μMO2 /min/g; P < 0.05; -42%) but not VTMPD /Asc . IR also decreased the CRC from 15.58 ± 3.85 to 6.19 ± 0.86 μMCa(2+) /min/g; P < 0.05; -42%). These alterations were not corrected by CsA (-77%, -49%, and -32% after IR for VM ax, VS ucc , and CRC, respectively). Further, CsA significantly increased ROS production in both hindlimbs (P < 0.05; +73%). In old rats, hindlimb IR impairs skeletal muscle mitochondrial function and increases oxidative stress. Cyclosporine A did not show protective effects.

Inhibition of the NLRP3 inflammasome limits the inflammatory injury following myocardial ischemia-reperfusion in the mouse

BACKGROUND

Successful reperfusion is the most effective strategy to reduce ischemic injury in acute myocardial infarction (AMI). Ischemic injury, however, also triggers a secondary ischemia-independent injury, known as reperfusion injury, contributing to the overall infarct size. We hypothesize that inhibition of the Nod-like Receptor Protein-3 (NLRP3) inflammasome limits infarct size following myocardial ischemia/reperfusion (I/R), by inhibiting the inflammatory component of the reperfusion injury.

METHODS

CD-1 male mice underwent transient ligation of the left anterior descending coronary artery for 30 or 75min followed by reperfusion. Infarct size was measured at 1, 3 and 24h. A NLRP3 inflammasome inhibitor (NLRP3inh) or vehicle was administrated immediately at time of reperfusion or with a delay of 1 or 3h of reperfusion.

RESULTS

A time-dependent increase in infarct size was measured at 1, 3, and 24h after reperfusion (11±2%, 30±5% and 43±4% of the area at risk respectively; P<0.001 for trend). NLRP3 myocardial expression was significantly increased at 24h and 6h vs 3h (P<0.01). Administration of the NLRP3inh at reperfusion did not reduce infarct size at 3h, while it significantly reduced infarct size at 24h (-56% vs vehicle, P<0.01). The NLRP3inh given 1h after reperfusion also significantly decreased caspase-1 activity and infarct size measured at 24h, whereas the NLRP3inh did not when given with a delay of 3h.

CONCLUSIONS

Pharmacological inhibition of the NLRP3 inflammasome within 1h of reperfusion limits the secondary inflammatory injury and infarct size following myocardial ischemia-reperfusion in the mouse.

Involvement of Cyclophilin D and Calcium in Isoflurane-induced Preconditioning

BACKGROUND

The mitochondrial permeability transition pore (PTP) has been established as an important mediator of ischemia-reperfusion-induced cell death. The matrix protein cyclophilin D (CypD) is the best known regulator of PTP opening. Therefore, the authors hypothesized that isoflurane, by inhibiting the respiratory chain complex I, another regulator of PTP, might reinforce the myocardial protection afforded by CypD inhibition.

METHODS

Adult mouse or isolated cardiomyocytes from wild-type or CypD knockout (CypD-KO) mice were subjected to ischemia or hypoxia followed by reperfusion or reoxygenation. Infarct size was assessed in vivo. Mitochondrial membrane potential and PTP opening were assessed using tetramethylrhodamine methyl ester perchlorate and calcein-cobalt fluorescence, respectively. Fluo-4 AM and rhod-2 AM staining allowed the measurement, by confocal microscopy, of Ca transient and Ca transfer from sarcoplasmic reticulum (SR) to mitochondria after caffeine stimulation.

RESULTS

Both inhibition of CypD and isoflurane significantly reduced infarct size (-50 and -37%, respectively) and delayed PTP opening (+63% each). Their combination had no additive effect (n = 6/group). CypD-KO mice displayed endogenous protection against ischemia-reperfusion. Isoflurane depolarized the mitochondrial membrane (-28%, n = 5), decreased oxidative phosphorylation (-59%, n = 5), and blunted the caffeine-induced Ca transfer from SR to mitochondria (-22%, n = 7) in the cardiomyocytes of wild-type mice. Importantly, this transfer was spontaneously decreased in the cardiomyocytes of CypD-KO mice (-25%, n = 4 to 5).

CONCLUSIONS

The results suggest that the partial inhibitory effect of isoflurane on respiratory complex I is insufficient to afford a synergy to CypD-induced protection. Isoflurane attenuates the Ca transfer from SR to mitochondria, which is also the prominent role of CypD, and finally prevents PTP opening.

Interaction of risk factors, comorbidities, and comedications with ischemia/reperfusion injury and cardioprotection by preconditioning, postconditioning, and remote conditioning

Pre-, post-, and remote conditioning of the myocardium are well described adaptive responses that markedly enhance the ability of the heart to withstand a prolonged ischemia/reperfusion insult and provide therapeutic paradigms for cardioprotection. Nevertheless, more than 25 years after the discovery of ischemic preconditioning, we still do not have established cardioprotective drugs on the market. Most experimental studies on cardioprotection are still undertaken in animal models, in which ischemia/reperfusion is imposed in the absence of cardiovascular risk factors. However, ischemic heart disease in humans is a complex disorder caused by, or associated with, cardiovascular risk factors and comorbidities, including hypertension, hyperlipidemia, diabetes, insulin resistance, heart failure, altered coronary circulation, and aging. These risk factors induce fundamental alterations in cellular signaling cascades that affect the development of ischemia/reperfusion injury per se and responses to cardioprotective interventions. Moreover, some of the medications used to treat these risk factors, including statins, nitrates, and antidiabetic drugs, may impact cardioprotection by modifying cellular signaling. The aim of this article is to review the recent evidence that cardiovascular risk factors and their medication may modify the response to cardioprotective interventions. We emphasize the critical need to take into account the presence of cardiovascular risk factors and concomitant medications when designing preclinical studies for the identification and validation of cardioprotective drug targets and clinical studies. This will hopefully maximize the success rate of developing rational approaches to effective cardioprotective therapies for the majority of patients with multiple risk factors.

Cyclosporine before PCI in Patients with Acute Myocardial Infarction

BACKGROUND

Experimental and clinical evidence suggests that cyclosporine may attenuate reperfusion injury and reduce myocardial infarct size. We aimed to test whether cyclosporine would improve clinical outcomes and prevent adverse left ventricular remodeling.

METHODS

In a multicenter, double-blind, randomized trial, we assigned 970 patients with an acute anterior ST-segment elevation myocardial infarction (STEMI) who were undergoing percutaneous coronary intervention (PCI) within 12 hours after symptom onset and who had complete occlusion of the culprit coronary artery to receive a bolus injection of cyclosporine (administered intravenously at a dose of 2.5 mg per kilogram of body weight) or matching placebo before coronary recanalization. The primary outcome was a composite of death from any cause, worsening of heart failure during the initial hospitalization, rehospitalization for heart failure, or adverse left ventricular remodeling at 1 year. Adverse left ventricular remodeling was defined as an increase of 15% or more in the left ventricular end-diastolic volume.

RESULTS

A total of 395 patients in the cyclosporine group and 396 in the placebo group received the assigned study drug and had data that could be evaluated for the primary outcome at 1 year. The rate of the primary outcome was 59.0% in the cyclosporine group and 58.1% in the control group (odds ratio, 1.04; 95% confidence interval [CI], 0.78 to 1.39; P=0.77). Cyclosporine did not reduce the incidence of the separate clinical components of the primary outcome or other events, including recurrent infarction, unstable angina, and stroke. No significant difference in the safety profile was observed between the two treatment groups.

CONCLUSIONS

In patients with anterior STEMI who had been referred for primary PCI, intravenous cyclosporine did not result in better clinical outcomes than those with placebo and did not prevent adverse left ventricular remodeling at 1 year. (Funded by the French Ministry of Health and NeuroVive Pharmaceutical; CIRCUS ClinicalTrials.gov number, NCT01502774; EudraCT number, 2009-013713-99.).

Tissue kallikrein is required for the cardioprotective effect of cyclosporin A in myocardial ischemia in the mouse

Clinical and experimental studies suggest that pharmacological postconditioning with Cyclosporin A (CsA) reduces infarct size in cardiac ischemia and reperfusion. CsA interacts with Cyclophilin D (CypD) preventing opening of the mitochondrial permeability transition pore (mPTP). Tissue kallikrein (TK) and its products kinins are involved in cardioprotection in ischemia. CypD knockout mice are resistant to the cardioprotective effects of both CsA and kinins suggesting common mechanisms of action. Using TK gene knockout mice, we investigated whether the kallikrein-kinin system is involved in the cardioprotective effect of CsA. Homozygote and heterozygote TK deficient mice (TK(-/-), TK(+/-)) and wild type littermates (TK(+/+)) were subjected to cardiac ischemia-reperfusion with and without CsA postconditioning. CsA reduced infarct size in TK(+/+) mice but had no effect in TK(+/-) and TK(-/-) mice. Cardiac mitochondria isolated from TK(-/-) mice had indistinguishable basal oxidative phosphorylation and calcium retention capacity compared to TK(+/+) mice but were resistant to CsA inhibition of mPTP opening. TK activity was documented in mouse heart and rat cardiomyoblasts mitochondria. By proximity ligation assay TK was found in close proximity to the mitochondrial membrane proteins VDAC and Tom22, and CypD. Thus, partial or total deficiency in TK induces resistance to the infarct size reducing effect of CsA in cardiac ischemia in mice, suggesting that TK level is a critical factor for cardioprotection by CsA. TK is required for the mitochondrial action of CsA and may interact with CypD. Genetic variability in TK activity has been documented in man and may influence the cardioprotective effect of CsA.

Role of the MPTP in conditioning the heart - translatability and mechanism

Mitochondria have long been known to be the gatekeepers of cell fate. This is particularly so in the response to acute ischaemia‐reperfusion injury (IRI). Following an acute episode of sustained myocardial ischaemia, the opening of the mitochondrial permeability transition pore (MPTP) in the first few minutes of reperfusion, mediates cell death. Preventing MPTP opening at the onset of reperfusion using either pharmacological inhibitors [such as cyclosporin A (CsA) ] or genetic ablation has been reported to reduce myocardial infarct (MI) size in animal models of acute IRI. Interestingly, the endogenous cardioprotective intervention of ischaemic conditioning, in which the heart is protected against MI by applying cycles of brief ischaemia and reperfusion to either the heart itself or a remote organ or tissue, appears to be mediated through the inhibition of MPTP opening at reperfusion. Small proof‐of‐concept clinical studies have demonstrated the translatability of this therapeutic approach to target MPTP opening using CsA in clinical settings of acute myocardial IRI. However, given that CsA is a not a specific MPTP inhibitor, more novel and specific inhibitors of the MPTP need to be discovered – the molecular identification of the MPTP should facilitate this. In this paper, we review the role of the MPTP as a target for cardioprotection, the potential mechanisms underlying MPTP inhibition in the setting of ischaemic conditioning, and the translatability of MPTP inhibition as a therapeutic approach in the clinical setting.

Linked Articles

This article is part of a themed section on Conditioning the Heart – Pathways to Translation. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue‐8

Distinct cardioprotective mechanisms of immediate, early and delayed ischaemic postconditioning

Cardioprotection against ischaemia/reperfusion injury in mice can be achieved by delayed ischaemic postconditioning (IPost) applied as late as 30 min after the onset of reperfusion. We determined the efficacy of delayed IPost in a rat model of myocardial infarction (MI) and investigated potential underlying mechanisms of this phenomenon. Rats were subjected to 20, 30 or 45 min of coronary artery occlusion followed by 120 min of reperfusion (I/R). Immediate and early IPost included six cycles of I/R (10/10 s) applied 10 s or 10 min after reperfusion onset. In the second series of experiments, the rats were subjected to 30 min of coronary occlusion followed by IPost applied 10 s, 10, 30, 45 or 60 min after the onset of reperfusion. Immediate and early IPost (applied 10 s or 10 min of reperfusion) established cardioprotection only when applied after a period of myocardial ischaemia lasting 30 min. Delayed IPost applied after 30 or 45 min of reperfusion reduced infarct sizes by 36 and 41 %, respectively (both P < 0.01). IPost applied 60 min after reperfusion onset was ineffective. Inhibition of RISK pathway (administration of ERK1/2 inhibitor PD-98059 or PI3K inhibitor LY-294002) abolished cardioprotection established by immediate IPost but had no effect on cardioprotection conferred by early IPost. Blockade of SAFE pathway using JAK/STAT inhibitor AG490 had no effect on the immediate or early IPost cardioprotection. Blockade of mitochondrial KATP (mitoKATP) channels (with 5-Hydroxydecanoate) abolished cardioprotection achieved by immediate and early IPost, but had no effect on cardioprotection when IPost was applied 30 or 45 min into the reperfusion period. Immediate IPost increased phosphorylation of PI3K-AKT and ERK1/2. Early or delayed IPost had no effect on phosphorylation of PI3K-AKT, ERK1/2 or STAT3. These data show that in the rat model, delayed IPost confers significant cardioprotection even if applied 45 min after onset of reperfusion. Cardioprotection induced by immediate and early postconditioning involves recruitment of RISK pathway and/or mitoKATP channels, while delayed postconditioning appears to rely on a different mechanism.

Extracellular signalling molecules in the ischaemic/reperfused heart - druggable and translatable for cardioprotection?

In patients with acute myocardial infarction, timely reperfusion is essential to limit infarct size. However, reperfusion also adds to myocardial injury. Brief episodes of ischaemia/reperfusion in the myocardium or on organ remote from the heart, before or shortly after sustained myocardial ischaemia effectively reduce infarct size, provided there is eventual reperfusion. Such conditioning phenomena have been established in many experimental studies and also translated to humans. The underlying signal transduction, that is the molecular identity of triggers, mediators and effectors, is not clear yet in detail, but several extracellular signalling molecules, such as adenosine, bradykinin and opioids, have been identified to contribute to cardioprotection by conditioning manoeuvres. Several trials have attempted the translation of cardioprotection by such autacoids into a clinical scenario of myocardial ischaemia and reperfusion. Adenosine and its selective agonists reduced infarct size in a few studies, but this benefit was not translated into improved clinical outcome. All studies with bradykinin or drugs which increase bradykinin's bioavailability reported reduced infarct size and some of them also improved clinical outcome. Synthetic opioid agonists did not result in a robust infarct size reduction, but this failure of translation may relate to the cardioprotective properties of the underlying anaesthesia per se or of the comparator drugs. The translation of findings in healthy, young animals with acute coronary occlusion/reperfusion to patients of older age, with a variety of co-morbidities and co-medications, suffering from different scenarios of myocardial ischaemia/reperfusion remains a challenge.

The mitochondrial permeability transition: a current perspective on its identity and role in ischaemia/reperfusion injury

The mitochondrial permeability transition pore (MPTP) is a non-specific pore that opens in the inner mitochondrial membrane (IMM) when matrix [Ca(2+)] is high, especially when accompanied by oxidative stress, high [Pi] and adenine nucleotide depletion. Such conditions occur during ischaemia and subsequent reperfusion, when MPTP opening is known to occur and cause irreversible damage to the heart. Matrix cyclophilin D facilitates MPTP opening and is the target of its inhibition by cyclosporin A that is cardioprotective. Less certainty exists over the composition of the pore itself, with structural and/or regulatory roles proposed for the adenine nucleotide translocase, the phosphate carrier and the FoF1 ATP synthase. Here we critically review the supporting data for the role of each and suggest that they may interact with each other through their bound cardiolipin to form the ATP synthasome. We propose that under conditions favouring MPTP opening, calcium-triggered conformational changes in these proteins may perturb the interface between them generating the pore. Proteins associated with the outer mitochondrial membrane (OMM), such as members of the Bcl-2 family and hexokinase (HK), whilst not directly involved in pore formation, may regulate MPTP opening through interactions between OMM and IMM proteins at "contact sites". Recent evidence suggests that cardioprotective protocols such as preconditioning inhibit MPTP opening at reperfusion by preventing the loss of mitochondrial bound HK2 that stabilises these contact sites. Contact site breakage both sensitises the MPTP to [Ca(2+)] and facilitates cytochrome c loss from the intermembrane space leading to greater ROS production and further MPTP opening. This article is part of a Special Issue entitled "Mitochondria: From Basic Mitochondrial Biology to Cardiovascular Disease".

Targeting mitochondria for cardioprotection: examining the benefit for patients

ABSTRACT: 

Mitochondria are critical for sustaining life, not only as the essential powerhouses of cells but as critical mediators of cell survival and death. Mitochondrial dysfunction has been identified as a key perturbation underlying numerous pathologies including myocardial ischemia–reperfusion injury and the subsequent development of impaired left ventricular systolic function and compensatory cardiac hypertrophy. This article outlines the role of mitochondrial dysfunction in these important cardiac pathologies and highlights current cardioprotective strategies and their clinical efficacy in acute myocardial infarction and heart failure patients. Finally, we explore novel mitochondrial targets and evaluate their potential future translation for clinical cardioprotection.