Ischemic postconditioning: experimental models and protocol algorithms

The antiarrhythmic dipeptide ZP1609 (danegaptide) when given at reperfusion reduces myocardial infarct size in pigs

Connexin 43 is located in the cardiomyocyte sarcolemma and in the mitochondrial membrane. Sarcolemmal connexin 43 contributes to the spread of myocardial ischemia/reperfusion injury, whereas mitochondrial connexin 43 contributes to cardioprotection. We have now investigated the antiarrhythmic dipeptide ZP1609 (danegaptide), which is an analog of the connexin 43 targeting antiarrhythmic peptide rotigaptide (ZP123), in an established and clinically relevant experimental model of ischemia/reperfusion in pigs. Pigs were subjected to 60 min coronary occlusion and 3 h reperfusion. ZP1609 (n = 10) was given 10 min prior to reperfusion (75 μg/kg b.w. bolus i.v. + 57 μg/kg/min i.v. infusion for 3 h). Immediate full reperfusion (IFR, n = 9) served as control. Ischemic postconditioning (PoCo, n = 9; 1 min LAD reocclusion after 1 min reperfusion; four repetitions) was used as a positive control of cardioprotection. Infarct size (TTC) was determined as the end point of cardioprotection. Systemic hemodynamics and regional myocardial blood flow during ischemia were not different between groups. PoCo and ZP1609 reduced infarct size vs. IFR (IFR, 46 ± 4 % of area at risk; mean ± SEM; PoCo, 31 ± 4 %; ZP1609, 25 ± 5 %; both p < 0.05 vs. IFR; ANOVA). There were only few arrhythmias during reperfusion such that no antiarrhythmic action of ZP1609 was observed. ZP1609 when given before reperfusion reduces infarct size to a similar extent as ischemic postconditioning. Further studies are necessary to define the mechanism/action of ZP1609 on connexin 43 in cardiomyocytes.

Mechanisms involved in postconditioning protection of cardiomyocytes against acute reperfusion injury

Experimental and clinical studies demonstrated that postconditioning confers protection against myocardial ischemia/reperfusion injury. However the underlying cellular mechanisms responsible for the beneficial effect of postconditioning are still poorly understood. The aim of the present study was to examine the role of cytosolic and mitochondrial Ca(2+)-handling. For this purpose adult rat cardiomyocytes were subjected to simulated in vitro ischemia (glucose-free hypoxia at pH6.4) followed by simulated reperfusion with a normoxic buffer (pH7.4; 2.5 mmol/L glucose). Postconditioning, i.e., 2 repetitive cycles of normoxic (5s) and hypoxic (2.5 min) superfusion, was applied during the first 5 min of reoxygenation. Mitochondrial membrane potential (ΔΨm), cytosolic and mitochondrial Ca(2+) concentrations, cytosolic pH and necrosis were analysed applying JC-1, fura-2, fura-2/manganese, BCECF and propidium iodide, respectively. Mitochondrial permeability transition pore (MPTP) opening was detected by calcein release. Hypoxic treatment led to a reduction of ΔΨm, an increase in cytosolic and mitochondrial Ca(2+) concentration, and acidification of cardiomyocytes. During the first minutes of reoxygenation, ΔΨm transiently recovered, but irreversibly collapsed after 7 min of reoxygenation, which was accompanied by MPTP opening. Simultaneously, mitochondrial Ca(2+) increased during reperfusion and cardiomyocytes developed spontaneous cytosolic Ca(2+) oscillations and severe contracture followed by necrosis after 25 min of reoxygenation. In postconditioned cells, the collapse in ΔΨm as well as the leak of calcein, the increase in mitochondrial Ca(2+), cytosolic Ca(2+) oscillations, contracture and necrosis were significantly reduced. Furthermore postconditioning delayed cardiomyocyte pH recovery. Postconditioning by hypoxia/reoxygenation was as protective as treatment with cyclosporine A. Combining cyclosporine A and postconditioning had no additive effect. The data of the present study demonstrate that postconditioning by hypoxia/reoxygenation prevents reperfusion injury by limiting mitochondrial Ca(2+) load and thus opening of the MPTP in isolated cardiomyocytes. These effects seem to be supported by postconditioning-induced delay in pH recovery and suppression of Ca(2+) oscillations.

Coronary microembolization during early reperfusion: infarct extension, but protection by ischaemic postconditioning

AIMS

Reperfusion injury following acute myocardial infarction impacts not only on the myocardium but also on the coronary microcirculation, and microembolization from the culprit lesion contributes to microvascular obstruction. Prior experimental studies have not accounted for microembolization in ischaemia/reperfusion injury and not considered microembolization as a confounder and target of protection by ischaemic postconditioning. We therefore investigated the impact of microembolization during reperfusion on infarct size and cardioprotection by postconditioning.

METHODS AND RESULTS

Anaesthetized, open-chest pigs were subjected to 90 min low-flow ischaemia. Immediate full reperfusion (n = 8) served as the control. Microembolization was induced by intracoronary infusion of 42 µm microspheres with the onset of reperfusion (n = 8). In a second step, postconditioning was induced by six cycles of 20s reperfusion/20s re-occlusion without (n = 8) and with superimposed microembolization (n = 8). Transmural blood flow and area at risk were determined by radioactive microspheres, infarct size by triphenyl tetrazolium chloride staining. Area at risk and transmural blood flow were not different between groups. Microembolization increased infarct size from 32 ± 3% of the area at risk to 47 ± 3% (P < 0.05). Embolizing particles were re-distributed away from the central infarcted area and accumulated in the infarct border, thus contributing to infarct extension. Postconditioning reduced infarct size without (21 ± 3%; P < 0.05 vs. immediate full reperfusion) and also with additional microembolization (26 ± 5%; P < 0.05 vs. immediate full reperfusion and microembolization); embolizing particles did not accumulate in the infarct border.

CONCLUSION

Microembolization at reperfusion augments infarct size, but postconditioning in the presence of microembolization still reduces infarct size and attenuates infarct expansion.

Influence of tumour necrosis factor alpha on the outcome of ischaemic postconditioning in the presence of obesity and diabetes

Obesity and diabetes contribute to cardiovascular disease and alter cytokine profile. The cytokine, tumour necrosis factor alpha (TNFα), activates a protective signalling cascade during ischaemic postconditioning (IPostC). However, most successful clinical studies with IPostC have not included obese and/or diabetic patients. We aimed to investigate the influence of TNFα on the outcome of IPostC in obese or diabetic mice. TNF knockout or wildtype mice were fed for 11 weeks with a high carbohydrate diet (HCD) to induce modest obesity. Diabetes was induced in a separate group by administration of a single intraperitoneal injection of streptozotocin. Hearts were then isolated and subjected to ischaemia (35 min of global ischaemia) followed by 45 min of reperfusion. HCD increased body weight, plasma insulin and leptin levels while the glucose level was unchanged. In streptozotocin-treated mice, blood glucose, plasma leptin and insulin were altered. Control, obese or diabetic mice were protected with IPostC in wiltype animals. In TNF knockout mice, IPostC failed to protect control and diabetic hearts while a slight protection was observed in obese hearts. Our data confirm a bidirectional role for TNFα associated with the severity of concomitant comorbidities and suggest that diabetic and/or modestly obese patients may still benefit from IPostC.

Uncoupled eNOS annihilates neuregulin-1β-induced cardioprotection: a novel mechanism in pharmacological postconditioning in myocardial infarction

Myocardial infarct size can be limited by pharmacological postconditioning (pPC) with cardioprotective agents. Cardioprotective effects of neuregulin-1β (NRG) via activation of protein kinase B (Akt) and downstream pathways like endothelial nitric oxide synthase (eNOS) have been postulated based on results from cell culture experiments. The purpose of this study was to investigate if eNOS may be involved in pPC with NRG. NRG application in an ex vivo mouse model (C57Bl6) of ischemia-reperfusion injury was analyzed. Unexpectedly, the infarct size increased when NRG was infused starting 5 min prior to reperfusion, even though protective Akt and GSK3β phosphorylation were enhanced. In eNOS deficient mice, however, NRG significantly reduced the infarct size. Co-infusion of NRG and L-arginine (Arg) lead to a reduction in infarct size in wild type animals. Electron paramagnetic resonance measurements revealed that NRG treatment prior to reperfusion leads to an enhanced release of reactive oxygen species compared to controls and this effect is blunted by co-infusion of Arg. This study documents the cardioprotective mechanisms of NRG signaling to be mediated by GSK3β inactivation. This is the first study to show that this protection fails in situations with dysfunctional eNOS. In eNOS deficient mice NRG exerts its protective effect via the GSK3β pathway, suggesting that the eNOS can limit cardioprotection. As dysfunctional eNOS has been described in cardiovascular risk factors like diabetes, hypertension, and hypercholesterolemia these findings can help to explain lack of postconditioning performance in models of cardiovascular co-morbidities.

Delayed postconditioning: not too late?

Ischemic postconditioning applied at the onset of reperfusion reduces myocardial infarction in both animals and humans. Our recent study on the mouse myocardium showed for the first time that delayed postconditioning (applied up to 30 min after the onset of reperfusion) can decrease infarct size. The existence of a longer cardioprotection window is conceptually relevant for clinical application and also in the case of a pharmacological strategy.

Moderate elevation of intracellular creatine by targeting the creatine transporter protects mice from acute myocardial infarction

Aims

Increasing energy storage capacity by elevating creatine and phosphocreatine (PCr) levels to increase ATP availability is an attractive concept for protecting against ischaemia and heart failure. However, testing this hypothesis has not been possible since oral creatine supplementation is ineffectual at elevating myocardial creatine levels. We therefore used mice overexpressing creatine transporter in the heart (CrT-OE) to test for the first time whether elevated creatine is beneficial in clinically relevant disease models of heart failure and ischaemia/reperfusion (I/R) injury.

Methods and results

CrT-OE mice were selected for left ventricular (LV) creatine 20–100% above wild-type values and subjected to acute and chronic coronary artery ligation. Increasing myocardial creatine up to 100% was not detrimental even in ageing CrT-OE. In chronic heart failure, creatine elevation was neither beneficial nor detrimental, with no effect on survival, LV remodelling or dysfunction. However, CrT-OE hearts were protected against I/R injury in vivo in a dose-dependent manner (average 27% less myocardial necrosis) and exhibited greatly improved functional recovery following ex vivo I/R (59% of baseline vs. 29%). Mechanisms contributing to ischaemic protection in CrT-OE hearts include elevated PCr and glycogen levels and improved energy reserve. Furthermore, creatine loading in HL-1 cells did not alter antioxidant defences, but delayed mitochondrial permeability transition pore opening in response to oxidative stress, suggesting an additional mechanism to prevent reperfusion injury.

Conclusion

Elevation of myocardial creatine by 20–100% reduced myocardial stunning and I/R injury via pleiotropic mechanisms, suggesting CrT activation as a novel, potentially translatable target for cardiac protection from ischaemia.

Reperfusion-triggered stress protein response in the myocardium is blocked by post-conditioning. Systems biology pathway analysis highlights the key role of the canonical aryl-hydrocarbon receptor pathway

AIMS

Ischaemic post-conditioning (IPost-Co) exerts cardioprotection by diminishing ischaemia/reperfusion injury. Yet, the mechanisms involved in such protection remain largely unknown. We have investigated the effects of IPost-Co in cardiac cells and in heart performance using molecular, proteomic and functional approaches.

METHODS AND RESULTS

Pigs underwent 1.5 h mid-left anterior descending balloon occlusion and then were sacrificed without reperfusion (ischaemia; n= 7), subjected to 2.5 h of cardiac reperfusion and sacrificed (n= 5); or subjected to IPost-Co before reperfusion and sacrificed 0.5 h (n= 4) and 2.5 h (n= 5) afterwards. A sham-operated group was included (n= 4). Ischaemic and non-ischaemic myocardium was obtained for molecular/histological analysis. Proteomic analysis was performed by two-dimensional electrophoresis followed by matrix-assisted laser desorption/ionization-time-of-flight identification. Potential protein networks involved were identified by bioinformatics and Ingenuity Pathway Analysis (IPA). Cardiac function was assessed by echocardiography. IPost-Co diminished (up to 2.5 h) reperfusion-induced apoptosis of both the intrinsic and extrinsic pathways whereas it did not affect reperfusion-induced Akt/mammalian target of rapamycin (mTOR)/P70S6K activation. Proteomic studies showed that IPost-Co reverted 43% of cardiac cytoplasmic protein changes observed during ischaemia and ischaemia + reperfusion. Systems biology assessment revealed significant changes in the aryl-hydrocarbon receptor (AhR) pathway (cell damage related). Bioinformatic data were confirmed since the expression of HSP90, AhR, ANRT, and β-tubulin (involved in AhR-signalling transduction) were accordingly modified after IPost-Co. IPost-Co rescued 52% of the left ventricle-at-risk compared with reperfusion alone and resulted in a ≈30% relative improvement in left ventricular ejection fraction (P <0.05).

CONCLUSION

IPost-Co improves cardiac function post-myocardial infarction and reduces reperfusion-induced cell damage by down-regulation of the AhR-signalling transduction pathway ultimately leading to infarct size reduction.

Remote ischemic perconditioning--a simple, low-risk method to decrease ischemic reperfusion injury: models, protocols and mechanistic background. A review

Interruption of blood flow can cause ischemic reperfusion injury, which sometimes has a fatal outcome. Recognition of the phenomenon known as reperfusion injury has led to initial interventional approaches to lessen the degree of damage. A number of efficient pharmacologic agents and surgical techniques (e.g., local ischemic preconditioning and postconditioning) are available. A novel, alternative approach to target organ protection is remote ischemic conditioning triggered by brief repetitive ischemia and reperfusion periods in distant organs. Among the different surgical techniques is so-called remote ischemic perconditioning, a method that applies short periods of ischemic reperfusion to a distant organ delivered during target organ ischemia. Although ischemic reperfusion injury is reduced by this technique, the explanation for this phenomenon is still unclear, and approximately only a dozen reports on the topic have appeared in the literature. In our study, therefore, we investigated the connective mechanisms, signal transduction, and effector mechanisms behind remote perconditioning, with a review on molecular background and favorable effects. In addition, we summarize the various treatment protocols and models to promote future experimental and clinical research.

Upregulation of cytochrome P450 2J3/11,12-epoxyeicosatrienoic acid inhibits apoptosis in neonatal rat cardiomyocytes by a caspase-dependent pathway

Short, nonlethal ischemic episodes administered to hearts directly after ischemic events (ischemic postconditioning, IPost) have an advantage over ischemic preconditioning (IPC). The endogenous cytochrome P450 2J3/11,12-epoxyeicosatrienoic acid (CYP2J3/11,12-EET) is upregulated by IPost, but not IPC, in the rat heart. The CYP epoxygenase inhibitor N-methylsulphonyl-6-(2-propargyloxyphenyl) hexanamide (MS-PPOH) reduces the cardioprotective effects of IPost, but not IPC. We proposed that upregulation of CYP2J3/11,12-EET during IPost induces cardioprotection by inhibiting cardiomyocyte apoptosis and that multiple apoptotic signals, including changes in mitochondrial membrane potential (MMP) and mitochondrial permeability transition pore (mPTP) opening, mitochondrial cytochrome c leakage, caspase-3 levels, and levels of protective kinases such as Bcl-2 and Bax, are involved in the process. Neonatal rat cardiomyocytes underwent 3-h hypoxia followed by 2-, 5-, or 6-h reoxygenation (H/R) or three cycles of 5-min reoxygenation followed by 5-min hypoxia before 90-min reoxygenation (HPost); or were transfected with pcDNA3.1-CYP2J3 for 48 h before H/R; or were treated with MS-PPOH for 10 min before HPost. For HPost alone, pcDNA3.1-CYP2J3 transfection attenuated cardiomyocyte apoptosis to 68.4% (p<0.05) of that with H/R. pcDNA3.1-CYP2J3 transfection significantly decreased MMP and inhibited mPTP opening induced by H/R, reduced mitochondrial cytochrome c leakage, cleaved caspase-3 protein expression, and increased the ratio of Bcl-2 to Bax expression. MS-PPOH abolished this effect. Therefore, upregulation of CYP2J3/11,12-EET during HPost is involved in cardioprotection by inhibiting apoptosis via a caspase-dependent pathway, and the apoptosis-suppressive effect may have important clinical implications during HPost.

Post-cardiac arrest myocardial dysfunction is improved with cyclosporine treatment at onset of resuscitation but not in the reperfusion phase

AIM OF STUDY

Significant myocardial dysfunction and high mortality occur after whole-body ischaemia-eperfusion injuries in the post-cardiac arrest status. The inhibition of mitochondrial permeability transition pore (mPTP) opening during ischaemia-reperfusion can ameliorate injuries in the specific organs. We investigated the effect and therapeutic window of pharmacological inhibition of mPTP opening in cardiac arrest.

METHODS

Forty male Wistar rats were resuscitated after cardiac arrest induced by 8.5 min of asphyxia. Cyclosporine (10 mg/kg) was administered intravenously at onset of resuscitation in protocol 1 study and administered 3 min after ROSC in protocol 2 with placebo control in both.

RESULTS

Left ventricular systolic (dP/dt 40), diastolic (maximal negative dP/dt) functions and cardiac output were improved in the group with cyclosporine treatment at onset of resuscitation compared to control group (p < 0.01, respectively). Seventy-two hour survival was better in the group with cyclosporine treatment at onset of resuscitation compared to control (p = 0.046). Left ventricular systolic and diastolic function, cardiac output and 72 h survival were not improved in the group with cyclosporine treatment 3 min after ROSC. The severity of mitochondrial damage under electronic microscopy, mPTP opening, mitochondrial respiratory control ratio and ADP:O ratio were ameliorated in the group with cyclosporine treatment at onset of resuscitation (p< 0.05, respectively) but not in the group with cyclosporine treatment at 3 min after ROSC.

CONCLUSIONS

Post-cardiac arrest myocardial dysfunction and survival can be improved by cyclosporine treatment at onset of resuscitation, but not by the cyclosporine treatment at 3 min after ROSC.

Cardioprotection from ischemia/reperfusion injury: basic and translational research

Because ischemic heart diseases (IHDs) are a major cause of mortality and heart failure, novel therapeutic approaches are expected to improve the clinical outcomes of patients with IHDs such as acute myocardial infarction and ischemic heart failure. Brief episodes of nonlethal ischemia and reperfusion before sustained ischemia or at the onset of reperfusion can reduce ischemia-reperfusion injury. These ischemic conditioning phenomena are termed "ischemic preconditioning" and "ischemic postconditioning", respectively. Furthermore, brief episodes of nonlethal ischemia and reperfusion applied to the organ or tissue distal to the heart reduce myocardial infarct size, known as "remote ischemic conditioning". The cardioprotection afforded by these ischemic conditionings can be used to treat patients with acute myocardial infarction or cardiac operations. Extensive research has determined that autacoids (eg, adenosine, bradykinin opioid) and cytokines, their respective receptors, kinase signaling pathways and mitochondrial modulation are involved in ischemic conditioning. Modification of these factors by pharmacological agents mimics the cardioprotection by ischemic conditioning and provides a novel therapeutic intervention for IHDs. Here, the potential mechanisms of ischemic conditioning and its "proof-of-concept" translational studies are reviewed. In the near future, large, multicenter, randomized, placebo-controlled, clinical trials will be required to determine whether pharmacological and ischemic conditioning can improve the clinical outcomes of patients with IHDs.

Protective effect of ischemic postconditioning against ischemia reperfusion-induced myocardium oxidative injury in IR rats

Brief episodes of myocardial ischemia-reperfusion (IR) employed during reperfusion after a prolonged ischemic insult may attenuate the total ischemia-reperfusion injury. This phenomenon has been termed ischemic postconditioning. In the present study, we studied the possible effect of ischemic postconditioning on an ischemic reperfusion (IR)-induced myocardium oxidative injury in rat model. Results showed that ischemic postconditioning could improve arrhythmia cordis, reduce myocardium infarction and serum creatin kinase (CK), lactate dehydrogenase (LDH) and aspartate transaminase (AST) activities in IR rats. In addition, ischemic postconditioning could still decrease myocardium malondialdehyde (MDA) level, and increased myocardium Na+-K+-ATPase, Ca2+-Mg2+-ATPase, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) and glutathione reductase (GR) activities. It can be concluded that ischemic postconditioning possesses strong protective effects against ischemia reperfusion-induced myocardium oxidative injury in IR rats.

Adjuvant early and late cardioprotective therapy: access to the heart

Coronary heart disease is still the leading cause of death in industrialized nations, occurring either as acute coronary occlusion and myocardial infarction or as chronic ischaemic cardiomyopathy caused by continuous obstruction of one or more coronary arteries. Even after successful reperfusion, an additional loss of otherwise vital cardiomyocytes may occur in the primary ischaemic area, called lethal reperfusion injury. In experimental settings, delivery of therapeutic agents targeting the reperfusion injury reduces the infarct size by 30%. In addition to the choice of therapeutic agent and time point, the mode of application may be crucial for the therapeutic success. Therefore, this review focuses on the current and future administration techniques for early and late post-myocardial infarction therapies.

Mesenchymal stem cell exosome: a novel stem cell-based therapy for cardiovascular disease

Cardiovascular disease is a major target for many experimental stem cell-based therapies and mesenchymal stem cells (MSCs) are widely used in these therapies. Transplantation of MSCs to treat cardiac disease has always been predicated on the hypothesis that these cells would engraft, differentiate and replace damaged cardiac tissues. However, experimental or clinical observations so far have failed to demonstrate a therapeutically relevant level of transplanted MSC engraftment or differentiation. Instead, they indicate that transplanted MSCs secrete factors to reduce tissue injury and/or enhance tissue repair. Here we review the evidences supporting this hypothesis including the recent identification of exosome as a therapeutic agent in MSC secretion. In particular, we will discuss the potential and practicality of using this relatively novel entity as a therapeutic modality for the treatment of cardiac disease, particularly acute myocardial infarction.

The role of mitochondrial permeability transition in reperfusion-induced cardiomyocyte death depends on the duration of ischemia

Mitochondrial permeability transition (MPT) is critical in cardiomyocyte death during reperfusion but it is not the only mechanism responsible for cell injury. The objectives of the study is to investigate the role of the duration of myocardial ischemia on mitochondrial integrity and cardiomyocyte death. Mitochondrial membrane potential (ΔΨm, JC-1) and MPT (calcein) were studied in cardiomyocytes from wild-type and cyclophilin D (CyD) KO mice refractory to MPT, submitted to simulated ischemia and 10 min reperfusion. Reperfusion after 15 min simulated ischemia induced a rapid recovery of ΔΨm, extreme cell shortening (contracture) and mitochondrial calcein release, and CyD ablation did not affect these changes or cell death. However, when reperfusion was performed after 25 min simulated ischemia, CyD ablation improved ΔΨm recovery and reduced calcein release and cell death (57.8 ± 4.9% vs. 77.3 ± 4.8%, P < 0.01). In a Langendorff system, CyD ablation increased infarct size after 30 min of ischemia (61.3 ± 6.4% vs. 45.3 ± 4.0%, P = 0.02) but reduced it when ischemia was prolonged to 60 min (52.8 ± 8.1% vs. 87.6 ± 3.7%, P < 0.01). NMR spectroscopy in rat hearts showed a rapid recovery of phosphocreatine after 30 min ischemia followed by a marked decay associated with contracture and LDH release, that were preventable with contractile blockade but not with cyclosporine A. In contrast, after 50 min ischemia, phosphocreatine recovery was impaired even with contractile blockade (65.2 ± 4% at 2 min), and cyclosporine A reduced contracture, LDH release and infarct size (52.1 ± 4.2% vs. 82.8 ± 3.6%, P < 0.01). In conclusion, the duration of ischemia critically determines the importance of MPT on reperfusion injury. Mechanisms other than MPT may play an important role in cell death after less severe ischemia.

The potential effects of anti-diabetic medications on myocardial ischemia-reperfusion injury

Heart disease and stroke account for 65% of the deaths in people with diabetes mellitus (DM). DM and hyperglycemia cause systemic inflammation, endothelial dysfunction, a hypercoagulable state with impaired fibrinolysis and increased platelet degranulation, and reduced coronary collateral blood flow. DM also interferes with myocardial protection afforded by preconditioning and postconditioning. Newer anti-diabetic agents should not only reduce serum glucose and HbA1c levels, but also improve cardiovascular outcomes. The older sulfonylurea agent, glyburide, abolishes the benefits of ischemic and pharmacologic preconditioning, but newer sulfonylurea agents, such as glimepiride, may not interfere with preconditioning. GLP-1 analogs and sitagliptin, an oral dipeptidyl peptidase IV inhibitor, limit myocardial infarct size in animal models by increasing intracellular cAMP levels and activating protein kinase A, whereas metformin protects the heart by activating AMP-activated protein kinase. Both thiazolidinediones (rosiglitazone and pioglitazone) limit infarct size in animal models. The protective effect of pioglitazone is dependent on downstream activation of cytosolic phospholipase A(2) and cyclooxygenase-2 with subsequent increased production of 15-epi-lipoxin A(4), prostacyclin and 15-d-PGJ(2). We conclude that agents used to treat DM have additional actions that have been shown to affect the ability of the heart to protect itself against ischemia-reperfusion injury in preclinical models. However, the effects of these agents in doses used in the clinical setting to minimize ischemia-reperfusion injury and to affect clinical outcomes in patients with DM have yet to be shown. The clinical implications as well as the mechanisms of protection should be further studied.

Cardioprotection by Ivabradine Through Heart Rate Reduction and Beyond

The present review summarizes the experimental and clinical evidence for the anti-ischemic action of the selective bradycardic agent ivabradine. Improvements in myocardial blood flow and contractile function during experimental myocardial ischemia and the clinical anti-anginal effect are largely mediated by heart rate reduction. However, a significant reduction in infarct size by ivabradine persists in the absence of heart rate reduction, and such protection can also be recruited when ivabradine is given only during early reperfusion. The mechanisms for such pleiotropic action of ivabradine remain to be resolved.

Delayed postconditioning in the mouse heart in vivo

BACKGROUND

Reperfusion during acute myocardial infarction remains the best treatment for reducing infarct size. Postconditioning, applied at the onset of reperfusion, reduces myocardial infarction both in animals and humans. The objective of this study was to identify the time delay to apply postconditioning at reperfusion, allowing preservation of cardioprotection in the mouse myocardium. This is a major issue in the management of acute myocardial infarction patients.

METHODS AND RESULTS

Mice were subjected to 40 minutes of ischemia and 60 minutes of reperfusion (IR(60')). Postconditioning protocols corresponding to repetitive ischemia (3 cycles of 1 minute of ischemia and 1 minute of reperfusion) were applied during early reperfusion at various time durations (Δt) after reopening of the coronary artery (Δt=10 seconds, 1, 5, 10, 15, 20, 30, and 45 minutes; PostC(Δt)). Infarct size/area at risk was reduced by 71% in PostC(Δ1) compared with IR(60') mice (P=5×10(-6)). There was a linear correlation (r(2)=0.91) between infarct size and Δt, indicating that the cardioprotective effect of delayed postconditioning was progressively attenuated when Δt time increased. The protective effect of PostC(Δ1) and PostC(Δ15) was still effective when the duration of reperfusion was prolonged to 24 hours (IR(24 hours); PostC(Δ1) and PostC(Δ15) versus IR(24 hours), P=0.001). Similar results were obtained for internucleosomal DNA fragmentation and lactate dehydrogenase release.

CONCLUSIONS

This study in our in vivo mouse model of myocardial IR shows for the first time that delaying the intervention of postconditioning to 30 minutes does not abrogate the cardioprotective effect of postconditioning. This finding provides evidence that the time window of protection afforded by postconditioning may be larger than initially reported.

Determination of the myocardial area at risk with pre- versus post-reperfusion imaging techniques in the pig model

The purpose of this study was to compare the accuracy of post-reperfusion cardiac magnetic resonance (CMR) and pre-reperfusion multidetector computed tomography (MDCT) imaging to measure the size of the area at risk (AAR), using pathology as a reference technique in a porcine acute myocardial infarction model. Fifteen pigs underwent balloon-induced coronary artery occlusion for 40 min followed by reperfusion. The AAR was assessed with arterial enhanced MDCT performed during occlusion, while two different T2 weighted (T2W) CMR imaging sequences and the contrast-enhanced (ce-) CMR endocardial surface length (ESL) were performed after 90 min of reperfusion. Animals were euthanized and the AAR was assessed by pathology. Additional measurements of the myocardial water content in the AAR, remote and the AAR border zones were performed. AAR by pathology best correlated with measurements made by MDCT (R(2) = 0.88; p < 0.001) with little bias on Bland-Altman plots (bias 2.5%, SD 6.1% LV area). AAR measurements obtained by T2W STIR, T2W ACUTE sequences or the ESL on ce-CMR showed a fair correlation with pathology (R(2) = 0.72, R(2) = 0.65 and R(2) = 0.69, respectively; all p ≤ 0.001), but significantly overestimated the size of the AAR with important bias (17.4 ± 10.8% LV area; 11.7 ± 11.0% LV area; 13.0 ± 10.3% LV area, respectively). The myocardial water content in the AAR border zones was significantly higher than the remote (82.8 vs. 78.8%; p < 0.001). Our data suggest that post-reperfusion imaging methods overestimated the AAR likely due to the presence of edema outside of the boundaries of the AAR. Pre-reperfusion arterial enhanced MDCT showed the greatest accuracy for the assessment of the AAR.

Pathophysiology of myocardial reperfusion injury: preconditioning, postconditioning, and translational aspects of protective measures

Heart diseases due to myocardial ischemia, such as myocardial infarction or ischemic heart failure, are major causes of death in developed countries, and their number is unfortunately still growing. Preliminary exploration into the pathophysiology of ischemia-reperfusion injury, together with the accumulation of clinical evidence, led to the discovery of ischemic preconditioning, which has been the main hypothesis for over three decades for how ischemia-reperfusion injury can be attenuated. The subcellular pathophysiological mechanism of ischemia-reperfusion injury and preconditioning-induced cardioprotection is not well understood, but extensive research into components, including autacoids, ion channels, receptors, subcellular signaling cascades, and mitochondrial modulators, as well as strategies for modulating these components, has made evolutional progress. Owing to the accumulation of both basic and clinical evidence, the idea of ischemic postconditioning with a cardioprotective potential has been discovered and established, making it possible to apply this knowledge in the clinical setting after ischemia-reperfusion insult. Another a great outcome has been the launch of translational studies that apply basic findings for manipulating ischemia-reperfusion injury into practical clinical treatments against ischemic heart diseases. In this review, we discuss the current findings regarding the fundamental pathophysiological mechanisms of ischemia-reperfusion injury, the associated protective mechanisms of ischemic pre- and postconditioning, and the potential seeds for molecular, pharmacological, or mechanical treatments against ischemia-reperfusion injury, as well as subsequent adverse outcomes by modulation of subcellular signaling mechanisms (especially mitochondrial function). We also review emerging translational clinical trials and the subsistent clinical comorbidities that need to be overcome to make these trials applicable in clinical medicine.

RISK and SAFE signaling pathway interactions in remote limb ischemic perconditioning in combination with local ischemic postconditioning

Local ischemic postconditioning (IPost) and remote ischemic perconditioning (RIPer) are promising methods to decrease ischemia-reperfusion (I/R) injury. We tested whether the use of the two procedures in combination led to an improvement in cardioprotection through a higher activation of survival signaling pathways. Rats exposed to myocardial I/R were allocated to one of the following four groups: Control, no intervention at myocardial reperfusion; IPost, three cycles of 10-s coronary artery occlusion followed by 10-s reperfusion applied at the onset of myocardial reperfusion; RIPer, 10-min limb ischemia followed by 10-min reperfusion initiated 20 min after coronary artery occlusion; IPost+RIPer, IPost and RIPer in combination. Infarct size was significantly reduced in both IPost and RIPer (34.25 ± 3.36 and 24.69 ± 6.02%, respectively) groups compared to Control (54.93 ± 6.46%, both p < 0.05). IPost+RIPer (infarct size = 18.04 ± 4.86%) was significantly more cardioprotective than IPost alone (p < 0.05). RISK pathway (Akt, ERK1/2, and GSK-3β) activation was enhanced in IPost, RIPer, and IPost+RIPer groups compared to Control. IPost+RIPer did not enhance RISK pathway activation as compared to IPost alone, but instead increased phospho-STAT-3 levels, highlighting the crucial role of the SAFE pathway. In IPost+RIPer, a SAFE inhibitor (AG490) abolished cardioprotection and blocked both Akt and GSK-3β phosphorylations, whereas RISK inhibitors (wortmannin or U0126) abolished cardioprotection and blocked STAT-3 phosphorylation. In our experimental model, the combination of IPost and RIPer improved cardioprotection through the recruitment of the SAFE pathway. Our findings also indicate that cross talk exists between the RISK and SAFE pathways.

Ischemia/reperfusion injury and cardioprotective mechanisms: Role of mitochondria and reactive oxygen species

Reperfusion therapy must be applied as soon as possible to attenuate the ischemic insult of acute myocardial infarction (AMI). However reperfusion is responsible for additional myocardial damage, which likely involves opening of the mitochondrial permeability transition pore (mPTP). In reperfusion injury, mitochondrial damage is a determining factor in causing loss of cardiomyocyte function and viability. Major mechanisms of mitochondrial dysfunction include the long lasting opening of mPTPs and the oxidative stress resulting from formation of reactive oxygen species (ROS). Several signaling cardioprotective pathways are activated by stimuli such as preconditioning and postconditioning, obtained with brief intermittent ischemia or with pharmacological agents. These pathways converge on a common target, the mitochondria, to preserve their function after ischemia/reperfusion. The present review discusses the role of mitochondria in cardioprotection, especially the involvement of adenosine triphosphate-dependent potassium channels, ROS signaling, and the mPTP. Ischemic postconditioning has emerged as a new way to target the mitochondria, and to drastically reduce lethal reperfusion injury. Several clinical studies using ischemic postconditioning during angioplasty now support its protective effects, and an interesting alternative is pharmacological postconditioning. In fact ischemic postconditioning and the mPTP desensitizer, cyclosporine A, have been shown to induce comparable protection in AMI patients.

Ischemic postconditioning: from receptor to end-effector

Ischemic preconditioning, a robust cardioprotective intervention, has limited clinical efficacy because it must be initiated before myocardial ischemia. Conversely, ischemic postconditioning, repeated brief reocclusions of a coronary artery after release of prolonged coronary occlusion, provides cardioprotection in clinically feasible settings, that is, coronary angioplasty. Ischemic postconditioning's signaling is being investigated to identify pharmacological triggers that could be used without angioplasty. In initial minutes of reperfusion H(+) washes out of previously ischemic cells. pH rises enabling mitochondrial permeability transition pores (MPTPs) to form leading to cessation of ATP production and cell necrosis. Coronary reocclusions maintain sufficient acidosis to keep MPTP closed while signaling is initiated that can generate endogenous antagonists of MPTP formation even after cellular pH normalizes. Reintroduction of oxygen generates reactive oxygen species that activate protein kinase C to increase sensitivity of adenosine A(2b) receptors allowing adenosine released from ischemic cells to bind leading to activation of phosphatidylinositol 3-kinase and extracellular signal-regulated kinase 1/2. Phosphatidylinositol 3-kinase activation results in phosphorylation of Akt promoting activation of nitric oxide synthase and nitric oxide production, which inhibits glycogen synthase kinase-3β, perhaps the final cytosolic signaling step before inhibition of MPTP formation. Interference with MPTP may be the final step that determines cell salvage.

Effect of apelin-apelin receptor system in postischaemic myocardial protection: a pharmacological postconditioning tool?

In the heart, a great part of ischaemia and reperfusion injuries occurs mainly during the first minutes of reperfusion. The opening of the mitochondrial permeability transition pores is the end point of the cascade to myocardial damage. Also, oxidative stress contributes to cell death. Postconditioning is a protective maneuver that can be selectively timed at the beginning of reperfusion. It is hypothesized that it acts via the reperfusion injury salvage kinase pathway, which includes nitric oxide-dependent and nitric oxide-independent cascades. Apelin is an endogenous peptide that can protect the heart from reperfusion injury if given at the beginning of reperfusion but not before ischaemia. It is hypothesized that it may trigger the reperfusion injury salvage kinase pathway via a specific apelin receptor. Apelin can also limit the oxidative stress by the activation of superoxide dismutase. Apelin and apelin receptor expression increase early after ischaemia and at the beginning of an ischaemic heart failure. These observations suggest that the endogenous release of the peptide can limit the severity of an infarction and ameliorate myocardial contractility compromised by the appearance of the failure. Due to its protective activities, apelin could be a therapeutic tool if administered with the same catheter used for angioplasty or after the maneuvers aimed at bypassing a coronary occlusion.

Contribution of delayed intracellular pH recovery to ischemic postconditioning protection

Ischemic postconditioning (PoCo) has been proven to be a feasible approach to attenuate reperfusion injury and enhance myocardial salvage in patients with acute myocardial infarction, but its mechanisms have not been completely elucidated yet. Recent studies demonstrate that PoCo may delay the recovery of intracellular pH during initial reperfusion, and that its ability to limit infarct size critically depends on this effect. Prolongation of postischemic intracellular acidosis inhibits hypercontracture, mitochondrial permeability transition, calpain-mediated proteolysis, and gap junction-mediated spread of injury during the first minutes of reflow. This role of prolonged acidosis does not exclude the participation of other pathways in PoCo-induced cardioprotection. On the contrary, it may allow these pathways to act by preventing immediate reperfusion-induced cell death. Moreover, the existence of interactions between intracellular acidosis and endogenous protection signaling cannot be excluded and needs to be investigated. The role of prolonged acidosis in PoCo cardioprotection has important implications in the design of optimal PoCo protocols and in the translation of cardioprotective strategies to patients with on-going myocardial infarction receiving coronary reperfusion.

Cardioprotective pathways during reperfusion: focus on redox signaling and other modalities of cell signaling

Post-ischemic reperfusion may result in reactive oxygen species (ROS) generation, reduced availability of nitric oxide (NO•), Ca(2+)overload, prolonged opening of mitochondrial permeability transition pore, and other processes contributing to cell death, myocardial infarction, stunning, and arrhythmias. With the discovery of the preconditioning and postconditioning phenomena, reperfusion injury has been appreciated as a reality from which protection is feasible, especially with postconditioning, which is under the control of physicians. Potentially cooperative protective signaling cascades are recruited by both pre- and postconditioning. In these pathways, phosphorylative/dephosphorylative processes are widely represented. However, cardioprotective modalities of signal transduction also include redox signaling by ROS, S-nitrosylation by NO• and derivative, S-sulfhydration by hydrogen sulfide, and O-linked glycosylation with beta-N-acetylglucosamine. All these modalities can interact and regulate an entire pathway, thus influencing each other. For instance, enzymes can be phosphorylated and/or nitrosylated in specific and/or different site(s) with consequent increase or decrease of their specific activity. The cardioprotective signaling pathways are thought to converge on mitochondria, and various mitochondrial proteins have been identified as targets of these post-transitional modifications in both pre- and postconditioning.

cGMP/PKG pathway mediates myocardial postconditioning protection in rat hearts by delaying normalization of intracellular acidosis during reperfusion

Ischemic postconditioning has been demonstrated to limit infarct size in patients, but its molecular mechanisms remain incompletely understood. Low intracellular pH (pHi) inhibits mitochondrial permeability transition, calpain activation and hypercontracture. Recently, delayed normalization of pHi during reperfusion has been shown to play an important role in postconditioning protection, but its relation with intracellular protective signaling cascades is unknown. The present study investigates the relation between the rate of pHi normalization and the cGMP/PKG pathway in postconditioned myocardium. In isolated Sprague-Dawley rat hearts submitted to transient ischemia both, postconditioning and acidic reperfusion protocols resulted in a similar delay in pHi recovery measured by (31)P-NMR spectroscopy (3.6±0.2min and 3.5±0.2min respectively vs. 1.4±0.2min in control group, P<0.01) and caused equivalent cardioprotection (48% and 41% of infarct reduction respectively, P<0.01), but only postconditioning increased myocardial cGMP levels (P=0.02) and activated PKG. Blockade of cGMP/PKG pathway by the addition of the guanylyl cyclase inhibitor ODQ or the PKG inhibitor KT5823 during reperfusion accelerated pHi recovery and abolished cardioprotection in postconditioned hearts, but had no effect in hearts subjected to acidic reperfusion suggesting that PKG signaling was upstream of delayed pHi normalization in postconditioned hearts. In isolated cardiomyocytes the cGMP analog 8-pCPT-cGMP delayed Na(+)/H(+)-exchange mediated pHi normalization after acidification induced by a NH(4)Cl pulse. These results demonstrate that the cGMP/PKG pathway contributes to postconditioning protection at least in part by delaying normalization of pHi during reperfusion, probably via PKG-dependent inhibition of Na(+)/H(+)-exchanger.

The combination of L-arginine and ischaemic post-conditioning at the onset of reperfusion limits myocardial injury in the pig

AIM

To investigate whether ischaemic post-conditioning (IPoC) combined with i.v. infusion of the nitric oxide (NO) substrate L-arginine at the onset of reperfusion exerts cardioprotective effect that is superior to either treatment given separately.

METHODS

Twenty-six anesthetized pigs were subjected to coronary artery (left anterior descending artery, LAD) ligation for 40 min followed by 4 h reperfusion. The pigs were randomized into five different groups receiving either i.v. vehicle, i.v. L-arginine, IPoC 4 × 60 s together with i.v. vehicle or IPoC together with i.v. L-arginine and a group with IPoC 8 × 30 s. All infusions were started 10 min before reperfusion.

RESULTS

The infarct size of the vehicle group was 82 ± 4% of the area at risk. L-Arginine alone (79 ± 8%), IPoC 4 × 60 s vehicle (86 ± 3%) or IPoC 8 × 30 s vehicle (94 ± 7%) did not affect infarct size. l-Arginine together with IPoC significantly reduced infarct size to 59 ± 4% (P < 0.01). Except for higher LAD flow during early reperfusion in the IPoC L-arginine group, haemodynamic parameters did not differ between the four main groups. Heart rate and rate pressure product were lower during ischaemia and reperfusion in the IPoC 8 × 30 s vehicle group. In comparison with the vehicle group, there were no changes in the expression of Akt, phosphorylated Akt Ser(473) , inducible NO synthase, endothelial NO synthase (eNOS) or phosphorylated eNOS Ser(1177) in the ischaemic/reperfused myocardium.

CONCLUSION

L-Arginine given systemically at the onset of reperfusion protects the pig heart against ischaemia and reperfusion injury only when combined with IPoC. These results indicate that the combination of the two treatment strategies exerts cardioprotection.

Endothelial NOS activity and myocardial oxygen metabolism define the salvageable ischemic time window for ischemic postconditioning

Ischemic postconditioning (IPOC) could be ineffective or even detrimental if the index ischemic duration is either too short or too long. The present study is to demonstrate that oxygen supply and metabolism defines a salvageable ischemic time window of IPOC in mice. C57BL/6 mice underwent coronary artery occlusion followed by reperfusion (I/R), with or without IPOC by three cycles of 10 s/10 s R/I. In vivo myocardial tissue oxygenation was monitored with electron paramagnetic resonance oximetry. Regional blood flow (RBF) was measured with a laser Doppler monitor. At the end of 60 min reperfusion, tissue from the risk area was collected, and mitochondrial enzyme activities were assayed. Tissue oximetry demonstrated that I/R induced a reperfusion hyperoxygenation state in the 30- and 45-min but not 15- and 60-min ischemia groups. IPOC attenuated the hyperoxygenation with 45 but not 30 min ischemia. RBF, eNOS phosphorylation, and mitochondrial enzyme activities were suppressed after I/R with different ischemic time, and IPOC afforded protection with 30 and 45 but not 60 min ischemia. Infarct size measurement indicated that IPOC reduced infarction with 30 and 45 min but not 60 min ischemia. Clearly, IPOC protected mouse heart with a defined ischemic time window between 30 and 45 min. This salvageable time window was accompanied by the improvement of RBF due to increased phosphorylated eNOS and the preservation of mitochondrial oxygen consumption due to conserved mitochondrial enzyme activities. Interestingly, this salvageable ischemic time window was mirrored by tissue hyperoxygenation status in the postischemic heart.

Synergistic protection of Danhong injection (丹红注射液) and ischemic postconditioning on myocardial reperfusion injury in minipigs

OBJECTIVE

To explore the synergistic protection of Danhong Injection (丹红注射液, DHI) and ischemic postconditioning on myocardial reperfusion injury in minipigs.

METHODS

Acute myocardial infarction model was made by balloon occlusion in left anterior descending coronary artery (LAD) of minipigs, and then postconditioning was simulated through inflation/deflation of the angioplasty balloon. Minipigs were divided into four groups: the sham operation group (SH group), the ischemia/reperfusion group (I/R group), the ischemic postconditioning group (POC group) and DHI combined with ischemic postconditioning group (PAD group, DHI 20 mL through ear vein), six in each group. After 24-h continuous observation, myocardial infarction size was assessed by triphenyltetrazolium staining (TTC). Morphological changes of ischemic myocardium were observed by light microscopy, and cardiomyocyte ultrastructure was studied with electron microscopy. The superoxide dismutase (SOD) and malondialdehyde (MDA) activity in heart homogenates were measured by a biochemical method.

RESULTS

The myocardial infarction size was smaller in the POC group than in the I/R group (0.26 ± 0.02 vs. 0.37 ± 0.09, P<0.05), and the PAD group (0.14 ± 0.08) displayed a significantly reduced infarction size relative to the I/R group (P<0.01) and POC group (P<0.05). The damage of myocardial tissue was severe in the I/R group shown by light and electron microscopy: myocardial fibers disorder, sarcoplasmic dissolution, myofilament fracture, mitochondria swelling and even vacuolization formation and a large number of inflammatory cell infiltrations. Compared with the I/R group, reduction of reperfusion injury in the PAD group included more orderly arranged myocardial fibers, less infiltration of inflammatory cells and maintenance of mitochondrial integrity. Compared with the I/R group, the damage of myocardial tissue in the POC group was improved, but not as significant as that in the PAD group. SOD levels in the POC group and the PAD group were significantly higher than those in the I/R group (96.96 ± 13.43, 112.25 ± 22.75 vs. 76.32 ± 10.63, P<0.05), and MDA was significantly lower in the POC group and the PAD group compared to the I/R group (1.27 ± 0.19, 1.09 ± 0.21 vs. 1.47 ± 0.16, P<0.05).

CONCLUSION

DHI and ischemic postconditioning show a synergistic cardioprotection on myocardial reperfusion injury in minipigs.

Translating novel strategies for cardioprotection: the Hatter Workshop Recommendations

Ischemic heart disease (IHD) is the leading cause of death worldwide. Novel cardioprotective strategies are therefore required to improve clinical outcomes in patients with IHD. Although a large number of novel cardioprotective strategies have been discovered in the research laboratory, their translation to the clinical setting has been largely disappointing. The reason for this failure can be attributed to a number of factors including the inadequacy of the animal ischemia–reperfusion injury models used in the preclinical cardioprotection studies and the inappropriate design and execution of the clinical cardioprotection studies. This important issue was the main topic of discussion of the UCL-Hatter Cardiovascular Institute 6th International Cardioprotection Workshop, the outcome of which has been published in this article as the “Hatter Workshop Recommendations”. These have been proposed to provide guidance on the design and execution of both preclinical and clinical cardioprotection studies in order to facilitate the translation of future novel cardioprotective strategies for patient benefit.

Postconditioning hormesis put in perspective: an overview of experimental and clinical studies

A beneficial effect of applying mild stress to cells or organisms, that were initially exposed to a high dose of stress, has been referred to as 'postconditioning hormesis'. The initial high dose of stress activates intrinsic self-recovery mechanisms. Modulation of these endogenous adaptation strategies by administration of a subsequent low dose of stress can confer effects that are beneficial to the biological system. Owing to its potentially therapeutic applications, postconditioning hormesis is subject to research in various scientific disciplines. This paper presents an overview of the dynamics of postconditioning hormesis and illustrates this phenomenon with a number of examples in experimental and clinical research.

Signaling pathways involved in postconditioning-induced cardioprotection of human myocardium, in vitro

We examined the respective role and relationship between protein kinase C (PKC), mitochondrial adenosine triphosphate-sensitive potassium (mitoK(ATP)) channel and p38 mitogen-activated protein kinase (MAPK) in postconditioning of human myocardium, in vitro. Isometrically contracting, isolated human right atrial trabeculae were exposed to 30 min hypoxia and 60 min reoxygenation. Phorbol 12-myristate 13-acetate (a PKC activator), diazoxide (a mitoK(ATP) opener) and anisomycin (a p38 MAPK activator) were superfused in early reoxygenation alone and with calphostin C (a PKC inhibitor), 5-hydroxy-decanoate (5-HD, a mitoK(ATP) channel inhibitor) and SB 202190 (a p38 MAPK inhibitor). Developed force at the end of the 60 min reoxygenation (FoC(60)) period was compared between groups (mean +/- SD). Phorbol 12-myristate 13-acetate (91 +/- 4% of baseline), diazoxide (85 +/- 5% of baseline) and anisomycin (90 +/- 4% of baseline) enhanced the FoC(60) as compared with the control group (53 +/- 7% of baseline, P < 0.0001). The enhanced FoC(60) induced by phorbol 12-myristate 13-acetate was abolished by calphostin C (52 +/- 5% of baseline) and 5-HD (56 +/- 3% of baseline), but not by SB 202190 (90 +/- 8%). The diazoxide-induced recovery of FoC(60) was attenuated by 5-HD (55 +/- 6% of baseline), but was not modified by calphostin C (87 +/- 5% of baseline) and SB 202190 (90 +/- 8% of baseline). The anisomycin-induced recovery of FoC(60) was abolished by calphostin C (61 +/- 9% of baseline) and SB 202190 (52 +/- 8% of baseline), but not by 5-HD (88 +/- 6% of baseline). In conclusion, PKC activation, opening of mitoK(ATP) channels and p38 MAPK activation in early reoxygenation induced the postconditioning of human myocardium, in vitro. Furthermore, PKC activation was upstream of the opening of mitoK(ATP) channels; p38 MAPK acted on PKC. Therefore, mitoK(ATP) and p38 MAPK seemed to be involved in two independent pathways.

Combined local ischemic postconditioning and remote perconditioning recapitulate cardioprotective effects of local ischemic preconditioning

Ischemic postconditioning (PostC) and perconditioning (PerC) provide practical methods for protecting the heart against ischemia-reperfusion (I/R) injury, but their combined effects have not been studied in detail. Using an in vivo rat I/R model, we tested 1) whether additive effects were produced when local PostC was preceded by varying doses of remote PerC, and whether the optimal PostC+PerC regime is additive to local ischemic preconditioning (IPC), and 2) how combined PostC+PerC alters the activity of the reperfusion injury salvage kinase pathway. The optimal combination of PerC and PostC therapy was produced by PerC delivered with four cycles of 5 min of limb ischemia followed by 5-min reperfusion. This resulted in lower infarct size (22.56 ± 4.45%) compared with rats with PostC alone (29.39 ± 3.66%) and PerC alone (33.49 ± 5.81%) and complementary differences in the generation of reactive oxygen species and apoptotic signaling. However, this optimal combination of PostC+PerC resulted in protection similar to local IPC alone (18.8 ± 2.54%, P = 0.13), and when added to IPC there was no additional protection (19.62 ± 2.89%, P = 0.675). Akt and ERK1/2 phosphorylation was induced by PostC and PerC and maximally by combined PostC+PerC treatment, and protection was abolished by phosphatidylinositol 3-kinase or ERK1/2 inhibitors. This study shows that neither PostC nor a maximized “dose” of PerC leads to optimal kinase signaling or cardioprotection compared with IPC alone. However, combined PostC+PerC may result in complementary effects on kinase signaling to recapitulate the effects of local IPC. Finally, combined PostC+PerC is not additive to IPC, suggesting that each works via a common pathway.

Postconditioning and protection from reperfusion injury: where do we stand? Position paper from the Working Group of Cellular Biology of the Heart of the European Society of Cardiology

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