Persistent beneficial effect of postconditioning against infarct size: role of mitochondrial K(ATP) channels during reperfusion

Mitochondrial connexin43 and mitochondrial KATP channels modulate triggered arrhythmias in mouse ventricular muscle

Connexin43 (Cx43) exits as hemichannels in the inner mitochondrial membrane. We examined how mitochondrial Cx43 and mitochondrial K_ATP channels affect the occurrence of triggered arrhythmias. To generate cardiac-specific Cx43-deficient (cCx43^-/-) mice, Cx43^flox/flox mice were crossed with α-MHC (Myh6)-cre^+/- mice. The resulting offspring, Cx43^flox/flox/Myh6-cre^+/- mice (cCx43^-/- mice) and their littermates (cCx43^+/+ mice), were used. Trabeculae were dissected from the right ventricles of mouse hearts. Cardiomyocytes were enzymatically isolated from the ventricles of mouse hearts. Force was measured with a strain gauge in trabeculae (22°C). To assess arrhythmia susceptibility, the minimal extracellular Ca²⁺ concentration ([Ca²⁺]_o,min), at which arrhythmias were induced by electrical stimulation, was determined in trabeculae. ROS production was estimated with 2',7'-dichlorofluorescein (DCF), mitochondrial membrane potential with tetramethylrhodamine methyl ester (TMRM), and Ca²⁺ spark frequency with fluo-4 and confocal microscopy in cardiomyocytes. ROS production within the mitochondria was estimated with MitoSoxRed and mitochondrial Ca²⁺ with rhod-2 in trabeculae. Diazoxide was used to activate mitochondrial K_ATP. Most of cCx43^-/- mice died suddenly within 8 weeks. Cx43 was present in the inner mitochondrial membrane in cCx43^+/+ mice but not in cCx43^-/- mice. In cCx43^-/- mice, the [Ca²⁺]_o,min was lower, and Ca²⁺ spark frequency, the slope of DCF fluorescence intensity, MitoSoxRed fluorescence, and rhod-2 fluorescence were higher. TMRM fluorescence was more decreased in cCx43^-/- mice. Most of these changes were suppressed by diazoxide. In addition, in cCx43^-/- mice, antioxidant peptide SS-31 and N-acetyl-L-cysteine increased the [Ca²⁺]_o,min. These results suggest that Cx43 deficiency activates Ca²⁺ leak from the SR, probably due to depolarization of mitochondrial membrane potential, an increase in mitochondrial Ca²⁺, and an increase in ROS production, thereby causing triggered arrhythmias, and that Cx43 hemichannel deficiency may be compensated by activation of mitochondrial K_ATP channels in mouse hearts.

A Novel Reperfusion Strategy for Primary Percutaneous Coronary Intervention in Patients with Acute ST-Segment Elevation Myocardial Infarction: A Prospective Case Series

BACKGROUND

Ischemia reperfusion injury (IRI) remains a major problem in patients with acute ST-segment elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PCI). We have developed a novel reperfusion strategy for PCI and named it "volume-controlled reperfusion (VCR)". The aim of the current study was to assess the safety and feasibility of VCR in patients with STEMI.

METHODS

Consecutive patients admitted to Beijing Chaoyang Hospital with STEMI were prospectively enrolled. The feasibility endpoint was procedural success. The safety endpoints included death from all causes, major vascular complications, and major adverse cardiac event (MACE), i.e., a composite of cardiac death, myocardial reinfarction, target vessel revascularization (TVR), and heart failure.

RESULTS

A total of 30 patients were finally included. Procedural success was achieved in 28 (93.3%) patients. No patients died during the study and no major vascular complications or MACE occurred during hospitalization. With the exception of one patient (3.3%) who underwent TVR three months after discharge, no patient encountered death (0.0%), major vascular complications (0.0%), or and other MACEs (0.0%) during the median follow-up of 16 months.

CONCLUSION

The findings of the pilot study suggest that VCR has favorable feasibility and safety in patients with STEMI. Further larger randomized trials are required to evaluate the effectiveness of VCR in STEMI patients.

Ex Vivo Lung Perfusion with K(ATP) Channel Modulators Antagonize Ischemia Reperfusion Injury

Ex vivo lung perfusion (EVLP) has been implemented to increase the number of donor lungs available for transplantation. The use of K(ATP) channel modulators during EVLP experiments may protect against lung ischemia-reperfusion injury and may inhibit the formation of reactive oxygen species. In a rat model of donation after circulatory death with 2 h warm ischemic time, we evaluated rat lungs for a 4-hour time in EVLP containing either mitochondrial-specific or plasma membrane and/or sarcolemmal-specific forms of K(ATP) channel modulators. Lung physiological data were recorded, and metabolic parameters were assessed. When compared to the control group, in the EVLP performed with diazoxide or 5-hydroxydecanoic acid (5-HD) we recorded significantly lower pulmonary vascular resistance and only in the diazoxide group recorded significant lung weight loss. In the perfusate of the 5-HD group, interleukin-1β and interleukin-1α were significantly lower when compared to the control group. Perfusate levels of calcium ions were significantly higher in both 5-HD and cromakalim groups, whereas the levels of calcium, potassium, chlorine and lactate were reduced in the diazoxide group, although not significantly when compared to the control. The use of a diazoxide mitochondrial-specific K(ATP) channel opener during EVLP improved lung physiological and metabolic parameters and reduced edema.

Cardioprotective Effect of Quercetin against Ischemia/Reperfusion Injury Is Mediated Through NO System and Mitochondrial K-ATP Channels

Objective

Quercetin (Que) is a plant-derived polyphenolic compound, that was shown to possess anti-inflammatory activity in myocardial ischemia/reperfusion (I/R) models in vivo; however, detailed mechanisms of its anti-inflammatory effects remain unclear. This study aimed to examine the effects of quercetin postconditioning (QPC) on I/R-induced inflammatory response in a rat model and evaluate the role of the mitochondrial K-ATP (mitoK_ATP) channels and NO system in this regard.

Materials and Methods

In this experimental study, hearts of male Wistar rats (250 ± 20 g) perused by Langendorff apparatus, were subjected to 30 minutes of global ischemia followed by 55 minutes reperfusion, and Que was added to the perfusion solution immediately at the onset of reperfusion. Creatine kinase (CK) levels in the coronary effluent were measured by spectrophotometry. Interleukin-1 (IL-1β), IL-6, and tumor necrosis factor-alpha (TNF-α) levels were analyzed by an enzyme-linked immunosorbent assay (ELISA) rat specific kit to assess the inflammatory condition of the myocardial tissue.

Results

Our results showed that QPC significantly improved left ventricular developed pressure (LVDP) (P<0.05), and decreased the CK release into the coronary effluent vs. control group (P<0.01). The levels of IL-1β (P<0.01), TNF-α (P<0.01), and IL-6 (P<0.05) were significantly diminished in Que-treated groups when compared to the control group. Inhibiting mitoK_ATPchannels by 100 μM 5-hydroxydecanoate and blocking NO system by 100 μM L-NAME reversed the cardioprotective effects of Que.

Conclusion

The findings of this study suggested that QPC exerts cardioprotective effects on myocardial I/R injury (MIRI) through inhibition of inflammatory reactions and improvement of contractility potential. Also, mitoK_ATP channels and NO system might be involved in this anti-inflammatory effect.

Postconditioning with Nitrates Protects Against Myocardial Reperfusion Injury: A New Use for an Old Pharmacological Agent

Early reperfusion remains the key therapy to salvage viable myocardium and must be applied as soon as possible following an acute myocardial infarction (AMI) to attenuate the ischemic insult. However, reperfusion injury may develop following reintroduction of blood and oxygen to vulnerable myocytes, which results in more severe cell death than in the preceding ischemic episode. Ischemic postconditioning (I-PostC) provides a cardioprotective effect in combination with pharmacological agents. Although nitrates have been tested in many experimental and clinical studies of acute AMI to evaluate the cardioprotective effect, few investigations have been focused on nitrates postconditioning in patients undergoing percutaneous coronary intervention (PCI). This review presents the manifestations of myocardial reperfusion injury (RI) and potential mechanisms underlying it, and provides the mechanisms involved in the cardioprotection of I-PostC. We also present a new therapeutic approach to attenuate RI by use of an ‘old’ agent – nitrates – in AMI patients.

Ischemic Postconditioning Reduces Reperfusion Arrhythmias by Adenosine Receptors and Protein Kinase C Activation but Is Independent of KATP Channels or Connexin 43

Ischemic postconditioning (IPoC) reduces reperfusion arrhythmias but the antiarrhythmic mechanisms remain unknown. The aim of this study was to analyze IPoC electrophysiological effects and the role played by adenosine A1, A2A and A3 receptors, protein kinase C, ATP-dependent potassium (KATP) channels, and connexin 43. IPoC reduced reperfusion arrhythmias (mainly sustained ventricular fibrillation) in isolated rat hearts, an effect associated with a transient delay in epicardial electrical activation, and with action potential shortening. Electrical impedance measurements and Lucifer-Yellow diffusion assays agreed with such activation delay. However, this delay persisted during IPoC in isolated mouse hearts in which connexin 43 was replaced by connexin 32 and in mice with conditional deletion of connexin 43. Adenosine A1, A2A and A3 receptor blockade antagonized the antiarrhythmic effect of IPoC and the associated action potential shortening, whereas exogenous adenosine reduced reperfusion arrhythmias and shortened action potential duration. Protein kinase C inhibition by chelerythrine abolished the protective effect of IPoC but did not modify the effects on action potential duration. On the other hand, glibenclamide, a KATP inhibitor, antagonized the action potential shortening but did not interfere with the antiarrhythmic effect. The antiarrhythmic mechanisms of IPoC involve adenosine receptor activation and are associated with action potential shortening. However, this action potential shortening is not essential for protection, as it persisted during protein kinase C inhibition, a maneuver that abolished IPoC protection. Furthermore, glibenclamide induced the opposite effects. In addition, IPoC delays electrical activation and electrical impedance recovery during reperfusion, but these effects are independent of connexin 43.

Interaction of ischaemic postconditioning and thrombectomy in patients with ST-elevation myocardial infarction

OBJECTIVE

The Third Danish Study of Optimal Acute Treatment of Patients with ST-segment Elevation Myocardial Infarction - Ischaemic Postconditioning (DANAMI-3-iPOST) did not show improved clinical outcome in patients with ST-segment elevation myocardial infarction (STEMI) treated with ischaemic postconditioning. However, the use of thrombectomy was frequent and thrombectomy may in itself diminish the effect of ischaemic postconditioning. We evaluated the effect of ischaemic postconditioning in patients included in DANAMI-3-iPOST stratified by the use of thrombectomy.

METHODS

Patients with STEMI were randomised to conventional primary percutaneous coronary intervention (PCI) or ischaemic postconditioning plus primary PCI. The primary endpoint was a combination of all-cause mortality and hospitalisation for heart failure.

RESULTS

From March 2011 until February 2014, 1234 patients were included with a median follow-up period of 35 (interquartile range 28 to 42) months. There was a significant interaction between ischaemic postconditioning and thrombectomy on the primary endpoint (p=0.004). In patients not treated with thrombectomy (n=520), the primary endpoint occurred in 33 patients (10%) who underwent ischaemic postconditioning (n=326) and in 35 patients (18%) who underwent conventional treatment (n=194) (adjusted hazard ratio (HR) 0.55 (95%confidence interval (CI) 0.34 to 0.89), p=0.016). In patients treated with thrombectomy (n=714), there was no significant difference between patients treated with ischaemic postconditioning (n=291) and conventional PCI (n=423) on the primary endpoint (adjusted HR 1.18 (95% CI 0.62 to 2.28), p=0.62).

CONCLUSIONS

In this post-hoc study of DANAMI-3-iPOST, ischaemic postconditioning, in addition to primary PCI, was associated with reduced risk of all-cause mortality and hospitalisation for heart failure in patients with STEMI not treated with thrombectomy.

TRIAL REGISTRATION NUMBER

NCT01435408.

Effect of Ischemic Postconditioning During Primary Percutaneous Coronary Intervention for Patients With ST-Segment Elevation Myocardial Infarction: A Randomized Clinical Trial

Importance

Ischemic postconditioning of the heart during primary percutaneous coronary intervention (PCI) induced by repetitive interruptions of blood flow to the ischemic myocardial region immediately after reopening of the infarct-related artery may limit myocardial damage.

Objective

To determine whether ischemic postconditioning can improve the clinical outcomes in patients with ST-segment elevation myocardial infarction (STEMI).

Design, Setting, And Participants

In this multicenter, randomized clinical trial, patients with onset of symptoms within 12 hours, STEMI, and thrombolysis in myocardial infarction (TIMI) grade 0-1 flow in the infarct-related artery at arrival were randomized to conventional PCI or postconditioning. Inclusion began on March 21, 2011, through February 2, 2014, and follow-up was completed on February 2, 2016. Analysis was based on intention to treat.

Interventions

Patients were randomly allocated 1:1 to conventional primary PCI, including stent implantation, or postconditioning performed as 4 repeated 30-second balloon occlusions followed by 30 seconds of reperfusion immediately after opening of the infarct-related artery and before stent implantation.

Main Outcome and Measures

A combination of all-cause death and hospitalization for heart failure.

Results

During the inclusion period, 1234 patients (975 men [79.0%] and 259 women [21.0%]; mean [SD] age, 62 [11] years) underwent randomization in the trial. Median follow-up was 38 months (interquartile range, 24-58 months). The primary outcome occurred in 69 patients (11.2%) who underwent conventional primary PCI and in 65 (10.5%) who underwent postconditioning (hazard ratio, 0.93; 95% CI, 0.66-1.30; P = .66). The hazard ratios were 0.75 (95% CI, 0.49-1.14; P = .18) for all-cause death and 0.99 (95% CI, 0.60-1.64; P = .96) for heart failure.

Conclusions and Relevance

Routine ischemic postconditioning during primary PCI failed to reduce the composite outcome of death from any cause and hospitalization for heart failure in patients with STEMI and TIMI grade 0-1 flow at arrival.

Trial Registration

clinicaltrials.gov Identifier: NCT01435408.

Mitochondria "THE" target of myocardial conditioning

Several interventions, such as ischemic preconditioning, remote pre/perconditioning, or postconditioning, are known to decrease lethal myocardial ischemia-reperfusion injury. While several signal transduction pathways become activated by such maneuvers, they all have a common end point, namely, the mitochondria. These organelles represent an essential target of the cardioprotective strategies, and the preservation of mitochondrial function is central for the reduction of ischemia-reperfusion injury. In the present review, we address the role of mitochondria in the different conditioning strategies; in particular, we focus on alterations of mitochondrial function in terms of energy production, formation of reactive oxygen species, opening of the mitochondrial permeability transition pore, and mitochondrial dynamics induced by ischemia-reperfusion.

Mitochondria in Cardiac Postconditioning

Mitochondria play a pivotal role in cardioprotection. Here we report some fundamental studies which considered the role of mitochondrial components (connexin 43, mitochondrial KATP channels and mitochondrial permeability transition pore) in postconditioning cardioprotection. We briefly discuss the role of mitochondria, reactive oxygen species and gaseous molecules in postconditioning. Also the effects of anesthetics-used as cardioprotective substances-is briefly considered in the context of postconditioning. The role of mitochondrial postconditioning signaling in determining the limitation of cell death is underpinned. Issues in clinical translation are briefly considered. The aim of the present mini-review is to discuss in a historical perspective the role of main mitochondria mechanisms in cardiac postconditioning.

Levosimendan protects human hepatocytes from ischemia-reperfusion injury

Background

Ischemia-reperfusion injury (IRI) is a major challenge in liver transplantation. The mitochondrial pathway plays a pivotal role in hepatic IRI. Levosimendan, a calcium channel sensitizer, was shown to attenuate apoptosis after IRI in animal livers. The aim of this study was to investigate the effect of levosimendan on apoptosis in human hepatocytes.

Methods

Primary human hepatocytes were either exposed to hypoxia or cultured under normoxic conditions. After the hypoxic phase, reoxygenation was implemented and cells were treated with different concentrations of levosimendan (10ng/ml, 100ng/ml, 1000ng/ml). The overall metabolic activity of the cells was measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), and aspartate aminotransferase (AST) levels were determined in order to quantify hepatic injury. Fluorescence-activated cell sorting (FACS) analysis was applied to measure necrosis and apoptosis. Finally, Western blotting was performed to analyze apoptotic pathway proteins.

Results

Administration of levosimendan during reperfusion increases the metabolic activity of human hepatocytes and decreases AST levels. Moreover, apoptosis after IRI is reduced in treated vs. untreated hepatocytes, and levosimendan prevents down-regulation of the anti-apoptotic protein Bcl-2 as well as up-regulation of the pro-apoptotic protein BAX.

Conclusion

The present study suggests a protective effect of levosimendan on human hepatocytes. Our findings suggest that treatment with levosimendan during reperfusion attenuates apoptosis of human hepatocytes by influencing BAX and Bcl-2 levels.

Cardioprotective Effect of the SDF-1α/CXCR4 Axis in Ischemic Postconditioning in Isolated Rat Hearts

BACKGROUND AND OBJECTIVES

Information about the role of the stromal cell-derived factor-1α (SDF-1α)/chemokine receptor type 4 (CXCR4) axis in ischemic postconditioning (IPOC) is currently limited. We hypothesized that the SDF-1α/CXCR4 signaling pathway is directly involved in the cardioprotective effect of IPOC.

METHODS

Isolated rat hearts were divided into four groups. The control group was subjected to 30-min of regional ischemia and 2-hour of reperfusion (n=12). The IPOC group was induced with 6 cycles of 10-second reperfusion and 10-second global ischemia (n=8) in each cycle. The CXCR4 antagonist, AMD3100, was applied before reperfusion in the IPOC group (AMD+IPOC group, n=11) and control group (AMD group, n=9). Hemodynamic changes with electrocardiography were monitored and infarct size was measured. The SDF-1α, lactate dehydrogenase (LDH) and creatine kinase (CK) concentrations in perfusate were measured. We also analyzed extracellular signal-regulated kinase 1/2 (ERK1/2) and Akt phosphorylation state expression.

RESULTS

IPOC significantly reduced infarct size, but AMD3100 attenuated the infarct reducing effect of IPOC. IPOC significantly decreased LDH and CK, but these effects were reversed by AMD3100. ERK1/2 and Akt phosphorylation increased with IPOC and these effects were blocked by AMD3100.

CONCLUSION

Based on the results of this study, SDF-1α/CXCR4 signaling may be involved in IPOC cardioprotection and this signaling pathway couples to the ERK1/2 and Akt pathways.

Ubiquinol-cytochrome c reductase core protein 1 may be involved in delayed cardioprotection from preconditioning induced by diazoxide

This study aimed to use long-term diazoxide treatment to establish a loss-of-cardioprotection model and then perform proteomics analysis to explore which proteins of mitochondrial inner membrane (MIM) are potentially involved in delayed cardioprotection. Rats received 1 to 8 weeks of diazoxide treatments (20 mg•kg-1•d-1) to establish a loss-of-cardioprotection model in different groups. Detection of serum cTnI levels and cell apoptosis assays in heart tissue were performed. Then, rats MIM after 0, 4 and 6 weeks of diazoxide treatment was isolated and proteomics analysis was performed. An invitro model of H9C2 cells was performed to explore the effects of targeted protein on delayed cardioprotection. The effect of delayed cardioprotection by diazoxide preconditioning disappeared when diazoxide treatments were given for six weeks or longer. Ubiquinol-cytochrome c reductase core protein 1 (UQCRC1) was identified in the proteomics analysis. UQCRC1 expression was upregulated by diazoxide treatment in H9C2 cells, and UQCRC1 down-regulation could increase the lactate dehydrogenase release and apoptosis rate after injury induced by oxygen glucose deprivation. These results showed that UQCRC1 might contribute to the loss-of-cardioprotection model induced by long-term diazoxide treatment and play a role in delayed cardioprotection.

Myocardial ischemia/reperfusion upregulates the transcription of the Neuregulin1 receptor ErbB3, but only postconditioning preserves protein translation: Role in oxidative stress

BACKGROUND

Neuregulin1 (Nrg1) and its receptors ErbB are crucial for heart development and for adult heart structural maintenance and function and Nrg1 has been proposed for heart failure treatment. Infarct size is the major determinant of heart failure and the mechanism of action and the role of each ErbB receptor remain obscure, especially in the post-ischemic myocardium. We hypothesized that Nrg1 and ErbB are affected at transcriptional level early after ischemia/reperfusion (I/R) injury, and that the protective postconditioning procedure (PostC, brief cycles of ischemia/reperfusion carried out after a sustained ischemia) can influence this pathway.

METHODS AND RESULTS

The Langendorff's heart was used as an ex-vivo model to mimic an I/R injury in the whole rat heart; after 30min of ischemia and 2h of reperfusion, with or without PostC, Nrg1 and ErbB expression were analysed by quantitative real-time PCR and Western blot. While no changes occur for ErbB2, ErbB4 and Nrg1, an increase of ErbB3 expression occurs after I/R injury, with and without PostC. However, I/R reduces ErbB3 protein, whereas PostC preserves it. An in vitro analysis with H9c2 cells exposed to redox-stress indicated that the transient over-expression of ErbB3 alone is able to increase cell survival (MTT assay), limiting mitochondrial dysfunction (JC-1 probe) and apoptotic signals (Bax/Bcl-2 ratio).

CONCLUSIONS

This study suggests ErbB3 as a protective factor against death pathways activated by redox stress and supports an involvement of this receptor in the pro-survival responses.

Role of ATP-Sensitive Potassium Channels in Remote Ischemic Preconditioning Induced Tissue Protection

Remote ischemic preconditioning (RIPC) is an innovative treatment strategy that alleviates ischemia-reperfusion injury, whereby short episodes of regional ischemia and reperfusion delivered to remote organs including hind limb, kidney and intestine, and so on provide protection to the heart. The RIPC is known to reduce infarct size, serum levels of cardiac enzymes, and myocardial dysfunction in various animal species as well as in patients. There have been a large number of studies suggesting that the ATP-sensitive potassium channels (KATP channel) play a significant role as a mediator or end effector in RIPC. The present review discusses the role of KATP channels and possible mechanisms in RIPC-induced cardioprotection.

Ischemic postconditioning and pinacidil suppress calcium overload in anoxia-reoxygenation cardiomyocytes via down-regulation of the calcium-sensing receptor

Ischemic postconditioning (IPC) and ATP sensitive potassium channel (KATP) agonists (e.g. pinacidil and diazoxide) postconditioning are effective methods to defeat myocardial ischemia-reperfusion (I/R) injury, but their specific mechanisms of reducing I/R injury are not fully understood. We observed an intracellular free calcium ([Ca²⁺]_i) overload in Anoxia/reoxygenation (A/R) cardiomyocytes, which can be reversed by KATP agonists diazoxide or pinacidil. The calcium-sensing receptor (CaSR) regulates intracellular calcium homeostasis. CaSR was reported to be involved in the I/R-induced apoptosis in rat cardiomyocytes. We therefore hypothesize that IPC and pinacidil postconditioning (PPC) reduce calcium overload in I/R cardiomyocytes by the down-regulation of CaSR. A/R model was established with adult rat caridomyocyte. mRNA and protein expression of CaSR were detected, IPC, PPC and KATP’s effects on [Ca²⁺]_i concentration was assayed too. IPC and PPC ameliorated A/R insult induced [Ca²⁺]_i overload in cardiomyocytes. In addition, they down-regulated the mRNA and protein level of CaSR as we expected. CaSR agonist spermine and KATP blocker glibenclamide offset IPC’s effects on CaSR expression and [Ca²⁺]_i modulation. Our data indicate that CaSR down-regulation contributes to the mitigation of calcium overload in A/R cardiomyocytes, which may partially represents IPC and KATP’s myocardial protective mechanism under I/R circumstances.

Non-cell autonomous cues for enhanced functionality of human embryonic stem cell-derived cardiomyocytes via maturation of sarcolemmal and mitochondrial KATP channels

Human embryonic stem cells (hESCs) is a potential unlimited ex vivo source of ventricular (V) cardiomyocytes (CMs), but hESC-VCMs and their engineered tissues display immature traits. In adult VCMs, sarcolemmal (sarc) and mitochondrial (mito) ATP-sensitive potassium (K_ATP) channels play crucial roles in excitability and cardioprotection. In this study, we aim to investigate the biological roles and use of sarcK_ATP and mitoK_ATP in hESC-VCM. We showed that SarcI_{K, ATP} in single hESC-VCMs was dormant under baseline conditions, but became markedly activated by cyanide (CN) or the known opener P1075 with a current density that was ~8-fold smaller than adult; These effects were reversible upon washout or the addition of GLI or HMR1098. Interestingly, sarcI_{K, ATP} displayed a ~3-fold increase after treatment with hypoxia (5% O₂). MitoI_{K, ATP} was absent in hESC-VCMs. However, the thyroid hormone T3 up-regulated mitoI_{K, ATP,} conferring diazoxide protective effect on T3-treated hESC-VCMs. When assessed using a multi-cellular engineered 3D ventricular cardiac micro-tissue (hvCMT) system, T3 substantially enhanced the developed tension by 3-folds. Diazoxide also attenuated the decrease in contractility induced by simulated ischemia (1% O₂). We conclude that hypoxia and T3 enhance the functionality of hESC-VCMs and their engineered tissues by selectively acting on sarc and mitoI_{K, ATP}.

Cardiac Mechano-Gated Ion Channels and Arrhythmias

Mechanical forces will have been omnipresent since the origin of life, and living organisms have evolved mechanisms to sense, interpret, and respond to mechanical stimuli. The cardiovascular system in general, and the heart in particular, is exposed to constantly changing mechanical signals, including stretch, compression, bending, and shear. The heart adjusts its performance to the mechanical environment, modifying electrical, mechanical, metabolic, and structural properties over a range of time scales. Many of the underlying regulatory processes are encoded intracardially and are, thus, maintained even in heart transplant recipients. Although mechanosensitivity of heart rhythm has been described in the medical literature for over a century, its molecular mechanisms are incompletely understood. Thanks to modern biophysical and molecular technologies, the roles of mechanical forces in cardiac biology are being explored in more detail, and detailed mechanisms of mechanotransduction have started to emerge. Mechano-gated ion channels are cardiac mechanoreceptors. They give rise to mechano-electric feedback, thought to contribute to normal function, disease development, and, potentially, therapeutic interventions. In this review, we focus on acute mechanical effects on cardiac electrophysiology, explore molecular candidates underlying observed responses, and discuss their pharmaceutical regulation. From this, we identify open research questions and highlight emerging technologies that may help in addressing them.

Ischemic postconditioning influences electron transport chain protein turnover in Langendorff-perfused rat hearts

Ischemia postconditioning (IPo) is a promising strategy in reducing myocardial ischemia reperfusion (I/R) injury (MIRI), but its specific molecular mechanism is incompletely understood. Langendorff-perfused isolated rat hearts were subjected to global I/R and received IPo in the absence or presence of the mitochondrial ATP-sensitive potassium channel (mitoKATP) blocker 5-hydroxydecanoate (5-HD). Myocardial mitochondria were extracted and mitochondrial comparative proteomics was analyzed. IPo significantly reduces post-ischemic myocardial infarction and improved cardiac function in I/R rat hearts, while 5-HD basically cancelled IPo's myocardial protective effect. Joint application of two-dimensional polyacrylamide gel electrophoresis (2DE) and MALDI-TOF MS identified eight differentially expressed proteins between groups. Expression of cardiac succinate dehydrogenase (ubiquinone) flavoprotein subunit (SDHA) increased more than two-fold after I/R, while IPo led to overexpression of dihydrolipoyl dehydrogenase (DLD), NADH dehydrogenase (ubiquinone) flavoprotein 1 and isoform CRA_b (NDUFV1). When the mitoKATP was blocked, MICOS complex subunit Mic60 (IMMT) and Stress-70 protein (Grp75) were over expressed, while DLDH, ATPase subunit A (ATPA) and rCG44606 were decreased. Seven of the differential proteins belong to electron transport chain (ETC) or metabolism regulating proteins, and five of them were induced by closing mitoKATP in I/R hearts. We thus conclude that IPo's myocardial protective effect relies on energy homeostasis regulation. DLD, SDHA, NDUFV1, Grp75, ATPA and rCG44606 may contribute to IPo's cardial protective effect.

Adenosine triphosphate-sensitive potassium channels and cardiomyopathies (Review)

Cardiomyopathies have been indicated to be one of the leading causes of heart failure. Though it was indicated that genetic defects, viral infection and trace element deficiency were among the causes of cardiomyopathy, the etiology has remained to be fully elucidated. Cardiomyocytes require large amounts of energy to maintain their normal biological functions. Adenosine triphosphate-sensitive potassium channels (KATP), composed of inward-rectifier potassium ion channel and sulfonylurea receptor subunits, are present on the cell surface and mitochondrial membrane of cardiac muscle cells. As metabolic sensors sensitive to changes in intracellular energy levels, KATP adapt electrical activities to metabolic challenges, maintaining normal biological functions of myocytes. It is implied that malfunctions, mutations and altered expression of KATP are associated with the pathogenesis of conditions including c hypertrophy, diabetes as well as dilated, ischemic and endemic cardiomyopathy. However, the current knowledge is only the tip of the iceberg and the roles of KATP in cardiomyopathies largely remain to be elucidated in future studies.

Ischemic postconditioning improves the expression of cellular membrane connexin 43 and attenuates the reperfusion injury in rat acute myocardial infarction

To investigate the effects of cellular membrane connexin 43 (Cx43) and the potential details in ischemic postconditioning (IPOC)-induced cardioprotection, ischemia/reperfusion (IR) models were generated in 8-week-old male Sprague-Dawley rats by ligating the left coronary artery anterior descending branch. The serum levels of myocardial creatases, nitric oxide (NO) and malondialdehyde (MDA) levels, infarct size, arrhythmia events, expression and distribution of Cx43, ultrastructure and apoptosis in the myocardium in different treatments with IR, IR + IPOC, IR + diazoxide or IR + IPOC + 5-hydroxydecanoate acid (5-HD) were investigated. Consequently, IPOC decreased infarct size (10.9 vs. 43.3%, P<0.01) and the levels of myocardial creatases, NO and MDA, and improved the expression (16.8 vs. 25.2% and 6.4 vs. 32.8%, after 1- and 3-h reperfusion, respectively; P<0.01) and distribution of Cx43, ultrastructure and apoptosis (19.2 vs. 42.9%, P<0.01) significantly. Diazoxide partly simulated the effects, and 5-HD attenuated but not completely abolished the effects of IPOC. In addition, the phosphorylated Cx43 (p-Cx43) level in the IR + IPOC group was lower than that in the IR + diazoxide group after 1-h reperfusion (26.1 vs. 29.4%, P>0.05); however, it was reversed after 3-h reperfusion and the p-Cx43 level in the IR + IPOC group was significantly higher than that in the IR + diazoxide group (32.8 vs. 18.7%, P<0.01). In conclusion, cell membrane Cx43 is also involved in the process of IPOC-induced cardioprotection and the improvement of membrane Cx43 is more dependent on mitochondrial K_ATP in the earlier phase of IPOC compared to the late phase of IPOC.

Genome-Wide Expression Profiling of Anoxia/Reoxygenation in Rat Cardiomyocytes Uncovers the Role of MitoKATP in Energy Homeostasis

Mitochondrial ATP-sensitive potassium channel (mitoK(ATP)) is a common end effector of many protective stimuli in myocardial ischemia-reperfusion injury (MIRI). However, the specific molecular mechanism underlying its myocardial protective effect is not well elucidated. We characterized an anoxia/reoxygenation (A/R) model using freshly isolated adult rat cardiomyocytes. MitoK(ATP) status was interfered with its specific opener diazoxide (DZ) or blocker 5-hydroxydecanote (5-HD). Digital gene expression (DGE) and bioinformatic analysis were deployed. Three energy metabolism related genes (MT-ND6, Idh2, and Acadl) were upregulated when mitoK(ATP) opened. In addition, as many as 20 differentially expressed genes (DEGs) were significantly enriched in five energy homeostasis correlated pathways (PPAR, TCA cycle, fatty acid metabolism, and peroxisome). These findings indicated that mitoK(ATP) opening in MIRI resulted in energy mobilization, which was confirmed by measuring ATP content in cardiomyocytes. These causal outcomes could be a molecular mechanism of myocardial protection of mitoKATP and suggested that the mitoK(ATP) opening plays a physiologic role in triggering cardiomyocytes' energy homeostasis during MIRI. Strategies of modulating energy expenditure during myocardial ischemia-reperfusion may be promising approaches to reduce MIRI.

Influence of levosimendan postconditioning on apoptosis of rat lung cells in a model of ischemia-reperfusion injury

Objective

To ascertain if levosimendan postconditioning can alleviate lung ischemia–reperfusion injury (LIRI) in rats.

Method

One hundred rats were divided into five groups: Sham (sham), ischemia–reperfusion group (I/R group), ischemic postconditioning (IPO group), levosimendan postconditioning (Levo group) and combination postconditioning group of levosimendan and 5-Hydroxydecanoic acid (Levo+5-HD group). The apoptotic index (AI) of lung tissue cells was determined using the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. Expression of active cysteine aspartate specific protease-3 ( active caspase-3), Bcl-2 and Bax in lung tissue was determined by immunohistochemical staining. The morphopathology of lung tissue was observed using light and electron microscopy.

Results

AI values and expression of active caspase-3, Bcl-2 and Bax of lung tissue in I/R and Levo+5-HD groups were significantly higher than those in the sham group ( P<0.05). AI values and expression of active caspase-3 and Bax were significantly lower, whereas that of Bcl-2 was higher significantly in the Levo group, compared with I/R and Levo+5-HD groups (P<0.05). Significant differences were not observed in comparisons between I/R and Levo+5-HD groups as well as IPO and Levo groups.

Conclusion

LIRI can be alleviated by levosimendan, which simulates an IPO protective function. A postulated lung-protective mechanism of action could involve opening of mitochondrial adenosine triphosphate-sensitive potassium channels, relieving Ca2+ overload, upregulation of expression of Bcl-2, and downregulation of expression of active caspase-3 and Bax.

Blocking of the ATP sensitive potassium channel ameliorates the ischaemia-reperfusion injury in the rat testis

There is increasing evidence that the effects of administered ATP sensitive potassium (KATP ) channel openers or blockers during ischaemia are still controversial in many organs/tissues. Testicular torsion detorsion which causes ischaemia-reperfusion (IR) injury, cannot be predicted, thus an effective drug should be administered during or after the ischaemia. The aim of this study was to examine whether the administration of KATP channel openers or blockers during ischaemia ameliorates IR injury in the testis. Eight-week-old male Sprague-Dawley rats were subjected to 2 h right testicular ischaemia followed by 24 h reperfusion. The selective mitochondrial (mito) KATP channel blocker, 5-hydroxydecanoate (5-HD) (40 mg/kg), the non-selective KATP channel blocker glibenclamide (5 mg/kg), the selective mito KATP channel opener diazoxide (10 mg/kg) and the non-selective KATP channel opener cromakalim (300 μg/kg) were administered intraperitoneally 15 min prior to the ischaemia or 75 min after the induction of ischaemia. Tissue damage was evaluated by malondialdehyde concentration, myeloperoxidase activity, histological evaluation and TdT-mediated dUTP nick end labelling assay in the testis. There was a significant increase in oxidative stress, neutrophil infiltration, histological damage and apoptosis in the testicular IR model. A significant reduction in the testicular IR injury was observed with the administration of glibenclamide, but not 5-HD, diazoxide or cromakalim during ischaemia. The administration of non-selective KATP channel blocker glibenclamide ameliorated the testicular IR injury. On the other hand, the selective mito KATP channel blocker, 5-HD and KATP channel openers did not reduce the testicular IR injury. These data suggest that blocking of the membrane KATP channel may have a protective effect during the testicular ischaemia. Glibenclamide could be an effective drug to manage the post-ischaemic injury caused by the testicular torsion-detorsion.

High‑dose fasudil preconditioning and postconditioning attenuate myocardial ischemia‑reperfusion injury in hypercholesterolemic rats

Fasudil may induce preconditioning and postconditioning against myocardial ischemia‑reperfusion injury in normal rats, however, their effectivenesses in hypercholesterolemia remains to be determined. The study aimed to investigate whether fasudil induces preconditioning and postconditioning in hypercholesterolemic rats and to determine the roles of the phosphoinositol 3‑kinase (PI3K)/Akt/endothelial nitric oxide synthase (eNOS) pathway and mitochondrial KATP (m‑KATP) channels in this process. Isolated rat hearts underwent 30 min global ischemia and 120 min reperfusion. Low‑ (1 mg/kg) or high‑dose (10 mg/kg) fasudil was administered 15 min prior to ischemia and at the initial onset of reperfusion. 5‑Hydroxydecanoic acid (5HD), an m‑KATP channel blocker, at 10 mg/kg was administered 5 min prior to reperfusion. Myocardial infarct size was estimated by 2,3,5‑triphenyltetrazolium chloride (TTC) staining and lactate dehydrogenase (LDH) and creatine kinase‑MB (CK‑MB) were analyzed from coronary effluents. Phosphorylation of Akt and eNOS was measured by immunoblotting. High‑dose fasudil‑induced preconditioning and postconditioning significantly reduced infarct size and the release of LDH and CK‑MB and increased the phosphorylation of Akt and eNOS compared with the control group, whereas low‑dose fasudil did not exert these beneficial effects. In addition, the cardioprotection of high‑dose fasudil‑induced preconditioning and postconditioning are blocked by 5HD. Low‑dose fasudil‑induced preconditioning and postconditioning are abrogated by hypercholesterolemia, while high‑dose fasudil restores the cardioprotection, which is involved in upregulation of the PI3K/Akt/eNOS pathway and inducing the opening of the m‑KATP channel.

Multiplicity of effectors of the cardioprotective agent, diazoxide

Diazoxide has been identified over the past 50years to have a number of physiological effects, including lowering the blood pressure and rectifying hypoglycemia. Today it is used clinically to treat these conditions. More recently, another important mode of action emerged: diazoxide has powerful protective properties against cardiac ischemia. The heart has intrinsic protective mechanisms against ischemia injury; one of which is ischemic preconditioning. Diazoxide mimics ischemic preconditioning. The purpose of this treatise is to review the literature in an attempt to identify the many effectors of diazoxide and discuss how they may contribute to diazoxide's cardioprotective properties. Particular emphasis is placed on the concentration ranges in which diazoxide affects its different targets and how this compares with the concentrations commonly used to study cardioprotection. It is concluded that diazoxide may have several potential effectors that may potentially contribute to cardioprotection, including KATP channels in the pancreas, smooth muscle, endothelium, neurons and the mitochondrial inner membrane. Diazoxide may also affect other ion channels and ATPases and may directly regulate mitochondrial energetics. It is possible that the success of diazoxide lies in this promiscuity and that the compound acts to rebalance multiple physiological processes during cardiac ischemia.

Curcumin promotes cardiac repair and ameliorates cardiac dysfunction following myocardial infarction

BACKGROUND AND PURPOSE

Curcumin, the natural yellow pigment extracted from the rhizomes of the plant curcuma longa, has been demonstrated to exhibit a variety of potent beneficial effects, acting as an antioxidant, anti-inflammatory and anti-fibrotic. In this study we tested the hypothesis that curcumin attenuates maladaptive cardiac repair and improves cardiac function after ischaemia and reperfusion by reducing degradation of extracellular matrix (ECM) and inhibiting synthesis of collagens via TGFβ/Smad-mediated signalling pathway.

EXPERIMENTAL APPROACH

Sprague-Dawley rats were subjected to 45 min of ischaemia followed by 7, 21 and 42 days of reperfusion respectively. Curcumin was fed orally at a dose of 150 mg·kg(-1) ·day(-1) only during reperfusion.

KEY RESULTS

Curcumin reduced the level of malondialdehyde, inhibited activity of MMPs, preserved ECM from degradation and attenuated collagen deposition, as it reduced the extent of collagen-rich scar and increased mass of viable myocardium. In addition to reducing collagen synthesis and fibrosis in the ischaemic/reperfused myocardium, curcumin significantly down-regulated the expression of TGFβ1 and phospho-Smad2/3, and up-regulated Smad7 and also increased the population of α-smooth muscle actin expressing myofibroblasts within the infarcted myocardium relative to the control. Echocardiography showed it significantly improved left ventricular end-diastolic volume, stroke volume and ejection fraction. The wall thickness of the infarcted middle anterior septum in the curcumin group was also greater than that in the control group.

CONCLUSION AND IMPLICATIONS

Dietary curcumin is effective at inhibiting maladaptive cardiac repair and preserving cardiac function after ischaemia and reperfusion. Curcumin has potential as a treatment for patients who have had a heart attack.

Combination of hypoxic preconditioning and postconditioning does not induce additive protection of ex vivo human skeletal muscle from hypoxia/reoxygenation injury

We previously demonstrated that hypoxic preconditioning (HPreC) or postconditioning (HPostC) protected ex vivo human skeletal muscle from hypoxia/reoxygenation injury. Here, we investigated if combined HPreC and HPostC could convey additive protection. Human rectus abdominis muscle strips were cultured in normoxic Krebs buffer for 5 hours (control) or in 3 hours hypoxic/2 hours normoxic buffer (treatment groups). HPreC and HPostC were induced by 1 cycle of 5 minutes hypoxia/5 minutes reoxygenation immediately before or after 3 hours hypoxia, respectively. Muscle injury, viability, and adenosine triphosphate (ATP) synthesis were assessed by measuring lactate dehydrogenase release, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide reduction, and ATP content, respectively. Hypoxia/reoxygenation caused lactate dehydrogenase to increase and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide reduction and ATP content to decrease (P < 0.05; n = 7). HPreC, HPostC, and combination of both were equally effective in protection of muscle from hypoxia/reoxygenation injury. Atractyloside (5 × 10 M), a mitochondrial permeability transition pore opener, abolished the protective effect of HPreC or HPostC. We conclude that HPreC and HPostC protect ex vivo human skeletal muscle against hypoxia/reoxygenation injury by closing the mitochondrial permeability transition pore. For that reason, they are equally effective and do not demonstrate an additive effect. Moreover, the potent effect of HPostC indicates ischemic postconditioning as an effective clinical intervention against reperfusion injury in autogenous skeletal muscle transplantation and replantation surgery.

Ischemic post-conditioning and vasodilator therapy during standard cardiopulmonary resuscitation to reduce cardiac and brain injury after prolonged untreated ventricular fibrillation

AIM OF THE STUDY

We investigated the effects of ischemic postconditioning (IPC) with and without cardioprotective vasodilatory therapy (CVT) at the initiation of cardiopulmonary resuscitation (CPR) on cardio-cerebral function and 48-h survival.

METHODS

Prospective randomized animal study. Following 15 min of ventricular fibrillation, 42 Yorkshire farm pigs weighing an average of 34 ± 2 kg were randomized to receive standard CPR (SCPR, n=12), SCPR+IPC (n=10), SCPR+IPC+CVT (n=10), or SCPR+CVT (n=10). IPC was delivered during the first 3 min of CPR with 4 cycles of 20s of chest compressions followed by 20-s pauses. CVT consisted of intravenous sodium nitroprusside (2mg) and adenosine (24 mg) during the first minute of CPR. Epinephrine was given in all groups per standard protocol. A transthoracic echocardiogram was obtained on all survivors 1 and 4h post-ROSC. The brains were extracted after euthanasia at least 24h later to assess ischemic injury in 7 regions. Ischemic injury was graded on a 0-4 scale with (0=no injury to 4 ≥ 50% neural injury). The sum of the regional scores was reported as cerebral histological score (CHS). 48 h survival was reported.

RESULTS

Post-resuscitation left ventricular ejection (LVEF) fraction improved in SCPR+CVT, SCPR+IPC+CVT and SCPR+IPC groups compared to SCPR (59% ± 9%, 52% ± 14%, 52% ± 14% vs. 35% ± 11%, respectively, p<0.05). Only SCPR+IPC and SCPR+IPC+CVT, but not SCPR+CVT, had lower mean CHS compared to SCPR (5.8 ± 2.6, 2.8 ± 1.8 vs. 10 ± 2.1, respectively, p<0.01). The 48-h survival among SCPR+IPC, SCPR+CVT, SCPR+IPC+CVT and SCPR was 6/10, 3/10, 5/10 and 1/12, respectively (Cox regression p<0.01).

CONCLUSIONS

IPC and CVT during standard CPR improved post-resuscitation LVEF but only IPC was independently neuroprotective and improved 48-h survival after 15 min of untreated cardiac arrest in pigs.

Mitochondrial ROMK channel is a molecular component of mitoK(ATP)

RATIONALE

Activation of the mitochondrial ATP-sensitive potassium channel (mitoK(ATP)) has been implicated in the mechanism of cardiac ischemic preconditioning, yet its molecular composition is unknown.

OBJECTIVE

To use an unbiased proteomic analysis of the mitochondrial inner membrane to identify the mitochondrial K(+) channel underlying mitoK(ATP).

METHODS AND RESULTS

Mass spectrometric analysis was used to identify KCNJ1(ROMK) in purified bovine heart mitochondrial inner membrane and ROMK mRNA was confirmed to be present in neonatal rat ventricular myocytes and adult hearts. ROMK2, a short form of the channel, is shown to contain an N-terminal mitochondrial targeting signal, and a full-length epitope-tagged ROMK2 colocalizes with mitochondrial ATP synthase β. The high-affinity ROMK toxin, tertiapin Q, inhibits mitoK(ATP) activity in isolated mitochondria and in digitonin-permeabilized cells. Moreover, short hairpin RNA-mediated knockdown of ROMK inhibits the ATP-sensitive, diazoxide-activated component of mitochondrial thallium uptake. Finally, the heart-derived cell line, H9C2, is protected from cell death stimuli by stable ROMK2 overexpression, whereas knockdown of the native ROMK exacerbates cell death.

CONCLUSIONS

The findings support ROMK as the pore-forming subunit of the cytoprotective mitoK(ATP) channel.

Mitochondrial K+ channels are involved in ischemic postconditioning in rat hearts

The mitochondrial calcium-activated potassium channel (mitoK(Ca)) and the mitochondrial ATP-sensitive potassium channel (mitoK(ATP)) are both involved in cardiac preconditioning. Here, we examined whether these two channels are also involved in ischemic or pharmacological postconditioning. Using Langendorff perfusion, rat hearts were made hypoxic for 45 min and then reoxygenated for 30 min. Ischemic postconditioning (IPT) was achieved through application of 3 cycles of 10 s of reperfusion and 10 s of ischemia before reoxygenation, with and without paxilline (Pax; a mitoK(Ca) blocker) or 5-hydroxydecanoate (5-HD; a mitoK(ATP) blocker). Pharmacological postconditioning was carried out for 5 min at the onset of reoxygenation using NS1619 (a mitoK(Ca) opener) or diazoxide (Dia; a mitoK(ATP) opener). Pax and 5-HD abolished IPT-induced cardioprotection from reoxygenation injury, whereas administration of NS1619 or Dia significantly improved cardiac contractile activity and reduced aspartate aminotransferase (an index of myocyte injury) release following reoxygenation. In addition, isolated rat myocytes were loaded with tetramethylrhodamine methyl ester (TMRE; fluorescent mitochondrial membrane potential indicator) and 2',7'-dichlorofluorescein [DCFH; fluorescent reactive oxygen species (ROS) indicator] or Fluo-4-acetoxymethyl ester (Fluo-4-AM; fluorescent calcium indicator). When TMRE-loaded myocytes were laser illuminated, the DCFH and Fluo-4 fluorescence increased, and TMRE fluorescence decreased. These effects were significantly inhibited by NS1619 and Dia. We therefore conclude that IPT may protect the heart through activation of mitoK(ATP) and mitoK(Ca) channels, and that opening of these channels at the onset of reoxygenation protects the heart from reoxygenation injury, most likely by reducing excess generation of ROS and the resultant Ca(2+) overload.

Endogenous cardioprotection by ischaemic postconditioning and remote conditioning

Persistent myocardial ischaemia causes cell death if not rescued by early reperfusion. Millions of years in nature's laboratory have evolved protective responses that 'condition' the heart (and other tissues) to adapt to stressors, and these responses are applicable to the relatively new societal stress of myocardial ischaemia and reperfusion injury. Conditioning can be applied before (preconditioning), during (perconditioning), or after (postconditioning) the ischaemic stressor by imposing short periods of non-lethal ischaemia separated by brief periods of reperfusion. This conditioning protects multiple cell types and induces or rebalances a number of physiological and molecular pathways that ultimately attenuate necrosis and apoptosis. The seemingly disparate pathways may converge directly or indirectly on the mitochondria as a final effector, but other pathways not affecting mitochondria broaden the mechanisms of cardioprotection. The potential downsides of imposing even brief ischaemia directly on the heart somewhat tempered the enthusiasm for applying conditioning stimuli to the heart, but this hurdle was surmounted by applying ischaemia to remote organs and tissues in pre-, per-, and postconditioning. Although the clinical translation of remote per- and postconditioning has been rapid compared with classical preconditioning, there are numerous basic questions that require further investigation, and wider adoption awaits large-scale randomized clinical trials. Pharmacological mimetics may provide another important therapeutic approach by which to treat evolving myocardial infarction.

Desflurane-induced post-conditioning against myocardial infarction is mediated by calcium-activated potassium channels: role of the mitochondrial permeability transition pore

BACKGROUND

Desflurane (DES)-induced preconditioning is mediated by large-conductance calcium-activated potassium channels (BK(Ca)). Whether BK(Ca) are involved in anaesthetic-induced post-conditioning is unknown. We tested the hypothesis that DES-induced post-conditioning is mediated by BK(Ca) upstream of the mitochondrial permeability transition pore (mPTP).

METHODS

Pentobarbital-anaesthetized male C57Black/6 mice were subjected to 45 min coronary artery occlusion (CAO) and 3 h reperfusion. Animals received either no intervention or dimethylsulphoxide (DMSO, 10 µl g(-1)). DES (1.0 MAC, 7.5 vol%) was administered for 18 min, starting 3 min before the end of CAO. The following agents were given either alone or in combination with DES: the BK(Ca) activator NS1619 (1 µg g(-1)), the BK(Ca) inhibitor iberiotoxin (IbTx, 0.05 µg g(-1)), the mPTP opener atractyloside (ATRA, 25 µg g(-1)), and the mPTP inhibitor cyclosporine A (CYC A, 10 µg g(-1)). Infarct size (IS) was determined with triphenyltetrazolium chloride and the area at risk with Evans Blue, respectively.

RESULTS

IS in control animals was 48(6)%. Neither DMSO, IbTx nor ATRA affected myocardial IS. DES alone or NS1619 alone or the combination reduced IS (P<0.05), CYC A alone or in combination with IbTx or DES also reduced IS (P<0.05). DES-induced reduction of myocardial IS was completely abolished by IbTx and was partially blocked by ATRA and ATRA partially blocked IS reduction by NS1619.

CONCLUSIONS

These data suggest that DES-induced post-conditioning against myocardial infarction is mediated by BK(Ca) and mPTP. Cardioprotection by BK(Ca) activator NS1619 might occur, at least in part, independently of mPTP.

Mitochondria in postconditioning

Several signal transduction pathways are activated by cardioprotective stimuli, including ischemic or pharmacological postconditioning. These pathways converge on a common target, the mitochondria, and cardioprotection by postconditioning is associated with preserved mitochondrial function after ischemia/reperfusion. The present review discusses the role of mitochondria in cardioprotection, especially the involvement of ATP-dependent potassium channels, reactive oxygen species, and the mitochondrial permeability transition pore, and focuses on the effects of postconditioning on mitochondrial function (i.e., their oxygen consumption and calcium retention capacity). The contribution of mitochondria to loss of protection by postconditioning in diseased or aged myocardium is also addressed.

Postconditioning protects against human endothelial ischaemia-reperfusion injury via subtype-specific KATP channel activation and is mimicked by inhibition of the mitochondrial permeability transition pore

AIMS

Intermittent early reperfusion (ischaemic postconditioning; PostC) reduces ischaemia-reperfusion (IR) injury. Using an in vivo model of endothelial IR injury in humans, we sought to determine the role of K(ATP) channels in PostC and whether inhibition of the mitochondrial permeability transition pore (mPTP) at the onset of reperfusion protected against endothelial IR injury.

METHODS AND RESULTS

Endothelial function (EF) in healthy volunteers was assessed using vascular ultrasound to measure the percentage increase in the diameter of the brachial artery in response to reactive hyperaemia [flow-mediated dilatation (FMD)]. In resistance vessels, venous occlusion plethysmography was used to measure the dilator response to acetylcholine (ACh) [area under ACh dose-response curve (ACh AUC)]. Measurements were made before and after IR injury. Ischaemic postconditioning consisted of three 10 s cycles of alternating ischaemia and reperfusion in the first minute of reperfusion. Oral glibenclamide and glimepiride were used to determine the role of K(ATP) channel subtypes in PostC. Intra-arterial cyclosporine was used to determine the role of mPTP in endothelial IR injury. Ischaemia-reperfusion reduced EF in the brachial artery (FMD 7.1 ± 0.9% pre-IR, 2.8 ± 0.4% post-IR; P < 0.001) and resistance vessels [ACh AUC (×10(4)) 2.1 ± 0.4 pre-IR, 1.5 ± 0.2 post-IR; P < 0.05]. Ischaemic postconditioning preserved EF in the brachial artery [FMD 6.8 ± 0.9% (P < 0.001 vs. post-IR)] and resistance vessels [ACh AUC (×10(4)) 1.9 ± 0.2 (P < 0.001 vs. post-IR)]. Protection by PostC was abolished by glibenclamide in the brachial artery [FMD 3.3 ± 0.2% (P < 0.001 vs. post-IR + PostC)] and in resistance vessels [ACh AUC (×10(4)) 1.1 ± 0.2 (P < 0.001 vs. post-IR + PostC)], whereas glimepiride had no effect. Cyclosporine preserved EF after IR injury in the resistance vessels [ACh AUC (×10(4)) 1.4 ± 0.2 post-IR vs. 2.2 ± 0.3 post-IR + cyclosporine; P < 0.05].

CONCLUSION

Protection by PostC against endothelial IR injury in humans depends on K(ATP) channel activation and is mimicked by inhibition of the mPTP at reperfusion.

Post-ischemic conditioning in the rat retina is dependent upon ischemia duration and is not additive with ischemic pre-conditioning

Ischemic pre-conditioning (IPC) provides neuroprotection in the rat retina from the damaging effects of severe ischemia. Recently, neuroprotection by retinal ischemic post-conditioning (Post-C), i.e., transient ischemia after more lengthy, damaging ischemia, was described, but its mechanisms are not yet known. One possible explanation of the effectiveness of Post-C is that it augments intrinsic neuroprotective mechanisms initiated during ischemia. Increasing duration of the damaging ischemic insult may therefore impact the effectiveness of Post-C. IPC, in contrast, sets in motion a series of neuroprotective events prior to the onset of ischemia. Thus, IPC and Post-C may operate by differing mechanisms. Accordingly, we examined the effect of retinal ischemic duration on post-ischemic outcome in vivo in rats after adding Post-C, and the impact of combining pre- and post-conditioning. Recovery after ischemia performed 24 h after IPC, or after Post-C performed 5 min after ischemia ended, was assessed functionally (electroretinography) and histologically at 7 days after ischemia. Durations of ischemia of 45 and 55 min were studied. Since recovery with IPC or Post-C alone, with 55 min of ischemia, did not achieve the same degree of effect (i.e., not complete recovery) exhibited in our previous studies of IPC using a different ischemia model, we also combined IPC and Post-C to test the hypothesis of the possible additive effects of the IPC and Post-C. We found that the recovery after Post-C was enhanced to a greater degree when ischemia was of longer duration. Post-C led to greater post-ischemic recovery compared to IPC. Both IPC and Post-C also attenuated structural damage to the retina. Contrary to our hypothesis, IPC and Post-C did not combine to enhance recovery after ischemia. In earlier studies, IPC attenuated post-ischemic apoptosis. To begin to examine the mechanism of Post-C, we studied its impact on apoptosis following ischemia. We examined apoptosis by determining the percentage of TUNEL-positive cells at 24 h after ischemia. Post-C attenuated apoptosis, but when combined with IPC, TUNEL was similar in the combined group to that of ischemia alone. We also examined the role of the recruitment of an inflammatory response in ischemia and Post-C. We found that inflammatory markers increased by ischemia were not altered by Post-C. We conclude that Post-C effectiveness depends upon the duration of ischemia; Post-C is not additive with IPC, and Post-C functions, in part, by preventing apoptotic damage to the inner retina. Post-C has considerable promise for clinical translation to eye diseases that cause blindness by ischemia.

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.

Attenuation of myocardial injury by postconditioning: role of hypoxia inducible factor-1alpha

Postconditioning (PostC) has regenerated interest as a mechanical intervention against myocardial ischemia/reperfusion injury, but its molecular mechanisms remain elusive. This study tested the hypothesis that hypoxia inducible factor-1alpha (HIF-1alpha) plays a role in PostC-induced cardioprotection. Male Wistar rats were subjected to 30 min ischemia followed by 3 h of reperfusion (Control). PostC with 3 cycles of 10 s reperfusion and 10 s re-occlusion was applied at the onset of reperfusion. Relative to the Sham group, HIF-1alpha protein level was increased by 2.9-fold in the Control group, but its level was enhanced by 5.8-fold with PostC (P < 0.01 vs. Control). However, HIF-1alpha protein level was further augmented by 2.0-fold and 3.3-fold, respectively, when the prolyl hydroxylase inhibitor, dimethyloxalylglycine (DMOG, 40 mg/kg, i.p.) was given at 24 h before ischemia in both Control and PostC groups. PostC reduced infarct size by 24% compared with the Control (27 +/- 4.2% vs. 36 +/- 5.2%, P < 0.01), consistent with significant lower levels of plasma creatine kinase activity, index of cardiomyocyte apoptosis and caspase-3 activity. Although pretreatment with DMOG significantly reduced infarct size relative to the Control, the infarct-sparing effect of PostC was remarkably enhanced when DMOG was given before PostC (18 +/- 2.0% vs. 27 +/- 4.2% in PostC alone, P < 0.05). There was a significant linear inverse relationship between HIF-1alpha protein level and infarct size (r = -0.799, P < 0.01) among all groups. Furthermore, along with up-regulated HIF-1alpha expression, the levels of iNOS mRNA and protein were significantly increased in the PostC alone and DMOG plus PostC groups. In conclusion, these data suggest that HIF-1alpha is involved in cardioprotection by PostC and pharmacological augmentation of HIF-1alpha expression that enhances the infarct-sparing effect of PostC; iNOS, the downstream gene of HIF-1alpha, may participate in signaling pathways in mediating PostC's protection.