The multidimensional physiological responses to postconditioning

Cyclic Nigerosyl-Nigerose as Oxygen Nanocarrier to Protect Cellular Models from Hypoxia/Reoxygenation Injury: Implications from an In Vitro Model

Heart failure (HF) prevalence is increasing among the aging population, and the mortality rate remains unacceptably high despite improvements in therapy. Myocardial ischemia (MI) and, consequently, ischemia/reperfusion injury (IRI), are frequently the basis of HF development. Therefore, cardioprotective strategies to limit IRI are mandatory. Nanocarriers have been proposed as alternative therapy for cardiovascular disease. Controlled reoxygenation may be a promising strategy. Novel nanocarriers, such as cyclic nigerosyl-nigerose (CNN), can be innovative tools for oxygen delivery in a controlled manner. In this study we analyzed new CNN-based formulations as oxygen nanocarriers (O₂-CNN), and compared them with nitrogen CNN (N₂-CNN). These different CNN-based formulations were tested using two cellular models, namely, cardiomyoblasts (H9c2), and endothelial (HMEC) cell lines, at different concentrations. The effects on the growth curve during normoxia (21% O₂, 5% CO₂ and 74% N₂) and their protective effects during hypoxia (1% O₂, 5% CO₂ and 94% N₂) and reoxygenation (21% O₂, 5% CO₂ and 74% N₂) were studied. Neither O₂-CNN nor N₂-CNN has any effect on the growth curve during normoxia. However, O₂-CNN applied before hypoxia induces a 15–30% reduction in cell mortality after hypoxia/re-oxygenation when compared to N₂-CNN. O₂-CNN showed a marked efficacy in controlled oxygenation, which suggests an interesting potential for the future medical application of soluble nanocarrier systems for MI treatment.

H2S Pretreatment Is Promigratory and Decreases Ischemia/Reperfusion Injury in Human Microvascular Endothelial Cells

Endothelial cell injury and vascular function strongly correlate with cardiac function following ischemia/reperfusion injury. Several studies indicate that endothelial cells are more sensitive to ischemia/reperfusion compared to cardiomyocytes and are critical mediators of cardiac ischemia/reperfusion injury. H₂S is involved in the regulation of cardiovascular system homeostasis and can act as a cytoprotectant during ischemia/reperfusion. Activation of ERK1/2 in endothelial cells after H₂S stimulation exerts an enhancement of angiogenesis while its inhibition significantly decreases H₂S cardioprotective effects. In this work, we investigated how H₂S pretreatment for 24 hours prevents the ischemia/reperfusion injury and promotes angiogenesis on microvascular endothelial cells following an ischemia/reperfusion protocol in vitro, using a hypoxic chamber and ischemic buffer to simulate the ischemic event. H₂S preconditioning positively affected cell viability and significantly increased endothelial cell migration when treated with 1 μM H₂S. Furthermore, mitochondrial function was preserved when cells were preconditioned. Since ERK1/2 phosphorylation was extremely enhanced in ischemia/reperfusion condition, we inhibited ERK both directly and indirectly to verify how H₂S triggers this pathway in endothelial cells. Taken together, our data suggest that H₂S treatment 24 hours before the ischemic insult protects endothelial cells from ischemia/reperfusion injury and eventually decreases myocardial injury.

α-Cyclodextrin and α-Cyclodextrin Polymers as Oxygen Nanocarriers to Limit Hypoxia/Reoxygenation Injury: Implications from an In Vitro Model

The incidence of heart failure (HF) is increasing worldwide and myocardial infarction (MI), which follows ischemia and reperfusion (I/R), is often at the basis of HF development. Nanocarriers are interesting particles for their potential application in cardiovascular disease. Impaired drug delivery in ischemic disease is challenging. Cyclodextrin nanosponges (NS) can be considered innovative tools for improving oxygen delivery in a controlled manner. This study has developed new α-cyclodextrin-based formulations as oxygen nanocarriers such as native α-cyclodextrin (α-CD), branched α-cyclodextrin polymer (α-CD POLY), and α-cyclodextrin nanosponges (α-CD NS). The three different α-CD-based formulations were tested at 0.2, 2, and 20 µg/mL to ascertain their capability to reduce cell mortality during hypoxia and reoxygenation (H/R) in vitro protocols. H9c2, a cardiomyoblast cell line, was exposed to normoxia (20% oxygen) or hypoxia (5% CO₂ and 95% N₂). The different formulations, applied before hypoxia, induced a significant reduction in cell mortality (in a range of 15% to 30%) when compared to samples devoid of oxygen. Moreover, their application at the beginning of reoxygenation induced a considerable reduction in cell death (12% to 20%). α-CD NS showed a marked efficacy in controlled oxygenation, which suggests an interesting potential for future medical application of polymer systems for MI treatment.

Application of ischemic postconditioning's algorithms in tissues protection: response to methodological gaps in preclinical and clinical studies

Ischaemic postconditioning (IPostC) was introduced for the first time by Zhao et al. as a feasible method for reduction of myocardial ischaemia–reperfusion (IR) injury. The cardioprotection by this protocol has been extensively evaluated in various species. Then, further research revealed that IPostC is a safe and convenient approach in limiting IR injury of non‐myocardial tissues such as lung, liver, kidney, intestine, skeletal muscle, brain and spinal cord. IPostC has been conducted with different algorithms, resulting in diverse effects. The possible important factors leading to these differences are the difference in activation levels of signalling pathways and protective mediators by any algorithm, presence or absence of IPostC effectors in each tissue, or intrinsic characteristics of the tissues as well as the methodological biases. Also, the conflicting results have been shown with the application of the same algorithm of IPostC in certain tissues or animal species. The effectiveness of IPostC may depend upon various parameters including the species and the tissues characteristics. For example, different heart rates and metabolic rates of the species and unequal amounts of perfusion and blood flow of the tissues should be considered as the important determinants of IPostC effectiveness and should be thought about in designing IPostC algorithms for future studies. Due to these discrepancies, there is still no optimal single IPostC algorithm applicable to any tissue or any species. This issue is the main topic of the present article.

Atorvastatin protects myocardium against ischemia-reperfusion arrhythmia by increasing Connexin 43 expression: A rat model

Atorvastatin has protective effects against myocardial ischemia-reperfusion injuries and ischemia-reperfusion arrhythmia. This study was designed to investigate whether atorvastatin is able to protect against myocardial ischemia-reperfusion injury by enhancing the expression of Connexin 43 (Cx43) via the activation of the phosphatidylinositol-3-kinase (PI3K)/Akt pathway and mitochondrial ATP-sensitive potassium (K(ATP)) channels. Isolated perfused rat hearts were treated with classic ischemia postconditioning (IPOST), atorvastatin, and atorvastatin combined with inhibitor of PI3K and K(ATP) channels, respectively, after 30min of LAD ischemia and then subjected to reperfusion for 120min. The QRS duration and the ischemia-reperfusion ventricular arrhythmia were assessed. The lactate dehydrogenase (LDH) and creatine kinase isoenzyme (CK-MB) levels were measured and the Cx43 expression was assessed by immunoblotting and immunohistochemistry. After 120min of reperfusion, atorvastatin and IPOST significantly decreased the QRS duration and inhibited ventricular arrhythmia. They also decreased the levels of LDH and CK-MB. Meanwhile, atorvastatin and IPOST also significantly enhanced the Cx43 expression and the phosphorylation of Cx43. Such protective effects were abolished in the presence of the inhibitor of PI3K or the inhibitor of mitochondrial K(ATP) channels. This study suggests that atorvastatin protected against myocardial ischemia-reperfusion injury and enhanced the expression of Cx43 by activating the PI3K/Akt pathway and mitochondrial K(ATP) channels.

Protein S-nitrosylation in preconditioning and postconditioning

The coronary artery disease is a leading cause of death and morbidity worldwide. This disease has a complex pathophysiology that includes multiple mechanisms. Among these is the oxidative/nitrosative stress. Paradoxically, oxidative/nitrosative signaling plays a major role in cardioprotection against ischemia/reperfusion injury. In this context, the gas transmitter nitric oxide may act through several mechanisms, such as guanylyl cyclase activation and via S-nitrosylation of proteins. The latter is a covalent modification of a protein cysteine thiol by a nitric oxide-group that generates an S-nitrosothiol. Here, we report data showing that nitric oxide and S-nitrosylation of proteins play a pivotal role not only in preconditioning but also in postconditioning cardioprotection.

Olmesartan restores the protective effect of remote ischemic perconditioning against myocardial ischemia/reperfusion injury in spontaneously hypertensive rats

OBJECTIVES

Remote ischemic perconditioning is the newest technique used to lessen ischemia/reperfusion injury. However, its effect in hypertensive animals has not been investigated. This study aimed to examine the effect of remote ischemic perconditioning in spontaneously hypertensive rats and determine whether chronic treatment with Olmesartan could influence the effect of remote ischemic perconditioning.

METHODS

Sixty rats were randomly divided into six groups: vehicle-sham, vehicle-ischemia/reperfusion injury, vehicle-remote ischemic perconditioning, olmesartan-sham, olmesartan-ischemia/reperfusion and olmesartan-remote ischemic perconditioning. The left ventricular mass index, creatine kinase concentration, infarct size, arrhythmia scores, HIF-1α mRNA expression, miR-21 expression and miR-210 expression were measured.

RESULTS

Olmesartan significantly reduced the left ventricular mass index, decreased the creatine kinase concentration, limited the infarct size and reduced the arrhythmia score. The infarct size, creatine kinase concentration and arrhythmia score during reperfusion were similar for the vehicle-ischemia/reperfusion group and vehicle-remote ischemic perconditioning group. However, these values were significantly decreased in the olmesartan-remote ischemic perconditioning group compared to the olmesartan-ischemia/reperfusion injury group. HIF-1α, miR-21 and miR-210 expression were markedly down-regulated in the Olmesartan-sham group compared to the vehicle-sham group and significantly up-regulated in the olmesartan-remote ischemic perconditioning group compared to the olmesartan-ischemia/reperfusion injury group.

CONCLUSION

The results indicate that (1) the protective effect of remote ischemic perconditioning is lost in vehicle-treated rats and that chronic treatment with Olmesartan restores the protective effect of remote ischemic perconditioning; (2) chronic treatment with Olmesartan down-regulates HIF-1α, miR-21 and miR-210 expression and reduces hypertrophy, thereby limiting ischemia/reperfusion injury; and (3) recovery of the protective effect of remote ischemic perconditioning is related to the up-regulation of HIF-1α, miR-21 and miR-210 expression.

Ischaemic conditioning: pitfalls on the path to clinical translation

The development of novel adjuvant strategies capable of attenuating myocardial ischaemia-reperfusion injury and reducing infarct size remains a major, unmet clinical need. A wealth of preclinical evidence has established that ischaemic 'conditioning' is profoundly cardioprotective, and has positioned the phenomenon (in particular, the paradigms of postconditioning and remote conditioning) as the most promising and potent candidate for clinical translation identified to date. However, despite this preclinical consensus, current phase II trials have been plagued by heterogeneity, and the outcomes of recent meta-analyses have largely failed to confirm significant benefit. As a result, the path to clinical application has been perceived as 'disappointing' and 'frustrating'. The goal of the current review is to discuss the pitfalls that may be stalling the successful clinical translation of ischaemic conditioning, with an emphasis on concerns regarding: (i) appropriate clinical study design and (ii) the choice of the 'right' preclinical models to facilitate clinical translation.

Postconditioning signalling in the heart: mechanisms and translatability

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

Ischemic conditioning: the challenge of protecting the diabetic heart

The successful clinical translation of novel therapeutic strategies to attenuate lethal myocardial ischemia-reperfusion injury and limit infarct size has been identified as a major unmet need, and is of particular importance in patients with type-2 diabetes. There is a wealth of preclinical evidence that ischemic conditioning (encompassing the three paradigms of preconditioning, postconditioning and remote conditioning) is profoundly cardioprotective and, via up-regulation of endogenous signaling cascades, renders the heart resistant to infarction. However, current phase II trials aimed at exploiting ischemic conditioning for the clinical treatment of myocardial ischemia-reperfusion injury have yielded mixed results, possibly reflecting the emerging concern that the efficacy of conditioning-induced cardioprotection may be compromised in the diabetic heart. Our goal in this review is to provide a summary of our present understanding of the effect of type-2 diabetes on the infarct-sparing effect of ischemic conditioning, and the challenges of limiting ischemia-reperfusion injury in the diabetic heart.

Silymarin component 2,3-dehydrosilybin attenuates cardiomyocyte damage following hypoxia/reoxygenation by limiting oxidative stress

Ischemic postconditioning and remote conditioning are potentially useful tools for protecting ischemic myocardium. This study tested the hypothesis that 2,3-dehydrosilybin (DHS), a flavonolignan component of Silybum marianum, could attenuate cardiomyocyte damage following hypoxia/reoxygenation by decreasing the generation of reactive oxygen species (ROS). After 5-6 days of cell culture in normoxic conditions the rat neonatal cardiomyocytes were divided into four groups. Control group (9 h at normoxic conditions), hypoxia/reoxygenation group (3 h at 1 % O₂, 94 % N₂and 5 % CO₂followed by 10 min of 10 micromol·l⁻¹DHS and 6 h of reoxygenation in normoxia) and postconditioning group (3 h of hypoxia, three cycles of 5 min reoxygenation and 5 min hypoxia followed by 6 h of normoxia). Cell viability assessed by propidium iodide staining was decreased after DHS treatment consistent with increased levels of lactatedehydrogenase (LDH) after reoxygenation. LDH leakage was significantly reduced when cardiomyocytes in the H/Re group were exposed to DHS. DHS treatment reduced H₂O₂production and also decreased the generation of ROS in the H/Re group as evidenced by a fluorescence indicator. DHS treatment reduces reoxygenation-induced injury in cardiomyocytes by attenuation of ROS generation, H₂O₂and protein carbonyls levels. In addition, we found that both the postconditioning protocol and the DHS treatment are associated with restored ratio of phosphorylated/total protein kinase C epsilon, relative to the H/Re group. In conclusion, our data support the protective role of DHS in hypoxia/reperfusion injury and indicate that DHS may act as a postconditioning mimic.

Overexpression of the muscle-specific protein, melusin, protects from cardiac ischemia/reperfusion injury

Melusin is a muscle-specific protein which interacts with β1 integrin cytoplasmic domain and acts as chaperone protein. Its overexpression induces improved resistance to cardiac overload delaying left ventricle dilation and reducing the occurrence of heart failure. Here, we investigated possible protective effect of melusin overexpression against acute ischemia/reperfusion (I/R) injury with or without Postconditioning cardioprotective maneuvers. Melusin transgenic (Mel-TG) mice hearts were subjected to 30-min global ischemia followed by 60-min reperfusion. Interestingly, infarct size was reduced in Mel-TG mice hearts compared to wild-type (WT) hearts (40.3 ± 3.5 % Mel-TG vs. 59.5 ± 3.8 % WT hearts; n = 11 animals/group; P < 0.05). The melusin protective effect was also demonstrated by measuring LDH release, which was 50 % lower in Mel-TG compared to WT. Mel-TG hearts had a higher baseline level of AKT, ERK1/2 and GSK3β phosphorylation, and displayed increased phospho-kinases level after I/R compared to WT mice. Post-ischemic Mel-TG hearts displayed also increased levels of the anti-apoptotic factor phospho-BAD. Importantly, pharmacological inhibition of PI3K/AKT (Wortmannin) and ERK1/2 (U0126) pathways abrogated the melusin protective effect. Notably, HSP90, a chaperone known to protect heart from I/R injury, showed high levels of expression in the heart of Mel-TG mice suggesting a possible collaboration of this molecule with AKT/ERK/GSK3β pathways in the melusin-induced protection. Postconditioning, known to activate AKT/ERK/GSK3β pathways, significantly reduced IS and LDH release in WT hearts, but had no additive protective effects in Mel-TG hearts. These findings implicate melusin as an enhancer of AKT and ERK pathways and as a novel player in cardioprotection from I/R injury.

The impact of ischemia-reperfusion injury on the effectiveness of primary angioplasty in ST-segment elevation myocardial infarction

The most effective method of reperfusion in patients with ST-segment elevation myocardial infarction (STEMI) is primary percutaneous coronary intervention (PCI), assisted by aspiration thrombectomy and administration of antiplatelet agents and anticoagulants. However, effective restoration of blood flow in the infarct-related artery may paradoxically result in further damage to the heart muscle. This phenomenon, called ischemia-reperfusion injury (IRI), can significantly reduce the beneficial effects of reperfusion therapy. The rapid restoration of blood flow to the previously ischemic area causes a number of pathophysiological mechanisms leading to increased necrosis of myocytes still viable at the end of the ischemic period. It has been postulated that there are several strategies that can reduce damage to the heart muscle. Attempts to translate the results of experimental trials has been disappointing. More recently, however, some of the clinical benefits of ischemic postconditioning in which reperfusion in patients with STEMI who are undergoing PCI is interrupted with short episodes of ischemia were demonstrated. This renewed the interest in the reperfusion phase as a target for cardioprotective therapy. Research in this field has also been reinforced by the discovery of new potential targets for treatment that protects against IRI, such as the kinase pathway to protect against damage (reperfusion injury salvage kinases – RISK) and mitochondrial permeability transition pore. It seems that these findings will help to develop strategies that will improve the efficiency of mechanical reperfusion and may translate into long-term clinical effects.

Reduction of myocardial infarct size with ischemic "conditioning": physiologic and technical considerations

A wealth of evidence has revealed that the heart can be "conditioned" and rendered less vulnerable to ischemia-reperfusion injury via the upregulation of endogenous protective signaling pathways. Three distinct conditioning strategies have been identified: (1) preconditioning, the phenomenon where brief episodes of myocardial ischemia (too brief to cause cardiomyocyte death) limit necrosis caused by a subsequent sustained ischemic insult; (2) postconditioning, the concept that relief of myocardial ischemia in a staged or stuttered manner attenuates lethal ischemia-reperfusion injury; and (3) remote conditioning, or upregulation of a cardioprotective phenotype initiated by ischemia in a remote organ or tissue and "transported" to the heart. Progress has been made in defining the technical requirements and limitations of each of the 3 ischemic conditioning models (including the timing and severity of the protective stimulus), as well as elucidating the molecular mechanisms (in particular, the receptor-mediated signaling pathways) responsible for conditioning-induced myocardial protection. Moreover, phase III clinical trials are in progress, seeking to capitalize on the protection that can be achieved by postconditioning and remote conditioning, and applying these strategies in patients undergoing cardiac surgery or angioplasty for the treatment of acute myocardial infarction. There is, however, a potentially important caveat to the clinical translation of myocardial conditioning: emerging data suggest that the efficacy of ischemic conditioning is compromised in aging, diabetic, and hypertensive cohorts, the specific populations in which myocardial protection is most relevant. Successful clinical application of myocardial conditioning will therefore require an understanding of the potential confounding consequences of these comorbidities on the "conditioned" phenotype.

The science and clinical translation of remote postconditioning

The treatment of reperfusion injury requires measures beyond timely reperfusion. Conventional postconditioning (PostC) of ischemic tissues offers a strategy to reduce reperfusion injury, but its adoption is challenged by requiring access and imposing additional ischemia to the ischemic organ. Generating protective signals by PostC in a tissue remote from the target organ such as the limb, i.e. remote PostC (rPostC), may present an alternative approach to exerting endogenous tissue protection. Because rPostC is only recently reported, the fundamental biology of rPostC is not well understood, and studies to date are largely observational. rPostC has been observed to reduce ischemia-reperfusion injury experimentally in heart, kidney, brain and skeletal muscle in multiple species, including rat, rabbit and pig. Both necrosis and apoptosis are reduced. As in remote ischemic preconditioning, rPostC requires a transfer or communication of protective factors or signals through humoral and/or neural pathways. Triggers of target organ protection include G-protein-coupled receptor ligands, metabolites of ischemia, or small thermolabile molecules. Some evidence suggests that reperfusion injury salvage kinases may be involved in rPostC, in agreement with both preconditioning and conventional PostC. Clinical studies investigating improvements in clinical outcomes or biomarkers with rPostC are encouraging.

The emerging application of remote ischemic conditioning in the clinical arena

Remote ischemic conditioning (RIC) is an intervention, in which intermittent episodes of ischemia and reperfusion in an organ or tissue distant from the target organ requiring protection, provide armour against lethal ischemia-reperfusion injury. Although the exact mechanisms underlying the protection mediated through RIC have not been clearly established, the release of humoral factors and the activation of neural pathways have been implicated. There is now clinical evidence suggesting that this form of protection can be induced by a simple, noninvasive, and cost-effective procedure such as inflation and deflation of a blood pressure cuff and that this intervention provides increased organ protection in a variety of clinical scenarios, for example, in myocardial infarction. Here we provide an overview of the history and evolution of RIC, the potential mechanisms underlying its protective effects, and published randomized clinical trials in cardiovascular procedures.

Mitochondrial pathways, permeability transition pore, and redox signaling in cardioprotection: therapeutic implications

Reperfusion therapy is the indispensable treatment of acute myocardial infarction (AMI) and must be applied as soon as possible to attenuate the ischemic insult. However, reperfusion is responsible for additional myocardial damage likely involving opening of the mitochondrial permeability transition pore (mPTP). A great part of reperfusion injury occurs during the first minute of reperfusion. The prolonged opening of mPTP is considered one of the endpoints of the cascade to myocardial damage, causing loss of cardiomyocyte function and viability. Opening of mPTP and the consequent oxidative stress due to reactive oxygen and nitrogen species (ROS/RNS) are considered among the major mechanisms of mitochondrial and myocardial dysfunction. Kinases and mitochondrial components constitute an intricate network of signaling molecules and mitochondrial proteins, which interact in response to stressors. Cardioprotective pathways are activated by stimuli such as preconditioning and postconditioning (PostC), obtained with brief intermittent ischemia or with pharmacological agents, which drastically reduce the lethal ischemia/reperfusion injury. The protective pathways converging on mitochondria may preserve their function. Protection involves kinases, adenosine triphosphate-dependent potassium channels, ROS signaling, and the mPTP modulation. Some clinical studies using ischemic PostC during angioplasty support its protective effects, and an interesting alternative is pharmacological PostC. In fact, the mPTP desensitizer, cyclosporine A, has been shown to induce appreciable protections in AMI patients. Several factors and comorbidities that might interfere with cardioprotective signaling are considered. Hence, treatments adapted to the characteristics of the patient (i.e., phenotype oriented) might be feasible in the future.

Magnesium orotate elicits acute cardioprotection at reperfusion in isolated and in vivo rat hearts

Orotic acid and its salts chronically administered have been shown to significantly improve cardiac function in pathological settings associated with ischemia–reperfusion (I/R) injury. The aim of our study was to investigate the effect of magnesium orotate (Mg-Or) administration at the onset of post-ischemic reperfusion on myocardial function and infarct size (IS). Ex-vivo experiments performed on isolated perfused rat hearts were used to compare Mg-Or administration with a control group (buffer treated), ischemic post-conditioning, orotic acid treatment, and MgCl2 treatment. Mg-Or administration was also investigated in an in-vivo model of regional I/R performed in rats undergoing reversible coronary ligation. The effect of Mg-Or on mitochondrial permeability transition pore (mPTP) opening after I/R was investigated in vitro to gain mechanistic insights. Both ex-vivo and in-vivo experiments showed a beneficial effect from Mg-Or administration at the onset of reperfusion on myocardial function and IS. In-vitro assays showed that Mg-Or significantly delayed mPTP opening after I/R. Our data suggest that Mg-Or administered at the very onset of reperfusion may preserve myocardial function and reduce IS. This beneficial effect may be related to a significant reduction of mPTP opening, a usual trigger of cardiac cell death following I/R.

Catestatin reduces myocardial ischaemia/reperfusion injury: involvement of PI3K/Akt, PKCs, mitochondrial KATP channels and ROS signalling

Catestatin (CST) limits myocardial ischaemia/reperfusion (I/R) injury with unknown mechanisms. Clearly phosphoinositide-3-kinase (PI3K), protein kinase C (PKC) isoforms, including intra-mitochondrial PKCε, mitochondrial KATP (mitoKATP) channels and subsequent reactive oxygen species (ROS)-signalling play important roles in postconditioning cardioprotection, preventing mitochondrial permeability transition pore (mPTP) opening. Therefore, we studied the role of these extra- and intra-mitochondrial factors in CST-induced protection. Isolated rat hearts and H9c2 cells underwent I/R and oxidative stress, respectively. In isolated hearts CST (75nM, CST-Post) given in early-reperfusion significantly reduced infarct size, limited post-ischaemic contracture, and improved recovery of developed left ventricular pressure. PI3K inhibitor, LY-294002 (LY), large spectrum PKC inhibitor, Chelerythrine (CHE), specific PKCε inhibitor (εV1-2), mitoKATP channel blocker, 5-Hydroxydecanoate (5HD) or ROS scavenger, 2-mercaptopropionylglycine (MPG) abolished the infarct-sparing effect of CST. Notably the CST-induced contracture limitation was maintained during co-infusion of 5HD, MPG or εV1-2, but it was lost during co-infusion of LY or CHE. In H9c2 cells challenged with H2O2, mitochondrial depolarization (an index of mPTP opening studied with JC1-probe) was drastically limited by CST (75nM). Our results suggest that the protective signalling pathway activated by CST includes mitoKATP channels, ROS signalling and prevention of mPTP opening, with a central role for upstream PI3K/Akt and PKCs. In fact, all inhibitors completely abolished CST-infarct-sparing effect. Since CST-anti-contracture effect cannot be explained by intra-mitochondrial mechanisms (PKCε activation and mitoKATP channel opening) or ROS signalling, it is proposed that these downstream signals are part of a reverberant loop which re-activates upstream PKCs, which therefore play a pivotal role in CST-induced protection.

Perconditioning and postconditioning: current knowledge, knowledge gaps, barriers to adoption, and future directions

The broad definition of "conditioning" is the application of a series of alternating intervals of brief ischemia (hypoxia) and reperfusion (reoxygenation) applied in the setting of prolonged ischemia causing myocardial infarction. While the conditioning stimulus is applied before the major (index) ischemic event in ischemic preconditioning, it is applied during the event in perconditioning, and applied after the event (reperfusion) in postconditioning. Studies on perconditioning have only recently demonstrated a reduction in infarct size by remote ischemia applied during transport of heart attack victims to the hospital before percutaneous coronary interventions (PCIs). The "conditioning" paradigm has been extended to include remote perconditioning and remote postconditioning. However, the biology of perconditioning is virtually unknown. Postconditioning has enjoyed enthusiastic attention from scientists that have done much to demonstrate that the model of triggers, mediators, and effectors used in preconditioning may also apply to postconditioning, with the addition and important contribution of physiological mechanisms resulting in cardioprotection, including gradual normalization of tissue pH, reduction in generation of reactive oxygen species, and avoidance of hypercontracture. This same schema has not been confirmed in perconditioning. However, the unknowns in both conditioning paradigms far outweigh the knowns. Why postconditioning does not exert cardioprotection in experimental models of comorbidities and aging, yet reduces postischemic injury and contractile dysfunction in older patients with multiple comorbidities is a conundrum for which no answers are forthcoming. The optimal algorithm is unknown, as is the interrelationship between the many molecular, cellular, and physiological pathways that purportedly "mediate" or "trigger" the conditioning responses. Whether there are common pathways engaged in all 3 forms of conditioning, and what nuances separate one form of conditioning from another are unanswered questions. Yet, the translational potential of per- and postconditioning will drive further experimental work and clinical trials, which will ask unprecedented cooperation and information sharing between basic and clinician scientists, and creative developments from industry.

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.

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.

Efficacy of cardioprotective 'conditioning' strategies in aging and diabetic cohorts: the co-morbidity conundrum

Evidence obtained in multiple experimental models has revealed that cardiac 'conditioning' strategies--including ischaemic preconditioning, postconditioning, remote conditioning and administration of pharmacological conditioning mimetics--are profoundly protective and significantly attenuate myocardial ischaemia-reperfusion injury. As a result, there is considerable interest in translating these cardioprotective paradigms from the laboratory to patients. However, the majority of studies investigating conditioning-induced cardioprotection have utilized healthy adult animals devoid of the risk factors and co-morbidities associated with cardiovascular disease and acute myocardial infarction. The aim of this article is to summarize the growing consensus that two well established risk factors, aging and diabetes mellitus, may render the heart refractory to the favourable effects of myocardial conditioning, and discuss the clinical implications of a loss in efficacy of cardiac conditioning paradigms in these patient populations.

Ischaemic postconditioning revisited: lack of effects on infarct size following primary percutaneous coronary intervention

AIMS

To assess the short- and long-term effects of postconditioning (p-cond) on infarct size, extent of myocardial salvage, and left ventricular ejection fraction (LVEF) in a series of patients presenting with evolving ST-elevation myocardial infarction (STEMI). Previous studies have shown that p-cond during primary percutaneous coronary intervention (PCI) confers protection against ischaemia-reperfusion injury and thus might reduce myocardial infarct size.

METHODS AND RESULTS

Seventy-nine patients undergoing PCI for a first STEMI with TIMI grade flow 0-1 and no collaterals were randomized to p-cond (n= 39) or controls (n= 40). Postconditioning was performed by applying four consecutive cycles of 1 min balloon inflation, each followed by 1 min deflation. Infarct size, myocardial salvage, and LVEF were assessed by cardiac-MRI 1 week and 6 months after MI. Postconditioning was associated with lower myocardial salvage (4.1 ± 7.2 vs. 9.1 ± 5.8% in controls; P= 0.004) and lower myocardial salvage index (18.9 ± 27.4 vs. 30.9 ± 20.5% in controls; P= 0.038). No significant differences in infarct size and LVEF were found between the groups at 1 week and 6 months after MI.

CONCLUSION

This randomized study suggests that p-cond during primary PCI does not reduce infarct size or improve myocardial function recovery at both short- and long-term follow-up and might have a potential harmful effect.

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.

Cardioprotection with postconditioning: loss of efficacy in murine models of type-2 and type-1 diabetes

Postconditioning (PostC), or relief of myocardial ischemia in a stuttered manner, has been shown to reduce infarct size, due in part to upregulation of survival kinase signaling. Virtually all of these data have, however, been obtained in healthy adult cohorts; the question of whether PostC-induced cardioprotection is maintained in the setting of clinically relevant comorbidities has remained largely unexplored. Accordingly, our aim was to assess the consequences of a major risk factor-diabetes-on the infarct-sparing effect of stuttered reflow. Isolated buffer-perfused hearts were obtained from normoglycemic C57BL/6J mice, BKS.Cg-m+/+Lepr(db)/J (db/db) mice (model of type-2 diabetes), C57BL/6J mice injected with streptozotocin (model of type-1 diabetes), and streptozotocin-injected mice in which normoglycemia was re-established by islet cell transplantation. All hearts underwent 30  min of ischemia and, within each cohort, hearts received either standard (control) reperfusion or three to six 10-s cycles of stuttered reflow. PostC reduced infarct size via upregulation of extracellular signal-regulated kinase 1/2 in normoglycemic mice. In contrast, diabetic hearts were refractory to PostC-induced cardioprotection-an effect that, in the type-1 model, was reversed by restoration of normoglycemia. We provide novel evidence for a profound-but potentially reversible-diabetes-induced defect in the cardioprotective efficacy of PostC.

Cardiac postconditioning

In the heart, ischemia/reperfusion damage occurs mainly during the first minutes of reperfusion. Recently, it has been shown that the heart can be protected against the extension of ischemia/reperfusion injury if brief coronary occlusions are performed just at the beginning of the reperfusion. This procedure has been called postconditioning (PostC). It can also be elicited by pharmacological intervention, that is, pharmacological PostC. In particular, PostC limits infarct size, apoptosis, endothelial dysfunction, neutrophil adherence, and arrhythmias. Similar to preconditioning, PostC may trigger signaling pathways, including reperfusion injury salvage kinase and survivor activating factor enhancement pathways. PostC-induced protection also involves intracellular acidosis and early redox-sensitive mechanisms. However, controversies exist on the nature of receptors and main pathway(s) involved in PostC. Protective pathways activated by PostC appear to converge on mitochondria and, in particular, on mitochondrial permeability transition pores. Preliminary clinical data indicate that drugs targeting mitochondrial permeability transition pore or reperfusion injury salvage kinases may confer benefits to patients with acute myocardial infarction above that provided by myocardial reperfusion alone. Future studies must define the principal protective cascades, the interdependence of the signaling pathways, and the optimal pharmacological target and agent(s) for protection. These studies must also consider the possible confounding effects of comorbidities and their drug treatments.

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.

Ischemic post-conditioning to counteract intestinal ischemia/reperfusion injury

Intestinal ischemia is a severe disorder with a variety of causes. Reperfusion is a common occurrence during treatment of acute intestinal ischemia but the injury resulting from ischemia/reperfusion (IR) may lead to even more serious complications from intestinal atrophy to multiple organ failure and death. The susceptibility of the intestine to IR-induced injury (IRI) appears from various experimental studies and clinical settings such as cardiac and major vascular surgery and organ transplantation. Whereas oxygen free radicals, activation of leukocytes, failure of microvascular perfusion, cellular acidosis and disturbance of intracellular homeostasis have been implicated as important factors in the pathogenesis of intestinal IRI, the mechanisms underlying this disorder are not well known. To date, increasing attention is being paid in animal studies to potential pre- and post-ischemia treatments that protect against intestinal IRI such as drug interference with IR-induced apoptosis and inflammation processes and ischemic pre-conditioning. However, better insight is needed into the molecular and cellular events associated with reperfusion-induced damage to develop effective clinical protection protocols to combat this disorder. In this respect, the use of ischemic post-conditioning in combination with experimentally prolonged acidosis blocking deleterious reperfusion actions may turn out to have particular clinical relevance.