Remote postconditioning. Brief renal ischemia and reperfusion applied before coronary artery reperfusion reduces myocardial infarct size via endogenous activation of adenosine receptors

Effect of remote ischemic conditioning on atrial fibrillation and outcome after coronary artery bypass grafting (RICO-trial)

Background

Pre- and postconditioning describe mechanisms whereby short ischemic periods protect an organ against a longer period of ischemia. Interestingly, short ischemic periods of a limb, in itself harmless, may increase the ischemia tolerance of remote organs, e.g. the heart (remote conditioning, RC). Although several studies have shown reduced biomarker release by RC, a reduction of complications and improvement of patient outcome still has to be demonstrated. Atrial fibrillation (AF) is one of the most common complications after coronary artery bypass graft surgery (CABG), affecting 27-46% of patients. It is associated with increased mortality, adverse cardiovascular events, and prolonged in-hospital stay. We hypothesize that remote ischemic pre- and/or post-conditioning reduce the incidence of AF following CABG, and improve patient outcome.

Methods/design

This study is a randomized, controlled, patient and investigator blinded multicenter trial. Elective CABG patients are randomized to one of the following four groups: 1) control, 2) remote ischemic preconditioning, 3) remote ischemic postconditioning, or 4) remote ischemic pre- and postconditioning. Remote conditioning is applied at the arm by 3 cycles of 5 minutes of ischemia and reperfusion. Primary endpoint is the incidence AF in the first 72 hours after surgery, detected using a Holter-monitor. Secondary endpoints include length-of-stay on the intensive care unit and in-hospital, and the occurrence of major adverse cardiovascular events at 30 days, 3 months and 1 year.

Based on an expected incidence in the control group of 27%, 195 patients per group are needed to detect with 80% power a reduction by 45% following either pre- or postconditioning, while allowing for a 10% dropout and at an alpha of 0.05. With the combined intervention expected to be stronger, we need 75 patients in this group to detect a reduction in incidence of AF of 60%.

Discussion

The RICO-trial (the effect of Remote Ischemic Conditioning on atrial fibrillation and Outcome) is a randomized controlled multicenter trial, designed to investigate whether remote ischemic pre- and/or post-conditioning of the arm reduce the incidence of AF following CABG surgery.

Trial registration

ClinicalTrials.gov under NCT01107184.

Postconditioning in acute myocardial infarction patients

Reperfusion therapy is the indispensable treatment of acute myocardial infarction (AMI) and must be applied as soon as possible to attenuate the ischemic insult. Evidence indicates that reperfusion is responsible for additional myocardial damage likely involving opening of the mitochondrial permeability transition pore. Ischemic postconditioning is a new way to dramatically reduce the lethal reperfusion injury. Several clinical studies using angioplasty postconditioning now support its protective effects in patients with an AMI. An interesting alternative is pharmacological postconditioning, which could be applied to a much larger number of patients. The mitochondrial permeability transition pore inhibitor cyclosporine A has been shown to generate a comparable protection in AMI patients. Future large-scale trials are needed to determine whether postconditioning may improve clinical outcome in ST-segment elevation MI patients.

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.

Contribution of delayed intracellular pH recovery to ischemic postconditioning protection

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

Targeting of adenosine receptors in ischemia-reperfusion injury

IMPORTANCE OF THE FIELD

Ischemia-reperfusion (IR) injury is a common problem after transplantation as well as myocardial infarction and stroke. IR initiates an inflammatory response leading to rapid tissue damage. Adenosine, produced in response to IR, is generally considered a protective signaling molecule and elicits its physiological responses through four distinct adenosine receptors. The short half-life, lack of specificity and rapid metabolism limits the use of adenosine as a therapeutic agent. Thus, intense research efforts have focused on the synthesis and implementation of specific adenosine receptor agonists and antagonists as potential therapeutic agents for a variety of inflammatory conditions including IR injury.

AREAS COVERED IN THIS REVIEW

Current knowledge on IR injury with a focus on lung, heart and kidney and studies that have advanced our understanding of the role of adenosine receptors and the therapeutic potential of adenosine receptor agonists and antagonists for the prevention of IR injury.

WHAT THE READER WILL GAIN

Insight into the role of adenosine receptor signaling in IR injury.

TAKE HOME MESSAGE

No therapies are currently available that specifically target IR injury; however, targeting of specific adenosine receptors may offer therapeutic strategies in this regard.

Remote postconditioning by humoral factors in effluent from ischemic preconditioned rat hearts is mediated via PI3K/Akt-dependent cell-survival signaling at reperfusion

Short non-lethal ischemic episodes administered to hearts prior to (ischemic preconditioning, IPC) or directly after (ischemic postconditioning, IPost) ischemic events facilitate myocardial protection. Transferring coronary effluent collected during IPC treatment to un-preconditioned recipient hearts protects from lethal ischemic insults. We propose that coronary IPC effluent contains hydrophobic cytoprotective mediators acting via PI3K/Akt-dependent pro-survival signaling at ischemic reperfusion. Ex vivo rat hearts were subjected to 30 min of regional ischemia and 120 min of reperfusion. IPC effluent administered for 10 min prior to index ischemia attenuated infarct size by ≥55% versus control hearts (P < 0.05). Effluent administration for 10 min at immediate reperfusion (reperfusion therapy) or as a mimetic of pharmacological postconditioning (remote postconditioning, RIPost) significantly reduced infarct size compared to control (P < 0.05). The IPC effluent significantly increased Akt phosphorylation in un-preconditioned hearts when administered before ischemia or at reperfusion, while pharmacological inhibition of PI3K/Akt-signaling at reperfusion completely abrogated the cardioprotection offered by effluent administration. Fractionation of coronary IPC effluent revealed that cytoprotective humoral mediator(s) released during the conditioning phase were of hydrophobic nature as all hydrophobic fractions with molecules under 30 kDa significantly reduced infarct size versus the control and hydrophilic fraction-treated hearts (P < 0.05). The total hydrophobic effluent fraction significantly reduced infarct size independently of temporal administration (before ischemia, at reperfusion or as remote postconditioning). In conclusion, the IPC effluent retains strong cardioprotective properties, containing hydrophobic mediator(s) < 30 kDa offering cytoprotection via PI3K/Akt-dependent signaling at ischemic reperfusion.

Remote pharmacological post-conditioning by intrathecal morphine: cardiac protection from spinal opioid receptor activation

BACKGROUND

Intrathecal morphine pre-conditioning attenuates cardiac ischemia-reperfusion injury via activation of central opioid receptors. We hypothesized that intrathecal morphine also post-conditions the myocardium in the rat.

METHODS

Intrathecal morphine at 0.3 μg/kg (LMPC), 3 μg/kg (MMPC) or 30 μg/kg (HMPC) was administered for 5 min before 120-min reperfusion following 30-min ischemia. Infarct size as a percentage of area at risk (IS/AAR) was determined using triphenyltetrazolium staining. MMPC was repeated following the intrathecal administration of nor BNI, NTD, CTOP, or naloxone methiodide (NM), kappa, delta, mu and non-specific opioid receptor antagonists, respectively. The role of peripheral opioid, adenosine and calcitonin gene-related peptide (CGRP) receptors was examined by the intravenous administration of NM, 8-ρ-sulfophenyl theophylline (8-SPT) and human CGRP fragment (CGRP(8-37)), respectively.

RESULTS

Morphine post-conditioning at all three doses was cardioprotective (IS/AAR of LMPC=37 ± 4%, MMPC=35 ± 5%, HMPC=32 ± 4%, control=50 ± 5%, P<0.01). The prior administration of opioid receptor antagonists intrathecally, as well as intravenous 8-SPT and CGRP(8-37) receptor antagonists, abolished this effect (nor BNI+MMPC=47 ± 7%, NTD+MMPC=49 ± 7%, CTOP+MMPC=45 ± 9%, NM+MMPC=47 ± 6% 8-SPT+MPC=46 ± 5% & CGRP(8-37)+MPC=53 ± 6%, P=0.63). However, the intravenous administration of NM did not prevent the protective effect (34 ± 4%, P<0.01).

CONCLUSIONS

Intrathecal morphine administration can induce pharmacological cardiac post-conditioning as it involves opioid receptor centrally but non-opioid receptors peripherally.

Potential therapeutic benefits of strategies directed to mitochondria

The mitochondrion is the most important organelle in determining continued cell survival and cell death. Mitochondrial dysfunction leads to many human maladies, including cardiovascular diseases, neurodegenerative disease, and cancer. These mitochondria-related pathologies range from early infancy to senescence. The central premise of this review is that if mitochondrial abnormalities contribute to the pathological state, alleviating the mitochondrial dysfunction would contribute to attenuating the severity or progression of the disease. Therefore, this review will examine the role of mitochondria in the etiology and progression of several diseases and explore potential therapeutic benefits of targeting mitochondria in mitigating the disease processes. Indeed, recent advances in mitochondrial biology have led to selective targeting of drugs designed to modulate and manipulate mitochondrial function and genomics for therapeutic benefit. These approaches to treat mitochondrial dysfunction rationally could lead to selective protection of cells in different tissues and various disease states. However, most of these approaches are in their infancy.

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

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

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

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

Cardioprotective role of remote ischemic periconditioning in primary percutaneous coronary intervention: enhancement by opioid action

OBJECTIVES

We sought to determine the potential of remote ischemic periconditioning (RIPC), and its combination with morphine, to reduce reperfusion injury in primary percutaneous coronary interventions.

BACKGROUND

Remote ischemic post-conditioning is implemented by applying cycles of ischemia and reperfusion on a remote organ, which result in release of circulating factors inducing the effects of post-conditioning on the myocardium.

METHODS

A total of 96 patients (59 men) were enrolled. The patients were randomized to groups as follows: 33 to each treatment group (Group A: RIPC; Group B: RIPC and morphine) and 30 to the control group (Group C). Measures of efficacy were achievement of full ST-segment resolution (primary), and reduction of ST-segment deviation score and peak troponin I during hospitalization.

RESULTS

A higher proportion of patients in Groups A (73%) and B (82%) achieved full ST-segment resolution after percutaneous coronary intervention, compared with control patients (53%) (p = 0.045). Peak troponin I was lowest in Group B, 103.3 +/- 13.3 ng/ml, in comparison to peak levels in Group A, 166.0 +/- 28.0 ng/ml, and the control group, 255.5 +/- 35.5 ng/ml (p = 0.0006). ST-segment deviation resolution was 87.3 +/- 2.7% in Group B, compared with 69.9 +/- 5.1% in Group A and 53.2 +/- 6.4% in the control group (p = 0.00002). In paired comparisons between groups, Group B did better than the control group in terms of both ST-segment reduction (p = 0.0001) and peak troponin I (p = 0.004), whereas Group A differences from the control group did not achieve statistical significance (p = 0.054 and p = 0.062, respectively).

CONCLUSIONS

These findings demonstrate a cardioprotective effect of RIPC and morphine during primary percutaneous coronary intervention for the prevention of reperfusion injury. This is in agreement with observations that the beneficial effect of RIPC is inhibited by the opioid receptor blocker naloxone.

Cardiac preconditioning for ischaemia: lost in translation

Coronary heart disease (CHD) is the leading cause of death worldwide. The development of novel treatment strategies for protecting the myocardium against the detrimental effects of acute ischaemia-reperfusion injury, termed cardioprotection, and for improving clinical outcomes in patients with CHD requires the use of appropriate animal disease models. The concept of cardioprotection was first conceived in the late 1960s and has evolved to include the endogenous cardioprotective phenomenon of ischaemic conditioning, a concept in which the heart can be protected from an episode of acute lethal ischaemia-reperfusion injury by applying brief non-lethal episodes of ischaemia and reperfusion either to the heart itself or to an organ or tissue that is remote from the heart. The brief conditioning episodes of ischaemia and reperfusion can be applied prior to the index ischaemic episode (ischaemic preconditioning), after the onset of the index ischaemic episode (ischaemic perconditioning), or at the onset of reperfusion (ischaemic postconditioning). Elucidation of the signal transduction pathways underlying ischaemic conditioning has identified a variety of pharmacological agents that are capable of reproducing its cardioprotective actions. Despite a wealth of preclinical, experimental animal data demonstrating clear cardioprotective benefits with these treatment strategies, their translation into clinical therapy has been hugely disappointing. This review explores the potential reasons behind this failure; it will focus primarily on the inadequacy of the experimental animal disease models that are currently being used to investigate novel cardioprotective strategies, which on the whole are not adequately representative of the clinical scenario, and finally, we will discuss potential solutions to remedy this problem.

Translation of remote ischaemic preconditioning into clinical practice

Reduction of the burden of ischaemia-reperfusion injury is the aim of most treatments for cardiovascular and cerebrovascular disease. Although many strategies have proven benefit in the experimental arena, few have translated to clinical practice. Scientific and practical reasons might explain this finding, but the unpredictability of acute ischaemic syndromes is one of the biggest obstacles to timely application of novel treatments. Remote ischaemic preconditioning-which is a powerful innate mechanism of multiorgan protection that can be induced by transient occlusion of blood flow to a limb with a blood-pressure cuff-could be close to becoming a clinical technique. Several proof-of-principle and clinical trials have been reported, suggesting that the technique has remarkable promise. We examine the history, development, and present state of remote preconditioning in cardiovascular disease.

Remote postconditioning is more potent than classic postconditioning in reducing the infarct size in anesthetized rabbits

PURPOSE

Postconditioning confers protection to the heart after a potentially lethal episode of prolonged ischemia. There is evidence that it may also be protective when applied at a distal artery. In the present study, we sought to determine whether remote postconditioning within the heart (local) or outside the heart (distal) is effective in salvaging the ischemic heart in vivo and to compare its effect with that of the classic postconditioning.

METHODS

Twenty seven open chest New Zealand white anesthetized male rabbits were divided into four groups and were exposed to 30 min regional myocardial ischemia (isc), after ligation of a prominent coronary artery, followed by 3 h reperfusion (rep) after releasing the snare. Control group (n = 7) was subjected to no additional interventions, postC group (n = 6) was subjected to four cycles of 1 min isc/1 min rep of the same coronary artery at the beginning of reperfusion, remote local postC group (n = 7) to four cycles of 1 min isc/1 min rep of another coronary artery 30 s before the end of index isc and remote distal postC group (n = 7) to four cycles of 1 min isc/1 min rep of another (carotid) artery again 30 s before the end of index isc. Infarct size (I) and area at risk (R) were delineated with the aid of TTC staining and green fluorescent microspheres respectively and their ratio was expressed in percent (%I/R).

RESULTS

Remote local and remote distal postC reduced the % I/R ratio (17.7 +/- 1.7% and 18.4 +/- 1.6%, respectively vs 47.0 +/- 2.5% in the control group, P < 0.01). Classic PostC had an intermediate protective effect (33.1 +/- 1.7%, P < 0.05 vs all the other groups).

CONCLUSION

Remote postconditioning consisted of 1 min isc/1 min rep protects the ischemic rabbit heart in vivo, independently of the site of the remote artery. This intervention seems to confer a stronger protection than the classic postconditioning.

Molecular aspects of ischaemic postconditioning

Preconditioning, a well established phenomenon had been used since 1980s to attenuate ischaemia-reperfusion induced injury. However, inability to predict the onset of ischaemia in clinical settings led to the discovery of a new concept of postconditioning (PoCo), in 2000s whereby brief repetitive cycles of ischaemia with intermittent reperfusion followed by prolonged ischaemia-elicited tissue protection. There is an impressive array of molecular mechanisms contributing to PoCo-mediated tissue-protection, which include triggers like adenosine (ADO), opioid, erythropoietin (EPO), endogenous nitric-oxide, reactive oxygen species, acetylcholine, tissue factors, pro-inflammatory cytokines and bradykinin; mediators like reperfusion injury salvage kinase pathways including phosphoinositide-3-kinase, extra-cellular signal regulated kinase(1/2) pathway, protein kinase G and protein kinase C; end-effectors like mitochondrial permeability transition pore and mitochondrial potassium ATP channel. The clinical applicability of PoCo has been extended with the use of PoCo mimetic agents like insulin, glucagon like peptide, EPO, statins and ADO before reperfusion in patients with ischaemia reperfusion injury. Remote PoCo has also emerged as a new concept; however, considerable research is required for understanding its molecular mechanisms. In this review, an exhaustive attempt has been made to unearth some molecular aspects of PoCo.

Limb remote ischemic postconditioning protects against focal ischemia in rats

Remote ischemic postconditioning (RIP) refers to an ischemia conducted in a distant organ that protects against a prior ischemia in another organ. We tested whether RIP protects against focal ischemia in the rat brain. Stroke was generated by a permanent occlusion of the left distal middle cerebral artery combined with a 30-min occlusion of the bilateral common carotid arteries (CCA) in male rats. After CCA release, RIP was generated by three cycles of 15-min occlusion/15-min release of the left-hind femoral artery. The results showed that rapid RIP performed immediately after CCA release reduced infarction by 67% measured at 2 days after stroke. In addition, delayed RIP initiated as late as 3 h, but not 6 h, still robustly reduced infarction by 43% 2 days after stroke. RIP's protective effect was abolished by injecting the protein synthesis inhibitor, cycloheximide, and the afferent nerve blocker, capsaicin, suggesting that RIP blocks ischemic injury by modulating protein synthesis and nerve activity. Nevertheless, rapid RIP did not reduce infarction size 2 months after stroke while it ameliorated the outcome of the behavioral test. In conclusion, RIP attenuates brain injury after focal ischemia.

Remote ischemic conditioning: evolution of the concept, mechanisms, and clinical application

Remote ischemic conditioning is a novel concept of protection against ischemia-reperfusion injury. Brief controlled episodes of intermittent ischemia of the arm or leg may confer a powerful systemic protection against prolonged ischemia in a distant organ. This conditioning phenomenon is clinically applicable and can be performed before--preconditioning, during--perconditioning, or after--postconditioning prolonged distant organ ischemia. The remote ischemic conditioning may have an immense impact on clinical practice in the near future.

Protective ischaemia in patients: preconditioning and postconditioning

Infarct size can be limited by reducing the determinants of infarct size or increasing collateral blood flow by treatment initiated before the ischaemic event. Reperfusion is the definitive treatment for permanently reducing infarct size and restoring some degree of contractile function to the affected myocardium. Innate survival mechanisms in the heart can be stimulated by short, non-lethal periods of ischaemia and reperfusion, applied either before or after the ischaemic event. Preconditioning, a series of transient intervals of ischaemia and reperfusion applied before the lethal 'index' ischaemic event, sets in motion molecular and cellular mechanisms that increase cardiomyocyte survival to a degree that had not hitherto been seen before. The cardioprotective ischaemic-reperfusion protocol applied at onset of reperfusion, termed 'postconditioning' (Postcon), is also associated with significant cardioprotection that can be applied at the point of reperfusion treatment in the catheterization laboratory or operating room. Both preconditioning and Postcon have been successfully applied to the clinical setting and have been found to reduce infarct size and other attributes of post-ischaemic injury. This review will summarize the physiological preclinical data on preconditioning and Postcon that are relevant to their translation to clinical therapeutics and treatment.

Sequential limb ischemia demonstrates remote postconditioning protection of murine skeletal muscle

BACKGROUND

Ischemic postconditioning, the process of exposing tissues to brief cycles of ischemia-reperfusion after critical ischemia, can mitigate local ischemia-reperfusion injury. Remote protection of skeletal muscle has never been demonstrated in postconditioning models of ischemia-reperfusion injury.

METHODS

Mice were subjected to 2 hours of ipsilateral hind limb ischemia followed by reperfusion. Contralateral limb ischemia was subsequently induced for 2 hours after either 0 (n = 6), 20 (n = 6), or 120 (n = 5) minutes of ipsilateral limb reperfusion. These groups were compared with animals subjected to bilateral simultaneous injury (n = 8) and sham animals that did not undergo ischemia (n = 6). The gastrocnemius muscles were harvested for histologic evaluation, and injury was recorded as the percentage of injured fibers.

RESULTS

The first limbs undergoing injury in the 20-minute interval group had a 59 percent injury reduction compared with contralateral limbs (16.0 +/- 2.4 percent versus 39.5 +/- 6.5 percent) after 24 hours of reperfusion and 62 percent reduction after 48 hours (24.4 +/- 3.0 percent versus 63.6 +/- 5.5 percent). In animals with no interval or a 120-minute interval between the onset of limb ischemia, there was no significant difference in injury between hind limbs. The injury in these groups was similar to that in hind limbs subjected to simultaneous bilateral ischemia.

CONCLUSIONS

A 20-minute reperfusion interval between hind limb ischemia significantly protects against injury in the initially ischemic limb, while similar injury is observed with simultaneous ischemia or an interval of 120 minutes. This study demonstrates remote postconditioning of skeletal muscle and may lead to the development of post hoc therapies.

Preconditioning and postconditioning: underlying mechanisms and clinical application

Coronary heart disease (CHD) is the leading cause of death world-wide. Its major pathophysiological manifestation is acute myocardial ischaemia-reperfusion injury. Innovative treatment strategies for protecting the myocardium against the detrimental effects of this form of injury are required in order to improve clinical outcomes in patients with CHD. In this regard, harnessing the endogenous protection elicited by the heart's ability to 'condition' itself, has recently emerged as a powerful new strategy for limiting myocardial injury, preserving left ventricular systolic function and potentially improving morbidity and mortality in patients with CHD. 'Conditioning' the heart to tolerate the effects of acute ischaemia-reperfusion injury can be initiated through the application of several different mechanical and pharmacological strategies. Inducing brief non-lethal episodes of ischaemia and reperfusion to the heart either prior to, during, or even after an episode of sustained lethal myocardial ischaemia has the capacity to dramatically reduce myocardial injury--a phenomenon termed ischaemic preconditioning (IPC), preconditioning or postconditioning, respectively. Intriguingly, similar levels of cardioprotection can be achieved by applying the brief episodes of non-lethal ischaemia and reperfusion to an organ or tissue remote from the heart, thereby obviating the need to 'condition' the heart directly. This phenomenon has been termed remote ischaemic 'conditioning', and it can offer widespread systemic protection to other organs which are susceptible to acute ischaemia-reperfusion injury such as the brain, liver, intestine or kidney. Furthermore, the identification of the signalling pathways which underlie the effects of 'conditioning', has provided novel targets for pharmacological agents allowing one to recapitulate the benefits of these cardioprotective phenomena--so-termed pharmacological preconditioning and postconditioning. Initial clinical studies, reporting beneficial effects of 'conditioning' the heart to tolerate acute ischaemia-reperfusion injury, have been encouraging. Larger multi-centred randomised studies are now required to determine whether these 'conditioning' strategies are able to impact on clinical outcomes. In this article, we provide an overview of 'conditioning' in all its various forms, describe the underlying mechanisms and review the recent clinical application of this emerging cardioprotective strategy.

Ischaemic and pharmacological preconditionings protect liver via adenosine and redox status following hepatic ischaemia/reperfusion in rats

Although IPC (ischaemic preconditioning) is considered as a protective strategy in HI/R (hepatic ischaemia/reperfusion), the mechanisms for this effect have not been fully elucidated. In the present study we investigate whether PPC (pharmacological preconditioning) by transient activation of A(1)R (adenosine A(1) receptor) protects against long-term HI/R and whether the protective effects of IPC depend on A(1)R activation and whether both preconditionings affect remote organs. Wistar rats underwent IPC and long-term HI/R. Another set of animals were pharmacologically preconditioned with the A(1)R-agonist CCPA [2-chloro-N(6)-cyclopentyladenosine; 0.1 mg/kg of body weight, i.p. (intraperitoneally)] 24 h before HI/R. In other groups, rats received an A(1)R-antagonist, DPCPX (1,3-dipropyl-8-cyclopentylxanthine; 0.1 mg/kg of body weight, i.p.) 24 h before HI/R. Hepatic damage was evaluated by transaminase [AST (aspartate transaminase), ALT (alanine transaminase)] release; inflammation was assessed by hepatic MPO (myeloperoxidase) and serum TNFalpha (tumour necrosis factor alpha) and NO; oxidative stress was estimated by MDA (malondialdehyde) and 4-HDA (4-hydroxyalkenals), SOD (superoxide dismutase) activity, GSH and ADA (adenosine deaminase) as adenosine metabolism. Both preconditionings protected liver and lung against HI/R as indicated by the reduction in transaminases, MPO, MDA+4-HDA, NO, TNFalpha and ADA activity as compared with HI/R (P<0.05). However, pre-treatment with DPCPX abolished the protective effects of IPC and PPC. Preconditionings induced a significant increase in hepatic MnSOD (manganese SOD) activity and NO generation compared with the sham group, and this activity was abolished by DPCPX pre-treatment. A(1)R activation induced hepatic delayed preconditioning and blockade of A(1)R abolished hepatic IPC. IPC, as well as PPC, were able to prevent lung damage. These protective effects are associated with a reduction in oxidative stress, inflammation and endogenous antioxidant preservation.

Preconditioning and postconditioning: new strategies for cardioprotection

Despite optimal therapy, the morbidity and mortality of coronary heart disease (CHD) remains significant, particularly in patients with diabetes or the metabolic syndrome. New strategies for cardioprotection are therefore required to improve the clinical outcomes in patients with CHD. Ischaemic preconditioning (IPC) as a cardioprotective strategy has not fulfilled it clinical potential, primarily because of the need to intervene before the index ischaemic event, which is impossible to predict in patients presenting with an acute myocardial infarction (AMI). However, emerging studies suggest that IPC-induced protection is mediated in part by signalling transduction pathways recruited at time of myocardial reperfusion, creating the possibility of harnessing its cardioprotective potential by intervening at time of reperfusion. In this regard, the recently described phenomenon of ischaemic postconditioning (IPost) has attracted great interest, particularly as it represents an intervention, which can be applied at time of myocardial reperfusion for patients presenting with an AMI. Interestingly, the signal transduction pathways, which underlie its protection, are similar to those recruited by IPC, creating a potential common cardioprotective pathway, which can be recruited at time of myocardial reperfusion, through the use of appropriate pharmacological agents given as adjuvant therapy to current myocardial reperfusion strategies such as thrombolysis and primary percutaneous coronary intervention for patients presenting with an AMI. This article provides a brief overview of IPC and IPost and describes the common signal transduction pathway they both appear to recruit at time of myocardial reperfusion, the pharmacological manipulation of which has the potential to generate new strategies for cardioprotection.

Remote ischaemic preconditioning: underlying mechanisms and clinical application

Remote ischaemic preconditioning (RIPC) represents a strategy for harnessing the body's endogenous protective capabilities against the injury incurred by ischaemia and reperfusion. It describes the intriguing phenomenon in which transient non-lethal ischaemia and reperfusion of one organ or tissue confers resistance to a subsequent episode of lethal ischaemia reperfusion injury in a remote organ or tissue. In its original conception, it described intramyocardial protection, which could be relayed from the myocardium served by one coronary artery to another. It soon became apparent that myocardial infarct size could be dramatically reduced by applying brief ischaemia and reperfusion to an organ or tissue remote from the heart before the onset of myocardial infarction. The concept of remote organ protection has now been extended beyond that of solely protecting the heart to providing a general form of inter-organ protection against ischaemia-reperfusion injury. This article reviews the history and evolution of the phenomenon that is RIPC, the potential mechanistic pathways underlying its cardioprotective effect, and its emerging application in the clinical setting.

Coronary effluent from a preconditioned heart activates the JAK-STAT pathway and induces cardioprotection in a donor heart

Preconditioning (PC) protects against ischemia-reperfusion (I/R) injury via the activation of the JAK-STAT pathway. We hypothesized that the mediators responsible for PC can be transferred to naive myocardium through the coronary effluent. Langendorff-perfused hearts from male Sprague-Dawley rats were randomized to paired donor/acceptor protocols with or without PC in the presence or absence of the JAK-2 inhibitor AG-490 ( n = 6 for each group). Warmed, oxygenated coronary effluent collected during the reperfusion phases of PC (3 cycles of 5 min ischemia and 5 min reperfusion) was administered to acceptor hearts. The hearts were then subjected to 30 min ischemia and 40 min reperfusion. The left ventricles were analyzed for phosphorylated (p)STAT-1, pSTAT-3, Bax, Bcl, Bcl-XL/Bcl-2-associated protein (BAD), and caspase-3 expression by Western blot. A separate group of hearts ( n = 6) was analyzed for STAT activation immediately after the transfer of the PC effluent (no I-R). Baseline cardiodynamics were not different among the groups. End-reperfusion maximal change in pressure over time (+dP/d tmax) was significantly ( P < 0.05) improved in acceptor PC (3,637 ± 199 mmHg/s) and donor PC (4,304 ± 347 mmHg/s) hearts over non-PC donor (2,020 ± 363 mmHg/s) and acceptor (2,624 ± 345 mmHg/s) hearts. Similar differences were seen for minimal change in pressure over time (−dP/d tmin). STAT-3 activation was significantly increased in donor and acceptor PC hearts compared with non-PC hearts. Conversely, pSTAT-1 and Bax expression was decreased in donor and acceptor PC hearts compared with non-PC hearts. No differences in Bcl, BAD, or caspase-3 expression were observed. Treatment with AG-490 attenuated the recovery of ±dP/d t in acceptor PC hearts and significantly reduced pSTAT-3 expression. The PC coronary effluent activates JAK-STAT signaling, limits apoptosis, and protects myocardial performance from I/R injury.

The paradigm of postconditioning to protect the heart

Ischaemic preconditioning limits the damage induced by subsequent ischaemia/reperfusion (I/R). However, preconditioning is of little practical use as the onset of an infarction is usually unpredictable. Recently, it has been shown that the heart can be protected against the extension of I/R injury if brief (10–30 sec.) coronary occlusions are performed just at the beginning of the reperfusion. This procedure has been called postconditioning (PostC). It can also be elicited at a distant organ, termed remote PostC, by intermittent pacing (dyssynchrony-induced PostC) and by pharmacological interventions, that is pharmacological PostC. In particular, brief applications of intermittent bradykinin or diazoxide at the beginning of reperfusion reproduce PostC protection. PostC reduces the reperfusion-induced injury, blunts oxidant-mediated damages and attenuates the local inflammatory response to reperfusion. PostC induces a reduction of infarct size, apoptosis, endothelial dysfunction and activation, neutrophil adherence and arrhythmias. Whether it reduces stunning is not clear yet. Similar to preconditioning, PostC triggers signalling pathways and activates effectors implicated in other cardioprotective manoeuvres. Adenosine and bradykinin are involved in PostC triggering. PostC triggers survival kinases (RISK), including A t and extracellular signal-regulated kinase (ERK). Nitric oxide, via nitric oxide synthase and non-enzymatic production, cyclic guanosine monophosphate (cGMP) and protein kinases G (PKG) participate in PostC. PostC-induced protection also involves an early redox-sensitive mechanism, and mitochondrial adenosine-5′ -triphosphate (ATP)-sensitive K⁺ and PKC activation. Protective pathways activated by PostC appear to converge on mitochondrial permeability transition pores, which are inhibited by acidosis and glycogen synthase kinase-3β (GSK-3β). In conclusion, the first minutes of reperfusion represent a window of opportunity for triggering the aforementioned mediators which will in concert lead to protection against reperfusion injury. Pharmacological PostC and possibly remote PostC may have a promising future in clinical scenario.

Interaction of cardiovascular risk factors with myocardial ischemia/reperfusion injury, preconditioning, and postconditioning

Therapeutic strategies to protect the ischemic myocardium have been studied extensively. Reperfusion is the definitive treatment for acute coronary syndromes, especially acute myocardial infarction; however, reperfusion has the potential to exacerbate lethal tissue injury, a process termed "reperfusion injury." Ischemia/reperfusion injury may lead to myocardial infarction, cardiac arrhythmias, and contractile dysfunction. Ischemic preconditioning of myocardium is a well described adaptive response in which brief exposure to ischemia/reperfusion before sustained ischemia markedly enhances the ability of the heart to withstand a subsequent ischemic insult. Additionally, the application of brief repetitive episodes of ischemia/reperfusion at the immediate onset of reperfusion, which has been termed "postconditioning," reduces the extent of reperfusion injury. Ischemic pre- and postconditioning share some but not all parts of the proposed signal transduction cascade, including the activation of survival protein kinase pathways. Most experimental studies on cardioprotection have been undertaken in animal models, in which ischemia/reperfusion is imposed in the absence of other disease processes. However, ischemic heart disease in humans is a complex disorder caused by or associated with known cardiovascular risk factors including hypertension, hyperlipidemia, diabetes, insulin resistance, atherosclerosis, and heart failure; additionally, aging is an important modifying condition. In these diseases and aging, the pathological processes are associated with fundamental molecular alterations that can potentially affect the development of ischemia/reperfusion injury per se and responses to cardioprotective interventions. Among many other possible mechanisms, for example, in hyperlipidemia and diabetes, the pathological increase in reactive oxygen and nitrogen species and the use of the ATP-sensitive potassium channel inhibitor insulin secretagogue antidiabetic drugs and, in aging, the reduced expression of connexin-43 and signal transducer and activator of transcription 3 may disrupt major cytoprotective signaling pathways thereby significantly interfering with the cardioprotective effect of pre- and postconditioning. The aim of this review is to show the potential for developing cardioprotective drugs on the basis of endogenous cardioprotection by pre- and postconditioning (i.e., drug applied as trigger or to activate signaling pathways associated with endogenous cardioprotection) and to review the evidence that comorbidities and aging accompanying coronary disease modify responses to ischemia/reperfusion and the cardioprotection conferred by preconditioning and postconditioning. We emphasize the critical need for more detailed and mechanistic preclinical studies that examine car-dioprotection specifically in relation to complicating disease states. These are now essential to maximize the likelihood of successful development of rational approaches to therapeutic protection for the majority of patients with ischemic heart disease who are aged and/or have modifying comorbid conditions.

Postconditioning: a mechanical maneuver that triggers biological and molecular cardioprotective responses to reperfusion

Infarct size is determined not only by the duration and severity of ischemia, but also by pathological processes initiated at reperfusion (reperfusion injury). Numerous pharmacological strategies have been reported which administer drugs at or just before the onset of reperfusion, with subsequent salubrious effects, notably a reduction in infarct size. However, few if any of these strategies have become standard of care in the catheterization laboratory setting. Postconditioning, defined as repeated brief cycles of reperfusion interrupted by ischemia (or hypoxia) applied at the onset of reperfusion, was recently introduced as a mechanical strategy to attenuate reperfusion injury. Postconditioning intervenes only during the first few minutes of reperfusion. However, it reduces endothelial activation and dysfunction, the inflammatory response to reperfusion, necrosis, and apoptosis both acutely and long-term. Cardioprotection has been demonstrated by multiple independent laboratories and in multiple species. Postconditioning stimulates G-protein coupled receptors by their cognate endogenously released ligands and surprisingly activates survival kinases that may converge on mitochondrial K(ATP) channels and the permeability transition pore. Postconditioning has been shown in two clinical studies to reduce infarct size in patients undergoing percutaneous coronary intervention in the catheterization laboratory, and at least five other studies are in some phase of implementation. This significant reduction in infarct size has implications for reduction in heart failure as a consequence of myocardial infarction, but this link has yet to be demonstrated. The salubrious effects of postconditioning are an indirect validation of the experimental and clinical importance of reperfusion injury in the setting of coronary artery occlusion.

Design, synthesis and cardioprotective effect of a new class of dual-acting agents: Phenolic tetrahydro-β-carboline RGD peptidomimetic conjugates

In this study, a new class of phenolic tetrahydro-beta-carboline RGD peptidomimetic conjugates was designed and synthesized. The radical scavenging activities of these newly synthesized compounds 12a-c were evaluated in PC12 cell survival assays. The NO scavenging activities of these compounds were confirmed in the acetylcholine-induced vasorelaxation assay. Compounds 12a-c were efficacious in a rat arterial thrombosis model, and were active in ADP- or PAF-induced in vitro platelet aggregation assays, which suggests these compounds also possess anti-thrombotic activity. The beneficial effects of dual-acting agent 12c were demonstrated on the ischemia-reperfusion induced cardiac infarct size and oxidative change in an in vivo rat model.

Transient limb ischemia induces remote preconditioning and remote postconditioning in humans by a K(ATP)-channel dependent mechanism

BACKGROUND

Transient limb ischemia administered before a prolonged ischemic insult has systemic protective effects against ischemia-reperfusion (IR) injury (remote ischemic preconditioning [RIPC]). It has been demonstrated that protection from IR can be achieved by brief periods of ischemia applied at a remote site during an injurious ischemic event (remote postconditioning [RPostC]). Using an in vivo model of endothelial IR injury, we sought to determine whether RPostC occurred in humans and whether it shared mechanistic similarities with RIPC.

METHODS AND RESULTS

Endothelial function was assessed by flow-mediated dilation before and after IR (20 minutes of arm ischemia followed by reperfusion). RIPC was induced by conditioning cycles of 5 minutes of ischemia and reperfusion on the contralateral arm or leg before IR. For RPostC induction, conditioning cycles were administered during the ischemic phase of IR. Oral glibenclamide was used to determine the dependence of RIPC and RPostC on K(ATP) channels. IR caused a significant reduction in flow-mediated dilation in healthy volunteers (baseline, 9.3+/-1.2% versus post-IR, 3.3+/-0.7%; P<0.0001) and patients with atherosclerosis (baseline, 5.5+/-0.6% versus post-IR, 2.3+/-0.5%; P<0.01). This reduction was prevented by RIPC (post-IR+RIPC: healthy volunteers, 7.2+/-0.5% [P<0.0001 versus post-IR]; patients, 4.5+/-0.3% [P<0.01 versus post-IR]) and RPostC (post-IR+RPostC: 8.0+/-0.5%; P<0.0001 versus post-IR). The protective effects of RIPC and RPostC were blocked by glibenclamide.

CONCLUSIONS

This study demonstrates for the first time in humans that RPostC can be induced by transient limb ischemia and is as effective as RIPC in preventing endothelial IR injury. RIPC and RPostC share mechanistic similarities, with protection being dependent on K(ATP) channel activation. These results suggest that remote conditioning stimuli could be protective in patients with acute ischemia about to undergo therapeutic reperfusion.

Limb ischemic postconditioning protects myocardium from ischemia-reperfusion injury

OBJECTIVE

To test the hypothesis that limb ischemic postconditioning protects the myocardium from reperfusion injury, and examine the mechanism involved.

DESIGN

Forty rabbits were randomly divided into four groups: Control, Ischemic Preconditioning, Ischemic Postconditioning and Remote Postconditioning. Myocardial infarct size and tissue myeloperoxidase activity were determined at the end of the experiment. Plasma creatine kinase and malondialdehyde activity were measured at baseline, the end of ischemia, and after 3 h of reperfusion respectively.

RESULTS

Myocardial infarct size was significantly reduced in Ischemic Preconditioning, Ischemic Postconditioning and Remote Postconditioning as compared to Control (p < 0.01). Results were confirmed by plasma creatine kinase activity. Plasma malondialdehyde was significantly less at 3 h of reperfusion in Ischemic Preconditioning, Ischemic Postconditioning and Remote Postconditioning than that in Control (p < 0.01). Neutrophil accumulation (myeloperoxidase activity) in the area at risk was less in Ischemic Preconditioning, Ischemic Postconditioning and Remote Postconditioning than that in Control (p < 0.01).

CONCLUSION

Remote postconditioning reduces myocardial infarction in rabbits. The mechanism involved might be reduced oxygen radical-induced injury and improved antioxidant action.

Post-conditioning Protects From Cardioplegia and Cold Ischemia via Inhibition of Mitochondrial Permeability Transition Pore

BACKGROUND

The aim of this study was to evaluate the role of the mitochondrial permeability transition pore (MPTP) in the protection achieved by post-conditioning of hearts submitted to hypothermic cardioplegia and ischemia.

METHODS

Isolated rat hearts (n = 30) underwent cold cardioplegia (4 degrees C, Celsior solution) and 8 hours of ischemia at 4 degrees C, followed by a 60-minute Langendorff reperfusion. Hearts were randomly assigned to one of two groups: post-conditioning (post-C, consisting of episodes of 30-second ischemia and 30-second reperfusion at onset of reperfusion) or control (no intervention). A sham group was added for which hearts were harvested and immediately reperfused without ischemia. Coronary flow, heart rate, dP/dt and rate-pressure product were measured. Infarct size was assessed by triphenyltetrazolium chloride (TTC) staining and lactate dehydrogenase (LDH), creatine phosphokinase (CPK) and troponin I release analysis. After reperfusion, heart mitochondria were isolated and calcium overload necessary to induce MPTP opening was measured. From the onset of reperfusion, all functional parameters were significantly improved in post-C vs control hearts.

RESULTS

Infarct size, measured both by TTC staining and LDH, and CPK and troponin I leakage were lower in post-C hearts (p < 0.01). Mean calcium load needed to induce MPTP opening was higher in post-C mitochondria vs controls (p < 0.01).

CONCLUSIONS

Post-conditioning protects the rat heart against cold ischemia-reperfusion injury. Our data suggest that this protection involves inhibition of MPTP opening.

Postconditioning the Human Heart with Adenosine in Heart Valve Replacement Surgery

BACKGROUND

The effect of adenosine postconditioning on myocardial protection in cardiac surgery remains uncertain. The present study evaluated the safety, feasibility, and beneficial effect of adenosine postconditioning as an adjunct to predominantly used cold-blood cardioplegic myocardial protection method in the setting of heart valve replacement operations.

METHODS

Sixty patients with rheumatic heart valve disease undergoing heart valve replacement operations were randomized to an adenosine (1.5 mg/kg) or saline (as control) bolus injection through an arterial catheter immediately after the aorta cross-clamp was removed. The surgical indications were similar in both groups, and heart valve replacement was successful in all patients.

RESULTS

The extubation time and postoperative hospital time were similar in both groups. Compared with the control group, however, the inotrope scores in the intensive care unit (ICU) were much lower (p < 0.01), and the ICU time was significantly shorter (p < 0.05) in adenosine group. More important, cardiac troponin I release was less in the adenosine group, especially at 12 and 24 hours after reperfusion (p < 0.01), and total cardiac troponin I release estimated with the area under curve was also significantly reduced during the first 24 hours after reperfusion (p < 0.01).

CONCLUSIONS

A 1.5-mg/kg bolus administration of adenosine through an arterial catheter immediately after the aorta cross-clamp is removed is feasible and well tolerated in patients undergoing heart valve replacement. An adenosine postconditioning adjunct to high potassium cold blood myocardial protection is related to less troponin I release, less inotropic drug use, and shorter ICU stay.

Adenosinergic cardioprotection: Multiple receptors, multiple pathways

Adenosine, formed primarily via hydrolysis of 5'-AMP, has been historically dubbed a "retaliatory" metabolite due to enhanced local release and beneficial actions during cellular/metabolic stress. From a cardiovascular perspective, evidence indicates the adenosinergic system is essential in mediation of intrinsic protection (e.g., pre- and postconditioning) and determining myocardial resistance to insult. Modulation of adenosine and its receptors thus remains a promising, though as yet not well-realized, approach to amelioration of injury in ischemic-reperfused myocardium. Adenosine exerts effects through A(1), A(2A), A(2B), and A(3) adenosine receptor subtypes (A(1)AR, A(2A)AR, A(2B)AR, and A(3)AR), which are all expressed in myocardial and vascular cells, and couple to G proteins to trigger a range of responses (generally, but not always, beneficial). Adenosine can also enhance tolerance to injurious stimuli via receptor-independent metabolic effects. Given adenosines contribution to preconditioning, it is no surprise that postreceptor signaling typically mimics that associated with preconditioning. This involves activation/translocation of PKC, PI3 kinase, and MAPKs, with ultimate effects at the level of mitochondrial targets-the mitochondrial K(ATP) channel and/or the mitochondrial permeability transition pore (mPTP). Nonetheless, differences in cytoprotective signaling and actions of the different adenosine receptor subtypes have been recently revealed. Our understanding of adenosinergic cytoprotection continues to evolve, with roles for the A(2) subtypes emerging, together with evidence of essential receptor "cross-talk" in mediation of protection. This review focuses on current research into adenosine-mediated cardioprotection, highlighting recent findings which, together with a wealth of prior knowledge, may ultimately facilitate adenosinergic approaches to clinical cardiac protection.