Remote preconditioning

A Dual Protective Effect of Intestinal Remote Ischemic Conditioning in a Rat Model of Total Hepatic Ischemia

The present study aimed to investigate the effects of intestinal remote ischemic preconditioning (iRIC) on ischemia-reperfusion injury (IRI) and gut barrier integrity in a rat model of total hepatic ischemia (THI). Male Wistar rats (n = 50; 250–300 g) were randomly allocated into two experimental groups: RIC/Control. Thirty minutes of THI was induced by clamping the hepatoduodenal ligament. iRIC was applied as 4-min of ischemia followed by 11-min of reperfusion by clamping the superior mesenteric artery. Animals were sacrificed at 1, 2, 6, 24 h post-reperfusion (n = 5/group/timepoint). RIC of the gut significantly improved microcirculation of the ileum and the liver. Tissue ATP-levels were higher following iRIC (Liver: 1.34 ± 0.12 vs. 0.97 ± 0.20 μmol/g, p = 0.04) and hepatocellular injury was reduced significantly (ALT: 2409 ± 447 vs. 6613 ± 1117 IU/L, p = 0.003). Systemic- and portal venous IL-6 and TNF-alpha levels were markedly lower following iRIC, demonstrating a reduced inflammatory response. iRIC led to a structural and functional preservation of the intestinal barrier. These results suggest that iRIC might confer a potent protection against the detrimental effects of THI in rats via reducing IRI and systemic inflammatory responses and at the same time by mitigating the dramatic consequences of severe intestinal congestion and bacterial translocation.

Additive Effect on Survival of Anaesthetic Cardiac Protection and Remote Ischemic Preconditioning in Cardiac Surgery: A Bayesian Network Meta-Analysis of Randomized Trials

INTRODUCTION

Cardioprotective properties of volatile agents and of remote ischemic preconditioning have survival effects in patients undergoing cardiac surgery. We performed a Bayesian network meta-analysis to confirm the beneficial effects of these strategies on survival in cardiac surgery, to evaluate which is the best strategy and if these strategies have additive or competitive effects.

METHODS

Pertinent studies were independently searched in BioMedCentral, MEDLINE/PubMed, Embase, and the Cochrane Central Register (updated November 2013). A Bayesian network meta-analysis was performed. Four groups of patients were compared: total intravenous anesthesia (with or without remote ischemic preconditioning) and an anesthesia plan including volatile agents (with or without remote ischemic preconditioning). Mortality was the main investigated outcome.

RESULTS

We identified 55 randomized trials published between 1991 and 2013 and including 6,921 patients undergoing cardiac surgery. The use of volatile agents (posterior mean of odds ratio = 0.50, 95% CrI 0.28-0.91) and the combination of volatile agents with remote preconditioning (posterior mean of odds ratio = 0.15, 95% CrI 0.04-0.55) were associated with a reduction in mortality when compared to total intravenous anesthesia. Posterior distribution of the probability of each treatment to be the best one, showed that the association of volatile anesthetic and remote ischemic preconditioning is the best treatment to improve short- and long-term survival after cardiac surgery, suggesting an additive effect of these two strategies.

CONCLUSIONS

In patients undergoing cardiac surgery, the use of volatile anesthetics and the combination of volatile agents with remote preconditioning reduce mortality when compared to TIVA and have additive effects. It is necessary to confirm these results with large, multicenter, randomized, double-blinded trials comparing these different strategies in cardiac and non-cardiac surgery, to establish which volatile agent is more protective than the others and how to best apply remote ischemic preconditioning.

Long-term, regular remote ischemic preconditioning improves endothelial function in patients with coronary heart disease

Remote ischemic preconditioning (RIPre) can prevent myocardial injury. The purpose of this study was to assess the beneficial effects of long-term regular RIPre on human arteries. Forty patients scheduled for coronary artery bypass graft (CABG) surgery were assigned randomly to a RIPre group (n=20) or coronary heart disease (CHD) group (n=20). Twenty patients scheduled for mastectomy were enrolled as a control group. RIPre was achieved by occluding arterial blood flow 5 min with a mercury sphygmomanometer followed by a 5-min reperfusion period, and this was repeated 4 times. The RIPre procedure was repeated 3 times a day for 20 days. In all patients, arterial fragments discarded during surgery were collected to evaluate endothelial function by flow-mediated dilation (FMD), CD34⁺ monocyte count, and endothelial nitric oxide synthase (eNOS expression). Phosphorylation levels of STAT-3 and Akt were also assayed to explore the underlying mechanisms. Compared with the CHD group, long-term regular RIPre significantly improved FMD after 20 days (8.5±2.4 vs 4.9±4.2%, P<0.05) and significantly reduced troponin after CABG surgery (0.72±0.31 and 1.64±0.19, P<0.05). RIPre activated STAT-3 and increased CD34⁺ endothelial progenitor cell counts found in arteries. Long-term, regular RIPre improved endothelial function in patients with CHD, possibly due to STAT-3 activation, and this may have led to an increase in endothelial progenitor cells.

Transient carotid ischemia as a remote conditioning stimulus for myocardial protection in anesthetized rabbits: Insights into intracellular signaling

BACKGROUND

We investigated the effectiveness of perconditioning (Perc) applied at different time points along with the role of RISK, SAFE, STAT5 and eNOS pathways.

METHODS AND RESULTS

Anesthetized rabbits were subjected to 30-min ischemia/3-hour reperfusion. Perc, consisted of 4 cycles of 1-min ischemia/reperfusion, was applied in the carotid artery at different time points. Perc was started and ended during ischemia, started during ischemia and ended at the beginning of reperfusion, started at the end of ischemia and ended at reperfusion and started and ended during reperfusion. The PI3K inhibitor wortmannin, or the JAK-2 inhibitor AG490, was also applied and the infarct size was assessed. In another series assigned to the previous groups, the phosphorylation of Akt, PI3K, ERKs1/2, GSK3β, STAT3, and STAT5 was evaluated. All Perc groups had smaller infarction compared to those without Perc, independently of PI3K or JAK-2 inhibition. STAT5 was the only molecule that was phosphorylated in parallel with cardioprotection. Since Src and angiotensin II mediate the STAT5 pathway, we administered the Scr inhibitor PP1 and the angiotensin II receptor antagonist valsartan. PP1 and valsartan prevented STAT5 phosphorylation, but did not abrogate the effect of Perc. Furthermore, the NOS inhibitor L-NAME was administered and abrogated the infarct size limiting effect of Perc. In parallel, the expression of cleaved caspase-3 was elevated only in the control and Perc-A-L-NAME groups.

CONCLUSION

Perc reduces infarction independently of RISK, SAFE and STAT5 pathways. Src kinase and angiotensin II play a predominant role in STAT5 activation. eNOS may protect the myocardium through inhibition of apoptosis.

What is Wrong With Cardiac Conditioning? We May be Shooting at Moving Targets

Early recanalization of the occluded culprit coronary artery clearly reduces infarct size in both animal models and patients and improves clinical outcomes. Unfortunately, reperfusion can seldom be accomplished before some myocardium infarcts. As a result there has been an intensive search for interventions that will make the heart resistant to infarction so that reperfusion could salvage more myocardium. A number of interventions have been identified in animal models, foremost being ischemic preconditioning. It protects by activating signaling pathways that prevent lethal permeability transition pores from forming in the heart’s mitochondria at reperfusion. Such conditioning can be accomplished in a clinically relevant manner either by staccato reperfusion (ischemic postconditioning) or by pharmacological activation of the conditioning signaling pathways prior to reperfusion. Unfortunately, clinical trials of ischemic postconditioning and pharmacologic conditioning have been largely disappointing. We suggest that this may be caused by inappropriate use as models intended to mimic the clinical scenario of young healthy animals that receive none of the many drugs currently given to our patients. Patients may be resistant to some forms of conditioning because of comorbidities, for example, diabetes, or they may already be conditioned by adjunct medications, for example, P2Y12 inhibitors or opioids. Incremental technological improvements in patient care may render some approaches to cardioprotection redundant, and thus the clinical target may be continually changing, while our animal models have not kept pace. In remote conditioning, a limb is subjected to ischemia/reperfusion prior to or during coronary reperfusion. Its mechanism is not as well understood as that of ischemic preconditioning, but the results have been very encouraging. In the present article, we will review ischemic, remote, and pharmacologic conditioning and possible confounders that could interfere with their efficacy in clinical trials in 2 settings of myocardial ischemia: (1) primary angioplasty in acute myocardial infarction and (2) elective angioplasty.

Remote ischemic conditioning: from experimental observation to clinical application: report from the 8th Biennial Hatter Cardiovascular Institute Workshop

In 1993, Przyklenk and colleagues made the intriguing experimental observation that ‘brief ischemia in one vascular bed also protects remote, virgin myocardium from subsequent sustained coronary artery occlusion’ and that this effect ‘…. may be mediated by factor(s) activated, produced, or transported throughout the heart during brief ischemia/reperfusion’. This seminal study laid the foundation for the discovery of ‘remote ischemic conditioning’ (RIC), a phenomenon in which the heart is protected from the detrimental effects of acute ischemia/reperfusion injury (IRI), by applying cycles of brief ischemia and reperfusion to an organ or tissue remote from the heart. The concept of RIC quickly evolved to extend beyond the heart, encompassing inter-organ protection against acute IRI. The crucial discovery that the protective RIC stimulus could be applied non-invasively, by simply inflating and deflating a blood pressure cuff placed on the upper arm to induce cycles of brief ischemia and reperfusion, has facilitated the translation of RIC into the clinical setting. Despite intensive investigation over the last 20 years, the underlying mechanisms continue to elude researchers. In the 8th Biennial Hatter Cardiovascular Institute Workshop, recent developments in the field of RIC were discussed with a focus on new insights into the underlying mechanisms, the diversity of non-cardiac protection, new clinical applications, and large outcome studies. The scientific advances made in this field of research highlight the journey that RIC has made from being an intriguing experimental observation to a clinical application with patient benefit.

Cardioprotection acquired through exercise: the role of ischemic preconditioning

A great bulk of evidence supports the concept that regular exercise training can reduce the incidence of coronary events and increase survival chances after myocardial infarction. These exercise-induced beneficial effects on the myocardium are reached by means of the reduction of several risk factors relating to cardiovascular disease, such as high cholesterol, hypertension, obesity etc. Furthermore, it has been demonstrated that exercise can reproduce the "ischemic preconditioning" (IP), which refers to the capacity of short periods of ischemia to render the myocardium more resistant to subsequent ischemic insult and to limit infarct size during prolonged ischemia. However, IP is a complex phenomenon which, along with infarct size reduction, can also provide protection against arrhythmia and myocardial stunning due to ischemia-reperfusion. Several clues demonstrate that preconditioning may be directly induced by exercise, thus inducing a protective phenotype at the heart level without the necessity of causing ischemia. Exercise appears to act as a physiological stress that induces beneficial myocardial adaptive responses at cellular level. The purpose of the present paper is to review the latest data on the role played by exercise in triggering myocardial preconditioning.

RISK and SAFE signaling pathway involvement in apolipoprotein A-I-induced cardioprotection

Recent findings indicate that apolipoprotein A-I (ApoA-I) may be a protective humoral mediator involved in remote ischemic preconditioning (RIPC). This study sought to determine if ApoA-I mediates its protective effects via the RISK and SAFE signaling pathways implicated in RIPC. Wistar rats were allocated to one of the following groups. Control: rats were subjected to myocardial ischemia/reperfusion (I/R) without any further intervention; RIPC: four cycles of limb I/R were applied prior to myocardial ischemia; ApoA-I: 10 mg/Kg of ApoA-I were intravenously injected prior to myocardial ischemia; ApoA-I + inhibitor: pharmacological inhibitors of RISK/SAFE pro-survival kinase (Akt, ERK1/2 and STAT-3) were administered prior to ApoA-I injection. Infarct size was significantly reduced in the RIPC group compared to Control. Similarly, ApoA-I injection efficiently protected the heart, recapitulating RIPC-induced cardioprotection. The ApoA-I protective effect was associated with Akt and GSK-3β phosphorylation and substantially inhibited by pretreatment with Akt and ERK1/2 inhibitors. Pretreatment with ApoA-I in a rat model of I/R recapitulates RIPC-induced cardioprotection and shares some similar molecular mechanisms with those of RIPC-involved protection of the heart.

Molecular mechanisms of ischemic conditioning: translation into patient outcomes

Following the initiation of an ischemic insult, reperfusion injury (RI) can result in numerous deleterious cardiac effects, including cardiomyocyte death. Experimental data have suggested that ischemic conditioning, when delivered either before or after the ischemic event, can provide considerable cardioprotection against RI. Ischemic conditioning involves delivering brief repetitive cycles of ischemia to the myocardium (local) or to another distal organ or structure (remote). This review will discuss recent advances in the molecular mechanisms involved in RI, the signaling pathways recruited by ischemic conditioning and conclude with an appraisal of the evidence for the use of ischemic conditioning in current clinical practice.

Role of hypoxia inducible factor-1α in remote limb ischemic preconditioning

Remote ischemic preconditioning (RIPC) has emerged as a feasible and attractive therapeutic procedure for heart protection against ischemia/reperfusion (I/R) injury. However, its molecular mechanisms remain poorly understood. Hypoxia inducible factor-1α (HIF-1α) is a transcription factor that plays a key role in the cellular adaptation to hypoxia and ischemia. This study's aim was to test whether RIPC-induced cardioprotection requires HIF-1α upregulation to be effective. In the first study, wild-type mice and mice heterozygous for HIF1a (gene encoding the HIF-1α protein) were subjected to RIPC immediately before myocardial infarction (MI). RIPC resulted in a robust HIF-1α activation in the limb and acute cardioprotection in wild-type mice. RIPC-induced cardioprotection was preserved in heterozygous mice, despite the low HIF-1α expression in their limbs. In the second study, the role of HIF-1α in RIPC was evaluated using cadmium (Cd), a pharmacological HIF-1α inhibitor. Rats were subjected to MI (MI group) or to RIPC immediately prior to MI (R-MI group). Cd was injected 18 0min before RIPC (Cd-R-MI group). RIPC induced robust HIF-1α activation in rat limbs and significantly reduced infarct size (IS). Despite Cd's inhibition of HIF-1α activation, RIPC-induced cardioprotection was preserved in the Cd-R-MI group. RIPC applied immediately prior to MI increased HIF-1α expression and attenuated IS in rats and wild-type mice. However, RIPC-induced cardioprotection was preserved in partially HIF1a-deficient mice and in rats pretreated with Cd. When considered together, these results suggest that HIF-1α upregulation is unnecessary in acute RIPC.

Conditioning the heart to prevent myocardial reperfusion injury during PPCI

For patients presenting with a ST-segment elevation myocardial infarction (STEMI), early myocardial reperfusion by primary percutaneous coronary intervention (PPCI) remains the most effective treatment strategy for limiting myocardial infarct size, preserving left ventricular systolic function, and preventing the onset of heart failure. Recent advances in PCI technology to improve myocardial reperfusion and the introduction of novel anti-platelet and anti-thrombotic agents to maintain the patency of the infarct-related coronary artery continue to optimize PPCI procedure. However, despite these improvements, STEMI patients still experience significant major adverse cardiovascular events. One major contributing factor has been the inability to protect the heart against the lethal myocardial reperfusion injury, which accompanies PPCI. Past attempts to translate cardioprotective strategies, discovered in experimental studies to prevent lethal myocardial reperfusion injury, into the clinical setting of PPCI have been disappointing. However, a number of recent proof-of-concept clinical studies suggest that the heart can be 'conditioned' to protect itself against lethal myocardial reperfusion injury, as evidenced by a reduction in myocardial infarct size. This can be achieved using either mechanical (such as ischaemic postconditioning, remote ischaemic preconditioning, therapeutic hypothermia, or hyperoxaemia) or pharmacological (such as cyclosporin-A, natriuretic peptide, exenatide) 'conditioning' strategies as adjuncts to PPCI. Furthermore, recent developments in cardiac magnetic resonance (CMR) imaging can provide a non-invasive imaging strategy for assessing the efficacy of these novel adjunctive therapies to PPCI in terms of key surrogate clinical endpoints such as myocardial infarct size, myocardial salvage, left ventricular ejection fraction, and the presence of microvascular obstruction or intramyocardial haemorrhage. In this article, we review the therapeutic potential of 'conditioning' to protect the heart against lethal myocardial reperfusion injury in STEMI patients undergoing PPCI.

Remote ischemic preconditioning: the surgeon's perspective

Since cardiac surgery began, surgeons have aimed to find methods of minimizing myocardial injury resulting from ischemia and reperfusion. The concept of somehow conditioning the heart in order to attenuate ischemia and reperfusion-related injury has evolved in cardiovascular research over decades, from ischemic preconditioning and postconditioning to, more recently, remote ischemic preconditioning (and postconditioning). Although many strategies have proven to be beneficial in the experimental arena, a few have been successfully translated into clinical practice. Remote ischemic preconditioning, with the use of brief episodes of ischemia and reperfusion of vascular territories remote from the heart, has been shown convincingly to decrease myocardial injury. To date, the translation of this powerful innate mechanism of myocardial and/or multiorgan protection from the animal lab to the operating theatre, using transient occlusion of blood flow to the upper limb with a blood-pressure cuff before cardiac surgery, has shown promising results, with several proof-of-principle and first randomized controlled clinical trials reporting benefits for patients undergoing cardiac surgery. If the efficacy of remote ischemic preconditioning can be conclusively proven, the clinical applications in cardiac surgery could be almost infinite, providing multiorgan protection in various surgical scenarios.

Interference of propofol with signal transducer and activator of transcription 5 activation and cardioprotection by remote ischemic preconditioning during coronary artery bypass grafting

OBJECTIVE

Remote ischemic preconditioning protects the myocardium from ischemia/reperfusion injury. We recently identified protection by remote ischemic preconditioning to be associated with the activation of signal transducer and activator of transcription 5 in left ventricular biopsy specimens of patients undergoing coronary artery bypass grafting during isoflurane anesthesia. Because remote ischemic preconditioning did not protect the heart during propofol anesthesia, we hypothesized that propofol anesthesia interferes with signal transducer and activator of transcription 5 activation.

METHODS

In a randomized, single-blind, placebo-controlled, prospective study, we analyzed an array of established cardioprotective proteins during propofol anesthesia with or without remote ischemic preconditioning in 24 nondiabetic patients with 3-vessel coronary artery disease.

RESULTS

Remote ischemic preconditioning (n = 12) compared with no remote ischemic preconditioning (n = 12) failed to decrease the area under the troponin I time curve (273 ± 184 ng/mL × 72 hours vs 365 ± 301 ng/mL × 72 hours; P = .374). Although phosphorylation of several protein kinases was increased from baseline to reperfusion, signal transducer and activator of transcription 5 phosphorylation was not increased and was not different between the remote ischemic preconditioning and no remote ischemic preconditioning groups.

CONCLUSIONS

Remote ischemic preconditioning during propofol anesthesia did not evoke either signal transducer and activator of transcription 5 activation or cardioprotection, implying interaction of propofol with cardioprotective signaling upstream of signal transducer and activator of transcription 5.

Investigating the signal transduction pathways underlying remote ischemic conditioning in the porcine heart

BACKGROUND

The mechanism underlying remote ischemic conditioning (RIC) remains unclear. We investigated whether RIC protects the heart through the activation of the adenosine receptor and the PI3K-Akt pathway at the onset of myocardial reperfusion.

METHODS AND RESULTS

Domestic pigs (27-35 kg) were subjected to in situ left anterior descending coronary artery ischemia (60 min) followed by reperfusion (180 min) and randomised to the following: (1) Control- No additional intervention; (2) Remote ischemic preconditioning (RIPC)- Four-5 min cycles of lower limb ischemia/reperfusion were administered prior to myocardial ischemia; (3) RIPC  +  Wort or 8-SPT: Wortmannin (Wort 20 μg/kg, a PI3K inhibitor) or 8-sulfophenyltheophylline (8-SPT 10 mg/kg, an adenosine receptor inhibitor) were administered intravenously 30 s before myocardial reperfusion to RIPC-treated animals; (4) Remote ischemic perconditioning (RIPerC)--Four-5 min cycles of lower limb ischemia/reperfusion were applied 1 min before myocardial reperfusion; (5) RIPerC  +  Wort or 8-SPT: Wort or 8-SPT were given 30 s before myocardial reperfusion to RIPerC-treated animals. Both RIPC and RIPerC reduced myocardial infarct size (13.3 ± 2.2% with RIPC, 18.2 ± 2.0% with RIPerC versus 48.8 ± 4.2% in control:P  < 0.05:N ≥ 5/group). Wortmannin abolished the infarct-limiting effects of RIPC (33.2 ± 6% with RIPC + Wort versus 13.3 ± 2.2% with RIPC:P < 0.05:N ≥ 5/group) but not RIPerC (18.0 ± 3.4% with RIPerC + Wort versus 18.2 ± 2.0% with RIPerC:P > 0.05:N ≥ 5/group). 8-SPT did not influence the infarct-limiting effects of either RIPC or RIPerC. Western blot analysis confirmed Wortmannin-sensitive PI3K and Akt activation at myocardial reperfusion in RIPC-treated hearts.

CONCLUSIONS

In the porcine heart, both RIPC and RIPerC both reduce myocardial infarct size and with RIPC but not RIPerC this cardioprotective effect is associated with the activation of the PI3K-Akt pathway at reperfusion.

The effect of acute versus delayed remote ischemic preconditioning on reperfusion induced ventricular arrhythmias

INTRODUCTION

The effect of remote ischemic preconditioning (RIPC) on arrhythmias in in vivo models is unknown. Our purpose was to determine effects of both acute and delayed RIPC on arrhythmias.

METHODS AND RESULTS

In the acute protocol anesthetized open chest rats were exposed to 5 minutes of proximal left coronary artery occlusion (CAO) and 10 minutes of reperfusion. Rats were either untreated (ischemia/reperfusion, IR group, n = 17) or received RIPC (n = 14) with 5 minutes bilateral femoral occlusions followed by 5 minutes of reperfusion times 3, started 30 minutes before CAO. At reperfusion, onset of ventricular tachycardia (VT) was delayed in RIPC group (25.7 seconds) versus IR (8.8 seconds; P = 0.04). Number of episodes of VT was 17.0 in IR versus 3.0 in the RIPC group (P = 0.01) and duration of VT was 54.1 seconds in IR versus 4.9 seconds in RIPC (P = 0.019). Number of ventricular premature complexes (VPC) was 26.0 in IR and 10.0 in RIPC rats (P = 0.04). Levels of reperfusion injury salvage kinases (RISK), that is, phospho-Akt and phospho-p70S6 in the risk area of IR and RIPC hearts were similarly higher compared to the nonischemic areas both at 1 and 10 minutes into reperfusion. Delayed RIPC was induced on day 1 and on day 2, myocardial IR was induced. Delayed RIPC did not affect VT or VPC.

CONCLUSION

Acute RIPC of the lower limbs induced a powerful delay in/and reduction in IR induced ventricular arrhythmias, but without evoking the RISK pathway; a late protective phase of RIPC on arrhythmias did not occur.

Cardioprotection during cardiac surgery

Coronary heart disease (CHD) is the leading cause of morbidity and mortality worldwide. For a large number of patients with CHD, coronary artery bypass graft (CABG) surgery remains the preferred strategy for coronary revascularization. Over the last 10 years, the number of high-risk patients undergoing CABG surgery has increased significantly, resulting in worse clinical outcomes in this patient group. This appears to be related to the ageing population, increased co-morbidities (such as diabetes, obesity, hypertension, stroke), concomitant valve disease, and advances in percutaneous coronary intervention which have resulted in patients with more complex coronary artery disease undergoing surgery. These high-risk patients are more susceptible to peri-operative myocardial injury and infarction (PMI), a major cause of which is acute global ischaemia/reperfusion injury arising from inadequate myocardial protection during CABG surgery. Therefore, novel therapeutic strategies are required to protect the heart in this high-risk patient group. In this article, we review the aetiology of PMI during CABG surgery, its diagnosis and clinical significance, and the endogenous and pharmacological therapeutic strategies available for preventing it. By improving cardioprotection during CABG surgery, we may be able to reduce PMI, preserve left ventricular systolic function, and reduce morbidity and mortality in these high-risk patients with CHD.

Protection by remote ischemic preconditioning during coronary artery bypass graft surgery with isoflurane but not propofol - a clinical trial

BACKGROUND

Remote ischemic preconditioning (RIPC) of the myocardium by limb ischemia/reperfusion may mitigate cardiac damage, but its interaction with the anesthetic regimen is unknown. We tested whether RIPC is associated with differential effects depending on background anesthesia. Specifically, we hypothesized that RIPC during isoflurane anesthesia attenuates myocardial injury in patients undergoing coronary artery bypass graft (CABG) surgery, and that effects may be different during propofol anesthesia.

METHODS

In a randomized, single-blinded, placebo-controlled prospective study, serum troponin I concentration (cTnI) (baseline, and 1, 6, 12, 24, 48, and 72 h postoperatively) were measured during isoflurane/sufentanil or propofol/sufentanil anesthesia with or without RIPC (three 5-min periods of intermittent left upper arm ischemia with 5 min reperfusion each) in non-diabetic patients (n = 72) with three-vessel coronary artery disease (ClinicalTrials.gov NCT01406678).

RESULTS

RIPC during isoflurane anesthesia (n = 20) decreased the area under the cTnI time curve (cTnI AUC) (-50%, 190 ± 105 ng/ml × 72 h vs. 383 ± 262 ng/ml × 72 h, P = 0.004), and the peak (7.3 ± 3.6 ng/ml vs. 11.8 ± 5.5, P = 0.004) and serial (P < 0.041) postoperative cTnI when compared to isoflurane alone (n = 19). In contrast, RIPC during propofol anesthesia (n = 14) did not alter the cTnI AUC [263 ± 157 ng/ml × 72 h vs. 372 ± 376 ng/ml × 72 h (n = 19), P = 0.318] or peak postoperative cTnI (10.1 ± 4.5 ng/ml vs. 12 ± 8.2, P = 0.444). None of the patients experienced harm or side effects from the intermittent left arm ischemia.

CONCLUSION

Thus, RIPC during isoflurane but not during propofol anesthesia decreased myocardial damage in patients undergoing CABG surgery. Accordingly, effects of RIPC evoked by upper limb ischemia/reperfusion depend on background anesthesia, with combined RIPC/isoflurane exerting greater beneficial effects under conditions studied.

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

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

The therapeutic potential of ischemic conditioning: an update

Novel approaches are required to improve clinical outcomes in patients with coronary heart disease (CHD). Ischemic conditioning--the practice of applying brief episodes of nonlethal ischemia and reperfusion to confer protection against a sustained episode of lethal ischemia and reperfusion injury--is one potential therapeutic strategy. Importantly, the protective stimulus can be applied before (ischemic preconditioning) or after (ischemic perconditioning) onset of the sustained episode of lethal ischemia, or even at the onset of myocardial reperfusion (ischemic postconditioning). Furthermore, the protective stimulus can be applied noninvasively by placing a blood-pressure cuff on an upper or lower limb to induce brief episodes of nonlethal ischemia and reperfusion (remote ischemic conditioning), a finding that has greatly facilitated the translation of ischemic conditioning to various clinical settings. In addition to mechanical approaches, elucidation of the signal-transduction pathways underlying ischemic conditioning has identified several novel targets for pharmacological conditioning. This Review highlights findings from proof-of-concept clinical studies conducted in the past 5-6 years, in which the therapeutic potential of ischemic and pharmacological conditioning has been realized. Large, randomized, controlled trials are now required to determine whether pharmacological and ischemic conditioning improve clinical end points and outcomes in patients with CHD.

Remote ischemic preconditioning reduces myocardial injury after coronary artery bypass surgery with crystalloid cardioplegic arrest

Remote ischemic preconditioning (RIPC) with transient upper limb ischemia reduces myocardial injury in patients undergoing on-pump coronary artery bypass grafting (CABG) with cross-clamp fibrillation or blood cardioplegia for myocardial protection. Whether or not such protection is still operative when standard crystalloid cardioplegic arrest is used is uncertain. Fifty-three consecutive, non-diabetic patients with triple-vessel disease and 64 +/- 12 years of age (mean +/- SD), who underwent elective CABG surgery with crystalloid (Bretschneider) cardioplegic arrest, were allocated in a prospective, randomized, single-blinded protocol to receive either a RIPC protocol (3 cycles of 5 min transient left upper arm ischemia induced by inflating a blood pressure cuff to 200 mmHg with 5 min of reperfusion) or control, respectively, after induction of anesthesia. Cardiac troponin I (cTnI) concentration was measured preoperatively and over 72 h postoperatively, and the area under the curve (AUC) was calculated. Peak postoperative cTnI concentration was significantly reduced from 13.7 +/- 7.7 ng/mL in controls to 8.9 +/- 4.4 ng/mL in RIPC (P = 0.008). Mean cTnI concentration was significantly lower at 6, 12, 24, and 48 h after surgery (ANOVA; P < 0.0001) in the RIPC patients (N = 27) than in controls (N = 26), resulting in a 44.5% reduction of cTnI (AUC at 72 h). RIPC by repetitive inflation of a cuff around the left upper arm before surgery enhances myocardial protection in patients undergoing CABG surgery with antegrade cold crystalloid cardioplegia.

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.

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.

Protocols and Mechanisms for Remote Ischemic Preconditioning: A Novel Method for Reducing Ischemia Reperfusion Injury

Ischemia reperfusion injury (IRI) results in damage to local and remote organs. Remote ischemic preconditioning (RIPC) is a strategy to protect against IRI by inducing a prior brief period(s) of IRI to an organ remote from that undergoing sustained injury. RIPC has been shown to protect organs against IRI; however, the protocols and mechanisms for RIPC are unclear. For this review, a Medline/Pubmed search (January 1985 to January 2007) was conducted and all relevant articles were included. RIPC protocols are organ and species specific and both humoral and neurogenic pathways are involved in triggering intracellular signal pathways for protection.

Effects of remote ischemic preconditioning on the flow pattern of the left anterior descending coronary artery in normal subjects

Remote ischemic preconditioning (RIPC) has been proposed as an effective method to improve both myocardial and vascular protection in human beings. The aim of this study was to identify the effect of RIPC on the flow pattern of left anterior descending coronary artery (LAD) by transthoracic Doppler echocardiography. 18 normal male volunteers were enrolled to this study. The Doppler signals of flow velocity were recorded at baseline, 1, 3, 6 and 9 min after reperfusion of each cycle to identify the effect of RIPC on the flow pattern of the LAD. In the study, the coronary mean velocity, peak diastolic velocity and mean diastolic velocity were increased (all P<0.05) in the first 3 min of reperfusion of each cycle while peak systolic velocity, mean systolic velocity and heart rate did not change compared with the baseline readings throughout RIPC. And the maximal coronary flow velocity was observed at the first minute of the second reperfusion. The result of this study proves that remote ischemic preconditioning produces hyperemia via the LAD during early reperfusion, which is characterized by an increase in diastolic flow velocity.

Is remote preconditioning as effective as direct ischemic preconditioning in preventing spinal cord ischemic injury?

BACKGROUND

Spinal cord injury remains a devastating complication of thoracic and thoracoabdominal aortic operations. The aim of this study was to assess the affectivity of direct ischemic preconditioning (PC) and remote PC in preventing spinal cord ischemic injury in an experimental model.

MATERIALS AND METHODS

Thirty-eight New Zealand white rabbits were divided into five groups: One group served as Sham group (n = 7). Rabbits in other groups had their abdominal aorta cross-clamped for 40 min. Before aortic occlusion, aorta was clamped twice at the same site of aortic occlusion for 5 min followed by 15 min of reperfusion after each ischemic episode in one group (Direct PC, n = 8), left renal artery was clamped twice for 5 min followed by 15 min of reperfusion after each renal ischemic episode in one group (Remote PC, n = 8), left renal artery was first clamped for 5 min followed by 15 min of reperfusion and then aorta was clamped for 5 min followed by 15 min of reperfusion in one group (Remote + Direct PC, n = 8), and no PC method was used in Control group (n = 7).

RESULTS

In all PC groups, neurological status of rabbits (Tarlov score) at post-ischemia 24th and 48th hours was better than the control group (P < 0.05), but worse than Sham group (P < 0.05). Mean viability index values in PC groups were higher than control group (P < 0.01). Post-ischemia serum NSE and MDA levels obtained in all three PC groups were significantly lower than control group (P < 0.05 and P < 0.01).

CONCLUSIONS

The use of direct ischemic PC and/or remote PC is an effective way of reducing spinal cord ischemic injury because of aortic occlusion, while direct PC is more effective. The combined use of direct PC and remote PC did not provide better protection.

Increased C reactive protein and cardiac enzyme levels after coronary stent implantation. Is there protection by remote ischaemic preconditioning?

AIM

To investigate whether remote ischaemic preconditioning (RIPC) can attenuate the inflammatory response and enzyme leakage that can occur after uncomplicated routine percutaneous coronary intervention (PCI).

METHODS

41 consecutive normotensive patients with stable angina and single-vessel disease were assigned to be exposed to RIPC (n = 20) or not (control group; n = 21) before elective PCI with stent implantation. RIPC was induced by three cycles of 5-min ischaemia-reperfusion of both upper limbs (inflation/deflation of blood pressure cuff). C reactive protein (CRP), creatine phosphokinase (CK), CK cardiac isoenzyme (CK-MB) and troponin I (TNI) were serially measured for 48 h.

RESULTS

No difference in baseline values was observed between the groups. The CRP rose significantly (p<0.001) and at 48 h was similarly increased (>fourfold) in both groups (15.7 (2.6) v 14.0 (3.3) mg/l, RIPC v control; p = NS). However, sub-group analysis on the basis of statin use showed that the highest rise was in the group of patients with RIPC not taking statins and was significantly greater than in patients with RIPC taking statins (23.8 (3.71) v 11.4 (3.0) mg/l, respectively, p<0.01). Both CK-MB and TNI leakage were raised (slightly but significantly) after PCI in controls at 24 h compared with baseline values. However, this small rise was significantly worse after RIPC (CK-MB, 1.33 (0.27) v 3.57 (0.97) ng/ml, p<0.01; TNI, 0.255 (0.059) v 0.804 (0.232) ng/ml, p<0.05, respectively at 24 h). The increase was more marked in the RIPC subgroup not taking statins.

CONCLUSIONS

RIPC does not reduce, but exacerbates, the enzyme and TNI release from the heart after single-vessel angioplasty with stent. Furthermore, the increased circulating CRP remains raised. It seems that there is an enhanced inflammatory response after RIPC in the absence of statin treatment.

Remote organ ischemic preconditioning protect brain from ischemic damage following asphyxial cardiac arrest

Ischemic preconditioning (IPC) is a phenomenon whereby an organ's adaptive transient resistance to a lethal ischemic insult occurs by preconditioning this organ with a sub-lethal/mild ischemic insult of short duration. Besides IPC, recent studies reported that a short sub-lethal ischemia and reperfusion in various organs can induce ischemic tolerance in another organ as well. This phenomenon is known as remote ischemic preconditioning (RPC). In the present study we tested the hypothesis that tolerance for ischemia can be induced in brain by RPC and IPC in a rat model of asphyxial cardiac arrest (ACA). RPC was induced by tightening the upper two-thirds of both hind limbs using a tourniquet for 15 or 30 min and IPC was induced by tightening bilateral carotid artery ligatures for 2 min. Eight minutes of ACA was induced 48 h after RPC or IPC. After 7 day of resuscitation, brains were extracted and examined for histopathological changes. In CA1 hippocampus, the number of normal neurons was 63% lower in cardiac-arrested rats as compared to the control group. The number of normal neurons in the 15 min RPC, 30 min RPC, and IPC groups was higher than the ACA group by 54, 70, and 67%, respectively. This study demonstrates that RPC and IPC are able to provide neuroprotection in a rat model of ACA. Besides direct application of RPC or IPC paradigms, the exploration of the mechanisms of observed neuroprotection by RPC and IPC may also lead to a possible therapy for CA patients.

Myocardial preconditioning and remote renal preconditioning--identifying a protective factor using proteomic methods?

It is still unknown whether remote ischemic preconditioning is mediated by a humoral or a neurogenic mechanism from the preconditioning to the preconditioned tissue. The purpose of the following study was to identify a possible humoral trigger of ischemic myocardial preconditioning and remote renal preconditioning. Open chest rats were subjected to a coronary artery occlusion period of 45 min followed by 2 h of reperfusion (Control animals; n = 6). The coronary preconditioned group (IPC, n = 6) was subjected to a preceding preconditioning period of 5 min coronary artery occlusion followed by 5 min of reperfusion, repeated three times. The renal preconditioned group (IPR, n = 6) was subjected to a preceding renal artery occlusion period of 10 min followed by 20 min of reperfusion. Area at risk (AAR) and infarcted area (IA) were determined at the end of each protocol. Blood samples were taken at the end of the preconditioning protocols from parallel experiments for proteomic analysis using two-dimensional gel electrophoresis (2-DE), matrix assisted laser desorption and ionization-time of flight-mass spectrometry (MALDI-TOF-MS), and liquid chromatography-electrospray ionization-tandem mass spectrometry (nanoLC-ESI-MS/MS). IA/AAR was 87.8 +/- 10.7% in the control group. IPC and IPR significantly reduced IA/AAR (58.2 +/- 9.3% and 56.9 +/- 9.0%, p < 0.001). Proteomic analyses detected four protein spots which were either up- (n = 3) or down-regulated in the preconditioned groups vs. the control group. The three up-regulated protein spots were identified as albumin fragments, whereas the down-regulated spot was identified as liver regeneration-related protein (LRRG03). Interestingly, albumin modification by brief ischemia has been recently shown and evaluated for the clinical diagnosis of sublethal myocardial ischemia. However, no differentially abundant proteins which possess a known signaling function could be found. Hence, though there is a differential protein expression in blood following IPC and IPR, our data are not in favor of a humoral mediator of remote preconditioning with a molecular weight of more than 8 kDa. Our results rather suggest either a neurogenic pathway or a mediator smaller than 8 kDa.

Harnessing the preconditioning phenomenon: does remote organ ischaemia provide the answer?

Despite progress in defining the cellular mechanisms of the ischaemic preconditioning phenomenon, its conversion into convenient clinical practice has been slow. The possibility that an innate mechanism of tissue resistance to ischaemia could be harnessed as a clinical tool is an attractive and enticing prospect.

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

OBJECTIVES

A series of brief coronary artery reperfusions and reocclusions applied during the early minutes of coronary artery reflow ("postconditioning") attenuates reperfusion injury. However, it is not known whether brief ischemia-reperfusion applied to a distant organ at the onset of myocardial reperfusion (i.e. "remote postconditioning", remote PostC) reduces infarct size in the reperfused myocardium. In an in vivo anesthetized rat model of myocardial infarction induced by coronary artery occlusion and reperfusion, this study tested the hypothesis that remote postC induced by a single 5 minute episode of renal artery (RA) occlusion and reperfusion applied immediately before the onset of coronary artery reperfusion protects the myocardium from reperfusion injury by mechanisms involving endogenous adenosine receptor activation.

METHODS

All rats were subjected to a total of 30 minutes of left coronary artery occlusion (LCAO) and 3 hours of reperfusion. The rats were randomized to one of six groups: 1) CONTROL: LCAO and reperfusion only with no other intervention; 2) Remote PostC: after 24 minutes of LCAO the RA was occluded for 5 minutes and released 1 min before coronary artery reperfusion; 3) Permanent RA occlusion: the RA was permanently occluded after 24 minutes LCAO continuing to the end of reperfusion; 4) Delayed Remote PostC: after 26 minutes LCAO the RA was occluded for 5 minutes, and its release was delayed until 1 min after coronary artery reperfusion; 5) CON + SPT: rats with LCAO and reperfusion received 10 mg/kg IV of the non-selective adenosine receptor antagonist 8-sulfophenyl theophylline [SPT] administered 5 minutes before coronary artery reperfusion; and 6) Remote PostC + SPT: after 24 minutes of LCAO the RA was occluded for 5 minutes and released 1 minute before coronary artery reperfusion in the presence of 10 mg/kg SPT given 5 min before coronary artery reperfusion.

RESULTS

Myocardial infarct size (percentage necrosis/area at risk, mean +/- SEM) was reduced by 50% in Remote PostC (25 +/- 4%) compared to CONTROL (49 +/- 4%, p = 0.003), consistent with a reduction in plasma CK activity (44 +/- 5 vs. 67 +/- 6 U/ml, p = 0.023). In contrast, permanent RA occlusion before LCAO and reperfusion failed to reduce myocardial infarct size (47 +/- 5%) vs CONTROL. Delaying the release of the RA occlusion (delayed Remote PostC) abrogated the myocardial infarct reduction observed with Remote PostC (48 +/- 6%). SPT alone had no effect on infarct size (47 +/- 4% in CON + SPT vs. 49 +/- 4% in CON); however, Remote PostC+SPT abrogated the myocardial infarct size reduction in Remote PostC (50 +/- 3% in Remote PostC + SPT vs. 25 +/- 4% in Remote PostC).

CONCLUSIONS

Remote renal postconditioning applied immediately before the onset of coronary artery reperfusion provides potent myocardial infarct size reduction likely exerted during the first minutes of coronary artery reperfusion. This inter-organ remote postconditioning phenomenon is likely mediated in part by release of adenosine by the ischemic-reperfused kidney and subsequent activation of adenosine receptors.

Mitochondrial KATPchannels in hindlimb remote ischemic preconditioning of skeletal muscle against infarction

We previously demonstrated in the pig that instigation of three cycles of 10 min of occlusion and reperfusion in a hindlimb by tourniquet application (∼300 mmHg) elicited protection against ischemia-reperfusion injury (infarction) in multiple distant skeletal muscles subsequently subjected to 4 h of ischemia and 48 h of reperfusion, but the mechanism was not studied. The aim of this project was to test our hypothesis that mitochondrial ATP-sensitive potassium (KATP) (mKATP) channels play a central role in the trigger and mediator mechanisms of hindlimb remote ischemic preconditioning (IPC) of skeletal muscle against infarction in the pig. We observed in the pig that hindlimb remote IPC reduced the infarct size of latissimus dorsi (LD) muscle flaps (8 × 13 cm) from 45 ± 2% to 22 ± 3% ( n = 10; P < 0.05). The nonselective KATPchannel inhibitor glibenclamide (0.3 mg/kg) or the selective mKATPchannel inhibitor 5-hydroxydecanoate (5-HD, 5 mg/kg), but not the selective sarcolemmal KATP(sKATP) channel inhibitor HMR-1098 (3 mg/kg), abolished the infarct-protective effect of hindlimb remote IPC in LD muscle flaps ( n = 10, P < 0.05) when these drugs were injected intravenously at 10 min before remote IPC. In addition, intravenous bolus injection of glibenclamide (1 mg/kg) or 5-HD (10 mg/kg) at the end of hindlimb remote IPC also abolished the infarct protection in LD muscle flaps ( n = 10; P < 0.05). Furthermore, intravenous injection of the specific mKATPchannel opener BMS-191095 (2 mg/kg) at 10 min before 4 h of ischemia protected the LD muscle flap against infarction to a similar extent as hindlimb remote IPC, and this infarct-protective effect of BMS-191095 was abolished by intravenous bolus injection of 5-HD (5 mg/kg) at 10 min before or after intravenous injection of BMS-191095 ( n = 10; P < 0.05). The infarct protective effect of BMS-191095 was associated with a higher muscle content of ATP at the end of 4 h of ischemia and a decrease in muscle neutrophilic myeloperoxidase activity at the end of 1.5 h of reperfusion compared with the time-matched control ( n = 10, P < 0.05). These observations led us to conclude that mKATPchannels play a central role in the trigger and mediator mechanisms of hindlimb remote IPC of skeletal muscle against infarction in the pig, and the opening of mKATPchannels in ischemic skeletal muscle is associated with an ATP-sparing effect during sustained ischemia and attenuation of neutrophil accumulation during reperfusion.

Noninvasive remote ischemic preconditioning for global protection of skeletal muscle against infarction

The aim of this study was to investigate the efficacy and mechanism of action of a noninvasive remote ischemic preconditioning (IPC) technique for the protection of multiple distant skeletal muscles against ischemic necrosis (infarction). It was observed in the pig that three cycles of 10-min occlusion and reperfusion in a hindlimb by tourniquet application reduced the infarction of latissimus dorsi (LD), gracilis (GC), and rectus abdominis (RA) muscle flaps by 55%, 60%, and 55%, respectively, compared with their corresponding control (n = 6, P < 0.01) when they were subsequently subjected to 4 h of ischemia and 48 h of reperfusion. This infarct-protective effect of remote IPC in LD muscle flaps was abolished by an intravenous bolus injection of the nonselective opioid receptor antagonist naloxone (3 mg/kg) 10 min before remote IPC and a continuous intravenous infusion (3 mg/kg) during remote IPC and by an intravenous bolus injection of the selective delta 1-opioid receptor antagonist 7-benzylidenealtrexone maleate (3 mg/kg). However, this infarct-protective effect of remote IPC was not affected by an intravenous bolus injection of the ganglionic blocker hexamethonium chloride (20 mg/kg) or the nonspecific adenosine receptor antagonist 8-(p-sulfophenyl)theophylline (10 mg/kg) or by a local intra-arterial injection of the adenosine1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (3 mg/muscle flap) given 10 min before remote IPC. It was also observed that this remote IPC of skeletal muscle against infarction was associated with a slower rate of muscle ATP depletion during the 4 h of sustained ischemia and a reduced muscle neutrophilic myeloperoxidase activity after 1.5 h of reperfusion. These observations led us to speculate that noninvasive remote IPC by brief cycles of occlusion and reperfusion in a pig hindlimb is effective in global protection of skeletal muscle against infarction. This infarct-protective effect is most likely triggered by the activation of opioid receptors in the skeletal muscle, and remote IPC is associated with an energy-sparing effect during sustained ischemia and attenuation of neutrophil accumulation during reperfusion.