Does nitric oxide generation contribute to the mechanism of remote ischemic preconditioning?

Improved endothelial-dependent and endothelial-independent skin vasodilator responses following remote ischemic preconditioning

One week of daily remote ischemic preconditioning (RIPC) improves cutaneous vasodilatory (VD) function. However, the underlying mechanisms and the number of sessions needed to optimize this adaptive response remain unclear. We hypothesized that the responses to localized heating of the skin will be greater after 2 wk as opposed to 1 wk of RIPC. Furthermore, 2 wk of repeated RIPC will augment cutaneous VD responses to thermal and pharmacological stimuli. In methods, twenty-four participants (24 ± 2 yr; 13 men, 11 women) performed repeated RIPC (7 daily sessions over 1 wk, n = 11; 12 sessions over 2 wk, n = 13), consisting of four repetitions of 5 min of arm blood flow occlusion separated by 5 min reperfusion. Laser speckle contrast imaging was used to measure skin blood flow responses, in perfusion units (PU), to local heating (T_loc = 42°C), acetylcholine (ACh), and sodium nitroprusside (SNP) before and after repeated RIPC. Data were expressed as cutaneous vascular conductance (CVC, in PU/mmHg). In results, the VD response to local heating increased after RIPC (∆CVC from baseline; 1 wk: 0.94 ± 0.11 to 1.19 ± 0.15, 2 wk: 1.18 ± 0.07 to 1.33 ± 0.10 PU/mmHg; P < 0.05) but the ∆CVC did not differ between weeks. SNP-induced VD increased after 2 wk of RIPC (∆CVC; 0.34 ± 0.07 to 0.63 ± 0.11 PU/mmHg; P < 0.05), but ACh-induced VD did not. In conclusion, repeated RIPC improves local heating- and SNP-mediated cutaneous VD. When compared with 1 wk of RIPC, 2 wk of RIPC does not induce further improvements in cutaneous VD function.NEW & NOTEWORTHY Repeated RIPC increases the cutaneous vasodilatory response to local heating and to sodium nitroprusside but not to acetylcholine. Thus, endothelial-independent and local heating-mediated cutaneous vasodilation are improved following RIPC. However, 2 wk of RIPC sessions are not more effective than 1 wk of RIPC sessions in enhancing local heating-mediated cutaneous vasodilation.

A Review of Humoral Factors in Remote Preconditioning of the Heart

A humoral mechanism of cardioprotection by remote ischemic preconditioning (RIP) has been clearly demonstrated in various models of ischemia-reperfusion including upper and lower extremities, liver, and the mesenteric and renal arteries. A wide range of humoral factors for RIP have been proposed including hydrophobic peptides, opioid peptides, adenosine, prostanoids, endovanilloids, endocannabinoids, calcitonin gene-related peptide, leukotrienes, noradrenaline, adrenomedullin, erythropoietin, apolipoprotein, A-I glucagon-like peptide-1, interleukin 10, stromal cell-derived factor 1, and microRNAs. Virtually, all of the components of ischemic preconditioning's signaling pathway such as nitric oxide synthase, protein kinase C, redox signaling, PI3-kinase/Akt, glycogen synthase kinase β, ERK1/2, mitoK_ATP channels, Connexin 43, and STAT were all found to play a role. The signaling pattern also depends on which remote vascular bed was subjected to ischemia and on the time between applying the rip and myocardial ischemia occurs. Because there is convincing evidence for many seemingly diverse humoral components in RIP, the most likely explanation is that the overall mechanism is complex like that seen in ischemic preconditioning where multiple components are both in series and in parallel and interact with each other. Inhibition of any single component in the right circumstance may block the resulting protective effect, and selectively activating that component may trigger the protection. Identifying the humoral factors responsible for RIP might be useful in developing drugs that confer RIP's protection in a more comfortable and reliable manner.

Seven consecutive days of remote ischaemic preconditioning improves cutaneous vasodilatory capacity in young adults

KEY POINTS

Remote ischaemic preconditioning (RIPC), induced by brief bouts of ischaemia followed by reperfusion, confers vascular adaptations that protect against subsequent bouts of ischaemia; however, the effect of RIPC repeated over several days on the human microcirculation is unknown. Using skin as a model, microvascular function was assessed at a control and a NO-inhibited area of skin before 1 day after and 1 week after administering seven consecutive days of repeated RIPC on the contralateral arm. Maximal vasodilatation was increased by ∼20-50% following 7 days of repeated RIPC, and this response remained elevated 1 week after stopping RIPC; however, NO-mediated vasodilatation was not affected by the RIPC stimulus. These data indicate that repeated RIPC augments maximal vasodilatation, but the underlying mechanism for this improvement is largely independent of NO. This finding suggests a role for other endothelium-derived mediators and/or for endothelium-independent adaptations with repeated RIPC.

ABSTRACT

Remote ischaemic preconditioning (RIPC), induced by intermittent periods of ischaemia followed by reperfusion, confers cardiovascular protection from subsequent ischaemic bouts. RIPC increases conduit and resistance vessel function; however, the effect of RIPC on the microvasculature remains unclear. Using human skin as a microvascular model, we hypothesized that cutaneous vasodilatory (VD) function elicited by localized heating would be increased following repeated RIPC. Ten participants (23 ± 1 years, 6 males, 4 females) performed RIPC for seven consecutive days. Each daily RIPC session consisted of 4 repetitions of 5 min of arm blood flow occlusion interspersed by 5 min reperfusion. Before, 1 day after and 1 week after the 7 days of RIPC, two microdialysis fibres were placed in ventral forearm skin for continuous infusion of Ringer solution or 20 mM l-NAME. Red blood cell flux was measured by laser Doppler flowmetry at each fibre site during local heating (T_loc  = 39°C) and during maximal VD elicited by heating (T_loc  = 43°C) and 28 mM sodium nitroprusside infusion. Data were normalized to cutaneous vascular conductance (flux/mmHg). Seven days of RIPC did not alter the nitric oxide (NO) contribution to the VD response to local heating (P > 0.05). However, the maximal VD was augmented (Pre: 2.5 ± 0.2, Post: 3.8 ± 0.5 flux/mmHg; P < 0.05) and remained elevated 1 week post RIPC (3.3 ± 0.4 flux/mmHg; P < 0.05). Repeated RIPC improves maximal VD but does not affect NO-mediated VD in the cutaneous microvasculature. This finding suggests that other factors may explain the vasodilatory adaptations that occur following repeated RIPC.

Endogenous Agmatine Induced by Ischemic Preconditioning Regulates Ischemic Tolerance Following Cerebral Ischemia

Ischemic preconditioning (IP) is one of the most important endogenous mechanisms that protect the cells against ischemia-reperfusion (I/R) injury. However, the exact molecular mechanisms remain unclear. In this study, we showed that changes in the level of agmatine were correlated with ischemic tolerance. Changes in brain edema, infarct volume, level of agmatine, and expression of arginine decarboxylase (ADC) and nitric oxide synthases (NOS; inducible NOS [iNOS] and neural NOS [nNOS]) were analyzed during I/R injury with or without IP in the rat brain. After cerebral ischemia, brain edema and infarct volume were significantly reduced in the IP group. The level of agmatine was increased before and during ischemic injury and remained elevated in the early reperfusion phase in the IP group compared to the experimental control (EC) group. During IP, the level of plasma agmatine was increased in the early phase of IP, but that of liver agmatine was abruptly decreased. However, the level of agmatine was definitely increased in the ipsilateral and contralateral hemisphere of brain during the IP. IP also increased the expression of ADC—the enzyme responsible for the synthesis of endogenous agmatine—before, during, and after ischemic injury. In addition, ischemic injury increased endogenous ADC expression in the EC group. The expression of nNOS was reduced in the I/R injured brain in the IP group. These results suggest that endogenous increased agmatine may be a component of the ischemic tolerance response that is induced by IP. Agmatine may have a pivotal role in endogenous ischemic tolerance.

Remote vs. local ischaemic preconditioning in the rat heart: infarct limitation, suppression of ischaemic arrhythmia and the role of reactive oxygen species

The unmet clinical need for myocardial salvage during ischaemia-reperfusion injury requires the development of new techniques for myocardial protection. In this study the protective effect of different local ischaemic preconditioning (LIPC) and remote ischaemic preconditioning (RIPC) protocols was compared in the rat model of myocardial ischaemia-reperfusion, using infarct size and ischaemic tachyarrhythmias as end-points. In addition, the hypothesis that there is involvement of reactive oxygen species (ROS) in the protective signalling by RIPC was tested, again in comparison with LIPC. The animals were subjected to 30-min coronary occlusion and 90-min reperfusion. RIPC protocol included either transient infrarenal aortic occlusion (for 5, 15 and 30 min followed by 15-min reperfusion) or 15-min mesenteric artery occlusion with 15-min reperfusion. Ventricular tachyarrhythmias during test ischaemia were quantified according to Lambeth Conventions. It was found that the infarct-limiting effect of RIPC critically depends on the duration of a single episode of remote ischaemia, which fails to protect the heart from infarction when it is too short or, instead, too prolonged. It was also shown that RIPC is ineffective in reducing the incidence and severity of ischaemia-induced ventricular tachyarrhythmias. According to our data, the infarct-limiting effect of LIPC could be partially eliminated by the administration of ROS scavenger N-2-mercaptopropionylglycine (90 mg/kg), whereas the same effect of RIPC seems to be independent of ROS signalling.

Reconciling the IPC and Two-Hit Models: Dissecting the Underlying Cellular and Molecular Mechanisms of Two Seemingly Opposing Frameworks

Inflammatory cascades and mechanisms are ubiquitous during host responses to various types of insult. Biological models and interventional strategies have been devised as an effort to better understand and modulate inflammation-driven injuries. Amongst those the two-hit model stands as a plausible and intuitive framework that explains some of the most frequent clinical outcomes seen in injuries like trauma and sepsis. This model states that a first hit serves as a priming event upon which sequential insults can build on, culminating on maladaptive inflammatory responses. On a different front, ischemic preconditioning (IPC) has risen to light as a readily applicable tool for modulating the inflammatory response to ischemia and reperfusion. The idea is that mild ischemic insults, either remote or local, can cause organs and tissues to be more resilient to further ischemic insults. This seemingly contradictory role that the two models attribute to a first inflammatory hit, as priming in the former and protective in the latter, has set these two theories on opposing corners of the literature. The present review tries to reconcile both models by showing that, rather than debunking each other, each framework offers unique insights in understanding and modulating inflammation-related injuries.

The Effect of Remote Ischemic Conditioning and Glyceryl Trinitrate on Perioperative Myocardial Injury in Cardiac Bypass Surgery Patients: Rationale and Design of the ERIC-GTN Study

Remote ischemic conditioning (RIC) using transient limb ischemia/reperfusion has been reported to reduce perioperative myocardial injury in patients undergoing coronary artery bypass grafting and/or valve surgery. The role of intravenous glyceryl trinitrate (GTN) therapy administered during cardiac surgery as a cardioprotective agent and whether it interferes with RIC cardioprotection is not clear and is investigated in the ERIC-GTN trial ( http://www.clinicaltrials.gov: NCT01864252). The ERIC-GTN trial is a single-site, double-blind, randomized, placebo-controlled study. Consenting adult patients (age > 18 years) undergoing elective coronary artery bypass grafting ± valve surgery with blood cardioplegia will be eligible for inclusion. Two hundred sixty patients will be randomized to 1 of 4 treatment groups following anesthetic induction: (1) RIC alone, a RIC protocol comprising three 5-minute cycles of simultaneous upper-arm and thigh cuff inflation/deflation followed by an intravenous (IV) placebo infusion; (2) GTN alone, a simulated sham RIC protocol followed by an IV GTN infusion; (3) RIC + GTN, a RIC protocol followed by an IV GTN infusion; and (4) neither RIC nor GTN, a sham RIC protocol followed by IV placebo infusion. The primary endpoint will be perioperative myocardial injury as quantified by the 72-hour area-under-the-curve serum high-sensitivity troponin T. The ERIC-GTN trial will determine whether intraoperative GTN therapy is cardioprotective during cardiac surgery and whether it affects RIC cardioprotection.

Remote Ischemic Preconditioning May Attenuate Renal Ischemia-Reperfusion Injury in a Porcine Model of Supraceliac Aortic Cross-Clamping

AIM

The effect of remote ischemic preconditioning (RIPC) in decreasing renal ischemia-reperfusion injury (IRI) during a suprarenal aortic cross-clamping was examined in a swine model.

MATERIALS AND METHODS

Four groups of pigs were examined: (a) ischemia-reperfusion (IR) group, renal IRI produced by 30 min of supraceliac aortic cross-clamping; (b) RIPC I group, the same renal IRI following RIPC by brief occlusion of the infrarenal aorta (15 min ischemia and 15 min reperfusion); (c) RIPC II group, the same renal IRI following RIPC by brief occlusion of the infrarenal aorta (3 cycles of 5 min ischemia and 5 min reperfusion); (d) sham group. Renal function was assessed before and after IRI by examining creatinine, neutrophil gelatinase-associated lipocalin (NGAL), TNF-α, malondialdehyde (MDA), cystatin C and C-reactive protein (CRP) from renal vein blood samples at specific time intervals.

RESULTS

Both RIPC groups presented significantly less impaired results compared to the IR group when considering MDA, cystatin C, CRP and creatinine. Between the two RIPC groups, RIPC II presented a better response with regard to CRP, NGAL, TNF-α, MDA and cystatin C.

CONCLUSIONS

Remote IR protocols and mainly repetitive short periods of cycles of IR ameliorate the biochemical kidney effects of IRI in a model of suprarenal aortic aneurysm repair.

Remote ischemic preconditioning for myocardial protection: update on mechanisms and clinical relevance

Ischemic heart disease is the leading cause of death for both men and women worldwide, accruing 7.4 million deaths in 2012. There has been a continued search for better cardioprotective modalities that would reduce myocardial ischemia-reperfusion injury. Among these attempts, a more convenient model of ischemic preconditioning, known as remote ischemic preconditioning (RIPC) was first introduced in 1993 by Przyklenk and colleagues who reported that brief regional occlusion-reperfusion episodes in one vascular bed of the heart render protection to remote myocardial tissue. Subsequently, major advances in myocardial RIPC came with the use of skeletal muscle as the ischemic stimulus. To date, numerous studies have revealed that RIPC applied to the kidney, liver, mesentery, and skeletal muscle, have all exhibited cardioprotective effects. The main purpose of this review article is to summarize the new advances in understanding the molecular mechanisms of RIPC during the past 5 years, including those related to capsaicin-activated C sensory fibers, hypoxia-inducible factor 1α, connexin 43, extracellular vesicles, microRNA-144, microRNA-1, and nitrite. In addition, we have discussed results from several recent human clinical trials with RIPC. Taken together, the emerging clinical evidence supports the concept that the effectiveness of RIPC paired with its low-cost and non-invasive features makes it an ideal treatment before reperfusion after sustained ischemia. More carefully designed studies are warranted to fully exploit the clinical benefits of RIPC and its potential implications in patients with cardiovascular disease.

Is red blood cell a mediator of remote ischaemic preconditioning?

Remote ischaemic preconditioning is emerging as a promising clinical technique which can afford immediate protection against coronary ischaemia. The mechanisms which mediate the signal transduction from remote organ to the heart are still unclear. The role of ATP sensitive potassium channels in ischaemic preconditioning has been established. It is known that the red blood cell (RBC) acts as a mediator of local autoregulation in adjusting oxygen supply to demand by sensing hypoxia and releasing ATP locally to achieve vasodilatation in the adjacent vascular beds. Our hypothesis links these two known mechanisms. Remote ischaemic preconditioning and local RBC autoregulation might share a common mechanism using the ATP sensitive potassium channels. Therefore, we hypothesize that the signal transduction by RBC might be partly responsible for this protection against ischaemia.

The role of gasotransmitters NO, H2S and CO in myocardial ischaemia/reperfusion injury and cardioprotection by preconditioning, postconditioning and remote conditioning

Ischaemic heart disease is one of the leading causes of morbidity and mortality worldwide. The development of cardioprotective therapeutic agents remains a partly unmet need and a challenge for both medicine and industry, with significant financial and social implications. Protection of the myocardium can be achieved by mechanical vascular occlusions such as preconditioning (PC), when brief episodes of ischaemia/reperfusion (I/R) are experienced prior to ischaemia; postconditioning (PostC), when the brief episodes are experienced at the immediate onset of reperfusion; and remote conditioning (RC), when the brief episodes are experienced in another vascular territory. The elucidation of the signalling pathways, which underlie the protective effects of PC, PostC and RC, would be expected to reveal novel molecular targets for cardioprotection that could be modulated by pharmacological agents to prevent reperfusion injury. Gasotransmitters including NO, hydrogen sulphide (H2S) and carbon monoxide (CO) are a growing family of regulatory molecules that affect physiological and pathological functions. NO, H2S and CO share several common properties; they are beneficial at low concentrations but hazardous in higher amounts; they relax smooth muscle cells, inhibit apoptosis and exert anti-inflammatory effects. In the cardiovascular system, NO, H2S and CO induce vasorelaxation and promote cardioprotection. In this review article, we summarize current knowledge on the role of the gasotransmitters NO, H2S and CO in myocardial I/R injury and cardioprotection provided by conditioning strategies and highlight future perspectives in cardioprotection by NO, H2S, CO, as well as their donor molecules.

The role of remote ischemic preconditioning in the treatment of atherosclerotic diseases

BACKGROUND

Remote ischemic preconditioning (RIPC) is the application of a transient and brief ischemic stimulus to a distant site from the organ or tissue that is afterward exposed to injury ischemia, and has been found to reduce ischemia-reperfusion injury (IRI) in various animal models. RIPC appears to offer two distinct phases of endothelial IRI protection, which are presumably mediated through neuronal and humoral pathways.

METHODS

We conducted a comprehensive literature review on the available published data about the potential effect of RIPC in patients undergoing IRI in one or more vital organs.

RESULTS

Our search highlighted 24 randomized clinical trials about the effect of RIPC on variable clinical settings (abdominal aortic aneurysm repair, open heart surgery, percutaneous coronary intervention, living donor renal transplantation, coronary angiography, elective decompression surgery, carotid endarterectomy, recent stroke, or transient ischemic attack combined with intracranial carotid artery stenosis). Most of the trials focused on postoperative cardiac or renal function after RIPC with conflicting results. Preconditioning protocols, age limits, comorbidities, and concomitant drug use varied significantly across trials, and therefore no firm conclusions can be drawn using the available data. However, no severe local adverse events were observed in any patient undergoing limb or arm preconditioning.

CONCLUSIONS

RIPC is a safe and well-tolerated procedure that may constitute a potentially promising innovative treatment in atherosclerotic diseases. Large, multicenter, randomized clinical trials are required to determine an optimal protocol for the RIPC procedure, and to evaluate further the potential benefits of RIPC in human ischemic injury.

Remote or conventional ischemic preconditioning--local liver metabolism in rats studied with microdialysis

BACKGROUND

Ischemic preconditioning (IPC) of the liver decreases liver injury secondary to ischemia and reperfusion. An attractive alternative to IPC is remote ischemic preconditioning (R-IPC), but these two methods have not previously been compared.

MATERIAL AND METHODS

Eighty-seven rats were randomized into four groups: sham operated (n = 15), 1 h segmental ischemia (IRI, n = 24), preceded by IPC (n = 24), or R-IPC (n = 24) (to the left hindleg). IPC and R-IPC were performed with 10 min ischemia and 10 min of reperfusion. Analyses of liver microdialysate (MD), serum transaminase levels, and liver histology were made.

RESULTS

Rats treated with IPC and R-IPC had significantly lower AST, 71.5 (19.6) IU/L respective 96.6 (12.4) at 4 h reperfusion than those subjected to IRI alone, 155 (20.9), P = 0.0004 and P = 0.04 respectively. IPC also had lower ALT levels, 41.6 (11.3) IU/L than had IRI 107.4 (15.5), P = 0.003. The MD glycerol was significantly higher during ischemia in the R-IPC [759 (84) μM] and the IRI [732 (67)] groups than in the IPC 514 (70) group, P = 0.022 and P = 0.046 respectively. The MD glucose after ischemia was lower in the IPC group 7.1 (1.2) than in the IRI group 12.7 (1.6), P = 0.005. Preconditioning to the liver caused an direct increase in lactate, glucose and glycerol in the ischemic segment compared with the control segment an effect not seen in the R-IPC and IRI groups.

CONCLUSIONS

IPC affects glucose metabolism in the rat liver, observed with MD. IPC reduces liver cell injury during ischemic and reperfusion in rats. R-IPC performed over the same length of time as IPC does not have the same effect as the latter on ALT levels and MD glycerol; this may suggest that R-IPC does not offer the same protection as IPC in this setting of rat liver IRI.

Pretreatment with the nitric oxide donor SNAP or nerve transection blocks humoral preconditioning by remote limb ischemia or intra-arterial adenosine

We have previously shown that remote ischemic preconditioning (rIPC) by transient limb ischemia leads to the release of a circulating factor(s) that induces potent myocardial protection. Intra-arterial injection of adenosine into a limb also leads to cardioprotection, but the mechanism of its signal transduction is poorly understood. Eleven groups of rabbits received saline control or rIPC or adenosine administration with additional pretreatment with the nitric oxide (NO) synthase blocker N(G)-nitro-l-arginine methyl ester, the NO donor S-nitroso-N-acetylpenicillamine, its non-NO-donating derivative N-acetylpenicillamine, or femoral nerve section. Blood was then drawn from each animal, and the dialysate of the plasma was used to perfuse a naïve heart from an untreated donor. Infarct size was measured after 30 min of global ischemia and 120 min reperfusion. When compared with that of the control, mean infarct size was significantly smaller in groups treated with rIPC alone (P < 0.01) and intra-arterial adenosine (P < 0.01). Pretreatment with N(G)-nitro-l-arginine methyl ester or N-acetylpenicillamine did not affect the level of protection induced by rIPC (P = not significant, compared with rIPC alone) or intra-arterial adenosine (P = not significant, compared with intra-arterial adenosine alone), but prior femoral nerve transection or pretreatment with S-nitroso-N-acetylpenicillamine abolished the cardioprotective effect of intra-arterial adenosine and rIPC. Intra-arterial adenosine, like rIPC, releases a blood-borne cardioprotective factor(s) that is dependent on an intact femoral nerve and is inhibited by pretreatment with a NO donor. These results may be important when designing or assessing the results of clinical trials of adenosine or rIPC cardioprotection, where NO donors are used as part of therapy.

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 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.

Remote ischemic preconditioning: a novel protective method from ischemia reperfusion injury--a review

BACKGROUND

Restoration of blood supply to an organ after a critical period of ischemia results in parenchymal injury and dysfunction of the organ referred to as reperfusion injury. Ischemia reperfusion injury is often seen in organ transplants, major organ resections and in shock. Ischemic preconditioning (IPC) is an adaptational response of briefly ischemic tissues which serves to protect against subsequent prolonged ischemic insults and reperfusion injury. Ischemic preconditioning can be mechanical or pharmacological. Direct mechanical preconditioning in which the target organ is exposed to brief ischemia prior to prolonged ischemia has the benefit of reducing ischemia-reperfusion injury (IRI) but its main disadvantage is trauma to major vessels and stress to the target organ. Remote (inter organ) preconditioning is a recent observation in which brief ischemia of one organ has been shown to confer protection on distant organs without direct stress to the organ.

AIM

To discuss the evidence for remote IPC (RIPC), underlying mechanisms and possible clinical applications of RIPC. METHODS OF SEARCH: A Pubmed search with the keywords "ischemic preconditioning," "remote preconditioning," "remote ischemic preconditioning," and "ischemia reperfusion" was done. All articles on remote preconditioning up to September 2006 have been reviewed. Relevant reference articles from within these have been selected for further discussion.

RESULTS

Experimental studies have demonstrated that the heart, liver, lung, intestine, brain, kidney and limbs are capable of producing remote preconditioning when subjected to brief IR. Remote intra-organ preconditioning was first described in the heart where brief ischemia in one territory led to protection in other areas. Translation of RIPC to clinical application has been demonstrated by the use of brief forearm ischemia in preconditioning the heart prior to coronary bypass and in reducing endothelial dysfunction of the contra lateral limb. Recently protection of the heart has been demonstrated by remote hind limb preconditioning in children who underwent surgery on cardiopulmonary bypass for congenital heart disease. The RIPC stimulus presumably induces release of biochemical messengers which act either by the bloodstream or by the neurogenic pathway resulting in reduced oxidative stress and preservation of mitochondrial function. Studies have demonstrated endothelial NO, Free radicals, Kinases, Opioids, Catecholamines and K(ATP) channels as the candidate mechanism in remote preconditioning. Experiments have shown suppression of proinflammatory genes, expression of antioxidant genes and modulation of gene expression by RIPC as a novel method of IRI injury prevention.

CONCLUSION

There is strong evidence to support RIPC. The underlying mechanisms and pathways need further clarification. The effective use of RIPC needs to be investigated in clinical settings.

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.

The Role of Nitric Oxide in the Neuroprotection of Limb Ischemic Preconditioning in Rats

Brief limb ischemia was reported to protect neurons against injury induced by subsequent cerebral ischemia-reperfusion, and this phenomenon is known as limb ischemic preconditioning (LIP). To explore the role of nitric oxide (NO) in neuroprotection of LIP in rats, we observed changes in the content of nitric oxide (NO) and activity of NO synthase (NOS) in the serum and CA1 hippocampus of rats after transient limb ischemic preconditioning (LIP), and the influence of N(G)-nitro-L-arginine methylester (L-NAME), a NOS inhibitor, on the neuroprotection of LIP against cerebral ischemia-reperfusion injury. Results showed that NO content and NOS activity in serum increased significantly after LIP compared with the sham group. The increase showed a double peak pattern, in which the first one appeared at time 0 (immediate time point) and the second one appeared at 48 h after the LIP (P < 0.01). The NO content and NOS activity in the CA1 hippocampus in LIP group showed similar change pattern with the changes in the serum, except for the first peak of up-regulation of NO content and NOS activity appeared at 6 h after LIP. Pretreatment with L-NAME before LIP blocked the neuroprotection of LIP against subsequent cerebral ischemic insult. The blocking effect of L-NAME was abolished with pretreatment of L-Arg. These findings indicated that NO may be associated with the tolerance of pyramidal cells in the CA1 hippocampus to ischemia induced by LIP in rats.

Transient limb ischemia induces remote preconditioning in liver among rats: the protective role of heme oxygenase-1

BACKGROUND

We have reported the protective role of heme oxygenase-1 (HO-1) in the mechanism of hypoxic preconditioning. We wish to investigate the role of HO-1 in remote preconditioning (RP) against hepatic ischemia/reperfusion (I/R) injury in rats.

METHODS

The remote preconditioning was produced by four cycles of 10-min ischemia-reperfusion of the hind limb of rats. Partial hepatic ischemia was produced in the left lobes for 45 min followed by 240 min of reperfusion. Zinc-protoporphyrin IX (ZnPP), a specific inhibitor of HO enzymatic activity, was intra-peritoneally injected 1 hr before the ischemia-reperfusion injury in separate groups of RP rats. Serum alanine transaminase (ALT) levels, expression of hepatic HO-1 protein and mRNA, immunohistochemical staining and HO enzymatic activity were measured.

RESULTS

HO-1 was induced in the livers of rats 4 hr after the RP stimuli, and the overexpression persisted for 24 hr. Immunohistochemical staining demonstrated induction of HO-1 in the hepatocytes. The peripheral lymphocytes did not express HO-1 after RP. RP diminished the elevation of serum ALT levels 4 hr after I/R injury (283.7+/-167.4 U L) when compared with controls (1297.7+/-729.3 U L) and RP+ ZnPP pretreated groups (1429.9+/-750.9 U L). The heme oxygenase activity in treated rats also correlated these results (286.8+/-34.3 pmol mg protein hr for the RP group, 156.3+/-27.5 pmol mg protein hr for the RP+ ZnPP pretreated group, and 170.6+/-19.4 pmol mg protein hr for the control group, 144.8+/-7.8 pmol mg protein hr for the control+ ZnPP pretreated group).

CONCLUSION

Our results indicated that the induction of HO-1 in remote preconditioning played a protective role against hepatic I/R injury.

Ischemic preconditioning of the rat brain as a method of endothelial protection from ischemic/repercussion injury

The studies reported here addressed the endothelium-protecting action of local and remote ischemic preconditioning of the brain in rats. Cerebral ischemia lasting 30 min was reproduced by thermocoagulation of the vertebral arteries with simultaneous clamping of the carotid arteries, the procedure being followed by reperfusion via the carotid arteries for 120 min (controls). The early and late phases of ischemic preconditioning and remote preconditioning were reproduced. Brain blood flow was recorded using high-frequency Doppler ultrasonography. The early and late phases of local ischemic preconditioning and the late phase of remote ischemic preconditioning were found to have endothelium-protecting actions apparent as improvements in the recovery of brain blood flow in the post-ischemic period in preconditioned rats, with lower levels of endothelial desquamation and cerebral edema. Blockade of nitric oxide synthesis eliminated the protective effects of both phases of preconditioning.

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.