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.     

Hypoxic preconditioning of ischaemic canine myocardium.

OBJECTIVE: The aim was to test whether a brief period of non-ischaemic hypoxia can precondition myocardium. METHODS: 60 anaesthetised adult mongrel dogs of either sex underwent 60 min occlusion of the left anterior descending coronary artery, followed by 5 h reperfusion. In treated groups, hearts were either preconditioned with 5 min coronary perfusion with hypoxic blood [O2 content 9.2(SEM 0.6) ml.litre-1] or 5 min occlusion followed by a 10 min reperfusion period prior to 60 min occlusion. The effect of these treatments on myocardial infarct size and regional contractile function was assessed. RESULTS: Infarct size, determined by tetrazolium staining, as a percentage of anatomical area at risk was markedly decreased in hypoxia preconditioned hearts, at 7.2(1.8)% v 22.4(4.6)% in controls (p < 0.01), but did not differ from ischaemia preconditioned hearts [4.6(1.7)%; p < 0.01 v control]. Anatomical area at risk, expressed as a percentage of left ventricular mass, and collateral blood flow to the inner two thirds of the ischaemic wall did not differ among the groups. Regional contractile function was depressed following ischaemic preconditioning but not following hypoxic preconditioning. During reperfusion following 60 min occlusion, marked paradoxical systolic lengthening was evident in ischaemia preconditioned and control hearts but not in hypoxia preconditioned myocardium. CONCLUSIONS: Five minutes of hypoxic and ischaemic preconditioning were equipotent in preventing infarction, whereas ischaemic preconditioning caused a greater decrement in postischaemic contractile function.     

p38 MAPK activation triggers pharmacologically-induced beta-adrenergic preconditioning, but not ischaemic preconditioning.

p38 Mitogen-activated protein kinase (p38 MAPK) is activated by short episodes of ischaemia-reperfusion as well as by sustained ischemia followed by reperfusion, Whether activation of this kinase is beneficial or deleterious to the ischaemic heart is still a subject of controversy. Since transient beta-adrenergic stimulation (5 min) stimulates p38 MAPK activation and mimics the cardioprotection of ischaemic preconditioning, it was used as a tool to further evaluate the role of this kinase in cardioprotection. The isolated perfused working rat heart, subjected to 25 min ischaemia and 30 min reperfusion was used as experimental model. p38 MAPK and ATF2 activation was determined using Western blots. The results showed that isoproterenol stimulated p38 MAPK in a dose- and time-dependent manner. Ischaemia-induced activation of p38 MAPK could be partially abolished by beta- and alpha1-adrenergic receptor blockade. Isoproterenol activation of the kinase could be abolished by alprenolol and verapamil, but not by 8-cyclopentyladenosine. p38 MAPK activation induced by either a multi-episode preconditioning protocol or isoproterenol (10(-7) M for 5 min) was associated with a significant reduction in p38 MAPK activation at all time intervals studied during 25 min global ischaemia and at 20 and 30 min of reperfusion, compared with the marked activation observed in untreated non-preconditioned hearts. In each case attenuation of p38 MAPK activation during ischaemia and during reperfusion was associated with improved functional recovery during reperfusion. Cyclic elevations in tissue cAMP during an ischaemic preconditioning protocol acted as trigger of cardioprotection, since pretreatment of such hearts with alprenolol abolished cardioprotection. Mechanical failure in such hearts was characterized by a significant stimulation of p38 MAPK activity during ischaemia and reperfusion. However, p38 MAPK activation during an ischaemic preconditioning protocol did not act as trigger: inhibition of p38 MAPK activation by SB 203580 during the preconditioning phase did not abolish cardioprotection. In fact, functional recovery was significantly better than that of untreated preconditioned hearts. On the other hand, SB 203580, when administered before and during the isoproterenol-preconditioning protocol abolished cardioprotection, suggesting that p38 MAPK activation by a beta -adrenergic-induced preconditioning protocol does act as trigger of cardioprotection. In addition, attenuation of p38 MAPK activity during sustained ischaemia and reperfusion as occurs in ischaemic- or isoproterenol-preconditioned hearts, is beneficial.     

Gap junctional uncoupling plays a trigger role in the antiarrhythmic effect of ischaemic preconditioning

OBJECTIVE: The aim of this study was to determine whether uncoupling of gap junctions (GJ) prior to ischaemia would modify the antiarrhythmic effect of ischaemic preconditioning (PC) in a canine model of ischaemia/reperfusion. METHODS: Twenty control dogs, anaesthetised with chloralose and urethane, were thoracotomised and subjected either to a 25 or a 60 min occlusion of the left anterior descending (LAD) coronary artery. This prolonged ischaemia was preceded 20 min earlier by a single 5 min LAD occlusion in preconditioned dogs (PC group; n=14) or by a 20 min intracoronary infusion of 50 microM carbenoxolone (CBX group; n=15), a relatively selective uncoupler of gap junctions. CBX was also infused in PC dogs (CBX+PC group; n=11). The severity of ischaemia (epicardial ST-segment changes, inhomogeneity of electrical activation) and of ventricular arrhythmias, such as ventricular premature beats (VPBs), ventricular tachycardiac (VT) episodes and ventricular fibrillation (VF), as well as changes in electrical impedance was assessed throughout the experiments. Connexin 43 (Cx43) phosphorylation and GJ permeability were determined at the end of the occlusion periods. RESULTS: Compared to the controls PC and, interestingly, CBX markedly reduced, e.g. the total number of VPBs (440+/-104 vs 47+/-11 and 60+/-15; P<0.05) during the prolonged occlusion. This protection was, however, attenuated when CBX was infused in PC dogs (VPBs: 203+/-32). Changes in electrical impedance, GJ permeability and Cx43 dephosphorylation were significantly less in the PC and CBX groups than in the controls but these were again increased in the CBX+PC group. CONCLUSIONS: Uncoupling of GJs prior to ischaemia either by PC or CBX preserves the electrical coupling of cells and results in an antiarrhythmic effect during a subsequent ischaemic insult, indicating that a partial closure of gap junctions may play a trigger role in the protection. In contrast, when CBX is administered in PC dogs the protection both against GJ uncoupling and arrhythmias is markedly attenuated, suggesting that the antiarrhythmic protection, at least in part, is mediated through GJs.     

Sulfonylureas and ischaemic preconditioning; a double-blind, placebo-controlled evaluation of glimepiride and glibenclamide.

AIMS: Glimepiride is a new sulfonylurea for diabetes treatment which is supposed to impact less on extra-pancreatic ATP-dependent K+ channels than the conventional drug glibenclamide. This study was performed to evaluate whether this results in a better maintenance of ATP-dependent K+ channel mediated ischaemic myocardial preconditioning. METHODS AND RESULTS: In a double-blind placebo-controlled study the period of total coronary occlusion during balloon angioplasty of high grade coronary artery stenoses was used as a model to compare the effects of both drugs. Quantification of myocardial ischaemia was achieved by recording the intracoronary ECG and the time to the occurrence of angina during vessel occlusion. All patients underwent three dilatations. The first dilatation (dilatation 1) served to determine the severity of ischaemia during vessel occlusion. During dilatation 2, baseline values were recorded. Thereafter, glimepiride (15 patients: 1.162 mg), glibenclamide (15 patients: 2.54 mg) or placebo (15 patients) were intravenously administered over 12 min. Dilatation 3 started 10 min after the beginning of the drug administration. Mean ST segment shifts in the placebo group decreased by 35% (dilatation 2: 0.23; dilatation 3:0.15 mV; CI -0.55 to 0.00 mV; P=0.049). A similar reduction also occurred in the glimepiride group, in which repetitive balloon occlusion led to a 34% reduction (dilatation 2: 0.35; dilatation 3: 0.23 mV; CI -0.21 to -0.02 mV; P=0.01). There was little influence however, on mean ST segment shifts in the glibenclamide group (dilatation 2 and dilatation 3: 0.24 mV; CI -0.10 to 0.25 mV; P=0.34). Accordingly, time to angina during balloon occlusion slightly increased (by 30%) in the placebo group (dilatation 2: 37 s; dilatation 3: 48 s; CI 0.0 to 15.0 s; P=0.16); increased by 13% in the glimepiride group (dilatation 2: 40 s; dilatation 3: 45 s; CI 0.0 to 14.0 s; P=0023); and remained unchanged in the glibenclamide group (dilatation 2 and dilatation 3: 30 s; CI -7.5 to 7.5 s; P=0.67). CONCLUSION: These results show that glimepiride maintains myocardial preconditioning, while glibenclamide might be able to prevent it.     

Role of nitric oxide and oxidative stress in ischaemic myocardial injury and preconditioning

Nitric oxide (NO) plays an important role in the physiologic modulation of coronary artery tone and myocardial function. However, increased formation of NO within the myocardium can also have detrimental effects, contributing to the pathophysiology of myocardial dysfunction in ischaemic heart diseases. The role of reactive nitrogen species in the pathogenesis of myocardial dysfunction after ischaemia has been investigated in numerous studies. They reveal divergent and opposed effects of nitric oxide: from a cardioprotective action leading to ischaemic preconditioning after short ischaemic periods to a cardiodepressive action after severe ischaemia/reperfusion injury and heart failure. This review describes the determining role of reactive oxygen species on these opposite myocardial effects of NO. The final action of NO, whether cardioprotective or cardiodepressive, strongly depends on the level of oxidative stress in the myocardium. Nitric oxide disrupts free radical and oxidant-mediated reactions, due to a strong attraction and interaction with superoxide.The level of oxidative stress is positively related to the severity of the ischaemic injury, making the results in different myocardial syndromes more concordant. If the increased production of NO is well in balance with a moderate increase in oxygen radicals, then NO will exert beneficial effects. However, if the oxygen radicals are produced in excess of NO as in prolonged ischaemic injury, then deleterious effects will be induced. Consequently, the balance between NO and free oxygen radicals is crucial in modulating the outcome after an ischaemic insult.     

Cardioprotective effects of chronic hypoxia and ischaemic preconditioning are not additive

The objective of the work was to examine whether adaptation to intermittent high altitude hypoxia and ischaemic preconditioning provide additive protection of the heart against subsequent acute ischaemic injury. Adult male rats were exposed to hypoxia (7000 m, 8 h/day, 24–30 exposures) in a hypobaric chamber. Susceptibility of their hearts to ischaemia-induced ventricular arrhythmias and infarction was evaluated in open-chest animals subjected to 30-min coronary artery occlusion and 4-h reperfusion. Preconditioning was induced by either two (PC1) or five (PC2) occlusions of the same artery for 5 min, each followed by 5-min reperfusion. Adaptation to hypoxia decreased the arrhythmia score from 2.75 ± 0.13 in normoxic controls to 2.17 ± 0.18. Both PC1 and PC2 reduced the arrhythmia score in the controls (0.15 ± 0.10 and 0.71 ± 0.24, respectively), as well as in the hypoxic groups (0.40 ± 0.15 and 0.27 ± 0.15, respectively). The infarct size was reduced from 66.6 ± 2.3% of the area at risk in the controls to 50.2 ± 1.9% in the adapted rats. PC1 conferred further protection in adapted animals (38.4 ± 2.8%) but this combined effect was of the same magnitude as that of preconditioning in the controls (37.5 ± 1.6%). Similar results were obtained using PC2. It is concluded that adaptation to hypoxia decreases the efficiency of ischaemic preconditioning; cardioprotective effects of these two phenomena are not additive. The results are consistent with the view that the mechanisms of protection conferred by chronic hypoxia and preconditioning may share the same signalling pathway. Received: 23 April 2001, Returned for revision: 22 May 2001, Revision received: 25 July 2001, Accepted: 20 August 2001