Possible mechanisms for levosimendaninduced cardioprotection

[摘要] Background and purpose. To limit ischaemic injury, rapid restoration of coronaryblood flow is required, which will in turn reduce infarct size. However, reperfusionitself causes myocyte death – a phenomenon termed lethal reperfusion-inducedinjury, which limits protection of the ischaemic myocardium. Thus the reperfusionof irreversibly damaged myocytes may accelerate the process of cell necrosis.Additive protection of the ischaemic myocardium in the form of adjunct therapyremains a topic of intensive research. Levosimendan, a calcium sensitizing agentwith positive inotropic effects has in several studies been found to alleviate thedamaging effects of reperfusion injury. Levosimendan has been shown to be aKATP channel opener. These channels have been implicated to play an importantrole in ischaemic preconditioning (IPC). With this knowledge, the aim of this studywas to determine whether levosimendan and IPC have certain cardioprotectivemechanisms in common and whether protection with pharmacologicalpreconditioning could be elicited with levosimendan. In this study, we investigatedwhether: 1) the isolated guinea pig heart could be protected by ischaemicpreconditioning (IPC) and postconditioning (IPostC), 2) the heart could bepharmacologically pre- and postconditioned, using levosimendan (LPC & LPostC),3) a combination of IPC & LPC had an additive protective effect on the heart, 4)the KATP (both mitochondrial and sarcolemmal) channels are involved in thisprotection and 5) the pro-survival kinases of the RISK (reperfusion injury salvagekinase) pathway are involved.Experimental approach. Isolated perfused guinea pig hearts were subjected tothree different IPC protocols (1x5, 2x5 and 3x5 minutes of ischaemia) orlevosimendan (0.1μM) preconditioning, before coronary artery occlusion (CAO –40min@36.5ºC), followed by 30 minutes of reperfusion. Hearts were alsosubjected to a combination of IPC & LPC, to establish whether they had additiveprotective effects. In addition, hearts were pre-treated with levosimendan directlybefore induction of sustained ischaemia (without washout of the drug –levosimendan pre-treatment (LPT)) for 10min. With the postconditioning protocol,iiithe hearts were subjected to 3x30second cycles of ischaemia/reperfusion orlevosimendan/vehicle. In a separate series of experiments, hearts were treatedwith KATP channel blockers (for both sarcolemmal & mitochondrial), before LPC,LPT and LPostC. The endpoints that were measured were: cardiac reperfusionfunction, myocardial infarct size and RISK pathway expression andphosphorylation (PKB/Akt and extracellular signal-regulated kinase – ERK42/44).Results. IPC, IPostC, LPC & LPostC decreased myocardial infarct sizesignificantly compared with their controls (21.9±2.2%, 21.4±2.2%, 20.6±3.1% and20.6±1.8% respectively vs. 46.4±1.8% for controls, p<0.05). The combination ofIPC & LPC had no additive protective effect. Pre-treating the hearts withlevosimendan (without washout), before index ischaemia, proved to be the mosteffective method of cardioprotection (infarct size: 5.8±0.9% vs. 46.4±1.8% forcontrols, p<0.001). With LPT a significant increase (p < 0.05 vs. control) inphosphorylation of ER42/44 was also observed. An increase in the activity of oneof the RISK pathway kinases, ERK42/44 seems to be one of the reasons for LPT'sefficacy. Treating the hearts with KATP channel blockers before subjecting them toLPC, LPT & LPostC abolished the protective effects induced by levosimendan,suggesting a role for the sarcolemmal and mitochondrial KATP channels inlevosimendan-induced cardioprotection.Conclusions and implications. 1) Isolated guinea pig hearts could be pre- andpostconditioned within the setting of ischaemia, 2) Hearts could bepharmacologically pre- and postconditioned with levosimendan, 3) levosimendanpre-treatment is the most effective way to reduce infarct size, possibly acting byincreasing the phosphorylation of ERK42/44, 4) Myocardial protection was notincreased by combining IPC & LPC (suggesting similar mechanisms of protection),5) LPC, LPT and LPostC were abolished by both sarcolemmal and mitochondrialKATP channel blockers..LPC and especially LPT, could be useful before elective cardiac surgery whileLPostC may be considered after acute coronary artery events.

[发布机构] Stellenbosch University