The Cardioprotective Effect Of Insulin Against Myocardial Ischemia/reperfusion Injury And Its Mechanism

BackgroundWith the widespread application of percutaneous coronary intervention(PCI) and coronary artery bypass grafting (CABG) in ischemia heartdisease,myocardial ischemia and reperfusion (I/R) injury received intensiveattention from heart disease experts. In past few years, except that applyingmedicines and the gene treatment method, the cardioprotective effect ofinsulin in myocardial ischemia/reperfusion has been one of the most intenselystudied topics in biomedical research and clinical practice. However, thesignaling mechanisms in the cardioprotective effect of insulin areincompletely understood.Previous works considered that besides improving glucose intake andmetabolism, insulin improves the function of myocardium via antiapoptosis.Meanwhile our previous work has demonstrated that insulin activate thesurvival signal pathway: PI3-K-Akt-eNOS pathway and it is required for insulin's antiapoptotic effects.However, it has recently been demonstrated that myocardialischemia/reperfusion activates the mitogen-activated protein kinase (MAPK)subfamily, namely c-Jun N-terminal kinases (JNK). The oxide materialsactivate the JNK protein and p-JNK further induces the programmed deathof myocardial cell, resulting in apoptosis. MAPKs signaling family are theimportant downstream proteins of insulin receptor as well as PKB/Akt, butits function in insulin protecting the I/R injury is unknown.Aim1. To determine whether systemic administration of insulin reducesmyocardial ischemia/reperfusion injury by reducing the degree ofpostischemic myocardial apoptosis.2. To investigate whether the JNK protein involves in the antiapoptoticeffects of insulin in myocardial ischemia/reperfusion injury, investigate themechanism(s) by which JNK protein may modulate the function of insulin.3. To explore whether the JNK and PI3-K/Akt pathways has a crosstalkin the antiapoptotic effects of insulin in myocardial ischemia/reperfusioninjury and its mechanism in myocardial apoptosis signaling.Methods1. The isolated adult SD rat heart were subjected to 30 min of ischemia/4h of reperfusion and treated with either vehicle or insulin (50 U/L). The heartrate (HR), the left ventricular developing presses (LVDP) and left ventricular±dp/dt maximum (±LVdp/dt max) were observed. After reperfusion, infarctsize (IS), area at risk (AAR) and apoptotic index were examined. Phosphorylation of Akt and JNK were evaluated by the method of WesternBlot.2. SD rats were randomly assigned to the following treatments: Sham,Control, Insulin, Ins+LY, Ins+SP and Ins+LY+SP. LY : LY294002, 15mmol/L;SP:SP600125, 10 mmol/L。3. In Ins+LY, Ins+SP and Ins+LY+SP groups, isolated rat hearts wereperfused with LY294002 (15 mmol/L) or/and SP600125 (10 mmol/L) for 15min before ischemia.Results1. Compared to control, administration of insulin leaded to theimprovement of HR,LVDP,±LVdp/dt max; And apoptotic index declinedfrom 55.1±2.7% to 31.9±1.4% (n=6, P<0.01), meanwhile the rate of infarctsize decreased 16.3%(n=6, P<0.01). Activity of Akt obviously increased (n=6,P<0.05), meanwhile activity of JNK also increased (n=6, P<0.01).2. Administration of PI3-K/Akt inhibitor LY294002 before ischemia, HR,LVDP,±LVdp/dt max of isolated rat hearts obviously decreased (n=6, P<0.01);apoptotic cells increase to 43.8±1.7%; infarct size was 43.5±5.0%, increased14.6% compared with insulin group (n=6, P<0.05). The activity of Aktdeclined but p-JNK had no difference (Ins vsC. Ins+LY, P<0.05).3. The activity of JNK declined in Ins+SP treatment group,meanwhilethe level of p-Akt also declined (vs. Insulin, n=6, P<0.05).4.Compared with Ins+LY gruoup,HR, LVDP,±LVdp/dt max of isolatedrat hearts obviously improveded in Ins+LY+SP group (n=6, P<0.01);apoptotic cells decrease to 29.0±3.0% (n=4, P<0.05); infarct size was 32.5±1.2% (n=4, P<0.05).Conclusion1. Administration of insulin during early stages of ischemic events canprotect myocardial tissue from reperfusion-related damage, and offer a potentially attractive intervention to improve outcome and prognosis aftermyocardial ischemia.2. Direct evidence indicated that Akt is required in the effect of insulinprotecting the I/R heart.3. JNK protein induces the apoptosis of I/R myocardium. SP600125inhibits the activity of JNK and exerts cardioprotective effect.4.Insulin simultaneously activates Akt and JNK signaling protein.p-JNK promotes the phosphorylation of Akt, thus induces the anti-apoptoticeffect in I/R myocardium. The crosstalk between Akt and JNK signalingprotein may exert significant role in insulin protecting I/R myocardium.