The Effects And Mechanism Of Nicorandil On The Cardiac Function In Patients With Acute Myocardial Infarction After Percutaneous Coronary Intervention

BackgroundAccording to the report of World Health Organization(WHO),there are 55 million people died in 2011,and 17 million of the death were caused by cardiovascular diseases(CVDs).It means that every 3 in 10 deaths were caused by CVDs,about 7 million people died from coronary heart disease(CHD),and 6.2 million people died from stroke among those death,moreover,the death caused by CHD in China is the second top in the world,It is estimated that from 2006 to 2015,there are approximate 558 billion dollars loss of national income in China which is caused by CHD,stroke and diabetes mellitus,The prevalence of cardiovascular disease has began to become a heavy burden of Chinese government.Therefore,how to reduce the morbidity and mortality of CHD is a challenge for every cardiovascular doctors in our country.Acute myocardial infarction(AMI)is the principal clinical manifestation of CHD,and also is the primary cause of death in patients with CHD.Many clinical trials confirmed that early reperfusion therapy of an occluded coronary artery improves survival in patients with acute myocardial infarction(AMI),the concept of Time is Myocardium and Time is Life was accepted by most of the cardiovascular doctors,primary percutaneous coronary intervention(PCI)is widely performed accoding the guidelines in the first-class hospitals domestically.Although early reperfusion therapy greatly improves the outcomes for patients with AMI,but its benefits are limited by reperfusion injury in some case,much of the patients gradually presented with cardiac dilatation,heart failure and arrhythmia after AMI,which is also called ischemic cardiomyopathy,and the long-term outcomes are very poor.The fundamental reason of ischemic cardiomyopathy is left ventricular(LV)remodeling after acute myocardial infarction(AMI)which is pathologically characterized by infarct area expansion,lengthening of noninfarcted segments in adj acent noninfarcted regions,global ventricular dilatation and dysfunction.All studies,both in animals and humans,showed that the key pathogenetic element of heart failure after acute myocardial infarction(AMI)poor clinical prognosis is constituted by myocardial remodeling.This is a complex pathologic process of ultrastructural rearrangement of the impaired heart induced by various neuro-humoral factors released by cardiac fibrocells in response to biomechanical stress connected to chronic haemodynamic overload.The typical molecular pathological features of myocardial remodeling are represented by cardiomyocytes hypertrophy and apoptosis,extracellular matrix alterations,mesenchymal fibrotic and phlogistic processes and by cardiac gene expression modifications with fetal genetic program reactivation.In the last decades,increasing knowledge of subtle molecular and cellular mechanisms involved in myocardial remodeling has led to the discovery of some new potential therapeutic targets capable of inducing its regression.As is well-known,Angiotensin-converting enzyme inhibitor(ACEI)and ?-adrenoceptor blocker are proved to limit Left Ventricular remodeling and reduce the mortality in patients with chronic heart failure(CHF)caused by AMI,and are the standard therapy for chronic heart failure(CHF)at present.Cell apoptosis is also called programed cell death(PCD),which has been revealed to play a important role in the pathogenesis of a number of human diseases.It accounts for at least part of cell death or cardiac functional deterioration in acute myocardial infarction or chronic heart failure(CHF).Apoptotic cell death is usually observed in pathological situations of the heart such as acute myocardial infarction or congestive heart failure.Since cardiac myocytes are terminally differentiated and are refractory to cell cycle entry,apoptotic cell death in the myocardium likely result in a cumulative decrease in cell number and progressive cardiac functional deterioration.Some study discovered that the activation of mitochondrial KATp channels inhibits oxidative stress induced apoptosis in isolated cardiac myocytes,but the precise molecular mechanisms by which mitochondrial KATP channel opening protects against apoptosis remain unclear.Other study found that the activation of mitochondrial KATP channels inhibits the depolarization of mitochondrial membrane potential,enhances the membrane stability,and prevent calcium overload in mitochondrial matrix induced by hypoxia.Mitochondrial matrix calcium overload is a well-documented trigger of the opening of permeability transition pore(PTP),the opening of PTP directly results in the leak of mitochondrial substance such as reactive oxygen species(ROS),cytochrome c and so on,and induces the cell apoptosis or necrosis.Potassium channels particularly those regulated by intracellular ATP are ubiquitous in the heart and blood vessels and are important modulators of cardiovascular function.In cardiac muscle tissue,KATP channel activation markedly shortens the action potential duration in ventricular and Purkinje fibers and lead to a reduction in cellular energy demands.Moreover,certain studies have shown that the KATP channel opening drugs could also modulate the mitochondrial KATP channel,which makes people realize that the mitochondrial KATP channel is an important target of KATP channel opening drugs and several studies have been developed.Mitochondrial respiration and ATP synthesis are the two major pathways in the energetics of the mitochondrial system.There are three important regulators of the respiratory rate:(1)the supply of ADP that regulates respiration by its rate of transfer into the mitochondria,(2)the ratio of NAD/NADH2 in the mitochondria,which regulates the activity of citrate cycle dehydrogenases and(3)the mitochondrial calcium concentration,which also regulates these dehydrogenases.Maintenance of proper mitochondrial transmembrane potential is essential for the survival of the cell as it drives the synthesis of ATP and maintains oxidative phosphorylation.During ischaemia,the cellular stores of ATP and creatine phosphate are depleted.Membrane permeability is increased and the cytosolic levels of Na+ and Ca2+ are raised.The mitochondria exhibit an altered respiration and a lower respiratory control ratio(RCR).The decreased 02 uptake may be due to impairment in myocardial energy production.The most dramatic decrease in respiratory activity during state 3 respiration indicates an impairment of electron transport coupling.A decrease in respiratory rate(states 3 and 4)and respiratory control ratio(RCR)has been reported in ischemic myocardium.Decrease in ADP/O ratio shows that the utilization of oxygen is delinked from oxidative phosphorylation and thus there will be decreased synthesis of ATP.Since mitochondrial membrane is rich in polyunsaturated fatty acids,enhanced lipid peroxidation could lead to decreased synthesis of ATP.There is a close association between ATP depletion and the metabolic changes on the onset of swelling,loss of ionic gradients and alterations in mitochondrial membrane structure and function.The significant rise in the mitochondrial cholesterol content suggests a redistribution of cholesterol in the ischaemic cell.A significant increase in mitochondrial cholesterol content is well associated with myocardial ischaemia.An alteration in mitochondrial membrane cholesterol content affects its fluidity;permeability of ions,activities of membrane bound enzymes and increased degradation of membrane phospholipids(PL).In myocardial mitochondria the primary role of PLis to stabilize the conformation of membrane bound enzymes.A significant increase in FFAs and a decrease in PL content were observed in the myocytes could be due to the accelerated degradation of membrane PL by phospholipases.Accelerated degradation of membrane PL by phospholipases and lysophospholipases has been related to membrane dysfunction and irreversible ischaemic injury.The accumulation of free fatty acids is a consequence of changes in myocardial lipid metabolism.Thus,in ischaemic heart,hydrolysis of PL prevails in myocardial mitochondria.These changes in the metabolism of the subcellular fractions may lead to damage of the membranes of the cardiac myocyte mitochondria,which may be the cause of disorders of electrolyte metabolism and contractile properties of the myocardium.Nicorandil as a dual effects drug of adenosine triphosphate(ATP)-sensitive K(KATP)channel opener and nicotinamide nitrate which can dilate the coronary artery,and has an extraordinary efficacy for myocardial ischemia and angina pectoris.It is widely used in the clinical practice.Animal experiments indicated that it can decrease the infarct size and incidence of arrhythmias after coronary artery reperfusion.clinical studies also have shown that intravenous administration of nicorandil in conjugation with reperfusion therapy in patients with AMI preserves microvascular integrity,decreases the incidence of no-reflow phenomenon,and improves myocardial viability and functional and clinical outcomes.in addition,some studies found that nicorandil was shown to have anti-free radical and neutrophil-modulating properties and also to attenuate polymorphonuclear leukocyte activation induced by ischemia and reperfusion in rats.Ischemic preconditioning(IPC)is a cardioprotective phenomenon in which short periods of myocardial ischemia result in myocardial resistance to the harmful effects of a subsequent episode of prolonged ischemia.Many studies indicated that the KATp channel is probably the final effector of IPC.Miura et al reported that nicorandil exerts its ischemic preconditioning effects and attenuates cardiac sympathetic nerve injury by activating KATp channels.Moreover,nicorandil administration has been reported to improve cardiac sympathetic nerve activity(CSNA)and attenuate LV remodeling in patients with acute myocardial infarction(AMI).Several studies indicated that intravenous administration with nicorandil could decrease the infarct size of acute myocardial infarction(AMI)and improve the cardiac systolic dysfunction after myocardial infarction.Masaharu Akao et al reported that the mitochondrial KATp channels opening plays a major role in cardioprotection afforded by nicorandil,which makes people realize that activation of mitochondrial KATP channels is a significant mechanism of ischemic preconditioning and amelioration for the myocardial ischemia/reperfusion injury.A lot of animal experiments confirmed the mimic effects of nicorandil with ischemic preconditioning(IPC).This drug has undergoing been reported to have an infarct size limiting effect in a number of animal experiments,clinical studies have documented beneficial effects of nicorandil in patients percutaneous coronary intervention(PCI)as well as coronary artery bypass graft(CABG).Moreover,nicorandil could also improve the prognosis in patients with acute myocardial infarction.Some studies indicated the cardioprotective effects of nicorandil are mediated by activation of KATP channels in the mitochondrial inner membrane.Several potential mechanisms have been proposed presently for nicorandil's cardioprotective effects:(1)vaso-dilatation,reduction in pre-and afterload;(2)improved myocardial perfusion;(3)pharmacological ischemic preconditioning;(4)prevention of Ca2+ overload by opening ATP-sensitive potassium channelscnannels30;and(5)free radical scavenging and neutrophil-modulating properties.Nowadays,Nicorandil has attracted keen interest of cardiology doctors due to its well-documented cardioprotective actions.A number of studies in animal models of ischemia/reperfusion indicate that nicorandil has cardioprotective effects,as evidenced by the preservation of cardiac function or infarct size reduction.Meanwhile,studies in patients undergoing percutaneous coronary intervention have shown that the administration of nicorandil reduces ST-segment elevation during ischemia.Similar beneficial effects of nicorandil in patients undergoing coronary artery bypass graft(CABG).Nicorandil also improved the results of exercise tolerance tests relative to placebo in early randomized,double blind,placebo-controlled trials,In the subsequent randomized,double-blind comparative studies in patients with angina pectoris,nicorandil has demonstrated equivalent efficacy to isosorbide dinitrate and mononitrate,metoprolol,,diltiazem,amlodipine and nifedipine.Moreover,nicorandil could also improve regional left ventricular wall motion in patients with acute myocardial infarction,and result in better clinical outcomes as assessed by the incidence of malignant arrhythmia or congestive heart failure.The results of IONA study which published on The Lancet in 2002 indicated that nicorandil was associated with a significant risk reduction of primary end-point events in coronary heart disease death,non-fatal myocardial infarction and unplanned hospitalization due to acute chest pain.The results of JCAD study which published in 2010 also indicated that compared with control group,the death from all causes,fatal myocardial infarction and congestive heart failure in the nicorandil group was significantly decreased.This results make people realize that nicorandil not only could improve the angina symptoms and the quality of life,but also reduce the mortality of patients with CHD,this is an important progress of drug treatament for CHD.At present,the mechanisms underlying nicorandil's protection of the myocardium during acute ischemic injury have been extensively reported,but little is known about nicorandil's effects in infarction-induced LV dilatation and contraction.The extent of changes in LV volume and function has been shown to be associated with short-and long-term prognosis in patients with heart failure caused by ischemic cardiomyopathy after acute myocardial Infarction.Therefore,we conducted this experimental study.ObjectivesThe objectives of this study is to evaluate the effects and underlying mechanism of nicorandil on the cardiac function in patients with acute myocardial infarction after percutaneous coronary intervention by series of clinical trials and animal experiments.1.To evaluate the effect of nicorandil on cardiac function in patients with acute myocardial infarction undergoing primary percutaneous coronary intervention.2.To evaluate the effect of nicorandil on cardiac function in patients with ischemic cardiomyopathy after acute myocardial infarction.3.To evaluate the effect of nicorandil on the apoptosis of cultured neonatal rat cardiomyocytes in vitro.4.To evaluate the effect of nicorandil on the mitochondrial respiration of rat cardiomyocyte.Methods[Cilnical Trails Portion]1.Effects of nicorandil on cardiac function in patients with acute myocardial infarction undergoing primary percutaneous coronary interventionFifty-eight patients with AMI were randomized into control(n=25)group and nicorandil treatment groups(n=33).In the nicorandil group,nicorandil(4 mg as a bolus injection followed by constant infusion at 8 mg/hour for 24 hours)was administered just after admission.reactive oxygen species(ROS)formation was assessed by measuring urinary excretion of 8-epi-prostaglandin F2?(PGF2?)and compared between the two groups.Furthermore,Cardiac function and the incidence of reperfusion injury and cardiac events were also compared.2.Effects of nicorandil on cardiac function in patients with ischemic cardiomyopathy after acute myocardial infarctionThirty-six patients with ischemic cardiomyopathy(LVEF<40%)who underwent successful PCI procedure before 6 months were recruited and treated by standard conventional therapy.Eighteen patients were randomly assigned to nicorandil(15 mg/d)group,whereas the other 18 patients assigned to control group.The delayed heart-to-mediastinum count ratio(H/M ratio),delayed total defect score(TDS),and washout rate(WR)were determined from 123I-meta-iodobenzylguanidine(MIBG)scintigraphy before and 6 months after treatment.Left ventricular end-diastolic volume(LVEDV)and LVEF were determined by echocardiography for the assessment of left ventricular function.[Animal Experiments Portion]1.The effect of nicorandil on apoptosis of cultured neonatal rat cardiomyocyte in vitroThe cultured neonatal rat cardiomyocytes were randomly divided into four groups:control group;hydrogen peroxide(H2O2)(100?mol/L)group;nicorandil(100?mol/L)plus H2O2(100?mol/L)group and nicorandil(100?mol/L)plus 5-hydroxydecanoate(5-HD)(500?mol/L)and H2O2(100?mol/L)group.We evaluated whether nicorandil inhibits the apoptosis of cardiomyocytes directly by using a number of apoptotic markers.2.The effect of nicorandil on mitochondrial respiration of rat cardiomyocytesThe experimental male Wistar rats were divided into three groups(n = 15,in each group):control group;isoproterenol-induced acute myocardial injury model group;nicorandil pretreatment group.After the experimental period,the animals were sacrificed by cervical decapitation.the levels of respiratory control ratio(RCR),ADP/O ratio,ATP concentration and oxidation of succinate were measured accordingly to evaluate the mitochondrial respiration of cardiomyocyte,The mitochondrial cholesterol,phospholipids(PL),triacylglycerol(TG)and free fatty acids(FFAs)were estimated after extracting the total lipid to evaluate the integrity of mitochondrial membrane.Results[Cilnical Trails Portion]1.Effects of nicorandil on cardiac function in patients with acute myocardial infarction undergoing primary percutaneous coronary interventionUrinary 8-epi-PGF2? excretion was increased 2-fold at 60 to 90 minutes after PCI in the control group,whereas it was unchanged after PCI in the nicorandil group(P<0.001,between the two groups).The incidence of no-reflow phenomenon was lower in the nicorandil group than in the control group(P=0.025,between the two groups).Left ventricular ejection fraction and cardiac index at 6 months were greater in the nicorandil group than in controls(P<0.001 and P=0.005,separately).Plasma NT-proBNP level was lower in the nicorandil group(P<0.001,compared with control group).Incidences of inhospital cardiac events and rehospitalization were lower in the nicorandil group than in controls(P<0.05,compared with control group).2.Effects of nicorandil on cardiac function in patients with ischemic cardiomyopathy after acute myocardial infarctionTotal defect score(TDS),H/M ratio,WR,LVEDV,and LVEF at baseline were similar for both groups(P>0.05,between the two groups).After 6 months treatment,in patients receiving nicorandil,TDS decreased from 50±6 to 40±11(P<0.001,compared between before and after nicorandil treatment),H/M ratio increased from 1.68±0.23 to 1.79±0.26(P =0.034,compared between before and after nicorandil treatment),and WR decreased from 46%±9%to 40%±12%(P=0.046,compared between before and after nicorandil treatment).In addition,LVEDV decreased from 178±31 to 157±30 mL(P=0.009,compared between before and after nicorandil treatment),and LVEF increased from 33%.6%to 39%±7%(P =0.008,compared between before and after nicorandil treatment).But in patients of control group,no significant changes were observed in these parameters(P>0.05,compared between before and after treatment).Moreover,there was a significant correlation between the percent change of LVEF and that of TDS from baseline to 6 months in the patients receiving nicorandil(r=-0.569,P<0.05).[Animal Experiments Portion]1.The effect of nicorandil on apoptosis of cultured neonatal rat cardiomyocytes in vitroThe cultured neonatal rat cardiomyocytes were exposed to H2O2(100?mol/L)group resulted in a higher apoptotic rate compared with those in the control group and nicorandil(100?mol/L)plus H2O2(100?mol/L)group(P<0.05)as shown by TUNEL positivity,cytochrome c translocation and caspase-3 activation.Moreover,the caspase-3 activation in Nicorandil group is significantly lower than that in the H2O2(100?mol/L)group(P<0.001,compared between the two groups).These protective effects of nicorandil were blocked by the mito-KATP channel antagonist 5-hydroxydecanoate(5-HD).2.The effect of nicorandil on mitochondrial respiration of rat cardiomyocytesA significant decline in the levels of RCR,ADP/O ratio,ATP concentration and oxidation of succinate in the cardiomyocyte mitochondria of isoproterenol induced acute myocardial injury rats model group compared with the control group(P<0.001 separately).But in the nicorandil groups the levels of RCR,ADP/O ratio,ATP concentration and oxidation of succinate in the cardiomyocyte mitochondria were significantly higher than the model group(P<0.05 separately).Compared with the control group,a significant increase(P<0.001 separately)in the levels of cholesterol,TG and FFAs with a significant decrease(P<0.001)in the PL content in the cardiomyocyte mitochondria of isoproterenol induced acute myocardial injury rat s model group.But in the nicorandil group,the levels of cholesterol,TG and FFAs were significantly lower than the model group(P=0,002?P<0,001 ? P<0.001),and the PL content was significantly higher than the model group(P=0.001).Conclusions1.Our findings indicated that nicorandil improves cardiac function and clinical outcomes in patients with AMI undergoing primary percutaneous coronary intervention.Suppression of ROS formation may be involved in the underlying mechanism.2.Our study demonstrates improvements in cardiac 123I-MIBG scintigraphic and echocardiographic parameters with nicorandil treatment.These findings indicate that nicorandil can improve cardiac sympathetic nerve activity and cardiac function in patients with ischemic cardiomyopathy after acute myocardial infraction.3.Our findings identified nicorandil as an direct inhibitor of apoptosis induced by oxidative stress in cardiomyocytes,and confirmed the critical role of mito-KATP channels opening in inhibiting apoptosis.4.Our study indicated that the protective effect of nicorandil on mitochondrial respiration and its membrane integrity of cardiomyocyte in the isoproterenol-induced acute myocardial injury rats model.