Protective Effect Of Gastrin On Myocardial Ischemia/reperfusion Injury

Background:Ischemic heart diseases(IHD) threaten human health worldwide. With the development of medical technology, ischemic myocardium can be reperfused by vascular reconstruction as early as possible after ischemic heart events. The reperfusion saves a lot of ischemic myocardium. However, it carries with an inherent risk, in that paradoxically, the process of that can induce fatal myocardial damage and the increase of the infarction area, termed ischemia/reperfusion(I/R) injury, which affects the prognosis. It has step into a period of I/R therapy today. So how to reduce the I/R induced myocardial damage is crucial for treating severe cardiovascular disease.The mechanisms of cardiac I/R injury are complex, among which cardiomyocyte apoptosis and necrosis are one of the key pathologic processes. Pharmacological inhibition of the apoptotic signaling induced by I/R injury attenuated cardiomyocyte apoptosis. Cardiomyocyte apoptosis is regulated by multiple genes which regulate apoptotic signaling cascades, such as anti-apoptosis gene and pro-survival kinase signaling cascades(PI3K/Akt, ERK1/2 and STAT3 signaling pathways). Some studies showed that ischemia preconditioning, ischemia postconditioning, distal ischemia preconditioning reduced I/R injury by regulating pro-survival kinase signaling cascades. Some chemical drugs such as edaravone also exert similar effect. However, the current methods have not fully block the I/R injury induced cardiac damage, and there are many factors in the process of applied to clinical use. Thus new strategies easy to apply to clinical use are needed.Previous studies found that the heart is better protected against myocardial I/R injury in the fed state compared to the fasted state with phosphorylation level of Akt increasing. It’s known that diet affects the secretion of gastrointestinal hormones. The increased rate of serum concentration of gastrin is higher than other gastrointestinal hormones after meal. Gastrin was reported to activate the pro-survival pathway, including PI3K/Akt, ERK1/2, and STAT3 pathways. So we speculated that elevated circulating gastrin during fed state may protect myocardium against I/R injury through activating the pro-survival kinase signaling cascades(PI3K/Akt, ERK1/2, and STAT3). Gastrin may be a novel strategy for the treatment of myocardial I/R injury.Purpose:To investigate the protective role of gastrin against myocardial I/R injury, and detect the underlying mechanism for the protective effect of gastrin.Method:1. In the first part, we study the protection and its mechanism of gastrin against myocardial I/R injury in vivo. Rat myocardial I/R injury were induced by ligation of the left anterior descending artery for 30 min and then re-open the suture for 24 hours. The release of myocardial enzyme(LDH, TnT-HSST) was detected 24 hours after ischemia, and myocardial infarction size was measured by TTC staining. Cardiomyocyte apoptosis was examined by Tunel staining and caspaes-3 expression. The expression and phosphorylation of Akt, ERK1/2, STAT3 were analyzed to identify the roles of these pathways in the cardioprotective effect of gastrin.2. In the second part, we study the protection and the mechanism of gastrin against myocardial I/R injury ex vivo. Isolated rat hearts were perfused with a langendorff device(global ischemia 40 min, reperfusion 60 min and drug pretreatment 20 min before ischemia). In this model, we can dislodge the influence of neurohumor and coronary flow by gastrin. The left ventricular function was recorded continually; the effluent of coronary sinus was collected at pre-ischemia and 60 min after reperfusion to detect cardiac enzyme(LDH, TnT-HSST). We measured myocardial infarction area by TTC staining and observated cell apoptosis by Tunel staining. The protein expression and/or phosphorylation of caspase-3, Akt, ERK1/2 and STAT3 protein were detected with Western blotting. We observed that gastrin pretreatment play a protective role in cardiac ischemia reperfusion injury with the inhibitor of Akt, ERK1/2 and STAT3 respectively.Result:1. Gastrin pretreatment inhibited the release of cardiac enzyme, reduced infarction size and decreased myocardial apoptosis after 24 hours on myocardial I/R injury in vivo, which was abolished by gastrin receptor inhibitor CI 988. Gastrin pretreatment increased Akt, ERK1/2 and STAT3 protein phosphorylation level.2. Gastrin pretreatment promoted the recovery of left ventricle function(LVDP, LVEDP, +dp/dtmax), reduced myocardial infarction area, inhibited myocardial enzyme(LDH, TnT-HSST) release and reduced the apoptosis of myocardial cells, was abolished by its receptor inhibitor CI 988 on myocardial I/R injury ex vivo. Gastrin pretreatment increased Akt, ERK1/2 and STAT3 protein phosphorylation expression, which was suppressed by CI 988. Gastrin induced beneficial effects against I/R injury, including infarction area and the release of myocardial enzyme increase, were also blocked by inhibitors of Akt, ERK1/2 and STAT3.Conculsion:Gastrin protects myocardium against I/R injury in vivo and ex vivo through both RISK(PI3K/Akt and ERK1/2) and SAFE(STAT3) signaling pathways, and this effect can be abolished by its receptor inhibitor CI 988.