An Experimental Study On The Effects Of Ginsenoside Rb1 Against Myocardial Ischemia/Reperfusion Injury In Streptozotocin-induced Diabetic Rats

Background:Patients with diabetes are more vulnerable to myocardial ischemic insult and less sensitive to cardioprotective agent than nondiabeic patients. The mortality rate in diabetic patients with acute coronary syndromes is double compared with their nondiabetic counterparts. Ischemic preconditioning and postconditioning play important roles in heart protection through various of signaling pathways, however, cardioprotective effects of them in diabetic hearts were reduced due to the impairment of cardioprotective signaling pathways. Shen-Fu (SF) is an important Chinese herbal medicine that has been used for the treatment of various diseases especial for cardiac diseases in Asia countries for thousands of years. One of our previous studies showed that SF attenuated myocardial ischemia/reperfusion (I/R) injury and enhance postoperative myocardial functional recovery in patients undergoing heart surgery with cardiopulmonary bypass. Ginsenoside Rbl, the major pharmacological extracts of SF, possesses a variety of biological activities. The mechanisms of ginsenoside Rbl-induced cardioprotection remain to be elucidated. Moreover, the pretreatment effects of ginsenoside Rbl on diabetic rats following myocardial I/R are not well understood.ParⅠObjective:To investigate whether myocardial I/R injury are aggravated in STZ-induced diabetic rats and whether ginsenoside Rbl can attenuate myocardial I/R injury in diabetic rats.Methods:Experimental diabetes was induced in the rats by a single intraperitoneal administration of STZ at a dose of 65mg/kg. Body weight and plasma glucose level were recorded every week after vehicle or STZ injection. Rats were divided into four groups,8 weeks after injection:(i) diabetes, (ii) diabetes treated with ginsenoside Rb1 10mg/kg, (iii) diabetes treated with ginsenoside Rb1 40mg/kg, (iv) non-diabetes. Rats were anesthetized followed by tracheotomy and artificial ventilation. A fourth-intercostal space thoracotomy was performed, and the pericardium was excised to expose the heart. The left anterior descending coronary artery (LAD) was occluded for 30 min. After 30 min ischemia, the ligature was loosened to allow blood reperfusion for 2 h. Ginsenoside Rbl 10 or 40mg/kg was administered 10 min before coronary artery ischemia, respectively. After 2h reperfusion, creatine kinase (CK) and lactate dehydrogenase (LDH) were measured. Myocardial infarct size, ultrastructural evidence of myocardial damage was also observed.Results:After 2h reperfusion, postischemic myocardial infarct size was significantly higher in the diabetic untreated group as compared to non-diabetic group (P<0.05), accompanied with increased ultrastructural injury, elevated plasma CK and LDH release were also observed(P<0.05). Ginsenoside Rbl reduced infarct size, CK and LDH release and ultrastructural injury compared to the diabetic control group. Ginsenoside Rbl at a doze of 40mg/kg which exerts better cardioprotective effects than the doze of 10mg/kg.Conclusion:STZ-induced diabetes significantly aggravates myocardial I/R injury. Ginsenoside Rbl exerts cardioprotective effects against myocardial I/R injury in diabetic rats at a dose of 40mg/kg.PartⅡObjective:The purpose of this part was to explore whether ginsenoside Rb1 can attenuate MI/R injury in diabetes through phosphatidylinositol 3-kinase (PI3K)/Akt signal pathway and explore the underlying mechanism.Methods:STZ-induced diabetic rats were randomly assigned to the sham, I/R, ginsenoside Rbl preconditioning, and ginsenoside Rbl plus wortmannin (a special PI3K inhibitor) group. Ginsenoside Rbl (40mg/kg) and wortmannin (15μg/kg) were administered prior to I/R procedure. After the treatment, diabetic hearts except the sham group were subjected to 30 min of coronary artery occlusion and 2h reperfusion. At the end of 2h reperfusion, myocardial infarction size, cardiomyocytes apoptosis, plasma CK and LDH level were assessed. The protein expressions of Akt, eNOS, bcl-2 and caspase-3 in cardiac tissues were analyzed by Western blotting.Results:Comparing with diabetic sham group, I/R caused a significant increase in CK and LDH, myocardial infarct size, cardiomyocyte apoptosis in diabetic I/R group. The expression of Bcl-2 was reduced and activated caspase-3 was increased. Ginsenoside Rb1 preconditioning significantly decreased infarct size, apoptosis, activated caspase-3 protein expression, and plasma level of CK and LDH accompany with increasement of p-Akt, p-eNOS and Bcl-2. Moreover, ginsenoside Rbl-induced cardioprotective effects were abolished by wortmannin.Conclusion:Ginsenoside Rbl protects hearts from I/R injury via PI3K/Akt- dependent pathway in STZ-induced diabetic rats.