Relationship between autophagy and diabetes mellitus-caused influence on ischemic preconditioning-induced cardioprotection in rats

Abstract

Objective To evaluate the relationship between autophagy and diabetes mellitus-caused influence on ischemic preconditioning(IP)-induced cardioprotection in rats. Methods Clean-grade healthy male Sprague-Dawley rats, aged 12 weeks, weighing 290-320 g, were used in this study.Diabetes mellitus was induced by high-fat and high-sucrose diet (lasting for 1 week) and intraperitoneal streptozotocin 50 mg/kg (for 2 consecutive days) and confirmed by fasting blood glucose level≥16.65 mmol/L (for 1 week). Thirty rats with diabetes mellitus, weighing 350-450 g, were divided into 3 groups (n=10 each) using a random number table method: sham operation group (DM-S group), myocardial ischemia-reperfusion (I/R) group (DM-IR group) and IP group (DM-IP group). Another 30 non-diabetic rats were selected and divided into 3 groups (n=10 each) using a random number table method: sham operation group (S group), myocardial I/R group (IR group) and IP group.Myocardial ischemia was induced by ligation of the anterior descending branch of left coronary artery for 30 min followed by 120 min reperfusion.IP was produced by 3 cycles of 5-min ischemia followed by 5-min reperfusion prior to establishment of myocardial I/R injury model in IP and DM-IP groups.Blood samples were collected from the internal jugular vein at the end of reperfusion for measuring serum concentrations of cardiac troponin I (cTnI) and creatine kinase-MB (CK-MB). The rats were then sacrificed and myocardial tissues were obtained for determination of myocardial infarct size and expression of microtubule-associated protein 1 light chain 3 Ⅱ (LC3 Ⅱ), Beclin-1, phosphatidyl-inositol 3-kinase (PI3K), protein kinase B (Akt), phosphorylated Akt (p-Akt) and mammalian target of rapamycin (mTOR) (by Western blot). p-Akt/Akt ratio was calculated. Results Compared with S group, the serum cTnI and CK-MB concentrations were significantly increased, the percentage of myocardial infarct size was increased, the expression of LC3Ⅱand Beclin-1 in myocardial tissues was up-regulated, the expression of PI3K and mTOR was down-regulated, and p-Akt/Akt ratio was decreased in IR group (P 0.05). Conclusion The mechanism by which diabetes mellitus abolishes IP-induced cardioprotection may be related to inhibiting activation of PI3K-Akt-mTOR signaling pathway and enhanced autophagy in rats. Key words: Autophagy; Diabetes mellitus; Ischemic preconditioning; Myocardial reperfusin injury