Effect of ischemic preconditioning on myocardial Bcl-2 expression and mitochondrial structure during heart valve replacement surgery / 中国病理生理杂志

ABSTRACT

AIM: To investigate the effect of ischemic preconditioning (IP) on myocardial Bcl-2 expression and mitochondrial structure during heart valve replacement surgery under cardiopulmonary bypass. METHODS: Fifty-four patients were prospectively randomized to receive or not ischemic preconditioning (IP) before cold cardioplegic arrest. Ischemic preconditioning in the IP patients (n=22) was induced by a single 2-min ischemia followed by 3-min reperfusion just before aortic clamping and cold crystalloid cardioplegia for myocardial protection. The control group (n=32) received no ischemic preconditioning before cold cardioplegic arrest. The levels of ejection fraction (EF), fractional shortening(FS) and stroke volume (SV) in both groups were measured and compared. troponin T (c-TnT) level, Bcl-2 protein expression and microscopic changes of myocardial mitochondrial structure were recorded for each group before and after surgery. RESULTS: The level of EF, FS and SV in IP group was higher than those in control group (P<0.05). No significant difference in preoperative c-TnT levels between two groups was observed. The level of c-TnT in IP group was lower than that in control group and with a declining trend over time of 6 h, 24 h, 48 h, 72 h and 5 d after surgery, respectively. The preoperative positive unit of Bcl-2 expression between two groups showed no statistical difference (P> 0.05). Postoperatively, the positive unit of Bcl-2 expression in IP group was 19.85±5.88, significantly increased as compared to the preoperative value (P<0.05). In control group, the positive unit of Bcl-2 expression was 14.17±3.39, showed no statistically significant difference to the preoperative value (P>0.05). Postoperative Bcl-2 expression between two groups showed a significant difference (P<0.05). In the control group, microscopic observation revealed swollen mitochondrion, with a hardly visible or disrupted membrane for some mitochondrion;mitochondrial crista were obviously dissolved and loose with a large number of vacuoles formation. However in IP group, myocardial mitochondrion appeared with intact membrane, concentrated mitochondrial cristae with high electron density and no vacuoles formation was observed. CONCLUSION: IP may up-regulate the expression of myocardial anti-apoptotic protein Bcl-2 to protect the mitochondrion, thus protecting cardiocytes and cardiac functions.