Objectives: Pretreatment with diazoxide, a mitochondrial ATP-sensitive potassium channel (mito KATP) opener, was found to protect the rat heart against ischaemia-reperfusion (I/R) injury by mimicking ischaemic preconditioning (IPC). However, the protection mechanisms have not been fully clarified yet.We hypothesize that molecular regulation of mitochondrial energetics is integral to this cardioprotective programme. We explored the involvement of peroxisome proliferator-activated receptor gamma coactivator-1-1alpha (PGC-1alpha) in the effect of IPC and diazoxide preconditioning (DPC) with regard to its role in protection against I/R injury.
Methods: 30 Wistar rats were used to establish the Langendorff isolated perfused heart model. Rats were randomly divided into 5 groups, 6 in each group: (1) the I/R group: after 30 min of equilibration perfusion, the heart was subjected to 30 min of ischaemia and 1 h of reperfusion; (2) the IPC group: after 10 min of equilibration perfusion, the heart was subjected to two times 5 min ischaemia and 5 min of reperfusion, followed by 30 min of ischaemia and 1 h of reperfusion; (3) the DPC group: after 10 min of equilibration perfusion, the heart was given two times a K-H perfusion solution containing diazoxide (100 micromol/l) for 5 min then a non-diazoxide K-H perfusion solution for 5 min, followed by 30 min of ischaemia and 1 h of reperfusion; (4) a blank control group: an equal amount of saline was used instead of diazoxide. The perfusion procedure was the same as in the DPC group; (5) the dimethyl sulfoxide (DMSO) group: DMSO was applied instead of diazoxide, and the perfusion procedure was the same as in the DPC group. Cardiac apex muscle was cut for frozen section. Immunohistochemistry staining of PGC-1alpha was performed and average absorbance was calculated. An electron microscope was used for Flameng scoring of the myocardial mitochondria.
Results: The average absorbance values of PGC-1alpha were: I/R group (3.88 +/- 1.72), IPC group (10.94 +/- 5.23), DPC group (8.40 +/- 3.64), blank control group (3.55 +/- 1.56) and DMSO group (4.16 +/- 0.52), respectively. The expression of PGC- 1alpha was significantly increased in the IPC and DPC groups and the differences were statistically significant compared to the I/R, blank control and DMSO groups, i.e., P < 0.01 for IPC group and P < 0.05 for DPC group. However, there was no significant difference between the IPC and DPC groups (P > 0.05). Flameng score: IPC group (0.44 +/- 0.13), DPC group (0.47 +/- 0.10), I/R group (1.78 +/- 0.14), blank control group (1.70 +/- 0.03) and DMSO group (1.68 +/- 0.06). The Flameng score of the IPC and DPC groups was statistically significantly different as compared to the I/R group, blank control group and DMSO group (P < 0.01), but no significant difference was detected between the IPC and DPC groups (P > 0.05).
Conclusion: IPC and DPC have a protective effect on myocardial mitochondria, and their mechanism of action may be related to activation and over-expression of PGC-1alpha.