Effect of caspase-3 inhibitor in neuronal apoptosis in rat cerebral cortex after ischemia-reperfusion injury

Abstract

To investigate the effect of z-DEVD-fmk, a caspase-3 inhibitor on the neuronal apoptosis in ischemia-reperfusion region (IRR) of rat cerebral cortex. Rats prepared by middle cerebral artery occlusion and reperfusion were used as the research model. The animals were divided into A group (untreated), B group (DMSO control) and C group (treated with z-DEVD-fmk). Before reperfusion, z-DEVD-fmk (7 microg/kg) was injected into the ischemic side of ventriculus cerebri of C group rats. The expression and activation of caspase-3, expression and cleavage of poly (ADP-ribose) polymerase (PARP), and apoptotic neurons in the temporal-parietal cortex IRRs (SPAB method) of all the rats were studied using Western blotting, in situ apoptotic detection (TUNEL method) and immunohistochemistry. In the cerebral IRRs of A, B, C groups reperfused for 1 h and 24 h, the quantities of caspase-3 precursor were 16.7 +/- 3.0, 11.5 +/- 3.0 and 47.5 +/- 3.5, and 76.1 +/- 3.5, 71.3 +/- 6.4 and 88.2 +/- 5.5, respectively; the caspase-3 fragments (12,000) 8.2 +/- 2.3, 9.4 +/- 1.2 and 4.3 +/- 1.6, and 59.0 +/- 6.3, 60.5 +/- 7.2 and 17.3 +/- 2.8, respectively; the PARP 12.6 +/- 3.0, 13.9 +/- 2.0 and 53.7 +/- 4.1, and 67.5 +/- 8.6, 61.1 +/- 6.6 and 93.6 +/- 4.1, respectively; the PARP fragments (24,000) 6.0 +/- 0.7, 6.6 +/- 1.2, 3.6 +/- 1.1, and 27.4 +/- 2.6, 25.8 +/- 3.2, 12.1 +/- 2.8 (relative quantity, x+/- s); the densities of apoptotic neurons 83.3 +/- 7.5, 84.3 +/- 5.7 and 45.7 +/- 4.0, and 197.4 +/- 11.8, 185.2 +/- 11.2 and 99.1 +/- 5.8 (cell number/0.1 mm(2), x+/- s). These results showed that in the cerebral IRRs of both A and B groups, all caspase-3 expression and activation, PARP expression and cleavage, and neuronal apoptosis were increased relevantly along with prolongation of the reperfusion time (P < 0.05 - 0.001). At each time point of the reperfusion, caspase-3 activation, PARP cleavage and neuronal apoptosis in the cerebral IRR of C group were significantly less than those of the former two groups (P < 0.05 - 0.001). The variations of the 5 parameters of A, B and C groups correlated positively with one another (r = 0.630 - 0.942, P < 0.01). The cells expressing PARP were mainly neurons in the cerebral IRRs of all the animals, but the difference of their number was not distinct among the 3 groups. It is an important mechanism resulting in apoptosis of the injured neurons in the cerebral IRR that caspase-3 expression and activation abnormally increased by the reperfusion have more PARP rapidly inactivated by over-cleavage. z-DEVD-fmk may decrease PARP cleavage by inhibiting activity and auto-activation of caspase-3, and prevent the injured neurons from apoptosis.