Roles of reactive oxygen species and phosphatidyl-inositol 3- kinase-Akt in neuroprotection against spinal cord ischemia-reperfusion injury by ischemic postconditioning or controlled low perfusion pressure in rats

Abstract

Objective To investigate the roles of reactive oxygen species (ROS) and phosphatidyl-inositol 3-kinase-Akt (PI3K-Akt) in neuroprotection against spinal cord ischemia-reperfusion (I/R) injury by ischemic postconditioning (IP) or controlled low perfusion pressure (LR). Methods One hundred and twenty-six adult male SD rats weighing 300-350 g were randomly divided into 7 groups (n = 18 each): group Ⅰ I/R; group ⅡIP; group Ⅲ LR; group Ⅳ IP + LY-294002 (IP + LY); group Ⅴ LR + LY-294002 (LR + LY); group Ⅵ IP +N-acetylcysteine (IP+ N) and group Ⅶ LR+ N-acetyl-cysteine (LR+ N). Spinal cord ischemia was induced by 9 min occlusion of the thoracic aorta combined with controlled hypotension (MAP = 40 mm Hg). In IP group the animals were subjected to 3 cycles of 30 s reperfusion interspersed with 30 s ischemia immediately after release of aortic occlusion. In LR group MAP was maintained at 40 mm Hg for another 5 min immediately after release of aortic occlusion, then increased to 100 mm Hg. In group Ⅳ-Ⅶ LY-294002 (PI3K inhibitor) 25 mg/kg or N-acetylcysteine (ROS scavenger) 100 mg/kg were administered at the onset of reperfusion. Twelve animals in each group were killed at 2 h of reperfusion. The lumbar segment of the spinal cord was removed for determination of the level of Akt phosphorylation and opening of mitochondrial permeability transition pore (mPTP). Neurological function was assessed and scored (15 = normal function, 0 = unable to move hind limb) at 4, 12, 24 and 48 h of reperfusion in another 6 animals in each group. The animals were then killed after last assessment and the lumbar segment of the spinal cord was removed for detection of apoptotic neurons. Results Compared with I/R group,both IP and LR significantly enhanced the level of Akt phosphorylation in the spinal cord, inhibited mPTP opening and neuronal apoptosis and increased neurological function scores. There was no significant difference in the protective effects exerted by IP and LR. The neuroprotective effects exerted by IP and LR were abolished by LY-294002 and N-acetylcysteine. Conclusion Ischemic postconditioning or controlled low perfusion pressure can protect the spinal cord from I/R injury by activating PI3K-Akt and inhibiting mitochondrial permeability. Key words: Reactive oxygen species; 1-Phosphatidylinositol 3-kinase; Protein kinases; Perfusion; Reperfusion injury; Spinal cord; Ischemic postconditioning