Effect of the free radical scavenger MCI-186 on spinal cord reperfusion after transient ischemia in the rabbit

Objective: Paraplegia remains a serious complication of aortic operations. The production of free radicals during reperfusion after transient ischemia is believed to induce secondary spinal neuronal injury, resulting in paraplegia. The aim of the present study was to clarify the protective effect and method of administration of antioxidants on the neurological and histological outcome in the animal model for reperfusion injury after transient spinal cord ischemia. Methods: New Zealand white rabbits underwent surgical exposure of the abdominal aorta that was clamped for 15 minutes to achieve spinal cord ischemia. Group A animals received two 10 mg/kg doses of 3-methyl-l-phenyl-2-pyrazolin-5-one (MCI-186) at the time of release of the aortic clamp and 30 minutes later. In group B, MCI-186, 5 mg/kg, was given three times, at the time of aorta clamp release, 30 minutes and 12 hours later. In group C (control group), one dose of vehicle was administered. Neurological status was assessed using modified Tarlov’s score until 168 hours after operation. Spinal cord sections were examined microscopically to determine the extent of ischemic neuronal damage. Results: Groups A and B animals had better neurological function than group C (p(0.001). In contrast, group C animals exhibited paraplegia or paraparesis with marked neuronal necrosis. The number of surviving neurons within examined sections of the spinal cord was significantly greater in group B than in group C (p(0.001). Conclusion: In a 15-minute ischemia-reperfusion model using rabbits, systemic repetitious administration of MCI-186, a free radical scavenger, was found to have a protective effect on the spinal cord neurons both neurologically and histologically. We postulate that the drug minimizes the delayed neuronal cell death for reperfusion injury after transient ischemia by reducing the free radical molecules. Moreover, it was thought that we could protect delayed neuronal cell death more effectively by administering MCI-18612 hours later.