Effect of different dosages of difluoromethylornithine on reperfusion injury after temporary middle cerebral artery occlusion

Alpha-Difluoromethylornithine (DFMO) is a specific irreversible inhibitor of ornithine decarboxylase (ODC), the first-step enzyme of polyamines. It has been shown that DFMO has neuroprotective effects on the infarction size after permanent focal and/or transient global cerebral ischemia. However, results using a model of temporary focal cerebral ischemia and reperfusion that more closely resembles the pathological changes observed in human stroke have not been reported. The aim of the present study was to determine the effect of DFMO therapy on postischemic injury size after reperfusion using a transient middle cerebral artery (MCA) occlusion model in rats. Male spontaneously hypertensive rats were anesthetized with halothane and subjected to 2 hours of temporary MCA occlusion with an intraluminal suture. Then 100, 300, and 500 mg/kg of DFMO (six, eight, and eight animals, respectively) or saline (11 animals) were injected intraperitoneally 5 minutes after the induction of ischemia. Physiological parameters including blood gases analysis, blood glucose, hemoglobin, rectal and temporal muscle temperatures, and regional cerebral blood flow were monitored during the surgical procedure. Ischemic injury volume was measured with 2,3,5-triphenyl tetrazolium chloride monohydrate at 24 hours after occlusion. There were no statistically significant differences regarding the physiological parameters during the procedure. Treatment with DFMO significantly reduced the ischemic injury volume in dosages of 300 and 500 mg/kg compared with the saline treatment. The total volume of ischemic brain injury was 256 ± 71, 174 ± 44, 178 ± 46 in 100 -, 300 -, 500-mg/kg DFMO group, respectively, and 271 ± 38 in the saline group (p < 0.05 for 300 and 500 mg/kg DFMO vs. saline). These results demonstrate for the first time that DFMO has neuroprotective effect on reperfusion injury after focal cerebral ischemia. This protective effects may result from either inhibition of ODC, the first and rate-limiting enzyme of polyamine biosynthesis, or from inhibition of polyamine turnover in the interconversion pathway, both of which may result in decreased levels of putrescine.