Neuroprotective efficacy and therapeutic time window of peroxynitrite decomposition catalysts in focal cerebral ischemia in rats

Free radicals have been implicated in cerebral ischemia reperfusion (IR) injury. Massive production of nitric oxide and superoxide results in continuous formation of peroxynitrite even several hours after IR insult. This can produce DNA strand nicks, hydroxylation and/or nitration of cytosolic components of neuron, leading to neuronal death. Peroxynitrite decomposition catalysts 5,10,15,20-tetrakis(N-methyl-4'-pyridyl)porphyrinato iron (III) (FeTMPyP) and 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato iron (III) (FeTPPS) have been demonstrated to protect neurons in in vitro cultures; however, their neuroprotective efficacy in cerebral IR injury has not been explored. In the present study, we investigated the efficacy and the therapeutic time window of FeTMPyP and FeTPPS in focal cerebral ischemia (FCI). FCI was induced according to the middle cerebral artery occlusion (MCAO) method. After 2 h of MCAO and 70 h of reperfusion, the extent of neurological deficits, infarct and edema volume were measured in Sprague-Dawley rats. FeTMPyP and FeTPPS were administered at different time points 2, 6, 9 and 12 h post MCAO. FeTMPyP and FeTPPS (3 mg kg(-1), i.v.) treatment at 2 and 6 h post MCAO produced significant reduction in infarct volume, edema volume and neurological deficits. However, treatment at latter time points did not produce significant neuroprotection. Significant reduction of peroxynitrite in blood and nitrotyrosine in brain sections was observed on FeTMPyP and FeTPPS treatment. As delayed treatment of FeTMPyP and FeTPPS produced neuroprotection, we tested whether treatment had any influence over the apoptotic neuronal death. DNA fragmentation and in situ nick end-labeling assays showed that FeTMPyP and FeTPPS treatment reduced IR injury-induced DNA fragmentation. In conclusion, peroxynitrite decomposition catalysts (FeTMPyP and FeTPPS) produced prominent neuroprotection even if administered 6 h post MCAO and the neuroprotective effect is at least in part due to the reduction of peroxynitrite and apoptosis.