Focal cerebral ischemia activates the nuclear protein poly(ADP-ribose) polymerase (PARP) by single DNA strand breaks which leads to energy depletion and cell death and significantly contributes to the pathogenesis of stroke. Apoptosis Inducing Factor (AIF) is a flavoprotein that is normally confined to the mithochondrial intermembrane space, yet translocates to the nucleus, as shown in several in vitro models of neuronal injury. Here we examined the AIF tranclocation changes in a rat model of focal cerebral ischemia and using INO-1001, a novel potent inhibitor of PARP, we determined the role of PARP activation in the process of AIF translocation in vivo. We used a standard rat middle cerebral artery occlusion model with 2h ischemia and 22h reperfusion. INO-1001 (3 mg/kg/24h) provided a 85% reduction in total hemispheric infarct size, when its administration began 2 hours after the MCA occlusion. INO-1001 attenuated the accumulation of poly(ADP-ribose) in the ischemic/reperfused hemisphere and reduced the accumulation of APP in the white matter of the affected hemisphere, consistently with protection against neuronal necrosis and axonal damage, respectively. Immunocytochemical analysis showed the appearance of AIF labeling in neuronal nuclei of the border zone ischemic area in the striatum after stroke. Cytoplasmatic (axonal) AIF staining was significantly diminished in the necrotic core of the striatum, while it was somewhat enhanced at the borderline ischemic territories of the white matter (ie. in the inner layer of the external capsule). Inhibition of PARP with INO-1001 reshifted the location of the apoptotic marker to the axons in the ipsilateral striatum. Thus, PARP inhibition provides marked protection in the rat model of MCA occlusion induced stroke, both in terms of histological damage (perykarial and axonal) and in terms of functional parameters. Moreover, PARP appears to be involved in the ischemic nuclear translocation of AIF. References: 1.Yu SW, Wang H, Poitras MF, Coombs C et al: Mediation of PARP-1-dependent cell death by apoptosis-inducing factor. Science, 2002; 297: 259-63 2.Virág L, Szabó C: The therapeutic potential of PARP inhibition. Pharmacological Reviews, 2002; 54: 375-429

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