The central hypothesis of this proposal is that hemoglobin is cytotoxic and will significantly worsen cellular injury produced by the original ischemic episode. This contribution of hemoglobin to neurological injury can be reduced by pretreatment with antioxidants, chelators, the hemoglobin binding protein haptoglobin, or agents that will plug the barrier, blocking the entry of hemoglobin. This proposal will focus on a rat model of focal ischemia and reperfusion that has been demonstrated to disrupt the blood-brain barrier. To attempt to model the clinical situation, stroma-free or purified human hemoglobin will be infused into the vasculature of rats at the start of reperfusion following focal ischemia. This procedure results in the direct deposition of hemoglobin into the ischemic area of the brain through the disrupted BBB. Increasing doses of hemoglobin will be administered to assess behavioral impairment and survivability. At different time intervals following stroke, the brains will be evaluated for infarct size, cerebral edema, and the degree of disruption of the blood-brain barrier. Neuronal degeneration will be assessed by conventional histology and fluorescence microscopy using fluoro-jade. Finally, animals will be pretreated with an antioxidant (polynitroxyl-albumin), an iron chelator (a starch deferoxamine conjugate), the normal hemoglobin-binding protein haptoglobin, or a subfraction of pentastarch that has been shown to physically plug the holes of a disrupted blood-brain barrier. These studies will delineate a hemoglobin-dependent contribution to neural injury following opening of the blood-brain barrier and will test several therapeutic candidates that could be used in the clinical setting of CABG surgery.
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