Neurotrophins are powerful neuroprotective agents in global or regional brain ischemia when the protein is injected directly into the ischemic brain. Intra-cerebral administration is necessary, because the neurotrophins do not cross the brain capillary endothelial wall, which forms the blood-brain barrier (BBB) in vivo, in the absence of BBB disruption. Presently, there is no neuroprotective agent available to stroke patients, because of the BBB problem. The present work develops neurotrophin chimeric peptides, which are enabled to cross the BBB and cause neuroprotection in the brain following delayed intravenous administration. A neurotrophin chimeric peptide is formed when the neurotrophin is conjugated or fused to a BBB transport vector. The latter is an endogenous peptide or peptidomimetic monoclonal antibody (MAb), which cross the BBB via receptor-mediated transcytosis (RMT) on endogenous BBB peptide transport systems. The model neurotrophins studied are brain-derived neurotrophic factor (BDNF) and basic fibroblast growth factor (bFGF). The model BBB transport vector used for rats is the murine OX26 MAb to the rat transferrin receptor (TfR). The neurotrophin is conjugated to the transport vector with avidin-biotin technology. The proposed work involves 3 Specific Aims. First, the BDNF and bFGF chimeric peptides will be engineered using hybridoma technology, chemical coupling reactions, and avidin-biotin systems. Second, the infarction volume in rats subjected to reversible middle cerebral artery occlusion (MCAO) and treated with varying combinations of the BDNF and bFGF chimeric peptides will be measured. The goal of this Aim is to prolong the therapeutic window beyond the present window of 1-2 hours during which neuroprotection is possible after a 1 hour MCAO. Infarction volumes will be measured at both 1 and 7 days after ischemia. Third, the effects of chronic treatment with BDNF or bFGF chimeric peptides on neurogenesis in the infarcted region will be investigated. Both BDNF and bFGF have been recently shown to induce the formation of new neurons within the adult brain following direct injection into the brain. This work will attempt to show that neurogenesis in the adult brain subjected to ischemia can be induced with the intravenous administration of BDNF and/or bFGF, providing the neurotrophin is enabled to cross the intact BBB in vivo. ? ?
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