TRANSPORT OF HUMAN RECOMBINANT BRAIN-DERIVED NEUROTROPHIC FACTOR (BDNF) THROUGH THE RAT BLOOD-BRAIN-BARRIER IN-VIVO USING VECTOR-MEDIATED PEPTIDE DRUG-DELIVERY

The blood-brain barrier (BBB) transport of brain-derived neurotrophic factor (BDNF) in anesthetized rats was examined in the present studies using vector-mediated peptide drug delivery. Following tritiation, th e BDNF was biotinylated via a disulfide linker and was coupled to a co valent conjugate of neutral avidin (NLA), which binds the biotinylated peptide with a high affinity, and the murine OX26 monoclonal antibody to the rat transferrin receptor. Owing to the abundance of transferri n receptors on brain capillary endothelium, the OX26 monoclonal antibo dy undergoes receptor-mediated transcytosis through the BBB, and the N LA-OX26 conjugate transports biotinylated peptide therapeutics through the BBB. The present studies show that while unconjugated BDNF was no t transported through the BBB in vivo, the conjugation of biotinylated BDNF to the NLA-OX26 vector resulted in a marked increase in the brai n delivery of BDNF, as defined by measurements of the percentage of th e injected dose (ID) delivered per gram of brain. Although BDNF was no t transported through the BBB in vivo, this cationic peptide was avidl y bound by isolated human brain capillaries via a low-affinity, high-c apacity system that was inhibited by protamine and by serum protein bi nding of BDNF In conclusion, these studies show that the delivery of u nconjugated BDNF to brain is nil owing to the combined effects of negl igible BBB transport and rapid systemic clearance of intravenous admin istered BDNF. The brain delivery of BDNF may be augmented by conjugati on of BDNF to BBB drug delivery vectors, such as the NLA-OX26 conjugat e.