Opioid peptide permeation across the blood-brain and blood-cerebrospinal fluid barriers
KeywordsHealth Sciences, Pharmacology.
AdvisorDavis, Thomas P.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractThe passage of peptides across the blood-brain or blood-cerebrospinal fluid barrier is extremely limited. Peptides can be hindered from entering the central nervous system due to the hydrophilic nature of peptides and their susceptibility to enzymatic degradation by various peptidases. This limitation can be overcome through chemical modifications of opioid peptides with the goal of increasing biological stability and blood-central nervous system permeation. In the present studies, an in vitro bovine brain microvessel endothelial cell model of the blood-brain barrier was characterized both functionally and enzymatically. This primary culture model was found to be reflective of the in vivo blood-brain barrier in reference to predicting a peptides relative lipophilicity. Bovine brain microvessel endothelial cells were also found to be quite active enzymatically as far as the peptidases known to be involved in the degradation of methionine enkephalin. The conformationally stable analog of methionine enkephalin, DPDPE, was also characterized for its ability to enter the CNS using the in situ brain perfusion technique. DPDPE was found to enter the brain by both saturable and non-saturable uptake mechanisms. Chlorohalogenation was also found to significantly improve the central nervous system entry as well as biological stability of a potent opioid agonist, biphalin. In addition, the mu-opioid receptor selective antagonist, CTAP, was also evaluated for its ability to enter the CNS. The amount of CTAP that crossed both the blood-brain and blood-cerebrospinal fluid barrier was quantitatively comparable to the mu-selective agonist, morphine. Biphalin was found to enter both spinal and supra-spinal sites that have been shown previously to express mu and delta opioid receptors. In situ brain perfusion experiments identified a saturable component that contributes to the brain entry of [¹²⁵125I-Tyr¹]biphalin. Further experiments revealed that [¹²⁵125I-Tyr¹]biphalin was entering the CNS by the large neutral amino acid transporter and not by the leucine enkephalin uptake system or DPDPE transport system. This research has provided important preliminary work for the characterization of peptide transport into the brain. The importance of using neuropharmaceutical drug delivery vectors in modern medicine needs attention for the evolution of successful drug design targeted for CNS entry.
Degree ProgramGraduate College
Pharmacology & Toxicology