Functional expression of multidrug resistance transporters, P-glycoprotein and the breast cancer resistance protein, in brain cellular compartments
By: by Gloria Lee.
Published: 2006
Language: eng
Number of pages: 309
ISBN-13: 9780494159040
Description: Multidrug resistance (MDR) is a clinical obstacle often encountered during pharmacological treatment of a variety of neurological disorders that include HIV neuropathy, brain neoplasia, and epilepsy. The expression of ATP-binding cassette (ABC) efflux transporters at the blood-brain barrier (BBB) may play a role in restricting permeability and accumulation of xenobiotics and therapeutics into the brain. Glial cells (microglia, astrocytes) are pathologically involved in these neurological disorders and are drug cellular targets. The goal of this Ph.D. project was to investigate the subcellular localization, protein/gene expression and activity of P-glycoprotein (P-gp) and BCRP that may confer MDR in brain compartments using well-characterized in vitro brain culture systems. P-gp gene/protein expression were detected in rat brain microvessel endothelial cells (RBE4) and a continuous rat brain microglia cell line (MLS-9). BCRP gene/protein expression were detected in RBE4, MLS-9 and primary cultures of human brain microvessel cells, rat astrocytes and microglia but at low levels compared to BCRP over-expressing MCF-MX100 cells. P-gp was localized along the plasma/nuclear membranes and plasmalemmal vesicles in RBE4, MLS-9 and in situ in rat brain capillaries by electron microscopy using C219, MRK16, MAB-448 monoclonal antibodies. Fluorescence microscopy using BXP-21 and BXP-53 monoclonal antibodies did not localize BCRP to the plasma membrane compared to MCF-MX100 in all brain compartments. Cellular accumulation of 3H-digoxin in the presence of P-gp inhibitors shows P-gp activity in RBE4 and MLS-9 cells. In addition, protease inhibitors are inhibitors and substrates for P-gp in RBE4 and MLS-9 cells. Compared to MCF-MX100 cells, BCRP transport of 3H-mitoxantrone and fluorescent pheophorbideA was not detected in our brain cultures. In conclusion, our results suggest a multi-level model of drug resistance in brain compartments at the plasma and intracellular membranes. The functional expression of P-gp in RBE4 and MLS-9 cells suggests an important role in restricting the permeability of drugs across the BBB as well as restricting drug accumulation in cellular targets within brain parenchyma. Low expression and lack of BCRP activity in our brain cultures, paralleling recent in situ and  in vivo studies, suggests that BCRP, unlike P-gp, may not serve a protective role, at least in non-diseased brain.
Notes: Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3727.

Thesis (Ph.D.)--University of Toronto, 2006.

Includes bibliographic references.

Electronic version licensed for access by U. of T. users.