Abstract
In the central nervous system, the primary targets of the human immunodeficiency virus-1 (HIV-1) are microglia, resulting in a disorder called HIV-1 dementia. P-glycoprotein (P-gp), a membrane-associated ATP-dependent efflux transporter, limits entry into the brain of numerous xenobiotics, including anti-HIV drugs (i.e., protease inhibitors). This project investigates the functional expression of P-gp in the endogenous immune cells of the brain, a parenchymal compartment not previously studied. We used a cell line (MLS-9) derived from rat microglia to study the transport of digoxin, a known P-gp substrate. Reverse transcriptase-polymerase chain reaction analysis detected mRNA for only mdr1b in MLS-9 cells, whereas both mdr1a and mdr1b mRNA were expressed in primary cultured microglia from which they were derived. Western blot analysis with the C219 antibody detected a single band at ∼170 to 180 kDa in MLS-9 cells, which is the size previously reported for P-gp. Immunocytochemical analysis with the monoclonal antibodies C219, MRK16, and MAB-448 labeled P-gp protein along the plasma membrane and nuclear envelope of MLS-9 cells. [3H]Digoxin accumulation by monolayers of MLS-9 cells was significantly enhanced in the presence of any of several P-gp inhibitors (verapamil, cyclosporin A, quinidine, PSC 833), protease inhibitors (i.e., saquinavir, indinavir, and ritonavir), and sodium azide, an ATPase inhibitor. These results provide the first evidence for the functional expression of P-gp in microglia and imply that entry of pharmacological agents, including protease inhibitors, may be prevented within the brain parenchyma, as well as at the blood-brain barrier.
Footnotes
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This work is supported by a grant from the Canadian Foundation for AIDS Research, the Ontario HIV Treatment Network (OHTN), and the Positive Action Fund, AIDS Bureau, Ontario Ministry of Health. Abstract selected for oral presentation at the 101st Annual Meeting of the American Society for Clinical Pharmacology and Therapeutics, Orlando, FL, March 2001.
- Abbreviations:
- HIV-1
- human immunodeficiency virus type 1
- CNS
- central nervous system
- P-gp
- P-glycoprotein, MDR, multidrug resistance
- RT-PCR
- reverse transcriptase-polymerase chain reaction
- PBS
- phosphate-buffered solution
- EBSS
- Earle's balanced saline solution
- MRP
- multidrug resistance-associated protein
- bp
- base pair(s)
- Received April 26, 2001.
- Accepted June 21, 2001.
- The American Society for Pharmacology and Experimental Therapeutics
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