Abstract
In the central nervous system, HIV-1 has a defined tropism for brain macrophages and microglia. Nucleoside analog drugs such as zidovudine improve the clinical and neuropsychological functions in HIV-demented patients. Multiple carrier-mediated transport systems can play an important role in the membrane permeation of nucleosides and nucleoside analog drugs in a number of cells. The purpose of this project was to characterize the uptake properties of the pyrimidine nucleoside probe thymidine by a continuous rat microglia cell line (MLS-9) grown as a monolayer on an impermeable substratum. Approximately 50% of thymidine (10 μM) uptake by the monolayer cells was found to be Na+dependent. Kinetics of specific thymidine uptake showed a single saturation system (Km = 44 μM at 37°C) and a Na+/thymidine stoichiometry of 2:1. Pyrimidine and purine nucleoside probes (50 μM) exerted a competitive inhibitory effect on specific thymidine uptake withKi values of 40, 38, 45, and 39 μM for adenosine, uridine, guanosine, and cytidine, respectively. In addition, nucleoside analog drugs significantly decreased specific thymidine uptake, with IC50 values of 135.1 μM for abacavir and 0.6 μM for zidovudine, which inhibited in a noncompetitive manner. These results suggest that a Na+-dependent nucleoside transport system is present in rat microglia and that long-range interactions between antiretroviral nucleoside analog drugs and the nucleoside substrates may occur at the transporter sites.
Footnotes
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Send reprint requests to: Dr. Reina Bendayan. Department of Pharmaceutical Sciences, Faculty of Pharmacy, University of Toronto, 19 Russell St., Toronto, Ontario M5S 2S2, Canada. E-mail:r.bendayan{at}utoronto.ca
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↵1 This work is supported by a grant from the Ontario HIV Treatment Network, the Canadian Foundation for AIDS Research, and the Medical Research Council (MT-13657). M. Hong is a recipient of an Ontario HIV Treatment Network Studentship Award.
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↵2 Current address: Department of Pharmaceutical Sciences, Faculty of Pharmacy, University of Toronto, Toronto, Ontario M5S 2S2, Canada.
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↵3 M. Hong, P. Pennefather, L. Schlichter, and R. Bendayan. Transport properties of thymidine by a rat microglia cell line. Abstract selected for presentation at the 100th Annual Meeting of the American Society for Clinical Pharmacology and Therapeutics, San Antonio, TX, March 1999.
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↵4 Current address: The Neuroscience Institute, University Health Network, Toronto, Ontario M5T 2S8 and Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A1, Canada.
- Abbreviations:
- CNS
- central nervous system
- NT
- nucleoside transporter
- es
- equilibrative, sensitive to NBMPR inhibition
- NBMPR
- 6-(4-nitrobenzyl)-thio-9-β-d-ribofuranosylpurine
- ei
- equilibrative, insensitive to NBMPR
- cif or N1
- concentrative, NBMPR insensitive, accepts formycin B as a permeant
- cit or N2
- concentrative, NBMPR insensitive, common permeant: thymidine
- cib or N3/N4
- concentrative, NBMPR insensitive, broad specificity
- cs or N5
- concentrative, NBMPR sensitive
- BBB
- blood brain barrier
- CSF
- cerebrospinal fluid
- ZDV
- zidovudine
- 3TC
- lamivudine
- ddI
- didanosine
- ddC
- zalcitabine
- NMG
- N-methyl-d-glucamine
- Received June 10, 1999.
- Accepted September 29, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
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A Na+-Dependent Nucleoside Transporter in Microglia
