A novel zidovudine uptake system in microglia.
ABSTRACT In the central nervous system (CNS), brain macrophages and microglia are the primary targets of productive human immunodeficiency virus 1 (HIV-1) infection. Zidovudine (ZDV), a thymidine derivative, has been reported to reduce the progression of the disease and prolong survival in patients with acquired immunodeficiency syndrome (AIDS) and AIDS dementia complex. Although a restricted ZDV distribution has been observed in the CNS, its accumulation in brain parenchyma has not been examined. We have investigated the uptake properties of radiolabeled ZDV by a continuous rat microglia cell line (MLS-9) grown as a monolayer on an impermeable surface. Although the organic cations verapamil, mepiperphenidol, quinidine, cimetidine, and N(1)-methylnicotinamide moderately inhibited ZDV uptake, the organic cation probes tetraethylammonium and 1-methyl-4-phenylpyridinium were weak inhibitors. ZDV uptake was significantly increased when the proton gradient was outward (pH(i) 6.3 < pH(o) 7.4; pH(i) approximately 7.1 < pH 8.0), whereas uptake decreased with extracellular acidification (pH(i) approximately 7.1 > pH(o) 6.0) or in the presence of the Na(+)/H(+) ionophore monensin. ZDV uptake was increased under depolarized membrane conditions (i.e., 138 mM K(+) in external medium) and decreased under hyperpolarized conditions (i.e., 2 mM K(+) in external medium), implying a membrane potential dependence. These results suggest that although ZDV transport system in microglia has some specificity features of an organic cation transporter, it involves a carrier, distinct from other cloned organic cation transporters, that is novel in its sensitivity to pH and membrane potential. This system may play a significant role in the transport of other weak organic cation substrates and/or metabolites in brain parenchyma.
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ABSTRACT: A novel organic anion transporter selectively expressed at the blood-brain barrier (BBB), originally designated BBB-specific anion transporter type 1 (BSAT1), and now classified as Slco1c1, has been cloned from a BBB genomics program as a partial cDNA; this study describes the cloning and expression of the full-length cDNA from a rat brain capillary cDNA library. Northern analysis revealed the selective expression of the transporter at the BBB, and the transporter was expressed after permanent transfection of human 293 cells with cDNA encoding either the full length or open reading frame mRNA. The full-length transporter cDNA was 2.6 kb, and the mRNA was highly expressed at the rat brain microvasculature, but not in kidney, liver, heart, or lung, or in glial cells or brain glial tumors. Blood-brain barrier-specific anion transporter type 1 expression in 293 cells was poor after the transfection of the full-length cDNA, whereas transporter expression in 293 cells was high after transfection of the open reading frame. The transporter showed asymmetric kinetic properties in comparison of the influx and efflux of model substrates, thyroxine (T4), triiodothyronine (T3), and estradiol-glucuronide (E2G). Thyroxine and T3 inhibited the influx of E2G, but E2G did not inhibit thyroxine influx, and T3 only weakly inhibited the influx of T4. Extracellular E2G stimulated the transefflux of intracellular T4. Blood-brain barrier-specific anion transporter type 1 is a novel organic anion transporter that is a sodium-independent exchanger that may participate in the active efflux of iodothyronines and steroid conjugates at the BBB.Journal of Cerebral Blood Flow & Metabolism 03/2008; 28(2):291-301. · 5.40 Impact Factor
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ABSTRACT: The primary aim of this study was to investigate intranasal (i.n.) administration as a potential route to enhance systemic and brain delivery of didanosine (ddI). A further aim was to investigate the potential use of chitosan nanoparticles as a delivery system to enhance the systemic and brain targeting efficiency of ddI following i.n. administration. Didanosine-loaded chitosan nanoparticles, were prepared through ionotropic gelation of chitosan with tripolyphosphonate anions, and characterized in terms of their size, drug loading, and in vitro release. The nanoparticles were administered i.n. to rats, compared to i.n. and intravenous (i.v.) administration of ddI in solution. The concentrations of ddI in blood, CSF, and brain tissues were analyzed by ultra performance liquid chromatography mass spectroscopy (UPLC/MS). The brain/plasma, olfactory bulb/plasma and CSF/plasma concentration ratios were significantly higher (P < 0.05) after i.n. administration of ddI nanoparticles or solution than those after i.v. administration of didanosine aqueous solution. The ratio of ddI concentration values of the nanoparticles to the solution at 180 min post-i.n. dosing was 2.1 and 1.9 in CSF and brain, respectively. Thus, both the i.n. route of administration and formulation of ddI in chitosan nanoparticles increased delivery of ddI to CSF and brain.Journal of Drug Targeting 12/2009; 18(5):381-8. · 2.77 Impact Factor
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ABSTRACT: Neuronal damage after stroke-associated brain hypoxia is a leading cause of long-term disability and death. The refractoriness to therapeutic strategies for neuroprotection after 3 h post brain ischemia is poorly understood. P-glycoprotein (P-gp), the multidrug resistance gene (MDR-1) product is normally expressed at blood-brain-barrier. P-gp neuronal expression has been demonstrated in refractory epilepsy and after brain ischemia. In this report we investigated the hypoxia-induced neuronal P-gp expression after local injection of CoCl(2) (1-200 mM) in the fronto-parietal cortex of male adult rats (Bregma -1.30 mm) by stereotaxic surgery. P-gp immunostaining of brain slides was analyzed using specific monoclonal antibodies and double immunolabeling was done with specific astrocytic and neuronal markers. Five days after injection of 1 mM CoCl(2), P-gp expression surrounding the lesion site was observed in neurons, astrocytic end-foot on capillary blood vessels and endothelial cells on blood vessels. Higher CoCl(2) doses (200 mM) resulted in additional P-gp immunostaining of the entire astrocytic and neuronal cytoplasm. Electron microscopy (EM) studies showed alterations in neurons as early as 6 h after the CoCl(2) injection. P-gp expression in hypoxic neurons and astrocytic end-foot could potentially impair of drugs access to the brain parenchyma thus suggesting the presence of two P-gp-based pumping systems (one in astrocytes and other in the hypoxic neurons) that are able to behave as a previously unnoticed obstacle for pharmacological strategies of neuroprotection.Journal of the Neurological Sciences 08/2007; 258(1-2):84-92. · 2.24 Impact Factor