Brain Microvessel Endothelial Cell Line Research Articles

Study on the reversal of epileptic drug resistance by tetramethylpyrazine in combination with carbamazepine through modulation of P-Glycoprotein expression in rat brain microvessel endothelial cell.

The purpose of this study was to detect the changes of P-Glycoprotein (P-GP) expression in rat brain microvessel endothelial cell line RBE4 after the action of Tetramethylpyrazine (TMP) on Carbamazepine (CBZ), so as to clarify the potential mechanism of TMP combined with CBZ against intractable epilepsy drug resistance. The RBE4 cell line was utilized for in vitro analysis. Cells were divided into control, CBZ, and CBZ-TMP group. The expression of P-GP was assessed using Western blot and reverse transcription polymerase chain reaction (RT-PCR). Intracellular concentration of CBZ was measured through high-performance liquid chromatography (HPLC). The differential expression of mRNA was evaluated by RNA sequencing. The intracellular concentration of CBZ in the CBZ-TMP group was significantly higher than that in other groups. The expression of P-GP in the CBZ group was significantly higher than that in the control group, while in the CBZ&TMP group, it was significantly lower than that in the other groups. Comparative analysis also revealed some differentially expressed genes. Compared with the CBZ group, FAM106A, SLC3A2, TENM2, etc. were upregulated most significantly in the CBZ&TMP group. ZBTB10, WDR7, STARD13, etc. were downregulated most significantly. Results suggest that TMP increases the intracellular concentration of CBZ, downregulates the expression of P-GP increased by CBZ, and modulates related cellular metabolism and signaling pathways, thus reversing the drug resistance mechanism of intractable epilepsy, providing a theoretical basis for the combination of traditional Chinese medicine and antiepileptic drugs.

Reduction in cardiolipin reduces expression of creatine transporter-1 and creatine transport in growing hCMEC/D3 human brain microvessel endothelial cells

The phospholipid cardiolipin (CL) regulates mitochondrial energy production. Endothelial cells of the blood-brain barrier (BBB) play a vital role in uptake of metabolites into the brain and are enriched in mitochondria. We examined how deficiency in BBB endothelial cell CL regulates the expression of selected drug and metabolite transporters and their function. Cardiolipin synthase-1 (hCLS1) was knocked down in a human brain microvessel endothelial cell line, hCMEC/D3, and CL levels and the mRNA expression of selected BBB drug and metabolite transporters examined. Mock transfected hCMEC/D3 cells served as controls. Incorporation of (14C)creatine and (14C)oleate into hCMEC/D3 cells was determined as a measure of solute metabolite transport. In addition, protein expression of the creatine transporter was determined. Knockdown of hCLS1 in hCMEC/D3 reduced CL and the mRNA expression of creatine transporter-1, p-glycoprotein and breast cancer resistance protein compared to controls. In contrast, mRNA expression of ATP binding cassette subfamily C members-1, -3, multidrug resistance-associated protein-4 variants 1, -2, and fatty acid transport protein-1 were unaltered. Although ATP production was unaltered by hCLS1 knockdown, incorporation of (14C)creatine into hCMEC/D3 cells was reduced compared to controls. The reduction in (14C)creatine incorporation was associated with a reduction in creatine transporter-1 protein expression. In contrast, incorporation of (14C)oleic acid into hCMEC/D3 cells and the mRNA expression of fatty acid transport protein-1 was unaltered by knockdown of hCLS1 compared to controls. Thus, knockdown of hCLS1 in hCMEC/D3, with a corresponding reduction in CL, results in alteration in expression of specific solute membrane transporters.

Is P-Glycoprotein Functionally Expressed in the Limiting Membrane of Endolysosomes? A Biochemical and Ultrastructural Study in the Rat Liver.

The drug efflux transporter P-glycoprotein (Pgp; ABCB1) plays an important role in drug absorption, disposition, and elimination. There is an ongoing debate whether, in addition to its localization at the plasma membrane, Pgp may also be expressed at the limiting membrane of endolysosomes (ELs), mediating active EL drug sequestration. If true, this would be an important mechanism to prevent drugs from reaching their intracellular targets. However, direct evidence demonstrating the functional expression of Pgp at the limiting membrane of ELs is lacking. This prompted us to perform a biochemical and ultrastructural study on the intracellular localization of Pgp in native rat liver. For this purpose, we established an improved subcellular fractionation procedure for the enrichment of ELs and employed different biochemical and ultrastructural methods to characterize the Pgp localization and function in the enriched EL fractions. Whereas the biochemical methods seemed to indicate that Pgp is functionally expressed at EL limiting membranes, transmission electron microscopy (TEM) indicated that this only occurs rarely, if at all. Instead, Pgp was found in the limiting membrane of early endosomes and intraluminal vesicles. In additional TEM experiments, using a Pgp-overexpressing brain microvessel endothelial cell line (hCMEC/D3-MDR1-EGFP), we examined whether Pgp is expressed at the limiting membrane of ELs when cells are exposed to high levels of the Pgp substrate doxorubicin. Pgp was seen in early endosomes but only rarely in endolysosomes, whereas Pgp immunogold labeling was detected in large autophagosomes. In summary, our data demonstrate the importance of combining biochemical and ultrastructural methods to investigate the relationship between Pgp localization and function.

Effects of Bmi1 gene on endothelial cells promoting glioma stem cell-like phenotype

To explore the effects of B-cell specific Maloney leukemia virus integration site 1 (Bmi1) gene on endothelial cells promoting glioma stem cell (GSC)-like phenotype. Glioblastoma cell line GL261 and brain micro-vessel endothelial cell line b.END3 were used. Transwell co-culture system, limit dilution assay, xenograft, real-time polymerase chain reaction (PCR), Western blot, fluorescence activating cell sorter (FACS) and gene knock-down assay were used to determine the GSC-like phenotype and Bmi1 gene expression in glioma cells. Compared with the control of GL261 cell alone, (1) more and larger tumor spheres formed after co-culturing with endothelial cells (62.5% ± 1.5% vs 25.0% ± 4.6% at 40 cells/well, P = 0.000). Xenografts generated by GL261 cells with b.END3 cells appeared earlier and were larger than that by GL261 cells alone ((0.798 ± 0.297) cm(3) vs (0.362 ± 0.123) cm(3), P = 0.000); (2) CD133 positive glioma cells increased after co-culturing with endothelial cells (8.48% ± 0.78% vs 4.81% ± 0.37%, P = 0.000); (3) the expression of Bmi1 in co-cultured glioma cells was up-regulated at mRNA level (2.72 ± 0.18 vs 1.00 ± 0.15, P = 0.000) and at protein level; (4) the above phenomenon was attenuated when Bmi1 gene expression was inhibited by siRNA in glioma cells, CD133 positive portion of Bmi1-knockdown GL261 cells co-culturing with b.END3 cells decreased than that of wildtype GL261 cells (0.34% ± 0.21% vs 1.70% ± 0.69%, P = 0.025). Endothelial cells promote GSC-like phenotype by up-regulating the expression of Bmi1 in glioma cells.

Glioma stem cells enhance endothelial cell migration and proliferation via the Hedgehog pathway

The aim of the present study was to determine the possible mechanism underlying the enhanced migration and proliferation of endothelial cells caused by glioma stem cells (GSCs). Tumor spheres enriched in GSCs derived from the mouse GL261 glioma cell line, and the brain microvessel endothelial cell line, b.END3, were used in this study. A Transwell co-culture system, RNAi experiments, quantitative polymerase chain reaction, western blotting and enzyme-linked immunosorbent, cell counting kit-8 (CCK-8) proliferation, Transwell migration and wound-healing assays were used in this study to determine the migration and proliferation ability, as well as the Hedgehog (HH) pathway-related gene expression in the b.END3 cells. Based on the results, it was demonstrated that the migration and proliferation of the endothelial cells were enhanced following co-culture with GSCs. The gene expression of the HH pathway-related genes, Sonic Hedgehog (Shh) and Hedgehog-interacting protein (Hhip) was altered in the endothelial cells when co-cultured with GSCs. Overexpression of glioma-associated oncogene homolog 1 indicated activation of the HH pathway. Following knockdown of smoothened (Smo) in the endothelial cells, the migration and proliferation abilities of the cells were inhibited. GSCs have little effect on enhancing these behaviors in endothelial cells following Smo-knockdown. Further investigation revealed that Shh levels in the supernatant of the co-culture system were elevated, indicating the importance of secreted Shh from the endothelial cells. In conclusion, GSCs enhanced the migration and proliferation of the endothelial cells in vitro, which was likely associated with the activation of the HH pathway in the endothelial cells, caused by the increased secretion of Shh.

Characterization of cellular uptake and toxicity of aminosilane-coated iron oxide nanoparticles with different charges in central nervous system-relevant cell culture models

BackgroundAminosilane-coated iron oxide nanoparticles (AmS-IONPs) have been widely used in constructing complex and multifunctional drug delivery systems. However, the biocompatibility and uptake characteristics of AmS-IONPs in central nervous system (CNS)-relevant cells are unknown. The purpose of this study was to determine the effect of surface charge and magnetic field on toxicity and uptake of AmS-IONPs in CNS-relevant cell types.MethodsThe toxicity and uptake profile of positively charged AmS-IONPs and negatively charged COOH-AmS-IONPs of similar size were examined using a mouse brain microvessel endothelial cell line (bEnd.3) and primary cultured mouse astrocytes and neurons. Cell accumulation of IONPs was examined using the ferrozine assay, and cytotoxicity was assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay.ResultsNo toxicity was observed in bEnd.3 cells at concentrations up to 200 μg/mL for either AmS-IONPs or COOH-AmS-IONPs. AmS-IONPs at concentrations above 200 μg/mL reduced neuron viability by 50% in the presence or absence of a magnetic field, while only 20% reductions in viability were observed with COOH-AmS-IONPs. Similar concentrations of AmS-IONPs in astrocyte cultures reduced viability to 75% but only in the presence of a magnetic field, while exposure to COOH-AmS-IONPs reduced viability to 65% and 35% in the absence and presence of a magnetic field, respectively. Cellular accumulation of AmS-IONPs was greater in all cell types examined compared to COOH-AmS-IONPs. Rank order of cellular uptake for AmS-IONPs was astrocytes > bEnd.3 > neurons. Accumulation of COOH-AmS-IONPs was minimal and similar in magnitude in different cell types. Magnetic field exposure enhanced cellular accumulation of both AmS- and COOH-AmS-IONPs.ConclusionBoth IONP compositions were nontoxic at concentrations below 100 μg/mL in all cell types examined. At doses above 100 μg/mL, neurons were more sensitive to AmS-IONPs, whereas astrocytes were more vulnerable toward COOH-AmS-IONPs. Toxicity appears to be dependent on the surface coating as opposed to the amount of iron-oxide present in the cell.

1α,25-Dihydroxyvitamin D3-liganded vitamin D receptor increases expression and transport activity of P-glycoprotein in isolated rat brain capillaries and human and rat brain microvessel endothelial cells.

Induction of the multidrug resistance protein 1 (MDR1)/P-glycoprotein (P-gp) by the vitamin D receptor (VDR) was investigated in isolated rat brain capillaries and rat (RBE4) and human (hCMEC/D3) brain microvessel endothelial cell lines. Incubation of isolated rat brain capillaries with 10 nM of the VDR ligand, 1α,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] for 4 h increased P-gp protein expression fourfold. Incubation with 1,25(OH)(2)D(3) for 4 or 24 h increased P-gp transport activity (specific luminal accumulation of NBD-CSA, the fluorescent P-gp substrate) by 25-30%. In RBE4 cells, Mdr1b mRNA was induced in a concentration-dependent manner by exposure to 1,25(OH)(2)D(3). Concomitantly, P-gp protein expression increased 2.5-fold and was accompanied by a 20-35% reduction in cellular accumulation of the P-gp substrates, rhodamine 6G (R6G), and HiLyte Fluor 488-labeled human amyloid beta 1-42 (hAβ(42)). In hCMEC/D3 cells, a 3 day exposure to 100 nM 1,25(OH)(2)D(3) increased MDR1 mRNA expression (40%) and P-gp protein (threefold); cellular accumulation of R6G and hAβ(42) was reduced by 30%. Thus, VDR activation up-regulates Mdr1/MDR1 and P-gp protein in isolated rat brain capillaries and rodent and human brain microvascular endothelia, implicating a role for VDR in increasing the brain clearance of P-gp substrates, including hAβ(42), a plaque-forming precursor in Alzheimer's disease.

Effects of resveratrol on uncoupling protein mRNA expression in brain microvessel endothelial cells under hyperglycemic condition <I>in vitro</I>

Objective To study the effect of hyperglycemia on uncoupling protein ( UCP) mRNA expression in mouse brain microvessel endothelial cell line bEnd. 3,and to investigate the regulatory effect of resveratrol on the expression. Methods Mouse bEnd. 3 cells were cultured in vitro. The mRNA levels of UCP1 -5 in bEnd. 3 cells were determined by RT -PCR after exposure to different concentrations of glucose( 5. 5、25 mmol/L) and resveratrol ( 25 μmol/L). Results We found that exposure to 25 mmol/L glucose for 24 h up-regulated the expression of UCP4 and UCP5 mRNA levels ( P 0. 05) ,but had no noticeable influence on the expression of UCP1 and UCP2 mRNA levels. Resveratrol increased UCP5 mRNA levels under baseline and hyperglycemia conditions ( P 0. 05) ,and it decreased reactive oxygen specices( ROS) induced by hyperglycemia condition ( P 0. 05). Conclusion High glucose stimulation can specifically up -regulate UCP4 and UCP5 mRNA expression in mouse brain microvessel endothelial cells. Resveratrol can greatly decrease ROS production induced by hyperglycemia condition and up-regulate UCP5 mRNA expression.

Up‐regulation of P‐glycoprotein by HIV protease inhibitors in a human brain microvessel endothelial cell line

A major concern regarding the chronic administration of antiretroviral drugs is the potential for induction of drug efflux transporter expression (i.e., P-glycoprotein, P-gp) at tissue sites that can significantly affect drug distribution and treatment efficacy. Previous data have shown that the inductive effect of human immunodeficiency virus protease inhibitors (PIs) is mediated through the human orphan nuclear receptor, steroid xenobiotic receptor (SXR or hPXR). The objectives of this study were to investigate transport and inductive properties on efflux drug transporters of two PIs, atazanavir and ritonavir, at the blood-brain barrier by using a human brain microvessel endothelial cell line, hCMEC/D3. Transport properties of PIs by the drug efflux transporters P-gp and multidrug resistance protein 1 (MRP1) were assessed by measuring the cellular uptake of (3)H-atazanavir or (3)H-ritonavir in P-gp and MRP1 overexpressing cells as well as hCMEC/D3. Whereas the P-gp inhibitor, PSC833, increased atazanavir and ritonavir accumulation in hCMEC/D3 cells by 2-fold, the MRP inhibitor MK571 had no effect. P-gp, MRP1, and hPXR expression and localization were examined by Western blot analysis and immunogold cytochemistry at the electron microscope level. Treatment of hCMEC/D3 cells for 72 hr with rifampin or SR12813 (two well-established hPXR ligands) or PIs (atazanavir or ritonavir) resulted in an increase in P-gp expression by 1.8-, 6-, and 2-fold, respectively, with no effect observed for MRP1 expression. In hCMEC/D3 cells, cellular accumulation of these PIs appears to be primarily limited by P-gp efflux activity. Long-term exposure of atazanavir or ritonavir to brain microvessel endothelium may result in further limitations in brain drug permeability as a result of the up-regulation of P-gp expression and function.

Antioxidants prevent the cytotoxicity of manganese in RBE4 cells

Manganese (Mn) is an essential trace element required for ubiquitous enzymatic reactions. Chronic overexposure to this metal may, however, promote potent neurotoxic effects. The mechanism of Mn toxicity is not well established, but several studies indicate that oxidative stress and mitochondria play major roles in the Mn-induced neurodegenerative processes that lead to dysfunction in the basal ganglia. The aim of this study was to address the toxic effects of MnCl 2 and MnSO 4 on the immortalized rat brain microvessel endothelial cell line (RBE4) and to characterize toxic mechanism associated with exposure to Mn. The cytotoxicity of Mn in RBE4 cells was evaluated using the LDH and the MTT assays. A significant increase was noted in LDH release from RBE4 cells exposed for 24 h to MnCl 2 at concentrations of 800 μM and MnSO 4 at concentrations ≥ 400 μM ( p < 0.05) when compared with control unexposed cells. The MTT assay established significant decrease in cellular viability upon exposure to MnCl 2 at concentrations ≥ 100 μM and to MnSO 4 at concentrations ≥ 50 μM ( p < 0.05). Thus, the cytotoxicity assays showed that the MTT assay was more sensitive than the LDH assay, suggesting that mitochondrial changes precede other toxic effects of Mn. In addition, upon exposure to MnCl 2 (200 and 800 μM), intracellular reduced glutathione (GSH) levels in RBE4 cells decreased as Mn exposure concentrations increased ( p < 0.05). To confirm the oxidative hypothesis of Mn cytotoxicity, co-exposure of MnCl 2 with antioxidant agents ( N-acetylcysteine [NAC] or Trolox) were carried out. The cellular viability was evaluated using the MTT assay. A significant decrease in Mn cytotoxicity was observed in co-exposed cells confirming that (1) oxidative stress plays a critical role in the mechanism of Mn toxicity, and (2) antioxidants may offer a useful therapeutic modality to reverse the aberrant effects of Mn.

Solid Lipid Nanoparticles Enhance the Delivery of the HIV Protease Inhibitor, Atazanavir, by a Human Brain Endothelial Cell Line

Protease inhibitors (PIs) exhibit low brain permeability. As a result, unchallenged HIV viral replication can lead to HIV-encephalitis and antiretroviral drug resistance. The objective of this study was to develop and evaluate a lipid nanoparticle system for enhanced brain delivery of the potent and frequently used HIV PI, atazanavir, using a well characterized human brain microvessel endothelial cell line (hCMEC/D3) representative of the blood-brain barrier. Solid lipid nanoparticles (SLNs) were prepared by a thin film hydration technique and analyzed for atazanavir encapsulation efficiency, particle size, morphology, zeta potential and drug release. Cell viability experiments demonstrate that SLNs exhibit no toxicity in hCMEC/D3 cells up to a concentration corresponding to 200 nM of atazanavir. Spherical SLNs with an average particle size of approximately 167 nm were formulated. Delivery of [3H]-atazanavir by SLNs led to a significantly higher accumulation by the endothelial cell monolayer as compared to the drug aqueous solution. Furthermore, release of Rhodamine-123 (a fluorescent probe) by SLNs also resulted in a higher cellular accumulation. These data suggest that SLNs could be a promising drug delivery system to enhance brain uptake of atazanavir and potentially other PIs.

Localization of P-glycoprotein at the nuclear envelope of rat brain cells

P-Glycoprotein is a plasma membrane drug efflux protein implicated in extrusion of cytotoxic compounds out of a cell. There is now evidence that suggests expression of this transporter at several subcellular sites, including the nucleus, mitochondria, and Golgi apparatus. This study investigated the localization and expression of P-glycoprotein at the nuclear membrane of rat brain microvessel endothelial (RBE4) and microglial (MLS-9) cell lines. Immunocytochemistry at the light and electron microscope levels using P-glycoprotein monoclonals antibodies demonstrated the localization of the protein at the nuclear envelope of RBE4 and MLS-9 cells. Western blot analysis revealed a single band of 170-kDa in purified nuclear membranes prepared from isolated nuclei of RBE4 and MLS-9 cells. These findings indicate that P-glycoprotein is expressed at the nuclear envelope of rat brain cells and suggest a role in multidrug resistance at this subcellular site.

Effect of hypoxia/reoxygenation on CD73 (ecto-5′-nucleotidase) in mouse microvessel endothelial cell lines

Cerebral ischemia and post-ischemic reperfusion commonly result in significant brain damage. Brain microvessel endothelial cells, the key target cells and regulating sites, can secrete adenosine which plays an important neuroprotective role in the ischemic brain. A primary determinant of localized production of adenosine at tissue interfaces is ecto-5′-nucleotidase (CD73). In our experiments, we used bEnd.3 cells, immortalized mouse brain microvessel endothelial cell lines, as the target cells to study the effect of hypoxia and posthypoxic reoxygenation on CD73 in brain microvessel endothelial cells. CD73 activity in bEnd.3 cells exposed to hypoxia significantly increased in time-dependent way. The upregulation of CD73 mRNA and protein expression induced by hypoxia in bEnd.3 cells were detected by RT-PCR and Western blot. However, for reoxygenation studies, CD73 activity, mRNA and protein expression decreased at the initial stages, but increased at prolonged reoxygenation. Our results suggest that hypoxia can induce upregulation of CD73 expression in brain microvessel endothelial cells, which can be reversed by reoxygenation of short duration. But CD73 expression increased gradually with the duration of reoxygenation. Then, we infer that CD73 in brain microvessel endothelial cells plays a very important role through forming adenosine during brain ischemia and reperfusion.

Induction of aquaporin 1 but not aquaporin 4 messenger RNA in rat primary brain microvessel endothelial cells in culture

Aquaporins (AQPs) are a family of proteins that mediate water transport across cells, but the extent to which they are involved in water transport across endothelial cells of the blood-brain barrier is not clear. Expression of AQP1 and AQP4 in rat brain microvessel endothelial cells was investigated in order to determine whether these isoforms were present and, in particular, to examine the hypothesis that brain endothelial expression of AQPs is dynamic and regulated by astrocytic influences. Reverse-transcriptase-polymerase chain reaction (RT-PCR) and immunocytochemistry showed that AQP1 mRNA and protein are present at very low levels in primary rat brain microvessel endothelial cells, and are up-regulated in passaged cells. Upon passage, endothelial cell expression of mdr1a mRNA is decreased, indicating loss of blood-brain barrier phenotype. In passage 4 endothelial cells, AQP1 mRNA levels are reduced by coculture above rat astrocytes, demonstrating that astrocytic influences are important in maintaining the low levels of AQP1 characteristic of the blood-brain barrier endothelium. Reverse-transcriptase-PCR revealed very low levels of AQP1 mRNA present in the RBE4 rat brain microvessel endothelial cell line, with no expression detected in primary cultures of rat astrocytes or in the C6 rat glioma cell line. In contrast, AQP4 mRNA is strongly expressed in astrocytes, but no expression is found in primary or passaged brain microvessel endothelial cells, or in RBE4 or C6 cells. Our results support the concept that expression of AQP1, which is seen in many non-brain endothelia, is suppressed in the specialized endothelium of the blood-brain barrier.

SATURABLE DISTRIBUTION OF TACRINE INTO THE STRIATAL EXTRACELLULAR FLUID OF THE RAT: EVIDENCE OF INVOLVEMENT OF MULTIPLE ORGANIC CATION TRANSPORTERS IN THE TRANSPORT

The kinetics and mechanism by which tacrine is distributed in the rat brain were examined. Tacrine levels in plasma and striatal extracellular fluid were used to evaluate the pharmacokinetics of this process. The K(D,brain) was decreased with the dose for tacrine, indicating that the distribution to the brain is saturable. The uptake of organic cations such as choline, 1-methyl-4-phenylpyridinium (MPP), tetraethylammonium (TEA), and carnitine was inhibited by the addition of tacrine to cultures of mouse immortalized brain capillary endothelial cells. In addition, the apical to basal transport and basal to apical transport of tacrine were inhibited by the addition of organic cations to cultures of LLC-PK1 cells, suggesting that tacrine transport across the blood-brain barrier (BBB) is mediated by organic cation transport system(s). Consistent with the in vitro results, a standard reverse transcription-polymerase chain reaction procedure was able to amplify the message of mOCT2 and mOCTN2, but not mOCT1, in MBEC4 (mouse brain microvessel endothelial cell line 4) cells. Similarly, mRNAs for rOCT2 and rOCTN2 were present in representative rat brain samples. To determine whether OCT2 and/or OCTN2 transport tacrine, these transporters were cloned and then transfected in SK-HEP1 and HEK 293 cells. The uptake of choline, MPP, and TEA was inhibited by the presence of tacrine in rOCT2-expressing SK-HEP1 cells, whereas the uptake of carnitine was inhibited by the presence of tacrine in rOCTN2-expressing HEK 293 cells. Collectively, these observations suggest that the transport of tacrine across the BBB is mediated, at least in part, by multiple organic cation transport systems in rats.

Involvement of P-glycoprotein in the transport of saquinavir and indinavir in rat brain microvessel endothelial and microglia cell lines.

Membrane-bound efflux transporters, such as P-glycoprotein (P-gp), may limit the brain entry and distribution of HIV-1 protease inhibitors and be in part responsible for HIV-1-associated dementia treatment failure. The purpose of this study was to characterize the transport properties of saquinavir and indinavir in a brain microvessel endothelial cell line and in microglia, the immune cells of the brain and primary HIV-1 cellular target. Biochemical and transport studies were performed in an immortalized rat brain endothelial cell line (RBE4), a rat microglia cell line (MLS-9), and a P-gp overexpressing Chinese hamster ovary cell line (CHRC5). Western blot analysis using the P-gp monoclonal antibody C219 detected a single band at approximately 170 to 180 kDa (a size previously reported for P-gp) in all cell lines. Cellular accumulation of [14C]saquinavir and [3H]indinavir by RBE4, MLS-9, and CHRC5 monolayers was significantly enhanced in the presence of P-gp inhibitors, HIV-1 protease inhibitors, the ATPase inhibitor sodium azide, and the ATP depleting agent 2',4'-dinitrophenol respectively. [14C]Saquinavir and [3H]indinavir efflux from both cell systems was rapid and significantly reduced in the presence of PSC833. These results provide evidence for P-gp mediated transport of saquinavir and indinavir in RBE4 and MLS-9 and suggest that this transporter can restrict, at least in part, the permeation of HIV-1 protease inhibitors at both the brain barrier site and in brain parenchyma.

Regulation of [(3)H]MPP(+) transport by phosphorylation/dephosphorylation pathways in RBE4 cells: role of ecto-alkaline phosphatase.

The aim of this study was to investigate the role of phosphorylation/dephosphorylation mechanisms at the blood-brain barrier (BBB) in the uptake of organic cations. The experiments were performed using RBE4 cells, an immortalized, rat brain microvessel endothelial cell line, an in vitro model of the BBB. The modulation of the uptake of 1-methyl-4-phenylpyridinium (MPP(+)), a model organic cation, at the apical membrane of RBE4 cells was studied. Agents that stimulate protein kinase A, but not protein kinase C, produced a moderate inhibition (approximately 18% reduction) of uptake of [(3)H]MPP(+) by RBE4 cells. Okadaic acid, an inhibitor of protein serine/threonine phosphatase, did not affect uptake of (3)H-MPP(+), but the alkaline phosphatase (ALP) inhibitor levamisole markedly reduced (3)H-MPP(+) uptake. The activity of membrane-bound ALP expressed on the apical surface of RBE4 cells was studied at pH 7.4 using p-nitrophenylphosphate as substrate. Kaempferol, progesterone, 3-isobutyl-1-methylxanthine, all- trans-retinoic acid and iron stimulated ecto-ALP activity and uptake of [(3)H]MPP(+) in RBE4. Orthovanadate (a protein tyrosine phosphatase inhibitor) markedly inhibited both ecto-ALP activity and uptake of [(3)H]MPP(+) by RBE4 cells. In conclusion, these results suggest that apical transporter(s) of MPP(+) in RBE4 cells may be under the control of phosphorylation/dephosphorylation mechanisms, being active in the dephosphorylated state. A physiological role for ALP in the modulation of organic cation transport in the BBB is suggested.

Transport of choline and its relationship to the expression of the organic cation transporters in a rat brain microvessel endothelial cell line (RBE4)

The present study was undertaken to elucidate the functional characteristics of choline uptake and deduce the relationship between choline uptake and the expression of organic cation transporters in the rat brain microvessel endothelial cell line RBE4. Confluent RBE4 cells were found to express a high affinity choline uptake system. The system is Na +-independent and shows a Michaelis–Menten constant of approx. 20 μM for choline. The choline analogue hemicholinium-3 inhibits choline uptake in these cells with an inhibition constant of approx. 50 μM. The uptake system is also susceptible for inhibition by various organic cations, including 1-methyl-4-phenylpyridinium, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, clonidine, procainamide, and tetramethylammonium. The prototypical organic cation tetraethylammonium shows very little affinity for the choline uptake system in these cells. The inhibition of choline uptake by hemicholinium-3 is competitive. Northern analysis and RT-PCR show that these cells do not express the organic cation transporters OCT2 and OCT3. These cells do express, however, low levels of OCT1, but the functional characteristics of choline uptake in these cells are very different from the known properties of choline uptake via OCT1. The Na +-coupled high affinity choline transporter CHT1 is not expressed in these cells as evidenced by RT-PCR. This corroborates the Na +-independent nature of choline uptake in these cells. It is concluded that RBE4 cells express an organic cation transporter that is responsible for choline uptake in these cells and that this transporter is not identical to any of the organic cation transporters thus far identified at the molecular level in mammalian cells.

Transport of [3H]MPP+ in an immortalized rat brain microvessel endothelial cell line (RBE 4).

The aim of this study was to characterize the transport of the organic cation 1-methyl-4-phenylpyridinium (MPP+) in an immortalized cell line of rat capillary cerebral endothelial cells (RBE 4). Verapamil (100 microM) and rhodamine 123 (10 microM), and decynium22 (2 microM) and corticosterone (100 microM) reduced cellular accumulation of [3H]MPP+ applied from the luminal and abluminal cell border, respectively. When cells were grown on plastic supports, [3H]MPP+ accumulated in the cells. The kinetic parameters of the saturable component were: Km=25 microM and Vmax=246 pmol per mg protein and 15 min. A selective organic anion transport inhibitor and selective inhibitors of the L- and A-type amino acid transporters did not affect [3H]MPP+ uptake. Uptake of [3H]MPP+ was Na+-independent and metabolic energy-, pH- and potential-dependent. It was inhibited by several organic cations (e.g., verapamil, quinidine, daunomycin, dopamine) but not by others (cimetidine, tetraethylammonium, N-methylnicotinamide). In conclusion, [3H]MPP+ is efficiently transported by RBE 4 cells in both abluminal-to-luminal and luminal-to-abluminal directions. Absorption of [3H]MPP+ seems to occur through a carrier-mediated mechanism belonging to the amphiphilic solute facilitator (ASF) family of transporters, but distinct from the known members of this family.

Immortalized mouse brain endothelial cells are ultrastructurally similar to endothelial cells and respond to astrocyte-conditioned medium.

Studies of brain microvessel endothelial cell physiology and blood-brain barrier properties are often hampered by the requirement of repeatedly producing and characterizing primary endothelial cell cultures. The use of viral oncogenes to produce several immortalized brain microvessel cell lines has been reported. The resulting cell lines express many properties of the blood-brain barrier phenotype but do not completely mimic primary endothelial cells in culture. As immortalized brain microvessel endothelial cell lines have not yet been produced from mice, we transformed mouse brain endothelial cells with the adenovirus E1A gene using a retroviral vector (DOL). Eight of 11 clones produced exhibited an endothelial-like cobblestone morphology and were characterized as endothelial with a panel of antibodies, lectins, and ultrastructural criteria. These cells are endothelial in origin and share ultrastructural features with primary cultures of endothelial cells. Examination of freeze fracture and transmission electron micrographs show adherens junctions exist between the transformed cells, and culture in astrocyte-conditioned medium induces the formation of gap junctions. This is one indication that responses to astrocyte-derived factors are retained by the transformed cell lines.