scholarly journals Coordinated Nuclear Receptor Regulation of the Efflux Transporter, Mrp2, and the Phase-Ii Metabolizing Enzyme, GSTπ, at the Blood—Brain Barrier

2008 ◽  
Vol 28 (6) ◽  
pp. 1222-1234 ◽  
Author(s):  
Björn Bauer ◽  
Anika M S Hartz ◽  
Jonathan R Lucking ◽  
Xiaodong Yang ◽  
Gary M Pollack ◽  
...  
Keyword(s):  
Blood Brain Barrier ◽  
Nuclear Receptor ◽  
Brain Barrier ◽  
Efflux Transporter ◽  
Transport Activity ◽  
Brain Capillaries ◽  
Blood Brain ◽  
Metabolizing Enzyme

Xenobiotic efflux pumps at the blood—brain barrier are critical modulators of central nervous system pharmacotherapy. We previously found expression of the ligand-activated nuclear receptor, pregnane X receptor (PXR), in rat brain capillaries, and showed increased expression and transport activity of the drug efflux transporter, P-glycoprotein, in capillaries exposed to PXR ligands (pregnenolone-16α-carbonitrile (PCN) and dexamethasone) in vitro and in vivo. Here, we show increased protein expression and transport activity of another efflux pump, multidrug resistance-associated protein isoform 2 (Mrp2), in rat brain capillaries after in vitro and in vivo exposure to PCN and dexamethasone. The phase-II drug-metabolizing enzyme, glutathione S-transferase-π (GSTπ), was found to be expressed in brain capillaries, where it colocalized to a large extent with Mrp2 at the endothelial cell luminal plasma membrane. Like Mrp2, GSTπ protein expression increased with PXR activation. Colocalization and coordinated upregulation suggest functional coupling of the metabolizing enzyme and efflux transporter. These findings indicate that, as in hepatocytes, brain capillaries possess a regulatory network consisting of nuclear receptors, metabolizing enzymes, and efflux transporters, which modulate blood—brain barrier function.

scholarly journals Protecting P-glycoprotein at the blood–brain barrier from degradation in an Alzheimer’s disease mouse model

2021 ◽  
Vol 18 (1) ◽  
Author(s):  
Yujie Ding ◽  
Yu Zhong ◽  
Andrea Baldeshwiler ◽  
Erin L. Abner ◽  
Björn Bauer ◽  
...  
Keyword(s):  
Mouse Model ◽  
Protein Expression ◽  
Blood Brain Barrier ◽  
Brain Barrier ◽  
Activity Levels ◽  
Transport Activity ◽  
Brain Capillaries ◽  
P Glycoprotein ◽  
Blood Brain

AbstractBackgroundFailure to clear Aβ from the brain is partly responsible for Aβ brain accumulation in Alzheimer’s disease (AD). A critical protein for clearing Aβ across the blood-brain barrier is the efflux transporter P-glycoprotein (P-gp). In AD, P-gp levels are reduced, which contributes to impaired Aβ brain clearance. However, the mechanism responsible for decreased P-gp levels is poorly understood and there are no strategies available to protect P-gp. We previously demonstrated in isolated brain capillariesex vivothat human Aβ40 (hAβ40) triggers P-gp degradation by activating the ubiquitin-proteasome pathway. In this pathway, hAβ40 initiates P-gp ubiquitination, leading to internalization and proteasomal degradation of P-gp, which then results in decreased P-gp protein expression and transport activity levels. Here, we extend this line of research and present results from anin vivostudy using a transgenic mouse model of AD (human amyloid precursor protein (hAPP)-overexpressing mice; Tg2576).MethodsIn our study, hAPP mice were treated with vehicle, nocodazole (NCZ, microtubule inhibitor to block P-gp internalization), or a combination of NCZ and the P-gp inhibitor cyclosporin A (CSA). We determined P-gp protein expression and transport activity levels in isolated mouse brain capillaries and Aβ levels in plasma and brain tissue.ResultsTreating hAPP mice with 5 mg/kg NCZ for 14 days increased P-gp levels to levels found in WT mice. Consistent with this, P-gp-mediated hAβ42 transport in brain capillaries was increased in NCZ-treated hAPP mice compared to untreated hAPP mice. Importantly, NCZ treatment significantly lowered hAβ40 and hAβ42 brain levels in hAPP mice, whereas hAβ40 and hAβ42 levels in plasma remained unchanged.ConclusionsThese findings provide in vivo evidence that microtubule inhibition maintains P-gp protein expression and transport activity levels, which in turn helps to lower hAβ brain levels in hAPP mice. Thus, protecting P-gp at the blood-brain barrier may provide a novel therapeutic strategy for AD and other Aβ-based pathologies.

scholarly journals Activation of PKC Isoform βI at the Blood–Brain Barrier Rapidly Decreases P-Glycoprotein Activity and Enhances Drug Delivery to the Brain

2010 ◽  
Vol 30 (7) ◽  
pp. 1373-1383 ◽  
Author(s):  
Robert R Rigor ◽  
Brian T Hawkins ◽  
David S Miller
Keyword(s):  
Rat Brain ◽  
Blood Brain Barrier ◽  
Brain Barrier ◽  
Brain Capillaries ◽  
P Glycoprotein ◽  
Blood Brain ◽  
Tnf Α ◽  
The Brain

P-glycoprotein is an ATP (adenosine triphosphate)-driven drug efflux transporter that is highly expressed at the blood–brain barrier (BBB) and is a major obstacle to the pharmacotherapy of central nervous system diseases, including brain tumors, neuro-AIDS, and epilepsy. Previous studies have shown that P-glycoprotein transport activity in rat brain capillaries is rapidly reduced by the proinflammatory cytokine, tumor necrosis factor-α (TNF-α) acting through protein kinase C (PKC)-dependent signaling. In this study, we used isolated rat brain capillaries to show that the TNF-α-induced reduction of P-glycoprotein activity was prevented by a PKCβI/II inhibitor, LY333531, and mimicked by a PKCβI/II activator, 12-deoxyphorbol-13-phenylacetate-20-acetate (dPPA). Western blotting of brain capillary extracts with phospho-specific antibodies showed that dPPA activated PKCβI, but not PKCβII. Moreover, in intact rats, intracarotid infusion of dPPA potently increased brain accumulation of the P-glycoprotein substrate, [3H]-verapamil without compromising tight junction integrity. Thus, PKCβI activation selectively reduced P-glycoprotein activity both in vitro and in vivo. Targeting PKCβI at the BBB may prove to be an effective strategy for enhancing the delivery of small molecule therapeutics to the brain.

scholarly journals Protecting P-glycoprotein at the Blood-Brain Barrier from Degradation in an Alzheimer’s Disease Mouse Model

2020 ◽  
Author(s):  
Yujie Ding ◽  
Yu Zhong ◽  
Andrea Baldeshwiler ◽  
Erin L. Abner ◽  
Björn Bauer ◽  
...  
Keyword(s):  
Mouse Model ◽  
Protein Expression ◽  
Blood Brain Barrier ◽  
Brain Barrier ◽  
Activity Levels ◽  
Transport Activity ◽  
Brain Capillaries ◽  
P Glycoprotein ◽  
Blood Brain

Abstract Background. Failure to clear Aβ from the brain is partly responsible for Aβ brain accumulation in Alzheimer’s disease (AD). A critical protein for clearing Aβ across the blood-brain barrier is the efflux transporter P-glycoprotein (P-gp). In AD, P-gp levels are reduced, which contributes to impaired Aβ brain clearance. However, the mechanism responsible for decreased P-gp levels is poorly understood and there are no strategies available to protect P-gp. We previously demonstrated in isolated brain capillaries ex vivo that human Aβ40 (hAβ40) triggers P-gp degradation by activating the ubiquitin-proteasome pathway. In this pathway, hAβ40 initiates P-gp ubiquitination, leading to internalization and proteasomal degradation of P-gp, which then results in decreased P-gp protein expression and transport activity levels. Here, we extend this line of research and present results from an in vivo study using a transgenic mouse model of AD (human amyloid precursor protein (hAPP)-overexpressing mice; Tg2576). Methods. In our study, hAPP mice were treated with vehicle, nocodazole (NCZ, microtubule inhibitor to block P-gp internalization), or a combination of NCZ and the P-gp inhibitor cyclosporin A (CSA). We determined P-gp protein expression and transport activity levels in isolated mouse brain capillaries and Aβ levels in plasma and brain tissue. Results. Treating hAPP mice with 5 mg/kg NCZ for 14 days protected P-gp from degradation. Consistent with this, P-gp-mediated hAβ42 transport in brain capillaries was increased in NCZ-treated hAPP mice compared to untreated hAPP mice. Importantly, NCZ treatment significantly lowered hAβ40 and hAβ42 brain levels in hAPP mice, whereas hAβ40 and hAβ42 levels in plasma remained unchanged. Conclusions. These findings provide in vivo proof that blocking P-gp internalization protects P-gp from degradation and maintains P-gp protein expression and transport activity levels, which in turn lowers hAβ brain levels. Thus, protecting P-gp at the blood-brain barrier may provide a novel therapeutic target for AD and other Aβ-based pathologies.

scholarly journals 17-β-Estradiol: A Powerful Modulator of Blood–Brain Barrier BCRP Activity

2010 ◽  
Vol 30 (10) ◽  
pp. 1742-1755 ◽  
Author(s):  
Anika MS Hartz ◽  
Anne Mahringer ◽  
David S Miller ◽  
Björn Bauer
Keyword(s):  
Blood Brain Barrier ◽  
Ex Vivo ◽  
Brain Barrier ◽  
Cancer Resistance ◽  
Transport Activity ◽  
Brain Capillaries ◽  
Therapeutic Drugs ◽  
Blood Brain ◽  
Capillary Membranes ◽  
Blood Brain Barrier Model

The ATP-driven efflux transporter, breast cancer resistance protein (BCRP), handles many therapeutic drugs, including chemotherapeutics, limiting their ability to cross the blood–brain barrier. This study provides new insight into rapid, nongenomic regulation of BCRP transport activity at the blood–brain barrier. Using isolated brain capillaries from rats and mice as an ex vivo blood–brain barrier model, we show that BCRP protein is highly expressed in brain capillary membranes and functionally active in intact capillaries. We show that nanomolar concentrations of 17-β-estradiol (E2) rapidly reduced BCRP transport activity in the brain capillaries. This E2-mediated effect occurred within minutes and did not involve transcription, translation, or proteasomal degradation, indicating a nongenomic mechanism. Removing E2 after 1 h fully reversed the loss of BCRP activity. Experiments using agonists and antagonists for estrogen receptor (ER)α and ERβ and brain capillaries from ERα and ERβ knockout mice demonstrated that E2 could signal through either receptor to reduce BCRP transport function. We speculate that this nongenomic E2-signaling pathway could potentially be used for targeting BCRP at the blood–brain barrier, in brain tumors, and in brain tumor stem cells to improve chemotherapy of the central nervous system.

Activation of PKC modulates blood-brain barrier endothelial cell permeability changes induced by hypoxia and posthypoxic reoxygenation

2005 ◽  
Vol 289 (5) ◽  
pp. H2012-H2019 ◽  
Author(s):  
Melissa A. Fleegal ◽  
Sharon Hom ◽  
Lindsay K. Borg ◽  
Thomas P. Davis
Keyword(s):  
Blood Brain Barrier ◽  
Paracellular Permeability ◽  
Cell Permeability ◽  
Brain Barrier ◽  
Cerebral Microvessels ◽  
Permeability Changes ◽  
Blood Brain ◽  
Brain Microvessel

The blood-brain barrier (BBB) is a metabolic and physiological barrier important for maintaining brain homeostasis. The aim of this study was to determine the role of PKC activation in BBB paracellular permeability changes induced by hypoxia and posthypoxic reoxygenation using in vitro and in vivo BBB models. In rat brain microvessel endothelial cells (RMECs) exposed to hypoxia (1% O2-99% N2; 24 h), a significant increase in total PKC activity was observed, and this was reduced by posthypoxic reoxygenation (95% room air-5% CO2) for 2 h. The expression of PKC-βII, PKC-γ, PKC-η, PKC-μ, and PKC-λ also increased following hypoxia (1% O2-99% N2; 24 h), and these protein levels remained elevated following posthypoxic reoxygenation (95% room air-5% CO2; 2 h). Increases in the expression of PKC-ε and PKC-ζ were also observed following posthypoxic reoxygenation (95% room air-5% CO2; 2 h). Moreover, inhibition of PKC with chelerythrine chloride (10 μM) attenuated the hypoxia-induced increases in [14C]sucrose permeability. Similar to what was observed in RMECs, total PKC activity was also stimulated in cerebral microvessels isolated from rats exposed to hypoxia (6% O2-94% N2; 1 h) and posthypoxic reoxygenation (room air; 10 min). In contrast, hypoxia (6% O2-94% N2; 1 h) and posthypoxic reoxygenation (room air; 10 min) significantly increased the expression levels of only PKC-γ and PKC-θ in the in vivo hypoxia model. These data demonstrate that hypoxia-induced BBB paracellular permeability changes occur via a PKC-dependent mechanism, possibly by differentially regulating the protein expression of the 11 PKC isozymes.

Refining In Vitro Neurotoxicity Testing — The Development of Blood–Brain Barrier Models

2003 ◽  
Vol 31 (3) ◽  
pp. 273-276 ◽  
Author(s):  
Hanna Tähti ◽  
Heidi Nevala ◽  
Tarja Toimela
Keyword(s):  
Blood Brain Barrier ◽  
Cell Lines ◽  
Three Dimensional ◽  
Brain Barrier ◽  
Culture Methods ◽  
Blood Brain ◽  
Capillary Endothelial Cells ◽  
In Vitro Bbb Model

The purpose of this paper is to review the current state of development of advanced in vitro blood–brain barrier (BBB) models. The BBB is a special capillary bed that separates the blood from the central nervous system (CNS) parenchyma. Astrocytes maintain the integrity of the BBB, and, without astrocytic contacts, isolated brain capillary endothelial cells in culture lose their barrier characteristics. Therefore, when developing in vitro BBB models, it is important to add astrocytic factors into the culture system. Recently, novel filter techniques and co-culture methods have made it possible to develop models which resemble the in vivo functions of the BBB in an effective way. With a BBB model, kinetic factors can be added into the in vitro batteries used for evaluating the neurotoxic potential of chemicals. The in vitro BBB model also represents a useful tool for the in vitro prediction of the BBB permeability of drugs, and offers the possibility to scan a large number of drugs for their potential to enter the CNS. Cultured monolayers of brain endothelial cell lines or selected epithelial cell lines, combined with astrocyte and neuron cultures, form a novel three-dimensional technique for the screening of neurotoxic compounds.

scholarly journals Proof-of-Concept Study of Drug Brain Permeability Between in Vivo Human Brain and an in Vitro iPSCs-Human Blood-Brain Barrier Model

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Gwenaëlle Le Roux ◽  
Rafika Jarray ◽  
Anne-Cécile Guyot ◽  
Serena Pavoni ◽  
Narciso Costa ◽  
...  
Keyword(s):  
Human Brain ◽  
Blood Brain Barrier ◽  
Brain Barrier ◽  
Pharmacokinetic Parameters ◽  
Pharmacokinetic Data ◽  
Apparent Permeability ◽  
Clinical Drug Development ◽  
Blood Brain

Abstract The development of effective central nervous system (CNS) drugs has been hampered by the lack of robust strategies to mimic the blood-brain barrier (BBB) and cerebrovascular impairments in vitro. Recent technological advancements in BBB modeling using induced pluripotent stem cells (iPSCs) allowed to overcome some of these obstacles, nonetheless the pertinence for their use in drug permeation study remains to be established. This mandatory information requires a cross comparison of in vitro and in vivo pharmacokinetic data in the same species to avoid failure in late clinical drug development. Here, we measured the BBB permeabilities of 8 clinical positron emission tomography (PET) radioligands with known pharmacokinetic parameters in human brain in vivo with a newly developed in vitro iPSC-based human BBB (iPSC-hBBB) model. Our findings showed a good correlation between in vitro and in vivo drug brain permeability (R2 = 0.83; P = 0.008) which contrasted with the limited correlation between in vitro apparent permeability for a set of 18 CNS/non-CNS compounds using the in vitro iPSCs-hBBB model and drug physicochemical properties. Our data suggest that the iPSC-hBBB model can be integrated in a flow scheme of CNS drug screening and potentially used to study species differences in BBB permeation.

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