scholarly journals Asymmetrical Transport of Amino Acids across the Blood—Brain Barrier in Humans

1990 ◽  
Vol 10 (5) ◽  
pp. 698-706 ◽  
Author(s):  
G. Moos Knudsen ◽  
K. D. Pettigrew ◽  
C. S. Patlak ◽  
M. M. Hertz ◽  
O. B. Paulson
Keyword(s):  
Amino Acids ◽  
Endothelial Cell ◽  
Amino Acid ◽  
Blood Brain Barrier ◽  
Extracellular Fluid ◽  
Brain Barrier ◽  
Reverse Direction ◽  
Single Membrane ◽  
Blood Brain ◽  
The Brain

Blood–brain barrier permeability to four large neutral and one basic amino acid was studied in 30 patients with the double indicator technique. The resultant 64 venous outflow curves were analyzed by means of two models that take tracer backflux and capillary heterogeneity into account. The first model considers the blood–brain barrier as a double membrane where amino acids from plasma enter the endothelial cell. When an endothelial cell volume of 0.001 ml/g was assumed, permeability from the blood into the endothelial cell was, for most amino acids, about 10–20 times larger than the permeability for the reverse direction. The second model assumes that the amino acids, after intracarotid injection, cross a single membrane barrier and enter a well-mixed compartment, the brain extracellular fluid, i.e., the endothelial cell is assumed to behave as a single membrane. With this model, for large neutral amino acids, the permeability out of the extracellular fluid space back to the blood was between 8 to 12 times higher than the permeability from the blood into the brain. Such a difference in permeabilities across the blood–brain barrier can almost entirely be ascribed to the effect of a nonlinear transport system combined with a relatively small brain amino acid metabolism. The significance of the possible presence of an energy-dependent A system at the abluminal side of the blood–brain barrier is discussed and related to the present findings. For both models, calculation of brain extraction by simple peak extraction values underestimates true unidirectional brain uptake by 17–40%. This raises methodological problems when estimating blood to brain transfer of amino acids with this traditional in vivo method.

scholarly journals In vitro models of the blood–brain barrier: An overview of commonly used brain endothelial cell culture models and guidelines for their use

2016 ◽  
Vol 36 (5) ◽  
pp. 862-890 ◽  
Author(s):  
Hans C Helms ◽  
N Joan Abbott ◽  
Malgorzata Burek ◽  
Romeo Cecchelli ◽  
Pierre-Olivier Couraud ◽  
...  
Keyword(s):  
Cell Culture ◽  
Endothelial Cell ◽  
Blood Brain Barrier ◽  
Brain Parenchyma ◽  
Brain Barrier ◽  
Blood Brain ◽  
Culture Models ◽  
Cell Culture Models ◽  
The Brain

The endothelial cells lining the brain capillaries separate the blood from the brain parenchyma. The endothelial monolayer of the brain capillaries serves both as a crucial interface for exchange of nutrients, gases, and metabolites between blood and brain, and as a barrier for neurotoxic components of plasma and xenobiotics. This “blood-brain barrier” function is a major hindrance for drug uptake into the brain parenchyma. Cell culture models, based on either primary cells or immortalized brain endothelial cell lines, have been developed, in order to facilitate in vitro studies of drug transport to the brain and studies of endothelial cell biology and pathophysiology. In this review, we aim to give an overview of established in vitro blood–brain barrier models with a focus on their validation regarding a set of well-established blood–brain barrier characteristics. As an ideal cell culture model of the blood–brain barrier is yet to be developed, we also aim to give an overview of the advantages and drawbacks of the different models described.

scholarly journals Structural, Molecular, and Functional Alterations of the Blood-Brain Barrier during Epileptogenesis and Epilepsy: A Cause, Consequence, or Both?

2020 ◽  
Vol 21 (2) ◽  
pp. 591 ◽  
Author(s):  
Wolfgang Löscher ◽  
Alon Friedman
Keyword(s):  
Endothelial Cells ◽  
Blood Brain Barrier ◽  
Defense Mechanism ◽  
Extracellular Fluid ◽  
Cell Types ◽  
Therapeutic Interventions ◽  
Brain Barrier ◽  
Transport Systems ◽  
Blood Brain ◽  
The Brain

The blood-brain barrier (BBB) is a dynamic, highly selective barrier primarily formed by endothelial cells connected by tight junctions that separate the circulating blood from the brain extracellular fluid. The endothelial cells lining the brain microvessels are under the inductive influence of neighboring cell types, including astrocytes and pericytes. In addition to the anatomical characteristics of the BBB, various specific transport systems, enzymes and receptors regulate molecular and cellular traffic across the BBB. While the intact BBB prevents many macromolecules and immune cells from entering the brain, following epileptogenic brain insults the BBB changes its properties. Among BBB alterations, albumin extravasation and diapedesis of leucocytes from blood into brain parenchyma occur, inducing or contributing to epileptogenesis. Furthermore, seizures themselves may modulate BBB functions, permitting albumin extravasation, leading to activation of astrocytes and the innate immune system, and eventually modifications of neuronal networks. BBB alterations following seizures are not necessarily associated with enhanced drug penetration into the brain. Increased expression of multidrug efflux transporters such as P-glycoprotein likely act as a ‘second line defense’ mechanism to protect the brain from toxins. A better understanding of the complex alterations in BBB structure and function following seizures and in epilepsy may lead to novel therapeutic interventions allowing the prevention and treatment of epilepsy as well as other detrimental neuro-psychiatric sequelae of brain injury.

scholarly journals CoQ10 Deficient Endothelial Cell Culture Model for the Investigation of CoQ10 Blood–Brain Barrier Transport

2020 ◽  
Vol 9 (10) ◽  
pp. 3236
Author(s):  
Luke Wainwright ◽  
Iain P. Hargreaves ◽  
Ana R. Georgian ◽  
Charles Turner ◽  
R. Neil Dalton ◽  
...  
Keyword(s):  
Cell Culture ◽  
Endothelial Cell ◽  
Blood Brain Barrier ◽  
Advanced Glycation Endproducts ◽  
Brain Barrier ◽  
High Dose ◽  
Blood Brain ◽  
Coq10 Deficiency ◽  
The Brain

Primary coenzyme Q10 (CoQ10) deficiency is unique among mitochondrial respiratory chain disorders in that it is potentially treatable if high-dose CoQ10 supplements are given in the early stages of the disease. While supplements improve peripheral abnormalities, neurological symptoms are only partially or temporarily ameliorated. The reasons for this refractory response to CoQ10 supplementation are unclear, however, a contributory factor may be the poor transfer of CoQ10 across the blood–brain barrier (BBB). The aim of this study was to investigate mechanisms of CoQ10 transport across the BBB, using normal and pathophysiological (CoQ10 deficient) cell culture models. The study identifies lipoprotein-associated CoQ10 transcytosis in both directions across the in vitro BBB. Uptake via SR-B1 (Scavenger Receptor) and RAGE (Receptor for Advanced Glycation Endproducts), is matched by efflux via LDLR (Low Density Lipoprotein Receptor) transporters, resulting in no “net” transport across the BBB. In the CoQ10 deficient model, BBB tight junctions were disrupted and CoQ10 “net” transport to the brain side increased. The addition of anti-oxidants did not improve CoQ10 uptake to the brain side. This study is the first to generate in vitro BBB endothelial cell models of CoQ10 deficiency, and the first to identify lipoprotein-associated uptake and efflux mechanisms regulating CoQ10 distribution across the BBB. The results imply that the uptake of exogenous CoQ10 into the brain might be improved by the administration of LDLR inhibitors, or by interventions to stimulate luminal activity of SR-B1 transporters.

scholarly journals Carrier-Mediated Delivery of Metabotropic Glutamate Receptor Ligands to the Central Nervous System: Structural Tolerance and Potential of the l-system Amino Acid Transporter at the Blood-Brain Barrier

2000 ◽  
Vol 20 (1) ◽  
pp. 168-174 ◽  
Author(s):  
Andreas Reichel ◽  
David J. Begley ◽  
N. Joan Abbott
Keyword(s):  
Central Nervous System ◽  
Amino Acid ◽  
Blood Brain Barrier ◽  
Brain Barrier ◽  
Side Chain ◽  
Large Neutral Amino Acid ◽  
Metabotropic Glutamate ◽  
Blood Brain ◽  
L System ◽  
The Brain

The brain endothelial large neutral amino acid carrier (l-system) is well suited for facilitated drug transport to the brain because of its high transport capacity and relatively broad structural substrate tolerance. The authors have examined the potential of this transporter for central nervous system (CNS) delivery of a new family of compounds derived from the large neutral amino acid phenylglycine. These compounds are highly selective for specific isoforms of metabotropic glutamate receptors (mGluRs) but will only become effective therapeutics for CNS diseases such as ischemic disorders, stroke, and epilepsy if they can effectively cross the blood-brain barrier. Using the immortalized rat brain endothelial cell line RBE4 as in vitro blood-brain barrier model, the authors have studied the interaction of phenylglycine and selected derivatives with the l-system-mediated transport of l-[3H]-histidine. The transport of l-histidine was characteristic of the l-system in vivo with the following kinetic parameters: Km 135 ± 18 μmol/L, Vmax 15.3 ± 1.13 nmol/min/mg protein, and KD 2.38 ± 0.84 μL/min/mg protein. The affinities of the l-system for phenylglycine and the derivatives investigated increased in the order S-4-carboxy-phenylglycine (Ki = 16 mmol/L) < R-phenylglycine (2.2 mmol/L) < S-3-hydroxy-phenylglycine (48 μmol/L) < S-phenylglycine (34 μmol/L), suggesting that a negative charge at the side chain or R-configuration is detrimental for carrier recognition, whereas neutral side chain substituents are well tolerated. The authors have further shown (1) that the mode of interaction with the l-system of S-phenylglycine and S-3-hydroxy-phenylglycine is competitive, and (2) that the transporter carries these two agents into the cell as shown by high-performance liquid chromatography (HPLC) analysis of the RBE4 cell contents. The study provides the first evidence for the potential of S-phenylglycine derivatives for carrier-mediated delivery to the CNS and outlines the substrate specificity of the l-system at the blood-brain barrier for this class of mGluR ligands. As the affinities of S-phenylglycine and S-3-hydroxy-phenylglycine for the l-system carrier are even higher than those of some natural substrates, these agents should efficiently enter CNS via this route. Possible strategies for a synergistic optimization of phenylglycine-derived therapeutics with respect to desired activity at the CNS target combined with carrier-mediated delivery to overcome the blood-brain barrier are discussed.

Metabolic fuel and amino acid transport into the brain in experimental hypothyroidism

1990 ◽  
Vol 122 (2) ◽  
pp. 156-162 ◽  
Author(s):  
Arshag D. Mooradian
Keyword(s):  
Amino Acids ◽  
Blood Brain Barrier ◽  
Brain Barrier ◽  
Transport Systems ◽  
Brain Uptake ◽  
Acid Transport ◽  
Brain Extraction ◽  
Blood Brain ◽  
Brain Uptake Index ◽  
The Brain

Abstract The effect of hypothyroidism in the adult rat on blood-brain barrier and muscle transport of hexoses, neutral amino acids, basic amino acids, monocarboxylic acids, and ketone bodies was examined using single arterial injection-tissue sampling technique. The cerebral blood flow and brain extraction of 3H2O (internal reference substance) was not altered in 3-month-old hypothyroid rats maintained on methimazole, 0.025% in the drinking water, for 7 weeks. The brain uptake index of D-β-hydroxybutyrate was significantly reduced in hypothyroid rats (2.4 ± 0.3 vs 4.6 ± 0.6% p<0.001). Hypothyroid rats given thyroid hormone replacement therapy had normal brain uptake of D-β-hydroxybutyrate (4.4 ± 0.8%). The brain uptake index of butyrate was also significantly reduced in hypothyroid rats (39.3 ± 2.1 vs 47.2 ± 0.74%, p<0.001). The brain uptake index of other test substances and muscle uptake of nutrients examined were not altered in hypothyroid rats. These studies indicate that of the four transport systems examined in two tissues, the blood-brain barrier monocarboxylic acid transport system is most susceptible to the hypothyroidism-induced changes.

Concentrations of Amino Acids in Extracellular Fluid After Opening of the Blood-Brain Barrier by Intracarotid Infusion of Protamine Sulfate

2008 ◽  
Vol 62 (1) ◽  
pp. 159-165 ◽  
Author(s):  
Irena Westergren ◽  
Britta Nystrom ◽  
Anders Hamberger ◽  
Claes Nordborg ◽  
Barbro B. Johansson
Keyword(s):  
Amino Acids ◽  
Blood Brain Barrier ◽  
Extracellular Fluid ◽  
Protamine Sulfate ◽  
Brain Barrier ◽  
Blood Brain

Amino acid assignment to one of three blood-brain barrier amino acid carriers

1976 ◽  
Vol 230 (1) ◽  
pp. 94-98 ◽  
Author(s):  
WH Oldendorf ◽  
J Szabo
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Blood Brain Barrier ◽  
Internal Standard ◽  
Basic Amino Acid ◽  
Brain Barrier ◽  
Carrier System ◽  
Blood Brain ◽  
Cross Inhibition ◽  
Amino Acid Carrier

The percentages of 22 14C-labeled amino acids remaining in rat brain 15 s after carotid injection were measured relative to a simultaneously injected diffusible internal standard, 3HOH. The injected solution also contained a nondiffusible internal standard, [113mIn]EDTA to correct for incomplete brain blood compartment washout. Self-inhibition and cross-inhibition was demonstrated by inclusion of unlabeled amino acids and carboxylic acids. All amino acids tested, excluding proline, alanine, and glycine, could be assigned to one, and only one, blood-brain barrier carrier system. The neutral carrier system transported phenylalanine, leucine, tyrosine, isoleucine, methionine, tryptophane, valine, DOPA, cysteine, histidine, threonine, glutamine, asparagine, and serine. Affinity for a basic amino acid carrier system was demonstrated for arginine, ornithine, and lysine. A third, low-capacity independent carrier system transporting aspartic and glutamic acids was demonstrated.

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