The Effects of Zinc Treatment on the Blood–Brain Barrier Permeability and Brain Element Levels During Convulsions

We evaluated the effect of zinc treatment on the blood–brain barrier (BBB) permeability and the levels of zinc (Zn), natrium (Na), magnesium (Mg), and copper (Cu) in the brain tissue during epileptic seizures. The Wistar albino rats were divided into four groups, each as follows: (1) control group, (2) pentylenetetrazole (PTZ) group: rats treated with PTZ to induce seizures, (3) Zn group: rats treated with ZnCl₂ added to drinking water for 2 months, and (4) Zn?+?PTZ group. The brains were divided into left, right hemispheres, and cerebellum?+?brain stem regions. Evans blue was used as BBB tracer. Element concentrations were analyzed by inductively coupled plasma optical emission spectroscopy. The BBB permeability has been found to be increased in all experimental groups (p?<?0.05). Zn concentrations in all brain regions in Zn-supplemented groups (p?<?0.05) showed an increase. BBB permeability and Zn level in cerebellum?+?brain stem region were significantly high compared to cerebral hemispheres (p?<?0.05). In all experimental groups, Cu concentration decreased, whereas Na concentrations showed an increase (p?<?0.05). Mg content in all the brain regions decreased in the Zn group and Zn?+?PTZ groups compared to other groups (p?<?0.001). We also found that all elements’ levels showed hemispheric differences in all groups. During convulsions, Zn treatment did not show any protective effect on BBB permeability. Chronic Zn treatment decreased Mg and Cu concentration and increased Na levels in the brain tissue. Our results indicated that Zn treatment showed proconvulsant activity and increased BBB permeability, possibly changing prooxidant/antioxidant balance and neuronal excitability during seizures.     

Effects of Metabotropic Glutamate Receptor Stimulation on Blood–Brain Barrier Permeability During Focal Cerebral Ischemia

This investigation was performed to evaluate whether ACPD [(1S, 3R)-1-aminocyclopentane-1, 3-dicarboxylic acid], a metabotropic glutamate receptor agonist, would enhance the degree of increase in blood-brain barrier (BBB) permeability caused by focal cerebral ischemia. In this study, male Wistar rats were placed in control (n = 7) and ACPD (n = 7) groups under isoflurane anesthesia. Twenty minutes after middle cerebral artery (MCA) occlusion, patches of 10(-5) M ACPD or normal saline were placed on the ischemic cortex (IC) for a period of 40 min. Patches were changed every 10 min. One hour after MCA occlusion, BBB permeability was determined by measuring the transfer coefficient (Ki) of [alpha-14C] aminoisobutyric acid. There were no statistical differences in systemic blood pressures and heart rates between these groups. Blood gases were within normal limits. In the control group, the Ki of ischemic cortex (IC) was 2.1 times that of the contralateral cortex (CC) (3.7+/-0.9 vs. 1.8+/-0.3 microl/g/min). In the ACPD group, the Ki of the IC was 3.3 times that of the CC (5.0+/-0.7 vs. 1.5+/-0.4 microl/g/min). The increase in Ki of the ACPD group in the ischemic cortex was significantly greater than that in the control group. There was no significant difference in the Ki of the CC between these groups. Our data suggest that activation metabotropic glutamate receptors in the cortex can further augment the increase in BBB permeability caused by focal ischemia.     

Inflammatory Mediators and Modulation of Blood–Brain Barrier Permeability

1. Unlike some interfaces between the blood and the nervous system (e.g., nerve perineurium), the brain endothelium forming the blood–brain barrier can be modulated by a range of inflammatory mediators. The mechanisms underlying this modulation are reviewed, and the implications for therapy of the brain discussed.2. Methods for measuring blood–brain barrier permeability in situ include the use of radiolabeled tracers in parenchymal vessels and measurements of transendothelial resistance and rate of loss of fluorescent dye in single pial microvessels. In vitro studies on culture models provide details of the signal transduction mechanisms involved.3. Routes for penetration of polar solutes across the brain endothelium include the paracellular tight junctional pathway (usually very tight) and vesicular mechanisms. Inflammatory mediators have been reported to influence both pathways, but the clearest evidence is for modulation of tight junctions.4. In addition to the brain endothelium, cell types involved in inflammatory reactions include several closely associated cells including pericytes, astrocytes, smooth muscle, microglia, mast cells, and neurons. In situ it is often difficult to identify the site of action of a vasoactive agent. In vitro models of brain endothelium are experimentally simpler but may also lack important features generated in situ by cell:cell interaction (e.g. induction, signaling).5. Many inflammatory agents increase both endothelial permeability and vessel diameter, together contributing to significant leak across the blood–brain barrier and cerebral edema. This review concentrates on changes in endothelial permeability by focusing on studies in which changes in vessel diameter are minimized.6. Bradykinin (Bk)² increases blood–brain barrier permeability by acting on B₂ receptors. The downstream events reported include elevation of [Ca²⁺]_i, activation of phospholipase A₂, release of arachidonic acid, and production of free radicals, with evidence that IL-1 potentiates the actions of Bk in ischemia.7. Serotonin (5HT) has been reported to increase blood–brain barrier permeability in some but not all studies. Where barrier opening was seen, there was evidence for activation of 5-HT₂ receptors and a calcium-dependent permeability increase.8. Histamine is one of the few central nervous system neurotransmitters found to cause consistent blood–brain barrier opening. The earlier literature was unclear, but studies of pial vessels and cultured endothelium reveal increased permeability mediated by H₂ receptors and elevation of [Ca²⁺]_i and an H₁ receptor-mediated reduction in permeability coupled to an elevation of cAMP.9. Brain endothelial cells express nucleotide receptors for ATP, UTP, and ADP, with activation causing increased blood–brain barrier permeability. The effects are mediated predominantly via a P_2U (P2Y₂) G-protein-coupled receptor causing an elevation of [Ca²⁺]_i; a P2Y₁ receptor acting via inhibition of adenyl cyclase has been reported in some in vitro preparations.10. Arachidonic acid is elevated in some neural pathologies and causes gross opening of the blood–brain barrier to large molecules including proteins. There is evidence that arachidonic acid acts via generation of free radicals in the course of its metabolism by cyclooxygenase and lipoxygenase pathways.11. The mechanisms described reveal a range of interrelated pathways by which influences from the brain side or the blood side can modulate blood–brain barrier permeability. Knowledge of the mechanisms is already being exploited for deliberate opening of the blood–brain barrier for drug delivery to the brain, and the pathways capable of reducing permeability hold promise for therapeutic treatment of inflammation and cerebral edema.     

Lifelong Consumption of Sodium Selenite: Gender Differences on Blood–Brain Barrier Permeability in Convulsive,Hypoglycemic Rats

The aim of this study was to compare the effects of hypoglycemia and induced convulsions on the blood-brain barrier permeability in rats with or without lifelong administration of sodium selenite. There is a significant decrease of the blood-brain barrier permeability in three brain regions of convulsive, hypoglycemic male rats treated with sodium selenite when compared to sex-matched untreated rats (p<0.05), but the decrease was not significant in female rats (p>0.05). The blood-brain barrier permeability of the left and right hemispheres of untreated, moderately hypoglycemic convulsive rats of both genders was better than their untreated counterparts (p<0.05). Our results suggest that moderate hypoglycemia and lifelong treatment with sodium selenite have a protective effect against blood-brain barrier permeability during convulsions and that the effects of sodium selenite are gender-dependent.     

Tight Junctions of the Blood–Brain Barrier

1. The blood–brain barrier is essential for the maintainance and regulation of the neural microenvironment. The blood–brain barrier endothelial cells comprise an extremely low rate of transcytotic vesicles and a restrictive paracellular diffusion barrier. The latter is realized by the tight junctions between the endothelial cells of the brain microvasculature, which are subject of this review. Morphologically, blood–brain barrier-tight junctions are more similar to epithelial tight junctions than to endothelial tight junctions in peripheral blood vessels.2. Although blood–brain barrier-tight junctions share many characteristics with epithelial tight junctions, there are also essential differences. However, in contrast to tight junctions in epithelial systems, structural and functional characteristics of tight junctions in endothelial cells are highly sensitive to ambient factors.3. Many ubiquitous molecular constituents of tight junctions have been identified and characterized including claudins, occludin, ZO-1, ZO-2, ZO-3, cingulin, and 7H6. Signaling pathways involved in tight junction regulation comprise, among others, G-proteins, serine, threonine, and tyrosine kinases, extra- and intracellular calcium levels, cAMP levels, proteases, and TNF. Common to most of these pathways is the modulation of cytoskeletal elements which may define blood–brain barrier characteristics. Additionally, cross-talk between components of the tight junction– and the cadherin–catenin system suggests a close functional interdependence of the two cell–cell contact systems.4. Recent studies were able to elucidate crucial aspects of the molecular basis of tight junction regulation. An integration of new results into previous morphological work is the central intention of this review.     

Astrocyte–Endotheliocyte Axis in the Regulation of the Blood–Brain Barrier

Neurochemical Research - The evolution of blood–brain barrier paralleled centralisation of the nervous system: emergence of neuronal masses required control over composition of the...     

Endothelial Vesicles in the Blood–Brain Barrier: Are They Related to Permeability?

1. Macromolecules cross capillary walls via large vascular pores that are thought to be formed by plasmalemmal vesicles. Early hypotheses suggested that vesicles transferred plasma constituents across the endothelial wall either by a shuttle mechanism or by fusing to form transient patent channels for diffusion. Recent evidence shows that the transcytotic pathway involves both movement of vesicles within the cell and a series of fusions and fissions of the vesicular and cellular membranes.2. The transfer of macromolecules across the capillary wall is highly specific and is mediated by receptors incorporated into specific membrane domains. Therefore, despite their morphological similarity, endothelial vesicles form heterogeneous populations in which the predominant receptor proteins incorporated in their membranes define the functions of individual vesicles.3. Blood–brain barrier capillaries have very low permeabilities to most hydrophilic molecules. Their low permeability to macromolecules has been presumed to be due to an inhibition of the transcytotic mechanism, resulting in a low density of endothelial vesicles.4. A comparison of vesicular densities and protein permeabilities in a number of vascular beds shows only a very weak correlation, therefore vesicle numbers alone cannot be used to predict permeability to macromolecules.5. Blood–brain barrier capillaries are fully capable of transcytosing specific proteins, for example, insulin and transferrin, although the details are still somewhat controversial.6. It has recently been shown that the albumin binding protein gp60 (also known as albondin), which facilitates the transcytosis of native albumin in other vascular beds, is virtually absent in brain capillaries.7. It seems likely that the low blood–brain barrier permeability to macromolecules may be due to a low level of expression of specific receptors, rather than to an inhibition of the transcytosis mechanism.     

MiR-539 Targets MMP-9 to Regulate the Permeability of Blood–Brain Barrier in Ischemia/Reperfusion Injury of Brain

Cerebral ischemia/reperfusion (I/R) injury severely threatens human life, while the potential mechanism underlying it is still need further exploration. The rat model of cerebral I/R injury was established using middle cerebral artery occlusion (MCAO). The rat microvascular endothelial cell line bEND.3 was exposed to oxygen–glucose deprivation/reperfusion (OGD/R) to mimic ischemic condition in vitro. Evans blue was performed to determine the blood–brain barrier (BBB) permeability. Real-time PCR and western blot were performed to determine gene expression in mRNA and protein level, individually. Luciferase reporter assay was conducted to determine the relationship between miR-539 and MMP-9. The infarct volume and BBB permeability of cerebral (I/R) rats were significantly greater than Sham group. The expression of miR-539 was decreased, while MMP-9 was increased in the brain tissues of I/R injury rats and OGD/R pretreated bEND.3. Up-regulated miR-539 in OGD/R pretreated bEND.3 significantly promoted the BBB permeability. MiR-539 targets MMP-9 to regulate its expression. OGD/R treatment significantly promoted the BBB permeability in bEND.3, miR-539 mimic transfection abolished the effects of OGD/R, while co-transfected with pcDNA-MMP-9 abolished the effects of miR-539 mimic. MiR-539 targets MMP-9 and further regulates the BBB permeability in cerebral I/R injury.     

Mechanisms of the Blood–Brain Barrier Disruption in HIV-1 Infection

Summary 1. Alterations of brain microvasculature and the disruption of the blood–brain barrier (BBB) integrity are commonly associated with human immunodeficiency virus type 1 (HIV-1) infection. These changes are most frequently found in human immunodeficiency virus-related encephalitis (HIVE) and in human immunodeficiency virus-associated dementia (HAD).2. It has been hypothesized that the disruption of the BBB occurs early in the course of HIV-1 infection and can be responsible for HIV-1 entry into the CNS.3. The current review discusses the mechanisms of injury to brain endothelial cells and alterations of the BBB integrity in HIV-infection with focus on the vascular effects of HIV Tat protein. In addition, this review describes the mechanisms of the BBB disruption due to HIV-1 or Tat protein interaction with selected risk factors for HIV infection, such as substance abuse and aging.This revised article was published online in May 2005 with a February 2005 cover date.     

Effect of P-glycoprotein Inhibition on the Penetration of Ceftriaxone Across the Blood–Brain Barrier

Neurochemical Research - Recent studies indicate that inhibition of the efflux transporter P-glycoprotein (P-gp) at the blood–brain barrier (BBB) may represent a putative strategy to increase...     

Resistin-Inhibited Neural Stem Cell-Derived Astrocyte Differentiation Contributes to Permeability Destruction of the Blood–Brain Barrier

Neurochemical Research - Neuroinflammation is an important part of the development of neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s and amyotrophic lateral...     

Lipopolysaccharide-Activated Microglia Induce Dysfunction of the Blood–Brain Barrier in Rat Microvascular Endothelial Cells Co-Cultured with Microglia

The blood–brain barrier (BBB) is formed by brain capillary endothelial cells, astrocytes, pericytes, microglia, and neurons. BBB disruption under pathological conditions such as neurodegenerative disease and inflammation is observed in parallel with microglial activation. To test whether activation of microglia is linked to BBB dysfunction, we evaluated the effect of lipopolysaccharide (LPS) on BBB functions in an in vitro co-culture system with rat brain microvascular endothelial cells (RBEC) and microglia. When LPS was added for 6 h to the abluminal side of RBEC/microglia co-culture at a concentration showing no effects on the RBEC monolayer, transendothelial electrical resistance was decreased and permeability to sodium-fluorescein was increased in RBEC. Immunofluorescence staining for tight junction proteins demonstrated that zonula occludens-1-, claudin-5-, and occludin-like immunoreactivities at the intercellular borders of RBEC were fragmented in the presence of LPS-activated microglia. These functional changes induced by LPS-activated microglia were blocked by the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor, diphenyleneiodonium chloride. The present findings suggest that LPS activates microglia to induce dysfunction of the BBB by producing reactive oxygen species through NADPH oxidase.     

Effect of Baicalin on Matrix Metalloproteinase-9 Expression and Blood–Brain Barrier Permeability Following Focal Cerebral Ischemia in Rats

Focal cerebral ischemia results in an increased expression of matrix metalloproteinase-9 (MMP-9), which induces vasogenic brain edema via disrupting the blood–brain barrier (BBB) integrity. Recent studies from our laboratory showed that baicalin reduces ischemic brain damage by inhibiting inflammatory reaction and neuronal apoptosis in a rat model of focal cerebral ischemia. In the present study, we first explored the effect of baicalin on the neuronal damage, brain edema and BBB permeability, then further investigated its potential mechanisms. Sprague–Dawley rats underwent permanent middle cerebral artery occlusion (MCAO). Baicalin was administrated by intraperitoneally injected twice at 2 and 12 h after the onset of MCAO. Neuronal damage, brain edema and BBB permeability were measured 24 h following MCAO. Expression of MMP-9 protein and mRNA were determined by western blot and RT–PCR, respectively. Expression of tight junction protein (TJP) occludin was detected by western blot. Neuronal damage, brain edema and BBB permeability were significantly reduced by baicalin administration following focal cerebral ischemia. Elevated expression of MMP-9 protein and mRNA were significantly down-regulated by baicalin administration. In addition, MCAO caused the decreased expression of occludin, which was significantly up-regulated by baicalin administration. Our study suggested that baicalin reduces MCAO-induced neuronal damage, brain edema and BBB permeability, which might be associated with the inhibition of MMP-9 expression and MMP-9-mediated occludin degradation.     

Cation Transport Specificity at the Blood–Brain Barrier

The molecular identification, expression and cloning of membrane-bound organic cation transporters are being completed in isolated in vitro membranes. In vivo studies, where cation specificity overlaps, need to complement this work. Method: Cross-inhibition of [³H]choline and [³H]thiamine brain uptake by in situ rat brain perfusion. Results: [³H]Choline brain uptake was not inhibited by thiamine at physiologic concentrations (100 nM). However, choline ranging from 100 nM to 250 M inhibited [³H]thiamine brain uptake, though not below levels observed at thiamine concentrations of 100 nM. Conclusion: (1) The molecular family of the blood–brain barrier (BBB) choline transporter may be elucidated in vitro by its interaction with physiologic thiamine levels, and (2) two cationic transporters at the BBB may be responsible for thiamine brain uptake.     

Diabetes-Related Alteration of Occludin Expression in Rat Blood–Spinal Cord Barrier

Occludin is an essential component of tight junctions, which are involved in controlling the integrity of the blood–brain barrier and blood–spinal cord barrier (BSCB). Diabetes-induced alteration of occludin in rat BSCB and the relationship between occludin level and disease course was examined. Diabetes was induced using streptozotocin. Occludin rat spinal cord mRNA levels were assessed by real-time quantitative RT-PCR. Protein levels were examined by western blot. Occludin expression in 1-month diabetic rats was significantly reduced compared to the controls (0.20 ± 0.01 vs 1.00 ± 0.01, respectively; P < 0.05). Expression was also significantly lower in the 3-month diabetic group (0.06 ± 0.02; P < 0.01). Occludin protein levels of 1-month (0.53 ± 0.01) and 3-month (0.31 ± 0.01) diabetic rats were also significantly reduced compared to controls (0.91 ± 0.06; P < 0.01 for both). Diabetes decreased BSCB occludin expression at the mRNA and protein level. This down-regulation appears to correlate with the course of the disease, and may be a causal factor of diabetes-induced increase of BSCB permeability.     

Neural Induction of the Blood–Brain Barrier: Still an Enigma

1. The study of the blood–brain barrier and its various realms offers a myriad of opportunities for scientific exploration. This review focuses on two of these areas in particular: the induction of the blood–brain barrier and the molecular mechanisms underlying this developmental process.2. The creation of the blood–brain barrier is considered a specific step in the differentiation of cerebral capillary endothelial cells, resulting in a number of biochemical and functional alterations. Although the specific endothelial properties which maintain the homeostasis in the central nervous system necessary for neuronal function have been well described, the inductive mechanisms which trigger blood–brain barrier establishment in capillary endothelial cells are unknown.3. The timetable of blood–brain barrier formation is still a matter of debate, caused largely by the use of varying experimental systems and by the general difficulty of quantitatively measuring the degree of blood–brain barrier tightness. However, there is a general consensus that a gradual formation of the blood–brain barrier starts shortly after intraneural neovascularization and that the neural microenvironment (neurons and/or astrocytes) plays a key role in inducing blood–brain barrier function in capillary endothelial cells. This view stems from numerous in vitro experiments using mostly cocultures of capillary endothelial cells and astrocytes and assays for easily measurable blood–brain barrier markers. In vivo, there are great difficulties in proving the inductive influence of the neuronal environment. Also dealt with in this article are brain tumors, the least understood in vivo systems, and the induction or noninduction of barrier function in the newly established tumor vascularization.4. Finally, this review tries to elucidate the question concerning the nature of the inductive signal eliciting blood–brain barrier formation in the cerebral microvasculature.     

Tissue Plasminogen Activator Enhances the Hypoxia/reoxygenation-induced Impairment of the Blood–brain Barrier in a Primary Culture of Rat Brain Endothelial Cells

Hemorrhagic transformation is a major complication associated with tissue plasminogen activator (tPA) therapy for ischemic stroke. We studied the effect of tPA on the blood–brain barrier (BBB) function with our in vitro monolayer model generated using rat brain microvascular endothelial cells subjected either to normoxia or to hypoxia/reoxygenation (H/R) with or without the administration of tPA. The barrier function was evaluated by the transendothelial electrical resistance (TEER), the permeability of sodium fluorescein and Evans’ blue-albumin (EBA), and the uptake of lucifer yellow (LY). The permeability of sodium fluorescein and EBA was used as an index of paracellular and transcellular transport, respectively. The administration of tPA increased the permeability of EBA and the uptake of LY under normoxia. It enhanced the increase in the permeability of both sodium fluorescein and EBA, the decrease in the TEER, and the disruption in the expression of ZO-1 under H/R conditions. Administration of tPA could cause an increase in the transcellular transport under normoxia, and both the transcellular and paracellular transport of the BBB under H/R conditions in vitro. Even in humans, tPA may lead to an opening of the BBB under non-ischemic conditions and have an additional effect on the ischemia-induced BBB disruption.     

Permeability Studies on In Vitro Blood–Brain Barrier Models: Physiology,Pathology, and Pharmacology

Summary 1. The specifically regulated restrictive permeability barrier to cells and molecules is the most important feature of the blood–brain barrier (BBB). The aim of this review was to summarize permeability data obtained on in vitro BBB models by measurement of transendothelial electrical resistance and by calculation of permeability coefficients for paracellular or transendothelial tracers.2. Results from primary cultures of cerebral microvascular endothelial cells or immortalized cell lines from bovine, human, porcine, and rodent origin are presented. Effects of coculture with astroglia, neurons, mesenchymal cells, blood cells, and conditioned media, as well as physiological influence of serum components, hormones, growth factors, lipids, and lipoproteins on the barrier function are discussed.3. BBB permeability results gained on in vitro models of pathological conditions including hypoxia and reoxygenation, neurodegenerative diseases, or bacterial and viral infections have been reviewed. Effects of cytokines, vasoactive mediators, and other pathogenic factors on barrier integrity are also detailed.4. Pharmacological treatments modulating intracellular cyclic nucleotide or calcium levels, and activity of protein kinases, protein tyrosine phosphatases, phospholipases, cyclooxygenases, or lipoxygenases able to change BBB integrity are outlined. Barrier regulation by drugs involved in the metabolism of nitric oxide and reactive oxygen species, as well as influence of miscellaneous treatments are also listed and evaluated.5. Though recent advances resulted in development of improved in vitro BBB model systems to investigate disease modeling, drug screening, and testing vectors targeting the brain, there is a need for checking validity of permeability models and cautious interpretation of data.This revised article was published online in May 2005 with a February 2005 cover date.