Adrenomedullin Improves the Blood–Brain Barrier Function Through the Expression of Claudin-5

Summary 1. Aims: Brain vascular endothelial cells secret Adrenomedullin (AM) has multifunctional biological properties. AM affects cerebral blood flow and blood–brain barrier (BBB) function. We studied the role of AM on the permeability and tight junction proteins of brain microvascular endothelial cells (BMEC).2. Methods: BMEC were isolated from rats and a BBB in vitro model was generated. The barrier functions were studied by measuring the transendothelial electrical resistance (TEER) and the permeability of sodium fluorescein and Evans’ blue albumin. The expressions of tight junction proteins were analyzed using immunocytochemistry and immunoblotting.3. Results: AM increased TEER of BMEC monolayer dose-dependently. Immunocytochemistry revealed that AM enhanced the claudin-5 expression at a cell–cell contact site in a dose-dependent manner. Immunoblotting also showed an overexpression of claudin-5 in AM exposure.4.Conclusions: AM therefore inhibits the paracellular transport in a BBB in vitro model through claudin-5 overexpression.     

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...     

The Effect of Butylphthalide on the Brain Edema,Blood–Brain Barrier of Rats After Focal Cerebral Infarction and the Expression of Rho A

The aim of this study was to explore the effect of butylphthalide on the brain edema, blood–brain barrier of rats of rats after focal cerebral infarction and the expression of Rho A. A total of 195 sprague–dawley male rats were randomly divided into control group, model group, and butylphthalide group (40 mg/kg, once a day, by gavage). The model was made by photochemical method. After surgery 3, 12, 24, 72, and 144 h, brain water content was done to see the effect of butylphthalide for the cerebral edema. Evans blue extravasation method was done to see the changes in blood–brain barrier immunohistochemistry, and Western blot was done to see the expression of Rho A around the infarction. Compared with the control group, the brain water content of model group and butylphthalide group rats was increased, the permeability of blood–brain barrier of model group and butylphthalide group rats was increased, and the Rho A protein of model group and butylphthalide group rats was increased. Compared with the model group, the brain water content of butylphthalide group rats was induced (73.67 ± 0.67 vs 74.14 ± 0.46; 74.89 ± 0.57 vs 75.61 ± 0.52; 77.49 ± 0.34 vs 79.33 ± 0.49; 76.31 ± 0.56 vs 78.01 ± 0.48; 72.36 ± 0.44 vs 73.12 ± 0.73; P < 0.05), the permeability of blood–brain barrier of butylphthalide group rats was induced (319.20 ± 8.11 vs 394.60 ± 6.19; 210.40 ± 9.56 vs 266.40 ± 7.99; 188.00 ± 9.22 vs 232.40 ± 7.89; 288.40 ± 7.86 vs 336.00 ± 6.71; 166.60 ± 6.23 vs 213.60 ± 13.79; P < 0.05), and the Rho A protein of butylphthalide group rats was decreased (western blot result: 1.2230 ± 0.0254 vs 1.3970 ± 0.0276; 1.5985 ± 0.0206 vs 2.0368 ± 0.0179; 1.4229 ± 0.0167 vs 1.7930 ± 0.0158;1.3126 ± 0.0236 vs 1.5471 ± 0.0158; P < 0.05). The butylphthalide could reduce the brain edema, protect the blood–brain barrier, and decrease the expression of Rho A around the infarction.     

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.     

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...     

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 Propofol Post-treatment on Blood–Brain Barrier Integrity and Cerebral Edema After Transient Cerebral Ischemia in Rats

Although propofol has been reported to offer neuroprotection against cerebral ischemia injury, its impact on cerebral edema following ischemia is not clear. The objective of this investigation is to evaluate the effects of propofol post-treatment on blood–brain barrier (BBB) integrity and cerebral edema after transient cerebral ischemia and its mechanism of action, focusing on modulation of aquaporins (AQPs), matrix metalloproteinases (MMPs), and hypoxia inducible factor (HIF)-1α. Cerebral ischemia was induced in male Sprague–Dawley rats (n = 78) by occlusion of the right middle cerebral artery for 1 h. For post-treatment with propofol, 1 mg kg^?1 min^?1 of propofol was administered for 1 h from the start of reperfusion. Nineteen rats undergoing sham surgery were also included in the investigation. Edema and BBB integrity were assessed by quantification of cerebral water content and extravasation of Evans blue, respectively, following 24 h of reperfusion. In addition, the expression of AQP-1, AQP-4, MMP-2, and MMP-9 was determined 24 h after reperfusion and the expression of HIF-1α was determined 8 h after reperfusion. Propofol post-treatment significantly reduced cerebral edema (P < 0.05) and BBB disruption (P < 0.05) compared with the saline-treated control. The expression of AQP-1, AQP-4, MMP-2, and MMP-9 at 24 h and of HIF-1α at 8 h following ischemia/reperfusion was significantly suppressed in the propofol post-treatment group (P < 0.05). Propofol post-treatment attenuated cerebral edema after transient cerebral ischemia, in association with reduced expression of AQP-1, AQP-4, MMP-2, and MMP-9. The decreased expression of AQPs and MMPs after propofol post-treatment might result from suppression of HIF-1α expression.     

LRP-1 Mediated Endocytosis of EFE Across the Blood–Brain Barrier; Protein–Protein Interaction and Molecular Dynamics Analysis

International Journal of Peptide Research and Therapeutics - Additional biological protection; blood brain barrier (BBB) to neuronal tissue is essential against invading infections and unwanted...     

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.     

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.     

The Blood–Brain Barrier and Bilirubin Encephalopathy

1. The pathogenesis of bilirubin encephalopathy is multifactorial, involving the transport of bilirubin or albumin/bilirubin across the blood–brain barrier and delivering bilirubin to target neurons.2. The relative importance of the blood–brain barrier, unconjugated bilirubin levels, serum binding, and tissue susceptibility in this process is only partially understood. Even at dangerously high serum levels, bilirubin traverses the intact blood–brain barrier slowly, requiring time for encephalopathy to occur, although deposition of bilirubin can be rapid if a surge in plasma unbound bilirubin is produced by administering a drug which competes with bilirubin for binding to albumin.3. There may be maturational changes in permeability both in the fetus and postnatally which protect the brain from bilirubin.4. Disruption or partial disruption of the blood–brain barrier by disease or hypoxic ischemic injury will facilitate transport of bilirubin/albumin into brain, but the relative affinities of albumin and target neurons will determine whether the tissue bilirubin load is sufficient for toxicity to occur.     

A New Function for the LDL Receptor: Transcytosis of LDL across the Blood–Brain Barrier

Lipoprotein transport across the blood–brain barrier (BBB) is of critical importance for the delivery of essential lipids to the brain cells. The occurrence of a low density lipoprotein (LDL) receptor on the BBB has recently been demonstrated. To examine further the function of this receptor, we have shown using an in vitro model of the BBB, that in contrast to acetylated LDL, which does not cross the BBB, LDL is specifically transcytosed across the monolayer. The C7 monoclonal antibody, known to interact with the LDL receptor-binding domain, totally blocked the transcytosis of LDL, suggesting that the transcytosis is mediated by the receptor. Furthermore, we have shown that cholesterol-depleted astrocytes upregulate the expression of the LDL receptor at the BBB. Under these conditions, we observed that the LDL transcytosis parallels the increase in the LDL receptor, indicating once more that the LDL is transcytosed by a receptor-mediated mechanism. The nondegradation of the LDL during the transcytosis indicates that the transcytotic pathway in brain capillary endothelial cells is different from the LDL receptor classical pathway. The switch between a recycling receptor to a transcytotic receptor cannot be explained by a modification of the internalization signals of the cytoplasmic domain of the receptor, since we have shown that LDL receptor messengers in growing brain capillary ECs (recycling LDL receptor) or differentiated cells (transcytotic receptor) are 100% identical, but we cannot exclude posttranslational modifications of the cytoplasmic domain, as demonstrated for the polymeric immunoglobulin receptor. Preliminary studies suggest that caveolae are likely to be involved in the potential transport of LDL from the blood to the brain.The maintenance of the homeostasis of brain interstitial fluid, which constitutes the special microenvironment for neurons, is established by the presence of the blood–brain barrier (BBB)¹ at the transition area from endothelial cells (ECs) to brain tissue. Of primary importance in the formation of a permeability barrier by these cells is the presence of continuous tight junctions that seal together the margins of the ECs and restrict the passage of substances from the blood to the brain. Furthermore, in contrast to ECs in many other organs, the brain capillary ECs contain no direct transendothelial passageways such as fenestrations or channels. But obviously, the BBB cannot be absolute. The brain is dependent upon the blood to deliver metabolic substrates and remove metabolic waste, and the BBB therefore facilitates the exchange of selected solutes. Carrier-mediated transport systems that facilitate the uptake of hexoses, amino acids, purine compounds, and mono-carboxylic acids have been revealed in the cerebral endothelium (Betz and Goldstein, 1978), but until now little information has come to light regarding the cerebral uptake of lipids.There is growing evidence that the brain is equipped with a relatively self-sufficient transport system for maintaining cholesterol and lipid homeostasis. The presence of a low density lipoprotein (LDL) receptor has been demonstrated by immunocytochemistry in rat and monkey brains; and apolipoprotein (apo) E and apo AI-containing particles have been detected in human cerebrospinal fluid (Pitas et al., 1987). Furthermore, enzymes involved in lipid metabolism have been located within the brain: LCAT mRNA has been shown to be expressed in rat brains and cholesteryl ester transfer protein, which plays a key role in cholesterol homeostasis, has been detected in human cerebrospinal fluid and seems to be synthesized in the brain (Albers et al., 1992). The distribution of the LDL receptor-related protein, a multifunctional receptor that binds apoE, is highly restricted and limited to the gray matter, primarily associated with neuronal cell population (Wolf et al., 1992). The difference in cellular expression of ligand (apoE) and receptor (LDL receptor-related protein) may provide a pathway for intracellular transport of apoE-containing lipoproteins in the central nervous system. All these data leave little doubt that the brain is equipped with a relatively self-sufficient transport system for cholesterol.Cholesterol could be derived from de novo synthesis within the brain and from plasma via the BBB. Malavolti et al. (1991) indicate the presence of unexpectedly close communications between extracerebral and brain cholesterol. Changes in the extracerebral cholesterol levels are readily sensed by the LDL receptor in the brain and promptly provoke appropriate modifications in its activity. Méresse et al. (1989a) provided direct evidence for the occurrence in vivo of an LDL receptor on the endothelium of brain capillaries. Furthermore, the fact that enzymes involved in the lipoprotein metabolism are present in the brain microvasculature (Brecher and Kuan, 1979) and that the entire fraction of the drug bound to lipoproteins is available for entry into the brain strongly suggest that this cerebral endothelial receptor plays a role in the interaction of plasma lipoproteins with brain capillaries. These results pinpoint the critical importance of the interactions between brain capillary ECs and lipoproteins. Owing to the fact that the neurological abnormalities that result from the inadequate absorption of dietary vitamin E can be improved by the oral administration of pharmacological doses of vitamin E, Traber and Kayden (1984) have suggested that LDL functions as a transport system for tocopherol to the brain. Furthermore, the trace amounts of apolipoprotein B that were detected by Salem et al. (1987) in cerebrospinal fluid from healthy patients using a very sensitive immunoblot technique confirm that, at most, small amounts of apolipoprotein B normally pass through the BBB. However, whether LDL is involved in the exchange is not known.Using an in vitro model of the BBB that imitates an in vivo situation by culturing capillary ECs and astrocytes on opposite sides of a filter (Dehouck et al., 1990a , 1992), we have demonstrated that in culture, like in vivo, in contrast to peripheral endothelium and in spite of the tight apposition of ECs and their contact with physiological concentrations of lipoproteins, brain capillary ECs express an LDL receptor (Méresse et al., 1991; Dehouck et al., 1994). The capacity of ECs to bind LDLs is greater when cocultured with astrocytes than in their absence. Futhermore, we have shown that the lipid requirement of astrocytes increases the expression of the LDL receptor on brain capillary ECs. Taken together, the presence of LDL receptors on brain capillary ECs and the modulation of the expression of these receptors by the lipid composition of astrocytes suggest that cholesterol used by cells in the central nervous system may be derived, at least in part, from the periphery via transport across the BBB.In the present study, we provide direct evidence that after binding to brain capillary ECs, there is a specific mechanism for the transport of LDL across the endothelial monolayer from the apical to the abluminal surface. This mechanism might be best explained by a process of receptor-mediated transcytosis. Preliminary results pinpoint the role of caveolae in the transcellular transport of LDL across the brain endothelium.     

Characterization and Modulation of Glucose Uptake in a Human Blood–Brain Barrier Model

The blood–brain barrier (BBB) plays a key role in limiting and regulating glucose access to glial and neuronal cells. In this work glucose uptake on a human BBB cell model (the hCMEC/D3 cell line) was characterized. The influence of some hormones and diet components on glucose uptake was also studied. ³H-2-deoxy-d-glucose ([³H]-DG) uptake for hCMEC/D3 cells was evaluated in the presence or absence of tested compounds. [³H]-DG uptake was sodium- and energy-independent. [³H]-DG uptake was regulated by Ca²⁺ and calmodulin but not by MAPK kinase pathways. PKC, PKA and protein tyrosine kinase also seem to be involved in glucose uptake modulation. Progesterone and estrone were found to decrease ³H-DG uptake. Catechin and epicatechin did not have any effect, but their methylated metabolites increased [³H]-DG uptake. Quercetin and myricetin decreased [³H]-DG uptake, and glucuronic acid-conjugated quercetin did not have any effect. These cells expressed GLUT1, GLUT3 and SGLT1 mRNA.     

Pericyte-derived Glial Cell Line-derived Neurotrophic Factor Increase the Expression of Claudin-5 in the Blood–brain Barrier and the Blood-nerve Barrier

The destruction of blood–brain barrier (BBB) and blood-nerve barrier (BNB) has been considered to be a key step in the disease process of a number of neurological disorders including cerebral ischemia, Alzheimer’s disease, multiple sclerosis, and diabetic neuropathy. Although glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) facilitate neuronal or axonal regeneration in the brain or peripheral nerves, their action in the BBB and BNB remains unclear. The purpose of the present study was to elucidate whether these neurotrophic factors secreted from the brain or peripheral nerve pericytes increase the barrier function of the BBB or BNB, using our newly established human brain microvascular endothelial cell (BMEC) line or peripheral nerve microvascular endothelial cell (PnMEC) line. GDNF increased the expression of claudin-5 and the transendothelial electrical resistance (TEER) of BMECs and PnMECs, whereas BDNF did not have this effect. Furthermore, we herein demonstrate that the GDNF secreted from the brain and peripheral nerve pericytes was one of the key molecules responsible for the up-regulation of claudin-5 expression and the TEER value in the BBB and BNB. These results indicate that the regulation of GDNF secreted from pericytes may therefore be a novel therapeutic strategy to modify the BBB or BNB functions and promote brain or peripheral nerve regeneration.     

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.     

Gender Difference in the Influence of Antioxidants on the Blood–Brain Barrier Permeability During Pentylenetetrazol-Induced Seizures in Hyperthermic Rat Pups

Our purpose in this study was to investigate the protective effects of selenium and vitamin E on the blood–brain barrier (BBB) permeability in rats with convulsion under hyperthermic conditions. To eliminate the effect of sex on BBB, we performed our study on 4- to 5-week-old prepubertal rat pups. Evans-blue was used as a BBB tracer. Convulsions were induced by administration of i.p. pentylenetetrazol. In the selenium group, 4 ppm selenium was added to the drinking water for 4–5 weeks. Vitamin E was administered at 700 mg/kg ip. It was shown that the convulsions, both under normothermic and hyperthermic conditions, caused widespread increase in the BBB permeability (p < 0.05). In addition, a significant difference was observed among female and male rats (f [1, 102] = 6.387, p < 0.05). In convulsions under normothermic conditions, there was a further increase in the BBB permeability (F[3, 102] = 43.534, p < 0.001) and a greater increase of permeability in males compared to females (F[1, 102] = 6.387, p < 0.05). Selenium and vitamin E significantly decreased the BBB destruction caused by convulsions under hyperthermic conditions in males (p < 0.05). Treatment with selenium or vitamin E has beneficial effects on the BBB breakdown during convulsions. But gender differences are very important in BBB permeability under pathological conditions and antioxidant treatments.     

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.