Ammonia selectively stimulates neutral amino acid transport across blood-brain barrier

The response to increased blood NH4+ of three blood-brain barrier transport systems, which are altered after portacaval anastomosis, was studied. NH4+ acetate was infused for 4 or 22 h to raise blood and brain NH4+, and brain glutamine, to levels similar to those observed after portacaval anastomosis. While brain glutamine content was much higher (16-20 mumol/g) than normal (6 mumol/g) at both times, the permeability of the blood-brain barrier to the neutral amino acid [14C]tryptophan was greater only after 22 h of infusion. After discontinuing the infusion for 5 h, tryptophan transport returned to normal, whereas brain glutamine remained elevated (13 mumol/g). Thus there seemed to be no relationship between the rate of transport and glutamine content. The permeability to [14C]sucrose was unaltered, showing that the integrity of the blood-brain barrier was maintained. Other changes that are characteristic of portacaval shunting, such as decreased basic amino acid ([14C]lysine) and monocarboxylic acid (3-[14C]hydroxybutyrate) transport, were not reproduced by 22 h of infusion. The results demonstrated that the continued presence of NH4+ could be responsible for the change in at least one of the transport systems that are affected by portacaval shunting.     

Transport of glucose across the blood-brain barrier: Reevaluation of the accelerative exchange diffusion

In an earlier study of glucose transport across the blood-brain barrier it was concluded that the kinetic transport constants increase as the brain glucose concentration increases, a finding that was attributed to accelerative exchange diffusion (Betz et al. 1975). The conclusion, however, relied upon application of a commonly used simplified treatment of tracer extraction data. In this study it is demonstrated that the simplified treatment is applicable only in the case of zero brain glucose concentration, and a more general model for determination of the kinetic constants is developed. Re-analysis by this model of the data of Betz et al. (1975)—comprising a range of brain glucose concentrations—gave kinetic constants which did not vary significantly over a wide range of brain glucose concentrations. For brain glucose concentrations up to about 12 mmol l^-1, the kinetic constants obtained for glucose transport across the blood-brain barrier are Km =6.18±0.38mmol l^-1 V_max= 1.65±0.06 μmol g-¹ min^-1     

Penetration of sugars across the blood-brain barrier

1. A cerebral perfusion method was used to measure the net uptake of arabinose from the circulatory system in cats.2. There was found to be discrimination between the optical isomers of this substance, with apparently greater uptake of the (-)-form.3. The uptake process was highly temperature dependent, with a Q(10) of 3.0.4. The uptake of arabinose was partially inhibited by 1 mM ouabain perfused concurrently. It was not significantly inhibited by dinitrophenol or phlorrhizin.5. Glucose inhibited competitively the uptake of (-)-arabinose.6. We conclude that the mechanism involved is of the carrier-mediated or of the active transport type, and that at least part of it is shared with glucose and probably other sugars.     

Migration of African trypanosomes across the blood-brain barrier

Subspecies of the extracellular parasite, Trypanosoma brucei, which are spread by the tsetse fly in sub-Saharan Africa, cause in humans Sleeping Sickness. In experimental rodent models the parasite can at a certain stage of disease pass through the blood-brain barrier across or between the endothelial cells and the vessel basement membranes. The laminin composition of the basement membranes determines whether they are permissive to parasite penetration. One cytokine, interferon-gamma, plays an important role in regulating the trypanosome trafficking into the brain. Treatment strategies aim at developing drugs that can impede penetration of trypanosomes into the brain and/or that can eliminate trypanosomes once they are inside the brain parenchyma, but have lower toxicity than the ones presently in use.     

Uptake across the blood-brain barrier and tissue distribution of enterostatin after peripheral administration in rats

Enterostatin, the N-terminal activation pentapeptide of procolipase that is produced by the pancreas, reduces food intake from high-fat diet when injected either peripherally or centrally to rats. We investigated uptake across the blood-brain barrier (BBB) and tissue distribution of enterostatin by giving radioactive-labeled enterostatin (3H-VPDPR) intravenously. Low levels of 3H-VPDPR were detected in many areas of the brain, with greatest radioactivity in the frontal cortex, hippocampus and cerebellum. Radioactivity was found in the plasma and all tissues, with the highest amount detected in the pancreas.     

Prostaglandins as inflammatory messengers across the blood-brain barrier

Upon immune challenge the brain launches a wide range of responses, such as fever, anorexia, and hyperalgesia that serve to maintain homeostasis. While these responses are adaptive during acute infections, they may be destructive during chronic inflammatory conditions. Research performed during the last decade has given us insight into how the brain monitors the presence of a peripheral inflammation and the mechanisms underlying the brain-mediated acute-phase reactions. Here we give a brief review on this subject, with focus on the role of prostaglandin E2 produced in cells associated with the blood-brain barrier in immune-to-brain signaling. The recent advances in this field have not only elucidated the mechanisms behind the anti-pyretic and anti-hyperalgesic effects of cyclooxygenase inhibitors, but have also identified novel and more-selective potential drug targets.     

Traversal of Candida albicans across human blood-brain barrier in vitro

Candida albicans is an opportunistic pathogen, which primarily affects neonates and immunocompromised individuals. The pathogen can invade the central nervous system, resulting in meningitis. At present, the pathogenesis of C. albicans meningitis is unclear. We used an in vitro model of the human blood-brain barrier to investigate the interaction(s) of C. albicans with human brain microvascular endothelial cells (BMEC). Binding of C. albicans to human BMEC was time and inoculum dependent. Invasion of C. albicans into human BMEC was demonstrated by using an enzyme-linked immunosorbent assay based on fluorescent staining of C. albicans with calcoflour. In contrast, avirulent Candida mutant strains and nonpathogenic yeast Saccharomyces cerevisiae were not able to bind and invade human BMEC. Morphological studies revealed that on association with human BMEC, C. albicans formed germ tubes and was able to bud intracellularly. Transmission electron microscopy showed various stages of C. albicans interactions with human BMEC, e.g., pseudopod-like structures on human BMEC membrane and intracellular vacuole-like structures retaining C. albicans. Of interest, C. albicans was able to bud and develop pseudohyphae inside human BMEC without apparent morphological changes of the host cells. In addition, C. albicans penetrates through human BMEC monolayers without a detectable change in transendothelial electrical resistance and inulin permeability. This is the first demonstration that C. albicans is able to adhere, invade, and transcytose across human BMEC without affecting monolayer integrity. A complete understanding of the interaction(s) of C. albicans with human BMEC should contribute to the understanding of the pathogenic mechanism(s) of C. albicans meningitis.     

Effects of apolipoproteins on dalargin transport across the blood-brain barrier

Antinociceptive activity of dalargin (7.5 mg/kg) adsorbed on poly(butyl)cyanoacrylate nanoparticles with different coating was studied on outbred albino mice by the tail-flick test. Poly(butyl)cyanoacrylate nanoparticles without coating did not increase the antinociceptive activity of dalargin and hence, did not increase its transport across the blood-brain barrier. Poly(butyl)cyanoacrylate nanoparticles coated with apolipoprotein B, apolipoprotein E, and polysorbate 80 increased the transport of dalargin across the blood-brain barrier. Delivery of dalargin to the brain was most effective in case of using poly(butyl)cyanoacrylate nanoparticles with polysorbate 80 coating and subsequent supercoating with apolipoprotein E. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 142, No. 12, pp. 659–662, December, 2006     

Transport of branched-chain amino acids in brain slices of developing and adult rats

The accumulation of labelled leucine, isoleucine and valine by cerebral slices of developing and adult rats was studied. The accumulation increased with age by 15–25%. It was strongly (from 52 to 86%) inhibited by a 100-fold excess of phenylalanine, tryptophan and another branched-chain amino acid, but moderately activated by GABA and glutamate. The inhibitions evoked by leucine and isoleucine were slightly stronger in young than in adult rats. The corresponding 2-oxoacid analogs of leucine, isoleucine and valine were also inhibitory but less effective. The 30-min accumulation of ³H-labelled branched-chain amino acids was ostensibly higher than the increase in their total concentrations in incubated slices, which apparently bespeaks lively homoexchange of endogenous intracellular and labelled extracellular amino acids.     

Decreased blood-brain barrier permeability to fluorescein in streptozotocin-treated rats

Investigations of the blood-brain barrier (BBB) in diabetes have yielded contradictory results. It is possible that diabetes differentially affects paracellular and transcellular permeabilities via modulation of tight junction and transport proteins, respectively. Fluorescein (FL), a marker for paracellular permeability, is a substrate for the transport proteins organic anion transporter (OAT)-3 and multidrug resistance protein (MRP)-2 at the BBB. Furthermore, MRP-2-mediated efflux of FL can be upregulated by glucose. In this study, streptozotocin-induced diabetes led to decreased brain distribution of FL measured by in situ brain perfusion, consistent with activation of an efflux transport system for FL at the BBB. This change was paralleled by increased protein expression of MRP-2, but not OAT-3, in cerebral microvessels. These data indicate that diabetes may lead to changes in efflux transporters at the BBB and have implications for delivery of therapeutics to the central nervous system.     

右美托咪定对脓毒血症大鼠血脑屏障的影响

目的探讨右美托咪定(dexmedetomidine,DEX)对内毒素血症大鼠模型血脑屏障及认知功能的影响。方法健康SD雄性大鼠24只,随机分为4组(n=6):空白对照组(C组)、脂多糖组(LPS组)、右美托咪定组(DEX组)和右美托咪定+脂多糖组(DEX+LPS组)。采用尾静脉注射LPS方法制备内毒素血症模型。各组大鼠进行Morris水迷宫实验,记录大鼠逃避潜伏期、穿越平台次数、在平台所在象限时间。处死大鼠,取海马组织,采用免疫组化法和Western blot检测各组大鼠海马组织血脑屏障(BBB)结构蛋白Occludin和ZO-1蛋白表达,采用ELISA方法检测各组大鼠海马组织炎症因子TNF-α、IL-1β和IL-6。结果 LPS组大鼠认知功能受损严重,海马组织Occludin和ZO-1蛋白的表达水平降低,炎症因子TNF-α、 IL-1β和IL-6含量显著升高;DEX+LPS组大鼠认知功能受损程度较LPS组轻,海马组织Occludin蛋白和ZO-1的蛋白表达升高,炎症因子TNF-α、IL-1β和IL-6含量显著降低。结论右美托咪定改善内毒素血症大鼠的认知功能,与上调Occludin以及ZO-1蛋白表达水平相关。     

6-hydroxydopamine and the blood-brain barrier in adult conscious rats

6-hydroxydopamine (6-OHDA), 15 or 50 mg . kg-1 given as bolus i.v. injection to adult conscious rats with aortic catheter, rapidly increased mean arterial pressure by 70-78 mmHg. The pressure returned to normal within 40-60 min. The cerebrovascular permeability in rats given 6-OHDA and sacrificed 10 or 60 min later was enhanced as indicated by extravasation of Evans blue albumin and significant increase of 125I human serum albumin content in brain tissue compared to control rats. When the increase in blood pressure was diminished by i.v. phentolamine, 6-OHDA treated rats did not differ from controls. It is concluded that the blood pressure elevation induced by i.v. 6-OHDA facilitates the entry of the drug into the brain parenchyma.     

Cerebrovascular sympathetic denervation and blood-brain barrier function in conscious rats

Electrical stimulation of the sympathetic nerves to the cerebrovascular bed enables the resistance vessels to better withstand a high blood pressure in terms of blood-brain barrier integrity. Sympathetic denervation could hence be expected to lead to a decrease in cerebrovascular tone and increased vulnerability of the blood-brain barrier. In the present study acute hypertension was induced in conscious unrestrained rats by administration of angiotensin or bicuculline. The albumin leakage into the brain, as studied by Evans blue-albumin and ¹²⁵I labelled human serum albumin. was not enhanced in acutely or chronically sympathectomized rats compared to controls.     

颈淋巴阻滞对大鼠血脑屏障通透性的影响

目的: 探讨大鼠颈淋巴阻滞后血脑屏障(BBB)通透性的变化。方法: 手术组大鼠采用Casley-Smith法阻滞颈淋巴,对照组大鼠不摘除颈淋巴结和不结扎淋巴管,只将它们分离暴露。每组于术后1、3、5、7、14、21 d,通过观察血清中S-100B的浓度、电镜观察镧离子示踪剂和BBB超微结构变化来确定BBB通透性的改变。结果: 各组血清中S100B浓度变化无显著差异,提示BBB没有破坏;电镜观察:对照组与手术组的超微结构变化相同,各组术后各时点血管腔外没有发现镧离子。结论: 颈淋巴阻滞对BBB通透性没有显著影响。     

雌激素对大鼠脑缺血再灌注后血脑屏障作用研究

目的观察雌激素对大鼠脑缺血再灌注后血脑屏障(blood-brain barrier,BBB)的通透性、Occludin表达的影响,探讨雌激素在脑缺血中的作用。方法随机将去势雌性大鼠分为假手术组、模型组、雌激素预处理组,选取缺血再灌后4 h,24 h,3 d3个时间点作为观察点,对各个时间点脑水肿情况、Occludin蛋白表达、血脑屏障通透性改变进行考察分析,并选取24 h和3 d作BBB超微结构电镜观察,脑水肿改变情况采用脑含水量百分数测定;蛋白质表达采用western blot方法;血脑屏障通透性改变采用伊文思蓝(EB)比色法。结果与假手术组比较,局灶性脑缺血再灌4 h模型组大鼠脑组织含水量及EB含量均增加(P0.05),随缺血再灌时间延长,脑组织含水量、脑组织EB含量持续增加,至24 h,达到高峰(P0.01),与同时间点模型组比较,各治疗组大鼠脑组织含水量、EB含量均有不同程度降低(P0.05或P0.01),以24 h组降低最为显著(P0.01)。电镜观察雌激素预处理组较模型组同时间点比较BBB TJ开放减轻,星形胶质细胞足突及毛细血管管周水肿较轻,以3 d组显著。Western blot检测Occludin蛋白表达,发现模型组4 h时Occludin蛋白表达较假手术组减弱,但无显著性差异(P0.05),24 h组Occludin蛋白表达较假手术组减弱,有显著性差异(P0.05),3 d组Occludin蛋白表达进一步减弱,有明显差异(P0.01),雌激素组4 h时Occludin蛋白表达较同时间点模型组比较无显著性差异(P0.05),雌激素24 h及3 d组Occludin蛋白表达较同时间点模型组比较均升高,有显著性差异(P0.05)。结论局灶性脑缺血大鼠动物血脑屏障超微结构可见紧密连接发生断裂,内皮细胞内小泡数量增加及星形胶质细胞足突肿胀,可能是大鼠局脑缺血时血管源性脑水肿的重要因素。大鼠局灶性脑缺血,随缺血再灌时间延长,紧密连接相关蛋白occludin的表达明显下降,提示occludin在调节紧密连接通透性变化的过程中有重要作用。雌激素上调紧密连接Occludin蛋白的表达,有可能是其维护血脑屏障完整性减轻脑水肿的机制之一。     

Tat-聚乙二醇修饰明胶-硅氧烷纳米粒跨血脑屏障研究

明胶-硅氧烷杂化材料具有低毒、表面易修饰、易重复合成等优点,并可介导外源基因在细胞内进行高效率转染,是一种潜在的高效基因载体材料。本文通过两步溶胶-凝胶反应合成明胶-硅氧烷纳米粒(GS NPs),经Tat多肽(KYGRRRQRRKKRGC)、聚乙二醇(PEG)表面修饰构成Tat-PEG-GS NPs。应用透射电镜(TEM)、粒径仪和活体成像系统对其粒径、形貌、zeta电位、跨血脑屏障入脑能力进行评价。结果得出,Tat-PEG-GS NPs粒径分布在150～200nm、zeta电位(32.27±2.47)mV;TEM观察显示Tat-PEG-GS NPs可跨过血脑屏障到达脑组织,活体成像显示Tat-PEG-GS NPs较PEG-GS NPs在脑部的荧光强,Tat-PEG-GS NPs比PEG-GS NPs在肝脏、脾脏的荧光低,差异具有统计学意义。证明Tat-PEG-GS NPs可以逃逸内皮网状吞噬系统的吞噬,跨过血脑屏障到达脑实质内,是一种有潜力的入脑纳米载体系统。