血脑屏障上的药物转运体P-糖蛋白

血脑屏障(Blood-brain Barrier,简称BBB)是维护脑内环境稳态的重要功能单位,它不仅可以阻止血液中的有害物质进入脑组织,而且能够清除脑内的有毒代谢产物。BBB上表达的转运系统在积极转运营养物质入脑和选择性外排药物的两个方面均发挥了重要作用。其中P-糖蛋白由于自身结构功能的特异性和作用底物的广泛性而备受关注。本文主要论述了BBB上P-糖蛋白的特性、表达、转运底物及其体内外研究的进展情况。P-糖蛋白作为BBB的重要组成部分在中枢神经系统治疗药物的摄取、分布和排泄中发挥了越来越重要的作用。因此,对P-糖蛋白的研究将有助于阐明药物脑部转运机制,为增加药物的BBB通透性、提高脑内靶点药物浓度提供新的研究思路。     

The blood-brain barrier in brain homeostasis and neurological diseases

Brain endothelial cells are unique among endothelial cells in that they express apical junctional complexes, including tight junctions, which quite resemble epithelial tight junctions both structurally and functionally. They form the blood-brain-barrier (BBB) which strictly controls the exchanges between the blood and the brain compartments by limiting passive diffusion of blood-borne solutes while actively transporting nutrients to the brain. Accumulating experimental and clinical evidence indicate that BBB dysfunctions are associated with a number of serious CNS diseases with important social impacts, such as multiple sclerosis, stroke, brain tumors, epilepsy or Alzheimer's disease. This review will focus on the implication of brain endothelial tight junctions in BBB architecture and physiology, will discuss the consequences of BBB dysfunction in these CNS diseases and will present some therapeutic strategies for drug delivery to the brain across the BBB.     

A New Brain Drug Delivery Strategy: Focused Ultrasound-Enhanced Intranasal Drug Delivery

Central nervous system (CNS) diseases are difficult to treat because of the blood-brain barrier (BBB), which prevents most drugs from entering into the brain. Intranasal (IN) administration is a promising approach for drug delivery to the brain, bypassing the BBB; however, its application has been restricted to particularly potent substances and it does not offer localized delivery to specific brain sites. Focused ultrasound (FUS) in combination with microbubbles can deliver drugs to the brain at targeted locations. The present study proposed to combine these two different platform techniques (FUS+IN) for enhancing the delivery efficiency of intranasally administered drugs at a targeted location. After IN administration of 40 kDa fluorescently-labeled dextran as the model drug, FUS targeted at one region within the caudate putamen of mouse brains was applied in the presence of systemically administered microbubbles. To compare with the conventional FUS technique, in which intravenous (IV) drug injection is employed, FUS was also applied after IV injection of the same amount of dextran in another group of mice. Dextran delivery outcomes were evaluated using fluorescence imaging of brain slices. The results showed that FUS+IN enhanced drug delivery within the targeted region compared with that achieved by IN only. Despite the fact that the IN route has limited drug absorption across the nasal mucosa, the delivery efficiency of FUS+IN was not significantly different from that of FUS+IV. As a new drug delivery platform, the FUS+IN technique is potentially useful for treating CNS diseases.     

血脑屏障与脑血管疾病的相关研究

血脑屏障（blood brain barrier,BBB）的主要结构包括：脑毛细血管内皮细胞及其间的紧密连接（tight junction,TJ）、基底膜、基 底膜下星型胶质细胞终足。血脑屏障是存在于血液和脑组织之间的一层屏障系统,在许多大脑疾患的病理过程中,BBB 的破坏导 致通透性增高都是不可避免的一个环节。BBB是保证中枢神经系统的正常生理功能的重要屏障系统。目前已有大量关于血脑屏 障通透性在脑血管疾病中的变化研究。本文分别从血脑屏障的结构和功能,药物通过血脑屏障的方法和功能,脑缺血损伤、阿尔 茨海默病、帕金森病和多发性硬化症等不同的脑病变与血脑屏障通透性的变化及中医药应用等方面做一综述。有针对性地对 BBB和大脑疾病进行进一步的研究与探索,将会为临床治疗相关疾病带来新的视角与机遇。     

聚乳酸纳米粒穿透血脑屏障的分析电镜研究

观察以聚乳酸 (D ,L-polylacticacid,PLA)为材料制备、经吐温-80(T-80)表面改性的纳米粒对血脑屏障的穿透效果并探讨其机制 ,分别将FITC-Dextran、叶绿素铜作为PLA纳米粒的示踪标记 ,应用荧光显微镜、透射电镜及分析电镜观察经静脉注射入小鼠体内的PLA纳米粒在脑组织中的分布、穿透血脑屏障的特性。荧光显微镜观察到小鼠脑组织中散在及沿毛细血管壁分布的荧光颗粒 ,透射电镜可观察到小鼠脑毛细血管内皮细胞及周围脑组织中圆形或类圆形的外源性纳米粒 ;进一步采用分析电镜对颗粒处组织进行能谱分析证实其为叶绿素铜标记的PLA纳米粒。证实了T-80修饰的PLA纳米粒具有穿透血脑屏障的特性 ,机制可能是毛细血管内皮细胞的胞吞转运作用 ,同时 ,为研究纳米粒在组织内的定位提供了新的标记方法.     

Strategies to overcome the barrier: use of nanoparticles as carriers and modulators of barrier properties

The blood–brain barrier (BBB) protects the brain from toxic substances within the bloodstream and keeps the brain’s homeostasis stable. On the other hand, it also represents the main obstacle in the treatment of many CNS diseases. Among different techniques, nanoparticles have emerged as promising tools to enhance brain drug delivery of therapeutic molecules. For successful drug delivery, nanoparticles may either modulate BBB integrity or exploit transport systems present on the endothelium. In this review, we present two different nanoparticles to enhance brain drug delivery. Poly(butyl cyanoacrylate) nanoparticles were shown to induce a reversible disruption of the BBB in vitro which may be exploited by simultaneous injection of the drug in question. By coating the poly(butyl cyanoacrylate) nanoparticles with, e.g., ApoE, it is also possible to circumvent the BBB via the LDL-receptor. Another example of the use of receptor-mediated endocytosis to enhance brain uptake of nanoparticles are poly(ethylene glycol)-coated Fe3O4 nanoparticles which are covalently attached to lactoferrin. These nanoparticles have been shown to facilitate the transport via the lactoferrin receptor, and so could then be used for magnetic resonance imaging.     

Sobetirome prodrug esters with enhanced blood–brain barrier permeability

There is currently great interest in developing drugs that stimulate myelin repair for use in demyelinating diseases such as multiple sclerosis. Thyroid hormone plays a key role in stimulating myelination during development and also controls the expression of important genes involved in myelin repair in adults. Because endogenous thyroid hormone in excess lacks a generally useful therapeutic index, it is not used clinically for indications other than hormone replacement; however, selective thyromimetics such as sobetirome offer a therapeutic alternative. Sobetirome is the only clinical-stage thyromimetic that is known to cross the blood–brain-barrier (BBB) and we endeavored to increase the BBB permeability of sobetirome using a prodrug strategy. Ester prodrugs of sobetirome were prepared based on literature reports of improved BBB permeability with other carboxylic acid containing drugs and BBB permeability was assessed in vivo. One sobetirome prodrug, ethanolamine ester 11, was found to distribute more sobetirome to the brain compared to an equimolar peripheral dose of unmodified sobetirome. In addition to enhanced brain levels, prodrug 11 displayed lower sobetirome blood levels and a brain/serum ratio that was larger than that of unmodified sobetirome. Thus, these data indicate that an ester prodrug strategy applied to sobetirome can deliver increased concentrations of the active drug to the central nervous system (CNS), which may prove useful in the treatment of CNS disorders.     

Alteration of blood-brain barrier function by methamphetamine and cocaine

The integrity of the blood-brain barrier (BBB) plays an important role in maintaining a safe neural microenvironment in the brain. Loss of BBB integrity has been recognized as a major cause of profound brain alterations. Psychoactive drugs such as methamphetamine (METH) or cocaine are well-known drugs of abuse that can alter the permeability of the BBB via various mechanisms. In addition, the neurotoxicity of METH is well documented, and alterations in BBB function can contribute to this toxicity. A great deal of effort has been devoted to understanding the cellular and molecular mechanisms of the action of these drugs in the central nervous system. However, only a few investigations have focused on the effects of METH and cocaine on BBB function. The aim of this short review is to summarize our present knowledge of this subject.     

Mouse models of neurological disorders: A view from the blood–brain barrier

The number of disease models that involve an aspect of blood–brain barrier (BBB) dysregulation have increased tremendously. The main factors contributing to this expansion have been an increased number of diseases in which the BBB is known to be involved, an increase in the known functions of the BBB, and an increase in the number of models and tools with which those diverse functions can be studied. In many cases, the BBB may be a target of disease; current thinking would include hypertensive encephalopathy and perhaps stroke in this category. Another category are those diseases in which special attributes of the BBB may predispose to disease; for example, the ability of a pathogen to cross the BBB often depends on the pathogen's ability to invoke transcytotic pathways in the brain endothelial or choroid plexus cell. Of special interest are those diseases in which the BBB may be the primary seat of disease or play a major role in the onset or progression of the disease. An increasing number of diseases are so categorized in which BBB dysfunction or dysregulation plays a major role; this review highlights such roles for the BBB including those proposed for Alzheimer's disease and obesity.     

Bioengineered microfluidic blood-brain barrier models in oncology research

Metastasis is the major reason for most brain tumors with up to a 50% chance of occurrence in patients with other types of malignancies. Brain metastasis occurs if cancer cells succeed to cross the ‘blood-brain barrier’ (BBB). Moreover, changes in the structure and function of BBB can lead to the onset and progression of diseases including neurological disorders and brain-metastases. Generating BBB models with structural and functional features of intact BBB is highly important to better understand the molecular mechanism of such ailments and finding novel therapeutic agents targeting them. Hence, researchers are developing novel in vitro BBB platforms that can recapitulate the structural and functional characteristics of BBB. Brain endothelial cells-based in vitro BBB models have thus been developed to investigate the mechanism of brain metastasis through BBB and facilitate the testing of brain targeted anticancer drugs. Bioengineered constructs integrated with microfluidic platforms are vital tools for recapitulating the features of BBB in vitro closely as possible. In this review, we outline the fundamentals of BBB biology, recent developments in the microfluidic BBB platforms, and provide a concise discussion of diverse types of bioengineered BBB models with an emphasis on the application of them in brain metastasis and cancer research in general. We also provide insights into the challenges and prospects of the current bioengineered microfluidic platforms in cancer research.     

Cyclodextrins promote protein aggregation posing risks for therapeutic applications

The presence of neurofibrillary tangles (NFTs) is a hallmark feature of various neurodegenerative disorders including Alzheimer’s (AD) and Niemann-Pick type C (NPC) diseases. NFTs have been correlated with elevated cholesterol levels and a cholesterol-scavenging compound, cyclodextrin, effectively modulates and traffics cholesterol from cell bodies in NPC disease models. Cyclodextrins are also used as drug carriers to the blood-brain barrier (BBB) and other tissues. While cyclodextrins have potential value in treating brain diseases, it is important to determine how cyclodextrins affect natively unfolded proteins such as beta-amyloid (Aβ) whose aggregation has been correlated with AD. We show that cyclodextrins drastically alter Aβ aggregation kinetics and induce morphological changes to Aβ that can enhance toxicity towards SH-SY5Y human neuroblastoma cells. These results suggest that care must be taken when using cyclodextrins for BBB delivery or for treatment of brain disease because cyclodextrins can promote toxic aggregation of Aβ.     

Targeted Brain Derived Neurotropic Factors (BDNF) Delivery across the Blood-Brain Barrier for Neuro-Protection Using Magnetic Nano Carriers: An In-Vitro Study

Parenteral use of drugs; such as opiates exert immunomodulatory effects and serve as a cofactor in the progression of HIV-1 infection, thereby potentiating HIV related neurotoxicity ultimately leading to progression of NeuroAIDS. Morphine exposure is known to induce apoptosis, down regulate cAMP response element-binding (CREB) expression and decrease in dendritic branching and spine density in cultured cells. Use of neuroprotective agent; brain derived neurotropic factor (BDNF), which protects neurons against these effects, could be of therapeutic benefit in the treatment of opiate addiction. Previous studies have shown that BDNF was not transported through the blood brain barrier (BBB) in-vivo.; and hence it is not effective in-vivo. Therefore development of a drug delivery system that can cross BBB may have significant therapeutic advantage. In the present study, we hypothesized that magnetically guided nanocarrier may provide a viable approach for targeting BDNF across the BBB. We developed a magnetic nanoparticle (MNP) based carrier bound to BDNF and evaluated its efficacy and ability to transmigrate across the BBB using an in-vitro BBB model. The end point determinations of BDNF that crossed BBB were apoptosis, CREB expression and dendritic spine density measurement. We found that transmigrated BDNF was effective in suppressing the morphine induced apoptosis, inducing CREB expression and restoring the spine density. Our results suggest that the developed nanocarrier will provide a potential therapeutic approach to treat opiate addiction, protect neurotoxicity and synaptic density degeneration.     

The role of peptides in blood-brain barrier nanotechnology.

The blood-brain barrier (BBB) regulates the passage of molecules between the bloodstream and the brain. Overcoming the difficulty of delivery drugs to specific areas of the brain is a major challenge. The BBB exerts a neuroprotective function as it hinders the delivery of diagnostic and therapeutic agents to the brain. Here, we provide an overview of the way in which peptides and nanotechnology are being exploited in tandem to address this problem. Peptides can be used as specialised coatings able to transport nanoparticles with specific properties, such as targeting. The nanoparticle can also carry a peptide drug. Furthermore, peptides can be used in less conventional approaches such as all-peptide nanoparticles. In summary, the combined use of peptides and nanotechnology offers tremendous hope in the treatment of brain disorders.     

Effects of oxysterols on the blood–brain barrier: Implications for Alzheimer’s disease

Altered brain cholesterol homeostasis plays a key role in neurodegenerative diseases such as Alzheimer’s disease (AD). For a long time, the blood–brain barrier (BBB) was basically considered as a barrier isolating the brain from circulating cholesterol, however, several lines of evidence now suggest that the BBB strictly regulates the exchanges of sterol between the brain and the peripheral circulation. Oxysterols, synthesized by neurons or by peripheral cells, cross the BBB easily and modulate the expression of several enzymes, receptors and transporters which are involved not only in cholesterol metabolism but also in other brain functions. This review article deals with the way oxysterols impact BBB cells. These perspectives open new routes for designing certain therapeutical approaches that target the BBB so that the onset and/or progression of brain diseases such as AD may be modulated.     

Blood-brain barrier-on-a-chip for brain disease modeling and drug testing

The blood-brain barrier (BBB) is an interface between cerebral blood and the brain parenchyma. As a gate keeper, BBB regulates passage of nutrients and exogeneous compounds. Owing to this highly selective barrier, many drugs targeting brain diseases are not likely to pass through the BBB. Thus, a large amount of time and cost have been paid for the development of BBB targeted therapeutics. However, many drugs validated in in vitro models and animal models have failed in clinical trials primarily due to the lack of an appropriate BBB model. Human BBB has a unique cellular architecture. Different physiologies between human and animal BBB hinder the prediction of drug responses. Therefore, a more physiologically relevant alternative BBB model needs to be developed. In this review, we summarize major features of human BBB and current BBB models and describe organ-on-chip models for BBB modeling and their applications in neurological complications.     

Potential of biopartitioning micellar chromatography as an in vitro technique for predicting drug penetration across the blood-brain barrier

The blood-brain barrier (BBB) is considered to be the main barrier to drug transport into the central nervous system (CNS). The BBB restricts the passive diffusion of many drugs from blood to brain. The ease with which any particular drug diffuses across the BBB is determined largely by the molecular features of drugs, and it is therefore possible to predict the BBB permeability of a drug from its molecular structure. Biopartitioning micellar chromatography (BMC), a mode of micellar liquid chromatography that uses micellar mobile phases of Brij35 in adequate experimental conditions, can be useful in mimicking the drug partitioning process into biological systems. Retention in BMC depends on the hydrophobicity, electronic and steric properties of drugs. In this paper, the usefulness of BMC for predicting the BBB penetration ability of drugs expressed as the brain/blood distribution coefficient (BB) is demonstrated. A multiple linear regression (MLR) model that relates the BB distribution coefficients data with BMC retention data and total molar charge is proposed. The model is obtained using 44 heterogeneous drugs including, neutral, anionic, and cationic compounds. A comparison with other reported methodologies to predict the BBB permeability is also presented.     

A novel LRP1-binding peptide L57 that crosses the blood brain barrier

The blood-brain barrier (BBB) is a major obstacle to drug delivery into the central nervous system (CNS), in particular for macromolecules such as peptides and proteins. However, certain macromolecules can reach the CNS via a receptor-mediated transcytosis (RMT) pathway, and low-density lipoprotein receptor-related protein 1 (LRP1) is one of the promising receptors for RMT. An LRP1 ligand peptide, Angiopep-2, was reported to pass through the BBB and deliver covalently conjugated drugs into the CNS. While conjugation of LRP1 ligands with drugs would be an effective approach for drug delivery to the CNS, no other reliable LRP1 ligands have been reported to date. In this study, we aimed to identify novel LRP1 ligands to further investigate LRP1-mediated RMT. Using phage display technology, we obtained a novel peptide, L57 (TWPKHFDKHTFYSILKLGKH-OH), with an EC₅₀ value of 45 nM for binding to cluster 4 (Ser3332–Asp3779) of LRP1. L57 was stable in mouse plasma for up to 20 min. In situ brain perfusion assay in mice revealed the significantly high BBB permeability of L57. In conclusion, we discovered L57, the first artificial LRP1-binding peptide with BBB permeability. Our findings will contribute to the development of RMT-based drugs for the treatment of CNS diseases.     

In Search of the Astrocytic Factor(s) Modulating Blood–Brain Barrier Functions in Brain Capillary Endothelial Cells In Vitro

Summary 1. The blood–brain barrier (BBB) is formed by brain capillary endothelial cells (ECs). There are various cell types, in particular astrocytes, but also pericytes and neurons, located in close vicinity to the capillary ECs which may influence formation and function of the BBB. Based on this consideration, this paper discusses various aspects of the influence of the surrounding cells on brain capillary ECs with special focus on the role of astrocytes.2. Based on the morphology of the BBB, important aspects of brain EC functions are summarized, such as transport functions and maintenance of low paracellular permeability. Moreover, various facets are discussed with respect to the influence of astrocytes, pericytes, microglia, and neurons on the BBB. Data on the role of glial cells in the ontogenesis of the BBB are presented subsequently. The knowledge on this subject is far from being complete, however, these data imply that the neural/neuronal environment rather than glial cells may be of importance in the maturation of the barrier.3. The role of glial cells in the induction and maintenance of the BBB is discussed under physiological as well as pathological conditions. Although the literature presents manifold evidence for a great variety of effects induced by astroglia, there are also many controversies, which may result from different cellular models and experimental conditions used in the respective studies. Numerous factors secreted by astrocytes have been shown to induce a BBB phenotype. On the molecular level, increased expression of barrier-relevant proteins (e.g., tight junction proteins) is documented in the presence of astrocyte-derived factors, and many studies demonstrate the improvement of physiological parameters, such as increased transendothelial resistance and decreased paracellular permeability, in different in vitro models of the BBB. Moreover, one has to take into account that the interaction of brain ECs and astrocytes is bi-directional, and that the other cell types surrounding the brain microvasculature also contribute to BBB function or dysfunction, respectively.4. In conclusion, it is expected that the present and future research focused on molecular mechanisms and signaling pathways will produce new and exciting insights into the complex network of BBB regulation: the cornerstone is laid.This revised article was published online in May 2005 with a February 2005 cover date.     

Control of the blood–brain barrier function in cancer cell metastasis

Cerebral metastases are the most common brain neoplasms seen clinically in the adults and comprise more than half of all brain tumours. Actual treatment options for brain metastases that include surgical resection, radiotherapy and chemotherapy are rarely curative, although palliative treatment improves survival and life quality of patients carrying brain‐metastatic tumours. Chemotherapy in particular has also shown limited or no activity in brain metastasis of most tumour types. Many chemotherapeutic agents used systemically do not cross the blood–brain barrier (BBB), whereas others may transiently weaken the BBB and allow extravasation of tumour cells from the circulation into the brain parenchyma. Increasing evidence points out that the interaction between the BBB and tumour cells plays a key role for implantation and growth of brain metastases in the central nervous system. The BBB, as the tightest endothelial barrier, prevents both early detection and treatment by creating a privileged microenvironment. Therefore, as observed in several in vivo studies, precise targetting the BBB by a specific transient opening of the structure making it permeable for therapeutic compounds, might potentially help to overcome this difficult clinical problem. Moreover, a better understanding of the molecular features of the BBB, its interrelation with metastatic tumour cells and the elucidation of cellular mechanisms responsible for establishing cerebral metastasis must be clearly outlined in order to promote treatment modalities that particularly involve chemotherapy. This in turn would substantially expand the survival and quality of life of patients with brain metastasis, and potentially increase the remission rate. Therefore, the focus of this review is to summarise the current knowledge on the role and function of the BBB in cancer metastasis.