P-糖蛋白在神经退行性疾病中的作用

神经退行性疾病( neurodegenerative disease)是一种以神经元退行性病变为基础的慢性进行性神经系统疾病,发病机制尚不明了,但一些内源性和外源性物质在脑部的异常聚集和沉积与其病因密切相关,且其往往是P糖蛋白的底物.近年来研究表明血脑屏障的p-糖蛋白在一些神经退行性疾病发展过程中表达会减少,这可能导致致病性内外源性物质的进一步聚集和沉积,恶化病情.本文对近年来有关P-糖蛋白在神经退行性疾病的发病和病情进展中的作用作一综述.     

Blood-brain barrier delivery

Neuropharmaceutics is the largest potential growth sector of the pharmaceutical industry. However, this growth is blocked by the problem of the blood-brain barrier (BBB). Essentially 100% of large-molecule drugs and >98% of small-molecule drugs do not cross the BBB. The BBB can be traversed because there are multiple endogenous transporters within this barrier. Therefore, brain drug development programs of the future need to be re-configured so that drugs are formulated to enable transport into the brain via endogenous BBB transporters.     

Blood-brain barrier efflux transport

Efflux transport at the blood-brain barrier (BBB) limits the brain tissue exposure to a variety of potential therapeutic agents, including compounds that are relatively lipophilic and would be predicted to permeate the endothelial lining of the brain microvasculature. Recent advances in molecular and cell biology have led to identification of several specific transport systems at the blood-brain interface. Refinement of classical pharmacokinetic experimentation has allowed assessment of the structural specificity of transporters, the impact of efflux transport on brain tissue exposure, and the potential for drug-drug interactions at the level of BBB efflux transport. The objective of this minireview is to summarize efflux transporter characteristics (location, specificity, and potential inhibition) for transport systems identified in the BBB. A variety of experimental approaches available to ascertain or predict the impact of efflux transport on net brain tissue uptake of substrates also are presented. The potential impact of efflux transport on the pharmacodynamics of agents acting in the central nervous system are illustrated. Finally, general issues regarding the role of identifying efflux transport as part of the drug development process are discussed.     

Blood-brain barrier interfaces and brain tumors

In the developing brain, capillaries are differentiated and matured into the blood-brain barrier (BBB), which is composed of cerebral endothelial cells, astrocyte end-feet, and pericytes. Since the BBB regulates the homeostasis of central nervous system (CNS), the maintenance of the BBB is important for CNS function. The disruption of the BBB may result in many brain disorders including brain tumors. However, the molecular mechanism of BBB formation and maintenance is poorly understood. Here, we summarize recent advances in the role of oxygen tension and growth factors on BBB development and maintenance, and in BBB dysfunction related with brain tumors.     

Blood-brain barrier transport of opioid analgesics

Opioid analgesics exhibit cationic properties under physiological conditions, and the mechanism underlying permeation of the blood-brain barrier thus cannot be fully explained by simple diffusion alone. Various types of transporters that exhibit substrate specificity are localized on the blood-brain barrier, and play a role in transporting substances from circulating blood and from brain interstitial fluid. Progress is being made in explaining the mechanisms, functions, and physiological roles of polyspecific organic cation transporters, but little evidence has indicated that these previously identified organic cation transporters are involved in the transport of opioid analgesics across the blood-brain barrier. Consequently, clarifying the role of transporters in the distribution of opioid analgesics into the brain and determining their transport molecule will not only provide clues to effective drug delivery to the brain, but will also contribute to optimizing pain relief treatment, and by extension play a role in drug discovery for analgesics. Currently there are enthusiastic discussions in the literature regarding the existence of putative transporters involved in the transport of opioid analgesics across the blood-brain barrier. This review article introduces the results of our research as well as recent findings on the involvement of transporters in the blood-brain barrier transport of opioid analgesics such as morphine, morphine metabolites, oxycodone, fentanyl, codeine, and pentazocine.     

Blood-brain barrier permeability and tPA-mediated neurotoxicity

Tissue type plasminogen activator (tPA) can induce neuronal apoptosis, disrupt the blood-brain barrier (BBB), and promote dilation of the cerebral vasculature. The timing, sequence and contributions of these and other deleterious effects of tPA and their contribution to post-ischemic brain damage after stroke, have not been fully elucidated. To dissociate the effects of tPA on BBB permeability, cerebral vasodilation and protease-dependent pathways, we developed several tPA mutants and PAI-1 derived peptides constructed by computerized homology modeling of tPA. Our data show that intravenous administration of human tPA to rats increases BBB permeability through a non-catalytic process that is associated with reversible neurotoxicity, brain damage, mortality and contributes significantly to its brief therapeutic window. Furthermore, our data show that inhibiting the effect of tPA on BBB function without affecting its catalytic activity, improves outcome and significantly extends its therapeutic window in mechanical as well as in thromboembolic models of stroke.     

Blood-brain barrier permeability to small and large molecules

The objective of this article is to provide the reader with an update of some of the BBB research highlights which have occurred in recent times, and to review the impact and contributions of immunogold electron microscopic studies on our understanding of the brain capillary endothelium. Glucose and monocarboxylic acids are two small molecules which this review will focus upon; and advances in immunogold characterization of the GLUT1 glucose transporter and the MCT1 and MCT2 monocarboxylic acid nutrient transporters will be discussed. Human serum albumin is chosen as a representative large molecule, and it has recently been shown that immunogold identification of this protein can serve as an indicator of compromised BBB function in a variety of pathophysiological conditions.     

The barrier function of CYP3A4 and P-glycoprotein in the small bowel

CYP3A4 present in small bowel enterocytes can catalyze substantial metabolism of some orally administered drugs and, thus, exerts a first-pass effect. Recent data indicate that the P-glycoprotein (the MDR 1 gene product) in the enterocyte brush border also limits the bioavailability of many of the same drugs that interact with CYP3A. It has been proposed that P-glycoprotein and CYP3A4 may be functionally linked because (a) the two proteins are co-localized within the digestive tract and within enterocytes, (b) they share many of the same substrates and (c) they are co-inducible in response to at least some xenobiotics. There are several potential mechanisms whereby the functions of P-glycoprotein and CYP3A4 could be complimentary. First, Pgp may limit absorption in the proximal small bowel, shifting it to more distal, less catalytically efficient segments that contain lower amounts of CYP3A4. Second, Pgp may function to prolong the duration of absorption. This might increase the duration of exposure of drug to and, hence, the extent of metabolism by enterocyte CYP3A4. Finally, Pgp may preferentially remove from the enterocyte primary drug metabolites that are themselves substrates for CYP3A4. This would limit product inhibition and facilitate primary metabolism catalyzed by CYP3A4. Characterization of the roles of CYP3A4 and Pgp in limiting oral drug availability may be aided by recent success in the development of human intestinal cell lines that stably express both CYP3A4 and Pgp.     

Effect of endotoxin on doxorubicin transport across blood-brain barrier and P-glycoprotein function in mice

The aim of this study was to investigate whether Klebsiella pneumoniae endotoxin modifies transport of doxorubicin, a P-glycoprotein substrate, across the blood-brain barrier and P-glycoprotein function in mice. Doxorubicin (30 mg/kg) was administered into the tail vein or fluorescein isothiocyanate-labeled dextran (FD-4) was infused (20 microg/min) into the right jugular vein of mice intravenously injected with endotoxin (10 mg/kg) 6 or 24 h earlier. Blood and brain samples were collected 4 h after injection of doxorubicin or 1 h after infusion of FD-4. We examined using Western blotting the influence of endotoxin on the expression of P-glycoprotein in brains obtained 6, 12 and 24 h after injection. Endotoxin did not change the plasma and brain concentrations and brain-to-plasma concentration ratio (K(p) value) of FD-4. No histopathological changes in brain capillaries were observed. These results suggest that endotoxin does not cause damage to brain capillaries. Plasma and brain concentrations of doxorubicin in mice treated 6 h earlier with endotoxin were significantly higher than those in control and mice treated 24 h earlier. However, endotoxin did not significantly change the K(p) value of doxorubicin. The protein level of P-glycoprotein was significantly, but slightly down-regulated 6 h after endotoxin treatment. However, the levels remained almost unchanged after 12 and 24 h. The present results suggest that Klebsiella pneumoniae endotoxin has no effect on the brain capillary integrity and doxorubicin transport across the blood-brain barrier in mice. It is likely that P-glycoprotein function might be sufficient to transport doxorubicin in spite of decreased levels of P-glycoprotein in the brain.     

载药纳米粒透过血脑屏障机制的研究进展

血脑屏障是维持中枢神经系统内环境稳定的结构基础,有效保护脑组织避免外源性有害物质侵害,但也阻碍许多治疗药物进入脑内,限制了中枢神经系统药物的临床应用。如何有效透过血脑屏障成为此类药物发挥治疗作用的关键环节。纳米粒作为一种新型药物载体,能携载药物透过血脑屏障进入脑组织,提高脑内药物浓度,实现脑内靶向给药。本文对载药纳米粒及其透过血脑屏障机制的研究进展作一综述。     

Blood-brain barrier drug discovery for central nervous system infections

Central nervous system (CNS) infections are formidable diseases with high rates of morbidity and mortality. Since the majority of antimicrobial agents discovered so far do not cross the blood-brain barrier (BBB), the treatment of CNS infections is a major challenge issue. The development of drugs to treat those diseases requires consideration of achievable brain concentrations by targeting the following question. How can the chemistry and biology of the BBB, and infectomics be exploited for the development of drugs against CNS infections? To date drug targeting approaches, such as chemistry-based, biology-based, and infectomics-based, have been implicated in the development of drugs for treatment of CNS infections. The chemistry-based strategies rely on lipid-mediated BBB drug transport as substances that readily permeate the BBB. These usually include small molecular weight of lipophilic or hydrophobic molecules. The biology-based strategies depend on endogenous BBB transport systems, including carrier-mediated transport (CMT), active efflux transport (AET), and receptor-mediated transport (RMT). These transporters play important roles in the influxes and/or effluxes of drugs including antimicrobial agents in brain capillary endothelial cells that form the BBB. Both microbial and host signatures of infectomes, which can be dissected by infectomics, provide invaluable fountains in the search for novel antimicrobial therapies. Key markers associated with the mechanisms of neuronal injury may be identified, and thus, provide important targets for the prevention and treatment of CNS infections. This review focuses on the major BBB drug targeting strategies in the development of therapeutics for CNS infections. A combination of these strategies will ultimately lead to improved treatments.     

Insulin therapy restores impaired function and expression of P-glycoprotein in blood-brain barrier of experimental diabetes

We aimed to investigate effects of insulin on function and expression of P-glycoprotein (P-GP) in the blood-brain barrier of streptozotocin (STZ)-induced diabetic rats. Brain-to-plasma concentration ratio of vincristine (VCR) in rats was used as an indicator of in vivo function of P-GP. Western blot and quantitative real time-polymerase chain reaction were used to determine protein levels of P-GP and its mdr1a/mdr1b mRNA levels, respectively, in cerebral cortex of rats. In vitro effects of insulin on function and expression of P-GP in primarily cultured rat brain microvessel endothelial cells (rBMECs) were evaluated using rhodamine 123 (Rho123) uptakes and Western blot, respectively. The results showed that 3- and 5-week insulin treatment alleviated the impaired efflux function, expression and mdr1a/mdr1b mRNA levels of P-GP in cerebral cortex of diabetic rats. The 3- and 5-week insulin treatments also significantly enhanced P-GP levels and mdr1a/mdr1b mRNA levels in the cerebral cortex of normal rats. Addition of insulin to the insulin-deficient diabetic rat serum normalized the impaired function and expression of P-GP in rBMECs cultured in diabetic rat serum. When incubated with normal culture medium containing different levels of insulin, the rBMECs exhibited the enhanced P-GP levels and the reduced Rho123 uptake in a concentration-dependent manner. So we may conclude that appropriate level of insulin plays an important role in maintaining the normal function of BBB through regulating the function and expression of P-GP in the diabetic and normal rats.     

血脑屏障上的P-糖蛋白与精神类药物

P-糖蛋白(P-gp)是ABC超家族的重要成员,而许多精神药物包括抗精神分裂症药物和抗抑郁症药物,都是P-gp的底物。本文对近年来国内外有关P-gp对精神药物限制进入血脑屏障的相关研究,进行了综述。     

Blood-brain barrier transport of morphine in patients with severe brain trauma

AIMS: In experimental studies, morphine pharmacokinetics is different in the brain compared with other tissues due to the properties of the blood-brain barrier, including action of efflux pumps. It was hypothesized in this clinical study that active efflux of morphine occurs also in human brain, and that brain injury would alter cerebral morphine pharmacokinetics. METHODS: Patients with traumatic brain injury, equipped with one to three microdialysis catheters in the brain and one in abdominal subcutaneous fat for metabolic monitoring, were studied. The cerebral catheter locations were classified as 'better' and 'worse' brain tissue, referring to the degree of injury. Morphine (10 mg) was infused intravenously over a 10-min period in seven patients in the intensive care setting. Tissue and plasma morphine concentrations were obtained during the subsequent 3-h period with microdialysis and regular blood sampling. RESULTS: The area under the concentration-time curve (AUC) ratio of unbound morphine in brain tissue to plasma was 0.64 (95% confidence interval 0.40, 0.87) in 'better' brain tissue (P < 0.05 vs. the subcutaneous fat/plasma ratio), 0.78 (0.49, 1.07) in 'worse' brain tissue and 1.00 (0.86, 1.13) in subcutaneous fat. The terminal half-life and T(max) were longer in the brain vs. plasma and fat, respectively. The relative recovery for morphine was higher in 'better' than in 'worse' brain tissue. The T(max) value tended to be shorter in 'worse' brain tissue. CONCLUSIONS: The unbound AUC ratio below unity in the 'better' human brain tissue demonstrates an active efflux of morphine across the blood-brain barrier. The 'worse' brain tissue shows a decrease in relative recovery for morphine and in some cases also an increase in permeability for morphine over the blood-brain barrier.     

Blood-brain barrier transport of cytokines: a mechanism for neuropathology

Cytokines circulating in the blood affect CNS function through a variety of pathways. One of these pathways is by being transported directly across the blood-brain barrier (BBB). Transport of blood-borne cytokines across the BBB is now known to be an operational pathway by which cytokines can directly affect CNS functions. Cytokine transport across the BBB, however, is a complex event. Not all cytokines are transported and, for those which are, transport rates differ among cytokines, among brain regions, with physiological circumstances, and with disease. Here we address some of the major principles and concepts relating to cytokine transport and BBB function which have emerged as important to neuroimmunology and neuropathology.     

胰岛素抵抗大鼠血脑屏障上P-糖蛋白表达和转运功能的研究

目的:建立胰岛素抵抗大鼠模型,观察胰岛素抵抗大鼠血脑屏障(BBB)上P-糖蛋白(P-gp)的表达和转运功能.方法:采用高脂饲料喂养制备胰岛素抵抗大鼠模型,用口服葡萄糖耐量、胰岛素耐量和胰岛素敏感性指数评价大鼠胰岛素抵抗.用伊文思蓝检测BBB通透性,用透射电镜观察BBB的完整性,用Westem blot测定BBB上P-gp的蛋白水平,用RT-PCR技术检测BBB上mdrla/mdrlb的mRNA水平,用Rh123累积实验测定BBB上P-gp的转运功能.结果:用高脂饲料喂养大鼠6周后,葡萄糖耐量和胰岛素耐量明显异常,空腹胰岛素含量显著升高,胰岛素敏感性显著下降.胰岛素抵抗大鼠BBB上P-gp表达水平和转运功能显著下降,但BBB通透性和完整性未发生明显改变.结论:胰岛素抵抗下调BBB上P-gp表达和转运功能.     

Blood-brain barrier permeability during acute and chronic electroconvulsive seizures.

The effect of chronic electroconvulsive seizure on the blood brain barrier permeability to albumin was investigated in the male rats. Evans blue was used as a blood brain barrier tracer. The following situations were studied: Acute electroshock: a. one electroshock stimulus, b. ten electroshock stimuli. Chronic electroshock: a) group of animals were pretreated with electroshock given as one electroshock (ES) every other day (ES x 7); b) chronic electroshock + one electroshock, c) chronic electroshock + ten repeated electroshocks. As a result, chronic electroshock per se does not effect the blood-brain barrier permeability.