Cereport (RMP-7) increases the permeability of human brain microvascular endothelial cell monolayers

Inhibiting PI3K/Akt-Signaling Pathway Improves Neurobehavior Changes in Anti-NMDAR Encephalitis Mice by Ameliorating Blood-Brain Barrier Disruption and Neuronal Damage

The disruption of the blood-brain barrier (BBB) is hypothesized to be involved in the progression of anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis, but its mechanism is still unclear. Recently, the phosphatidylinositol 3-kinase (PI3K)/threonine kinase (Akt) pathway is involved in the regulation of the BBB in various diseases. This study is aimed to investigate the mechanism of BBB damage and neurobehavior changes in anti-NMDAR encephalitis mice. Female C57BL/6J mice were actively immunized to establish an anti-NMDAR encephalitis mouse model and evaluate the neurobehavior changes of mice. To study its potential mechanism, LY294002 (PI3K inhibitor, 8 mg/kg) and Recilisib (PI3K agonist, 10 mg/kg) were treated by intraperitoneal injection, respectively. Anti-NMDAR encephalitis mice showed neurological deficits, increased BBB permeability, open endothelial tight junctions (TJs), and decreased expression of TJ-related proteins zonula occludens (ZO)-1 and Claudin-5. However, administration of PI3K inhibitor significantly reduced the expression of p-PI3K and p-Akt, improved neurobehavior function, decreased BBB permeability, and upregulated the expressions of ZO-1 and Claudin-5. Furthermore, PI3K inhibition reversed the decline of NMDAR NR1 in the membranes of hippocampal neurons, which reduced the loss of neuron-specific nucleoprotein (NeuN) and microtubule-associated protein 2 (MAP2). In contrast, administration of the PI3K agonist Recilisib showed a tendency to exacerbate BBB breakdown and neurological deficits. Our results showed that the activation of PI3K/Akt, along with the changes in TJ-related proteins ZO-1 and Claudin-5, may be closely related to BBB damage and neurobehavior changes in anti-NMDAR encephalitis mice. PI3K inhibition attenuates BBB disruption and neuronal damage in mice, thereby improving neurobehavior.

Transient Opening of the Blood-Brain Barrier by Vasoactive Peptides to Increase CNS Drug Delivery: Reality Versus Wishful Thinking?

BACKGROUND

The blood-brain barrier inhibits the central nervous system penetration of 98% of small molecule drugs and virtually all biologic agents, which has limited progress in treating neurologic disease. Vasoactive peptides have been shown in animal studies to transiently disrupt the blood-brain barrier and regadenoson is currently being studied in humans to determine if it can improve drug delivery to the brain. However, many other vasoactive peptides could potentially be used for this purpose.

METHODS

We performed a review of the literature evaluating the physiologic effects of vasoactive peptides on the vasculature of the brain and systemic organs. To assess the likelihood that a vasoactive peptide might transiently disrupt the blood-brain barrier, we devised a four-tier classification system to organize the available evidence.

RESULTS

We identified 32 vasoactive peptides with potential blood-brain barrier permeabilityaltering properties. To date, none of these are shown to open the blood-brain barrier in humans. Twelve vasoactive peptides increased blood-brain barrier permeability in rodents. The remaining 20 had favorable physiologic effects on blood vessels but lacked specific information on permeability changes to the blood-brain barrier.

CONCLUSION

Vasoactive peptides remain an understudied class of drugs with the potential to increase drug delivery and improve treatment in patients with brain tumors and other neurologic diseases. Dozens of vasoactive peptides have yet to be formally evaluated for this important clinical effect. This narrative review summarizes the available data on vasoactive peptides, highlighting agents that deserve further in vitro and in vivo investigations.

Adult precision medicine: learning from the past to enhance the future

Despite therapeutic advances for other malignancies, gliomas remain challenging solid tumors to treat. Complete surgical resection is nearly impossible due to gliomas’ diffuse infiltrative nature, and treatment is hampered by restricted access to the tumors due to limited transport across the blood–brain barrier. Recent advances in genomic studies and next-generation sequencing techniques have led to a better understanding of gliomas and identification of potential aberrant signaling pathways. Targeting the specific genomic abnormalities via novel molecular therapies has opened a new avenue in the management of gliomas, with encouraging results in preclinical studies and early clinical trials. However, molecular characterization of gliomas revealed significant heterogeneity, which poses a challenge for targeted therapeutic approaches. In this context, leading neuro-oncology researchers and clinicians, industry innovators, and patient advocates convened at the inaugural annual Remission Summit held in Orlando, FL in February 2019 to discuss the latest advances in immunotherapy and precision medicine approaches for the treatment of adult and pediatric brain tumors and outline the unanswered questions, challenges, and opportunities that lay ahead for advancing the duration and quality of life for patients with brain tumors. Here, we provide historical context for precision medicine in other cancers, present emerging approaches for gliomas, discuss their limitations, and outline the steps necessary for future success. We focus on the advances in small molecule targeted therapy, as the use of immunotherapy as an emerging precision medicine modality for glioma treatment has recently been reviewed by our colleagues.

Neurolysin substrates bradykinin, neurotensin and substance P enhance brain microvascular permeability in a human in vitro model

Increased brain microvascular permeability and disruption of blood-brain barrier (BBB) function are among hallmarks of several acute neurodegenerative disorders, including stroke. Numerous studies suggest the involvement of bradykinin (BK), neurotensin (NT) and substance P (SP) in BBB impairment and oedema formation after stroke; however, there is paucity of data in regard to the direct effects of these peptides on the brain microvascular endothelial cells (BMECs) and BBB. The present study aimed to evaluate the direct effects of BK, NT and SP on the permeability of BBB in an in vitro model based on human induced pluripotent stem cell (iPSC)-derived BMECs. Our data indicate that all three peptides increase BBB permeability in a concentration-dependent manner in an in vitro model formed from two different iPSC lines (CTR90F and CTR65M) and widely used hCMEC/D3 human BMECs. The combination of BK, NT and SP at a sub-effective concentration also resulted in increased BBB permeability in the iPSC-derived model indicating potentiation of their action. Furthermore, we observed abrogation of BK, NT and SP effects with pretreatment of pharmacological blockers targeting their specific receptors. Additional mechanistic studies indicate that the short-term effects of these peptides are not mediated through alteration of tight-junction proteins claudin-5 and occludin, but likely involve redistribution of F-actin and secretion of vascular endothelial growth factor. This is the first experimental study to document the increased permeability of the BBB in response to direct action of NT in an in vitro model. In addition, our study confirms the expected but not well-documented, direct effect of SP on BBB permeability and adds to the well-recognised actions of BK on BBB. Lastly, we demonstrate that peptidase neurolysin can neutralise the effects of these peptides on BBB, suggesting potential therapeutic implications.

Recent progress in translational engineered in vitro models of the central nervous system

The complexity of the human brain poses a substantial challenge for the development of models of the CNS. Current animal models lack many essential human characteristics (in addition to raising operational challenges and ethical concerns), and conventional in vitro models, in turn, are limited in their capacity to provide information regarding many functional and systemic responses. Indeed, these challenges may underlie the notoriously low success rates of CNS drug development efforts. During the past 5 years, there has been a leap in the complexity and functionality of in vitro systems of the CNS, which have the potential to overcome many of the limitations of traditional model systems. The availability of human-derived induced pluripotent stem cell technology has further increased the translational potential of these systems. Yet, the adoption of state-of-the-art in vitro platforms within the CNS research community is limited. This may be attributable to the high costs or the immaturity of the systems. Nevertheless, the costs of fabrication have decreased, and there are tremendous ongoing efforts to improve the quality of cell differentiation. Herein, we aim to raise awareness of the capabilities and accessibility of advanced in vitro CNS technologies. We provide an overview of some of the main recent developments (since 2015) in in vitro CNS models. In particular, we focus on engineered in vitro models based on cell culture systems combined with microfluidic platforms (e.g. 'organ-on-a-chip' systems). We delve into the fundamental principles underlying these systems and review several applications of these platforms for the study of the CNS in health and disease. Our discussion further addresses the challenges that hinder the implementation of advanced in vitro platforms in personalized medicine or in large-scale industrial settings, and outlines the existing differentiation protocols and industrial cell sources. We conclude by providing practical guidelines for laboratories that are considering adopting organ-on-a-chip technologies.

A Mechanistic Rationale for PDE-4 Inhibitors to Treat Residual Cognitive Deficits in Acquired Brain Injury

Patients with acquired brain injury (ABI) suffer from cognitive deficits that interfere significantly with their daily lives. These deficits are long-lasting and no treatment options are available. A better understanding of the mechanistic basis for these cognitive deficits is needed to develop novel treatments. Intracellular cyclic adenosine monophosphate (cAMP) levels are decreased in ABI. Herein, we focus on augmentation of cAMP by PDE4 inhibitors and the potentially synergistic mechanisms in traumatic brain injury. A major acute pathophysiological event in ABI is the breakdown of the blood-brain-barrier (BBB). Intracellular cAMP pathways are involved in the subsequent emergence of edema, inflammation and hyperexcitability. We propose that PDE4 inhibitors such as roflumilast can improve cognition by modulation of the activity in the cAMP-Phosphokinase A-Ras-related C3 botulinum toxin substrate (RAC1) inflammation pathway. In addition, PDE4 inhibitors can also directly enhance network plasticity and attenuate degenerative processes and cognitive dysfunction by increasing activity of the canonical cAMP/phosphokinase-A/cAMP Responsive Element Binding protein (cAMP/PKA/CREB) plasticity pathway. Doublecourtin and microtubule-associated protein 2 are generated following activation of the cAMP/PKA/CREB pathway and are decreased or even absent after injury. Both proteins are involved in neuronal plasticity and may consist of viable markers to track these processes. It is concluded that PDE4 inhibitors may consist of a novel class of drugs for the treatment of residual symptoms in ABI attenuating the pathophysiological consequences of a BBB breakdown by their anti-inflammatory actions via the cAMP/PKA/RAC1 pathway and by increasing synaptic plasticity via the cAMP/PKA/CREB pathway. Roflumilast improves cognition in young and elderly humans and would be an excellent candidate for a proof of concept study in ABI patients.

Peripheral white blood cell count as a screening tool for ventriculostomy-related infections

One of the most common complications following external ventricular drain (EVD) placement is infection. Routine cultures of cerebrospinal fluid (CSF) are often used to screen for infection, however several days may pass before infection is discovered. In this study, we compared the predictive value of daily recorded vital sign parameters and peripheral white blood count (WBC) in identifying ventriculostomy-related infections. Patients with EVDs who had CSF cultures for microorganisms performed between January 2011 and July 2017 were assigned to either an infected and/or uninfected study group. Clinical parameters were then compared using t-test, chi squared and multiple logistic regression analyses. Patients of any age and gender were included. One hundred seventy uninfected and 10 infected subjects were included in the study. Nine of the 10 infected patients had an elevated WBC (>10.4 × 10³/μL), with a significantly greater WBC (15.9 × 10³/μL) than the uninfected group (10.4 × 10³/μL) (p-value ≤ 0.0001). Using logistic regression, we found no association between patient vital signs and CSF infection except for WBC (p = .003). As a diagnostic marker for CSF infection, the sensitivity and specificity of WBC elevation greater than 15 × 10³/μL was 70% (7/10) and 90.2% (147/163), respectively. This study serves as a 'proof of concept' that WBC could be useful as potential screening tool for early detection of CSF infection post-EVD placement. Future investigation using a large, multicenter prospective study is needed to further assess the applicability of this parameter.

Characterisation of a mouse cerebral microvascular endothelial cell line (bEnd.3) after oxygen glucose deprivation and reoxygenation

Studies have utilised immortalised mouse cerebral endothelial cells (bEnd.3) exposed to oxygen glucose deprivation (OGD) to study blood-brain barrier (BBB) disruption after ischaemia. However, there is a paucity of literature describing the duration of OGD (and reoxygenation [RO]) required to best simulate BBB disruption in vivo. In this study we assessed BBB disruption in bEnd.3 cells after exposure to a range of OGD periods, and also after OGD + RO. Exposure of bEnd.3 monolayers to 4, 6, 16, or 24 hours of OGD resulted in a significant increase in permeability. The hyperpermeability after 16 or 24 hours was associated with decreased expression of tight junction proteins (occludin and claudin-5). Furthermore, there was a decrease in cell viability and increased expression of the pro-apoptotic protein, cleaved caspase-3. Exposure of bEnd.3 monolayers to 1 hour OGD+ 23 hours RO exacerbated hyperpermeability relative to 1 hour OGD, which was associated with decreased expression levels of occludin and ZO-1, but no change in cell viability or caspase-3. 4 hours OGD + 23 hours RO exacerbated hyperpermeability, decreased expression levels of tight junction proteins, decreased cell viability, and increased caspase-3 expression. Thus, bEnd.3 cells exhibit hyperpermeability, a loss of tight junction proteins, and undergo cell death, after exposure to prolonged periods of OGD. Moreover, they exhibit exacerbated hyperpermeability, a loss of tight junction proteins, and increased expression of caspase-3 after OGD + RO. These findings will facilitate the use of this cell line in studies of BBB disruption and for the testing of therapeutics.

dNP2 is a blood-brain barrier-permeable peptide enabling ctCTLA-4 protein delivery to ameliorate experimental autoimmune encephalomyelitis

Central nervous system (CNS)-infiltrating effector T cells play critical roles in the development and progression of multiple sclerosis (MS). However, current drugs for MS are very limited due to the difficulty of delivering drugs into the CNS. Here we identify a cell-permeable peptide, dNP2, which efficiently delivers proteins into mouse and human T cells, as well as various tissues. Moreover, it enters the brain tissue and resident cells through blood vessels by penetrating the tightly organized blood-brain barrier. The dNP2-conjugated cytoplasmic domain of cytotoxic T-lymphocyte antigen 4 (dNP2-ctCTLA-4) negatively regulates activated T cells and shows inhibitory effects on experimental autoimmune encephalomyelitis in both preventive and therapeutic mouse models, resulting in the reduction of demyelination and CNS-infiltrating T helper 1 and T helper 17 cells. Thus, this study demonstrates that dNP2 is a blood-brain barrier-permeable peptide and dNP2-ctCTLA-4 could be an effective agent for treating CNS inflammatory diseases such as MS.

Neuroprotection against degeneration of sk-N-mc cells using neuron growth factor-encapsulated liposomes with surface cereport and transferrin

Liposomes with Cereport (RMP-7) and transferrin (Tf) (RMP-7/Tf/liposomes) were employed to target the blood-brain barrier (BBB) and to inhibit the degeneration of neurons insulted with fibrillar β-amyloid peptide 1-42 (Aβ1-42). Neuron growth factor (NGF)-encapsulated RMP-7/Tf/liposomes (RMP-7/Tf/NGF-liposomes) were used to permeate a monolayer of human brain-microvascular endothelial cells (HBMECs) regulated by human astrocytes (HAs) and to treat Aβ1-42 -attacked SK-N-MC cells. An increase in RMT-7 concentration increased the particle size, zeta potential, propidium iodide (PI) permeability, and NGF permeability, but decreased the cross-linking efficiency of RMT-7, viability of HBMECs and HAs, and transendothelial electrical resistance (TEER). In addition, an increase in Tf concentration enhanced the particle size, viability of HBMECs, HAs, and SK-N-MC cells, PI permeability, and NGF permeability, but reduced the zeta potential, cross-linking efficiency of RMT-7 and Tf, and TEER. RMP-7/Tf/NGF-liposomes can transport NGF across the BBB and improve the neuroprotection for Alzheimer's disease therapy in preclinical trials.

Recent progress in tight junction modulation for improving bioavailability

INTRODUCTION

Currently, there are many novel drugs that belong to class III or IV of the Biopharmaceutics Classification System, showing low bioavailability. Tight junction (TJ) modulation offers an approach to increase bioavailability of pharmaceutical compounds. Furthermore, some diseases are accompanied by disturbed barrier function or TJ dysregulation and thus represent a second application for TJ modulators.

AREAS COVERED

This review contains a summary of three different TJ modulators: AT1002, PN159 and labradimil. Within this summary, the authors provide a description of their effects on TJs, their adverse effects and their success in clinical trials. Furthermore, the authors present the current understanding of TJ regulation and highlight opportunities to develop new TJ modulators; they also review the problems that might occur.

EXPERT OPINION

The development of new mechanism-based (MB) TJ modulators is a very promising field of research. MB approaches are expected to have the best future prospects. Further elucidation of signaling pathways and TJ regulation will be necessary for advancing MB TJ modulator research.

Phosphodiesterase inhibitor modulation of brain microvascular endothelial cell barrier properties

BACKGROUND AND PURPOSE

Brain microvascular disorders, including cerebral microscopic hemorrhage, have high prevalence but few treatment options. To develop new strategies for these disorders, we analyzed the effects of several phosphodiesterase (PDE) inhibitors on human brain microvascular endothelial cells (HBECs).

METHODS

We modified barrier properties and response to histamine of HBECs using cilostazol (PDE3 inhibitor), rolipram (PDE4 inhibitor), and dipyridamole (non-specific PDE inhibitor).

RESULTS

Cilostazol and dipyridamole altered the distribution of endothelial F-actin. Cilostazol increased expression of tight junction protein claudin-5 by 118% compared to control (p<.001). Permeability to albumin was decreased by cilostazol (21% vs control, p<.05), and permeability to dextran (70Kd) was decreased by both cilostazol (37% vs control, p<.001) and dipyridamole (44% vs control, p<.0001). Cilostazol increased trans-endothelial electrical resistance (TEER) after 12h by 111% compared to control (p<.0001). Protein kinase A (PKA) inhibitors H89 and KT5720 attenuated the TEER increase by cilostazol. Transient increased permeability in response to histamine was significantly mitigated by cilostazol, but not by other PDE inhibitors.

CONCLUSIONS

These findings demonstrate distinctive effects of cilostazol and other PDE inhibitors on HBECs, including enhanced barrier characteristics and mitigation of response to histamine. PKA-mediated effects of cilostazol were prominent in this model. These in vitro findings are consistent with therapeutic potential of PDE inhibitors in human brain microvascular disorders.

Modern methods for delivery of drugs across the blood-brain barrier

The blood-brain barrier (BBB) is a highly regulated and efficient barrier that provides a sanctuary to the brain. It is designed to regulate brain homeostasis and to permit selective transport of molecules that are essential for brain function. Unfortunately, drug transport to the brain is hampered by this almost impermeable, highly selective and well coordinated barrier. With progress in molecular biology, the BBB is better understood, particularly under different pathological conditions. This review will discuss the barrier issue from a biological and pathological perspective to provide a better insight to the challenges and opportunities associated with the BBB. Modern methods which can take advantage of these opportunities will be reviewed. Applications of nanotechnology in drug transport, receptor-mediated targeting and transport, and finally cell-mediated drug transport will also be covered in the review. The challenge of delivering an effective therapy to the brain is formidable; solutions will likely involve concerted multidisciplinary approaches that take into account BBB biology as well as the unique features associated with the pathological condition to be treated.

Assessment of activation of the plasma kallikrein-kinin system in frontal and temporal cortex in Alzheimer's disease and vascular dementia

Decreased cerebral blood flow and blood-brain barrier disruption are features of Alzheimer's disease (AD). The plasma kallikrein-kinin system modulates cerebrovascular tone through release of vasoactive bradykinin (BK). Cerebroventricular infusion of Aβ1-40 enhances BK release, suggesting that the activity of this system may be elevated in AD. We investigated the profile of the activating protease of this system, plasma kallikrein (PK), in frontal and temporal brain tissue from postmortem confirmed cases of AD, vascular dementia (VaD), and controls. Measurements of neuron specific enolase messenger ribonucleic acid (mRNA) and protein were used to adjust for neuronal loss. Adjusted PK mRNA was significantly increased in the frontal cortex in AD, and the frontal and temporal cortex in VaD. Similar trends were seen for PK protein level in AD and VaD. PK activity was significantly increased in the frontal and temporal cortex in AD. Increased PK activity in AD is likely to contribute to increased BK release and may thereby influence cerebral blood flow and vascular permeability.

Crosstalk of tight junction components with signaling pathways

Tight junctions (TJs) regulate the passage of ions and molecules through the paracellular pathway in epithelial and endothelial cells. TJs are highly dynamic structures whose degree of sealing varies according to external stimuli, physiological and pathological conditions. In this review we analyze how the crosstalk of protein kinase C, protein kinase A, myosin light chain kinase, mitogen-activated protein kinases, phosphoinositide 3-kinase and Rho signaling pathways is involved in TJ regulation triggered by diverse stimuli. We also report how the phosphorylation of the main TJ components, claudins, occludin and ZO proteins, impacts epithelial and endothelial cell function.

Bradykinin-induced blood-brain tumor barrier permeability increase is mediated by adenosine 5'-triphosphate-sensitive potassium channel

Bradykinin has been shown to selectively transiently increase the permeability of the blood-brain barrier (BBB). This study was performed to determine whether ATP-sensitive potassium (K(ATP)) channels mediate the increase in permeability of brain tumor microvessels induced by BK. Using a rat brain glioma (C6) model, we found increased expression of K(ATP) channels at tumor sites via Western blot analysis, after intracarotid infusion of bradykinin at a dose of 10 microg/kg/min for 15 min. A significant increase (73.58%) of the integrated density value (IDV) of the K(ATP) channel Kir6.2 subunit was observed in rats with glioma after 10 min of bradykinin perfusion. The over-expression of K(ATP) channels with bradykinin was significantly attenuated by the K(ATP) channel antagonist glibenclamide. Immunohistochemistry and immunolocalization experiments showed that the over-expression of K(ATP) channels was more obvious near tumor capillaries of 10 microm in diameter. I(KATP) modulation by bradykinin in cultured C6 cells was also studied using the patch-clamp technique in a whole-cell configuration. Administration of bradykinin led to a significant opening of K(ATP) channels in a time-dependent manner. This led to the conclusion that the bradykinin-mediated BBB permeability increase is due to accelerated formation of K(ATP) channels, which are thus as an important target in the biochemical regulation of this process.

Tight junction protein expression and barrier properties of immortalized mouse brain microvessel endothelial cells

Understanding the molecular and biochemical mechanisms regulating the blood-brain barrier is aided by in vitro model systems. Many studies have used primary cultures of brain microvessel endothelial cells for this purpose. However, primary cultures limit the generation of material for molecular and biochemical assays since cells grow slowly, are prone to contamination by other neurovascular unit cells, and lose blood-brain barrier characteristics when passaged. To address these issues, immortalized cell lines have been generated. In these studies, we assessed the suitability of the immortalized mouse brain endothelial cell line, bEnd3, as a blood-brain barrier model. RT-PCR and immunofluorescence indicated expression of multiple tight junction proteins. bEnd3 cells formed barriers to radiolabeled sucrose, and responded like primary cultures to disrupting stimuli. Exposing cells to serum-free media on their basolateral side significantly decreased paracellular permeability; astrocyte-conditioned media did not enhance barrier properties. The serum-free media-induced decrease in permeability was correlated with an increase in claudin-5 and zonula occludens-1 immunofluorescence at cell-cell contracts. We conclude that bEnd3 cells are an attractive candidate as a model of the blood-brain barrier due to their rapid growth, maintenance of blood-brain barrier characteristics over repeated passages, formation of functional barriers and amenability to numerous molecular interventions.

ATP participates in the regulation of microvessel permeability

We demonstrated previously that stimulation of the P2Y receptor enhanced the macromolecular permeability of cultured endothelial cell monolayers via the paracellular pathway. To determine whether the P2Y receptor participates in the regulation of permeability in intact microvessels, we have examined the effects of exogenous and endogenous ATP on the permeation of the surface tissue of perfused rat tail caudal artery using a fluorescein isothiocyanate-dextran (FD-4; MW 4400; 1.0 mg mL(-1)). The permeation of FD-4 was assessed by a confocal fluorescence imaging system. We found that 2-methylthioadenosine 5'-triphosphate, a P2Y receptor agonist, enhanced the fluorescence intensity of FD-4 in the surface of the rat caudal artery tissue and that it was inhibited by pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid, a P2 receptor antagonist. Also, noradrenaline, a sympathetic neurotransmitter, and bradykinin, an inflammatory autacoid, enhanced the fluorescence intensity of FD-4 in the surface tissue of the rat caudal artery. The enhancement by noradrenaline was significantly inhibited by the P2 receptor antagonist. In addition, noradrenaline and bradykinin caused the release of ATP, ADP, AMP and adenosine from the endothelium of the rat caudal artery. These results indicated that the exogenous and endogenous ATP increased the macromolecular permeability of blood capillaries via the P2Y receptor. Such purinergic regulation of endothelial permeability may function in physiological and pathophysiological conditions.

Permeability studies on in vitro blood-brain barrier models: physiology, pathology, and pharmacology

(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.

Microspheres based on inulin for the controlled release of serine protease inhibitors: preparation, characterization and in vitro release

The pharmacological activity of serine protease inhibitors, potential drugs for the treatment of thrombosis, is often linked to the presence of amidine functions. With the aim of developing a suitable formulation for these compounds, inulin and inulin acetate associated or not with 1,12-dodecanedicarboxylic acid, were chosen to prepare microspheres. Using a coacervation method, these biocompatible polymers led to microspheres of about 0.5-5 microm. The encapsulation of a water-soluble model drug (E,E)-bis(amidinobenzylidene)cycloheptanone [(E,E)-BABCH] in these microspheres was studied. In this investigation, factorial designs were used to determine the joint influence of several variables (drug mass, speed and time of formulation stirring, centrifugation time) for an optimum encapsulation efficiency. Results revealed that encapsulation efficiency reached 65% whatever the nature of the biopolymer, by using a stirring time of 30 min, a high stirring speed and a centrifugation time of 15 min. (E,E)-BABCH release from microspheres was examined in an in vitro model. The profiles were characterized by three phases strongly dependent on the microspheres and the diacid association displayed a crucial role. With inulin and inulin acetate, the initial phase was a rapid 'drug burst'. Within the first 5 min, 58-62% of the drug were delivered. Microspheres of inulin acetate associated with 1,12-dodecanedicarboxylic acid, showed a slower release with only 32% of the drug delivered after 15 min. After a slow diffusion phase (33 h), an increasing rate until complete drug release was observed for 2.5 days.

Protection against hypoxia-induced increase in blood-brain barrier permeability: role of tight junction proteins and NFkappaB

Co-culture with glial cells and glia-conditioned media can induce blood-brain barrier properties in microvessel endothelial cells and protect against hypoxia-induced blood-brain barrier breakdown. We examined the effect of two types of glia-conditioned media on brain microvessel endothelial cell permeability and tight junction protein expression, and studied potential mechanisms of action. We found that C6-glioma-conditioned media, but not rat astrocyte-conditioned media, protected against an increase in permeability induced by exposure to 1% oxygen for 24 hours. This hypoxic stress caused an increase in the expression of tight junction proteins claudin-1 and actin, particularly in cells treated with C6-conditioned media. We found that C6-conditioned media has a significantly higher level of both basic fibroblast growth factor and vascular endothelial growth factor. Treatment with C6-conditioned media for 1 or 3 days protects against hypoxia-induced permeability increases, and this protective effect may be mediated by signal transduction pathways terminating at the transcription factor NFkappaB.

Endovascular restorative neurosurgery: a novel concept for molecular and cellular therapy of the nervous system

The amalgam of molecular biology and neurosurgery offers immense promise for neurorestoration and the management of neurodegenerative deficiencies, developmental disorders, neoplasms, stroke, and trauma. This article summarizes present strategies for and impediments to gene therapy and stem cell therapy of the central nervous system and advances the concept of a potential new approach, namely endovascular restorative neurosurgery. The objectives of gene transfer to the central nervous system are efficient transfection of host cells, selective sustained expression of the transgene, and lack of toxicity or immune excitation. The requisite elements of this process are the identification of candidate diseases, the construction of vehicles for gene transfer, regulated expression, and physical delivery. In the selection of target disorders, the underlying genetic events to be overcome, as well as their spatial and temporal distributions, must be considered. These factors determine the requirements for the physical dispersal of the transgene, the duration of transgene expression, and the quantity of transgene product needed to abrogate the disease phenotype. Vehicles for conveying the transgene to the central nervous system include viral vectors (retroviruses, lentiviruses, adenoviruses, adeno-associated viruses, and herpes simplex virus), liposomes, and genetically engineered cells, including neural stem cells. Delivery of the transgene into the brain presents several challenges, including limited and potentially risky access through the cranium, sensitivity to volumetric changes, restricted diffusion, and the blood-brain barrier. Genetic or cellular therapeutic agents may be injected directly into the brain parenchyma (via stereotaxy or craniotomy), into the cerebrospinal fluid (in the ventricles or cisterns), or into the bloodstream (intravenously or intra-arterially). The advantages of the endovascular route include the potential for widespread distribution, the ability to deliver large volumes, limited perturbation of neural tissue, and the feasibility of repeated administration.

Zonula occludens toxin increases the permeability of molecular weight markers and chemotherapeutic agents across the bovine brain microvessel endothelial cells

The purpose of this study was to examine the ability of Zonula occludens toxin (Zot) to reversibly open tight junctions in bovine brain microvessel endothelial cells (BBMECs) to enhance drug delivery via the paracellular pathway. Transport across BBMEC monolayers was examined for molecular weight markers and chemotherapeutic agents ([(14)C]sucrose, [(14)C]inulin, [(3)H]propranolol, [(3)H]doxorubicin, and [(14)C]paclitaxel) with Zot (0.0-4.0 microg/mL). TEER of monolayers was measured to assess effect and reversibility of Zot. Cell viability of BBMEC in the presence of Zot was assessed by trypan blue exclusion staining. Apparent permeability (P(app)), enhancement ratio (R), and percent increase in transport determined were statistically compared by ANOVA. A significant increase (p < 0.05) in P(app) was observed for the transport of [(14)C]sucrose, [(14)C]inulin, [(3)H]doxorubicin, and [(14)C]paclitaxel at a 4.0 microg/mL concentration of Zot. A significant concentration-dependent decrease in TEER was observed on treatment with Zot with rapid reversal to baseline after removal. Zot (4 micro/ml) was found to be nontoxic to the BBMECs after 2 hours incubation. In conclusion, Zot increased paracellular transport across the BBMEC in a reversible, concentration-dependent manner. Modulation of paracellular transport with Zot may be used to increase the brain permeability of potent central nervous system-active drugs, including anticancer agents.

Astrocyte-endothelial interactions and blood-brain barrier permeability

The blood-brain barrier (BBB) is formed by brain endothelial cells lining the cerebral microvasculature, and is an important mechanism for protecting the brain from fluctuations in plasma composition, and from circulating agents such as neurotransmitters and xenobiotics capable of disturbing neural function. The barrier also plays an important role in the homeostatic regulation of the brain microenvironment necessary for the stable and co-ordinated activity of neurones. The BBB phenotype develops under the influence of associated brain cells, especially astrocytic glia, and consists of more complex tight junctions than in other capillary endothelia, and a number of specific transport and enzyme systems which regulate molecular traffic across the endothelial cells. Transporters characteristic of the BBB phenotype include both uptake mechanisms (e.g. GLUT-1 glucose carrier, L1 amino acid transporter) and efflux transporters (e.g. P-glycoprotein). In addition to a role in long-term barrier induction and maintenance, astrocytes and other cells can release chemical factors that modulate endothelial permeability over a time-scale of seconds to minutes. Cell culture models, both primary and cell lines, have been used to investigate aspects of barrier induction and modulation. Conditioned medium taken from growing glial cells can reproduce some of the inductive effects, evidence for involvement of diffusible factors. However, for some features of endothelial differentiation and induction, the extracellular matrix plays an important role. Several candidate molecules have been identified, capable of mimicking aspects of glial-mediated barrier induction of brain endothelium; these include TGFbeta, GDNF, bFGF, IL-6 and steroids. In addition, factors secreted by brain endothelial cells including leukaemia inhibitory factor (LIF) have been shown to induce astrocytic differentiation. Thus endothelium and astrocytes are involved in two-way induction. Short-term modulation of brain endothelial permeability has been shown for a number of small chemical mediators produced by astrocytes and other nearby cell types. It is clear that endothelial cells are involved in both long- and short-term chemical communication with neighbouring cells, with the perivascular end feet of astrocytes being of particular importance. The role of barrier induction and modulation in normal physiology and in pathology is discussed.

Bacterial invasion and transcytosis in transfected human brain microvascular endothelial cells

Most cases of neonatal bacterial meningitis develop as a result of a hematogenous spread, but it is not clear how circulating bacteria cross the blood-brain barrier. Attempts to answer these questions have been hampered by the lack of a reliable model of the human blood-brain barrier. Human brain microvascular endothelial cells (HBMEC) were isolated and transfected with a pBR322 based plasmid containing simian virus 40 large T antigen (SV40-LT). The transfected HBMEC exhibited similar brain endothelial cell characteristics as the primary HBMEC, i.e. gamma glutamyl transpeptidase and a high transendothelial electrical resistance. Escherischia coli and Citrobacter spp, two important Gram-negative bacilli causing neonatal meningitis, were found to transcytose across primary and transfected HBMEC, without affecting the integrity of the monolayer. In addition, E. coli and C. freundii invaded transfected HBMEC as shown previously with primary HBMEC. We conclude that E. coli and C. freundii are able to invade and transcytose HBMEC and these bacterial-HBMEC interactions are similar between primary and transfected HBMEC. Therefore, our transfected HBMEC should be useful for studying pathogenesis of CNS infections.

beta-amyloid-induced migration of monocytes across human brain endothelial cells involves RAGE and PECAM-1

In patients with amyloid beta-related cerebrovascular disorders, e.g. , Alzheimer's disease, one finds increased deposition of amyloid peptide (Abeta) and increased presence of monocyte/microglia cells in the brain. However, relatively little is known of the role of Abeta in the trafficking of monocytes across the blood-brain barrier (BBB). Our studies show that interaction of Abeta(1-40) with monolayer of human brain endothelial cells results in augmented adhesion and transendothelial migration of monocytic cells (THP-1 and HL-60) and peripheral blood monocytes. The Abeta-mediated migration of monocytes was inhibited by antibody to Abeta receptor (RAGE) and platelet endothelial cell adhesion molecule (PECAM-1). Additionally, Abeta-induced transendothelial migration of monocytes were inhibited by protein kinase C inhibitor and augmented by phosphatase inhibitor. We conclude that interaction of Abeta with RAGE expressed on brain endothelial cells initiates cellular signaling leading to the transendothelial migration of monocytes. We suggest that increased diapedesis of monocytes across the BBB in response to Abeta present either in the peripheral circulation or in the brain parenchyma may play a role in the pathophysiology of Abeta-related vascular disorder.