Establishment and characterization of spinal cord microvascular endothelial cell lines

Modeling of Blood-Brain Barrier (BBB) Dysfunction and Immune Cell Migration Using Human BBB-on-a-Chip for Drug Discovery Research

Blood-brain barrier (BBB) dysfunction is a key feature in neuroimmunological and neurodegenerative diseases. In this study, we developed a microfluidic human BBB-on-a-chip to model barrier dysfunction and immune cell migration using immortalized TY10 brain endothelial cells, pericytes, and astrocytes. It was found that immortalized TY10 brain endothelial cells developed a microvascular structure under flow. Pericytes were localized on the basal side surrounding the TY10 microvascular structure, showing an in vivo-like structure. Barrier integrity increased under co-culture with pericytes. In addition, both ethylenediaminetetraacetic acid (EDTA) and anti-Claudin-5 (CLDN5) neutralizing antibody caused a decrease in the transendothelial electrical resistance (TEER). EDTA caused the leakage of 20 kDa dextran, suggesting different effects on the BBB based on the mechanism of action, whereas anti-CLDN5 antibody did not cause leakage. In the tri-culture model, human T cells migrated through endothelial vessels towards basal C-X-C motif chemokine ligand 12 (CXCL12). The live-imaging analysis confirmed the extravasation of fluorescence-labelled T cells in a CXCL12-concentration- and time-dependent manner. Our BBB model had an in vivo-like structure and successfully represented barrier dysfunction and transendothelial T cell migration. In addition, our study suggests that the inhibition of CLDN5 attenuates the BBB in humans. This platform has various potential uses in relation to the BBB in both drug discovery research and in elucidating the mechanisms of central nervous system diseases.

Functional analysis of human brain endothelium using a microfluidic device integrating a cell culture insert

The blood-brain barrier (BBB) is a specialized brain endothelial barrier structure that regulates the highly selective transport of molecules under continuous blood flow. Recently, various types of BBB-on-chip models have been developed to mimic the microenvironmental cues that regulate the human BBB drug transport. However, technical difficulties in complex microfluidic systems limit their accessibility. Here, we propose a simple and easy-to-handle microfluidic device integrated with a cell culture insert to investigate the functional regulation of the human BBB endothelium in response to fluid shear stress (FSS). Using currently established immortalized human brain microvascular endothelial cells (HBMEC/ci18), we formed a BBB endothelial barrier without the substantial loss of barrier tightness under the relatively low range of FSS (0.1-1 dyn/cm2). Expression levels of key BBB transporters and receptors in the HBMEC/ci18 cells were dynamically changed in response to the FSS, and the effect of FSS reached a plateau around 1 dyn/cm2. Similar responses were observed in the primary HBMECs. Taking advantage of the detachable cell culture insert from the device, the drug efflux activity of P-glycoprotein (P-gp) was analyzed by the bidirectional permeability assay after the perfusion culture of cells. The data revealed that the FSS-stimulated BBB endothelium exhibited the 1.9-fold higher P-gp activity than that of the static culture control. Our microfluidic system coupling with the transwell model provides a functional human BBB endothelium with secured transporter activity, which is useful to investigate the bidirectional transport of drugs and its regulation by FSS.

Design and Validation of a Human Brain Endothelial Microvessel-on-a-Chip Open Microfluidic Model Enabling Advanced Optical Imaging

We describe here the design and implementation of an in vitro microvascular open model system using human brain microvascular endothelial cells. The design has several advantages over other traditional closed microfluidic platforms: (1) it enables controlled unidirectional flow of media at physiological rates to support vascular function, (2) it allows for very small volumes which makes the device ideal for studies involving biotherapeutics, (3) it is amenable for multiple high resolution imaging modalities such as transmission electron microscopy (TEM), 3D live fluorescence imaging using traditional spinning disk confocal microscopy, and advanced lattice light sheet microscopy (LLSM). Importantly, we miniaturized the design, so it can fit within the physical constraints of LLSM, with the objective to study physiology in live cells at subcellular level. We validated barrier function of our brain microvessel-on-a-chip by measuring permeability of fluorescent dextran and a human monoclonal antibody. One potential application is to investigate mechanisms of transcytosis across the brain microvessel-like barrier of fluorescently-tagged biologics, viruses or nanoparticles.

Drug Clearance from Cerebrospinal Fluid Mediated by Organic Anion Transporters 1 (Slc22a6) and 3 (Slc22a8) at Arachnoid Membrane of Rats

Although arachnoid mater epithelial cells form the blood-arachnoid barrier (BAB), acting as a blood-CSF interface, it has been generally considered that the BAB is impermeable to water-soluble substances and plays a largely passive role. Here, we aimed to clarify the function of transporters at the BAB in regulating CSF clearance of water-soluble organic anion drugs based on quantitative targeted absolute proteomics (QTAP) and in vivo analyses. Protein expression levels of 61 molecules, including 19 ATP-binding-cassette (ABC) transporters and 32 solute-carrier (SLC) transporters, were measured in plasma membrane fraction of rat leptomeninges using QTAP. Thirty-three proteins were detected; others were under the quantification limits. Expression levels of multidrug resistance protein 1 (Mdr1a/P-gp/Abcb1a) and breast cancer resistance protein (Bcrp/Abcg2) were 16.6 and 3.27 fmol/μg protein (51.9- and 9.82-fold greater than in choroid plexus, respectively). Among those organic anion transporters detected only at leptomeninges, not choroid plexus, organic anion transporter 1 (oat1/Slc22a6) showed the greatest expression (2.73 fmol/μg protein). On the other hand, the protein expression level of oat3 at leptomeninges was 6.65 fmol/μg protein, and the difference from choroid plexus was within two-fold. To investigate oat1's role, we injected para-aminohippuric acid (PAH) with or without oat1 inhibitors into cisterna magna (to minimize the contribution of choroid plexus function) of rats. A bulk flow marker, FITC-inulin, was not taken up from CSF up to 15 min, whereas uptake clearance of PAH was 26.5 μL/min. PAH uptake was completely blocked by 3 mM cephalothin (inhibits both oat1 and oat3), while 17% of PAH uptake was inhibited by 0.2 mM cephalothin (selectively inhibits oat3). These results indicate that oat1 and oat3 at the BAB provide a distinct clearance pathway of organic anion drugs from CSF independently of choroid plexus.

Identification of galectin-3 as a possible antibody target for secondary progressive multiple sclerosis

Background:

Recent studies have revealed that the disruption of the blood–brain barrier (BBB) might contribute to the induction of neurodegeneration in the progressive stage of multiple sclerosis (MS).

Objective:

We investigated a potential target for the serum auto-antibodies responsible for the BBB impairment in patients with secondary progressive MS (SPMS).

Methods:

We identified undetermined target antigens in human brain microvascular endothelial cells (BMECs) that reacted with auto-antibodies in sera from SPMS patients using a proteomic approach. In addition, we examined how the identified auto-antibodies compromise the BBB integrity.

Results:

We found that 10 of 11 SPMS sera had auto-antibodies against galectin-3, although the patients with other neurological diseases did not have these antibodies. Downregulation of galectin-3 led to elevated intercellular adhesion molecule-1 (ICAM-1) and phospho-nuclear factor-kappa (NFκ) B p65 expression in the BMECs. Exposure to SPMS patients’ sera also increased the protein levels of ICAM-1 and phospho-NFκB p65 in BMECs, but these effects induced by anti-galectin-3 immunoreactivity were canceled by the downregulation of galectin-3.

Conclusion:

Galectin-3 is a possible immunological target molecule of the pathogenic auto-antibodies and contributes to the persistent BBB breakdown in patients with SPMS. These antibodies may also serve as a novel biomarker for SPMS.

In vitro blood-brain barrier permeability predictions for GABAA receptor modulating piperine analogs

The alkaloid piperine from black pepper (Piper nigrum L.) and several synthetic piperine analogs were recently identified as positive allosteric modulators of γ-aminobutyric acid type A (GABAA) receptors. In order to reach their target sites of action, these compounds need to enter the brain by crossing the blood-brain barrier (BBB). We here evaluated piperine and five selected analogs (SCT-66, SCT-64, SCT-29, LAU397, and LAU399) regarding their BBB permeability. Data were obtained in three in vitro BBB models, namely a recently established human model with immortalized hBMEC cells, a human brain-like endothelial cells (BLEC) model, and a primary animal (bovine endothelial/rat astrocytes co-culture) model. For each compound, quantitative UHPLC-MS/MS methods in the range of 5.00-500ng/mL in the corresponding matrix were developed, and permeability coefficients in the three BBB models were determined. In vitro predictions from the two human BBB models were in good agreement, while permeability data from the animal model differed to some extent, possibly due to protein binding of the screened compounds. In all three BBB models, piperine and SCT-64 displayed the highest BBB permeation potential. This was corroborated by data from in silico prediction. For the other piperine analogs (SCT-66, SCT-29, LAU397, and LAU399), BBB permeability was low to moderate in the two human BBB models, and moderate to high in the animal BBB model. Efflux ratios (ER) calculated from bidirectional permeability experiments indicated that the compounds were likely not substrates of active efflux transporters.

Validation of an immortalized human (hBMEC) in vitro blood-brain barrier model

We recently established and optimized an immortalized human in vitro blood-brain barrier (BBB) model based on the hBMEC cell line. In the present work, we validated this mono-culture 24-well model with a representative series of drug substances which are known to cross or not to cross the BBB. For each individual compound, a quantitative UHPLC-MS/MS method in Ringer HEPES buffer was developed and validated according to current regulatory guidelines, with respect to selectivity, precision, and reliability. Various biological and analytical challenges were met during method validation, highlighting the importance of careful method development. The positive controls antipyrine, caffeine, diazepam, and propranolol showed mean endothelial permeability coefficients (P e) in the range of 17-70 × 10(-6) cm/s, indicating moderate to high BBB permeability when compared to the barrier integrity marker sodium fluorescein (mean P e 3-5 × 10(-6) cm/s). The negative controls atenolol, cimetidine, and vinblastine showed mean P e values < 10 × 10(-6) cm/s, suggesting low permeability. In silico calculations were in agreement with in vitro data. With the exception of quinidine (P-glycoprotein inhibitor and substrate), BBB permeability of all control compounds was correctly predicted by this new, easy, and fast to set up human in vitro BBB model. Addition of retinoic acid and puromycin did not increase transendothelial electrical resistance (TEER) values of the BBB model.

Pertussis Toxin Exploits Specific Host Cell Signaling Pathways for Promoting Invasion and Translocation of Escherichia coli K1 RS218 in Human Brain-derived Microvascular Endothelial Cells

Pertussis toxin (PTx), an AB5 toxin and major virulence factor of the whooping cough-causing pathogen Bordetella pertussis, has been shown to affect the blood-brain barrier. Dysfunction of the blood-brain barrier may facilitate penetration of bacterial pathogens into the brain, such as Escherichia coli K1 (RS218). In this study, we investigated the influence of PTx on blood-brain barrier permissiveness to E. coli infection using human brain-derived endothelial HBMEC and TY10 cells as in vitro models. Our results indicate that PTx acts at several key points of host cell intracellular signaling pathways, which are also affected by E. coli K1 RS218 infection. Application of PTx increased the expression of the pathogen binding receptor gp96. Further, we found an activation of STAT3 and of the small GTPase Rac1, which have been described as being essential for bacterial invasion involving host cell actin cytoskeleton rearrangements at the bacterial entry site. In addition, we showed that PTx induces a remarkable relocation of VE-cadherin and β-catenin from intercellular junctions. The observed changes in host cell signaling molecules were accompanied by differences in intracellular calcium levels, which might act as a second messenger system for PTx. In summary, PTx not only facilitates invasion of E. coli K1 RS218 by activating essential signaling cascades; it also affects intercellular barriers to increase paracellular translocation.