A face-to-face comparison of claudin-5 transduced human brain endothelial (hCMEC/D3) cells with porcine brain endothelial cells as blood-brain barrier models for drug transport studies

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.

Microvascular blood-brain barrier alterations in isolated brain capillaries of mice over-expressing alpha-synuclein (Thy1-aSyn line 61)

Dysfunction of the blood-brain barrier (BBB) is suggested to play a critical role in the pathological mechanisms of Parkinson's disease (PD). PD-related pathology such as alpha-synuclein accumulation and inflammatory processes potentially affect the integrity of the BBB early in disease progression, which in turn may alter the crosstalk of the central and peripheral immune response. Importantly, BBB dysfunction could also affect drug response in PD. Here we analyzed microvascular changes in isolated brain capillaries and brain sections on a cellular and molecular level during disease progression in an established PD mouse model that overexpresses human wild-type alpha-synuclein (Thy1-aSyn, line 61). BBB alterations observed in Thy1-aSyn mice included reduced vessel density, reduced aquaporin-4 coverage, reduced P-glycoprotein expression, increased low-density lipoprotein receptor-related protein 1 expression, increased pS129-alpha-synuclein deposition, and increased adhesion protein and matrix metalloprotease expression together with alterations in tight junction proteins. Striatal capillaries presented with more dysregulated BBB integrity markers compared to cortical capillaries. These alterations of BBB integrity lead, however, not to an overt IgG leakage in brain parenchyma. Our data reveals intricate alterations in key proteins of BBB function together with histological evidence for altered structure of the brain vasculature. Thy1-aSyn mice represent a useful model to investigate therapeutic targeting of BBB alterations in synucleinopathies.

TGF-Beta Modulates the Integrity of the Blood Brain Barrier In Vitro, and Is Associated with Metabolic Alterations in Pericytes

The blood-brain barrier (BBB) is a selectively permeable boundary that separates the circulating blood from the extracellular fluid of the brain and is an essential component for brain homeostasis. In glioblastoma (GBM), the BBB of peritumoral vessels is often disrupted. Pericytes, being important to maintaining BBB integrity, can be functionally modified by GBM cells which induce proliferation and cell motility via the TGF-β-mediated induction of central epithelial to mesenchymal transition (EMT) factors. We demonstrate that pericytes strengthen the integrity of the BBB in primary endothelial cell/pericyte co-cultures as an in vitro BBB model, using TEER measurement of the barrier integrity. In contrast, this effect was abrogated by TGF-β or conditioned medium from TGF-β secreting GBM cells, leading to the disruption of a so far intact and tight BBB. TGF-β notably changed the metabolic behavior of pericytes, by shutting down the TCA cycle, driving energy generation from oxidative phosphorylation towards glycolysis, and by modulating pathways that are necessary for the biosynthesis of molecules used for proliferation and cell division. Combined metabolomic and transcriptomic analyses further underscored that the observed functional and metabolic changes of TGF-β-treated pericytes are closely connected with their role as important supporting cells during angiogenic processes.

Tumor Treating Fields (TTFields) Induce Cell Junction Alterations in a Human 3D In Vitro Model of the Blood-Brain Barrier

In a recent study, we showed in an in vitro murine cerebellar microvascular endothelial cell (cerebEND) model as well as in vivo in rats that Tumor-Treating Fields (TTFields) reversibly open the blood-brain barrier (BBB). This process is facilitated by delocalizing tight junction proteins such as claudin-5 from the membrane to the cytoplasm. In investigating the possibility that the same effects could be observed in human-derived cells, a 3D co-culture model of the BBB was established consisting of primary microvascular brain endothelial cells (HBMVEC) and immortalized pericytes, both of human origin. The TTFields at a frequency of 100 kHz administered for 72 h increased the permeability of our human-derived BBB model. The integrity of the BBB had already recovered 48 h post-TTFields, which is earlier than that observed in cerebEND. The data presented herein validate the previously observed effects of TTFields in murine models. Moreover, due to the fact that human cell-based in vitro models more closely resemble patient-derived entities, our findings are highly relevant for pre-clinical studies.

Advances in BBB on Chip and Application for Studying Reversible Opening of Blood-Brain Barrier by Sonoporation

The complex structure of the blood-brain barrier (BBB), which blocks nearly all large biomolecules, hinders drug delivery to the brain and drug assessment, thus decelerating drug development. Conventional in vitro models of BBB cannot mimic some crucial features of BBB in vivo including a shear stress environment and the interaction between different types of cells. There is a great demand for a new in vitro platform of BBB that can be used for drug delivery studies. Compared with in vivo models, an in vitro platform has the merits of low cost, shorter test period, and simplicity of operation. Microfluidic technology and microfabrication are good tools in rebuilding the BBB in vitro. During the past decade, great efforts have been made to improve BBB penetration for drug delivery using biochemical or physical stimuli. In particular, compared with other drug delivery strategies, sonoporation is more attractive due to its minimized systemic exposure, high efficiency, controllability, and reversible manner. BBB on chips (BOC) holds great promise when combined with sonoporation. More details and mechanisms such as trans-endothelial electrical resistance (TEER) measurements and dynamic opening of tight junctions can be figured out when using sonoporation stimulating BOC, which will be of great benefit for drug development. Herein, we discuss the recent advances in BOC and sonoporation for BBB disruption with this in vitro platform.

A human-derived neurovascular unit in vitro model to study the effects of cellular cross-talk and soluble factors on barrier integrity

The blood-brain barrier (BBB) restricts paracellular and transcellular diffusion of compounds and is part of a dynamic multicellular structure known as the "neurovascular unit" (NVU), which strictly regulates the brain homeostasis and microenvironment. Several neuropathological conditions (e.g., Parkinson's disease and Alzheimer's disease), are associated with BBB impairment yet the exact underlying pathophysiological mechanisms remain unclear. In total, 90% of drugs that pass animal testing fail human clinical trials, in part due to inter-species discrepancies. Thus, in vitro human-based models of the NVU are essential to better understand BBB mechanisms; connecting its dysfunction to neuropathological conditions for more effective and improved therapeutic treatments. Herein, we developed a biomimetic tri-culture NVU in vitro model consisting of 3 human-derived cell lines: human cerebral micro-vascular endothelial cells (hCMEC/D3), human 1321N1 (astrocyte) cells, and human SH-SY5Y neuroblastoma cells. The cells were grown in Transwell hanging inserts in a variety of configurations and the optimal setup was found to be the comprehensive tri-culture model, where endothelial cells express typical markers of the BBB and contribute to enhancing neural cell viability and neurite outgrowth. The tri-culture configuration was found to exhibit the highest transendothelial electrical resistance (TEER), suggesting that the cross-talk between astrocytes and neurons provides an important contribution to barrier integrity. Lastly, the model was validated upon exposure to several soluble factors [e.g., Lipopolysaccharides (LPS), sodium butyrate (NaB), and retinoic acid (RA)] known to affect BBB permeability and integrity. This in vitro biological model can be considered as a highly biomimetic recapitulation of the human NVU aiming to unravel brain pathophysiology mechanisms as well as improve testing and delivery of therapeutics.

Development of a multicellular in vitro model of the meningeal blood-CSF barrier to study Neisseria meningitidis infection

Background

Bacterial meningitis is a life-threatening disease that occurs when pathogens such as Neisseria meningitidis cross the meningeal blood cerebrospinal fluid barrier (mBCSFB) and infect the meninges. Due to the human-specific nature of N. meningitidis, previous research investigating this complex host–pathogen interaction has mostly been done in vitro using immortalized brain endothelial cells (BECs) alone, which often do not retain relevant barrier properties in culture. Here, we developed physiologically relevant mBCSFB models using BECs in co-culture with leptomeningeal cells (LMCs) to examine N. meningitidis interaction.

Methods

We used BEC-like cells derived from induced pluripotent stem cells (iBECs) or hCMEC/D3 cells in co-culture with LMCs derived from tumor biopsies. We employed TEM and structured illumination microscopy to characterize the models as well as bacterial interaction. We measured TEER and sodium fluorescein (NaF) permeability to determine barrier tightness and integrity. We then analyzed bacterial adherence and penetration of the cell barrier and examined changes in host gene expression of tight junctions as well as chemokines and cytokines in response to infection.

Results

Both cell types remained distinct in co-culture and iBECs showed characteristic expression of BEC markers including tight junction proteins and endothelial markers. iBEC barrier function as determined by TEER and NaF permeability was improved by LMC co-culture and remained stable for seven days. BEC response to N. meningitidis infection was not affected by LMC co-culture. We detected considerable amounts of BEC-adherent meningococci and a relatively small number of intracellular bacteria. Interestingly, we discovered bacteria traversing the BEC-LMC barrier within the first 24 h post-infection, when barrier integrity was still high, suggesting a transcellular route for N. meningitidis into the CNS. Finally, we observed deterioration of barrier properties including loss of TEER and reduced expression of cell-junction components at late time points of infection.

Conclusions

Here, we report, for the first time, on co-culture of human iPSC derived BECs or hCMEC/D3 with meningioma derived LMCs and find that LMC co-culture improves barrier properties of iBECs. These novel models allow for a better understanding of N. meningitidis interaction at the mBCSFB in a physiologically relevant setting.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12987-022-00379-z.

Chlorpyrifos, permethrin and cyfluthrin effect on cell survival, permeability, and tight junction in an in-vitro model of the human blood-brain barrier (BBB)

The blood-brain barrier (BBB) is a structural and functional interface between the plasma and the human brain. Predictive BBB in-vitro models like immortalized human capillary microvascular endothelial cells (HCMEC/D3) can be used to explore the BBB disruption potential of daily exposed chemicals. The present study was focused on investigating the human BBB permeation potential of one organophosphate pesticide, chlorpyrifos (CPF), and two pyrethroids, permethrin (PMT) and cyfluthrin (CFT). HCMEC/D3 cells were exposed to the chemical and the time-dependent pass across BBB along with permeation coefficient (Papp) was calculated. Transendothelial electrical resistance (TEER) was measured for the cells to check the monolayer formation and later to check the reduction in integrity after chemical exposure. Real time PCR was conducted to investigate the effect of chemicals on the expression BBB´s tight and adherens junction proteins. Calculated Papp value for three chemicals was in the following order: CPF>CFT>PMT, where CPF showed the highest permeation coefficient. TEER calculation showed that the integrity decreased after CPF exposure which was in concordance with Papp value whereas for other chemicals, no change in TEER after exposure was observed. In addition, the transwell study showed a higher efflux ratio (ER) (>2) of CFT indicating that CFT could be a substrate for active transport. For CPF and PMT, ER was less than 2, so no active transport seems to be involved. The evaluation of the mRNA expression analysis revealed a statistically significant decrease in Occludin (OCLN) gene expression for CPF, VE-Cadherin (CDH5) for PMT and Zonula Occludens (ZO1) expression for CFT. Our study showed that CPF has the highest potential for inducing cell death, higher permeation, and capability to induce BBB dysfunction than among the above-mentioned chemicals. Additionally, the results of the permeation study could be useful to build a human PBPK model using in vitro-to-in vivo extrapolation approach.

Modeling the blood-brain barrier for treatment of central nervous system (CNS) diseases

The blood-brain barrier (BBB) is the most specialized biological barrier in the body. This configuration of specialized cells protects the brain from invasion of molecules and particles through formation of tight junctions. To learn more about transport to the brain, in vitro modeling of the BBB is continuously advanced. The types of models and cells selected vary with the goal of each individual study, but the same validation methods, quantification of tight junctions, and permeability assays are often used. With Transwells and microfluidic devices, more information regarding formation of the BBB has been observed. Disease models have been developed to examine the effects on BBB integrity. The goal of modeling is not only to understand normal BBB physiology, but also to create treatments for diseases. This review will highlight several recent studies to show the diversity in model selection and the many applications of BBB models in in vitro research.

Influence of nanoparticle size on blood-brain barrier penetration and the accumulation of anti-seizure medicines in the brain

Anti-seizure medicines constitute a common yet important modality to treat epilepsy. However, some of them are associated with serious side effects including hepatotoxicity and hypersensitivity. Furthermore, the blood-brain barrier (BBB) is an insurmountable obstacle for brain drug delivery. Fortunately, the introduction of the nanoparticles for drug delivery is a feasible approach to overcome these obstacles. Encapsulating drugs into nanoparticles and delivering them to specific sites shows great potential for improving the efficiency of drug delivery and reducing systemic toxicity. Several in vivo studies have investigated the effect of nanoparticle size on biodistribution in mice, but very few have investigated its effects on efficient drug delivery while crossing the BBB. Therefore, we designed a methoxy poly(lactide-co-glycolide)-b-poly(ethylene glycol) methyl ether (mPEG-PLGA) nanoparticle delivery system and explored the cell uptake efficiency of nanoparticles with different sizes and their ability to penetrate the BBB while carrying carbamazepine (CBZ). CBZ-loaded nanoparticles could significantly reduce the cytotoxicity of CBZ to L929 cells at high concentrations. Results from the endocytosis experiment involving human cerebral microvessel endothelial cell/D3 showed that the DiR-loaded mPEG_5K-PLGA_10K nanoparticles possessed the highest cell uptake efficiency. The endocytosis efficiency was 90% at 30 min, which far exceeded that of the other groups. Moreover, similar results were obtained from subsequent experiments where fluorescence images of the isolated organs of the mice were acquired. To summarize, our study demonstrated that drug delivery to the brain using nanocarriers is size dependent. Nanoparticles with the smallest particle size can be internalized more effectively, and easily penetrate the BBB, and accumulate in the brain.

Similarities and differences in the localization, trafficking, and function of P-glycoprotein in MDR1-EGFP-transduced rat versus human brain capillary endothelial cell lines

Background

In vitro models based on brain capillary endothelial cells (BCECs) are among the most versatile tools in blood–brain barrier research for testing drug penetration into the brain and how this is affected by efflux transporters such as P-glycoprotein (Pgp). However, compared to freshly isolated brain capillaries or primary BCECs, the expression of Pgp in immortalized BCEC lines is markedly lower, which prompted us previously to transduce the widely used human BCEC line hCMEC/D3 with a doxycycline-inducible MDR1-EGFP fusion plasmid. The EGFP-labeled Pgp in these cells allows studying the localization and trafficking of the transporter and how these processes are affected by drug exposure. Here we used this strategy for the rat BCEC line RBE4 and performed a face-to-face comparison of RBE4 and hCMEC/D3 wild-type (WT) and MDR1-EGFP transduced cells.

Methods

MDR1-EGFP-transduced variants were derived from WT cells by lentiviral transduction, using an MDR1-linker-EGFP vector. Localization, trafficking, and function of Pgp were compared in WT and MDR1-EGFP transduced cell lines. Primary cultures of rat BCECs and freshly isolated rat brain capillaries were used for comparison.

Results

All cells exhibited typical BCEC morphology. However, significant differences were observed in the localization of Pgp in that RBE4-MDR1-EGFP cells expressed Pgp primarily at the plasma membrane, whereas in hCMEC/D3 cells, the Pgp-EGFP fusion protein was visible both at the plasma membrane and in endolysosomal vesicles. Exposure to doxorubicin increased the number of Pgp-EGFP-positive endolysosomes, indicating a lysosomotropic effect. Furthermore, lysosomal trapping of doxorubicin was observed, likely contributing to the protection of the cell nucleus from damage. In cocultures of WT and MDR1-EGFP transduced cells, intercellular Pgp-EGFP trafficking was observed in RBE4 cells as previously reported for hCMEC/D3 cells. Compared to WT cells, the MDR1-EGFP transduced cells exhibited a significantly higher expression and function of Pgp. However, the junctional tightness of WT and MDR1-EGFP transduced RBE4 and hCMEC/D3 cells was markedly lower than that of primary BCECs, excluding the use of the cell lines for studying vectorial drug transport.

Conclusions

The present data indicate that MDR1-EGFP transduced RBE4 cells are an interesting tool to study the biogenesis of lysosomes and Pgp-mediated lysosomal drug trapping in response to chemotherapeutic agents and other compounds at the level of the blood–brain barrier.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12987-021-00266-z.

Endothelial genetic deletion of CD147 induces changes in the dual function of the blood-brain barrier and is implicated in Alzheimer's disease

AIMS

The blood-brain barrier (BBB) is a specialized and indispensable structure in brain blood vessels that is damaged during Alzheimer's disease (AD). CD147 is expressed on the BBB and deeply engaged in the AD pathological process. In this study, we aimed to provide a better understanding of the roles of CD147 in BBB function in health and neurodegenerative disease.

METHODS AND RESULTS

We measured CD147 expression in mouse brains and demonstrated that CD147 is exclusively expressed in brain endothelial cells (BECs), and its expression decreases with age. After constructing endothelial-specific CD147 knockout mice, we performed RNA-sequencing on BECs isolated from mice of different ages as well as a range of database analyses. We found that endothelial CD147 is essential for the dual functions of the BBB, including barrier maintenance and transporter regulation. This study also shows that CD147 plays a pivotal role in neurodegenerative diseases, particularly in AD.

CONCLUSIONS

Our findings suggested that targeting CD147 in BECs may represent a novel therapeutic strategy, which promoted the design of future experimental investigations and the mechanistic understanding of neurodegenerative diseases.

Development of Real-Time Transendothelial Electrical Resistance Monitoring for an In Vitro Blood-Brain Barrier System

Three-dimensional (3D) cell cultures and organs-on-a-chip have been developed to construct microenvironments that resemble the environment within the human body and to provide a platform that enables clear observation and accurate assessments of cell behavior. However, direct observation of transendothelial electrical resistance (TEER) has been challenging. To improve the efficiency in monitoring the cell development in organs-on-a-chip, in this study, we designed and integrated commercially available TEER measurement electrodes into an in vitro blood-brain barrier (BBB)-on-chip system to quantify TEER variation. Moreover, a flowing culture medium was added to the monolayered cells to simulate the promotion of continuous shear stress on cerebrovascular cells. Compared with static 3D cell culture, the proposed BBB-on-chip integrated with electrodes could measure TEER in a real-time manner over a long period. It also allowed cell growth angle measurement, providing instant reports of cell growth information online. Overall, the results demonstrated that the developed system can aid in the quantification of the continuous cell-pattern variations for future studies in drug testing.

Tight Junction Modulating Bioprobes for Drug Delivery System to the Brain: A Review

The blood-brain barrier (BBB), which is composed of endothelial cells, pericytes, astrocytes, and neurons, separates the brain extracellular fluid from the circulating blood, and maintains the homeostasis of the central nervous system (CNS). The BBB endothelial cells have well-developed tight junctions (TJs) and express specific polarized transport systems to tightly control the paracellular movements of solutes, ions, and water. There are two types of TJs: bicellular TJs (bTJs), which is a structure at the contact of two cells, and tricellular TJs (tTJs), which is a structure at the contact of three cells. Claudin-5 and angulin-1 are important components of bTJs and tTJs in the brain, respectively. Here, we review TJ-modulating bioprobes that enable drug delivery to the brain across the BBB, focusing on claudin-5 and angulin-1.