Paracellular barrier and tight junction protein expression in the immortalized brain endothelial cell lines bEND.3, bEND.5 and mouse brain endothelial cell 4

The Progress in Molecular Transport and Therapeutic Development in Human Blood-Brain Barrier Models in Neurological Disorders

The blood-brain barrier (BBB) is responsible for maintaining homeostasis within the central nervous system (CNS). Depending on its permeability, certain substances can penetrate the brain, while others are restricted in their passage. Therefore, the knowledge about BBB structure and function is essential for understanding physiological and pathological brain processes. Consequently, the functional models can serve as a key to help reveal this unknown. There are many in vitro models available to study molecular mechanisms that occur in the barrier. Brain endothelial cells grown in culture are commonly used to modeling the BBB. Current BBB platforms include: monolayer platforms, transwell, matrigel, spheroidal, and tissue-on-chip models. In this paper, the BBB structure, molecular characteristic, as well as its dysfunctions as a consequence of aging, neurodegeneration, or under hypoxia and neurotoxic conditions are presented. Furthermore, the current modelling strategies that can be used to study BBB for the purpose of further drugs development that may reach CNS are also described.

Implementation of the neuro-glia-vascular unit through co-culture of adult neural stem cells and vascular cells and transcriptomic analysis of diverse Aβ assembly types

BACKGROUND

The blood-brain barrier (BBB) is a specialized layer between blood vessels and tissue in the brain, which is comprised of a neuro-glia-vascular (NGV) unit, thus play a vital role in various brain diseases.

NEW METHOD

We developed the in vitro NGV units by co-culturing brain microvascular endothelial cells (BMECs; bEnd.3) and primary neural stem cells extracted from subventricular zone of adult mice. This approach was designed to mimic the RNA profile conditions found in the microvessels of a mouse brain and confirmed through various comparative transcriptome analyses.

RESULTS

Optimal NGV unit development was achieved by adjusting cell density-dependent co-culture ratios. Specifically, the morphogenic development and neuronal association of astrocyte endfeet were well observed in the contact region with BMECs in the NGV unit. Through transcriptome analysis, we compared co-cultured bEnd.3/NSCs with monocultured bEnd.3 or NSCs and additionally compared them with previously reported mouse brain vascular tissue to show that this NGV unit model is a suitable in vitro model for neurological disease such as Alzheimer's disease (AD).

COMPARISON WITH EXISTING METHOD(S)

This in vitro NGV unit was formed from neural stem cells and vascular cells in the brain of adult mice, not embryos. It is very useful for studying brain disease mechanisms by identifying proteins and genes associated with diseases progress.

CONCLUSIONS

We suggest that this simple in vitro NGV model is appropriate to investigate the relationship between BBB changes and pathological factors in the fields of neurovascular biology and cerebrovascular diseases including AD.

5-Aza-2'-Deoxycytidine Ameliorates Choroidal Neovascularization by Inhibiting the Wnt/β-Catenin Signaling Pathway

Purpose

Choroidal neovascularization (CNV) can constitute the final pathology of many ocular diseases and result in severe vision loss. Studies have demonstrated that DNA methylation is critical in retinal development, aging, and disorders. The current work investigated the effects and underlying mechanism of 5-Aza-2'-deoxycytidine (5-aza-dC), a suppressor of DNA methylation, in the pathological progression of CNV.

Methods

The DNA methylation profiles of retinal pigment epithelial (RPE)/choroidal complexes in normal and laser-induced CNV mice were assessed by Arraystar Mouse RefSeq Promoter Arrays. The CNV area and blood flow density and intensity were observed by optical coherence tomography angiography, and fluorescence leakage was examined by fundus fluorescein angiography in CNV mice with systemic administration of 5-aza-dC. The effects of 5-aza-dC on the biological functions of bEnd.3 cells were estimated by related assays. Notum gene promoter methylation was measured using bisulfite sequencing PCR. Methyltransferases and Wnt signaling-related genes were detected in animal and cell culture experiments by real-time PCR and immunoblot.

Results

Methyltransferases were upregulated, but Notum (a secretion inhibitor of Wnt signaling) was downregulated in the RPE/choroidal complexes of mice with experimental CNV. Intraperitoneal injection of 5-aza-dC inactivated the Wnt pathway and ameliorated the lesion area and the intensity and density of blood flow, as well as the degree of leakage in CNV. In vitro, vascular endothelial growth factor A (VEGFA) stimulation promoted methyltransferases expression and suppressed Notum expression, consequently activating Wnt signaling, whereas exogenous 5-aza-dC reversed VEGFA-induced hyperpermeability, proliferation, migration, and tube formation in bEnd.3 cells via demethylation of Notum promoter.

Conclusions

We observed that 5-aza-dC attenuates the growth of CNV by inhibiting the Wnt signaling pathway via promoter demethylation of the Wnt antagonist Notum. These findings provide a theoretical basis for methylation-based treatment with the Notum gene as a potential target for CNV treatment.

Wnt7a Decreases Brain Endothelial Barrier Function Via β-Catenin Activation

The blood-brain barrier consists of tightly connected endothelial cells protecting the brain's microenvironment from the periphery. These endothelial cells are characterized by specific tight junction proteins such as Claudin-5 and Occludin, forming the endothelial barrier. Disrupting these cells might lead to blood-brain barrier dysfunction. The Wnt/β-catenin signaling pathway can regulate the expression of these tight junction proteins and subsequent barrier permeability. The aim of this study was to investigate the in vitro effects of Wnt7a mediated β-catenin signaling on endothelial barrier integrity. Mouse brain endothelial cells, bEnd.3, were treated with recombinant Wnt7a protein or XAV939, a selective inhibitor of Wnt/β-catenin mediated transcription to modulate the Wnt signaling pathway. The involvement of Wnt/HIF1α signaling was investigated by inhibiting Hif1α signaling with Hif1α siRNA. Wnt7a stimulation led to activation and nuclear translocation of β-catenin, which was inhibited by XAV939. Wnt7a stimulation decreased Claudin-5 expression mediated by β-catenin and decreased endothelial barrier formation. Wnt7a increased Hif1α and Vegfa expression mediated by β-catenin. However, Hif1α signaling pathway did not regulate tight junction proteins Claudin-5 and Occludin. Our data suggest that Wnt7a stimulation leads to a decrease in tight junction proteins mediated by the nuclear translocation of β-catenin, which hampers proper endothelial barrier formation. This process might be crucial in initiating endothelial cell proliferation and angiogenesis. Although HIF1α did not modulate the expression of tight junction proteins, it might play a role in brain angiogenesis and underlie pathogenic mechanisms in Wnt/HIF1α signaling in diseases such as cerebral small vessel disease.

3D Bioprinting of Neurovascular Tissue Modeling with Collagen-Based Low-Viscosity Composites

In vitro neurovascular unit (NVU) models are valuable for investigating brain functions and developing drugs. However, it remains challenging to recapitulate the native architectural features and ultra-soft extracellular matrix (ECM) properties of the natural NVU. Cell-laden bioprinting is promising to prepare complex living tissues, but hard to balance the fidelity and cell growth. This study proposes a novel two-stage methodology for biomanufacturing functional 3D neurovascular constructs in vitro with low modulus of ECM. At the shaping stage, a low-viscosity alginate/collagen is printed through an embedded approach; at the culturing stage, the alginate is removed through targeted lysing. The low-viscosity and rapid crosslinking properties provide a printing resolution of ≈10 µm, and the lysis processing can decrease the hydrogels' modulus to ≈1 kPa and adjust the porosity of the microstructure, providing cells with an environment closing to the brain ECM. A 3D hollow coaxial neurovascular model is fabricated, in which the endothelial cells has expressed tight junction proteins and shown selective permeability, and the astrocytes outside of the endothelial layer are found to spread out with branches and directly interact with endothelial cells. The present study offers a promising modeling method for better understanding the NVU function and screening neuro-drugs.

A dual-targeting peptide for glioblastoma screened by phage display peptide library biopanning combined with affinity-adaptability analysis

The obstruction of blood-brain barrier (BBB) and the poor specific targeting are still the major obstacles and challenges of targeted nano-pharmaceutical therapy for glioblastoma (GBM) up to now. It is critical to find appropriate targeting ligands that can effectively mediate the nano-pharmaceuticals to penetrate brain capillary endothelial cells (BCECs) and then specifically bind to glioblastoma cells (GCs). Herein, a dual-targeting ligand for GBM was screened by the combination of phage display peptide library biopanning and affinity-adaptability analysis. Based on the acquisition of sub-library of peptide which exhibited the specific affinity to both BCECs and GCs, a comparison parameter of relative affinity was deliberately introduced to evaluate the relative affinity of candidate peptides to U251-MG cells and bEnd.3 cells. The optimized WTW peptide (sequenced as WTWEYTK) was provided with a high relative affinity (RU/B = 2.44), implying that its high affinity to U251-MG cells and moderate affinity to bEnd.3 cells might synergistically promote its receptor-mediated internalization and transport, the dissociation from bEnd.3, and the binding to U251-MG. The results of BBB model trials in vitro showed that the BBB penetration efficiency and GBM accumulation of WTW peptide were significantly higher than those of WSL peptide, GNH peptide, and REF peptide. Results of orthotopic GBM xenograft model assays in vivo also indicated that WTW peptide had successfully penetrated the BBB and improved accumulation in GBM. The screened WTW peptide might be the potential dual-targeting ligand to motivate the advancement of GBM targeted therapy.

A novel 4-cell in-vitro blood-brain barrier model and its characterization by confocal microscopy and TEER measurement

The blood-brain barrier (BBB) is a protective cellular anatomical layer with a dynamic micro-environment, tightly regulating the transport of materials across it. To achieve in-vivo characteristics, an in-vitro BBB model requires the constituent cell types to be layered in an appropriate order. A cost-effective in-vitro BBB model is desired to facilitate central nervous system (CNS) drug penetration studies. Enhanced integrity of tight junctions observed during the in-vitro BBB establishment and post-experiment is essential in these models. We successfully developed an in-vitro BBB model mimicking the in-vivo cell composition and a distinct order of seeding primary human brain cells. Unlike other in-vitro BBB models, our work avoids the need for pre-coated plates for cell adhesion and provides better cell visualization during the procedure. We found that using bovine collagen-I coating, followed by bovine fibronectin coating and poly-L-lysine coating, yields better adhesion and layering of cells on the transwell membrane compared to earlier reported use of collagen and poly-L-lysine only. Our results indicated better cell visibility and imaging with the polyester transwell membrane as well as point to a higher and more stable Trans Endothelial Electrical Resistance values in this plate. In addition, we found that the addition of zinc induced higher claudin 5 expressions in neuronal cells. Dolutegravir, a drug used in the treatment of HIV, is known to appear in moderate concentrations in the CNS. Thus, dolutegravir was used to assess the functionality of the final model and cells. Using primary cells and an in-house coating strategy substantially reduces costs and provides superior imaging of cells and their tight junction protein expression. Our 4-cell-based BBB model is a suitable experimental model for the drug screening process.

New Indole-3-Propionic Acid and 5-Methoxy-Indole Carboxylic Acid Derived Hydrazone Hybrids as Multifunctional Neuroprotectors

In light of the known neuroprotective properties of indole compounds and the promising potential of hydrazone derivatives, two series of aldehyde-heterocyclic hybrids combining those pharmacophores were synthesized as new multifunctional neuroprotectors. The obtained derivatives of indole-3-propionic acid (IPA) and 5-methoxy-indole carboxylic acid (5MICA) had good safety profiles: Hemolytic effects < 5% (200 μM) and IC₅₀ > 150 µM were found in the majority of the SH-SY5Y and bEnd3 cell lines. The 2,3-dihydroxy, 2-hydroxy-4-methoxy, and syringaldehyde derivatives of 5MICA exhibited the strongest neuroprotection against H₂O₂-induced oxidative stress in SH-SY5Y cells and 6-OHDA-induced neurotoxicity in rat-brain synaptosomes. All the compounds suppressed the iron-induced lipid peroxidation. The hydroxyl derivatives were also the most active in terms of deoxyribose-degradation inhibition, whereas the 3,4-dihydroxy derivatives were able to decrease the superoxide-anion generation. Both series of compounds showed an increased inhibition of hMAO-B, with greater expression detected in the 5MICA hybrids. The in vitro BBB model with the bEnd3 cell line showed that some compounds increased the permeability of the endothelial monolayer while maintaining the tight junctions. The combined results demonstrated that the derivatives of IPA and 5MICA showed strong neuroprotective, antioxidant, MAO-B inhibitory activity and could be considered as prospective multifunctional compounds for the treatment of neurodegenerative disorders.

Deep Tissue Penetration of Bottle-Brush Polymers via Cell Capture Evasion and Fast Diffusion

Drug nanocarriers (NCs) capable of crossing the vascular endothelium and deeply penetrating into dense tissues of the CNS could potentially transform the management of neurological diseases. In the present study, we investigated the interaction of bottle-brush (BB) polymers with different biological barriers in vitro and in vivo and compared it to nanospheres of similar composition. In vitro internalization and permeability assays revealed that BB polymers are not internalized by brain-associated cell lines and translocate much faster across a blood-brain barrier model compared to nanospheres of similar hydrodynamic diameter. These observations performed under static, no-flow conditions were complemented by dynamic assays performed in microvessel arrays on chip and confirmed that BB polymers can escape the vasculature compartment via a paracellular route. BB polymers injected in mice and zebrafish larvae exhibit higher penetration in brain tissues and faster extravasation of microvessels located in the brain compared to nanospheres of similar sizes. The superior diffusivity of BBs in extracellular matrix-like gels combined with their ability to efficiently cross endothelial barriers via a paracellular route position them as promising drug carriers to translocate across the blood-brain barrier and penetrate dense tissue such as the brain, two unmet challenges and ultimate frontiers in nanomedicine.

Imatinib inhibits pericyte-fibroblast transition and inflammation and promotes axon regeneration by blocking the PDGF-BB/PDGFRβ pathway in spinal cord injury

Background

Fibrotic scar formation and inflammation are characteristic pathologies of spinal cord injury (SCI) in the injured core, which has been widely regarded as the main barrier to axonal regeneration resulting in permanent functional recovery failure. Pericytes were shown to be the main source of fibroblasts that form fibrotic scar. However, the mechanism of pericyte-fibroblast transition after SCI remains elusive.

Methods

Fibrotic scarring and microvessels were assessed using immunofluorescence staining after establishing a crush SCI model. To study the process of pericyte-fibroblast transition, we analyzed pericyte marker and fibroblast marker expression using immunofluorescence. The distribution and cellular origin of platelet-derived growth factor (PDGF)-BB were examined with immunofluorescence. Pericyte-fibroblast transition was detected with immunohistochemistry and Western blot assays after PDGF-BB knockdown and blocking PDGF-BB/PDGFRβ signaling in vitro. Intrathecal injection of imatinib was used to selectively inhibit PDGF-BB/PDGFRβ signaling. The Basso mouse scale score and footprint analysis were performed to assess functional recovery. Subsequently, axonal regeneration, fibrotic scarring, fibroblast population, proliferation and apoptosis of PDGFRβ⁺ cells, microvessel leakage, and the inflammatory response were assessed with immunofluorescence.

Results

PDGFRβ⁺ pericytes detached from the blood vessel wall and transitioned into fibroblasts to form fibrotic scar after SCI. PDGF-BB was mainly distributed in the periphery of the injured core, and microvascular endothelial cells were one of the sources of PDGF-BB in the acute phase. Microvascular endothelial cells induced pericyte-fibroblast transition through the PDGF-BB/PDGFRβ signaling pathway in vitro. Pharmacologically blocking the PDGF-BB/PDGFRβ pathway promoted motor function recovery and axonal regeneration and inhibited fibrotic scar formation. After fibrotic scar formation, blocking the PDGFRβ receptor inhibited proliferation and promoted apoptosis of PDGFRβ⁺ cells. Imatinib did not alter pericyte coverage on microvessels, while microvessel leakage and inflammation were significantly decreased after imatinib treatment.

Conclusions

We reveal that the crosstalk between microvascular endothelial cells and pericytes promotes pericyte-fibroblast transition through the PDGF-BB/PDGFRβ signaling pathway. Our finding suggests that blocking the PDGF-BB/PDGFRβ signaling pathway with imatinib contributes to functional recovery, fibrotic scarring, and inflammatory attenuation after SCI and provides a potential target for the treatment of SCI.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41232-022-00223-9.

Four Chemotherapeutic Compounds That Limit Blood-Brain-Barrier Invasion by Toxoplasma gondii

Background: Toxoplasma gondii, an intracellular protozoan parasite, exists in the host brain as cysts, which can result in Toxoplasmic Encephalitis (TE) and neurological diseases. However, few studies have been conducted on TE, particularly on how to prevent it. Previous proteomics studies have showed that the expression of C3 in rat brains was up-regulated after T. gondii infection. Methods: In this study, we used T. gondii to infect mice and bEnd 3 cells to confirm the relation between T. gondii and the expression of C3. BEnd3 cells membrane proteins which directly interacted with C3a were screened by pull down. Finally, animal behavior experiments were conducted to compare the differences in the inhibitory ability of TE by four chemotherapeutic compounds (SB290157, CVF, NSC23766, and Anxa1). Results: All chemotherapeutic compounds in this study can inhibit TE and cognitive behavior in the host. However, Anxa 1 is the most suitable material to inhibit mice TE. Conclusion: T. gondii infection promotes TE by promoting host C3 production. Anxa1 was selected as the most appropriate material to prevent TE among four chemotherapeutic compounds closely related to C3.

Comparative studies between the murine immortalized brain endothelial cell line (bEnd.3) and induced pluripotent stem cell-derived human brain endothelial cells for paracellular transport

Brain microvascular endothelial cells, forming the anatomical site of the blood-brain barrier (BBB), are widely used as in vitro complements to in vivo BBB studies. Among the immortalized cells used as in vitro BBB models, the murine-derived bEnd.3 cells offer culturing consistency and low cost and are well characterized for functional and transport assays, but result in low transendothelial electrical resistance (TEER). Human-induced pluripotent stem cells differentiated into brain microvascular endothelial cells (ihBMECs) have superior barrier properties, but the process of differentiation is time-consuming and can result in mixed endothelial-epithelial gene expression. Here we performed a side-by-side comparison of the ihBMECs and bEnd.3 cells for key paracellular diffusional transport characteristics. The TEER across the ihBMECs was 45- to 68-fold higher than the bEnd.3 monolayer. The ihBMECs had significantly lower tracer permeability than the bEnd.3 cells. Both, however, could discriminate between the paracellular permeabilities of two tracers: sodium fluorescein (MW: 376 Da) and fluorescein isothiocyanate (FITC)-dextran (MW: 70 kDa). FITC-dextran permeability was a strong inverse-correlate of TEER in the bEnd.3 cells, whereas sodium fluorescein permeability was a strong inverse-correlate of TEER in the ihBMECs. Both bEnd.3 cells and ihBMECs showed the typical cobblestone morphology with robust uptake of acetylated LDL and strong immuno-positivity for vWF. Both models showed strong claudin-5 expression, albeit with differences in expression location. We further confirmed the vascular endothelial- (CD31 and tube-like formation) and erythrophagocytic-phenotypes and the response to inflammatory stimuli of ihBMECs. Overall, both bEnd.3 cells and ihBMECs express key brain endothelial phenotypic markers, and despite differential TEER measurements, these in vitro models can discriminate between the passage of different molecular weight tracers. Our results highlight the need to corroborate TEER measurements with different molecular weight tracers and that the bEnd.3 cells may be suitable for large molecule transport studies despite their low TEER.

The Effect of Normoxic and Hypoxic U-87 Glioblastoma Paracrine Secretion on the Modulation of Brain Endothelial Cells

Background: Glioblastoma multiforme (GBM) is a highly invasive brain tumour, characterized by its ability to secrete factors promoting its virulence. Brain endothelial cells (BECs) in the GBM environment are physiologically modulated. The present study investigated the modulatory effects of normoxically and hypoxically induced glioblastoma U-87 cell secretions on BECs. Methods: Conditioned media (CM) were derived by cultivating U-87 cells under hypoxic incubation (5% O₂) and normoxic incubation (21% O₂). Treated bEnd.3 cells were evaluated for mitochondrial dehydrogenase activity, mitochondrial membrane potential (ΔΨm), ATP production, transendothelial electrical resistance (TEER), and endothelial tight-junction (ETJ) gene expression over 96 h. Results: The coculture of bEnd.3 cells with U-87 cells, or exposure to either hypoxic or normoxic U-87CM, was associated with low cellular viability. The ΔΨm in bEnd.3 cells was hyperpolarized after hypoxic U-87CM treatment (p < 0.0001). However, normoxic U-87CM did not affect the state of ΔΨm. BEC ATP levels were reduced after being cocultured with U-87 cells, or with hypoxic and normoxic CM (p < 0.05). Suppressed mitochondrial activity in bEnd.3 cells was associated with increased transendothelial permeability, while bEnd.3 cells significantly increased the gene expression levels of ETJs (p < 0.05) when treated with U-87CM. Conclusions: Hypoxic and normoxic glioblastoma paracrine factors differentially suppressed mitochondrial activity in BECs, increasing the BECs’ barrier permeability.

Cav-1 Protein Levels in Serum and Infarcted Brain Correlate with Hemorrhagic Volume in a Mouse Model of Thromboembolic Stroke, Independently of rt-PA Administration

Thrombolytic therapy with recombinant tissue plasminogen activator (rt-PA) is currently the only FDA-approved drug for acute ischemic stroke. However, its administration is still limited due to the associated increased risk of hemorrhagic transformation (HT). rt-PA may exacerbate blood-brain barrier (BBB) injury by several mechanisms that have not been fully elucidated. Caveolin-1 (Cav-1), a major structural protein of caveolae, has been linked to the endothelial barrier function. The effects of rt-PA on Cav-1 expression remain largely unknown. Here, Cav-1 protein expression after ischemic conditions, with or without rt-PA administration, was analyzed in a murine thromboembolic middle cerebral artery occlusion (MCAO) and in brain microvascular endothelial bEnd.3 cells subjected to oxygen/glucose deprivation (OGD). Our results show that Cav-1 is overexpressed in endothelial cells of infarcted area and in bEnd.3 cell line after ischemia but there is disagreement regarding rt-PA effects on Cav-1 expression between both experimental models. Delayed rt-PA administration significantly reduced Cav-1 total levels from 24 to 72 h after reoxygenation and increased pCav-1/Cav-1 at 72 h in the bEnd.3 cells while it did not modify Cav-1 immunoreactivity in the infarcted area at 24 h post-MCAO. Importantly, tissue Cav-1 positively correlated with Cav-1 serum levels at 24 h post-MCAO and negatively correlated with the volume of hemorrhage after infarction, the latter supporting a protective role of Cav-1 in cerebral ischemia. In addition, the negative association between baseline serum Cav-1 levels and hemorrhagic volume points to a potential usefulness of baseline serum Cav-1 levels to predict hemorrhagic volume, independently of rt-PA administration.

The HIV-1 matrix protein p17 does cross the Blood-Brain Barrier

Human immunodeficiency virus type-1(HIV-1)-associated neurocognitive disorder (HAND) remains an important neurological manifestation in HIV-1-infected (HIV⁺) patients. Furthermore, the HIV-1 matrix protein p17 (p17) detection in the central nervous system (CNS) and its ability to form toxic assemblies in the brain has been recently confirmed. Here we show for the first time using both an in vitro blood-brain barrier (BBB) model and in vivo biodistribution studies in healthy mice that p17 can cross the BBB. There is fast brain uptake with 0.35 ± 0.19% of injected activity per gram of tissue (I.A./g) two minutes after administration, followed by brain accumulation with 0.28 ± 0.09% I.A./g after 1 h. The interaction of p17 with the chemokine receptor 2 (CXCR2) at the surface of brain endothelial cells triggers transcytosis. The present study supports the hypothesis of a direct role of free p17 in neuronal dysfunction in HAND by demonstrating its intrinsic ability to reach the CNS. IMPORTANCE The number of patients affected by HIV-1-associated neurocognitive disorder (HAND) ranges from 30 to 50% of HIV-infected (HIV⁺) patients. The mechanisms leading to HAND development need to be elucidated, but the role of secreted viral proteins, chemokines, and proinflammatory molecules appears to be clear. In particular, the blood-brain barrier (BBB) represents a route for entry into the central nervous system (CNS) thus playing an important role in HAND. Several findings suggest a key role for the HIV-1 matrix protein p17 (p17) as a microenvironmental factor capable of inducing neurocognitive disorders. Here we show, the ability of the p17 to cross the BBB and to reach the CNS thus playing a crucial role in neuronal dysfunction in HAND.

Advances in Non-Animal Testing Approaches towards Accelerated Clinical Translation of Novel Nanotheranostic Therapeutics for Central Nervous System Disorders

Nanotheranostics constitute a novel drug delivery system approach to improving systemic, brain-targeted delivery of diagnostic imaging agents and pharmacological moieties in one rational carrier platform. While there have been notable successes in this field, currently, the clinical translation of such delivery systems for the treatment of neurological disorders has been limited by the inadequacy of correlating in vitro and in vivo data on blood-brain barrier (BBB) permeation and biocompatibility of nanomaterials. This review aims to identify the most contemporary non-invasive approaches for BBB crossing using nanotheranostics as a novel drug delivery strategy and current non-animal-based models for assessing the safety and efficiency of such formulations. This review will also address current and future directions of select in vitro models for reducing the cumbersome and laborious mandate for testing exclusively in animals. It is hoped these non-animal-based modelling approaches will facilitate researchers in optimising promising multifunctional nanocarriers with a view to accelerating clinical testing and authorisation applications. By rational design and appropriate selection of characterised and validated models, ranging from monolayer cell cultures to organ-on-chip microfluidics, promising nanotheranostic particles with modular and rational design can be screened in high-throughput models with robust predictive power. Thus, this article serves to highlight abbreviated research and development possibilities with clinical translational relevance for developing novel nanomaterial-based neuropharmaceuticals for therapy in CNS disorders. By generating predictive data for prospective nanomedicines using validated in vitro models for supporting clinical applications in lieu of requiring extensive use of in vivo animal models that have notable limitations, it is hoped that there will be a burgeoning in the nanotherapy of CNS disorders by virtue of accelerated lead identification through screening, optimisation through rational design for brain-targeted delivery across the BBB and clinical testing and approval using fewer animals. Additionally, by using models with tissue of human origin, reproducible therapeutically relevant nanomedicine delivery and individualised therapy can be realised.

Drug Penetration into the Central Nervous System: Pharmacokinetic Concepts and In Vitro Model Systems

Delivery of most drugs into the central nervous system (CNS) is restricted by the blood-brain barrier (BBB), which remains a significant bottleneck for development of novel CNS-targeted therapeutics or molecular tracers for neuroimaging. Consistent failure to reliably predict drug efficiency based on single measures for the rate or extent of brain penetration has led to the emergence of a more holistic framework that integrates data from various in vivo, in situ and in vitro assays to obtain a comprehensive description of drug delivery to and distribution within the brain. Coupled with ongoing development of suitable in vitro BBB models, this integrated approach promises to reduce the incidence of costly late-stage failures in CNS drug development, and could help to overcome some of the technical, economic and ethical issues associated with in vivo studies in animal models. Here, we provide an overview of BBB structure and function in vivo, and a summary of the pharmacokinetic parameters that can be used to determine and predict the rate and extent of drug penetration into the brain. We also review different in vitro models with regard to their inherent shortcomings and potential usefulness for development of fast-acting drugs or neurotracers labeled with short-lived radionuclides. In this regard, a special focus has been set on those systems that are sufficiently well established to be used in laboratories without significant bioengineering expertise.

Adenosine A2A Receptor Activation Enhances Blood-Tumor Barrier Permeability in a Rodent Glioma Model

The blood-tumor barrier (BTB) limits the entry of effective chemotherapeutic agents into the brain for treatment of malignant tumors like glioblastoma. Poor drug entry across the BTB allows infiltrative glioma stem cells to evade therapy and develop treatment resistance. Regadenoson, an FDA-approved adenosine A2A receptor (A2AR) agonist, has been shown to increase drug delivery across the blood-brain barrier in non-tumor-bearing rodents without a defined mechanism of enhancing BTB permeability. Here, we characterize the time-dependent impact of regadenoson on brain endothelial cell interactions and paracellular transport, using mouse and rat brain endothelial cells and tumor models. In vitro, A2AR activation leads to disorganization of cytoskeletal actin filaments by 30 minutes, downregulation of junctional protein expression by 4 hours, and reestablishment of endothelial cell integrity by 8 hours. In rats bearing intracranial gliomas, regadenoson treatment results in increase of intratumoral temozolomide concentrations, yet no increased survival noted with combined temozolomide therapy. These findings demonstrate regadenoson's ability to induce brain endothelial structural changes among glioma to increase BTB permeability. The use of vasoactive mediators, like regadenoson, which transiently influences paracellular transport, should further be explored to evaluate their potential to enhance central nervous system treatment delivery to aggressive brain tumors. IMPLICATIONS: This study provides insight on the use of a vasoactive agent to increase exposure of the BTB to chemotherapy with intention to improve glioma treatment efficacy.

ATN-161 Ameliorates Ischemia/Reperfusion-induced Oxidative Stress, Fibro-inflammation, Mitochondrial damage, and Apoptosis-mediated Tight Junction Disruption in bEnd.3 Cells

We have previously demonstrated the significance of endothelial cell-expressed α5β1 integrin in ischemic stroke, having shown that α5β1 integrin endothelial cell-selective knockout mice are significantly resistance to ischemic stroke injury via preservation of the tight junction protein claudin-5 and subsequent stabilization of the blood–brain barrier (BBB). In addition, inhibition of α5β1 by the small peptide noncompetitive integrin α5 inhibitor, ATN-161, is beneficial in a mouse model of ischemic stroke through reduction of infarct volume, edema, stabilization of the BBB, and reduced inflammation and immune cell infiltration into the brain. In continuation with our previous findings, we have further evaluated the mechanistic role of ATN-161 in vitro and found that oxygen and glucose deprivation and reperfusion (OGD/R)-induced inflammation, oxidative stress, apoptosis, mitochondrial depolarization, and fibrosis attenuate tight junction integrity via induction of α5, NLRP3, p-FAK, and p-AKT signaling in mouse brain endothelial cells. ATN-161 treatment (10 µM) effectively inhibited OGD/R-induced extracellular matrix (ECM) deposition by reducing integrin α5, MMP-9, and fibronectin expression, as well as reducing oxidative stress by reducing mitochondrial superoxide radicals, intracellular ROS, inflammation by reducing NLRP3 inflammasome, tight junction loss by reducing claudin-5 and ZO-1 expression levels, mitochondrial damage by inhibiting mitochondrial depolarization, and apoptosis via regulation of p-FAK and p-AKT levels. Taken together, our results further support therapeutically targeting α5 integrin with ATN-161, a safe, well-tolerated, and clinically validated peptide, in ischemic stroke.

IL-17A Damages the Blood-Retinal Barrier through Activating the Janus Kinase 1 Pathway

Blood-retinal barrier (BRB) dysfunction underlies macular oedema in many sight-threatening conditions, including diabetic macular oedema, neovascular age-related macular degeneration and uveoretinitis. Inflammation plays an important role in BRB dysfunction. This study aimed to understand the role of the inflammatory cytokine IL-17A in BRB dysfunction and the mechanism involved. Human retinal pigment epithelial (RPE) cell line ARPE19 and murine brain endothelial line bEnd.3 were cultured on transwell membranes to model the outer BRB and inner BRB, respectively. IL-17A treatment (3 days in bEnd.3 cells and 6 days in ARPE19 cells) disrupted the distribution of claudin-5 in bEnd.3 cells and ZO-1 in ARPE19 cells, reduced the transepithelial/transendothelial electrical resistance (TEER) and increased permeability to FITC-tracers in vitro. Intravitreal (20 ng/1 μL/eye) or intravenous (20 ng/g) injection of recombinant IL-17A induced retinal albumin leakage within 48 h in C57BL/6J mice. Mechanistically, IL-17A induced Janus kinase 1 (JAK1) phosphorylation in bEnd.3 but not ARPE19 cells. Blocking JAK1 with Tofacitinib prevented IL-17A-mediated claudin-5 dysmorphia in bEnd.3 cells and reduced albumin leakage in IL-17A-treated mice. Our results suggest that IL-17A can damage the BRB through the activating the JAK1 signaling pathway, and targeting this pathway may be a novel approach to treat inflammation-induced macular oedema.

Biology and Models of the Blood-Brain Barrier

The blood-brain barrier (BBB) is one of the most selective endothelial barriers. An understanding of its cellular, morphological, and biological properties in health and disease is necessary to develop therapeutics that can be transported from blood to brain. In vivo models have provided some insight into these features and transport mechanisms adopted at the brain, yet they have failed as a robust platform for the translation of results into clinical outcomes. In this article, we provide a general overview of major BBB features and describe various models that have been designed to replicate this barrier and neurological pathologies linked with the BBB. We propose several key parameters and design characteristics that can be employed to engineer physiologically relevant models of the blood-brain interface and highlight the need for a consensus in the measurement of fundamental properties of this barrier.

High-Resolution Insights Into the in vitro Developing Blood-Brain Barrier: Novel Morphological Features of Endothelial Nanotube Function

High-resolution electron microscopy (HREM) imaging of the in vitro blood-brain barrier (BBB), is a promising modality for investigating the dynamic morphological interplay underpinning BBB development. The successful establishment of BBB integrity is grounded in the brain endothelial cells (BEC’s) ability to occlude its paracellular spaces of brain capillaries through the expression of the intercellular tight junction (TJ) proteins. The impermeability of these paracellular spaces are crucial in the regulation of transcellular transport systems to achieve homeostasis of the central nervous system. To-date research describing morphologically, the dynamics by which TJ interaction is orchestrated to successfully construct a specialized barrier remains undescribed. In this study, the application of HREM illuminates the novel, dynamic and highly restrictive BEC paracellular pathway which is founded based on lateral membrane alignment which is the functional imperative for the mechanical juxtapositioning of TJ zones that underpin molecular bonding and sealing of the paracellular space. For the first time, we report on the secretion of a basement membrane in vitro, which allow BECs to orientate themselves into distinct basolateral and apicolateral domains and establish a 3-dimensional BEC construct. We report for the first time, on the expression of nanovesicles bound to the plasma membrane surfaces of the BECs. These membrane-bound vesicles are reported to possess an array of DNA/RNA constituents and chemotaxic properties affecting the formation of nanotubes that span the paracellular space between BECs, facilitating BBB construction, alluding to a functional role in mediating cell-to-cell communication. This study suggests that novel, ultrathin nanotubular (NT) structures are involved in functional roles in bringing into alignment the paracellular space of BECs. Immortalized mouse BECs (b.End3, b.End5) and primary rat cardiac microvascular ECs were used to further validate the in vitro BBB model by profiling variances in peripheral EC monolayer development. These cardiac capillary ECs presented with an opposite topographical profile: large fenestra and intercellular spaces, devoid of morphological ultrastructures. This comparative study alludes to the role of NT facilitation in TJ-induced hemifusion of apicolateral BEC membranes, as a structural event forming the basis for establishing a polarized BBB.

Cerebral Apolipoprotein D Exits the Brain and Accumulates in Peripheral Tissues

Apolipoprotein D (ApoD) is a secreted lipocalin associated with neuroprotection and lipid metabolism. In rodent, the bulk of its expression occurs in the central nervous system. Despite this, ApoD has profound effects in peripheral tissues, indicating that neural ApoD may reach peripheral organs. We endeavor to determine if cerebral ApoD can reach the circulation and accumulate in peripheral tissues. Three hours was necessary for over 40% of all the radiolabeled human ApoD (hApoD), injected bilaterally, to exit the central nervous system (CNS). Once in circulation, hApoD accumulates mostly in the kidneys/urine, liver, and muscles. Accumulation specificity of hApoD in these tissues was strongly correlated with the expression of lowly glycosylated basigin (BSG, CD147). hApoD was observed to pass through bEnd.3 blood brain barrier endothelial cells monolayers. However, cyclophilin A did not impact hApoD internalization rates in bEnd.3, indicating that ApoD exit from the brain is either independent of BSG or relies on additional cell types. Overall, our data showed that ApoD can quickly and efficiently exit the CNS and reach the liver and kidneys/urine, organs linked to the recycling and excretion of lipids and toxins. This indicated that cerebral overexpression during neurodegenerative episodes may serve to evacuate neurotoxic ApoD ligands from the CNS.

Delivery of Thyronamines (TAMs) to the Brain: A Preliminary Study

Recent reports highlighted the significant neuroprotective effects of thyronamines (TAMs), a class of endogenous thyroid hormone derivatives. In particular, 3-iodothyronamine (T1AM) has been shown to play a pleiotropic role in neurodegeneration by modulating energy metabolism and neurological functions in mice. However, the pharmacological response to T1AM might be influenced by tissue metabolism, which is known to convert T1AM into its catabolite 3-iodothyroacetic acid (TA1). Currently, several research groups are investigating the pharmacological effects of T1AM systemic administration in the search of novel therapeutic approaches for the treatment of interlinked pathologies, such as metabolic and neurodegenerative diseases (NDDs). A critical aspect in the development of new drugs for NDDs is to know their distribution in the brain, which is fundamentally related to their ability to cross the blood–brain barrier (BBB). To this end, in the present study we used the immortalized mouse brain endothelial cell line bEnd.3 to develop an in vitro model of BBB and evaluate T1AM and TA1 permeability. Both drugs, administered at 1 µM dose, were assayed by high-performance liquid chromatography coupled to mass spectrometry. Our results indicate that T1AM is able to efficiently cross the BBB, whereas TA1 is almost completely devoid of this property.

Drug delivery and targeting to brain tumors: considerations for crossing the blood-brain barrier

Introduction: The blood-brain barrier (BBB) selectively impedes the transportation of drug molecules into the brain, which makes the drug delivery and targeting of brain tumors very challenging.Areas covered: Having surveyed the recent literature, comprehensive insights are given into the impacts of the BBB on the advanced drug delivery and targeting modalities for brain tumors.Expert opinion: Brain capillary endothelial cells form the BBB in association with astrocytes, pericytes, neurons, and extracellular matrix. Coop of these forms the complex setting of neurovascular unite. The BBB maintains the brain homeostasis by restrictive controlling of the blood circulating nutrients/substances trafficking. Despite substantial progress on therapy of brain tumors, there is no impeccable strategy to safely deliver chemotherapeutics into the brain. Various strategies have been applied to deliver chemotherapeutics into the brain (e.g. BBB opening, direct delivery by infusion, injection, microdialysis, and implants, and smart nanosystems), which hold different pros and cons. Of note, smart nanoscale multifunctional nanomedicines can serve as targeting, imaging, and treatment modality for brain tumors. Given that aggressive brain tumors (e.g. gliomas) are often unresponsive to any treatments, an in-depth understanding of the molecular/cellular complexity of brain tumors might help the development of smart and effective treatment modalities.

Bioengineering the neurovascular niche to study the interaction of neural stem cells and endothelial cells

The ability of mammalian neural stem cells (NSCs) to self-renew and differentiate throughout adulthood has made them ideal to study neurogenesis and attractive candidates for neurodegenerative disease therapies. In the adult mammalian brain, NSCs are maintained in the neurovascular niche (NVN) where they are found near the specialized blood vessels, suggesting that brain endothelial cells (BECs) are prominent orchestrators of NSC fate. However, most of the current knowledge of the mammalian NVN has been deduced from nonhuman studies. To circumvent the challenges of in vivo studies, in vitro models have been developed to better understand the reciprocal cellular mechanisms of human NSCs and BECs. This review will cover the current understanding of mammalian NVN biology, the effects of endothelial cell-derived signals on NSC fate, and the in vitro models developed to study the interactions between NSCs and BECs.

Nanoparticles Based on Quaternary Ammonium Chitosan-methyl-β-cyclodextrin Conjugate for the Neuropeptide Dalargin Delivery to the Central Nervous System: An In Vitro Study

Peptide oral administration is a hard goal to reach, especially if the brain is the target site. The purpose of the present study was to set up a vehicle apt to promote oral absorption of the neuropeptide dalargin (DAL), allowing it to cross the intestinal mucosal barrier, resist enzymatic degradation, and transport drugs to the brain after crossing the blood–brain barrier. Therefore, a chitosan quaternary ammonium derivative was synthesized and conjugated with methyl-β-cyclodextrin to prepare DAL-medicated nanoparticles (DAL-NP). DAL-NP particle size was 227.7 nm, zeta potential +8.60 mV, encapsulation efficiency 89%. DAL-NP protected DAL from degradation by chymotrypsin or pancreatin and tripled DAL degradation time compared to non-encapsulated DAL. Use of DAL-NP was safe for either Caco-2 or bEnd.3 cells, with the latter selected as a blood–brain barrier model. DAL-NP could also cross either the Caco-2 or bEnd.3 monolayer by the transepithelial route. The results suggest a potential DAL-NP ability to transport to the brain a DAL dose fraction administered orally, although in vivo experiments will be needed to confirm the present data obtained in vitro.

Drug Development for Central Nervous System Diseases Using In vitro Blood-brain Barrier Models and Drug Repositioning

An important goal of biomedical research is to translate basic research findings into practical clinical implementation. Despite the advances in the technology used in drug discovery, the development of drugs for central nervous system diseases remains challenging. The failure rate for new drugs targeting important central nervous system diseases is high compared to most other areas of drug discovery. The main reason for the failure is the poor penetration efficacy across the blood-brain barrier. The blood-brain barrier represents the bottleneck in central nervous system drug development and is the most important factor limiting the future growth of neurotherapeutics. Meanwhile, drug repositioning has been becoming increasingly popular and it seems a promising field in central nervous system drug development. In vitro blood-brain barrier models with high predictability are expected for drug development and drug repositioning. In this review, the recent progress of in vitro BBB models and the drug repositioning for central nervous system diseases will be discussed.

Evaluation of the Influence of Astrocytes on In Vitro Blood-Brain Barrier Models

In vitro blood-brain barrier (BBB) models are a useful tool to screen the permeability and toxicity of new drugs. Currently, many different in vitro BBB models coexist, but none stands out as being notably better than the rest. Therefore, there is still a need to evaluate the quality of BBB models under various conditions and assess their ability to mimic the in vivo situation. In this study, two brain endothelial cell lines (bEnd.3 and hCMEC/D3) and two epithelial-like cell lines (MDCKII and Caco-2) were selected for BBB modelling purposes. They were grown as monolayers of a single cell type, under the following conditions: in coculture with either primary or immortalised astrocytes; or in the presence of primary or immortalised astrocyte-derived conditioned media. A total of 20 different BBB models were established in this manner, in order to assess the effects of the astroglial components on the BBB phenotype in each case. To this end, six parameters were studied: the expression of selected tight junction proteins; the enzyme activities of alkaline phosphatase and of gamma glutamyl transpeptidase; the transendothelial/transepithelial electrical resistance (TEER); restriction in paracellular transport; and efflux transporter inhibition were each evaluated and correlated. The results showed that coculturing with either primary or immortalised astrocytes led to a general improvement in all parameters studied, evidencing the contribution of this cell type to effective BBB formation. Furthermore, the permeability coefficient (P _e) of the tracer molecule, Lucifer Yellow, correlated with three of the six parameters studied. In addition, this study highlights the potential for the use of the Lucifer Yellow P _e value as an indicator of barrier integrity in in vitro BBB models, which could be useful for screening the permeability of new drugs.

The Fabp5/calnexin complex is a prerequisite for sensitization of mice to experimental autoimmune encephalomyelitis

We previously showed that calnexin (Canx)-deficient mice are desensitized to experimental autoimmune encephalomyelitis (EAE) induction, a model that is frequently used to study inflammatory demyelinating diseases, due to increased resistance of the blood-brain barrier to immune cell transmigration. We also discovered that Fabp5, an abundant cytoplasmic lipid-binding protein found in brain endothelial cells, makes protein-protein contact with the cytoplasmic C-tail domain of Canx. Remarkably, both Canx-deficient and Fabp5-deficient mice commonly manifest resistance to EAE induction. Here, we evaluated the importance of Fabp5/Canx interactions on EAE pathogenesis and on the patency of a model blood-brain barrier to T-cell transcellular migration. The results demonstrate that formation of a complex comprised of Fabp5 and the C-tail domain of Canx dictates the permeability of the model blood-brain barrier to immune cells and is also a prerequisite for EAE pathogenesis.

Advanced glycation end-products disrupt brain microvascular endothelial cell barrier: The role of mitochondria and oxidative stress

During diabetes mellitus, advanced glycation end-products (AGEs) are major contributors to the development of alterations in cerebral capillaries, leading to the disruption of the blood-brain barrier (BBB). Consequently, this is often associated with an amplified oxidative stress response in microvascular endothelial cells. As a model to mimic brain microvasculature, the bEnd.3 endothelial cell line was used to investigate cell barrier function. Cells were exposed to native bovine serum albumin (BSA) or modified BSA (BSA-AGEs). In the presence or absence of the antioxidant compound, N-acetyl-cysteine, cell permeability was assessed by FITC-dextran exclusion, intracellular free radical formation was monitored with H₂DCF-DA probe, and mitochondrial respiratory and redox parameters were analyzed. We report that, in the absence of alterations in cell viability, BSA-AGEs contribute to an increase in endothelial cell barrier permeability and a marked and prolonged oxidative stress response. Decreased mitochondrial oxygen consumption was associated with these alterations and may contribute to reactive oxygen species production. These results suggest the need for further research to explore therapeutic interventions to restore mitochondrial functionality in microvascular endothelial cells to improve brain homeostasis in pathological complications associated with glycation.

Neuroinflammaging underlies emotional disturbances and circadian rhythm disruption in young male senescence-accelerated mouse prone 8 mice

Aging causes psychological dysfunction and neurodegeneration, and can lead to cognitive impairments. Although numerous studies have reported that neurodegeneration and subsequent cognitive impairments are involved in neuroinflammation, relationship between psychological disturbance and neuroinflammation with aging (neuroinflammaging) remains unclear. Here, to clarify the relationship, we examined whether neuroinflammaging affects emotional behaviors in senescence-accelerated mouse prone 8 (SAMP8) mice. Microglial inflammatory responses to a subsequent lipopolysaccharide (LPS) challenge were significantly enhanced in male SAMP8 mice relative to normal aging senescence-accelerated mouse resistant 1 (SAMR1) mice at 17 weeks, but not 8 weeks of age. LPS injection also significantly increased brain and systemic inflammation in SAMP8 mice at 17 weeks. In a battery of behavioral tests, SAMP8 mice at 17 weeks, but not 8 weeks, exhibited anxiety- and depression-like behaviors and circadian rhythm disruption. Taken together, SAMP8 mice at 17 weeks possess a brain microenvironment in which it is easier to trigger neuroinflammatory priming; this may lead to an emergence of anxiety- and depression-like behaviors and circadian rhythm disruption. These findings provide new insights into the temporal relationship between neuroinflammaging and emotion.

Transport of PEGylated-PLA nanoparticles across a blood brain barrier model, entry into neuronal cells and in vivo brain bioavailability

Treatments of neurodegenerative diseases (NDDs) are severely hampered by the presence of the blood-brain barrier (BBB) precluding efficient brain drug delivery. The development of drug nanocarriers aims at increasing the brain therapeutic index would represent a real progress in brain disease management. PEGylated polyester nanoparticles (NPs) are intensively tested in clinical trials for improved drug delivery. Our working hypothesis was that some surface parameters and size of NPs could favor their penetration across the BBB and their neuronal uptake. Polymeric material PEG-b-PLA diblocks were synthesized by ring opening polymerisation (ROP) with PEG₂₀₀₀ or PEG₅₀₀₀. A library of polymeric PEG-b-PLA diblocks NPs with different physicochemical properties was produced. The toxicity, endocytosis and transcytosis through the brain microvascular endothelial cells were monitored as well as the neuronal cells uptake. In vitro results lead to the identification of favourable surface parameters for the NPs endocytosis into vascular endothelial cells. NPs endocytosis took place mainly by macropinocytosis while transcytosis was partially controlled by their surface chemistry and size. In vivo assays on a zebrafish model showed that the kinetic of NPs in circulation is dependent on PEG coating properties. In vivo findings also showed a low but similar translocation of PEG-b-PLA diblocks NPs to the CNS, regardless of their properties. In conclusion, modulation of surface PEG chain length and NPs size impact the endocytosis rate of NPs but have little influence on cell barriers translocation; while in vivo biodistribution is influenced by surface PEG chain density.

Vascularized neural constructs for ex-vivo reconstitution of blood-brain barrier function

Ex-vivo blood-brain barrier (BBB) model is of great value for studying brain function and drug development, but it is still challenging to engineer macroscale three-dimensional (3D) tissue constructs to recapitulate physiological and functional aspects of BBB. Here, we describe a delicate 3D vascularized neural constructs for ex-vivo reconstitution of BBB function. The tissue-engineered tissue construct is based on a multicomponent 3D co-culture of four types of cells, which typically exist in the BBB and were spatially defined and organized to mimic the in vivo BBB structure and function. A porous polycaprolactone/poly (d,l-lactide-co-glycolide) (PCL/PLGA) microfluidic perfusion system works as the vasculature network, which was made by freeze-coating a 3D-printed sacrificial template. Endothelial cells were seeded inside the channels of the network to form 3D interconnected blood vessels; while other types of cells, including pericytes, astrocytes, and neurons, were co-cultured in a collagen matrix wrapping the vasculature network to derive a vascularized neural construct that recapitulates in vivo BBB function with great complexity and delicacy. Using this model, we successfully reconstituted BBB function with parameters that are similar to the in vivo condition, and demonstrated the identification of BBB-penetrating therapeutics by examining the molecular delivery to neuronal cells when relevant biologic molecules were applied to the vasculature circulation system of the neural construct.

The Traditional Chinese Medicine Compound, GRS, Alleviates Blood-Brain Barrier Dysfunction

Introduction

Traditional Chinese medicine (TCM) provides unique advantages for treatment of ischemic stroke, an aging-related vascular disease. Shengmai powder (GRS) is composed of three active components, specifically, ginsenoside Rb1, ruscogenin and schisandrin A, at a ratio of 6:0.75:6. The main objective of this study was to evaluate the effects of GRS on blood–brain barrier (BBB) dysfunction under conditions of middle cerebral artery occlusion/reperfusion (MCAO/R).

Methods

C57BL/6J mice subjected to MCAO/R were used as a model to assess the protective effects of varying doses of GRS (6.4, 12.8, and 19.2 mg/kg) on BBB dysfunction.

Results

GRS reduced cerebral infarct volume and degree of brain tissue damage, improved behavioral scores, decreased water content and BBB permeability, and restored cerebral blood flow. Moreover, GRS promoted expression of zona occludens-1 (ZO-1) and claudin-5 while inhibiting matrix metalloproteinase 2/9 (MMP-2/9) expression and myosin light chain (MLC) phosphorylation. In vitro, GRS (1, 10, and 100 ng/mL) enhanced the viability of bEnd.3 cells subjected to oxygen glucose deprivation/reoxygenation (OGD/R) and decreased sodium fluorescein permeability.

Conclusion

Consistent with in vivo findings, ZO-1 and claudin-5 were significantly upregulated by GRS in bEnd.3 cells under OGD/R and MMP-2/9 levels and MLC phosphorylation reduced through the Rho-associated coil-forming protein kinase (ROCK)/cofilin signaling pathway. Based on the collective findings, we propose that the TCM compound, GRS, plays a protective role against I/R-induced BBB dysfunction.

Engineering Shelf-Stable Coating for Microfluidic Organ-on-a-Chip Using Bioinspired Catecholamine Polymers

The conceptualization of body-on-a-chip in 2004 resulted in a new approach for studying human physiology in three-dimensional culture. Despite pioneering works and the progress made in replicating human physiology on-a-chip, the stability, reliability, and preservation of cell-culture-treated microfluidic chips remain a challenge. The development of a reliable surface treatment technique to more efficiently and reproducibly modify microfluidic channels would significantly simplify the process of creating and implementing organ-on-a-chip (OOC) systems. In this work, a new flow-based coating technique using bioinspired polymers was implemented to create reliable, reproducible, ready-to-use microfluidic cell culture chips for OOC studies. Single-channel polydimethylsiloxane microfluidic chips were coated with the bioinspired catecholamine polymers, polydopamine (PDA) and polynorepinephrine (PNE), using a flow-based coating technique. The functionality of the resulting microfluidic chips was evaluated by extensive surface characterizations, at 130 °C, in the presence of various cleaning and culture media in static and flow conditions regularly used in OOCs and tested for shelf life by storing the coated microfluidic chips for 4 months at room temperature. Microfluidic chips coated with polycatecholamine were then seeded with the mouse cancer cell line Cath.a.differentiated (CAD) and with the normal human cerebral microvascular endothelial cell line human cerebral microvascular endothelial cells (hCMEC)/D3. Cell viability, cell phenotype, and cell functionality were assessed to evaluate the performance of both the coatings and the surface treatment technique. Both PDA- and PNE-coated microfluidic chips maintained high viability, phenotype, and functionality of CAD cells and hCMEC/D3 cells. In addition, CAD cells retained high viability when they were cultured in both the polymer-coated chips, which were stored at room temperature for up to 120 days. These results suggest that flow-based techniques to coat surfaces with polycatecholamines can be used to generate ready-to-use microfluidic OOC chips that offer long-term stability and reliability for the culture of cell types with application in pathophysiological studies and drug screening.

Evaluation of long-term rt-PA effects on bEnd.3 endothelial cells under ischemic conditions; changes in ZO-1 expression and glycosylation of the bradykinin B2 receptor

Recombinant tissue plasminogen activator (rt-PA) has proven effective in the treatment of acute ischemic stroke, despite the increased risk of hemorrhagic transformation (HT), its major associated complication. Although it is known that HT is related to blood brain barrier (BBB) disruption, the underlying mechanisms are not well established. We assessed time-dependent effects of rt-PA on the bEnd.3 murine brain endothelial cell line subjected either to normoxia or to 2.5 h of oxygen and glucose deprivation (OGD), evaluating a longer period than has previously been done, beyond 6 h post-reoxygenation. Parameters of cell viability, metabolic activity, ionic and transcellular permeability, as well as levels of claudin-5, zonula occludens-1 (ZO-1) and bradykinin B2 receptor (B2R) protein expression were analyzed at 24, 48 and 72 h post-reoxygenation with or without the administration of rt-PA. rt-PA treatment increased both the ionic and transcellular permeability until 72 h and did not modify cell viability or metabolic activity or the expression of claudin-5, ZO-1 and B2R under normoxia at any analyzed time. Under OGD conditions, rt-PA exacerbated OGD effects on metabolic activity from 48 to 72 h, increased transcellular permeability from 24 to 72 h, significantly decreased ZO-1 protein levels at the plasma membrane and increased B2R glycosylation at 72 h post-reoxygenation. Our findings suggest that a long-term analysis is necessary to elucidate time-dependent molecular mechanisms associated to BBB breakdown due to rt-PA administration under ischemia. Thus, protective BBB therapies after ischemic stroke and rt-PA treatment should be explored at least until 72 h after OGD and rt-PA administration.

Lanthanum chloride causes blood–brain barrier disruption through intracellular calcium-mediated RhoA/Rho kinase signaling and myosin light chain kinase

Lanthanum caused endothelial barrier hyperpermeability, loss of VE-cadherin and rearrangement of the actin cytoskeleton, though intracellular Ca²⁺-mediated RhoA/ROCK and MLCK pathways.

IVIVC Assessment of Two Mouse Brain Endothelial Cell Models for Drug Screening

Since most preclinical drug permeability assays across the blood-brain barrier (BBB) are still evaluated in rodents, we compared an in vitro mouse primary endothelial cell model to the mouse b.End3 and the acellular parallel artificial membrane permeability assay (PAMPA) models for drug screening purposes. The mRNA expression of key feature membrane proteins of primary and bEnd.3 mouse brain endothelial cells were compared. Transwell^® monolayer models were further characterized in terms of tightness and integrity. The in vitro in vivo correlation (IVIVC) was obtained by the correlation of the in vitro permeability data with log BB values obtained in mice for seven drugs. The mouse primary model showed higher monolayer integrity and levels of mRNA expression of BBB tight junction (TJ) proteins and membrane transporters (MBRT), especially for the efflux transporter Pgp. The IVIVC and drug ranking underlined the superiority of the primary model (r² = 0.765) when compared to the PAMPA-BBB (r² = 0.391) and bEnd.3 cell line (r² = 0.019) models. The primary monolayer mouse model came out as a simple and reliable candidate for the prediction of drug permeability across the BBB. This model encompasses a rapid set-up, a fair reproduction of BBB tissue characteristics, and an accurate drug screening.

Cilostazol ameliorates ischemia/reperfusion-induced tight junction disruption in brain endothelial cells by inhibiting endoplasmic reticulum stress

Endoplasmic reticulum (ER) stress is essential for brain ischemia/reperfusion (I/R) injury. However, whether it contributes to I/R-induced blood-brain barrier (BBB) injury remains unclear. cilostazol exerts protective effects toward I/R-induced BBB injury, with unclear mechanisms. This study explored the potential role of ER stress in I/R-induced endothelial cell damage and determined whether the therapeutic potential of cilostazol, with respect to I/R-induced endothelial cell damage, is related to inhibition of ER stress. We found that exposing brain endothelial cells (bEnd.3) to oxygen-glucose deprivation/reoxygenation (OGD/R) significantly activated ER stress and diminished the barrier function of cell monolayers; treatment with the ER stress inhibitor 4-phenylbutyric acid (4-PBA) or cilostazol prevented OGD/R-induced ER stress and preserved barrier function. Furthermore, OGD/R induced the expression and secretion of matrix metalloproteinase-9 and nuclear translocation of phosphorylated NF-κB. These changes were partially reversed by 4-PBA or cilostazol treatment. In vivo, 4-PBA or cilostazol significantly attenuated I/R-induced ER stress and ameliorated Evans blue leakage and tight junction loss. These results demonstrate that I/R-induced ER stress participates in BBB disruption. Targeting ER stress could be a useful strategy to protect the BBB from ischemic stroke, and cilostazol is a promising therapeutic agent for this process.-Nan, D., Jin, H., Deng, J., Yu, W., Liu, R., Sun, W., Huang, Y. Cilostazol ameliorates ischemia/reperfusion-induced tight junction disruption in brain endothelial cells by inhibiting endoplasmic reticulum stress.

The endo-lysosomal system of bEnd.3 and hCMEC/D3 brain endothelial cells

Background

Brain endothelial cell-based in vitro models are among the most versatile tools in blood–brain barrier research for testing drug penetration to the central nervous system. Transcytosis of large pharmaceuticals across the brain capillary endothelium involves the complex endo-lysosomal system. This system consists of several types of vesicle, such as early, late and recycling endosomes, retromer-positive structures, and lysosomes. Since the endo-lysosomal system in endothelial cell lines of in vitro blood–brain barrier models has not been investigated in detail, our aim was to characterize this system in different models.

Methods

For the investigation, we have chosen two widely-used models for in vitro drug transport studies: the bEnd.3 mouse and the hCMEC/D3 human brain endothelial cell line. We compared the structures and attributes of their endo-lysosomal system to that of primary porcine brain endothelial cells.

Results

We detected significant differences in the vesicular network regarding number, morphology, subcellular distribution and lysosomal activity. The retromer-positive vesicles of the primary cells were distinct in many ways from those of the cell lines. However, the cell lines showed higher lysosomal degradation activity than the primary cells. Additionally, the hCMEC/D3 possessed a strikingly unique ratio of recycling endosomes to late endosomes.

Conclusions

Taken together our data identify differences in the trafficking network of brain endothelial cells, essentially mapping the endo-lysosomal system of in vitro blood–brain barrier models. This knowledge is valuable for planning the optimal route across the blood–brain barrier and advancing drug delivery to the brain.

Electronic supplementary material

The online version of this article (10.1186/s12987-019-0134-9) contains supplementary material, which is available to authorized users.

Proteomics analysis of HSV-1-induced alterations in mouse brain microvascular endothelial cells

Herpes simplex virus 1 (HSV-1) is a predominant cause of herpes simplex encephalitis (HSE), leading to a high mortality rate and severe neurological sequelae worldwide. HSE is typically accompanied by the blood-brain barrier (BBB) disruption, but the underlying mechanisms are unclear. To explore the disruption mechanisms of the BBB, quantitative analysis of the cellular proteome was carried out to investigate the proteomic changes that occur after infection. In this study, bEnd.3 cells were infected with HSV-1, followed by liquid chromatography-tandem mass spectrometry. A total of 6761 proteins were identified in three independent mass spectrometry analyses. Compared to the uninfected cells, 386 and 293 differentially expressed proteins were markedly upregulated or downregulated, respectively. Bioinformatic analysis showed that the activator protein-1 factor, including Fos, Jun, and ATF family proteins and cell adhesion molecules were significantly changed. Further validation of the changes observed for these proteins was carried out by western blotting and quantitative real-time PCR. Transendothelial electrical resistance (TEER) studies were performed to explore the effects of ATF3, Fra1, or JunB overexpression on the function of bEnd.3 cells. Characterization of the differential expression of these proteins in bEnd.3 cells will facilitate further exploration of BBB disruption upon HSV-1 infection.

Mimicking brain tumor-vasculature microanatomical architecture via co-culture of brain tumor and endothelial cells in 3D hydrogels

Glioblastoma (GBM) is an aggressive malignant brain tumor with median survival of 12 months and 5-year survival rate less than 5%. GBM is highly vascularized, and the interactions between tumor and endothelial cells play an important role in driving tumor growth. To study tumor-endothelial interactions, the gold standard co-culture model is transwell culture, which fails to recapitulate the biochemical or physical cues found in tumor niche. Recently, we reported the development of poly(ethylene-glycol)-based hydrogels as 3D niche that supported GBM proliferation and invasion. To further mimic the microanatomical architecture of tumor-endothelial interactions in vivo, here we developed a hydrogel-based co-culture model that mimics the spatial organization of tumor and endothelial cells. To increase the physiological relevance, patient-derived GBM cells and mouse brain endothelial cells were used as model cell types. Using hydrolytically-degradable alginate fibers as porogens, endothelial cells were deployed and patterned into vessel-like structures in 3D hydrogels with high cell viability and retention of endothelial phenotype. Co-culture led to a significant increase in GBM cell proliferation and decrease in endothelial cell expression of cell adhesion proteins. In summary, we have developed a novel 3D co-culture model that mimics the in vivo spatial organization of brain tumor and endothelial cells. Such model may provide a valuable tool for future mechanistic studies to elucidate the effects of tumor-endothelial interactions on tumor progression in a more physiologically-relevant manner.

Nanoparticle encapsulation increases the brain penetrance and duration of action of intranasal oxytocin

The blood-brain barrier (BBB) limits the therapeutic use of large molecules as it prevents them from passively entering the brain following administration by conventional routes. It also limits the capacity of researchers to study the role of large molecules in behavior, as it often necessitates intracerebroventricular administration. Oxytocin is a large-molecule neuropeptide with pro-social behavioral effects and therapeutic promise for social-deficit disorders. Although preclinical and clinical studies are using intranasal delivery of oxytocin to improve brain bioavailability, it remains of interest to further improve the brain penetrance and duration of action of oxytocin, even with intranasal administration. In this study, we evaluated a nanoparticle drug-delivery system for oxytocin, designed to increase its brain bioavailability through active transport and increase its duration of action through encapsulation and sustained release. We first evaluated transport of oxytocin-like large molecules in a cell-culture model of the BBB. We then determined in vivo brain transport using bioimaging and cerebrospinal fluid analysis in mice. Finally, we determined the pro-social effects of oxytocin (50 μg, intranasal) in two different brain targeting and sustained-release formulations. We found that nanoparticle formulation increased BBB transport both in vitro and in vivo. Moreover, nanoparticle-encapsulated oxytocin administered intranasally exhibited greater pro-social effects both acutely and 3 days after administration, in comparison to oxytocin alone, in mouse social-interaction experiments. These multimodal data validate this brain targeting and sustained-release formulation of oxytocin, which can now be used in animal models of social-deficit disorders as well as to enhance the brain delivery of other neuropeptides.

Shuxuetong injection protects cerebral microvascular endothelial cells against oxygen-glucose deprivation reperfusion

Shuxuetong injection composed of leech (Hirudo nipponica Whitman) and earthworm (Pheretima aspergillum) has been used for the clinical treatment of acute stroke for many years in China. However, the precise neuroprotective mechanism of Shuxuetong injection remains poorly understood. Here, cerebral microvascular endothelial cells (bEnd.3) were incubated in glucose-free Dulbecco’s modified Eagle’s medium containing 95% N₂/5% CO₂ for 6 hours, followed by high-glucose medium containing 95% O₂ and 5% CO₂ for 18 hours to establish an oxygen-glucose deprivation/reperfusion model. This in vitro cell model was administered Shuxuetong injection at 1/32, 1/64, and 1/128 concentrations (diluted 32-, 64-, and 128-times). Cell Counting Kit-8 assay was used to evaluate cell viability. A fluorescence method was used to measure lactate dehydrogenase, and a fluorescence microplate reader used to detect intracellular reactive oxygen species. A fluorescent probe was also used to measure mitochondrial superoxide production. A cell resistance meter was used to measure transepithelial resistance and examine integrity of monolayer cells. The fluorescein isothiocyanate-dextran test was performed to examine blood-brain barrier permeability. Real-time reverse transcription polymerase chain reaction was performed to analyze mRNA expression levels of tumor necrosis factor alpha, interleukin-1β, interleukin-6, and inducible nitric oxide synthase. Western blot assay was performed to analyze expression of caspase-3, intercellular adhesion molecule 1, vascular cell adhesion molecule 1, occludin, vascular endothelial growth factor, cleaved caspase-3, B-cell lymphoma 2, phosphorylated extracellular signal-regulated protein kinase, extracellular signal-regulated protein kinase, nuclear factor-κB p65, I kappa B alpha, phosphorylated I kappa B alpha, I kappa B kinase, phosphorylated I kappa B kinase, claudin-5, and zonula occludens-1. Our results show that Shuxuetong injection increases bEnd.3 cell viability and B-cell lymphoma 2 expression, reduces cleaved caspase-3 expression, inhibits production of reactive oxygen species and mitochondrial superoxide, suppresses expression of tumor necrosis factor alpha, interleukin-1β, interleukin-6, inducible nitric oxide synthase mRNA, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1, markedly increases transepithelial resistance, decreases blood-brain barrier permeability, upregulates claudin-5, occludin, and zonula occludens-1 expression, reduces nuclear factor-κB p65 and vascular endothelial growth factor expression, and reduces I kappa B alpha, extracellular signal-regulated protein kinase 1/2, and I kappa B kinase phosphorylation levels. Overall, these findings suggest that Shuxuetong injection has protective effects on brain microvascular endothelial cells after oxygen-glucose deprivation/reperfusion. Moreover, its protective effect is associated with reduction of mitochondrial superoxide production, inhibition of the inflammatory response, and inhibition of vascular endothelial growth factor, extracellular signal-regulated protein kinase 1/2, and the nuclear factor-κB p65 signaling pathway.

Physiological implications of DHEAS-induced non-classical steroid hormone signaling

In the spermatogenic cell line GC-2, dehydroepiandrosterone sulfate (DHEAS), activates the Src/Ras/c-Raf/Erk1/2/CREB(ATF-1) signaling cascade. Since DHEAS is present in the gonads, and since spermatogenesis and maturation of spermatogonia to haploid spermatozoa requires activation of Erk1/2, the triggering of these signaling events by DHEAS might have physiological relevance. In the Sertoli cell line TM4, DHEAS-induces activation of Erk1/2, CREB, and ATF-1, stimulates expression of claudin-3 and claudin-5 and augments transepithelial resistance, indicating the formation of tight junctions between adjacent Sertoli cells. Thus, by influencing the formation and dynamics of tight junctions at the blood-testis barrier, which protects germ cells from cells of the immune system, DHEAS might play a crucial role in the regulation and maintenance of male fertility. In bEnd.3 brain-derived endothelial cells, DHEAS stimulates the expression of zonula occludens-1 and claudin-3 and promotes tight junction formation between neighboring cells, which at the blood-brain barrier protects the brain from harmful factors and cells. If DHEAS supports the integrity of the blood-brain barrier also in vivo, the current findings might lead to new strategies for the prevention or treatment of neurological disorders associated with barrier defects.