Comparative study of four immortalized human brain capillary endothelial cell lines, hCMEC/D3, hBMEC, TY10, and BB19, and optimization of culture conditions, for an in vitro blood-brain barrier model for drug permeability studies

Δ9-tetrahydrocannabinol induces blood-brain barrier disruption: Involving the activation of CB1R and oxidative stress

Cannabis abuse has increased with the continuous relaxation of cannabis policies. However, the mechanism by which Δ9-tetrahydrocannabinol (THC) negatively affects the central nervous system, especially the blood-brain barrier (BBB), remains unclear. THC exposure models were established in vivo and in vitro. The BBB properties were examined using Western blotting (WB), immunofluorescence staining (IF), transendothelial electrical resistance (TEER), and flux of sodium fluorescein (SF). The oxidative stress regulators were examined using IF and assay kits. The activation of cannabinoid receptor 1 (CB1R) was examined using WB and IF. The THC exposure caused barrier integrity damage and endothelial dysfunction in murine and hCMEC/D3 cells, conclude albumin leakage, increased SF permeability and reduced TEER value. The expression of tight junction proteins, including claudin 5, occludin, and junctional adhesion molecules, was decreased. Additionally, key oxidative stress regulators, including reactive oxygen species, hydrogen peroxide, malonaldehyde levels, and antioxidant enzyme activities, including catalase, glutathione peroxidase, glutathione S-transferase, and superoxide dismutase, and heme oxygenase 1, were increased. Activation of CB1R has been detected in brain microvascular endothelial cells in vivo and in vitro. Furthermore, inhibition of oxidative stress and CB1R could mitigate the aforementioned conditions and BBB damage after THC exposure. The effect of THC on murine and human brain microvascular endothelial cells revealed that THC-induced BBB damage was partly mediated by CB1R activation, triggering the oxidative stress response. This study provides new theoretical insights into the mechanisms of THC-induced BBB damage and offers novel scientific evidence for the potential neurotoxicity and adverse reactions induced by THC.

The microvascular endothelium of the blood-brain barrier is highly restrictive to JC Polyomavirus neuroinvasion

JC Polyomavirus is the causative agent of progressive multifocal leukoencephalopathy (PML), an often-fatal demyelinating disease. Unfortunately, a diagnosis of PML occurs only after patients have suffered irreversible neuropathologies. The first step in the initiation of PML is viral entry to the brain, but the route and mechanisms responsible for neuroinvasion have not been well established. To gain a better understanding of this, we asked whether purified virus or virus associated with extracellular vesicles (EVs) could penetrate two different cell culture models of the blood-brain barrier. In one model, we used the hCMEC/D3 brain endothelial cell line, and in the other, we used pluripotent stem cells induced to a brain endothelial cell phenotype (iPSC-EC). We found that neither cell type was permissive to viral infection, but the virus bound and was internalized by both in a sialic acid-dependent manner. Despite virus internalization into these cells, very few virions or virus-associated extracellular vesicles (virus-EVs) penetrated the barriers. The small amount of virus or virus-EVs that did pass through either barrier was sufficient to establish infection in human glial cells. Our findings demonstrate that limited amounts of infectious virions and virus-associated EVs can traverse the brain microvascular endothelium and establish infection.IMPORTANCEThe human polyomavirus, JC Polyomavirus (JCPyV), causes a rapidly progressing demyelinating disease in immunocompromised or immunomodulated patients. Demyelinating lesions are often seen surrounding blood vessels in the brain. In this paper, we used two models to recapitulate a minimal blood-brain barrier and found that both were highly restrictive of virus penetration. A small amount of virus succeeded in crossing both barriers and was sufficient to establish infection of human glia. These data have direct implications for mechanisms used by JCPyV to invade the CNS and cause neurological disease.

Recent advances in blood-brain barrier-on-a-chip models

The blood-brain barrier is a physiological barrier between the vascular system and the nervous system. Under healthy conditions, it restricts the passage of most biomolecules into the brain, making drug development exceedingly challenging. Conventional cell-based in vitro models provide valuable insights into certain features of the BBB. Nevertheless, these models often lack the three-dimensional structure and dynamic interactions of the surrounding microenvironment, which greatly influence cell functionality. Consequently, considerable efforts have been made to enhance in vitro models for drug development and disease research. Recently, microfluidic organ-on-a-chip systems have emerged as promising candidates to better mimic the dynamic nature of the BBB. This review provides a comprehensive overview of recent BBB-on-chip devices. The typical building blocks, chip designs, the perfusion infrastructure, and readouts used to characterize and evaluate BBB formation are presented, analyzed, and discussed in detail. STATEMENT OF SIGNIFICANCE: The blood-brain barrier (BBB) is a highly selective barrier that controls what can enter the brain. While it protects the brain from harmful substances, it also hinders the delivery of treatments for neurological diseases such as Alzheimer's and Parkinson's. Due to its complexity, studying the BBB in living organisms remains difficult. However, recent advances in "organ-on-a-chip" technology have allowed scientists to create small, engineered models that replicate the BBB. These models provide a powerful platform to study diseases and test potential drugs with greater accuracy than traditional methods. Organ-on-a-chip devices are designed to mimic the behavior of organs or tissues in the human body, offering a more realistic and controlled environment for research. This review highlights recent breakthroughs in BBB-on-a-chip technology, showing how these models enhance current research and have the potential to transform the way we study brain diseases and develop new drugs. By integrating biology and engineering, BBB-on-a-chip technology has the potential to transform neuroscience research, improve drug development, and enhance our understanding of brain disorders.

Targeted and Untargeted Proteomics-based Comparison of Adenoviral Infected hCMEC/D3 and hBMEC as a Human Brain Endothelial Cells to Study the OATP2B1 Transporter

The blood-brain barrier (BBB) is essential for central nervous system (CNS) homeostasis by regulating permeability between the bloodstream and brain. This study evaluates the immortalized human brain capillary endothelial cell lines hCMEC/D3 and hBMEC for their use as a brain endothelial cells to investigate the OATP2B1 transporter following adenoviral infection. We assessed the impact of adenoviral-mediated OATP2B1 expression on BBB marker proteins and transporters using targeted and untargeted mass spectrometry-based proteomics. Targeted proteomics identified measurable levels of endothelial markers PECAM1 and CDH5 in hCMEC/D3, whereas these markers were undetectable in hBMEC. Both cell lines exhibited similar Pgp levels, while BCRP was absent in hCMEC/D3. The expression of uptake transporters was also evaluated, revealing comparable levels of GLUT1, ENT1, MCT1 and OAT7 in hCMEC/D3 and hBMEC. Although OATP2B1 levels did not significantly increase post-infection in targeted proteomics, untargeted proteomics confirmed enhanced OATP2B1 expression. Other BBB markers and transporters remained unaffected in both cell lines. Notably, hCMEC/D3 demonstrated a stronger BBB phenotype, indicated by higher expression of BBB markers and transporters, while adenoviral infection was more effective in hBMEC. The differences between targeted and untargeted proteomics underscore the need for diverse methods to verify protein expression levels. This comparative analysis provides insights into the strengths and limitations of hCMEC/D3 and hBMEC for BBB research, particularly regarding drug transport mechanisms.

Impact of Tick-Borne Orthoflaviviruses Infection on Compact Human Brain Endothelial Barrier

Tick-borne encephalitis remains a significant burden on human health in the endemic areas in Central Europe and Eastern Asia. The causative agent, tick-borne encephalitis virus (TBEV), is a neurotropic virus belonging to the genus of Orthoflavivirus. After TBEV enters the central nervous system (CNS), it mainly targets neurons, causing encephalitis and leading to life-long disabilities, coma and, in rare cases, death. The neuroinvasive mechanisms of orthoflaviviruses are poorly understood. Here we investigate the mechanism of TBEV neuroinvasion, hypothesizing that TBEV influences blood-brain barrier (BBB) properties and uses transcellular routes to cross the endothelial barrier and enter the CNS. To test this hypothesis, we employed an in vitro transwell system consisting of endothelial cell monolayers cultured on insert membranes and studied the barrier properties following inoculation to tick-borne orthoflaviviruses. It was shown that TBEV and closely related but naturally attenuated Langat virus (LGTV) crossed the intact endothelial cell monolayer without altering its barrier properties. Interestingly, transendothelial migration of TBEV was significantly affected when two cellular surface antigens, the laminin-binding protein and vimentin, were blocked with specific antibodies. Taken together, these results indicate that orthoflaviviruses use non-destructive transcellular routes through endothelial cells to establish infection within the CNS.

A guide for blood-brain barrier models

Understanding the intricate mechanisms underlying brain-related diseases hinges on unraveling the pivotal role of the blood-brain barrier (BBB), an essential dynamic interface crucial for maintaining brain equilibrium. This review offers a comprehensive analysis of BBB physiology, delving into its cellular and molecular components while exploring a wide range of in vivo and in vitro BBB models. Notably, recent advancements in 3D cell culture techniques are explicitly discussed, as they have significantly improved the fidelity of BBB modeling by enabling the replication of physiologically relevant environments under flow conditions. Special attention is given to the cellular aspects of in vitro BBB models, alongside discussions on advances in stem cell technologies, providing valuable insights into generating robust cellular systems for BBB modeling. The diverse array of cell types used in BBB modeling, depending on their sources, is meticulously examined in this comprehensive review, scrutinizing their respective derivation protocols and implications. By synthesizing diverse approaches, this review sheds light on the improvements of BBB models to capture physiological conditions, aiding in understanding BBB interactions in health and disease conditions to foster clinical developments.

Hepatic and extra-hepatic metabolism of propylene glycol ethers in the context of central nervous system toxicity

Propylene glycol ethers (PGEs) are mixtures of an α-isomer and a β-isomer (β-PGE) that is oxidized via alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) to potentially neurotoxic alkoxy propionic acids (β-metabolites). While the liver is the primary organ for ADH- and ALDH-mediated metabolism, the contribution to the metabolism of β-PGEs by the blood-brain barrier (BBB) and the brain remains unknown. Here, we aimed to assess the neurotoxic potential of PGEs after systemic exposure by (1) comparing 3D HepaRG and human liver subcellular fraction (S9) for the in vitro determination of the kinetics of hepatic metabolism for β-PGEs, (2) evaluating the BBB-permeability of PGEs and β-metabolites, (3) determining the presence of ADH1 and ALDH2 and the extent of metabolization of β-PGEs in the BBB and brain. The results show that 3D HepaRG and S9 served as competent systems to estimate the enzymatic kinetic (clearance) for β-metabolite formation. We observed that PGEs and the β-metabolites could cross the BBB, based on their permeance across a cellular barrier consisting of the hCMEC/D3 cell line. Metabolic enzymes were not exclusive to the liver, as expression of ADH1 and ALDH2 was demonstrated using RT-qPCR, Western blot, and immunostainings in the BBB in vitro models and in BrainSpheres. Furthermore, LC-MS/MS quantification of the β-metabolites in all in vitro models revealed that 3D HepaRG had a similar metabolic capacity to primary human hepatocytes and that the amount of β-metabolite formed per protein in the BBB was approximately 10-30 % of that in the liver. We also demonstrated active metabolism in the BrainSpheres. In conclusion, the hepatic in vitro models provided data that will help to refine toxicokinetic models and predict internal exposures, thereby supporting the risk assessment of PGEs. In addition, the high permeance of the PGEs and the β-metabolites across the BBB increases the plausibility of neurotoxicity upon systemic exposure. This is further supported by the presence of active ADH1 and ALDH2 enzymes in the BBB in vitro systems and in BrainSpheres, suggesting metabolite formation in the central nervous system. Hence, we suggest that BBB-permeance and extra-hepatic metabolism of the β-PGEs may contribute to the neurotoxicity of PGEs.

Involvement of RhoA/ROCK Signaling Pathway in Methamphetamine-Induced Blood-Brain Barrier Disruption

Methamphetamine (METH) is a powerful addictive psychostimulant that gives rise to severe abusers worldwide. While many studies have reported on the neurotoxicity of METH, blood-brain barrier (BBB) dysfunction has recently attracted attention as an essential target in METH-induced pathological changes in the brain. However, its mechanism has not been fully understood. We found that METH increased paracellular permeability and decreased vascular integrity through FITC-dextran and trans-endothelial electrical resistance (TEER) assay in primary human brain endothelial cells (HBMECs). Also, redistribution of tight junction proteins (zonula occluden-1 and claudin-5) and reorganization of F-actin cytoskeleton were observed in METH-exposed HBMECs. To determine the mechanism of METH-induced BBB disruption, the RhoA/ROCK signaling pathway was examined in METH-treated HBMECs. METH-activated RhoA, followed by an increase in the phosphorylation of downstream effectors, myosin light chain (MLC) and cofilin, occurs in HBMECs. Pretreatment with ROCK inhibitors Y-27632 and fasudil reduced the METH-induced increase in phosphorylation of MLC and cofilin, preventing METH-induced redistribution of junction proteins and F-actin cytoskeletal reorganization. Moreover, METH-induced BBB leakage was alleviated by ROCK inhibitors in vitro and in vivo. Taken together, these results suggest that METH induces BBB dysfunction by activating the RhoA/ROCK signaling pathway, which results in the redistribution of junction proteins via F-actin cytoskeletal reorganization.

Functional assessment of immortalized human brain microvascular endothelial cells with different passage numbers: A case study for a prospective proposal on variability management of in vitro blood-brain barrier models

In vitro blood-brain barrier (BBB) models, primarily consisting of brain microvascular endothelial cells (BMEC), are expected to play pivotal roles in evaluating drug permeability into the brain. However, these models often exhibit functional variability due to various factors, raising practical concerns that can hinder their use in drug development studies. By investigating cell passage numbers as one such factor, we aim to assess how BBB model functionality is affected and to propose a practical strategy for managing this variability. In transwell-BBB models - but not in spheroidal-BBB models - the intercellular barrier integrity was somewhat compromised when higher-passage human immortalized BMEC (HBMEC/ci18) were used. Nonetheless, a clear in vitro-in vivo correlation (IVIVC) curve could still be obtained with these transwell-BBB models, similar to those with lower passage number HBMEC/ci18, presumably allowing for reasonable estimation of in vivo drug permeability. Therefore, changes in functional levels of BBB models do not always significantly diminish their practical value in drug BBB permeability studies. Additionally, the IVIVC curve integrity may serve as an indicator for assessing acceptable BBB model functionality. These findings provide valuable insights for the future application of in vitro human BBB models in drug development studies.

Decreasing β-Catenin Leads to Altered Endothelial Morphology, Increased Barrier Permeability and Cognitive Impairment During Chronic Methamphetamine Exposure

Cognitive impairment induced by chronic methamphetamine (METH) exposure exhibits similarities to neurodegenerative disorders and is associated with blood-brain barrier (BBB) dysfunction. However, the potential involvement of β-catenin in maintaining BBB integrity during METH exposure remains unexplored. In this study, Y-maze and novel object recognition tests were conducted to assess cognitive impairment in mice exposed chronically to methamphetamine for 2 and 4 weeks. Gd-DTPA and Evans blue leakage tests revealed disruption of the BBB in the hippocampus, while chronic METH exposure for 2 and 4 weeks significantly decreased β-catenin levels along with its transcriptionally regulated protein, claudin5. Additionally, various neural injury-related proteins, such as APP, Aβ1-42, p-tau (Thr181) and p-tau (Ser396), as well as neuroinflammation-related proteins, such as IL-6, IL-1β, and TNF-α, exhibited increased levels following chronic METH exposure. Furthermore, plasma analysis indicated elevated levels of p-Tau (total), neurofilament light chain, and GFAP. In vitro experiments demonstrated that exposure to METH resulted in dose-dependent and time-dependent reductions in cellular activity and connectivity of bEnd.3 and hcmec/D3 cells. Furthermore, β-catenin exhibited decreased levels and altered subcellular localization, transitioning from the cell membrane to the cytoplasm and nucleus upon METH exposure. Overexpression of β-catenin was found to alleviate endothelial toxicity and attenuate junctional weakening induced by METH. The aforementioned findings underscore the crucial involvement of β-catenin in endothelial cells during chronic METH exposure-induced disruption of the BBB, thereby presenting a potential novel target for addressing METH-associated cerebrovascular dysfunction and cognitive impairment.

Regulatory Network Inference of Induced Senescent Midbrain Cell Types Reveals Cell Type-Specific Senescence-Associated Transcriptional Regulators

Cellular senescence of brain cell types has become an increasingly important perspective for both aging and neurodegeneration, specifically in the context of Parkinson's Disease (PD). The characterization of classical hallmarks of senescence is a widely debated topic, whereby the context in which a senescence phenotype is being investigated, such as the cell type, the inducing stressor, and/or the model system, is an extremely important aspect to consider when defining a senescent cell. Here, we describe a cell type-specific profile of senescence through the investigation of various canonical senescence markers in five human midbrain cell lines using chronic 5-Bromodeoxyuridine (BrdU) treatment as a model of DNA damage-induced senescence. We used principal component analysis (PCA) and subsequent regulatory network inference to define both unique and common senescence profiles in the cell types investigated, as well as revealed senescence-associated transcriptional regulators (SATRs). Functional characterization of one of the identified regulators, transcription factor AP4 (TFAP4), further highlights the cell type-specificity of the expression of the various senescence hallmarks. Our data indicates that SATRs modulate cell type-specific profiles of induced senescence in key midbrain cell types that play an important role in the context of aging and PD.

Astaxanthin-loaded brain-permeable liposomes for Parkinson's disease treatment via antioxidant and anti-inflammatory responses

Parkinson's disease is a neurodegenerative disorder characterized by cardinal motor symptoms resulting from the loss of dopaminergic neurons in the substantia nigra pars compacta. Although current medications may alleviate its symptoms, Parkinson's disease remains incurable. Astaxanthin is an antioxidant and anti-inflammatory agent; however, its high susceptibility to oxidative degradation and low aqueous solubility limit its therapeutic efficacy. This study aimed to improve the pharmaceutical properties and neuroprotective effects of astaxanthin for Parkinson's disease treatment by using lactoferrin-conjugated astaxanthin-loaded liposomes (Lf-ASX-LPs). We successfully formulated Lf-ASX-LPs with high encapsulation efficiency (97.6%) and favorable physical characteristics (diameter: 109.8 ± 1.1 nm; polydispersity index: 0.18 ± 0.01; zeta potential: - 9.5 ± 1.1 mV). Lf-functionalized liposomes demonstrated enhanced cellular uptake and permeation in a Transwell® study, showing a 16.7-fold higher internalization in SH-SY5Y cells over 24 h than those without Lf conjugation. Additionally, Lf functionalization enhanced brain penetration ability, as demonstrated by a biodistribution study using nude mice, compared to LPs without Lf conjugation. In vitro, Lf-ASX-LPs reduced cell loss by 20.1% and oxygen species by 30.0%, ameliorated the reduction in mitochondrial membrane potential under 1-methyl-4-phenylpyridinium-induced toxicity by 40.1%, and reduced extracellular nitric oxide levels under lipopolysaccharide-induced toxicity by 32.0%, indicating cytoprotective and antioxidant effects. In a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Parkinson's disease mouse model, treatment with Lf-ASX-LPs resulted in 5.0-, 3.1-, and 5.6-fold increases in dopamine levels, TH+ fiber density, and TH+ neurons, respectively, restoring dopaminergic neuron damage. The developed formulation also alleviated behavioral impairment and neuroinflammation, reducing astrocyte and microglial activation in the striatum and substantia nigra of the MPTP-treated animals. Thus, our formulation of Lf-ASX-LPs represents a promising strategy for providing neuroprotection and retarding Parkinson's disease progression.

HDAC6 inhibitor-loaded brain-targeted nanocarrier-mediated neuroprotection in methamphetamine-driven Parkinson's disease

The dynamic equilibrium between acetylation and deacetylation is vital for cellular homeostasis. Parkinson's disease (PD), a neurodegenerative disorder marked by α-synuclein (α-syn) accumulation and dopaminergic neuron loss in the substantia nigra, is associated with a disruption of this balance. Therefore, correcting this imbalance with histone deacetylase (HDAC) inhibitors represents a promising treatment strategy for PD. CAY10603 (CAY) is a potent and selective HDAC6 inhibitor. However, because of its poor water solubility and short biological half-life, it faces clinical limitations. Herein, we engineered lactoferrin-decorated CAY-loaded poly(lactic-co-glycolic acid) nanoparticles (denoted as PLGA@CAY@Lf NPs) to effectively counter methamphetamine (Meth)-induced PD. PLGA@CAY@Lf NPs showed enhanced blood-brain barrier crossing and significant brain accumulation. Notably, CAY released from PLGA@CAY@Lf NPs restored the disrupted acetylation balance in PD, resulting in neuroprotection by reversing mitochondrial dysfunction, suppressing reactive oxygen species, and inhibiting α-syn accumulation. Additionally, PLGA@CAY@Lf NPs treatment normalized dopamine and tyrosine hydroxylase levels, reduced neuroinflammation, and improved behavioral impairments. These findings underscore the potential of PLGA@CAY@Lf NPs in treating Meth-induced PD and suggest that an innovative HDAC6-inhibitor-based strategy can be used to treat PD.

Bioactive compounds regulate appetite through the melanocortin system: a review

Obesity, a significant health crisis, arises from an imbalance between energy intake and expenditure. Enhancing appetite regulation has garnered substantial attention from researchers as a novel and effective strategy for weight management. The melanocortin system, situated in the hypothalamus, is recognized as a critical node in the regulation of appetite. It integrates long-term and short-term hormone signals from the periphery as well as nutrients, forming a complex network of interacting feedback mechanisms with the gut-brain axis, significantly contributing to the regulation of energy homeostasis. Appetite regulation by bioactive compounds has been a focus of intensive research due to their favorable safety profiles and easy accessibility. These bioactive compounds, derived from a variety of plant and animal sources, modulate the melanocortin system and influence appetite and energy homeostasis through multiple pathways: central nervous system, peripheral hormones, and intestinal microbiota. Here, we review the anatomy, function, and receptors of the melanocortin system, outline the long-term and short-term regulatory hormones that act on the melanocortin system, and discuss the bioactive compounds and their mechanisms of action that exert a regulatory effect on appetite by targeting the melanocortin system. This review contributes to a better understanding of how bioactive compounds regulate appetite via the melanocortin system, thereby providing nutritional references for citizens' dietary preferences.

An In Vitro Model of the Blood-Brain Barrier for the Investigation and Isolation of the Key Drivers of Barriergenesis

The blood-brain barrier (BBB) tightly regulates substance transport between the bloodstream and the brain. Models for the study of the physiological processes affecting the BBB, as well as predicting the permeability of therapeutic substances for neurological and neurovascular pathologies, are highly desirable. Existing models, such as Transwell utilizing-models, do not mimic the extracellular environment of the BBB with their stiff, semipermeable, non-biodegradable membranes. To help overcome this, we engineered electrospun membranes from poly L-lactic acid in combination with a nanometric coating of poly(ethyl acrylate) (PEA) that drives fibrillogenesis of fibronectin, facilitating the synergistic presentation of both growth factors and integrin binding sites. Compared to commercial semi-porous membranes, these membranes significantly improve the expression of BBB-related proteins in brain endothelial cells. PEA-coated membranes in combination with different growth factors and extracellular protein coatings reveal nerve growth factor (NGF) and fibroblast growth factor (FGF-2) caused formation of better barriers in vitro. This BBB model offers a robust platform for studying key biochemical factors influencing barrier formation that marries the simplicity of the Transwell model with the highly tunable electrospun PEA-fibronectin membranes. This enables the generation of high-throughput drug permeability models without the need of complicated co-culture conditions.

Complex regulation of tau phosphorylation by the endothelin system in brain microvascular endothelial cells (BMVECs): link to barrier function

Endothelin-1 (ET-1), the most potent vasoconstrictor identified to date, contributes to cerebrovascular dysfunction. ET-1 levels in postmortem brain specimens from individuals diagnosed with Alzheimer's disease (AD) and related dementias (ADRD) were shown to be related to cerebral hypoxia and disease severity. ET-1-mediated vascular dysfunction and ensuing cognitive deficits have also been reported in experimental models of AD and ADRD. Moreover, studies also showed that ET-1 secreted from brain microvascular endothelial cells (BMVECs) can affect neurovascular unit integrity in an autocrine and paracrine manner. Vascular contributions to cognitive impairment and dementia (VCID) is a leading ADRD cause known to be free of neuronal tau pathology, a hallmark of AD. However, a recent study reported cytotoxic hyperphosphorylated tau (p-tau) accumulation, which fails to bind or stabilize microtubules in BMVECs in VCID. Thus, the study aimed to determine the impact of ET-1 on tau pathology, microtubule organization, and barrier function in BMVECs. Cells were stimulated with 1 μM ET-1 for 24 h in the presence/absence of ETA (BQ123; 20 μM) or ETB (BQ788; 20 μM) receptor antagonists. Cell lysates were assayed for an array of phosphorylation site-specific antibodies and microtubule organization/stabilization markers. ET-1 stimulation increased p-tau Thr231 but decreased p-tau Ser199, Ser262, Ser396, and Ser214 levels only in the presence of ETA or ETB antagonism. ET-1 also impaired barrier function in the presence of ETA antagonism. These novel findings suggest that (1) dysregulation of endothelial tau phosphorylation may contribute to cerebral microvascular dysfunction and (2) the ET system may be an early intervention target to prevent hyperphosphorylated tau-mediated disruption of BMVEC barrier function.

Microfluidic Preparation and Evaluation of Multivesicular Liposomes Containing Gastrodin for Oral Delivery across the Blood-Brain Barrier

In this study, multivesicular liposomes (MVLs) were prepared by microfluidic technology and used for delivering gastrodin (GAS), a water-soluble drug, across the blood-brain barrier (BBB). The formulations and preparation parameters in preparing gastrodin multivesicular liposomes (GAS-MVLs) were both optimized. Some properties of GAS-MVLs including morphology, particle size, encapsulation efficiency, and in vitro release were evaluated. An in vitro BBB model was established by coculturing mouse brain endothelial cells (bEnd.3) and astrocytes (C8-D1A). The permeability of GAS-MVLs across the BBB model was evaluated. Finally, the permeability of GAS-MVLs across BBB was evaluated by in vivo pharmacokinetics in mice. The concentrations of GAS in the blood and brain were determined by high-performance liquid chromatography (HPLC), and then brain-targeting efficiency (BTE), relative uptake rate (Re), and peak concentration ratio (Ce) were calculated. The results showed that, using a Y-type microfluidic chip and setting the flow rate ratio of the second aqueous phase to the W/O emulsion phase at 23, with a total flow rate of 0.184 m/s, the prepared GAS-MVLs showed an obvious multivesicular structure and a relatively narrow distribution of particle sizes. The prepared GAS-MVLs were spherical with a dense structure. The average particle size was 2.09 ± 0.17 μm. The average encapsulation rate was (34.47 ± 0.39)%. The particle size of MVLs prepared by the microfluidic method was much smaller than that prepared by the traditional method, which was usually larger than 10 μm. After 6 h from the beginning of the administration, the apparent transmittance of GAS-MVLs in the in vitro BBB model was 67.71%, which was 1.92 times higher than that of the GAS solution. In vivo pharmacokinetic study showed that the intracerebral area under curve (AUC) of GAS-MVLs was 5.68 times higher than that of the GAS solution, and the e peak concentration (Cmax) was 2.036 times higher than that of the GAS solution. BTE was 1.945, intracerebral Re was 5.688, and Ce was 2.036. Both in vitro and in vivo experiment results showed that GAS-MVLs prepared by microfluidic technology in this study significantly delivered GAS across BBB and enriched GAS in the brain. It provides a possibility for brain-targeting delivery of GAS in the prevention and treatment of central nervous system diseases by oral administration and lays the foundation for further development of oral brain-targeted preparations of GAS.

In vitro modelling of the neurovascular unit for ischemic stroke research: Emphasis on human cell applications and 3D model design

Ischemic stroke has garnered global medical attention as one of the most serious cerebrovascular diseases. The mechanisms involved in both the development and recovery phases of ischemic stroke are complex, involving intricate interactions among different types of cells, each with its own unique functions. To better understand the possible pathogenesis, neurovascular unit (NVU), a concept comprising neurons, endothelial cells, mural cells, glial cells, and extracellular matrix components, has been used in analysing various brain diseases, particularly in ischemic stroke, aiming to depict the interactions between cerebral vasculature and neural cells. While in vivo models often face limitations in terms of reproducibility and the ability to precisely mimic human pathophysiology, it is now important to establish in vitro NVU models for ischemic stroke research. In order to accurately portray the pathological processes occurring within the brain, a diverse array of NVU 2D and 3D in vitro models, each possessing unique characteristics and advantages, have been meticulously developed. This review presents a comprehensive overview of recent advancements in in vitro models specifically tailored for investigating ischemic stroke. Through a systematic categorization of these developments, we elucidate the intricate links between NVU components and the pathogenesis of ischemic stroke. Furthermore, we explore the distinct advantages offered by innovative NVU models, notably 3D models, which closely emulate in vivo conditions. Additionally, an examination of current therapeutic modalities for ischemic stroke developed utilizing in vitro NVU models is provided. Serving as a valuable reference, this review aids in the design and implementation of effective in vitro models for ischemic stroke research.

Neurons enhance blood-brain barrier function via upregulating claudin-5 and VE-cadherin expression due to glial cell line-derived neurotrophic factor secretion

Blood-brain barrier (BBB) prevents neurotoxins from entering central nervous system. We aimed to establish and characterize an in vitro triple co-culture BBB model consisting of brain endothelial cells hCMEC/D3, astrocytoma U251 cells, and neuroblastoma SH-SY5Y cells. Co-culture of SH-SY5Y and U251 cells markedly enhanced claudin-5 and VE-cadherin expression in hCMEC/D3 cells, accompanied by increased transendothelial electrical resistance and decreased permeability. Conditioned medium (CM) from SH-SY5Y cells (S-CM), U251 cells (U-CM), and co-culture of SH-SY5Y and U251 cells (US-CM) also promoted claudin-5 and VE-cadherin expression. Glial cell line-derived neurotrophic factor (GDNF) levels in S-CM and US-CM were significantly higher than CMs from hCMEC/D3 and U-CM. Both GDNF and US-CM upregulated claudin-5 and VE-cadherin expression, which were attenuated by anti-GDNF antibody and GDNF signaling inhibitors. GDNF increased claudin-5 expression via the PI3K/AKT/FOXO1 and MAPK/ERK pathways. Meanwhile, GDNF promoted VE-cadherin expression by activating PI3K/AKT/ETS1 and MAPK/ERK/ETS1 signaling. The roles of GDNF in BBB integrity were validated using brain-specific Gdnf silencing mice. The developed triple co-culture BBB model was successfully applied to predict BBB permeability. In conclusion, neurons enhance BBB integrity by upregulating claudin-5 and VE-cadherin expression through GDNF secretion and established triple co-culture BBB model may be used to predict drugs' BBB permeability.

RGD-coated polymeric microbubbles promote ultrasound-mediated drug delivery in an inflamed endothelium-pericyte co-culture model of the blood-brain barrier

Drug delivery to central nervous pathologies is compromised by the blood-brain barrier (BBB). A clinically explored strategy to promote drug delivery across the BBB is sonopermeation, which relies on the combined use of ultrasound (US) and microbubbles (MB) to induce temporally and spatially controlled opening of the BBB. We developed an advanced in vitro BBB model to study the impact of sonopermeation on the delivery of the prototypic polymeric drug carrier pHPMA as a larger molecule and the small molecule antiviral drug ribavirin. This was done under standard and under inflammatory conditions, employing both untargeted and RGD peptide-coated MB. The BBB model is based on human cerebral capillary endothelial cells and human placental pericytes, which are co-cultivated in transwell inserts and which present with proper transendothelial electrical resistance (TEER). Sonopermeation induced a significant decrease in TEER values and facilitated the trans-BBB delivery of fluorescently labeled pHPMA (Atto488-pHPMA). To study drug delivery under inflamed endothelial conditions, which are typical for e.g. tumors, neurodegenerative diseases and CNS infections, tumor necrosis factor (TNF) was employed to induce inflammation in the BBB model. RGD-coated MB bound to and permeabilized the inflamed endothelium-pericyte co-culture model, and potently improved Atto488-pHPMA and ribavirin delivery. Taken together, our work combines in vitro BBB bioengineering with MB-mediated drug delivery enhancement, thereby providing a framework for future studies on optimization of US-mediated drug delivery to the brain.

Neisseria meningitidis activates pyroptotic pathways in a mouse model of meningitis: role of a two-partner secretion system

There is evidence that in infected cells in vitro the meningococcal HrpA/HrpB two-partner secretion system (TPS) mediates the exit of bacteria from the internalization vacuole and the docking of bacteria to the dynein motor resulting in the induction of pyroptosis. In this study we set out to study the role of the HrpA/HrpB TPS in establishing meningitis and activating pyroptotic pathways in an animal model of meningitis using a reference serogroup C meningococcal strain, 93/4286, and an isogenic hrpB knockout mutant, 93/4286ΩhrpB. Survival experiments confirmed the role of HrpA/HrpB TPS in the invasive meningococcal disease. In fact, the ability of the hrpB mutant to replicate in brain and spread systemically was impaired in mice infected with hrpB mutant. Furthermore, western blot analysis of brain samples during the infection demonstrated that: i. N. meningitidis activated canonical and non-canonical inflammasome pyroptosis pathways in the mouse brain; ii. the activation of caspase-11, caspase-1, and gasdermin-D was markedly reduced in the hrpB mutant; iii. the increase in the amount of IL-1β and IL-18, which are an important end point of pyroptosis, occurs in the brains of mice infected with the wild-type strain 93/4286 and is strongly reduced in those infected with 93/4286ΩhrpB. In particular, the activation of caspase 11, which is triggered by cytosolic lipopolysaccharide, indicates that during meningococcal infection pyroptosis is induced by intracellular infection after the exit of the bacteria from the internalizing vacuole, a process that is hindered in the hrpB mutant. Overall, these results confirm, in an animal model, that the HrpA/HrpB TPS plays a role in the induction of pyroptosis and suggest a pivotal involvement of pyroptosis in invasive meningococcal disease, paving the way for the use of pyroptosis inhibitors in the adjuvant therapy of the disease.

Engineering a 3D Biomimetic Peptides Functionalized-Polyethylene Glycol Hydrogel Model Cocultured with Endothelial Cells and Astrocytes: Enhancing In Vitro Blood-Brain Barrier Biomimicry

The blood-brain barrier (BBB) poses a significant challenge for drug delivery and is linked to various neurovascular disorders. In vitro BBB models provide a tool to investigate drug permeation across the BBB and the barrier's response to external injury events. Yet, existing models lack fidelity in replicating the BBB's complexity, hindering a comprehensive understanding of its functions. This study introduces a three-dimensional (3D) model using polyethylene glycol (PEG) hydrogels modified with biomimetic peptides that represent recognition sequences of key proteins in the brain. Hydrogels were functionalized with recognition sequences for laminin (IKVAV) and fibronectin peptides (RGD) and chemically cross-linked with matrix metalloprotease-sensitive peptides (MMPs) to mimic the extracellular matrix of the BBB. Astrocytes and endothelial cells were seeded within and on the surface of the hydrogels, respectively. The barrier integrity was assessed through different tests including transendothelial electrical resistance (TEER), the permeability of sodium fluorescence (Na-F), the permeability of Evan's blue bound to albumin (EBA), and the expression of zonula occluden-1 (ZO-1) in seeded endothelial cells. Hydrogels with a combination of RGD and IKVAV peptides displayed superior performance, exhibiting significantly higher TEER values (55.33 ± 1.47 Ω·cm2) at day 5 compared to other 2D controls including HAECs-monoculture and HAECs-cocultured with NHAs seeded on well inserts and 3D controls including RGD hydrogel and RGD-IKVAV monoculture with HAECs and RGD hydrogel cocultured with HAECs and NHAs. The designed 3D system resulted in the lowest Evan's blue permeability at 120 min (0.215 ± 0.055 μg/mL) compared to controls. ZO-1 expression was significantly higher and formed a relatively larger network in the functionalized hydrogel cocultured with astrocytes and endothelial cells compared to the controls. Thus, the designed 3D model effectively recapitulates the main BBB structure and function in vitro and is expected to contribute to a deeper understanding of pathological CNS angiogenesis and the development of effective CNS medications.

Shaping the Neurovascular Unit Exploiting Human Brain Organoids

Brain organoids, three-dimensional cell structures derived from pluripotent stem cells, closely mimic key aspects of the human brain in vitro, providing a powerful tool for studying neurodevelopment and disease. The neuroectodermal induction protocol employed for brain organoid generation primarily gives rise to the neural cellular component but lacks the vital vascular system, which is crucial for the brain functions by regulating differentiation, migration, and circuit formation, as well as delivering oxygen and nutrients. Many neurological diseases are caused by dysfunctions of cerebral microcirculation, making vascularization of human brain organoids an important tool for pathogenetic and translational research. Experimentally, the creation of vascularized brain organoids has primarily focused on the fusion of vascular and brain organoids, on organoid transplantation in vivo, and on the use of microfluidic devices to replicate the intricate microenvironment of the human brain in vitro. This review summarizes these efforts and highlights the importance of studying the neurovascular unit in a forward-looking perspective of leveraging their use for understanding and treating neurological disorders.

Loss of Direct Vascular Contact to Astrocytes in the Hippocampus as an Initial Event in Alzheimer's Disease. Evidence from Patients, In Vivo and In Vitro Experimental Models

Alzheimer's disease (AD) is characterized by the accumulation of aggregated amyloid peptides in the brain parenchyma and within the walls of cerebral vessels. The hippocampus-a complex brain structure with a pivotal role in learning and memory-is implicated in this disease. However, there is limited data on vascular changes during AD pathological degeneration in this susceptible structure, which has distinctive vascular traits. Our aim was to evaluate vascular alterations in the hippocampus of AD patients and PDAPP-J20 mice-a model of AD-and to determine the impact of Aβ40 and Aβ42 on endothelial cell activation. We found a loss of physical astrocyte-endothelium interaction in the hippocampus of individuals with AD as compared to non-AD donors, along with reduced vascular density. Astrocyte-endothelial interactions and levels of the tight junction protein occludin were altered early in PDAPP-J20 mice, preceding any signs of morphological changes or disruption of the blood-brain barrier in these mice. At later stages, PDAPP-J20 mice exhibited decreased vascular density in the hippocampus and leakage of fluorescent tracers, indicating dysfunction of the vasculature and the BBB. In vitro studies showed that soluble Aβ40 exposure in human brain microvascular endothelial cells (HBMEC) was sufficient to induce NFκB translocation to the nucleus, which may be linked with an observed reduction in occludin levels. The inhibition of the membrane receptor for advanced glycation end products (RAGE) prevented these changes in HBMEC. Additional results suggest that Aβ42 indirectly affects the endothelium by inducing astrocytic factors. Furthermore, our results from human and mouse brain samples provide evidence for the crucial involvement of the hippocampal vasculature in Alzheimer's disease.

Circulating low-molecular-weight (poly)phenol metabolites in the brain: unveiling in vitro and in vivo blood-brain barrier transport

Circulating metabolites resulting from colonic metabolism of dietary (poly)phenols are highly abundant in the bloodstream, though still marginally explored, particularly concerning their brain accessibility. Our goal is to disclose (poly)phenol metabolites' blood-brain barrier (BBB) transport, in vivo and in vitro, as well as their role at BBB level. For three selected metabolites, benzene-1,2-diol-3-sulfate/benzene-1,3-diol-2-sulfate (pyrogallol-sulfate - Pyr-sulf), benzene-1,3-diol-6-sulfate (phloroglucinol-sulfate - Phlo-sulf), and phenol-3-sulfate (resorcinol-sulfate - Res-sulf), BBB transport was assessed in human brain microvascular endothelial cells (HBMEC). Their potential in modulating in vitro BBB properties at circulating concentrations was also studied. Metabolites' fate towards the brain, liver, kidney, urine, and blood was disclosed in Wistar rats upon injection. Transport kinetics in HBMEC highlighted different BBB permeability rates, where Pyr-sulf emerged as the most in vitro BBB permeable metabolite. Pyr-sulf was also the most potent regarding BBB properties improvement, namely increased beta(β)-catenin membrane expression and reduction of zonula occludens-1 membrane gaps. Whereas no differences were observed for transferrin, increased expression of caveolin-1 upon Pyr-sulf and Res-sulf treatments was found. Pyr-sulf was also capable of modulating gene and protein expression of some solute carrier transporters. Notably, each of the injected metabolites exhibited a unique tissue distribution in vivo, with the remarkable ability to almost immediately reach the brain.

3D Brain Vascular Niche Model Captures Invasive Behavior and Gene Signatures of Glioblastoma

Glioblastoma (GBM) is a lethal brain cancer with no effective treatment; understanding how GBM cells respond to tumor microenvironment remains challenging as conventional cell cultures lack proper cytoarchitecture while in vivo animal models present complexity all at once. Developing a culture system to bridge the gap is thus crucial. Here, we employed a multicellular approach using human glia and vascular cells to optimize a 3-dimensional (3D) brain vascular niche model that enabled not only long-term culture of patient derived GBM cells but also recapitulation of key features of GBM heterogeneity, in particular invasion behavior and vascular association. Comparative transcriptomics of identical patient derived GBM cells in 3D and in vivo xenotransplants models revealed that glia-vascular contact induced genes concerning neural/glia development, synaptic regulation, as well as immune suppression. This gene signature displayed region specific enrichment in the leading edge and microvascular proliferation zones in human GBM and predicted poor prognosis. Gene variance analysis also uncovered histone demethylation and xylosyltransferase activity as main themes for gene adaption of GBM cells in vivo . Furthermore, our 3D model also demonstrated the capacity to provide a quiescence and a protective niche against chemotherapy. In summary, an advanced 3D brain vascular model can bridge the gap between 2D cultures and in vivo models in capturing key features of GBM heterogeneity and unveil previously unrecognized influence of glia-vascular contact for transcriptional adaption in GBM cells featuring neural/synaptic interaction and immunosuppression.

Empirical analysis of lead neurotoxicity mode of action and its application in health risk assessment

The mode of action (MOA) framework is proposed to inform a biological link between chemical exposures and adverse health effects. Despite a significant increase in knowledge and awareness, the application of MOA in human health risk assessment (RA) remains limited. This study aims to discuss the adoption of MOA for health RA within a regulatory context, taking our previously proposed but not yet validated MOA for lead neurotoxicity as an example. We first conducted a quantitative weight of evidence (qWOE) assessment, which revealed that the MOA has a moderate confidence. Then, targeted bioassays were performed within an in vitro blood-brain barrier (BBB) model to quantitatively validate the scientific validity of key events (KEs) in terms of essentiality and concordance of empirical support (dose/temporal concordance), which increases confidence in utilizing the MOA for RA. Building upon the quantitative validation data, we further conducted benchmark dose (BMD) analysis to map dose-response relationships for the critical toxicity pathways, and the lower limit of BMD at a 5% response (BMDL5) was identified as the point of departure (POD) value for adverse health effects. Notably, perturbation of the Aryl Hydrocarbon Receptor (AHR) signaling pathway exhibited the lowest POD value, measured at 0.0062 μM. Considering bioavailability, we further calculated a provisional health-based guidance value (HBGV) for children's lead intake, determining it to be 2.56 μg/day. Finally, the health risk associated with the HBGV was assessed using the hazard quotient (HQ) approach, which indicated that the HBGV established in this study is a relative safe reference value for lead intake. In summary, our study described the procedure for utilizing MOA in health RA and set an example for MOA-based human health risk regulation.

Organ-on-a-Chip Approach for Accelerating Blood-Brain Barrier Nanoshuttle Discovery

Organ-on-a-chip, which recapitulates the dynamics of in vivo vasculature, has emerged as a promising platform for studying organ-specific vascular beds. However, its practical advantages in identifying vascular-targeted drug delivery systems (DDS) over traditional in vitro models remain underexplored. This study demonstrates the reliability and efficacy of the organ-on-a-chip in screening efficient DDS by comparing its performance with that of a conventional transwell, both designed to simulate the blood-brain barrier (BBB). The BBB nanoshuttles discovered through BBB Chip-based screening demonstrated superior functionality in vivo compared to those identified using transwell methods. This enhanced effectiveness is attributed to the BBB Chip's accurate replication of the structure and dynamics of the endothelial glycocalyx, a crucial protective layer within blood vessels, especially under shear stress. This capability of the BBB Chip has enabled the identification of molecular shuttles that efficiently exploit the endothelial glycocalyx, thereby enhancing transendothelial transport efficacy. Our findings suggest that organ-on-a-chip technology holds considerable promise for advancing research in vascular-targeted DDS due to its accurate simulation of molecular transport within endothelial systems.

Progresses in the establishment, evaluation, and application of in vitro blood-brain barrier models

The blood-brain barrier (BBB) is a barrier between the circulatory system and the central nervous system (CNS), contributing to CNS protection and maintaining the brain homeostasis. Establishment of in vitro BBB models that are closer to the microenvironment of the human brain is helpful for evaluating the potential and efficiency of a drug penetrating BBB and thus the clinical application value of the drug. The in vitro BBB models not only provide great convenience for screening new drugs that can access to CNS but also help people to have a deeper study on the mechanism of substances entering and leaving the brain, which makes people have greater opportunities in the treatment of CNS diseases. Up to now, although much effort has been paid to the researches on the in vitro BBB models and many progresses have been achieved, no unified method has been described for establishing a BBB model and there is much work to do and many challenges to be faced with in the future. This review summarizes the research progresses in the establishment, evaluation, and application of in vitro BBB models.

Recent advances in cell-based in vitro models for predicting drug permeability across brain, intestinal, and pulmonary barriers

INTRODUCTION

Recent years have witnessed remarkable progress in the development of cell-based in vitro models aimed at predicting drug permeability, particularly focusing on replicating the barrier properties of the blood-brain barrier (BBB), intestinal epithelium, and lung epithelium.

AREA COVERED

This review provides an overview of 2D in vitro platforms, including monocultures and co-culture systems, highlighting their respective advantages and limitations. Additionally, it discusses tools and techniques utilized to overcome these limitations, paving the way for more accurate predictions of drug permeability. Furthermore, this review delves into emerging technologies, particularly microphysiological systems (MPS), encompassing static platforms such as organoids and dynamic platforms like microfluidic devices. Literature searches were performed using PubMed and Google Scholar. We focus on key terms such as in vitro permeability models, MPS, organoids, intestine, BBB, and lungs.

EXPERT OPINION

The potential of these MPS to mimic physiological conditions more closely offers promising avenues for drug permeability assessment. However, transitioning these advanced models from bench to industry requires rigorous validation against regulatory standards. Thus, there is a pressing need to validate MPS to industry and regulatory agency standards to exploit their potential in drug permeability prediction fully. This review underscores the importance of such validation processes to facilitate the translation of these innovative technologies into routine pharmaceutical practice.

Calcium and IL-6 regulate the anterograde trafficking and plasma membrane residence of the iron exporter ferroportin to modulate iron efflux

Iron is an essential element for proper cell functioning, but unbalanced levels can cause cell death. Iron metabolism is controlled at the blood-tissue barriers provided by microvascular endothelial cells. Dysregulated iron metabolism at these barriers is a factor in both neurodegenerative and cardiovascular diseases. Mammalian iron efflux is mediated by the iron efflux transporter ferroportin (Fpn). Inflammation is a factor in many diseases and correlates with increased tissue iron accumulation. Evidence suggests treatment with interleukin 6 (IL-6) increases intracellular calcium levels and calcium is known to play an important role in protein trafficking. We have shown that calcium increases plasma membrane localization of the iron uptake proteins ZIP8 and ZIP14, but if and how calcium modulates Fpn trafficking is unknown. In this article, we examined the effects of IL-6 and calcium on Fpn localization to the plasma membrane. In HEK cells expressing a doxycycline-inducible GFP-tagged Fpn, calcium increased Fpn-GFP membrane presence by 2 h, while IL-6 increased membrane-localized Fpn-GFP by 3 h. Calcium pretreatment increased Fpn-GFP mediated 55Fe efflux from cells. Endoplasmic reticulum calcium stores were shown to be important for Fpn-GFP localization and iron efflux. Use of calmodulin pathway inhibitors showed that calcium signaling is important for IL-6-induced Fpn relocalization. Studies in brain microvascular endothelial cells in transwell culture demonstrated an initial increase in 55Fe flux with IL-6 that is reduced by 6 h coinciding with upregulation of hepcidin. Overall, this research details one pathway by which inflammatory signaling mediated by calcium can regulate iron metabolism, likely contributing to inflammatory disease mechanisms.

A human pluripotent stem cell-derived in vitro model of the blood-brain barrier in cerebral malaria

BACKGROUND

Blood-brain barrier (BBB) disruption is a central feature of cerebral malaria (CM), a severe complication of Plasmodium falciparum (Pf) infections. In CM, sequestration of Pf-infected red blood cells (Pf-iRBCs) to brain endothelial cells combined with inflammation, hemolysis, microvasculature obstruction and endothelial dysfunction mediates BBB disruption, resulting in severe neurologic symptoms including coma and seizures, potentially leading to death or long-term sequelae. In vitro models have advanced our knowledge of CM-mediated BBB disruption, but their physiological relevance remains uncertain. Using human induced pluripotent stem cell-derived brain microvascular endothelial cells (hiPSC-BMECs), we aimed to develop a novel in vitro model of the BBB in CM, exhibiting enhanced barrier properties.

METHODS

hiPSC-BMECs were co-cultured with HB3var03 strain Pf-iRBCs up to 9 h. Barrier integrity was measured using transendothelial electrical resistance (TEER) and sodium fluorescein permeability assays. Localization and expression of tight junction (TJ) proteins (occludin, zonula occludens-1, claudin-5), cellular adhesion molecules (ICAM-1, VCAM-1), and endothelial surface markers (EPCR) were determined using immunofluorescence imaging (IF) and western blotting (WB). Expression of angiogenic and cell stress markers were measured using multiplex proteome profiler arrays.

RESULTS

After 6-h of co-culture with Pf-iRBCs, hiPSC-BMECs showed reduced TEER and increased sodium fluorescein permeability compared to co-culture with uninfected RBCs, indicative of a leaky barrier. We observed disruptions in localization of occludin, zonula occludens-1, and claudin-5 by IF, but no change in protein expression by WB in Pf-iRBC co-cultures. Expression of ICAM-1 and VCAM-1 but not EPCR was elevated in hiPSC-BMECs with Pf-iRBC co-culture compared to uninfected RBC co-culture. In addition, there was an increase in expression of angiogenin, platelet factor-4, and phospho-heat shock protein-27 in the Pf-iRBCs co-culture compared to uninfected RBC co-culture.

CONCLUSION

These findings demonstrate the validity of our hiPSC-BMECs based model of the BBB, that displays enhanced barrier integrity and appropriate TJ protein localization. In the hiPSC-BMEC co-culture with Pf-iRBCs, reduced TEER, increased paracellular permeability, changes in TJ protein localization, increase in expression of adhesion molecules, and markers of angiogenesis and cellular stress all point towards a novel model with enhanced barrier properties, suitable for investigating pathogenic mechanisms underlying BBB disruption in CM.

Human in vitro blood barrier models: architectures and applications

Blood barriers serve as key points of transport for essential molecules as well as lines of defense to protect against toxins. In vitro modeling of these barriers is common practice in the study of their physiology and related diseases. This review describes a common method of using an adaptable, low cost, semipermeable, suspended membrane to experimentally model three blood barriers in the human body: the blood-brain barrier (BBB), the gut-blood barrier (GBB), and the air-blood barrier (ABB). The GBB and ABB both protect from the outside environment, while the BBB protects the central nervous system from potential neurotoxic agents in the blood. These barriers share several commonalities, including the formation of tight junctions, polarized cellular monolayers, and circulatory system contact. Cell architectures used to mimic barrier anatomy as well as applications to study function, dysfunction, and response provide an overview of the versatility enabled by these cultural systems.

Teriflunomide Promotes Blood-Brain Barrier Integrity by Upregulating Claudin-1 via the Wnt/β-catenin Signaling Pathway in Multiple Sclerosis

The blood-brain barrier (BBB) and tight junction (TJ) proteins maintain the homeostasis of the central nervous system (CNS). The dysfunction of BBB allows peripheral T cells infiltration into CNS and contributes to the pathophysiology of multiple sclerosis (MS). Teriflunomide is an approved drug for the treatment of MS by suppressing lymphocytes proliferation. However, whether teriflunomide has a protective effect on BBB in MS is not understood. We found that teriflunomide restored the injured BBB in the EAE model. Furthermore, teriflunomide treatment over 6 months improved BBB permeability and reduced peripheral leakage of CNS proteins in MS patients. Teriflunomide increased human brain microvascular endothelial cell (HBMEC) viability and promoted BBB integrity in an in vitro cell model. The TJ protein claudin-1 was upregulated by teriflunomide and responsible for the protective effect on BBB. Furthermore, RNA sequencing revealed that the Wnt signaling pathway was affected by teriflunomide. The activation of Wnt signaling pathway increased claudin-1 expression and reduced BBB damage in cell model and EAE rats. Our study demonstrated that teriflunomide upregulated the expression of the tight junction protein claudin-1 in endothelial cells and promoted the integrity of BBB through Wnt signaling pathway.

Porous Membrane Electrical Cell-Substrate Impedance Spectroscopy for Versatile Assessment of Biological Barriers In Vitro

Cell culture models of endothelial and epithelial barriers typically use porous membrane inserts (e.g., Transwell inserts) as a permeable substrate on which barrier cells are grown, often in coculture with other cell types on the opposite side of the membrane. Current methods to characterize barrier function in porous membrane inserts can disrupt the barrier or provide bulk measurements that cannot isolate barrier cell resistance alone. Electrical cell-substrate impedance sensing (ECIS) addresses these limitations, but its implementation on porous membrane inserts has been limited by costly manufacturing, low sensitivity, and lack of validation for barrier assessment. Here, we present porous membrane ECIS (PM-ECIS), a cost-effective method to adapt ECIS technology to porous substrate-based in vitro models. We demonstrate high fidelity patterning of electrodes on porous membranes that can be incorporated into well plates of a variety of sizes with excellent cell biocompatibility with mono- and coculture set ups. PM-ECIS provided sensitive, real-time measurement of isolated changes in endothelial cell barrier impedance with cell growth and barrier disruption. Barrier function characterized by PM-ECIS resistance correlated well with permeability coefficients obtained from simultaneous molecular tracer permeability assays performed on the same cultures, validating the device. Integration of ECIS into conventional porous cell culture inserts provides a versatile, sensitive, and automated alternative to current methods to measure barrier function in vitro, including molecular tracer assays and transepithelial/endothelial electrical resistance.

Neurological impairment is crucial for tire rubber-derived contaminant 6PPDQ-induced acute toxicity to rainbow trout

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPDQ) has attracted significant attention due to its highly acute lethality to sensitive salmonids. However, studies investigating the mechanisms underlying its acute toxicity have been lacking. In this work, we demonstrated the sensitivity of rainbow trout to 6PPDQ-induced mortality. Moribund trout exhibited significantly higher brain concentrations of 6PPDQ compared to surviving trout. In an in vitro model using human brain microvascular endothelial cells, 6PPDQ can penetrate the blood-brain barrier and enhance blood-brain barrier permeability without compromising cell viability. The time spent in the top of the tank increased with rising 6PPDQ concentrations, as indicated by locomotion behavior tests. Furthermore, 6PPDQ influenced neurotransmitter levels and mRNA expression of neurotransmission-related genes in the brain and exhibited strong binding affinity to target neurotransmission-related proteins using computational simulations. The integrated biomarker response value associated with neurotoxicity showed a positive linear correlation with trout mortality. These findings significantly contribute to filling the knowledge gap between neurological impairments and apical outcomes, including behavioral effects and mortality, induced by 6PPDQ.

Silica Nanoparticles Decrease Glutamate Uptake in Blood-Brain Barrier Components

Glutamate is the major excitatory amino acid in the vertebrate brain, playing an important role in most brain functions. It exerts its activity through plasma membrane receptors and transporters, expressed both in neurons and glia cells. Overstimulation of neuronal glutamate receptors is linked to cell death in a process known as excitotoxicity, that is prevented by the efficient removal of the neurotransmitter through glutamate transporters enriched in the glia plasma membrane and in the components of the blood-brain barrier (BBB). Silica nanoparticles (SiO2-NPs) have been widely used in biomedical applications and directed to enter the circulatory system; however, little is known about the potential adverse effects of SiO2-NPs exposure on the BBB transport systems that support the critical isolation function between the central nervous system (CNS) and the peripheral circulation. In this contribution, we investigated the plausible SiO2-NPs-mediated disruption of the glutamate transport system expressed by BBB cell components. First, we evaluated the cytotoxic effect of SiO2-NPs on human brain endothelial (HBEC) and Uppsala 87 Malignant glioma (U-87MG) cell lines. Transport kinetics were evaluated, and the exposure effect of SiO2-NPs on glutamate transport activity was determined in both cell lines. Exposure of the cells to different SiO2-NP concentrations (0.4, 4.8, 10, and 20 µg/ml) and time periods (3 and 6 h) did not affect cell viability. We found that the radio-labeled D-aspartate ([3H]-D-Asp) uptake is mostly sodium-dependent, and downregulated by its own substrate (glutamate). Furthermore, SiO2-NPs exposure on endothelial and astrocytes decreases [3H]-D-Asp uptake in a dose-dependent manner. Interestingly, a decrease in the transporter catalytic efficiency, probably linked to a diminution in the affinity of the transporter, was detected upon SiO2-NPs. These results favor the notion that exposure to SiO2-NPs could disrupt BBB function and by these means shed some light into our understanding of the deleterious effects of air pollution on the CNS.

Acetylcholine Analog-Modified Albumin Nanoparticles for the Enhanced and Synchronous Brain Delivery of Saponin Components of Panax Notoginseng

BACKGROUND

Panax notoginseng saponins (PNS) are commonly used first-line drugs for treating cerebral thrombosis and stroke in China. However, the synchronized and targeted delivery of active ingredients in traditional Chinese medicine (TCM) poses a significant challenge for modern TCM formulations.

METHODS

Bovine serum albumin (BSA) was modified using 2-methacryloyloxyethyl phosphorylcholine (MPC), an analog of acetylcholine, and subsequently adsorbed the major PNS onto the modified albumin to produce MPC-BSA@PNS nanoparticles (NPs). This novel delivery system facilitated efficient and synchronized transport of PNS across the blood-brain barrier (BBB) through active transport mediated by nicotinic acetylcholine receptors.

RESULTS

In vitro experiments demonstrated that the transport rates of R1, Rg1, Rb1, and Rd across the BBB were relatively synchronous in MPC-BSA@PNS NPs compared to those in the PNS solution. Additionally, animal experiments revealed that the brain-targeting efficiencies of R1 + Rg1 + Rb1 in MPC-BSA@PNS NPs were 2.02 and 7.73 times higher than those in BSA@PNS NPs and the free PNS group, respectively.

CONCLUSIONS

This study presents a simple and feasible approach for achieving the targeted delivery of complex active ingredient clusters in TCM.

Palmitoylation of hIFITM1 inhibits JEV infection and contributes to BBB stabilization

Human brain microvascular endothelial cells (hBMECs) are the main component cells of the blood-brain barrier (BBB) and play a crucial role in responding to viral infections to prevent the central nervous system (CNS) from viral invasion. Interferon-inducible transmembrane protein 1 (IFITM1) is a multifunctional membrane protein downstream of type-I interferon. In this study, we discovered that hIFITM1 expression was highly upregulated in hBMECs during Japanese encephalitis virus (JEV) infection. Depletion of hIFITM1 with CRISPR/Cas9 in hBMECs enhanced JEV replication, while overexpression of hIFITM1 restricted the viruses. Additionally, overexpression of hIFITM1 promoted the monolayer formation of hBMECs with a better integrity and a higher transendothelial electrical resistance (TEER), and reduced the penetration of JEV across the BBB. However, the function of hIFITM1 is governed by palmitoylation. Mutations of palmitoylation residues in conserved CD225 domain of hIFITM1 impaired its antiviral capacity. Moreover, mutants retained hIFITM1 in the cytoplasm and lessened its interaction with tight junction protein Occludin. Taken together, palmitoylation of hIFITM1 is essential for its antiviral activity in hBMECs, and more notably, for the maintenance of BBB homeostasis.

Host-microbe interactions at the blood-brain barrier through the lens of induced pluripotent stem cell-derived brain-like endothelial cells

Microbe-induced meningoencephalitis/meningitis is a life-threatening infection of the central nervous system (CNS) that occurs when pathogens are able to cross the blood-brain barrier (BBB) and gain access to the CNS. The BBB consists of highly specialized brain endothelial cells that exhibit specific properties to allow tight regulation of CNS homeostasis and prevent pathogen crossing. However, during meningoencephalitis/meningitis, the BBB fails to protect the CNS. Modeling the BBB remains a challenge due to the specialized characteristics of these cells. In this review, we cover the induced pluripotent stem cell-derived, brain-like endothelial cell model during host-pathogen interaction, highlighting the strengths and recent work on various pathogens known to interact with the BBB. As stem cell technologies are becoming more prominent, the stem cell-derived, brain-like endothelial cell model has been able to reveal new insights in vitro, which remain challenging with other in vitro cell-based models consisting of primary human brain endothelial cells and immortalized human brain endothelial cell lines.

Loss of filamentous actin, tight junction protein expression, and paracellular barrier integrity in frataxin-deficient human brain microvascular endothelial cells-implications for blood-brain barrier physiology in Friedreich's ataxia

Introduction: Friedreich's Ataxia (FRDA) is the most prevalent inherited ataxia. FRDA results from loss of Frataxin (FXN), an essential mitochondrial iron trafficking protein. FRDA starts with an early burst of neurodegeneration of the dorsal root ganglion and cerebellar dentate nuclei, followed by progressive brain iron accumulation in the latter. End stage disease includes cardiac fibrosis that contributes to hypertrophic cardiomyopathy. The microvasculature plays an essential barrier role in both brain and heart homeostasis, thus an investigation of this tissue system in FRDA is essential to the delineation of the cellular dysfunction in this genetic disorder. Previous reports have identified cytoskeletal alterations in non-barrier forming FRDA cell models, but physiological consequences are limited. Methods: We investigated brain microvascular endothelial cell integrity in FRDA in a model of the blood-brain barrier (BBB). We have knocked down FXN in immortalized human brain microvascular endothelial cells (hBMVEC), which compose the microcapillaries of the BBB, by using shRNA. We confirmed known cellular pathophysiologies of FXN-knockdown including decreased energy metabolism, markers of oxidative stress, and increased cell size. Results: We investigated cytoskeletal architecture, identifying decreased filamentous actin and Occludin and Claudin-5 tight junction protein expression in shFXN hBMVECs. This was consistent with decreased transendothelial electrical resistance (TEER) and increased paracellular tracer flux during early barrier formation. shFXN hBMVEC start with only 67% barrier integrity of the controls, and flux a paracellular tracer at 800% of physiological levels. Discussion: We identified that insufficient FXN levels in the hBMVEC BBB model causes changes in cytoskeletal architecture and tight junction protein abundance, co-incident with increased barrier permeability. Changes in the integrity of the BBB may be related to patient brain iron accumulation, neuroinflammation, neurodegeneration, and stroke. Furthermore, our findings implicate other barrier cells, e.g., the cardiac microvasculature, loci of disease pathology in FRDA.

Alzheimer's disease brain endothelial-like cells reveal differential drug transporter expression and modulation by potentially therapeutic focused ultrasound

The blood-brain barrier (BBB) has a key function in maintaining homeostasis in the brain, partly modulated by transporters, which are highly expressed in brain endothelial cells (BECs). Transporters mediate the uptake or efflux of compounds to and from the brain and they can also challenge the delivery of drugs for the treatment of Alzheimer's disease (AD). Currently there is a limited understanding of changes in BBB transporters in AD. To investigate this, we generated brain endothelial-like cells (iBECs) from induced pluripotent stem cells (iPSCs) with familial AD (FAD) Presenilin 1 (PSEN1) mutation and identified AD-specific differences in transporter expression compared to control (ctrl) iBECs. We first characterized the expression levels of 12 BBB transporters in AD-, Ctrl-, and isogenic (PSEN1 corrected) iBECs to identify any AD specific differences. We then exposed the cells to focused ultrasound (FUS) in the absence (FUSonly) or presence of microbubbles (MB) (FUS+MB), which is a novel therapeutic method that can be used to transiently open the BBB to increase drug delivery into the brain, however its effects on BBB transporter expression are largely unknown. Following FUSonly and FUS+MB, we investigated whether the expression or activity of key transporters could be modulated. Our findings demonstrate that PSEN1 mutant FAD (PSEN1AD) possess phenotypical differences compared to control iBECs in BBB transporter expression and function. Additionally, we show that FUSonly and FUS+MB can modulate BBB transporter expression and functional activity in iBECs, having potential implications on drug penetration and amyloid clearance. These findings highlight the differential responses of patient cells to FUS treatment, with patient-derived models likely providing an important tool for modelling therapeutic effects of FUS.

In Vitro Blood-Brain Barrier Models for Neuroinfectious Diseases: A Narrative Review

The blood-brain barrier (BBB) is a complex, dynamic, and adaptable barrier between the peripheral blood system and the central nervous system. While this barrier protects the brain and spinal cord from inflammation and infection, it prevents most drugs from reaching the brain tissue. With the expanding interest in the pathophysiology of BBB, the development of in vitro BBB models has dramatically evolved. However, due to the lack of a standard model, a range of experimental protocols, BBB-phenotype markers, and permeability flux markers was utilized to construct in vitro BBB models. Several neuroinfectious diseases are associated with BBB dysfunction. To conduct neuroinfectious disease research effectively, there stems a need to design representative in vitro human BBB models that mimic the BBB's functional and molecular properties. The highest necessity is for an in vitro standardised BBB model that accurately represents all the complexities of an intact brain barrier. Thus, this in-depth review aims to describe the optimization and validation parameters for building BBB models and to discuss previous research on neuroinfectious diseases that have utilized in vitro BBB models. The findings in this review may serve as a basis for more efficient optimisation, validation, and maintenance of a structurally- and functionally intact BBB model, particularly for future studies on neuroinfectious diseases.

An Improved In Vitro Blood-Brain Barrier Model for the Evaluation of Drug Permeability Using Transwell with Shear Stress

The development of drugs targeting the central nervous system (CNS) is challenging because of the presence of the Blood-Brain barrier (BBB). Developing physiologically relevant in vitro BBB models for evaluating drug permeability and predicting the activity of drug candidates is crucial. The transwell model is one of the most widely used in vitro BBB models. However, this model has limitations in mimicking in vivo conditions, particularly in the absence of shear stress. This study aimed to overcome the limitations of the transwell model using immortalized human endothelial cells (hCMEC/D3) by developing a novel dish design for an orbital shaker, providing shear stress. During optimization, we assessed cell layer integrity using trans-endothelial electrical resistance measurements and the % diffusion of lucifer yellow. The efflux transporter activity and mRNA expression of junctional proteins (claudin-5, occludin, and VE-cadherin) in the newly optimized model were verified. Additionally, the permeability of 14 compounds was evaluated and compared with published in vivo data. The cell-layer integrity was substantially increased using the newly designed annular shaking-dish model. The results demonstrate that our model provided robust conditions for evaluating the permeability of CNS drug candidates, potentially improving the reliability of in vitro BBB models in drug development.

Brain-Penetrating Peptide Shuttles across the Blood-Brain Barrier and Extracellular-like Space

Systemic delivery of therapeutics into the brain is greatly impaired by multiple biological barriers─the blood-brain barrier (BBB) and the extracellular matrix (ECM) of the extracellular space. To address this problem, we developed a combinatorial approach to identify peptides that can shuttle and transport across both barriers. A cysteine-constrained heptapeptide M13 phage display library was iteratively panned against an established BBB model for three rounds to select for peptides that can transport across the barrier. Using next-generation DNA sequencing and in silico analysis, we identified peptides that were selectively enriched from successive rounds of panning for functional validation in vitro and in vivo. Select peptide-presenting phages exhibited efficient shuttling across the in vitro BBB model. Two clones, Pep-3 and Pep-9, exhibited higher specificity and efficiency of transcytosis than controls. We confirmed that peptides Pep-3 and Pep-9 demonstrated better diffusive transport through the extracellular matrix than gold standard nona-arginine and clinically trialed angiopep-2 peptides. In in vivo studies, we demonstrated that systemically administered Pep-3 and Pep-9 peptide-presenting phages penetrate the BBB and distribute into the brain parenchyma. In addition, free peptides Pep-3 and Pep-9 achieved higher accumulation in the brain than free angiopep-2 and may exhibit brain targeting. In summary, these in vitro and in vivo studies highlight that combinatorial phage display with a designed selection strategy can identify peptides as promising carriers, which are able to overcome the multiple biological barriers of the brain and shuttle different-sized molecules from small fluorophores to large macromolecules for improved delivery into the brain.

Simple design for membrane-free microphysiological systems to model the blood-tissue barriers

Microphysiological systems (MPS) incorporate physiologically relevant microanatomy, mechanics, and cells to mimic tissue function. Reproducible and standardized in vitro models of tissue barriers, such as the blood-tissue interface (BTI), are critical for next-generation MPS applications in research and industry. Many models of the BTI are limited by the need for semipermeable membranes, use of homogenous cell populations, or 2D culture. These factors limit the relevant endothelial-epithelial contact and 3D transport, which would best mimic the BTI. Current models are also difficult to assemble, requiring precise alignment and layering of components. The work reported herein details the engineering of a BTI-on-a-chip (BTI Chip) that addresses current disadvantages by demonstrating a single layer, membrane-free design. Laminar flow profiles, photocurable hydrogel scaffolds, and human cell lines were used to construct a BTI Chip that juxtaposes an endothelium in direct contact with a 3D engineered tissue. A biomaterial composite, gelatin methacryloyl and 8-arm polyethylene glycol thiol, was used for in situ fabrication of a tissue structure within a Y-shaped microfluidic device. To produce the BTI, a laminar flow profile was achieved by flowing a photocurable precursor solution alongside phosphate buffered saline. Immediately after stopping flow, the scaffold underwent polymerization through a rapid exposure to UV light (<300 mJ/cm2). After scaffold formation, blood vessel endothelial cells were introduced and allowed to adhere directly to the 3D tissue scaffold, without barriers or phase guides. Fabrication of the BTI Chip was demonstrated in both an epithelial tissue model and blood-brain barrier (BBB) model. In the epithelial model, scaffolds were seeded with human dermal fibroblasts. For the BBB models, scaffolds were seeded with the immortalized glial cell line, SVGP12. The BTI Chip microanatomy was analyzed post facto by immunohistochemistry, showing the uniform production of a patent endothelium juxtaposed with a 3D engineered tissue. Fluorescent tracer molecules were used to characterize the permeability of the BTI Chip. The BTI Chips were challenged with an efflux pump inhibitor, cyclosporine A, to assess physiological function and endothelial cell activation. Operation of physiologically relevant BTI Chips and a novel means for high-throughput MPS generation was demonstrated, enabling future development for drug candidate screening and fundamental biological investigations.

Development of an apolipoprotein E mimetic peptide-lipid conjugate for efficient brain delivery of liposomes

Liposomes are versatile carriers that can encapsulate various drugs; however, for delivery to the brain, they must be modified with a targeting ligand or other modifications to provide blood-brain barrier (BBB) permeability, while avoiding rapid clearance by reticuloendothelial systems through polyethylene glycol (PEG) modification. BBB-penetrating peptides act as brain-targeting ligands. In this study, to achieve efficient brain delivery of liposomes, we screened the functionality of eight BBB-penetrating peptides reported previously, based on high-throughput quantitative evaluation methods with in vitro BBB permeability evaluation system using Transwell, in situ brain perfusion system, and others. For apolipoprotein E mimetic tandem dimer peptide (ApoEdp), which showed the best brain-targeting and BBB permeability in the comparative evaluation of eight peptides, its lipid conjugate with serine-glycine (SG)5 spacer (ApoEdp-SG-lipid) was newly synthesized and ApoEdp-modified PEGylated liposomes were prepared. ApoEdp-modified PEGylated liposomes were effectively associated with human brain capillary endothelial cells via the ApoEdp sequence and permeated the membrane in an in vitro BBB model. Moreover, ApoEdp-modified PEGylated liposomes accumulated in the brain 3.9-fold higher than PEGylated liposomes in mice. In addition, the ability of ApoEdp-modified PEGylated liposomes to localize beyond the BBB into the brain parenchyma in mice was demonstrated via three-dimensional imaging with tissue clearing. These results suggest that ApoEdp-SG-lipid modification is an effective approach for endowing PEGylated liposomes with the brain-targeting ability and BBB permeability.

Microfluidic models of the neurovascular unit: a translational view

The vasculature of the brain consists of specialized endothelial cells that form a blood-brain barrier (BBB). This barrier, in conjunction with supporting cell types, forms the neurovascular unit (NVU). The NVU restricts the passage of certain substances from the bloodstream while selectively permitting essential nutrients and molecules to enter the brain. This protective role is crucial for optimal brain function, but presents a significant obstacle in treating neurological conditions, necessitating chemical modifications or advanced drug delivery methods for most drugs to cross the NVU. A deeper understanding of NVU in health and disease will aid in the identification of new therapeutic targets and drug delivery strategies for improved treatment of neurological disorders.To achieve this goal, we need models that reflect the human BBB and NVU in health and disease. Although animal models of the brain's vasculature have proven valuable, they are often of limited translational relevance due to interspecies differences or inability to faithfully mimic human disease conditions. For this reason, human in vitro models are essential to improve our understanding of the brain's vasculature under healthy and diseased conditions. This review delves into the advancements in in vitro modeling of the BBB and NVU, with a particular focus on microfluidic models. After providing a historical overview of the field, we shift our focus to recent developments, offering insights into the latest achievements and their associated constraints. We briefly examine the importance of chip materials and methods to facilitate fluid flow, emphasizing their critical roles in achieving the necessary throughput for the integration of microfluidic models into routine experimentation. Subsequently, we highlight the recent strides made in enhancing the biological complexity of microfluidic NVU models and propose recommendations for elevating the biological relevance of future iterations.Importantly, the NVU is an intricate structure and it is improbable that any model will fully encompass all its aspects. Fit-for-purpose models offer a valuable compromise between physiological relevance and ease-of-use and hold the future of NVU modeling: as simple as possible, as complex as needed.

Nanofibrous Membrane Promotes and Sustains Vascular Endothelial Barrier Function

The vascular endothelium serves as a physical barrier between the circulating blood and surrounding tissue and acts as a critical regulator of various physiological processes. In vitro models involving vasculature rely on the maintenance of the endothelial barrier function. In this study, we fabricated 2D aligned nanofibrous membranes with distinct pore sizes via electrospinning and investigated the effect of membrane pore size on endothelial barrier function. Our results demonstrated that the use of the nanofibrous membranes promoted the formation of a tight vascular endothelium and sustained barrier function for over one month in comparison with conventional transwell setups. Moreover, the examination of the nucleocytoplasmic localization of yes-associated protein (YAP) in the endothelial cells indicated that nanofibrous membrane promoted YAP expression and its nuclear localization, critical to endothelial barrier function. Furthermore, the comparison of permeability between random and aligned nanofibrous membranes underscored the importance of pore size in preserving barrier function. Our findings offer a valuable strategy for creating more physiologically relevant in vitro vascular models and contribute to the understanding of endothelial barrier formation and maintenance mechanisms.

Costunolide and parthenolide: Novel blood-brain barrier permeable sesquiterpene lactones to improve barrier tightness

Sesquiterpene lactones - such as those found in chicory - are considered promising bioactive compounds. These small molecules have shown several health benefits for various diseases, including brain disorders. However, it is unknown whether these compounds can cross the blood-brain barrier (BBB), and which could be the effects on brain microvascular endothelial cells. We show that six sesquiterpene lactones evaluated in an in vitro model of the BBB have different capacities to be transported through the barrier. Costunolide presented more than 20 % of transport while lactucin, 11β-13-dihydrolactucin, 11β-13-dihydrolactucopicrin, and parthenolide presented between 10 % and 20 %, whilst almost no transport was detected for lactucopicrin. Furthermore, costunolide and parthenolide reduced P-gp ABC transporter expression alongside an increase in caveolin-1, the main protein of caveolae. Remarkably, these two compounds improved barrier tightness by increasing the expression of both tight and adherens junctions. These findings open a new avenue to explore costunolide and parthenolide as promising compounds for brain therapies.