In Vitro Models of the Blood–Cerebrospinal Fluid Barrier and Their Applications in the Development and Research of (Neuro)Pharmaceuticals

Sensor-integrated gut-on-a-chip for monitoring senescence-mediated changes in the intestinal barrier

The incidence of inflammatory bowel disease among the elderly has significantly risen in recent years, posing a growing socioeconomic burden to aging societies. Moreover, non-gastrointestinal diseases, also prevalent in this demographic, have been linked to intestinal barrier dysfunction, thus highlighting the importance of investigating aged-mediated changes within the human gut. While gastrointestinal pathology often involves an impaired gut barrier, the impact of aging on the human gastrointestinal barrier function remains unclear. To explore the effect of senescence, a key hallmark of aging, on gut barrier integrity, we established and evaluated an in vitro gut-on-a-chip model tailored to investigate barrier changes by the integration of an impedance sensor. Here, a microfluidic gut-on-a-chip system containing integrated membrane-based electrode microarrays is used to non-invasively monitor epithelial barrier formation and senescence-mediated changes in barrier integrity upon treating Caco-2 cells with 0.8 μg mL-1 doxorubicin (DXR), a chemotherapeutic which induces cell cycle arrest. Results of our microfluidic human gut model reveal a DXR-mediated increase in impedance and cell hypertrophy as well as overexpression of p21, and CCL2, indicative of a senescent phenotype. Combined with the integrated electrodes, monitoring ∼57% of the cultivation area in situ and non-invasively, the developed chip-based senescent-gut model is ideally suited to study age-related malfunctions in barrier integrity.

On the origin of metal species in the human brain: a perspective on key physicochemical properties

Normal functioning of the human brain is dependent on adequate regulation of essential metal nutrients. However, it is also highly sensitive to metal-mediated toxicity, linked to various neurodegenerative disorders. Exposure to environmental metal sources (especially to particulate air pollution) can stimulate toxicity and neuropathologic effects, which is particularly evident in populations chronically exposed to high levels of air pollution. Identifying the sources of metal-rich deposits in the human brain is important in not only distinguishing the effects of environmentally acquired metals from endogenous metal dysregulation, but also for tracing pollutant sources which may be subject to exposure control. This perspective reviews evidence for key physicochemical properties (size/morphology, chemical composition, oxidation state, magnetic properties, and isotopic composition) concerning their capacity to distinguish sources of metals in the brain. The scope for combining analytical techniques to study properties in tandem is also discussed.

Trojan Horse Delivery Strategies of Natural Medicine Monomers: Challenges and Limitations in Improving Brain Targeting

Central nervous system (CNS) diseases, such as brain tumors, Alzheimer's disease, and Parkinson's disease, significantly impact patients' quality of life and impose substantial economic burdens on society. The blood-brain barrier (BBB) limits the effective delivery of most therapeutic drugs, especially natural products, despite their potential therapeutic effects. The Trojan Horse strategy, using nanotechnology to disguise drugs as "cargo", enables them to bypass the BBB, enhancing targeting and therapeutic efficacy. This review explores the applications of natural products in the treatment of CNS diseases, discusses the challenges posed by the BBB, and analyzes the advantages and limitations of the Trojan Horse strategy. Despite the existing technical challenges, future research is expected to enhance the application of natural drugs in CNS treatment by integrating nanotechnology, improving delivery mechanisms, and optimizing targeting characteristics.

Choroid plexus organoids reveal mechanisms of Streptococcus suis translocation at the blood-cerebrospinal fluid barrier

Streptococcus suis is a globally emerging zoonotic pathogen that can cause invasive disease commonly associated with meningitis in pigs and humans. To cause meningitis, S. suis must invade the central nervous system (CNS) by crossing the neurovascular unit, also known as the blood-brain barrier (BBB), or vascularized choroid plexus (ChP) epithelium known as the blood-cerebrospinal fluid barrier (BCSFB). Recently developed ChP organoids have been shown to accurately replicate the cytoarchitecture and physiological functions of the ChP epithelium in vivo. Here, we used human induced pluripotent stem cells (iPSC)-derived ChP organoids as an in vitro model to investigate S. suis interaction and infection at the BCSFB. Our study revealed that S. suis is capable of translocating across the epithelium of ChP organoids without causing significant cell death or compromising the barrier integrity. Plasminogen (Plg) binding to S. suis in the presence of tissue plasminogen activator (tPA), which converts immobilized Plg to plasmin (Pln), significantly increased the basolateral to apical translocation across ChP organoids into the CSF-like fluid in the lumen. S. suis was able to replicate at the same rate in CSF and laboratory S. suis culture medium but reached a lower final density. The analysis of transcriptomes in ChP organoids after S. suis infection indicated inflammatory responses, while the addition of Plg further suggested extracellular matrix (ECM) remodeling. To our knowledge, this is the first study using ChP organoids to investigate bacterial infection of the BCSFB. Our findings highlight the potential of ChP organoids as a valuable tool for studying the mechanisms of bacterial interaction and infection of the human ChP in vitro.

Viruses and the Brain-A Relationship Prone to Trouble

Neurological disorders, some of which are associated with viral infections, are growing due to the aging and expanding population. Despite strong defenses of the central nervous system, some viruses have evolved ways to breach them, which often result in dire consequences. In this review, we recount the various ways by which different viruses can enter the CNS, and we describe the consequences of such invasions. Consequences may manifest as acute disease, such as encephalitis, meningitis, or result in long-term effects, such as neuromuscular dysfunction, as occurs in poliomyelitis. We discuss evidence for viral involvement in the causation of well-known chronic neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis, as well as vascular dementia in the elderly. We also describe the approaches currently available to control a few of the neural viral infections. These include antivirals that are effective against human immunodeficiency virus and herpes simplex virus, as well as vaccines valuable for controlling rabies virus, poliomyelitis virus, and some flavivirus infections. There is an urgent need to better understand, at a molecular level, how viruses contribute to acute and, especially, chronic neurological diseases and to develop more precise and effective vaccines and therapies.

Penetration of linezolid and tedizolid in cerebrospinal fluid of mouse and impact of blood-brain barrier disruption

Penetration of antimicrobial treatments into the cerebrospinal fluid is essential to successfully treat infections of the central nervous system. This penetration is hindered by different barriers, including the blood-brain barrier, which is the most impermeable. However, inflammation may lead to structural alterations of these barriers, modifying their permeability. The impact of blood-brain barrier disruption on linezolid and tedizolid (antibiotics that may be alternatives to treat nosocomial meningitis) penetration in cerebrospinal fluid (CSF) remains unknown. The aim of this study is to evaluate the impact of blood brain barrier disruption on CSF penetration of linezolid and tedizolid. Female C57BI/6 J mice were used. Blood-brain barrier disruption was induced by an intraperitoneal administration of lipopolysaccharide. Linezolid (40 mg/kg) or tedizolid-phosphate (20 mg/kg) were injected intraperitoneally. All the plasma and CSF samples were analyzed with a validated UPLC-MS/MS method. Pharmacokinetic parameters were calculated using a non-compartmental approach based on the free drug concentration. The penetration ratio from the plasma into the CSF was calculated by the AUC0-8h (Area Under Curve) ratio (AUC0-8hCSF/AUC0-8hplasma). Linezolid penetration ratio was 46.5% in control group and 46.1% in lipopolysaccharide group. Concerning tedizolid, penetration ratio was 5.5% in control group and 15.5% in lipopolysaccharide group. In conclusion, CSF penetration of linezolid is not impacted by blood-brain barrier disruption, unlike tedizolid, whose penetration ratio increased.

The Blood-Cerebrospinal Fluid Barrier Dysfunction in Brain Disorders and Stroke: Why, How, What For?

Ischemic stroke (IS) results in the interruption of blood flow to the brain, which can cause significant damage. The pathophysiological mechanisms of IS include ionic imbalances, oxidative stress, neuroinflammation, and impairment of brain barriers. Brain barriers, such as the blood-brain barrier (BBB) and the blood-cerebrospinal fluid (CSF) barrier (B-CSF), protect the brain from harmful substances by regulating the neurochemical environment. Although the BBB is widely recognized for its crucial role in protecting the brain and its involvement in conditions such as stroke, the B-CSF requires further study. The B-CSF plays a fundamental role in regulating the CSF environment and maintaining the homeostasis of the central nervous system (CNS). However, the impact of B-CSF impairment during pathological events such as IS is not yet fully understood. In conditions like IS and other neurological disorders, the B-CSF can become compromised, allowing the entry of inflammatory substances and increasing neuronal damage. Understanding and preserving the integrity of the B-CSF are crucial for mitigating damage and facilitating recovery after ischemic stroke, highlighting its fundamental role in regulating the CNS during adverse neurological conditions.

In vitro models of the choroid plexus and the blood-cerebrospinal fluid barrier: advances, applications, and perspectives

The choroid plexus (CP), a highly vascularized endothelial-epithelial convolute, is placed in the ventricular system of the brain and produces a large part of the cerebrospinal fluid (CSF). Additionally, the CP is the location of a blood-CSF barrier (BCSFB) that separates the CSF from the blood stream in the CP endothelium. In vitro models of the CP and the BCSFB are of high importance to investigate the biological functions of the CP and the BCSFB. Since the CP is involved in several serious diseases, these in vitro models promise help in researching the processes contributing to the diseases and during the development of treatment options. In this review, we provide an overview on the available models and the advances that have been made toward more sophisticated and "in vivo near" systems as organoids and microfluidic lab-on-a-chip approaches. We go into the applications and research objectives for which the various modeling systems can be used and discuss the possible future prospects and perspectives.

Advances in Intrathecal Nanoparticle Delivery: Targeting the Blood-Cerebrospinal Fluid Barrier for Enhanced CNS Drug Delivery

The blood-cerebrospinal fluid barrier (BCSFB) tightly regulates molecular exchanges between the bloodstream and cerebrospinal fluid (CSF), creating challenges for effective central nervous system (CNS) drug delivery. This review assesses intrathecal (IT) nanoparticle (NP) delivery systems that aim to enhance drug delivery by circumventing the BCSFB, complementing approaches that target the blood-brain barrier (BBB). Active pharmaceutical ingredients (APIs) face hurdles like restricted CNS distribution and rapid clearance, which diminish the efficacy of IT therapies. NPs can be engineered to extend drug circulation times, improve CNS penetration, and facilitate sustained release. This review discusses key pharmacokinetic (PK) parameters essential for the effectiveness of these systems. NPs can quickly traverse the subarachnoid space and remain within the leptomeninges for extended periods, often exceeding three weeks. Some designs enable deeper brain parenchyma penetration. Approximately 80% of NPs in the CSF are cleared through the perivascular glymphatic pathway, with microglia-mediated transport significantly contributing to their paravascular clearance. This review synthesizes recent progress in IT-NP delivery across the BCSFB, highlighting critical findings, ongoing challenges, and the therapeutic potential of surface modifications and targeted delivery strategies.

Current status and advances to improving drug delivery in diffuse intrinsic pontine glioma

Diffuse midline glioma (DMG), including tumors diagnosed in the brainstem (diffuse intrinsic pontine glioma - DIPG), is the primary cause of brain tumor-related death in pediatric patients. DIPG is characterized by a median survival of <12 months from diagnosis, harboring the worst 5-year survival rate of any cancer. Corticosteroids and radiation are the mainstay of therapy; however, they only provide transient relief from the devastating neurological symptoms. Numerous therapies have been investigated for DIPG, but the majority have been unsuccessful in demonstrating a survival benefit beyond radiation alone. Although many barriers hinder brain drug delivery in DIPG, one of the most significant challenges is the blood-brain barrier (BBB). Therapeutic compounds must possess specific properties to enable efficient passage across the BBB. In brain cancer, the BBB is referred to as the blood-brain tumor barrier (BBTB), where tumors disrupt the structure and function of the BBB, which may provide opportunities for drug delivery. However, the biological characteristics of the brainstem's BBB/BBTB, both under normal physiological conditions and in response to DIPG, are poorly understood, which further complicates treatment. Better characterization of the changes that occur in the BBB/BBTB of DIPG patients is essential, as this informs future treatment strategies. Many novel drug delivery technologies have been investigated to bypass or disrupt the BBB/BBTB, including convection enhanced delivery, focused ultrasound, nanoparticle-mediated delivery, and intranasal delivery, all of which are yet to be clinically established for the treatment of DIPG. Herein, we review what is known about the BBB/BBTB and discuss the current status, limitations, and advances of conventional and novel treatments to improving brain drug delivery in DIPG.

Current progress and challenges in the development of brain tissue models: How to grow up the changeable brain in vitro?

In vitro modeling of brain tissue is a promising but not yet resolved problem in modern neurobiology and neuropharmacology. Complexity of the brain structure and diversity of cell-to-cell communication in (patho)physiological conditions make this task almost unachievable. However, establishment of novel in vitro brain models would ultimately lead to better understanding of development-associated or experience-driven brain plasticity, designing efficient approaches to restore aberrant brain functioning. The main goal of this review is to summarize the available data on methodological approaches that are currently in use, and to identify the most prospective trends in development of neurovascular unit, blood-brain barrier, blood-cerebrospinal fluid barrier, and neurogenic niche in vitro models. The manuscript focuses on the regulation of adult neurogenesis, cerebral microcirculation and fluids dynamics that should be reproduced in the in vitro 4D models to mimic brain development and its alterations in brain pathology. We discuss approaches that are critical for studying brain plasticity, deciphering the individual person-specific trajectory of brain development and aging, and testing new drug candidates in the in vitro models.

Preclinical Study on Biodistribution of Mesenchymal Stem Cells after Local Transplantation into the Brain

Therapeutic efficacy of mesenchymal stem cells (MSCs) is determined by biodistribution and engraftment in vivo. Compared to intravenous infusion, biodistribution of locally transplanted MSCs are partially understood. Here, we performed a pharmacokinetics (PK) study of MSCs after local transplantation. We grafted human MSCs into the brains of immune-compromised nude mice. Then we extracted genomic DNA from brains, lungs, and livers after transplantation over a month. Using quantitative polymerase chain reaction with human Alu-specific primers, we analyzed biodistribution of the transplanted cells. To evaluate the role of residual immune response in the brain, MSCs expressing a cytosine deaminase (MSCs/CD) were used to ablate resident immune cells at the injection site. The majority of the Alu signals mostly remained at the injection site and decreased over a week, finally becoming undetectable after one month. Negligible signals were transiently detected in the lung and liver during the first week. Suppression of Iba1-positive microglia in the vicinity of the injection site using MSCs/CD prolonged the presence of the Alu signals. After local transplantation in xenograft animal models, human MSCs remain predominantly near the injection site for limited time without disseminating to other organs. Transplantation of human MSCs can locally elicit an immune response in immune compromised animals, and suppressing resident immune cells can prolong the presence of transplanted cells. Our study provides valuable insights into the in vivo fate of locally transplanted stem cells and a local delivery is effective to achieve desired dosages for neurological diseases.

Advancements in the Application of Nanomedicine in Alzheimer's Disease: A Therapeutic Perspective

Alzheimer's disease (AD) is a progressive neurodegenerative disease that affects most people worldwide. AD is a complex central nervous system disorder. Several drugs have been designed to cure AD, but with low success rates. Because the blood-brain and blood-cerebrospinal fluid barriers are two barriers that protect the central nervous system, their presence has severely restricted the efficacy of many treatments that have been studied for AD diagnosis and/or therapy. The use of nanoparticles for the diagnosis and treatment of AD is the focus of an established and rapidly developing field of nanomedicine. Recent developments in nanomedicine have made it possible to effectively transport drugs to the brain. However, numerous obstacles remain to the successful use of nanomedicines in clinical settings for AD treatment. Furthermore, given the rapid advancement in nanomedicine therapeutics, better outcomes for patients with AD can be anticipated. This article provides an overview of recent developments in nanomedicine using different types of nanoparticles for the management and treatment of AD.

The application of nanotechnology in treatment of Alzheimer's disease

The buildup of beta-amyloid plaques in the brain results in Alzheimer's disease (AD), a neurodegenerative condition. A permanent treatment for AD is not yet available. Only a slowing down of its advancement is possible with the current pharmaceutical options. Nevertheless, nanotechnology has proven to be advantageous in medical applications. It has a lot of potential for AD therapy, particularly in diagnosing the condition and providing an alternative course of treatment. In this review, we outline the developments and benefits of nanomedicines in treating AD. Prospective nanomedicines for diagnosing and surveillance therapeutic interventions for AD and other diseases of the central nervous system (CNS) may be clinically accessible, persuading the development of investigation in this field.