T lymphocytes impair P-glycoprotein function during neuroinflammation

The impact of ATP-binding cassette transporters in the diseased brain: Context matters

ATP-binding cassette (ABC) transporters facilitate the movement of diverse molecules across cellular membranes, including those within the CNS. While most extensively studied in microvascular endothelial cells forming the blood-brain barrier (BBB), other CNS cell types also express these transporters. Importantly, disruptions in the CNS microenvironment during disease can alter transporter expression and function. Through this comprehensive review, we explore the modulation of ABC transporters in various brain pathologies and the context-dependent consequences of these changes. For instance, downregulation of ABCB1 may exacerbate amyloid beta plaque deposition in Alzheimer's disease and facilitate neurotoxic compound entry in Parkinson's disease. Upregulation may worsen neuroinflammation by aiding chemokine-mediated CD8 T cell influx into multiple sclerosis lesions. Overall, ABC transporters at the BBB hinder drug entry, presenting challenges for effective pharmacotherapy. Understanding the context-dependent changes in ABC transporter expression and function is crucial for elucidating the etiology and developing treatments for brain diseases.

Antigen-specific immunotherapy via delivery of tolerogenic dendritic cells for multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system resulting from loss of immune tolerance. Many disease-modifying therapies for MS have broad immunosuppressive effects on peripheral immune cells, but this can increase risks of infection and attenuate vaccine-elicited immunity. A more targeted approach is to re-establish immune tolerance in an autoantigen-specific manner. This review discusses methods to achieve this, focusing on tolerogenic dendritic cells. Clinical trials in other autoimmune diseases also provide learnings with regards to clinical translation of this approach, including identification of autoantigen(s), selection of appropriate patients and administration route and frequency.

Emerging Role of ABC Transporters in Glia Cells in Health and Diseases of the Central Nervous System

ATP-binding cassette (ABC) transporters play a crucial role for the efflux of a wide range of substrates across different cellular membranes. In the central nervous system (CNS), ABC transporters have recently gathered significant attention due to their pivotal involvement in brain physiology and neurodegenerative disorders, such as Alzheimer's disease (AD). Glial cells are fundamental for normal CNS function and engage with several ABC transporters in different ways. Here, we specifically highlight ABC transporters involved in the maintenance of brain homeostasis and their implications in its metabolic regulation. We also show new aspects related to ABC transporter function found in less recognized diseases, such as Huntington's disease (HD) and experimental autoimmune encephalomyelitis (EAE), as a model for multiple sclerosis (MS). Understanding both their impact on the physiological regulation of the CNS and their roles in brain diseases holds promise for uncovering new therapeutic options. Further investigations and preclinical studies are warranted to elucidate the complex interplay between glial ABC transporters and physiological brain functions, potentially leading to effective therapeutic interventions also for rare CNS disorders.

Universal method for the isolation of microvessels from frozen brain tissue: A proof-of-concept multiomic investigation of the neurovasculature

The neurovascular unit, comprised of vascular cell types that collectively regulate cerebral blood flow to meet the needs of coupled neurons, is paramount for the proper function of the central nervous system. The neurovascular unit gatekeeps blood-brain barrier properties, which experiences impairment in several central nervous system diseases associated with neuroinflammation and contributes to pathogenesis. To better understand function and dysfunction at the neurovascular unit and how it may confer inflammatory processes within the brain, isolation and characterization of the neurovascular unit is needed. Here, we describe a singular, standardized protocol to enrich and isolate microvessels from archived snap-frozen human and frozen mouse cerebral cortex using mechanical homogenization and centrifugation-separation that preserves the structural integrity and multicellular composition of microvessel fragments. For the first time, microvessels are isolated from postmortem ventromedial prefrontal cortex tissue and are comprehensively investigated as a structural unit using both RNA sequencing and Liquid Chromatography with tandem mass spectrometry (LC-MS/MS). Both the transcriptome and proteome are obtained and compared, demonstrating that the isolated brain microvessel is a robust model for the NVU and can be used to generate highly informative datasets in both physiological and disease contexts.

Central Versus Peripheral Drug Exposure Ratio, a Key Differentiator for Siponimod Over Fingolimod?

INTRODUCTION

Siponimod, a potent and selective sphingosine-1-phosphate (S1P1,5) agonist, is the only therapeutic agent that has shown efficacy against disability progression, decline in cognitive processing speed, total brain volume loss, gray matter atrophy and signs of demyelination in patients with secondary progressive multiple sclerosis (SPMS). Although the pathophysiology of progression in SPMS and primary progressive MS (PPMS) is thought to be similar, fingolimod, the prototype S1P1,3,45 agonist, failed to show efficacy against disability progression in PPMS. Differentiating siponimod from fingolimod at the level of their central effects is believed to be the key to a better understanding of the underlying characteristics that could make siponimod uniquely efficacious in progressive MS (PMS).

METHODS

Here, we compared the central vs. peripheral dose-dependent drug exposures for siponimod and fingolimod in healthy mice and mice with experimental autoimmune encephalomyelitis (EAE).

RESULTS

Siponimod treatment achieved dose-dependent efficacy and dose-proportional increases in steady-state drug blood levels, with a central nervous system (CNS)/blood drug-exposure ratio (CNS/bloodDER) of ~ 6 in both healthy and EAE mice. In contrast, fingolimod treatments achieved dose-proportional increases in fingolimod and fingolimod-phosphate blood levels, with respective CNS/bloodDER that were markedly increased (≥ threefold) in EAE vs. healthy mice.

CONCLUSION

If proven to have translational value, these observations would suggest that CNS/bloodDER may be a key differentiator for siponimod over fingolimod for clinical efficacy in PMS.

Intrinsic blood-brain barrier dysfunction contributes to multiple sclerosis pathogenesis

Blood-brain barrier (BBB) breakdown and immune cell infiltration into the CNS are early hallmarks of multiple sclerosis (MS). The mechanisms leading to BBB dysfunction are incompletely understood and generally thought to be a consequence of neuroinflammation. Here, we have challenged this view and asked if intrinsic alterations in the BBB of MS patients contribute to MS pathogenesis. To this end, we made use of human induced pluripotent stem cells derived from healthy controls and MS patients and differentiated them into brain microvascular endothelial cell (BMEC)-like cells as in vitro model of the BBB. MS-derived BMEC-like cells showed impaired junctional integrity, barrier properties and efflux pump activity when compared to healthy controls. Also, MS-derived BMEC-like cells displayed an inflammatory phenotype with increased adhesion molecule expression and immune cell interactions. Activation of Wnt/β-catenin signalling in MS-derived endothelial progenitor cells enhanced barrier characteristics and reduced the inflammatory phenotype. Our study provides evidence for an intrinsic impairment of BBB function in MS patients that can be modelled in vitro. Human iPSC-derived BMEC-like cells are thus suitable to explore the molecular underpinnings of BBB dysfunction in MS and will assist in the identification of potential novel therapeutic targets for BBB stabilization.

Regulation of P-Glycoprotein in the Brain

Maintenance of the tightly regulated homeostatic environment of the brain is facilitated by the blood-brain barrier (BBB). P-glycoprotein (P-gp), an ATP-binding cassette transporter, is expressed on the luminal surface of the endothelial cells in the BBB, and actively exports a wide variety of substrates to limit exposure of the vulnerable brain environment to waste buildup and neurotoxic compounds. Downregulation of P-gp expression and activity at the BBB have been reported with ageing and in neurodegenerative diseases. Upregulation of P-gp at the BBB contributes to poor therapeutic outcomes due to altered pharmacokinetics of CNS-acting drugs. The regulation of P-gp is highly complex, but unravelling the mechanisms involved may help the development of novel and nuanced strategies to modulate P-gp expression for therapeutic benefit. This review summarises the current understanding of P-gp regulation in the brain, encompassing the transcriptional, post-transcriptional and post-translational mechanisms that have been identified to affect P-gp expression and transport activity.

Full spectrum of vitamin D immunomodulation in multiple sclerosis: mechanisms and therapeutic implications

Vitamin D deficiency has been associated with the risk of multiple sclerosis, disease activity and progression. Results from in vitro experiments, animal models and analysis of human samples from randomized controlled trials provide comprehensive data illustrating the pleiotropic actions of Vitamin D on the immune system. They globally result in immunomodulation by decreasing differentiation of effector T and B cells while promoting regulatory subsets. Vitamin D also modulates innate immune cells such as macrophages, monocytes and dendritic cells, and acts at the level of the blood–brain barrier reducing immune cell trafficking. Vitamin D exerts additional activity within the central nervous system reducing microglial and astrocytic activation. The immunomodulatory role of Vitamin D detected in animal models of multiple sclerosis has suggested its potential therapeutic use for treating multiple sclerosis. In this review, we focus on recent published data describing the biological effects of Vitamin D in animal models of multiple sclerosis on immune cells, blood–brain barrier function, activation of glial cells and its potential neuroprotective effects. Based on the current knowledge, we also discuss optimization of therapeutic interventions with Vitamin D in patients with multiple sclerosis, as well as new technologies allowing in-depth analysis of immune cell regulations by vitamin D.

Regulation of P-glycoprotein by miR-27a-3p at the Brain Endothelial Barrier

Multi-drug resistance P-glycoprotein (P-gp/MDR1) is one of the most clinically relevant ABC transporters, highly enriched at the blood-brain barrier (BBB) with a broad substrate spectrum including therapeutic drugs and metabolic waste products. Altered P-gp transport function has been implicated in multi-drug resistance and in the pathogenesis and progression of neurological diseases. Recent studies have shown that P-gp expression is modulated by micro-RNAs in peripheral organs. Particularly, miR-27a-3p has been shown to play a critical role in the regulation of P-gp in multi-drug resistant cancer cells. In brain disorders, altered levels of miR-27a-3p were reported in several diseases associated with alterations in P-gp expression at the BBB. However, effect of altered miR-27a-3p expression on P-gp expression at the BBB remains to be determined. In this study, we investigated the role of miR-27a-3p in the regulation of P-gp expression and activity at the brain endothelium. Levels of miR-27a-3p were modulated by mimic and inhibitor transfection in an in-vitro model of human brain endothelial hCMEC/D3 cells. Effect of miR-27a-3p modulation on P-gp expression and activity was examined and the underlying regulatory mechanisms explored. Our results showed that transfection of hCMEC/D3 cells with miR-27a-3p mimic induces expression and activity of P-gp while miR-27a-3p inhibition exerted opposite effects. Mechanistic studies revealed that miR-27a-3p regulates P-gp by mediating Glycogen Synthase Kinase 3 Beta (GSK3ß) inhibition and activating Wnt/ß-catenin signaling. These findings shed light on miR-27a-3p/GSK3ß/ß-catenin as a novel axis that could be exploited to modulate P-gp efflux activity at the brain endothelium and help improving CNS diseases treatment or brain protection.

Pro-resolving lipid mediator lipoxin A4 attenuates neuro-inflammation by modulating T cell responses and modifies the spinal cord lipidome

The chronic neuro-inflammatory character of multiple sclerosis (MS) suggests that the natural process to resolve inflammation is impaired. This protective process is orchestrated by specialized pro-resolving lipid mediators (SPMs), but to date, the role of SPMs in MS remains largely unknown. Here, we provide in vivo evidence that treatment with the SPM lipoxin A4 (LXA4) ameliorates clinical symptoms of experimental autoimmune encephalomyelitis (EAE) and inhibits CD4+ and CD8+ T cell infiltration into the central nervous system (CNS). Moreover, we show that LXA4 potently reduces encephalitogenic Th1 and Th17 effector functions, both in vivo and in isolated human T cells from healthy donors and patients with relapsing-remitting MS. Finally, we demonstrate that LXA4 affects the spinal cord lipidome by significantly reducing the levels of pro-inflammatory lipid mediators during EAE. Collectively, our findings provide mechanistic insight into LXA4-mediated amelioration of neuro-inflammation and highlight the potential clinical application of LXA4 for MS.

Disease-Induced Modulation of Drug Transporters at the Blood-Brain Barrier Level

The blood–brain barrier (BBB) is a highly selective and restrictive semipermeable network of cells and blood vessel constituents. All components of the neurovascular unit give to the BBB its crucial and protective function, i.e., to regulate homeostasis in the central nervous system (CNS) by removing substances from the endothelial compartment and supplying the brain with nutrients and other endogenous compounds. Many transporters have been identified that play a role in maintaining BBB integrity and homeostasis. As such, the restrictive nature of the BBB provides an obstacle for drug delivery to the CNS. Nevertheless, according to their physicochemical or pharmacological properties, drugs may reach the CNS by passive diffusion or be subjected to putative influx and/or efflux through BBB membrane transporters, allowing or limiting their distribution to the CNS. Drug transporters functionally expressed on various compartments of the BBB involve numerous proteins from either the ATP-binding cassette (ABC) or the solute carrier (SLC) superfamilies. Pathophysiological stressors, age, and age-associated disorders may alter the expression level and functionality of transporter protein elements that modulate drug distribution and accumulation into the brain, namely, drug efficacy and toxicity. This review focuses and sheds light on the influence of inflammatory conditions and diseases such as Alzheimer’s disease, epilepsy, and stroke on the expression and functionality of the BBB drug transporters, the consequential modulation of drug distribution to the brain, and their impact on drug efficacy and toxicity.

PM2.5 exposure as a risk factor for multiple sclerosis. An ecological study with a Bayesian mapping approach

Some environmental factors are associated with an increased risk of multiple sclerosis (MS). Air pollution could be a main one. This study was conducted to investigate the association of particulate matter 2.5 (PM_2.5) concentrations with MS prevalence in the province of Pavia, Italy. The overall MS prevalence in the province of Pavia is 169.4 per 100,000 inhabitants. Spatial ground-level PM_2.5 gridded data were analysed, by municipality, for the period 2010-2016. Municipalities were grouped by tertiles according to PM_2.5 concentration. Ecological regression and Bayesian statistics were used to analyse the association between PM_2.5 concentrations, degree of urbanization, deprivation index and MS risk. MS risk was higher among persons living in areas with an average winter PM_2.5 concentration above the European annual limit value (25 μg/m³). The Bayesian map revealed sizeable MS high-risk clusters. The study found a relationship between low MS risk and lower PM_2.5 levels, strengthening the suggestion that air pollution may be one of the environmental risk factors for MS.

P-Glycoprotein: One Mechanism, Many Tasks and the Consequences for Pharmacotherapy of Cancers

P-glycoprotein or multidrug resistance protein (MDR1) is an adenosine triphosphate (ATP) binding cassette transporter (ABCB1) intensely investigated because it is an obstacle to successful pharmacotherapy of cancers. P-glycoprotein prevents cellular uptake of a large number of structurally and functionally diverse compounds, including most cancer therapeutics and in this way causes multidrug resistance (MDR). To overcome MDR, and thus improve cancer treatment, an understanding of P-glycoprotein inhibition at the molecular level is required. With this goal in mind, we propose rules that predict whether a compound is a modulator, substrate, inhibitor, or inducer of P-glycoprotein. This new set of rules is derived from a quantitative analysis of the drug binding and transport properties of P-glycoprotein. We further discuss the role of P-glycoprotein in immune surveillance and cell metabolism. Finally, the predictive power of the proposed rules is demonstrated with a set of FDA approved drugs which have been repurposed for cancer therapy.

Brain-homing CD4+ T cells display glucocorticoid-resistant features in MS

Objective

To study whether glucocorticoid (GC) resistance delineates disease-relevant T helper (Th) subsets that home to the CNS of patients with early MS.

Methods

The expression of key determinants of GC sensitivity, multidrug resistance protein 1 (MDR1/ABCB1) and glucocorticoid receptor (GR/NR3C1), was investigated in proinflammatory Th subsets and compared between natalizumab-treated patients with MS and healthy individuals. Blood, CSF, and brain compartments from patients with MS were assessed for the recruitment of GC-resistant Th subsets using fluorescence-activated cell sorting (FACS), quantitative polymerase chain reaction (qPCR), immunohistochemistry, and immunofluorescence.

Results

An MS-associated Th subset termed Th17.1 showed a distinct GC-resistant phenotype as reflected by high MDR1 and low GR expression. This expression ratio was further elevated in Th17.1 cells that accumulated in the blood of patients with MS treated with natalizumab, a drug that prevents their entry into the CNS. Proinflammatory markers C-C chemokine receptor 6, IL-23R, IFN-γ, and GM-CSF were increased in MDR1-expressing Th17.1 cells. This subset predominated the CSF of patients with early MS, which was not seen in the paired blood or in the CSF from patients with other inflammatory and noninflammatory neurologic disorders. The potential of MDR1-expressing Th17.1 cells to infiltrate brain tissue was confirmed by their presence in MS white matter lesions.

Conclusion

This study reveals that GC resistance coincides with preferential CNS recruitment of pathogenic Th17.1 cells, which may hamper the long-term efficacy of GCs in early MS.

Dysfunction of ABC transporters at the blood-brain barrier: Role in neurological disorders

ABC (ATP-binding cassette) transporters represent one of the largest and most diverse superfamily of proteins in living species, playing an important role in many biological processes such as cell homeostasis, cell signaling, drug metabolism and nutrient uptake. Moreover, using the energy generated from ATP hydrolysis, they mediate the efflux of endogenous and exogenous substrates from inside the cells, thereby reducing their intracellular accumulation. At present, 48 ABC transporters have been identified in humans, which were classified into 7 different subfamilies (A to G) according to their phylogenetic analysis. Nevertheless, the most studied members with importance in drug therapeutic efficacy and toxicity include P-glycoprotein (P-gp), a member of the ABCB subfamily, the multidrug-associated proteins (MPRs), members of the ABCC subfamily, and breast cancer resistance protein (BCRP), a member of the ABCG subfamily. They exhibit ubiquitous expression throughout the human body, with a special relevance in barrier tissues like the blood-brain barrier (BBB). At this level, they play a physiological function in tissue protection by reducing or limiting the brain accumulation of neurotoxins. Furthermore, dysfunction of ABC transporters, at expression and/or activity level, has been associated with many neurological diseases, including epilepsy, multiple sclerosis, Alzheimer's disease, and amyotrophic lateral sclerosis. Additionally, these transporters are strikingly associated with the pharmacoresistance to central nervous system (CNS) acting drugs, because they contribute to the decrease in drug bioavailability. This article reviews the signaling pathways that regulate the expression and activity of P-gp, BCRP and MRPs subfamilies of transporters, with particular attention at the BBB level, and their mis-regulation in neurological disorders.

ABC Transporters in Neurological Disorders: An Important Gateway for Botanical Compounds Mediated Neuro-Therapeutics

Neurodegeneration is a distinguishing feature of many age related disorders and other vector borne neuroinflammatory diseases. There are a number of factors that can modulate the pathology of these disorders. ATP-binding cassette (ABC) transporters are primarily involved in the maintenance of normal brain homeostasis by eliminating toxic peptides and compounds from the brain. Also, ABC transporters protect the brain from the unwanted effects of endogenous and exogenous toxins that can enter the brain parenchyma. Therefore, these transporters have the ability to determine the pathological outcomes of several neurological disorders. For instance, ABC transporters like P-glycoprotein (ABCB1), and BCRP (ABCG2) have been reported to facilitate the clearance of peptides such as amyloid-β (Aβ) that accumulate in the brain during Alzheimer's disease (AD) progression. Other members such as ABCA1, ABCA2, ABCC8, ABCC9, ABCG1 and ABCG4 also have been reported to be involved in the progression of various brain disorders such as HIV-associated dementia, Multiple sclerosis (MS), Ischemic stroke, Japanese encephalitis (JE) and Epilepsy. However, these defective transporters can be targeted by numerous botanical compounds such as Verapamil, Berberine and Fascalpsyn as a therapeutic target to treat these neurological outcomes. These compounds are already reported to modulate ABC transporter activity in the CNS. Nonetheless, the exact mechanisms involving the ABC transporters role in normal brain functioning, their role in neuronal dysfunction and how these botanical compounds ensure and facilitate their therapeutic action in association with defective transporters still remain elusive. This review therefore, summarizes the role of ABC transporters in neurological disorders, with a special emphasis on its role in AD brains. The prospect of using botanical/natural compounds as modulators of ABC transporters in neurological disorders is discussed in the latter half of the article.

P-glycoprotein Inhibitor Tariquidar Potentiates Efficacy of Astragaloside IV in Experimental Autoimmune Encephalomyelitis Mice

ATP-binding cassette (ABC) transporters, such as P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP), often reduce drug efficacy and are the major cause of drug resistance. Astragaloside IV (ASIV), one of the bioactive saponins isolated from Astragalus membranaceus, has been demonstrated to alleviate the progression of experimental autoimmune encephalomyelitis (EAE) in mice, an animal model for multiple sclerosis (MS). In the present study, we found for the first time that ASIV induced the upregulation of P-gp and BCRP in the central nervous system (CNS) microvascular endothelial cells of EAE mice. Further study disclosed that tariquidar, a P-gp inhibitor, could facilitate the penetration of ASIV into CNS. On bEnd.3 cells, a mouse brain microvascular endothelial cell line, tariquidar benefited the net uptake and transport of ASIV. Additional molecular docking experiment suggested that ASIV might be a potential substrate of P-gp. In EAE mice, tariquidar was demonstrated to enhance the efficacy of ASIV, as shown by attenuated clinical symptom and reduced incidence rate as well as mitigated inflammatory infiltration and decreased demyelination in the CNS. Collectively, our findings implicate that P-gp inhibitor can promote the therapeutic efficacy of ASIV on EAE mice, which may boost its clinical usage together with ASIV in the therapy of MS.

ABC Family Transporters

The transport of specific molecules across lipid membranes is an essential function of all living organisms. The processes are usually mediated by specific transporters. One of the largest transporter families is the ATP-binding cassette (ABC) family. More than 40 ABC transporters have been identified in human, which are divided into 7 subfamilies (ABCA to ABCG) based on their gene structure, amino acid sequence, domain organization, and phylogenetic analysis. Of them, at least 11 ABC transporters including P-glycoprotein (P-GP/ABCB1), multidrug resistance-associated proteins (MRPs/ABCCs), and breast cancer resistance protein (BCRP/ABCG2) are involved in multidrug resistance (MDR) development. These ABC transporters are expressed in various tissues such as the liver, intestine, kidney, and brain, playing important roles in absorption, distribution, and excretion of drugs. Some ABC transporters are also involved in diverse cellular processes such as maintenance of osmotic homeostasis, antigen processing, cell division, immunity, cholesterol, and lipid trafficking. Several human diseases such as cystic fibrosis, sitosterolemia, Tangier disease, intrahepatic cholestasis, and retinal degeneration are associated with mutations in corresponding transporters. This chapter will describe function and expression of several ABC transporters (such as P-GP, BCRP, and MRPs), their substrates and inhibitors, as well as their clinical significance.

Multiple sclerosis and air pollution exposure: Mechanisms toward brain autoimmunity

The association between neurodegenerative diseases and environmental exposures, in particular air pollution, has been noticed in the last two decades, but the importance of this environmental factor in multiple sclerosis (MS) pathogenesis has not been considered extensively. However, recent evidence suggests that major mechanisms involved in MS pathogenesis, such as inflammatory factors expression, free radicals overproduction, the blood brain barrier (BBB) breakdown, neuroinflammation, vitamin D deficiency and mitochondrial dysfunction could also occur due to exposure to air pollutants. A prospective hypothesis is suggested here in which exposure to air pollutants may initiate destructive mechanisms inducing inflammatory-oxidative cascades, reduction of immunological self-tolerance and neurodegeneration leading to brain autoimmunity.

Age-associated physiological and pathological changes at the blood-brain barrier: A review

The age-associated decline of the neurological and cognitive functions becomes more and more serious challenge for the developed countries with the increasing number of aged populations. The morphological and biochemical changes in the aging brain are the subjects of many extended research projects worldwide for a long time. However, the crucial role of the blood-brain barrier (BBB) impairment and disruption in the pathological processes in age-associated neurodegenerative disorders received special attention just for a few years. This article gives an overview on the major elements of the blood-brain barrier and its supporting mechanisms and also on their alterations during development, physiological aging process and age-associated neurodegenerative disorders (Alzheimer's disease, multiple sclerosis, Parkinson's disease, pharmacoresistant epilepsy). Besides the morphological alterations of the cellular elements (endothelial cells, astrocytes, pericytes, microglia, neuronal elements) of the BBB and neurovascular unit, the changes of the barrier at molecular level (tight junction proteins, adheres junction proteins, membrane transporters, basal lamina, extracellular matrix) are also summarized. The recognition of new players and initiators of the process of neurodegeneration at the level of the BBB may offer new avenues for novel therapeutic approaches for the treatment of numerous chronic neurodegenerative disorders currently without effective medication.

Inhibition of T-cell activation attenuates hypertension, TNFα, IL-17, and blood-brain barrier permeability in pregnant rats with angiogenic imbalance

PROBLEM

Angiogenic imbalance during pregnancy is associated with immune activation, hypertension, increased T cell infiltration, and neurological insults.

METHOD OF STUDY

On gestational day (GD) 12, timed-pregnant rats were infused with anti-angiogenic factors sFlt-1 and sEndoglin (4.7 and 7 μg/kg) to create HELLP syndrome via mini-osmotic pumps for 8 days, with a subset of these rats having Orencia (2 mg/kg) infused on GD13. On GD19, blood-brain barrier (BBB) permeability was evaluated via Evan's Blue infusion, blood was collected for T-cell measurements, inflammatory cytokine secretion. Brain tissues were also collected to examine inflammatory cytokine infiltration.

RESULTS

T-cell attenuation with Orencia decreased circulating CD4(+) and CD8(+) T cells, circulating tumor necrosis factor alpha (TNFα) and IL-17, BBB permeability and significantly decreased biochemical evidence of HELLP compared to untreated HELLP rats.

CONCLUSIONS

These data support the hypothesis that T cells have a critical role in contributing to the pathophysiology that is seen in angiogenic imbalance during pregnancy.

Transporters as Drug Targets in Neurological Diseases

Membrane transport proteins have central physiological function in maintaining cerebral homeostasis. These transporters are expressed in almost all cerebral cells in which they regulate the movement of a wide range of solutes, including endogenous substrates, xenobiotic, and therapeutic drugs. Altered activity/expression of central nervous system (CNS) transporters has been implicated in the onset and progression of multiple neurological diseases. Neurological diseases are heterogeneous diseases that involve complex pathological alterations with only a few treatment options; therefore, there is a great need for the development of novel therapeutic treatments. To that end, transporters have emerged recently to be promising therapeutic targets to halt or slow the course of neurological diseases. The objective of this review is to discuss implications of transporters in neurological diseases and summarize available evidence for targeting transporters as decent therapeutic approach in the treatment of neurological diseases.

Inhibition of cerebral vascular inflammation by brain endothelium-targeted oligodeoxynucleotide complex

The present study generated a novel DNA complex to specifically target endothelial NF-κB to inhibit cerebral vascular inflammation. This DNA complex (GS24-NFκB) contains a DNA decoy which inhibits NF-κB activity, and a DNA aptamer (GS-24), a ligand of transferrin receptor (TfR), which allows for targeted delivery of the DNA decoy into cells. The results indicate that GS24-NFκB was successfully delivered into a murine brain-derived endothelial cell line, bEND5, and inhibited inflammatory responses induced by tumor necrosis factor α (TNF-α) or oxygen-glucose deprivation/re-oxygenation (OGD/R) via down-regulation of the nuclear NF-κB subunit, p65, as well as its downstream inflammatory cytokines, inter-cellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule (VCAM-1). The inhibitory effect of the GS24-NFκB was demonstrated by a significant reduction in TNF-α or OGD/R induced monocyte adhesion to the bEND5 cells after GS24-NFκB treatment. Intravenous (i.v.) injection of GS24-'NFκB (15mg/kg) was able to inhibit the levels of phoseph-p65 and VCAM-1 in brain endothelial cells in a mouse lipopolysaccharide (LPS)-induced inflammatory model in vivo. In conclusion, our approach using DNA nanotechnology for DNA decoy delivery could potentially be utilized for inhibition of inflammation in ischemic stroke and other neuro-inflammatory diseases affecting cerebral vasculature.

Identifying immune mechanisms mediating the hypertension during preeclampsia

Preeclampsia (PE) is a pregnancy-associated disorder that affects 5-8% of pregnancies and is a major cause of maternal, fetal, and neonatal morbidity and mortality. Hallmark characteristics of PE are new onset hypertension after 20 wk gestation with or without proteinuria, chronic immune activation, fetal growth restriction, and maternal endothelial dysfunction. However, the pathophysiological mechanisms that lead to the development of PE are poorly understood. Recent data from studies of both clinical and animal models demonstrate an imbalance in the subpopulations of CD4+ T cells and a role for these cells as mediators of inflammation and hypertension during pregnancy. Specifically, it has been proposed that the imbalance between two CD4+ T cell subtypes, regulatory T cells (Tregs) and T-helper 17 cells (Th17s), is involved in the pathophysiology of PE. Studies from our laboratory highlighting how this imbalance contributes to vasoactive factors, endothelial dysfunction, and hypertension during pregnancy will be discussed in this review. Therefore, the purpose of this review is to highlight hypertensive mechanisms stimulated by inflammatory factors in response to placental ischemia, thereby elucidating a role.

Regulation of ABC efflux transporters at blood-brain barrier in health and neurological disorders

The strength of the blood-brain barrier (BBB) in providing protection to the central nervous system from exposure to circulating chemicals is maintained by tight junctions between endothelial cells and by a broad range of transporter proteins that regulate exchange between CNS and blood. The most important transporters that restrict the permeability of large number of toxins as well as therapeutic agents are the ABC transporters. Among them, P-gp, BCRP, MRP1 and MRP2 are the utmost studied. These efflux transporters are neuroprotective, limiting the brain entry of neurotoxins; however, they could also restrict the entry of many therapeutics and contribute to CNS pharmacoresistance. Characterization of several regulatory pathways that govern expression and activity of ABC efflux transporters in the endothelium of brain capillaries have led to an emerging consensus that these processes are complex and contain several cellular and molecular elements. Alterations in ABC efflux transporters expression and/or activity occur in several neurological diseases. Here, we review the signaling pathways that regulate expression and transport activity of P-gp, BCRP, MRP1 and MRP2 as well as how their expression/activity changes in neurological diseases. This article is part of a Special Issue entitled SI: Neuroprotection.

Current perspectives on the link between neuroinflammation and neurogenesis

The link between neuroinflammation and neurogenesis is an area of intensive research in contemporary neuroscience. The burgeoning amount of evidence accumulated over the past decade has been incredible, and now there remains the figuring out of minutia to give us a more complete picture of what individual, synergistic, and antagonistic events are occurring between neurogenesis and neuroinflammation. An intricate study of the inflammatory microenvironment influenced by the presence of the various inflammatory components like cytokines, chemokines, and immune cells is essential for: 1) understanding how neurogenesis can be affected in such a specialized niche and 2) applying the knowledge gained for the treatment of cognitive and/or motor deficits arising from inflammation-associated diseases like stroke, traumatic brain injury, Alzheimer's disease, and Parkinson's disease. This review is written to provide the reader with up-to-date information explaining how these inflammatory components are effecting changes on neurogenesis.

Differential drug resistance acquisition to doxorubicin and paclitaxel in breast cancer cells

BACKGROUND

Several signal transduction pathways have been reported being involved in the acquisition of P-glycoprotein (P-gp) mediated multi-drug resistance (MDR) upon exposure to anti-cancer drugs, whereas there is evidence indicating that the expression and activity of P-gp were not equally or even reversely modulated by different drugs.

METHODS

To further illustrate this drug-specific effect, possible mechanisms that enable breast cancer cells MCF-7 to acquire MDR to either paclitaxel (PTX) or doxorubicin (DOX) were investigated in a time-dependent manner.

RESULTS

The results suggested that at least two pathways participated in this process. One was the short and transient activation of NF-κB, the second one was the relatively prolonged induction of PXR. Both PXR and NF-κB pathways took part in the PTX drug resistance acquisition, whereas DOX did not exert a significant effect on the PXR-mediated induction of P-gp. Furthermore, the property of NF-κB activation shared by DOX and PTX was not identical. An attempt made in the present study demonstrated that the acquired resistance to DOX was via or partially via NF-κB activation but not its upstream receptor TLR4, while PTX can induce the drug resistance via TLR4-NF-κB pathway.

CONCLUSIONS

To our knowledge, this report is among the first to directly compare the time dependence of NF-κB and PXR pathways. The current study provides useful insight into the distinct ability of DOX and PTX to induce P-gp mediated MDR in breast cancer. Different strategies may be required to circumvent MDR in the presence of different anti-cancer drugs.

P-glycoprotein regulates trafficking of CD8(+) T cells to the brain parenchyma

The trafficking of cytotoxic CD8(+) T lymphocytes across the lining of the cerebral vasculature is key to the onset of the chronic neuro-inflammatory disorder multiple sclerosis. However, the mechanisms controlling their final transmigration across the brain endothelium remain unknown. Here, we describe that CD8(+) T lymphocyte trafficking into the brain is dependent on the activity of the brain endothelial adenosine triphosphate-binding cassette transporter P-glycoprotein. Silencing P-glycoprotein activity selectively reduced the trafficking of CD8(+) T cells across the brain endothelium in vitro as well as in vivo. In response to formation of the T cell-endothelial synapse, P-glycoprotein was found to regulate secretion of endothelial (C-C motif) ligand 2 (CCL2), a chemokine that mediates CD8(+) T cell migration in vitro. Notably, CCL2 levels were significantly enhanced in microvessels isolated from human multiple sclerosis lesions in comparison with non-neurological controls. Endothelial cell-specific elimination of CCL2 in mice subjected to experimental autoimmune encephalomyelitis also significantly diminished the accumulation of CD8(+) T cells compared to wild-type animals. Collectively, these results highlight a novel (patho)physiological role for P-glycoprotein in CD8(+) T cell trafficking into the central nervous system during neuro-inflammation and illustrate CCL2 secretion as a potential link in this mechanism.

Lesional-targeting of neuroprotection to the inflammatory penumbra in experimental multiple sclerosis

Progressive multiple sclerosis is associated with metabolic failure of the axon and excitotoxicity that leads to chronic neurodegeneration. Global sodium-channel blockade causes side effects that can limit its use for neuroprotection in multiple sclerosis. Through selective targeting of drugs to lesions we aimed to improve the potential therapeutic window for treatment. This was assessed in the relapsing-progressive experimental autoimmune encephalomyelitis ABH mouse model of multiple sclerosis using conventional sodium channel blockers and a novel central nervous system-excluded sodium channel blocker (CFM6104) that was synthesized with properties that selectively target the inflammatory penumbra in experimental autoimmune encephalomyelitis lesions. Carbamazepine and oxcarbazepine were not immunosuppressive in lymphocyte-driven autoimmunity, but slowed the accumulation of disability in experimental autoimmune encephalomyelitis when administered during periods of the inflammatory penumbra after active lesion formation, and was shown to limit the development of neurodegeneration during optic neuritis in myelin-specific T cell receptor transgenic mice. CFM6104 was shown to be a state-selective, sodium channel blocker and a fluorescent p-glycoprotein substrate that was traceable. This compound was >90% excluded from the central nervous system in normal mice, but entered the central nervous system during the inflammatory phase in experimental autoimmune encephalomyelitis mice. This occurs after the focal and selective downregulation of endothelial p-glycoprotein at the blood-brain barrier that occurs in both experimental autoimmune encephalomyelitis and multiple sclerosis lesions. CFM6104 significantly slowed down the accumulation of disability and nerve loss in experimental autoimmune encephalomyelitis. Therapeutic-targeting of drugs to lesions may reduce the potential side effect profile of neuroprotective agents that can influence neurotransmission. This class of agents inhibit microglial activity and neural sodium loading, which are both thought to contribute to progressive neurodegeneration in multiple sclerosis and possibly other neurodegenerative diseases.

Control of spasticity in a multiple sclerosis model using central nervous system-excluded CB1 cannabinoid receptor agonists

The purpose of this study was the generation of central nervous system (CNS)-excluded cannabinoid receptor agonists to test the hypothesis that inhibition of spasticity, due to CNS autoimmunity, could be controlled by affecting neurotransmission within the periphery. Procedures included identification of chemicals and modeling to predict the mode of exclusion; induction and control of spasticity in the ABH mouse model of multiple sclerosis; conditional deletion of CB1 receptor in peripheral nerves; side-effect profiling to demonstrate the mechanism of CNS-exclusion via drug pumps; genome-wide association study in N2(129×ABH) backcross to map polymorphic cannabinoid drug pump; and sequencing and detection of cannabinoid drug-pump activity in human brain endothelial cell lines. Three drugs (CT3, SAB378 and SAD448) were identified that control spasticity via action on the peripheral nerve CB1 receptor. These were peripherally restricted via drug pumps that limit the CNS side effects (hypothermia) of cannabinoids to increase the therapeutic window. A cannabinoid drug pump is polymorphic and functionally lacking in many laboratory (C57BL/6, 129, CD-1) mice used for transgenesis, pharmacology, and toxicology studies. This phenotype was mapped and controlled by 1-3 genetic loci. ABCC1 within a cluster showing linkage is a cannabinoid CNS-drug pump. Global and conditional CB1 receptor-knockout mice were used as controls. In summary, CNS-excluded CB1 receptor agonists are a novel class of therapeutic agent for spasticity.

Immune responses at brain barriers and implications for brain development and neurological function in later life

For a long time the brain has been considered an immune-privileged site due to a muted inflammatory response and the presence of protective brain barriers. It is now recognized that neuroinflammation may play an important role in almost all neurological disorders and that the brain barriers may be contributing through either normal immune signaling or disruption of their basic physiological mechanisms. The distinction between normal function and dysfunction at the barriers is difficult to dissect, partly due to a lack of understanding of normal barrier function and partly because of physiological changes that occur as part of normal development and ageing. Brain barriers consist of a number of interacting structural and physiological elements including tight junctions between adjacent barrier cells and an array of influx and efflux transporters. Despite these protective mechanisms, the capacity for immune-surveillance of the brain is maintained, and there is evidence of inflammatory signaling at the brain barriers that may be an important part of the body's response to damage or infection. This signaling system appears to change both with normal ageing, and during disease. Changes may affect diapedesis of immune cells and active molecular transfer, or cause rearrangement of the tight junctions and an increase in passive permeability across barrier interfaces. Here we review the many elements that contribute to brain barrier functions and how they respond to inflammation, particularly during development and aging. The implications of inflammation–induced barrier dysfunction for brain development and subsequent neurological function are also discussed.

Retinoic acid induces blood-brain barrier development

The blood-brain barrier (BBB) is crucial in the maintenance of a controlled environment within the brain to safeguard optimal neuronal function. The endothelial cells (ECs) of the BBB possess specific properties that restrict the entry of cells and metabolites into the CNS. The specialized BBB endothelial phenotype is induced during neurovascular development by surrounding cells of the CNS. However, the molecular differentiation of the BBB endothelium remains poorly understood. Retinoic acid (RA) plays a crucial role in the brain during embryogenesis. Because radial glial cells supply the brain with RA during the developmental cascade and associate closely with the developing vasculature, we hypothesize that RA is important for the induction of BBB properties in brain ECs. Analysis of human postmortem fetal brain tissue shows that the enzyme mainly responsible for RA synthesis, retinaldehyde dehydrogenase, is expressed by radial glial cells. In addition, the most important receptor for RA-driven signaling in the CNS, RA-receptor β (RARβ), is markedly expressed by the developing brain vasculature. Our findings have been further corroborated by in vitro experiments showing RA- and RARβ-dependent induction of different aspects of the brain EC barrier. Finally, pharmacologic inhibition of RAR activation during the differentiation of the murine BBB resulted in the leakage of a fluorescent tracer as well as serum proteins into the developing brain and reduced the expression levels of important BBB determinants. Together, our results point to an important role for RA in the induction of the BBB during human and mouse development.

Early brain injury alters the blood-brain barrier phenotype in parallel with β-amyloid and cognitive changes in adulthood

Clinical studies suggest that traumatic brain injury (TBI) hastens cognitive decline and development of neuropathology resembling brain aging. Blood-brain barrier (BBB) disruption following TBI may contribute to the aging process by deregulating substance exchange between the brain and blood. We evaluated the effect of juvenile TBI (jTBI) on these processes by examining long-term alterations of BBB proteins, β-amyloid (Aβ) neuropathology, and cognitive changes. A controlled cortical impact was delivered to the parietal cortex of male rats at postnatal day 17, with behavioral studies and brain tissue evaluation at 60 days post-injury (dpi). Immunoglobulin G extravasation was unchanged, and jTBI animals had higher levels of tight-junction protein claudin 5 versus shams, suggesting the absence of BBB disruption. However, decreased P-glycoprotein (P-gp) on cortical blood vessels indicates modifications of BBB properties. In parallel, we observed higher levels of endogenous rodent Aβ in several brain regions of the jTBI group versus shams. In addition at 60 dpi, jTBI animals displayed systematic search strategies rather than relying on spatial memory during the water maze. Together, these alterations to the BBB phenotype after jTBI may contribute to the accumulation of toxic products, which in turn may induce cognitive differences and ultimately accelerate brain aging.

Inflammatory events at blood-brain barrier in neuroinflammatory and neurodegenerative disorders: implications for clinical disease

Proper function of the neurovasculature is required for optimal brain function and preventing neuroinflammation and neurodegeneration. Within this review, we discuss alterations of the function of the blood-brain barrier in neurologic disorders such as multiple sclerosis, epilepsy, and Alzheimer's disease and address potential underlying mechanisms.

Targeting blood-brain barrier sphingolipid signaling reduces basal P-glycoprotein activity and improves drug delivery to the brain

P-glycoprotein, an ATP-driven drug efflux pump, is a major obstacle to the delivery of small-molecule drugs across the blood-brain barrier and into the CNS. Here we test a unique signaling-based strategy to overcome this obstacle. We used a confocal microscopy-based assay with isolated rat brain capillaries to map a signaling pathway that within minutes abolishes P-glycoprotein transport activity without altering transporter protein expression or tight junction permeability. This pathway encompasses elements of proinflammatory- (TNF-α) and sphingolipid-based signaling. Critical to this pathway was signaling through sphingosine-1-phosphate receptor 1 (S1PR1). In brain capillaries, S1P acted through S1PR1 to rapidly and reversibly reduce P-glycoprotein transport activity. Sphingosine reduced transport by a sphingosine kinase-dependent mechanism. Importantly, fingolimod (FTY720), a S1P analog recently approved for treatment of multiple sclerosis, also rapidly reduced P-glycoprotein activity; similar effects were found with the active, phosphorylated metabolite (FTY720P). We validated these findings in vivo using in situ brain perfusion in rats. Administration of S1P, FTY720, or FTY729P increased brain uptake of three radiolabeled P-glycoprotein substrates, (3)H-verapamil (threefold increase), (3)H-loperamide (fivefold increase), and (3)H-paclitaxel (fivefold increase); blocking S1PR1 abolished this effect. Tight junctional permeability, measured as brain (14)C-sucrose accumulation, was not altered. Therefore, targeting signaling through S1PR1 at the blood-brain barrier with the sphingolipid-based drugs, FTY720 or FTY720P, can rapidly and reversibly reduce basal P-glycoprotein activity and thus improve delivery of small-molecule therapeutics to the brain.

Sphingosine 1-phosphate receptor 5 mediates the immune quiescence of the human brain endothelial barrier

Background

The sphingosine 1-phosphate (S1P) receptor modulator FTY720P (Gilenya®) potently reduces relapse rate and lesion activity in the neuroinflammatory disorder multiple sclerosis. Although most of its efficacy has been shown to be related to immunosuppression through the induction of lymphopenia, it has been suggested that a number of its beneficial effects are related to altered endothelial and blood–brain barrier (BBB) functionality. However, to date it remains unknown whether brain endothelial S1P receptors are involved in the maintenance of the function of the BBB thereby mediating immune quiescence of the brain. Here we demonstrate that the brain endothelial receptor S1P₅ largely contributes to the maintenance of brain endothelial barrier function.

Methods

We analyzed the expression of S1P₅ in human post-mortem tissues using immunohistochemistry. The function of S1P₅ at the BBB was assessed in cultured human brain endothelial cells (ECs) using agonists and lentivirus-mediated knockdown of S1P₅. Subsequent analyses of different aspects of the brain EC barrier included the formation of a tight barrier, the expression of BBB proteins and markers of inflammation and monocyte transmigration.

Results

We show that activation of S1P₅ on cultured human brain ECs by a selective agonist elicits enhanced barrier integrity and reduced transendothelial migration of monocytes in vitro. These results were corroborated by genetically silencing S1P₅ in brain ECs. Interestingly, functional studies with these cells revealed that S1P₅ strongly contributes to brain EC barrier function and underlies the expression of specific BBB endothelial characteristics such as tight junctions and permeability. In addition, S1P₅ maintains the immunoquiescent state of brain ECs with low expression levels of leukocyte adhesion molecules and inflammatory chemokines and cytokines through lowering the activation of the transcription factor NFκB.

Conclusion

Our findings demonstrate that S1P₅ in brain ECs contributes to optimal barrier formation and maintenance of immune quiescence of the barrier endothelium.

The Role of ATP-Binding Cassette Transporters in Neuro-Inflammation: Relevance for Bioactive Lipids

ATP-binding cassette (ABC) transporters are highly expressed by brain endothelial cells that form the blood–brain barrier (BBB). These efflux pumps play an important role in maintaining brain homeostasis as they actively hinder the entry of unwanted blood-derived compounds into the central nervous system (CNS). Consequently, their high activity at the BBB has been a major hurdle for the treatment of several brain diseases, as they prevent numerous drugs to reach their site of action within the brain. Importantly, recent data indicate that endogenous substrates for ABC transporters may include inflammatory mediators, such as prostaglandins, leukotrienes, cytokines, chemokines, and bioactive lipids, suggesting a potential role for ABC transporters in immunological responses, and more specifically in inflammatory brain disorders, such as multiple sclerosis (MS). In this review, we will give a comprehensive overview of recent findings that illustrate this novel role for ABC transporters in neuro-inflammatory processes. Moreover, we will provide first insights into underlying mechanisms and focus on the importance for bioactive lipids, in particular platelet-activating factor, herein. A thorough understanding of these events may form the basis for the development for selective treatment modalities to dampen the neuro-inflammatory attack in MS and thereby reducing tissue damage.

The biology that underpins the therapeutic potential of cannabis-based medicines for the control of spasticity in multiple sclerosis

Cannabis-based medicines have recently been approved for the treatment of pain and spasticity in multiple sclerosis (MS). This supports the original perceptions of people with MS, who were using illegal street cannabis for symptom control and pre-clinical testing in animal models of MS. This activity is supported both by the biology of the disease and the biology of the cannabis plant and the endocannabinoid system. MS results from disease that impairs neurotransmission and this is controlled by cannabinoid receptors and endogenous cannabinoid ligands. This can limit spasticity and may also influence the processes that drive the accumulation of progressive disability.

Autoimmunity in 2010

There is now growing evidence that autoimmunity is the common trait connecting multiple clinical phenotypes albeit differences in tissue specificity, pathogenetic mechanisms, and therapeutic approaches cannot be overlooked. Over the past years we witnessed a constant growth of the number of publications related to autoimmune diseases in peer-reviewed journals of the immunology area. Original data referred to factors from common injury pathways (i.e. T helper 17 cells, serum autoantibodies, or vitamin D) and specific diseases such as multiple sclerosis, systemic lupus erythematosus, and rheumatoid arthritis. As an example, the issue of a latitudinal gradient in the prevalence and incidence rates has been proposed for all autoimmune diseases and was recently coined as geoepidemiology to suggest new environmental triggers for tolerance breakdown. The present article is aimed at reviewing the articles that were published over the past year in the major autoimmunity and immunology journals.

ATP-binding cassette transporters and their roles in protecting the brain

The blood-brain barrier is a network of endothelial cells that are tightly attached with each other via specialized cell-cell contacts. This passive diffusion barrier is complemented by ATP-binding cassette (ABC) transporters, which are localized on the surface of the endothelial cells. ABC transporters play important roles in the maintenance of blood-brain barrier integrity, as they carry a wide range of organic molecules, cell metabolites, and nutrients both out of the brain and into the brain. Recent studies have unraveled important roles of ABC transporters in the preservation of tissue homeostasis, pointing out the fact that ABC transporters protect both brain parenchymal cells and microvascular cells from injury. As such, ABC transporters have been involved in the pathogenesis of age-related neurodegenerative diseases, such as Parkinson and Alzheimer diseases, recently. This has led to the idea that neurodegenerative processes might be targeted by restoration of transport processes across the blood-brain barrier.

Adenosine triphosphate-binding cassette transporters mediate chemokine (C-C motif) ligand 2 secretion from reactive astrocytes: relevance to multiple sclerosis pathogenesis

Adenosine triphosphate-binding cassette efflux transporters are highly expressed at the blood-brain barrier and actively hinder passage of harmful compounds, thereby maintaining brain homoeostasis. Since, adenosine triphosphate-binding cassette transporters drive cellular exclusion of potential neurotoxic compounds or inflammatory molecules, alterations in their expression and function at the blood-brain barrier may contribute to the pathogenesis of neuroinflammatory disorders, such as multiple sclerosis. Therefore, we investigated the expression pattern of different adenosine triphosphate-binding cassette efflux transporters, including P-glycoprotein, multidrug resistance-associated proteins-1 and -2 and breast cancer resistance protein in various well-characterized human multiple sclerosis lesions. Cerebrovascular expression of P-glycoprotein was decreased in both active and chronic inactive multiple sclerosis lesions. Interestingly, foamy macrophages in active multiple sclerosis lesions showed enhanced expression of multidrug resistance-associated protein-1 and breast cancer resistance protein, which coincided with their increased function of cultured foamy macrophages. Strikingly, reactive astrocytes display an increased expression of P-glycoprotein and multidrug resistance-associated protein-1 in both active and inactive multiple sclerosis lesions, which correlated with their enhanced in vitro activity on astrocytes derived from multiple sclerosis lesions. To investigate whether adenosine triphosphate-binding cassette transporters on reactive astrocytes can contribute to the inflammatory process, primary cultures of reactive human astrocytes were generated through activation of Toll-like receptor-3 to mimic the astrocytic phenotype as observed in multiple sclerosis lesions. Notably, blocking adenosine triphosphate-binding cassette transporter activity on reactive astrocytes inhibited immune cell migration across a blood-brain barrier model in vitro, which was due to the reduction of astrocytic release of the chemokine (C-C motif) ligand 2. Our data point towards a novel (patho)physiological role for adenosine triphosphate-binding cassette transporters, suggesting that limiting their activity by dampening astrocyte activation may open therapeutic avenues to diminish tissue damage during multiple sclerosis pathogenesis.

Amyloid efflux transporter expression at the blood-brain barrier declines in normal aging

Reduced clearance of amyloid β peptides (Aβ) across the blood-brain barrier contributes to amyloid accumulation in Alzheimer disease. Amyloid β efflux transport is via the endothelial low-density lipoprotein receptor-related protein 1 (LRP-1) and P-glycoprotein (P-gp), whereas Aβ influx transport is via the receptor for advanced glycation end products. Because age is the major risk factor for developing Alzheimer disease, we measured LRP-1 and P-gp expression and associated transporter expression with Aβ accumulation in aging rats. Quantitative LRP-1 and P-gp microvessel expression was measured by immunohistochemistry (IHC); LRP-1 and P-gp expression were assessed in microvessel isolates by Western blotting. There was an age-dependent loss of capillary LRP-1 across all ages (3-36 months) by IHC (linear trend p = 0.0004) and between 3 and 20 months by Western blotting (linear trend p < 0.0001). There was a late (30-36 months) P-gp expression loss by IHC (p < 0.05) and Western blotting (p = 0.0112). Loss of LRP-1 correlated with Aβ42 accumulation (p = 0.0121) and very nearly with Aβ40 (p = 0.0599) across all ages. Expression of LRP-1 correlated negatively with the expression of receptor for advanced glycation end products (p < 0.0004). These data indicate that alterations in LRP-1 and P-gp expression seem to contribute progressively to Aβ accumulation in aging.