Tumor necrosis factor alpha and endothelin-1 increase P-glycoprotein expression and transport activity at the blood-brain barrier

Nongenomic ERα-AMPK Signaling Regulates Sex-Dependent Bcrp Transport Activity at the Blood-Brain Barrier

The blood-brain barrier (BBB) is an extensive capillary network that protects the brain from environmental and metabolic toxins while limiting drug delivery to the central nervous system (CNS). The ATP-binding cassette transporter breast cancer resistance protein (Bcrp) reduces drug delivery across the BBB by actively transporting its clinical substrates back into peripheral circulation before their entry into the CNS compartment. 17β-Estradiol (E2)-elicited changes in Bcrp transport activity and expression have been documented previously. We report a novel signaling mechanism by which E2 decreases Bcrp transport activity in mouse brain capillaries via rapid nongenomic signaling through estrogen receptor α. We extended this finding to investigate the effects of different endocrine-disrupting compounds (EDCs) and selective estrogen receptor modulators (SERMs) on Bcrp transport function. We also demonstrate sex-dependent expression of Bcrp and E2-sensitive Bcrp transport activity at the BBB ex vivo. This work establishes an explanted tissue-based model by which to interrogate EDCs and SERMs as modulators of nongenomic estrogenic signaling with implications for sex and hormonal regulation of therapeutic delivery into the CNS.

Neuroinflammatory Responses and Blood-Brain Barrier Injury in Chronic Alcohol Exposure: Role of Purinergic P2X7 Receptor Signaling

Alcohol consumption leads to neuroinflammation and blood-brain barrier (BBB) damage, resulting in neurological impairment. We previously demonstrated that ethanol-induced disruption of barrier function in human brain endothelial cells was associated with mitochondrial injury, increased ATP and extracellular vesicle (EV) release, and purinergic receptor P2X7R activation. Therefore, we aimed to evaluate the effect of P2X7r blockade on peripheral and neuro-inflammation in EtOH-exposed mice. In a chronic intermittent ethanol (CIE)-exposed mouse model, P2X7R was inhibited by two different methods: Brilliant Blue G (BBG) or gene knockout. We assessed blood ethanol concentration (BEC), plasma P2X7R and P-gp, number of extra-cellular vesicles (EV), serum ATP and EV-ATP levels. Brain microvessel gene expression and EV mtDNA copy numbers were measured by RT2 PCR array and digital PCR, respectively. A RT2 PCR array of brain microvessels revealed significant upregulation of proinflammatory genes involved in apoptosis, vasodilation, and platelet activation in CIE-exposed animals, which were decreased 15-50-fold in BBG-treated CIE-exposed animals. Plasma P-gp levels and serum P2X7R shedding were significantly increased in CIE-exposed animals. Pharmacological or genetic suppression of P2X7R decreased P2X7R shedding to levels equivalent to those in control group. The increase in EV number and EV-ATP content in the CIE-exposed mice was significantly reduced by P2X7R inhibition. CIE mice showed augmented EV-mtDNA copy numbers which were reduced in EVs after P2X7R inhibition or receptor knockout. These observations suggested that P2X7R signaling plays a critical role in ethanol-induced brain injury. Increased eATP, EV-ATP, EV numbers, and EV-mtDNA copy numbers highlight a new mechanism of brain injury during alcohol exposure via P2X7R and biomarkers of such damage. In this study, for the first time, we report the in vivo involvement of P2X7R signaling in CIE-induced brain injury.

Hopping the Hurdle: Strategies to Enhance the Molecular Delivery to the Brain through the Blood-Brain Barrier

Modern medicine has allowed for many advances in neurological and neurodegenerative disease (ND). However, the number of patients suffering from brain diseases is ever increasing and the treatment of brain diseases remains an issue, as drug efficacy is dramatically reduced due to the existence of the unique vascular structure, namely the blood-brain barrier (BBB). Several approaches to enhance drug delivery to the brain have been investigated but many have proven to be unsuccessful due to limited transport or damage induced in the BBB. Alternative approaches to enhance molecular delivery to the brain have been revealed in recent studies through the existence of molecular delivery pathways that regulate the passage of peripheral molecules. In this review, we present recent advancements of the basic research for these delivery pathways as well as examples of promising ventures to overcome the molecular hurdles that will enhance therapeutic interventions in the brain and potentially save the lives of millions of patients.

ABCB1 and ABCG2 Regulation at the Blood-Brain Barrier: Potential New Targets to Improve Brain Drug Delivery

The drug efflux transporters ABCB1 and ABCG2 at the blood-brain barrier limit the delivery of drugs into the brain. Strategies to overcome ABCB1/ABCG2 have been largely unsuccessful, which poses a tremendous clinical problem to successfully treat central nervous system (CNS) diseases. Understanding basic transporter biology, including intracellular regulation mechanisms that control these transporters, is critical to solving this clinical problem.In this comprehensive review, we summarize current knowledge on signaling pathways that regulate ABCB1/ABCG2 at the blood-brain barrier. In Section I, we give a historical overview on blood-brain barrier research and introduce the role that ABCB1 and ABCG2 play in this context. In Section II, we summarize the most important strategies that have been tested to overcome the ABCB1/ABCG2 efflux system at the blood-brain barrier. In Section III, the main component of this review, we provide detailed information on the signaling pathways that have been identified to control ABCB1/ABCG2 at the blood-brain barrier and their potential clinical relevance. This is followed by Section IV, where we explain the clinical implications of ABCB1/ABCG2 regulation in the context of CNS disease. Lastly, in Section V, we conclude by highlighting examples of how transporter regulation could be targeted for therapeutic purposes in the clinic. SIGNIFICANCE STATEMENT: The ABCB1/ABCG2 drug efflux system at the blood-brain barrier poses a significant problem to successful drug delivery to the brain. The article reviews signaling pathways that regulate blood-brain barrier ABCB1/ABCG2 and could potentially be targeted for therapeutic purposes.

Transcranial Focal Electric Stimulation Avoids P-Glycoprotein Over-Expression during Electrical Amygdala Kindling and Delays Epileptogenesis in Rats

Recent evidence suggests that P-glycoprotein (P-gp) overexpression mediates hyperexcitability and is associated with epileptogenesis. Transcranial focal electrical stimulation (TFS) delays epileptogenesis and inhibits P-gp overexpression after a generalized seizure. Here, first we measured P-gp expression during epileptogenesis and second, we assessed if TFS antiepileptogenic effect was related with P-gp overexpression avoidance. Male Wistar rats were implanted in right basolateral amygdala and stimulated daily for electrical amygdala kindling (EAK), P-gp expression was assessed during epileptogenesis in relevant brain areas. Stage I group showed 85% increase in P-gp in ipsilateral hippocampus (p < 0.001). Stage III group presented 58% and 57% increase in P-gp in both hippocampi (p < 0.05). Kindled group had 92% and 90% increase in P-gp in both hippocampi (p < 0.01), and 93% and 143% increase in both neocortices (p < 0.01). For the second experiment, TFS was administrated daily after each EAK stimulation for 20 days and P-gp concentration was assessed. No changes were found in the TFS group (p > 0.05). Kindled group showed 132% and 138% increase in P-gp in both hippocampi (p < 0.001) and 51% and 92% increase in both cortices (p < 0.001). Kindled + TFS group presented no changes (p > 0.05). Our experiments revealed that progression of EAK is associated with increased P-gp expression. These changes are structure-specific and dependent on seizure severity. EAK-induced P-gp overexpression would be associated with neuronal hyperexcitability and thus, epileptogenesis. P-gp could be a novel therapeutical target to avoid epileptogenesis. In accordance with this, TFS inhibited P-gp overexpression and interfered with EAK. An important limitation of the present study is that P-gp neuronal expression was not evaluated under the different experimental conditions. Future studies should be carried out to determine P-gp neuronal overexpression in hyperexcitable networks during epileptogenesis. The TFS-induced lessening of P-gp overexpression could be a novel therapeutical strategy to avoid epileptogenesis in high-risk patients.

LncRNA H19 Regulates P-glycoprotein Expression Through the NF-κB Signaling Pathway in the Model of Status Epilepticus

Pharmaco-resistance is a challenging problem for treatment of status epilepticus (SE) in the clinic. P-glycoprotein (P-gp) is one of the most important multi-drug transporters that contribute to drug resistance of SE. Long noncoding RNAs (lncRNAs) have been increasingly recognized as versatile regulators of P-gp in tumors and epilepsy. However, the function of lncRNAs in drug resistance of SE remains largely unknown. In the present study, pilocarpine-induced rat model is used to explore the expression profiles of lncRNAs in the hippocampus of SE using RNA sequencing. Our results implied that the level of lncRNA H19 was significantly increased in the hippocampus of SE rats, which was positively correlated with the level of P-gp. While downregulation of H19 could inhibit the expression of P-gp and alleviate neural damage in the hippocampus of SE rats. Furthermore, it was revealed that H19 regulates P-gp expression through the nuclear factor-kappaB (NF-κB) signaling pathway by functioning as a competing endogenous RNA against microRNA-29a-3p. Overall, our study indicated that H19 regulates P-gp expression and neural damage induced by SE through the NF-κB signaling pathway, which provides a promising target to overcome drug resistance and alleviate brain damage for SE.

Expression of GnT-III decreases chemoresistance via negatively regulating P-glycoprotein expression: Involvement of the TNFR2-NF-κB signaling pathway

The phenomenon of multidrug resistance (MDR) is called chemoresistance with respect to the treatment of cancer, and it continues to be a major challenge. The role of N-glycosylation in chemoresistance, however, remains poorly understood. Here, we established a traditional model for adriamycin resistance in K562 cells, which are also known as K562/adriamycin-resistant (ADR) cells. Lectin blot, mass spectrometry, and RT-PCR analysis showed that the expression levels of N-acetylglucosaminyltransferase III (GnT-III) mRNA and its products, bisected N-glycans, are significantly decreased in K562/ADR cells, compared with the levels in parent K562 cells. By contrast, the expression levels of both P-glycoprotein (P-gp) and its intracellular key regulator, NF-κB signaling, are significantly increased in K562/ADR cells. These upregulations were sufficiently suppressed by the overexpression of GnT-III in K562/ADR cells. We found that the expression of GnT-III consistently decreased chemoresistance for doxorubicin and dasatinib, as well as activation of the NF-κB pathway by tumor necrosis factor (TNF) α, which binds to two structurally distinct glycoproteins, TNF receptor 1 (TNFR1) and TNF receptor 2 (TNFR2), on the cell surface. Interestingly, our immunoprecipitation analysis revealed that only TNFR2, but not TNFR1, contains bisected N-glycans. The lack of GnT-III strongly induced TNFR2's autotrimerization without ligand stimulation, which was rescued by the overexpression of GnT-III in K562/ADR cells. Furthermore, the deficiency of TNFR2 suppressed P-gp expression while it increased GnT-III expression. Taken together, these results clearly show that GnT-III negatively regulates chemoresistance via the suppression of P-gp expression, which is regulated by the TNFR2-NF/κB signaling pathway.

Recent advances in the in vitro and in vivo methods to assess impact of P-glycoprotein and breast cancer resistance protein transporters in central nervous system drug disposition

One challenge in central nervous system (CNS) drug discovery has been ensuring the blood-brain barrier (BBB) penetration of compounds at an efficacious concentration that provides suitable safety margins for clinical investigation. Research providing for the accurate prediction of brain penetration of compounds during preclinical discovery is important to a CNS program. In the BBB, P-glycoprotein (P-gp) (ABCB1) and breast cancer resistance protein (BCRP) (ABCG2) transporters have been demonstrated to play a major role in the active efflux of endogenous compounds and xenobiotics out of the brain microvessel cells and back to the systemic circulation. In the past 10 years, there has been significant technological improvement in the sensitivity of quantitative proteomics methods, in vivo imaging, in vitro methods of organoid and microphysiological systems, as well as in silico quantitative physiological based pharmacokinetic and systems pharmacology models. Scientists continually leverage these advancements to interrogate the distribution of compounds in the CNS which may also show signals of substrate specificity of P-gp and/or BCRP. These methods have shown promise toward predicting and quantifying the unbound concentration(s) within the brain relevant for efficacy or safety. In this review, the authors have summarized the in vivo, in vitro, and proteomics advancements toward understanding the contribution of P-gp and/or BCRP in restricting the entry of compounds to the CNS of either healthy or special populations. Special emphasis has been provided on recent investigations on the application of a proteomics-informed approach to predict steady-state drug concentrations in the brain. Moreover, future perspectives regarding the role of these transporters in newer modalities are discussed.

Lipopolysaccharide-Induced Functional Alteration of P-glycoprotein in the Ex Vivo Rat Inner Blood-Retinal Barrier

At the inner blood-retinal barrier (BRB), P-glycoprotein (P-gp) contributes to maintaining the homeostasis of substance concentration in the retina by transporting drugs and exogenous toxins from the retina to the circulating blood. Under inflammatory conditions, P-gp activities have been reported to be altered in various tissues. The purpose of this study was to clarify the alterations in P-gp activity at the inner BRB due to lipopolysaccharide (LPS), an inflammatory agent, and the molecular mechanisms of the alterations induced by LPS. Ex vivo P-gp activity was evaluated as luminal accumulation of 7-nitro-2,1,3-benzoxadiazole-cyclosporin A (NBD-CSA), a fluorescent P-gp substrate, in freshly prepared rat retinal capillaries. The luminal NBD-CSA accumulation was significantly decreased in the presence of LPS, indicating that P-gp activity at the inner BRB is reduced by LPS. This LPS-induced attenuation of the luminal NBD-CSA accumulation was abolished by inhibiting toll-like receptor 4 (TLR4), a receptor for LPS. Furthermore, an inhibitor/antagonist of tumor necrosis factor receptor 1, endothelin B receptor, nitric oxide synthase, or protein kinase C (PKC) significantly restored the LPS-induced decrease in the luminal NBD-CSA accumulation. Consequently, it is suggested that the TLR4/PKC pathway is involved in the reduction in P-gp function in the inner BRB by LPS.

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.

The Impact of P-Glycoprotein on Opioid Analgesics: What's the Real Meaning in Pain Management and Palliative Care?

Opioids are widely used in cancer and non-cancer pain management. However, many transporters at the blood-brain barrier (BBB), such as P-glycoprotein (P-gp, ABCB1/MDR1), may impair their delivery to the brain, thus leading to opioid tolerance. Nonetheless, opioids may regulate P-gp expression, thus altering the transport of other compounds, namely chemotherapeutic agents, resulting in pharmacoresistance. Other kinds of painkillers (e.g., acetaminophen, dexamethasone) and adjuvant drugs used for neuropathic pain may act as P-gp substrates and modulate its expression, thus making pain management challenging. Inflammatory conditions are also believed to upregulate P-gp. The role of P-gp in drug-drug interactions is currently under investigation, since many P-gp substrates may also act as substrates for the cytochrome P450 enzymes, which metabolize a wide range of xenobiotics and endobiotics. Genetic variability of the ABCB1/MDR1 gene may be accountable for inter-individual variation in opioid-induced analgesia. P-gp also plays a role in the management of opioid-induced adverse effects, such as constipation. Peripherally acting mu-opioid receptors antagonists (PAMORAs), such as naloxegol and naldemedine, are substrates of P-gp, which prevent their penetration in the central nervous system. In our review, we explore the interactions between P-gp and opioidergic drugs, with their implications in clinical practice.

TNF-α and IL-1β Modulate Blood-Brain Barrier Permeability and Decrease Amyloid-β Peptide Efflux in a Human Blood-Brain Barrier Model

The blood-brain barrier (BBB) is a selective barrier and a functional gatekeeper for the central nervous system (CNS), essential for maintaining brain homeostasis. The BBB is composed of specialized brain endothelial cells (BECs) lining the brain capillaries. The tight junctions formed by BECs regulate paracellular transport, whereas transcellular transport is regulated by specialized transporters, pumps and receptors. Cytokine-induced neuroinflammation, such as the tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), appear to play a role in BBB dysfunction and contribute to the progression of Alzheimer’s disease (AD) by contributing to amyloid-β (Aβ) peptide accumulation. Here, we investigated whether TNF-α and IL-1β modulate the permeability of the BBB and alter Aβ peptide transport across BECs. We used a human BBB in vitro model based on the use of brain-like endothelial cells (BLECs) obtained from endothelial cells derived from CD34+ stem cells cocultivated with brain pericytes. We demonstrated that TNF-α and IL-1β differentially induced changes in BLECs’ permeability by inducing alterations in the organization of junctional complexes as well as in transcelluar trafficking. Further, TNF-α and IL-1β act directly on BLECs by decreasing LRP1 and BCRP protein expression as well as the specific efflux of Aβ peptide. These results provide mechanisms by which CNS inflammation might modulate BBB permeability and promote Aβ peptide accumulation. A future therapeutic intervention targeting vascular inflammation at the BBB may have the therapeutic potential to slow down the progression of AD.

Transporter Regulation in Critical Protective Barriers: Focus on Brain and Placenta

Drug transporters play an important role in the maintenance of chemical balance and homeostasis in different tissues. In addition to their physiological functions, they are crucial for the absorption, distribution, and elimination of many clinically important drugs, thereby impacting therapeutic efficacy and toxicity. Increasing evidence has demonstrated that infectious, metabolic, inflammatory, and neurodegenerative diseases alter the expression and function of drug transporters. However, the current knowledge on transporter regulation in critical protective barriers, such as the brain and placenta, is still limited and requires more research. For instance, while many studies have examined P-glycoprotein, it is evident that research on the regulation of highly expressed transporters in the blood–brain barrier and blood–placental barrier are lacking. The aim of this review is to summarize the currently available literature in order to better understand transporter regulation in these critical barriers.

Neuroimmune Crosstalk Between the Peripheral and the Central Immune System in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal disease characterized by the degeneration and death of motor neurons. Systemic neuroinflammation contributes to the pathogenesis of ALS. The proinflammatory milieu depends on the continuous crosstalk between the peripheral immune system (PIS) and central immune system (CIS). Central nervous system (CNS) resident immune cells interact with the peripheral immune cells via immune substances. Dysfunctional CNS barriers, including the blood–brain barrier, and blood–spinal cord barrier, accelerate the inflammatory process, leading to a systemic self-destructive cycle. This review focuses on the crosstalk between PIS and CIS in ALS. Firstly, we briefly introduce the cellular compartments of CIS and PIS, respectively, and update some new understanding of changes specifically occurring in ALS. Then, we will review previous studies on the alterations of the CNS barriers, and discuss their crucial role in the crosstalk in ALS. Finally, we will review the moveable compartments of the crosstalk, including cytokines, chemokines, and peripheral immune cells which were found to infiltrate the CNS, highlighting the interaction between PIS and CIS. This review aims to provide new insights into pathogenic mechanisms and innovative therapeutic approaches for ALS.

Addressing Blood–Brain Barrier Impairment in Alzheimer’s Disease

The blood–brain barrier (BBB) plays a vital role in maintaining the specialized microenvironment of the brain tissue. It facilitates communication while separating the peripheral circulation system from the brain parenchyma. However, normal aging and neurodegenerative diseases can alter and damage the physiological properties of the BBB. In this review, we first briefly present the essential pathways maintaining and regulating BBB integrity, and further review the mechanisms of BBB breakdown associated with normal aging and peripheral inflammation-causing neurodegeneration and cognitive impairments. We also discuss how BBB disruption can cause or contribute to Alzheimer’s disease (AD), the most common form of dementia and a devastating neurological disorder. Next, we document overlaps between AD and vascular dementia (VaD) and briefly sum up the techniques for identifying biomarkers linked to BBB deterioration. Finally, we conclude that BBB breakdown could be used as a biomarker to help diagnose cognitive impairment associated with normal aging and neurodegenerative diseases such as AD.

Blood-Brain Barrier Transporters: Opportunities for Therapeutic Development in Ischemic Stroke

Globally, stroke is a leading cause of death and long-term disability. Over the past decades, several efforts have attempted to discover new drugs or repurpose existing therapeutics to promote post-stroke neurological recovery. Preclinical stroke studies have reported successes in identifying novel neuroprotective agents; however, none of these compounds have advanced beyond a phase III clinical trial. One reason for these failures is the lack of consideration of blood-brain barrier (BBB) transport mechanisms that can enable these drugs to achieve efficacious concentrations in ischemic brain tissue. Despite the knowledge that drugs with neuroprotective properties (i.e., statins, memantine, metformin) are substrates for endogenous BBB transporters, preclinical stroke research has not extensively studied the role of transporters in central nervous system (CNS) drug delivery. Here, we review current knowledge on specific BBB uptake transporters (i.e., organic anion transporting polypeptides (OATPs in humans; Oatps in rodents); organic cation transporters (OCTs in humans; Octs in rodents) that can be targeted for improved neuroprotective drug delivery. Additionally, we provide state-of-the-art perspectives on how transporter pharmacology can be integrated into preclinical stroke research. Specifically, we discuss the utility of in vivo stroke models to transporter studies and considerations (i.e., species selection, co-morbid conditions) that will optimize the translational success of stroke pharmacotherapeutic experiments.

Lentiviral Infections Persist in Brain despite Effective Antiretroviral Therapy and Neuroimmune Activation

HIV infection persists in different tissue reservoirs among people with HIV (PWH) despite effective antiretroviral therapy (ART). In the brain, lentiviruses replicate principally in microglia and trafficking macrophages. The impact of ART on this viral reservoir is unknown. We investigated the activity of contemporary ART in various models of lentivirus brain infection. HIV-1 RNA and total and integrated DNA were detected in cerebral cortex from all PWH (n = 15), regardless of ART duration or concurrent plasma viral quantity and, interestingly, integrated proviral DNA levels in brain were significantly higher in the aviremic ART-treated group (P < 0.005). Most ART drugs tested (dolutegravir, ritonavir, raltegravir, and emtricitabine) displayed significantly lower 50% effective concentration (EC₅₀) values in lymphocytes than in microglia, except tenofovir, which showed 1.5-fold greater activity in microglia (P < 0.05). In SIV-infected Chinese rhesus macaques, despite receiving suppressive (n = 7) or interrupted (n = 8) ART, brain tissues had similar SIV-encoded RNA and total and integrated DNA levels compared to brains from infected animals without ART (n = 3). SIV and HIV-1 capsid antigens were immunodetected in brain, principally in microglia/macrophages, regardless of ART duration and outcome. Antiviral immune responses were comparable in the brains of ART-treated and untreated HIV- and SIV-infected hosts. Both HIV-1 and SIV persist in brain tissues despite contemporary ART, with undetectable virus in blood. ART interruption exerted minimal effect on the SIV brain reservoir and did not alter the neuroimmune response profile. These studies underscore the importance of augmenting ART potency in different tissue compartments. IMPORTANCE Antiretroviral therapy (ART) suppresses HIV-1 in plasma and CSF to undetectable levels. However, the impact of contemporary ART on HIV-1 brain reservoirs remains uncertain. An active viral reservoir in the brain during ART could lead to rebound systemic infection after cessation of therapy, development of drug resistance mutations, and neurological disease. ART's impact, including its interruption, on brain proviral DNA remains unclear. The present studies show that in different experimental platforms, contemporary ART did not suppress viral burden in the brain, regardless of ART component regimen, the duration of therapy, and its interruption. Thus, new strategies for effective HIV-1 suppression in the brain are imperative to achieve sustained HIV suppression.

Engineered nanomaterials induce alterations in biological barriers: focus on paracellular permeability

Engineered nanoparticles (ENPs) are widely used in medical diagnosis and treatment, as food additives and as energy materials. ENPs may exert adverse or beneficial effects on the human body, which may be linked to interactions with biological barriers. In this review, the authors summarize the influences of four typical metal/metal oxide nanomaterials (Ag, TiO₂, Au, ZnO nanoparticles) on the paracellular permeability of biological barriers. Disruptions on tight junctions, adhesion junctions, gap junctions and desmosomes via complex signaling pathways, such as the MAPK, PKC and ROCK signaling pathways, affect paracellular permeability. Reactive oxygen species and cytokines underlie the mechanism of ENP-triggered alterations in paracellular permeability. This review provides the information necessary for the cautious application of nanoparticles in medicine and life sciences in the future.

Neuroinflammatory Triangle Presenting Novel Pharmacological Targets for Ischemic Brain Injury

Ischemic stroke is one of the leading causes of morbidity and mortality globally. Hundreds of clinical trials have proven ineffective in bringing forth a definitive and effective treatment for ischemic stroke, except a myopic class of thrombolytic drugs. That, too, has little to do with treating long-term post-stroke disabilities. These studies proposed diverse options to treat stroke, ranging from neurotropic interpolation to venting antioxidant activity, from blocking specific receptors to obstructing functional capacity of ion channels, and more recently the utilization of neuroprotective substances. However, state of the art knowledge suggests that more pragmatic focus in finding effective therapeutic remedy for stroke might be targeting intricate intracellular signaling pathways of the 'neuroinflammatory triangle': ROS burst, inflammatory cytokines, and BBB disruption. Experimental evidence reviewed here supports the notion that allowing neuroprotective mechanisms to advance, while limiting neuroinflammatory cascades, will help confine post-stroke damage and disabilities.

Inflammation Induces Changes in the Functional Expression of P-gp, BCRP, and MRP2: An Overview of Different Models and Consequences for Drug Disposition

The ATP-binding cassette (ABC) transporters play a key role in drug pharmacokinetics. These membrane transporters expressed within physiological barriers can be a source of pharmacokinetic variability. Changes in ABC transporter expression and functionality may consequently affect the disposition of substrate drugs, resulting in different drug exposure. Inflammation, present in several acute and chronic diseases, has been identified as a source of modulation in drug transporter expression leading to variability in drug response. Its regulation may be particularly dangerous for drugs with a narrow therapeutic index. In this context, numerous in vitro and in vivo models have shown up- or downregulation in the expression and functionality of ABC transporters under inflammatory conditions. Nevertheless, the existence of contradictory data and the lack of standardization for the models used have led to a less conclusive interpretation of these data.

Fungal brain infection modelled in a human-neurovascular-unit-on-a-chip with a functional blood-brain barrier

The neurovascular unit, which consists of vascular cells surrounded by astrocytic end-feet and neurons, controls cerebral blood flow and the permeability of the blood-brain barrier (BBB) to maintain homeostasis in the neuronal milieu. Studying how some pathogens and drugs can penetrate the human BBB and disrupt neuronal homeostasis requires in vitro microphysiological models of the neurovascular unit. Here we show that the neurotropism of Cryptococcus neoformans-the most common pathogen causing fungal meningitis-and its ability to penetrate the BBB can be modelled by the co-culture of human neural stem cells, brain microvascular endothelial cells and brain vascular pericytes in a human-neurovascular-unit-on-a-chip maintained by a stepwise gravity-driven unidirectional flow and recapitulating the structural and functional features of the BBB. We found that the pathogen forms clusters of cells that penetrate the BBB without altering tight junctions, suggesting a transcytosis-mediated mechanism. The neurovascular-unit-on-a-chip may facilitate the study of the mechanisms of brain infection by pathogens, and the development of drugs for a range of brain diseases.

Increased brain penetration of diphenhydramine and memantine in rats with adjuvant-induced arthritis

Brain penetration of cationic drugs is an important determinant of their efficacy and side effects. However, the effects of alterations in the activity of uptake transporters in the brain under inflammatory conditions on the brain penetration of cationic drugs are not fully understood. The aim of this study was to examine changes in brain penetration of cationic drugs, including diphenhydramine (DPHM), memantine (MMT), and cimetidine (CMD), and changes in the expression of uptake transporters such as organic cation transporter (Oct) in brain microvascular endothelial cells (BMECs) under inflammatory conditions. To clarify the effects of inflammation on the brain penetration of DPHM, MMT, and CMD, we performed brain microdialysis studies in a rat model of adjuvant-induced arthritis (AA). Further, differences in transporter mRNA expression levels between BMECs from control and AA rats were evaluated. Brain microdialysis showed that the unbound brain-to-plasma partition coefficient (K_p,uu,brain) for DPHM and MMT was significantly lower in AA rats compared with control rats. OCT mRNA levels were increased and proton-coupled organic cation (H⁺/OC) antiporter mRNA levels were decreased in AA rats compared with control rats. Taken together, our findings suggest that inflammation decreases the brain penetration of H⁺/OC antiporter substrates such as DPHM and MMT.

Tissue-Nonspecific Alkaline Phosphatase in Central Nervous System Health and Disease: A Focus on Brain Microvascular Endothelial Cells

Tissue-nonspecific alkaline phosphatase (TNAP) is an ectoenzyme bound to the plasma membranes of numerous cells via a glycosylphosphatidylinositol (GPI) moiety. TNAP's function is well-recognized from earlier studies establishing its important role in bone mineralization. TNAP is also highly expressed in cerebral microvessels; however, its function in brain cerebral microvessels is poorly understood. In recent years, few studies have begun to delineate a role for TNAP in brain microvascular endothelial cells (BMECs)-a key component of cerebral microvessels. This review summarizes important information on the role of BMEC TNAP, and its implication in health and disease. Furthermore, we discuss current models and tools that may assist researchers in elucidating the function of TNAP in BMECs.

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.

Changes of blood-brain-barrier function and transfer of amyloid beta in rats with collagen-induced arthritis

Background

Rheumatoid arthritis (RA) is characterized by synovial inflammation, cartilage damage, and systemic inflammation. RA is also associated with the occurrence of neuroinflammation and neurodegenerative diseases. In this study, the impacts of RA on the function of the blood-brain barrier (BBB) and the disposition of amyloid beta (Aβ), including BBB transport and peripheral clearance of Aβ, were investigated in rats with collagen-induced arthritis (CIA), an animal model with similarity to clinical and pathological features of human RA.

Methods

CIA was induced in female Lewis rats. In addition to neuroinflammation, the integrity and function of the BBB were examined. The expression of Aβ-transporting proteins at brain blood vessels was measured. Blood-to-brain influx and plasma clearance of Aβ were determined.

Results

Both microgliosis and astrogliosis were significantly increased in the brain of CIA rats, compared with controls. In terms of BBB function, the BBB permeability of sodium fluorescein, a marker compound for BBB integrity, was significantly increased in CIA rats. Moreover, increased expression of matrix metalloproteinase-3 (MMP-3) and MMP-9 and decreased expression of tight junction proteins, zonula occludens-1 (ZO-1) and occludin, were observed in brain microvessels of CIA rats. In related to BBB transport of Aβ, protein expression of the receptor of advanced glycation end product (RAGE) and P-glycoprotein (P-gp) was significantly increased in brain microvessels of CIA rats. Notably, much higher expression of RAGE was identified at the arterioles of the hippocampus of CIA rats. Following an intravenous injection of human Aβ, significant higher brain influx of Aβ was observed in the hippocampus of CIA rats.

Conclusions

Neuroinflammation and the changes of BBB function were observed in CIA rats. The increased RAGE expression at cerebral blood vessels and enhanced blood-to-brain influx of Aβ indicate the imbalanced BBB clearance of Aβ in RA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02086-2.

The effects of drug transporters on the efficacy of methotrexate in the treatment of rheumatoid arthritis

The ATP-binding cassette (ABC) and solute carrier (SLC) transporter families consist of common drug transporters that mediate the efflux and uptake of drugs, respectively, and play an important role in the absorption, distribution, metabolism and excretion of drugs in vivo. Rheumatoid arthritis (RA) is an autoimmune disease characterized by erosive arthritis, and there are many RA patients worldwide. Methotrexate (MTX), the first-choice treatment for RA, can reduce the level of inflammation, prevent joint erosion and functional damage, and greatly reduce pain in RA patients. However, many patients show resistance to MTX, greatly affecting the efficacy of MTX. Many factors, such as irrational drug use and heredity, are associated with drug resistance. Considering the effect of drug transporters on drugs, many studies have compared the expression of drug transporters in drug-resistant and drug-sensitive patients, and abnormal transporter expression and transport activity have been found in patients with MTX resistance. Thus, drug transporters are involved in drug resistance. This article reviews the effects of transporters on the efficacy of MTX in the treatment of RA.

Neural Progenitor Cell-Derived Extracellular Vesicles Enhance Blood-Brain Barrier Integrity by NF-κB (Nuclear Factor-κB)-Dependent Regulation of ABCB1 (ATP-Binding Cassette Transporter B1) in Stroke Mice

Supplemental Digital Content is available in the text.

Objective:

Extracellular vesicles (EVs) derived from neural progenitor cells enhance poststroke neurological recovery, albeit the underlying mechanisms remain elusive. Since previous research described an enhanced poststroke integrity of the blood-brain barrier (BBB) upon systemic transplantation of neural progenitor cells, we examined if neural progenitor cell-derived EVs affect BBB integrity and which cellular mechanisms are involved in the process.

Approach and Results:

Using in vitro models of primary brain endothelial cell (EC) cultures as well as co-cultures of brain ECs (ECs) and astrocytes exposed to oxygen glucose deprivation, we examined the effects of EVs or vehicle on microvascular integrity. In vitro data were confirmed using a mouse transient middle cerebral artery occlusion model. Cultured ECs displayed increased ABCB1 (ATP-binding cassette transporter B1) levels when exposed to oxygen glucose deprivation, which was reversed by treatment with EVs. The latter was due to an EV-induced inhibition of the NF-κB (nuclear factor-κB) pathway. Using a BBB co-culture model of ECs and astrocytes exposed to oxygen glucose deprivation, EVs stabilized the BBB and ABCB1 levels without affecting the transcellular electrical resistance of ECs. Likewise, EVs yielded reduced Evans blue extravasation, decreased ABCB1 expression as well as an inhibition of the NF-κB pathway, and downstream matrix metalloproteinase 9 (MMP-9) activity in stroke mice. The EV-induced inhibition of the NF-κB pathway resulted in a poststroke modulation of immune responses.

Conclusions:

Our findings suggest that EVs enhance poststroke BBB integrity via ABCB1 and MMP-9 regulation, attenuating inflammatory cell recruitment by inhibition of the NF-κB pathway.

Increased penetration of diphenhydramine in brain via proton-coupled organic cation antiporter in rats with lipopolysaccharide-induced inflammation

Uptake transporters in brain microvascular endothelial cells (BMECs) are involved in the penetration of basic (cationic) drugs such as diphenhydramine (DPHM) into the brain. Lipopolysaccharide (LPS)-induced inflammation alters the expression levels and activities of uptake transporters, which change the penetration of DPHM into the brain. A brain microdialysis study showed that the unbound brain-to-plasma partition coefficient (K_p,uu,brain) for DPHM in LPS rats was approximately two times higher than that in control rats. The transcellular transport of DPHM to BMECs was increased when BMECs were cultured with serum from LPS rats. Compared with control rats or BMECs, the brain uptake of DPHM in LPS rats was increased and the intracellular accumulation of DPHM was increased under a high intracellular pH in BMECs from LPS rats, respectively. Treatment of BMECs with transporter inhibitors or inflammatory cytokines had little impact on the intracellular accumulation of DPHM in BMECs. This study suggests that LPS-induced inflammation promotes unidentified proton-coupled organic cation (H⁺/OC) antiporters that improve the penetration of DPHM into rat brain via the blood-brain barrier.

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The unbound brain-to-plasma partition coefficient for diphenhydramine (DPHM) was increased in lipopolysaccharide-induced inflammation in rats.

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The uptake of DPHM to brain microvascular endothelial cells (BMECs) was promoted by treatments of serum from rats with inflammation.

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Treatment of BMECs with transporter inhibitors or inflammatory cytokines had little impact on the intracellular accumulation of DPHM in BMECs.

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LPS-induced inflammation promotes unidentified proton-coupled organic cation antiporters that improve the brain penetration of DPHM.

Regulation of blood-brain barrier integrity by microglia in health and disease: A therapeutic opportunity

The blood-brain barrier (BBB) is a critical regulator of CNS homeostasis. It possesses physical and biochemical characteristics (i.e. tight junction protein complexes, transporters) that are necessary for the BBB to perform this physiological role. Microvascular endothelial cells require support from astrocytes, pericytes, microglia, neurons, and constituents of the extracellular matrix. This intricate relationship implies the existence of a neurovascular unit (NVU). NVU cellular components can be activated in disease and contribute to dynamic remodeling of the BBB. This is especially true of microglia, the resident immune cells of the brain, which polarize into distinct proinflammatory (M1) or anti-inflammatory (M2) phenotypes. Current data indicate that M1 pro-inflammatory microglia contribute to BBB dysfunction and vascular "leak", while M2 anti-inflammatory microglia play a protective role at the BBB. Understanding biological mechanisms involved in microglia activation provides a unique opportunity to develop novel treatment approaches for neurological diseases. In this review, we highlight characteristics of M1 proinflammatory and M2 anti-inflammatory microglia and describe how these distinct phenotypes modulate BBB physiology. Additionally, we outline the role of other NVU cell types in regulating microglial activation and highlight how microglia can be targeted for treatment of disease with a focus on ischemic stroke and Alzheimer's disease.

David S. Miller: Scientist, Mentor, Friend-a tribute and thank you

David S. Miller was Acting Scientific Director of the Division of Intramural Research at the National Institute of Environmental Health Sciences, National Institutes of Health, and Head of the Intracellular Regulation Group in the Laboratory of Toxicology and Pharmacology before he retired in 2016. David received his Ph.D. in biochemistry from the University of Maine in 1973. David was a Group Leader at the Michigan Cancer Foundation before joining the NIEHS in 1985. His research covered a wide range from renal excretory transport mechanisms to regulation of transporters at the blood–CSF and blood–brain barriers, from fish, amphibians and birds to mammals. David was an outstanding scientist with irresistible enthusiasm for science and an incredible ability to think outside the box while being an exceptional mentor and friend.

Overexpression of ABCC2 and NF-Κβ/p65 with Reduction in Cisplatin and 4OH-Tamoxifen Sensitivity in MCF-7 Breast Cancer Cells: The Influence of TNF-α

Background: TNF-α, as a pro-inflammatory cytokine in the tumor microenvironment is able to regulate the expression and function of various ATP binding cassette (ABC) transporters involved in clinical drug resistance and among them, ABCC2 transporter is represented to contribute to cancer multidrug resistance (MDR) by drug efflux. Methods: In this study, we aimed to evaluate the effects of TNF-α and/or E2 (17β-estradiol) on the mRNA and protein expression levels of ABCC2 and NF-κB (p65) transcription factor in estrogen receptor positive (ER+) MCF-7 cells by QRT-PCR and Western blot analysis. Also, we used MTT assay to study the cell sensitivity against the active form of tamoxifen (4OH-TAM), a hypothetical substrate and Cisplatin (Cis), a well-known substrate for ABCC2 used in endocrine and chemo-therapy of breast cancers, respectively. Data were analyzed by one-way ANOVA and Tukey tests. Significance was considered in P-values < 0.05. Results: The expression levels of ABCC2 and the active form of NF-κB (p65) were significantly increased following 20-day concomitant treatment with TNF-α and E2, compared to untreated cells as control. Also, the viability assay showed that 20-day TNF-α+E2 treatment led to more sensitivity reduction of MCF-7 cells to Cis and 4OH-TAM compared to E2-treated and untreated cells. Conclusion: Based on our findings, there is a positive correlation between ABCC2 overexpression, over-activity of NF-ҡB/p65 and decreasing the sensitivity of MCF-7 cells to Cis and 4OH-TAM following TNF-α treatment in MCF-7 cells. Further experiments are needed to elucidate possible mechanistic relationship of these findings and their clinical significance in order to circumvent the drug-resistance in breast tumors.

HMGB1 promoted P-glycoprotein at the blood-brain barrier in MCAO rats via TLR4/NF-κB signaling pathway

P-glycoprotein (P-gp) is located on the luminal surface of brain vascular endothelium and its status may determine the delivery of the agents into the brain tissues. Previous study showed that upregulation of P-gp at the blood-brain barrier (BBB) after ischemic stroke were mediated by nuclear factor-B (NF-kB) and tumour necrosis factor-α (TNF-α). Based on middle cerebral artery occlusion (MCAO) rats and oxygen-glucose deprivation (OGD) in co-culture of rat brain microvessel endothelial cells (rBMECs) and astrocytes system, the present data indicated that potentiated P-gp expression and activity in brain microvessels or rBMECs were associated with the increase in high-mobility group box 1 (HMGB1), Toll-like receptor 4 (TLR4) and activation of NF-kB and that HMGB1 can release from nucleus to the cytoplasm in activated astrocytes, then into the medium. Moreover, changes in TLR4, TIR domain-containing adaptor protein (TIRAP), NF-kB and P-gp in rBMECs were attenuated by addition of 1 mM ethyl pyruvate (EP), 10 μM TAK-242 and 10 μM pyrrolidine dithiocarbamate (PDTC), respectively. These results demonstrated that HMGB1 promoted P-gp at the BBB after cerebral ischemia via TLR4/NF-κB signaling pathway.

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.

Inhibition of human microsomal PGE2 synthase-1 reduces seizure-induced increases of P-glycoprotein expression and activity at the blood-brain barrier

The cause of antiseizure drug (ASD) resistance in epilepsy is poorly understood. Here, we focus on the transporter P-glycoprotein (P-gp) that is partly responsible for limited ASD brain uptake, which is thought to contribute to ASD resistance. We previously demonstrated that cyclooxygenase-2 (COX-2) and the prostaglandin E receptor, prostanoid E receptor subtype 1, are involved in seizure-mediated P-gp up-regulation. Thus, we hypothesized that inhibiting microsomal prostaglandin E₂ (PGE2) synthase-1 (mPGES-1), the enzyme generating PGE2, prevents blood-brain barrier P-gp up-regulation after status epilepticus (SE). To test our hypothesis, we exposed isolated brain capillaries to glutamate ex vivo and used a combined in vivo-ex vivo approach by isolating brain capillaries from humanized mPGES-1 mice to study P-gp levels. We demonstrate that glutamate signaling through the NMDA receptor, cytosolic phospholipase A2, COX-2, and mPGES-1 increases P-gp protein expression and transport activity levels. We show that mPGES-1 is expressed in human, rat, and mouse brain capillaries. We show that BI1029539, an mPGES-1 inhibitor, prevented up-regulation of P-gp expression and transport activity in capillaries exposed to glutamate and in capillaries from humanized mPGES-1 mice after SE. Our data provide key signaling steps underlying seizure-induced P-gp up-regulation and suggest that mPGES-1 inhibitors could potentially prevent P-gp up-regulation in epilepsy.-Soldner, E. L. B., Hartz, A. M. S., Akanuma, S.-I., Pekcec, A., Doods, H., Kryscio, R. J., Hosoya, K.-I., Bauer, B. Inhibition of human microsomal PGE2 synthase-1 reduces seizure-induced increases of P-glycoprotein expression and activity at the blood-brain barrier.

2,4,6-Tribromophenol Exposure Decreases P-Glycoprotein Transport at the Blood-Brain Barrier

2,4,6-Tribromophenol (TBP, CAS No. 118-79-6) is a brominated chemical used in the production of flame-retardant epoxy resins and as a wood preservative. In marine environments, TBP is incorporated into shellfish and consumed by predatory fish. Food processing and water treatment facilities produce TBP as a byproduct. 2,4,6-Tribromophenol has been detected in human blood and breast milk. Biologically, TBP interferes with estrogen and thyroid hormone signaling, which regulate important transporters of the blood-brain barrier (BBB). The BBB is a selectively permeable barrier characterized by brain microvessels which are composed of endothelial cells mortared by tight-junction proteins. ATP-binding cassette (ABC) efflux transporters on the luminal membrane facilitate the removal of unwanted endobiotics and xenobiotics from the brain. In this study, we examined the in vivo and ex vivo effects of TBP on two important transporters of the BBB: P-glycoprotein (P-gp, ABCB1) and Multidrug Resistance-associated Protein 2 (MRP2, ABCC2), using male and female rats and mice. 2,4,6-Tribromophenol exposure ex vivo resulted in a time- (1-3 h) and dose- (1-100 nM) dependent decrease in P-gp transport activity. MRP2 transport activity was unchanged under identical conditions. Immunofluorescence and western blotting measured decreases in P-gp expression after TBP treatment. ATPase assays indicate that TBP is not a substrate and does not directly interact with P-gp. In vivo dosing with TBP (0.4 µmol/kg) produced decreases in P-gp transport. Co-treatment with selective protein kinase C (PKC) inhibitors prevented the TBP-mediated decreases in P-gp transport activity.

Inflammatory pathway interactions and cancer multidrug resistance regulation

Multidrug resistances against chemotherapeutics are among the major challenges related to cancer treatment. Recent studies have demonstrated that different conditions may tune the expression and activity of MDR transporters. For instance, inflammation occurs through a complex cytological process and chemical reactions in the most tumor microenvironment; it can play a critical role in cancer development and is capable of altering the expression and function of MDR transporters. Cytokines, interleukins, and prostaglandins are potent inflammatory mediators that can modulate the expression of MDRs at transcriptional and post-transcriptional levels in the most human cancer cells and tissues and potentially contribute to balance bioavailability of chemotherapeutic agents. Since cancer cases are usually accompanied by inflammatory responses, glucocorticoids and NSAIDs are the primary useful combination chemotherapies in a variety of cancer treatment protocols. In addition to the anti-inflammatory activities of these agents, they exert diverse modulatory effects on MDR-mediated drug resistance via specific mechanisms. Several factors, including cell and MDR-protein types, pharmacokinetics, and pharmacogenetics, mainly influence the regulatory mechanisms. Uncovering the networks between inflammation and multidrug resistance will be clinically helpful in the treatment of malignant cancers and decreasing the cancer mortality rates.

Changes of Blood-Brain Barrier and Brain Parenchymal Protein Expression Levels of Mice under Different Insulin-Resistance Conditions Induced by High-Fat Diet

PURPOSE

The purpose of the present study was to investigate changes of blood-brain barrier (BBB) and brain parenchymal protein expression due to type II diabetes mellitus (T2DM) induced by a high-fat diet (HFD) by using SWATH-based quantitative proteomics.

METHODS

Mice were fed a HFD for 2 or 10 weeks, and then SWATH-based quantitative proteomic analysis, western blot analysis, immunohistochemistry and functional transport studies were performed.

RESULTS

In brain capillaries, expression levels of BBB transporters (Glut1, P-glycoprotein) and tight-junction proteins (claudin-5, occludin) were significantly reduced in HFD mice at 2 weeks, but recovered to the levels in the normal diet (ND) group at 10 weeks. P-glycoprotein function at the BBB was reduced at 2 weeks. In the cerebral cortex and hippocampus, neurofilament, which is important for neuronal function, was decreased in HFD mice at 2 weeks, but recovered at 10 weeks.

CONCLUSION

Our results suggest that changes in the status of insulin resistance influence expression of BBB transporters, which in turn may alter the expression of cognitive function-related proteins.

TNF-α Modulates P-Glycoprotein Expression and Contributes to Cellular Proliferation via Extracellular Vesicles

P-glycoprotein (Pgp/ABCB1) overexpression is associated with multidrug resistance (MDR) phenotype and, consequently, failure in cancer chemotherapy. However, molecules involved in cell death deregulation may also support MDR. Tumor necrosis factor-alpha (TNF-α) is an important cytokine that may trigger either death or tumor growth. Here, we examined the role of cancer cells in self-maintenance and promotion of cellular malignancy through the transport of Pgp and TNF-α molecules by extracellular vesicles (membrane microparticles (MP)). By using a classical MDR model in vitro, we identified a positive correlation between endogenous TNF-α and Pgp, which possibly favored a non-cytotoxic effect of recombinant TNF-α (rTNF-α). We also found a positive feedback involving rTNF-α incubation and TNF-α regulation. On the other hand, rTNF-α induced a reduction in Pgp expression levels and contributed to a reduced Pgp efflux function. Our results also showed that parental and MDR cells spontaneously released MP containing endogenous TNF-α and Pgp. However, these MP were unable to transfer their content to non-cancer recipient cells. Nevertheless, MP released from parental and MDR cells elevated the proliferation index of non-tumor cells. Collectively, our results suggest that Pgp and endogenous TNF-α positively regulate cancer cell malignancy and contribute to changes in normal cell behavior through MP.

ABC transporters in drug-resistant epilepsy: mechanisms of upregulation and therapeutic approaches

Drug-resistant epilepsy (DRE) affects approximately one third of epileptic patients. Among various theories that try to explain multidrug resistance, the transporter hypothesis is the most extensively studied. Accordingly, the overexpression of efflux transporters in the blood-brain barrier (BBB), mainly from the ATP binding cassette (ABC) superfamily, may be responsible for hampering the access of antiepileptic drugs into the brain. P-glycoprotein and other efflux transporters are known to be upregulated in endothelial cells, astrocytes and neurons of the neurovascular unit, a functional barrier critically involved in the brain penetration of drugs. Inflammation and oxidative stress involved in the pathophysiology of epilepsy together with uncontrolled recurrent seizures, drug-associated induction and genetic polymorphisms are among the possible causes of ABC transporters overexpression in DRE. The aforementioned pathological mechanisms will be herein discussed together with the multiple strategies to overcome the activity of efflux transporters in the BBB - from direct transporters inhibition to down-regulation of gene expression resorting to RNA interference (RNAi), or by targeting key modulators of inflammation and seizure-mediated signalling.

Role of astroglia in diet-induced central neuroplasticity

Obesity, characterized by increased adiposity that develops when energy intake outweighs expenditure, is rapidly becoming a serious health crisis that affects millions of people worldwide and is associated with severe comorbid disorders including hypertension, cardiovascular disease, and type II diabetes. Obesity is also associated with the dysregulation of central neurocircuits involved in the control of autonomic, metabolic, and cognitive functions. Systemic inflammation associated with diet-induced obesity (DIO) has been proposed to be responsible for the development of these comorbidities as well as the dysregulation of central neurocircuits. A growing body of evidence suggests, however, that exposure to a high-fat diet (HFD) may cause neuroinflammation and astroglial activation even before systemic inflammation develops, which may be sufficient to cause dysregulation of central neurocircuits involved in energy homeostasis before the development of obesity. The purpose of this review is to summarize the current literature exploring astroglial-dependent modulation of central circuits following exposure to HFD and DIO, including not only dysregulation of neurocircuits involved in energy homeostasis and feeding behavior, but also the dysregulation of learning, memory, mood, and reward pathways.

Isolation of Cerebral Capillaries from Fresh Human Brain Tissue

Understanding blood-brain barrier function under physiological and pathophysiological conditions is critical for the development of new therapeutic strategies that hold the promise to enhance brain drug delivery, improve brain protection, and treat brain disorders. However, studying the human blood-brain barrier function is challenging. Thus, there is a critical need for appropriate models. In this regard, brain capillaries isolated from human brain tissue represent a unique tool to study barrier function as close to the human in vivo situation as possible. Here, we describe an optimized protocol to isolate capillaries from human brain tissue at a high yield and with consistent quality and purity. Capillaries are isolated from fresh human brain tissue using mechanical homogenization, density-gradient centrifugation, and filtration. After the isolation, the human brain capillaries can be used for various applications including leakage assays, live cell imaging, and immune-based assays to study protein expression and function, enzyme activity, or intracellular signaling. Isolated human brain capillaries are a unique model to elucidate the regulation of the human blood-brain barrier function. This model can provide insights into central nervous system (CNS) pathogenesis, which will help the development of therapeutic strategies for treating CNS disorders.

Opioids and the Blood-Brain Barrier: A Dynamic Interaction with Consequences on Drug Disposition in Brain

Background:

Opioids are widely used in pain management, acting via opioid receptors and/or Toll-like receptors (TLR) present at the central nervous system (CNS). At the blood-brain barrier (BBB), several influx and efflux transporters, such as the ATP-binding cassette (ABC)

P-glycoprotein (P-gp, ABCB1), Breast Cancer Resistance Protein (BCRP, ABCG2) and multidrug resistance-associated proteins (MRP, ABCC) transporters, and solute carrier transporters (SLC), are responsible for the transport of xenobiotics from the brain into the bloodstream or vice versa.

Objective:

ABC transporters export several clinically employed opioids, altering their neuro-

pharmacokinetics and CNS effects. In this review, we explore the interactions between opioids

and ABC transporters, and decipher the molecular mechanisms by which opioids can modify their expression at the BBB.

Results:

P-gp is largely implicated in the brain-to-blood efflux of opioids, namely morphine and oxycodone. Long-term ex-posure to morphine and oxycodone has proven to up-regulate the expression of ABC transporters, such as P-gp, BCRP and MRPs, at the BBB, which may lead to increased tolerance to the antinociceptive effects of such drugs. Recent studies uncov-er two mechanisms by which morphine may up-regulate P-gp and BCRP at the BBB: 1) via a glutamate, NMDA-receptor and COX-2 signaling cascade, and 2) via TLR4 activation, subsequent development of neuro-

inflammation, and activation of NF-κB, presumably via glial cells.

Conclusion:

The BBB-opioid interaction can culminate in bilateral consequences, since ABC transporters condition the brain disposition of opioids, while opioids also affect the expression of ABC transporters at the BBB, which may result in increased CNS drug pharmacoresistance.

Blood-brain barrier regulation in psychiatric disorders

The blood-brain barrier (BBB) is a dynamic interface between the peripheral blood supply and the cerebral parenchyma, controlling the transport of material to and from the brain. Tight junctions between the endothelial cells of the cerebral microvasculature limit the passage of large, negatively charged molecules via paracellular diffusion whereas transcellular transportation across the endothelial cell is controlled by a number of mechanisms including transporter proteins, endocytosis, and diffusion. Here, we review the evidence that perturbation of these processes may underlie the development of psychiatric disorders including schizophrenia, autism spectrum disorder (ASD), and affective disorders. Increased permeability of the BBB appears to be a common factor in these disorders, leading to increased infiltration of peripheral material into the brain culminating in neuroinflammation and oxidative stress. However, although there is no common mechanism underpinning BBB dysfunction even within each particular disorder, the tight junction protein claudin-5 may be a clinically relevant target given that both clinical and pre-clinical research has linked it to schizophrenia, ASD, and depression. Additionally, we discuss the clinical significance of the BBB in diagnosis (genetic markers, dynamic contrast-enhanced-magnetic resonance imaging, and blood biomarkers) and in treatment (drug delivery).

Lysophosphatidic acid and amitriptyline signal through LPA1R to reduce P-glycoprotein transport at the blood-brain barrier

The blood-brain barrier is a microvascular network that (1) provides neuroprotection from metabolic and environmental toxins and (2) limits the delivery of therapeutics to the central nervous system (CNS). The ATP-binding cassette transporter P-glycoprotein contributes to the latter by actively pumping clinical substrates back into circulation before they can reach the brain parenchyma. Targeting P-glycoprotein has proven effective in increasing the delivery of therapeutics to their cerebral targets. We provide a novel mechanism to achieve this end in functioning, intact rat brain capillaries, whereby the bioactive phospholipid lysophosphatidic acid (LPA) and tricyclic antidepressant (TCA) amitriptyline reduce basal P-glycoprotein transport activity through a distinct lysophosphatidic acid 1 receptor-mediated signaling cascade that requires G-protein coupling, Src kinase, and ERK 1/2. Furthermore, we demonstrate the ability of LPA and TCA amitriptyline to decrease induced P-glycoprotein transport activity in a human SOD1 transgenic rat model of amyotrophic lateral sclerosis. This work may translate to new clinical strategies for increasing the cerebral penetration of therapeutics in patients suffering from CNS diseases marked by exacerbated pharmacoresistance.

Neuroimmune Axes of the Blood-Brain Barriers and Blood-Brain Interfaces: Bases for Physiological Regulation, Disease States, and Pharmacological Interventions

Central nervous system (CNS) barriers predominantly mediate the immune-privileged status of the brain, and are also important regulators of neuroimmune communication. It is increasingly appreciated that communication between the brain and immune system contributes to physiologic processes, adaptive responses, and disease states. In this review, we discuss the highly specialized features of brain barriers that regulate neuroimmune communication in health and disease. In section I, we discuss the concept of immune privilege, provide working definitions of brain barriers, and outline the historical work that contributed to the understanding of CNS barrier functions. In section II, we discuss the unique anatomic, cellular, and molecular characteristics of the vascular blood-brain barrier (BBB), blood-cerebrospinal fluid barrier, and tanycytic barriers that confer their functions as neuroimmune interfaces. In section III, we consider BBB-mediated neuroimmune functions and interactions categorized as five neuroimmune axes: disruption, responses to immune stimuli, uptake and transport of immunoactive substances, immune cell trafficking, and secretions of immunoactive substances. In section IV, we discuss neuroimmune functions of CNS barriers in physiologic and disease states, as well as pharmacological interventions for CNS diseases. Throughout this review, we highlight many recent advances that have contributed to the modern understanding of CNS barriers and their interface functions.

Beyond Competitive Inhibition: Regulation of ABC Transporters by Kinases and Protein-Protein Interactions as Potential Mechanisms of Drug-Drug Interactions

ATP-binding cassette (ABC) transporters are transmembrane efflux transporters mediating the extrusion of an array of substrates ranging from amino acids and lipids to xenobiotics, and many therapeutic compounds, including anticancer drugs. The ABC transporters are also recognized as important contributors to pharmacokinetics, especially in drug-drug interactions and adverse drug effects. Drugs and xenobiotics, as well as pathologic conditions, can influence the transcription of ABC transporters, or modify their activity or intracellular localization. Kinases can affect the aforementioned processes for ABC transporters as do protein interactions. In this review, we focus on the ABC transporters ABCB1, ABCB11, ABCC1, ABCC4, and ABCG2 and illustrate how kinases and protein-protein interactions affect these transporters. The clinical relevance of these factors is currently unknown; however, these examples suggest that our understanding of drug-drug interactions will benefit from further knowledge of how kinases and protein-protein interactions affect ABC transporters.

Pro-inflammatory and anti-inflammatory compounds exert similar effects on P-glycoprotein in blood–brain barrier endothelial cells

Objectives

The effects of anti-inflammatory glucocorticoids dexamethasone (DX) and hydrocortisone (HC), pro-inflammatory cytokine interleukin-1β (IL-1β) and dietary long-chain polyunsaturated fatty acids (PUFAs) on expression and activity of the ATP-binding cassette transporter P-glycoprotein (P-GP) were studied in porcine brain endothelial cells (PBECs).

Methods

Primary PBECs were treated for 24 h with glucocorticoids, IL-1β and long-chain PUFAs. P-GP activity was determined by measuring intracellular calcein accumulation and P-GP expression by Western blotting. The effect of PUFAs on membrane fluidity was assessed by fluorescence recovery after photobleaching (FRAP).

Key findings

Dexamethasone, HC and IL-1β significantly increased P-GP expression and activity. The effect of IL-1β was attenuated by the IL-1 receptor antagonist (IL-1RA). This is the first report of the combined actions of IL-1β and IL-1RA on P-GP expression and the first evidence of glucocorticoid-mediated P-GP up-regulation in PBECs. Arachidonic acid (AA), docosahexaenoic acid (DHA) and eicosapentenoic acid (EPA) significantly decreased P-GP activity without affecting expression or membrane fluidity. AA, DHA and EPA counteracted IL-1β-mediated increases in P-GP activity, while AA and EPA, but not DHA, counteracted glucocorticoid-mediated increase in P-GP activity.

Conclusions

While glucocorticoids and IL-1β possess opposing actions in inflammation, they demonstrate functional consistency by increasing P-GP expression and activity in PBECs.