ABCC1: a gateway for pharmacological compounds to the ischaemic brain

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.

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.

A versatile vessel casting method for fine mapping of vascular networks using a hydrogel-based lipophilic dye solution

Efficient labeling of the vasculature is important for understanding the organization of vascular networks. Here, we propose VALID, a vessel-labeling method that enables visualization of vascular networks with tissue clearing and light-sheet microscopy. VALID transforms traditional lipophilic dye solution into hydrogel by introducing gelatin and restrains the dye aggregation, resulting in complete and uniform vessel-labeling patterns with high signal-to-background ratios. VALID also enhances the compatibility of lipophilic dyes with solvent-based tissue-clearing protocols, which was hard to achieve previously. Using VALID, we combined lipophilic dyes with solvent-based tissue-clearing techniques to perform 3D reconstructions of vasculature within mouse brain and spinal cord. We also employed VALID for 3D visualization and quantification of microvascular damage in a middle cerebral artery occlusion mouse model. VALID should provide a simple, cost-effective vessel-labeling protocol that would significantly widen the applications of lipophilic dyes in research on cerebrovascular complications.

Relationship between blood-brain barrier changes and drug metabolism under high-altitude hypoxia: obstacle or opportunity for drug transport?

The blood-brain barrier is essential for maintaining the stability of the central nervous system and is also crucial for regulating drug metabolism, changes of blood-brain barrier's structure and function can influence how drugs are delivered to the brain. In high-altitude hypoxia, the central nervous system's function is drastically altered, which can cause disease and modify the metabolism of drugs in vivo. Changes in the structure and function of the blood-brain barrier and the transport of the drug across the blood-brain barrier under high-altitude hypoxia, are regulated by changes in brain microvascular endothelial cells, astrocytes, and pericytes, either regulated by drug metabolism factors such as drug transporters and drug-metabolizing enzymes. This article aims to review the effects of high-altitude hypoxia on the structure and function of the blood-brain barrier as well as the effects of changes in the blood-brain barrier on drug metabolism. We also hypothesized and explore the regulation and potential mechanisms of the blood-brain barrier and associated pathways, such as transcription factors, inflammatory factors, and nuclear receptors, in regulating drug transport under high-altitude hypoxia.

Integrated Bioinformatics Analysis of the Hub Genes Involved in Irinotecan Resistance in Colorectal Cancer

Different drug combinations including irinotecan remain some of the most important therapeutic modalities in treating colorectal cancer (CRC). However, chemotherapy often leads to the acquisition of cancer drug resistance. To bridge the gap between in vitro and in vivo models, we compared the mRNA expression profiles of CRC cell lines (HT29, HTC116, and LoVo and their respective irinotecan-resistant variants) with patient samples to select new candidate genes for the validation of irinotecan resistance. Data were downloaded from the Gene Expression Omnibus (GEO) (GSE42387, GSE62080, and GSE18105) and the Human Protein Atlas databases and were subjected to an integrated bioinformatics analysis. The protein–protein interaction (PPI) network of differently expressed genes (DEGs) between FOLFIRI-resistant and -sensitive CRC patients delivered several potential irinotecan resistance markers: NDUFA2, SDHD, LSM5, DCAF4, COX10 RBM8A, TIMP1, QKI, TGOLN2, and PTGS2. The chosen DEGs were used to validate irinotecan-resistant cell line models, proving their substantial phylogenetic heterogeneity. These results indicated that in vitro models are highly limited and favor different mechanisms than in vivo, patient-derived ones. Thus, cell lines can be perfectly utilized to analyze specific mechanisms on their molecular levels but cannot mirror the complicated drug resistance network observed in patients.

Use of PET Imaging to Assess the Efficacy of Thiethylperazine to Stimulate Cerebral MRP1 Transport Activity in Wild-Type and APP/PS1-21 Mice

Multidrug resistance-associated protein 1 (MRP1, encoded by the ABCC1 gene) may contribute to the clearance of amyloid-beta (Aβ) peptides from the brain into the blood and stimulation of MRP1 transport activity may be a therapeutic approach to enhance brain Aβ clearance. In this study, we assessed the effect of thiethylperazine, an antiemetic drug which was shown to stimulate MRP1 activity in vitro and to decrease Aβ load in a rapid β-amyloidosis mouse model (APP/PS1-21), on MRP1 transport activity by means of positron emission tomography (PET) imaging with the MRP1 tracer 6-bromo-7-[11C]methylpurine. Groups of wild-type, APP/PS1-21 and Abcc1(-/-) mice underwent PET scans before and after a 5-day oral treatment period with thiethylperazine (15 mg/kg, once daily). The elimination rate constant of radioactivity (kelim) was calculated from time-activity curves in the brain and the lungs as a measure of tissue MRP1 activity. Treatment with thiethylperazine had no significant effect on MRP1 activity in the brain and the lungs of wild-type and APP/PS1-21 mice. This may either be related to a lack of an MRP1-stimulating effect of thiethylperazine in vivo or to other factors, such as substrate-dependent MRP1 stimulation, insufficient target tissue exposure to thiethylperazine or limited sensitivity of the PET tracer to measure MRP1 stimulation.

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.

Blood-Brain Barrier Mechanisms in Stroke and Trauma

The brain microenvironment is tightly regulated. The blood-brain barrier (BBB), which is composed of cerebral endothelial cells, astrocytes, and pericytes, plays an important role in maintaining the brain homeostasis by regulating the transport of both beneficial and detrimental substances between circulating blood and brain parenchyma. After brain injury and disease, BBB tightness becomes dysregulated, thus leading to inflammation and secondary brain damage. In this chapter, we overview the fundamental mechanisms of BBB damage and repair after stroke and traumatic brain injury (TBI). Understanding these mechanisms may lead to therapeutic opportunities for brain injury.

Nebulization of Low-Dose S-Nitrosoglutathione in Diabetic Stroke Enhances Benefits of Reperfusion and Prevents Post-Thrombolysis Hemorrhage

The COVID-19 pandemic has escalated the occurrence of hypoxia including thrombotic stroke worldwide, for which nitric oxide (NO) therapy seems very promising and translatable. Therefore, various modes/routes of NO-delivery are now being tested in different clinical trials for safer, faster, and more effective interventions against ischemic insults. Intravenous (IV) infusion of S-Nitrosoglutathione (GSNO), the major endogenous molecular pool of NO, has been reported to protect against mechanical cerebral ischemia-reperfusion (IR); however, it has been never tested in any kind of “clinically” relevant thromboembolic stroke models with or without comorbidities and in combination with the thrombolytic reperfusion therapy. Moreover, “IV-effects” of higher dose of GSNO following IR-injury have been contradicted to augment stroke injury. Herein, we tested the hypothesis that nebulization of low-dose GSNO will not alter blood pressure (BP) and will mitigate stroke injury in diabetic mice via enhanced cerebral blood flow (CBF) and brain tissue oxygenation (PbtO2). GSNO-nebulization (200 μg/kgbwt) did not alter BP, but augmented the restoration of CBF, improved behavioral outcomes and reduced stroke injury. Moreover, GSNO-nebulization increased early reoxygenation of brain tissue/PbtO2 as measured at 6.5 h post-stroke following thrombolytic reperfusion, and enervated unwanted effects of late thrombolysis in diabetic stroke. We conclude that the GSNO-nebulization is safe and effective for enhancing collateral microvascular perfusion in the early hours following stroke. Hence, nebulized-GSNO therapy has the potential to be developed and translated into an affordable field therapy against ischemic events including strokes, particularly in developing countries with limited healthcare infrastructure.

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.

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.

Mechanisms of glutathione-conjugate efflux from the brain into blood: Involvement of multiple transporters in the course

Accumulation of detrimental glutathione-conjugated metabolites in the brain potentially causes neurological disorders, and must therefore be exported from the brain. However, in vivo mechanisms of glutathione-conjugates efflux from the brain remain unknown. We investigated the involvement of transporters in glutathione-conjugates efflux using 6-bromo-7-[¹¹C]methylpurine ([¹¹C]1), which enters the brain and is converted into its glutathione conjugate, S-(7-[¹¹C]methylpurin-6-yl)glutathione ([¹¹C]2). In mice of control and knockout of P-glycoprotein/breast cancer resistance protein and multidrug resistance-associated protein 2 ([Mrp2]^-/-), [¹¹C]2 formed in the brain was rapidly cleared, with no significant difference in efflux rate. In contrast, [¹¹C]2 formed in the brain of Mrp1^-/- mice was slowly cleared, whereas [¹¹C]2 microinjected into the brain of control and Mrp1^-/- mice was 75% cleared within 60 min, with no significant difference in efflux rate. These suggest that Mrp1 contributes to [¹¹C]2 efflux across cell membranes, but not BBB. Efflux rate of [¹¹C]2 formed in the brain was significantly lower in Mrp4^-/- and organic anion transporter 3 (Oat3)^-/- mice compared with control mice. In conclusion, Mrp1, Oat3, and Mrp4 mediate [¹¹C]2 efflux from the brain. Mrp1 may contribute to [¹¹C]2 efflux from brain parenchymal cells, while extracellular [¹¹C]2 is likely cleared across the BBB, partly by Oat3 and Mrp4.

Deactivation of ATP-Binding Cassette Transporters ABCB1 and ABCC1 Does Not Influence Post-ischemic Neurological Deficits, Secondary Neurodegeneration and Neurogenesis, but Induces Subtle Microglial Morphological Changes

ATP-binding cassette (ABC) transporters prevent the access of pharmacological compounds to the ischemic brain, thereby impeding the efficacy of stroke therapies. ABC transporters can be deactivated by selective inhibitors, which potently increase the brain accumulation of drugs. Concerns have been raised that long-term ABC transporter deactivation may promote neuronal degeneration and, under conditions of ischemic stroke, compromise neurological recovery. To elucidate this issue, we exposed male C57BL/6 mice to transient intraluminal middle cerebral artery occlusion (MCAO) and examined the effects of the selective ABCB1 inhibitor tariquidar (8 mg/kg/day) or ABCC1 inhibitor MK-571 (10 mg/kg/day), which were administered alone or in combination with each other over up to 28 days, on neurological recovery and brain injury. Mice were sacrificed after 14, 28, or 56 days. The Clark score, RotaRod, tight rope, and open field tests revealed reproducible motor-coordination deficits in mice exposed to intraluminal MCAO, which were not influenced by ABCB1, ABCC1, or combined ABCB1 and ABCC1 deactivation. Brain volume, striatum volume, and corpus callosum thickness were not altered by ABCB1, ABCC1 or ABCB1, and ABCC1 inhibitors. Similarly, neuronal survival and reactive astrogliosis, evaluated by NeuN and GFAP immunohistochemistry in the ischemic striatum, were unchanged. Iba1 immunohistochemistry revealed no changes of the overall density of activated microglia in the ischemic striatum of ABC transporter inhibitor treated mice, but subtle changes of microglial morphology, that is, reduced microglial cell volume by ABCB1 deactivation after 14 and 28 days and reduced microglial ramification by ABCB1, ABCC1 and combined ABCB1 and ABCC1 deactivation after 56 days. Endogenous neurogenesis, assessed by BrdU incorporation analysis, was not influenced by ABCB1, ABCC1 or combined ABCB1 and ABCC1 deactivation. Taken together, this study could not detect any exacerbation of neurological deficits or brain injury after long-term ABC transporter deactivation in this preclinical stroke model.

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.

Effects of oxygen-glucose deprivation (OGD) on barrier properties and mRNA transcript levels of selected marker proteins in brain endothelial cells/astrocyte co-cultures

Ischemic stroke has been shown to induce breakdown of the blood-brain barrier, although these changes are not fully characterized. Oxygen-glucose deprivation (OGD) has been used to investigate the effects of ischemia in cultured brain capillary endothelial cells, however this involves a change of medium which in itself may affect the cells. The aim of the present study was to investigate the effect of OGD and simple medium exchange followed by 48 h of reperfusion on barrier properties of primary bovine endothelial cells co-cultured with rat astrocytes. Barrier properties were evaluated by transendothelial electrical resistance measurements, passive permeability of flux markers, RT-qPCR and immunocytochemistry. Both OGD and simple medium exchange caused an increase in endothelial monolayer permeability. This correlated with reduced transcript levels of a number of tight junction and tight junction-associated proteins (claudin-1, claudin-5, occludin, ZO-1, tricellulin, marveld3 and PECAM-1), as well as with altered transcript level of several transporters and receptors (GLUT-1, HB-EGF, InsR, TfR, two members of the low density lipoprotein receptor family, LDLR and LRP-1, and the efflux transporter BCRP). In contrast, effects induced specifically by OGD were transient de-localization of claudin-5 from the junction zone, increased InsR localization at the plasma membrane and transient downregulation of MRP-1 and P-gp transcript levels. In conclusion, OGD caused changes in claudin-5 and InsR localization, as well as in MRP-1 and P-gp transcript levels. Our results however also indicated that medium exchange alone caused changes in functional barrier properties and expression levels of wide range of proteins.

Disease-Associated Changes in Drug Transporters May Impact the Pharmacokinetics and/or Toxicity of Drugs: A White Paper From the International Transporter Consortium

Drug transporters are critically important for the absorption, distribution, metabolism, and excretion (ADME) of many drugs and endogenous compounds. Therefore, disruption of these pathways by inhibition, induction, genetic polymorphisms, or disease can have profound effects on overall physiology, drug pharmacokinetics, drug efficacy, and toxicity. This white paper provides a review of changes in transporter function associated with acute and chronic disease states, describes regulatory pathways affecting transporter expression, and identifies opportunities to advance the field.

Modulation of Opioid Transport at the Blood-Brain Barrier by Altered ATP-Binding Cassette (ABC) Transporter Expression and Activity

Opioids are highly effective analgesics that have a serious potential for adverse drug reactions and for development of addiction and tolerance. Since the use of opioids has escalated in recent years, it is increasingly important to understand biological mechanisms that can increase the probability of opioid-associated adverse events occurring in patient populations. This is emphasized by the current opioid epidemic in the United States where opioid analgesics are frequently abused and misused. It has been established that the effectiveness of opioids is maximized when these drugs readily access opioid receptors in the central nervous system (CNS). Indeed, opioid delivery to the brain is significantly influenced by the blood-brain barrier (BBB). In particular, ATP-binding cassette (ABC) transporters that are endogenously expressed at the BBB are critical determinants of CNS opioid penetration. In this review, we will discuss current knowledge on the transport of opioid analgesic drugs by ABC transporters at the BBB. We will also examine how expression and trafficking of ABC transporters can be modified by pain and/or opioid pharmacotherapy, a novel mechanism that can promote opioid-associated adverse drug events and development of addiction and tolerance.

Neurosteroid Transport in the Brain: Role of ABC and SLC Transporters

Neurosteroids, comprising pregnane, androstane, and sulfated steroids can alter neuronal excitability through interaction with ligand-gated ion channels and other receptors and have therefore a therapeutic potential in several brain disorders. They can be formed in brain cells or are synthesized by an endocrine gland and reach the brain by penetrating the blood–brain barrier (BBB). Especially sulfated steroids such as pregnenolone sulfate (PregS) and dehydroepiandrosterone sulfate (DHEAS) depend on transporter proteins to cross membranes. In this review, we discuss the involvement of ATP-binding cassette (ABC)- and solute carrier (SLC)-type membrane proteins in the transport of these compounds at the BBB and in the choroid plexus (CP), but also in the secretion from neurons and glial cells. Among the ABC transporters, especially BCRP (ABCG2) and several MRP/ABCC subfamily members (MRP1, MRP4, MRP8) are expressed in the brain and known to efflux conjugated steroids. Furthermore, several SLC transporters have been shown to mediate cellular uptake of steroid sulfates. These include members of the OATP/SLCO subfamily, namely OATP1A2 and OATP2B1, as well as OAT3 (SLC22A3), which have been reported to be expressed at the BBB, in the CP and in part in neurons. Furthermore, a role of the organic solute transporter OSTα-OSTβ (SLC51A/B) in brain DHEAS/PregS homeostasis has been proposed. This transporter was reported to be localized especially in steroidogenic cells of the cerebellum and hippocampus. To date, the impact of transporters on neurosteroid homeostasis is still poorly understood. Further insights are desirable also with regard to the therapeutic potential of these compounds.

Bile Acids Increase Doxorubicin Sensitivity in ABCC1-expressing Tumour Cells

Tumour cells possess or acquire various mechanisms to circumvent the cytotoxic effects of chemotherapy drugs. One such mechanism involves the overexpression of ABC transporters that facilitate the extrusion of a variety of structurally distinct chemotherapy drugs from the cytoplasm into the extracellular space. While specific ABC transporter inhibitors have been developed, many affect other ABC transporters, particularly at elevated concentrations. It is also unclear whether they show clear efficacy for combatting drug resistance in cancer patients with minimal host toxicity. In this study, we demonstrate the ability of two bile acids [β-cholanic acid (urso-cholanic acid) and deoxycholic acid] to specifically inhibit ABCC1-mediated drug transport, augmenting doxorubicin accumulation in breast and lung tumour cells selected for doxorubicin resistance through overexpression of the ABCC1 (but not ABCB1) drug transporter. The bile acids could also restore uptake and sensitivity to doxorubicin in human endothelial kidney cells genetically engineered to overexpress the ABCC1 drug transporter. These observations suggest a previously unreported role for bile acids as ABCC1 inhibitors or regulators. Given its additional properties of minimal clinical toxicity in humans and its ability to inhibit aldo-keto reductases involved in anthracycline resistance and anthracycline-induced cardiotoxicity, β-cholanic acid merits further in vivo and clinical investigation.

3D visualization and quantification of microvessels in the whole ischemic mouse brain using solvent-based clearing and light sheet microscopy

The visualization of cerebral microvessels is essential for understanding brain remodeling after stroke. Injection of dyes allows for the evaluation of perfused vessels, but has limitations related either to incomplete microvascular filling or leakage. In conventional histochemistry, the analysis of microvessels is limited to 2D structures, with apparent limitations regarding the interpretation of vascular circuits. Herein, we developed a straight-forward technique to visualize microvessels in the whole ischemic mouse brain, combining the injection of a fluorescent-labeled low viscosity hydrogel conjugate with 3D solvent clearing followed by automated light sheet microscopy. We performed transient middle cerebral artery occlusion in C57Bl/6j mice and acquired detailed 3D vasculature images from whole brains. Subsequent image processing, rendering and fitting of blood vessels to a filament model was employed to calculate vessel length density, resulting in 0.922 ± 0.176 m/mm³ in healthy tissue and 0.329 ± 0.131 m/mm³ in ischemic tissue. This analysis showed a marked loss of capillaries with a diameter ≤ 10 µm and a more moderate loss of microvessels in the range > 10 and ≤ 20 µm, whereas vessels > 20 µm were unaffected by focal cerebral ischemia. We propose that this protocol is highly suitable for studying microvascular injury and remodeling post-stroke.

The neuroprotective effect of focused ultrasound: New perspectives on an old tool

INTRODUCTION

Transcranial focused ultrasound (tFUS) is a novel technique that can noninvasively modulate the cortical function. Moreover, there are rapidly replicating evidence suggesting the role of tFUS for targeted neuroprotective drug delivery by increasing the permeability of the central nervous system barrier that results with increased neuroprotective activity. In contrast to the indirect neuroprotective effect, there is rare evidence suggesting the direct parenchymal neuroprotective effect of transcranial focused ultrasound (tFUS). In the light of these findings, we aimed to review the direct and indirect neuroprotective effect of FUS in various animal models of Stroke, Parkinson's Disease, Alzheimer's Disease and Major Depressive Disorder.

METHODS

A literary search was conducted, utilizing search terms "animal", "focused ultrasound", "neuroprotection", "Alzheimer's Disease", "Parkinson's Disease ", "Stroke", "Neurodegenerative disease" and "Major Depressive Disorder". Items were excluded if they failed to: (1) include patients, (2) editorials, and letters.

RESULTS

This mini-review article presents an up-to-date review of the neuroprotective effects of tFUS in animal studies and suggests the dual neurotherapeutic role of tFUS in various neurodegenerative diseases.

CONCLUSION

Future well-conducted human studies are emergently needed to assess the neuroprotective effects of FUS.

Stroke and Drug Delivery--In Vitro Models of the Ischemic Blood-Brain Barrier

Stroke is a major cause of death and disability worldwide. Both cerebral hypoperfusion and focal cerebral infarcts are caused by a reduction of blood flow to the brain, leading to stroke and subsequent brain damage. At present, only few medical treatments of stroke are available, with the Food and Drug Administration-approved tissue plasminogen activator for treatment of acute ischemic stroke being the most prominent example. A large number of potential drug candidates for treatment of ischemic brain tissue have been developed and subsequently failed in clinical trials. A deeper understanding of permeation pathways across the barrier in ischemic and postischemic brain endothelium is important for development of new medical treatments. The blood-brain barrier, that is, the endothelial monolayer lining the brain capillaries, changes properties during an ischemic event. In vitro models of the blood-brain barrier are useful tools to investigate the effects of induced ischemia under controlled conditions. In the present mini review, we aim to give a brief overview of the in vitro models of ischemia. Special focus is given to the expression of uptake and efflux transport pathways in the ischemic and postischemic endothelium. Finally, we will point toward future challenges within the field of in vitro models of brain ischemia.

ABC transporters at the blood-brain barrier

INTRODUCTION

The blood-brain barrier (BBB) possesses an outstanding ability to protect the brain against xenobiotics and potentially poisonous metabolites. Owing to this, ATP binding cassette (ABC) export proteins have garnered significant interest in the research community. These transport proteins are predominantly localized to the luminal membrane of brain microvessels, where they recognize a wide range of different substrates and transport them back into the blood circulation.

AREAS COVERED

This review summarizes recent findings on these transport proteins, including their expression in the endothelial cell membrane and their substrate recognition. Signaling cascades underlying the expression and function of these proteins will be discussed as well as their role in diseases such as Alzheimer's disease, epilepsy, amyotrophic lateral sclerosis and brain tumors.

EXPERT OPINION

ABC transporters represent an integral part of the human transportome and are of particular interest at the blood-brain barrier they as they significantly contribute to brain homeostasis. In addition, they appear to be involved in myriad CNS diseases. Therefore studying their mechanisms of action as well as their signaling cascades and responses to internal and external stimuli will help us understand the pathogenesis of these diseases.

Method parameters' impact on mortality and variability in mouse stroke experiments: a meta-analysis

Although hundreds of promising substances have been tested in clinical trials, thrombolysis currently remains the only specific pharmacological treatment for ischemic stroke. Poor quality, e.g. low statistical power, in the preclinical studies has been suggested to play an important role in these failures. Therefore, it would be attractive to use animal models optimized to minimize unnecessary mortality and outcome variability, or at least to be able to power studies more exactly by predicting variability and mortality given a certain experimental setup. The possible combinations of methodological parameters are innumerous, and an experimental comparison of them all is therefore not feasible. As an alternative approach, we extracted data from 334 experimental mouse stroke articles and, using a hypothesis-driven meta-analysis, investigated the method parameters’ impact on infarct size variability and mortality. The use of Swiss and C57BL6 mice as well as permanent occlusion of the middle cerebral artery rendered the lowest variability of the infarct size while the emboli methods increased variability. The use of Swiss mice increased mortality. Our study offers guidance for researchers striving to optimize mouse stroke models.

Pharmacogenetics and induction/consolidation therapy toxicities in acute lymphoblastic leukemia patients treated with AIEOP-BFM ALL 2000 protocol

Drug-related toxicities represent an important clinical concern in chemotherapy, genetic variants could help tailoring treatment to patient. A pharmacogenetic multicentric study was performed on 508 pediatric acute lymphoblastic leukemia patients treated with AIEOP-BFM 2000 protocol: 28 variants were genotyped by VeraCode and Taqman technologies, deletions of GST-M1 and GST-T1 by multiplex PCR. Toxicities were derived from a central database: 251 patients (49.4%) experienced at least one gastrointestinal (GI) or hepatic (HEP) or neurological (NEU) grade III/IV episode during the remission induction phase: GI occurred in 63 patients (12.4%); HEP in 204 (40.2%) and NEU in 44 (8.7%). Logistic regression model adjusted for sex, risk and treatment phase revealed that ITPA rs1127354 homozygous mutated patients showed an increased risk of severe GI and NEU. ABCC1 rs246240 and ADORA2A rs2236624 homozygous mutated genotypes were associated to NEU and HEP, respectively. These three variants could be putative predictive markers for chemotherapy-related toxicities in AIEOP-BFM protocols.

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.

Improved Antidepressant Remission in Major Depression via a Pharmacokinetic Pathway Polygene Pharmacogenetic Report

Objective

Major depressive disorder (MDD) is projected to be a leading cause of disability globally by 2030. Only a minority of patients remit with antidepressants. If assay of polymorphisms influencing central nervous system (CNS) bioavailability could guide prescribers to more effectively dose patients, remission rates may improve and the burden of disease from MDD reduce. Hepatic and blood brain barrier (BBB) polymorphisms appear to influence antidepressant CNS bioavailability.

Methods

A 12-week prospective double blind randomized genetically guided versus unguided trial of antidepressant dosing in Caucasian adults with MDD (n=148) was conducted.

Results

Subjects receiving genetically guided prescribing had a 2.52-fold greater chance of remission (95% confidence interval [CI]=1.71–3.73, z=4.66, p<0.0001). The number needed to genotype (NNG)=3 (95% CI=1.7–3.5) to produce an additional remission.

Conclusion

These data suggest that a pharmacogenetic dosing report (CNSDose^®) improves antidepressant efficacy. The effect size was sufficient that translation to clinical care may arise if results are independently replicated.

ABC transporter-driven pharmacoresistance in Amyotrophic Lateral Sclerosis

Amyotrophic Lateral Sclerosis (ALS) is a slowly progressing neurodegenerative disease that affects motor neurons of the nervous system. Despite the identification of many potential therapeutics targeting pathogenic mechanisms in in vitro models, there has been limited progress in translating them into a successful pharmacotherapy in the animal model of ALS. Further, efforts to translate any promising results from preclinical trials to effective pharmacotherapies for patients have been unsuccessful, with the exception of riluzole, the only FDA-approved medication, which only modestly extends survival both in the animal model and in patients. Thus, it is essential to reconsider the strategies for developing ALS pharmacotherapies. Growing evidence suggests that problems identifying highly effective ALS treatments may result from an underestimated issue of drug bioavailability and disease-driven pharmacoresistance, mediated by the ATP-binding cassette (ABC) drug efflux transporters. ABC transporters are predominately localized to the lumen of endothelial cells of the blood-brain and blood-spinal cord barriers (BBB, BSCB) where they limit the entry into the central nervous system (CNS) of a wide range of neurotoxicants and xenobiotics, but also therapeutics. In ALS, expression and function of ABC transporters is increased at the BBB/BSCB and their expression has been detected on neurons and glia in the CNS parenchyma, which may further reduce therapeutic action in target cells. Understanding and accounting for the contribution of these transporters to ALS pharmacoresistance could both improve the modest effects of riluzole and set in motion a re-evaluation of previous ALS drug disappointments. In addition, identifying pathogenic mechanisms regulating ABC transporter expression and function in ALS may lead to the development of new therapeutic strategies. It is likely that novel pharmacological approaches require counteracting pharmacoresistance to improve therapeutic efficacy. This article is part of a Special Issue entitled ALS complex pathogenesis.

Genetic Modulation of Neurocognitive Function in Glioma Patients

PURPOSE

Accumulating evidence supports the contention that genetic variation is associated with neurocognitive function in healthy individuals and increased risk for neurocognitive decline in a variety of patient populations, including cancer patients. However, this has rarely been studied in glioma patients.

EXPERIMENTAL DESIGN

To identify the effect of genetic variants on neurocognitive function, we examined the relationship between the genotype frequencies of 10,967 single-nucleotide polymorphisms in 580 genes related to five pathways (inflammation, DNA repair, metabolism, cognitive, and telomerase) and neurocognitive function in 233 newly diagnosed glioma patients before surgical resection. Four neuropsychologic tests that measured memory (Hopkins Verbal Learning Test-Revised), processing speed (Trail Making Test A), and executive function (Trail Making Test B, Controlled Oral Word Association) were examined.

RESULTS

Eighteen polymorphisms were associated with processing speed and 12 polymorphisms with executive function. For processing speed, the strongest signals were in IRS1 rs6725330 in the inflammation pathway (P = 2.5 × 10(-10)), ERCC4 rs1573638 in the DNA repair pathway (P = 3.4 × 10(-7)), and ABCC1 rs8187858 in metabolism pathway (P = 6.6 × 10(-7)). For executive function, the strongest associations were in NOS1 rs11611788 (P = 1.8 × 10(-8)) and IL16 rs1912124 (P = 6.0 × 10(-7)) in the inflammation pathway, and POLE rs5744761 (P = 6.0 × 10(-7)) in the DNA repair pathway. Joint effect analysis found significant gene polymorphism-dosage effects for processing speed (Ptrend = 9.4 × 10(-16)) and executive function (Ptrend = 6.6 × 10(-15)).

CONCLUSIONS

Polymorphisms in inflammation, DNA repair, and metabolism pathways are associated with neurocognitive function in glioma patients and may affect clinical outcomes.

Importance of ABCC1 for cancer therapy and prognosis

Multidrug resistance presents one of the most important causes of cancer treatment failure. Numerous in vitro and in vivo data have made it clear that multidrug resistance is frequently caused by enhanced expression of ATP-binding cassette (ABC) transporters. ABC transporters are membrane-bound proteins involved in cellular defense mechanisms, namely, in outward transport of xenobiotics and physiological substrates. Their function thus prevents toxicity as carcinogenesis on one hand but may contribute to the resistance of tumor cells to a number of drugs including chemotherapeutics on the other. Within 48 members of the human ABC superfamily there are several multidrug resistance-associated transporters. Due to the well documented susceptibility of numerous drugs to efflux via ABC transporters it is highly desirable to assess the status of ABC transporters for individualization of treatment by their substrates. The multidrug resistance associated protein 1 (MRP1) encoded by ABCC1 gene is one of the most studied ABC transporters. Despite the fact that its structure and functions have already been explored in detail, there are significant gaps in knowledge which preclude clinical applications. Tissue-specific patterns of expression and broad genetic variability make ABCC1/MRP1 an optimal candidate for use as a marker or member of multi-marker panel for prediction of chemotherapy resistance. The purpose of this review was to summarize investigations about associations of gene and protein expression and genetic variability with prognosis and therapy outcome of major cancers. Major advances in the knowledge have been identified and future research directions are highlighted.

Current preclinical studies on neuroinflammation and changes in blood-brain barrier integrity by MDMA and methamphetamine

The blood-brain barrier (BBB) is essential in the maintenance of brain homeostasis both by preserving normal brain functioning and also by protecting the brain from exposure to a range of potentially harmful substances. This review presents some of the evidence of BBB disruption following exposure to the substituted amphetamines 3,4-methylenedioxymethamphetamine (MDMA, 'ecstasy') and methamphetamine (METH), two drugs of abuse which are widely consumed recreationally by younger sectors of the population. Both MDMA and METH have been shown to produce disruption of the BBB as reflected by IgG extravasation and Evans Blue leakage. In particular, METH decreases the expression of basal lamina proteins associated with an increase in matrix metalloproteinase activity. These changes in BBB integrity appear to be related to MDMA-induced activation of the mitogen-activated protein kinase (MAPK) JNK1/2. The consequences of the disruption in the BBB by these two drugs remain to be established, but there is evidence in the literature that, at least in the case of METH, increased matrix metalloproteinase (MMP) activity may be related to increased behavioural sensitization and reward perhaps because of the modification of the passage of the drug into the CNS. In addition, the high incidence of AIDS-related neurologic disease in METH users may also be related to increased entry into the brain of virally derived neurotoxic products. This article is part of the Special Issue entitled 'CNS Stimulants'.

Mrp1 is essential for sphingolipid signaling to p-glycoprotein in mouse blood-brain and blood-spinal cord barriers

At the blood-brain and blood-spinal cord barriers, P-glycoprotein, an ATP-driven drug efflux pump, is a major obstacle to central nervous system (CNS) pharmacotherapy. Recently, we showed that signaling through tumor necrosis factor-α (TNF-α), sphingolipids, and sphingosine-1-phosphate receptor 1 (S1PR1) rapidly and reversibly reduced basal P-glycoprotein transport activity in the rat blood-brain barrier. The present study extends those findings to the mouse blood-brain and blood-spinal cord barriers and, importantly, identifies multidrug resistance-associated protein 1 (Mrp1, Abcc1) as the transporter that mediates S1P efflux from brain and spinal cord endothelial cells. In brain and spinal cord capillaries isolated from wild-type mice, TNF-α, sphingosine, S1P, the S1PR agonist fingolimod (FTY720), and its active, phosphorylated metabolite, FTY720P, reduced P-glycoprotein transport activity; these effects were abolished by a specific S1PR1 antagonist. In brain and spinal cord capillaries isolated from Mrp1-null mice, neither TNF-α nor sphingosine nor FTY720 reduced P-glycoprotein transport activity. However, S1P and FTY720P had the same S1PR1-dependent effects on transport activity as in capillaries from wild-type mice. Thus, deletion of Mrp1 alone terminated endogenous signaling to S1PR1. These results identify Mrp1 as the transporter essential for S1P efflux from the endothelial cells and thus for inside-out S1P signaling to P-glycoprotein at the blood-brain and blood-spinal cord barriers.

A study on the effect of JNK inhibitor, SP600125, on the disruption of blood-brain barrier induced by methamphetamine

Methamphetamine (METH) is a widely consumed drug with high abuse potential. Studies in animals have shown that the drug produces dopaminergic neurotoxicity following both single high-dose and repeated low-dose administration. In addition, METH produces an increase in matrix metalloproteinase expression and loss of BBB integrity. We have examined the effect of repeated low-dose METH on MMP-9/2 expression and activity and laminin expression and the role of MMPs and JNK 1/2 phosphorylation on the changes induced by the drug in BBB integrity. Mice were given METH (4 mg/kg, i.p., three times separated by 3 h) and killed at different times after the last dose. Striatal MMP-9/2 activity was determined by zymography and expression of MMPs, laminin and phosphorylated JNK 1/2 was determined by western blot. BBB integrity was determined by IgG immunoreactivity. SP600125 and BB-94 were used to inhibit JNK and MMPs respectively. METH increased striatal MMP-9 expression and activity, IgG immunoreactivity and p-JNK 1/2 expression and decreased laminin expression. Increased IgG immunoreactivity colocalized with areas of greater MMP-9 activity. JNK inhibition prevented METH-induced changes in MMP-9 activity, laminin degradation and BBB leakage. BB-94 also prevented laminin degradation and BBB leakage. The decrease in BBB integrity induced by METH is mediated by the JNK pathway which activates MMP-9 causing degradation of laminin and BBB leakage.

The abluminal endothelial membrane in neurovascular remodeling in health and disease

After brain injury, blood-brain barrier (BBB) integrity can be compromised as a consequence of the breakdown of cell-cell interactions in the neurovascular unit, resulting in the loss of the characteristic endothelial luminal-to-abluminal structure. During the process of restoration of the BBB and vascularization, the endothelial cells are continuously reshaped, with both the luminal and abluminal membranes serving as sites of signaling. Here, we focus on the bidirectional signaling processes that are rapidly initiated between endothelial and perivascular cells and occur in certain brain diseases or in response to injury. The goal of these processes is (i) the reemergence of endothelial cell polarity, (ii) the remodeling of extracellular matrix interactions, (iii) the realignment of pericytes and astrocytic endfeet with endothelial cells, and (iv) the restitution of a well-organized and stable BBB. This abluminal membrane exemplifies how the brain vasculature responds to stressors and may represent promising targets for therapeutic interventions of brain diseases.

ATP-binding cassette transporters in immortalised human brain microvascular endothelial cells in normal and hypoxic conditions

Background

Rapid reperfusion following ischemia is the most effective therapy in stroke therapy. However, the success may be compromised by ischemia & reperfusion (I/R) injury and at the human blood–brain barrier (BBB), therefore the effects on transendothelial transport are of special interest. Current studies suggest the ATP-binding cassette (ABC) transporters to be regulated upon ischemic stroke in a way that impedes the effects of drug therapy. The immortalised human brain microvascular endothelial cell line hCMEC/D3 provides most of the unique properties of the BBB with respect to transport and might be a reliable in vitro model to study transendothelial transport after I/R.

Methods

We exposed hCMEC/D3 cells to 24 hours of hypoxia alone and to hypoxia followed by 60 min of reoxygenisation as an in vitro model for I/R. Western blot showed mild upregulation of hypoxia inducible factor (HIF-1α) after hypoxia alone and RNA lysates were analysed with a well-established real-time RT-PCR-based TaqMan low-density array detecting 47 of 48 known human ABC transporters.

Results

No significant increases of ABC mRNA expression levels were detected neither in hypoxic nor in I/R samples. However, slight decrease of ABCC1 in hypoxic and I/R samples and of ABCA10 and ABCD3 in I/R samples was observed.

Conclusion

Our data suggests that hCMEC/D3 cell line and – at the moment – in vitro models in general are a poor basis for stroke research but may be enhanced by co-culturing more cells of the neurovascular unit inducing an overall ischemic response at the BBB.

Apolipoprotein-E controls adenosine triphosphate-binding cassette transporters ABCB1 and ABCC1 on cerebral microvessels after methamphetamine intoxication

BACKGROUND AND PURPOSE

Methamphetamine is a powerful addictive, which has been associated with ischemic stroke and brain hemorrhage in humans. Whether and how methamphetamine influences the expression of tight junctions and adenosine triphosphate-binding cassette transporters, which have previously been shown to be regulated by apolipoprotein-E (ApoE) under conditions of brain ischemia, was unknown.

METHODS

C57BL/6J mice received intraperitoneal injections of methamphetamine (3 times 4 mg/kg separated by 3 hours) either alone or in combination with the ApoE receptor-2 inhibitor receptor-associated protein (40 μg/kg) or the inducible nitric oxide synthase inhibitor 1400W (5 mg/kg). Animals were euthanized 3 or 24 hours after methamphetamine exposure. Tissue responses were evaluated with Western blots, immunoprecipitation, and immunohistochemistry using total brain and cerebral microvessel extracts.

RESULTS

Methamphetamine induced a transient activation of stress kinases c-Jun N-terminal kinase 1/2 and p38 in the brain parenchyma and increased intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 expression on cerebral microvessels without inducing loss of tight junction proteins and without inducing IgG extravasation. Methamphetamine transiently increased the expression of the luminal adenosine triphosphate-binding cassette transporter ABCB1 on cerebral microvessels and reduced the expression of the abluminal transporter ABCC1. Elevated expression of ApoE was noted in the brain parenchyma by methamphetamine, activating ApoE receptor-2 on brain capillaries, deactivating c-Jun N-terminal kinase 1/2 and c-Jun, and regulating ABCB1 and ABCC1 expression. Indeed, ApoE receptor-2 and inducible nitric oxide synthase inhibition prevented the ABCB1 and ABCC1 expression changes.

CONCLUSIONS

Acute exposure to methamphetamine at doses comparable to those consumed in drug addiction does not induce tight junction breakdown but differentially regulates adenosine triphosphate-binding cassette transporters through the ApoE/ApoE receptor-2/c-Jun N-terminal kinase 1/2 pathway.

Vascular endothelial growth factor induces contralesional corticobulbar plasticity and functional neurological recovery in the ischemic brain

Vascular endothelial growth factor (VEGF) is a potent angiogenic factor, which also has neuroprotective activity. In view of these dual actions on vessels and neurons, we were interested whether VEGF promotes long distance axonal plasticity in the ischemic brain. Herein, we show that VEGF promotes neurological stroke recovery in mice when delivered in a delayed way starting 3 days after middle cerebral artery occlusion. Using anterograde tract-tracing experiments that we combined with histochemical and molecular biological studies, we demonstrate that although VEGF promoted angiogenesis predominantly in the ischemic hemisphere, pronounced axonal sprouting was induced by VEGF in the contralesional, but not the ipsilesional corticobulbar system. Corticobulbar plasticity was accompanied by the deactivation of the matrix metalloproteinase MMP9 in the lesioned hemisphere and the transient downregulation of the axonal growth inhibitors NG2 proteoglycan and brevican and the guidance molecules ephrin B1/2 in the contralesional hemisphere. The regulation of matrix proteinases, growth inhibitors, and guidance molecules offers insights how brain plasticity is controlled in the ischemic brain.

ABC Transporters and the Alzheimer's Disease Enigma

Alzheimer's disease (AD) is considered the "disease of the twenty-first century." With a 10-fold increase in global incidence over the past 100 years, AD is now reaching epidemic proportions and by all projections, AD patient numbers will continue to rise. Despite intense research efforts, AD remains a mystery and effective therapies are still unavailable. This represents an unmet need resulting in clinical, social, and economic problems. Over the last decade, a new AD research focus has emerged: ATP-binding cassette (ABC) transporters. In this article, we provide an overview of the ABC transporters ABCA1, ABCA2, P-glycoprotein (ABCB1), MRP1 (ABCC1), and BCRP (ABCG2), all of which are expressed in the brain and have been implicated in AD. We summarize recent findings on the role of these five transporters in AD, and discuss their potential to serve as therapeutic targets.

Intracerebroventricularly delivered VEGF promotes contralesional corticorubral plasticity after focal cerebral ischemia via mechanisms involving anti-inflammatory actions

Vascular endothelial growth factor (VEGF) has potent angiogenic and neuroprotective effects in the ischemic brain. Its effect on axonal plasticity and neurological recovery in the post-acute stroke phase was unknown. Using behavioral tests combined with anterograde tract tracing studies and with immunohistochemical and molecular biological experiments, we examined effects of a delayed i.c.v. delivery of recombinant human VEGF(165), starting 3 days after stroke, on functional neurological recovery, corticorubral plasticity and inflammatory brain responses in mice submitted to 30 min of middle cerebral artery occlusion. We herein show that the slowly progressive functional improvements of motor grip strength and coordination, which are induced by VEGF, are accompanied by enhanced sprouting of contralesional corticorubral fibres that branched off the pyramidal tract in order to cross the midline and innervate the ipsilesional parvocellular red nucleus. Infiltrates of CD45+ leukocytes were noticed in the ischemic striatum of vehicle-treated mice that closely corresponded to areas exhibiting Iba-1+ activated microglia. VEGF attenuated the CD45+ leukocyte infiltrates at 14 but not 30 days post ischemia and diminished the microglial activation. Notably, the VEGF-induced anti-inflammatory effect of VEGF was associated with a downregulation of a broad set of inflammatory cytokines and chemokines in both brain hemispheres. These data suggest a link between VEGF's immunosuppressive and plasticity-promoting actions that may be important for successful brain remodeling. Accordingly, growth factors with anti-inflammatory action may be promising therapeutics in the post-acute stroke phase.

The ATP-binding cassette transporters ABCB1 and ABCC1 are not regulated by hypoxia in immortalised human brain microvascular endothelial cells

BACKGROUND

ATP-binding cassette transporters at the blood-brain barrier are actively regulated upon ischemic stroke in a way that impedes the access of pharmacological compounds to the brain tissue. The luminal endothelial transporter ABCB1 was recently shown to be increased, whereas the abluminal transporter ABCC1 was decreased on ischemic brain capillaries. In vitro studies using epithelial cells suggested that ABCB1 is regulated during hypoxia in a hypoxia-inducible factor (HIF)-1α-dependent way.

METHODS

In order to investigate whether hypoxia might be responsible for the expression changes of ABCB1 and ABCC1 in the ischemic brain, the immortalised human brain microvascular endothelial cell line hCMEC/D3 was exposed to hypoxia (1%) or anoxia (0%). Cell lysates were analysed by Western blot to detect the protein expression of ABCB1, ABCC1, HIF-1α and HIF-2α.

RESULTS

During hypoxia, an accumulation of HIF-1α and HIF-2α was noticed in hCMEC/D3 cells that followed different time kinetics. Both HIF-1α and HIF-2α abundance increased within 4 h of hypoxia. HIF-1α levels decreased to below detection levels within 16 h of hypoxia, whereas HIF-2α remained elevated even after 48 h. No changes of ABCB1 and ABCC1 expression were detected, neither on the mRNA nor protein level.

CONCLUSION

Our data suggests that other factors than hypoxia may be responsible for the expression changes of ATP-binding cassette transporters in the ischemic brain.

Liver X receptor activation enhances blood-brain barrier integrity in the ischemic brain and increases the abundance of ATP-binding cassette transporters ABCB1 and ABCC1 on brain capillary cells

The blood-brain barrier (BBB) consists of dense contacts between endothelial cells, the tight junctions, which are complemented by membrane-bound transporters belonging to the ATP-binding cassette (ABC) transporter family. Liver X receptors (LXR) have previously been shown to stabilize the integrity of atherosclerotic noncerebral arteries. Their effects on ischemic cerebral vessels are still unknown. By delivering LXR agonists, T0901317 and GW3965, to mice submitted to 30 minutes intraluminal middle cerebral artery occlusion, we show that LXR activation reduces brain swelling and decreases BBB permeability by upregulating LXR's target calpastatin that deactivates calpain-1/2, stabilizing p120 catenin. p120 catenin specifically interacts with RhoA and Cdc42, inactivating the former and overactivating the latter, thus restoring the postischemic expression, phosphorylation and interaction of the tight junction proteins occludin and zona occludens-1. Moreover, LXR activation deactivates matrix metalloproteases-2/9 and inhibits microvascular apoptosis by deactivating JNK1/2 and caspase-3. In addition to the cholesterol transporters ABCA1 and ABCG1, which have previously been shown to be upregulated by LXR in noncerebral vessels, LXR activation increases the abundance of the drug transporters ABCB1 and ABCC1 on ischemic brain capillaries, as we further show. That LXR activation promotes endothelial integrity in different ways makes this receptor attractive as target for stroke therapies.

Translational pharmacokinetics: challenges of an emerging approach to drug development in stroke

INTRODUCTION

There is increasing recognition of the importance of translational pharmacokinetics in stroke research, lack of which has been cited as one of the main contributing factors to failure of Phase III trials.

AREAS COVERED

The article reviews the translational issues in administration, distribution and sampling in the pharmacokinetics of putative therapeutic drugs in stroke. In addition, the role of translational pharmacometrics in drug development is discussed. The review uses the anti-inflammatory agent, IL-1 receptor antagonist, as an example. The reader will gain an insight into the pitfalls that are commonplace in translating pharmacokinetics from the preclinical to the clinical scenario. The reader will also gain an understanding of the complexities of blood-central nervous system (CNS) barriers in relation to brain pharmacokinetics and the increasing use of translational pharmacometrics in stroke research.

EXPERT OPINION

The translation of preclinical to clinical pharmacokinetics is a discipline that is traditionally overlooked and is likely to be a key factor responsible for failure of clinical trials. With a clear comprehensive insight into the benefits and limitations of translational pharmacokinetics in stroke, translational pharmacokinetics can be safely used to enhance the efficacy of clinical trials in stroke and their likelihood of success.

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.

Post-acute delivery of erythropoietin induces stroke recovery by promoting perilesional tissue remodelling and contralesional pyramidal tract plasticity

The promotion of post-ischaemic motor recovery remains a major challenge in clinical neurology. Recently, plasticity-promoting effects have been described for the growth factor erythropoietin in animal models of neurodegenerative diseases. To elucidate erythropoietin's effects in the post-acute ischaemic brain, we examined how this growth factor influences functional neurological recovery, perilesional tissue remodelling and axonal sprouting of the corticorubral and corticobulbar tracts, when administered intra-cerebroventricularly starting 3 days after 30 min of middle cerebral artery occlusion. Erythropoietin administered at 10 IU/day (but not at 1 IU/day), increased grip strength of the contralesional paretic forelimb and improved motor coordination without influencing spontaneous locomotor activity and exploration behaviour. Neurological recovery by erythropoietin was associated with structural remodelling of ischaemic brain tissue, reflected by enhanced neuronal survival, increased angiogenesis and decreased reactive astrogliosis that resulted in reduced scar formation. Enhanced axonal sprouting from the ipsilesional pyramidal tract into the brainstem was observed in vehicle-treated ischaemic compared with non-ischaemic animals, as shown by injection of dextran amines into both motor cortices. Despite successful remodelling of the perilesional tissue, erythropoietin enhanced axonal sprouting of the contralesional, but not ipsilesional pyramidal tract at the level of the red and facial nuclei. Moreover, molecular biological and histochemical studies revealed broad anti-inflammatory effects of erythropoietin in both hemispheres together with expression changes of plasticity-related molecules that facilitated contralesional axonal growth. Our study establishes a plasticity-promoting effect of erythropoietin after stroke, indicating that erythropoietin acts via recruitment of contralesional rather than of ipsilesional pyramidal tract projections.

Apolipoprotein E controls ATP-binding cassette transporters in the ischemic brain

The adenosine triphosphate-binding cassette transporters ABCB1 and ABCC1 show coordinated changes in abundance at the luminal and abluminal membranes of ischemic cerebral capillaries that impede the brain access of pharmacological compounds. We found that apolipoprotein E (ApoE) was present on ischemic microvessels but not contralateral controls. ApoE signaled through ApoE receptor-2 (ApoER2), which was constitutively expressed on brain microvessels, to decrease c-Jun amino-terminal kinase 1 and 2 and c-Jun activities. ApoE regulated the postischemic abundance of ABCB1 and ABCC1, thereby controlling drug accumulation in the ischemic brain. Our data suggest that inhibition of ApoE signaling may enable improved delivery of drugs to the brain.

Combination of tissue-plasminogen activator with erythropoietin induces blood-brain barrier permeability, extracellular matrix disaggregation, and DNA fragmentation after focal cerebral ischemia in mice

BACKGROUND AND PURPOSE

After 1 clinical study in which recombinant erythropoietin (EPO) protected against ischemic stroke and improved clinical outcome, the German multicenter EPO trial recently reported increased mortality in stroke patients receiving EPO after tissue-plasminogen activator (t-PA)-induced thrombolysis. The reasons for the adverse effects of EPO in t-PA-treated patients are unknown.

METHODS

Mice were submitted to 90 minutes of middle cerebral artery occlusion. Immediately after reperfusion, animals were treated with normal saline or t-PA (10 mg/kg). Animals subsequently received injections of normal saline or EPO that were administered after reperfusion and 12 hours later (2500 IU/kg each). Ischemic injury and brain edema were analyzed at 24 hours after reperfusion by cresyl violet staining and terminal transferase biotinylated-dUTP nick end labeling. Blood-brain barrier integrity was assessed by histochemistry for extravasated serum IgG. Matrix metalloproteinase activity was evaluated by gelatinase zymography.

RESULTS

EPO did not influence ischemic infarct size but reduced brain swelling. This effect was abolished by t-PA, which exacerbated serum IgG extravasation in ischemic tissue. Gelatinase zymographies revealed that EPO promoted matrix metalloproteinase-9 activity that was markedly elevated by t-PA. Add-on treatment with t-PA increased the density of DNA-fragmented cells in ischemic tissue of EPO-treated, but not vehicle-treated, mice.

CONCLUSIONS

Our data demonstrate a hitherto unknown interaction of t-PA with EPO at the blood-brain interface, ie, promotion of vascular permeability and extracellular matrix breakdown, which may account for the unfavorable actions of EPO in t-PA-treated patients. After t-PA-induced thrombolysis, EPO may not be suitable as stroke treatment.