Marked differences in the effect of antiepileptic and cytostatic drugs on the functionality of P-glycoprotein in human and rat brain capillary endothelial cell lines

Effect of Apolipoprotein E isoforms on the Abundance and Function of P-glycoprotein in Human Brain Microvascular Endothelial Cells

BACKGROUND

Individuals with Alzheimer's disease (AD) often require many medications; however, these medications are dosed using regimens recommended for individuals without AD. This is despite reduced abundance and function of P-glycoprotein (P-gp) at the blood-brain barrier (BBB) in AD, which can impact brain exposure of drugs. The fundamental mechanisms leading to reduced P-gp abundance in sporadic AD remain unknown; however, it is known that the apolipoprotein E (apoE) gene has the strongest genetic link to sporadic AD development, and apoE isoforms can differentially alter BBB function. The aim of this study was to assess if apoE affects P-gp abundance and function in an isoform-dependent manner using a human cerebral microvascular endothelial cell (hCMEC/D3) model.

METHODS

This study assessed the impact of apoE isoforms on P-gp abundance (by western blot) and function (by rhodamine 123 (R123) uptake) in hCMEC/D3 cells. Cells were exposed to recombinant apoE3 and apoE4 at 2 - 10 µg/mL over 24 - 72 hours. hCMEC/D3 cells were also exposed for 72 hours to astrocyte-conditioned media (ACM) from astrocytes expressing humanised apoE isoforms.

RESULTS

P-gp abundance in hCMEC/D3 cells was not altered by recombinant apoE4 relative to recombinant apoE3, nor did ACM containing human apoE isoforms alter P-gp abundance. R123 accumulation in hCMEC/D3 cells was also unchanged with recombinant apoE isoform treatments, suggesting no change to P-gp function, despite both abundance and function being altered by positive controls SR12813 (5 µM) and PSC 833 (5 µM), respectively.

CONCLUSIONS

Different apoE isoforms have no direct influence on P-gp abundance or function within this model, and further in vivo studies would be required to address whether P-gp abundance or function are reduced in sporadic AD in an apoE isoform-specific manner.

Human brain microvascular endothelial cells release different types of P-glycoprotein-containing extracellular vesicles upon exposure to doxorubicin

In the brain, the efflux transporter P-glycoprotein (Pgp) is predominantly located on the luminal membrane of microvascular endothelial cells (BMECs) that form the blood-brain barrier. In addition, Pgp is localized in intracellular organelles involved in Pgp traffic and cycling and, by the release of extracellular vesicles (EVs), in intercellular Pgp transfer to cells with low Pgp expression. We recently described that drug exposure of a human BMEC line (hCMEC/D3) induces the release of Pgp-EGFP-containing EVs; however, the nature of the Pgp-enriched vesicles was not characterized. The two main categories of EVs are exosomes and microvesicles, which differ in origin, size, and molecular cargo. In the present study, we performed similar experiments with hCMEC/D3 cells in the absence and presence of doxorubicin and isolated and characterized the EVs released by the cells during the experiments by differential ultracentrifugation with/without subsequent sucrose gradient fractionation of EV pellets, proteomic profiling, EV size analysis, and confocal fluorescence microscopy. Using cocultures of hCMEC/D3 wildtype cells and cells transduced with MDR1-EGFP or monocultures of hCMEC/D3-MDR1-EGFP cells, we found release of both Pgp-enriched exosomes and microvesicles but analysis of the exosomal marker protein Rab7 indicated that doxorubicin increased particularly the release of exosomes. Transfer experiments with isolated EVs demonstrated EV endocytosis by recipient cells. EV release from BMECs in response to anticancer drugs such as doxorubicin likely serves different functions, including non-genetic intercellular transfer of a resistance phenotype to neighboring BMECs and a mechanism of drug extrusion that contributes to brain protection against potentially toxic chemotherapeutic drugs.

Valproic Acid-Induced Upregulation of Multidrug Efflux Transporter ABCG2/BCRP via PPARα-Dependent Mechanism in Human Brain Endothelial Cells

Despite the progress made in the development of new antiepileptic drugs (AEDs), poor response to them is a rising concern in epilepsy treatment. Of several hypotheses explaining AED treatment failure, the most promising theory is the overexpression of multidrug transporters belonging to ATP-binding cassette (ABC) transporter family at blood-brain barrier. Previous data show that AEDs themselves can induce these transporters, in turn affecting their own brain bioavailability. Presently, this induction and the underlying regulatory mechanism involved at human blood-brain barrier is not well elucidated. Herein, we sought to explore the effect of most prescribed first- and second-line AEDs on multidrug transporters in human cerebral microvascular endothelial cells, hCMEC/D3. Our work demonstrated that exposure of these cells to valproic acid (VPA) induced mRNA, protein, and functional activity of breast cancer resistance protein (BCRP/ABCG2). On examining the substrate interaction status of AEDs with BCRP, VPA, phenytoin, and lamotrigine were found to be potential BCRP substrates. Furthermore, we observed that siRNA-mediated knockdown of peroxisome proliferator-activated receptor alpha (PPARα) or use of PPARα antagonist, resulted in attenuation of VPA-induced BCRP expression and transporter activity. VPA was found to increase PPARα expression and trigger its translocation from cytoplasm to nucleus. Findings from chromatin immunoprecipitation and luciferase assays showed that VPA enhances the binding of PPARα to its response element in the ABCG2 promoter, resulting in elevated ABCG2 transcriptional activity. Taken together, these in vitro findings highlight PPARα as the potential molecular target to prevent VPA-mediated BCRP induction, which may have important implications in VPA pharmacoresistance. SIGNIFICANCE STATEMENT: Induction of multidrug transporters at blood-brain barrier can largely affect the bioavailability of the substrate antiepileptic drugs in the brains of patients with epilepsy, thus affecting their therapeutic efficacy. The present study reports a mechanistic pathway of breast cancer resistance protein (BCRP/ABCG2) upregulation by valproic acid in human brain endothelial cells via peroxisome proliferator-activated receptor alpha involvement, thereby providing a potential strategy to prevent valproic acid pharmacoresistance in epilepsy.

Oligodendroglioma: A Review of Management and Pathways

Anaplastic oligodendrogliomas are a type of glioma that occurs primarily in adults but are also found in children. These tumors are genetically defined according to the mutations they harbor. Grade II and grade III tumors can be differentiated most of the times by the presence of anaplastic features. The earliest regimen used for the treatment of these tumors was procarbazine, lomustine, and vincristine. The treatment modalities have shifted over time, and recent studies are considering immunotherapy as an option as well. This review assesses the latest management modalities along with the pathways involved in the pathogenesis of this malignancies.

Similarities and differences in the localization, trafficking, and function of P-glycoprotein in MDR1-EGFP-transduced rat versus human brain capillary endothelial cell lines

Background

In vitro models based on brain capillary endothelial cells (BCECs) are among the most versatile tools in blood–brain barrier research for testing drug penetration into the brain and how this is affected by efflux transporters such as P-glycoprotein (Pgp). However, compared to freshly isolated brain capillaries or primary BCECs, the expression of Pgp in immortalized BCEC lines is markedly lower, which prompted us previously to transduce the widely used human BCEC line hCMEC/D3 with a doxycycline-inducible MDR1-EGFP fusion plasmid. The EGFP-labeled Pgp in these cells allows studying the localization and trafficking of the transporter and how these processes are affected by drug exposure. Here we used this strategy for the rat BCEC line RBE4 and performed a face-to-face comparison of RBE4 and hCMEC/D3 wild-type (WT) and MDR1-EGFP transduced cells.

Methods

MDR1-EGFP-transduced variants were derived from WT cells by lentiviral transduction, using an MDR1-linker-EGFP vector. Localization, trafficking, and function of Pgp were compared in WT and MDR1-EGFP transduced cell lines. Primary cultures of rat BCECs and freshly isolated rat brain capillaries were used for comparison.

Results

All cells exhibited typical BCEC morphology. However, significant differences were observed in the localization of Pgp in that RBE4-MDR1-EGFP cells expressed Pgp primarily at the plasma membrane, whereas in hCMEC/D3 cells, the Pgp-EGFP fusion protein was visible both at the plasma membrane and in endolysosomal vesicles. Exposure to doxorubicin increased the number of Pgp-EGFP-positive endolysosomes, indicating a lysosomotropic effect. Furthermore, lysosomal trapping of doxorubicin was observed, likely contributing to the protection of the cell nucleus from damage. In cocultures of WT and MDR1-EGFP transduced cells, intercellular Pgp-EGFP trafficking was observed in RBE4 cells as previously reported for hCMEC/D3 cells. Compared to WT cells, the MDR1-EGFP transduced cells exhibited a significantly higher expression and function of Pgp. However, the junctional tightness of WT and MDR1-EGFP transduced RBE4 and hCMEC/D3 cells was markedly lower than that of primary BCECs, excluding the use of the cell lines for studying vectorial drug transport.

Conclusions

The present data indicate that MDR1-EGFP transduced RBE4 cells are an interesting tool to study the biogenesis of lysosomes and Pgp-mediated lysosomal drug trapping in response to chemotherapeutic agents and other compounds at the level of the blood–brain barrier.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12987-021-00266-z.

Entry of antiepileptic drugs (valproate and lamotrigine) into the developing rat brain

Background: Women with epilepsy face difficult choices whether to continue antiepileptic drug treatment during pregnancy, as uncontrolled seizures carry great risk to mother and fetus but continuing treatment may have adverse effects on baby’s development. This study aimed at evaluating antiepileptic drug entry into developing brain. Methods: Anaesthetised pregnant, non-pregnant adult females, postnatal and fetal rats were injected intraperitoneally with different doses, single or in combinations, of valproate and lamotrigine, all within clinical range. Injectate included 3H-labelled drug. After 30min, CSF, blood and brain samples were obtained; radioactivity was measured using liquid scintillation counting. Some animals were also exposed to valproate in feed throughout pregnancy and into neonatal period. Drug levels were measured by liquid chromatography coupled to mass spectrometry (LC-MS). Results are given as CSF or tissue/plasma% as index of drug entry. Results: Entry of valproate into brain and CSF was higher at E19 and P4 compared to adult but was not dose-dependent;  placental transfer increased significantly at highest dose of 100mg/Kg. Lamotrigine entry into the brain was dose dependent only at E19. Chronic valproate treatment, or combination of valproate and lamotrigine had little effect on either drug entry, except for reduced valproate brain entry in adult brain with chronic treatment. Placental transfer decreased significantly after chronic valproate treatment. LC-MS measurement of valproate in adults confirmed that rat plasma values were within the clinical range and CSF/plasma and brain/plasma ratios for LC-MS and 3H-valproate were similar. Conclusion: Results suggest that entry of valproate may be higher in developing brain, the capacity of barrier mechanism is mostly unaffected by doses within the clinical range, with or without addition of lamotrigine. Chronic valproate exposure may result in upregulation in cellular mechanisms restricting its entry into the brain. Entry of lamotrigine was little different at different ages and was not dose dependent.

Entry of antiepileptic drugs (valproate and lamotrigine) into the developing rat brain

Background: Women with epilepsy face difficult choices whether to continue antiepileptic drug treatment during pregnancy, as uncontrolled seizures carry great risk to mother and fetus but continuing treatment may have adverse effects on baby’s development. This study aimed at evaluating antiepileptic drug entry into developing brain.

Methods: Anaesthetised pregnant, non-pregnant adult females, postnatal and fetal rats were injected intraperitoneally with different doses, single or in combinations, of valproate and lamotrigine, within clinical range. Injectate included  ³H-labelled drug. After 30min, CSF, blood and brain samples were obtained; radioactivity measured using liquid scintillation counting. Some animals were also exposed to valproate in feed throughout pregnancy and into neonatal period. Drug levels measured by liquid chromatography coupled to mass spectrometry (LC-MS). Results given as CSF or tissue/plasma% as index of drug entry.

Results: Entry of valproate into brain and CSF was higher at E19 and P4 compared to adult and was dose-dependent except at E19; placental transfer increased significantly at highest dose of 100mg/kg. Lamotrigine entry into the brain was dose dependent only at E19. Chronic valproate treatment, or combination of valproate and lamotrigine had little effect on either drug entry, except for reduced valproate brain entry in adult brain with chronic treatment. Placental transfer decreased significantly after chronic valproate treatment. LC-MS measurement of valproate in adults confirmed that rat plasma values were within the clinical range and CSF/plasma and brain/plasma ratios for LC-MS and  ³H-valproate were similar.

Conclusion: Results suggest that entry of valproate may be higher in developing brain, the capacity of barrier mechanism is mostly unaffected by doses within the clinical range, with or without addition of lamotrigine. Chronic valproate exposure may result in upregulation in cellular mechanisms restricting its entry into the brain. Entry of lamotrigine was little different at different ages and was not dose dependent.

Novel Intrinsic Mechanisms of Active Drug Extrusion at the Blood-Brain Barrier: Potential Targets for Enhancing Drug Delivery to the Brain?

The blood-brain barrier (BBB) limits the pharmacotherapy of several brain disorders. In addition to the structural and metabolic characteristics of the BBB, the ATP-driven, drug efflux transporter P-glycoprotein (Pgp) is a selective gatekeeper of the BBB; thus, it is a primary hindrance to drug delivery into the brain. Here, we review the complex regulation of Pgp expression and functional activity at the BBB with an emphasis on recent studies from our laboratory. In addition to traditional processes such as transcriptional regulation and posttranscriptional or posttranslational modification of Pgp expression and functionality, novel mechanisms such as intra- and intercellular Pgp trafficking and intracellular Pgp-mediated lysosomal sequestration in BBB endothelial cells with subsequent disposal by blood neutrophils are discussed. These intrinsic mechanisms of active drug extrusion at the BBB are potential therapeutic targets that could be used to modulate P-glycoprotein activity in the treatment of brain diseases and enhance drug delivery to the brain.

A face-to-face comparison of claudin-5 transduced human brain endothelial (hCMEC/D3) cells with porcine brain endothelial cells as blood-brain barrier models for drug transport studies

BACKGROUND

Predictive in vitro models of the human blood-brain barrier (BBB) are essential in early drug discovery and development. Among available immortalized human brain capillary endothelial cell lines (BCECs), the hCMEC/D3 cell line has become the most widely used in vitro BBB model. However, monolayers of hCMEC/D3 cells form only moderately restrictive barriers, most likely because the major tight junction protein, claudin-5, is markedly downregulated. Thus, hCMEC/D3 monolayers cannot be used for vectorial drug transport experiments, which is a major disadvantage of this model.

METHODS

Here we transduced hCMEC/D3 cells with a claudin-5 plasmid and compared the characteristics of these cells with those of hCMEC/D3 wildtype cells and primary cultured porcine BCECs.

RESULTS

The claudin-5 transduced hCMEC/D3 exhibited expression levels (and junctional localization) of claudin-5 similar to those of primary cultured porcine BCECs. The transduced cells exhibited increased TEER values (211 Ω cm²) and reduced paracellular mannitol permeability (8.06%/h), indicating improved BBB properties; however, the barrier properties of porcine BCECs (TEER 1650 Ω cm²; mannitol permeability 3.95%/h) were not reached. Hence, vectorial transport of a selective P-glycoprotein substrate (N-desmethyl-loperamide) was not observed in claudin-5 transduced hCMEC/D3 (or wildtype) cells, whereas such drug transport occurred in porcine BCECs.

CONCLUSIONS

The claudin-5 transduced hCMEC/D3 cells provide a tool to studying the contribution of claudin-5 to barrier tightness and how this can be further enhanced by additional transfections or other manipulations of this widely used in vitro model of the BBB.

Heat Shock Proteins Accelerate the Maturation of Brain Endothelial Cell Glucocorticoid Receptor in Focal Human Drug-Resistant Epilepsy

Pharmacoresistance in epilepsy is a major challenge to successful clinical therapy. Glucocorticoid receptor (GR) dysregulation can affect the underlying disease pathogenesis. We recently reported that local drug biotransformation at the blood-brain barrier is upregulated by GR, which controls drug-metabolizing enzymes (e.g., cytochrome P450s, CYPs) and efflux drug transporters (MDR1) in human epileptic brain endothelial cells (EPI-ECs). Here, we establish that this mechanism is influenced upstream by GR and its association with heat shock proteins/co-chaperones (Hsps) during maturation, which differentially affect human epileptic (EPI) tissue and brain endothelial cells. Overexpressed GR, Hsp90, Hsp70, and Hsp40 were found in EPI vs. NON-EPI brain regions. Elevated neurovascular GR expression and co-localization with Hsps was evident in the EPI regions with cortical dysplasia, predominantly in the brain micro-capillaries and neurons. A corresponding increase in ATPase activity (*p < 0.05) was found in the EPI regions. The GR-Hsp90/Hsp70 binding patterns indicated a faster chaperone-promoted maturation of GR, leading to its overactivation in both the tissue and EPI-ECs derived from EPI/focal regions and GR silencing in EPI-ECs slowed such GR-Hsp interactions. Significantly accelerated GR nuclear translocation was determined in EPI-ECs following treatment with GR modulators/ligands dexamethasone, rifampicin, or phenytoin. Our findings reveal that overexpressed GR co-localizes with Hsps in the neurovasculature of EPI brain, increased GR maturation by Hsps accelerates EPI GR machinery, and furthermore this change in EPI and NON-EPI GR-Hsp interaction alters with the age of seizure onset in epileptic patients, together affecting the pathophysiology and drug regulation in the epileptic brain endothelium.

Investigating Maternal Brain Alterations in Preeclampsia: the Need for a Multidisciplinary Effort

PURPOSE OF REVIEW

To provide insight into the mechanisms underlying cerebral pathophysiology and to highlight possible methods for evaluation, screening, and surveillance of cerebral complications in preeclampsia.

RECENT FINDINGS

The pathophysiology of eclampsia remains enigmatic. Animal studies show that the cerebral circulation in pregnancy and preeclampsia might be affected with increased permeability over the blood-brain barrier and altered cerebral blood flow due to impaired cerebral autoregulation. The increased blood pressure cannot be the only underlying cause of eclampsia and cerebral edema, since some cases of eclampsia arise without simultaneous hypertension. Findings from animal studies need to be confirmed in human tissues. Evaluation of brain alterations in preeclampsia and eclampsia is challenging and demands a multidisciplinary collaboration, since no single method can accurately and fully describe how preeclampsia affects the brain. Cerebral complications of preeclampsia are significant factors in maternal morbidity and mortality worldwide. No single method can accurately describe the full picture of how preeclampsia affects the brain vasculature and parenchyma. We recommend an international and multidisciplinary effort not only to overcome the issue of limited sample availability but also to optimize the quality of research.

Effects of carbamazepine on the P-gp and CYP3A expression correlated with PXR or NF-κB activity in the bEnd.3 cells

Drug-resistant epilepsy (DRE) is present in 20-30% of all patients who develop epilepsy. Growing evidences demonstrated that glutamate released during seizures to increase the brain P-glycoprotein (P-gp) expression. Carbamazepine (CBZ) is known to influence the P-gp and cytochrome P450 (CYP) expression. However, the exact molecular mechanism is still unknown. We investigated that the effects of NF-κB and pregnane X receptor (PXR) activity on P-gp and CYP3A expression in mouse brain endothelial (bEnd.3) cells treated with l-glutamate (mimicking the seizure conditions), CBZ (mimicking the AED treating conditions) or both (l-glutamate plus CBZ) through qPCR and Western blotting assay. Mean fluorescence intensity was used to observe P-gp efflux function by analysis of intracellular Rhodamine123 (Rho123) accumulation. P-gp, CYP3A, PXR and NF-κB p65 were elevated in bEnd.3 cells incubated with l-glutamate, CBZ or CBZ pretreated by l-glutamate for 30 min. Both the mRNA and protein levels of P-gp and CYP3A were remarkably reduced by PXR or NF-κB p65 knock-down by siRNA transfections. The decreased intracellular accumulation of Rho123 suggested that the expression of P-gp was enhanced in bEnd.3 cells. These data suggested that overexpression of P-gp and CYP3A during seizures and treated with CBZ may be regulated by PXR or NF-κB p65 activity and expression, which revealed a mechanism underlying the development of DRE.

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.

In Vitro Assessment of the Effect of Antiepileptic Drugs on Expression and Function of ABC Transporters and Their Interactions with ABCC2

ABC transporters have a significant role in drug disposition and response and various studies have implicated their involvement in epilepsy pharmacoresistance. Since genetic studies till now are inconclusive, we thought of investigating the role of xenobiotics as transcriptional modulators of ABC transporters. Here, we investigated the effect of six antiepileptic drugs (AEDs) viz. phenytoin, carbamazepine, valproate, lamotrigine, topiramate and levetiracetam, on the expression and function of ABCB1, ABCC1, ABCC2 and ABCG2 in Caco2 and HepG2 cell lines through real time PCR, western blot and functional activity assays. Further, the interaction of AEDs with maximally induced ABCC2 was studied. Carbamazepine caused a significant induction in expression of ABCB1 and ABCC2 in HepG2 and Caco2 cells, both at the transcript and protein level, together with increased functional activity. Valproate caused a significant increase in the expression and functional activity of ABCB1 in HepG2 only. No significant effect of phenytoin, lamotrigine, topiramate and levetiracetam on the transporters under study was observed in either of the cell lines. We demonstrated the interaction of carbamazepine and valproate with ABCC2 with ATPase and 5,6-carboxyfluorescein inhibition assays. Thus, altered functionality of ABCB1 and ABCC2 can affect the disposition and bioavailability of administered drugs, interfering with AED therapy.

SLC and ABC Transporters: Expression, Localization, and Species Differences at the Blood-Brain and the Blood-Cerebrospinal Fluid Barriers

The blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCSFB) separate the brain and cerebrospinal fluid (CSF) from the systemic circulation and represent a barrier to the uptake of both endogenous compounds and xenobiotics into the brain. For compounds whose passive diffusion is limited due to their ionization or hydrophilicity, membrane transporters can facilitate their uptake across the BBB or BCSFB. Members of the solute carrier (SLC) and ATP-binding case (ABC) families are present on these barriers. Differences exist in the localization and expression of transport proteins between the BBB and BCSFB, resulting in functional differences in transport properties. This review focuses on the expression, membrane localization, and different isoforms present at each barrier. Diseases that affect the central nervous system including brain tumors, HIV, Alzheimer's disease, Parkinson's disease, and stroke affect the integrity and expression of transporters at the BBB and BCSFB and will be briefly reviewed.

Inhibition of mTOR Pathway by Rapamycin Decreases P-glycoprotein Expression and Spontaneous Seizures in Pharmacoresistant Epilepsy

The mammalian target of rapamycin (mTOR) has been demonstrated to mediate multidrug resistance in various tumors by inducing P-glycoprotein (P-gp) overexpression. Here, we investigated the correlation between the mTOR pathway and P-gp expression in pharmacoresistant epilepsy. Temporal cortex specimens were obtained from patients with refractory mesial temporal lobe epilepsy (mTLE) and age-matched controls who underwent surgeries at West China Hospital of Sichuan University between June 2014 and May 2015. We established a rat model of epilepsy kindled by coriaria lactone (CL) and screened pharmacoresistant rats (non-responders) using phenytoin. Non-responders were treated for 4 weeks with vehicle only or with the mTOR pathway inhibitor rapamycin at doses of 1, 3, and 6 mg/kg. Western blotting and immunohistochemistry were used to detect the expression of phospho-S6 (P-S6) and P-gp at different time points (1 h, 8 h, 1 day, 3 days, 1 weeks, 2 weeks, and 4 weeks) after the onset of treatment. Overexpression of P-S6 and P-gp was detected in both refractory mTLE patients and non-responder rats. Rapamycin showed an inhibitory effect on P-S6 and P-gp expression 1 week after treatment in rats. In addition, the expression levels of P-S6 and P-gp in the 6 mg/kg group were significantly lower than those in the 1 mg/kg or the 3 mg/kg group at the same time points (all P < 0.05). Moreover, rapamycin decreased the duration and number of CL-induced seizures, as well as the stage of non-responders (all P < 0.05). The current study indicates that the mTOR signaling pathway plays a critical role in P-gp expression in drug-resistant epilepsy. Inhibition of the mTOR pathway by rapamycin may be a potential therapeutic approach for pharmacoresistant epilepsy.

Intercellular transfer of P-glycoprotein in human blood-brain barrier endothelial cells is increased by histone deacetylase inhibitors

The blood–brain barrier (BBB) controls the entry of compounds into the brain, thereby regulating brain homeostasis. Efflux transporters such as P-glycoprotein (Pgp) significantly contribute to BBB function. Multiple signaling pathways modulate the expression and activity of Pgp in response to xenobiotics and disease. A non-genetic way of intercellular transfer of Pgp occurs in cancer cells, but whether this also occurs in non-cancer cells such as endothelial cells that form the BBB is not known. A human brain endothelial cell line (hCMEC/D3) was used to study whether cell-to-cell Pgp transfer occurs during co-culturing with Pgp-EGFP expressing hCMEC/D3 cells. The Pgp-EGFP fusion protein was transferred from donor to recipient cells by cell-to-cell contact and Pgp-EGFP enriched vesicles, which were exocytosed by donor cells and endocytosed by adherent recipient cells. Flow cytometry experiments with the Pgp substrate eFLUXX-ID Gold demonstrated that the transferred Pgp is functional in the recipient cells. Exposure of the donor cells with inhibitors of histone deacetylases (HDACs) resulted in an enhanced intercellular Pgp transfer. Non-genetic transfer of a resistance phenotype and its regulation by HDACs is a novel mechanism of altering BBB functionality. This mechanism may have important implications for understanding drug-induced alterations in Pgp expression and activity.

Knockout of P-glycoprotein does not alter antiepileptic drug efficacy in the intrahippocampal kainate model of mesial temporal lobe epilepsy in mice

Pharmacoresistance to antiepileptic drugs (AEDs) is a major challenge in epilepsy therapy, affecting at least 30% of patients. Thus, there is considerable interest in the mechanisms responsible for such pharmacoresistance, with particular attention on the specific cellular and molecular factors that lead to reduced drug sensitivity. Current hypotheses of refractory epilepsy include the multidrug transporter hypothesis, which posits that increased expression or function of drug efflux transporters, such as P-glycoprotein (Pgp), in brain capillaries reduces the local concentration of AEDs in epileptic brain regions to subtherapeutic levels. In the present study, this hypothesis was addressed by evaluating the efficacy of six AEDs in wildtype and Pgp deficient Mdr1a/b(-/-) mice in the intrahippocampal kainate model of mesial temporal lobe epilepsy. In this model, frequent focal electrographic seizures develop after an initial kainate-induced status epilepticus. These seizures are resistant to major AEDs, but the mechanisms of this resistance are unknown. In the present experiments, the focal nonconvulsive seizures were resistant to carbamazepine and phenytoin, whereas high doses of valproate and levetiracetam exerted moderate and phenobarbital and diazepam marked anti-seizure effects. All AEDs suppressed generalized convulsive seizures. No significant differences between wildtype and Pgp-deficient mice were observed in anti-seizure drug efficacies. Also, the individual responder and nonresponder rates in each experiment did not differ between mouse genotypes. This does not argue against the multidrug transporter hypothesis in general, but indicates that Pgp is not involved in the mechanisms explaining that focal electrographic seizures are resistant to some AEDs in the intrahippocampal mouse model of partial epilepsy. This was substantiated by the finding that epileptic wildtype mice do not exhibit increased Pgp expression in this model.

Seizures in oligodendroglial tumors

Epilepsy develops in more than 70-90% of oligodendroglial tumors and represents a favorable indicator for long-term survival if present as the first clinical sign. Presence of IDH1 mutation is frequently associated with seizures in oligodendrogliomas, next to alterations of glutamate and GABA metabolism in the origin of glioma-associated epilepsy. Treatment by surgery or radiotherapy results in seizure freedom in about two-thirds of patients, and chemotherapy to a seizure reduction in about 50%. Symptomatic anticonvulsive therapy with levetiracetam and valproic acid as monotherapy are both evidence-based drugs for the partial epilepsies, and their effective use in brain tumors is supported by a large amount of additional data. Pharmacoresistance against anticonvulsants is more prevalent among oligodendrogliomas, occurring in about 40% despite polytherapy with two anticonvulsants or more. Toxic signs of anticonvulsants in brain tumors involve cognition, bone marrow and skin. Previous neurosurgery, radiation therapy or chemotherapy add to the risks of cognitive dysfunction.