Overexpression of multidrug resistance-associated protein 2 in the brain of pentylenetetrazole-kindled rats

In Silico and In Vivo: Evaluating the Therapeutic Potential of Kaempferol, Quercetin, and Catechin to Treat Chronic Epilepsy in a Rat Model

Recently, alternative therapies are gaining popularity in the treatment of epilepsy. The present study aimed to find out the antiepileptic potential of quercetin, catechin, and kaempferol. In vivo and in silico experiments were conducted to investigate their therapeutic potential. 25 mg/kg/day of pentylenetetrazole was administered for 4 weeks after epilepsy was induced in the rats; this was followed by the behavioral studies and histological analysis of rat brain slices. Binding affinities of kaempferol, quercetin, and catechin were assessed by performing in silico studies. Kaempferol, quercetin, and catechin were found to have the highest binding affinity with the synaptic vesicle 2A (SV2A) protein, comparable to standard levetiracetam (LEV). The mRNA levels of SV2A, as well as the expression of TNF, IL 6, IL 1 beta, NFkB, IL 1Ra, IL 4, and IL 10, were investigated using qPCR. Our results indicate for the first time that SV2A is also a transporter of understudied phytoflavonoids, due to which a significant improvement was observed in epileptic parameters. The mRNA levels of SV2A were found to be significantly elevated in the PF-treated rats when compared with those of the control rats with epilepsy. Additionally, downregulation of the pro-inflammatory cytokines and upregulation of the anti-inflammatory cytokines were also noted in the PF-treated groups. It is concluded that kaempferol, quercetin, and catechin can effectively decrease the epileptic seizures in our chronic epilepsy rat model to a level that is comparable to the antiepileptic effects induced by levetiracetam drug.

Drug-resistant epilepsy: From multiple hypotheses to an integral explanation using preclinical resources

Drug-resistant epilepsy affects approximately one-third of the patients with epilepsy. The pharmacoresistant condition in epilepsy is mainly explained by six hypotheses. In addition, several experimental models have been used to understand the mechanisms involved in pharmacoresistant epilepsy and to identify novel therapies to control this condition. However, the global prevalence of this disease persists without changes. Several factors can explain this situation. First of all, the pharmacoresistant epilepsy is explained by different and independent hypotheses. Each hypothesis indicates specific mechanisms to explain the drug-resistant condition in epilepsy. However, there are different findings suggesting common mechanisms between the different hypotheses. Other important situation is that the experimental models designed for the screening of drugs with potential anticonvulsant effect do not consider factors such as age, gender, type of epilepsy, and comorbid disorders. The present review focuses on indicating the limitations for each hypothesis and the relationships among them. The relevance to consider central and peripheral phenomena associated with the drug-resistant condition in different types of epilepsy is also indicated. The necessity to establish a global hypothesis that integrates all the phenomena associated with the pharmacoresistant epilepsy is proposed. This article is part of the Special Issue "NEWroscience 2018".

Activation of adenosine receptors modulates the efflux transporters in brain capillaries and restores the anticonvulsant effect of carbamazepine in carbamazepine resistant rats developed by window-pentylenetetrazole kindling

Up-regulation of efflux transporters in brain capillaries may lead to the decreased therapeutic efficacy of antiepileptic drugs in patients with Drug Resistant Epilepsy. Adenosine receptor activation in brain capillaries can modulate blood-brain barrier permeability by decreasing the protein levels and function of efflux transporters. Therefore, we aimed to investigate whether the activation of adenosine receptors improves convulsions outcome in carbamazepine (CBZ) resistant animals and modulates the protein levels of efflux transporters (P-GP, MRP1, MRP2) in brain capillaries. We employed the window-pentylenetetrazol (PTZ) kindling model to develop CBZ resistant rats by CBZ administration during the post-kindling phase, and tested if these animals displayed subsequent resistance to other antiepileptic drugs. Crucially, we investigated if the administration of a broad-spectrum adenosine agonist (NECA) improves convulsions control in CBZ resistant rats. Of potential therapeutic relevance, in CBZ resistant rats NECA restored the anticonvulsant effect of CBZ. We also evaluated how the resistance to CBZ and the activation of adenosine receptors with NECA affect protein levels of efflux transporters in brain capillaries, as quantified by western blot. While CBZ resistance was associated with the up-regulation of both P-GP/MRP2 in brain capillaries, with the administration of NECA in CBZ resistant rats, we observed a decrease of P-GP and an increase of MRP2 levels, in brain capillaries. Since the activation of adenosine receptors improves the outcome of convulsions probably through the modulation of the efflux transporters protein levels in brain capillaries, adenosine agonists could be useful as an adjunct therapy for the control of Drug Resistant Epilepsy.

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

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

Contributions of Drug Transporters to Blood-Brain Barriers

Blood-brain interfaces comprise the cerebral microvessel endothelium forming the blood-brain barrier (BBB) and the epithelium of the choroid plexuses forming the blood-cerebrospinal fluid barrier (BCSFB). Their main functions are to impede free diffusion between brain fluids and blood; to provide transport processes for essential nutrients, ions, and metabolic waste products; and to regulate the homeostasis of central nervous system (CNS), all of which are attributed to absent fenestrations, high expression of tight junction proteins at cell-cell contacts, and expression of multiple transporters, receptors, and enzymes. Existence of BBB is an important reason that systemic drug administration is not suitable for the treatment of CNS diseases. Some diseases, such epilepsy, Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and diabetes, alter BBB function via affecting tight junction proteins or altering expression and function of these transporters. This chapter will illustrate function of BBB, expression of transporters, as well as their alterations under disease status.

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

Background:

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

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

Objective:

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

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

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

Results:

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

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

Conclusion:

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

Altered Function and Expression of ABC Transporters at the Blood-Brain Barrier and Increased Brain Distribution of Phenobarbital in Acute Liver Failure Mice

This study investigated alterations in the function and expression of P-glycoprotein (P-GP), breast cancer resistance protein (BCRP), and multidrug resistance-associated protein 2 (MRP2) at the blood–brain barrier (BBB) of acute liver failure (ALF) mice and its clinical significance. ALF mice were developed using intraperitoneal injection of thioacetamide. P-GP, BCRP, and MRP2 functions were determined by measuring the ratios of brain-to-plasma concentration of rhodamine 123, prazosin, and dinitrophenyl-S-glutathione, respectively. The mRNA and proteins expression levels of P-GP, BCRP, and MRP2 were evaluated with quantitative real-time PCR and western blot, respectively. MDCK-MDR1 and HCMEC/D3 cells were used to document the effects of the abnormally altered components in serum of ALF mice on the function and expression of P-GP. The clinical significance of alteration in P-GP function and expression was investigated by determining the distribution of the P-GP substrate phenobarbital (60 mg/kg, intravenous administration) in the brain and loss of righting reflex (LORR) induced by the drug (100 mg/kg). The results showed that ALF significantly downregulated the function and expression of both P-GP and BCRP, but increased the function and expression of MRP2 in the brain of mice. Cell study showed that increased chenodeoxycholic acid may be a reason behind the downregulated P-GP function and expression. Compared with control mice, ALF mice showed a significantly higher brain concentration of phenobarbital and higher brain-to-plasma concentration ratios. In accordance, ALF mice showed a significantly larger duration of LORR and shorter latency time of LORR by phenobarbital, inferring the enhanced pharmacological effect of phenobarbital on the central nervous system (CNS). In conclusion, the function and expression of P-GP and BCRP decreased, while the function and expression of MRP2 increased in the brain of ALF mice. The attenuated function and expression of P-GP at the BBB might enhance phenobarbital distribution in the brain and increase phenobarbital efficacy on the CNS of ALF mice.

Significance of the expression of MRP1 and MRP2 in peripheral blood mononuclear cells of children with intractable epilepsy

Intactable epilepsy (IE) is relatively common in pediatric epilepsy. The resistance mechanism of IE has been previously investigated. Multidrug-resistant associated protein 1 (MRP1) and MRP2 are associated with drug transport. The aim of the present study was to investigate the expression of MRP1 and MRP2 in peripheral blood mononuclear cells of children with IE. Fifty outpatient or inpatient children were included in the study as the experimental group. Additionally, 50 children with epilepsy controlled by anti-epileptic drugs (AEDs) and 50 healthy children without epilepsy, who served as the control group, were included in the present study. Expression of MRP1 and MRP2 in the peripheral blood mononuclear cells of children in all the groups was detected using RT-PCR and western blot analysis. The results showed that the relative expression of MRP1 and MRP2 mRNA in the peripheral blood mononuclear cells of children with IE (MRP1, 0.795±0.042; MRP2, 0.804±0.023) was higher than that in epilepsy controlled by AEDs (MRP1, 0.682±0.030; MRP2, 0.675±0.021) and healthy children without epilepsy (MRP1, 0.665±0.031; MRP2, 0.654±0.029) (P<0.01). The mean relative expression of MRP1 and MRP2 protein in the peripheral blood mononuclear cells of children with IE (MRP1, 2.027±0.034; MRP2, 1.902±0.021) was higher than that in children with epilepsy controlled by AEDs (MRP1, 1.131±0.042; MRP2, 1.086±0.027) and healthy children without epilepsy (MRP1, 1.093±0.023; MRP2, 1.045±0.018) (P<0.01). The difference in the MRP1 and MRP2 mRNA and protein expression between the children with epilepsy controlled by AEDs and healthy children without epilepsy was not statistically significant (P>0.05). In conclusion, a higher expression of MRP1 and MRP2 in the peripheral blood mononuclear cells of children with IE may be relevant to the drug-resistant mechanism of IE.

Reversal of P-glycoprotein overexpression by Ginkgo biloba extract in the brains of pentylenetetrazole-kindled and phenytoin-treated mice

The purpose of this study was to investigate the combined effects of Ginkgo biloba extract and phenytoin (PHT) sodium as a dose regimen simulating the clinical treatment of patients with epilepsy, on P-glycoprotein (P-GP) overexpression in a pentylenetetrazole-kindled mouse model of epilepsy. Epilepsy was induced by intraperitoneal administration of pentylenetetrazole (40 mg/kg) for 7 days followed by intragastric administration of PHT (40 mg/kg) for 14 days. Thirty mice that developed seizures were randomly divided into three groups and administered PHT as well as the following treatments: saline (negative control); verapamil (20 mg/kg, positive control); and G. biloba (30 mg/kg). Seizure severity was recorded 30 minutes after treatment on Day 4 of drug administration, after which the mice were euthanized, and their brains isolated. Western blots and immunohistochemistry were performed to analyze the expression of P-GP and caspase-3, respectively, in the brain tissue. High-performance liquid chromatography was used to measure the concentrations of PHT in the brains of the treated mice. After 4 consecutive days of treatment, the seizure severity in the mice in the G. biloba extract group was more significantly reduced than the seizure severity in the saline control group, and a significant difference was observed between the G. biloba extract and verapamil control groups (p < 0.05). P-GP expression in the brain more significantly decreased in the mice treated with G. biloba extract and verapamil than it did in the saline-treated control group (p < 0.05). Compared with the saline-treated control group, the mice treated with G. biloba extract and verapamil showed significantly increased brain PHT concentrations (p < 0.05). Furthermore, caspase-3 expression in the brain tissue of the G. biloba extract group was significantly lower than that in the vehicle control group (p < 0.05); this finding demonstrated the neuroprotective effects of G. biloba. Therefore, this study showed that treatment with G. biloba extract in combination with PHT prevented the upregulation of P-GP expression in mice. Moreover, G. biloba extract decreased seizure severity in pentylenetetrazole-kindled/PHT-treated mice through a mechanism that might be related to the reduction of P-GP expression in the brain.

Pharmacoresistant Epilepsy: A Current Update on Non-Conventional Pharmacological and Non-Pharmacological Interventions

Uncontrolled seizure or epilepsy is intricately related with an increase risk of pharmacoresistant epilepsy. The failure to achieve seizure control with the first or second drug trial of an anticonvulsant medication given at the appropriate daily dosage is termed as pharmacoresistance, despite the fact that these drugs possess different modes of action. It is one of the devastating neurological disorders act as major culprit of mortality in developed as well as developing countries with towering prevalence. Indeed, the presence of several anti-epileptic drug including carbamazepine, phenytoin, valproate, gabapentin etc. But no promising therapeutic remedies available to manage pharmacoresistance in the present clinical scenario. Hence, utility of alternative strategies in management of resistance epilepsy is increased which further possible by continuing developing of promising therapeutic interventions to manage this insidious condition adequately. Strategies include add on therapy with adenosine, verapamil etc or ketogenic diet, vagus nerve stimulation, focal cooling or standard drugs in combinations have shown some promising results. In this review we will shed light on the current pharmacological and non pharmacological mediator with their potential pleiotropic action on pharmacoresistant epilepsy.

The effect of organic anion transporter 3 inhibitor probenecid on bumetanide levels in the brain: an integrated in vivo microdialysis study in the rat

Objectives

Recent data highlight the potential of bumetanide as a treatment for neonatal seizures and autism, as it facilitates the excitatory to inhibitory switch in gamma-aminobutyric acid signalling. This study examines the extent of blood-brain barrier (BBB) permeation of bumetanide, a key determinant of the efficacy of centrally acting drugs. Furthermore, the impact of efflux transporter organic anion transporter 3 (oat3) inhibition on bumetanide pharmacokinetics was investigated.

Methods

Bumetanide levels in extracellular fluid (ECF) and plasma in the presence and absence of oat3 inhibitor probenecid were monitored using integrated microdialysis.

Key findings

Following a bumetanide bolus/continuous infusion of 10 mg/kg and 6 mg/kg/h, bumetanide was detected in hippocampal ECF at the estimated concentration of 131 ± 55 ng/ml. Plasma bumetanide levels were ∼20 mg/l at steady state. Coadministration of probenecid resulted in an increase in bumetanide levels in both ECF and plasma, indicating that oat3 inhibition influences the pharmacokinetics of bumetanide primarily in the periphery.

Conclusion

Although bumetanide reached detectable levels in hippocampal ECF, bumetanide concentration in ECF was low relative to systemic concentration. Oat3 inhibition by probenecid resulted in increased bumetanide concentrations in brain and plasma. As an acute treatment in neonatal seizures, the bumetanide/probenecid combination may hold therapeutic potential.

Hyperammonemia enhances the function and expression of P-glycoprotein and Mrp2 at the blood-brain barrier through NF-κB

Ammonia is considered to be the main neurotoxin responsible for hepatic encephalopathy resulting from liver failure. Liver failure has been reported to alter expression and activity of P-glycoprotein (P-gp) and multidrug resistance-associated protein 2 (Mrp2) at the blood-brain barrier (BBB). The aim of this study was to investigate whether ammonia is involved in abnormalities of expression and activity of P-gp and Mrp2 at the BBB. Hyperammonemic rats were developed by an intraperitoneal injection of ammonium acetate (NH4 Ac, 4.5 mmol/kg). Results showed that Mrp2 function markedly increased in cortex and hippocampus of rats at 6 h following NH4 Ac administration. Significant increase in function of P-gp was observed in hippocampus of rats. Meanwhile, such alterations were in line with the increase in mRNA and protein levels of P-gp and Mrp2. Significant increase in levels of nuclear amount of nuclear factor-κB (NF-κB) p65 was also observed. Primarily cultured rat brain microvessel endothelial cells (rBMECs) were used for in vitro study. Data indicated that 24 h exposure to ammonia significantly increased function and expression of P-gp and Mrp2 in rBMECs, accompanied with activation of NF-κB. Furthermore, such alterations induced by ammonia were reversed by NF-κB inhibitor. In conclusion, this study demonstrates that hyperammonemia increases the function and expression of P-gp and Mrp2 at the BBB via activating NF-κB pathway. Hyperammonemia, a proverbial main factor responsible for neurocognitive disorder and blood-brain barrier (BBB) dysfunction resulting from liver failure, could increase the expression and activity of P-glycoprotein and multidrug resistance-associated protein 2 (Mrp2) at the BBB both in vivo and in vitro. Furthermore, the NF-κB activation stimulated by hyperammonemia may be the potential mechanism underlying such abnormalities induced by hyperammonemia.