Inhibition of the Multidrug Transporter P-Glycoprotein Improves Seizure Control in Phenytoin-treated Chronic Epileptic Rats

Tolerability of tariquidar - A third generation P-gp inhibitor as add-on medication to antiseizure medications in drug-resistant epilepsy

PURPOSE

P-glycoprotein (P-gp) has been hypothesized to be involved in drug-resistance of epilepsy by actively extruding antiseizure medications (ASMs) from the brain. The P-gp inhibitor tariquidar (TQD) has been shown to effectively inhibit P-gp at the human blood-brain barrier, improving brain entry of several ASMs. A potential strategy to overcome drug-resistance is the co-administration of P-gp inhibitors such as TQD to ASMs. Here we present data on the tolerability of single-dose TQD as a potential add-on medication to ASMs.

METHODS

We performed a multi-centre cohort study including drug-resistant epilepsy patients and healthy controls from the United Kingdom and Austria. TQD was administered intravenously at five different doses (2 mg/kg or 3 mg/kg of TQD were given to drug-resistant epilepsy patients and healthy controls, higher doses of TQD at 4 mg/kg, 6 mg/kg and 8 mg/kg as well as a prolonged infusion aiming at a dose of 6 mg/kg were only given to healthy controls). Adverse events were recorded and graded using the Common Terminology Criteria (CTCAE) scale. Additionally, TQD plasma concentration levels were measured and compared between drug-resistant patients and healthy controls.

RESULTS

In total, 108 participants received TQD once at variable doses and it was overall well tolerated. At doses of 2 or 3 mg/kg TQD, only two of the 19 drug-resistant epilepsy patients and a third of the healthy controls (n = 14/42) reported adverse events probably related to TQD. The majority of those adverse events (96 %) were reported as mild. One drug-resistant epilepsy patient reported adverse events 24-hours after TQD administration possibly related to TQD-induced increased ASMs levels in the brain.

CONCLUSIONS

TQD is an effective and well tolerated P-gp inhibitor as a single dose and could potentially be used intermittently in conjunction with ASMs to improve efficacy. This promising strategy to overcome drug-resistance in epilepsy should be investigated further in clinical randomised controlled trials.

A Narrative Review of the Published Pre-Clinical Evaluations: Multiple Effects of Arachidonic Acid, its Metabolic Enzymes and Metabolites in Epilepsy

Arachidonic acid (AA), an important polyunsaturated fatty acid in the brain, is hydrolyzed by a direct action of phospholipase A2 (PLA2) or through the combined action of phospholipase C and diacylglycerol lipase, and released into the cytoplasm. Various derivatives of AA can be synthesized mainly through the cyclooxygenase (COX), lipoxygenase (LOX) and cytochrome P450 (P450) enzyme pathways. AA and its metabolic enzymes and metabolites play important roles in a variety of neurophysiological activities. The abnormal metabolites and their catalytic enzymes in the AA cascade are related to the pathogenesis of various central nervous system (CNS) diseases, including epilepsy. Here, we systematically reviewed literatures in PubMed about the latest randomized controlled trials, animal studies and clinical studies concerning the known features of AA, its metabolic enzymes and metabolites, and their roles in epilepsy. The exclusion criteria include non-original studies and articles not in English.

Epilepsy in Africa: a multifaceted perspective on diagnosis, treatment, and community support

Epilepsy is the most widespread neurological disorder in Africa, affecting an estimated 25 million people. The disorder is characterized by recurrent seizures, which can be caused by a variety of factors, including past trauma, central nervous system infections, and genetic disorders. Diagnosis and treatment of epilepsy are challenging in African patients due to several factors, including the low socioeconomic status of the residents and limited access to appropriate medication. Phenobarbital remains the only drug widely available to patients, but it is not always effective and can have significant side effects. In addition to the medical challenges, individuals with epilepsy also face a lot of social stigmas in Africa. Widespread superstitions and false beliefs lead to prejudices against these people, making it difficult for them to live fulfilling social lives. With the development of new treatment modalities, such as gene therapy, stem cell therapy, and P-glycoprotein inhibitors, it is more important now than ever to increase the research output for the African region to create the best possible treatment and maximize patient outcomes.

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.

Simulated Microgravity Alters P-Glycoprotein Efflux Function and Expression via the Wnt/β-Catenin Signaling Pathway in Rat Intestine and Brain

The drug efflux transporter permeability glycoprotein (P-gp) plays an important role in oral drug absorption and distribution. Under microgravity (MG), the changes in P-gp efflux function may alter the efficacy of oral drugs or lead to unexpected effects. Oral drugs are currently used to protect and treat multisystem physiological damage caused by MG; whether P-gp efflux function changes under MG remains unclear. This study aimed to investigate the alteration of P-gp efflux function, expression, and potential signaling pathway in rats and cells under different simulated MG (SMG) duration. The altered P-gp efflux function was verified by the in vivo intestinal perfusion and the brain distribution of P-gp substrate drugs. Results showed that the efflux function of P-gp was inhibited in the 7 and 21 day SMG-treated rat intestine and brain and 72 h SMG-treated human colon adenocarcinoma cells and human cerebral microvascular endothelial cells. P-gp protein and gene expression levels were continually down-regulated in rat intestine and up-regulated in rat brain by SMG. P-gp expression was regulated by the Wnt/β-catenin signaling pathway under SMG, verified by a pathway-specific agonist and inhibitor. The elevated intestinal absorption and brain distribution of acetaminophen levels also confirmed the inhibited P-gp efflux function in rat intestine and brain under SMG. This study revealed that SMG alters the efflux function of P-gp and regulates the Wnt/β-catenin signaling pathway in the intestine and the brain. These findings may be helpful in guiding the use of P-gp substrate drugs during spaceflight.

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

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

P-glycoprotein: new insights into structure, physiological function, regulation and alterations in disease

The multidrug resistance phenomenon presents a major threat to the pharmaceutical industry. This resistance is a common occurrence in several diseases and is mediated by multidrug transporters that actively pump substances out of the cell and away from their target regions. The most well-known multidrug transporter is the P-glycoprotein transporter. The binding sites within P-glycoprotein can accommodate a variety of compounds with diverse structures. Hence, numerous drugs are P-glycoprotein substrates, with new ones being identified every day. For many years, the mechanisms of action of P-glycoprotein have been shrouded in mystery, and scientists have only recently been able to elucidate certain structural and functional aspects of this protein. Although P-glycoprotein is highly implicated in multidrug resistant diseases, this transporter also performs various physiological roles in the human body and is expressed in several tissues, including the brain, kidneys, liver, gastrointestinal tract, testis, and placenta. The expression levels of P-glycoprotein are regulated by different enzymes, inflammatory mediators and transcription factors; alterations in which can result in the generation of a disease phenotype. This review details the discovery, the recently proposed structure and the regulatory functions of P-glycoprotein, as well as the crucial role it plays in health and disease.

A sensitive LC-MS/MS method for quantification of phenytoin and its major metabolite with application to in vivo investigations of intravenous and intranasal phenytoin delivery

Phenytoin is a powerful antiseizure drug with complex pharmacokinetic properties, making it an interesting model drug to use in preclinical in vivo investigations, especially with regards to formulations aiming to improve drug delivery to the brain. Moreover, it has a major metabolite, 5‐(4‐hydroxyphenyl)‐5‐phenylhydantoin, which can be simultaneously studied to achieve a better assessment of its behaviour in the body. Here, we describe the development and validation of a sensitive LCMS/MS method for quantification of phenytoin and 5‐(4‐hydroxyphenyl)‐5‐phenylhydantoin in rat plasma and brain which can be used in such preclinical studies. Calibration curves produced covered a range of 7.81 to 250 ng/mL (plasma) and 23.4 to 750 ng/g (brain tissue) for both analytes. The method was validated for specificity, sensitivity, accuracy, and precision and found to be within the acceptable limits of ±15% over this range in both tissue types. The method when applied in two in vivo investigations: validation of a seizure model and to study the behaviour of a solution of intranasally administered phenytoin as a foundation for future studies into direct nose‐to‐brain delivery of phenytoin using specifically developed particulate systems, was highly sensitive for detecting phenytoin and 5‐(4‐hydroxyphenyl)‐5‐phenylhydantoin in rat plasma and brain.

The ABCB1, ABCC2 and RALBP1 polymorphisms are associated with carbamazepine response in epileptic patient: a systematic review

Despite a dramatic increase in treatment options over the past 30 years, Carbamazepine (CBZ) is still considered the standard of care and the most prescribed initial treatment for focal epilepsy. Hence, the identification of genetic biomarkers that influence the response, resistance and toxicity to CBZ remains a challenge. Several research studies have looked into this to highlight the polymorphisms responsible for the variability in the response to CBZ in patients with epilepsy. The aim of this review is to compare the different results published in the literature The systematic review included thirty-nine studies (2005-2021), Meta-analyses were performed on more than twelve polymorphisms in three genes (ABCB1, ABCC2, RALBP1) involved in CBZ cell transport. The current challenges are to identify other new biomarkers of antiepileptic drugs that can only materialize with large-scale collaborative research efforts.

Emerging therapeutic targets for epilepsy: Preclinical insights

INTRODUCTION

Around 30% of patients with epilepsy suffer from drug-resistant seizures. Drug-resistant seizures may have significant consequences such as sudden death in epilepsy, injuries, memory disturbances, and childhood learning and developmental problems. Conventional and newer available antiepileptic drugs (AEDs) work via numerous mechanisms - mainly through inhibition of voltage-operated Na⁺ and/or Ca²⁺ channels, excitation of K⁺ channels, enhancement of GABA-mediated inhibition and/or blockade of glutamate-produced excitation. However, the discovery and development of novel brain targets may improve the future pharmacological management of epilepsy and hence is of pivotal importance.

AREAS COVERED

This article examines novel drug targets such as brain multidrug efflux transporters and inflammatory pathways; it progresses to discuss possible strategies for the management of drug-resistant seizures. Reduction of the consequences of blood brain barrier dysfunction and enhancement of anti-oxidative defense are discussed.

EXPERT OPINION

Novel drug targets comprise brain multidrug efflux transporters, TGF-β, Nrf2-ARE or m-TOR signaling and inflammatory pathways. Gene therapy and antagomirs seem the most promising targets. Epileptic foci may be significantly suppressed by viral-vector-mediated gene transfer, leading to an increased in situ concentration of inhibitory factors (for instance, galanin). Also, antagomirs offer a promising possibility of seizure inhibition by silencing micro-RNAs involved in epileptogenesis and possibly in seizure generation.

Pharmacogenetics of Drug-Resistant Epilepsy (Review of Literature)

Pharmacogenomic studies in epilepsy are justified by the high prevalence rate of this disease and the high cost of its treatment, frequent drug resistance, different response to the drug, the possibility of using reliable methods to assess the control of seizures and side effects of antiepileptic drugs. Candidate genes encode proteins involved in pharmacokinetic processes (drug transporters, metabolizing enzymes), pharmacodynamic processes (receptors, ion channels, enzymes, regulatory proteins, secondary messengers) and drug hypersensitivity (immune factors). This article provides an overview of the literature on the influence of genetic factors on treatment in epilepsy.

Multi-omic strategies applied to the study of pharmacoresistance in mesial temporal lobe epilepsy

Mesial temporal lobe epilepsy (MTLE) is the most common type of focal epilepsy in adults, and hippocampal sclerosis (HS) is a frequent histopathological feature in patients with MTLE. Pharmacoresistance is present in at least one-third of patients with MTLE with HS (MTLE+HS). Several hypotheses have been proposed to explain the mechanisms of pharmacoresistance in epilepsy, including the effect of genetic and molecular factors. In recent years, the increased knowledge generated by high-throughput omic technologies has significantly improved the power of molecular genetic studies to discover new mechanisms leading to disease and response to treatment. In this review, we present and discuss the contribution of different omic modalities to understand the basic mechanisms determining pharmacoresistance in patients with MTLE+HS. We provide an overview and a critical discussion of the findings, limitations, new approaches, and future directions of these studies to improve the understanding of pharmacoresistance in MTLE+HS. However, it is important to point out that, as with other complex traits, pharmacoresistance to anti-seizure medications is likely a multifactorial condition in which gene-gene and gene-environment interactions play an important role. Thus, studies using multidimensional approaches are more likely to unravel these intricate biological processes.

Understanding mechanisms of drug resistance in epilepsy and strategies for overcoming it

INTRODUCTION

The present evidence indicates that approximately 70% of patients with epilepsy can be successfully treated with antiepileptic drugs (AEDs). A significant proportion of patients are not under sufficient control, and pharmacoresistant epilepsy is clearly associated with poor quality of life and increased morbidity and mortality. There is a great need for newer therapeutic options able to reduce the percentage of drug-resistant patients.

AREAS COVERED

A number of hypotheses trying to explain the development of pharmacoresistance have been put forward. These include: target hypothesis (altered AED targets), transporter (overexpression of brain efflux transporters), pharmacokinetic (overexpression of peripheral efflux transporters in the intestine or kidneys), intrinsic severity (initial high seizure frequency), neural network (aberrant networks), and gene variant hypothesis (genetic polymorphisms).

EXPERT OPINION

A continuous search for newer AEDs or among non-AEDs (blockers of efflux transporters, interleukin antagonists, cyclooxygenase inhibitors, mTOR inhibitors, angiotensin II receptor antagonists) may provide efficacious drugs for the management of drug-resistant epilepsy. Also, combinations of AEDs exerting synergy in preclinical and clinical studies (for instance, lamotrigine + valproate, levetiracetam + valproate, topiramate + carbamazepine) might be of importance in this respect. Preclinically antagonistic combinations must be avoided (lamotrigine + carbamazepine, lamotrigine + oxcarbazepine).

Chronic limbic epilepsy models for therapy discovery: Protocols to improve efficiency

OBJECTIVE

There have been recommendations to improve therapy discovery for epilepsy by incorporating chronic epilepsy models into the preclinical process, but unpredictable seizures and difficulties in maintaining drug levels over prolonged periods have been obstacles to using these animals. We report new protocols in which drugs are administered through a new chronic gastric tube to rats with higher seizure frequencies to minimize these obstacles.

METHODS

Adult rats with spontaneous limbic seizures following an episode of limbic status epilepticus induced by electrical hippocampal stimulation were monitored with long-term video- electroencephalography (EEG). Animals with a predetermined baseline seizure frequency received an intragastric tube for drug administration. Carbamazepine, levetiracetam, phenobarbital, and phenytoin were tested with either an acute protocol (an increasing single dose every other day for a maximum of three doses) or with a chronic protocol (multiple administrations of one dose for a week). Drug levels were obtained to correlate the effect with the level.

RESULTS

With the acute protocol, all four drugs induced a clear dose-related response. Similar dose-related responses were seen following the week-long dosing protocol for carbamazepine, phenobarbital, and phenytoin, and these responses were associated with drug levels that were in the human therapeutic range. The response to chronic levetiracetam was much less robust. The gastric tube route of administration was well tolerated over a number of months.

SIGNIFICANCE

Using rats with stable, higher seizure frequencies made it possible to identify the potential of a drug to suppress seizures in a realistic model of epilepsy with drug levels that are similar to those of human therapeutic levels. The acute protocol provided a full dose response in 1 week. The chronic administration protocol further differentiated drugs that may be effective long term. The gastric tube facilitates a less stressful, humane, and consistent administration of multiple doses.

Direct N1-Selective Alkylation of Hydantoins Using Potassium Bases

Hydantoins, including the antiepileptic drug phenytoin, contain an amide nitrogen and an imide nitrogen, both of which can be alkylated. However, due to the higher acidity of its proton, N³ can be more easily alkylated than N¹ under basic conditions. In this study, we explored methods for direct N¹-selective methylation of phenytoin and found that conditions using potassium bases [potassium tert-butoxide (^tBuOK) and potassium hexamethyldisilazide (KHMDS)] in tetrahydrofuran (THF) gave N¹-monomethylated phenytoin in good yield. The applicable scope of this reaction system was found to include various hydantoins and alkyl halides. To explore the function of methylated hydantoins, the effects of a series of methylated phenytoins on P-glycoprotein were examined, but none of methylated products showed inhibitory activity toward rhodamine 123 efflux by P-glycoprotein.

The Influence of Pharmacogenetics on the Clinical Relevance of Pharmacokinetic Drug-Drug Interactions: Drug-Gene, Drug-Gene-Gene and Drug-Drug-Gene Interactions

Drug interactions are a well-known cause of adverse drug events, and drug interaction databases can help the clinician to recognize and avoid such interactions and their adverse events. However, not every interaction leads to an adverse drug event. This is because the clinical relevance of drug-drug interactions also depends on the genetic profile of the patient. If inhibitors or inducers of drug metabolising enzymes (e.g., CYP and UGT) are added to the drug therapy, phenoconcversion can occur. This leads to a genetic phenotype that mismatches the observable phenotype. Drug-drug-gene and drug-gene-gene interactions influence the toxicity and/or ineffectivness of the drug therapy. To date, there have been limited published studies on the impact of genetic variations on drug-drug interactions. This review discusses the current evidence of drug-drug-gene interactions, as well as drug-gene-gene interactions. Phenoconversion is explained, the and methods to calculate the phenotypes are described. Clinical recommendations are given regarding the integratation of the PGx results in the assessment of the relevance of drug interactions in the future.

Association between ABCB1 polymorphisms and response to antiepileptic drugs among Jordanian epileptic patients

BACKGROUND

Genetic polymorphisms of drug efflux transporters as ATP-binding cassette subfamily B, member 1 (ABCB1) have been suggested to modulate antiepileptic drugs (AEDs) response. We aimed to explore the association of ABCB1 polymorphisms and AEDs resistance among epileptic patients.

METHODS

A total of 86 Jordanian epileptic patients treated with AEDs was included in the study. DNA was extracted from blood samples and genotyping and haplotypes analyses were conducted for Nine single nucleotide polymorphisms (SNPs) on the ABCB1 gene.

RESULTS

Data revealed that none of the examined SNPs were associated with resistance to AEDs neither on the level of alleles nor genotypes. However, strong association was found between rs2235048 (OR = 10.6; 95%CI = [1.89-59.8], p= 0.01), rs1045642 (OR = 14; 95%CI = [1.3-156.7], p= 0.02), rs2032582 (OR = 9.1; 95%CI = [1.4-57.3], p= 0.04) and rs1128503 (OR = 18.7; 95%CI = [1.6-222.9], p= 0.02), ABCB1 polymorphisms and resistance to AEDs among females but not males. Haplotype analysis revealed statistically significant associations. The strongest significant associations were for haplotypes containing 2677G_1236 T in two-SNPshaplotypes (OR = 4.2; 95%CI = [1.2-14.9], p = 0.024); three-SNPs-haplotypes (OR = 4.2; 95% CI = [1.2-14.9], p = 0.02); four-SNPs-haplotypes (OR = 4.1; 95%CI = [1.2-14.3], p = 0.026).

CONCLUSION

Data suggests that there is a gender dependent association between ABCB1 genetic polymorphisms and response to AEDs. Additionally, ABCB1 haplotypes influence the response to AEDs. Further investigation is needed to confirm the results of this study.

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.

Relationship between Delta Rhythm, Seizure Occurrence and Allopregnanolone Hippocampal Levels in Epileptic Rats Exposed to the Rebound Effect

Abrupt withdrawal from antiepileptic drugs is followed by increased occurrence of epileptic seizures, a phenomenon known as the “rebound effect”. By stopping treatment with levetiracetam (LEV 300 mg/kg/day, n = 15; vs. saline, n = 15), we investigated the rebound effect in adult male Sprague-Dawley rats. LEV was continuously administered using osmotic minipumps, 7 weeks after the intraperitoneal administration of kainic acid (15 mg/kg). The effects of LEV were determined by comparing time intervals, treatments, and interactions between these main factors. Seizures were evaluated by video-electrocorticographic recordings and power band spectrum analysis. Furthermore, we assessed endogenous neurosteroid levels by liquid chromatography-electrospray-tandem mass spectrometry. LEV significantly reduced the percentage of rats experiencing seizures, reduced the seizure duration, and altered cerebral levels of neurosteroids. In the first week of LEV discontinuation, seizures increased abruptly up to 700% (p = 0.002, Tukey’s test). The power of delta band in the seizure postictal component was related to the seizure occurrence after LEV withdrawal (r² = 0.73, p < 0.001). Notably, allopregnanolone hippocampal levels were positively related to the seizure occurrence (r² = 0.51, p = 0.02) and to the power of delta band (r² = 0.67, p = 0.004). These findings suggest a role for the seizure postictal component in the rebound effect, which involves an imbalance of hippocampal neurosteroid levels.

Noninvasive transcranial focal stimulation affects the convulsive seizure-induced P-glycoprotein expression and function in rats

Transcranial focal stimulation (TFS) is a noninvasive neuromodulation strategy that reduces seizure activity in different experimental models. Nevertheless, there is no information about the effects of TFS in the drug-resistant phenotype associated with P-glycoprotein (Pgp) overexpression. The present study focused on determining the effects of TFS on Pgp expression after an acute seizure induced by 3-mercaptopropionic acid (MPA). P-glycoprotein expression was analyzed by western blot in the cerebral cortex and hippocampus of rats receiving 5 min of TFS (300 Hz, 50 mA, 200 μs, biphasic charge-balanced squared pulses) using a tripolar concentric ring electrode (TCRE) prior to administration of a single dose of MPA. An acute administration of MPA induced Pgp overexpression in cortex (68 ± 13.4%, p < 0.05 vs the control group) and hippocampus (48.5 ± 14%, p < 0.05, vs the control group). This effect was avoided when TFS was applied prior to MPA. We also investigated if TFS augments the effects of phenytoin in an experimental model of drug-resistant seizures induced by repetitive MPA administration. Animals with MPA-induced drug-resistant seizures received TFS alone or associated with phenytoin (75 mg/kg, i.p.). TFS alone did not modify the expression of the drug-resistant seizures. However, TFS combined with phenytoin reduced seizure intensity, an effect associated with a lower prevalence of major seizures (50%, p = 0.03 vs phenytoin alone). Our experiments demonstrated that TFS avoids the Pgp overexpression induced after an acute convulsive seizure. In addition, TFS augments the phenytoin effects in an experimental model of drug-resistant seizures. According with these results, it is indicated that TFS may represent a new neuromodulatory strategy to revert the drug-resistant phenotype.

Astrocytes as Guardians of Neuronal Excitability: Mechanisms Underlying Epileptogenesis

Astrocytes are key homeostatic regulators in the central nervous system and play important roles in physiology. After brain damage caused by e.g., status epilepticus, traumatic brain injury, or stroke, astrocytes may adopt a reactive phenotype. This process of reactive astrogliosis is important to restore brain homeostasis. However, persistent reactive astrogliosis can be detrimental for the brain and contributes to the development of epilepsy. In this review, we will focus on physiological functions of astrocytes in the normal brain as well as pathophysiological functions in the epileptogenic brain, with a focus on acquired epilepsy. We will discuss the role of astrocyte-related processes in epileptogenesis, including reactive astrogliosis, disturbances in energy supply and metabolism, gliotransmission, and extracellular ion concentrations, as well as blood-brain barrier dysfunction and dysregulation of blood flow. Since dysfunction of astrocytes can contribute to epilepsy, we will also discuss their role as potential targets for new therapeutic strategies.

The Relationship Between Clinico-Pathological Properties and p-Glycoprotein Expression in Hippocampal Sclerosis Among Patients with Mesial Temporal Lobe Epilepsy Who Undergo Selective Amygdalohippocampectomy Operation

INTRODUCTION

The overproduction of the efflux transporters in the blood-brain barrier is considered to play a role in the development of drug resistance in mesial temporal lobe epilepsy (MTLE) patients. The aim of the present study was to investigate the relationship of clinical features of patients with MTLE accompanied by hippocampal sclerosis (HS) and the p-glycoprotein (p-gp) expression and neuronal loss in the hippocampus.

METHODS

This study included a total of 33 patients who underwent selective amygdala-hippocampectomy operation. A detailed medical history of each patient, including age, side of HS, sex, age of habitual seizure onset, duration of habitual seizures, type and age of initial precipitating injury, presence and duration of latent period, presence and duration of silent period, monthly seizure frequency within 1 year prior to operation, mean age at the time of operation was evaluated retrospectively.

RESULTS

The p-gp expression was significantly higher in the patient group with a seizure frequency of more than 15 days per month and a disease duration of more than 20 years. There was no significant difference between the p-gp expression and the clinical features of the MTLE-HS patients.

CONCLUSION

These results suggest that p-gp expression is affected by disease duration and seizure frequency rather than a patient's clinical and pathological properties. In patients with HS-MTLE, potential use of the p-gp inhibitors as additional therapy and developing novel drugs not carried by multidrug carriers expressed in blood-brain barrier should be regarded as the new treatment targets.

The evolution of the pilocarpine animal model of status epilepticus

The pilocarpine animal model of status epilepticus is a well-established, clinically translatable model that satisfies all of the criteria essential for an animal model of status epilepticus: a latency period followed by spontaneous recurrent seizures, replication of behavioural, electrographic, metabolic, and neuropathological changes, as well as, pharmacoresistance to anti-epileptic drugs similar to that observed in human status epilepticus. However, this model is also characterized by high mortality rates and studies in recent years have also seen difficulties in seizure induction due to pilocarpine resistant animals. This can be attributed to differences in rodent strains, species, gender, and the presence of the multi-transporter, P-glycoprotein at the blood brain barrier. The current paper highlights the various alterations made to the original pilocarpine model over the years to combat both the high mortality and low induction rates. These range from the initial lithium-pilocarpine model to the more recent Reduced Intensity Status Epilepticus (RISE) model, which finally brought the mortality rates down to 1%. These modifications are essential to improve animal welfare and future experimental outcomes.

Long Non-coding RNA KCNQ1OT1 Contributes to Antiepileptic Drug Resistance Through the miR-138-5p/ABCB1 Axis in vitro

Compelling evidence has verified that long non-coding RNAs (lncRNAs) play a critical role on drug resistance in various diseases, especially cancer. However, the role of lncRNAs underlying multidrug resistance in epilepsy remains to be clarified. In the present study, we investigated the potential regulatory mechanism of the lncRNA KCNQ1OT1 in regulating antiepileptic drug (AED) resistance in human brain microvascular endothelial cells (HBMECs). The results revealed that expression of P-glycoprotein (P-gp) and KCNQ1OT1 was significantly elevated in phenytoin-resistant HBMECs (HBMEC/PHT). Meanwhile, the activity of nuclear factor-kappa B (NF-κB) was increased in HBMECs/PHT cells. Microarray analysis indicated that miR-138-5p was downregulated in HBMEC/PHT cells. Interestingly, bioinformatics prediction tools indicated miR-138-5p could directly target the transcripts of KCNQ1OT1 and NF-κB p65, and these results were confirmed by luciferase assays. Moreover, KCNQ1OT1 downregulation or miR-138-5p upregulation in vitro could inhibit P-gp expression and suppress NF-κB signaling pathway activation. Additionally, knockdown of KCNQ1OT1 or overexpression of miR-138-5p could increase the accumulation of rhodamine 123 (Rh123) and AEDs in HBMEC/PHT cells. Collectively, our results suggested that KCNQ1OT1 contributes to AED resistance through the miR-138-5p/NF-κB/ABCB1 axis in HBMEC/PHT cells, and these results provide a promising therapeutic target for the treatment of medically intractable epilepsy.

Cyclooxygenase-2 (COX-2) inhibitors: future therapeutic strategies for epilepsy management

Epilepsy, a common multifactorial neurological disease, affects about 69 million people worldwide constituting nearly 1% of the world population. Despite decades of extensive research on understanding its underlying mechanism and developing the pharmacological treatment, very little is known about the biological alterations leading to epileptogenesis. Due to this gap, the currently available antiepileptic drug therapy is symptomatic in nature and is ineffective in 30% of the cases. Mounting evidences revealed the pathophysiological role of neuroinflammation in epilepsy which has shifted the focus of epilepsy researchers towards the development of neuroinflammation-targeted therapeutics for epilepsy management. Markedly increased expression of key inflammatory mediators in the brain and blood-brain barrier may affect neuronal function and excitability and thus may increase seizure susceptibility in preclinical and clinical settings. Cyclooxygenase-2 (COX-2), an enzyme synthesizing the proinflammatory mediators, prostaglandins, has widely been reported to be induced during seizures and is considered to be a potential neurotherapeutic target for epilepsy management. However, the efficacy of such therapy involving COX-2 inhibition depends on various factors viz., therapeutic dose, time of administration, treatment duration, and selectivity of COX-2 inhibitors. This article reviews the preclinical and clinical evidences supporting the role of COX-2 in seizure-associated neuroinflammation in epilepsy and the potential clinical use of COX-2 inhibitors as a future strategy for epilepsy treatment.

Cytosolic phospholipase A2 is a key regulator of blood-brain barrier function in epilepsy

Blood-brain barrier dysfunction in epilepsy contributes to seizures and resistance to antiseizure drugs. Reports show that seizures increase brain glutamate levels, leading to barrier dysfunction. One component of barrier dysfunction is overexpression of the drug efflux transporters P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP). Based on our previous studies, we hypothesized that glutamate released during seizures activates cytosolic phospholipase A2 (cPLA2), resulting in P-gp and BCRP overexpression. We exposed isolated rat brain capillaries to glutamate ex vivo and used an in vivo-ex vivo approach of isolating brain capillaries from rats after status epilepticus (SE) and in chronic epileptic (CE) rats. Glutamate increased cPLA2, P-gp, and BCRP protein and activity levels in isolated brain capillaries. We confirmed the role of cPLA2 in the signaling pathway in brain capillaries from male and female mice lacking cPLA2. We also demonstrated, in vivo, that cPLA2 inhibition prevents overexpression of P-gp and BCRP at the blood-brain barrier in rats after status epilepticus and in CE rats. Our data support the hypothesis that glutamate signals cPLA2 activation, resulting in overexpression of blood-brain barrier P-gp and BCRP.-Hartz, A. M. S., Rempe, R. G., Soldner, E. L. B., Pekcec, A., Schlichtiger, J., Kryscio, R., Bauer, B. Cytosolic phospholipase A2 is a key regulator of blood-brain barrier function in epilepsy.

ABC Transporter-Mediated Multidrug-Resistant Cancer

ATP-binding cassette (ABC) transporters are involved in active pumping of many diverse substrates through the cellular membrane. The transport mediated by these proteins modulates the pharmacokinetics of many drugs and xenobiotics. These transporters are involved in the pathogenesis of several human diseases. The overexpression of certain transporters by cancer cells has been identified as a key factor in the development of resistance to chemotherapeutic agents. In this chapter, the localization of ABC transporters in the human body, their physiological roles, and their roles in the development of multidrug resistance (MDR) are reviewed. Specifically, P-glycoprotein (P-GP), multidrug resistance-associated proteins (MRPs), and breast cancer resistance protein (BCRP/ABCG2) are described in more detail. The potential of ABC transporters as therapeutic targets to overcome MDR and strategies for this purpose are discussed as well as various explanations for the lack of efficacy of ABC drug transporter inhibitors to increase the efficiency of chemotherapy.

Pharmacoresistance - Epidemiology, mechanisms, and impact on epilepsy treatment

Understanding the natural history of and factors associated with pharmacoresistant epilepsy provides the foundation for formulating mechanistic hypotheses that can be evaluated to drive the development of novel treatments. This article reviews the modern definition of drug-resistant epilepsy, its prevalence and incidence, risk factors, hypothesized mechanisms, and the implication of recognizing pharmacoresistance in therapeutic strategies. This article is part of the special issue entitled 'New Epilepsy Therapies for the 21st Century - From Antiseizure Drugs to Prevention, Modification and Cure of 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.

Silymarin as a flavonoid-type P-glycoprotein inhibitor with impact on the pharmacokinetics of carbamazepine, oxcarbazepine and phenytoin in rats

P-glycoprotein (P-gp) is an efflux transporter involved in drug-resistant epilepsy and some flavonoids have been targeted as effective P-gp inhibitors. Herein, we assessed the impact of silymarin on the pharmacokinetics of three antiepileptic drugs (AEDs) in rats. Animals were pretreated with silymarin, verapamil (positive control) or vehicle (negative control) 1 h before AEDs administration (carbamazepine (25 mg/kg), oxcarbazepine (OXC) (50 mg/kg), or phenytoin (100 mg/kg)). Multiple blood samples were collected after AED dosing, and a non-compartmental analysis was performed. An independent study was also conducted to investigate the effects of silymarin on the OXC plasma-to-brain distribution. Silymarin altered the pharmacokinetics of OXC, increasing its peak plasma concentration by 50% and its extent of systemic exposure by 41%, which had also impact on brain drug concentrations. These findings support that the co-administration of silymarin and OXC should continue to be explored as a strategy to reverse the pharmacoresistance in epilepsy.

Variability in expression of the human MDR1 drug efflux transporter and genetic variation of the ABCB1 gene: implications for drug-resistant epilepsy

Among individuals diagnosed with epilepsy, as many as one in three develop resistance to antiepileptic drugs (AEDs) thus rendering their seizures refractory to treatment. Despite current antiepileptic drugs (AEDs) having a variety of modes of action, seizures in drug-resistant individuals often persist even after treatment with two or more drugs. The underlying cause of this broad resistance is currently under debate, but two dominant theories have emerged and have been widely studied. Here we discuss current literature investigating the "transporter theory", the idea that individuals present with drug resistance due to genetic variability in the ABCB1 gene encoding the efflux transporter multidrug resistance protein 1 (MDR1). Results of in vitro and in vivo studies suggest that variability in the expression of the MDR1 transporter may be closely tied to drug resistance. While there is much support for this hypothesis from molecular and mechanistic studies, population-based studies of ABCB1 polymorphisms are divergent in their conclusions, and there is need for additional investigations.

Understanding the controversial drug targets in epilepsy and pharmacoresistant epilepsy

Accumulating experimental data suggests a number of successful drug targets against epilepsy which eventually failed in the clinical setup. Mammalian target of rapamycin inhibitors, multi-drug resistance transporter inhibitors, cyclo-oxygenase-2 inhibitors, statins, etc. are the most promising and well studied among them. Drugs aiming at these targets produced beneficial response in most of the in vitro and in vivo seizure models. However, in certain situations, they have produced differential rather controversial results. Their effects varied with the seizure model, species, time and route of administration, different drugs from the same class, etc. This review emphasises on such drugs which presented with variability in their beneficial effects against seizures and epilepsy. This review critically summarises the preclinical evidence of these targets in the context of seizures and the probable reasons for their variability and clinical failures.

MicroRNA-298 Reverses Multidrug Resistance to Antiepileptic Drugs by Suppressing MDR1/P-gp Expression in vitro

P-glycoprotein (P-gp), a critical multidrug transporter, recognizes and transports various antiepileptic drugs (AEDs) through the blood-brain barrier (BBB). This may decrease the concentrations of AEDs in brain tissues and cause multidrug resistance (MDR) in patients with refractory epilepsy. Compelling evidence indicates that microRNAs (miRNAs) modulate MDR in various cancers by regulating P-gp expression. Furthermore, a previous study showed that miR-298 mediates MDR in breast cancer cells by downregulating P-gp expression. Based on the therapeutic results obtained from tumor cells, we aimed to determine whether miR-298 reverses MDR to AEDs by regulating P-gp expression in the BBB. We first established different drug-resistant cell lines, including PHT-resistant HBMECs (human brain microvascular endothelial cells) and doxorubicin (DOX)-resistant U87-MG (human malignant glioma) cells, by inducing P-gp overexpression. Quantitative real-time PCR (qRT-PCR) analysis revealed reduced expression of miR-298 in both HBMEC/PHT and U87-MG/DOX cells, and the luciferase reporter assay identified the direct binding of miR-298 to the 3′-untranslated region (3′-UTR) of P-gp. Moreover, ectopic expression of miR-298 downregulated P-gp expression at the mRNA and protein levels, thereby increasing the intracellular accumulation of AEDs in drug-resistant HBMEC/PHT and U87-MG/DOX cells. Thus, our findings suggest that miR-298 reverses MDR to AEDs by inhibiting P-gp expression, suggesting a potential target for overcoming MDR in refractory epilepsy.

Phenytoin Could Potentially Increase Hepatic Clearance of 99mTc-Sestamibi in Myocardial Perfusion Imaging

Myocardial perfusion imaging (MPI) is one of the most commonly used nuclear medicine imaging modalities for coronary artery disease evaluation and risk stratification. The authors present incidental image findings in a patient who underwent MPI twice because of development of seizures just before the first SPECT-MPI acquisition. The projection images for first MPI done without medication (phenytoin) showed the retention of hepatic tracer activity. After a few days from restarting of phenytoin, the repeat MPI showed complete hepatic clearance of tracer. This case highlights the possible pharmacokinetic interaction between phenytoin intake and Tc-sestamibi, resulting in faster hepatic clearance of the radiotracer.

Verapamil as an Adjuvant Treatment for Drug-Resistant Epilepsy

Almost one-third of the people suffering from epilepsy continue to have seizures in spite of using appropriate antiepileptics. Pharmacoresistance is defined as the failure to achieve seizure control with two or more anticonvulsant medications at appropriate daily dosage. Here, we discuss one such gentleman whose seizures had been intractable despite multiple antiepileptic drugs in maximum tolerable doses. Verapamil, a calcium channel blocker, was used for its P-glycoprotein inhibition properties to overcome the pharmacoresistance in this patient with satisfactory seizure control. There are a few studies with limited patients on the successful usage of verapamil in a patient with pharmacoresistant status epilepticus (SE). We intend to publish this case report to draw interest among the critical care physicians on pharmacoresistant SE, the different hypotheses that prevail, its causes and the available management strategies.

Recent Advances in Radiotracer Imaging Hold Potential for Future Refined Evaluation of Epilepsy in Veterinary Neurology

Non-invasive nuclear imaging by positron emission tomography and single photon emission computed tomography has significantly contributed to epileptic focus localization in human neurology for several decades now. Offering functional insight into brain alterations, it is also of particular relevance for epilepsy research. Access to these techniques for veterinary medicine is becoming more and more relevant and has already resulted in first studies in canine patients. In view of the substantial proportion of drug-refractory epileptic dogs and cats, image-guided epileptic focus localization will be a prerequisite for selection of patients for surgical focus resection. Moreover, radiotracer imaging holds potential for a better understanding of the pathophysiology of underlying epilepsy syndromes as well as to forecast disease risk after epileptogenic brain insults. Importantly, recent advances in epilepsy research demonstrate the suitability and value of several novel radiotracers for non-invasive assessment of neuroinflammation, blood–brain barrier alterations, and neurotransmitter systems. It is desirable that veterinary epilepsy patients will also benefit from these promising developments in the medium term. This paper reviews the current use of radiotracer imaging in the veterinary epilepsy patient and suggests possible future directions for the technique.

Role of P-glycoprotein inhibitors in children with drug-resistant epilepsy

OBJECTIVE

The role of P-glycoprotein (Pgp), one of the known multidrug transporters, has been suggested in drug-resistant epilepsy (DRE). The following study aimed to measure the serum level of Pgp as a possible indicator of tissue Pgp overexpression in patients with DRE and to assess the efficacy of verapamil (as a Pgp inhibitor agent) in these patients.

MATERIAL AND METHODS

A group of 24 patients with DRE were recruited and subdivided into two groups, one receiving verapamil and the other receiving a placebo in a double-blind randomized study. Pgp serum levels were measured at enrollment and 12 months later. Twenty medically controlled epileptic patients served as a control group.

RESULTS

A significant statistical increase was found in the Pgp level of patients when compared the control group. Patients on both verapamil and the placebo showed improvement in seizure frequency and severity where statistical analysis showed no significant differences.

CONCLUSION

Pgp serum levels in patients with DRE were significantly elevated compared to patients with medically controlled epilepsy. The effect of verapamil as Pgp inhibitor on DRE requires further evaluation and research.

BCRP expression in schwannoma, plexiform neurofibroma and MPNST

Background

peripheral nerve sheath tumors comprise a broad spectrum of neoplasms. Vestibular schwannomas and plexiform neurofibromas are symptomatic albeit benign, but a subset of the latter pre-malignant lesions will transform to malignant peripheral nerve sheath tumors (MPNST). Surgery and radiotherapy are the primary strategies to treat these tumors. Intrinsic resistance to drug therapy characterizes all three tumor subtypes. The breast cancer resistance protein BCRP is a transmembrane efflux transporter considered to play a key role in various biological barriers such as the blood brain barrier. At the same time it is associated with drug resistance in various tumors. Its potential role in drug resistant tumors of the peripheral nervous system is largely unknown.

Objective

to assess if BCRP is expressed in vestibular schwannomas, plexiform neurofibromas and MPNST.

Material and methods

immunohistochemical staining for BCRP was performed on a tissue microarray composed out of 22 vestibular schwannomas, 10 plexiform neurofibromas and 18 MPNSTs.

Results

sixteen out of twenty-two vestibular schwannomas (73%), nine out of ten plexiform neurofibromas (90%) and six out of eighteen MPNST (33%) expressed BCRP in the vasculature. Tumor cells were negative.

Conclusion

BCRP is present in the vasculature of vestibular schwannomas, plexiform neurofibromas and MPSNT. Therefore, it may reduce the drug exposure of underlying tumor tissues and potentially cause failure of drug therapy.

Drug-Resistant Epilepsy: Multiple Hypotheses, Few Answers

Epilepsy is a common neurological disorder that affects over 70 million people worldwide. Despite the recent introduction of new antiseizure drugs (ASDs), about one-third of patients with epilepsy have seizures refractory to pharmacotherapy. Early identification of patients who will become refractory to ASDs could help direct such patients to appropriate non-pharmacological treatment, but the complexity in the temporal patterns of epilepsy could make such identification difficult. The target hypothesis and transporter hypothesis are the most cited theories trying to explain refractory epilepsy, but neither theory alone fully explains the neurobiological basis of pharmacoresistance. This review summarizes evidence for and against several major theories, including the pharmacokinetic hypothesis, neural network hypothesis, intrinsic severity hypothesis, gene variant hypothesis, target hypothesis, and transporter hypothesis. The discussion is mainly focused on the transporter hypothesis, where clinical and experimental data are discussed on multidrug transporter overexpression, substrate profiles of ASDs, mechanism of transporter upregulation, polymorphisms of transporters, and the use of transporter inhibitors. Finally, future perspectives are presented for the improvement of current hypotheses and the development of treatment strategies as guided by the current understanding of refractory epilepsy.

Influence of the dual combination of silymarin and (-)-epigallocatechin gallate, natural dietary flavonoids, on the pharmacokinetics of oxcarbazepine in rats

Considering the potential of flavonoids in reversing the P-glycoprotein (P-gp)-mediated multidrug resistance, this work aimed to assess the combined effects of silymarin and (-)-epigallocatechin gallate (EPG) on the pharmacokinetics of the P-gp substrates oxcarbazepine (OXC) and licarbazepine (LIC). Rats were pre-treated intraperitoneally with silymarin (25 mg/kg), EPG (25 mg/kg), silymarin/EPG (12.5/12.5 mg/kg; 6.25/18.75 mg/kg; 18.75/6.25 mg/kg) or verapamil (25 mg/kg, reference P-gp inhibitor) before the intraperitoneal administration of OXC (50 mg/kg). Pre-treatment with dual silymarin/EPG combinations originated peak plasma concentrations of OXC and LIC (pharmacologically active metabolite of OXC) similar to those achieved in the presence of verapamil (positive control). Moreover, the effects promoted by silymarin/EPG combinations on the magnitude of systemic drug exposure to OXC and LIC were also reflected in the corresponding drug levels attained in the brain (biophase). These findings evidence the synergistic effect of silymarin and EPG in enhancing the degree of systemic exposure to OXC and LIC in rats, which occurred in a comparable extent to that observed with verapamil. Hence, our findings support the combination of flavonoid-type P-gp inhibitors and P-gp substrate antiepileptic drugs as a potential therapeutic strategy for the management of pharmacoresistant epilepsy.

Status epilepticus in dogs and cats, part 1: etiopathogenesis, epidemiology, and diagnosis

OBJECTIVE

To review current knowledge of the etiopathogenesis, diagnosis, and consequences of status epilepticus (SE) in veterinary patients.

DATA SOURCES

Human and veterinary literature, including clinical and laboratory research and reviews.

ETIOPATHOGENESIS

Status epilepticus is a common emergency in dogs and cats, and may be the first manifestation of a seizure disorder. It results from the failure of termination of an isolated seizure. Multiple factors are involved in SE, including initiation and maintenance of neuronal excitability, neuronal network synchronization, and brain microenvironmental contributions to ictogenesis. Underlying etiologies of epilepsy and SE in dogs and cats are generally classified as genetic (idiopathic), structural-metabolic, or unknown.

DIAGNOSIS

Diagnosis of convulsive SE is usually made based on historical information and the nature of the seizures. Patient specific variables, such as the history, age of seizure onset, and physical and interictal neurological examination findings can help hone the rule out list, and are used to guide selection and prioritization of diagnostic tests. Electroencephalographic monitoring is routinely used in people to diagnose SE and guide patient care decisions, but is infrequently performed in veterinary medicine. Nonconvulsive status epilepticus has been recognized in veterinary patients; routine electroencephalography would aid in the diagnosis of this phenomenon in dogs and cats.

CLINICAL SEQUELAE

Status epilepticus is a medical emergency that can result in life-threatening complications involving the brain and systemic organs. Status epilepticus often requires comprehensive diagnostic testing, treatment with multiple anticonvulsant agents, and intensive supportive care.

P-gp Protein Expression and Transport Activity in Rodent Seizure Models and Human Epilepsy

A cure for epilepsy is currently not available, and seizure genesis, seizure recurrence, and resistance to antiseizure drugs remain serious clinical problems. Studies show that the blood-brain barrier is altered in animal models of epilepsy and in epileptic patients. In this regard, seizures increase expression of blood-brain barrier efflux transporters such as P-glycoprotein (P-gp), which is thought to reduce brain uptake of antiseizure drugs, and thus, contribute to antiseizure drug resistance. The goal of the current study was to assess the viability of combining in vivo and ex vivo preparations of isolated brain capillaries from animal models of seizures and epilepsy as well as from patients with epilepsy to study P-gp at the blood-brain barrier. Exposing isolated rat brain capillaries to glutamate ex vivo upregulated P-gp expression to levels that were similar to those in capillaries isolated from rats that had status epilepticus or chronic epilepsy. Moreover, the fold-increase in P-gp protein expression seen in animal models is consistent with the fold-increase in P-gp observed in human brain capillaries isolated from patients with epilepsy compared to age-matched control individuals. Overall, the in vivo/ex vivo approach presented here allows detailed analysis of the mechanisms underlying seizure-induced changes of P-gp expression and transport activity at the blood-brain barrier. This approach can be extended to other blood-brain barrier proteins that might contribute to drug-resistant epilepsy or other CNS disorders as well.

Extracellular HMGB1 Modulates Glutamate Metabolism Associated with Kainic Acid-Induced Epilepsy-Like Hyperactivity in Primary Rat Neural Cells

BACKGROUND/AIMS

Neuroinflammatory processes have been implicated in the pathophysiology of seizure/epilepsy. High mobility group box 1 (HMGB1), a non-histone DNA binding protein, behaves like an inflammatory cytokine in response to epileptogenic insults. Kainic acid (KA) is an excitotoxic reagent commonly used to induce epilepsy in rodents. However, the molecular mechanism by which KA-induced HMGB1 affords the initiation of epilepsy, especially the role of extracellular HMGB1 in neurotransmitter expression, remains to be elucidated.

METHODS

Experimental early stage of epilepsy-related hyperexcitability was induced in primary rat neural cells (PRNCs) by KA administration. We measured the localization of HMGB1, cell viability, mitochondrial activity, and expression level of glutamate metabolism-associated enzymes.

RESULTS

KA induced the translocation of HMGB1 from nucleus to cytosol, and its release from the neural cells. The translocation is associated with post-translational modifications. An increase in extracellular HMGB1 decreased PRNC cell viability and mitochondrial activity, downregulated expression of glutamate decarboxylase67 (GAD67) and glutamate dehydrogenase (GLUD1/2), and increased intracellular glutamate concentration and major histocompatibility complex II (MHC II) level.

CONCLUSIONS

That a surge in extracellular HMGB1 approximated seizure initiation suggests a key pathophysiological contribution of HMGB1 to the onset of epilepsy-related hyperexcitability.

Increasing nerve agent treatment efficacy by P-glycoprotein inhibition

One of the shortcomings of current treatment of nerve agent poisoning is that not all drugs effectively penetrate the blood-brain barrier (BBB), whereas most nerve agents easily do. P-glycoprotein (Pgp) efflux transporters at the BBB may contribute to this aspect. It was previously shown that Pgp inhibition by tariquidar enhanced the efficacy of nerve agent treatment when administered as a pretreatment. In the present study soman-induced seizures were also substantially prevented when the animals were intravenously treated with tariquidar post-poisoning, in addition to HI-6 and atropine. In these animals, approximately twice as much AChE activity was present in their brain as compared to control rats. The finding that tariquidar did not affect distribution of soman to the brain indicates that the potentiating effects were a result of interactions of Pgp inhibition with drug distribution. In line with this, atropine appeared to be a substrate for Pgp in in vitro studies in a MDR1/MDCK cell model. This indicates that tariquidar might induce brain region specific effects on atropine distribution, which could contribute to the therapeutic efficacy increase found. Furthermore, the therapeutic enhancement by tariquidar was compared to that of the less specific and less potent Pgp inhibitor cyclosporine A. This compound appeared to induce a protective effect similar to tariquidar. In conclusion, treatment with a Pgp inhibitor resulted in enhanced therapeutic efficacy of HI-6 and atropine in a soman-induced seizure model in the rat. The mechanism underlying these effects should be further investigated. To that end, the potentiating effect of nerve agent treatment should be addressed against a broader range of nerve agents, for oximes and atropine separately, and for those at lower doses. In particular when efficacy against more nerve agents is shown, a Pgp inhibitor such as tariquidar might be a valid addition to nerve agent antidotes.

Cellular and regional specific changes in multidrug efflux transporter expression during recovery of vasogenic edema in the rat hippocampus and piriform cortex

In the present study, we investigated the characteristics of drug efflux transporter expressions following status epilepticus (SE). In the hippocampus and piriform cortex (PC), vasogenic edema peaked 3-4 days after SE. The expression of breast cancer resistance protein (BCRP), multidrug resistance protein-4 (MRP4), and p-glycoprotein (p-GP) were decreased 4 days after SE when vasogenic edema was peaked, but subsequently increased 4 weeks after SE. Multidrug resistance protein-1 (MRP1) expression gradually decreased in endothelial cells until 4 weeks after SE. These findings indicate that SE-induced vasogenic edema formation transiently reduced drug efflux pump expressions in endothelial cells. Subsequently, during recovery of vasogenic edema drug efflux pump expressions were differentially upregulated in astrocytes, neuropils, and endothelial cells. Therefore, we suggest that vasogenic edema formation may be a risk factor in pharmacoresistent epilepsy. [BMB Reports 2015; 48(6): 348-353]