Mechanisms of action of antiepileptic drugs: the search for synergy

Can glial cells save neurons in epilepsy?

Epilepsy is a neurological disorder caused by the pathological hyper-synchronization of neuronal discharges. The fundamental research of epilepsy mechanisms and the targets of drug design options for its treatment have focused on neurons. However, approximately 30% of patients suffering from epilepsy show resistance to standard anti-epileptic chemotherapeutic agents while the symptoms of the remaining 70% of patients can be alleviated but not completely removed by the current medications. Thus, new strategies for the treatment of epilepsy are in urgent demand. Over the past decades, with the increase in knowledge on the role of glia in the genesis and development of epilepsy, glial cells are receiving renewed attention. In a normal brain, glial cells maintain neuronal health and in partnership with neurons regulate virtually every aspect of brain function. In epilepsy, however, the supportive roles of glial cells are compromised, and their interaction with neurons is altered, which disrupts brain function. In this review, we will focus on the role of glia-related processes in epileptogenesis and their contribution to abnormal neuronal activity, with the major focus on the dysfunction of astroglial potassium channels, water channels, gap junctions, glutamate transporters, purinergic signaling, synaptogenesis, on the roles of microglial inflammatory cytokines, microglia-astrocyte interactions in epilepsy, and on the oligodendroglial potassium channels and myelin abnormalities in the epileptic brain. These recent findings suggest that glia should be considered as the promising next-generation targets for designing anti-epileptic drugs that may improve epilepsy and drug-resistant epilepsy.

Role of Impaired Astrocyte Gap Junction Coupling in Epileptogenesis

The gap-junction-coupled astroglial network plays a central role in the regulation of neuronal activity and synchronisation, but its involvement in the pathogenesis of neuronal diseases is not yet understood. Here, we present the current state of knowledge about the impact of impaired glial coupling in the development and progression of epilepsy and discuss whether astrocytes represent alternative therapeutic targets. We focus mainly on temporal lobe epilepsy (TLE), which is the most common form of epilepsy in adults and is characterised by high therapy resistance. Functional data from TLE patients and corresponding experimental models point to a complete loss of astrocytic coupling, but preservation of the gap junction forming proteins connexin43 and connexin30 in hippocampal sclerosis. Several studies further indicate that astrocyte uncoupling is a causal event in the initiation of TLE, as it occurs very early in epileptogenesis, clearly preceding dysfunctional changes in neurons. However, more research is needed to fully understand the role of gap junction channels in epilepsy and to develop safe and effective therapeutic strategies targeting astrocytes.

From HDAC to Voltage-Gated Ion Channels: What's Next? The Long Road of Antiepileptic Drugs Repositioning in Cancer

Simple Summary

Although in the last decades the clinical outcome of cancer patients considerably improved, the major drawbacks still associated with chemotherapy are the unwanted side effects and the development of drug resistance. Therefore, a continuous effort in trying to discover new tumor markers, possibly of diagnostic, prognostic and therapeutic value, is being made. This review is aimed at highlighting the anti-tumor activity that several antiepileptic drugs (AEDs) exert in breast, prostate and other types of cancers, mainly focusing on their ability to block the voltage-gated Na⁺ and Ca⁺⁺ channels, as well as to inhibit the activity of histone deacetylases (HDACs), all well-documented tumor markers and/or molecular targets. The existence of additional AEDs molecular targets is highly suspected. Therefore, the repurposing of already available drugs as adjuvants in cancer treatment would have several advantages, such as reductions in dose-related toxicity CVs will be sent in a separate mail to the indicated address of combined treatments, lower production costs, and faster approval for clinical use.

Abstract

Cancer is a major health burden worldwide. Although the plethora of molecular targets identified in the last decades and the deriving developed treatments, which significantly improved patients’ outcome, the occurrence of resistance to therapies remains the major cause of relapse and mortality. Thus, efforts in identifying new markers to be exploited as molecular targets in cancer therapy are needed. This review will first give a glance on the diagnostic and therapeutic significance of histone deacetylase (HDAC) and voltage gated ion channels (VGICs) in cancer. Nevertheless, HDAC and VGICs have also been reported as molecular targets through which antiepileptic drugs (AEDs) seem to exert their anticancer activity. This should be claimed as a great advantage. Indeed, due to the slowness of drug approval procedures, the attempt to turn to off-label use of already approved medicines would be highly preferable. Therefore, an updated and accurate overview of both preclinical and clinical data of commonly prescribed AEDs (mainly valproic acid, lamotrigine, carbamazepine, phenytoin and gabapentin) in breast, prostate, brain and other cancers will follow. Finally, a glance at the emerging attempt to administer AEDs by means of opportunely designed drug delivery systems (DDSs), so to limit toxicity and improve bioavailability, is also given.

Multimodal Characterization of Seizures in Zebrafish Larvae

Epilepsy accounts for a significant proportion of the world's disease burden. Indeed, many research efforts are produced both to investigate the basic mechanism ruling its genesis and to find more effective therapies. In this framework, the use of zebrafish larvae, owing to their peculiar features, offers a great opportunity. Here, we employ transgenic zebrafish larvae expressing GCaMP6s in all neurons to characterize functional alterations occurring during seizures induced by pentylenetetrazole. Using a custom two-photon light-sheet microscope, we perform fast volumetric functional imaging of the entire larval brain, investigating how different brain regions contribute to seizure onset and propagation. Moreover, employing a custom behavioral tracking system, we outline the progressive alteration of larval swim kinematics, resulting from different grades of seizures. Collectively, our results show that the epileptic larval brain undergoes transitions between diverse neuronal activity regimes. Moreover, we observe that different brain regions are progressively recruited into the generation of seizures of diverse severity. We demonstrate that midbrain regions exhibit highest susceptibility to the convulsant effects and that, during periods preceding abrupt hypersynchronous paroxysmal activity, they show a consistent increase in functional connectivity. These aspects, coupled with the hub-like role that these regions exert, represent important cues in their identification as epileptogenic hubs.

Update on Antiseizure Medications 2022

EDITORS NOTE

The article "Update on Antiseizure Medications 2022" by Dr Abou-Khalil was first published in the February 2016 Epilepsy issue of Continuum: Lifelong Learning in Neurology as "Antiepileptic Drugs," and at the request of the Editor-in-Chief was updated by Dr Abou-Khalil for the 2019 issue and again for this issue.

Effects of Pregabalin, Nimodipine, and Their Combination in the Inhibition of Status Epilepticus and the Prevention of Death in Mice

Objectives

The current study aims to evaluate the combined antiepileptic effects of pregabalin (PGB) and nimodipine (NMD) in an acute seizure model of epilepsy in mice.

Materials and Methods

This study assessed the combined antiepileptic effects of PGB with NMD on death protection in mice. Pentylenetetrazole was used to induce seizures. Both drugs were used singly and in combination to judge anticonvulsant effects on an acute seizure model of epilepsy in mice. Diazepam (DZ) and valproate (VPT) were used as standard antiepileptic drugs.

Results

The death protection in mice by both these drugs was observed in percentage and deliberated as marked change when the outcome of the tested drug was equal to ED₅₀ of PGB and measured highly marked when the result was more than ED₅₀ for PGB. Treatment with pregabalin and nimodipine combination revealed substantial mortality protection at 30+2.5 mg/kg dose and highly marked at doses from 35+5 mg/kg to 55+15 mg/kg, these effects were superior to individual effects of PGB, showing synergism, however lesser then classic drugs valproate and diazepam.

Conclusion

NMD showed synergistic anticonvulsant effect with PGB. However, clinical studies are required to establish the effectiveness of this combination in humans.

Subicular Caspase-1 Contributes to Pharmacoresistance in Temporal Lobe Epilepsy

OBJECTIVE

Unidentified mechanisms largely restrict the viability of effective therapies in pharmacoresistant epilepsy. Our previous study revealed that hyperactivity of the subiculum is crucial for the genesis of pharmacoresistance in temporal lobe epilepsy (TLE), but the underlying molecular mechanism is not clear.

METHODS

Here, we examined the role of subicular caspase-1, a key neural pro-inflammatory enzyme, in pharmacoresistant TLE.

RESULTS

We found that the expression of activated caspase-1 in the subiculum, but not the CA1, was upregulated in pharmacoresistant amygdaloid-kindled rats. Early overexpression of caspase-1 in the subiculum was sufficient to induce pharmacoresistant TLE in rats, whereas genetic ablation of caspase-1 interfered with the genesis of pharmacoresistant TLE in both kindled rats and kainic acid-treated mice. The pro-pharmacoresistance effect of subicular caspase-1 was mediated by its downstream inflammasome-dependent interleukin-1β. Further electrophysiological results showed that inhibiting caspase-1 decreased the excitability of subicular pyramidal neurons through influencing the excitation/inhibition balance of presynaptic input. Importantly, a small molecular caspase-1 inhibitor CZL80 attenuated seizures in pharmacoresistant TLE models, and decreased the neuronal excitability in the brain slices obtained from patients with pharmacoresistant TLE.

INTERPRETATION

These results support the subicular caspase-1-interleukin-1β inflammatory pathway as a novel alternative mechanism hypothesis for pharmacoresistant TLE, and present caspase-1 as a potential target. ANN NEUROL 2021.

Astrocytes and Epilepsy

Changes in astrocyte channels, transporters, and metabolism play a critical role in seizure generation and epilepsy. In particular, alterations in astrocyte potassium, glutamate, water and adenosine homeostasis and gap junctional coupling have all been associated with hyperexcitability and epileptogenesis (largely in temporal lobe epilepsy). Distinct astrocytic changes have also been identified in other types of epilepsy, such as tuberous sclerosis, tumor-associated epilepsy and post-traumatic epilepsy. Together, the emerging literature on astrocytes and epilepsy provides powerful rationale for distinct new therapeutic targets that are astrocyte-specific.

Clinical Management of Drug Resistant Epilepsy: A Review on Current Strategies

Drug resistant epilepsy (DRE) is defined as the persistence of seizures despite at least two syndrome-adapted antiseizure drugs (ASD) used at efficacious daily dose. Despite the increasing number of available ASD, about a third of patients with epilepsy still suffer from drug resistance. Several factors are associated with the risk of evolution to DRE in patients with newly diagnosed epilepsy, including epilepsy onset in the infancy, intellectual disability, symptomatic epilepsy and abnormal neurological exam. Pharmacological management often consists in ASD polytherapy. However, because quality of life is driven by several factors in patients with DRE, including the tolerability of the treatment, ASD management should try to optimize efficacy while anticipating the risks of drug-related adverse events. All patients with DRE should be evaluated at least once in a tertiary epilepsy center, especially to discuss eligibility for non-pharmacological therapies. This is of paramount importance in patients with drug resistant focal epilepsy in whom epilepsy surgery can result in long-term seizure freedom. Vagus nerve stimulation, deep brain stimulation or cortical stimulation can also improve seizure control. Lastly, considering the effect of DRE on psychologic status and social integration, comprehensive care adaptations are always needed in order to improve patients' quality of life.

Epilepsy: Workup and Management in Adults

When managing epilepsy, there is a temptation to focus care with respect to the last and the next seizure. However, epilepsy is a multifaceted chronic condition and should be treated as such. Epilepsy comes with many physical risks, psychological effects, and socioeconomic ramifications, demanding a long-term commitment from the treating physician. Patients with epilepsy, compared to other chronically ill patient populations, have a worse quality of life, family function, and less social support. The majority of patients are well controlled on antiseizure drugs. However, approximately one-third will continue to have seizures despite optimized medical management. The primary aim of this article is to explore the long-term management of chronic epilepsy, and to address some of the particular needs of patients with chronic epilepsy.

Is the mechanism of action of antiseizure drugs a key element in the choice of treatment?

About 25 antiseizure drugs are available for the treatment of patients with epilepsy. The choice of the most suited drug for a specific patient is primarily based on the results of the pivotal randomized clinical trials and on the patient's characteristics and comorbidities. Whether or not the mechanism of action of the antiseizure drugs should be also taken into account to better predict the patient's response to the treatment remains a matter of debate. Despite the apparent complexity and diversity of antiseizure drug mechanisms of action, the reality unfortunately remains that they are very close, in particular with regard to their relationship with the pathophysiology of epilepsy. With the only exception of the association between lamotrigine and sodium valproate, there are no clinical data that formally support a synergistic association between certain antiseizure drugs in terms of efficacy. However, anticipating risk of adverse events by limiting as far as possible the combination of drugs, which share the same mechanisms of action, is undoubtedly an important driver of daily therapeutic decisions.

Astrocyte Glutamate Uptake and Signaling as Novel Targets for Antiepileptogenic Therapy

Astrocytes regulate and respond to extracellular glutamate levels in the central nervous system (CNS) via the Na⁺-dependent glutamate transporters glutamate transporter-1 (GLT-1) and glutamate aspartate transporter (GLAST) and the metabotropic glutamate receptors (mGluR) 3 and mGluR5. Both impaired astrocytic glutamate clearance and changes in metabotropic glutamate signaling could contribute to the development of epilepsy. Dysregulation of astrocytic glutamate transporters, GLT-1 and GLAST, is a common finding across patients and preclinical seizure models. Astrocytic metabotropic glutamate receptors, particularly mGluR5, have been shown to be dysregulated in both humans and animal models of temporal lobe epilepsy (TLE). In this review, we synthesize the available evidence regarding astrocytic glutamate homeostasis and astrocytic mGluRs in the development of epilepsy. Modulation of astrocyte glutamate uptake and/or mGluR activation could lead to novel glial therapeutics for epilepsy.

Update on Antiepileptic Drugs 2019

PURPOSE OF REVIEW

This article is an update from the article on antiepileptic drug (AED) therapy published in the last Continuum issue on epilepsy and is intended to cover the vast majority of agents currently available to the neurologist in the management of patients with epilepsy. Treatment of epilepsy starts with AED monotherapy. Knowledge of the spectrum of efficacy, clinical pharmacology, and modes of use for individual AEDs is essential for optimal treatment for epilepsy. This article addresses AEDs individually, focusing on key pharmacokinetic characteristics, indications, and modes of use.

RECENT FINDINGS

Since the previous version of this article was published, three new AEDs, brivaracetam, cannabidiol, and stiripentol, have been approved by the US Food and Drug Administration (FDA), and ezogabine was removed from the market because of decreased use as a result of bluish skin pigmentation and concern over potential retinal toxicity.Older AEDs are effective but have tolerability and pharmacokinetic disadvantages. Several newer AEDs have undergone comparative trials demonstrating efficacy equal to and tolerability at least equal to or better than older AEDs as first-line therapy. The list includes lamotrigine, oxcarbazepine, levetiracetam, topiramate, zonisamide, and lacosamide. Pregabalin was found to be less effective than lamotrigine. Lacosamide, pregabalin, and eslicarbazepine have undergone successful trials of conversion to monotherapy. Other newer AEDs with a variety of mechanisms of action are suitable for adjunctive therapy. Most recently, the FDA adopted a policy that a drug's efficacy as adjunctive therapy in adults can be extrapolated to efficacy in monotherapy. In addition, efficacy in adults can be extrapolated for efficacy in children 4 years of age and older. Both extrapolations require data demonstrating that an AED has equivalent pharmacokinetics between its original approved use and its extrapolated use. In addition, the safety of the drug in pediatric patients has to be demonstrated in clinical studies that can be open label. Rational AED combinations should avoid AEDs with unfavorable pharmacokinetic interactions or pharmacodynamic interactions related to mechanism of action.

SUMMARY

Knowledge of AED pharmacokinetics, efficacy, and tolerability profiles facilitates the choice of appropriate AED therapy for patients with epilepsy.

Homeostatic activity regulation as a mechanism underlying the effect of brain stimulation

Hyperexcitability of the neural network often occurs after brain injuries or degeneration and is a key pathophysiological feature in certain neurological diseases such as epilepsy, neuropathic pain, and tinnitus. Although the standard approach of pharmacological treatments is to directly suppress the hyperexcitability through reducing excitation or enhancing inhibition, different techniques for stimulating brain activity are often used to treat refractory neurological conditions. However, it is unclear why stimulating brain activity would be effective for controlling hyperexcitability. Recent studies suggest that the pathogenesis in these disorders exhibits a transition from an initial activity loss after acute injury or progressive neurodegeneration to subsequent development of hyperexcitability. This process mimics homeostatic activity regulation and may contribute to developing network hyperexcitability that underlies neurological symptoms. This hypothesis also predicts that stimulating brain activity should be effective in reducing hyperexcitability due to homeostatic activity regulation and in relieving symptoms. Here we review current evidence of homeostatic plasticity in the development of hyperexcitability in some neurological diseases and the effects of brain stimulation. The homeostatic plasticity hypothesis may provide new insights into the pathophysiology of neurological diseases and may guide the use of brain stimulation techniques for treating them.

Analysis of risk factors for antiepileptic drug-induced adverse psychotropic effects in Chinese outpatients with epilepsy

Antiepileptic drugs (AEDs) have adverse psychotropic effects (APEs). To explore the risk factors for AED-induced APEs, we compared Chinese outpatients with epilepsy with and without AED-induced APEs. We reviewed the medical data of outpatients with epilepsy enrolled in the Epilepsy Long-term Follow Up Registry Study (ELFURS) between January 1, 2003 and December 31, 2015. Data on demographics, comorbidities, variables related to epilepsy, AED use, and APEs were collected. APEs were determined by experienced epileptologists based on the definition of "adverse drug reaction (ADR)" proposed by the World Health Organization (WHO) in 1972, and the causality relationship between APEs and suspected medications was assessed based on the WHO-UMC scale. APEs included effects on memory, sleep, behavior, mood, psychotic symptoms, and others in this study. We divided the study population into patients with and without AED-induced APEs and then compared the differences between the two groups using univariate and multivariate methods. A total of 3074 eligible patients were included in this study (1001 patients with AED-induced APEs and 2073 patients without AED-induced APEs). Of all APEs, the effects on memory and sleep were most pronounced. The results show that the female sex (odds ratio [OR] 1.242, 95% confidence interval [CI] 1.055-1.463), psychotic disorder comorbidities (OR 1.815, 95% CI 1.159-2.841), polytherapy with AEDs (OR 1.400, 95% CI 1.061-1.847), and the duration of epilepsy (OR 1.010, 95% CI 1.000-1.020) are significant nondrug risk factors for AED-induced APEs. Recognizing risk factors for APEs may help determine optimal treatment strategies for epilepsy.

A novel action of lacosamide on GABAA currents sets the ground for a synergic interaction with levetiracetam in treatment of epilepsy

Epilepsy is one of the most common chronic neurological diseases, and its pharmacological treatment holds great importance for both physicians and national authorities, especially considering the high proportion of drug-resistant patients (about 30%). Lacosamide (LCM) is an effective and well-tolerated new-generation antiepileptic drug (AED), currently licensed as add-on therapy for partial-onset seizures. However, LCM mechanism of action is still a matter of debate, although its effect on the voltage sensitive sodium channels is by far the most recognized. This study aimed to retrospectively analyze a cohort of 157 drug-resistant patients treated with LCM to describe the most common and effective therapeutic combinations and to investigate if the LCM can affect also GABA_A-mediated neurotransmission as previously shown for levetiracetam (LEV). In our cohort, LEV resulted the compound most frequently associated with LCM in the responder subgroup. We therefore translated this clinical observation into the laboratory bench by taking advantage of the technique of "membrane micro-transplantation" in Xenopus oocytes and electrophysiological approaches to study human GABA_A-evoked currents. In cortical brain tissues from refractory epileptic patients, we found that LCM reduces the use-dependent GABA impairment (i.e., "rundown") that it is considered one of the specific hallmarks of drug-resistant epilepsies. Notably, in line with our clinical observations, we found that the co-treatment with subthreshold concentrations of LCM and LEV, which had no effect on GABA_A currents on their own, reduced GABA impairment in drug-resistant epileptic patients, and this effect was blocked by PKC inhibitors. Our findings demonstrate, for the first time, that LCM targets GABA_A receptors and that it can act synergistically with LEV, improving the GABAergic function. This novel mechanism might contribute to explain the clinical efficacy of LCM-LEV combination in several refractory epileptic patients.

Individualizing Treatment Approaches for Epileptic Patients with Glucose Transporter Type1 (GLUT-1) Deficiency

Monogenic and polygenic mutations are important contributors in patients suffering from epilepsy, including metabolic epilepsies which are inborn errors of metabolism with a good respond to specific dietetic treatments. Heterozygous variation in solute carrier family 2, facilitated glucose transporter member 1 (SLC2A1) and mutations of the GLUT1/SLC2A2 gene results in the failure of glucose transport, which is related with a glucose type-1 transporter (GLUT1) deficiency syndrome (GLUT1DS). GLUT1 deficiency syndrome is a treatable disorder of glucose transport into the brain caused by a variety of mutations in the SLC2A1 gene which are the cause of different neurological disorders also with different types of epilepsy and related clinical phenotypes. Since patients continue to experience seizures due to a pharmacoresistance, an early clinical diagnosis associated with specific genetic testing in SLC2A1 pathogenic variants in clinical phenotypes could predict pure drug response and might improve safety and efficacy of treatment with the initiation of an alternative energy source including ketogenic or analog diets in such patients providing individualized strategy approaches.

Exhaled Breath Markers for Nonimaging and Noninvasive Measures for Detection of Multiple Sclerosis

Multiple sclerosis (MS) is the most common chronic neurological disease affecting young adults. MS diagnosis is based on clinical characteristics and confirmed by examination of the cerebrospinal fluids (CSF) or by magnetic resonance imaging (MRI) of the brain or spinal cord or both. However, neither of the current diagnostic procedures are adequate as a routine tool to determine disease state. Thus, diagnostic biomarkers are needed. In the current study, a novel approach that could meet these expectations is presented. The approach is based on noninvasive analysis of volatile organic compounds (VOCs) in breath. Exhaled breath was collected from 204 participants, 146 MS and 58 healthy control individuals. Analysis was performed by gas-chromatography mass-spectrometry (GC-MS) and nanomaterial-based sensor array. Predictive models were derived from the sensors, using artificial neural networks (ANNs). GC-MS analysis revealed significant differences in VOC abundance between MS patients and controls. Sensor data analysis on training sets was able to discriminate in binary comparisons between MS patients and controls with accuracies up to 90%. Blinded sets showed 95% positive predictive value (PPV) between MS-remission and control, 100% sensitivity with 100% negative predictive value (NPV) between MS not-treated (NT) and control, and 86% NPV between relapse and control. Possible links between VOC biomarkers and the MS pathogenesis were established. Preliminary results suggest the applicability of a new nanotechnology-based method for MS diagnostics.

Selecting Rational Drug Combinations in Epilepsy

Monotherapy remains the standard initial therapy of epilepsy, but when the first antiepileptic drug (AED) fails, combination therapy may be considered. The choice of combination therapy should take into consideration pharmacokinetic interactions, as well as pharmacodynamic interactions related to mechanism of action. There is evidence that an AED combination with different mechanisms of action is more likely to be successful than a combination with the same mechanisms. The combination of lamotrigine and valproate has been demonstrated to be synergistic in its efficacy. However, there are limited data to support other synergistic AED combinations.

The Role of Sodium Bicarbonate in the Management of Some Toxic Ingestions

Adverse reactions to commonly prescribed medications and to substances of abuse may result in severe toxicity associated with increased morbidity and mortality. According to the Center for Disease Control, in 2013, at least 2113 human fatalities attributed to poisonings occurred in the United States of America. In this article, we review the data regarding the impact of systemic sodium bicarbonate administration in the management of certain poisonings including sodium channel blocker toxicities, salicylate overdose, and ingestion of some toxic alcohols and in various pharmacological toxicities. Based on the available literature and empiric experience, the administration of sodium bicarbonate appears to be beneficial in the management of a patient with the above-mentioned toxidromes. However, most of the available evidence originates from case reports, case series, and expert consensus recommendations. The potential mechanisms of sodium bicarbonate include high sodium load and the development of metabolic alkalosis with resultant decreased tissue penetration of the toxic substance with subsequent increased urinary excretion. While receiving sodium bicarbonate, patients must be monitored for the development of associated side effects including electrolyte abnormalities, the progression of metabolic alkalosis, volume overload, worsening respiratory status, and/or worsening metabolic acidosis. Patients with oliguric/anuric renal failure and advanced decompensated heart failure should not receive sodium bicarbonate.

Synergistic anticonvulsant effects of pregabalin and amlodipine on acute seizure model of epilepsy in mice

Status epilepticus is a life threatening neurological medical emergency. It may cause serious damage to the brain and even death in many cases if not treated properly. There is limited choice of drugs for the short term and long term management of status epilepticus and the dugs recommended for status epilepticus possess various side effects. The present study was designed to investigate synergistic anticonvulsant effects of pregabalin with amlodipine on acute seizure model of epilepsy in mice. Pentylenetetrazole was used to induce acute seizures which mimic status epilepticus. Pregabalin and amlodipine were used in combination to evaluate synergistic anti-seizure effects on acute seizure model of epilepsy in mice. Diazepam and valproate were used as reference dugs. The acute anti-convulsive activity of pregabalin with amlodipine was evaluated in vivo by the chemical induced seizures and their anti-seizure effects were compared with pentylenetetrazole, reference drugs and to their individual effects. The anti-seizure effects of tested drugs were recorded in seconds on seizure characteristics such as latency of onset of threshold seizures, rearing and fallings and Hind limbs tonic extensions. The seizure protection and mortality to the animals exhibited by the drugs were recorded in percentage. Combination regimen of pregabalin with amlodipine exhibited dose dependent significant synergistic anticonvulsant effects on acute seizures which were superior to their individual effects and equivalent to reference drugs.

Non-health care facility anticonvulsant medication errors in the United States

INTRODUCTION

This study provides an epidemiological description of non-health care facility medication errors involving anticonvulsant drugs.

METHODS

A retrospective analysis of National Poison Data System data was conducted on non-health care facility medication errors involving anticonvulsant drugs reported to US Poison Control Centers from 2000 through 2012.

RESULTS

During the study period, 108,446 non-health care facility medication errors involving anticonvulsant pharmaceuticals were reported to US Poison Control Centers, averaging 8342 exposures annually. The annual frequency and rate of errors increased significantly over the study period, by 96.6 and 76.7%, respectively. The rate of exposures resulting in health care facility use increased by 83.3% and the rate of exposures resulting in serious medical outcomes increased by 62.3%. In 2012, newer anticonvulsants, including felbamate, gabapentin, lamotrigine, levetiracetam, other anticonvulsants (excluding barbiturates), other types of gamma aminobutyric acid, oxcarbazepine, topiramate, and zonisamide, accounted for 67.1% of all exposures.

CONCLUSIONS

The rate of non-health care facility anticonvulsant medication errors reported to Poison Control Centers increased during 2000-2012, resulting in more frequent health care facility use and serious medical outcomes. Newer anticonvulsants, although often considered safer and more easily tolerated, were responsible for much of this trend and should still be administered with caution.

Optical mapping of neuronal activity during seizures in zebrafish

Mapping neuronal activity during the onset and propagation of epileptic seizures can provide a better understanding of the mechanisms underlying this pathology and improve our approaches to the development of new drugs. Recently, zebrafish has become an important model for studying epilepsy both in basic research and in drug discovery. Here, we employed a transgenic line with pan-neuronal expression of the genetically-encoded calcium indicator GCaMP6s to measure neuronal activity in zebrafish larvae during seizures induced by pentylenetretrazole (PTZ). With this approach, we mapped neuronal activity in different areas of the larval brain, demonstrating the high sensitivity of this method to different levels of alteration, as induced by increasing PTZ concentrations, and the rescuing effect of an anti-epileptic drug. We also present simultaneous measurements of brain and locomotor activity, as well as a high-throughput assay, demonstrating that GCaMP measurements can complement behavioural assays for the detection of subclinical epileptic seizures, thus enabling future investigations on human hypomorphic mutations and more effective drug screening methods. Notably, the methodology described here can be easily applied to the study of many human neuropathologies modelled in zebrafish, allowing a simple and yet detailed investigation of brain activity alterations associated with the pathological phenotype.

Treatment-refractory posttraumatic stress disorder (TRPTSD): a review and framework for the future

Post-traumatic stress disorder (PTSD) is a serious psychiatric consequence of trauma that occurs in a proportion of individuals exposed to life-threatening events. Trauma-focused psychotherapy is often recommended as first choice for those who do not recover spontaneously. But many individuals require medications. In the US, only paroxetine (PRX) and sertraline (SRT) are FDA approved for PTSD. But response and remission rates with these medications are low, so numerous other pharmacologic interventions have been tried. To date, there has not been a systematic review of the data on what are the best next-step pharmacologic strategies for individuals who fail standard treatments. To that end, we review 168 published trials of medications other than PRX or SRT and provide a detailed analysis of the 88/168 studies that describe alternative pharmacologic interventions in patients refractory to other treatment. We also review clinical factors relevant to treatment-refractory PTSD; the neurobiology of extinction, as well as evidence-based psychotherapy and neuromodulation strategies for this condition.

Pharmacotherapy in pediatric epilepsy: from trial and error to rational drug and dose selection - a long way to go

INTRODUCTION

Whereas ongoing efforts in epilepsy research focus on the underlying disease processes, the lack of a physiologically based rationale for drug and dose selection contributes to inadequate treatment response in children. In fact, limited information on the interindividual variation in pharmacokinetics and pharmacodynamics of anti-epileptic drugs (AEDs) in children drive prescription practice, which relies primarily on dose regimens according to a mg/kg basis. Such practice has evolved despite advancements in pediatric pharmacology showing that growth and maturation processes do not correlate linearly with changes in body size.

AREAS COVERED

In this review we aim to provide 1) a comprehensive overview of the sources of variability in the response to AEDs, 2) insight into novel methodologies to characterise such variation and 3) recommendations for treatment personalisation.

EXPERT OPINION

The use of pharmacokinetic-pharmacodynamic principles in clinical practice is hindered by the lack of biomarkers and by practical constraints in the evaluation of polytherapy. The identification of biomarkers and their validation as tools for drug development and therapeutics will require some time. Meanwhile, one should not miss the opportunity to integrate the available pharmacokinetic data with modeling and simulation concepts to prevent further delays in the development of personalised treatments for pediatric patients.

Synergism of perampanel and zonisamide in the rat amygdala kindling model of temporal lobe epilepsy

OBJECTIVE

Anticonvulsive monotherapy fails to be effective in one third of patients with epilepsy resulting in the need for polytherapy regimens. However, with the still limited knowledge, drug choices for polytherapy remain empirical. Here we report experimental data from a chronic epilepsy model for the combination of perampanel and zonisamide, which can render guidance for clinical studies and individual drug choices.

METHODS

The anticonvulsant effects of the combination of perampanel and zonisamide were evaluated in a rat amygdala kindling model. Furthermore, the potential for motor impairment was evaluated. The type of interaction was quantitatively assessed based on isobolographic analysis.

RESULTS

When administered alone, zonisamide dose-dependently increased the afterdischarge threshold in fully kindled rats. Moreover, data confirmed efficacy of perampanel to inhibit seizure initiation and progression with an impact on propagation of activity from the focus. Pronounced threshold increases were observed following administration of a constant zonisamide dosage combined with different doses of perampanel. Isobolographic analysis of drug responses, which is based on individual drug dose-effect data, revealed a synergistic interaction substantiating the high efficacy of the combination. Furthermore, rotarod data indicated that the combination has a favorable tolerability profile when zonisamide is coadministered with low doses of perampanel. Plasma concentration analysis argued against a pharmacokinetic interaction as a basis for the synergism.

SIGNIFICANCE

The findings clearly indicate a pronounced synergistic anticonvulsant effect for the combination of the noncompetitive α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist perampanel with zonisamide, which modulates voltage-sensitive sodium channels and T-type calcium currents. Consequently, polytherapy using these two antiepileptic drugs might be efficacious for clinical management of partial-onset seizures. The findings indicate that the impact of dose ratios on tolerability needs be taken into account. With regard to conclusions about the extent of the synergism and its implications further antiepileptic drug combinations need to be evaluated allowing direct comparison.

Homology modelling and molecular docking studies of human placental cadherin protein for its role in teratogenic effects of anti-epileptic drugs

Anti-epileptic drugs (AEDs) have high risk of teratogenic side effects, including neural tube defects while mother is on AEDs for her own prevention of convulsions during pregnancy. The present study investigated the interaction of major marketed AEDs and human placental (hp)-cadherin protein, in-silico, to establish the role of hp-cadherin protein in teratogenicity and also to evaluate the importance of Ca(2+) ion in functioning of the protein. A set of 21 major marketed AEDs were selected for the study and 3D-structure of hp-cadherin was constructed using homology modelling and energy minimized using MD simulations. Molecular docking studies were carried out using selected AEDs as ligand with hp-cadherin (free and bound Ca(2+) ion) to study the behavioural changes in hp-cadherin due to presence of Ca(2+) ion. The study reflected that four AEDs (Gabapentin, Pregabalin, Remacimide and Vigabatrine) had very high affinity towards hp-cadherin and thus the later may have prominent role in the teratogenic effects of these AEDs. From docking simulation analysis it was observed that Ca(2+) ion is required to make hp-cadherin energetically favourable and sterically functional.

A Potential Role for Felbamate in TSC- and NF1-Related Epilepsy: A Case Report and Review of the Literature

A 15-year-old girl with maternal inheritance of neurofibromatosis type 1 (NF1) and paternal inheritance of tuberous sclerosis complex (TSC) developed intractable epilepsy at age 5. Her seizures were refractory to adequate doses of four antiepileptic medications until felbamate was initiated at age 7. She has since remained seizure-free on felbamate monotherapy. Although felbamate has multiple mechanisms of action, it is thought to have its most potent antiepileptic effects through inhibition of the N-methyl-D-aspartate receptor (NMDAR). Previous studies have shown that the NMDAR is altered in varying epilepsy syndromes and notably in the cortical tubers found in TSC. The aim of this paper is to examine how felbamate monotherapy was able to achieve such robust antiepileptic effects in a unique patient and possibly offer a novel therapeutic approach to patients suffering from TSC- and NF-related epilepsy.

Identification of a neurovascular signaling pathway regulating seizures in mice

OBJECTIVE

A growing body of evidence suggests that increased blood-brain barrier (BBB) permeability can contribute to the development of seizures. The protease tissue plasminogen activator (tPA) has been shown to promote BBB permeability and susceptibility to seizures. In this study, we examined the pathway regulated by tPA in seizures.

METHODS

An experimental model of kainate-induced seizures was used in genetically modified mice, including mice deficient in tPA (tPA (-/-) ), its inhibitor neuroserpin (Nsp (-/-) ), or both (Nsp:tPA (-/-) ), and in mice conditionally deficient in the platelet-derived growth factor receptor alpha (PDGFRα).

RESULTS

Compared to wild-type (WT) mice, Nsp (-/-) mice have significantly reduced latency to seizure onset and generalization; whereas tPA (-/-) mice have the opposite phenotype, as do Nsp:tPA (-/-) mice. Furthermore, interventions that maintain BBB integrity delay seizure propagation, whereas osmotic disruption of the BBB in seizure-resistant tPA (-/-) mice dramatically reduces the time to seizure onset and accelerates seizure progression. The phenotypic differences in seizure progression between WT, tPA (-/-) , and Nsp (-/-) mice are also observed in electroencephalogram recordings in vivo, but absent in ex vivo electrophysiological recordings where regulation of the BBB is no longer necessary to maintain the extracellular environment. Finally, we demonstrate that these effects on seizure progression are mediated through signaling by PDGFRα on perivascular astrocytes.

INTERPRETATION

Together, these data identify a specific molecular pathway involving tPA-mediated PDGFRα signaling in perivascular astrocytes that regulates seizure progression through control of the BBB. Inhibition of PDGFRα signaling and maintenance of BBB integrity might therefore offer a novel clinical approach for managing seizures.

Eslicarbazepine acetate for the treatment of focal epilepsy: an update on its proposed mechanisms of action

Eslicarbazepine acetate (ESL) is a once daily antiepileptic drug (AED) approved by the European Medicines Agency (EMA), the Food and Drug Administration (FDA) and Health Canada as an adjunctive therapy in adults with partial-onset seizures (POS). In humans and in relevant animal laboratory species, ESL undergoes extensive first pass hydrolysis to its major active metabolite eslicarbazepine that represents ∼95% of circulating active moieties. ESL and eslicarbazepine showed anticonvulsant activity in animal models. ESL may not only suppress seizure activity but may also inhibit the generation of a hyperexcitable network. Data reviewed here suggest that ESL and eslicarbazepine demonstrated the following in animal models: (1) the selectivity of interaction with the inactive state of the voltage-gated sodium channel (VGSC), (2) reduction in VGSC availability through enhancement of slow inactivation, instead of alteration of fast inactivation of VGSC, (3) the failure to cause a paradoxical upregulation of persistent Na⁺ current (I_NaP), and (4) the reduction in firing frequencies of excitatory neurons in dissociated hippocampal cells from patients with epilepsy who were pharmacoresistant to carbamazepine (CBZ). In addition, eslicarbazepine effectively inhibited high- and low-affinity hCa_V3.2 inward currents with greater affinity than CBZ. These preclinical findings may suggest the potential for antiepileptogenic effects; furthermore, the lack of effect upon K_V7.2 outward currents may translate into a reduced potential for eslicarbazepine to facilitate repetitive firing.

Eslicarbazepine and the enhancement of slow inactivation of voltage-gated sodium channels: a comparison with carbamazepine, oxcarbazepine and lacosamide

This study aimed at evaluating the effects of eslicarbazepine, carbamazepine (CBZ), oxcarbazepine (OXC) and lacosamide (LCM) on the fast and slow inactivated states of voltage-gated sodium channels (VGSC). The anti-epileptiform activity was evaluated in mouse isolated hippocampal slices. The anticonvulsant effects were evaluated in MES and the 6-Hz psychomotor tests. The whole-cell patch-clamp technique was used to investigate the effects of eslicarbazepine, CBZ, OXC and LCM on sodium channels endogenously expressed in N1E-115 mouse neuroblastoma cells. CBZ and eslicarbazepine exhibit similar concentration dependent suppression of epileptiform activity in hippocampal slices. In N1E-115 mouse neuroblastoma cells, at a concentration of 250 μM, the voltage dependence of the fast inactivation was not influenced by eslicarbazepine, whereas LCM, CBZ and OXC shifted the V0.5 value (mV) by -4.8, -12.0 and -16.6, respectively. Eslicarbazepine- and LCM-treated fast-inactivated channels recovered similarly to control conditions, whereas CBZ- and OXC-treated channels required longer pulses to recover. CBZ, eslicarbazepine and LCM shifted the voltage dependence of the slow inactivation (V0.5, mV) by -4.6, -31.2 and -53.3, respectively. For eslicarbazepine, LCM, CBZ and OXC, the affinity to the slow inactivated state was 5.9, 10.4, 1.7 and 1.8 times higher than to the channels in the resting state, respectively. In conclusion, eslicarbazepine did not share with CBZ and OXC the ability to alter fast inactivation of VGSC. Both eslicarbazepine and LCM reduce VGSC availability through enhancement of slow inactivation, but LCM demonstrated higher interaction with VGSC in the resting state and with fast inactivation gating.

Systems biology, complexity, and the impact on antiepileptic drug discovery

The number of available anticonvulsant drugs increased in the period spanning over more than a century, amounting to the current panoply of nearly two dozen so-called antiepileptic drugs (AEDs). However, none of them actually prevents/reduces the post-brain insult development of epilepsy in man, and in no less than a third of patients with epilepsy, the seizures are not drug-controlled. Plausibly, the enduring limitation of AEDs' efficacy derives from the insufficient understanding of epileptic pathology. This review pinpoints the unbalanced reductionism of the analytic approaches that overlook the intrinsic complexity of epilepsy and of the drug resistance in epilepsy as the core conceptual flaw hampering the discovery of truly antiepileptogenic drugs. A rising awareness of the complexity of epileptic pathology is, however, brought about by the emergence of nonreductionist systems biology (SB) that considers the networks of interactions underlying the normal organismic functions and of SB-based systems (network) pharmacology that aims to restore pathological networks. By now, the systems pharmacology approaches of AED discovery are fairly meager, but their forthcoming development is both a necessity and a realistic prospect, explored in this review.

Antiseizure drugs differentially modulate θ-burst induced long-term potentiation in C57BL/6 mice

OBJECTIVE

Cognitive comorbidities are increasingly recognized as an equal (or even more disabling) aspect of epilepsy. In addition, the actions of some antiseizure drugs (ASDs) can impact learning and memory. Accordingly, the National Institute of Neurological Disorders and Stroke (NINDS) epilepsy research benchmarks call for the implementation of standardized protocols for screening ASDs for their amelioration or exacerbation of cognitive comorbidities. Long-term potentiation (LTP) is a widely used model for investigating synaptic plasticity and its relationship to learning and memory. Although the effects of some ASDs on LTP have been examined, none of these studies employed physiologically relevant induction stimuli such as theta-burst stimulation (TBS). To systematically evaluate the effects of multiple ASDs in the same preparation using physiologically relevant stimulation protocols, we examined the effects of a broad panel of existing ASDs on TBS-induced LTP in area CA1 of in vitro brain slices, prepared in either normal or sucrose-based artificial cerebrospinal fluid (ACSF), from C57BL/6 mice.

METHODS

Coronal brain slices containing the dorsal hippocampus were made using either standard or sucrose-based ACSF. Recordings were obtained from four slices at a time using the Scientifica Slicemaster high throughput recording system. Slices exposed to ASDs were paired with slices from the opposite hemisphere that served as controls. Field excitatory postsynaptic potentials (fEPSPs) were recorded, and all ASDs were applied to slices by bath perfusion for 20 min prior to the induction stimulus. LTP was induced by TBS or by high-frequency stimulation (HFS). The following ASDs were examined: 100 μM phenobarbital (PB), 80 μM phenytoin (PHT), 50 μM carbamazepine (CBZ), 600 μM valproate (VPA), 60 μM topiramate (TPM), 60 μM lamotrigine (LTG), 100 μM levetiracetam (LEV), 10 μM ezogabine (EZG), and 30 μM tiagabine (TGB).

RESULTS

Among voltage-gated sodium channel inhibitors, CBZ significantly attenuated TBS-induced LTP, PHT attenuated both TBS-induced LTP and post-tetanic potentiation (PTP), and LTG failed to affect LTP but did attenuate PTP. ASDs that modulate γ-aminobutyric acid (GABA)ergic synaptic transmission, such as PB and TGB, significantly attenuated LTP in brain slices prepared in sucrose-based ACSF but not standard ACSF. Third generation ASDs, such as LEV and TPM, did not affect LTP in ACSF- or sucrose-prepared brain slices. Although EZG failed to affect LTP, it did significantly attenuate PTP under both slicing conditions. VPA failed to affect LTP in area CA1, both in C57BL/6 mice and Sprague-Dawley rats, using TBS or HFS. However, VPA did attenuate TBS-induced LTP in the dentate gyrus (DG).

SIGNIFICANCE

The results of experiments describe herein provide a comprehensive summary of the effects of many commonly used ASDs on short- and long-term synaptic plasticity while, for the first time, using physiologically relevant LTP induction protocols and slice preparations from mice. Furthermore, methodologic variables, such as brain slice preparation protocols, were explored. These results provide comparative knowledge of ASD effects on synaptic plasticity in the mouse hippocampus and may ultimately contribute to an understanding of the differences in the cognitive side effect profiles of ASDs and the prediction of cognitive dysfunction associated with novel investigational ASDs.

Synergism of lacosamide with established antiepileptic drugs in the 6-Hz seizure model in mice

PURPOSE

Lacosamide (LCM, Vimpat) is an anticonvulsant with a unique mode of action. This provides lacosamide with the potential to act additively or even synergistically with other antiepileptic drugs (AEDs). The objective of this study was to determine the presence of such interactions by isobolographic analysis.

METHODS

The anticonvulsant effect of LCM in combination with other AEDs including carbamazepine (CBZ), phenytoin (PHT), valproate (VPA), lamotrigine (LTG), topiramate (TPM), gabapentin (GBP), and levetiracetam (LEV) at fixed dose ratios of 1:3, 1:1, and 3:1, was evaluated in the 6-Hz-induced seizure model in mice. In addition, the impact of the combinations of LCM with the other AEDs on motor coordination was assessed in the rotarod test. Finally, AED concentrations were measured in blood and brain to evaluate potential pharmacokinetic drug interactions.

KEY FINDINGS

All studied AEDs produced dose-dependent anticonvulsant effects against 6-Hz-induced seizures. Combinations of LCM with CBZ, LTG, TPM, GBP, or LEV were synergistic. All other LCM/AED combinations displayed additive effects with a tendency toward synergism. Furthermore, no enhanced adverse effects were observed in the rotarod test by combining LCM with other AEDs. No pharmacokinetic interactions were seen on brain AED concentrations. Coadministration of LCM and TPM led to an increase in plasma levels of LCM, whereas the plasma concentration of PHT was increased by coadministration of LCM.

SIGNIFICANCE

The synergistic anticonvulsant interaction of LCM with various AEDs, without exacerbation of adverse motor effects, highlights promising properties of LCM as add-on therapy for drug refractory epilepsy.

Nefiracetam attenuates post-ischemic nonconvulsive seizures in rats and protects neuronal cell death induced by veratridine and glutamate

AIMS

Stroke patients are at a high risk of developing post-ischemic seizures and cognitive impairment. Nefiracetam (NEF), a pyrrolidone derivative, has been shown to possess both anti-epileptic and cognitive-enhancing properties. In this study the anti-seizure effects of NEF were evaluated in a rat model of post-ischemic nonconvulsive seizures (NCSs). Its potential mechanisms were investigated in neuronal cell culture assays of neurotoxicity associated with ischemic brain injury and epileptogenesis.

MAIN METHODS

In the in vivo study, rats received 24h permanent middle cerebral artery occlusion. NEF was administered intravenously either at 15 min post-injury but prior to the first NCS event (30 mg/kg, pre-NCS treatment) or immediately after the first NCS occurred (30 or 60 mg/kg, post-NCS treatment). In the in vitro study, neuronal cell cultures were exposed to veratridine or glutamate and treated with NEF (1-500 nM).

KEY FINDINGS

The NEF pre-NCS treatment significantly reduced the NCS frequency and duration, whereas the higher NEF dose (60 mg/kg) was required to achieve similar effects when given after NCS occurred. The NEF treatment also dose-dependently (5-500 nM) protected against neuronal cell death induced by veratridine as measured by MTT cell viability assay, but higher doses (250-500 nM) were required against glutamate toxicity.

SIGNIFICANCE

The anti-seizure property of NEF was demonstrated in a clinically relevant rat model of post-ischemic NCS. The preferential effects of NEF against in vitro veratridine toxicity suggest the involvement of its modulation of sodium channel malfunction. Future studies are warranted to study the mechanisms of NEF against ischemic brain injury and post-ischemic seizures.

Synergistic GABA-enhancing therapy against seizures in a mouse model of Dravet syndrome

Seizures remain uncontrolled in 30% of patients with epilepsy, even with concurrent use of multiple drugs, and uncontrolled seizures result in increased morbidity and mortality. An extreme example is Dravet syndrome (DS), an infantile-onset severe epilepsy caused by heterozygous loss of function mutations in SCN1A, the gene encoding the brain type-I voltage-gated sodium channel NaV1.1. Studies in Scn1a heterozygous knockout mice demonstrate reduced excitability of GABAergic interneurons, suggesting that enhancement of GABA signaling may improve seizure control and comorbidities. We studied the efficacy of two GABA-enhancing drugs, clonazepam and tiagabine, alone and in combination, against thermally evoked myoclonic and generalized tonic-clonic seizures. Clonazepam, a positive allosteric modulator of GABA-A receptors, protected against myoclonic and generalized tonic-clonic seizures. Tiagabine, a presynaptic GABA reuptake inhibitor, was protective against generalized tonic-clonic seizures but only minimally protective against myoclonic seizures and enhanced myoclonic seizure susceptibility at high doses. Combined therapy with clonazepam and tiagabine was synergistic against generalized tonic-clonic seizures but was additive against myoclonic seizures. Toxicity determined by rotorod testing was additive for combination therapy. The synergistic actions of clonazepam and tiagabine gave enhanced seizure protection and reduced toxicity, suggesting that combination therapy may be well tolerated and effective for seizures in DS.

Identification of compounds with anti-convulsant properties in a zebrafish model of epileptic seizures

The availability of animal models of epileptic seizures provides opportunities to identify novel anticonvulsants for the treatment of people with epilepsy. We found that exposure of 2-day-old zebrafish embryos to the convulsant agent pentylenetetrazole (PTZ) rapidly induces the expression of synaptic-activity-regulated genes in the CNS, and elicited vigorous episodes of calcium (Ca(2+)) flux in muscle cells as well as intense locomotor activity. We then screened a library of ∼2000 known bioactive small molecules and identified 46 compounds that suppressed PTZ-inducedtranscription of the synaptic-activity-regulated gene fos in 2-day-old (2 dpf) zebrafish embryos. Further analysis of a subset of these compounds, which included compounds with known and newly identified anticonvulsant properties, revealed that they exhibited concentration-dependent inhibition of both locomotor activity and PTZ-induced fos transcription, confirming their anticonvulsant characteristics. We conclude that this in situ hybridisation assay for fos transcription in the zebrafish embryonic CNS is a robust, high-throughput in vivo indicator of the neural response to convulsant treatment and lends itself well to chemical screening applications. Moreover, our results demonstrate that suppression of PTZ-induced fos expression provides a sensitive means of identifying compounds with anticonvulsant activities.

Antiepileptic drug therapy: does mechanism of action matter?

This article represents a synthesis of presentations made by the authors during a scientific meeting held in London on 7 June 2010 and organized by GlaxoSmithKline. Each speaker produced a short précis of his lecture to answer a specific question, resulting in an overview of what we know about the relevance of the mechanisms of action of antiepileptic drugs in determining appropriate combination therapies for the treatment of drug-resistant epilepsy.

Experimental re-evaluation of flunarizine as add-on antiepileptic therapy

Background:

Experimental studies have found several calcium channel blockers with anticonvulsant property. Flunarizine is one of the most potent calcium channel blockers, which has shown anticonvulsant effect against pentylenetetrazole (PTZ) and maximal electroshock (MES)-induced seizures. However, further experimental and clinical trials have shown varied results. We conducted a PTZ model experimental study to re-evaluate the potential of flunarizine for add-on therapy in the management of refractory epilepsy.

Materials and Methods:

Experiments were conducted in PTZ model involving Swiss strain mice. Doses producing seizures in 50% and 99% mice, i.e. CD₅₀ and CD₉₉ values of PTZ were obtained from the dose-response study. Animals received graded, single dose of sodium valproate (100–300 mg/kg), lamotrigine (3–12 mg/kg) and flunarizine (5–20 mg/kg), and then each group of mice was injected with CD₉₉ dose of PTZ (65mg/kg i.p.). Another group of mice received single ED₅₀ dose (dose producing seizure protection in 50% mice) of sodium valproate and flunarizine separately in left and right side of abdomen. Results were analysed by Kruskal–Wallis ANOVA on Ranks test.

Results:

As compared to control, sodium valproate at 250 mg/kg and 300 mg/kg produced statistical significant seizure protection. At none of the pre-treatment dose levels of lamotrigine, the seizure score with PTZ differed significantly from that observed in the vehicle-treated group. Pre-treatment with flunarizine demonstrated dose-dependent decrease in the seizure score to PTZ administration. As compared to control group, flunarizine at 20 mg/kg produced statistical significant seizure protection.

Conclusion:

As combined use of sodium valproate and flunarizine has shown significant seizure protection in PTZ model, flunarizine has a potential for add-on therapy in refractory cases of partial seizures. It is therefore, we conclude that further experimental studies and multicenter clinical trials involving large sample size are needed to establish flunarizine as add-on therapy in refractory epilepsy.