Localization and photoaffinity labelling of the levetiracetam binding site in rat brain and certain cell lines

Discovery of E2730, a novel selective uncompetitive GAT1 inhibitor, as a candidate for anti-seizure medication

OBJECTIVE

As of 2022, 36 anti-seizure medications (ASMs) have been licensed for the treatment of epilepsy, however, adverse effects (AEs) are commonly reported. Therefore, ASMs with a wide margin between therapeutic effects and AEs are preferred over ASMs that are associated with a narrow margin between efficacy and risk of AEs. E2730 was discovered using in vivo phenotypic screening and characterized as an uncompetitive, yet selective, inhibitor of γ-aminobutyric acid (GABA) transporter 1 (GAT1). Here, we describe the preclinical characteristics of E2730.

METHODS

Anti-seizure effects of E2730 were evaluated in several animal models of epilepsy: corneal kindling, 6 Hz-44 mA psychomotor seizure, amygdala kindling, Fragile X syndrome, and Dravet syndrome models. Effects of E2730 on motor coordination were assessed in accelerating rotarod tests. The mechanism of action of E2730 was explored by [3 H]E2730 binding assay. The GAT1-selectivity over other GABA transporters was examined by GABA uptake assay of GAT1, GAT2, GAT3, or betaine/GABA transporter 1 (BGT-1) stably expressing HEK293 cells. To further investigate the mechanism for E2730-mediated inhibition of GAT1, in vivo microdialysis and in vitro GABA uptake assays were conducted under conditions of different GABA concentrations.

RESULTS

E2730 showed anti-seizure effects in the assessed animal models with an approximately >20-‍fold margin between efficacy and motor incoordination. [3 H]E2730 binding on brain synaptosomal membrane was abolished in GAT1-deficient mice, and E2730 selectively inhibited GAT1-mediated GABA uptake over other GABA transporters. In addition, results of GABA uptake assays showed that E2730-mediated inhibition of GAT1 positively correlated to the level of ambient GABA in vitro. E2730 also increased extracellular GABA concentration in hyperactivated conditions but not under basal levels in vivo.

SIGNIFICANCE

E2730 is a novel, selective, uncompetitive GAT1 inhibitor, which acts selectively under the condition of increasing synaptic activity, contributing to a wide margin between therapeutic effect and motor incoordination.

Assessment of the toxic effects of levetiracetam on biochemical, functional, and redox parameters of salivary glands in male Wistar rats

Levetiracetam (LEV) is an anticonvulsant for epilepsy. The toxic effects of this medication in tissues have been associated with redox state imbalance, which can lead to salivary gland dysfunction. Therefore, the current work investigated the effects of LEV on the biochemical, functional, and redox parameters of the parotid and submandibular glands in rats. For this, male Wistar rats (Rattus norvegicus albinus) were randomly divided into 3 groups (n = 10/group): Control (0.9% saline solution), LEV100 (100 mg/kg), and LEV300 (300 mg/kg). After 21 consecutive days of intragastric gavage treatments, pilocarpine stimulated saliva secretion was collected for salivary biochemical analysis. The extracted salivary glands were utilized for histomorphometry and redox state analyses. Our results showed that LEV300 increased plasma hepatotoxicity markers and reduced salivary amylase activity and the acinar surface area of the parotid gland. Total oxidant capacity and oxidative damage to lipids and proteins were higher in the parotid gland, while total antioxidant capacity and uric acid levels were reduced in the submandibular gland of the LEV100 group compared to Control. On the other hand, total oxidant capacity, oxidative damage to lipids and proteins, total antioxidant capacity, and uric acid levels were lower in both salivary glands of the LEV300 group compared to Control. Superoxide dismutase and glutathione peroxidase activities were lower in the salivary glands of treated animals compared to Control. In conclusion our data suggest that treatment with LEV represents a potentially toxic agent, that contributes to drug-induced salivary gland dysfunction.

Perinatal hypoxia and thalamus brain region: increased efficiency of antiepileptic drug levetiracetam to inhibit GABA release from nerve terminals

Levetiracetam (LV), 2S-(2-oxo-1-pyrrolidiny1) butanamide, is an antiepileptic drug. The exact mechanisms of anticonvulsant effects of LV remain unclear. In this study, rats (Wistar strain) underwent hypoxia and seizures at the age of 10–12 postnatal days (pd). [3H]GABA release was analysed in isolated from thalamus nerve terminals (synaptosomes) during development at the age of pd 17–19 and pd 24–26 (infantile stage), pd 38–40 (puberty) and pd 66–73 (young adults) in control and after perinatal hypoxia. The extracellular level of [3H]GABA in the preparation of thalamic synaptosomes increased during development at the age of pd 38–40 and pd 66–73 as compared to earlier ones. LV did not influence the extracellular level of [3H]GABA in control and after perinatal hypoxia at all studied ages. Exocytotic [3H]GABA release in control increased at the age of pd 24–26 as compared to pd 17–19. After hypoxia, exocytotic [3H]GABA release from synaptosomes also increased during development. LV elevated [3H]GABA release from thalamic synaptosomes at the age of pd 66–73 after hypoxia and during blockage of GABA uptake by NO-711 only. LV realizes its antiepileptic effects at the presynaptic site through an increase in exocytotic release of [3H]GABA in thalamic synaptosomes after perinatal hypoxia at pd 66–73. LV exhibited a more significant effect in thalamic synaptosomes after perinatal hypoxia than in control ones. The action of LV is age-dependent, and the drug was inert at the infantile stage that can be useful for an LV application strategy in child epilepsy therapy. Keywords: brain development, exocytosis, GABA, levetiracetam, perinatal hypoxia, thalamic synaptosomes

Glutathione and Related Molecules in Parkinsonism

Glutathione (GSH) is the most abundant intrinsic antioxidant in the central nervous system, and its substrate cysteine readily becomes the oxidized dimeric cystine. Since neurons lack a cystine transport system, neuronal GSH synthesis depends on cystine uptake via the cystine/glutamate exchange transporter (xCT), GSH synthesis, and release in/from surrounding astrocytes. Transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2), a detoxifying master transcription factor, is expressed mainly in astrocytes and activates the gene expression of various phase II drug-metabolizing enzymes or antioxidants including GSH-related molecules and metallothionein by binding to the antioxidant response element (ARE) of these genes. Accumulating evidence has shown the involvement of dysfunction of antioxidative molecules including GSH and its related molecules in the pathogenesis of Parkinson’s disease (PD) or parkinsonian models. Furthermore, we found several agents targeting GSH synthesis in the astrocytes that protect nigrostriatal dopaminergic neuronal loss in PD models. In this article, the neuroprotective effects of supplementation and enhancement of GSH and its related molecules in PD pathology are reviewed, along with introducing new experimental findings, especially targeting of the xCT-GSH synthetic system and Nrf2–ARE pathway in astrocytes.

Synthesis and Preclinical Evaluation of 11C-UCB-J as a PET Tracer for Imaging the Synaptic Vesicle Glycoprotein 2A in the Brain

The synaptic vesicle glycoprotein 2A (SV2A) is found in secretory vesicles in neurons and endocrine cells. PET with a selective SV2A radiotracer will allow characterization of drugs that modulate SV2A (e.g., antiepileptic drugs) and potentially could be a biomarker of synaptic density (e.g., in neurodegenerative disorders). Here we describe the synthesis and characterization of the SV2A PET radiotracer (11)C-UCB-J ((R)-1-((3-((11)C-methyl-(11)C)pyridin-4-yl)methyl)-4-(3,4,5-trifluorophenyl)pyrrolidin-2-one) in nonhuman primates, including whole-body biodistribution.

METHODS

(11)C-UCB-J was prepared by C-(11)C-methylation of the 3-pyridyl trifluoroborate precursor with (11)C-methyl iodide via the Suzuki-Miyaura cross-coupling method. Rhesus macaques underwent multiple scans including coinjection with unlabeled UCB-J (17, 50, and 150 μg/kg) or preblocking with the antiepileptic drug levetiracetam at 10 and 30 mg/kg. Scans were acquired for 2 h with arterial sampling and metabolite analysis to measure the input function. Regional volume of distribution (VT) was estimated using the 1-tissue-compartment model. Target occupancy was assessed using the occupancy plot; the dissociation constant (Kd) was determined by fitting self-blocking occupancies to a 1-site model, and the maximum number of receptor binding sites (Bmax) values were derived from baseline VT and from the estimated Kd and the nondisplaceable distribution volume (VND).

RESULTS

(11)C-UCB-J was synthesized with greater than 98% purity. (11)C-UCB-J exhibited high free fraction (0.46 ± 0.02) and metabolized at a moderate rate (39% ± 5% and 24% ± 3% parent remaining at 30 and 90 min) in plasma. In the monkey brain, (11)C-UCB-J displayed high uptake and fast kinetics. VT was high (∼25-55 mL/cm(3)) in all gray matter regions, consistent with the ubiquitous expression of SV2A. Preblocking with 10 and 30 mg/kg of levetiracetam resulted in approximately 60% and 90% occupancy, respectively. Analysis of the self-blocking scans yielded a Kd estimate of 3.4 nM and Bmax of 125-350 nM, in good agreement with the in vitro inhibition constant (Ki) of 6.3 nM and regional Bmax in humans. Whole-body biodistribution revealed that the liver and the brain are the dose-limiting organs for males and females, respectively.

CONCLUSION

(11)C-UCB-J exhibited excellent characteristics as an SV2A PET radiotracer in nonhuman primates. The radiotracer is currently undergoing first-in-human evaluation.

Audiogenic reflex seizures in cats

OBJECTIVES

This study aimed to characterise feline audiogenic reflex seizures (FARS).

METHODS

An online questionnaire was developed to capture information from owners with cats suffering from FARS. This was collated with the medical records from the primary veterinarian. Ninety-six cats were included.

RESULTS

Myoclonic seizures were one of the cardinal signs of this syndrome (90/96), frequently occurring prior to generalised tonic-clonic seizures (GTCSs) in this population. Other features include a late onset (median 15 years) and absence seizures (6/96), with most seizures triggered by high-frequency sounds amid occasional spontaneous seizures (up to 20%). Half the population (48/96) had hearing impairment or were deaf. One-third of cats (35/96) had concurrent diseases, most likely reflecting the age distribution. Birmans were strongly represented (30/96). Levetiracetam gave good seizure control. The course of the epilepsy was non-progressive in the majority (68/96), with an improvement over time in some (23/96). Only 33/96 and 11/90 owners, respectively, felt the GTCSs and myoclonic seizures affected their cat's quality of life (QoL). Despite this, many owners (50/96) reported a slow decline in their cat's health, becoming less responsive (43/50), not jumping (41/50), becoming uncoordinated or weak in the pelvic limbs (24/50) and exhibiting dramatic weight loss (39/50). These signs were exclusively reported in cats experiencing seizures for >2 years, with 42/50 owners stating these signs affected their cat's QoL.

CONCLUSIONS AND RELEVANCE

In gathering data on audiogenic seizures in cats, we have identified a new epilepsy syndrome named FARS with a geriatric onset. Further studies are warranted to investigate potential genetic predispositions to this condition.

Exploring the interaction of SV2A with racetams using homology modelling, molecular dynamics and site-directed mutagenesis

The putative Major Facilitator Superfamily (MFS) transporter, SV2A, is the target for levetiracetam (LEV), which is a successful anti-epileptic drug. Furthermore, SV2A knock out mice display a severe seizure phenotype and die after a few weeks. Despite this, the mode of action of LEV is not known at the molecular level. It would be extremely desirable to understand this more fully in order to aid the design of improved anti-epileptic compounds. Since there is no structure for SV2A, homology modelling can provide insight into the ligand-binding site. However, it is not a trivial process to build such models, since SV2A has low sequence identity to those MFS transporters whose structures are known. A further level of complexity is added by the fact that it is not known which conformational state of the receptor LEV binds to, as multiple conformational states have been inferred by tomography and ligand binding assays or indeed, if binding is exclusive to a single state. Here, we explore models of both the inward and outward facing conformational states of SV2A (according to the alternating access mechanism for MFS transporters). We use a sequence conservation analysis to help guide the homology modelling process and generate the models, which we assess further with Molecular Dynamics (MD). By comparing the MD results in conjunction with docking and simulation of a LEV-analogue used in radioligand binding assays, we were able to suggest further residues that line the binding pocket. These were confirmed experimentally. In particular, mutation of D670 leads to a complete loss of binding. The results shed light on the way LEV analogues may interact with SV2A and may help with the on-going design of improved anti-epileptic compounds.

Current pharmacological treatment approaches for alcohol dependence

INTRODUCTION

At present, the substances acamprosate, naltrexone and disulfiram are available for pharmacotherapy in alcohol dependence, but clinical studies found only modest effect sizes of these treatment options.

AREAS COVERED

This article focuses on current pharmacological treatment approaches for alcohol dependence, which have been evaluated in randomized, placebo-controlled trials (RCTs).

EXPERT OPINION

Besides the opioid system modulator nalmefene, which has recently been approved as a medication for the reduction of alcohol consumption, several compounds have been investigated in patients with alcohol dependence using a randomized, placebo-controlled design. In these studies, the antiepileptic drugs topiramate and gabapentin were found to be effective in improving several drinking-related outcomes, whereas levetiracetam failed to show efficacy in the treatment of alcohol dependence. Clinical studies using (low-dose) baclofen, a selective GABA-B receptor agonist, produced conflicting results, so that results of further trials are needed. Varenicline has also shown mixed results in two RCTs, but might possibly be useful in patients with comorbid nicotine dependence. The α1 adrenergic antagonist prazosin is currently under investigation in alcohol dependence with and without comorbid posttraumatic stress disorder (PTSD). Finally, first clinical evidence suggests that the 5-HT3 antagonist ondansetron might possibly be used in future within a pharmacogenetic treatment approach in alcohol dependence.

Discovery of heterocyclic nonacetamide synaptic vesicle protein 2A (SV2A) ligands with single-digit nanomolar potency: opening avenues towards the first SV2A positron emission tomography (PET) ligands

The role of the synaptic vesicle protein 2A (SV2A) protein, target of the antiepileptic drug levetiracetam, is still mostly unknown. Considering its potential to provide in vivo functional insights into the role of SV2A in epileptic patients, the development of an SV2A positron emission tomography (PET) tracer has been undertaken. Using a 3D pharmacophore model based on close analogues of levetiracetam, we report the rationale design of three heterocyclic non-acetamide lead compounds, UCB-A, UCB-H and UCB-J, the first single-digit nanomolar SV2A ligands with suitable properties for development as PET tracers.

Expression of SV2 isoforms during rodent brain development

Background

SV2A, SV2B and SV2C are synaptic vesicle proteins that are structurally related to members of the major facilitator superfamily (MFS). The function and transported substrate of the SV2 proteins is not clearly defined although they are linked to neurotransmitters release in a presynaptic calcium concentration-dependent manner. SV2A and SV2B exhibit broad expression in the central nervous system while SV2C appears to be more restricted in defined areas such as striatum. SV2A knockout mice start to display generalized seizures at a late developmental stage, around post-natal day 7 (P7), and die around P15. More recently, SV2A was demonstrated to be the molecular target of levetiracetam, an approved anti-epileptic drug (AED). The purpose of this work was to precisely analyze and quantify the SV2A, SV2B and SV2C expression during brain development to understand the contribution of these proteins in brain development and their impact on epileptic seizures.

Results

First, we systematically analyzed by immunohistofluorescence, the SV2A, SV2B and SV2C expression during mouse brain development, from embryonic day 12 (E12) to P30. This semi-quantitative approach suggests a modulation of SV2A and SV2B expression in hippocampus around P7. This is the reason why we used various quantitative approaches (laser microdissection of whole hippocampus followed by qRT-PCR and western blot analysis) indicating that SV2A and SV2B expression increased between P5 and P7 and remained stable between P7 and P10. Moreover, the increase of SV2A expression in the hippocampus at P7 was mainly observed in the CA1 region while SV2B expression in this region remains stable.

Conclusions

The observed alterations of SV2A expression in hippocampus are consistent with the appearance of seizures in SV2A−/− animals at early postnatal age and the hypothesis that SV2A absence favors epileptic seizures around P7.

Levetiracetam: the first SV2A ligand for the treatment of epilepsy

Levetiracetam is a multiple action drug that primarily acts through an interaction with the synaptic vesicle protein 2A. Levetiracetam is the first drug of its kind to be approved for the treatment of epilepsy and is now the most prescribed among the newer antiepileptic drugs. The discovery process identifying levetiracetam's antiepileptic potential was unique because it challenged several dogmas of antiepileptic drug discovery, and thereby encountered skepticism from the epilepsy community. This was contrasted by a very successful development programme leading to rapid regulatory approval by the FDA. The history of levetiracetam proves that a small core group of committed scientists and physicians, who dare to challenge the conventional scientific doctrine, can be successful in bringing to market a truly novel therapy for epilepsy patients.

Combining modelling and mutagenesis studies of synaptic vesicle protein 2A to identify a series of residues involved in racetam binding

LEV (levetiracetam), an antiepileptic drug which possesses a unique profile in animal models of seizure and epilepsy, has as its unique binding site in brain, SV2A (synaptic vesicle protein 2A). Previous studies have used a chimaeric and site-specific mutagenesis approach to identify three residues in the putative tenth transmembrane helix of SV2A that, when mutated, alter binding of LEV and related racetam derivatives to SV2A. In the present paper, we report a combined modelling and mutagenesis study that successfully identifies another 11 residues in SV2A that appear to be involved in ligand binding. Sequence analysis and modelling of SV2A suggested residues equivalent to critical functional residues of other MFS (major facilitator superfamily) transporters. Alanine scanning of these and other SV2A residues resulted in the identification of residues affecting racetam binding, including Ile273 which differentiated between racetam analogues, when mutated to alanine. Integrating mutagenesis results with docking analysis led to the construction of a mutant in which six SV2A residues were replaced with corresponding SV2B residues. This mutant showed racetam ligand-binding affinity intermediate to the affinities observed for SV2A and SV2B.

Region-specific changes in gene expression in rat brain after chronic treatment with levetiracetam or phenytoin

PURPOSE

It is commonly assumed that antiepileptic drugs (AEDs) act similarly in the various parts of the brain as long as their molecular targets are present. A few experimental studies on metabolic effects of vigabatrin, levetiracetam, valproate, and lamotrigine have shown that these drugs may act differently in different brain regions. We examined effects of chronic treatment with levetiracetam or phenytoin on mRNA levels to detect regional drug effects in a broad, nonbiased manner.

METHODS

mRNA levels were monitored in three brain regions with oligonucleotide-based microarrays.

RESULTS

Levetiracetam (150 mg/kg for 90 days) changed the expression of 65 genes in pons/medulla oblongata, two in hippocampus, and one in frontal cortex. Phenytoin (75 mg/kg), in contrast, changed the expression of only three genes in pons/medulla oblongata, but 64 genes in hippocampus, and 327 genes in frontal cortex. Very little overlap between regions or drug treatments was observed with respect to effects on gene expression.

DISCUSSION

We conclude that chronic treatment with levetiracetam or phenytoin causes region-specific and highly differential effects on gene expression in the brain. Regional effects on gene expression could reflect regional differences in molecular targets of AEDs, and they could influence the clinical profiles of AEDs.

Effect of levetiracetam on hippocampal protein expression and cell proliferation in rats

PURPOSE

Levetiracetam (LEV) is a broad-spectrum antiepileptic drug (AED) with possibly also antiepileptogenic properties. LEV has a specific binding site in the central nervous system and reduces brain excitability; however, the precise mechanism of action (MOA) of LEV remains unclear. To further unravel the potential MOA pathways of LEV we investigated altered protein expression and cell proliferation in rat hippocampal tissue during LEV administration.

METHODS

On day 1 of the experiment, rats were randomly assigned to a treatment group (LEV, 600 mg/kg/day, n=10) and a control group (saline, n=10). On days 2 and 3 rats were injected with bromodeoxyuridine (50 mg/kg, i.p., BID). After 7 days of treatment rats were killed and their brains removed. The right hemisphere was processed for histochemistry. The left hippocampus was dissected and frozen for proteomic analysis. Proteins were extracted from the tissue and two-dimensional gel electrophoresis was performed.

RESULTS

Treatment with LEV did not influence hippocampal cell proliferation. Multivariate analysis of differential protein expression, determined by proteomic analysis, revealed a significant clustering of control and treatment groups. The proteins which most contribute to the difference between groups were identified with mass spectrometry. The identified proteins were either involved in cytoskeleton, energy metabolism, neurotransmission, signal transduction, myelinization or stress response.

DISCUSSION

LEV does not affect hippocampal cell proliferation but has significant effects on the expression of proteins involved in a variety of physiological processes involved in physiological processes that play an important role in the currently identified MOAs of AEDs such as neurotransmission and signal transduction.

Antiepileptic Drug Discovery and Development: What Have We Learned and Where Are We Going?

Current marketed antiepileptic drugs (AEDs) consist of a variety of structural classes with different mechanisms of action. These agents typically have non-overlapping efficacy and side-effect profiles presenting multiple treatment options for the patient population. However, approximately 30% of seizure sufferers fail to respond to current therapies often because poorly tolerated side-effects limit adequate dosing. The scope of this review is to summarize selected advances in 2nd and 3rd generation AEDs as well as compounds in development with novel mechanisms of action.

Proteomic searches comparing two (R)-lacosamide affinity baits: An electrophilic arylisothiocyanate and a photoactivated arylazide group

We have advanced a novel strategy to search for lacosamide ((R)-1) targets in the brain proteome where protein binding is expected to be modest. Our approach used lacosamide agents containing affinity bait (AB) and chemical reporter (CR) units. The affinity bait moiety is designed to irreversibly react with the target, and the CR group permits protein detection and capture. In this study, we report the preparation and evaluation of (R)-N-(4-azido)benzyl 2-acetamido-3-(prop-2-ynyloxy)propionamide ((R)-3) and show that this compound exhibits potent anticonvulsant activities in the MES seizure model in rodents. We compared the utility of (R)-3 with its isostere, (R)-N-(4-isothiocyanato)benzyl 2-acetamido-3-(prop-2-ynyloxy)propionamide ((R)-2), in proteomic studies designed to identify potential (R)-1 targets. We showed that despite the two-fold improved anticonvulsant activity of (R)-3 compared with (R)-2, (R)-2 was superior in revealing potential binding targets in the mouse brain soluble proteome. The difference in these agents utility has been attributed to the reactivity of the affinity baits (i.e., (R)-2: aryl isothiocyanate moiety; (R)-3: photoactivated aryl azide intermediates) in the irreversible protein modification step, and we conclude that this factor is a critical determinant of successful target detection where ligand (drug) binding is modest. The utility of (R)-2 and (R)-3 in in situ proteome studies is explored.

Levetiracetam attenuates hippocampal expression of synaptic plasticity-related immediate early and late response genes in amygdala-kindled rats

BACKGROUND

The amygdala-kindled rat is a model for human temporal lobe epilepsy and activity-dependent synaptic plasticity. Hippocampal RNA isolated from amygdala-kindled rats at different kindling stages was analyzed to identify kindling-induced genes. Furthermore, effects of the anti-epileptic drug levetiracetam on kindling-induced gene expression were examined.

RESULTS

Cyclooxygenase-2 (Cox-2), Protocadherin-8 (Pcdh8) and TGF-beta-inducible early response gene-1 (TIEG1) were identified and verified as differentially expressed transcripts in the hippocampus of kindled rats by in situ hybridization and quantitative RT-PCR. In addition, we identified a panel of 16 additional transcripts which included Arc, Egr3/Pilot, Homer1a, Ania-3, MMP9, Narp, c-fos, NGF, BDNF, NT-3, Synaptopodin, Pim1 kinase, TNF-alpha, RGS2, Egr2/krox-20 and beta-A activin that were differentially expressed in the hippocampus of amygdala-kindled rats. The list consists of many synaptic plasticity-related immediate early genes (IEGs) as well as some late response genes encoding transcription factors, neurotrophic factors and proteins that are known to regulate synaptic remodelling. In the hippocampus, induction of IEG expression was dependent on the afterdischarge (AD) duration. Levetiracetam, 40 mg/kg, suppressed the development of kindling measured as severity of seizures and AD duration. In addition, single animal profiling also showed that levetiracetam attenuated the observed kindling-induced IEG expression; an effect that paralleled the anti-epileptic effect of the drug on AD duration.

CONCLUSIONS

The present study provides mRNA expression data that suggest that levetiracetam attenuates expression of genes known to regulate synaptic remodelling. In the kindled rat, levetiracetam does so by shortening the AD duration thereby reducing the seizure-induced changes in mRNA expression in the hippocampus.

Brivaracetam and seletracetam, two new SV2A ligands, improve paroxysmal dystonia in the dt sz mutant hamster

Previous examinations demonstrated antidystonic effects of the synaptic vesicle protein 2A (SV2A) ligand levetiracetam in the dt(sz) mutant hamster, an animal model of paroxysmal non-kinesiogenic dyskinesia in which dystonic episodes can be induced by stress. In the present study, we examined the effects of the two new, high affinity SV2A ligands, brivaracetam and seletracetam, in comparison to levetiracetam on the severity of dystonia in mutant hamsters. Seletracetam (50 and 75 mg/kg i.p.) and brivaracetam (75 mg/kg i.p.) reduced the severity of dystonia to a comparable extent as levetiracetam (50 and 75 mg/kg i.p.). These data confirm the therapeutic potential of these pyrrolidone derivatives for the treatment of paroxysmal dystonia.

New molecular targets for antiepileptic drugs: alpha(2)delta, SV2A, and K(v)7/KCNQ/M potassium channels

Many currently prescribed antiepileptic drugs (AEDs) act via voltage-gated sodium channels, through effects on gamma-aminobutyric acid-mediated inhibition, or via voltage-gated calcium channels. Some newer AEDs do not act via these traditional mechanisms. The molecular targets for several of these nontraditional AEDs have been defined using cellular electrophysiology and molecular approaches. Here, we describe three of these targets: alpha(2)delta, auxiliary subunits of voltage-gated calcium channels through which the gabapentinoids gabapentin and pregabalin exert their anticonvulsant and analgesic actions; SV2A, a ubiquitous synaptic vesicle glycoprotein that may prepare vesicles for fusion and serves as the target for levetiracetam and its analog brivaracetam (which is currently in late-stage clinical development); and K(v)7/KCNQ/M potassium channels that mediate the M-current, which acts a brake on repetitive firing and burst generation and serves as the target for the investigational AEDs retigabine and ICA-105665. Functionally, all of the new targets modulate neurotransmitter output at synapses, focusing attention on presynaptic terminals as critical sites of action for AEDs.

Brivaracetam: a rational drug discovery success story

Levetiracetam, the alpha-ethyl analogue of the nootropic piracetam, is a widely used antiepileptic drug (AED) that provides protection against partial seizures and is also effective in the treatment of primary generalized seizure syndromes including juvenile myoclonic epilepsy. Levetiracetam was discovered in 1992 through screening in audiogenic seizure susceptible mice and, 3 years later, was reported to exhibit saturable, stereospecific binding in brain to a approximately 90 kDa protein, later identified as the ubiquitous synaptic vesicle glycoprotein SV2A. A large-scale screening effort to optimize binding affinity identified the 4-n-propyl analogue, brivaracetam, as having greater potency and a broadened spectrum of activity in animal seizure models. Recent phase II clinical trials demonstrating that brivaracetam is efficacious and well tolerated in the treatment of partial onset seizures have validated the strategy of the discovery programme. Brivaracetam is among the first clinically effective AEDs to be discovered by optimization of pharmacodynamic activity at a molecular target.

Levetiracetam: the profile of a novel anticonvulsant drug-part I: preclinical data

The objective of this article was to review and summarize the available reports on the preclinical profile of the novel anticonvulsant drug levetiracetam (LEV). Therefore, a careful search was conducted in the MEDLINE database and combined with guidelines from regulatory agencies, proceedings of professional scientific meetings, and information provided by the manufacturers. This article provides detailed information on the anticonvulsant effects of LEV in various animal models of epilepsy and on its pharmacology in laboratory animals. The mechanism of action of LEV is reviewed, with special regard to its recently discovered binding site, the synaptic vesicle protein 2A. In general, LEV is shown to be a safe, broad-spectrum anticonvulsant drug with highly beneficial pharmacokinetic properties and a distinct mechanism of action. The clinical studies with LEV will be discussed in the second part of this review article to be published subsequently.

Levetiracetam for the treatment of hot flashes: a phase II study

GOALS OF WORK

The objectives of this pilot trial were to assess the potential efficacy and safety of levetiracetam for the treatment of hot flashes, a major cause of morbidity among breast cancer survivors.

PATIENTS AND METHODS

Women, aged 18 years or more, with a history of breast cancer or those who wished to avoid estrogen because of a perceived increased risk of breast cancer, who were experiencing bothersome hot flashes (more than or equal to 14 times per week, for more than or equal to 1 month before study entry), were included. During the baseline week, general demographic characteristics, hot flash information, and quality of life data were obtained. At the beginning of week 2, patients were started on levetiracetam for a total of 4 weeks. Information about hot flashes, quality of life, and toxicity were collected during these 4 weeks and compared with the baseline week.

MAIN RESULTS

After treatment with levetiracetam for 4 weeks (N = 19), mean hot flash scores (frequency times mean severity) were reduced by 57%, and mean hot flash frequencies were reduced by 53%, compared to the baseline week; both these reductions were greater than what would be expected with a placebo (20-25% reduction). There were significant improvements in abnormal sweating (p = 0.004), hot flash distress (p = 0.0002), and satisfaction of hot flash control (p = 0.0001), when comparing data from the fourth week of treatment to the baseline week. Twenty-nine percent of the subjects did not complete the study because of treatment-related adverse events, with the most frequently reported side effects being somnolence, fatigue, and dizziness, usually with mild to moderate intensity.

CONCLUSION

The results of this pilot trial suggest that levetiracetam might be an effective therapy for the treatment of hot flashes. Further data are needed to test this hypothesis, evaluating the efficacy and toxicity of this agent.

The efficacy and tolerability of levetiracetam in pharmacoresistant epileptic dogs

Twenty-two dogs with idiopathic epilepsy which were pharmacoresistant to phenobarbitone and bromide were treated with levetiracetam as an add-on medication. Records of eight dogs were used retrospectively to determine a safe, efficient levetiracetam dosage. Fourteen dogs were entered into a prospective, open label, non-comparative study. After 2 months of levetiracetam oral treatment (10 mg/kg TID), 8/14 dogs responded significantly to the treatment and seizure frequency was reduced by 50%. In dogs that remained refractory, the dosage was increased to 20 mg/kg TID for 2 months. One further dog responded to levetiracetam treatment. Levetiracetam responders had a significant decrease in seizure frequency of 77% (7.9+/-5.2 to 1.8+/-1.7 seizures/month) and a decrease in seizure days per month of 68% (3.8+/-1.7 to 1.2+/-1.1 seizure days/month). However, 6/9 responders experienced an increase in seizure frequency and seizure days after 4-8 months continuing with the levetiracetam treatment at the last effective dosage. Levetiracetam was well tolerated by all dogs and sedation was the only side-effect reported in just one of the 14 dogs.

Prospective assessment of levetiracetam pharmacokinetics during dose escalation in 4- to 12-year-old children with partial-onset seizures on concomitant carbamazepine or valproate

PURPOSE

To assess the multiple-dose pharmacokinetics of levetiracetam and its major metabolite ucb L057 in children with partial-onset seizures and determine whether it is affected by adjunctive carbamazepine or valproate. To correlate levetiracetam concentrations in plasma and saliva and to assess its safety and clinical response.

METHODS

Design was an open-label, multicenter study. Twenty-one children (4-12 years old) with epilepsy taking carbamazepine (13) or valproate (8) received adjunctive levetiracetam. Levetiracetam was initiated at 20 mg/(kg day) and titrated at 2-week intervals to 40 and then 60 mg/(kg day). Twelve-hour pharmacokinetics were determined at the end of each 2-week period. Efficacy was estimated from the partial seizure frequency per week and Global Evaluation Scale.

RESULTS

Levetiracetam was rapidly absorbed following oral dosing, with median t(max) of 0.5 h. Dose proportional increases were observed for C(max) and AUC((0-12)) over the dose range; t(1/2) was 4.9 h. Pharmacokinetics of levetiracetam and ucb L057 were not markedly different with concomitant carbamazepine or valproate; clearance was only 7-13% faster and AUC was decreased by only 15-24% in those on carbamazepine compared to valproate. Levetiracetam did not affect trough carbamazepine or valproate. Concentration in saliva and plasma were strongly correlated. Seizure frequency declined by 50% or more in 43% of subjects in the intent-to-treat population (n=21) and in 56% of those with seizures at baseline (n=16). Marked or moderate improvement occurred in 80% and 75% of patients based on Global Evaluation Scale ratings by investigators and parents/guardians, respectively. Levetiracetam was well tolerated.

CONCLUSION

Levetiracetam exhibits simple pharmacokinetics in children, with rapid absorption and dose-proportional kinetics. Small but not clinically relevant differences were observed between subjects receiving carbamazepine and valproate, suggesting significant dose adjustment is usually not necessary. This substantiates prior assessments that levetiracetam clearance is higher in children than adults, necessitating a higher dose in children on a mg/kg basis, and suggests it is useful add-on therapy for children with partial-onset seizures regardless of baseline therapy.

Modulation of AMPA Receptors in Cultured Cortical Neurons Induced by the Antiepileptic Drug Levetiracetam

PURPOSE

The present study explores the hypothesis that the antiepileptic mechanism of action of levetiracetam (LEV) is related to effects on alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor channels in mouse cortical neurons in culture.

METHODS

The neurons were subjected to the whole-cell configuration of the patch-clamp recording technique and were 8-12 days old in culture.

RESULTS

Kainate elicited concentration-dependent (EC(50)= 80 microM) inward currents in all the patched cells. LEV (5-200 microM) itself did not induce inward or outward currents on all patched neurons, whereas it was effective on the kainate- and AMPA-induced current because it significantly decreased the amplitude of these currents. LEV was also able to significantly decrease the total membrane conductance during kainate perfusion, indicating that its effect was not dependent on the cellular voltage membrane potential. Further evidence that LEV modulated the ionotropic non-NMDA receptors came from the analysis of miniature excitatory postsynaptic currents (mEPSCs). In fact, LEV significantly decreased both the amplitude and the frequency of mEPSCs, as shown by the relative cumulative distributions.

CONCLUSIONS

These results reveal that AMPA receptors are modulated by LEV because a significant decrease in the kainate- and AMPA-induced currents and a decrease in amplitude and in frequency of mEPSCs have been observed in cortical neurons in culture. The described effect of LEV on AMPA receptors in cortical neurons is probably due to the etheromeric composition of the receptors and may be considered as a possible new antiepileptic mechanism of action.

Effect of levetiracetam on molecular regulation of hippocampal glutamate and GABA transporters in rats with chronic seizures induced by amygdalar FeCl3 injection

Enhancement of the glutamatergic excitatory synaptic transmission efficacy in the FeCl3 induced epilepsy model is associated with changes in the levels of glutamate and GABA transporter proteins. This study examined the effect of levetiracetam (LEV) on glutamate overflow and glutamate/GABA transporters expression in rats with epileptogenesis induced by the amygdalar injection of 1.0 microl of 100 mM FeCl3 (epileptic rat) and in control rats receiving amygdalar acidic saline injection (non-epileptic rat). In amygdalar acidic saline injected rats, 40 mM KCl-evoked glutamate overflow was significantly suppressed by both 32 and 100 microM LEV co-perfusion. In unilateral amygdalar FeCl3 injected rats, 32 microM LEV was ineffective, but the 100 microM LEV statistically suppressed glutamate overflow. Western blotting was employed to determine the hippocampal expression of glutamate/GABA transporters in epileptic or non-epileptic rats. The rats were treated for 14 days with 54 mg/kg LEV or vehicle intraperitoneally injection. Following 14 days of treatment, the ipsilateral hippocampus was removed for a Western blot analysis. In non-epileptic rats, the expression increased for all of the glutamate and GABA transporters (GLAST, GLT-1, EAAC-1, GAT-1 and GAT-3) while the glutamate transporter regulating protein (GTRAP3-18) decreased in comparison to those of normal rats that were treated with the vehicle. In epileptic rats receiving LEV, the EAAC-1 and GAT-3 levels increased while GTRAP3-18 (89%) decreased in comparison to those of the epileptic rats treated with the vehicle. GTRAP3-18 inhibitor regulates glutamate-binding affinity to EAAC-1. The anti-epileptic action of LEV may be partially due to a reduction of glutamate-induced excitotoxicity and an enhancement of the GABAergic inhibition as observed with the inhibitory effect on the 40 mM KCl-evoked glutamate overflow. These conclusions are supported by the increase in the expression of glial glutamate transporters (GLAST and GLT-1), and the increase in the expression of EAAC-1 and GAT-3 associated with a decrease in GTRAP3-18. The increased expression of EAAC-1 and the decreased expression of GTRAP3-18 in association with the up-regulation of GAT-3 due to such continual LEV administration was thus found to enhance GABA synthesis and reverse the transport of GABA both in non-epileptic and epileptic rats. The suppression of glutamate excitation and the enhancement of GABA inhibition in the rats with continual LEV administration is a result of the up-regulation of glutamate and GABA transporters with the down-regulation of GTRAP3-18. These observations together demonstrated the critical molecular mechanism of the anti-epileptic activity of LEV.

Levetiracetam Reduces Anesthetic-Induced Hyperalgesia in Rats

BACKGROUND

As part of an increase in excitability, small doses of pentobarbital, propofol, and midazolam induce an increased sensitivity to pain. Specific therapy to prevent or reduce this excitability may offer advantages over current clinical management with analgesics and sedatives. The pharmacological profile of the novel antiepileptic drug, levetiracetam, suggests that it may reduce the intensity of the excitatory stages of anesthesia.

METHODS

We examined the influence of levetiracetam on the reduction of the nociceptive reflex threshold in rats by sedative doses of pentobarbital, propofol, and midazolam. Measurements of nociceptive reflex threshold to pressure and heat were made and then repeated after intraperitoneal injection of saline or one of three doses of levetiracetam (100, 200, 500 mg/kg). Pentobarbital (30 mg/kg), propofol (30 mg/kg), or midazolam (1.9 mg/kg) were then administered. The reflex threshold was measured every 10 min, starting at 5 min after the sedative injection, until 65 min had elapsed.

RESULTS

Levetiracetam did not alter nociceptive reflex threshold in nonsedated animals (P = 0.11) or influence the degree or duration of sedation. The three anesthetic/sedative drugs reduced the nociceptive reflex threshold by 20%-30% of control values. Levetiracetam reduced the hyperreflexia associated with pentobarbital and midazolam (P < 0.05), but not propofol.

CONCLUSIONS

These findings support further investigation into the role of levetiracetam in the prevention of anesthetic-induced excitability.

A new frontier in epilepsy: novel antiepileptogenic drugs

Epilepsy is a hetergenous syndrome characterized by recurrently and repeatedly occurring seizures. Although able to inhibit the epileptic seizures, the currently available antiepileptic drugs (AEDs) have no effects on epileptogenesis. Such AEDs should be classified as drugs against ictogenesis, which are transient events in ion and/or receptor-gated channels related with triggering to evoke seizures. Epileptogenesis involves long-term and histological/biochemical/physiological alterations formed in brain structures over a long period, ranging from months to years. This review focuses on the effects of AEDs on epileptogenesis and novel candidates of antiepileptogenic drugs using a genetically defined epilepsy model animal, the spontaneous epileptic rat (SER).

Levetiracetam for cerebellar tremor in multiple sclerosis: an open-label pilot tolerability and efficacy study

PURPOSE

Disabling tremor is frequent in multiple sclerosis (MS) and its treatment remains challenging. We conducted an open-label trial to evaluate the effect of levetiracetam (LEV) to treat cerebellar tremor in MS patients.

PATIENTS AND METHODS

Fourteen MS patients, aged 27 to 57 years, with cerebellar tremor. Tremor duration ranged from 3 to 14 years. The tremor clinical rating scale, the spiral drawings scale, and ataxia clinical scale were used to assess the severity of tremor. Data about the tremor-induced disability were obtained by using the specific Activities of Daily Living Questionnaire (ADL). LEV was orally administered at a starting dose of 500 mg twice daily for one week followed by increments of 500 mg twice daily each week up to the target dose of 50 mg/Kg/day. Patients were evaluated at baseline and two weeks after the end of titration phase. The Wilcoxon matched-pairs test was used for statistical analysis.

RESULTS

Eleven patients completed the trial. LEV administration was associated with subjective and objective improvement of the tremor, with significant lowering of all tremor measurements' sum of scores as well as of ADL mean score between the baseline and follow-up. No correlation was found between the degree of improvement of the tremor and the disease duration or progression. LEV was well tolerated by subjects who completed the study.

CONCLUSIONS

LEV could be useful for the management of cerebellar tremor in MS and the good tolerability makes it easy to test. LEV long-term efficacy should be confirmed in extended studies.

Binding characteristics of levetiracetam to synaptic vesicle protein 2A (SV2A) in human brain and in CHO cells expressing the human recombinant protein

A specific binding site for the antiepileptic drug levetiracetam (2S-(oxo-1-pyrrolidinyl)butanamide, Keppra) in rat brain, referred to as the levetiracetam binding site, was discovered several years ago. More recently, this binding site has been identified as the synaptic vesicle protein 2A (SV2A), a protein present in synaptic vesicles [Lynch, B., Lambeng, N., Nocka, K., Kensel-Hammes, P., Bajjalieh, S.M., Matagne, A., Fuks, B., 2004. The synaptic vesicle protein SV2A is the binding site for the antiepileptic drug levetiracetam. Proc. Natl. Acad. Sci. USA, 101, 9861-9866.]. In this study, we characterized the binding properties of levetiracetam in post-mortem human brain and compared them to human SV2A expressed in Chinese hamster ovary (CHO) cells. The results showed that the binding properties of levetiracetam and [3H]ucb 30889, an analogue that was previously characterized as a suitable ligand for levetiracetam binding site/SV2A in rat brain [Gillard, M., Fuks, B., Michel, P., Vertongen, P., Massingham, R. Chatelain, P., 2003. Binding characteristics of [3H]ucb 30889 to levetiracetam binding sites in rat brain. Eur. J. Pharmacol. 478, 1-9.], are almost identical in human brain samples (cerebral cortex, hippocampus and cerebellum) and in CHO cell membranes expressing the human SV2A protein. Moreover, the results are also similar to those previously obtained in rat brain. [3H]ucb 30889 binding in human brain and to SV2A was saturable and reversible. At 4 degrees C, its binding kinetics were best fitted assuming a two-phase model in all tissues. The half-times of association for the fast component ranged between 1 to 2 min and represent 30% to 36% of the sites whereas the half-times for the slow component ranged from 20 to 29 min. In dissociation experiments, the half-times were from 2 to 4 min for the fast component (33% to 49% of the sites) and 20 to 41 min for the slow component. Saturation binding curves led to Kd values for [3H]ucb 30889 of 53+/-7, 55+/-9, 70+/-11 and 75+/-33 nM in human cerebral cortex, hippocampus, cerebellum and CHO cells expressing SV2A respectively. Bmax values around 3-4 pmol/mg protein were calculated in all brain regions. Some of the saturation curves displayed curvilinear Scatchard plots indicating the presence of high and low affinity binding sites. When this was the case, Kd values from 25 to 30 nM for the high affinity sites (24% to 34% of total sites) and from 200 to 275 nM for the low affinity sites were calculated. This was observed in all brain regions and in CHO cell membranes expressing the SV2A protein. It cannot be explained by putative binding of [3H]ucb 30889 to SV2B or C isoforms but may reflect different patterns of SV2A glycosylation or the formation of SV2A oligomers. Competition experiments were performed to determine the affinities for SV2A of a variety of compounds including levetiracetam, some of its analogues and other molecules known to interact with levetiracetam binding sites in rat brain such as bemegride, pentylenetetrazol and chlordiazepoxide. We found an excellent correlation between the affinities of these compounds measured in human brain, rat brain and CHO cells expressing human SV2A. In conclusion, we report for the first time that the binding characteristics of native levetiracetam binding sites/SV2A in human brain and rat brain share very similar properties with human recombinant SV2A expressed in CHO cells.

Characterization of [(3)H]ucb 30889 binding to synaptic vesicle protein 2A in the rat spinal cord

The novel antiepileptic drug levetiracetam ((2S-(2-oxo-1-pyrrolidinyl)butanamide, KEPPRA possesses a specific binding site in brain, which has very recently been identified as the synaptic vesicle protein SV 2 A. The aim of this study was to evaluate the presence of a levetiracetam binding site in the spinal cord and compare its properties to that in rat brain. We used [(3)H]ucb 30889 ((2S)-2-[4-(3-azidophenyl)-2-oxopyrrolidin-1-yl]butanamide), a levetiracetam analogue, to perform binding assays, photoaffinity labelling and autoradiography experiments, and revealed the presence of SV 2 A by Western-blot analysis. [(3)H]ucb 30889 binding kinetics at 4 degrees C were biphasic and saturation binding curves were compatible with the labelling of a homogenous population of binding sites with a K(d) similar to that in brain. Competition curves with ligands known to interact with levetiracetam binding sites and photolabelling experiments indicated that [(3)H]ucb 30889 labels the same 90 kDa protein in both spinal cord and brain. Levetiracetam binding site was localised in the grey matter of the spinal cord and its expression was not modified in a model of neuropathic pain. This study demonstrates the presence of a specific levetiracetam binding site in the rat spinal cord, which is similar to that found in rat brain.

Solubilization and immunopurification of rat brain synaptic vesicle protein 2A with maintained binding properties

This study reports the solubilization of the rat synaptic vesicle protein SV2A, the brain binding site for the antiepileptic drug levetiracetam (LEV), and its characterization. N-dodecyl-beta-D-maltoside (DDM) was the best detergent at achieving a high percentage of SV2A solubilization and at maintaining the binding characteristics of a tritiated form of a more potent analogue of LEV, [3H]ucb 30889 ((2S)-2-[4-(3-azidophenyl)-2-oxopyrrolidin-1-yl]butanamide). Scatchard analysis revealed that approximately 25% of SV2A proteins from brain membranes are solubilized by DDM under optimal conditions. Competition binding experiments with a variety of LEV analogues indicated that [3H]ucb 30889 labels the same binding site in both crude homogenates and soluble extracts, with still high stereoselectivity. After immunoprecipitation of SV2A from solubilized rat brain membranes, binding properties of [3H]ucb 30889 to SV2A and association with synaptotagmin I were maintained. The two other isoforms SV2B and SV2C were found to be co-immunoprecipitated with SV2A. The solubilization and immunopurification of SV2A with unmodified ligand affinities and synaptotagmin I interaction provides the starting point for future protein-protein interactions and structural studies.

Levetiracetam in the Treatment of Idiopathic Generalized Epilepsies

Since its introduction into clinical practice in 1999, levetiracetam, the S enantiomer of piracetam, has rapidly found a secure place, initially in the therapy of partial onset seizures and subsequently in the treatment of idiopathic generalized epilepsies (IGE). It has many of the properties of an "ideal" antiepileptic drug, including rapid absorption, linear pharmokinetics, and sparse drug interactions. Tolerabiliy is generally excellent in both adults and children, although tiredness is a common dose-limiting adverse effect. Occasionally the drug can precipitate behavioral abnormalities, especially in patients with learning disability. There is a wide safety margin in overdose. In common with most antiepileptic drugs its mode of action remains uncertain. Levetiracetam binds to a specific site in the brain, influences intracellular calcium currents and reverses negative allosteric modulators of GABA- and glycine-gated currents in vitro. Its effectiveness has been demonstrated in animal models of epilepsy and in clinical trials of partial onset and IGE. Treatment of IGEs may be straightforward, with many patients demonstrating an excellent and robust response to valproate monotherapy. However, there remains a significant minority of patients for whom valproate is unsuitable, including those who experience unacceptable adverse effects (e.g., weight gain or hair loss) and women of childbearing age in whom the teratogenic potential of valproate is unacceptable. Therapeutic response to lamotrigine in this group is often disappointing, and many clinicians now are turning to the choice of levetiracetam. Efficacy in generalized tonic-clonic seizures and myoclonus is usually apparent and some patients experience improvement in typical absences. Experience of combinations of levetiracetam with other antiepileptic drugs is limited in IGE and the responses are largely anecdotal. In our hands, patients with refractory IGEs may respond to combinations of levetiracetam with valproate, lamotrigine, and phenobarbital, and adverse effects when they occur are usually limited to tiredness. Levetiracetam does not interact with the oral contraceptive pill, simplifying treatment in women of childbearing age. Although animal data look encouraging, questions over levetiracetam's teratogenic potential and overall safety in pregnancy will remain for many years to come.

Long-lasting antiepileptic effects of levetiracetam against epileptic seizures in the spontaneously epileptic rat (SER): differentiation of levetiracetam from conventional antiepileptic drugs

PURPOSE

Some evidence suggests that levetiracetam (LEV) possesses antiepileptogenic characteristics. The purpose of this study was to investigate the time course of seizure protection by LEV compared with that of phenytoin (PHT), phenobarbital (PB), valproate (VPA), and carbamazepine (CBZ) in the spontaneously epileptic rat (SER). The SER is a double mutant (tm/tm, zi/zi) showing both tonic convulsions and absence-like seizures.

METHODS

The effect of single (40, 80, and 160 mg/kg, i.p.) and 5-day (80 mg/kg/day, i.p.) administration of LEV on tonic convulsions and absence-like seizures in SERs were studied. Tonic convulsions induced by blowing air onto the animal's head at 5-min intervals for 30 min and spontaneous absence-like seizures characterized by 5- to 7-Hz spike-wave-like complexes in the cortical and hippocampal EEG were recorded for 30 min. In the single-administration study, observations for seizure activity were performed once before and 3 times (45, 75, and 135 min) after drug administration. In the 5-day administration study, seizure observation was performed 4 times for 30 min (once before and 3 times after drug administration) during the 5-day drug-administration period, and continued once a day until 8 days after the final administration. The antiepileptic effects of 5-day administration of conventional AEDs (PHT, PB, VPA, and CBZ) were examined by using similar methods.

RESULTS

Tonic convulsions and absence-like seizures were inhibited by a single administration of LEV at 80 and 160 mg/kg, i.p., but not significantly at 40 mg/kg, i.p. When LEV was repeatedly administered at 80 mg/kg/day, i.p., for 5 days to SERs, the inhibitory effects on seizures increased with administration time. The number of tonic convulsions and absence-like seizures were significantly reduced to 39.1% and 38.4% compared with previous values, respectively, after 5-day LEV administration. Furthermore, significant inhibition of tonic convulsions was detected <or=3 days after the final administration, and significant inhibition of absence-like seizures was still observed 8 days after the final injection of LEV. This demonstrates long-lasting seizure protection by LEV after cessation of treatment. PHT, PB, VPA, and CBZ inhibited tonic convulsions more potently compared with LEV in SERs. The maximal antiseizure effects of these drugs were reached after the initial administration, with almost the same antiseizure effects observed through day 5, despite continued drug administration. Moreover, a long-lasting treatment effect was not observed with any of these drugs except for PHT and CBZ, both of which showed moderately prolonged antiseizure effects.

CONCLUSIONS

These results show that LEV is effective in the treatment of both convulsive and absence-like seizures in SERs after single- and multiple-dose administration. Interestingly, in the 5-day administration study, it was found that the antiepileptic effects for tonic convulsions and absence-like seizures were observed both during the drug-administration period and <or=8 days after the final administration of LEV. This long-lasting effect suggests that LEV may possess an antiepileptogenic effect that it does not share with PHT, PB, VPA, and CBZ.

Separation of Antiepileptogenic and Antiseizure Effects of Levetiracetam in the Spontaneously Epileptic Rat (SER)

PURPOSE

The long-lasting antiseizure effects of levetiracetam (LEV) have been observed in the spontaneously epileptic rat (SER) that expresses both tonic and absence-like seizures. Furthermore, the antiepileptogenic effects of LEV in addition to antiseizure effects have been reported in the amygdala-kindling model in rats. This suggests that the long-lasting seizure protection of LEV may be at least partly due to its antiepileptogenic effects. Therefore this study aimed to differentiate the antiseizure and potential antiepileptogenic effects of LEV by administering LEV continuously to SERs before the appearance of any seizure expression.

METHODS

LEV was administered to the SERs at 80 mg/kg/day (i.p.) from postnatal weeks 5 to 8. The period of observation for tonic convulsions was from postnatal week 5 to 13. Absence-like seizures were recorded by using conventional EEG in weeks 12 and 13.

RESULTS

After age 7-8 weeks, SERs exhibit spontaneous tonic convulsions. Development of tonic convulsions was significantly inhibited in the LEV group, compared with the control group, by the middle of week 9. A significant reduction of tonic convulsions also was observed in the LEV group until week 13 (5 weeks after termination of the administration). In week 12, the absence-like seizures were significantly lower in the LEV group, compared with the control group.

CONCLUSIONS

This study demonstrates a significant inhibition of seizures after prolonged treatment with LEV before the developmental expression of seizure activity in SERs. This effect is suggested to be due to an antiepileptogenic effect and not an antiseizure effect of LEV, because the half-life of the drug in plasma is short (2-3 h in rats) after single and long-term administration. Furthermore, the inhibition of seizure expression in SERs was still apparent 5 weeks after termination of LEV treatment. These results further suggest that LEV possesses not only antiseizure effects but also antiepileptogenic properties.

The antiepileptic drug levetiracetam decreases the inositol 1,4,5-trisphosphate-dependent [Ca2+]I increase induced by ATP and bradykinin in PC12 cells

The present study explores the hypothesis that the new anti-epileptic drug levetiracetam (LEV) could interfere with the inositol 1,4,5-trisphosphate (IP(3))-dependent release of intracellular Ca(2+) initiated by G(q)-coupled receptor activation, a process that plays a role in triggering and maintaining seizures. We assessed the effect of LEV on the amplitude of [Ca(2+)](i) response to bradykinin (BK) and ATP in single Fura-2/acetoxymethyl ester-loaded PC12 rat pheochromocytoma cells, which express very high levels of LEV binding sites. LEV dose-dependently reduced the [Ca(2+)](i) increase, elicited either by 1 microM BK or by 100 microM ATP (IC(50), 0.39 +/- 0.01 microM for BK and 0.20 +/- 0.01 microM for ATP; Hill coefficients, 1.33 +/- 0.04 for BK and 1.38 +/- 0.06 for ATP). Interestingly, although the discharge of ryanodine stores by a process of calcium-induced calcium release also took place as part of the [Ca(2+)](i) response to BK, LEV inhibitory effect was mainly exerted on the IP(3)-dependent stores. In fact, the drug was still effective after the pharmacological blockade of ryanodine receptors. Furthermore, LEV did not affect Ca(2+) stored in the intracellular deposits since it did not reduce the amplitude of [Ca(2+)](i) response either to thapsigargin or to ionomycin. In conclusion, LEV inhibits Ca(2+) release from the IP(3)-sensitive stores without reducing Ca(2+) storage into these deposits. Because of the relevant implications of IP(3)-dependent Ca(2+) release in neuron excitability and epileptogenesis, this novel effect of LEV could provide a useful insight into the mechanisms underlying its antiepileptic properties.

The synaptic vesicle protein SV2A is the binding site for the antiepileptic drug levetiracetam

Here, we show that the synaptic vesicle protein SV2A is the brain binding site of levetiracetam (LEV), a new antiepileptic drug with a unique activity profile in animal models of seizure and epilepsy. The LEV-binding site is enriched in synaptic vesicles, and photoaffinity labeling of purified synaptic vesicles confirms that it has an apparent molecular mass of approximately 90 kDa. Brain membranes and purified synaptic vesicles from mice lacking SV2A do not bind a tritiated LEV derivative, indicating that SV2A is necessary for LEV binding. LEV and related compounds bind to SV2A expressed in fibroblasts, indicating that SV2A is sufficient for LEV binding. No binding was observed to the related isoforms SV2B and SV2C. Furthermore, there is a high degree of correlation between binding affinities of a series of LEV derivatives to SV2A in fibroblasts and to the LEV-binding site in brain. Finally, there is a strong correlation between the affinity of a compound for SV2A and its ability to protect against seizures in an audiogenic mouse animal model of epilepsy. These experimental results suggest that SV2A is the binding site of LEV in the brain and that LEV acts by modulating the function of SV2A, supporting previous indications that LEV possesses a mechanism of action distinct from that of other antiepileptic drugs. Further, these results indicate that proteins involved in vesicle exocytosis, and SV2 in particular, are promising targets for the development of new CNS drug therapies.

Piracetam and TRH analogues antagonise inhibition by barbiturates, diazepam, melatonin and galanin of human erythrocyte D-glucose transport

1 Nootropic drugs increase glucose uptake into anaesthetised brain and into Alzheimer's diseased brain. Thyrotropin-releasing hormone, TRH, which has a chemical structure similar to nootropics increases cerebellar uptake of glucose in murine rolling ataxia. This paper shows that nootropic drugs like piracetam (2-oxo 1 pyrrolidine acetamide) and levetiracetam and neuropeptides like TRH antagonise the inhibition of glucose transport by barbiturates, diazepam, melatonin and endogenous neuropeptide galanin in human erythrocytes in vitro. 2 The potencies of nootropic drugs in opposing scopolamine-induced memory loss correlate with their potencies in antagonising pentobarbital inhibition of erythrocyte glucose transport in vitro (P<0.01). Less potent nootropics, D-levetiracetam and D-pyroglutamate, have higher antagonist Ki's against pentobarbital inhibition of glucose transport than more potent L-stereoisomers (P<0.001). 3 Piracetam and TRH have no direct effects on net glucose transport, but competitively antagonise hypnotic drug inhibition of glucose transport. Other nootropics, like aniracetam and levetiracetam, while antagonising pentobarbital action, also inhibit glucose transport. Analeptics like bemigride and methamphetamine are more potent inhibitors of glucose transport than antagonists of hypnotic action on glucose transport. 4 There are similarities between amino-acid sequences in human glucose transport protein isoform 1 (GLUT1) and the benzodiazepine-binding domains of GABAA (gamma amino butyric acid) receptor subunits. Mapped on a 3D template of GLUT1, these homologies suggest that the site of diazepam and piracetam interaction is a pocket outside the central hydrophilic pore region. 5 Nootropic pyrrolidone antagonism of hypnotic drug inhibition of glucose transport in vitro may be an analogue of TRH antagonism of galanin-induced narcosis.

Binding characteristics of [3H]ucb 30889 to levetiracetam binding sites in rat brain

Levetiracetam (2S-(2-oxo-1-pyrrolidinyl)butanamide, KEPPRA, a novel antiepileptic drug, has been shown to bind to a specific binding site located in brain (levetiracetam binding site [Eur. J. Pharmacol. 286 (1995) 137]). However, [3H]levetiracetam displayed only micromolar affinity for these sites making it an unsuitable probe for further characterization. The present study describes the binding properties of an analogue of levetiracetam: [3H]ucb 30889, (2S)-2-[4-(3-azidophenyl)-2-oxopyrrolidin-1-yl]butanamide. [3H]ucb 30889 binds reversibly to specific binding sites in rat brain. Kinetics at 4 degrees C were biphasic with half-times of association and dissociation of, respectively, 3 and 4 min for the fast component and 47 and 61 min for the slow component. [3H]ucb 30889 saturation binding curves were compatible with the labelling of a homogenous population of binding sites having a B(max) of 4496+/-790 fmol/mg protein (mean+/-S.D., n=5) and a K(d) of 62+/-20 nM (mean+/-S.D., n=5), a 20-fold increase in affinity compared to [3H]levetiracetam. Competition binding curves with ligands known to interact with levetiracetam binding sites and tissue distribution restricted to the brain indicated that [3H]ucb 30889 and [3H]levetiracetam bind to the same site. Although levetiracetam binding sites and GABA(A) (gamma-aminobutyric acid) receptors share some ligands such as pentobarbital and pentylenetetrazol, experiments performed with [35S]TBPS (tert-butyl-bicyclo[2.2.2]phosporothionate), a probe for the GABA(A) Cl(-) channel do not support the hypothesis that levetiracetam binding sites are part of the GABA(A) receptor complex. Preliminary autoradiography studies in rat brain revealed that [3H]ucb 30889 labels specific sites in all brain regions and that this binding is concentration-dependently displaced by levetiracetam.