Targeting α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptors in epilepsy

LC-MS metabolomics profiling of Salvia aegyptiaca L. and S. lanigera Poir. with the antimicrobial properties of their extracts

BACKGROUND

Salvia L. (Lamiaceae) found in almost all countries in temperate and tropical regions. Both S. aegyptiaca L. and S. lanigera Poir. have a rather wide distribution in Egypt (Mediterranean region, Gebel Elba and nearly the whole Sinai). Salvia species showed antibacterial and antifungal activities against several groups of food microorganisms and pathogens, so they are considered as a natural foods preservatives.

AIM

Investigate the phytochemical profiles of S. aegyptiaca & S. lanigera collected from their natural habitats in Egypt and test the antimicrobial activities of both species against some bacteria and fungi pathogenic strains.

METHODOLOGY

In the present study, S. aegyptiaca and S. lanigera were collected from their natural habitat. Total phenolics and flavonoids contents were measured for aerial parts of both Salvia spp.. The separation and identification of the pure active materials of both Salvia sp. by using LC-MS system (UHPLC-TSQ Quantum Mass Spectrometer). The antimicrobial activities of the ethanol, water and benzene extracts of the two species were tested against different pathogenic strains and compared with the standard antimicrobial drug (Gentamycin). Antimicrobial activity was determined by using agar disk diffusion method.

RESULTS

The phenolics content in S. lanigera 132.61±6.23 mg/g and S. aegyptiaca 125.19±4.97 mg/g, while the flavonoids content was 35.68±1.84 and 40.63±2.11 mg/g, respectively. Through LC-MS analysis, two compounds were detected in both species; heptadecanoyl coenzyme A, that the highest percentage (13.5%) in S. aegyptiaca and (11.5 %) in S. lanigera. Oenin, in a peak area of 3.1% in S. aegyptiaca and 1.2 % in S. lanigera. Ethanol extract of the two species had the most inhibitory effect against all tested microorganisms that exceeded the effect of the standard, except for Mucor reinelloids which was more sensitive to the water extract. Moreover, S. lanigera ethanol extract showed larger inhibition zone than S. aegyptiaca in all tested microorganisms except for Pseudomonas aeruginosa.

CONCLUSION

This study shows the important phytochemicals that improve the antibacterial and antifungal activities of Salvia aegyptiaca and S. lanigera.

Non-competitive AMPA glutamate receptors antagonism by perampanel as a strategy to counteract hippocampal hyper-excitability and cognitive deficits in cerebral amyloidosis

Pathological accumulation of Aβ oligomers has been linked to neuronal networks hyperexcitability, potentially underpinned by glutamatergic AMPA receptors (AMPARs) dysfunction. We aimed to investigate whether the non-competitive block of AMPARs was able to counteract the alteration of hippocampal epileptic threshold, and of synaptic plasticity linked to Aβ oligomers accumulation, being this glutamate receptor a valuable specific therapeutic target. In this work, we showed that the non-competitive AMPARs antagonist perampanel (PER) which, per se, did not affect physiological synaptic transmission, was able to counteract Aβ-induced hyperexcitability. Moreover, AMPAR antagonism was able to counteract Aβ-induced hippocampal LTP impairment and hippocampal-based cognitive deficits in Aβ oligomers-injected mice, while retaining antiseizure efficacy. Beside this, AMPAR antagonism was also able to reduce the increased expression of proinflammatory cytokines in this mice model, also suggesting the presence of an anti-inflammatory activity. Thus, targeting AMPARs might be a valuable strategy to reduce both hippocampal networks hyperexcitability and synaptic plasticity deficits induced by Aβ oligomers accumulation.

The Roles of Glutamate Receptors and Their Antagonists in Status Epilepticus, Refractory Status Epilepticus, and Super-Refractory Status Epilepticus

Status epilepticus (SE) is a neurological emergency with a high mortality rate. When compared to chronic epilepsy, it is distinguished by the durability of seizures and frequent resistance to benzodiazepine (BZD). The Receptor Trafficking Hypothesis, which suggests that the downregulation of γ-Aminobutyric acid type A (GABAA) receptors, and upregulation of N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors play major roles in the establishment of SE is the most widely accepted hypothesis underlying BZD resistance. NMDA and AMPA are ionotropic glutamate receptor families that have important excitatory roles in the central nervous system (CNS). They are both essential in maintaining the normal function of the brain and are involved in a variety of neuropsychiatric diseases, including epilepsy. Based on animal and human studies, antagonists of NMDA and AMPA receptors have a significant impact in ending SE; albeit most of them are not yet approved to be in clinically therapeutic guidelines, due to their psychomimetic adverse effects. Although there is still a dearth of randomized, prospective research, NMDA antagonists such as ketamine, magnesium sulfate, and the AMPA antagonist, perampanel, are regarded to be reasonable optional adjuvant therapies in controlling SE, refractory SE (RSE) or super-refractory SE (SRSE), though there are still a lack of randomized, prospective studies. This review seeks to summarize and update knowledge on the SE development hypothesis, as well as clinical trials using NMDA and AMPA antagonists in animal and human studies of SE investigations.

Tailoring Materials for Epilepsy Imaging: From Biomarkers to Imaging Probes

Excising epileptic foci (EF) is the most efficient approach for treating drug-resistant epilepsy (DRE). However, owing to the vast heterogeneity of epilepsies, EF in one-third of patients cannot be accurately located, even after exhausting all current diagnostic strategies. Therefore, identifying biomarkers that truly represent the status of epilepsy and fabricating probes with high targeting specificity are prerequisites for identifying the "concealed" EF. However, no systematic summary of this topic has been published. Herein, the potential biomarkers of EF are first summarized and classified into three categories: functional, molecular, and structural aberrances during epileptogenesis, a procedure of nonepileptic brain biasing toward epileptic tissue. The materials used to fabricate these imaging probes and their performance in defining the EF in preclinical and clinical studies are highlighted. Finally, perspectives for developing the next generation of probes and their challenges in clinical translation are discussed. In general, this review can be helpful in guiding the development of imaging probes defining EF with improved accuracy and holds promise for increasing the number of DRE patients who are eligible for surgical intervention.

Interweaving epilepsy and neurodegeneration: Vitamin E as a treatment approach

Epilepsy is the most common neurological disorder, affecting nearly 50 million people worldwide. The condition can be manifested either due to genetic predisposition or acquired from acute insult which leads to alteration of cellular and molecular mechanisms. Evaluating the latest and the current knowledge in regard to the mechanisms underlying molecular and cellular alteration, hyperexcitability is a consequence of an imbalanced state wherein enhance excitatory glutamatergic and reduced inhibitory GABAergic signaling is considered to be accountable for seizures associated damage. However, neurodegeneration contributing to epileptogenesis has become increasingly appreciated. The components at the helm of neurodegenerative alterations during epileptogenesis include GABAergic neuronal and receptor changes, neuroinflammation, alteration in axonal transport, oxidative stress, excitotoxicity, and other cellular as well as functional changes. Targeting neurodegeneration with vitamin E as an antioxidant, anti-inflammatory and neuroprotective may prove to be one of the therapeutic approaches useful in managing epilepsy. In this review, we discuss and converse about the seizure-induced episodes as a link for the development of neurodegenerative and pathological consequences of epilepsy. We also put forth a summary of the potential intervention with vitamin E therapy in the management of epilepsy.

X-linked neonatal-onset epileptic encephalopathy associated with a gain-of-function variant p.R660T in GRIA3

The X-linked GRIA3 gene encodes the GLUA3 subunit of AMPA-type glutamate receptors. Pathogenic variants in this gene were previously reported in neurodevelopmental diseases, mostly in male patients but rarely in females. Here we report a de novo pathogenic missense variant in GRIA3 (c.1979G>C; p. R660T) identified in a 1-year-old female patient with severe epilepsy and global developmental delay. When exogenously expressed in human embryonic kidney (HEK) cells, GLUA3_R660T showed slower desensitization and deactivation kinetics compared to wildtype (wt) GLUA3 receptors. Substantial non-desensitized currents were observed with the mutant but not for wt GLUA3 with prolonged exposure to glutamate. When co-expressed with GLUA2, the decay kinetics were similarly slowed in GLUA2/A3_R660T with non-desensitized steady state currents. In cultured cerebellar granule neurons, miniature excitatory postsynaptic currents (mEPSCs) were significantly slower in R660T transfected cells than those expressing wt GLUA3. When overexpressed in hippocampal CA1 neurons by in utero electroporation, the evoked EPSCs and mEPSCs were slower in neurons expressing R660T mutant compared to those expressing wt GLUA3. Therefore our study provides functional evidence that a gain of function (GoF) variant in GRIA3 may cause epileptic encephalopathy and global developmental delay in a female subject by enhancing synaptic transmission.

Glutamate is the excitatory neurotransmitter in brain, abnormality of which causes excitotoxicity and diseases. Here we identified a pathogenic missense variant in GRIA3 gene in a female patient with severe epilepsy and global developmental delay. The X-linked GRIA3 gene encodes GLUA3, a subunit of glutamate receptors. Through electrophysiological analysis of the mutant GLUA3 in a cell line and mouse neurons, we found this mutant makes strengthened glutamate receptors. This study thus indicates that the variant causes epileptic encephalopathy and global developmental delay by enhancing glutamate signaling in brain.

Visualization of AMPA receptors in living human brain with positron emission tomography

Although aberrations in the number and function of glutamate AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid) receptors are thought to underlie neuropsychiatric disorders, no methods are currently available for visualizing AMPA receptors in the living human brain. Here we developed a positron emission tomography (PET) tracer for AMPA receptors. A derivative of 4-[2-(phenylsulfonylamino)ethylthio]-2,6-difluoro-phenoxyacetamide radiolabeled with ¹¹C ([¹¹C]K-2) showed specific binding to AMPA receptors. Our clinical trial with healthy human participants confirmed reversible binding of [¹¹C]K-2 in the brain according to Logan graphical analysis (UMIN000020975; study design: non-randomized, single arm; primary outcome: dynamics and distribution volumes of [¹¹C]K-2 in the brain; secondary outcome: adverse events of [¹¹C]K-2 during the 4-10 d following dosing; this trial met prespecified endpoints). In an exploratory clinical study including patients with epilepsy, we detected increased [¹¹C]K-2 uptake in the epileptogenic focus of patients with mesial temporal lobe epilepsy, which was closely correlated with the local AMPA receptor protein distribution in surgical specimens from the same individuals (UMIN000025090; study design: non-randomized, single arm; primary outcome: correlation between [¹¹C]K-2 uptake measured with PET before surgery and AMPA receptor protein density examined by biochemical study after surgery; secondary outcome: adverse events during the 7 d following PET scan; this trial met prespecified endpoints). Thus, [¹¹C]K-2 is a potent PET tracer for AMPA receptors, potentially providing a tool to examine the involvement of AMPA receptors in neuropsychiatric disorders.

Perampanel attenuates epileptiform phenotype in C6 glioma

Epileptic seizures are frequent in patients with glioma, and anticonvulsive treatment is often indicated. Glioma cells release glutamate via the X_c- antiporter system, which appears to be a major pathomechanism of glioma-associated seizures and excitotoxicity. In addition, the proliferation and survival of the tumor cells are promoted. Therefore, anticonvulsants that attenuate glutamate-mediated receptor activation could be especially effective. In this study, we investigated the effects of AMPA receptor antagonist perampanel in rat C6 glioma model. In first pilot experiments, perampanel reduced glucose uptake but had no impact of extracellular glutamate level in vitro. To analyze the effects of perampanel in vivo, we injected C6 cells orthotopically into the neocortex of Wistar rats in order to establish a model of glioma-associated epilepsy. Spontaneous recurrent discharges in brain slices were abolished upon perfusion with the AMPA receptor blocker perampanel, supporting the major role of glutamatergic excitation. With respect to the tumor progression, no effect of perampanel on survival of the animals or on glioma size was determined. Our data demonstrate that perampanel inhibit epileptiform discharges in organotypic brain slices of glioma, but failed to attenuate tumor growth or promote animal survival.

Mutational Analysis and Modeling of Negative Allosteric Modulator Binding Sites in AMPA Receptors

The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) constitute a subclass of the ionotropic glutamate receptor superfamily, which functions as glutamate-gated cation channels to mediate the majority of excitatory neurotransmission in the central nervous system. AMPARs are therapeutic targets in a range of brain disorders associated with abnormal glutamate hyperactivity. Multiple classes of AMPAR inhibitors have been developed during the past decades, including competitive antagonists, ion channel blockers, and negative allosteric modulators (NAMs). At present, the NAM is the only class of AMPAR ligands that have been developed into safe and useful drugs in humans in the form of perampanel (Fycompa), which was recently approved for treatment of epilepsy. Compared with the detailed understanding of other AMPAR ligand classes, surprisingly little information has been available regarding the molecular mechanism of perampanel and other classes of NAMs at AMPARs; including the location and structure of NAM binding pockets in the receptor complex. However, structures of the AMPAR GluA2 in complex with NAMs were recently reported that unambiguously identified the NAM binding sites. In parallel with this work, our aim with the present study was to identify specific residues involved in the formation of the NAM binding site for three prototypical AMPAR NAMs. Hence, we have performed a mutational analysis of the AMPAR region that links the four extracellular ligand-binding domains to the central ion channel in the transmembrane domain region. Furthermore, we perform computational ligand docking of the NAMs into structural models of the homomeric GluA2 receptor and optimize side chain conformations around the NAMs to model how NAMs bind in this specific site. The new insights provide potentially valuable input for structure-based drug design of new NAMs. SIGNIFICANCE STATEMENT: The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors are glutamate-gated ion channels that mediate the majority of excitatory neurotransmission in the brain. Negative allosteric modulators of AMPA receptors are considered to have significant therapeutic potential in diseases linked to glutamate hyperactivity. The present work employs mutational analysis and molecular modeling of the binding site for prototypical NAMs to provide new molecular insight into how NAMs interact with the AMPA receptor, which is of potential use for future design of new types of NAMs.

Disruption of the GluA2/GAPDH complex using TAT-GluA2NT1-3-2 peptide protects against AMPAR-mediated excitotoxicity after epilepsy

Excitotoxicity and neuronal death following epilepsy involve α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs). It forms a protein complex with glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and co-internalizes upon activation of AMPA receptors after epilepsy. Disruption of the GluA2/GAPDH complex with an interfering peptide, TAT-GluA2NT1-3-2, protects cells against AMPAR-mediated excitotoxicity, which have been identified in in-vitro and in-vivo models of brain ischemia. We postulated that disruption of the GluA2/GAPDH interaction with the TAT-GluA2NT1-3-2 peptide would also protect against AMPAR-induced neuronal injury in an in-vivo model of status epilepticus (SE). In the present study, we divided pilocarpine-induced SE Wistar rats into three main groups: the TAT-GluA2NT1-3-2 peptide group, the TAT-GluA2NT-scram peptide group, and the normal saline group, and injected different doses of peptides stereotaxically into the hippocampus of SE rats to investigate whether the GluA2/GAPDH interaction could be disrupted by our TAT-GluA2NT1-3-2 peptide and determine its most appropriate dose. Then, the dose was administered stereotaxically at different time points after SE to determine the best administration time of neuronal protection. We found that the TAT-GluA2NT1-3-2 peptide can disrupt the GluA2/GAPDH interaction and protects against epilepsy-induced neuronal damage. The GluA2/GAPDH interaction may be a novel therapeutic target for epilepsy.

Excitotoxicity, neuroinflammation and oxidant stress as molecular bases of epileptogenesis and epilepsy-derived neurodegeneration: The role of vitamin E

Glutamate-mediated excitotoxicity, neuroinflammation, and oxidative stress are common underlying events in neurodegeneration. This pathogenic "triad" characterizes the neurobiology of epilepsy, leading to seizure-induced cell death, increased susceptibility to neuronal synchronization and network alterations. Along with other maladaptive changes, these events pave the way to spontaneous recurrent seizures and progressive degeneration of the interested brain areas. In vivo models of epilepsy are available to explore such epileptogenic mechanisms, also assessing the efficacy of chemoprevention and therapy strategies at the pre-clinical level. The kainic acid model of pharmacological excitotoxicity and epileptogenesis is one of the most investigated mimicking the chronicization profile of temporal lobe epilepsy in humans. Its pathogenic cues include inflammatory and neuronal death pathway activation, mitochondrial disturbances and lipid peroxidation of several regions of the brain, the most vulnerable being the hippocampus. The importance of neuroinflammation and lipid peroxidation as underlying molecular events of brain damage was demonstrated in this model by the possibility to counteract the related maladaptive morphological and functional changes of this organ with vitamin E, the main fat-soluble cellular antioxidant and "conditional" co-factor of enzymatic pathways involved in polyunsaturated lipid metabolism and inflammatory signaling. The present review paper provides an overview of the literature supporting the potential for a timely intervention with vitamin E therapy in clinical management of seizures and epileptogenic processes associated with excitotoxicity, neuroinflammation and lipid peroxidation, i.e. the pathogenic "triad".

De-palmitoylation by N-(tert-Butyl) hydroxylamine inhibits AMPAR-mediated synaptic transmission via affecting receptor distribution in postsynaptic densities

AIMS

Palmitoylation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) subunits or their "scaffold" proteins produce opposite effects on AMPAR surface delivery. Considering AMPARs have long been identified as suitable drug targets for central nervous system (CNS) disorders, targeting palmitoylation signaling to regulate AMPAR function emerges as a novel therapeutic strategy. However, until now, much less is known about the effect of palmitoylation-deficient state on AMPAR function. Herein, we set out to determine the effect of global de-palmitoylation on AMPAR surface expression and its function, using a special chemical tool, N-(tert-Butyl) hydroxylamine (NtBuHA).

METHODS

BS³ protein cross-linking, Western blot, immunoprecipitation, patch clamp, and biotin switch assay.

RESULTS

Bath application of NtBuHA (1.0 mM) reduced global palmitoylated proteins in the hippocampus of mice. Although NtBuHA (1.0 mM) did not affect the expression of ionotropic glutamate receptor subunits, it preferentially decreased the surface expression of AMPARs, not N-methyl-d-aspartate receptors (NMDARs). Notably, NtBuHA (1.0 mM) reduces AMPAR-mediated excitatory postsynaptic currents (mEPSCs) in the hippocampus. This effect may be largely due to the de-palmitoylation of postsynaptic density protein 95 (PSD95) and protein kinase A-anchoring proteins, both of which stabilized AMPAR synaptic delivery. Furthermore, we found that changing PSD95 palmitoylation by NtBuHA altered the association of PSD95 with stargazin, which interacted directly with AMPARs, but not NMDARs.

CONCLUSION

Our data suggest that the palmitoylation-deficient state initiated by NtBuHA preferentially reduces AMPAR function, which may potentially be used for the treatment of CNS disorders, especially infantile neuronal ceroid lipofuscinosis (Batten disease).

Pharmacology of epileptogenesis and related comorbidities in the WAG/Rij rat model of genetic absence epilepsy

Animal studies currently represent the best source of information also in the field of epileptogenesis research. Many animal models have been proposed and studied so far both from the pathophysiological and pharmacological point of view. Furthermore, they are widely used for the identification of potentially clinically valuable biomarkers. The WAG/Rij rat model, similarly to other genetic animal strains, represents a suitable animal model of absence epileptogenesis accompanied by depressive-like and cognitive comorbidities. Generally, animal models of epileptogenesis are characterized by an identifiable initial insult (e.g. traumatic brain injury), a latent phase lasting up to the appearance of the first spontaneous seizure and a chronic phase characterized by recurrent spontaneous seizures. In most of genetic models: the initial insult should be defined as the mutation causing epilepsy, which is not clearly defined in the WAG/Rij rat model; the latent phase ends at the appearance of the first spontaneous seizure, which is about 2-3 months of age in WAG/Rij rats and thereafter the chronic phase. WAG/Rij rats also display depressive-like comorbidity around the age of 4 months, which is apparently linked to the development of absence seizures considering both its ontogeny and the fact that drugs affecting absence seizures development also block the development of depressive-like behavior. Finally, WAG/Rij rats also display cognitive impairment in some memory tasks, however, this has not been yet definitively linked to absence seizures development and may represent an epiphenomenon. This review is focused on the effects of pharmacological treatments against epileptogenesis and their effects on comorbidities.

Perampanel as adjunctive therapy in highly refractory epilepsies: Real-world data from an Italian tertiary care epilepsy centre

Perampanel (PER) is a selective non-competitive α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor antagonist, licensed as adjunctive therapy in focal epilepsy and primary generalized tonic-clonic seizures (pGTCSs). We performed a retrospective study on highly refractory adult patients taking PER, with 1-year follow-up. Retention rate represented the primary outcome of our work; seizure frequency reduction (≥50%), "switch rate" and proportion of adverse events (AEs) were evaluated as secondary endpoints. Eighty-nine subjects (47 females, age range: 19-78 years) were included. Seventy-three had focal epilepsy (FE), 9 generalized epilepsy and 7 epileptic encephalopathy. All patients were highly drug-resistant (medication failures: 5-17). Retention rate was 87.6%, 63% and 51.7% at 3, 6 and 12 months. Responders were 27/89 (30.3%), with 8/27 seizure-free. The number of previous treatment failures and the concomitant use of enzyme inducers negatively influenced clinical response, whereas no correlation was documented between PER dose and outcome. Responder proportion was more satisfying in structural FE than in FE of unknown etiology (33% versus 20%), and in secondarily GTCSs than focal seizures (54% vs 28%), whereas pGTCSs showed a lower reponse rate (25%). Mild-to-moderate AEs (mainly dizziness, gait disturbances and psychiatric effects) were reported by 40% of patients; serious psychiatric AEs usually occurred in subjects with psychiatric comorbidities. Our study confirms the tolerability and effectiveness of PER in highly drug-resistant patients with different epilepsy syndromes and aetiologies.

Endophilin A1 mediates seizure activity via regulation of AMPARs in a PTZ-kindled epileptic mouse model

Endophilin A1 is a member of the endophilin A family and is primarily expressed in the central nervous system. Endophilin A1 can mediate neuronal excitability by regulating neuronal synaptic plasticity, which indicates that the protein may be involved in epilepsy. However, to date, its role in epilepsy remains unclear. To explore the role of endophilin A1 in epilepsy, we aimed to investigate the expression patterns of endophilin A1 in patients with temporal lobe epilepsy (TLE) and in a pentylenetetrazole (PTZ)-kindled epileptic mouse model and to conduct behavioral and electrophysiological analyses after lentivirus-mediated knockdown of endophilin A1 in the hippocampus of epileptic mice. This study found that the expression of endophilin A1 was significantly up-regulated in the temporal neocortex of TLE patients and in the hippocampus and adjacent temporal cortex of the PTZ-kindled epileptic mouse model. Behavioral analyses indicated that knockdown of endophilin A1 in the mouse hippocampus increased the latency of the first seizure and reduced the frequency and duration of seizure activity. Whole-cell patch-clamp recordings of pyramidal neurons in the hippocampal CA3 area indicated that knockdown of endophilin A1 in the mouse hippocampus resulted in a reduced frequency of action potentials and decreased amplitudes of miniature excitatory postsynaptic currents (mEPSCs) and evoked AMPA-dependent EPSCs. Moreover, western blotting analysis showed that the surface expression of the AMPAR GluR2 subunit was also decreased after endophilin A1 knockdown, and co-immunoprecipitation indicated an association between endophilin A1 and AMPAR GluR2 in the mouse hippocampus. Further, when AMPARs were activated by CX546, the antiepileptic function of endophilin A1 knockdown was decreased. Based on these results, endophilin A1 plays a critical role in epilepsy, and its suppression in the mouse hippocampus can restrain neuronal excitability and seizure activity via regulating AMPARs.

Aryl- and heteroaryl-substituted phenylalanines as AMPA receptor ligands

A series of racemic unnatural amino acids was rationally designed on the basis of recently published X-ray structures of the GluA2 LBD with bound phenylalanine-based antagonists. Twelve new diaryl- or aryl/heteroaryl-substituted phenylalanine derivatives were synthesized and evaluated in vitro in radioligand binding assays at native rat ionotropic glutamate receptors. The most interesting compound in this series, (RS)-2-amino-3-(3'-hydroxy-5-(1H-pyrazol-4-yl)-[1,1'-biphenyl]-3-yl)propanoic acid 7e, showed the binding affinity of 4.6 μm for native AMPA receptors and over fourfold lower affinity for kainic acid receptors. Furthermore, 7e was evaluated at recombinant homomeric rat GluA2 and GluA3 receptors. Recently reported X-ray structures 5CBR and 5CBS, representing two distinct antagonist binding modes, were used as templates for molecular docking of the synthesized series. Binding data supported with molecular modeling confirmed that aryl/heteroaryl-substituted phenylalanine analogues effectively bind to AMPA receptors with low micromolar affinity and high selectivity over native NMDA and kainate receptors. These properties make 7e a promising lead for the further development of new AMPA receptor ligands.

AMPA receptors and perampanel behind selected epilepsies: current evidence and future perspectives

INTRODUCTION

The alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors are the major mediators of glutamate-mediated excitatory neurotransmission, and are critical for synchronization and spread of epileptic activity. Areas covered: AMPA receptor antagonists have been also developed as antiepileptic drugs and perampanel (PER) is the first highly selective, non-competitive AMPA-type glutamate receptor antagonist that is available on the market. It is approved as adjunctive therapy for the treatment of partial-onset seizures with or without secondary generalization, and for primary generalized tonic-clonic seizures in idiopathic generalized epilepsy, in patients aged ≥ 12 years. This article reviews the role of AMPA receptors in the neuronal hyperexcitability underlying epilepsy, the mechanism of action and clinical experience on the anti-seizure activity of PER. Moreover, the rationale for targeting AMPA receptor in specific epileptic disorders, including brain tumor-related epilepsy, mesial temporal lobe epilepsy with/without hippocampal sclerosis, and status epilepticus is evaluated. Finally, the pharmacological rationale for the development of AMPA receptor antagonists in other neurological disorders beyond epilepsy is considered. Expert opinion: Further research aimed at better understanding the pharmacology and blocking mechanism of PER and other AMPA receptor antagonists will drive future development of therapeutic agents that target epilepsy and other neurological diseases.

Pharmacological characterization and binding modes of novel racemic and optically active phenylalanine-based antagonists of AMPA receptors

In order to map out molecular determinants for the competitive blockade of AMPA receptor subtypes, a series of racemic aryl-substituted phenylalanines was synthesized and pharmacologically characterized in vitro at native rat ionotropic glutamate receptors. Most of the compounds showed micromolar affinity and preference for AMPA receptors. Individual stereoisomers of selected compounds were further evaluated at recombinant homomeric rat GluA2 and GluA3 receptors. The most potent compound, (-)-2-amino-3-(6-chloro-2',5'-dihydroxy-5-nitro-[1,1'-biphenyl]-3-yl)propanoic acid, the expected R-isomer showing K_i of 1.71 μM at the GluA2 subtype, was found to competitively antagonize GluA2(Q)_i receptors in TEVC electrophysiological experiments (K_b = 2.13 μM). Molecular docking experiments allowed us to compare two alternative antagonist binding modes for the synthesized phenylalanines at the GluA2 binding core, showing the direction for further structural modifications.

Alterations in Properties of Glutamatergic Transmission in the Temporal Cortex and Hippocampus Following Pilocarpine-Induced Acute Seizures in Wistar Rats

Temporal lobe epilepsy (TLE) is the most common type of focal epilepsy in humans, and is often developed after an initial precipitating brain injury. This form of epilepsy is frequently resistant to pharmacological treatment; therefore, the prevention of TLE is the prospective approach to TLE therapy. The lithium-pilocarpine model in rats replicates some of the main features of TLE in human, including the pathogenic mechanisms of cell damage and epileptogenesis after a primary brain injury. In the present study, we investigated changes in the properties of glutamatergic transmission during the first 3 days after pilocarpine-induced acute seizures in Wistar rats (PILO-rats). Using RT-PCR and electrophysiological techniques, we compared the changes in the temporal cortex (TC) and hippocampus, brain areas differentially affected by seizures. On the first day, we found a transient increase in a ratio of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl d-aspartate (NMDA) receptors in the excitatory synaptic response in pyramidal neurons of the CA1 area of the dorsal hippocampus, but not in the TC. This was accompanied by an increase in the slope of input-output (I/O) curves for fEPSPs recorded in CA1, suggesting an enhanced excitability in AMPARs in this brain area. There was no difference in the AMPA/NMDA ratio in control rats on the third day. We also revealed the alterations in NMDA receptor subunit composition in PILO-rats. The GluN2B/GluN2A mRNA expression ratio increased in the dorsal hippocampus but did not change in the ventral hippocampus or the TC. The kinetics of NMDA-mediated evoked EPSCs in hippocampal neurons was slower in PILO-rats compared with control animals. Ifenprodil, a selective antagonist of GluN2B-containing NMDARs, diminished the area and amplitude of evoked EPSCs in CA1 pyramidal cells more efficiently in PILO-rats compared with control animals. These results demonstrate that PILO-induced seizures lead to more severe alterations in excitatory synaptic transmission in the dorsal hippocampus than in the TC. Seizures affect the relative contribution of AMPA and NMDA receptor conductances in the synaptic response and increase the proportion of GluN2B-containing NMDARs in CA1 pyramidal neurons. These alterations disturb normal circuitry functions in the hippocampus, may cause neuron damage, and may be one of the important pathogenic mechanisms of TLE.

Current role of perampanel in pediatric epilepsy

Perampanel is among the latest AEDs approved, indicated for the treatment of partial-onset seizures with or without secondary generalization, and for primary generalized tonic-clonic seizures, in patients aged 12 years and older. This paper summarizes the clinical recommendations on the current role of perampanel in the treatment of pediatric epilepsies and future directions for research. The optimal dosage should be comprised between 4 and 12 mg/day, with 8 mg/day being the most common dosage used. The rate and severity of adverse events, including psychiatric symptoms, can be decreased by starting at low doses, and titrating slowly. Overall, perampanel presents an acceptable risk/benefit ratio, but special caution should be made to the risk of seizure aggravation and behavioral problems. The favorable cognitive profile, the ease of use of the titration scheme and the once-daily formulation offer advantage over other AEDs and make this drug particularly suitable for adolescent population. Perampanel is a welcome addition to the armamentarium of the existing AEDs, as it represents a new approach in the management of epilepsy, with a novel mechanism of action and a potential to have a considerable impact on the treatment of adolescents with epilepsy.

Development of novel N-3-bromoisoxazolin-5-yl substituted 2,3-benzodiazepines as noncompetitive AMPAR antagonists

In this work, we designed and synthesized novel N-3-bromoisoxazolin-5-yl substituted 2,3-benzodiazepines as noncompetitive AMPAR antagonists, with the aim that this heterocycle could establish favourable interactions with a putative binding pocket of the receptor, like the thiadiazole nucleus of GYKI 47409 does. Within this investigation, we identified some active molecules and, among these 2,3-benzodiazepines, 4c showed a much improved inhibitory potency as compared with unsubstituted 2,3-benzodiazepines.

EGAR, A Food Protein-Derived Tetrapeptide, Reduces Seizure Activity in Pentylenetetrazole-Induced Epilepsy Models Through α-Amino-3-Hydroxy-5-Methyl-4-Isoxazole Propionate Receptors

A primary pathogeny of epilepsy is excessive activation of α-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors (AMPARs). To find potential molecules to inhibit AMPARs, high-throughput screening was performed in a library of tetrapeptides in silico. Computational results suggest that some tetrapeptides bind stably to the AMPAR. We aligned these sequences of tetrapeptide candidates with those from in vitro digestion of the trout skin protein. Among salmon-derived products, Glu-Gly-Ala-Arg (EGAR) showed a high biological affinity toward AMPAR when tested in silico. Accordingly, natural EGAR was hypothesized to have anticonvulsant activity, and in vitro experiments showed that EGAR selectively inhibited AMPAR-mediated synaptic transmission without affecting the electrophysiological properties of hippocampal pyramidal neurons. In addition, EGAR reduced neuronal spiking in an in vitro seizure model. Moreover, the ability of EGAR to reduce seizures was evaluated in a rodent epilepsy model. Briefer and less severe seizures versus controls were shown after mice were treated with EGAR. In conclusion, the promising experimental results suggest that EGAR inhibitor against AMPARs may be a target for antiepilepsy pharmaceuticals. Epilepsy is a common brain disorder characterized by the occurrence of recurring, unprovoked seizures. Twenty to 30 % of persons with epilepsy do not achieve adequate seizure control with any drug. Here we provide a possibility in which a natural and edible tetrapeptide, EGAR, can act as an antiepileptic agent. We have combined computation with in vitro experiments to show how EGAR modulates epilepsy. We also used an animal model of epilepsy to prove that EGAR can inhibit seizures in vivo. This study suggests EGAR as a potential pharmaceutical for the treatment of epilepsy.

Perampanel effects in the WAG/Rij rat model of epileptogenesis, absence epilepsy, and comorbid depressive-like behavior

OBJECTIVE

Perampanel (PER), a selective non-competitive α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-receptor antagonist, exhibits broad-spectrum anticonvulsant activity in several seizure models, but its potential disease-modifying effects have not been investigated. Because of the relevance of AMPA receptors in epileptogenesis and psychiatric comorbidities, we studied the effects of PER in the WAG/Rij rat model of epileptogenesis, absence epilepsy, and depressive-like comorbidity.

METHODS

We investigated the effects of acute, subchronic, and chronic treatment with PER (0.25-3 mg/kg) on absence seizures, their development, and related psychiatric/neurologic comorbidity in WAG/Rij rats. Depression-related behavior was studied by using the forced swimming and the sucrose preference test; anxiety-related behavior by using the open field and elevated plus maze test; and memory by using the passive avoidance test.

RESULTS

PER (3 mg/kg/day orally for 17 weeks starting from P30) significantly reduced the development of absence seizures at 6 months of age (1 month after treatment withdrawal), but this effect was not maintained when reassessed 4 months later. Attenuated absence seizure development was accompanied by reduced depressive-like behavior in the forced swimming test (FST), whereas no effects were observed on anxiety-related behavior and memory. Subchronic (1 and 3 mg/kg/day orally for 1 week) and acute PER (0.25-1 mg/kg, i.p.) dosing did not affect established absence seizures and behavior.

SIGNIFICANCE

These results suggest that AMPA receptors are involved in mechanisms of epileptogenesis in an established model of absence epilepsy, and that these mechanisms differ from those responsible for seizure generation and spread when epilepsy has become established.

Changes of AMPA receptor properties in the neocortex and hippocampus following pilocarpine-induced status epilepticus in rats

Temporal lobe epilepsy (TLE) is the most common type of epilepsy in humans. The lithium-pilocarpine model in rodents reproduces some of the main features of human TLE. Three-week-old Wistar rats were used in this study. The changes in AMPA receptor subunit composition were investigated in several brain areas, including the medial prefrontal cortex (mPFC), the temporal cortex (TC), and the dorsal (DH) and ventral hippocampus (VH) during the first week following pilocarpine-induced status epilepticus (PILO-induced SE). In the hippocampus, GluA1 and GluA2 mRNA expression slightly decreased after PILO-induced SE and returned to the initial level on the seventh day. We did not detect any significant changes in mRNA expression of the GluA1 and GluA2 subunits in the TC, whereas in the mPFC we observed a significant increase of GluA1 mRNA expression on the third day and a decrease in GluA2 mRNA expression during the entire first week. Accordingly, the GluA1/GluA2 expression ratio increased in the mPFC, and the functional properties of the pyramidal cell excitatory synapses were disturbed. Using whole-cell voltage-clamp recordings, we found that on the third day following PILO-induced SE, isolated mPFC pyramidal neurons showed an inwardly rectifying current-voltage relation of kainate-evoked currents, suggesting the presence of GluA2-lacking calcium-permeable AMPARs (CP-AMPARs). IEM-1460, a selective antagonist of CP-AMPARs, significantly reduced the amplitude of evoked EPSC in pyramidal neurons from mPFC slices on the first and third days, but not on the seventh day. The antagonist had no effects on EPSC amplitude in slices from control animals. Thus, our data demonstrate that PILO-induced SE affects subunit composition of AMPARs in different brain areas, including the mPFC. SE induces transient (up to few days) incorporation of CP-AMPARs in the excitatory synapses of mPFC pyramidal neurons, which may disrupt normal circuitry functions.

Perspectives on treatment options for mesial temporal lobe epilepsy with hippocampal sclerosis

INTRODUCTION

Mesial temporal lobe epilepsy associated with hippocampal sclerosis (MTLE-HS) is a syndrome that is often refractory to drug treatment. The effects on specific syndromes are not currently available from the pre-marketing clinical development of new AEDs; this does not allow the prediction of whether new drugs will be more effective in the treatment of some patients.

AREAS COVERED

We have reviewed all the existing literature relevant to the understanding of a potential effectiveness in MTLE-HS patients for the latest AEDs, namely brivaracetam, eslicarbazepine, lacosamide, perampanel and retigabine also including the most relevant clinical data and a brief description of their pharmacological profile. Records were identified using predefined search criteria using electronic databases (e.g., PubMed, Cochrane Library Database of Systematic Reviews). Primary peer-reviewed articles published up to the 15 June 2015 were included.

EXPERT OPINION

All the drugs considered have the potential to be effective in the treatment of MTLE-HS; in fact, they possess proven efficacy in animal models; currently considered valuable tools for predicting drug efficacy in TLE. Furthermore, for some of these (e.g., lacosamide and eslicarbazepine) data are already available from post-marketing studies while brivaracetam acting on SV2A like levetiracetam might have the same potential effectiveness with the possibility to be more efficacious considering its ability to inhibit voltage gated sodium channels; finally, perampanel and retigabine are very effective drugs in animal models of TLE.

Perampanel in the management of partial-onset seizures: a review of safety, efficacy, and patient acceptability

Perampanel (PER) is a novel antiepileptic drug recently introduced for the adjunctive treatment in epilepsy patients aged 12 years or older with partial-onset seizures with or without secondary generalization in the US and Europe. Its antiepileptic action is based on noncompetitive inhibition of postsynaptic AMPA receptors, decreasing excitatory synaptic transmission. Evaluation of efficacy in three placebo-controlled randomized Phase III studies showed that add-on therapy of PER decreased seizure frequencies significantly compared to placebo at daily doses between 4 mg/day and 12 mg/day. PER's long half-life of 105 hours allows for once-daily dosing that is favorable for patient compliance with intake. Long-term extension studies showed a 62.5%-69.6% adherence of patients after 1 year of treatment, comparing favorably with other second-generation antiepileptic drugs. Whereas these trials demonstrated an overall favorable tolerability profile of PER, nonspecific central nervous system adverse effects like somnolence, dizziness, headache, and fatigue may occur. In addition, neuropsychiatric disturbances ranging from irritability to suicidality were reported in several case reports; both placebo-controlled and prospective long-term extension trials showed a low incidence of such behavioral and psychiatric complaints. For early recognition of neuropsychiatric symptoms like depression, anxiety, and aggression, slow titration and close monitoring during drug introduction are mandatory. This allows on the one hand to recognize patients particularly susceptible to adverse effects of the drug, and on the other hand to render the drug's full potential of seizure control available for the vast majority of patient groups tolerating the drug well.