Precision treatment with nicotine in autosomal dominant sleep-related hypermotor epilepsy (ADSHE): An observational study of clinical outcome and serum cotinine levels in 17 patients

Channelopathies in epilepsy: an overview of clinical presentations, pathogenic mechanisms, and therapeutic insights

Pathogenic variants in genes encoding ion channels are causal for various pediatric and adult neurological conditions. In particular, several epilepsy syndromes have been identified to be caused by specific channelopathies. These encompass a spectrum from self-limited epilepsies to developmental and epileptic encephalopathies spanning genetic and acquired causes. Several of these channelopathies have exquisite responses to specific antiseizure medications (ASMs), while others ASMs may prove ineffective or even worsen seizures. Some channelopathies demonstrate phenotypic pleiotropy and can cause other neurological conditions outside of epilepsy. This review aims to provide a comprehensive exploration of the pathophysiology of seizure generation, ion channels implicated in epilepsy, and several genetic epilepsies due to ion channel dysfunction. We outline the clinical presentation, pathogenesis, and the current state of basic science and clinical research for these channelopathies. In addition, we briefly look at potential precision therapy approaches emerging for these disorders.

Advancements in the use of xenopus oocytes for modelling neurological disease for novel drug discovery

INTRODUCTION

Introduced about 50 years ago, the model of Xenopus oocytes for the expression of recombinant proteins has gained a broad spectrum of applications. The authors herein review the benefits brought from using this model system, with a focus on modeling neurological disease mechanisms and application to drug discovery.

AREAS COVERED

Using multiple examples spanning from ligand gated ion channels to transporters, this review presents, in the light of the latest publications, the benefits offered from using Xenopus oocytes. Studies range from the characterization of gene mutations to the discovery of novel treatments for disorders of the central nervous system (CNS).

EXPERT OPINION

Development of new drugs targeting CNS disorders has been marked by failures in the translation from preclinical to clinical studies. As progress in genetics and molecular biology highlights large functional differences arising from a single to a few amino acid exchanges, the need for drug screening and functional testing against human proteins is increasing. The use of Xenopus oocytes to enable precise modeling and characterization of clinically relevant genetic variants constitutes a powerful model system that can be used to inform various aspects of CNS drug discovery and development.

Nicotinic acetylcholine receptors in neurological and psychiatric diseases

Neuronal nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels that are widely distributed both pre- and post-synaptically in the mammalian brain. By modulating cation flux across cell membranes, neuronal nAChRs regulate neuronal excitability and the release of a variety of neurotransmitters to influence multiple physiologic and behavioral processes including synaptic plasticity, motor function, attention, learning and memory. Abnormalities of neuronal nAChRs have been implicated in the pathophysiology of neurologic disorders including Alzheimer's disease, Parkinson's disease, epilepsy, and Tourette´s syndrome, as well as psychiatric disorders including schizophrenia, depression, and anxiety. The potential role of nAChRs in a particular illness may be indicated by alterations in the expression of nAChRs in relevant brain regions, genetic variability in the genes encoding for nAChR subunit proteins, and/or clinical or preclinical observations where specific ligands showed a therapeutic effect. Over the past 25 years, extensive preclinical and some early clinical evidence suggested that ligands at nAChRs might have therapeutic potential for neurologic and psychiatric disorders. However, to date the only approved indications for nAChR ligands are smoking cessation and the treatment of dry eye disease. It has been argued that progress in nAChR drug discovery has been limited by translational gaps between the preclinical models and the human disease as well as unresolved questions regarding the pharmacological goal (i.e., agonism, antagonism or receptor desensitization) depending on the disease.

The importance of ligand gated ion channels in sleep and sleep disorders

On average, humans spend about 26 years of their life sleeping. Increased sleep duration and quality has been linked to reduced disease risk; however, the cellular and molecular underpinnings of sleep remain open questions. It has been known for some time that pharmacological modulation of neurotransmission in the brain can promote either sleep or wakefulness thereby providing some clues about the molecular mechanisms at play. However, the field of sleep research has developed an increasingly detailed understanding of the requisite neuronal circuitry and key neurotransmitter receptor subtypes, suggesting that it may be possible to identify next generation pharmacological interventions to treat sleep disorders within this same space. The aim of this work is to examine the latest physiological and pharmacological findings highlighting the contribution of ligand gated ion channels including the inhibitory GABA_A and glycine receptors and excitatory nicotinic acetylcholine receptors and glutamate receptors in the sleep-wake cycle regulation. Overall, a better understanding of ligand gated ion channels in sleep will help determine if these highly druggable targets could facilitate a better night's sleep.

Nicotinic acetylcholine receptors and epilepsy

Despite recent advances in understanding the causes of epilepsy, especially the genetic, comprehending the biological mechanisms that lead to the epileptic phenotype remains difficult. A paradigmatic case is constituted by the epilepsies caused by altered neuronal nicotinic acetylcholine receptors (nAChRs), which exert complex physiological functions in mature as well as developing brain. The ascending cholinergic projections exert potent control of forebrain excitability, and wide evidence implicates nAChR dysregulation as both cause and effect of epileptiform activity. First, tonic-clonic seizures are triggered by administration of high doses of nicotinic agonists, whereas non-convulsive doses have kindling effects. Second, sleep-related epilepsy can be caused by mutations on genes encoding nAChR subunits widely expressed in the forebrain (CHRNA4, CHRNB2, CHRNA2). Third, in animal models of acquired epilepsy, complex time-dependent alterations in cholinergic innervation are observed following repeated seizures. Heteromeric nAChRs are central players in epileptogenesis. Evidence is wide for autosomal dominant sleep-related hypermotor epilepsy (ADSHE). Studies of ADSHE-linked nAChR subunits in expression systems suggest that the epileptogenic process is promoted by overactive receptors. Investigation in animal models of ADSHE indicates that expression of mutant nAChRs can lead to lifelong hyperexcitability by altering i) the function of GABAergic populations in the mature neocortex and thalamus, ii) synaptic architecture during synaptogenesis. Understanding the balance of the epileptogenic effects in adult and developing networks is essential to plan rational therapy at different ages. Combining this knowledge with a deeper understanding of the functional and pharmacological properties of individual mutations will advance precision and personalized medicine in nAChR-dependent epilepsy.