The α2δ Subunit and Absence Epilepsy: Beyond Calcium Channels?

Scavenger Receptor Class B Type I Modulates Epileptic Seizures and Receptor α2δ-1 Expression

Scavenger receptor class B type I (SR-BI) is abundant in adult mouse and human brains, but its function in the central nervous system (CNS) remains unclear. This study explored the role of SR-BI in epilepsy and its possible underlying mechanism. Expression patterns of SR-BI in the brains of mice with kainic acid (KA)-induced epilepsy were detected using immunofluorescence staining, quantitative real-time polymerase chain reaction (qPCR), and Western blotting(WB). Behavioral analysis was performed by 24-hour video monitoring and hippocampal local field potential (LFP) recordings were employed to verify the role of SR-BI in epileptogenesis. RNA sequencing (RNA-seq) was used to obtain biological information on SR-BI in the CNS. WB, qPCR, and co-immunoprecipitation (Co-IP) were performed to identify the relationship between SR-BI and the gabapentin receptor α2δ-1.The results showed that SR-BI was primarily co-localized with astrocytes and its expression was down-regulated in the hippocampus of KA mice. Notably, overexpressing SR-BI alleviated the epileptic behavioral phenotype in KA mice. Hippocampal transcriptomic analysis revealed 1043 differentially expressed genes (DEGs) in the SR-BI-overexpressing group. Most DEGs confirmed by RNA-seq analysis were associated with synapses, neuronal projections, neuron development, and ion binding. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis demonstrated that the DEGs were enriched in the glutamatergic synapse pathway. Furthermore, the gabapentin receptor α2δ-1 decreased with SR-BI overexpression in epileptic mice. Overall, these findings highlight the important role of SR-BI in regulating epileptogenesis and that the gabapentin receptor α2δ-1 is a potential downstream target of SR-BI.

Pharmacodynamic rationale for the choice of antiseizure medications in the paediatric population

In the landscape of paediatric epilepsy treatment, over 20 anti-seizure medications (ASMs) have gained approval from Drug Regulatory Agencies, each delineating clear indications. However, the complexity of managing drug-resistant epilepsy often necessitates the concurrent use of multiple medications. This therapeutic challenge highlights a notable gap: the absence of standardized guidelines, compelling clinicians to rely on empirical clinical experience when selecting combination therapies. This comprehensive review aims to explore current evidence elucidating the preferential utilization of specific ASMs or their combinations, with a primary emphasis on pharmacodynamic considerations. The fundamental objective underlying rational polytherapy is the strategic combination of medications, harnessing diverse mechanisms of action to optimize efficacy while mitigating shared side effects. Moreover, the intricate interplay between epilepsy and comorbidities partly may influence the treatment selection process. Despite advancements, unresolved queries persist, notably concerning the mechanisms underpinning drug resistance and the paradoxical exacerbation of seizures. By synthesizing existing evidence and addressing pertinent unresolved issues, this review aims to contribute to the evolving landscape of paediatric epilepsy treatment strategies, paving the way for more informed and efficacious therapeutic interventions.

A Meta-analysis of Randomized Controlled Trials Comparing the Efficacy and Safety of Pregabalin and Gabapentin in the Treatment of Postherpetic Neuralgia

OBJECTIVE

To systematically evaluate the clinical efficacy of pregabalin and gabapentin in the treatment of postherpetic neuralgia (PHN), including the difference in pain control and occurrence of adverse reactions.

METHODS

PubMed, MEDLINE, EMBASE, Cochrane Library, and Web of Science databases were searched for randomized controlled trials (RCTs) comparing the efficacy of pregabalin and gabapentin in patients with PHN. Data from studies meeting the inclusion criteria were extracted and the Cochrane Risk of Bias risk assessment tool was used to evaluate the quality of the included studies. Revman 5.3 and Stata17 were used to perform the meta-analysis and to detect publication bias.

RESULTS

A total of 14 RCTs with 3545 patients were included in this study, including 926 in the pregabalin treatment group, 1256 in the gabapentin treatment group, and 1363 in the placebo control group. Pregabalin was better than gabapentin in alleviating pain and improving the global perception of change in pain and sleep (P < 0.05). Gabapentin was associated with a lower incidence of adverse events than pregabalin (P < 0.05). Funnel plot and Begg's and Egger's tests showed no significant publication bias.

CONCLUSION

Pregabalin appears to have a better overall therapeutic effect than gabapentin for patients with PHN, but gabapentin has a lower incidence of adverse reactions and a better safety profile. Clinicians should comprehensively consider patient factors and fully evaluate the advantages and disadvantages of each treatment option to select the most suitable drugs for patient use. Considering the limited quantity and quality of the existing literature, high-quality RCTs are needed to confirm the advantages of pregabalin over gabapentin in the treatment of PHN and guide clinical decision-making.

The Clinical Application and Progress of Mirogabalin on Neuropathic Pain as a Novel Selective Gabapentinoids

Background

Neuropathic pain is a complex sort of pain that is detrimental to individuals' health, both physically and mentally, but merely a small portion of them could witness pain alleviation. Mirogabalin, by distinctive binding characteristics of voltage-gated calcium channels, has won approval from the Japanese authority as a third member of gabapentinoids in Japan. Our review was aimed at encompassing the bulk of clinical research on mirogabalin, which included clinical trials, special considerations, coadministration studies, case reports, and cost-effectiveness studies.

Methods

A review was carried out on a series of platforms, such as PubMed, MEDLINE, and Scopus, up to December 2021 using the keywords as follows: "mirogabalin OR mirogabalin besylate OR Tarlige OR DS-5565" AND "neuropathic pain OR Neuropathy."

Results

Mirogabalin demonstrated analgesic activity and manageable adverse reactions and provides a new alternative for individuals with PHN or DPNP in 3 phase II and 4 III trials. Mirogabalin alleviated pain markedly in comparison with placebo. Administration of mirogabalin on a long-term basis is a flexible dosage regimen for patients with PHN. It is noteworthy that mirogabalin should be administrated cautiously when combined with probenecid and cimetidine on account of a slight increase in pharmacodynamics effects of mirogabalin.

Conclusion

The development of mirogabalin allows further optimization of individual treatment strategies so as to provide more therapeutic choices in this medical domain.

Pathophysiological Roles of Auxiliary Calcium Channel α2δ Subunits

α2δ proteins serve as auxiliary subunits of voltage-gated calcium channels, which are essential components of excitable cells such as skeletal and heart muscles, nerve cells of the brain and the peripheral nervous system, as well as endocrine cells. Over the recent years, α2δ proteins have been identified as critical regulators of synaptic functions, including the formation and differentiation of synapses. These functions require signalling mechanisms which are partly independent of calcium channels. Hence, in light of these features it is not surprising that the genes encoding for the four α2δ isoforms have recently been linked to neurological and neurodevelopmental disorders including epilepsy, autism spectrum disorders, schizophrenia, and depressive and bipolar disorders. Despite the increasing number of identified disease-associated mutations, the underlying pathophysiological mechanisms are only beginning to emerge. However, a thorough understanding of the pathophysiological role of α2δ proteins ideally serves two purposes: first, it will contribute to our understanding of general pathological mechanisms in synaptic disorders. Second, it may support the future development of novel and specific treatments for brain disorders. In this context, it is noteworthy that the antiepileptic and anti-allodynic drugs gabapentin and pregabalin both act via binding to α2δ proteins and are among the top sold drugs for treating neuropathic pain. In this book chapter, we will discuss recent developments in our understanding of the functions of α2δ proteins, both as calcium channel subunits and as independent regulatory entities. Furthermore, we present and summarize recently identified and likely pathogenic mutations in the genes encoding α2δ proteins and discuss potential underlying pathophysiological consequences at the molecular and structural level.

Cacna2d2 inhibits axonal regeneration following surgical decompression in a rat model of cervical spondylotic myelopathy

Background

Cervical spondylotic myelopathy (CSM) is a clinically symptomatic condition due to spinal cord compression, leading to spinal cord dysfunction. Surgical decompression is the main treatment of CSM, but the mechanisms of axonal regeneration after surgical decompression are still fragmentary.

Methods

In a rat model of CSM, the cacna2d2 (α2δ2) expression levels in anterior horn of spinal cord were observed following compression and decompression by western blot and immunofluorescence. The expression levels of 5 hydroxytryptamine (5HT) and GAP43 were also analyzed by immunofluorescence. Furthermore, gabapentin intervention was performed for 4 weeks after decompression to analyze the changes of behaviors and anterior horn of spinal cords.

Results

Following decompression, the expression levels of α2δ2 in the anterior horn of spinal cord were decreased, but the expression levels of 5HT andGAP43 were increased. Compared with the vehicle treated rats, gabapentin treatment for 4 weeks ameliorated the behaviors of rats and improved the damaged anterior horn of spinal cord. Besides, inhibition of α2δ2 through gabapentin intervention enhanced the axonal regeneration in the anterior horn of damaged spinal cord.

Conclusions

Inhibition of α2δ2 could enhance axonal recovery in anterior horn of damaged spinal cord induced by CSM after surgical decompression, providing a potential method for promoting axon regeneration following surgery.

Piperazinyl Bicyclic Derivatives as Selective Ligands of the α2δ-1 Subunit of Voltage-Gated Calcium Channels

The synthesis and pharmacological activities of a new series of piperazinyl quinazolin-4-(3H)-one derivatives acting toward the α2δ-1 subunit of voltage-gated calcium channels (Ca_vα2δ-1) are reported. Different positions of a micromolar HTS hit were explored, and best activities were obtained for compounds containing a small alkyl group in position 3 of the quinazolin-4-(3H)-one scaffold and a 3-methyl-piperazin-1-yl- or 3,5-dimethyl-piperazin-1-yl-butyl group in position 2. The activity was shown to reside in the R enantiomer of the chain in position 2, and several eutomers reached single digit nanomolar affinities. Final modification of the central scaffold to reduce lipophilicity provided the pyrido[4,3-d]pyrimidin-4(3H)-one 16RR, which showed high selectivity for Ca_vα2δ-1 versus Ca_vα2δ-2, probably linked to its improved analgesic efficacy-safety ratio in mice over pregabalin.

Different functions of two putative Drosophila α2δ subunits in the same identified motoneurons

Voltage gated calcium channels (VGCCs) regulate neuronal excitability and translate activity into calcium dependent signaling. The α₁ subunit of high voltage activated (HVA) VGCCs associates with α₂δ accessory subunits, which may affect calcium channel biophysical properties, cell surface expression, localization and transport and are thus important players in calcium-dependent signaling. In vertebrates, the functions of the different combinations of the four α₂δ and the seven HVA α₁ subunits are incompletely understood, in particular with respect to partially redundant or separate functions in neurons. This study capitalizes on the relatively simpler situation in the Drosophila genetic model containing two neuronal putative α₂δ subunits, straightjacket and CG4587, and one Ca_v1 and Ca_v2 homolog each, both with well-described functions in different compartments of identified motoneurons. Straightjacket is required for normal Ca_v1 and Ca_v2 current amplitudes and correct Ca_v2 channel function in all neuronal compartments. By contrast, CG4587 does not affect Ca_v1 or Ca_v2 current amplitudes or presynaptic function, but is required for correct Ca_v2 channel allocation to the axonal versus the dendritic domain. We suggest that the two different putative α₂δ subunits are required in the same neurons to regulate different functions of VGCCs.

Neuronal α2δ proteins and brain disorders

α2δ proteins are membrane-anchored extracellular glycoproteins which are abundantly expressed in the brain and the peripheral nervous system. They serve as regulatory subunits of voltage-gated calcium channels and, particularly in nerve cells, regulate presynaptic and postsynaptic functions independently from their role as channel subunits. α2δ proteins are the targets of the widely prescribed anti-epileptic and anti-allodynic drugs gabapentin and pregabalin, particularly for the treatment of neuropathic pain conditions. Recently, the human genes (CACNA2D1-4) encoding for the four known α2δ proteins (isoforms α2δ-1 to α2δ-4) have been linked to a large variety of neurological and neuropsychiatric disorders including epilepsy, autism spectrum disorders, bipolar disorders, schizophrenia, and depressive disorders. Here, we provide an overview of the hitherto identified disease associations of all known α2δ genes, hypothesize on the pathophysiological mechanisms considering their known physiological roles, and discuss the most immanent future research questions. Elucidating their specific physiological and pathophysiological mechanisms may open the way for developing entirely novel therapeutic paradigms for treating brain disorders.

Emerging roles for α2δ subunits in calcium channel function and synaptic connectivity

Central nervous system function requires the proper formation and function of synapses. The α2δ auxiliary subunits of voltage-gated calcium channels have emerged as regulators of a number of critical events associated with regulation of synaptic function, including channel trafficking and localization, as well as the initial establishment of synaptic structures. In this review, we will discuss some of these recent studies which have uncovered novel mechanisms for α2δ function at the synapse, including the regulation of calcium channel α1 subunit specificity and the promotion of dendritic spine growth. Moreover, we will cover recent advances that have been made in understanding the consequences of aberrant α2δ signaling in injury and disease.

Genetic Associations between Voltage-Gated Calcium Channels and Psychiatric Disorders

Psychiatric disorders are mental, behavioral or emotional disorders. These conditions are prevalent, one in four adults suffer from any type of psychiatric disorders world-wide. It has always been observed that psychiatric disorders have a genetic component, however, new methods to sequence full genomes of large cohorts have identified with high precision genetic risk loci for these conditions. Psychiatric disorders include, but are not limited to, bipolar disorder, schizophrenia, autism spectrum disorder, anxiety disorders, major depressive disorder, and attention-deficit and hyperactivity disorder. Several risk loci for psychiatric disorders fall within genes that encode for voltage-gated calcium channels (CaVs). Calcium entering through CaVs is crucial for multiple neuronal processes. In this review, we will summarize recent findings that link CaVs and their auxiliary subunits to psychiatric disorders. First, we will provide a general overview of CaVs structure, classification, function, expression and pharmacology. Next, we will summarize tools to study risk loci associated with psychiatric disorders. We will examine functional studies of risk variations in CaV genes when available. Finally, we will review pharmacological evidence of the use of CaV modulators to treat psychiatric disorders. Our review will be of interest for those studying pathophysiological aspects of CaVs.

The Anticonvulsant Effects of Ketogenic Diet on Epileptic Seizures and Potential Mechanisms

Background:

Epilepsy is a syndrome of brain dysfunction induced by the aberrant excitability of certain neurons. Despite advances in surgical technique and anti-epileptic drug in recent years, recurrent epileptic seizures remain intractable and lead to a serious morbidity in the world. The ketogenic diet refers to a high-fat, low-carbohydrate and adequate-protein diet.Currently, its beneficial effects on epileptic seizure reduction have been well established. However, the detailed mechanisms underlying the anti-epileptic effects of ketogenic diet are still poorly understood. In this article, the possible roles of ketogenic diet on epilepsy were discussed.

Methods:

Data was obtained from the websites including Web of Science, Medline, Pubmed,Scopus, based on these keywords: “Ketogenic diet” and “epilepsy”.

Results:

As shown in both clinical and basic studies, the therapeutic effects of ketogenic diet might involve neuronal metabolism, neurotransmitter function, neuronal membrane potential and neuron protection against ROS.

Conclusion:

In this review, we systematically reviewed the effects and possible mechanisms of ketogenic diet on epilepsy, which may optimize the therapeutic strategies against epilepsy.

5-HT3 Receptors: A Potential Therapeutic Target for Epilepsy

BACKGROUND

Epilepsy is a syndrome of brain dysfunction caused by spontaneous, abnormal discharge. Many anti-epileptic drugs have developed in past decades. 5-HT is an important neurotransmitter in the central and peripheral nervous system of the human body which is involved in a number of physiological activities, such as sensation, movement, and behavior. 5-HT subtype have been divided into seven sub-groups from 5-HT1 to 5HT7. However, the role of 5-HT3 receptor on epilepsy is unclear. Therefore, in this article, the possible role of 5-HT3 receptor on epilepsy was systemically reviewed.

METHODS

Data were collected from Web of Science, Medline, Pubmed, Scopus, through searching of these keywords: "5-HT3" and "epilepsy".

RESULTS

An increasing number of studies have shown that the activation of the 5-HT3 receptor can inhibit epileptic seizures, while inhibition of the 5-HT3 receptor can promote spike waves.

CONCLUSION

In this review, we discuss the relationship between the 5HT3 receptor and epilepsy; this review may provide a new insight for clinical application of epilepsy treatment.

Early Gabapentin Treatment during the Latency Period Increases Convulsive Threshold, Reduces Microglial Activation and Macrophage Infiltration in the Lithium-Pilocarpine Model of Epilepsy

The lithium-pilocarpine model of epilepsy reproduces several features of temporal lobe epilepsy in humans, including the chronological timeline of an initial latency period followed by the development of spontaneous seizures. Epilepsy therapies in humans are implemented, as a rule, after the onset of the spontaneous seizures. We here studied the potential effect on epileptogenesis of starting an early treatment during the latency period, in order to prevent the development of spontaneous seizures. Adult male Wistar rats were treated with 3 mEq/kg LiCl, and 20 h later 30 mg/kg pilocarpine. Once status epilepticus (SE) was achieved, it was allowed to last for 20 min, and then motor seizures were controlled with the administration of 20 mg/kg diazepam. At 1DPSE (DPSE, days post-status epilepticus), animals started to receive 400 mg/kg/day gabapentin or saline for 4 days. At 5DPSE, we observed that SE induced an early profuse microglial and astroglial reactivity, increased synaptogenic trombospondin-1 expression and reduced AQP4 expression in astroglial ending feet. Blood brain barrier (BBB) integrity seemed to be compromised, as infiltrating NG2+ macrophages and facilitated access to the CNS was observed by transplanting eGFP+ blood cells and bone marrow-derived progenitors in the SE animals. The early 4-day gabapentin treatment successfully reduced microglial cell reactivity and blood-borne cell infiltration, without significantly altering the mRNA of proinflammatory cytokines IL-1β and TNFα immediately after the treatment. After 21DSPE, another group of animals that developed SE and received 4 days of gabapentin treatment, were re-exposed to subconvulsive accumulative doses of pilocarpine (10 mg/kg/30 min) and were followed by recording the Racine scale reached. Early 4-day gabapentin treatment reduced the Racine scale reached by the animals, reduced animal mortality, and reduced the number of animals that achieved SE (34% vs. 72%). We conclude that early gabapentin treatment following SE, during the latency period, is able to reduce neuroinflammation and produces a persistent effect that limits seizures and increases convulsive threshold, probably by restricting microglial reactivity and spurious synaptogenesis.