Response of Voltage-Gated Sodium and Calcium Channels Subtypes on Dehydroepiandrosterone Treatment in Iron-Induced Epilepsy

Increased NaV1.2 expression and its interaction with CaM contribute to the hyperexcitability induced by prolonged inhibition of CaMKII

OBJECTIVE

Dysfunction of calcium/calmodulin (CaM)-dependent kinase II (CaMKII) has been involved in hyperexcitability-related disorders including epilepsy. However, the relationship between CaMKII and neuronal excitability remains unclear.

METHODS

Neuronal excitability was detected in vivo and in vitro by electroencephalography (EEG), patch clamp and multi-electrode array (MEA), respectively. Next, we assessed the currents of voltage-gated sodium channels (VGSCs) by patch clamp, and  mRNA and protein expressions of VGSCs were determined by real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and western blot, respectively. Meanwhile, the association between the nuclear receptor subfamily 4 group A member 2 (NR4A2) and promoters of Scn2a, was determined by chromatin immunoprecipitation (ChIP)-qPCR. In addition, we utilized co-immunoprecipitation (Co-IP), immunofluorescence labeling, and pull-down to determine the interaction between VGSCs and CaM.

RESULTS

Prolonged CaMKII inhibition by KN93, an inhibitor of CaMKII, for 24 h and CaMKII knockdown induced more seizure-like events in Wistar rats, TRM rats and C57BL/6 mice, and led to hyperexcitability in primary hippocampal neurons and human induced-pluripotent stem cell (hiPSC)-derived cortical neurons. In addition, prolonged CaMKII inhibition resulted in elevated persistent sodium current (INaP)/transient sodium current (INaT) and increased mRNA and protein expressions of NaV1.2. Meanwhile, prolonged CaMKII inhibition by KN93 decreased NR4A2 expression and contributed to a transcriptional repression role of NR4A2 in Scn2a regulation, leading to increased NaV1.2 expression. Moreover, an increased interaction between NaV1.2 and CaM was attributable to enhanced binding of CaM to the isoleucine-glutamine (IQ) domain at the C-terminus of the NaV1.2 channel, which may also lead to the potentiation in INaP/INaT and channel activity. Furthermore, a peptide that antagonized CaM binding to NaV1.2 IQ domain (ACNp) rescued hyperexcitability following prolonged CaMKII inhibition.

SIGNIFICANCE

We unveiled that prolonged CaMKII inhibition induced hyperexcitability through increasing the expression of NaV1.2 and its association with CaM. Thus, our study uncovers a novel signaling mechanism by which CaMKII maintains appropriate neuronal excitability.

Treatment options for post-traumatic epilepsy: an update on clinical and translational aspects

INTRODUCTION

Post-traumatic epilepsy (PTE) accounts for 10% to 20% of all symptomatic epilepsies and 5% of all forms of epilepsy, and drug resistance is reported in up to 45% of cases.

AREAS COVERED

This is a focused narrative review that discusses the available data on the current and new PTE treatments, giving particular attention to the last 10 years.

EXPERT OPINION

Despite the disappointing results of many antiseizure medications (ASMs) in preventing epileptogenicity, it is still unclear whether the early intervention could lead to different clinical phenotypes in terms, for example, of seizure severity, drug resistance and comorbidity patterns. The same applies to compounds targeting neuroinflammation, oxidative stress and neurotransmission modulation. The heterogeneity of etiologies leading to PTE has limited the investigation and implementation of specific interventions. New studies must focus on identifying common pathways and mechanisms shared by different etiological processes, identifying biomarkers, and validating animal models of epileptogenesis concerning PTE. Drug repurposing research will facilitate rapid translation into clinical research. Multitarget drug combinations will also receive increasing attention. In terms of non-pharmacological treatments, Vagus Nerve Stimulation seems to be a good option, while epilepsy surgery and Deep Brain Stimulation deserve further attention.

Eugenol attenuates aluminium-induced neurotoxicity in rats by inhibiting the activation of STAT3 and NF-кB

Aluminium is a common metallic toxicant that easily penetrates the brain and exerts severe pathological effects e.g., oxidative stress, inflammation and neurodegeneration. Eugenol is a natural phenolic compound possessing numerous therapeutic properties including antioxidant, anti-inflammatory and neuroprotective. The compound has also been reported to interfere with important transcription factors like STAT3 and NF-кB. Thus, the present study intended to explore the therapeutic potential of eugenol in aluminium neurotoxicity. Rats were administered AlCl3 (100 mg/kg b. wt., orally) and eugenol (200 mg/kg b. wt., orally) alone or in combination for 45 days. The results revealed that AlCl3 administration increases acetylcholinesterase (AChE) activity, lipid peroxidation (LPO), and protein oxidation (PO) along with decreasing superoxide dismutase (SOD) and catalase (CAT) activities, and glutathione (GSH) content in the cortex and hippocampus regions of the brain. Moreover, AlCl3 induces neuronal loss and astroglial activation in both brain areas. The study further revealed that AlCl3 also increases the expression of transcription factors STAT3 and NF-кB in neurons and astrocytes of the cortex and hippocampus. However, co-administration of eugenol with AlCl3 restored the enzymatic activities of AChE, SOD and CAT, and GSH content, and rescued the cortex and hippocampus from LPO, PO, neuronal loss and astroglial activation. Furthermore, the study reported that eugenol reverses the expression pattern of STAT3 and NF-кB in AlCl3-intoxicated rats. In conclusion, the study suggests that eugenol ameliorates oxidative stress, neuronal loss and reactive astrogliosis in aluminium-induced neurotoxicity by inhibiting signalling molecules, STAT3 and NF-кB.

Recent Advances in Pathophysiology and Therapeutic Approaches in Epilepsy

Epilepsy is a severe neurological disorder involving spontaneous and recurrent seizures, affecting a large number of people worldwide [...].

Dehydroepiandrosterone Attenuates Astroglial Activation, Neuronal Loss and Dendritic Degeneration in Iron-Induced Post-Traumatic Epilepsy

Iron-induced experimental epilepsy in rodents reproduces features of post-traumatic epilepsy (PTE) in humans. The neural network of the brain seems to be highly affected during the course of epileptogenesis and determines the occurrence of sudden and recurrent seizures. The aim of the current study was to evaluate astroglial and neuronal response as well as dendritic arborization, and the spine density of pyramidal neurons in the cortex and hippocampus of epileptic rats. We also evaluated the effect of exogenous administration of a neuroactive steroid, dehydroepiandrosterone (DHEA), in epileptic rats. To induce epilepsy, male Wistar rats were given an intracortical injection of 100 mM solution (5 µL) of iron chloride (FeCl3). After 20 days, DHEA was administered intraperitoneally for 21 consecutive days. Results showed epileptic seizures and hippocampal Mossy Fibers (MFs) sprouting in epileptic rats, while DHEA treatment significantly reduced the MFs’ sprouting. Astroglial activation and neuronal loss were subdued in rats that received DHEA compared to epileptic rats. Dendritic arborization and spine density of pyramidal neurons was diminished in epileptic rats, while DHEA treatment partially restored their normal morphology in the cortex and hippocampus regions of the brain. Overall, these findings suggest that DHEA’s antiepileptic effects may contribute to alleviating astroglial activation and neuronal loss along with enhancing dendritic arborization and spine density in PTE.

Structure-function of DHEA binding proteins

Dehydroepiandrosterone (3β-hydroxy-5-androsten-17-one, DHEA) and its sulfated metabolite DHEA-S are the most abundant circulating steroids and are precursors for active sex steroid hormones, estradiol and testosterone. DHEA has a broad range of reported effects in the central nervous system (CNS), cardiovascular system, adipose tissue, kidney, liver, and in the reproductive system. The mechanisms by which DHEA and DHEA-S initiate their biological effects are diverse. DHEA and DHEA-S may directly bind to plasma membrane (PM) receptors, including a DHEA-specific, G-protein coupled receptor (GPCR) in endothelial cells; various neuroreceptors, e.g., aminobutyric-acid-type A (GABA(A)), N-methyl-d-aspartate (NMDA) and sigma-1 (S1R) receptors (NMDAR and SIG-1R). DHEA and DHEA-S directly bind the nuclear androgen and estrogen receptors (AR, ERα, or ERβ) although with significantly lower binding affinities compared to the steroid hormones, e.g., testosterone, dihydrotestosterone, and estradiol, which are the cognate ligands for AR and ERs. Thus, extra-gonadal metabolism of DHEA to the sex hormones must be considered for many of the biological benefits of DHEA. DHEA also actives GPER1 (G protein coupled estrogen receptor 1). DHEA activates constitutive androstane receptor CAR (CAR) and proliferator activated receptor (PPARα) by indirect dephosphorylation. DHEA affects voltage-gated sodium and calcium ion channels and DHEA-2 activates TRPM3 (Transient Receptor Potential Cation Channel Subfamily M Member 3). This chapter updates our previous 2018 review pertaining to the physiological, biochemical, and molecular mechanisms of DHEA and DHEA-S activity.

Ameliorative effect of curcumin on altered expression of CACNA1A and GABRD in the pathogenesis of FeCl3-induced epilepsy

The pivotal role played by ion-channel dysregulations in the pathogenesis of epilepsy has always garnered much attention. Since mutation of ion-channel proteins CACNA1A and GABRD have been associated with epilepsy, it is important to determine the post-traumatic epilepsy-associated changes in expression levels of these ion channel proteins. Additionally, curcumin is already known for its antiepileptic and neuroprotective potential in FeCl₃-induced model of post-traumatic epilepsy. Thus, we investigated FeCl₃-induced epilepsy mediated differential expression of CACNA1A and GABRD in the cortical region of the rat brain. Furthermore, we investigated the effect of curcumin on the expression of both proteins. For this, epilepsy was induced by intracortical FeCl₃ injection (5 μl of 100 mM). Additionally, curcumin (conc. 1000 ppm; 75 mg/kg of b.wt.; for 14 and 28 days) was administered, mixed with normal food pellets. Results obtained from EEG-MUA and Morris water maze assay demonstrate the progression of epilepsy after FeCl₃ injection. Additionally, western blotting and histological studies show the downregulation of CACNA1A and GABRD during epileptogenesis. It was observed that epilepsy-associated decline in learning and memory of animals might be linked with the dysregulation of both proteins. Results also demonstrated that curcumin administration ameliorated epilepsy-associated change in expression of both CACNA1A and GABRD proteins. In conclusion, the neuroprotective effect of curcumin against iron-induced epilepsy might be accompanied by the alleviated upregulation of these channel proteins.