Hippocampal low-frequency stimulation inhibits afterdischarge and increases GABA (A) receptor expression in amygdala-kindled pharmacoresistant epileptic rats

Systematic review of rodent studies of deep brain stimulation for the treatment of neurological, developmental and neuropsychiatric disorders

Deep brain stimulation (DBS) modulates local and widespread connectivity in dysfunctional networks. Positive results are observed in several patient populations; however, the precise mechanisms underlying treatment remain unknown. Translational DBS studies aim to answer these questions and provide knowledge for advancing the field. Here, we systematically review the literature on DBS studies involving models of neurological, developmental and neuropsychiatric disorders to provide a synthesis of the current scientific landscape surrounding this topic. A systematic analysis of the literature was performed following PRISMA guidelines. 407 original articles were included. Data extraction focused on study characteristics, including stimulation protocol, behavioural outcomes, and mechanisms of action. The number of articles published increased over the years, including 16 rat models and 13 mouse models of transgenic or healthy animals exposed to external factors to induce symptoms. Most studies targeted telencephalic structures with varying stimulation settings. Positive behavioural outcomes were reported in 85.8% of the included studies. In models of psychiatric and neurodevelopmental disorders, DBS-induced effects were associated with changes in monoamines and neuronal activity along the mesocorticolimbic circuit. For movement disorders, DBS improves symptoms via modulation of the striatal dopaminergic system. In dementia and epilepsy models, changes to cellular and molecular aspects of the hippocampus were shown to underlie symptom improvement. Despite limitations in translating findings from preclinical to clinical settings, rodent studies have contributed substantially to our current knowledge of the pathophysiology of disease and DBS mechanisms. Direct inhibition/excitation of neural activity, whereby DBS modulates pathological oscillatory activity within brain networks, is among the major theories of its mechanism. However, there remain fundamental questions on mechanisms, optimal targets and parameters that need to be better understood to improve this therapy and provide more individualized treatment according to the patient's predominant symptoms.

SEW2871 reduces seizures via the sphingosine 1-phosphate receptor-1 pathway in the pentylenetetrazol and phenobarbitone kindling model of drug-refractory epilepsy

Epilepsy is a prevalent neurological disorder characterized by neuronal hypersynchronous discharge in the brain, leading to central nervous system (CNS) dysfunction. Despite the availability of anti-epileptic drugs (AEDs), resistance to AEDs is the greatest challenge in treating epilepsy. The role of sphingosine-1-phosphate-receptor 1 (S1PR1) in drug-resistant epilepsy is unexplored. This study investigated the effects of SEW2871, a potent S1PR1 agonist, on a phenobarbitone (PHB)-resistant pentylenetetrazol (PTZ)-kindled Wistar rat model. We measured the messenger ribonucleic acid (mRNA) expression of multi-drug resistance 1 (MDR1) and multi-drug resistance protein 5 (MRP5) as indicators for drug resistance. Rats received PHB + PTZ for 62 days to develop a drug-resistant epilepsy model. From day 48, SEW2871 (0.25, 0.5, 0.75 mg/kg, intraperitoneally [i.p.]) was administered for 14 days. Seizure scoring, behaviour, oxidative markers like reduced glutathione, catalase, superoxide dismutase, inflammatory markers like interleukin 1 beta tumour necrosis factor alpha, interferon gamma and mRNA expression (MDR1 and MRP5) were assessed, and histopathological assessments were conducted. SEW2871 demonstrated dose-dependent improvements in seizure scoring and neurobehavioral parameters with a reduction in oxidative and inflammation-induced neuronal damage. The S1PR1 agonist also downregulated MDR1 and MRP5 gene expression and significantly decreased the number of dark-stained pyknotic nuclei and increased cell density with neuronal rearrangement in the rat brain hippocampus. These findings suggest that SEW2871 might ameliorate epileptic symptoms by modulating drug resistance through downregulation of MDR1 and MRP5 gene expression.

An Atomic Level Investigation of Sodium Ions Regulating Agonist and Antagonist Binding in the Active Site of a Novel Target 5HT2BR Against Drug-Resistant Epilepsy

The study investigates the movement of sodium ions inside the ligand-binding pocket of the class-A GPCR serotonin receptor (5HT_2BR), a primary target for modern drugs. The available PDBs are mutant chimeras, so a 3D structure is modeled and validated by structural similarity (84.05%), Ramachandran favorable residues (93.01%), and clash score. Using MD simulations (500 ns), the ion active site is tracked in the presence and absence of ions and ligands. The ions enter the active site along helices III, VI, and VII, and the primary residue (ASP^3.32) interacts with ions via H-bond (stronger- ~2.4 Å). The radial distribution function around ASP^3.32 rises promptly at intermediate distances (2 Å < r < 4 Å), suggesting a higher probability of finding sodium ions at these distances. The ions stabilize the receptor at a better RMSD and promote stronger interactions (3-H-bonds, 1-π-bond~3.35 Å) with the agonist, and not the antagonist (no H-bond). Simulating unrestrained ligands further confirms this pattern, suggesting that ions might promote agonist binding but not be a prerequisite for antagonist action. The study highlights the mechanistic evaluation of sodium ions mobility in 5HT_2BR modulation and ligand binding, showing potential in drug development.

Designing the 5HT2BR structure and its modulation as a therapeutic target for repurposing approach in drug-resistant epilepsy

The study intends to repurpose FDA drugs and investigate the mechanism of (5HT_2BR) activation by comprehending inter-residue interactions. The 5HT_2BR is a novel thread, and its role in reducing seizures in Dravet syndrome is emerging. The crystal structure (5HT_2BR) is a chimera with mutations; hence 3D-structure is modeled (4IB4: 5HT_2BR_M). The structure is cross-validated to simulate the human receptor using enrichment analysis (ROC: 0.79) and SAVESv6.0. Virtual screening of 2456 approved drugs yielded the best hits that are subjected to MM/GBSA and molecular dynamic (MD) simulations. The 2 top drugs Cabergoline (-53.44 kcal/mol) and Methylergonovine (-40.42 kcal/mol), display strong binding affinity, and ADMET/SAR analysis also suggests their non-mutagenic or non-carcinogenic nature. Methylergonovine has a weaker binding affinity and lower potency than standards [Ergotamine (agonist) and Methysergide (antagonist)] due to its higher K_i (1.32 M) and K_d (6.44 ×10^-8 M) values. Compared to standards, Cabergoline has moderate binding affinity and potency [K_i = 0.85 M and K_d = 5.53 × 10-8 M]. The top 2 drugs primarily interact with conserved residues (ASP135, LEU209, GLY221, ALA225, and THR140) as in agonists, unlike the antagonist. The top 2 drugs, upon binding to the 5HT_2BR_M, modify the helices VI, V, and III and shift the RMSD 2.48 Å and 3.07 Å. LEU209 forms a latch with residues 207-214 (forms a lid) in the 5HT_2BR_M receptor, which enhances agonist binding and prevents drug escape. Methylergonovine and Cabergoline interact more stongly with ALA225 than the antagonist. The post-MD analysis of Cabergoline suggests a better MM/GBSA value (-89.21 kcal/mol) than Methylergonovine (-63.54 kcal/mol). In this study, Cabergoline and Methylergonovine's agonistic mechanism and solid binding properties suggest their strong role in regulating the 5HT_2BR and might target drug-resistant epilepsy.

Animal Models of Drug-Resistant Epilepsy as Tools for Deciphering the Cellular and Molecular Mechanisms of Pharmacoresistance and Discovering More Effective Treatments

In the last 30 years, over 20 new anti-seizure medicines (ASMs) have been introduced into the market for the treatment of epilepsy using well-established preclinical seizure and epilepsy models. Despite this success, approximately 20-30% of patients with epilepsy have drug-resistant epilepsy (DRE). The current approach to ASM discovery for DRE relies largely on drug testing in various preclinical model systems that display varying degrees of ASM drug resistance. In recent years, attempts have been made to include more etiologically relevant models in the preclinical evaluation of a new investigational drug. Such models have played an important role in advancing a greater understanding of DRE at a mechanistic level and for hypothesis testing as new experimental evidence becomes available. This review provides a critical discussion of the pharmacology of models of adult focal epilepsy that allow for the selection of ASM responders and nonresponders and those models that display a pharmacoresistance per se to two or more ASMs. In addition, the pharmacology of animal models of major genetic epilepsies is discussed. Importantly, in addition to testing chemical compounds, several of the models discussed here can be used to evaluate other potential therapies for epilepsy such as neurostimulation, dietary treatments, gene therapy, or cell transplantation. This review also discusses the challenges associated with identifying novel therapies in the absence of a greater understanding of the mechanisms that contribute to DRE. Finally, this review discusses the lessons learned from the profile of the recently approved highly efficacious and broad-spectrum ASM cenobamate.

Allosteric modulation of conserved motifs and helices in 5HT2BR: Advances drug discovery and therapeutic approach towards drug resistant epilepsy

The 5HT2BR, class-A GPCR is a new target, and its significance for seizure reduction in Dravet syndrome is just now gaining interest, suggesting its specific role in epileptic seizure management. Homology modeling of human 5HT2BR (P41595), was performed using a template 4IB4, the modeled structure was cross-validated (stereo chemical hindrance, Ramachandran plot, enrichment analysis) to mimic a closer native structure. Virtual screening (8532 compounds), drug-likeliness, mutagenicity, and carcinogenicity profiling prioritized six compounds for molecular dynamics (500 ns), Rgyr, DCCM. The receptor's C-alpha fluctuation upon bound agonist (6.91 Å), known antagonist (7.03 Å), and LAS 52115629 (5.83 Å) binding varies, leading to receptor stabilization. The residues C-alpha side-chain in active site strongly interacts (hydrogen bonds) with bound agonist (100% interaction: ASP135), known antagonist (95%:ASP135), and LAS 52115629 (100%:ASP135). The Rgyr for receptor-ligand complex, LAS 52115629 (25.68 Å), lies close to bound agonist-Ergotamine, and DCCM analysis also shows strong positive correlations for LAS 52115629 as compared to known drugs. LAS 52115629 is less likely to cause toxicity than known drugs. The structural parameters in the modeled receptor's conserved motifs (DRY, PIF, NPY) were altered for receptor activation upon ligand-binding, which otherwise was in the in-activated state. The ligand (LAS 52115629)-binding further alters the helices-III, V, VI (G-protein bound), and VII, which form potential interacting sites with the receptor and are proven necessary for activating the receptor. Therefore, LAS 52115629 can act as a potential 5HT2BR agonist, targeting drug-resistant epilepsy.Communicated by Ramaswamy H. Sarma.

The Expression of ZnT3 and GFAP Is Potentiated in the Hippocampus of Drug-Resistant Epileptic Rats Induced by Amygdala Kindling

OBJECTIVE

The first-line treatment for epilepsy, a chronic neurological disorder characterized by spontaneous seizures, includes the application of anticonvulsant drug therapy. Only one-third of patients are incapable of complete controlling of their seizures after the administration of ≥2 pharmaceuticals. Here, we aimed to observe the ultrastructure changes and the expression of ZnT3 and GFAP in the hippocampus of drug-resistant epileptic rats.

METHODS

A total of 50 healthy adult male SD rats were used to generate the model ofepilepsy by amygdala kindling. After the rats were successfully kindled, pharmacoresistant epileptic (PRE) rats were selected according to their response to phenobarbital and phenytoin. The ultrastructure as well as the expression of zinc transporter 3 (ZnT3, a member of a growing family of mammalian zinc transporters) and glial fibrillary acidic protein (GFAP) were compared among PRE, pharmacosensitive epileptic (PRE), and normal (NRC) rats.

RESULTS

The PRE rats displayed severe synapses, neuronal degeneration, and necrosis. Moreover, the expression of ZnT3 and GFAP was significantly increased in both PRE and PSE rats; compared with NRC rats, the promotion of this expression was more pronounced in the PRE rats.

CONCLUSIONS

Taken together, obvious synapses, neuronal degeneration, necrosis, mossy fiber sprouting, and astrogliosis were found in the drug-resistant epileptic rat model induced by amygdala kindling.

Influence of hippocampal low-frequency stimulation on GABAA R α1, ICER and BNDF expression level in brain tissues of amygdala-kindled drug-resistant temporal lobe epileptic rats

This study investigated the therapeutic effect of hippocampal low-frequency stimulation (Hip-LFS) and its influence on the type A γ-aminobutyric acid receptor α1 subunit (GABA_A R α1 subunit), inducible cAMP early repressor (ICER) and brain-derived neurotrophic factors (BNDF). The model of epilepsy was induced by chronic electrical stimulation in amygdala. Drug-resistant and drug-sensitive epileptic rats were selected by testing their seizure response to phenytoin and phenobarbital. The changes of GABA_A R α1 subunit, ICER and BDNF expression were detected via immunohistochemistry and western blot. The expression levels of ICER and BDNF were increased remarkably but the GABA_A R α1 subunit decreased significantly in the drug-resistant epileptic rats. However, the expression levels of ICER, BDNF were decreased and the expression of the GABA_A R α1 subunit increased significantly in the drug-resistant epileptic rats after two weeks of Hip-LFS. Meanwhile, the seizure degree was reduced and the electroencephalograms were improved. The present study demonstrated thatincreased ICER and BDNF might be associated with the development of drug-resistance. The effect of Hip-LFS in the treatment of drug-resistant epileptic rats might be associated with increasing the levels of the ICER and the BDNF.