Embelin Protects Against Acute Pentylenetetrazole-Induced Seizures and Positively Modulates Cognitive Function in Adult Zebrafish

Behavioral and neurotransmitter changes on antiepileptic drugs treatment in the zebrafish pentylenetetrazol-induced seizure model

Epilepsy, a recurrent neurological disorder involving abnormal neurotransmitter kinetics in the brain, has emerged as a global health concern. The mechanism of epileptic seizures is thought to involve a relative imbalance between excitatory and inhibitory neurotransmitters. Despite the recent advances in clinical and basic research on the pathogenesis of epilepsy, the complex relationship between the neurotransmitter changes and behavior with and without antiepileptic drugs (AEDs) during seizures remains unclear. To investigate the effects of AEDs such as levetiracetam (LEV), carbamazepine (CBZ), and fenfluramine (FFR) on key neurotransmitters in the pentylenetetrazol (PTZ)-induced seizures in adult zebrafish, we examined the changes in glutamic acid, gamma-aminobutyric acid (GABA), serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), choline, acetylcholine, norepinephrine, dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), and adenosine. In this study, we observed that 5-HT and DA levels in the brain increased immediately after PTZ-induced seizures. Behavioral tests clearly showed that all of these AEDs suppressed the PTZ-induced seizures. Upon treatment of PTZ-induced seizures with these AEDs, CBZ decreased the glutamic acid and FFR increased the GABA levels; however, no neurotransmitter changes were observed in the brain after LEV administration. Thus, we demonstrated a series of neurotransmitter changes linked to behavioral changes during PTZ-induced epileptic seizures when LEV, CBZ, or FFR were administered. These findings will lead to a more detailed understanding of the pathogenesis of epilepsy associated with behavioral and neurotransmitter changes under AED treatment.

Antibacterial and Anti-Quorum Sensing Properties of Silver Nanoparticles Phytosynthesized Using Embelia ruminata

The rise in antibiotic resistance (AR) poses an imminent threat to human health. Nanotechnology, together with mechanisms such as quorum sensing (QS), which relies on communication between bacterial cells, may decrease the selective pressure for AR. Thus, this study aimed to investigate the effectiveness of silver nanoparticles (AgNPs) synthesized at room temperature (Rt) and 80 °C using Embelia ruminata leaf, stem-bark, and fruit extracts as antibacterial and anti-QS agents. The phytosynthesized AgNPs solutions were subjected to various characterization assays and assessed for their antibacterial activities. Quantitative QS assays were performed using Chromobacterium subtsugae CV017 and Chromobacterium violaceum ATCC 12472. Synthesized AgNPs were spherical-to-near-spherical in shape, poly-dispersed, and crystalline, with a size range of 21.06-32.15 nm. Fruit AgNPs showed stronger antibacterial activity than AgNPs from other plant organs against selected bacterial strains. In the QS assays, fruit 80 °C AgNPs demonstrated the most significant violacein inhibition in an assay performed using the short-chain acyl homoserine lactone CV017 biosensor, while the leaf and fruit Rt AgNPs demonstrated the most violacein inhibition in an assay performed using the long-chain acyl homoserine lactone ATCC 12472 biosensor. The investigations carried out in this study lay the groundwork for future innovative research into antibacterial and anti-QS strategies using E. ruminata.

Chemically-induced epileptic seizures in zebrafish: A systematic review

The use of zebrafish as a model organism is gaining evidence in the field of epilepsy as it may help to understand the mechanisms underlying epileptic seizures. As zebrafish assays became popular, the heterogeneity between protocols increased, making it hard to choose a standard protocol to conduct research while also impairing the comparison of results between studies. We conducted a systematic review to comprehensively profile the chemically-induced seizure models in zebrafish. Literature searches were performed in PubMed, Scopus, and Web of Science, followed by a two-step screening process based on inclusion/exclusion criteria. Qualitative data were extracted, and a sample of 100 studies was randomly selected for risk of bias assessment. Out of the 1058 studies identified after removing duplicates, 201 met the inclusion criteria. We found that the most common chemoconvulsants used in the reviewed studies were pentylenetetrazole (n = 180), kainic acid (n = 11), and pilocarpine (n = 10), which increase seizure severity in a dose-dependent manner. The main outcomes assessed were seizure scores and locomotion. Significant variability between the protocols was observed for administration route, duration of exposure, and dose/concentration. Of the studies subjected to risk of bias assessment, most were rated as low risk of bias for selective reporting (94%), baseline characteristics of the animals (67%), and blinded outcome assessment (54%). Randomization procedures and incomplete data were rated unclear in 81% and 68% of the studies, respectively. None of the studies reported the sample size calculation. Overall, these findings underscore the need for improved methodological and reporting practices to enhance the reproducibility and reliability of zebrafish models for studying epilepsy. Our study offers a comprehensive overview of the current state of chemically-induced seizure models in zebrafish, highlighting the common chemoconvulsants used and the variability in protocol parameters. This may be particularly valuable to researchers interested in understanding the underlying mechanisms of epileptic seizures and screening potential drug candidates in zebrafish models.

Treating Epilepsy with Natural Products: Nonsense or Possibility?

Epilepsy is a neurological disease characterized by recurrent seizures that can lead to uncontrollable muscle twitching, changes in sensitivity to sensory perceptions, and disorders of consciousness. Although modern medicine has effective antiepileptic drugs, the need for accessible and cost-effective medication is urgent, and products derived from plants could offer a solution. For this review, we have focused on natural compounds that have shown anticonvulsant activity in in vivo models of epilepsy at relevant doses. In some cases, the effects have been confirmed by clinical data. The results of our search are summarized in tables according to their molecular targets. We have critically evaluated the data we present, identified the most promising therapeutic candidates, and discussed these in the text. Their perspectives are supported by both pharmacokinetic properties and potential interactions. This review is intended to serve as a basis for future research into epilepsy and related disorders.

Zebrafish: A Pharmacological Model for Learning and Memory Research

Learning and memory are essential to organism survival and are conserved across various species, especially vertebrates. Cognitive studies involving learning and memory require using appropriate model organisms to translate relevant findings to humans. Zebrafish are becoming increasingly popular as one of the animal models for neurodegenerative diseases due to their low maintenance cost, prolific nature and amenability to genetic manipulation. More importantly, zebrafish exhibit a repertoire of neurobehaviors comparable to humans. In this review, we discuss the forms of learning and memory abilities in zebrafish and the tests used to evaluate the neurobehaviors in this species. In addition, the pharmacological studies that used zebrafish as models to screen for the effects of neuroprotective and neurotoxic compounds on cognitive performance will be summarized here. Lastly, we discuss the challenges and perspectives in establishing zebrafish as a robust model for cognitive research involving learning and memory. Zebrafish are becoming an indispensable model in learning and memory research for screening neuroprotective agents against cognitive impairment.

Bisphenol F Impaired Zebrafish Cognitive Ability through Inducing Neural Cell Heterogeneous Responses

The central nervous system (CNS) is a sensitive target for endocrine-disrupting chemicals, such as bisphenol analogues. Bisphenol A (BPA) usage is associated with the occurrence of many neurological diseases. With the restricted use of BPA, bisphenol F (BPF) has been greatly introduced for industrial manufacture and brings new hazards to public CNS health. To understand how BPF affects the neural system, we performed a cognitive test for zebrafish that are continuously exposed to environmentally relevant concentrations (0.5 and 5.0 μg/L) of BPF since embryonic stage and identified suppressed cognitive ability in adulthood. Single-cell RNA sequencing of neural cells revealed a cell composition shift in zebrafish brain post BPF exposure, including increase in microglia and decrease in neurons; these changes were further validated by immune staining. At the same time, a significant inflammatory response and increased phagocytic activity were detected in zebrafish brain post BPF exposure, which were consistent with the activation of microglia. Cell-specific transcriptomic profiles showed that abnormal phagocytosis, activated brain cell death, and apoptosis occurred in microglia post BPF exposure, which are responsible for the neuron loss. In addition, certain neurological diseases were affected by BPF in both excitatory and inhibitory neurons, such as the movement disorder and neural muscular disease, however, with distinctly involved genes. These findings indicate that BPF exposure could lead to an abnormal cognitive behavior of zebrafish through inducing heterogeneous changes of neural cells in brain and revealed the dominating role of microglia in mediating this effect.

Naturally Occurring HMGB1 Inhibitor, Glycyrrhizin, Modulates Chronic Seizures-Induced Memory Dysfunction in Zebrafish Model

Glycyrrhizin (GL) is a well-known pharmacological inhibitor of high mobility group box 1 (HMGB1) and is abundantly present in the licorice root (Glycyrrhiza radix). HMGB1 protein, a key mediator of neuroinflammation, has been implicated in several neurological disorders, including epilepsy. Epilepsy is a devastating neurological disorder with no effective disease-modifying treatment strategies yet, suggesting a pressing need for exploring novel therapeutic options. In the current investigation, using a second hit pentylenetetrazol (PTZ) induced chronic seizure model in adult zebrafish, regulated mRNA expression of HMGB1 was inhibited by pretreatment with GL (25, 50, and 100 mg/kg, ip). A molecular docking study suggests that GL establishes different binding interactions with the various amino acid chains of HMGB1 and Toll-like receptor-4 (TLR4). Our finding suggests that GL pretreatment reduces/suppresses second hit PTZ induced seizure, as shown by the reduction in the seizure score. GL also regulates the second hit PTZ induced behavioral impairment and rescued second hit PTZ related memory impairment as demonstrated by an increase in the inflection ratio (IR) at the 3 h and 24 h T-maze trial. GL inhibited seizure-induced neuronal activity as demonstrated by reduced C-fos mRNA expression. GL also modulated mRNA expression of BDNF, CREB-1, and NPY. The possible mechanism underlying the anticonvulsive effect of GL could be attributed to its anti-inflammatory activity, as demonstrated by the downregulated mRNA expression level of HMGB1, TLR4, NF-kB, and TNF-α. Overall, our finding suggests that GL exerts an anticonvulsive effect and ameliorates seizure-related memory disruption plausibly through regulating of the HMGB1-TLR4-NF-kB axis.

Effects of new antiseizure drugs on seizure activity and anxiety-like behavior in adult zebrafish

Several studies with larvae and adult zebrafish have shown that old and new antiseizure drugs (ASDs) produce discrepant results in seizure tests, locomotor activity or anxiety models. In this study, the pentylenetetrazole seizure test (PTZ) was performed to assess the effectiveness of four new ASDs: lamotrigine (LTG), topiramate (TPM), felbamate (FBM), and levetiracetam (LEV) in the subsequent stages of seizures in adult fish. All ASDs were administered intraperitoneally (i.p.). The time of maximal anticonvulsant effect and the dose-response relationship of the drugs were assessed. The effects of studied ASDs on the locomotor activity and the anxiety-like behavior in the color preference test were also investigated. Furthermore, drug concentrations in zebrafish homogenates were determined. LTG, TPM, and LEV significantly increased the seizure latency at three subsequent stages of seizures (SI-SIII), while FBM was effective only at SI. Locomotor activity decreased after TPM treatment. TPM and FBM exhibited a strong anxiolytic-like effect in the color preference test. LEV at the highest dose tested had a weak anxiolytic-like effect. The HPLC analysis showed average concentrations of the studied ASDs in the fish body during their maximum anticonvulsant activity. The present study shows that FBM cannot inhibit all subsequent PTZ seizure stages in the adult fish. Except for LTG, the studied drugs affected the anxiety-like behavior of treated animals. Furthermore, only TPM significantly changed locomotion parameters. Our findings support the need to accurately characterize the efficacy of new ASDs at different stages of the PTZ-induced seizures in adult zebrafish.

Anti-High Mobility Group Box-1 Monoclonal Antibody Attenuates Seizure-Induced Cognitive Decline by Suppressing Neuroinflammation in an Adult Zebrafish Model

Epilepsy is a chronic brain disease afflicting around 70 million global population and is characterized by persisting predisposition to generate epileptic seizures. The precise understanding of the etiopathology of seizure generation is still elusive, however, brain inflammation is considered as a major contributor to epileptogenesis. HMGB1 protein being an initiator and crucial contributor of inflammation is known to contribute significantly to seizure generation via activating its principal receptors namely RAGE and TLR4 reflecting a potential therapeutic target. Herein, we evaluated an anti-seizure and memory ameliorating potential of an anti-HMGB1 monoclonal antibody (mAb) (1, 2.5 and 5 mg/kg, I.P.) in a second hit Pentylenetetrazol (PTZ) (80 mg/kg, I.P.) induced seizure model earlier stimulated with Pilocarpine (400 mg/kg, I.P.) in adult zebrafish. Pre-treatment with anti-HMGB1 mAb dose-dependently lowered the second hit PTZ-induced seizure but does not alter the disease progression. Moreover, anti-HMGB1 mAb also attenuated the second hit Pentylenetetrazol induced memory impairment in adult zebrafish as evidenced by an increased inflection ration at 3 and 24 h trail in T-maze test. Besides, decreased level of GABA and an upregulated Glutamate level was observed in the second hit PTZ induced group, which was modulated by pre-treatment with anti-HMGB1 mAb. Inflammatory responses occurred during the progression of seizures as evidenced by upregulated mRNA expression of HMGB1, TLR4, NF-κB, and TNF-α, in a second hit PTZ group, which was in-turn downregulated upon pre-treatment with anti-HMGB1 mAb reflecting its anti-inflammatory potential. Anti-HMGB1 mAb modulates second hit PTZ induced changes in mRNA expression of CREB-1 and NPY. Our findings indicates anti-HMGB1 mAb attenuates second hit PTZ-induced seizures, ameliorates related memory impairment, and downregulates the seizure induced upregulation of inflammatory markers to possibly protect the zebrafish from the incidence of further seizures through via modulation of neuroinflammatory pathway.

Effects of classic antiseizure drugs on seizure activity and anxiety-like behavior in adult zebrafish

The zebrafish is extensively used as a model organism for studying several disorders of the central nervous system (CNS), including epilepsy. Some antiseizure drugs (ASDs) have been shown to produce discrepant results in larvae and adults zebrafish, therefore, their anticonvulsant efficacy in subsequent stages of the pentylenetetrazole (PTZ)-induced seizures should be more precisely characterized. The purpose of this study was to investigate behavioral effects of five classic ASDs: valproate (VPA), phenytoin (PHT), carbamazepine (CBZ), diazepam (DZP), and phenobarbital (PB) administered intraperitoneally (i.p.) in the PTZ-induced seizure test in adult zebrafish. We determined the time of maximal effect and the dose-response relationship of the studied ASDs. Furthermore, we assessed changes in the locomotor activity and the anxiety-like behavior in the color preference test. Moreover, drug concentrations in zebrafish homogenates were examined. VPA, DZP, and PB significantly increased the seizure latency at three subsequent stages of seizures (SI-SIII). PHT produced the anticonvulsant-like effect at SI and SII, while CBZ was effective at SII and SIII. Only DZP decreased zebrafish locomotor activity. A strong anxiolytic-like effect was observed after administration of PHT and PB. A weak anxiolytic-like effect occurred after treatment with VPA and DZP. The HPLC analysis showed the average concentrations of the studied ASDs in the fish body during the maximum anticonvulsant activity of each drug. Our results confirm the advantages of using zebrafish with the mature CNS over larval models and its utility to investigate some neuropharmacological properties of the tested drugs.