Cholecystokinin-8 sulfate modulates the anticonvulsant efficacy of vigabatrin in an experimental model of partial complex epilepsy in the rat

Differential toxic and antiepileptic features of Vigabatrin raceme and its enantiomers

BACKGROUND

The study aimed to investigate the potential pharmacological and toxicological differences between Vigabatrin (VGB) and its enantiomers S-VGB and R-VGB. The researchers focused on the toxic effects and antiepileptic activity of these compounds in a rat model.

METHODS

The epileptic rat model was established by intraperitoneal injection of kainic acid, and the antiepileptic activity of VGB, S-VGB, and VGB was observed, focusing on the improvements in seizure latency, seizure frequency and sensory, motor, learning and memory deficits in epileptic rats, as well as the hippocampal expression of key molecular associated with synaptic plasticity and the Wnt/β-catenin/GSK 3β signaling pathway. The acute toxic test was carried out and the LD50 was calculated, and tretinal damages in epileptic rats were also evaluated.

RESULT

The results showed that S-VGB exhibited stronger antiepileptic and neuroprotective effects with lower toxicity compared to VGB raceme. These findings suggest that S-VGB and VGB may modulate neuronal damage, glial cell activation, and synaptic plasticity related to epilepsy through the Wnt/β-catenin/GSK 3β signaling pathway. The study provides valuable insights into the potential differential effects of VGB enantiomers, highlighting the potential of S-VGB as an antiepileptic drug with reduced side effects.

CONCLUSION

S-VGB has the highest antiepileptic effect and lowest toxicity compared to VGB and R-VGB.

CDKL5-mediated developmental tuning of neuronal excitability and concomitant regulation of transcriptome

Cyclin-dependent kinase-like 5 (CDKL5) is a serine-threonine kinase enriched in the forebrain to regulate neuronal development and function. Patients with CDKL5 deficiency disorder (CDD), a severe neurodevelopmental condition caused by mutations of CDKL5 gene, present early-onset epilepsy as the most prominent feature. However, spontaneous seizures have not been reported in mouse models of CDD, raising vital questions on the human-mouse differences and the roles of CDKL5 in early postnatal brains. Here, we firstly measured electroencephalographic (EEG) activities via a wireless telemetry system coupled with video-recording in neonatal mice. We found that mice lacking CDKL5 exhibited spontaneous epileptic EEG discharges, accompanied with increased burst activities and ictal behaviors, specifically at postnatal day 12 (P12). Intriguingly, those epileptic spikes disappeared after P14. We next performed an unbiased transcriptome profiling in the dorsal hippocampus and motor cortex of Cdkl5 null mice at different developmental timepoints, uncovering a set of age-dependent and brain region-specific alterations of gene expression in parallel with the transient display of epileptic activities. Finally, we validated multiple differentially expressed genes, such as glycine receptor alpha 2 and cholecystokinin, at the transcript or protein levels, supporting the relevance of these genes to CDKL5-regulated excitability. Our findings reveal early-onset neuronal hyperexcitability in mouse model of CDD, providing new insights into CDD etiology and potential molecular targets to ameliorate intractable neonatal epilepsy.

Cholecystokinin-Mediated Neuromodulation of Anxiety and Schizophrenia: A "Dimmer-Switch" Hypothesis

Cholecystokinin (CCK), the most abundant brain neuropeptide, is involved in relevant behavioral functions like memory, cognition, and reward through its interactions with the opioid and dopaminergic systems in the limbic system. CCK excites neurons by binding two receptors, CCK1 and CCK2, expressed at low and high levels in the brain, respectively. Historically, CCK2 receptors have been related to the induction of panic attacks in humans. Disturbances in brain CCK expression also underlie the physiopathology of schizophrenia, which is attributed to the modulation by CCK1 receptors of the dopamine flux in the basal striatum. Despite this evidence, neither CCK2 receptor antagonists ameliorate human anxiety nor CCK agonists have consistently shown neuroleptic effects in clinical trials. A neglected aspect of the function of brain CCK is its neuromodulatory role in mental disorders. Interestingly, CCK is expressed in pivotal inhibitory interneurons that sculpt cortical dynamics and the flux of nerve impulses across corticolimbic areas and the excitatory projections to mesolimbic pathways. At the basal striatum, CCK modulates the excitability of glutamate, the release of inhibitory GABA, and the discharge of dopamine. Here we focus on how CCK may reduce rather than trigger anxiety by regulating its cognitive component. Adequate levels of CCK release in the basal striatum may control the interplay between cognition and reward circuitry, which is critical in schizophrenia. Hence, it is proposed that disturbances in the excitatory/ inhibitory interplay modulated by CCK may contribute to the imbalanced interaction between corticolimbic and mesolimbic neural activity found in anxiety and schizophrenia.

Cannabinoids, TRPV and nitric oxide: the three ring circus of neuronal excitability

Endocannabinoid system is considered a relevant player in the regulation of neuronal excitability, since it contributes to maintaining the balance of the synaptic ionic milieu. Perturbations to bioelectric conductances have been implicated in the pathophysiological processes leading to hyperexcitability and epileptic seizures. Cannabinoid influence on neurosignalling is exerted on classic receptor-mediated mechanisms or on further molecular targets. Among these, transient receptor potential vanilloid (TRPV) are ionic channels modulated by cannabinoids that are involved in the transduction of a plethora of stimuli and trigger fundamental downstream pathways in the post-synaptic site. In this review, we aim at providing a brief summary of the most recent data about the cross-talk between cannabinoid system and TRPV channels, drawing attention on their role on neuronal hyperexcitability. Then, we aim to unveil a plausible point of interaction between these neural signalling systems taking into consideration nitric oxide, a gaseous molecule inducing profound modifications to neural performances. From this novel perspective, we struggle to propose innovative cellular mechanisms in the regulation of hyperexcitability phenomena, with the goal of exploring plausible CB-related mechanisms underpinning epileptic seizures.

Neuropeptides: A promising target for treating seizures

Seizures are serious neurological disorders affecting nearly 50 million people worldwide. Seizures are characterized by abnormal, repetitive and synchronised firing of the neurons which is produced as a result of imbalance in the levels of the excitatory and inhibitory neurotransmitters. Neuropeptides are found to regulate seizures by rectifying this imbalance. These neuropeptides are stored in the dense core synaptic vesicles, and are released on excitation. This review focuses on certain neuropeptides which can alleviate both, the effects of seizures as well as epileptogenesis. Thus making it an attractive target for the management of seizures.

Involvement of TRPV1 channels in the activity of the cannabinoid WIN 55,212-2 in an acute rat model of temporal lobe epilepsy

The exogenous cannabinoid agonist WIN 55,212-2, (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl) pyrrolo[1,2,3-de]-1,4-benzoxazin-6-Yl]-1-naphthalenylmethanone (WIN), has revealed to play a role on modulating the hyperexcitability phenomena in the hippocampus. Cannabinoid-mediated mechanisms of neuroprotection have recently been found to imply the modulation of transient receptor potential vanilloid 1 (TRPV1), a cationic channel subfamily that regulate synaptic excitation. In our study, we assessed the influence of pharmacological manipulation of TRPV1 function, alone and on WIN antiepileptic activity, in the Maximal Dentate Activation (MDA) acute model of temporal lobe epilepsy. Our results showed that the TRPV1 agonist, capsaicin, increased epileptic outcomes; whilst antagonizing TRPV1 with capsazepine exerts a protective role on paroxysmal discharge. When capsaicin is co-administered with WIN effective dose of 10mg/kg is able to reduce its antiepileptic strength, especially on the triggering of MDA response. Accordingly, capsazepine at the protective dose of 2mg/kg managed to potentiate WIN antiepileptic effects, when co-treated. Moreover, WIN subeffective dose of 5mg/kg was turned into effective when capsazepine comes into play. This evidence suggests that systemic administration of TRPV1-active drugs influences electrically induced epilepsy, with a noticeable protective activity for capsazepine. Furthermore, results from the pharmacological interaction with WIN support an interplay between cannabinoid and TRPV1 signaling that could represent a promising approach for a future pharmacological strategy to challenge hyperexcitability-based diseases.

A prospective study on changes in blood levels of cholecystokinin-8 and leptin in patients with refractory epilepsy treated with the ketogenic diet

OBJECTIVE

To evaluate the changes in serum CCK-8 and leptin levels in patients with refractory epilepsy treated with the ketogenic diet (KD).

METHODS

In this prospective study, patients aged between one and 40 years with refractory epilepsy were included. CCK-8 and leptin were measured in serum at baseline and after three and 12 months of treatment with the KD using an enzyme-linked Immunoabsorbant Assay. Seizure frequency and responsiveness were calculated.

RESULTS

Fifty-four patients were included; 26 patients (48%) were still on the KD at 12 months. After three and 12 months, respectively, 39% and 26% were responders. CCK-8 values were statistically significantly increased at three months (p=0.005) and 12 months (p=0.012). In responders, at three months follow-up, this increase of CCK-8 was significant (p=0.020), whereas in the non-responders it was not (p=0.34). Leptin values were decreased at three and 12 months, the decrease at three months being statistically significant in post-pubertal men (p=0.028) and post-pubertal women (p=0.007).

SIGNIFICANCE

In responders to the KD, serum CCK-8 increased statistically significantly during treatment at three months. Serum leptin decreased statistically significantly at three months in men and in post-pubertal women. It is plausible that the increase of CCK-8 and the decrease of leptin contribute to the anti-convulsive effect of the KD.

Increased cholecystokinin labeling in the hippocampus of a mouse model of epilepsy maps to spines and glutamatergic terminals

The neuropeptide cholecystokinin (CCK) is abundant in the CNS and is expressed in a subset of inhibitory interneurons, particularly in their axon terminals. The expression profile of CCK undergoes numerous changes in several models of temporal lobe epilepsy. Previous studies in the pilocarpine model of epilepsy have shown that CCK immunohistochemical labeling is substantially reduced in several regions of the hippocampal formation, consistent with decreased CCK expression as well as selective neuronal degeneration. However, in a mouse pilocarpine model of recurrent seizures, increases in CCK-labeling also occur and are especially striking in the hippocampal dendritic layers of strata oriens and radiatum. Characterizing these changes and determining the cellular basis of the increased labeling were the major goals of the current study. One possibility was that the enhanced CCK labeling could be associated with an increase in GABAergic terminals within these regions. However, in contrast to the marked increase in CCK-labeled structures, labeling of GABAergic axon terminals was decreased in the dendritic layers. Likewise, cannabinoid receptor 1-labeled axon terminals, many of which are CCK-containing GABAergic terminals, were also decreased. These findings suggested that the enhanced CCK labeling was not due to an increase in GABAergic axon terminals. The subcellular localization of CCK immunoreactivity was then examined using electron microscopy, and the identities of the structures that formed synaptic contacts were determined. In pilocarpine-treated mice, CCK was observed in dendritic spines and these were proportionally increased relative to controls, whereas the proportion of CCK-labeled terminals forming symmetric synapses was decreased. In addition, CCK-positive axon terminals forming asymmetric synapses were readily observed in these mice. Double labeling with vesicular glutamate transporter 1 and CCK revealed colocalization in numerous terminals forming asymmetric synapses, confirming the glutamatergic identity of these terminals. These data raise the possibility that expression of CCK is increased in hippocampal pyramidal cells in mice with recurrent, spontaneous seizures.

Exploring the genomic basis of pharmacoresistance in epilepsy: an integrative analysis of large-scale gene expression profiling studies on brain tissue from epilepsy surgery

Some patients with pharmacoresistant epilepsy undergo therapeutic resection of the epileptic focus. At least 12 large-scale microarray studies on brain tissue from epilepsy surgery have been published over the last 10 years, but they have failed to make a significant impact upon our understanding of pharmacoresistance, because (1) doubts have been raised about their reproducibility, (2) only a small number of the gene expression changes found in each microarray study have been independently validated and (3) the results of different studies have not been integrated to give a coherent picture of the genetic changes involved in epilepsy pharmacoresistance. To overcome these limitations, we (1) assessed the reproducibility of the microarray studies by calculating the overlap between lists of differentially regulated genes from pairs of microarray studies and determining if this was greater than would be expected by chance alone, (2) used an inter-study cross-validation technique to simultaneously verify the expression changes of large numbers of genes and (3) used the combined results of the different microarray studies to perform an integrative analysis based on enriched gene ontology terms, networks and pathways. Using this approach, we respectively (1) demonstrate that there are statistically significant overlaps between the gene expression changes in different publications, (2) verify the differential expression of 233 genes and (3) identify the biological processes, networks and genes likely to be most important in the development of pharmacoresistant epilepsy. Our analysis provides novel biologically plausible candidate genes and pathways which warrant further investigation to assess their causal relevance.