Pharmacokinetic-pharmacodynamic influence of N-palmitoylethanolamine, arachidonyl-2'-chloroethylamide and WIN 55,212-2 on the anticonvulsant activity of antiepileptic drugs against audiogenic seizures in DBA/2 mice

Cannabinoid treatments in epilepsy and seizure disorders

Cannabis has been used to treat convulsions and other disorders since ancient times. In the last few decades, preclinical animal studies and clinical investigations have established the role of cannabidiol (CBD) in treating epilepsy and seizures and support potential therapeutic benefits for cannabinoids in other neurological and psychiatric disorders. Here, we comprehensively review the role of cannabinoids in epilepsy. We briefly review the diverse physiological processes mediating the central nervous system response to cannabinoids, including Δ9-tetrahydrocannabinol (Δ9-THC), cannabidiol, and terpenes. Next, we characterize the anti- and proconvulsive effects of cannabinoids from animal studies of acute seizures and chronic epileptogenesis. We then review the clinical literature on using cannabinoids to treat epilepsy, including anecdotal evidence and case studies as well as the more recent randomized controlled clinical trials that led to US Food and Drug Administration approval of CBD for some types of epilepsy. Overall, we seek to evaluate our current understanding of cannabinoids in epilepsy and focus future research on unanswered questions.

The immune system and metabolic products in epilepsy and glioma-associated epilepsy: emerging therapeutic directions

Epilepsy has a profound impact on quality of life. Despite the development of new antiseizure medications (ASMs), approximately one-third of affected patients have drug-refractory epilepsy and are nonresponsive to medical treatment. Nearly all currently approved ASMs target neuronal activity through ion channel modulation. Recent human and animal model studies have implicated new immunotherapeutic and metabolomic approaches that may benefit patients with epilepsy. In this Review, we detail the proinflammatory immune landscape of epilepsy and contrast this with the immunosuppressive microenvironment in patients with glioma-related epilepsy. In the tumor setting, excessive neuronal activity facilitates immunosuppression, thereby contributing to subsequent glioma progression. Metabolic modulation of the IDH1-mutant pathway provides a dual pathway for reversing immune suppression and dampening seizure activity. Elucidating the relationship between neurons and immunoreactivity is an area for the prioritization and development of the next era of ASMs.

Cenobamate enhances the anticonvulsant effect of other antiseizure medications in the DBA/2 mouse model of reflex epilepsy

Clinical studies documented that cenobamate (CNB) has a marked efficacy compared to other antiseizure medications (ASMs) in reducing focal seizures. To date, different aspects of CNB need to be clarified, including its efficacy against generalized seizures. Similarly, the pattern of drug-drug interactions between CNB and other ASMs also compels further investigation. This study aimed to detect the role of CNB on generalized seizures using the DBA/2 mouse model. We have also studied the effects of an adjunctive CNB treatment on the antiseizure properties of some ASMs against reflex seizures. The effects of this adjunctive treatment on motor performance, body temperature, and brain levels of ASMs were also evaluated. CNB was able to antagonize seizures in DBA/2 mice. CNB, at 5 mg/kg, enhanced the antiseizure activity of ASMs, such as diazepam, clobazam, levetiracetam, perampanel, phenobarbital, topiramate, and valproate. No synergistic effects were observed when CNB was co-administered with some Na+ channel blockers. The increase in antiseizure activity was associated with a comparable intensification in motor impairment; however, the therapeutic index of combined treatment of ASMs with CNB was more favorable than the combination with vehicle except for carbamazepine, phenytoin, and oxcarbazepine. Since CNB did not significantly influence the brain levels of the ASMs studied, we suggest that pharmacokinetic interactions seem not probable. Overall, this study shows the ability of CNB to counteract generalized reflex seizures in mice. Moreover, our data documented an evident synergistic antiseizure effect for the combination of CNB with ASMs including phenobarbital, benzodiazepines, valproate, perampanel, topiramate, and levetiracetam.

Audiogenic epileptic DBA/2 mice strain as a model of genetic reflex seizures and SUDEP

Epilepsy is a chronic neurological disease characterized by abnormal brain activity, which results in repeated spontaneous seizures. Sudden unexpected death in epilepsy (SUDEP) is the leading cause of seizure-related premature death, particularly in drug-resistant epilepsy patients. The etiology of SUDEP is a structural injury to the brain that is not fully understood, but it is frequently associated with poorly controlled and repeated generalized tonic-clonic seizures (GTCSs) that cause cardiorespiratory and autonomic dysfunctions, indicating the involvement of the brainstem. Both respiratory and cardiac abnormalities have been observed in SUDEP, but not much progress has been made in their prevention. Owing to the complexity of SUDEP, experimental animal models have been used to investigate cardiac and/or respiratory dysregulation due to or associated with epileptic seizures that may contribute to death in humans. Numerous rodent models, especially mouse models, have been developed to better understand epilepsy and SUDEP physiopathology. This review synthesizes the current knowledge about dilute brown agouti coat color (DBA/2) mice as a possible SUDEP model because respiratory arrest (RA) and sudden death induced by audiogenic generalized seizures (AGSs) have been observed in these animals. Respiratory/cardiac dysfunction, brainstem arousal system dysfunction, and alteration of the neurotransmitter systems, which are observed in human SUDEP, have also been observed in these mice. In particular, serotonin (5-HT) alteration and adenosine neurotransmission appear to contribute to not only the pathophysiological mechanisms of medication but also seizure-related respiratory dysfunctions in this animal model. These neurotransmitter systems could be the relevant targets for medication development for chronic epilepsy and SUDEP prevention. We reviewed data on AGSs in DBA/2 mice and the relevance of this model of generalized tonic-clonic epilepsy to human SUDEP. Furthermore, the advantages of using this strain prone to AGSs for the identification of possible new therapeutic targets and treatment options have also been assessed.

Is It Time to Test the Antiseizure Potential of Palmitoylethanolamide in Human Studies? A Systematic Review of Preclinical Evidence

Antiseizure medications are the cornerstone pharmacotherapy for epilepsy. They are not devoid of side effects. In search for better-tolerated antiseizure agents, cannabinoid compounds and other N-acylethanolamines not directly binding cannabinoid receptors have drawn significant attention. Among these, palmitoylethanolamide (PEA) has shown neuroprotective, anti-inflammatory, and analgesic properties. All studies examining PEA’s role in epilepsy and acute seizures were systematically reviewed. Preclinical studies indicated a systematically reduced PEA tone accompanied by alterations of endocannabinoid levels. PEA supplementation reduced seizure frequency and severity in animal models of epilepsy and acute seizures, in some cases, similarly to available antiseizure medications but with a better safety profile. The peripheral-brain immune system seemed to be more effectively modulated by subchronic pretreatment with PEA, with positive consequences in terms of better responding to subsequent epileptogenic insults. PEA treatment restored the endocannabinoid level changes that occur in a seizure episode, with potential preventive implications in terms of neural damage. Neurobiological mechanisms for PEA antiseizure effect seemed to include the activation of the endocannabinoid system and the modulation of neuroinflammation and excitotoxicity. Although no human study was identified, there is ground for testing the antiseizure potential of PEA and its safety profile in human studies of epilepsy.

The Endocannabinoid System in Glial Cells and Their Profitable Interactions to Treat Epilepsy: Evidence from Animal Models

Epilepsy is one of the most common neurological conditions. Yearly, five million people are diagnosed with epileptic-related disorders. The neuroprotective and therapeutic effect of (endo)cannabinoid compounds has been extensively investigated in several models of epilepsy. Therefore, the study of specific cell-type-dependent mechanisms underlying cannabinoid effects is crucial to understanding epileptic disorders. It is estimated that about 100 billion neurons and a roughly equal number of glial cells co-exist in the human brain. The glial population is in charge of neuronal viability, and therefore, their participation in brain pathophysiology is crucial. Furthermore, glial malfunctioning occurs in a wide range of neurological disorders. However, little is known about the impact of the endocannabinoid system (ECS) regulation over glial cells, even less in pathological conditions such as epilepsy. In this review, we aim to compile the existing knowledge on the role of the ECS in different cell types, with a particular emphasis on glial cells and their impact on epilepsy. Thus, we propose that glial cells could be a novel target for cannabinoid agents for treating the etiology of epilepsy and managing seizure-like disorders.

Human epithelial stem cell survival within their niche requires "tonic" cannabinoid receptor 1-signalling-Lessons from the hair follicle

The endocannabinoid system (ECS) regulates multiple aspects of human epithelial physiology, including inhibition/stimulation of keratinocyte proliferation/apoptosis, respectively. Yet, how the ECS impacts on human adult epithelial stem cell (eSC) functions remains unknown. Scalp hair follicles (HFs) offer a clinically relevant, prototypic model system for studying this directly within the native human stem cell niche. Here, we show in organ-cultured human HFs that, unexpectedly, selective activation of cannabinoid receptor-1 (CB1)-mediated signalling via the MAPK (MEK/Erk 1/2) and Akt pathways significantly increases the number and proliferation of cytokeratin CK15+ or CK19+ human HF bulge eSCs in situ, and enhances CK15 promoter activity in situ. In striking contrast, CB1-stimulation promotes apoptosis in the differentiated progeny of these eSCs (CK6+ HF keratinocytes). Instead, intrafollicular CB1 gene knockdown or CB1 antagonist treatment significantly reduces human HF eSCs numbers and stimulates their apoptosis, while CB1 knockout mice exhibit a reduced bulge eSCs pool in vivo. This identifies "tonic" CB1 signalling as a required survival stimulus for adult human HF eSCs within their niche. This novel concept must be taken into account whenever the human ECS is targeted therapeutically.

Cannabinoids in Audiogenic Seizures: From Neuronal Networks to Future Perspectives for Epilepsy Treatment

Cannabinoids and Cannabis-derived compounds have been receiving especial attention in the epilepsy research scenario. Pharmacological modulation of endocannabinoid system's components, like cannabinoid type 1 receptors (CB1R) and their bindings, are associated with seizures in preclinical models. CB1R expression and functionality were altered in humans and preclinical models of seizures. Additionally, Cannabis-derived compounds, like cannabidiol (CBD), present anticonvulsant activity in humans and in a great variety of animal models. Audiogenic seizures (AS) are induced in genetically susceptible animals by high-intensity sound stimulation. Audiogenic strains, like the Genetically Epilepsy Prone Rats, Wistar Audiogenic Rats, and Krushinsky-Molodkina, are useful tools to study epilepsy. In audiogenic susceptible animals, acute acoustic stimulation induces brainstem-dependent wild running and tonic-clonic seizures. However, during the chronic protocol of AS, the audiogenic kindling (AuK), limbic and cortical structures are recruited, and the initially brainstem-dependent seizures give rise to limbic seizures. The present study reviewed the effects of pharmacological modulation of the endocannabinoid system in audiogenic seizure susceptibility and expression. The effects of Cannabis-derived compounds in audiogenic seizures were also reviewed, with especial attention to CBD. CB1R activation, as well Cannabis-derived compounds, induced anticonvulsant effects against audiogenic seizures, but the effects of cannabinoids modulation and Cannabis-derived compounds still need to be verified in chronic audiogenic seizures. The effects of cannabinoids and Cannabis-derived compounds should be further investigated not only in audiogenic seizures, but also in epilepsy related comorbidities present in audiogenic strains, like anxiety, and depression.

Cannabinoid Receptor Type 1 (CB1R) Expression in Limbic Brain Structures After Acute and Chronic Seizures in a Genetic Model of Epilepsy

The endocannabinoid system (ECS) is related to several physiological processes, associated to the modulation of brain excitability, with impact in the expression of susceptibility and control of epileptic seizures. The cannabinoid receptor type 1 (CB1R) is widely expressed in the brain, especially in forebrain limbic structures. Changes in CB1R expression are associated with epileptic seizures in animal models and humans. The Wistar Audiogenic Rat (WAR) strain is a genetic model of epilepsy capable of mimicking tonic-clonic and limbic seizures in response to intense sound stimulation. The WAR strain presents several behavioral and physiological alterations associated with seizure susceptibility, but the ECS has never been explored in this strain. Therefore, the aim of the present study was to characterize CB1R expression in forebrain limbic structures important to limbic seizure expression in WARs. We used a detailed anatomical analysis to assess the effects of acute and chronic audiogenic seizures on CB1R expression in several layers and regions of hippocampus and amygdala. WARs showed increased CB1R immunostaining in the inner molecular layer of the hippocampus, when compared to control Wistar rats. Acute and chronic audiogenic seizures increased CB1R immunostaining in several regions of the dorsal hippocampus and amygdala of WARs. Also, changes in CB1R expression in the amygdala, but not in the hippocampus, were associated with limbic recruitment and limbic seizure severity in WARs. Our results suggest that endogenous alterations in CB1R immunostaining in WARs could be associated with genetic susceptibility to audiogenic seizures. We also demonstrated CB1R neuroplastic changes associated with acute and chronic seizures in the amygdala and hippocampus. Moreover, the present study brings important information regarding CB1R and seizure susceptibility in a genetic model of seizures and supports the relationship between ECS and epilepsy.

Divergent Effects of Systemic and Intracollicular CB Receptor Activation Against Forebrain and Hindbrain-Evoked Seizures in Rats

Cannabinoid (CB) receptor agonists are of growing interest as targets for anti-seizure therapies. Here we examined the effect of systemic administration of the CB receptor agonist WIN 55,212-2 (WIN) against audiogenic seizures (AGSs) in the Genetically Epilepsy Prone Rat (GEPR)-3 strain, and against seizures evoked focally from the Area Tempestas (AT). We compared these results to the effect of focal administration of the CB1/2 receptor agonist CP 55940 into the deep layers of the superior colliculus (DLSC), a brain site expressing CB1 receptors. While systemic administration of WIN dose-dependently decreased AGS in GEPR-3s, it was without effect in the AT model. By contrast, intra-DLSC infusion of CP 55940 decreased seizures in both models. To determine if the effects of systemic WIN were dependent upon activation of CB1 receptors in the DSLC, we next microinjected the CB1 receptor antagonist SR141716, before WIN systemic treatment, and tested animals for AGS susceptibility. The pretreatment of the DLSC with SR141716 was without effect on its own and did not alter the anti-convulsant action of WIN systemic administration. Thus, while CB receptors in the DLSC are a potential site of anticonvulsant action, they are not necessary for the effects of systemically administered CB agonists.

Alzheimer's Disease, a Lipid Story: Involvement of Peroxisome Proliferator-Activated Receptor α

Alzheimer's disease (AD) is the leading cause of dementia in the elderly. Mutations in genes encoding proteins involved in amyloid-β peptide (Aβ) production are responsible for inherited AD cases. The amyloid cascade hypothesis was proposed to explain the pathogeny. Despite the fact that Aβ is considered as the main culprit of the pathology, most clinical trials focusing on Aβ failed and suggested that earlier interventions are needed to influence the course of AD. Therefore, identifying risk factors that predispose to AD is crucial. Among them, the epsilon 4 allele of the apolipoprotein E gene that encodes the major brain lipid carrier and metabolic disorders such as obesity and type 2 diabetes were identified as AD risk factors, suggesting that abnormal lipid metabolism could influence the progression of the disease. Among lipids, fatty acids (FAs) play a fundamental role in proper brain function, including memory. Peroxisome proliferator-activated receptor α (PPARα) is a master metabolic regulator that regulates the catabolism of FA. Several studies report an essential role of PPARα in neuronal function governing synaptic plasticity and cognition. In this review, we explore the implication of lipid metabolism in AD, with a special focus on PPARα and its potential role in AD therapy.

Cryo-EM Structure of the Human Cannabinoid Receptor CB2-Gi Signaling Complex

Drugs selectively targeting CB2 hold promise for treating neurodegenerative disorders, inflammation, and pain while avoiding psychotropic side effects mediated by CB1. The mechanisms underlying CB2 activation and signaling are poorly understood but critical for drug design. Here we report the cryo-EM structure of the human CB2-G_i signaling complex bound to the agonist WIN 55,212-2. The 3D structure reveals the binding mode of WIN 55,212-2 and structural determinants for distinguishing CB2 agonists from antagonists, which are supported by a pair of rationally designed agonist and antagonist. Further structural analyses with computational docking results uncover the differences between CB2 and CB1 in receptor activation, ligand recognition, and G_i coupling. These findings are expected to facilitate rational structure-based discovery of drugs targeting the cannabinoid system.

Antiepileptogenic Effect of Subchronic Palmitoylethanolamide Treatment in a Mouse Model of Acute Epilepsy

Research on the antiepileptic effects of (endo-)cannabinoids has remarkably progressed in the years following the discovery of fundamental role of the endocannabinoid (eCB) system in controlling neural excitability. Moreover, an increasing number of well-documented cases of epilepsy patients exhibiting multi-drug resistance report beneficial effects of cannabis use. Pre-clinical and clinical research has increasingly focused on the antiepileptic effectiveness of exogenous administration of cannabinoids and/or pharmacologically induced increase of eCBs such as anandamide (also known as arachidonoylethanolamide [AEA]). Concomitant research has uncovered the contribution of neuroinflammatory processes and peripheral immunity to the onset and progression of epilepsy. Accordingly, modulation of inflammatory pathways such as cyclooxygenase-2 (COX-2) was pursued as alternative therapeutic strategy for epilepsy. Palmitoylethanolamide (PEA) is an endogenous fatty acid amide related to the centrally and peripherally present eCB AEA, and is a naturally occurring nutrient that has long been recognized for its analgesic and anti-inflammatory properties. Neuroprotective and anti-hyperalgesic properties of PEA were evidenced in neurodegenerative diseases, and antiepileptic effects in pentylenetetrazol (PTZ), maximal electroshock (MES) and amygdaloid kindling models of epileptic seizures. Moreover, numerous clinical trials in chronic pain revealed that PEA treatment is devoid of addiction potential, dose limiting side effects and psychoactive effects, rendering PEA an appealing candidate as antiepileptic compound or adjuvant. In the present study, we aimed at assessing antiepileptic properties of PEA in a mouse model of acute epileptic seizures induced by systemic administration of kainic acid (KA). KA-induced epilepsy in rodents is assumed to resemble to different extents human temporal lobe epilepsy (TLE) depending on the route of KA administration; intracerebral (i.c.) injection was recently shown to most closely mimic human TLE, while systemic KA administration causes more widespread pathological damage, both in brain and periphery. To explore the potential of PEA to exert therapeutic effects both in brain and periphery, acute and subchronic administration of PEA by intraperitoneal (i.p.) injection was assessed on mice with systemically administered KA. Specifically, we investigated: (i) neuroprotective and anticonvulsant properties of acute and subchronic PEA treatment in KA-induced seizure models, and (ii) temporal dynamics of eCB and eicosanoid (eiC) levels in hippocampus and plasma over 180 min post seizure induction in PEA-treated and non-treated KA-injected mice vs. vehicle injected mice. Finally, we compared the systemic PEA treatment with, and in combination with, pharmacological blockade of fatty acid amide hydrolase (FAAH) in brain and periphery, in terms of anticonvulsant properties and modulation of eCBs and eiCs. Here, we demonstrate that subchronic administration of PEA significantly alleviates seizure intensity, promotes neuroprotection and induces modulation of the plasma and hippocampal eCB and eiC levels in systemic KA-injected mice.

Reward-related limbic memory and stimulation of the cannabinoid system: An upgrade in value attribution?

While a lot is known about the mechanisms promoting aversive learning, the impact of rewarding factors on memory has received comparatively less attention. This research investigates reward-related explicit memory in male rats, by taking advantage of the emotional-object recognition test. This is based on the prior association, during conditioned learning, between a rewarding experience (the encounter with a receptive female rat) and an object; afterwards rat discrimination and recognition of the 'emotional object' is recorded in the presence of a novel object, as a measure of positive limbic memory formation. Since endocannabinoids are critical for processing reward and motivation, the consequences of the stimulation of cannabinoid signalling are also assessed by the administration of WIN 55,212-2 at pre- and post-conditioning time. Our results show that rats encode the association between object and rewarding experience, form positive limbic memory of the emotional object, and retrieve this information in the face of novelty. Stimulation of the cannabinoid system at pre-conditioning time is able to strengthen reward-related explicit memory in the presence of novelty, whereas post-conditioning activation increases approach behaviour to novel stimuli. The assessment of limbic memory by the emotional-object recognition test can help unveiling the addictive and confounding properties of psychotropic drugs.

Effects of arachidonyl-2'-chloroethylamide (ACEA) on the protective action of various antiepileptic drugs in the 6-Hz corneal stimulation model in mice

Accumulating evidence indicates that cannabinoid CB1 receptor ligands play a pivotal role in seizures, not only in preclinical studies on animals, but also in clinical settings. This study was aimed at characterizing the influence of arachidonyl-2'-chloroethylamide (ACEA-a selective cannabinoid CB1 receptor agonist) co-administered with phenylmethylsulfonyl fluoride (PMSF) on the anticonvulsant potency of various antiepileptic drugs (clobazam, lacosamide, levetiracetam, phenobarbital, tiagabine and valproate) in the 6-Hz corneal stimulation model. Psychomotor seizures in male albino Swiss mice were evoked by a current (32 mA, 6 Hz, 3 s stimulus duration) delivered via corneal electrodes. Potential adverse effects produced by the antiepileptic drugs in combination with ACEA+PMSF were assessed using the chimney test (motor performance), passive avoidance task (remembering and acquisition of learning), and grip-strength test (muscular strength). Brain concentrations of antiepileptic drugs were measured by HPLC to exclude any pharmacokinetic contribution to the observed effect. ACEA (5 mg/kg, i.p.) + PMSF (30 mg/kg, i.p.) significantly potentiated the anticonvulsant potency of levetiracetam (P<0.05), but not that of clobazam, lacosamide, phenobarbital, tiagabine or valproate in the 6-Hz corneal stimulation model. Moreover, ACEA+PMSF did not significantly affect total brain concentrations of levetiracetam in mice. No behavioral side effects were observed in animals receiving combinations of the studied antiepileptic drugs with ACEA+PMSF. In conclusion, the combined administration of ACEA+PMSF with levetiracetam is associated with beneficial anticonvulsant pharmacodynamic interaction in the 6-Hz corneal stimulation model. The selective activation of cannabinoid CB1 receptor-mediated neurotransmission in the brain may enhance levetiracetam-related suppression of seizures in epilepsy patients, contributing to the efficacious treatment of epilepsy in future.