Anticonvulsant effects of acetaminophen in mice: Comparison with the effects of nonsteroidal anti-inflammatory drugs

A Narrative Review of the Published Pre-Clinical Evaluations: Multiple Effects of Arachidonic Acid, its Metabolic Enzymes and Metabolites in Epilepsy

Arachidonic acid (AA), an important polyunsaturated fatty acid in the brain, is hydrolyzed by a direct action of phospholipase A2 (PLA2) or through the combined action of phospholipase C and diacylglycerol lipase, and released into the cytoplasm. Various derivatives of AA can be synthesized mainly through the cyclooxygenase (COX), lipoxygenase (LOX) and cytochrome P450 (P450) enzyme pathways. AA and its metabolic enzymes and metabolites play important roles in a variety of neurophysiological activities. The abnormal metabolites and their catalytic enzymes in the AA cascade are related to the pathogenesis of various central nervous system (CNS) diseases, including epilepsy. Here, we systematically reviewed literatures in PubMed about the latest randomized controlled trials, animal studies and clinical studies concerning the known features of AA, its metabolic enzymes and metabolites, and their roles in epilepsy. The exclusion criteria include non-original studies and articles not in English.

Electrophysiologic and anti-inflammatorial effects of cyclooxygenase inhibition in epileptiform activity

The aim of our study is to investigate the electrophysiological and anti-inflammatory effects of diclofenac potassium on epileptiform activity, which is the liquid form of diclofenac, and frequently used clinically for inflammatory process by inhibiting cyclooxygenase enzyme (COX). Wistar rats aged 2-4 months were divided into Epilepsy, Diazepam, Diclofenac potassium, and Diazepam+diclofenac potassium groups. Diazepam and diclofenac potassium were administered intraperitoneally 30 min after the epileptiform activity was created with penicillin injected intracortically under anesthesia. After the electrophysiological recording was taken in the cortex for 125 min, interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) were evaluated by the ELISA in the serums. No change was observed between the groups in serum IL-1β, IL-6, and TNF-α values. It was observed that the co-administration of diclofenac potassium and diazepam at 51-55, 56-60, 61-65, 111-115, and 116-120 min was more effective in reducing spike amplitude than diclofenac potassium alone (p < 0.05). Single-dose diclofenac potassium did not have an anti-inflammatory effect in epileptiform activity but both diazepam and diclofenac potassium reduced the epileptiform activity.

Pharmacological induction of AMFR increases functional EAAT2 oligomer levels and reduces epileptic seizures in mice

Dysregulation of excitatory amino acid transporter 2 (EAAT2) contributes to the development of temporal lobe epilepsy (TLE). Several strategies for increasing total EAAT2 levels have been proposed. However, the mechanism underlying the oligomeric assembly of EAAT2, impairment of which inhibits the formation of functional oligomers by EAAT2 monomers, is still poorly understood. In the present study, we identified E3 ubiquitin ligase AMFR as an EAAT2-interacting protein. AMFR specifically increased the level of EAAT2 oligomers rather than inducing protein degradation through K542-specific ubiquitination. By using tissues from humans with TLE and epilepsy model mice, we observed that AMFR and EAAT2 oligomer levels were simultaneously decreased in the hippocampus. Screening of 2386 FDA-approved drugs revealed that the most common analgesic/antipyretic medicine, acetaminophen (APAP), can induce AMFR transcriptional activation via transcription factor SP1. Administration of APAP protected against pentylenetetrazol-induced epileptogenesis. In mice with chronic epilepsy, APAP treatment partially reduced the occurrence of spontaneous seizures and greatly enhanced the antiepileptic effects of 17AAG, an Hsp90 inhibitor that upregulates total EAAT2 levels, when the 2 compounds were administered together. In summary, our studies reveal an essential role for AMFR in regulating the oligomeric state of EAAT2 and suggest that APAP can improve the efficacy of EAAT2-targeted antiepileptic treatments.

Screening of prototype antiseizure and anti-inflammatory compounds in the Theiler's murine encephalomyelitis virus model of epilepsy

OBJECTIVE

Infection with Theiler's murine encephalomyelitis virus (TMEV) in C57Bl/6J mice results in handling-induced seizures and is useful for evaluating compounds effective against infection-induced seizures. However, to date only a few compounds have been evaluated in this model, and a comprehensive study of antiseizure medications (ASMs) has not yet been performed. Furthermore, as the TMEV infection produces marked neuroinflammation, an evaluation of prototype anti-inflammatory compounds is needed as well.

METHODS

Male C57Bl/6J mice were inoculated with TMEV (day 0) followed by daily administrations of test compounds (day 3-7) and subsequent handling sessions (day 3-7). Doses of ASMs, comprising several mechanistic classes, were selected based on previously published data demonstrating the effect of these compounds in reducing seizures in the 6 Hz model of pharmacoresistant seizures. Doses of anti-inflammatory compounds, comprising several mechanistic classes, were selected based on published evidence of reduction of inflammation or inflammation-related endpoints.

RESULTS

Several prototype ASMs reduced acute seizures following TMEV infection: lacosamide, phenytoin, ezogabine, phenobarbital, tiagabine, gabapentin, levetiracetam, topiramate, and sodium valproate. Of these, phenobarbital and sodium valproate had the greatest effect (>95% seizure burden reduction). Prototype anti-inflammatory drugs celecoxib, dexamethasone, and prednisone also moderately reduced seizure burden.

SIGNIFICANCE

The TMEV model is utilized by the Epilepsy Therapy Screening Program (ETSP) as a tool for evaluation of novel compounds. Compounds reducing seizures in the TMEV comprise distinct mechanistic classes, some with mechanisms of action that extend beyond traditional ASMs.

Evaluation of Anticonvulsant Activity of Dual COX-2/5-LOX Inhibitor Darbufelon and Its Novel Analogues

Neuroinflammation is an integral part of epilepsy pathogenesis and other convulsive conditions, and non-steroidal anti-inflammatory drugs (NSAIDs) present a potent tool for the contemporary search and design of novel anticonvulsants. In the present paper, evaluation of the anticonvulsant activity of the potential NSAID dual COX-2/5-LOX inhibitor darbufelone methanesulfonate using an scPTZ model in mice in dose 100 mg/kg is reported. Darbufelone possesses anticonvulsant properties in the scPTZ model and presents interest for in-depth studies as a possible anticonvulsant multi-target agent with anti-inflammatory activity. The series of 4-thiazolidinone derivatives have been synthesized following the analogue-based drug design and hybrid-pharmacophore approach using a darbufelone matrix. The synthesized derivatives showed a significant protection level for animals in the scPTZ model and are promising compounds for the design of potential anticonvulsants with satisfactory drug-like parameters.

Inflammatory and immune mechanisms underlying epileptogenesis and epilepsy: From pathogenesis to treatment target

Epilepsy is a brain disease associated with epileptic seizures as well as with neurobehavioral outcomes of this condition. In the last century, inflammation emerged as a crucial factor in epilepsy etiology. Various brain insults through activation of neuronal and non-neuronal brain cells initiate a series of inflammatory events. Growing observations strongly suggest that abnormal activation of critical inflammatory processes contributes to epileptogenesis, a gradual process by which a normal brain transforms into the epileptic brain. Increased knowledge of inflammatory pathways in epileptogenesis has unveiled mechanistic targets for novel antiepileptic therapies. Molecules specifically targeting the pivotal inflammatory pathways may serve as promising candidates to halt the development of epilepsy. The present paper reviews the pieces of evidence conceptually supporting the potential role of inflammatory mechanisms and the relevant blood-brain barrier (BBB) disruption in epileptogenesis. Also, it discusses the mechanisms underlying inflammation-induced neuronal-glial network impairment and highlights innovative neuroregulatory actions of typical inflammatory molecules. Finally, it presents a brief analysis of observations supporting the therapeutic role of inflammation-targeting tiny molecules in epileptic seizures.

A Guide to Targeting the Endocannabinoid System in Drug Design

The endocannabinoid system (ECS) is one of the most crucial systems in the human organism, exhibiting multi-purpose regulatory character. It is engaged in a vast array of physiological processes, including nociception, mood regulation, cognitive functions, neurogenesis and neuroprotection, appetite, lipid metabolism, as well as cell growth and proliferation. Thus, ECS proteins, including cannabinoid receptors and their endogenous ligands’ synthesizing and degrading enzymes, are promising therapeutic targets. Their modulation has been employed in or extensively studied as a treatment of multiple diseases. However, due to a complex nature of ECS and its crosstalk with other biological systems, the development of novel drugs turned out to be a challenging task. In this review, we summarize potential therapeutic applications for ECS-targeting drugs, especially focusing on promising synthetic compounds and preclinical studies. We put emphasis on modulation of specific proteins of ECS in different pathophysiological areas. In addition, we stress possible difficulties and risks and highlight proposed solutions. By presenting this review, we point out information pivotal in the spotlight of ECS-targeting drug design, as well as provide an overview of the current state of knowledge on ECS-related pharmacodynamics and show possible directions for needed research.

Acetaminophen (Paracetamol) Metabolites Induce Vasodilation and Hypotension by Activating Kv7 Potassium Channels Directly and Indirectly

OBJECTIVE

Intravenous acetaminophen/paracetamol (APAP) is well documented to cause hypotension. Since the patients receiving intravenous APAP are usually critically ill, any severe hemodynamic changes, as with those associated with APAP, can be life-threatening. The mechanism underlying this dangerous iatrogenic effect of APAP was unknown. Approach and Results: Here, we show that intravenous APAP caused transient hypotension in rats, which was attenuated by the Kv7 channel blocker, linopirdine. APAP metabolite N-acetyl-p-benzoquinone imine caused vasodilatation of rat mesenteric arteries ex vivo. This vasodilatation was sensitive to linopirdine and also the calcitonin gene-related peptide antagonist, BIBN 4096. Further investigation revealed N-acetyl-p-benzoquinone imine stimulates calcitonin gene-related peptide release from perivascular nerves, causing a cAMP-dependent activation of Kv7 channels. We also show that N-acetyl-p-benzoquinone imine enhances Kv7.4 and Kv7.5 channels overexpressed in oocytes, suggesting that it can activate Kv7.4 and Kv7.5 channels directly, to elicit vasodilatation.

CONCLUSIONS

Direct and indirect activation of Kv7 channels by the APAP metabolite N-acetyl-p-benzoquinone imine decreases arterial tone, which can lead to a drop in blood pressure. Our findings provide a molecular mechanism and potential preventive intervention for the clinical phenomenon of intravenous APAP-dependent transient hypotension.

The paracetamol metabolite N-acetylp-benzoquinone imine reduces excitability in first- and second-order neurons of the pain pathway through actions on KV7 channels

Paracetamol (acetaminophen, APAP) is one of the most frequently used analgesic agents worldwide. It is generally preferred over nonsteroidal anti-inflammatory drugs because it does not cause typical adverse effects resulting from the inhibition of cyclooxygenases, such as gastric ulcers. Nevertheless, inhibitory impact on these enzymes is claimed to contribute to paracetamols mechanisms of action which, therefore, remained controversial. Recently, the APAP metabolites N-arachidonoylaminophenol (AM404) and N-acetyl-p-benzoquinone imine (NAPQI) have been detected in the central nervous system after systemic APAP administration and were reported to mediate paracetamol effects. In contrast to nonsteroidal anti-inflammatory drugs that rather support seizure activity, paracetamol provides anticonvulsant actions, and this dampening of neuronal activity may also form the basis for analgesic effects. Here, we reveal that the APAP metabolite NAPQI, but neither the parent compound nor the metabolite AM404, reduces membrane excitability in rat dorsal root ganglion (DRG) and spinal dorsal horn (SDH) neurons. The observed reduction of spike frequencies is accompanied by hyperpolarization in both sets of neurons. In parallel, NAPQI, but neither APAP nor AM404, increases currents through KV7 channels in DRG and SDH neurons, and the impact on neuronal excitability is absent if KV7 channels are blocked. Furthermore, NAPQI can revert the inhibitory action of the inflammatory mediator bradykinin on KV7 channels but does not affect synaptic transmission between DRG and SDH neurons. These results show that the paracetamol metabolite NAPQI dampens excitability of first- and second-order neurons of the pain pathway through an action on KV7 channels.

Screening for physical and behavioral dependence on non-opioid analgesics in a German elderly hospital population

OBJECTIVE

To provide further evidence of dependence on non-opioid analgesics (NOAs).

METHODS

Post-hoc-analysis of a cross-sectional study of a ≥ -65-year-old non-demented German general hospital population. Four hundred in-patients (75 ± 6.4 years; 63% females) were included and screened for current and past dependence on NOAs using a structured interview (SKID-I) based on DSM-IV-TR. The addiction section of SKID-I was expanded to the following NOAs: gabapentinoids, acetaminophen, metamizole, flupirtine, and non-steroidal anti-inflammatory drugs (NSAIDs).

RESULTS

We found twenty-eight seniors (7%) who fulfilled the criteria for a NOA-dependence. Of whom, twenty-four and four patients were currently dependent and in remission, respectively. According to SKID-I, twenty-one (75%) patients were mildly, five patients (17.9%) moderately, and two (7.1%) patients severely dependent on NOAs. All patients showed at least one sign of physical dependence (tolerance and/or withdrawal symptoms) and most of them reported additional behavioral dependence symptoms. Whereas there was one dependence on gabapentinoids or acetaminophen only, NSAIDs and metamizole were involved in the majority of cases (n = 25; 89.3%). Of note, ten (35.7%) seniors had a de-novo substance dependence exclusively on NOAs - including 2 females with signs of a de-novo dependence on metamizole, a NOA which yet has been not in the focus of addiction medicine.

CONCLUSION

This cross-sectional study provides further evidence of the existence of a physical and behavioral dependence on NOAs including NSAIDs. Furthermore, preliminary evidence of a de-novo dependence on metamizole is provided which needs further verification.

An update of cyclooxygenase (COX)-inhibitors in epilepsy disorders

INTRODUCTION

Neuroinflammation has a critical role in brain disorders. Cyclooxygenase (COX) is one of the principal drug targets for the reduction of neuroinflammation; however, studies have yielded mixed results for COX-inhibitors in the treatment of diverse acute and chronic models of epilepsy.

AREAS COVERED

The article covers the effects of COX-inhibitors in epilepsy disorders. A considerable emphasis has been placed on the antiepileptic and 'disease-modifying' properties of COX-1 and COX-2 inhibitors in various preclinical epilepsy models.

EXPERT OPINION

The effect of COX-inhibitors on epilepsy is inconclusive. Studies have indicated beneficial effects in preclinical models; however, proconvulsant or no effects have also been observed. These molecules may have a bidirectional role with early neuroprotective and delayed neurotoxic effects. Further systematic preclinical studies to establish the use of COX-inhibitors in epilepsy are necessary.