Effective treatments of prolonged status epilepticus in developing rats

Dapsone Protects Against Lithium-Pilocarpine-Induced Status Epilepticus in Rats through Targeting Tumor Necrosis Factor-α and Nitrergic Pathway

Background and Purpose

Status epilepticus (SE) results in permanent neuronal brain damage in the central nervous system. One of the complex etiologies underlying SE pathogenesis is neuroinflammation. Dapsone has been recently considered as a potential neuroprotective agent in neuroinflammatory conditions. Therefore, the present study aims to investigate effects of dapsone on lithium-pilocarpine-induced SE in rats and assess whether tumor necrosis factor-alpha (TNF-α) and nitric oxide (NO) pathway participate in this effect.

Methods

SE was established by injecting lithium chloride (127 mg/kg, intraperitoneally [i.p.]) and pilocarpine (60 mg/kg, i.p.). The animals received pre-treatment dapsone (2, 5, 10, and 20 mg/kg, oral gavage) and post-treatment dapsone (10 mg/kg). Subsequently, seizure score and mortality rate were documented. To assess the underlying signaling pathway, L-Nω-Nitro-L-arginine methyl ester hydrochloride (a non-specific NO synthase [NOS] inhibitor), 7-nitroindazole (a specific neuronal NOS inhibitor), and aminoguanidine (a specific inducible NOS inhibitor) were administered 15 minutes before dapsone (10 mg/kg) pre- or post-treatment. Hippocampal tissue TNF-α and NO concentrations were quantified using the enzyme-linked immunosorbent assay method.

Results

Dapsone (10 mg/kg) pre-and post-treatment significantly attenuated the increased seizure score and mortality rate due to lithium-pilocarpine-induced SE. The development of SE in animals was associated with higher TNF-α and NO metabolites levels, which notably decreased in the dapsone-treated rats. Moreover, co-administration of NOS inhibitors with dapsone markedly reversed the anti-epileptic effects of dapsone and caused an escalation in TNF-α level but a significant reduction in NO concentration level.

Conclusions

It seems that dapsone may exert an anti-epileptic effect on lithium-pilocarpine-induced SE through TNF-α inhibition and modulation of the nitrergic pathway.

Linking acute symptomatic neonatal seizures, brain injury and outcome in preterm infants

Neonatal seizures (NS) are the most frequent sign of neurological dysfunction in newborn infants. With increased survival of preterm neonates, the current clinical focus has shifted from preventing death to improving long-term neurological outcome. In the context of acute symptomatic NS, the main negative prognostic factors include etiology, and severity of brain injury, but also prolonged seizures and especially status epilepticus. However, the reasons for the detrimental contribution of seizures to outcome are still unclear, and evidence has been collected both in favor of seizures being an epiphenomenon of brain injury and of independently contributing to further damage. In this narrative focused review, we will discuss both hypotheses, with special emphasis on data relating to preterm infants. We will also identify present controversies and possible future lines of research.

Epileptogenesis in neonatal brain

Epilepsy is a chronic neurological disorder affecting 65 million people worldwide. The etiologies of seizures can often be identified as genetic, metabolic, structural, immunologic or infectious, but in many cases the cause is unknown with the current diagnostic tools. Epileptogenesis is a process during which genetic or other acquired etiologies/insults lead to functional, structural, or network reorganization changes in the brain that may lead to the development of, or progression of, spontaneous seizures. During development, there are continuous changes in the structure, function, and network operation that also show sex specificity, which may alter the mechanisms underlying the generation of seizures (ictogenesis) and epileptogenesis. Understanding the mechanisms of early life epileptogenesis will enable the development of rationally designed age- and sex-appropriate therapies that would improve the overall quality of patients' lives. Here, we discuss some of these processes that may affect seizure generation and epileptogenesis in the neonatal brain.

Status epilepticus: Role for etiology in determining response to benzodiazepines

OBJECTIVE

Clinical factors contributing to benzodiazepine failure in treating status epilepticus (SE) include suboptimal dosing and seizure duration. As many benzodiazepine-refractory episodes of SE arise from acute etiologies, we sought to determine whether etiology impacts SE treatment.

METHODS

The potency of diazepam to terminate SE induced by lithium-pilocarpine (LiPilo-SE) or kainic acid (KA-SE) in 3-week-old rats was studied by video-electroencephalography. Synaptic γ-aminobutyric acid type A receptor (GABAR)-mediated currents were recorded from dentate granule cells using voltage-clamp electrophysiology. Surface expression of γ2 subunit-containing GABARs and Kv4.2 potassium channels in hippocampal slices was determined using a biotinylation assay. Expression of phosphorylated forms of β2/3 and γ2 subunits was determined using phosphospecific antibodies and Western blotting.

RESULTS

Diazepam failed to terminate late SE in LiPilo-SE animals but was successful in terminating KA-SE of 1- and 3-hour duration. One hour after SE onset, GABAR-mediated synaptic inhibition and γ2 subunit-containing GABAR surface expression were reduced in LiPilo-SE animals. These were unchanged in KA-SE animals at 1 and 3 hours. Phosphorylation of γ2 subunit residue S327 was unchanged in both models, although GABAR β3 subunit S408/409 residues were dephosphorylated in the LiPilo-SE animals. Kv4.2 potassium channel surface expression was increased in LiPilo-SE animals but reduced in KA-SE animals.

INTERPRETATION

SE-model-dependent differences support a novel hypothesis that the development of benzodiazepine pharmacoresistance may be etiologically predetermined. Further studies are required to investigate the mechanisms that underlie such etiological differences during SE and whether etiology-dependent protocols for the treatment of SE need to be developed. Ann Neurol 2018;83:830-841.

Not all that glitters is gold: A guide to critical appraisal of animal drug trials in epilepsy

Preclinical studies have produced numerous drugs with antiseizure properties that currently are the standard of care. One third of the human population with epilepsy still continues to have seizures despite the ongoing discoveries. The recognized clinical gaps of care that need to be addressed are the identification of antiepileptogenic and disease‐modifying treatments, and treatments for refractory seizures or for seizures and epilepsies with limited or unsatisfactory treatments, such as early life epileptic encephalopathies. In this invited review, we provide a historical summary of the international efforts to reevaluate the strategies adopted in preclinical epilepsy therapy discovery studies. We discuss issues that may affect the quality, interpretation, and validation of preclinical studies and their translation to successful therapies for humans affected with epilepsy. These include the selection of animal models and the study design; research practices that affect rigor (such as appropriate use of statistics and reporting of study methods and results, their validation across models, labs, and preclinical‐clinical studies); the need to harmonize research methods and outcome assessment; and the importance of improving translation to clinically appropriate situations. The epilepsy research community is incrementally adopting collaborative research, including consortia or multicenter studies to meet these needs. Improving the infrastructure that can support these efforts will be instrumental in future success.

Phosphatase inhibition prevents the activity-dependent trafficking of GABAA receptors during status epilepticus in the young animal

OBJECTIVES

To determine if the activity-dependent trafficking of γ2 subunit-containing γ-aminobutyric acid type A receptors (GABAA Rs) that has been observed in older animals and posited to contribute to benzodiazepine pharmacoresistance during status epilepticus (SE) is age-dependent, and to evaluate whether blockade of protein phosphatases can inhibit or reverse the activity-dependent plasticity of these receptors.

METHODS

The efficacy and potency of diazepam 0.2-10 mg/kg administered 3 or 60 min after the onset of a lithium/pilocarpine-induced seizure in postnatal day 15-16 rats was evaluated using video-electroencephalography (EEG) recordings. The surface expression of γ2 subunit-containing GABAA Rs was assessed using a biotinylation assay, and GABAA R-mediated miniature inhibitory postsynaptic currents (mIPSCs) were recorded using whole-cell patch-clamp recording techniques from dentate granule cells in hippocampal slices acutely obtained 60 min after seizure onset (SE-treated). The effect of the protein phosphatase inhibitors FK506 and okadaic acid (OA) on the surface expression of these receptors was determined in organotypic slice cultures exposed to high potassium and N-methyl-d-aspartate (NMDA) or in SE-treated slices.

RESULTS

Diazepam terminated seizures of 3 min but not 60 min duration, even at the highest dose. In the SE-treated slices, the surface expression of γ2 subunit-containing GABAA Rs was reduced and the amplitude of the mIPSCs was diminished. Inhibition of protein phosphatases prevented the activity-induced reduction of the γ2 subunit-containing GABAA Rs in organotypic slice cultures. Furthermore, treatment of SE-treated slices with FK506 or OA restored the surface expression of the γ2 subunit-containing GABAA Rs and the mIPSC amplitude.

SIGNIFICANCE

This study demonstrates that the plasticity of γ2 subunit-containing GABAA Rs associated with the development of benzodiazepine resistance in young and adult animals is similar. The findings of this study suggest that the mechanisms regulating the activity-dependent trafficking of GABAA Rs during SE can be targeted to develop novel adjunctive therapy for the treatment of benzodiazepine-refractory SE.

Effective termination of status epilepticus by rational polypharmacy in the lithium-pilocarpine model in rats: Window of opportunity to prevent epilepsy and prediction of epilepsy by biomarkers

The pilocarpine rat model, in which status epilepticus (SE) leads to epilepsy with spontaneous recurrent seizures (SRS), is widely used to study the mechanisms of epileptogenesis and develop strategies for epilepsy prevention. SE is commonly interrupted after 30-90min by high-dose diazepam or other anticonvulsants to reduce mortality. It is widely believed that SE duration of 30-60min is sufficient to induce hippocampal damage and epilepsy. However, resistance to diazepam develops during SE, so that an SE that is longer than 30min is difficult to terminate, and SE typically recurs several hours after diazepam, thus forming a bias for studies on epileptogenesis or antiepileptogenesis. We developed a drug cocktail, consisting of diazepam, phenobarbital, and scopolamine that allows complete and persistent SE termination in the lithium-pilocarpine model. A number of novel findings were obtained with this cocktail. (a) In contrast to previous reports with incomplete SE suppression, a SE of 60min duration did not induce epilepsy, whereas epilepsy with SRS developed after 90 or 120min SE; (b) by comparing groups of rats with 60 and 90min of SE, development of epilepsy could be predicted by behavioral hyperexcitability and decrease in seizure threshold, indicating that these read-outs are suited as biomarkers of epileptogenesis; (c) CA1 damage was prevented by the cocktail, but rats exhibited cell loss in the dentate hilus, which was related to development of epilepsy. These data demonstrate that the duration of SE needed for induction of epileptogenesis in this model is longer than previously thought.

Serotonin 1A receptor inhibits the status epilepticus induced by lithium-pilocarpine in rats

Status epilepticus (SE) is a life-threatening neurological emergency associated with a high mortality rate. The serotonin 1A (5-HT1A) receptor is a possible target for the treatment of SE, but its role in animal models and the precise area of brain involved remain controversial. The hippocampus is a candidate site due to its key role in the development of SE and the existence of a high density of 5-HT1A receptors. Therefore, we investigated the effects of subcutaneous and intrahippocampal activation of 5-HT1A receptors in lithium-pilocarpine-induced SE, and tested whether the hippocampus is a true effector site. We developed SE in male Sprague-Dawley rats by giving lithium chloride (LiCl; 3 meq/kg, i.p.) 22-24 h prior to pilocarpine (25 mg/kg, i.p.), and found that 8-OH-DPAT, a 5-HT1A receptor agonist administered subcutaneously (s.c.) at 0.5 or 1.0 mg/kg 1 h before pilocarpine injection increased the latency to the first epileptiform spikes, the electrographic SE, and the behavioral generalized seizures (GS), while reducing the total EEG seizure time (P <0.01). The duration of GS was shortened only by 1.0 mg/kg 8-OH-DPAT s.c. (P <0.05). All these effects were inhibited by combined administration of WAY-100635 (1.0 mg/kg, s.c.) (P <0.05), an antagonist of the 5-HT1A receptor, but WAY-100635 alone and low doses of 8-OHDPAT (0.01 and 0.1 mg/kg) did not alter seizure activity. Furthermore, intrahippocampal 8-OH-DPAT only shortened the GS duration (P <0.05). These findings imply that the 5-HT1A receptor is a promising therapeutic target against the generation and propagation of SE, and hippocampal receptors are involved in reducing the seizure severity.

Issues related to development of new antiseizure treatments

This report represents a summary of the discussions led by the antiseizure treatment working group of the International League Against Epilepsy (ILAE)/American Epilepsy Society (AES) Working Groups joint meeting in London (London Meeting). We review here what is currently known about the pharmacologic characteristics of current models of refractory seizures, both for adult and pediatric epilepsy. In addition, we address how the National Institute of Neurological Disorders and Stroke (NINDS)-funded Anticonvulsant Screening Program (ASP) is evolving to incorporate appropriate animal models in the search for molecules that might be sufficiently novel to warrant further pharmacologic development. We also briefly address what we believe is necessary, going forward, to achieve the goal of stopping seizures in all patients, with a call to arms for funding agencies, the pharmaceutical industry, and basic researchers.

Neuronal degeneration is observed in multiple regions outside the hippocampus after lithium pilocarpine-induced status epilepticus in the immature rat

Although hippocampal sclerosis is frequently identified as a possible epileptic focus in patients with temporal lobe epilepsy, neuronal loss has also been observed in additional structures, including areas outside the temporal lobe. The claim from several researchers using animal models of acquired epilepsy that the immature brain can develop epilepsy without evidence of hippocampal neuronal death raises the possibility that neuronal death in some of these other regions may also be important for epileptogenesis. The present study used the lithium pilocarpine model of acquired epilepsy in immature animals to assess which structures outside the hippocampus are injured acutely after status epilepticus. Sprague-Dawley rat pups were implanted with surface EEG electrodes, and status epilepticus was induced at 20 days of age with lithium pilocarpine. After 72 h, brain tissue from 12 animals was examined with Fluoro-Jade B, a histochemical marker for degenerating neurons. All animals that had confirmed status epilepticus demonstrated Fluoro-Jade B staining in areas outside the hippocampus. The most prominent staining was seen in the thalamus (mediodorsal, paratenial, reuniens, and ventral lateral geniculate nuclei), amygdala (ventral lateral, posteromedial, and basomedial nuclei), ventral premammillary nuclei of hypothalamus, and paralimbic cortices (perirhinal, entorhinal, and piriform) as well as parasubiculum and dorsal endopiriform nuclei. These results demonstrate that lithium pilocarpine-induced status epilepticus in the immature rat brain consistently results in neuronal injury in several distinct areas outside of the hippocampus. Many of these regions are similar to areas damaged in patients with temporal lobe epilepsy, thus suggesting a possible role in epileptogenesis.

The control of kainic acid-induced status epilepticus

In the present study the effectiveness of different diazepam-ketamine combinations to control kainic acid-induced status epilepticus in rats was evaluated. We show that electrographic monitoring is mandatory to enable reliable assessment of status epilepticus control as the number of false positives is extremely high when status epilepticus control is only behaviourally assessed. Diazepam and ketamine synergistically blocked all electrographical seizure activity.

Harmful effect of kainic acid on brain ischemic damage is not related to duration of status epilepticus

Status epilepticus is common in infants and may have long-term consequences on the brain persisting into adulthood. Vascular ischemia is a common cause of stroke in adulthood. The extent of stroke in 15-day-old rats is larger when previously exposed to kainic acid-induced status epilepticus. In this paper, we assess whether shortening the duration of seizures modifies subsequent susceptibility to middle cerebral artery occlusion. We administered pentobarbital 50 mg/kg to abort seizures after 1 h. Although administration of pentobarbital aborted seizures, it had no effect on volume of infarction following ischemia. This study indicates that there is dissociation between stopping status epilepticus and modifying its long-term consequences.

Resistance to antiepileptic drugs and expression of P-glycoprotein in two rat models of status epilepticus

Status epilepticus (SE) is a neurological emergency, characterized by continuous or intermittent seizures without full recovery of consciousness between seizures, which can result in death or neurological sequelae. In about one third of patients, SE is unresponsive to sequential treatment with first- and second-line antiepileptic drugs (AEDs). At least in part, this drug resistance may be due to AED target alterations induced by SE, such as reduced membrane expression of GABA(A) receptors. Apart from target alterations by receptor trafficking, SE is known to increase the brain expression of drug efflux transporters such as P-glycoprotein (Pgp), which might reduce concentrations of AEDs at their brain targets. However, it is not known whether overexpression of Pgp develops rapidly enough after onset of SE to be of any functional consequence for drug treatment. Therefore, we studied whether overexpression of Pgp at the blood-brain barrier is involved in refractory SE. Two rat SE models were used, the lithium/pilocarpine model and induction of SE by sustained electrical stimulation of the basolateral amygdala (BLA). Four AEDs, diazepam (DZP), phenobarbital (PB) and phenytoin (PHT) or fosphenytoin (FPHT) were administered at different times after onset of SE. In the pilocarpine model, once self-sustained SE was established, none of the AEDs alone was effective in terminating SE, but sequential injection of PB and DZP stopped SE. Administration of the Pgp inhibitor tariquidar did not prevent or counteract resistance to AEDs. In the BLA model, DZP and PB terminated SE in the majority of rats, whereas PHT or FPHT were ineffective. Immunohistochemical staining of Pgp did not indicate any increase of Pgp expression in brain capillary endothelial cells during SE, whereas significant overexpression was determined in both models 48 h after SE. The data suggest that, at least under the conditions of the present study, alterations in Pgp are not critically involved in refractory SE.