Especially Valuable Epilepsy Cure Advice

Current Research Advances, ,

Introduction 

Despite an extensive research effort and a wealth of available antiseizure medications, a cure for epilepsy remains elusive.  Riley and Danzer (2024) in a recent review discuss the reasons for this.  The path to a cure begins with preclinical research that focuses on the disease initiation termed epileptogenesis and its associated co-morbidities.  Epileptogenesis and disease-dependent co-morbidities, e.g. cognitive decline are key therapeutic targets for a cure.  Riley and Danzer (2024) provide especially valuable epilepsy cure advice by their critique of current preclinical models and proposed improvements.  The especially valuable epilepsy cure advice provided by these scientists is summarized below in a series of insights.

Preclinical animal model types:  acute, acquired and genetic

Especially valuable epilepsy cure advice – Insight 1 

In the development of antiseizure medications (Assessment 6 – Epilepsy Medication – Need to Know Information), the model of choice is the acutely provoked seizure model.  It is known that “acutely evoked seizures generated by normal brains, however, are mechanistically different from spontaneous seizures generated by epileptic brains” (Riley and Danzer, 2024).  Despite this, there are over 25 approved antiseizure medications. Many more are presently in clinical trials (Novel Anti-seizure Drugs – Ongoing Research). 

It is clear that antiseizure medications do not provide a cure for epilepsy.  Seizures return with drug cessation. As supported by clinical trial results, antiseizure medications have no ameliorating effects on epileptogenesis (origin of the seizure) or associated disease comorbidities e.g. cognitive decline.  Epilepsy cure advice proposes that basic preclinical research investigate ways to slow disease progression and initiate beneficial changes even when therapy is withdrawn (Riley and Danzer, 2024).  Since development of antiseizure medications will not yield a cure, a change in research focus is needed.

Especially valuable epilepsy cure advice – Insight 2 

Some of the preclinical epilepsy models are acquired epilepsy models induced by any number of traumatic brain injuries that go on to change the normal brain to an epileptic one.   These model will play an important role in finding a cure for epilepsy. 

However, in these models, it is important to distinguish between the effect of therapy on injury reduction per se and its effect on prevention of induced epileptogenesis.  Thus, determination of timing between these events is key.  Not surprisingly, early therapeutic interventions are more successful. This is because they reduce the effect of injury per se. Such therapy is obviously impractical in real life where brain injury is unpredictable.  Although the goal is epileptogenic therapy and disease modification, injury reduction in traumatic brain injury, where known, is still very important.

Especially valuable epilepsy cure advice – Insight 3 

Epilepsy is chronic.  Patients endure this disease for years.  Therefore, animal models need to be long term.   However, animal models are rarely chronic due to expense and time/labor commitment.  Yet chronic models would be the best ones to study.  Additional advantages of chronic models are many. They include the ability to obtain a baseline EEG, group animals according to similar seizure types, reduce variability and actually use fewer animals (Riley and Danzer, 2024).  Biomarkers would greatly facilitate investigations in epileptogenesis with chronic models (Engel and Pitkänen, 2020).  Sadly, there markers are still in early stages of development.

Especially valuable epilepsy cure advice – Insight 4 

Genetic models target a subset of epilepsies.  In these models, the time of expression of  abnormal gene(s) needs accurate determination to be relevant to epileptogenesis.  Additionally, long term studies with genetic models would be of considerable value.

Especially valuable epilepsy cure advice – Insight 5 

The epilepsy therapy screening program (ETSP)originated over 40 years ago. It provided essential data for many of the antiseizure medications approved by the FDA.  Historically, the ETSP has focused on identification of antiseizure medications for patients who are drug resistant. Currently, “the ETSP contract site has, for the first time, adopted a strategy to explore the potential of novel compounds to prevent epilepsy or to be disease modifying” (Wilcox et al., 2020).  The Neurological Diseases and Stroke of the National Institute of Health at the University of Utah funds and administers this program.  

Scientists now use several epilepsy models. These are an infection-induced model of temporal lobe epilepsy, genetic models and the validated KA-SE (Kainic Acid-Status Epilepticus) model. The latter produces spontaneous seizures.  The KA-SE model mimics temporal lobe epilepsy in humans both in epileptogenesis and disease progression. 

Analysis of therapies in these models has potential to achieve a cure. However, evaluation of therapies in novel etiologically relevant  models face many challenges.  These include lack of a positive control, need to develop an appropriate study design, determination of time window to treat following the brain insult, the duration of treatment and dose, and how long post treatment to observe animals.  These all remain for future evaluation but are realistically achievable.

Conclusions 

A number of researchers, notably those mentioned above and others, are providing especially valuable epilepsy cure advice.  It is important to move away from discovery of antiseizure medications that only suppress symptoms of epilepsy. These medications do nothing to prevent epileptogenesis or modify disease progression. They have failed to identify a cure for epilepsy.  Therapy testing in relevant animal models in essential to meet this goal.

References https://pubmed.ncbi.nlm.nih.gov/

1.  Riley VA, Danzer SC. Preclinical Testing Strategies for Epilepsy Therapy Development.Epilepsy Curr. 2024 Oct 25;25(1):51-57. doi: 10.1177/15357597241292197

2.  Engel J, Jr, Pitkänen A. Biomarkers for epileptogenesis and its treatment. Neuropharmacology. 2020;167:107735 doi: 10.1016/j.neuropharm.2019.107735

3.  Wilcox KS, West PJ, Metcalf CS. The current approach of the Epilepsy Therapy Screening Program contract site for identifying improved therapies for the treatment of pharmacoresistant seizures in epilepsy. Neuropharmacology. 2020;166:107811 doi: 10.1016/j.neuropharm.2019.107811

Novel Anti-seizure Drugs – Ongoing Research

Current Research Advances, ,

Introduction 

There is a urgent need for novel anti-seizure drugs that are both efficacious, safe and absent undesirable side effects.  In particular, the number of epilepsy patients who are drug resistant remains at an unacceptably high rate of 30%.  Untreated epilepsy has dire consequences including injury and death.  Additionally, those who are seizure free with drug therapy are not free from unwanted neurological side effects such as headaches, somnolence, and memory impairment.  Therefore, research for novel anti-seizure drugs that prevent seizures at doses absent of side effects is desperately needed but incredibly challenging (see Blog 15 for overview).  This blog discusses some of the novel anti-seizure drugs – ongoing research.

Specifically, this blog reviews three of 5 novel anti-seizure drugs that have met their goals in early clinical trials with positive data on anti-seizure efficacy (1).  Novel anti-seizure drugs introduced here are A) azetukalner (XEN1101),  B) bexicaserin (LP352), and C)  soticletstat (TAK-935). 

A) Azetukalner – Novel Anti-Seizure Drug Candidate

Azetukalner is a potassium channel opener that selectively acts on specific channels designated Kv7.2/7.3.  Importantly, azetukalner, by opening potassium channels, accelerates the movement of potassium ions through Kv7.2/7.3 channels across the nerve membrane.  This is an critical action because it lowers the membrane potential and essentially dampens excitable (seizure) nerve activity that promotes a seizure.  Thus, the rational is that the selectivity of azetukalner allows it to bypass all the other ion channels, potassium or otherwise, and focus only on excitable nerves where Kv7.2/7.3 channels need assistance.

Selectivity

Based on in vitro findings, azetukalner is 4 fold more selective for potassium Kv7.2/7.3 channels compared to closely related potassium (Kv) channels.  Additionally, oral dosing in classic seizure rodent models (electrical and chemical) reduced seizures to a greater extent than a current standard drug, retigabine, a nonselective Kv7 potassium opener (2), used now only experimentally.

Clinical Results

Two clinical trials evaluated azetukalner for efficacy and safety.  The first was a randomized double-blind trial of 8 weeks with escalating doses (10, 20, and 25 mg) in adults with focal onset seizures, baseline median number of 13.5 seizures per month (3).   Most importantly, a reduction in monthly seizure frequency was slightly over 50% with the highest dose compared to an 18% reduction of seizure frequency in the control group.

The second trial was an open-label trial that allowed participants in the first trial to continue with the medication (20 mg dose).  Data after one year for those who chose to continue show that nearly 15% were seizure free. After 2 years, nearly 24% were seizure free (4).  This trial had no control group. The dropout rate was approximately 25%. Nevertheless, the results are considered good in light of the difficult to treat seizures in this group of patients (4).

Treatment Related Adverse Effects

Adverse effects from this long term trial were considered mild to moderate.  They ranged from dizziness, headache, coronavirus infection, somnolence, falls and memory impairment at rates of 12.7-21.8% (4).

B)  Bexicaserin – Novel Anti-Seizure Drug Candidate

Bexicaserin is a 5HT2C serotonin receptor stimulant (agonist).  Importantly, 5HT2C is one of three serotonin receptors. Specifically, it is the one that plays a major role in seizure activity such that activation damps seizures. 

Selectivity

Bexicaserin is “super” selective (more than 1000 fold) for the 5HT2C receptor compared to the other serotonin receptors as demonstrated in vitro studies.  In this regard it’s selectivity stands out against current drugs in this category e.g. fenfluramine (5) and lorcaserin (6).  Furthermore, bexicaserin also had no effect on an extensive battery of other known brain receptors (7). In animal models of genetically or drug-induced seizure activity (zebra fish, see blog 18; mice), bexicaserin reduced seizure activity. 

Clinical Results

A phase 1b/2a randomized clinical trial tested 41 patients with developmental epileptic encephalopathies (serious epilepsy affecting brain development). Patients receiving 6 month treatment with increasing doses of bexicaserin (6-12 mg/day) exhibited reduced median motor seizure activity by slightly more than 50% compared to start of the study (8). Noteably, a Phase 3 trial (NCT06660394) with bexicaserin is currently recruiting children and adults with Dravet Syndrome, a developmental epileptic encephalopathy.

Treatment Related Adverse Effects

The two main adverse reactions affecting 20% or more of participants were somnolence and decreased appetite (8). 

C.  Soticlestat – Novel Anit-Seizure Drug Candidate

Soticlestat inhibits the metabolism of cholesterol in the brain (9).  Drug action prevents the formation of cholesterol-24 hydroxylase (24HC). 24HC is a known facilitator of nerve excitability.  Specifically, 24HC increases the concentration of glutamate, a pro-excitability transmitter. Additionally, it modulates NMDA (N-methyl-D-aspartate) “excitable”  receptors and enhances inflammation, three actions that support abnormal brain excitability (10).   Therefore, reducing 24HC  would diminish these activities.

Preclnical Results

Results in mouse models of epilepsy showed soticlestat as an efficacious antiseizure chemical entity worthy of clinical evaluation. 

Clinical Results

The most recent trial (ELEKTRA) was a phase 2 randomized double-blind trial of 126 patients for 12 weeks (up to 300 mg/d). It reported significant (median 50%) seizure frequency reduction in children and adolescents with Dravet Syndrome.  However, it did not significantly reduce seizure frequency in patients with Lennox–Gastaut syndrome, another difficult to treat epilepsy (11). An interesting asset of this drug is that efficacy can be followed by measuring the concentration of 24HC in the blood.  Thus, as 24HC declines with soticlestat use, seizure frequency also declines.

Phase 3 trial (NCT05163314) is in progress (ClinicalTrials.gov).  The clinical trial goal is the determination of safety and tolerability. This is a trial of projected 400 patients with Dravet syndrome or Lennox-Gastaut Syndrome worldwide taking solticlestat (100mg/d) for 4 years.

Treatment Related Adverse Events

Adverse effects of soticlestat were comparable to placebo with 5% experiencing lethargy and constipation to a greater degree than placebo. 

Critique 

The three novell anti-seizure drugs, working toward FDA approval, each act by a different mechanism.   Azetukalner opens a potassium channel subtype, bexicaserin stimulates a serotonin receptor subtype and soticlestat blocks cholesterol metabolism in the brain.  The variety of targets speaks to the complexity of seizures and the lack of clear knowledge about epilepsy.  All three drugs have completed phase 2 trials with evidence of efficacy and safety. 

Despite the fact that these drugs reduce seizure frequency up to 50% in different epilepsies, these drugs are far from ideal.  Selectivity of azetukalner for the Kv7,2/7.3 channels is only 4  time greater than it is for other Kv channels.  This modest selectivity most likely disappears in human, leading to general suppression of neuronal activity supporting side effects of somnolence and memory impairment.  Bexicaserin exhibits a 1000 fold selectivity for the 5HT2C receptors compared to same class subtypes.   This impressive selectivity will most likely be maintained in humans.  However, stimulation of 5HT2C does more than dampen seizures and affects multiple functions such as appetite and mood. The multiple functionality of this serotonin receptor would brings in undesired side effects.

Soticlestat is a truly novel drug that targets the destructive brain metabolite of cholesterol.  Its unique effect knocks out three potential mechanisms supporting seizures and has the greatest chance of reducing seizures with the least induction of side effects.  Furthermore, its effects can be track with measurement of 24HC in blood. 

Patients with epilepsy deserve medications that prevent seizure without blocking other vital brain activities.  Patients with epilepsy eagerly await the results of Phase 3 clinical trials for these compounds.

References

1.  Bailer M, Johannessen SI, Koepp MJ, Perucca E, Perucca P et al. Progress report on new medications for seizures and epilepsy: A summary of the 17th Eilat Conference on New Antiepileptic Drugs and Devices (EILAT XVII). II. Drugs in more advanced clinical development Epilepsia  . 2024 Oct;65(10):2858-2882.  doi: 10.1111/epi.18075. 

2.  Gunthorpe MJ, Large CH, Sankar R. The mechanism of action of retigabine (ezogabine), a first-in-class K+ channel opener for the treatment of epilepsy Epilepsia . 2012 Mar;53(3):412-24.  doi: 10.1111/j.1528-1167.2011.03365.x. 

3.  French JA, Porter RJ, Perucca E, Brodie MJ, Rogawski MA, Pimstone S, et al. Efficacy and safety of XEN1101, a novel potassium channel opener, in adults with focal epilepsy: a phase 2b randomized clinical trial. JAMA Neurol. 2023;80(11):1145–54.

4.  French JAm Porter RJ, Perucca E, Brodie MJ Rogawski MA et al. Interim analysis of the long-term efficacy and safety of azetukalner in an ongoing open-label extension study following a phase 2b clinical trial (X-TOLE) in adults with focal epilepsy Epilepsia Open. 2025 Apr;10(2):539-548. doi: 10.1002/epi4.70015. 

5.  Sourbron J, Lagae L. Fenfluramine: a plethora of mechanisms? Front Pharmacol. 2023 May 12;14:1192022. doi: 10.3389/fphar.2023.1192022

References

6.  Gutafson A, King C, Rey JA. Lorcaserin (Belviq)A Selective Serotonin 5-HT2C Agonist In the Treatment of Obesity Pharmacy and Therapeutics. 2013 Sep;38(9):525-530, 534.

7.  Ren A, Zhu Z, Lehmann J, Kasem M, Schrader TO, Dang H et al. Diazepine Agonists of the 5‑HT2C Receptor with Unprecedented Selectivity: Discovery of Bexicaserin (LP352). J. Med. Chem. 2025, 68, 10599−10618 https://doi.org/10.1021/acs.jmedchem.4c02923

8.  Kaye R, Orevillo C, Dlugos DJ, Scheffer IE. Efficacy and safety of bexicaserin (LP352) in adolescents and adult participants with developmental and epileptic encephalopathies: Results of the phase 1B/2A pacific study. In 76th Annual Meeting of the American Academy of Neurology, April 13−18, 2024, Denver, CO, 2024

9.  Nishi T, Kondo S, Miyamoto M, Watanabe S, Hasegawa S, Kondo S, et al. Soticlestat, a novel cholesterol 24-hydroxylase inhibitor shows a therapeutic potential for neural hyperexcitation in mice. Sci Rep. 2020;10(1):17081

10.  Kondo S, Murthy V, Asgharnejad M, Benitez A, Nakashima K, Hawkins N, White HS. A review of the putative antiseizure and antiepileptogenic mechanisms of action for soticlestat. Epilepsia. 2025 May;66(5):1394-1405. doi: 10.1111/epi.18287.

11.  Hahn CD, Jiang Y, Villanueva V, Zolonowska M, Arkilo D et al. A phase 2, randomized, double-blind, placebo-controlled study to evaluate the efficacy and safety of soticlestat as adjunctive therapy in pediatric patients with Dravet syndrome or Lennox-Gastaut syndrome. (ELEKTRA) Epilepsia. 2022 Oct;63(10):2671-2683.  doi: 10.1111/epi.17367. 

Progress in Imaging Epilepsy

Current Research Advances, , , , , ,

Magnet resonance imaging (MRI), is frequently used, along with other data, to generate a diagnosis of epilepsy.   The MRI is a noninvasive imaging tool that scans the structure of the whole brain to identify abnormalities.  The MRI, alone, gives no information on physiological and pathological functions, only structure.  Fortunately, adjuncts and variants of the MRI and related techniques used to image epilepsy record changes in biological function.  Progress in imaging epilepsy improve diagnostic accuracy as well as expand understanding of epilepsy.  This blog will discuss progress in imaging epilepsy.

Progress in Imaging Epilepsy – MRI-related

MRI dependent imaging include 1) functional MRI and associated improvements,  2) diffusion MRI and 3) 1H-magnetic resonance spectroscopic imaging (MRSI).   The original MRI, using magnetic fields, detects subtle changes in brain structure, e.g. volume and contour differences in neuronal clusters particularly when newer technical adjustments are utilized (1).  Thus MRI imaging successfully identified differences in brains of normal individuals and those with temporal lobe epilepsy (1).  It is equally useful in detecting tumors and areas of traumatic brain injury.

1)  Functional MRI and advancements. 

The functional MRI (fMRI), a variant of the MRI, is also a non invasive technique.  It tracks blood oxygen levels in the brain.  The method relies on the observation that active neurons (e.g. those involved in brain-related activities such as thinking) consume more oxygen than quiescent neurons.  Thus, areas of high blood oxygen use pinpoint sites of activated functional neurons.  This technique succeeded in mapping areas involved in cognition, stress, and emotions (1).  Therefore, combining an EEG with a fMRI improves location of epileptogenic neurons triggering and supporting a seizure.  Such information is especially important in ablation surgery for drug-resistant patients with severe epilepsy (1).  fMRI is successfully used to follow the path of propagation of the seizure throughout the brain, providing evidence on how one part of the brain influences another during epilepsy progression (1).

2)  Diffusion-weighted MRI/Diffusion Tensor MRI.  

These imaging techniques measure tissue water movement in cells and surrounding space in the brain.  Each technique does it slightly differently with the oldest of the two as the diffusion-weighted MRI (3).  These techniques are advantageous in the diagnosis of pediatric epilepsy (4) and assessment of acute stroke(3) .  Research results using this imaging track and define the connectivity between neurons during brain-related activities, expanding knowledge of brain physiology (3).

3)  1H-magnetic resonance spectroscopic imaging (MRSI).

This is an old technique that is generating renewed interest due to its enhanced magnetic resonance sensitivity (5).  MRSI detects substances whose molecular components contain high amounts of 1H protons.  The main substances are N-acetyl-aspartate (NAA), creatine, and choline.  Results of numerous studies show that the ratio of NAA to creatine provides information on abnormal neuronal activity associated with oxidative stress.  This imaging opens up research on the relation between oxidative stress and neurotransmitters such as GABA (gamma amino butyric acid), a neurotransmitter implicated in epilepsy (5).

Progress in Imaging Epilepsy – Radioactive Imaging.

In contrast to the MRI, PET and SPECT are invasive imaging methods that inject radioactive substances to study brain activity in disease.

1)  PET stands for Positron Emission Tomography.

This imaging technique employs a positron emitting chemical (tracer) such as a radioactive variant of glucose (fluorodeoxyglucose).  Active neurons and auxiliary cells take up the sugar thus highlighting an area of brain activity.  This is used to identify tumors which are more metabolically active than normal tissue.  PET is also valuable in tracing blood flow in metabolic regions during a seizure.  While capture of a seizure during a PET scan is rare, measurement of activity between seizures is more likely and provides important information.  Here, areas of low metabolism (hypometabolism) indicate sites of epileptic origin and are useful aids in surgical ablations (1).

The PET also uses radioactive analogues of neurotransmitters to uncover changes in brain receptor activity in epilepsy (6).  Additionally, PET imaging reveals an increase in a specific marker of brain inflammation, the translocator protein (TSPO).  TSPO is elevated in epilepsy (7).  Its elevation indicates that auxiliary cells (glial cells) are active and contributing to brain inflammation (8).  See earlier blog on the role of inflammation in epilepsy (Neuroinflammation of Epilepsy – new diagnostic tools)

2)  SPECT stands for Single photon emission computed tomography. 

This  imaging technique is similar to PET but differs in that the radioactive tracers emit a different type of radiation.  Gamma rays are detected by SPECT.  For epilepsy diagnosis, SPECT is used secondarily to PET (9).  It is considered important for surgical candidates with drug resistant epilepsy in which no structural lesions are found.  This technique is highly successful in localization of  the site of seizure origin in pediatric epilepsy (10).

Progress in Imaging Epilepsy – Magnetoencephalography

Magnetoencephalography (MEG) differs radically from the above discussed techniques.  Specifically, it does not use magnetism or radioactivity to “shake up or interact with” with molecules in brain to define structure and function (11).  Rather, the MEG detects magnetic fields generated or given off from nerves after they transmit their signal (termed postsynaptic activity).  Because magnetic waves are received without distortion, the location of epileptogenic foci are more accurately identified.   MEG is considered an advanced version of the EEG.  Similar to the EEG, it is non invasive.  However, the EEG records electrical activity without the ability to assign origin to such activity.  In contrast, the MEG accurately locates the origin of abnormal nerve activity.  MEG associated with PET or MRI data is of great assistance in surgical ablations for severe epilepsy (11).  Additionally, findings from this technique suggest the existence of connectivity between several areas of the brain during seizures, expanding understanding of the complexity of epilepsy (1).  

Conclusions

This blog describes a number of sophisticated imaging techniques and methods used to assist with the diagnosis of epilepsy, illustrating progress in imaging epilepsy.  These include variations of the classic MRI, radioactive imaging and an upgraded version of the EEG.  The majority of these methods provide critical data to pinpoint epileptogenic foci for surgical ablations in cases of drug-resistant severe epilepsy.  Although accessed less frequently for research, the insights that have been gained thus far are invaluable.   These techniques offer potential for deeper understanding of the pathology of epilepsy and hence better therapy and a possible cure.

References http://pubmed

1.  Goodman AM, Szaflarski JP. Recent Advances in Neuroimaging of Epilepsy.  Neurotherapeutics. 2021 Apr;18(2):811-826. doi: 10.1007/s13311-021-01049-y.

2.   Chang C, Huang C, Zhou N, Li SX, Ver Hoef L, Gao Y. The bumps under the hippocampus. Hum Brain Mapp . 2018 Jan;39(1):472-490.  doi: 10.1002/hbm.238563. 

3.  Ranzenberger LR, Das JM, Snyder T.  Diffusion Tensor Imaging  StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan. 2023 Nov 12.

4   Szmuda M, Szmuda T, Springer J et al., Diffusion tensor tractography imaging in pediatric epilepsy – A systematic review.  Neurol Neurochir Pol . 2016;50(1):1-6.  doi: 10.1016/j.pjnns.2015.10.003. 

5 Pan JW, Kuzniecky RI Utility of magnetic resonance spectroscopic imaging for human epilepsy. .Quant Imaging Med Surg. 2015 Apr;5(2):313-22. doi: 10.3978/j.issn.2223-4292.2015.01.036.

6.  Sarikaya I. PET studies in epilepsy.  Am J Nucl Med Mol Imaging. 2015 Oct 12;5(5):416-30. eCollection 2015.

7.  Galovic, M, Koepp, M. Advances of molecular imaging in epilepsy. Curr Neurol Neurosci Rep  2016 Jun;16(6):58.  doi: 10.1007/s11910-016-0660-7.

8.  Zhang L, Hu K, Shao T, Hou L, Zhang S, Ye W, Josephson L, Meyer JH, Zhang MR, Vasdev N, Wang J, Xu H, Wang L, Liang SH Recent developments on PET radiotracers for TSPO and their applications in neuroimaging.  .Acta Pharm Sin B. 2021 Feb;11(2):373-393. doi: 10.1016/j.apsb.2020.08.006.

9.  Cendes F, Theodore WH, Brinkmann BH, Sulc V, Cascino GD.Neuroimaging of epilepsy. Handb Clin Neurol. 2016;136:985-1014. doi: 10.1016/B978-0-444-53486-6.00051-X.

10.  Juhász C, John F.Utility of MRI, PET, and ictal SPECT in presurgical evaluation of non-lesional pediatric epilepsy.Seizure. 2020 Apr;77:15-28. doi: 10.1016/j.seizure.2019.05.008. 


11.  Pan R, Yang C, Li Z, Ren J, Duan Y. Magnetoencephalography-based approaches to epilepsy classification.  Front Neurosci. 2023 Jul 12;17:1183391. doi: 10.3389/fnins.2023.1183391

Delay in Epilepsy Diagnosis

Epilepsy Topics, ,

Introduction

Several clinicians has reported that for many patients, a diagnosis of epilepsy occurs months to years after an initial seizure.  An epilepsy diagnostic delay is not only concerning but comes with significant consequences.  This blog will discuss the prevalence, possible reasons for an epilspy diagnostic delay and proposed solutions to minimize delays.

Prevalence of an Epilepsy Diagnostic Delay

Findings from several studies indicate that almost half (40-50%) of patients do not seek medical attention after a first seizure.  Specifically, a delay of approximately 9 months (Firkin, 2015) to 16 months (Gasparini et al., 2013) is documented.  In a recent review that averaged results from many studies, on average, 38% of patients delayed in seeking medical help with approximately 16% of patients waiting a year or more (Alessi 2021).

Parviainen et al., (2020), in a retrospective study (assessing previously recorded clinical data),found that out of 177 patients prior to diagnosis, 45% had 3-10 seizures and 5% experienced 50-100 seizures.  In this analysis, the average time from first seizure to diagnosis was 50 months.  The greatest extent of delay occurred in patients 18-30 years of age. The second greatest extent occurred in those 30-50 years of age.  It is clear that the delay in epileptic diagnosis is real and prominent.

Explanation for the Epilepsy Diagnosis Delay

Scientist offer several explanations to explain an epilepsy diagnostic delay.  In general, a delay has been attributed to:

 a) lack of medical care availability,

 b) lack of awareness of the seizure and

c) medical attention but lack of a diagnosis (Parvianen et al., 2020).  

Lack of Access to Medical Care

Firstly, several studies discount the lack of medical availability studies as a viable explanation.  This is because the countries conducting these studies are ones with free medical care for all (Gasparini et al., 2013; Firkin, 2015).  However, this factor may still be important in countries with limited access to medical care.

Lack of Awareness to a Seizure

Secondly, lack of awareness of a seizure is a reasonable explanation.   Scientists postulate that activation of brain tissue around the seizure lesion impairs consciousness or memory of the seizure.   Additionally, brief or what is termed as non disruptive seizures (absence seizures, monoclonic jerks) do not attract attention from those nearby and hence are missed by an observer.  Thus, the patient and bystander do not recognize the symptoms of a seizure.  However, this is not a full explanation since even those with a convulsive seizure (with temporary loss of consciousness), clearly an obvious event, often delay in seeking medical help (Gasparini et al., 2013).

Medical Attention without a Diagnosis

Thirdly, patients with seizures may seek medical advice but if classically accepted diagnostic criteria are not met, these patients are unlikely to get a diagnosis of epilepsy.  A diagnosis of epilepsy depends on a detailed history of seizures by the patient and if possible by an observer (usually a family member or friend).  Absent this, the physician relies on the presence of brain lesions detected with an MRI, CAT scan or seizure activity with an EEG.  A twenty minute EEG rarely picks up a seizure. The MRI/CAT scans detect precipitants of a seizure such as tumors and stroke but not subtle neurological abnormalities.   Not surprisingly, seizures in patients with a tumor or stoke have the least extent of diagnostic delay (Yang et al., 2022).

Lack of diagnostic data promotes uncertainty. Hence, physicians are reluctant to declare a diagnosis of epilepsy.   Adding to this is the possibility of a false positive, albeit with a 5% occurrence (Oto et al.,2017).  Conditions such as cardiogenic syncope (enlarged heart providing insufficient blood to the brain) and psychogenic non epileptic seizure (caused by psychological stress) which appear as seizures but are not cases of epilepsy, contribute to uncertainly in a diagnosis of actual epilepsy. 

Another explanation not offered in scientific journals is the social consequence of an epilepsy diagnosis which revokes the driver’s license for 6 months to several years depending on the state.  This brings possible repercussion for both work and every day living.

Thus current explanations for diagnostic delay are a) an inability to recognize the symptoms of a seizure by patient and observer, b) the absence of tangible evidence of a seizure (EEG, MRI, CAT, history), and c) possibly, serious concern for changes in living/working conditions.

Proposed Solutions to Minimize Delay

There are several proposed solutions.  One suggestion is to emphasize to physicians that it is better to proceed with an uncertain diagnosis. But, at the same time, acknowledge the need for continual review (Oto et al., 2017) .  This is difficult in practice because a false positive would subject the patient to unnecessary medication and state laws prohibiting patients with epilepsy from driving, as noted above. 

A second suggestion is to better educate both physicians and the public in general, on the symptomatology of a seizure.  If the patient cannot remember the seizure, it is important that an observer provide an accurate observation.  Education of the public on early warning signs of a heart attack and some cancers have met with success.

A third suggestion is to invest in improved diagnostics.  Results of a recent clinical trial showed the benefit of smart phone videography as elevating the predictive value of an epileptic seizure and distinguishing between epileptic and non epileptic seizures (Tatum et al., 2020).  This might become a reasonable point of education.  Genetic testing has become of increasing value and has success in the identification of a genetic mutation(s) in approximately 50% of epilepsies (Striano and Minassian, 2020). Additionally, several neuroinflammatory biomarkers such as High-Mobility Group Box 1 (see Blog 19) are highly intertwined with epilepsy and are currently investigated as meaningful adjuncts to diagnosis of epilepsy.  Additional work would be appropriate.  

Conclusions 

Nearly half of all individuals who experience a seizure receive a diagnosis of epilepsy after a considerable delay of months to years.  This is distressing to clinicians who understand the need for early disease treatment.  Currently, epileptic diagnostic delay is only partially understood.  Some explanations are memory of a seizure is near impossible, bystanders do not understand seizure symptoms and physicians are reluctant to give a diagnosis if classical signs e.g. abnormal EEG are lacking.   Education of seizure symptoms for physicians and public as well as development of meaningful diagnostic tools are desperately needed.

References (pubmed)

1. Firkin AL, Marco DJT, Saya S, et al. Epilepsia 2015;56:1534–41.  2. Gasparini S, Ferlazzo E, Beghi E, et al. Family history and frontal lobe seizures predict long-term remission in newly diagnosed cryptogenic focal epilepsy. Epilepsy Res 2013;107:101–108. 3. Alessi N, Perucca P, McIntosh AM. Missed, mistaken, stalled: identifying components of delay to diagnosis in epilepsy. Epilepsia 2021;62:1494–504. 4. Parviainen L, Kälviäinen R, Jutila L. Impact of diagnostic delay on seizure outcome in newly diagnosed focal epilepsy. Epilepsia Open. 2020 Dec 8;5(4):605-610. 5. Yang M, Tan KM, Carney, et al. Diagnostic delay in focal epilepsy: Association with brain pathology and age. Seizure. 2022 Mar;96:121-127. 6. Oto MM. The misdiagnosis of epilepsy: appraising risks and managing uncertainty. Seizure. 2017;44:143–6. 7. Tatum WO, Hirsch LJ, Gelfand MA  et al. Assessment of the Predictive Value of Outpatient Smartphone Videos for Diagnosis of Epileptic Seizures. JAMA Neurol. 2020 May 1;77(5):593-600. 8. Striano P, Minassian BA. From Genetic Testing to Precision Medicine in Epilepsy Neurotherapeutics. 2020 Apr;17(2):609-615.

Neuroinflammation of Epilepsy – new diagnostic tools

Current Research Advances, , ,

Key Mediators of Neuroinflammation

Over the past ten years, the number of research papers focused on neuroinflammation of epilepsy has escalated dramatically (Ngadimon et al., 2024).  Thus, neuroinflammation is central to both the initiation (epileptogenesis) of epilepsy and the support for repetitive seizures.  A great deal is known about the inflammatory pathways active in epilepsy (Aguilar-Castillo et al., 2024; Ngadimon et al., 2024).  Furthermore, several key mediators of neuroinflammation are now potential biomarkers of epilepsy (Aguilar-Castillo et al., 2024).  These select biomarkers are possible new diagnostic tools poised to replace the traditional EEG. 

This blog will discuss one of the key mediators of neuroinflammation of epilepsy, termed High-Mobility Group Box 1, also known as HMGB1 (Aguilar-Castillo et al., 2024; Ngadimon et al., 2024; Chen et al., 2023) .  HMGB1 has the potential to be an innovative and relevant diagnostic tool to identify and monitor the disease of epilepsy.

Unmet Medical Needs – Biomarkers and Selective Drugs

Several key neuroinflammatory mediators including HMGB1 and others are present in serum and importantly are associated with the severity and frequency of seizures (see studies below) (Ngadimon et al, 2024).  The ability of the traditional EEG to diagnosis new onset epilepsy is poor and its predictive capability for repeat seizures is limited.  It is, therefore, critical to pursue research to fill this unmet medical need and to identify novel molecules exclusive to epilepsy as valid diagnostic and prognostic tools.

Key Mediators of Neuroinflammation as drug targets

Moreover, select neuroinflammatory mediators and their target receptors have potential as targets for new drug therapy (Maroso et al., 2010).  Current anti-seizure drugs, although there are many, have adverse side effects that cause many patients to discontinue use (Chen et al., 2023).  These drugs suppress seizures but do nothing about the progression of the disease.  Furthermore, 30% of epileptic patients do not benefit from present day drugs. They are considered drug-resistant.  Thus, there is a need to develop more selective drugs.  Therefore, focus on development of drugs that inhibit the epilepsy-promoting effects of key mediators of neuroinflammation should prove of value.

Neuroinflammation of epilepsy – instigator?

Neuroinflammation is an inflammatory disturbance in and among the cells of the brain.  “Increasing evidence indicates that neuroinflammation is a common consequence of epileptic seizure activity, and also contributes to epileptogenesis as well as seizure initiation (ictogenesis) and perpetuation.” (Webster et al., 2017).  Approximately half of all acquired epilepsies occur following a prior neurological injury that produces neuroinflammation.  Neurological injuries are injuries such as a brain tumor/infection, traumatic brain injury, or exposure to destructive nerve agents (Klein et al., 2018; Chen et al., 2023).  Neuroinflammation is also the common denominator between epilepsy and sleep disorders (see blog 11)

Animal Models, Human Epileptic Tissue

Results of studies in animal models of epilepsy and data from human epileptic tissue specimens, define the brain pathways and mechanisms of neuroinflammation.  In general, a latent phase follows a brain injury and progresses to a chronic phase.  These changes eventually heighten the excitability of nerves, giving rise to seizures.  Neuroinflammation is characterized by abnormal alterations in brain support cells e.g. astrocytes and glial cells, harmful modifications in the blood-brain barrier (making it more porous susceptible to entry of unwanted cells and proteins), infiltration of immune cells, nerve cell death and reorganization of remaining neurons (Klein et al., 2018; Chen et al., 2023)(see Figure below). 

Importantly, these revisions produce an abundance of significant pro-inflammatory substances whose effects modify nerve activity favoring excitability.  High-Mobility Group Box 1 (HMGB1) is among one of the significant pro-inflammatory substances. Data show its amplified presence enhances nerve excitability and participates in continued hyper excitability (Maroso et al., 2010; Kamasak et al., 2020).

High-Mobility Group Box 1 (HMGB1) -Major Culprit?

HMGB1 is a nuclear protein with a normal activity of assisting DNA in gene expression (“turning genes off and on”), maintenance and repair.  Therefore, residing in the nucleus it remains beneficial.  However, stress-induced movement to the cytoplasm and the extracellular fluid renders it harmful.  Thus, when released from cells, actively or via cell death, HMGB1 acts as a pro-inflammatory initiator binding to one of two receptors (Toll-like Receptor 4, TLR4 and receptor for advanced glycation endproducts, RAGE) (Paudel et al., 2018; Chen et al., 2023). 

HMGB1 Consequences

This interaction sets off a cascade of changes that continue to generate other proinflammatory factors (cytokines, chemokines, growth factors, lipids) that support continued inflammation, keep the vicious cycle going by enabling more HMGB1 release and induce unwanted nerve hyperactivity. Thus, HMGB1 is one of the key mediators of neuroinflammation.

HMGB1 – Role in humans with epilepsy

As reviewed by Aronica and Crino (2011), there are several studies using resected (surgically removed) human epilepsy foci.  These specimens clearly show the presence of neuroinflammation.  Compared to normal brain tissue, specific inflammation mediators and their receptors are present in large amounts in tissue from epilepsy patients.  It is suggested that these distinct changes account for the neuroinflammation and are responsible for promotion of neuronal hyperactivity.  In particular, elevated levels of HMGB1and its receptor TLR4 were identified in human epilepsy foci, specifically in proactive astrocytes and microglia  (Aronica and Crino, 2011).  This positions HMGB1 as one of the key mediators of neuroinflammation.

Biochemical Analysis

More recently, biochemical analysis of  brain tissue removed from patients with intractable epilepsy compared to normal tissue showed HMGB1 not only in the nuclei of  neurons and glia cells (normal tissue location) but also in the cytoplasm where its release would be expected (Shi et al., 2018).  HMGB1, its two receptors (TLR4, RAGE) were significantly elevated in tissue from epilepsy patients compared to normal controls (Shi et al., 2018).

Activated and possibly damaged brain cells release HMGB1 in epileptic regions and, therefore, it should be detectable in serum.  Indeed, three studies reported elevated HMGB1 levels in children with epilepsy (Zhu et al., 2018), adults with drug resistant epilepsy (Walker et al., 2022) and case-control study of 105 epilepsy patients compared to 100 healthy controls (Kan et al, 2019). 

Serum Levels of HMGB1

The insights gained from these studies are important. The first study measured HMGB1 24 hours prior to a seizure.  Thus, the high levels of HMGB1 (and other inflammatory mediators) was predictive of seizure onset and frequency in children (Zhu et al., 2018), a prognostic benefit.  In the second study, drug-resistant epilepsy patients showed higher HMGB1 levels compared to those controlled with drugs and normal controls.  This suggests a possible screening tool to identify those resistant to standard drugs, all of which dampen ion channels and have no effect on neuroinflammation (Walker et al, 2022). 

Significant Human Study

The third study found that the levels of HMGB1 and TLR4 were higher in patients with more than 3 seizure/month and these levels additionally correlated with duration of the seizure of greater than 5 minutes.  HMGB1 levels were independent of the type of seizure (partial, general) or length of the disease (Kan et al., 2019).  These are important findings but are correlative.  Additional studies such as long term clinical trials are required to establish cause-and-effect. 

Conclusions

Clearly there is a need for validated and precise diagnostic tools to promptly and correctly identify the beginning stage and progression of epilepsy.  Misdiagnosis or delayed diagnosis prove fatal.  The neuroinflammatory mediator, HMGB1, is a reasonable diagnostic and prognostic candidate since it is one of the key mediators of neuroinflammation.  Initial stages of epilepsy exhibit higher levels of HMGB1 and serum levels correlate with onset, frequency and duration of epilepsy in humans.  However, the information at present, although promising, is limited and requires more studies, better assays to detect all forms of HMGB1 and definitely a serious research effort with a large clinical trial.

Figure By: Paudel YN, Shaikh MF, Chakraborti A, Kumari Y, Aledo-Serrano Á, Aleksovska K, Alvim MKM, Othman I.HMGB1: A Common Biomarker and Potential Target for TBI, Neuroinflammation, Epilepsy, and Cognitive Dysfunction. Front Neurosci. 2018 Sep 11;12:628. doi: 10.3389/fnins.2018.00628.

References  (http://Pubmed)

1.  Ngadimon IW, Shaikh MF, Mohan D, Cheong WL, Khoo S. Mapping epilepsy biomarkers: a bibliometric and content analysis.  Drug Discov Today. 2024 Dec;29(12):104247. doi: 10.1016/j.drudis.2024.104247.

2.  Aguilar-Castillo MJ, Cabezudo-García P, García-Martín G, Lopez-Moreno Y, Estivill-Torrús G, Ciano-Petersen NL, Oliver-Martos B, Narváez-Pelaez M, Serrano-Castro PJ.A Systematic Review of the Predictive and Diagnostic Uses of Neuroinflammation Biomarkers for Epileptogenesis. Int J Mol Sci. 2024 Jun 12;25(12):6488. doi: 10.3390/ijms25126488.

3.  Chen Y, Nagib MM, Yasmen N, Sluter MN, Littlejohn TL, Yu Y, Jiang J.  Neuroinflammatory mediators in acquired epilepsy: an update Inflamm Res. 2023 Apr;72(4):683-701. doi: 10.1007/s00011-023-01700-8. 

4.  Maroso M, Balosso S, Ravizza T, Liu J, Aronica E, Iyer AM, et al. Toll-like receptor 4 and high-mobility group box-1 are involved in ictogenesis and can be targeted to reduce seizures. Nat Med. 2010;16:413–419. doi: 10.1038/nm.2127 Webster KM, Sun M, Crack P, O’Brien TJ, Shultz SR, Semple BD Inflammation in epileptogenesis after traumatic brain injury. .J Neuroinflammation. 2017 Jan 13;14(1):10. doi: 10.1186/s12974-016-0786-1.

5.  Klein P, Dingledine R, Aronica E, Bernard C, Blümcke I, Boison D, Brodie MJ, Brooks-Kayal AR, Engel J Jr, Forcelli PA, Hirsch LJ, Kaminski RM, Klitgaard H, Kobow K, Lowenstein DH, Pearl PL, Pitkänen A, Puhakka N, Rogawski MA, Schmidt D, Sillanpää M, Sloviter RS, Steinhäuser C, Vezzani A, Walker MC, Löscher W Commonalities in epileptogenic processes from different acute brain insults: Do they translate?.Epilepsia. 2018 Jan;59(1):37-66. doi: 10.1111/epi.13965.

6.  Kamaşak T, Dilber B, Yaman SÖ, Durgut BD, Kurt T, Çoban E, et al. HMGB-1, TLR4, IL-1R1, TNF-α, and IL-1β: novel epilepsy markers? Epileptic Disord. (2020) 22:183–93. 10.1684/epd.2020.1155.

7. Aronica E, Crino PB. Inflammation in epilepsy: clinical observations. Epilepsia. 2011;52(Suppl 3):26–32. doi: 10.1111/j.1528-1167.2011.03033.x.

8.  Shi Y, Zhang L, Teng J, Miao W. HMGB1 mediates microglia activation via the TLR4/NF-κB pathway in coriaria lactone induced epilepsy. Mol Med Rep. (2018) 17:5125–31. 10.3892/mmr.2018.8485.

9.  Zhu M, Chen J, Guo H, Ding L, Zhang Y, Xu Y. high mobility group protein B1 (HMGB1) and Interleukin-1β as prognostic biomarkers of epilepsy in children. J Child Neurol. (2018) 33:909–17. 10.1177/0883073818801654. 

10.  Walker LE, Sills GJ, Jorgensen A, Alapirtti T, Peltola J, Brodie MJ, Marson AG, Vezzani A, Pirmohamed M. High-mobility group box 1 as a predictive biomarker for drug-resistant epilepsy: a proof-of-concept study. Epilepsia. 2022;63:e1–6. 10.1111/epi.17116.

11.  Kan M, Song L, Zhang X, Zhang J, Fang P. Circulating high mobility group box-1 and toll-like receptor 4 expressions increase the risk and severity of epilepsy. Braz J Med Biol Res. 2019. 10.1590/1414-431X20197374.

12. Paudel YN, Shaikh MF, Chakraborti A, Kumari Y, Aledo-Serrano Á, Aleksovska K, Alvim MKM, Othman I.HMGB1: A Common Biomarker and Potential Target for TBI, Neuroinflammation, Epilepsy, and Cognitive Dysfunction. Front Neurosci. 2018 Sep 11;12:628. doi: 10.3389/fnins.2018.00628.

Zebrafish – a valuable animal model

Current Research Advances, , ,

The zebrafish (Danio rerio), approximately 2-4 cm in length, has become a valuable animal model for investigations of neurological diseases and for use in high intensity screening to discover disease-ameliorating drugs.  In particular, this tiny non-mammalian animal has been of use in research into the genetics and pathophysiology of epilepsy and in the evaluation of anti-seizure drugs.  This blog will discuss this model and some of its contributions to understanding epilepsy.

Animal Models

There are many experimental models of epilepsy.  The greatest research effort has focused on rodent models of epilepsy (chemically or electrically-induced seizure, acute or chronic).  Interest in both experimental and natural models of epilepsy in the non-human primates (monkeys) has risen in recent years as has interest in smaller, non-mammalian models (amoeba, roundworm, fruit fly, zebrafish).  To be of scientific value, scientists must rigorously validate all models.  They must demonstrate neuronal electrical activity, neurotransmitter release, gene expression and response to antiseizure drugs comparable to that observed in patients with epilepsy.  As a result, animal models have contributed significantly to the identification of the multiple causes of epilepsy, genetic and environmental and are absolutely essential to the development of safe and effective antiseizure drugs.

Zebrafish Attributes that Make for a Successful Animal Model

Although rodent models of epilepsy have contributed considerably to our understanding of this disease,  rodents are expensive to breed, house and treat.  In contrast, the zebrafish is inexpensive to breed, maintain and treat.  Thus, large numbers are readily cared for with minimal expense.  Zebrafish mature quickly (~3 months), are highly fertile, giving rise to large numbers of offspring and can live in captivity up to 5 years.  The immature form, the larva, is transparent facilitating visual experimentation especially in observing gene expression and nerve activity.  Larvae and embryos are ideal for screening of large numbers of drugs for antiseizure activity.

Additionally and importantly, the zebrafish model relates well to rodent models and patients with epilepsy.  Firstly, 77% of zebrafish genes are similar to those in humans and approximately 80% of disease-associated genes are also present in zebrafish.  EEG recordings in drug-induced seizures in larvae and adult fish are similar to those observed in patients with epilepsy. 

Zebrafish mutants exist with alterations in genes involved in a number of human epileptic syndromes e.g. Dravet’s syndrome (see blog 17). Zebrafish mutants also show similar electrophysical activity as well as responses to anti-seizure drugs as evident in humans.  Additionally, zebrafish express brain neurotransmitters such as gamma-aminobutyric acid, glycine and acetylcholine. These are the same ones involved in human epilepsy. Neurotransmitters in zebrafish increase or decrease in response to seizure-producing and anti-seizure drugs as reported for rodents.

Contribution from Zebrafish Mutants

Many rare and not so rare genetically driven epilepses in humans have been successfully developed in zebrafish mutants.  One epilepsy of interest is Dravet syndrome, a grave pediatric epilepsy with severe seizures and associated cognitive deficits.  The disease origin is attributed in large part to a mutated neuronal sodium channel.  Zebrafish mutants lacking key elements of the sodium channel as in Dravet syndrome were developed and characterized (Baraban et al., 2013).  Mutant zebrafish exhibit abnormal brain electrical activity, related hyperactive locomotion and convulsions.  Furthermore, anti-seizure drugs that reduce seizures in Dravet syndrome also reduce seizures in zebrafish. Moreover, those that are ineffective in Dravet syndrome fail in mutated zebrafish. 

Zebrafish Mutants and Drug Evaluation

Using this model, over 300 chemicals and known drugs were tested (Baraban et al., 2017).  One drug, chemizole, an FDA approved antihistamine with a good safety profile, was highly effective.  This is a surprise but significant finding.   Since other antihistamines were ineffective, the mechanism of action of chemizole in seizure reduction suggests a unique unknown target. This is an opportunity to develop a new potentially novel antiseizure drug for Dravet syndrome.

Contribution from the proconvulsant-treated Zebrafish

The proconvulsant-treated zebrafish (also shortened to the PTZ-treated zebrafish) is a validated and reliable model of epilepsy.  It is used to identify the initial neuronal changes in epilepsy, to identify new anti-seizure drugs and recently to study the negative role of seizures on cognition.  PTZ (pentylenetetrazole) is a proconvulsant. Researchers treat zebrafish with PTZ to generate seizure activity comparable to generalized absence and myoclonic seizures in humans (Gawel et al., 2020).  Specifically, scientists anesthetize the zebrafish and inject the zebrafish intraperitonally (space between skin and intestines) with PTZ and/or an anti-seizure drug. Scientists then return the zebrafish to the testing tank for observations depending on the experimental protocol.   PTZ-induced seizures in zebrafish are dose and time-dependent and ameliorated by anti-seizure drugs such as valporic acid and diazepam (see blog 5).  Changes in locomotor activity following PTZ administration correlates with EEG activity.  

PTZ (proconvulsant)-treated Zebrafish results

As with Zebrafish mutants, researchers use the PTZ-treated zebrafish to screen for novel anti-seizure drugs.  Another interesting use is the study of the negative role of seizures in memory and learning.  Kundap et al., (2017) approached this by developing a T-maze for fish to evaluate memory and behavior.  In this study, researchers collected data on seizure activity, memory, neurotransmitter release and gene expression.  Interestingly, not only did seizure activity affect performance in the T-maze but the anti-seizure drugs that reduced seizure activity also reduced memory.  Tested drugs were phenytoin (Dilantin) oxcarbazepin (Trileptal), gabapentin (Gralise), diazepam (Diastat), rivastigmine (used in dementia ).  The authors conclude that this study provides “proof-of-concept” that the PTZ-treated zebrafish is a valuable model to study the negative effects of repetitive seizures on cognition.  These results emphasize the need to use cautiously those anti-seizure drugs that are additive to the harmful effects of seizure on memory.

Zebrafish Rendition

Conclusions

Investigations with validated animal models are an essential strategy to reveal the genetics and pathophysiology of epilepsy. Also, validated animal models are necessary to develop candidate drugs to eliminate seizures and cure epilepsy.  Although the most frequently used models for epilepsy are rodent models, the smaller, less expensive and equally useful model is the zebrafish.  Its many attributes and its validated relevance to genetics and etiology of human epilepsies may make it the model of choice for anti-seizure drug screening.

References

Baraban SC, Dinday MT, Hortopan GA. Drug screening in Scn1a mutant zebra-fish identifies clemizole as a potential Dravet syndrome treatment. Nat Com-mun 2013;4:2410.

Cunliffe VT et al., Epilepsy research methods update. Understanding the causes of epileptic seizures and identifying new treatments using non-mammalian model organisms Seizure 24 (2015) 44–51.

Gawel K et al., Seizing the moment: Zebrafish epilepsy models. Neuroscience and Biobehavioral Reviews 116 (2020) 1–20.

Kandratavicius L et al.,  Animal models of epilepsy: use and limitations.   Neuropsychiatric Disease and Treatment (2014):10 1693–1705.

Kundap UP et al., Zebrafish as a Model for Epilepsy-Induced Cognitive Dysfunction: A Pharmacological, Biochemical and Behavioral Approach Front. Pharmacol. 8:515, 2017.

Niemyer JE et al., Seizures initiate in zones of relative hyperexcitation in a zebrafish epilepsy model Brain (2022): 145; 2347–2360.

Precision Medicine – Promising Future

Current Research Advances, , ,

Introduction

There is a rising number of epilepsies that have been associated with genetic mutations called genetic variants (see Blog 14) .  For example, some of these epilepsies result from gene variants in ion channels that produce a loss of function or a gain of function.  Such changes promote seizures and other neurological deficits.  Specifically, the common gene variants account for 30% of adult general epilepsies. As more genetic expertise is developed, this number is expected to significantly increase.  Ongoing research from Ingo Helbig and collaborators at the Children’s Hospital of Philadelphia, Perelman School of Medicine and other University neurological departments) suggests that precision medicine is the promising future therapy of genetic-based epilepsies.

Precision Medicine

As reviewed by Knowles et al., (2022), precision medicine is an encompassing approach to optimal treatment.  In particular, it is based on classifying patients according to measurable biology, susceptibility to disease, and response to treatment to assure an efficacious intervention for those who would benefit and avoid those who would not.  For genetic epilepsies, “ideal precision treatment would correct a well-defined genetic mechanism in the context of individualized factors, to impart freedom from seizures and comorbidities” (Knowles et al., 2022).  However, this calls for integration of genetic analysis, natural history and clinical data into searchable databases.  Already, genetic testing alone yields better treatment and less hospitalizations.  Adding natural history and clinical data to genetic analysis would achieve considerably more treatment success.

Achievements Toward Precision Medicine

Identification of genetic variants in certain epilepsies allows for the application of molecular biology techniques to interfere with unwanted mRNA produced by genetic variants.  Therefore, appropriately designed oligonucleotides as well as vector-promoter-gene complexes successfully treat animal models of epilepsy. Currently, evaluation of the latter is ongoing in a clinical trial (NCT05419492) (https://clinicaltrials.gov/ct2/show/) for a genetic epilepsy. 

The discovery of the gene termed SCN8A exemplifies the feasibility of  rapid trajectory from gene identification to precision medicine.  Specifically, SCN8A (voltage-gated sodium channel gene) was discovered in 1995 in mice. Later, its pathological variants were associated with epileptic encephalopathies (seizures with neurological pathology).  By 2019, following intense research, the testing of a specific sodium channel inhibitor (NBI-921352) for the genetic variant was initiated.  Presently, “NBI-921352 is entering phase II proof-of-concept trials for the treatment of SCN8A-developmental epileptic encephalopathy (SCN8A-DEE) and adult focal-onset seizures” (Johnson et al., 2022).  Although this is impressive, “coordinated and systematic streamlining of the epilepsy precision medicine pipeline” from gene discovery to effective therapy is the essential goal (Knowles et al., 2022).

Challenges for Precision Medicine

Technological improvements in genome-wide association studies (GWAS) have facilitated the ability to screen large groups of patients to detect genetic variants associated with disease.  The result is the creation of large available, searchable databases of genetic variants.  However, not only must the gene variant associated with the disease be considered but more importantly, the unique expression of the gene variant in a particular patient must be defined. 

The expression of a gene variant is termed the phenotype of the disease. The phenotype includes all of the clinical observations and measurements in the patient relevant to the epilepsy. Therefore, gene expression may take many forms creating multiplicities and complexities of expression (heterogeneity) from patient to patient. Hence, the correct association of a gene variant with a defined phenotype poses a serious challenge.  According to Helbig and Tayoun, (2016) accurately defining the phenotype of a rare genetic variant, e.g. STXBP1 producing an epileptic encephalopathy represents a “hurdle” due to the phenotypic spectrum that it produces. 

To address this challenge, Helbig et al., (2019) characterized the phenotype of patients with “missense variant in AP2M1” (coding a protein needed for uptake mechanisms on the cell membrane).  The use of the searchable database, Human Phenotype Ontology, set up in 2008 to formalize the phenotypes of all diseases, enhanced this work.  More recently, the International League Against Epilepsy added neurological data and guidelines to it (Kohler et al., 2021).  This database presents “a standardized format to provide both terminology and semantics to a broad range of phenotypic features, including neurological features” (Helbig and Tayoun, 2016).  Consequently, with this type of analysis, researchers (Helbig and Tayou) were able to show “significant phenotypic overlap in individuals with the recurrent AP2M1”. 

Conclusions

To successfully treat epilepsy and its comorbidities both the genotype and phenotype of the epilepsy requires accurate assessment.  Researchers at Children’s Hospital of Pennsylvania and the Perelman School of Medicine and their collaborators are focused on this assessment.  The challenge lies in the interpretation of the epilepsy phenotype since both severe and less severe epilepsies are driven by the same genetic variants.  Sorting out this phenotypic heterogeneity will be worthwhile and lead to benefits of precision medicine for all patients.

References (pubmed)

Clatot J et al., SCN1A gain-of-function mutation causing an early onset epileptic encephalopathy. Epilepsia.64(5):  1318-1330, 2023.

Ganesan S, et al., A longitudinal footprint of genetic epilepsies using automated electronic medical record interpretation. Genet Med. 22(12):  2060-2070, 2020.

Helbig I et al., A Recurrent Missense Variant in AP2M1 Impairs Clathrin-Mediated Endocytosis and Causes Developmental and Epileptic Encephalopathy.  Am J Hum Genet .104(6):  1060-1072, 2019.

Helbig I, Tayoun ANA. Understanding Genotypes and Phenotypes in Epileptic Encephalopathies. Mol Syndromol  7:  172–181, 2016.

Kohler S et al.,  Human Phenotype Ontology in 2021, Nucleic Acids Research  49, Database issue D1207–D1217, 2021.

Knowles JK et al., Precision medicine for genetic epilepsy on the horizon: Recent advances, present challenges, and suggestions for continued progress. Epilepsia. 63(10):   2461–2475, 2022.

Lewis-Smith D et al., Phenotypic homogeneity in childhood epilepsies evolves in gene-specific patterns across 3251 patient-years of clinical data. Eur J Hum Genet. 29(11):  1690-1700, 2021.

Seiffert S et al., KCNC2 variants of uncertain significance are also associated to various forms of epilepsy. Front Neurol. 14: 1212079, 2023.

Xian J et al., Delineating clinical and developmental outcomes in STXBP1-related disorders. medRxiv. 2023 May 11;2023.05.10.23289776. doi: 10.1101/2023.05.10.23289776. Preprint

Early Detection of Seizures

Current Research Advances, , , ,

For decades,  the early detection of a seizure was a serious research effort.  It was obvious that if a seizure could be detected before its initiation, the patient would be better prepared to seek help to suppress the seizure.  However, early detection of a seizure with a lead time of hours proved to be unattainable.  Over the past decade, early detection of a seizure within minutes not hours of its initiation seemed a more reasonable objective.  This blog will focus on the state of research on early detection of seizures with advances developed by the epilepsy laboratory at Johns Hopkins University.

Introduction

As reviewed by Jouny et al., (2011), “The window of opportunity is the time of the earliest detectable changes in the EEG and the onset of disabling clinical symptoms”.  Thus, this provides a definition of early detection.  It may sound straightforward but there are numerous challenges to early detection of seizures. Jouny et al., reviews some of them.

1. Early detection of seizures –  Sensitivity and specificity

Early detection is just that.  Firstly, it must detect the earliest change in the electrical (neuronal) activity that leads to a seizure (called a true positive) and not an electrical event that would not lead to a seizure (called false positive).  Stated another way, the seizure is termed the ictal event and non seizure activity is the interictal activity.  Secondly, early detection must distinguish between lots of interictal activity and a smaller amount of ictal activity.  Many times initially there is little neuronal difference in the two.  Therefore, both sensitivity and specificity are required elements of any measurement targeting early detection of a seizure.

2.  Early detection of seizures – Capacity of microelectrodes.  

Microelectrodes in high density arrays are useful in obtaining detailed data of abnormal neuronal activity (termed pathological high frequency oscillations) indicative of  localized seizures. Specifically, researchers attach microelectrodes to the EEG or intracellular electrodes to capture as much information as possible.  Seizures that spread over extensive areas, unfortunately, surpass the present day recording capabilities of the microelectrode arrays.

3.  Early detection of seizures – Sampling rate.

Higher sampling rates are desirable but this produces more data for analysis.  This requires more powerful computers and better electronics.  Improvements here are needed to detect unique potential changes that distinguish the initiation of the seizure and the seizure itself from all the electrical activity in between.

Current Advances in Early Detection of Seizures.

Early detection devices depend on what is called support vector machines (SVM) which are a type of machine learning algorithms.  “Several algorithms have been developed for early-seizure-onset detection with real-time capabilities for scalp-EEG” (Ehrens et al., 2022).  In particular, they include early detection algorithms worldwide from labs in the Netherlands (Bogaarts et al., 2016); in India (Sridevi et al., 2019); in Italy (Chisci et al., 2010); in Austria/Netherlands (Fürbass et al., 2015); in Germany (Meier et al., 2008; Manzouri et al., 2021); in Canada (Saab and Gotman, 2005) and in the US, (Minasyan et al., 2010, Yidiz et al., 2022, Ehrens et al., 2022). 

Application of early detection algorithms

Early detection devices are appropriately evaluated in an epilepsy monitoring unit (EMU).  The EMU needs to gather reams of data for precise surgical intervention in patients with epilepsy that are resistant to drugs.  The Johns Hopkins Epilepsy Laboratory developed an “dynamical and self-adapting algorithm” (Ehrenss et al., 2022) which detects in real time the seizure phase of early onset as well as the seizure itself.  It is patient specific and does not require prior EEG training.  Basically, the ” algorithm uses a dynamic training set, based on a 20-min dataset that is updating every second” and ” requires no prior training because the algorithm compares the past 20 minutes of activity with the current activity and looks for novelty” (Ehrens et al., 2022)  A processing time of 0.5 seconds allows  algorithm processing, removal of artifacts, and extraction of essential features in the 20 minute learning session.

One-class SVM in early detection of seizures.

This algorithm, referred to as a one-class SVM, was tested in 35 patients with epilepsy (male: female, 62%:38%, 34 years average age) in the Johns Hopkins Hospital EMU.  “Patients were implanted intracranially with a combination of subdural grids, strips and/or depth electrodes to record cortical EEG and stereo EEG signals respectively ” (Ehrens et la., 2022).   For other information on intracranial recordings, check out Blog 10.

As presented above, the algorithm collected EEG data, eliminated non-neural artifacts and identified features essential to seizure identification  This preprocessing trains the one-class SVM and determines novelty.  The output is “post processed” such that it will then identify and signal the detection of an epileptiform event in real time. 

Although multiple SVM configurations were evaluated, the single SVM configuration yielded the best results.  The John Hopkins Laboratory SVM achieved a rate of 87% for true positives and a rate of 1.25% for false positive/hour.  That is, the SVM algorithm detected a seizure correctly 87% of the time and was wrong 1.25% of the time.  The true positive rate increased another 6% points and the false positives declined by half with removal of artifacts post analysis.  The mean detection latency (early detection) was 10.4 seconds. 

Conclusions

There is definitely a need for devices capable of early detection of seizures.  In the EMU, early detection alerts the staff and enables immediate treatment of the patient with epilepsy.  Outside the EMU, an early detection device would dramatically enhance the quality of life of patients with epilepsy.  The algorithm (one class SVM) is moving closer to achieving these goals.  Presently, 100% sensitivity of early detection is achievable in 74% of patients in the EMU setting with the unique algorithm developed at Johns Hopkins Laboratory (Ehrens et al., 2022). 

References (pubmed)

Bogaarts JG et al.,. Improved epileptic seizure detection combining dynamic feature normalization with EEG novelty detection. Med Biol Eng Comput  54:1883–92, 2016.

Chisci L. et al., Real-time epileptic seizure prediction using AR models and support vector machines. IEEE Trans Biomed Eng. 57(5):1124-32, 2010.

Ehrens et al., Dynamic training of a novelty classifier algorithm for real-time detection of early seizure onset.  Clin Neurophysiol.  135: 85–95, 2022.

Furbass F. et al., Prospective multi-center study of an automatic online seizure detection system for epilepsy monitoring units Clin Neurophysiol. 126(6):1124-1131, 2015.

Jouny CC. et al., Improving Early Seizure Detection Epilepsy Behav.  22(Suppl 1): S44–S48, 2011.

Manzouri F et al., A Comparison of Energy-Efficient Seizure Detectors for Implantable Neurostimulation Devices Front Neurol 12:703797, 2022.

Meier R et al., Detecting epileptic seizures in long-term human EEG: a new approach to automatic online and real-time detection and classification of polymorphic seizure patterns J Clin Neurophysiol. 25(3):119-31, 2008.

Minasyan GR et al., -specific early seizure detection from scalp electroencephalogram J Clin Neurophysiol. 27(3):163-78, 2010.

Saab ME, Gotman J. A system to detect the onset of epileptic seizures in scalp EEG Clin Neurophysiol. 116(2):427-42, 2005.

Sridevi V, et al.,. Improved Patient-Independent System for Detection of Electrical Onset of Seizures. J Clin Neurophysiol 36:14–24, 2019.

Yidiz I et al., Unsupervised seizure identification on EEG Comput Methods Programs Biomed. 215:106604, 2022.

Anti-Seizure Drugs of the Future

Future Anti-seizure Drugs, ,

Introduction

There are now more than 30 anti-seizure drugs available to treat seizures, the manifestation of epilepsy.  Despite the ongoing effort to develop novel drugs over the past century, none of the drugs in use today cure epilepsy.  Additionally, approximately 30% of patients with epilepsy are not helped with these drugs and many patients taking anti-seizure medications experience adverse reactions.  Thus, there is a need for future anti-seizure drugs with specificity, with no adverse side effects, with greater tolerability and with a potential to cure epilepsy.  This blog will briefly review the development of present day anti-seizure drugs and describe the pipeline of future anti-seizure drugs.

History of Anti-seizure Drugs

A detailed history of the development of anti-seizure drugs has been reviewed by Loscher and Klein (2021).   Potassium bromide  (1850s) and phenobarbital (1910) were the first two drugs to treat epilepsy.  Modification of the barbital structure gave rise to the first generation of anti-seizure drugs (e.g. phenytoin, acetazolamide, ethosuximide of the 13 available by 1958).

Second generation anti-seizure drugs appeared from 1960 to 1975 with structures different from first generation anti-seizure drugs and included (valproate, carbamazepine and the benzodiazepines).  Subsequently, third generation anti-seizure drugs were developed with the objective of “targeting” a specific molecular component of excessive neuronal activity e.g. sodium channel or a neurotransmitter.  Third generation drugs of which there are 20 or more include for example, lamotrigine (lamictal), vigabatrin (sabril), levetiracetam (Kappra), and cenobamate (xcopri).

The specific CNS targets on which the third generation of drugs exert their anti-seizure effects have been reviewed in Assessment 6 – Epilepsy Medication – Need to Know Information.  Some of the third generation anti-seizure drugs exhibit fewer side effects such as reduced potential for teratogenicity (harm to fetal formation), reduced skin sensitivities (allergies), less interference with other drugs and hence greater tolerability.  However, “most novel (third-generation) anti-seizure medications are not more effective than older drugs” Losher and Klein, (2021).  Consequently, the number of patients failing to experience seizure suppression has not changed despite considerable drug discovery effort. 

Experimental Identification of Anti-seizure drugs

The majority, if not all, of the anti-seizure drugs on the market were identified in select rodent models of seizures.  The main ones are 1) MES or maximal electroshock useful in identification of drugs effective against generalized tonic-clonic seizure e.g. grand mal seizure, 2) 6-Hz seizure test and chronic kindling models important in the identification of  drugs suppressing focal-onset seizures and 3) genetic rat models for identification of drugs affecting generalized absence seizures (Loscher and Klein, 2021).  Significant drug discovery assistance has been provided by the Epilepsy Therapy Screening Program supported by National Institute of Neurological Disorders and Stroke (Kehne et al., 2017). 

Why third generation drugs are not more efficacious than older drug?

The main answer relates to preclinical drug discovery.  The standard rodent models of epilepsy have been undeniably important in anti-seizure drug development.  But as emphasized by Loscher and Schmidt (2011) there is now a clear need for additional animal models and new innovative models that can identify more efficacious anti-seizure drugs in general and anti-seizure drugs effective in patients resistant to current drugs.  More importantly, newer more relevant models, although more complex and time-consuming are needed to identify drugs capable of the prevention and cure of epilepsy.   

Another reason for the failure of third generation anti-seizure drugs to achieve greater efficacy relates to the clinical trial protocols.  For drug approval, new drugs are compared to either placebo or a low dose of an approved drug.  This lowers the bar to development of  greatly improved drugs.  The result is that comparison of efficacy head-to-head of a new drug and an approved drug remains unknown, stalling progress.   Ideally, the best clinical trial compares an approved drug with a new drug at several doses.  Expense and large number of required recruits limit this trial type.  Sadly, several  large pharmaceutical firms, which could handle large clinical trials, have discontinued their epilepsy programs; remaining smaller companies are focusing on rare genetic epilepsies.

Future Drugs in the Pipeline

There are over 20 drugs currently in Phase I, II and a few in Phase III trials.  There are 8 promising compounds still in preclinical studies but nearing a phase I clinical trial.  Many of these novel compounds have mechanisms of action different from approved drugs on the market.  The following mechanisms are of interest.

Positive Allosteric Modulators

There are 8 compounds in this group.  Five of the eight new compounds act on the GABA-A receptor.  This receptor exerts inhibitory effects on neuronal activity.  Many available drugs already target the GABA-A receptor, either through augmentation of this receptor, prevention of the GABA-A neurotransmitter degradation or reuptake.  In contrast, future compounds in development seek to stimulate a regulatory site on the receptor so as to modulate its effects on nerve transmission.  Other compounds in this group target the excitatory glutamate receptors (mGlu2 or AMPA) via positive allosteric modulation.  In this case, modulation serves to suppress nerve activity.

Potassium Channel Openers

Despite the withdrawal of the first generation potassium channel opener, retigabine, due to limited use and toxicities, there are two second generation potassium channel openers in phase II trials and one in preclinical studies.  The expectation is that enhancing the opening of potassium channels will hyperpolarize the nerve membrane and dampen excessive nerve activity.

Calcium Channel Inhibitors/Sodium Channel Modulators

Two novel compounds are in phase I and II that block T-type calcium channels and one in preclinical studies that is considered broad spectrum in blocking both calcium channels and sodium channels.  There are already several approved calcium channel blockers such as ethosuximide (zarontin), methsuximide (celontin), eslicarbazepine (aptiom) and possibly valproate (Loscher and Klein, 2021).

One novel inhibitor of the sodium channel (NaV 1.6) is in phase I trial and another compound which acts as an modulator of sodium channel activity is in preclinical studies.  There are also several sodium channel inhibitors already on the market.

Anti-inflammatory Mechanisms

Compounds in development are focused on different inflammatory mechanisms.  These include general anti-inflammatory activity, inhibition of specific inflammatory enzymes, inhibition of leukocyte migration into the brain, and antagonism of an inflammatory receptor e.g. Il-1 or its production.  Unfortunately,  inhibition of leukocyte migration has already failed in a Phase IIa  trial and data from others are considered mediocre.

Multiple Mechanisms

Compounds in this group modulate multiple targets.  For example, one compound will modulate specific proteins that carry the neurotransmitter to the nerve terminal.  The same compound will also exert benzodiazepine-like effects.  Another compound stimulates serotonin receptors and inhibits sigma-1 receptors involved in protein synthesis in nerves.  Others block sodium and calcium channels plus modulating other receptors.  Thus far this approach has not been successful with generally poor efficacy or poor reproducibility in different trials.

Other Mechanisms

Several compounds will treat rare but devastating infancy and early childhood-onset epilepsies such as Dravet and Lennox-Gastaut syndromes.  Two of these compounds seek to reduce brain metabolism, with either inhibition of the breakdown of glucose or the formation of cholesterol.  Others act by stimulating protein formation or inhibiting formation of acetylcholine, a neurotransmitter involved in memory.

Fate of Future Drugs

Future anti-seizure drugs include compounds with novel mechanisms of action (positive allosteric modulation) and known mechanisms of action (T-type calcium channel inhibitors).  Dampening inflammation or combining multiple mechanisms in one compound does not seem of value.  Whether these unique compounds will succeed in becoming an antiseizure drug to help those currently without drug therapy or become fourth generation drugs no better than previous drugs, remains to be determined.

As emphasized in several reviews, the major problem of understanding epilepsy remains unresolved.  That is, there are a wide variety of epilepsies, most with unknown causes.  It is, therefore, impossible to match a specific drug with a known mechanism of action to a person with epilepsy for which this  is only a general description of the seizure.  Drug selection by the physician is and remains empirical.  Rational drug selection even from a large assortment does not exist for the patient with epilepsy. 

Better Efficacy and Tolerability?

Will these future drugs exhibit a better efficacy and safety profile than the third generation drugs?  There is an awareness for improved safety and tolerability.  This was true for third generation drugs.  Some of the third generation drugs exhibit different pharmacokinetics and interact less if at all with other drugs. 

The fact remains that all these drugs, current and future are developed to suppress seizures. This dampens CNS activity.  And they all were screened in standard preclinical seizure models.  As a result, all will influence numerous other pathways in the brain to cause minor to major unwanted changes.  Specificity in anti-seizure drug discovery is needed but this is impossible since epilepsy itself remains a black box.  Perhaps better drugs will come with more relevant animal models.  At present correcting genetic defects responsible for some epilepsies is the most promising approach and will benefit a few that desperately need it.

References

Loscher W. Kleins P. The Pharmacology and Clinical Efficacy of Antiseizure Medications:

From Bromide Salts to Cenobamate and Beyond. CNS Drugs (2021) 35:935–963

Kehne JH, Klein BD, Raeissi S, Sharma S. The National Institute of Neurological Disorders and Stroke (NINDS) Epilepsy Therapy Screening Program (ETSP) Neurochem Res (2017) 42:1894–1903

Loscher W Schmidt D. Modern antiepileptic drug development has failed to deliver: Ways out of the current dilemma Epilepsia, 52(4):657–678, 2011

Gene Therapy for Epilepsy

Future Therapy, , , ,

Introduction

Epilepsy is treated today with anti-seizure medications and in select cases, with surgery.  Although there are over 25 possible anti-seizure drugs, approximately 30% of patients with epilepsy do not respond to drug treatment and those who do, frequently endure adverse side effects.  Thus, there is an urgency to find better therapies.  One potential future strategy is gene therapy for epilepsy (see other strategies, Noncoding RNAs: diagnosis/cure for epilepsy?).

Gene therapy for diseases other than epilepsy have shown success (https://learn.genetics.utah.edu/ content/genetherapy/success/).  These diseases include immune deficiency diseases, hereditary blindness, hemophila and Parkinson’s disease.  In the future, epilepsy may also benefit from gene therapy.   This blog is based on several excellent reviews (see References below) that describe the reality of this future therapy.

What is gene therapy?

Gene therapy is a special technique whereby a gene carried by a vector is injected into a patient.  The selected gene is one that would replace, optimize or inhibit the disease-producing gene.  The vector can be viral or synthetic.  Viral vectors are either adeno-associated viruses, lentiviruses or a herpes simplex viruses.  These viruses are modified so that they can no longer divide and infect.  Therefore, they serve only as carriers.  Synthetic vectors are non viral vectors such as lipids and polymers.  Although not as efficient as viral vectors, synthetic vectors get into the brain readily and are easily manufactured.

What genes are important in epilepsy?

Researchers have identified several genes that influence different aspects of epilepsy.  Genes identified thus far are

a)  membrane channels that conduct ions e.g. sodium and potassium;

b)  receptors at the junction of nerves e.g. the NMDA receptor;

c)  neuromodulators influencing nerve excitability e.g. neuropeptide Y;

d)  genes involved in influencing DNA function e.g. adenosine and associated enzyme, adenosine kinase.

Ideally, gene therapy for epilepsy has three areas of focus.  This includes gene therapy for prevention of  disease initiation, eradication of seizures and amelioration of those brain areas subsequently changed by epilepsy.  It is thought that seizure inhibition is likely to be the first successful target for gene therapy.

Assessment of gene therapy

Animal Models

Gene therapy has been primarily investigated in animal (mouse, rat) models of epilepsy.  Most models evaluate one aspect of epilepsy.  Accordingly, there exists the PTZ model in which an injection of convulsant-inducing pentylenetetrazol causes generalized seizures.  This acute model has been helpful in screening for anti-convulsant drugs.  Another model (termed latent) requires a waiting period for seizure development following a particular insult (pilocarpine, kainic acid).  The initial phase is thought to mimic known injuries e.g. stroke, fever, trauma in man.  This type of model has considerable value in that the initiating changes, the seizures and associated cognitive changes may be investigated.  There also exist models of spontaneous seizures. 

Promising results in animal models

Ion Channels – target of gene therapy

Most of the current anti-seizure drugs block the defective sodium channel located on nerves. Drug-induced inhibition reduces the nerve impulse and dampens the unwanted excitability of the seizure.  Conversely, super activation of the potassium channel has a similar effect.  Therefore, gene therapy to correct defective sodium and potassium channels is reasonable. 

In mouse models analogous to infant epilepsies, several studies showed that gene therapy for the sodium channel inhibited seizures and improved other brain deficiencies.   In two rat models of epilepsy (focal neocortical and temporal lobe), gene therapy of a modified potassium channel effectively suppressed seizures.

Neurotransmitter Receptors – target of gene therapy

Nerves communicate with one another via release of small molecules called neurotransmitters that act on specific receptors.  Two neurotransmitters of interest in epilepsy are gamma-aminobutyric acid (GABA)  and N-methyl-D-aspartic acid (NMDA).  The former acts on its receptor to inhibit nerve activity and the latter acts on its receptor to enhance it.  Thus, these neurotransmitter receptors are potential gene therapy targets. 

Enhancing the number and/or activity of  the receptors stimulated by GABA  decreases seizure activity in animal models.  Conversely, modification of the receptors responding to the excitatory stimulation of NMDA attenuates seizures in animal models. 

Neuromodulators – target of gene therapy

There exist an abundance of neuromodulators that not only influence the extent of neuronal traffic but also affect nerve cell integrity.  Neuromodulators are thought to play a role in collateral changes with epilepsy.  

Several modulators of nerve excitability such as neuropeptide Y (NPY), dynorphin, fibroblast growth factor 2, brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor have been evaluated in animal models.  Vector carriers varied from adenovirus (NPY) to synthetic carriers (glial cell neurotrophin) injected directly into the brain.  Depending on the models, diminished seizures or reduced abnormal nerve cell growth  was reported. The effects were stable for months to one year.

DNA modulators – target of gene therapy

Adenosine and its metabolic enzyme, adenosine kinase play a role in epilepsy.  An increase in the enzyme activity results in a decline in the concentration of adenosine.  Adenosine is an important player in gene expression.  Hence, it influences what genes are “on” and which are “off”.  Patients with epilepsy are deficient in adenosine.  In rat models, implantation of a synthetic vector-releasing adenosine into the epileptic brain beneficially influences gene expression, retards abnormal neuronal growth and decreases seizure frequency.

Clinical trial using gene therapy

There is one clinical trial in progress to evaluate the safety and efficacy of gene therapy in epilepsy. This is the ENDEAVOR trial.  Its protocol is to test adenoviral-delivered sodium channel gene to infants 6-36 months with Dravet Syndrome.  Dravet syndrome is a severe form of epilepsy with seizures, mental and growth retardation and sudden death potential.  Many with Dravet Syndrome have a single mutation in the sodium channel making gene therapy possible.  This trial will evaluate the safety and efficacy of ETX101 (vector-promoter-gene complex) injected into a cerebral ventricle (https://clinicaltrials.gov/ct2/show/NCT05419492).

Challenges

Gene therapy has the potential to cure some forms of epilepsy. The ENDEAVER trial is one to follow. 

However, there remain considerable challenges to overcome.  These challenges include the complexity of genetic mutations.   Although there are a few epilepsies tied to one gene,  most epilepsies involve multiple genes..  Even when only one gene is identified, there is no guarantee that the defective gene acts the same way in each patient with that particular type of epilepsy.  Vector selection is also a challenge since the vector must deliver the gene to the correct cell type, gain access to the brain when given intravenously, persist for an adequate amount of time and not induce an unwanted immunological response.  Much of this has been and continues to be resolved in animal models, but gene therapy still awaits well-designed safety and efficacy studies in man.

Gene Therapy

References

Balestrini S, SisodiyaSM. Pharmacogenomics in epilepsy.  Neuroscience Letters 667: 27–39, 2018.

Bouza AA, Isom LL. Chapter 14: Voltage-gated sodium channel β subunits and their related diseases. Handb Exp Pharmacol. 246:   423–450, 2018.

Thakran S et al., Genetic Landscape of Common Epilepsies:  Advancing towards Precision in Treatment Int. J. Mol. Sci. 21: 7784, 2020.

Zhang L, Wang Y. Gene therapy in epilepsy Biomedicine & Pharmacotherapy 143: 112075, 2021.