A Caenorhabditis elegans assay of seizure-like activity optimised for identifying antiepileptic drugs and their mechanisms of action

J Neurosci Methods. 2018 Nov 1:309:132-142. doi: 10.1016/j.jneumeth.2018.09.004. Epub 2018 Sep 3.

Abstract

Background: Epilepsy affects around 1% of people, but existing antiepileptic drugs (AEDs) only offer symptomatic relief and are ineffective in approximately 30% of patients. Hence, new AEDs are sorely needed. However, a major bottleneck is the low-throughput nature of early-stage AED screens in conventional rodent models. This process could potentially be expedited by using simpler invertebrate systems, such as the nematode Caenorhabditis elegans.

New method: Head-bobbing convulsions were previously reported to be inducible by pentylenetetrazol (PTZ) in C. elegans with loss-of-function mutations in unc-49, which encodes a GABAA receptor. Given that epilepsy-linked mutations in human GABAA receptors are well documented, this could represent a clinically-relevant system for early-stage AED screens. However, the original agar plate-based assay is unsuited to large-scale screening and has not been validated for identifying AEDs. Therefore, we established an alternative streamlined, higher-throughput approach whereby mutants were treated with PTZ and AEDs via liquid-based incubation.

Results: Convulsions induced within minutes of PTZ exposure in unc-49 mutants were strongly inhibited by the established AED ethosuximide. This protective activity was independent of ethosuximide's suggested target, the T-type calcium channel, as a null mutation in the worm cca-1 ortholog did not affect ethosuximide's anticonvulsant action.

Comparison with existing method: Our streamlined assay is AED-validated, feasible for higher throughput compound screens, and can facilitate insights into AED mechanisms of action.

Conclusions: Based on an epilepsy-associated genetic background, this C. elegans unc-49 model of seizure-like activity presents an ethical, higher throughput alternative to conventional rodent seizure models for initial AED screens.

Keywords: Anticonvulsant; Caenorhabditis elegans; Calcium channel; Drug screens; Epilepsy; Ethosuximide; GABA receptor; Pentylenetetrazol.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Anticonvulsants / administration & dosage*
  • Caenorhabditis elegans
  • Caenorhabditis elegans Proteins / genetics
  • Convulsants / administration & dosage
  • Disease Models, Animal*
  • Drug Evaluation, Preclinical / methods*
  • Ethosuximide / administration & dosage
  • Pentylenetetrazole / administration & dosage
  • Receptors, GABA-A / genetics
  • Seizures / chemically induced
  • Seizures / prevention & control*

Substances

  • Anticonvulsants
  • Caenorhabditis elegans Proteins
  • Convulsants
  • Receptors, GABA-A
  • Unc-49 protein, C elegans
  • Ethosuximide
  • Pentylenetetrazole