A novel anticonvulsant modulates voltage-gated sodium channel inactivation and prevents kindling-induced seizures

Authors

  • Muhammad N. Ashraf,

    1. H.E.J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi, Pakistan
    2. Department of Psychiatry and Behavioural Neurosciences, Faculty of Medicine, McMaster University, Hamilton, Ontario, Canada
    3. Robarts Research Institute, Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
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  • Cezar Gavrilovici,

    1. Robarts Research Institute, Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
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  • Syed U. Ali Shah,

    1. H.E.J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi, Pakistan
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  • Farzana Shaheen,

    1. H.E.J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi, Pakistan
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  • Muhammad I. Choudhary,

    1. H.E.J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi, Pakistan
    2. Dr. Panjwani Center for Molecular Medicine and Drug Research, International Center for Chemical and Biological Sciences, University of Karachi, Karachi, Pakistan
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  • Atta-ur Rahman,

    1. H.E.J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi, Pakistan
    2. Dr. Panjwani Center for Molecular Medicine and Drug Research, International Center for Chemical and Biological Sciences, University of Karachi, Karachi, Pakistan
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  • Margaret Fahnestock,

    1. Department of Psychiatry and Behavioural Neurosciences, Faculty of Medicine, McMaster University, Hamilton, Ontario, Canada
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  • Shabana U. Simjee,

    1. H.E.J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi, Pakistan
    2. Dr. Panjwani Center for Molecular Medicine and Drug Research, International Center for Chemical and Biological Sciences, University of Karachi, Karachi, Pakistan
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  • Michael O. Poulter

    Corresponding author
    1. Robarts Research Institute, Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
    • H.E.J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi, Pakistan
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Address correspondence and reprint requests to Michael O. Poulter, Director Graduate Program in Neuroscience UWO, Molecular BrainResearch Group, Robarts Research Institute, Dept of Physiology & Pharmacology, Faculty of Medicine, University of Western Ontario, 100 Perth Drive, London Ontario, Canada N6A 5K8. E-mail: mpoulter@robarts.ca

Abstract

Here, we explore the mechanism of action of isoxylitone (ISOX), a molecule discovered in the plant Delphinium denudatum, which has been shown to have anticonvulsant properties. Patch-clamp electrophysiology assayed the activity of ISOX on voltage-gated sodium channels (VGSCs) in both cultured neurons and brain slices isolated from controls and rats with experimental epilepsy (kindling model). Quantitative transcription polymerase chain reaction (qRT-PCR) (QPCR) assessed brain-derived neurotrophic factor (BDNF) mRNA expression in kindled rats, and kindled rats treated with ISOX. ISOX suppressed sodium current (INa) showing an IC50 value of 185 nM in cultured neurons. ISOX significantly slowed the recovery from inactivation (ISOX τ = 18.7 ms; Control τ = 9.4 ms; p < 0.001). ISOX also enhanced the development of inactivation by shifting the Boltzmann curve to more hyperpolarized potentials by −11.2 mV (p < 0.05). In naive and electrically kindled cortical neurons, the IC50 for sodium current block was identical to that found in cultured neurons. ISOX prevented kindled stage 5 seizures and decreased the enhanced BDNF mRNA expression that is normally associated with kindling (< 0.05). Overall, our data show that ISOX is a potent inhibitor of VGSCs that stabilizes steady-state inactivation while slowing recovery and enhancing inactivation development. Like many other sodium channel blocker anti-epileptic drugs, the suppression of BDNF mRNA expression that usually occurs with kindling is likely a secondary outcome that nevertheless would suppress epileptogenesis. These data show a new class of anti-seizure compound that inhibits sodium channel function and prevents the development of epileptic seizures.

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Isoxylitones, isolated from Delphinium denudatum root prevent seizure induction. Activity was tested on voltage-gated sodium channels (VGSCs) in both cultured neurons and brain slices isolated from controls and rats with experimental epilepsy (kindling model). Isoxylitones enhanced sodium channel inactivation with an IC50 of about 200 nM. Our findings suggest isoxylitones as a potential novel anticonvulsant agent.

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