Elsevier

Brain Research

Volume 1657, 15 February 2017, Pages 347-354
Brain Research

Research report
Antiepileptic drugs prevent seizures in hyperbaric oxygen: A novel model of epileptiform activity

https://doi.org/10.1016/j.brainres.2016.12.032Get rights and content

Highlights

  • Hyperbaric oxygen (HBO2) can trigger epileptiform seizures.

  • Some antiepileptic drugs (AEDs) prevent or delay seizure onset in HBO2.

  • AEDs with known mechanisms-of-action can probe events leading to seizures in HBO2.

  • HBO2 seizures and other seizure disorders may have some common mechanisms.

  • HBO2 is uniquely suited to investigate the oxidative stress hypothesis of seizure disorders.

Abstract

Breathing oxygen at sufficiently elevated pressures can trigger epileptiform seizures. Therefore, we tested the hypothesis that pre-treatment with FDA-approved antiepileptic drugs could prevent seizure onset in hyperoxia at 5 atmospheres absolute. We selected drugs from two putative functional categories, Na+-channel antagonists and GABA enhancers, each administered intraperitoneally at four doses in separate groups of C57BL/6 mice. The drugs varied in efficacy at the doses used. Of the five tested Na+-channel antagonists, carbamazepine and lamotrigine more than tripled seizure latency compared to values seen in vehicle controls. Primidone, zonisamide and oxcarbazepine were less effective. Of the four GABA reuptake inhibitors, tiagabine and vigabatrin also increased seizure latency by more than three times control values; valproic acid was less effective, and the GABA synthesis promoter gabapentin was intermediate in effectiveness. We infer that Na+-channel function and GABA neurotransmission may be critical targets in the pathophysiology of CNS O2 toxicity. Because these essential components of neuronal excitation and inhibition are also implicated in the pathogenesis of other seizure disorders, including generalized epilepsy, we propose that, at some level, common pathways are involved in these pathologies, although the initiating insults differ. Furthermore, hyperoxic exposures are not known to cause the spontaneously-recurring seizures that characterize true clinical epilepsy. Nonetheless, experimental studies of hyperbaric oxygen toxicity could provide new insights into molecular mechanisms of seizure disorders of various etiologies. In addition, the neuropathology of hyperbaric oxygen is particularly relevant to the hypothesis held by some investigators that oxidative stress is an etiological factor in clinical epilepsies.

Introduction

Oxygen is a convulsant when breathed for a sufficient time at partial pressures of 2.5 atmospheres absolute (ATA) or above, and latency to onset of epileptiform patterns on the EEG and tonic-clonic neuromotor responses is inversely proportional to inspired Po2. This has been well established in human and animal studies that have been conducted for many years, primarily to devise procedures for protecting personnel exposed to hyperbaric oxygen (HBO2) in certain occupational and therapeutic environments (Balentine, 1982, Behnke et al., 1935, Clark and Thom, 2003, Donald, 1947a, Donald, 1947b, Paton, 1967). Vulnerable groups include military and civilian divers, crew attempting escape from a disabled submarine and patients undergoing hyperbaric oxygen therapy.

Although many drugs have been developed to prevent seizures of various etiologies, particularly those of broad clinical relevance, none have been specifically formulated to protect against seizures in HBO2, and it is unlikely that pharmaceutical companies would undertake the research needed to do so, since the human population at risk is small. Up to now, the only reliable methods for avoiding neurotoxicity in HBO2 have been to limit the dose and duration of hyperbaric oxygenation.

Although the events or conditions that initiate seizures in hyperbaric oxygen and in other seizure disorders may differ, the final common pathways and ultimate molecular targets may be similar. Indeed, some investigators have proposed that oxidative stress plays a contributory role in epilepsy (Patel, 2004, Pearson et al., 2015, Zsurka and Kunz, 2015). We reasoned, therefore, that antiepileptic drugs (AEDs) could prevent or delay seizures of CNS O2 toxicity and as a corollary, AEDs with known mechanisms-of-action might be used as investigative probes to further elucidate events that evoke hyperoxic seizures, although the true mechanisms of action of some of these drugs are not completely understood and may not fit neatly into their nominal functional classes. Furthermore, if a broad range of AEDs are found to prevent or delay seizures in HBO2, and if there are parallels between the ictal events in HBO2 and those seen in other seizure disorders, the hyperbaric model could elucidate mechanisms of various seizure-related disorders, including those due to the acquired and idiopathic epilepsies, traumatic brain injury and other causes. However, it must be understood that most animal models used in epilepsy research only simulate the seizures of epilepsy rather than epilepsy itself (Loscher, 2011), and this would apply to HBO2 as well.

In this study we assessed the ability of nine FDA-approved AEDs, administered individually, to increase seizure latency in mice exposed to 100% oxygen at 5 ATA for 60 min. This level and duration of hyperoxia reliably elicits seizures in this species in a reasonable period of time (60 min or less) without producing a significant degree of direct cardiopulmonary injury (Demchenko et al., 2007).

Since abnormal propagation of excitatory neurotransmission and attenuation of inhibitory neurotransmission are established pathogenic factors in clinical epilepsies (Jefferys, 2010) and are also assumed to be factors in CNS O2 toxicity (Colton and Colton, 1982, Dean et al., 2003, Demchenko and Piantadosi, 2006), we chose to evaluate the protective efficacy in HBO2 of AEDs from two functional classes relevant to excitatory and inhibitory functions: sodium-channel antagonists and GABA transmission enhancers. We compared our findings with published values for the efficacy of the same AEDs in a well-established animal model of epileptic seizures, maximal electroshock (MES).

Section snippets

Seizure activity in vehicle-treated mice

The 24 mice treated with vehicle (0.9% NaCl or DMSO) and exposed to HBO2 at 5 ATA exhibited neuromotor responses that progressed in 2 or 3 stages, comparable to those of the Racine Scale (Racine, 1972). In stage I, restlessness, intensive grooming, slight tremors, twitching vibrissae and transient muscular spasms were observed. In stage II, persistent, rhythmic spasms appeared in the face and body along with bilateral forelimb clonus and escape behaviors. Stage III, if it occurred, was

Discussion

We have demonstrated that a range of FDA-approved AEDs, of two functional classes, can significantly delay seizure onset in extreme hyperoxia. Although other investigators have tested the protective efficacy of two such drugs in HBO2, CBZ and VGB (Bitterman and Halpern, 1995, Hall et al., 2013, Harel et al., 1978, Reshef et al., 1991, Tzuk-Shina et al., 1991), we know of no study in which the anticonvulsant efficacies of multiple AEDs were compared in hyperbaric hyperoxia.

Among the Na+-channel

Conclusions

The findings presented here support our hypothesis and its corollary: a range of FDA-approved AEDs can prevent or delay seizures in extreme hyperoxia, and AEDs with known mechanisms-of-action can serve as investigative probes to elucidate seizure mechanisms in HBO2. Thus, some of the AEDs we tested increased seizure latency to more than triple that observed in vehicle controls. Furthermore, the significant protective efficacy in HBO2 of AEDs known to block Na+-channel function or to enhance

Grants

This work was supported by the Office of Naval Research, United States, Grant N00014-15-1-2072 (to C.A. Piantadosi) and the Russian Federation for Basic Research Grant 15-04-05970 (to I.T. Demchenko).

Methods and materials

Experiments were performed on conscious C57BL/6 mice (weighing 19-25 g and approximately 2.5 months in age) at the Center for Hyperbaric Medicine and Environmental Physiology, Duke University Medical Center (Durham, NC, USA), and at the Institute of Evolutionary Physiology and Biochemistry, Russian Academy Sciences (St. Petersburg, Russia). Animal use protocols were approved independently by the Institutional Animal Care and Use Committee of Duke University and the Ethical Review Board of the

References (66)

  • I.E. Leppik

    Zonisamide: chemistry, mechanism of action, and pharmacokinetics

    Seizure-Eur. J. Epilepsy

    (2004)
  • W. Loscher

    Critical review of current animal models of seizures and epilepsy used in the discovery and development of new antiepileptic drugs

    Seizure-Eur. J. Epilepsy

    (2011)
  • W. Loscher et al.

    Strategies in antiepileptic drug development - is rational drug design superior to random screening and structural variation

    Epilepsy Res.

    (1994)
  • R.J. Mailloux

    Redox regulation of mitochondrial function with emphasis on cysteine oxidation reactions

    Redox Biol.

    (2014)
  • Z.H. Pan

    Redox modulation of recombinant human GABAA receptors

    Neuroscience

    (2000)
  • M. Patel

    Mitochondrial dysfunction and oxidative stress: cause and consequence of epileptic seizures

    Free Radical Biol. Med.

    (2004)
  • J.N. Pearson

    Reactive oxygen species mediate cognitive deficits in experimental temporal lobe epilepsy

    Neurobiol. Dis.

    (2015)
  • Y.H. Raol et al.

    Experimental models of seizures and epilepsies

    Anim. Models Mol. Pathol.

    (2012)
  • K.J. Reinikainen

    Comparison of oxcarbazepine and carbamazepine: a double-blind study

    Epilepsy Res.

    (1987)
  • A. Reshef

    The effect of carbamazepine and ethosuximide on hyperoxic seizures

    Epilepsy Res.

    (1991)
  • M.A. Rogawski

    Molecular targets versus models for new antiepileptic drug discovery

    Epilepsy Res.

    (2006)
  • S. Taverna

    Valproate selectively reduces the persistent fraction of Na+ current in neocortical neurons

    Epilepsy Res.

    (1998)
  • L. Thomas

    Vigabatrin and behaviour disorders: a retrospective survey

    Epilepsy Res.

    (1996)
  • T. Tzuk-Shina

    The effect of vigabatrin on central-nervous-system oxygen-toxicity in rats

    Eur. J. Pharmacol.

    (1991)
  • G. Zsurka et al.

    Mitochondrial dysfunction and seizures: the neuronal energy crisis

    Lancet Neurol.

    (2015)
  • J. Aicardi

    Vigabatrin as initial therapy for infantile spasms: a European retrospective survey

    Epilepsia

    (1996)
  • B.W. Allen

    Two faces of nitric oxide: implications for cellular mechanisms of oxygen toxicity

    J. Appl. Physiol.

    (2009)
  • M. Ängehagen

    Novel mechanisms of action of three antiepileptic drugs, vigabatrin, tiagabine, and topiramate

    Neurochem. Res.

    (2003)
  • J.D. Balentine

    Pathology of Oxygen Toxicity

    (1982)
  • A.R. Behnke

    The effect of oxygen on man at pressures from 1 to 4 atmospheres

    Am. J. Physiol.

    (1935)
  • V. Biton

    Double-blind, placebo-controlled study of lamotrigine in primary generalized tonic-clonic seizures

    Neurology

    (2005)
  • N. Bitterman et al.

    The effect of flumazenil on Cns oxygen-toxicity in the rat

    Methods Find. Exp. Clin. Pharmacol.

    (1995)
  • A. Chmielewska et al.

    Mass versus molar doses, similarities and differences

    Pharmazie

    (2008)
  • Cited by (0)

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