Original research article
Anticonvulsant active inhibitor of GABA transporter subtype 1, tiagabine, with activity in mouse models of anxiety, pain and depression

https://doi.org/10.1016/j.pharep.2014.11.003Get rights and content

Abstract

Background

Tiagabine, a selective inhibitor of GABA transporter subtype 1 is used as an add-on therapy of partial seizures in humans but its mechanism of action suggests other potential medical indications for this drug. In this research we assess its pharmacological activity in several screening models of seizures, pain, anxiety and depression in mice.

Methods

For pharmacological tests tiagabine was administered intraperitoneally 60 min before the assay. Behavioral tests were performed using models of chemically and electrically induced seizures, thermal acute pain and formalin-induced tonic pain. Anxiolytic-like properties were evaluated using the four plate test and the elevated plus maze test. Antidepressant-like activity was assessed in the forced swim test. In addition, to exclude false positive results in these assays, the influence of tiagabine on animals’ locomotor activity and motor coordination was investigated, too.

Results

Tiagabine demonstrated anticonvulsant properties in chemically induced seizures (pentylenetetrazole and pilocarpine seizures). At the dose of 100 mg/kg it also elevated the seizure threshold for electrically induced seizures by 31.6% (p < 0.01), but it had no activity in the maximal electroshock seizure test. Tiagabine showed anxiolytic-like and antidepressant-like effects. Although it apparently reduced animals’ nociceptive responses in pain tests, these activities rather resulted from its sedative and motor-impairing properties demonstrated in the locomotor activity and the rotarod tests, respectively.

Conclusions

The results obtained in the present study suggest that tiagabine, apart its anticonvulsant effect, has anxiolytic-like, sedative and antidepressant-like properties. In view of this, it can be potentially used in the treatment of anxiety and mood disorders.

Introduction

In the mammalian central nervous system (CNS) γ-aminobutyric acid (GABA) is the most abundant inhibitory neurotransmitter which mediates numerous physiological processes. The augmentation of its neurotransmission is responsible for anticonvulsant, anxiolytic, muscle relaxant and sedative effects [1].

The release of GABA into the synaptic cleft is stimulated by depolarization of presynaptic neurons with subsequent diffusion toward the target receptors located on the postsynaptic surface [2]. The termination of GABA action results from its removal from the synaptic cleft either to neurons, or glial cells where this neurotransmitter is metabolized. So far, four plasma membrane GABA transporters (GAT) belonging to solute carrier family 6 (SLC6) have been discovered. These proteins are implicated in GABA re-uptake [3]. In the recent years, much attention has been paid to the biological role of GAT, and to the best of our knowledge regarding GAT has greatly expanded from being a simple machinery serving for GABA re-utilization to proteins whose distinct expression in the CNS limits the synaptic overspill of GABA and prevents overactivation of GABA receptors at extrasynaptic loci [4].

The cloning of plasma membrane GAT in the early 1990s brought about an unfortunate discrepancy in the nomenclature of species-homologue transporters, due to mouse GAT2 being homologue of other species betaine-GABA transporter-1 (BGT-1). In view of this, the nomenclature of GAT differs in accordance to the species of a mammal. In mice there are mGAT1, mGAT2, mGAT3 and mGAT4 [5]. The corresponding plasma membrane GABA transporters in humans are called GAT-1, BGT-1, GAT-2 and GAT-3 [5], [6].

A deficiency or complete loss of GABA function is observed in several types of neurological and psychiatric disorders, such as epilepsy, anxiety, chronic pain, and depression [2], [7]. Numerous studies confirmed that the enhancement of GABAergic tone might contribute to a therapeutic effect in these disorders, and therefore this strategy holds promise for the treatment of several diseases in which GABA function is reduced.

In the CNS the augmentation of GABA action can be achieved by the inhibition of its re-uptake from the synaptic cleft and this effect can be achieved by GAT inhibition. Tiagabine (Fig. 1), a derivative of nipecotic acid, has been developed and marketed as an add-on treatment of partial epilepsy [3], [8], [9]. This anticonvulsant drug is a highly selective GAT1 inhibitor with IC50 value of 0.8 μM [10], [11]. The selectivity toward GAT1 is thought to limit its activity to regions of the CNS in which GAT1 plays a significant role (the cortex, cerebellum, and hippocampus) [12], and it is expected that this drug, apart from its anticonvulsant activity, may present anxiolytic, antinociceptive, and antidepressant properties which are attributed to GAT1 inhibition [7]. Although the concept of anxiolytic, antidepressant-like and antinociceptive properties of brain GAT1 inhibition is not new, so far, there are limited and rather conflicting data from animal studies regarding other than anticonvulsant properties of tiagabine. Hence, in this study selected mouse models of seizures, acute and tonic pain, anxiety and depression were used to assess pharmacological profile of this drug.

Section snippets

Animals

Behavioral experiments were carried out in male Albino Swiss (CD-1) mice weighing 18–22 g. The mice were kept in cages, in groups of 10 animals. They had free access to food and water before experiments, and were maintained at room temperature 22–24 °C, under 12:12 (light/dark) cycle. For the assays the animals were selected in a random way, and each mouse was used only once. After the experiments the animals were euthanized by cervical dislocation. All the procedures used in behavioral tests

Anticonvulsant activity in pentylenetetrazole-induced seizure test

Tiagabine demonstrated protective properties against PTZ-induced seizures. In comparison to the control group, it prolonged the latency time to first clonus at a wide range of doses (6.25–50 mg/kg; F[5,72] = 12.93; p < 0.0001, Fig. 2a), and it reduced the number of seizure episodes in PTZ-treated mice compared to vehicle-treated group that received PTZ (F[5,72] = 9.187; p < 0.0001, Fig. 2b).

Anticonvulsant activity in pilocarpine-induced seizure test

In this test tiagabine had an overall effect on both the latency time to the occurrence of prodromal symptoms, and

Discussion

In the present study pharmacological properties of tiagabine, a selective inhibitor of GAT1 transporter subtype, were assessed in selected behavioral screening tests in mice. Using this GAT1-selective pharmacological tool we aimed to establish whether the inhibition of GAT1 might be a potential mechanism underlying the effectiveness of this drug in mouse models of chemically and electrically evoked seizures, anxiety, pain and depression.

Physiologically GAT proteins participate in the re-uptake

Conflict of interest

None declared.

Funding

This work was financially supported by the National Science Centre grant No. DEC-2012/05/B/NZ7/02705.

References (51)

  • M. Dudra-Jastrzebska et al.

    Pharmacodynamic and pharmacokinetic interaction profiles of levetiracetam in combination with gabapentin, tiagabine and vigabatrin in the mouse pentylenetetrazole-induced seizure model: an isobolographic analysis

    Eur J Pharmacol

    (2009)
  • E.B. Nielsen et al.

    Characterization of tiagabine (NO-328), a new potent and selective GABA uptake inhibitor

    Eur J Pharmacol

    (1991)
  • P.E. Schauwecker

    Strain differences in seizure-induced cell death following pilocarpine-induced status epilepticus

    Neurobiol Dis

    (2012)
  • G. Curia et al.

    The pilocarpine model of temporal lobe epilepsy

    J Neurosci Methods

    (2008)
  • F. Stief et al.

    Functional GABA uptake at inhibitory synapses in CA1 of chronically epileptic rats

    Epilepsy Res

    (2005)
  • M. Chrościńska-Krawczyk et al.

    Effect of caffeine on the anticonvulsant effects of oxcarbazepine, lamotrigine and tiagabine in a mouse model of generalized tonic–clonic seizures

    Pharmacol Rep

    (2009)
  • J.J. Łuszczki et al.

    Interactions of pregabalin with gabapentin, levetiracetam, tiagabine and vigabatrin in the mouse maximal electroshock-induced seizure model: a type II isobolographic analysis

    Epilepsy Res

    (2012)
  • J. Łuszczki et al.

    Interactions of tiagabine with some antiepileptics in the maximal electroshock in mice

    Pharmacol Biochem Behav

    (2003)
  • N.O. Dalby et al.

    Anticonvulsant properties of two GABA uptake inhibitors NNC 05-2045 and NNC 05-2090, not acting preferentially on GAT-1

    Epilepsy Res

    (1997)
  • B.S. Meldrum et al.

    Molecular targets for antiepileptic drug development

    Neurotherapeutics

    (2007)
  • C.G.S. Smith et al.

    GABA transporter type 1 (GAT-1) uptake inhibition reduces stimulated aspartate and glutamate release in the dorsal spinal cord in vivo via different GABAergic mechanisms

    Neuropharmacology

    (2007)
  • A. Ipponi et al.

    Tiagabine antinociception in rodents depends on GABA receptor B activation: parallel antinociception testing and medial thalamus GABA microdialysis

    Eur J Pharmacol

    (1999)
  • J.J. Łuszczki et al.

    Isobolographic characterization of interactions between vigabatrin and tiagabine in two experimental models of epilepsy

    Prog Neuropsychopharmacol Biol Psychiatry

    (2007)
  • H. Shannon et al.

    Comparison of the effects of anticonvulsant drugs with diverse mechanisms of action in the formalin test in rats

    Neuropharmacology

    (2005)
  • K.K. Madsen et al.

    Neuronal and non-neuronal GABA transporters as targets for antiepileptic drugs

    Pharmacol Ther

    (2010)
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