The AMPA receptor antagonist NBQX exerts anti-seizure but not antiepileptogenic effects in the intrahippocampal kainate mouse model of mesial temporal lobe epilepsy

Highlights

• The AMPA receptor antagonist NBQX acts antiepileptogenic in a neonatal rat model.

• We studied whether such effect also occurs in an adult mouse model of epilepsy.

• Epilepsy with spontaneous recurrent seizures was induced by intrahippocampal kainate.

• Treatment with NBQX after kainate did not prevent development of epilepsy.

• In epileptic mice, NBQX and perampanel suppressed difficult-to-treat partial seizures.

Abstract

The AMPA receptor subtype of glutamate receptors, which mediates fast synaptic excitation, is of primary importance in initiating epileptiform discharges, so that AMPA receptor antagonists exert anti-seizure activity in diverse animal models of partial and generalized seizures. Recently, the first AMPA receptor antagonist, perampanel, was approved for use as adjunctive therapy for the treatment of resistant partial seizures in patients. Interestingly, the competitive AMPA receptor antagonist NBQX has recently been reported to prevent development of spontaneous recurrent seizures (SRS) in a neonatal seizure model in rats, indicating the AMPA antagonists may exert also antiepileptogenic effects. This prompted us to evaluate competitive (NBQX) and noncompetitive (perampanel) AMPA receptor antagonists in an adult mouse model of mesial temporal lobe epilepsy. In this model, SRS develop after status epilepticus (SE) induced by intrahippocampal injection of kainate. Focal electrographic seizures in this model are resistant to several major antiepileptic drugs. In line with previous studies, phenytoin was not capable of blocking such seizures in the present experiments, while they were markedly suppressed by NBQX and perampanel. However, perampanel was less tolerable than NBQX in epileptic mice, so that only NBQX was subsequently tested for antiepileptogenic potential. When mice were treated over three days after kainate-induced SE with NBQX (20 mg/kg t.i.d.), no effect on development or frequency of seizures was found in comparison to vehicle controls. These results suggest that AMPA receptor antagonists, while being effective in suppressing resistant focal seizures, are not exerting antiepileptogenic effects in an adult mouse model of partial epilepsy.

Introduction

Diverse brain insults, including traumatic brain injury, stroke, brain infections, tumors, and prolonged acute symptomatic seizures, such as complex febrile seizures or status epilepticus (SE), can induce “epileptogenesis,” a process by which normal brain tissue is transformed into tissue capable of generating spontaneous seizures (Löscher and Brandt, 2010, Pitkänen, 2010). About 40% of all epilepsies are due to such brain insults, so that the lack of treatments for preventing epilepsy in patients at risk is a major unmet medical need (Löscher et al., 2013). Among the various drugs and drug targets that have been explored for antiepileptogenic effects in recent years (Pitkänen and Lukasiuk, 2009, Löscher and Brandt, 2010, Pitkänen, 2010, Pitkänen and Lukasiuk, 2011), drugs that modulate excitatory transmission by blocking glutamate receptors of the AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) subtype have received relatively little attention, although AMPA receptors have long been suggested to play an important role in ictogenesis and epileptogenesis (Meldrum, 1994, Rogawski and Donevan, 1999, Löscher and Schmidt, 2012, Rogawski, 2013). Competitive and non-competitive AMPA receptor antagonists such as the quinoxalinedione NBQX (2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo[f]quinoxaline-2,3-dione) or the 2,3-benzodiazepine GYKI 52466 (1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine) have been shown to inhibit the development of kindling (Namba et al., 1994, Rogawski et al., 2001), which is considered a model of epileptogenesis, although the classic kindling protocol does not induce development of spontaneous recurrent seizures (SRS), the hallmark of epilepsy (Löscher, 1998). Recently, Lippman-Bell et al. (2013) reported that NBQX treatment following neonatal seizures blocks the development of later-life SRS in rats, indicating a marked antiepileptogenic effect. This interesting study prompted us to evaluate whether NBQX is also capable of preventing or modifying development of spontaneous seizures in an adult mouse model of mesial temporal lobe epilepsy (TLE), the most common type of symptomatic epilepsy in adult patients. In this model, spontaneous seizures develop after an SE that is induced by unilateral intrahippocampal injection of the glutamate receptor agonist kainate (Bouilleret et al., 1999). Spontaneous seizures in this model are resistant to several clinically used antiepileptic drugs (AEDs), thus reflecting the frequent resistance to AEDs in human TLE (Riban et al., 2002, Gouder et al., 2003, Maroso et al., 2011, Klein et al., 2014, Klein et al., 2015). We therefore also investigated whether NBQX is more efficacious than standard treatment in suppressing spontaneous seizures in mice with chronic epilepsy. Recently, the first AMPA receptor antagonist, perampanel, has been approved for add-on treatment of partial seizures such as occurring in TLE (Löscher and Schmidt, 2012, Rogawski and Hanada, 2013, Hanada, 2014), so that this drug was included in our experiments. Because we previously showed that NMDA (N-methyl-d-aspartate) receptor antagonists synergistically potentiate the anti-seizure effect of NBQX on partial seizures (Löscher et al., 1993, Löscher and Hönack, 1994, Potschka et al., 1998), we also tested whether the anti-seizure activity of perampanel can be potentiated by an NMDA antagonist.