Treatment of early and late kainic acid-induced status epilepticus with the noncompetitive AMPA receptor antagonist GYKI 52466

Abstract

Purpose: Benzodiazepines such as diazepam may fail to effectively treat status epilepticus because benzodiazepine-sensitive GABA(A) receptors are progressively internalized with continued seizure activity. Ionotropic glutamate receptors, including AMPA receptors, are externalized, so that AMPA receptor antagonists, which are broad-spectrum anticonvulsants, could be more effective treatments for status epilepticus. We assessed the ability of the noncompetitive AMPA receptor antagonist GYKI 52466 to protect against kainic acid-induced status epilepticus in mice.

Methods: Groups of animals treated with kainic acid received GYKI 52466 (50 mg/kg followed in 15 min by 50 mg/kg) or diazepam (25 mg/kg followed in 20 min by 12.5 mg/kg) beginning at 5 min of continuous seizure activity or 25 min later. The duration of seizure activity was determined by EEG recording from epidural cortical electrodes.

Results: Both GYKI 52466 and diazepam rapidly terminated electrographic and behavioral seizures when administered early. However, diazepam-treated animals exhibited more seizure recurrences. With late administration, GYKI 52466 also rapidly terminated seizures and they seldom recurred, whereas diazepam was slow to produce seizure control and recurrences were common. Although both treatments caused sedation, GYKI 52466-treated animals retained neurological responsiveness whereas diazepam-treated animals did not. GYKI 52466 did not affect blood pressure whereas diazepam caused a sustained drop in mean arterial pressure.

Discussion: Noncompetitive AMPA receptor antagonists represent a promising approach for early treatment of status epilepticus; they may also be effective at later times when there is refractoriness to benzodiazepines.

Figure 1

Representative EEG recordings from epidural cortical electrodes in vehicle-, GYKI 52466- and diazepam-treated mice. Status epilepticus was induced by injection of kainic acid (45 mg/kg, i.p.). After 5 min of status epilepticus, the mice were treated either with 10% cyclodextrin in saline (vehicle), two successive 50 mg/kg GYKI 52466 doses separated by 15 min, or 25 mg/kg and 12.5 mg/kg doses of diazepam separated by 15 min. Both active treatments initially eliminated the epileptiform EEG activity as illustrated in the 30 min posttreatment traces; behavioral seizure activity was also terminated. The status epilepticus EEG pattern recurred in the diazepam-treated animal at 1 h post treatment, which was accompanied by subtle behavioral seizures. Each trace represents a 10 s epoch. Scale bar (upper left), 500 μV. Epilepsia © ILAE

Figure 2

Effects of early and late treatment with GYKI 52466 and diazepam on the duration of EEG seizure activity. Status epilepticus was induced by i.p. injection of kainic acid (vehicle and 5 min treatment group: 45 mg/kg, i.p.; 30 min treatment group: 40 mg/kg, i.p.). GYKI 52466 and diazepam treatment was initiated either 5 min or 30 min after onset of status epilepticus. (A) Mean time to the first termination of continuous seizure activity. (B) Mean cumulative time of seizure activity during the 5 h monitoring period. None of the animals in the vehicle treated group exhibited a break in seizure activity so that the time to first termination and total duration are identical. Each group consisted of 4–6 animals; the total number of mice was 26. Bars indicate mean ± - SEM. Dashed lines indicate comparisons with vehicle: NS, not significant; *p < 0.05; **p < 0.01. Bold symbols indicate comparisons between corresponding GYKI 52466 and diazepam groups. Epilepsia © ILAE

Figure 3

Outcome of the treatment experiment of Fig. 2. (A) Fifteen min after the second treatment dose, mice were mechanically stimulated on the vibrissae and snout to evaluate responsiveness. Animals exhibiting movement of all four limbs were designated as “responsive.” Responsiveness could not be assessed in the vehicle control group as all animals experienced ongoing behavioral seizures (ND). Animals in the 30 min diazepam group also experienced subtle ongoing seizure activity that may have affected the assessment of responsiveness. (B) Comparison of percent survival in the different treatment groups. All animals in the GYKI 52466 group survived whereas some animals died in the diazepam-treated and control groups (the difference did not reach statistical significance by the Fisher’s exact test). Note that animals in the 30 min groups received a lower dose of kainic acid (40 mg/kg), which was not associated with lethality. Epilepsia © ILAE

Figure 4

Effects of GYKI 52466 and diazepam on pulse rate (A, B) and mean arterial blood pressure (MAP) (C, D). (A, C) Data points indicate the mean ± SEM of 10 baseline measurements and 20 measurements following treatment with 50 mg/kg GYKI 52466 or 25 mg/kg diazepam. The measurements were made at ~1 min intervals. There were 10 mice in each treatment group. (B, D) Circles indicate percentage change in the mean of all after-treatment pulse rate or MAP values with respect to mean of all baseline values for each animal. Bars indicate mean ± SEM of the mean percentage change values for the 10 animals in each group. The overall reductions in pulse rate for the GYKI 52466 and diazepam groups were significant by the Wilcoxon matched-pairs signed-rank test (p < 0.01). The overall reduction in MAP for the diazepam but not the GYKI 52466 group was significant (p < 0.01). The overall reduction in pulse rate was significantly greater in the GYKI 52466 group than the diazepam group by the Wilcoxon two sample test (p < 0.01). The overall reduction in MAP was significantly greater in the diazepam group than in the GYKI 52466 group (p < 0.001). Epilepsia © ILAE