Inhibitory effect of anti-seizure medications on ionotropic glutamate receptors: special focus on AMPA receptor subunits.

Objective: The purpose of the current analysis was to investigate the direct inhibitory effects of perampanel and other anti-seizure medications (ASMs) on the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), N-methyl-D-aspartic acid (NMDA), and kainate glutamate receptor subtypes using electrophysiological assessments.

Methods: AMPA receptor subunit-expressing cell lines (hGluA1-4, including two kinds of Q/R RNA-editing variants of hGluA2), NMDA receptor-expressing cells (hNR1/hNR2B), and kainate receptor-expressing cells (hGluK2) were developed in house. The effects of perampanel, and other ASMs including topiramate, phenobarbital, lamotrigine, gabapentin, carbamazepine, valproate, levetiracetam, and lacosamide, on AMPA, NMDA, and kainate receptors were evaluated by automated patch-clamp technique. In the same way, 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo[f]quinoxaline (NBQX) and GYKI 52466 were evaluated as reference compounds of AMPA receptor antagonists. For the AMPA receptor functional assay, AMPA currents were elicited by AMPA in the presence of cyclothiazide. NMDA with glycine was used as a stimulant for the NMDA receptor assays, while glutamate was used for the kainate receptor assays. The mean 50 % inhibitory concentration (IC) values were determined based on sigmoidal-curve fitting using GraphPad Prism software.

Results: Perampanel inhibited functions of hGluA1-4, but did not inhibit hNR1/hNR2B and hGluK2 up to 25 μM, the maximum soluble concentration. The IC values were 660 nM for hGluA1, 780 nM for hGluA2(R), 1200 nM for hGluA2(Q), 1200 nM for hGluA3, and 1800 nM for hGluA4. NBQX and GYKI 52466 also inhibited the function of all AMPA receptor subunits, but did not inhibit hNR1/hNR2B and hGluK2. The IC values for NBQX were 880 nM for hGluA1, 290 nM for hGluA2(R), 310 nM for hGluA2(Q), 330 nM for hGluA3, and 630 nM for hGluA4. For GYKI 52466, IC values were 25,000 nM for hGluA1, 30,000 nM for hGluA2(R), 42,000 nM for hGluA2(Q), 28,000 nM for hGluA3, and 53,000 nM for hGluA4. Phenobarbital inhibited hGluA2(R) at an IC value of 730,000 nM. The majority of other ASMs evaluated in this study did not show a direct inhibitory effect on almost any of the glutamate receptor functions examined up to 1 M. However, lamotrigine and carbamazepine inhibited hNR1/hNR2B function at IC values of 930,000 and 1,000,000 nM, respectively.

Significance: Only a few ASMs evaluated in this study showed direct interaction with ionotropic glutamate receptors. Perampanel is the only ASM that had a potent inhibitory effect on all AMPA receptor subtypes, but did not inhibit NMDA or kainate receptor subunits; while phenobarbital inhibited GluA2(R), and carbamazepine and lamotrigine inhibited the NMDA receptor at high concentration ranges.