Screening for Activity Against AMPA Receptors Among Anticonvulsants-Focus on Phenytoin.

M Y Dron,O I Barygin,A S Zhigulin,D B Tikhonov

doi:10.3389/fphar.2021.775040

Abstract

The interest in AMPA receptors as a target for epilepsy treatment increased substantially after the approval of perampanel, a negative AMPA receptor allosteric antagonist, for the treatment of partial-onset seizures and generalized tonic-clonic seizures. Here we performed a screening for activity against native calcium-permeable AMPA receptors (CP-AMPARs) and calcium-impermeable AMPA receptors (CI-AMPARs) among different anticonvulsants using the whole-cell patch-clamp method on isolated Wistar rat brain neurons. Lamotrigine, topiramate, levetiracetam, felbamate, carbamazepine, tiagabin, vigabatrin, zonisamide, and gabapentin in 100-µM concentration were practically inactive against both major subtypes of AMPARs, while phenytoin reversibly inhibited them with IC50 of 30 ± 4 μM and 250 ± 60 µM for CI-AMPARs and CP-AMPARs, respectively. The action of phenytoin on CI-AMPARs was attenuated in experiments with high agonist concentrations, in the presence of cyclothiazide and at pH 9.0. Features of phenytoin action matched those of the CI-AMPARs pore blocker pentobarbital, being different from classical competitive inhibitors, negative allosteric inhibitors, and CP-AMPARs selective channel blockers. Close 3D similarity between phenytoin and pentobarbital also suggests a common binding site in the pore and mechanism of inhibition. The main target for phenytoin in the brain, which is believed to underlie its anticonvulsant properties, are voltage-gated sodium channels. Here we have shown for the first time that phenytoin inhibits CI-AMPARs with similar potency. Thus, AMPAR inhibition by phenytoin may contribute to its anticonvulsant properties as well as its side effects.

Highlights

Epilepsies are among the most common chronic brain disorders (Scharfman, 2007)
Lamotrigine, topiramate, levetiracetam, felbamate, carbamazepine, tiagabin, vigabatrin, zonisamide, and gabapentin were practically inactive against both CP-AMPARs and CI-AMPARs. These data agree well with the results of Fukushima et al (2020), who did not find significant activity of different anticonvulsants, except perampanel, against hGluA1-4 receptors. Phenytoin reversibly inhibited both CP-AMPARs and CI-AMPARs in our experiments, and we decided to study its molecular mechanisms of action in more detail
We have shown for the first time that phenytoin is more active against CI-AMPARs

Summary

Introduction

Epilepsies are among the most common chronic brain disorders (Scharfman, 2007). They affect 0.5–1% of people around the world (Sirven, 2015). Despite the constant development of new antiseizure drugs during the last decades (Rho and White, 2018), 20–30% patients cannot control seizures even with modern medications. The search for new anticonvulsant drugs and detailed. AMPA Receptor Inhibition by Phenytoin understanding of the mechanisms of action of older ones are extremely important for effective selection of therapy for each patient. Seizures may produce neurodegeneration within the brain, and different antiseizure drugs have different potential to prevent it (Miziak et al, 2020)

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Conclusion