AMPA受體拮抗劑Perampanel對於Dravet症候群動物模式之治療效果及抗癲癇機轉

Abstract

Dravet症候群，又稱為嬰兒期嚴重肌陣攣性癲癇（SMEI），是一種罕見且具耐藥性的癲癇性腦部病變。Dravet症候群患者除了會表現出自發性反復癲癇發作外，也容易在高溫下被誘導出癲癇發作症狀。大約90％的Dravet症候群患者與電壓敏感型鈉離子通道（voltage-gate sodium channel）Nav1.1亞型之SCN1A基因的功能喪失突變相關，進而導致PV+ GABAergic中樞神經元功能失調和GABA的釋放不足，造成整體腦神經迴路的過度興奮。此外，我們先前的研究發現Scn1aE1099X/+小鼠具有異常過度神經新生的情形，這可能在epileptogenesis當中扮演了關鍵性的角色。由於臨床上valproic acid、clobazam和stiripentol等藥物藉由促進GABA神經傳遞所達到的治療效果相當有限，因此我們換個角度思考抑制glutamate的神經傳遞是否能更有效地控制患者的病情。AMPA受體為一glutamate受體，在中樞神經系統中負責快速的突觸訊號傳遞，而perampanel為目前臨床上唯一被使用的AMPA受體拮抗劑。在這篇研究當中，我們使用Scn1aE1099X/+小鼠來探索perampanel的治療效果和當中可能涉及的抗癲癇機制。首先，我們評估了Perampanel對Dravet症候群小鼠自發性反覆癲癇發作的影響。結果表示，perampanel不僅可以預防自發性複發性癲癇發作的發生，而且可以減少EEG紀錄當中interictal spikes的次數。在高溫誘導癲癇發作的實驗中，我們發現1 mg / kg和2 mg / kg的perampanel無論在敏感性和嚴重性上均對高溫誘導癲癇發作均具有顯著的改善效果。在高溫誘導癲癇發作的實驗中，我們進一步測試了其他抗癲癇藥（如stiripentol，valproic acid和phenytoin）的治療效果。在這些藥物中，只有valproic acid可以降低高溫誘導癲癇發作的敏感性，但是皆無法改善高溫誘導癲癇發作的嚴重程度。為了評估perampanel除了單純抑制AMPA受體所介導的電流外是否還有其他抗癲癇作用，我們進行了連續七天給予Perampanel的實驗。在給予perampanel一星期後，我們注意到perampanel具有降低Dravet症候群小鼠海馬迴中AMPA受體次單元GluA1的蛋白質表達的能力。此外，perampanel還可以改善Dravet症候群小鼠異常過度神經新生的活性。這些發現提供了證據，說明perampanel是個相當具有潛力的Dravet症候群治療藥物。

Dravet syndrome (DS), also known as Severe Myoclonic Epilepsy in Infancy (SMEI), is a catastrophic and drug-resistant epileptic encephalopathy. Patients with Dravet syndrome exhibit spontaneous recurrent seizures and are prone to induce seizure symptoms under high temperatures. About 90% of patients with Dravet syndrome are associated with loss-of-function mutations in the sodium voltage-gated channel alpha subunit 1 (SCN1A) gene, which in turn leads to the dysfunction of PV+ GABAergic interneurons and insufficient GABA release, causing excessive excitation of the overall brain neural circuit. Our previous study discovered that Scn1aE1099X/+ mice had aberrant excessive neurogenesis, which may play a key role in epileptogenesis. Since the therapeutic effects of promoting GABA neurotransmission by valproic acid, clobazam and stiripentol are quite limited clinically, we considered whether inhibiting glutamate neurotransmission can control the patient's condition more effectively. AMPA receptor is one of the glutamate receptors that mediates fast synaptic transmission in the central nervous system, and perampanel is the first and only clinically used AMPA receptor antagonist. In this study, we used Scn1aE1099X/+ mice to explore the therapeutic effects and possible antiepileptic mechanisms of perampanel. First, we evaluated the effect of perampanel on spontaneous recurrent seizure in Dravet syndrome mice. Results showed that perampanel can not only prevent the occurrence of spontaneous recurrent seizures, but also decrease the number of interictal spikes in EEG recording. In the hyperthermia-induced seizure experiment, we found that both 1 mg/kg and 2 mg/kg of perampanel have significant therapeutic effects on hyperthermia-induced seizures in both susceptibility and severity. We further tested the therapeutic effect of other anti-epileptic drugs such as stiripentol, valproic acid and phenytoin in the hyperthermia-induced seizure experiment. Among these drugs, only valproic acid had the ability to decrease hyperthermia-induced seizure susceptibility, but none of the drugs affected hyperthermia-induced seizure severity. To evaluate whether perampanel has other antiepileptic effects apart from only inhibiting the AMPA receptor-mediated currents, we conducted an experiment in which perampanel was administered for seven consecutive days. After one week of perampanel administration, we noticed that it has the ability to decrease the protein level of AMPA receptor subunits GluA1 in hippocampus in Dravet syndrome mice. In addition, perampanel can also decrease the aberrant neurogenesis activity in Dravet syndrome mice. These findings provide evidence that perampanel is a promising drug for Dravet syndrome therapy.