摘要:背景:本研究為台奧國際交流合作計畫之延伸,協同主持人邱教授團隊之動物模式研究已證實由奧地利團隊設計製出的嶄新化合物:化合物6,有助於治療類精神分裂和抽動症(tics)。化合物6 為一pyrazoloquinolinone compound,乃GABAA(γ-aminobutyric acid type A)接受器之α6次單位的專一作用子(ligand),已知GABAA 之α6 次單位(α6GABAA)接受器只存在於三種神經細胞,其中之一為與偏頭痛致病機轉密切相關的三叉神經節。偏頭痛是嚴重型頭痛伴隨噁心、嘔吐、及自律神經發作,如眼睛畏光、怕吵等。約佔群體15%,因症狀嚴重,易生活失能,因此造成社會和家庭沉重的負擔,有必要進一步了解其疾病機轉和藥物作用方式,才能發展有效的治療。目前已知三叉神經血管系統中樞(含三叉神經核和頸椎前緣)及周邊組織(三叉神經節和大腦腦膜之神經末梢及血管)的敏感化是造成偏頭痛的主因。藥物治療主要的機轉為調節鈉、鈣離子通道、AMPA/kainate 接受器、及GABAA 接受器等,以降低三叉頸神經之興奮性、減少腦膜神經性血管擴張(極可能經由抑制calcitonin gene related peptide (CGRP)釋出之機轉)、抑制局部腦血流、及啟動cortical spreading depression,然而確切之作用機轉仍不清楚。已知仍有20%偏頭痛患者對目前現有的抗偏頭痛藥物療效不佳,有必要開發新的治療偏頭痛藥物。又10%偏頭痛患者有抽動症共病,三叉神經節的α6GABAA 次單位接受器是否偏頭痛之致病機轉相關?其正變構調節劑(positive allosteric modulators)是否有抗偏頭痛的作用?有必要進一步研究。實驗方法:本研究團隊已建立以辣椒素(capsaicin)誘發的偏頭痛動物模式,以辣椒素注入公鼠(8-10 週)之枕骨大孔,檢視三叉神經血管系統之中樞神經核和周邊三叉神經節及腦膜神經末梢和血管的變化。中樞部分將測量並量化c-Fos 免疫活性,此乃神經元活化之標記,量化的方法則根據本團隊之前研究所得之公式。周邊部分則以免疫染色呈現神經胜肽CGRP 之活化或釋出,即偏頭痛神經性發炎之表徵。並以diazepam 為陰性對照組,Ro 15-4513 和loreclezole 為陽性對照組。除了檢視化合物6 之外,將進一步研究其改良衍生物,即化合物6 重氫化之RV-I-29,LAU 463 和LAU 159,並比較與化合物6 之差異,將可列出值得開發之藥物清單。結論:化合物6 及其他三種α6GABAA 次單位接受器正變構調節劑為全新之化合物,尚未被應用在偏頭痛之研究。檢視這些α6GABAA 次單位接受器正變構調節劑之抗偏頭痛效果,一方面可以開發新的可能臨床上有效治療偏頭痛藥物,造福頑固型偏頭痛患者,尤其是有合併抽動症之病患;另一方面也有助於了解偏頭痛之致病機轉、精進臨床治療之成效,及未來發展新的抗偏頭痛藥物。
Abstract: Background: This proposal is an extension from a Taiwan-Austria international collaborating project fundedby MoST to the co-PI. In that bilateral project, the co-PI’s lab using several animal models mimickingschizophrenia and tics found several effective pyrazoloquinolinone compounds, such as Compound 6, whichwere developed by the Austrian partner’s lab and are the first-in-class high affinity positive allostericmodulators (PAMs) selectively acting on γ-aminobutyric acid type A receptors (GABAARs) containing theα6 subunit (α6GABAARs). α6GABAARs are only expressed in three neuronal tissues, including thetrigeminal ganglia (TG), which plays an important role in the pathogenesis of migraine. Migraine, a severeheadache characterized with concurrent nausea, vomiting, and autonomic instability, is a prevalent disablingcondition affecting about 15% of people with a high societal and individual burden. Trigemino-vascularactivation via both peripheral and central sensitizations is an essential neuropathogenic mechanism ofmigraine. Although there are several pharmacological treatments available clinically, 20% of migraineurs arerefractory. These agents were found to reduce superior sagittal sinus-evoked firing of neurons in thetrigeminocervical complex (TCC), attenuate neurogenic dural vasodilation, which is likely through inhibitingthe release of calcitonin gene related peptide (CGRP) from prejunctional trigeminal neurons, and inhibitpropagation of cortical spreading depression in rats and cats. Recent genetic studies suggest the involvementof two ion channel changes in the neuropathogenesis of migraine, TWIK-related spinal cord potassium(TRESK) and transient receptor potential M8 (TRPM8) that are enriched in peripheral sensory neurons,including TG. We, therefore, hypothesize that the PAM of α6GABAARs can inhibit the TG firing activity,leading to an anti-migraine activity. Thus, α6GABAAR-selective PAMs may have the potential as a novelantimigraine therapy. We will validate this hypothesis by examining effects of several PAMs of α6GABAARson a migraine model induced by intracisternal injection of capsaicin, which has been established in the PI’slab. Our preliminary results have shown that systemic administration of Compound 6 was effective in thismodel.Methods: The migraine model induced by intra-cisternal (i.c.) capsaicin in Wistar rats (8-10 weeks) weestablished will be used. The c-Fos immunoreactivity, an activated neuron marker, in the TCC (the centralend of the trigeminovascular system) will be quantified by the formulas we have established. In the periphery,protein extravasation with CGRP release and expression, phenomena of neurogenic inflammation, will bemeasured by immunohistochemistry in dura mater and TG. Diazepam that is ineffective at α6GABAAR, willbe tested as negative control whereas Ro 15-4513 and loreclezole are both α6GABAAR PAMs as positivecontrols. In addition to Compound 6, three newly developed PAMs on GABAARs with improved metabolicproperties based on Compound 6, the deuterated derivative of compound 6 (RV-I-29), LAU 463, and LAU159 will be explored and compared with compound 6 for generating the selectivity profile of interest inmigraine therapy.Conclusions: Developing a novel drug is of benefit for those refractory to current migraine therapy.Furthermore, it may help understand the exact pathogenesis of migraine, improve clinical practice anddevelop new anti-migraine drugs in the future. In our experience, there are 10% of pediatric migraineurscomorbid with tics. These may be potential anti-migraine drugs for those with intractable migraine orcomorbidity with tics.