當歸與蓮子心中之化合物保護大鼠初代皮質神經細胞對抗Aβ1-42的傷害

Abstract

阿滋海默症(Alzheimer’s disease, AD)是一種漸進式的神經退化性疾病 (progressive neurodegenerative disorder)，病患會有記憶減退，判斷力和理解力下降的現象，是老人失智症中最常見的一種。由阿滋海默症病患腦部的病理切片可發現細胞外的老年斑塊沉積(senile plaques)和細胞內神經糾結(neurofibrillary tangles)的現象，老年斑塊主要是由類澱粉胜肽(amyloid-β peptide, Aβ)構成，近來有研究指出，類澱粉胜肽寡聚合物（oligomer）為主要造成細胞毒性的分子。因此，本研究以『Aβ1-42類澱粉胜肽寡聚合物誘發大鼠初代皮質神經細胞毒性』為阿滋海默症之模式，並以具有神經保護功效的銀杏萃取物（EGb 761）做為正控制組，篩選具有抗Aβ1-42毒性的試驗樣品，包含蓮子心(seed embryo of Nelumbo nucifera)中的葒草素（orientin）、異葒草素（isoorientin）、金絲桃苷（hyperoside）、異檞皮苷（isoquercitrin），以及當歸(Angelica sinensis)中主要的活性成分藳本內酯（Z-ligustilide）。根據MTT assay評估細胞存活率的結果，異葒草素（isoorientin）及異檞皮苷（isoquercitrin）最有效的劑量為5 μM，而藳本內酯（Z-ligustlie）、葒草素（orientin）及金絲桃苷（hyperoside）最有效的劑量為25 μM。五種試驗樣品的保護效果依序為：葒草素（orientin）> Z-藁本內酯（Z-ligustilide）> 異葒草素（isoorientin）> 金絲桃苷（hyperoside）> 異檞皮苷（isoquercitrin）。而墨漬點法（dot blot assay），結果除了EG761，其餘樣品皆不能抑制Aβ聚集，顯示這些樣品可能透過加速Aβ聚集形成纖維，減少具有毒性的oligomer而有保護神經細胞的能力。

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder characterized by cognitive decline in memory, orientation, judgment, and reasoning; it is also the most common form of dementia among the elderly people. Pathologically, AD is manifested by oxidative stress induced neuronal cell death, deposition of amyloid-β (Aβ) peptide into senile plaques in the extracellular space, and formation of neurofibrillary tangles inside the neurons. Recent studies suggest that soluble Aβ oligomers may be the primary toxic species in AD. Therefore, the objective of this study is to find the potential phytochemicals that can protect neuron against Aβ oligomer induced toxicity. Flavonoids, a large group of natural compounds, have been proven to possess neuroprotective effects through its antioxidative ability. Flavonoids isolated from lotus (Nelumbo nucifera) seed embryo were identified to be orientin. isoorientin, isoquercirtrin and hyperoside. Also, Z-ligustilide is an active compound in Angelica sinensis. Using Ginkgo biloba extract (EGb761) as positive control, we plan on tesing the above phytochemicals for the potential neuroprotective effect against Aβ1-42 induced toxicity in primary rat cortical neurons. According to the results of cell viability assessed by the MTT colorimetric assay, the most effective dose of isoorientin and isoquercitrin is 5 μM, and Z-ligustlie、orientin and hyperoside is 25 μM. The protctive effect are as follows: orientin > Z-ligustlie > isoorientin > hyperoside > isoquercitrin. In dot blot assay, only EGb761 was found to inhibit the Aβ1-42 fibrillization, indicating that these compounds may protect neuron through accelerating Aβ assembly.