β 澱粉樣蛋白 (Amyloid β-protein，Aβ) 是造成神經細胞凋亡引起神經退化導致海默氏症(Alzheimer's disease，AD) 的主要病理因素，目前並無有效治療 AD 的藥物。本研究利用 Aβ25-35 造成神經細胞 PC12 凋亡的細胞模式來探討中藥訶子 (Terminalia chebula Retz) 的甲醇萃取物(Tech-MeOH) 是否具有神經保護作用及可能作用機制。研究結果顯示Tech-MeOH 非常有效抑制 Aβ_(25-35) 造成神經細胞 PC12 凋亡，並從Tech-MeOH 分離出純化合物 Tech-ME-A (證實為ellagic acid)。機制探討發現 Aβ_(25-35) 會隨著時間活化 glycogen synthase kinase 3 (GSK-3)，在 4 小時達到最高峰。而Tech-MeOH、ellagic acid 及 AR-A014418 (一種 GSK-3 抑制劑) 都可以顯著抑制 GSK-3 的活性，並且逆轉 Aβ_(25-35) 所誘發的 PC12 細胞凋亡；蛋白質訊息分子機制探討，發現它們最可能是藉由修飾 PI3K/Akt 依賴的 GSK-3 抑制作用而間接活化了 CREB 及其相關的抗凋亡蛋白 BcL-2 表現增加及抑制凋亡蛋白 caspase 3。我們結論認為從訶子的甲醇萃取物(Tech-MeOH) 及進一步分離純化的 ellagic acid 都可藉由修飾 PI3K/Akt 途徑抑制 GSK-3 的活化及相關機制而降低 Aβ_(25-35) 所造成之細胞凋亡作用。
Amyloid beta protein (Aβ) is a key pathological protein that induces neuronal apoptosis and mediates degeneration in Alzheimer's disease (AD). There is no effective medication for AD treatment so far. To explore whether methanol-soluble extract from the fruit of Terminalia chebula Retzius (Tech-MeOH) is neuroprotective, Aβ_(25-35)-induced apoptosis of rat pheochromocytoma cells (PC12 cells) was used to examine the protective potential and mechanisms involved. The Tech-MeOH extract was effective in the inhibition of Aβ_(25-35)-induced PC12 cells apoptosis and an active pure compound named ellagic acid (Tech-ME-A) was isolated. Mechanism elucidation showed that Aβ_(25-35) induced time-dependent activation of GSK-3 which peaked at 4hr after Aβ_(25-35) induction. However, both Tech-MeOH and Tech-ME-A, as well as a GSK-3 inhibitor (ARA014418) all significantly prevented GSK-3 activation, most possibly through modulation of phosphatidylinositol-3 kinase (PI3K)/Akt-dependent repression of GSK-3 activity, in turn, activated CREB-dependent upregulation of BcL2 and down-regulation of caspase 3. We conclude that methanol-soluble extract and ellagic acid isolated from T. chebula showed anti-apoptotic effects through modulation of PI3k/Akt-dependent inhibition of GSK-3 activity to reduce Aβ_(25-35) toxicity.
