- 學位論文
評估兩種海藻糖類似物在阿茲海默氏症模式鼠之潛在療效
Evaluation of the therapeutic potential of two trehalose analogs in Alzheimer's disease
摘要
AD為常見的神經退化性疾病，通常伴隨著海馬迴的損傷以及認知功能上的缺失。其重要病理特徵為類澱粉斑塊(Aβ)的堆積以及tau蛋白的過度磷酸化所導致的神經纖維糾結。近期有研究顯示海藻糖對AD模式鼠具有改善認知功能障礙的效果，進而能夠有效抑制類澱粉斑塊的聚集並降低其造成的毒性。但是在哺乳動物的消化道中海藻糖(trehalose)會被海藻糖水解酶(trehalase)分解成葡萄糖，因此在攝取後較無法有效地作用在目標組織，造成其效力的降低。 因此在本研究中，我們探討兩種不會被海藻糖水解酶所分解的海藻糖類似物，乳果糖(lactulose)與蜜二糖(melibiose)，對於AD模式鼠是否具有潛在的神經保護效果。首先使用經Aβ25-35寡聚體處理之小鼠海馬迴初級神經細胞，建立一個初步的篩藥平台，發現乳果糖能顯著保護神經細胞的分支數目，最後篩選出乳果糖進入動物實驗。我們先對小鼠進行海藻糖或乳果糖管餵5-6天後，以立體定位手術注射Aβ25-35寡聚體至小鼠之雙側海馬迴以誘發AD病徵，並以此模式分析海藻糖與乳果糖對於小鼠之行為以及相關病理特徵上之影響與其相關分子機制。在此實驗中發現乳果糖與海藻糖能夠改善小鼠的空間學習能力以及短期記憶的能力，且能夠降低小鼠海馬迴中Aβ堆積。另外，乳果糖與海藻糖亦能減少小鼠海馬迴中星狀膠細胞的數量，顯示神經損傷有降低的現像，並且提升與自噬作用中相關蛋白質的表現量，我們推論乳果糖與海藻糖透過促進自噬作用進而清除對細胞造成毒性與損害的Aβ，以對抗於海馬迴CA1區域急性注射Aβ25-35寡聚體所造成的傷害。在上述的各種分析中，乳果糖與海藻糖的功效不相上下，但是在改善長期記憶與突觸功能蛋白表現方面，乳果糖更勝於海藻糖，因此我們認為乳果糖具有被開發成為AD預防性或治療性藥物之潛力。
並列摘要
Alzheimer’s disease (AD) is the most common neurodegenerative disease associated with progressive damage in hippocampal neurons and cognitive dysfunctions. Both the accumulation of beta-amyloid peptides (Aβ) and tau protein phosphorylation are regarded as crucial events in the initiation of AD. Recently, a study shows that trehalose might invoke a suite of neuroprotective mechanisms that can contribute to improving cognitive performance in AD, and is also effective in inhibiting Aβ aggregation and reducing its cytotoxicity. However trehalose is digested into glucose by trehalase and which reduces its’s efficacy in the disease target tissues. Two trehalase-indigestible trehalose analogs, lactulose and melibiose, were identified and could be novel therapeutics for AD. In the study, we first examined the potential of lactulose and melibiose in AD treatment using mouse primary hippocampal neuronal culture under the toxicity of oligomeric Aβ25-35. Lactulose was further chosen to be tested in vivo. Lactulose and trehalose were applied individually to C57BL/6J mice under bilateral intrahippocampal CA1 injection of oligomeric Aβ25-35. We found that administration of lactulose and trehalose attenuated the short-term memory and the cognitive impairment. From pathological analysis, we further found that the pretreatment of lactulose and trehalose decreased the levels of Aβ deposition, neuroinflammation, and increasing the levels of autophagy pathway related proteins. These results suggest that both lactulose and trehalose might reduce the Aβ aggregation through autophagy. Except for the improvements as described, lactulose was even better than trehalose in the enhancement of long-term memory and synaptic protein expression level of AD mouse model. Therefore, lactulose could be potential to be developed into a preventive and/or therapeutic compound for AD.