阿茲海默氏症 (Alzheimer’s disease, AD)，俗稱老年癡呆症，是一種好發在老年人的神經退化性疾病。在腦中的主要病理特徵是：1）神經細胞內的神經纖維化糾結，與2）貝它糊蛋白斑塊沉澱。貝它糊蛋白斑塊沉澱是腦中貝它糊蛋白Amyloid-β (Aβ)不正常的聚集而成，目前被廣泛地認為是造成阿茲海默氏症的主要原因之ㄧ。根據近年來的研究發現，腦中Aβ的聚集可能是由於腦中Aβ不正常的代謝或清除所造成的。而不正常聚集的Aβ則具有神經毒性，會導致神經細胞死亡。有研究指出，血紅素中的血質會與Aβ結合，並共存在阿茲海默氏症患者的腦中。先前實驗室的研究發現，血質會與Aβ結合，並會在西方墨點法中呈現較多的Aβ寡聚體。但由於當血質與Aβ結合後會具有過氧化酶的能力，因此上述的觀察有可能是肇因於西方墨點法冷光顯影階段受過氧化酶干擾的結果。因此，本實驗的目的之一是探討血質對於Aβ聚集的影響。又因Aβ的聚集具有神經毒性，而此特性與阿茲海默氏症的病因息息相關。所以，以血質對於Aβ毒性的影響也是本研究的重點。首先，SDS-膠電泳/銀染色法顯示血質會導致較多的Aβ寡聚體形成，支持我們原先的觀察。然而，表面電漿共振感測結果卻顯示血質對於Aβ聚集沒有顯著的影響。以穿透式電子顯微鏡負染色法我發現血質並不會改變Aβ纖維化的過程。此外，腦室內注射血紅素並不會改變阿茲海默氏症雙重基因轉殖鼠腦中Aβ的濃度。最後，血質也似乎不會改變Aβ對於人類神經纖維瘤母細胞汹纡SH-SY5Y胝汹所造成的毒性。總結這個研究，血質似乎會促進Aβ寡聚體形成，但對Aβ纖維化卻無顯著的影響。至於血質對Aβ神經毒性的研究，因血質是在Aβ聚集後才加入，因此建議未來血質應加在剛溶解的Aβ中，如此才能研究血質對Aβ的聚集，進而對Aβ神經毒性的影響。

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder with a complex etiology and pathogenesis. The pivotal histopathologies of the brains of AD patients are the intracellular accumulation of neurofibrillary tangles and the extracellular deposition of amyloid plaques. The formation of amyloid plaque is due to abnormal aggregation of the 40 to 42 amino acids amyloid-β peptide (Aβ) peptides. The汹 aggregated Aβ is neurotoxic; hence, is considered culprit for AD pathogenesis. Recent evidence indicated that the accumulation and aggregation of Aβ is a consequence of abnormal metabolism and/or deceased clearance of Aβ from brain. Therefore, it has been suggested that molecules binding to Aβ may be responsible for the misfolding, clearance, transport and stability of Aβ. Previously, the heme moiety was identified as Aβ binding site of hemoglobin by Western blotting analyses. However, the results observed in Western blot may be an artifact due to the peroxidase activity of heme/Aβ complex. Therefore, one of the specific aims of this study is to validate the effect of heme on Aβ aggregation. Furthermore, the conformation-dependent toxicity of Aβ also render us to investigate the effect of heme on Aβ toxicity. The silver stain results revealed that heme indeed facilitated the Aβ oligomer formation as resolved by SDS-PAGE. However, results obtained from the surface plasmon resonance (SPR) biosensor that is known to monitor protein interactions, indicated heme did not alter the aggregation of Aβ1-40 and Aβ1-42. Transmission electron microscope/negative stain suggested that heme did not inhibit the fibrilization of Aβ. Intraventricular injection of hemoglobin did not change the levels of soluble or insoluble Aβ1-40 or Aβ1-42 in AD double transgenic mice. Finally, addition of heme did not alter the toxicity of already aggregated Aβ. Taken together, heme seems to promote initial Aβ oligomer formation, but does not affect the fibrillar formation of Aβ. For the Aβ toxicity, heme does not influence the toxicity of the already aggregated Aβ. In the future, heme should be added to the freshly dissolved Aβ to study effect of heme-induced Aβ conformation change and related toxicity.

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