The isolation and mechanism elucidation of neuroprotective components against amyloid β -induced toxicity from Uncaria hirsuta Haviland

• Main Authors: I-Ju Chen, 陳怡如
• Other Authors: Young-Ji Shiao
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/34698568115103722110

碩士 === 國立陽明大學 === 生物藥學研究所 === 90 === β-Amyloid (Aβ) has been proposed to play an important role in the pathogenesis of Alzheimer’s disease (AD). Deposits of insoluble Aβ are found in the brains of patients with AD and are one of the pathological hallmarks of the disease. Previous studies have shown that aggregated Aβ can induce caspase-dependent apoptosis and death by oxidative stress in cultured neurons. Uncaria hirsuta Haviland, a traditional Chinese herb, has been used combinatory with other herbal drugs for the treatment of cognitive disorder. However, which is the major component of Uncaria hirsuta Haviland to protect neurons against Aβ-mediated toxicity and its neuroprotective mechanisms is not clear yet. In present study, 25 fractions were extracted from Uncaria hirsuta Haviland by using column chromatography. From the ethyl acetate extract, five fractions and a pure compound, catechin, were identified to be neuroprotective by using MTT reduction assay and cell morphology observation. Among five fractions, A567, B3 and B9 were picked for further studies since they are partial purified and still possessed neuroprotective activity. Fraction A567 and B3 abrogated the Aβ-induced caspase 3 and 2 activation, and A567 also decreased the caspase 8 activation. In contrast, B9 potentiated the activity of caspase 8, 3, 9 and 2. Besides affecting the activity of caspases, fraction A567, B3 and B9 reduced mitochondria cytochrome c release and nucleus condensation induced by Aβ. These results suggest that these three fractions inhibit Aβ-induced apoptosis. In addition, fraction A567, B3 and B9 reduced Aβ-induced oxidative stress. In the trolox equilibrium antioxidant capacity (TEAC) assay, fraction B9 possessed higher and A567 and B3 possessed very low antioxidant capacity. Antioxidants, such as epigallocatechin and probucol, facilitated the caspase-dependent neuroprotective effect of fraction A567, therefore conferring a significant neuroprotective ability against Aβ-mediated toxicity. Our results demonstrate that the neuroprotective mechanisms of Uncaria hirsuta Haviland on Aβ-induced toxicity is mediated by abrogating the activation of caspase cascade. The inhibition of caspase cascade in combination with antioxidative activity will further eliminate Aβ-mediated neurotoxicity.