Analyses on oxidative stress and amyloid β protein in brains of mice with modified apolipoprotein E gene

阿尔茨海默病(AD)是以大脑皮质淀粉样蛋白(Aβ，Aβ)广泛沉积为特征的疾病。Aβ的产生是由氧化应激诱导的，而Aβ被报道通过产生活性氧等引起氧化应激等。此外，载脂蛋白E(ApoE)-ε4型是所有类型AD最强大的危险因素之一，在体外已被阐明其抗氧化作用不如apoE-ε3型。我们已经证明，携带载脂蛋白E-ε4同型的AD患者的颞叶皮质中含有比携带ε3同型的患者更多的硫代巴比妥酸反应物质，这表明载脂蛋白E-E4的低抗氧化活性可能与其与AD的关联有关。我们首先测量了载脂蛋白E基因敲除小鼠和野生型小鼠大脑中的硫代巴比妥酸反应物质，结果表明前者的硫代巴比妥酸反应物质明显多于后者，这表明载脂蛋白E具有抗氧化活性。然后，我们测量了apoE3敲门小鼠和apoE4敲门小鼠脑内的TBARS，发现全脑匀浆中的TBARS没有差异，但apoE4敲门小鼠的纯化脂筏部分的TBARS比apoE3敲门小鼠的更多，但没有统计学意义。我们进一步通过双侧颈动脉闭塞(BCAO)的方法观察了慢性低灌流对大鼠脑的影响。BCAO大鼠脑内A-β-40和A-β-42含量均高于假手术对照组。免疫细胞化学检测显示BACE1的表达高于对照组。综上所述，慢性低灌流可诱导BACE1的表达促进AD的沉积，其机制可能部分是通过诱发氧化应激来实现的，因此有必要进一步研究载脂蛋白E-参与AD的发病机制及其与氧化应激和Aβ生成的关系。

Alzheimer's disease (AD) is characterized by the extensive deposition of amyloid β protein (Aβ) in brain cortex. Aβ generation reveals to be induced by oxidative stress, and Aβ is reported to evoke oxidative stress through generating reactive oxygen species, etc. In addition, apolipoprotein E (apoE)-ε4 genotype, one of the most powerful risk factors for all types of AD, has been elucidated in vitro to show less anti-oxidant effect than apoE-ε3 genotype. We have already shown that temporal cortices from patients with AD carrying apoE-ε4 homotypes contained more thiobarbituric acid-reactive substances (TBARS) than those carrying ε3 homotypes, suggesting that the lower antioxidant activity of apoe-E4 could contribute to its association with AD.We first measured TBARS in brains from apoE-knockout and wild type mice, elucidating that the former showed significantly more TBARS than the latter, suggesting antioxidant activities of apoE. We measured then TBARS in brains from human apoE3-knockin and apoE4-knockin mice, revealing that no differences in whole brain homogenates, but more TBARS with no significance in purified lipid raft fractions from apoE4-knockin than those from apoE3-knockin mice.We further investigated effects of chronic hypoperfusion on rat brains by bilateral carotid artery occlusions (BCAO). Both Aβ40 and Aβ42 were more increased in BCAO rat brains than those from sham-operated rats employed as controls. Immunocytochemical studies showed more expression of BACE1 than controls. Taking all these findings together in consideration, chronic hypoperfusion could induce BACE1 expression facilitating AD-deposion, the mechanism of which might be partly by evoking oxidative stress.Further studies are necessary to clarify the pathomechanism by which apoE-64 could be risk for AD and its relations to oxidative stress and Aβ generation.