Chronic Intranasal Treatment with an Anti-Aβ30-42 scFv Antibody Ameliorates Amyloid Pathology in a Transgenic Mouse Model of Alzheimer's Disease

Amyloid-beta peptide (Aβ)-directed active and passive immunization therapeutic strategies reduce brain levels of Aβ, decrease the severity of beta-amyloid plaque pathology and reverse cognitive deficits in mouse models of Alzheimer's disease (AD). As an alternative approach to passive immunization with full IgG molecules, single-chain variable fragment (scFv) antibodies can modulate or neutralize Aβ-related neurotoxicity and inhibit its aggregation in vitro. In this study, we characterized a scFv derived from a full IgG antibody raised against the C-terminus of Aβ, and studied its passage into the brains of APP transgenic mice, as well as its potential to reduce Aβ-related pathology. We found that the scFv entered the brain after intranasal application, and that it bound to beta-amyloid plaques in the cortex and hippocampus of APP transgenic mice. Moreover, the scFv inhibited Aβ fibril formation and Aβ-mediated neurotoxicity in vitro. In a preventative therapeutic approach chronic intranasal treatment with scFv reduced congophilic amyloid angiopathy (CAA) and beta-amyloid plaque numbers in the cortex of APPswe/PS1dE9 mice. This reduction of CAA and plaque pathology was associated with a redistribution of brain Aβ from the insoluble fraction to the soluble peptide pool. Due to their lack of the effector domain of full IgG, scFv may represent an alternative tool for the treatment of Aβ-related pathology without triggering Fc-mediated effector functions. Additionally, our observations support the possibility that Aβ-directed immunotherapy can reduce Aβ deposition in brain vessels in transgenic mice.以β淀粉样肽（Amyloid-beta peptide, Aβ）为靶点的主动与被动免疫治疗策略，可降低阿尔茨海默病（Alzheimer's disease, AD）模型小鼠脑内Aβ水平，减轻β淀粉样斑块病理严重程度，并逆转认知功能缺陷。作为完整免疫球蛋白G（Immunoglobulin G, IgG）分子被动免疫的替代方案，单链可变片段（single-chain variable fragment, scFv）抗体可调节或中和Aβ相关神经毒性，并在体外抑制其聚集。本研究对一株源自针对Aβ羧基末端的完整IgG抗体的scFv进行了特性鉴定，并探究了其穿透血脑屏障进入APP转基因小鼠脑组织的能力，以及其减轻Aβ相关病理的潜在效用。研究结果显示，经鼻内给药后，该scFv可进入脑组织，并结合APP转基因小鼠大脑皮层与海马体中的β淀粉样斑块。此外，该scFv在体外可抑制Aβ纤维形成及Aβ介导的神经毒性。在预防性治疗方案中，对APPswe/PS1dE9小鼠进行长期鼻内scFv给药，可降低其皮层内嗜刚果红淀粉样血管病（congophilic amyloid angiopathy, CAA）的发生程度与β淀粉样斑块数量。这种CAA与斑块病理的减轻，与脑内Aβ从不可溶组分向可溶性肽池的重新分布相关。由于缺乏完整IgG的效应结构域，scFv可作为治疗Aβ相关病理的替代工具，且不会触发Fc介导的效应功能。此外，本研究结果支持以下可能性：以Aβ为靶点的免疫治疗可降低转基因小鼠脑血管内的Aβ沉积。