Targeting Soluble Amyloid-Beta Oligomers With a Novel Nanobody.

The classical amyloid cascade hypothesis postulates that the aggregation of amyloid plaques and the accumulation of intracellular hyperphosphorylated Tau tangles, together, lead to profound neuronal death. However, emerging research has demonstrated that soluble amyloid-b oligomers (SAbOs) accumulate early, prior to amyloid plaque formation. SAbOs induce memory impairment and disrupt cognitive function independent of amyloid-b plaques, and even in the absence of plaque formation. This work describes the development and characterization of a novel anti-SAbO (E3) nanobody generated from an alpaca immunized with SAbO. In-vitro assays and in-vivo studies using 5XFAD mice indicate that the fluorescein (FAM)-labeled E3 nanobody recognizes both SAbOs and amyloid-b plaques. The E3 nanobody traverses across the blood-brain barrier and binds to amyloid species in the brain of 5XFAD mice. Imaging of mouse brains reveals that SAbO and amyloid-b plaques are not only different in size, shape, and morphology, but also have a distinct spatial distribution in the brain. SAbOs are associated with neurons, while amyloid plaques reside in the extracellular matrix. The results of this study demonstrate that the SAbO nanobody can serve as a diagnostic agent with potential theragnostic applications in Alzheimer's disease.