Effect of Different Anti-Aβ Antibodies on Aβ Fibrillogenesis as Assessed by Atomic Force Microscopy

Extensive data suggest that the conversion of the amyloid-β (Aβ) peptide from soluble to insoluble forms is a key factor in the pathogenesis of Alzheimerʹs disease (AD). In recent years, atomic force microscopy (AFM) has provided useful insights into the physicochemical processes involving Aβ morphology, and it can now be used to explore factors that either inhibit or promote fibrillogenesis. We used ex situ AFM to explore the impact of anti-Aβ antibodies directed against different domains of Aβ on fibril formation. For the AFM studies, two monoclonal antibodies (m3D6 and m266.2) were incubated in solution with Aβ1–42 with a molar ratio of 1:10 (antibody to Aβ) over several days. Fibril formation was analyzed quantitatively by determining the number of fibrils per μm2 and by aggregate size analysis. m3D6, which is directed against an N-terminal domain of Aβ (amino acid residues 1–5) slowed down fibril formation. However, m266.2, which is directed against the central domain of Aβ (amino acid residues 13–28) appeared to completely prevent the formation of fibrils over the course of the experiment. Inhibition of fibril formation by both antibodies was also confirmed by thioflavin-T (ThT) fluorescence experiments carried out with Aβ1–40 incubated for five days. However, unlike AFM results, ThT did not differentiate between the samples incubated with m3D6 versus m266.2. These results indicate that AFM can be not only reliably used to study the effect of different molecules on Aβ aggregation, but that it can provide additional information such as the role of epitope specificity of antibodies as potential inhibitors of fibril formation.