Epitope mapping and neuroprotective properties of a human single chain FV antibody that binds an internal epitope of amyloid-beta 1-42

Active and passive immunotherapy targeted at the amyloid-beta (Aβ) peptide has been proposed as therapeutic approach against Alzheimer's disease (AD), and efforts towards the generation and application of antibody-based reagents that are capable of preventing and clearing amyloid aggregates are currently under active investigation. Previously, we selected and characterized a new anti-Aβ 1-42 phage-displayed scFv antibody, designated clone b4.4, using a non-immune human scFv antibody library and demonstrated that a peptide based on the sequence of the Ig heavy chain (V H) complementarity-determining region (HCDR3) of this antibody fragment bound to Aβ 1-42 and had neuroprotective potential against Aβ 1-42 mediated neurotoxicity in rat hippocampal cultured neurons. In the present study, using novel computational methods and in vitro experiments we demonstrated that b4.4 binds to the central region of Aβ 1-42. We also demonstrated that this scFv antibody binds to Aβ-derived diffusible ligands (ADDLs) and neutralizes the toxicity of both fibrillar and oligomeric forms of Aβ 1-42 tested in vitro in SH-SY5Y cell cultures.