Monoclonal Antibody Against the Turn of the 42-Residue Amyloid β-Protein at Positions 22 and 23

Aggregation of the 42-mer amyloid beta-protein (A beta 42) plays a critical role in the pathogenesis of Alzheimer's disease (AD). We have proposed a toxic conformer with a turn at positions 22 and 23, as well as a nontoxic conformer with a turn at positions 25 and 26, in A beta 42 aggregates from systematic proline scanning and solid-state NMR studies. Although recent clinical trials of immunization targeting A beta 42 aggregates have proved useful, some adverse effects were reported. One of the reasons was hypothesized to be excessive immunoreactions derived from the unintended removal of nontoxic A beta 42, which plays an important role in the physiological function. To develop a monoclonal antibody for toxic A beta 42, E22P-A beta 10-35, a minimum moiety for neurotoxicity containing the turn at positions 22 and 23, was used for the generation of antibodies, following the selection of clones using A beta 42 mutants of E22P (turn-inducing) and E22V (turn-preventing). The obtained clone (11A1) showed a high binding affinity (K-D = 10.3 nM) for A beta 42 using surface plasmon resonance. 11A1 also inhibited the neurotoxicity of A beta 42 in PC12 cells. Immunohistochemical studies showed that not only extracellular but intracellular amyloid was stained in human AD brains. In Western blotting analyses using human brains, low-molecular weight-oligomers rather than the monomer of A beta were readily recognized by 11A1. These results imply that 11A1 could detect toxic A beta 42 oligomers with the turn at positions 22 and 23 and that 11A1 could be applicable for the therapeutic targeting of toxic A beta 42 in AD.