Attenuated amyloid-β aggregation and neurotoxicity owing to methionine oxidation

Aggregation of the amyloid-beta (A beta) peptide into amyloid plaques is a characteristic feature of Alzheimer's disease neuropathogenesis. We and others have previously demonstrated delayed A beta aggregation as a consequence of oxidizing a single methionine residue at position 35 (Met-35). Here, we examined the consequences of Met-35 oxidation on the extremely aggregation-prone peptides A beta I-42 and A beta I-40Arctic with respect to protofibril and oligomer formation as well as neurotoxicity. Size exclusion chromatography and mass spectrometry demonstrated that monomer/dimers prevailed over larger oligomers after oxidizing Met-35, and consequently protofibril formation and aggregation of both A beta I-42 and A beta I-40Arctic were delayed. The oxidized peptides completely lacked neurotoxic effects in cortical neuronal cultures under these conditions, in contrast to the neurotoxic properties of the unoxidized peptides. We conclude that oxidation of Met-35 significantly attenuates aggregation of A beta I-42 and A beta I-40Arctic, and thereby reduces neurotoxicity.