The Aβ Peptide of Alzheimer's Disease Directly Produces Hydrogen Peroxide through Metal Ion Reduction

Abstract

Oxidative stress markers characterize the neuropathology both of Alzheimer's disease and of amyloid-bearing transgenic mice. The neurotoxicity of amyloid Aβ peptides has been linked to peroxide generation in cell cultures by an unknown mechanism. We now show that human Aβ directly produces hydrogen peroxide (H₂O₂) by a mechanism that involves the reduction of metal ions, Fe(III) or Cu(II), setting up conditions for Fenton-type chemistry. Spectrophotometric experiments establish that the Aβ peptide reduces Fe(III) and Cu(II) to Fe(II) and Cu(I), respectively. Spectrochemical techniques are used to show that molecular oxygen is then trapped by Aβ and reduced to H₂O₂ in a reaction that is driven by substoichiometric amounts of Fe(II) or Cu(I). In the presence of Cu(II) or Fe(III), Aβ produces a positive thiobarbituric-reactive substance (TBARS) assay, compatible with the generation of the hydroxyl radical (OH·). The amounts of both reduced metal and TBARS reactivity are greatest when generated by Aβ1−42 ≫ Aβ1−40 > rat Aβ1−40, a chemical relationship that correlates with the participation of the native peptides in amyloid pathology. These findings indicate that the accumulation of Aβ could be a direct source of oxidative stress in Alzheimer's disease.