Zinc, iron and copper are concentrated in senile plaques of Alzheimer disease. Copper and iron catalyze the Fenton-Haber-Weiss reaction, which likely contributes to oxidative stress in neuronal cells. In this study, we found that ascorbate oxidase activity and the intensity of ascorbate radicals measured using ESR spectroscopy, generated by free Cu(II), was decreased in the presence of amyloid-beta (Abeta), the major component of senile plaques. Specifically, the ascorbate oxidase activity was strongly inhibited (85% decrease) in the presence of Abeta1-16 or Abeta1-42, whereas it was only slightly inhibited in the presence of Abeta1-12 or Abeta25-35 (<20% inhibition). Ascorbate-dependent hydroxyl radical generation by free Cu(II) decreased in the presence of Abeta in the identical order of Abeta1-42, Abeta1-16 > Abeta1-12 and was abolished in the presence of 2-fold molar excess glycylhystidyllysine (GHK). Ascorbate oxidase activity and ascorbate-dependent hydroxyl radical generation by free Fe(III) were inhibited by Abeta1-42, Abeta1-16, and Abeta1-12. Although Cu(II)-Abeta shows a significant SOD-like activity, the rate constant for the reaction of superoxide with Cu(II)-Abeta was much slower than that with SOD. Overall, our results suggest that His6, His13, and His14 residues of Abeta1-42 control the redox activity of transition metals present in senile plaques.

Abstract-The lipid peroxidation product 4-hydroxy-2-nonenal (HNE) is proposed to be a toxic factor in the pathogenesis of Alzheimer's disease. The primary products of lipid peroxidation are phospholipid hydroperoxides and degraded reactive aldehydes, such as HNE, as secondary peroxidation products. In this study, we investigated the role of amyloid-β peptide (Aβ) in the formation of phospholipid hydroperoxides and HNE by copper ion bound to Aβ. The Aβ 1-42 -Cu 2+ (1:1 molar ratio) complex showed an activity to form phospholipid hydroperoxides from phospholipid, 1-palmitoyl-2-linoleoyl phosphatidylcholine (PLPC), through Cu 2+ reduction in the presence of ascorbic acid. The phospholipid hydroperoxides were considered to be racemic mixture of 9-hydroperoxide and 13-hydroperoxide of linoleoyl residue. When Cu 2+ was bound to two molar equivalents of Aβ 1-42 (2 Aβ 1-42 -Cu 2+ ), lipid peroxidation was inhibited.