A prochelator activated by beta-secretase inhibits Abeta aggregation and suppresses copper-induced reactive oxygen species formation

Abstract

The intersection of the amyloid cascade hypothesis and the implication of metal ions in Alzheimer's disease progression has sparked an interest in using metal-binding compounds as potential therapeutic agents. In the present work, we describe a prochelator SWH that is enzymatically activated by beta-secretase to produce a high affinity copper chelator CP. Because beta-secretase is responsible for the amyloidogenic processing of the amyloid precursor protein, this prochelator strategy imparts disease specificity toward copper chelation not possible with general metal chelators. Furthermore, once activated, CP efficiently sequesters copper from amyloid-beta, prevents and disassembles copper-induced amyloid-beta aggregation, and diminishes copper-promoted reactive oxygen species formation.

Figure 1

The β-secretase substrate has weak metal affinity, but after selective proteolytic cleavage, the product sequesters copper from Aβ, preventing aggregation. When copper is coordinated to Aβ it catalyzes production of ROS, but sequestration by CP prevents such deleterious reactions.

Figure 2

Turbidity of 10 μM Aβ samples in HEPES buffer pH 7.4, as determined by the normalized change in A_405nm Where indicated, 1 equiv of Cu(Gly)₂, ZnCl₂, CP, or SWH were added and incubated at 37 °C for 1 h to monitor aggregation prevention (blue bars). Products from SW or SWH plus BACE reactions were also tested for disaggregation of preformed CuAβ aggregates (green dotted bars).

Figure 3

Effect of peptides on deoxyribose degradation by OH^• generated by Cu-promoted Fenton chemistry. A decrease in A/A₀ indicates a protective effect. Conditions: 100 μM H₂O₂, 10 μM Cu(SO₄), 2 mM ascorbic acid, and 15 mM 2-deoxyribose in 50 mM NaH₂PO₄ buffered to pH 7.4.