The Interaction Between Copper Ions And Different Aggregated Forms Of Aβ In Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease, and manifests as neurological disorders and cognitive impairment. Excessive oxidative stress andβ-amyloid (Aβ) peptide deposition are both hallmark of AD. Aβis a metal protein which can combine with copper and has electrochemical activity. Cu(II) may be reduced by Aβand then to convert O₂ into H₂O₂. The free H₂O₂ may be the source of all forms of oxides in AD brain. However, whether Aβis to promote or inhibit the oxidative stress is still controversial. And researches have shown that in the course of interaction between Aβand copper, Aβcan be induced further aggregation by copper. Thus it is necessary to study the relationship of different aggregated forms of Aβand copper-related oxidative stress. This paper studied the interaction between three different forms of Aβand copper, and demonstrated that there are different interaction behavior between three different aggregated forms of Aβ(monomer, oligomer and fibril) and copper. In addition, the paper also compared the toxicity of three different forms of Aβ.The three different aggregated forms of Aβwere first prepared. Their aggregation processes were detected by ThT, and they were characterized by SEC and TEM quantitatively and qualitatively, respectively. Then TCEP-DTNB and H₂DCF-DA experiments were used to detect the different behavior of H₂O₂ production when three different forms of Aβinteracted with copper. Among them, in the entire range of copper concentration (from 0.2-1.4μM), monomer had the effect to inhibit the production of H₂O₂. The effect of oligomer and fibril were both determined by the concentration of copper which means that there was an inflection point (Cu(II): 0.8μM). When the concentration of copper was less than the inflection point, both oligomer and fibril can promote the generation of H₂O₂, while they can inhibit the H₂O₂ production when the concentration of copper exceed the inflection point. Under the inflection point of copper concentration (0.8μM), the properties of three forms of Aβwere investigated in terms of H₂O₂ production. It was found that oligomer can produce the highest amount of H₂O₂.By means of the reduction assay, the amounts of produced Cu(I) were measured when the three forms of Aβwere incubated with Cu(II). The results showed that oligomer can promote the most amount of Cu(I) generation. Interestingly monomer produced even higher amount of Cu(I) than fibril. Subsequently, the amounts of generated Cu(I) and H₂O₂ were measured in the presence of ascorbic acid without using Aβto determine the direct relationship between the generation of Cu(I) and H₂O₂. It was found that there was a positive correlation between the amount of Cu(I) and the generation of H₂O₂ when there was absent of the impact factor of conformation. Thus, the key factor in these different behaviors for H₂O₂ generation may be the different conformations of the aggregated state. The moderate folded, stacked state such as oligomer is essential for the high production of H₂O₂. That may be one of the reasons for that oligomeric form of Aβ42 is potentially the most toxic species...