A comprehensive study on the generation of reactive oxygen species in Cu-Aβ-catalyzed redox processes.

In the amyloid plaques, a signature of AD, abnormally high Cu concentrations are found bound to Aβ. Most of previous studies reported that Cu-Aβ could contribute to oxidative stress, as HO and •OH are catalytically generated by Cu-Aβ with the assistance of biological reductant, with only one recent report stated that free O is also generated in the Cu-Aβ catalyzed processes, where an indirect technique was applied. To comprehensively investigate the free radicals produced during this Cu-Aβ-mediated process with a biological reductant, DNA-cleavage assay, an indirect method, and two direct methods including electron paramagnetic resonance (EPR) spectroscopy and transient absorption spectroscopy (TAS), both having qualitative and quantitative power, were employed in this work. All the experimental results obtained from the three methods demonstrated that Cu-Aβ in the biological reducing environment was not only able to catalyze the production of HO and •OH, but also to generate free O. The results further indicated that O was the precursor of HO and •OH. It is also important to note that the results obtained from EPR spectroscopy and TAS provided direct evidence for the presence of O and •OH. By virtue of the direct techniques, we also found that the longest peptide fragments of Aβ, Aβ, and Aβ produced the least radicals with a lowest rate. More interestingly, the fibrillar forms of Aβ generated less O and •OH compared with oligomeric and monomeric forms.