RESUMO
Extensive research has linked the amyloid-beta (Aß) peptide to neurological dysfunction in Alzheimer's disease (AD). Insoluble Aß plaques in the AD patient brain contain high concentrations of advanced glycation end-products (AGEs) as well as transition metal ions. This research elucidated the roles of Aß, sugars, and Cu2+ in the oxidative stress mechanism of AD at the molecular level. Mass spectral (MS) analysis of the reactions of Aß with two representative sugars, ribose-5-phosphate (R5P) and methylglyoxal (MG), revealed Lys-16 and Arg-5 as the primary glycation sites. Quantitative analysis of superoxide [Formula: see text] production by a cyt c assay showed that Lys-16 generated four times as much [Formula: see text] as Arg-5. Lys-16 and Arg-5 in Aß1-40 are both adjacent to histidine residues, which are suggested to catalyze glycation. Additionally, Lys-16 is close to the central hydrophobic core (Leu-17-Ala-21) and to His-13, both of which are known to lower the pKa of the residue, leading to increased deprotonation of the amine and an enhanced glycation reactivity compared to Arg-5. Gel electrophoresis results indicated that all three components of AD plaques-Aß1-40, sugars, and Cu2+-are necessary for DNA damage. It is concluded that the glycation of Aß1-40 with sugars generates significant amounts of [Formula: see text], owing to the rapid glycation of Lys-16 and Arg-5. In the presence of Cu2+, [Formula: see text] converts to hydroxyl radical (HO·), the source of oxidative stress in AD.
