Disclosure of a fundamental clue for the elucidation of the myricetin mechanism of action as amyloid aggregation inhibitor by mass spectrometry

Progression of Alzheimer’s disease involves aggregation of amyloid-beta (Abeta) peptides, a complex process that involves the formation of several soluble intermediates and ends up with the deposition of ordered fibrillar architectures. The determination of the Abeta42 selfassembly species targeted by an inhibitor is a key step in the identification of new inhibitors endowed with a suitable profile. In this context, the subtle characterization of myricetin (Myr)mode of action at a molecular level was performed by using different MS techniques, which allowed the monitoring of the modifications induced by Myr on the first occurring Abeta42 self-assembly species. Results showed a persistent level of monomer and decreased formation of ordered Abeta42 aggregates in the presence of Myr, further, nano-LC-nano-ESIQTOF, MALDI-TOF, and ESI-IT highlighted the formation of a new oxidizedAbeta42 species, which is less prone to aggregation, in the presence of Myr. Coupling tryptic digestion and nano-LC-nano-ESI-QTOF also allowed the identification of Met35 as the specific site of oxidation along the Abeta aminoacid chain. Therefore, the detailed investigation by different MS techniques allowed better understanding of the molecular modification at the basis of the antiaggregating properties of Myr and highlighted its oxidizing action on the residue Met35 in Abeta monomers.