An improved capillary electrophoresis method for in vitro monitoring of the challenging early steps of Aβ1-42 peptide oligomerization: Application to anti-Alzheimer's drug discovery

We report an improved CE method to monitor in vitro the self-assembly of monomeric amyloid beta-peptide (42 amino acids amyloid beta-peptide, A beta(1-42)) and in particular the crucial early steps involved in the formation of the neurotoxic oligomers. In order to start the kinetics from the beginning, sample preparation was optimized to provide samples containing exclusively the monomeric form. The CE method was also improved using a dynamic coating and by reducing the separation distance. Using this method, the disappearance of the monomer as well as the progressive formation of four species during the self-assembly process can now be monitored and quantified over time. The hydrodynamic radius of the species present at the initial kinetics step was estimated around 1.8 nm by Taylor dispersion analysis while SDS-PAGE analyses showed the predominance of the monomer. These results confirmed that the A beta(1-42) species present at this initial time was the monomer. Methylene blue, an anti-Alzheimer disease candidate, was then evaluated. In spite of an oligomerization inhibition, the enhanced disappearance of the A beta(1-42) monomer provoked by methylene blue was demonstrated for the first time. This method, allowing the monomeric and smallest oligomeric species to be monitored, represents a new accurate and precise way to evaluate compounds for drug discovery.