Abstract
Alzheimer Disease (AD) is one of the major public health challenges of the 21st century and its development is centered around the amyloid hypothesis which states that extracellular formation of amyloid plaques and the intracellular accumulation of neurofibrillary Tau tangles (NFTs) are caused by the aggregation of β-amyloid (Aβ) peptides. Several biophysical techniques have been employed for studying the aggregation process of Aβ peptides such as thioflavin T (ThT) assay, dynamic light scattering (DLS), capillary electrophoresis (CE), electron microscopy (EM) and atomic force microscopy (AFM). Despite the useful information these methods provide, not all of them are suitable for monitoring the early stages of the process. The main objective of this thesis is to apply Taylor dispersion analysis (TDA) for the monitoring of the Aβ peptide aggregation mechanism. TDA is a modern technique that can size and quantify soluble species ranging from 0.1 nm to a few hundred nm. TDA has yet been employed for a real-time monitoring of the Aβ peptide aggregation. TDA revealed that the aggregation process of Aβ(1-40) and Aβ(1-42) isoforms occurs through distinct pathways. These results have been correlated with ThT assay and DLS. The co-aggregation of Aβ(1-40):Aβ(1-42) mixtures was further explored by TDA and AFM, highlighting the influence of the peptide ratios on the kinetics and the formation of potentially toxic oligomeric species. Finally, the aggregation process of Aβ peptides by TDA was conducted using a simultaneous UV-LIF detection in the presence of FITC-tagged Aβ peptides. This study demonstrated that the aggregation pathways of the native Aβ peptides are altered by the presence of the fluorophore. In conclusion, TDA provided a complete speciation of the different soluble species (monomer, oligomers, protofibrils) during Aβ aggregation, which brings valuable information on the mechanism of aggregation.Keywords: Alzheimer disease; β-amyloid peptides; Taylor dispersion analysis; aggregation studies; atomic force microscopy; ThT assay; dynamic light scattering.