Influence of the Physiochemical Properties of Superparamagnetic Iron Oxide Nanoparticles on Amyloid β Protein Fibrillation in Solution

Superparamagnetic iron oxide nanoparticles (SPIONs) are recognized as promising nanodiagnostic materials due to their biocompatibility, unique magnetic properties, and their application as multimodal contrast agents. As coated SPIONs have potential use in the diagnosis and treatment of various brain diseases such as Alzheimer's, a comprehensive understanding of their interactions with A beta and other amyloidogenic proteins is essential prior to their clinical application. Here we demonstrate the effect of thickness and surface charge of the coating layer of SPIONs on the kinetics of fibrillation of A beta in aqueous solution. A size and surface area dependent "dual" effect on A beta fibrillation was observed. While lower concentrations of SPIONs inhibited fibrillation, higher concentrations increased the rate of A beta fibrillation. With respect to coating charge, it is evident that the positively charged SPIONs are capable of promoting fibrillation at significantly lower particle concentrations compared with negatively charged or uncharged SPIONs. This suggests that in addition to the presence of particles, which affect the concentration of monomeric protein in solution (and thereby the nucleation time), there are also effects of binding on the protein conformation.