<i>In Vitro</i> Amyloid-β Binding and Inhibition of Amyloid-β Self-Association by Therapeutic Albumin

Abstract

Background: A promising approach for treating Alzheimer’s disease relies on the net efflux of the amyloid-β (Aβ) peptide from the brain to peripheral plasma, as a result of plasma Aβ clearance promoted by plasma removal and therapeutic albumin replacement. Objective: To assess the binding of therapeutic albumin (Albutein ® , Grifols) to monomeric and aggregated Aβ according to methods previously tested on the interactions between Aβ and research-grade albumin. Methods: Albumin integrity and the interactions with albumin stabilizers (octanoic acid and N-Ac-Trp) were assessed through one-dimensional (1D) 1 H-NMR and saturation transfer difference (STD) NMR spectra. The interactions between monomeric Aβ 1-40 and albumin were probed by 2D 1 H- 15 N HSQC spectra of labeled Aβ 1-40 . The formation of cross-β structured Aβ 1-42 assemblies was monitored by ThT fluorescence. The interactions between self-assembled Aβ 1-42 and albumin were probed by Trp fluorescence. Results: NMR spectra indicated that both therapeutic and research-grade albumin are similarly well-folded proteins. No significant changes in either HSQC peak position or intensity were observed upon addition of albumin to 15 N-labeled Aβ 1-40 , which rules out binding of albumin to monomeric Aβ with dissociation constant in the µM or lower range. When aggregated Aβ 1-42 was added to albumin, quenching of Trp fluorescence was observed, which indicates albumin binding to Aβ 1-42 aggregates. The relative potency of therapeutic albumin as an Aβ self-association inhibitor was in the same order of magnitude as research-grade albumin. Conclusions: Albutein ® inhibited Aβ self-association by selectively binding Aβ aggregates rather than monomers and by preventing further growth of the Aβ assemblies.