In Vitro Amyloid-β Binding and Inhibition of Amyloid-β Self-Association by Therapeutic Albumin

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) 1H-NMR and saturation transfer difference (STD) NMR spectra. The interactions between monomeric Aβ1-40 and albumin were probed by 2D 1H-15 N HSQC spectra of labeled Aβ1-40. The formation of cross-β structured Aβ1-42 assemblies was monitored by ThT fluorescence. The interactions between self-assembled Aβ1-42 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 15N-labeled Aβ1-40, which rules out binding of albumin to monomeric Aβ with dissociation constant in the μM or lower range. When aggregated Aβ1-42 was added to albumin, quenching of Trp fluorescence was observed, which indicates albumin binding to Aβ1-42 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.