An aminosterol breaks the autocatalytic cycle of Aβ42 aggregation and protects cell membranes from its soluble aggregates.

Aberrant aggregates of the 42-residue form of the amyloid-β peptide (Aβ42) are cytotoxic in Alzheimer's disease (AD). Cost-effective and chronically safe disease-modifying therapeutics are needed to address the AD medical emergency worldwide. To increase our understanding of the mechanisms of Aβ42-induced cytotoxicity and to investigate clinically relevant aminosterols, we study the impact of claramine on the aggregation kinetics and properties of Aβ42 aggregates, as well as the ability of these proteotoxic species to bind and disrupt cell membranes. Whereas previously studied aminosterols accelerated Aβ42 aggregation, we show that claramine potently inhibits Aβ42 amyloid fibril formation. We find that claramine stabilizes soluble Aβ42, speeding up primary and secondary nucleation into species with antiparallel β-sheet structure that are elongation incompetent, thereby depleting Aβ42 monomers from the aggregation reaction. This steroid-polyamine also dissociates Aβ42 fibrillar aggregates, resulting in the abrogation of the autocatalytic capacity of Aβ42 fibrils, and it also inhibits the aggregation of a tau fragment relevant to AD. Upon exposure of human neuroblastoma cells to stabilized Aβ42 oligomers, claramine effectively neutralized Aβ42 oligomer-induced cytotoxicity by preventing their binding to cell membranes. Owing to the unique mechanism of action of aminosterols to reduce the toxicity of soluble Aβ42 aggregates by protecting cell membranes, and the newly characterized ability of claramine to inhibit Aβ42 fibril formation and dissociate fibrillar Aβ42 resulting in the interruption of the positive feedback loop in Aβ42 aggregation, our findings further emphasize the relevance of this family of natural products as potential treatments for AD and other protein misfolding diseases.