The discovery of a novel series of amyloid-β antiaggregants based on the structure of 3-hydroxyanthranilic acid: a detailed analysis of the mechanism of action underpinning antiaggregant activity

Abstract

Alzheimer’s disease (AD) is the fourth leading cause of death in the industrialized nations, yet there are no disease-stabilizing therapies currently in use. The amyloid hypothesis suggests that oligomeric species of the amyloidogenic protein amyloid-β (Aβ) are the principle neurotoxic species in Alzheimer’s disease brain; therefore compounds which inhibit the self-association of Aβ may serve as putative therapeutics which address the underlying pathogenesis of AD. 3-hydroxyanthranilic acid (3HAA) is a compound endogenous to the brain which previous work has determined is a modulator of Aβ secondary structure. The thioflavin T (ThT) fibrillogenesis assay has confirmed that 3HAA is a potent inhibitor of amyloid-β fibril formation, and a comparison of its antifibrillogenic to several known polyphenol antiaggregants has confirmed that 3HAA is among the most potent small-molecule inhibitors of Aβ fibril formation known. Here, 3HAA was assessed as a platform for the development of a novel series of antiaggregant compounds. Analyses of several analogues of 3HAA confirm that the o-aminophenol motif underlies the observed antifibrillogenic activity of the compound that has led to the development of a serious of o-aminophenol-containing compounds which are novel inhibitors of Aβ aggregation. These compounds, as well as a series of plant-derived polyphenol-containing antiaggregants, were assessed in vitro for antifibrillogenic activity using the ThT fibrillogenesis assay and antioligomeric activity using a modified sandwich enzyme-linked immunosorbent assay (ELISA); results from these assays suggest that disparate mechanism underlie their observed antifibrillogenic activity. Here, in vitro assessments of antiaggregant activity were supplemented with both molecular modeling studies of compound binding to monomeric Aβ and nuclear magnetic resonance studies to assess compound binding in situ. Taken together these studies indicate that multiple mechanisms of action underlie the observed antiaggregant activity of these compounds – all of which involve the stabilization of fibrillogenically inactive monomeric forms of Aβ. These studies have clarified the mechanism of action of both o-aminophenol-containing antiaggregants and polyphenol-containing antiaggregants and provide a framework for the development of future antiaggregants with putative clinical application in the treatment of AD.