Potent anti-amyloidogenic and fibril-destabilizing effects of polyphenols in vitro: Implications for the prevention and therapeutics of Alzheimer's disease

Abstract

Cerebral deposition of amyloid β-peptide (Aβ) in the brain is an invariant feature of Alzheimer's disease (AD). A consistent protective effect of wine consumption on AD has been documented by epidemiological studies. In the present study, we used fluorescence spectroscopy with thioflavin T and electron microscopy to examine the effects of wine-related polyphenols (myricetin, morin, quercetin, kaempferol (+)-catechin and (-)-epicatechin) on the formation, extension, and destabilization of β-amyloid fibrils (fAβ) at pH 7.5 at 37°C in vitro. All examined polyphenols dose-dependently inhibited formation of fAβ from fresh Aβ(1-40) and Aβ(1-42), as well as their extension. Moreover, these polyphenols dose-dependently destabilized preformed fAβs. The overall activity of the molecules examined was in the order of: myricetin = morin = quercetin > kaempferol > (+)-catechin = (-)-epicatechin. The effective concentrations (EC50) of myricetin, morin and quercetin for the formation, extension and destabilization of fAβs were in the order of 0.1-1 μM. In cell culture experiments, myricetin-treated fAβ were suggested to be less toxic than intact fAβ, as demonstrated by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay. Although the mechanisms by which these polyphenols inhibit fAβ formation from Aβ, and destabilize pre-formed fAβ in vitro are still unclear, polyphenols could be a key molecule for the development of preventives and therapeutics for AD.