Cyanidin-3-O-glucoside inhibits Aβ40 fibrillogenesis, disintegrates preformed fibrils, and reduces amyloid cytotoxicity

Alzheimer's disease (AD) is mainly caused by the fibrillogenesis of amyloid-beta protein (A beta). Therefore, the development of effective inhibitors against A beta fibrillogenesis offers great hope for the treatment of AD. Cyanidin-3-O-glucoside (Cy-3G) is a commonly found anthocyanin that is mainly present in fruits, with established neuroprotective effects in situ. However, it remains unknown if Cy-3G can prevent A beta fibrillogenesis and alleviate the corresponding cytotoxicity. In this study, extensive biochemical, biophysical, biological and computational experiments were combined to address this issue. It was found that Cy-3G significantly inhibits A beta 40 fibrillogenesis and disintegrates mature A beta fibrils, and its inhibitory capacity is dependent on the Cy-3G concentration. The circular dichroism results showed that Cy-3G and A beta 40 at a molar ratio of 3 : 1 slightly prevents the structural transformation of A beta 40 from its initial random coil to the beta-sheet-rich structure. Co-incubation of A beta 40 with Cy-3G significantly reduced the production of intracellular reactive oxygen species induced by A beta 40 fibrillogenesis and thus reduced A beta 40-induced cytotoxicity. Molecular dynamics simulations revealed that Cy-3G disrupted the beta-sheet structure of the A beta 40 trimer. Cy-3G was found to mainly interact with the N-terminal region, the central hydrophobic cluster and the beta-sheet region II via hydrophobic and electrostatic interactions. The ten hot spot residues D7, Y10, E11, F19, F20, E22, I31, I32, M35 and V40 were also identified. These findings not only enable a comprehensive understanding of the inhibitory effect of Cy-3G on A beta 40 fibrillogenesis, but also allow the identification of a valuable dietary ingredient that possesses great potential to be developed into functional foods to alleviate AD.