Inhibition of amyloid fibrillation of apo-carbonic anhydrase by flavonoid compounds.

Flavonoids are polyphenol compounds abundantly found in plants and reported to have an inhibitory effect on amyloid fibrillation. The number and position of hydroxyl groups, as well as the arrangement of flavonoids rings, may influence their inhibitory effects. In this study, we investigate the effect of structural characteristics of flavonoids on amyloid fibril formation. For this purpose, five compounds (i.e., biochanin A, daidzein, quercetin, chrysin and fisetin) were selected that represent a variety in the number and position of their hydroxyl groups. The inhibitory effect of these flavonoids on the amyloid fibril formation of apo-carbonic anhydrase (apo-BCA), as a model protein, was evaluated using thioflavin T and transmission electron microscopy. The results showed that fisetin possessed the most significant inhibitory effect. Interestingly, upon apo-BCA acetylation, none of the tested flavonoids could inhibit the fibrillation process, which indicates that the interactions of these compounds with the amine groups of lysine residues could be somewhat important.