Inhibitory activities of flavonoids from Scutellaria baicalensis Georgi on amyloid aggregation related to type 2 diabetes and the possible structural requirements for polyphenol in inhibiting the nucleation phase of hIAPP aggregation

Abstract

Human islet amyloid polypeptide (hIAPP)-mediated cytotoxicity is identified as a potential target for developing new anti-diabetic molecules. Herein, we investigated the effect of the major bioactive compounds of Scutellaria baicalensis Georgi (S. baicalensis), including baicalein, baicalin, wogonin and oroxylin A, on hIAPP aggregation. We found that all of these compounds inhibited hIAPP fibril formation in a dose-dependent manner. But baicalein and baicalin, especially baicalein are more effective than wogonin and oroxylin A in stabilizing hIAPP monomers and eliminating toxic hIAPP assembly, suggesting that flavonoids with ortho-hydroxyl group on the A-ring exhibited higher anti-hIAPP nucleation potential than those without this structure. This stimulated our interest in further studying the possible structure-activity relationship between polyphenol and hIAPP aggregation inhibition. Our results demonstrated that flavonoids with ortho-hydroxyl group on the B-ring are also more effective against hIAPP nucleation than those without this structure. These results suggest that the ortho-hydroxybenzene structure is a key structural feature required for polyphenols to effectively inhibit hIAPP nucleation. This was further confirmed by the effects of polyphenol and phenols in inhibiting hIAPP nucleation. The conclusion that pyrogallol-type polyphenols are potential lead inhibitors may provide a valuable structural template for the further development of polyphenol-based inhibitor of amyloid peptides.