Inhibition of Aromatase and α-Amylase by Flavonoids and Proanthocyanidins from Sorghum bicolor Bran Extracts

We compared the ability of simple flavonoids and proanthocyanidins in Sorghum bicolor bran extracts to inhibit enzymes in vitro. In particular, aromatase is a target for breast cancer therapy, and inhibition of alpha-amylase can reduce the glycemic effect of dietary starches. Proanthocyanidin-rich sumac sorghum bran extract inhibited alpha-amylase at a lower concentration (50% inhibitory concentration [IC50] = 1.4 mu g/mL) than did proanthocyanidin-free black sorghum bran extract (IC50 = 11.4 mu g/mL). Sumac sorghum bran extract inhibited aromatase activity more strongly than black sorghum bran extract (IC50 = 12.1 mu g/mL vs. 18.8 mu g/mL, respectively). Bovine serum albumin (BSA), which binds proanthocyanidins, reduced inhibition by sumac but not black sorghum bran extract. When separated on Sephadex LH-20, sumac sorghum proanthocyanidins inhibited both enzymes but showed reduced inhibition with BSA. Flavonoids from either cultivar had higher IC50 values than proanthocyanidins, and BSA had little effect on their inhibition. Proanthocyanidins and simple flavonoids in LH-20 fractions both inhibited aromatase with mixed kinetics and affected K-m and V-max. The results show that potential health benefits of sorghum bran may include actions of monomeric flavanoids as well as proanthocyanidins.