Berry components inhibit α-glucosidase in vitro: synergies between acarbose and polyphenols from black currant and rowanberry.

Polyphenol-rich extracts from certain berries inhibited α-glucosidase activity in vitro. The two most effective berry extracts, from black currant and rowanberry, inhibited α-glucosidase with IC(50) values respectively of 20 and 30μg GAE/ml and were as effective as the pharmaceutical inhibitor, acarbose. These berry extracts differed greatly in their polyphenol composition: black currant was dominated by anthocyanins (∼70% of total) whereas rowanberry was enriched in chlorogenic acids (65% total) and had low levels of anthocyanins. Both black currant and rowanberry extracts potentiated the inhibition caused by acarbose and could replace the inhibition lost by reducing the acarbose dose. However, no additive effects were noted when black currant and rowanberry extracts were added in combination. The mechanisms underlying the synergy between acarbose and the berry polyphenols and the lack of synergy between the berry components are discussed. These extracts exhibited the potential to replace acarbose (or reduce the dose required) in its current clinical use in improving post-prandial glycaemic control in type 2 diabetics. As a result, these polyphenols may offer a dietary means for type 2 diabetics to exercise glycaemic control.