Influence of gallic acid on α-amylase and α-glucosidase inhibitory properties of acarbose

Acarbose is an antidiabetic drug which acts by inhibiting alpha-amylase and alpha-glucosidase activities but with deleterious side effects. Gallic acid (GA) is a phenolic acid that is widespread in plant foods. We therefore investigated the influence of GA on alpha-amylase and alpha-glucosidase inhibitory properties of acarbose (in vitro). Aqueous solutions of acarbose and GA were prepared to a final concentration of 25 mu M each. Thereafter, mixtures of the samples (50% acarbose + 50% GA; 75% acarbose + 25% GA; and 25% acarbose + 75% GA) were prepared. The results revealed that the combination of 50% acarbose and 50% GA showed the highest alpha-glucosidase inhibitory effect, while 75% acarbose + 25% GA showed the highest alpha-amylase inhibitory effect. Furthermore, all the samples caused the inhibition of Fe2+-induced lipid peroxidation (in vitro) in rat pancreatic tissue homogenate, with the combination of 50% acarbose and 50% GA causing the highest inhibition. All the samples also showed antioxidant properties (reducing property, 2,2'-azino-bis (-3-ethyl-benzthiazoline-6-sulphonate [ABTS*] and 1,1-dipheny1-2-picrylhydrazyl [DPPI-1] free radicals scavenging abilities, and Fe2+ chelating ability). Therefore, combinations of GA with acarbose could be employed as antidiabetic therapy, with a possible reduction of side effects of acarbose; nevertheless, the combination of 50% acarbose and 50% GA seems the best. Copyright (C) 2016, Food and Drug Administration, Taiwan. Published by Elsevier Taiwan LLC.