Identification and inhibitory activities of ellagic acid- and kaempferol-derivatives from Mongolian oak cups against α-glucosidase, α-amylase and protein glycation linked to type II diabetes and its complications and their influence on HepG2 cells' viability

This study was to characterize phenolic composition of 50% ethanol crude extract (ECE) by UPLC-QTOF-MS/MS and to investigate anti-diabetic activities of the ECE and its four fractions from Mongolian oak cups. The results show that 24 phenolics were identified from the ECE, and ellagic acid (EA)-and kaempferol-derivatives were the main phenolic components in oak cups. Dominant constituents in each of the four fractions were subsequently characterized by HPLC fingerprints. Acid hydrolysis exhibited that oak cups contained both ellagitannins and gallotannins, and ellagitannins were the dominant hydrolysable tannins. Furthermore, ECE and its four fractions exhibited much more drastic inhibitory activities against a-glucosidase than a-amylase, and formation of advanced glycation end-products was inhibited differently by ECE and Frs I-IV. Overall, EA-and kaempferol-derivatives in oak cups were the main anti-diabetic contributors, and EA-derivatives exhibited superior inhibition against a-glucosidase and glycation while kaempferol-derivatives showed stronger a-amylase inhibitory activity. In addition, Frs I-IV affected cell viability differently and kaempferol-derivatives in Fr. IV resulted in its highest anticancer activity. Aforementioned results first indicated that oak cups, being underutilized plant byproducts, should be a novel dietary phytonutrient for diabetes management with inhibitory activities against a-glucosidase, a-amylase and formation of AGEs, as well as for cancer treatment. (C) 2017 The Authors. Production and hosting by Elsevier B.V. on behalf of King Saud University.