In vitro anti-hyperglycemic, antioxidant activities and intestinal glucose uptake evaluation of Endiandra kingiana extracts

Optimal control of postprandial hyperglycemia is essentially important in the management of diabetes mellitus. The present investigation was undertaken to evaluate the in vitro anti-hyperglycemic, antioxidant properties and intestinal glucose uptake inhibition of Endiandra kingiana (E. kingiana) extracts. Previously, our group has identified and characterized the bioactive compounds of E. kingiana extracts, which had discovered several polyketides; endiandric acids and kingianins. Here, the inhibitory potential of bark-ethyl acetate (BEA), bark-methanol (BM), leaf-ethyl acetate (LEA), and leaf-methanol (LM) extracts of E. kingiana against carbohydrate-hydrolyzing enzymes with their mode of inhibitions were evaluated. Further, the antioxidant activities and inhibitory potential on glucose uptake in Caco-2 human intestinal cell monolayers were determined. Our finding showed that BEA extract exhibited the most potent inhibition activities against α-amylase (IC50 = 2.32 μg/mL) and α-glucosidase (IC50 = 1.83 μg/mL) by following inhibition mode of competitive and non-competitive manners, respectively. Meanwhile, BM extract exhibited notable antioxidant capabilities, as evidenced by strongest free radical scavenging (IC50 = 1.18 μg/mL) and reducing power effect (118.53 mM Fe2+ equivalent/g extract) in couple with highest total phenolic contents (10.17 mg GAE/g extract) compared to other extracts. Mechanistically, both BEA and BM extracts of E. kingiana significantly inhibited glucose uptake in Caco-2 cell monolayers under sodium-dependent condition. Collectively, these findings suggest that BM and BEA extracts of E. kingiana exert in vitro anti-hyperglycemic and antioxidant properties, which can be further utilized as a potential candidate for treatment of hyperglycemia–induced oxidative stress conditions.