The α-Glucosidase and α-Amylase Enzyme Inhibitory of Hydroxytyrosol and Oleuropein

Fatma Hadrich, Zouhaier Bouallagui, Han Junkyu, Hiroko Isoda, Sami Sayadi

To date, numerous studies have reported on the antidiabetic properties of various plant extracts through inhibition of carbohydrate-hydrolysing enzymes. The objective of this research was to evaluate the inhibitory effect of the hydroxytyrosol and the oleuropein against α-amylase and α-glucosidase. The hydroxytyrosol was purified from olive leaves. The result shows that the hydroxytyrosol had the strongest α-glucosidase inhibitory effect with IC50 values of 150 μM with mild inhibition against α-amylase. The enzyme kinetic studies, using Lineweaver-Burk indicated that, in the presence of the hydroxytyrosol, the Michaelis-Menton constant (Km) remained constant but the maximal velocity (Vmax) decreased, revealing a non-competitive type of inhibition with inhibition constants; Ki for the formation of the inhibitor-enzyme complex and Kis for the formation of the inhibitor-enzyme-substrate complex of 104.3 and 150.1 μM, respectively. On the other hand, oleuropein showedan uncompetitive inhibition. The concentrations used in this work were below cytotoxic levels observed at 400 μM. However, at 600 μM, the hydroxytyrosol significantly decreased viability of the Caco-2 cells (p < 0.05) and in the case of the oleuropein, there's an increase in cell number compared to control (p < 0.05). These results suggest that the hydroxytyrosol and oleuropein are two potential effective α-glucosidase inhibitors for management of postprandial hyperglycemia.