Mechanism of interaction between urolithin A and -glucosidase: Analysis by inhibition kinetics, fluorescence spectroscopy, isothermal titration calorimetry and molecular docking

In this study, the mechanism of interaction between urolithin A, a gut metabolite of ellagitannins, and a-glucosidase was characterized by inhibition kinetics, fluorescence spectroscopy, isothermal titration calorimetry, and molecular docking. Urolithin A exhibited potential reversible inhibitory activity for a-glucosidase in an uncompetitive manner with an IC50 value of (28.03 +/- 0.59) mu M. The results of fluorescence titration and isothermal titration calorimetry analysis showed that urolithin A statically quenched the endogenous fluorescence of a-glucosidase, which was a spontaneous exothermic process, mainly driven by hydrogen bond and/or van der Waals force. Synchronous fluorescence spectroscopy revealed that urolithin A increased the polarity of tryptophan microenvironment and the hydrophobicity of tyrosine microenvironment. The combination of urolithin A with acarbose, a competitive a-glucosidase inhibitor, showed an additive inhibitory effect. Furthermore, molecular docking showed that urolithin A formed hydrogen bonds with key residues Arg269, Thr273, and His258, which are the sites outside the active center of a-glucosidase. These findings could highlight the value of ellagitannin rich diet as an antihyperglycemic food in the prevention of postprandial hyperglycemia, and indicate that urolithin A may be a promising lead compound of a-glucosidase inhibitor.