Beta-Glucuronidase Inhibition By Constituents Of Mulberry Bark

Intestinal bacterial beta -glucuronidases, the key enzymes responsible for the hydrolysis of various glucuronides into free aglycone, have been recognized as key targets for treating various intestinal diseases. This study aimed to investigate the inhibitory effects and mechanisms of the Mulberry bark constituents on E. coli beta -glucuronidase ( Ec GUS), the most abundant beta -glucuronidases produced by intestinal bacteria. The results showed that the flavonoids isolated from Mulberry bark could strongly inhibit E. coli beta -glucuronidase, with IC (50) values ranging from 1.12 mu M to 10.63 mu M, which were more potent than D-glucaric acid-1,4-lactone. Furthermore, the mode of inhibition of 5 flavonoids with strong E. coli beta -glucuronidase inhibitory activity (IC (50) <= 5 mu M) was carefully investigated by a set of kinetic assays and in silico analyses. The results demonstrated that these flavonoids were noncompetitive inhibitors against E. coli beta -glucuronidase-catalyzed 4-nitrophenyl beta -D-glucuronide hydrolysis, with K (i) values of 0.97 mu M, 2.71 mu M, 3.74 mu M, 3.35 mu M, and 4.03 mu M for morin ( 1 ), sanggenon C ( 2 ), kuwanon G ( 3 ), sanggenol A ( 4 ), and kuwanon C ( 5 ), respectively. Additionally, molecular docking simulations showed that all identified flavonoid-type E. coli beta -glucuronidase inhibitors could be well-docked into E. coli beta -glucuronidase at nonsubstrate binding sites, which were highly consistent with these agents noncompetitive inhibition mode. Collectively, our findings demonstrated that the flavonoids in Mulberry bark displayed strong E. coli beta -glucuronidase inhibition activity, suggesting that Mulberry bark might be a promising dietary supplement for ameliorating beta -glucuronidase-mediated intestinal toxicity.