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Planta Med 2021; 87(08): 631-641
DOI: 10.1055/a-1402-6431
Biological and Pharmacological Activity
Original Papers

Beta-Glucuronidase Inhibition by Constituents of Mulberry Bark

Yue Bai
1   College of Basic Medical Sciences, Dalian Medical University, Dalian, China
,
Lu Chen
1   College of Basic Medical Sciences, Dalian Medical University, Dalian, China
,
Yun-Feng Cao
3   Dalian Runsheng Kangtai Medical Laboratory Co. Ltd, Dalian, China
,
Xu-Dong Hou
1   College of Basic Medical Sciences, Dalian Medical University, Dalian, China
,
Shou-Ning Jia
4   Qinghai Hospital of Traditional Chinese Medicine, Xining, China
,
Qi Zhou
1   College of Basic Medical Sciences, Dalian Medical University, Dalian, China
,
Yu-Qi He
2   The Key Laboratory of the Basic Pharmacology of the Ministry of Education, School of Pharmacy, Zunyi Medical University, Zunyi, China
,
Jie Hou
1   College of Basic Medical Sciences, Dalian Medical University, Dalian, China
› Author AffiliationsSupported by: Program for Innovative Leading Talents of Qinghai Province 2018 & 2019
Supported by: Innovative Entrepreneurship Program of High-level Talents in Dalian 2017RQ121
Supported by: Natural Science Foundation of Liaoning Province 20180530025
Supported by: Key R&D and Transformation Science and Technology Cooperation Project of Qinghai Province 2019-HZ-819
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Abstract

Intestinal bacterial β-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 β-glucuronidase (EcGUS), the most abundant β-glucuronidases produced by intestinal bacteria. The results showed that the flavonoids isolated from Mulberry bark could strongly inhibit E. coli β-glucuronidase, with IC50 values ranging from 1.12 µM to 10.63 µM, which were more potent than D-glucaric acid-1,4-lactone. Furthermore, the mode of inhibition of 5 flavonoids with strong E. coli β-glucuronidase inhibitory activity (IC50 ≤ 5 µM) 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 β-glucuronidase-catalyzed 4-nitrophenyl β-D-glucuronide hydrolysis, with Ki values of 0.97 µM, 2.71 µM, 3.74 µM, 3.35 µM, and 4.03 µM 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 β-glucuronidase inhibitors could be well-docked into E. coli β-glucuronidase at nonsubstrate binding sites, which were highly consistent with these agentsʼ noncompetitive inhibition mode. Collectively, our findings demonstrated that the flavonoids in Mulberry bark displayed strong E. coli β-glucuronidase inhibition activity, suggesting that Mulberry bark might be a promising dietary supplement for ameliorating β-glucuronidase-mediated intestinal toxicity.

Key words

Mulberry bark - Moraceae - Morus alba - intestinal bacterial - β-Glucuronidase - enzyme inhibition - flavonoid

Supporting Information

    The following is included in supporting information: the SDS-PAGE of purified EcGUS; the standard curve of Michaelis-Menten after reaction of EcGUS with the substrate (PNPG); the inhibitory effects of the crude extract of Mulberry bark on EcGUS-mediated PNPG hydrolysis, the standard curve of the hydrolytic product (p-nitrophenol) after the reaction of EcGUS with the substrate (PNPG); time-dependent inhibition assays of 5 compounds; the stereodiagram of the flavonoids isolated from Mulberry bark docked with the crystal structure of EcGUS; a stereoview of the crystal structure of EcGUS (PDB ID: 3K46) docked with the substrate PNPG. Also included are the 2D interactions between PNPG and EcGUS; the inhibition kinetics of positive inhibitor on EcGUS; the stereodiagram of positive inhibitor combined with the crystal structure of EcGUS; the 2D interactions and stereodiagram of kuwanon G (a, b), sanggenol A (c, d), and kuwanon C (e, f) combined with the crystal structure of EcGUS (orange: kuwanon G, chartreuse: sanggenol A, marine: kuwanon C); isoboles indexes of morin and kuwanon H (KH) against EcGUS-mediated PNPG hydrolysis.

  • Supporting Information


Publication History

Received: 07 November 2020

Accepted after revision: 28 February 2021

Article published online:
17 March 2021

© 2021. Thieme. All rights reserved.

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