Discovery and Characterization of the Key Constituents in Ginkgo biloba Leaf Extract With Potent Inhibitory Effects on Human UDP-Glucuronosyltransferase 1A1.

Hui-Lin Pang,Guang-Bo Ge,Ping Wang,Yang-Liu Xia,Tong-Yi Dou,Ya-Di Zhu,Qi-Hang Zhou,Chun-Zhi Ai,Guang-Hao Zhu,Hong Ma

doi:10.3389/fphar.2022.815235

Abstract

Human UDP-glucuronosyltransferase 1A1 (hUGT1A1) is one of the most essential phase II enzymes in humans. Dysfunction or strong inhibition of hUGT1A1 may result in hyperbilirubinaemia and clinically relevant drug/herb-drug interactions (DDIs/HDIs). Recently, a high-throughput fluorescence-based assay was constructed by us to find the compounds/herbal extracts with strong inhibition against intracellular hUGT1A1. Following screening of over one hundred of herbal products, the extract of Ginkgo biloba leaves (GBL) displayed the most potent hUGT1A1 inhibition in HeLa-UGT1A1 cells (Hela cells overexpressed hUGT1A1). Further investigations demonstrated that four biflavones including bilobetin, isoginkgetin, sciadopitysin and ginkgetin, are key constituents responsible for hUGT1A1 inhibition in living cells. These biflavones potently inhibit hUGT1A1 in both human liver microsomes (HLM) and living cells, with the IC50 values ranging from 0.075 to 0.41 μM in living cells. Inhibition kinetic analyses and docking simulations suggested that four tested biflavones potently inhibit hUGT1A1-catalyzed NHPN-O-glucuronidation in HLM via a mixed inhibition manner, showing the K i values ranging from 0.07 to 0.74 μM. Collectively, our findings uncover the key constituents in GBL responsible for hUGT1A1 inhibition and decipher their inhibitory mechanisms against hUGT1A1, which will be very helpful for guiding the rational use of GBL-related herbal products in clinical settings.

Highlights

Human UDP-glucuronosyltransferases1A1 is one of the most essential enzymes responsible for the biotransformation and detoxification of the endogenous toxins, and for the metabolic elimination of numerous therapeutic and diet-derived xenobiotics (Ouzzine et al, 2003; Kiang et al, 2005)
These four biflavones, which were cell-permeable and are active in living cells indicated by comparable IC50 values of Human UDP-glucuronosyltransferase 1A1 (hUGT1A1) inhibition between HeLa-UGT1A1 cells and human liver microsomes (HLM), were further revealed to inhibit hUGT1A1-catalyzed NHPN-O-glucuronidation through mixed-inhibition modes, which was consistent with the observations that these four compounds tightly bound on hUGT1A1 in both the catalytic pocket and an allosteric pocket of hUGT1A1 in docking simulations
The results demonstrated that Ginkgo biloba leaves (GBL) extract used in the present study displayed the most potent hUGT1A1 inhibition potency, with the inhibition rate exceeding 95% at the dose of 100 μg/ml

Summary

Introduction

Human UDP-glucuronosyltransferases1A1 (hUGT1A1) is one of the most essential enzymes responsible for the biotransformation and detoxification of the endogenous toxins (e.g., bilirubin), and for the metabolic elimination of numerous therapeutic and diet-derived xenobiotics (Ouzzine et al, 2003; Kiang et al, 2005). Partial or complete loss of hepatic and intestinal UGT1A1 activity may affect the pharmacokinetic behaviours of the UGT1A1-substrate drugs, which in turn, enhance the in vivo effects of UGT1A1-. It should be noted that in some cases, the UGT1A1 inhibitors with improved safety profiles can be used to increase the plasma exposure of phenolic drugs and to achieve desired in vivo therapeutic effects, by reducing the first pass metabolism mediated by intestinal UGT1A1 (Liu D. et al, 2019)

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