Inhibition of human carboxylesterases by ginsenosides: structure\u2013activity relationships and inhibitory mechanism

Zhao-Hui Sun,Hai-Bin Liu,Ling Yang,Guang-Bo Ge,Yun-Qing Song,Li-Wei Zou,Tong-Yi Dou,Jing Chen,Da-Cheng Hao

doi:10.1186/s13020-019-0279-0

Abstract

BackgroundHuman carboxylesterases (hCES) are key serine hydrolases responsible for the hydrolysis of a wide range of endogenous and xenobiotic esters. Although it has been reported that some ginsenosides can modulate the activities of various enzymes, the inhibitory effects of ginsenosides on hCES have not been well-investigated.MethodsIn this study, more than 20 ginsenosides were collected and their inhibitory effects on hCES1A and hCES2A were assayed using the highly specific fluorescent probe substrates for each isoenzyme. Molecular docking simulations were also performed to investigate the interactions between ginsenosides and hCES.ResultsAmong all tested ginsenosides, Dammarenediol II (DM) and 20S-O-β-(d-glucosyl)-dammarenediol II (DMG) displayed potent inhibition against both hCES1A and hCES2A, while protopanaxadiol (PPD) and protopanaxatriol (PPT) exhibited strong inhibition on hCES2A and high selectivity over hCES1A. Introduction of O-glycosyl groups at the core skeleton decreased hCES inhibition activity, while the hydroxyl groups at different sites might also effect hCES inhibition. Inhibition kinetic analyses demonstrated that DM and DMG functioned as competitive inhibitors against hCES1A-mediated d-luciferin methyl ester (DME) hydrolysis. In contrast, DM, DMG, PPD and PPT inhibit hCES2A-mediated fluorescein diacetate (FD) hydrolysis via a mixed manner.ConclusionThe structure–inhibition relationships of ginsenosides as hCES inhibitors was investigated for the first time. Our results revealed that DM and DMG were potent inhibitors against both hCES1A and hCES2A, while PPD and PPT were selective and strong inhibitors against hCES2A.

Highlights

Human carboxylesterases are key serine hydrolases responsible for the hydrolysis of a wide range of endogenous and xenobiotic esters
These results suggested that some ginsenosides showed moderate to strong inhibition on human carboxylesterases 1A (hCES1A) and human carboxylesterases 2A (hCES2A), which prompted us to further research the inhibitory mechanism of these ginsenosides on Human carboxylesterases (hCES)
The Lineweaver–Burk plots clearly showed that Dammarenediol II (DM), 20S-O-β-(d-glucosyl)dammarenediol II (DMG), PPD, and PPT inhibited hCES2A-catalyzed fluorescein diacetate (FD) hydrolysis via a mixed-inhibition manner, with the Ki values of 1.22 μM, 2.83 μM, 0.70 μM and 0.95 μM (Table 2), respectively. These findings suggested that DM, DMG, PPD, and PPT could bind on hCES2A at two distinct ligand-binding sites, which was much different from the binding modes of DM and DMG on hCES1A

Summary

Introduction

Human carboxylesterases (hCES) are key serine hydrolases responsible for the hydrolysis of a wide range of endogenous and xenobiotic esters. It has been reported that some ginsenosides can modulate the activities of various enzymes, the inhibitory effects of ginsenosides on hCES have not been well-investigated. Ginseng products and most of ginsenosides have been found with excellent safety profiles, recent reports have shown that ginsenosides and its metabolites can modulate the treatment outcomes of some therapeutic drugs that can inhibit some key human drug metabolizing enzymes, including UDP-glucuronosyltransferase 2B7 (UGT2B7) and cytochrome P450 3A (CYP3A4) [20, 21]. In view of the wide applications of ginseng products and the combined use of ginseng products and clinical drugs, it is necessary to systematically examine the interactions of ginsenosides with human drug metabolizing enzymes. The interactions of natural ginsenosides or their bacterial metabolites with other key drug metabolizing enzymes (including the esterases) have not been well-investigated

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