Deciphering Molecular Mechanism Underlying Hypolipidemic Activity of Echinocystic Acid

Li Han,Peng Lai,Jun-Rong Du

doi:10.1155/2014/823154

Li Han, Peng Lai + Show 1 more

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https://doi.org/10.1155/2014/823154

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Abstract

Our previous study showed that a triterpene mixture, consisting of echinocystic acid (EA) and oleanolic acid (OA) at a ratio of 4 : 1, dose-dependently ameliorated the hyperlipidemia and atherosclerosis in rabbits fed with high fat/high cholesterol diets. This study was aimed at exploring the mechanisms underlying antihyperlipidemic effect of EA. Molecular docking simulation of EA was performed using Molegro Virtual Docker (version: 4.3.0) to investigate the potential targets related to lipid metabolism. Based on the molecular docking information, isotope labeling method or spectrophotometry was applied to examine the effect of EA on the activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, acyl-CoA:cholesterol acyltransferase (ACAT), and diacylglycerol acyltransferase (DGAT) in rat liver microsomes. Our results revealed a strong affinity of EA towards ACAT and DGAT in molecular docking analysis, while low binding affinity existed between EA and HMG-CoA reductase as well as between EA and cholesteryl ester transfer protein. Consistent with the results of molecular docking, in vitro enzyme activity assays showed that EA inhibited ACAT and DGAT, with IC50 values of 103 and 139 μM, respectively, and exhibited no significant effect on HMG-CoA reductase activity. The present findings suggest that EA may exert hypolipidemic effect by inhibiting the activity of ACAT and DGAT.

Highlights

Hyperlipidemia is a key pathogenic factor for the development of cardiovascular and cerebrovascular diseases, such as atherosclerosis, hypertension, coronary heart disease, and brain stroke [1]
Our previous study demonstrated that oral administration of a pentacyclic triterpene mixture isolated from G. sinensis fruits (6 or 12 mg/kg/day), consisting of echinocystic acid (EA) and oleanolic acid (OA) at a ratio of 4 : 1, effectively improved the hyperlipidemia and subsequent atherosclerosis in rabbits fed with high fat/high cholesterol diets, suggesting the main constitute EA might be responsive to the hypolipidemic effect of triterpene extract from G. sinensis fruits in vivo [7]
To predict the potential targets of lipid-lowering effects of EA, we performed the molecular docking of EA with hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, diacylglycerol acyltransferase (DGAT), acyl-CoA:cholesterol acyltransferase (ACAT), and cholesteryl ester transfer protein (CETP) by Molegro Virtual Docker (MVD) 4.3.0 tool using Rerank scoring function, respectively

Summary

Introduction

Hyperlipidemia is a key pathogenic factor for the development of cardiovascular and cerebrovascular diseases, such as atherosclerosis, hypertension, coronary heart disease, and brain stroke [1]. Phytochemical and pharmacological studies have demonstrated that triterpenoidal saponins are the main active constitutes of G. sinensis [6]. Our previous study demonstrated that oral administration of a pentacyclic triterpene mixture isolated from G. sinensis fruits (6 or 12 mg/kg/day), consisting of echinocystic acid (EA) and oleanolic acid (OA) at a ratio of 4 : 1, effectively improved the hyperlipidemia and subsequent atherosclerosis in rabbits fed with high fat/high cholesterol diets, suggesting the main constitute EA might be responsive to the hypolipidemic effect of triterpene extract from G. sinensis fruits in vivo [7]. It is reported that OA significantly inhibited the diacylglycerol acyltransferase (DGAT) from rat liver microsomes, lowered plasma cholesterol by inhibiting intestinal acyl-CoA:cholesterol acyltransferase (ACAT) activity in high-fat-fed hamsters, and protected against isoproterenolinduced myocardial ischemia in rats via antihyperlipidemic, antioxidative, and antiarrhythmic properties as well as its membrane-stabilizing action [8,9,10]. EA isolated from G. sinensis fruits prevented rat acute myocardial ischemia induced by isoproterenol and vasopressin [11]

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