Comparative Effect of Aqueous and Methanolic Bupleuri Radix Extracts on Hepatic Uptake of High-Density Lipoprotein and Identification of the Potential Target in HFD-Fed Mice.

Zhibin Tan,Yijia Huang,Cheng Cao,Shuling Wang,Fenglian Chen

doi:10.1155/2019/9074289

Abstract

Our previous study found saikosaponin b2 (SSb2) increased high-density lipoprotein (HDL) uptake in HepG2 cells. SSb2 is only found in aqueous Bupleuri Radix extract, and it is one of the secondary saponins derived from saikosaponin d (SSd), which exists in the methanolic extract. This study aimed to compare the effect of aqueous extract of Bupleuri Radix on hepatic uptake of HDL with methanolic extract and to reveal the underlying mechanism of enhancing HDL uptake in mice fed with high-fat diet (HFD). Cellular HDL uptake in each group was quantified by flow cytometry. Bioactive components bound to the HepG2 cytomembrane were detected with HPLC-DAD. RNA sequencing was performed to screen the underlying target on hepatic HDL-uptake, and western blotting was conducted to verify differential protein expression. Significant increases of HDL uptake by HepG2 cells were observed in all groups of aqueous extract of Bupleuri Radix, while no effect or negative effect was observed in the methanolic extract. Saikosaponin b1 (SSb1) and SSb2 were detected in the desorption elute of the aqueous extract from the HepG2 cytomembrane, while saikosaponin a (SSa) and SSd were not found. Remarkable upregulation of FGF21 in HFD-fed mice liver was affirmed after treatment with aqueous extract. This study suggested that aqueous Bupleuri Radix extract could promote hepatic HDL uptake in vitro but methanolic extract could not, and FGF21 might be the potential target.

Highlights

Bupleuri Radix, the root of Bupleurum chinense DC. or Bupleurum scorzonerifolium Willd. [1], is a widely used herbal medicine in China, which regulates functions of the internal organs to relieve fever, disperse the stagnation of liver-qi, and uplift yang-qi
It was clearly observed that either aqueous or methanolic extract had no influence on the viability of HepG2 cells at concentrations of 5, 10, and 15 mg/mL after culturing for 24 h, compared with the negative control group. ese findings indicated that Bupleuri Radix extracts exhibited cytotoxicity against HepG2 cell lines in a concentrationdependent manner, but they could be safely administered to cells at a low concentration of 5, 10, or 15 mg/mL
A variety of studies [16, 17] have claimed that primary saikosaponins (SSa, saikosaponin d (SSd), SSc, etc.) have unstable chemical structure and immensely switch into secondary saikosaponins (SSb1, saikosaponin b2 (SSb2), SSh, etc.) when Bupleuri Radix is extracted in boiling water, while they are stable in extraction with methanol

Summary

Introduction

Bupleuri Radix, the root of Bupleurum chinense DC. or Bupleurum scorzonerifolium Willd. [1], is a widely used herbal medicine in China, which regulates functions of the internal organs to relieve fever, disperse the stagnation of liver-qi, and uplift yang-qi. SSa and SSd are characteristic components in crude plant material of Bupleuri Radix, and they are configurational isomers and have an oxygen ether ring in common, which is unstable and splits during decocting process with boiling water, triggering structure transformation into secondary saikosaponins, SSb1 and SSb2, respectively. The conventional extraction of Chinese medicinal herbs is decocting with boiling water, and of note, crude plant material of Bupleuri Radix needs to be processed with vinegar [11] before used for liver diseases as prescribed in Evidence-Based Complementary and Alternative Medicine ancient documents of Chinese traditional medicine, but with the innovation of modernization and internationalization of Chinese herbal medicines, ethanol extraction is vastly applied in the production. Whether primary or secondary saikosaponins are active ingredients in the Bupleuri Radix extract is unclear as yet

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Conclusion