Bioactive components and mechanisms of Chinese poplar propolis alleviates oxidized low-density lipoprotein-induced endothelial cells injury

Huasong Chang,Wenwen Yuan,Haizhu Wu,Xusheng Yin,Hongzhuan Xuan

doi:10.1186/s12906-018-2215-8

Abstract

BackgroundPropolis, a polyphenol-rich natural product, has been used as a functional food in anti-inflammation. However, its bioactive components and mechanisms have not been fully elucidated.To discover the bioactive components and anti-inflammatory mechanism, we prepared and separated 8 subfractions from ethyl acetate extract of Chinese propolis (EACP) and investigated the mechanism in oxidized low density lipoprotein (ox-LDL) induced human umbilical vein endothelial cells (HUVECs) damage.MethodsEight subfractions were prepared and separated from ethyl acetate extract of Chinese propolis (EACP) with different concentrations of methanol-water solution, and analysed its chemical constituents by HPLC-DAD/Q-TOF-MS. Then 80% confluent HUVECs were stimulated with 40 μg/mL ox-LDL. Cell viability and apoptosis were evaluated by Sulforhodamine B (SRB) assay and Hoechst 33,258 staining, respectively. Levels of caspase 3, PARP, LC3B, p62, p-mTOR, p-p70S6K, p-PI3K, p-Akt, LOX-1 and p-p38 MAPK were assessed by western blotting and immunofluorescence assay, respectively. Reactive oxygen species (ROS) and mitochondrial membrane potential (MMP) were measured with fluorescent probes.ResultsEach subfraction exhibited similar protective effect although the contents of chemical constituents were different. EACP attenuated ox-LDL induced HUVECs apoptosis, depressed the ratio of LC3-II/LC3-I and enhanced the p62 level. In addition, treatment with EACP also activated the phosphorylation of PI3K/Akt/mTOR, and deactivated the level of LOX-1 and phosphorylation of p38 MAPK. The overproduction of ROS and the damage of MMP were also ameliorated after ECAP treatment.ConclusionsThese findings indicated that the bioactive component of propolis on anti-inflammatory activity was not determined by a single constituent, but a complex interaction including flavonoids, esters and phenolic acids. EACP attenuated ox-LDL induced HUVECs injury by inhibiting LOX-1 level and depressed ROS production against oxidative stress in ox-LDL induced HUVECs, further to activate PI3K/Akt/mTOR pathway and deactivate p38 MAPK to inhibit apoptosis and autophagy, which provide novel insights into the potential application of propolis on modulating chronic inflammation.

Highlights

Propolis, a polyphenol-rich natural product, has been used as a functional food in anti-inflammation
Effect of 8 subfractions and extract of Chinese propolis (EACP) on cell viability in oxidized low density lipoprotein (ox-LDL) induced human umbilical vein endothelial cells (HUVECs) injury To discover the bioactive components of EACP in HUVECs stimulated by ox-LDL, we first tested the cell viability of the 8 subfractions separated from EACP on ox-LDL induced HUVECs
We deduced that the bioactive components of propolis on the protection effects in ox-LDL induced HUVECs were not determined by a single component

Summary

Introduction

A polyphenol-rich natural product, has been used as a functional food in anti-inflammation. Oxidized low density lipoprotein (ox-LDL) is considered to play a critical role in the pathogenesis of atherosclerosis by inducing intracellular lipid accumulation and foam cell formation [2]. During this process, ox-LDL up-regulates the expression of adhesion molecules and recruits the monocytes to the sub endothelial space, leading to the impairment of endothelial cells and decrease of antioxidant capability [3]. Propolis is a resinous material that honey bee (Apis mellifera L.) collect from various plant-derived substances [5, 6] It has widely used as a functional food since ancient time for its widely pharmacological activities, such as antimicrobial, antioxidant, anti-inflammatory, immunomodulatory, and cardioprotective effects [7]. Another report indicated that propolis exhibited strong free-radical scavenging activity and significant in vitro anti-inflammatory effects by modulating key inflammatory mediators of mRNA transcription, inhibiting the production of specific inflammatory cytokines, and blocking the activation of nuclear factor NF-κB [10]

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