Abstract
The biological activities of propolis are varied from plant sources and the prominent antioxidant effects of Chinese propolis (poplar type) have been extensively reported. Oxidative stress is associated with inflammation and induces many diseases. In the study, to evaluate antioxidant capacities and clarify the underlying molecular mechanisms of ethanol extracts of Chinese propolis (EECP) and ethanol extracts of poplar gums (EEPG), we analyzed their compositions by HPLC, evaluating their free radical scavenging activities and reducing power by chemical analysis methods. Moreover, we studied the roles of EECP and EEPG on the elimination of ROS and expressions of antioxidant genes (HO-1, TrxR1, GCLM, and GCLC) in RAW264.7 cells. We further investigated the effects of MAPKs on the antioxidant genes expression by specific inhibitors. The nucleus translocation effects of Nrf2 were also measured by confocal microscopy analysis. The results indicated that EECP had higher TPC and FDC values but regarding TFC values were not significant. EECP also possessed more contents of 11 compounds than EEPG. Both phytochemical analysis and cell experiment reflected that EECP exerted stronger antioxidant activities than EEPG. EECP and EEPG enhanced endogenous antioxidant defenses by eliminating reactive oxygen species directly and activating Erk-Nrf2-HO1, GCLM, and TrxR1 signal pathways.
Highlights
Poplar-type propolis is a resinous substance collected by honey bees from buds of poplar trees
The results showed that both total flavonoids content (TFC) values and Flavanone and Dihydroflavonol Contents (FDC) values of ethanol extracts of Chinese propolis (EECP) were significant higher than ethanol extracts of poplar gums (EEPG) but TFC values
The results indicated that EECP and EEPG induced the expression of Heme oxygenase -1 GCLC (HO-1), Glutamate-cysteine ligase modifier subunit Thioredoxin reductase 1 (TrxR1) (GCLM), and TrxR1 by activating the phosphorylation of Erk
Summary
Poplar-type propolis is a resinous substance collected by honey bees from buds of poplar trees. Poplar-type propolis has been studied extensively with broad spectrum biological and pharmacological properties, such as antioxidant [1, 2], anti-inflammatory [3], antiproliferative [4], anticardiovascular diseases [5], antidiabetes [6], and hepatoprotective [7] activities. A large number of biological activities of propolis are based on its complex chemical compositions [8], which are mainly dependent on the plant sources. The previous study reveals that poplar bud (Populus nigra) extract contains kinds of phenolic compositions and displays good antioxidant property [9]. The previous studies have distinguished propolis from poplar gums based on its chemical compositions [11, 12]. The relationship between Chinese propolis and poplar buds based on antioxidant capacities and their antioxidant molecular mechanisms is still unclear
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