Non-Targeted Metabolomic Analysis of Ethanol Extract of Propolis and Its Anti-Inflammatory Effects in LPS-Induced BV2 Microglial Cells via the TLR4 Signaling Pathway

Propolis contains abundant flavonoid and phenolic compounds, whose composition and concentration vary significantly in different geographical origins, thereby affecting its bioactive properties including anti-inflammatory, antioxidant, and antimicrobial activities. In this study, the flavonoid and phenolic content in the ethanol extract of propolis (EEP) from Henan (HN) and Shandong (SD) provinces was quantitatively analyzed, and the results showed that concentrations of both bioactive components in HN were slightly higher than those in SD. The non-targeted metabolomics technology was further employed to analyze the components of EEP, and a total of 10683 metabolites were detected. In the comparison between the samples of HN and SD, there were a total of 1436 differential metabolites, with 553 decreased and 883 increased in the HN sample. Among them, there were 205 differential metabolites related to flavonoids and phenols, with 108 decreased and 97 increased in the HN sample. However, a greater number of carboxylic acids and derivatives, fatty derivatives and organooxygen metabolites were found at higher relative levels in the HN sample. As a result, the EEP of the HN sample was selected to investigate its inhibitory effect on inflammation in lipopolysaccharide (LPS)-induced BV2 microglia cells. The results showed that LPS promoted the M1 polarization of BV2 microglia. However, treatment with EEP at concentrations of 10 µg/mL, 5 µg/mL, and 2.5 µg/mL could partially restore the cell morphology to its non-activated state. Meanwhile, LPS stimulation increased the protein levels of IL-1β, IL-6 and TNF-α significantly, as well as the relative gene expression levels of <i>IL-1β</i>, <i>IL-6</i>, <i>TNF-α</i>, <i>COX-2</i>, <i>iNOS</i> and TLR4. After treatment with the EEP, the expression levels of these three proteins and six genes were significantly decreased. These findings revealed that EEP effectively inhibited the M1 polarization of LPS-induced BV2 cells and decreased the expression of inflammatory factors, indicating its potential as a therapeutic agent for neuroinflammation.