Propolis, owing to its antibacterial and anti-inflammatory properties, acts as a cariostatic agent, capable of preventing the accumulation of dental plaque and inhibiting inflammation. The anti-inflammatory properties of propolis are attributed to caffeic acid phenethyl ester (CAPE), which is present in European propolis. The objective of the conducted study was to assess the anti-inflammatory effects of the Polish ethanolic extract of propolis (EEP) and isolated CAPE on stimulated with LPS and IFN-α, as well as the combination of LPS and IFN-α. The cytotoxicity of the tested compounds was determined using the MTT assay. The concentrations of specific cytokines released by the HGF-1 cell line following treatment with EEP (25-50 µg/mL) or CAPE (25-50 µg/mL) were assessed in the culture supernatant. In the tested concentrations, both CAPE and EEP did not exert cytotoxic effects. Our results demonstrate that CAPE reduces TNF-α and IL-6 in contrast to EEP. Propolis seems effective in stimulating HGF-1 to release IL-6 and IL-8. A statistically significant difference was observed for IL-8 in HGF-1 stimulated by LPS+IFN-α and treated EEP at a concentration of 50 µg/mL (p = 0.021201). Moreover, we observed that CAPE demonstrates a stronger interaction with IL-8 compared to EEP, especially when CAPE was administered at a concentration of 50 µg/mL after LPS + IFN-α stimulation (p = 0.0005). Analysis of the phenolic profile performed by high-performance liquid chromatography allowed identification and quantification in the EEP sample of six phenolic acids, five flavonoids, and one aromatic ester-CAPE. Propolis and its compound-CAPE-exhibit immunomodulatory properties that influence the inflammatory process. Further studies may contribute to explaining the immunomodulatory action of EEP and CAPE and bring comprehensive conclusions.
Keywords: caffeic acid phenethyl ester; cytokines; in vitro model; inflammation; polyphenols; propolis.