In vitro immunomodulatory activity of a Turkish propolis extract encapsulated in poly-ε-caprolactone nanoparticles

Comprehensive studies highlight various biological and pharmacological activities of propolis, which are associated mainly with its phenolic content. However, the undesirable properties of propolis, such as strong sticky behavior, pungent taste and low water solubility, are the main barriers to its widespread use. The objective of the present study was to entrap Turkish propolis extract in a poly-ε-caprolactone (PCL) polymer to eliminate its undesirable features and investigate its effects on several immune response-related biomarkers in vitro in comparison with its crude form. Similar experiments were also conducted with quercetin, which is a phenolic compound that possesses anti-inflammatory activity, for comparison. The single emulsion‒solvent evaporation method was used to fabricate propolis-PCL (256 ± 1.7 nm) and quercetin-PCL (249 ± 2.6 nm) nanoparticles, with satisfactory polydispersity index values (0.08 ± 0.005 and 0.07 ± 0.02, respectively). The in vitro release rates of the nanoparticles displayed an initial burst stage, followed by a persistent release stage extending for more than 300 h. The cumulative release rates for propolis-PCL nanoparticles at neutral (pH 7.4) and acidic (pH 6.8) conditions were 70 % and 77 %, respectively. Propolis-PCL significantly increased the production of the cytokines IL-4 and IFN-γ (approximately 2-fold, p < 0.001), while it also inhibited nitric oxide generation (by more than 3-fold, p < 0.001) in lipopolysaccharide-induced macrophages. In conclusion, the data obtained in this study demonstrate for the first time that propolis-PCL nanoparticles possess regulatory effects on the immune response and that these nanoparticles can be used to develop propolis products with high immunomodulatory properties.