Synergistic Inhibition of PMA-induced U937 Macrophage Differentiation by Robinia pseudoacacia Honey and Propolis

Macrophage differentiation of U937 monocytes is induced by PMA stimulation, which is driven by the expression and phosphorylation of numerous intracellular proteins. We prepared honey, propolis, and a mixture of honey and propolis called Honeypolis, and confirmed the inhibition of macrophage differentiation by PMA. PMA at 10 ng/mL promoted U937 macrophage differentiation, accompanied by increased expression and phosphorylation of TLR4, CK2-α, PPAR-γ, NF-κB, and SOCS3. Furthermore, the U937 cells differentiated into macrophages and became adherent to the culture dish. However, when propolis and Honeypolis were co-treated with PMA, macrophage differentiation was inhibited and cell morphology remained unchanged, and adherent cells were not observed. In addition, propolis and honeypolis were affected the expression and phosphoryaltion of intracellular protein molecules, decreasing the expression of TLR4, CK2-α, SOCS3, and PPAR-γ and the phosphorylation of NF-κB and PPAR-γ. In addition, propolis and honeypolis regulated the major protein of MAPK such as p38 phosphorylation and SAPK/JNK phosphorylation and expression. Especially, honeypolis showed a higher effect on protein expression and phosphorylation than propolis, indicating that the combination of honey and propolis exhibited a synergistic functional effect. In conclusion, our results show that both propolis and honeypolis inhibit PMA-induced U937 macrophage differentiation. And our study suggests that propolis has the immunosuppressive effects, and our results provided in vitro data for immunosuppressive agents application.