Blockade of RANKL/RANK signaling pathway by epigallocatechin gallate alleviates mast cell-mediated inflammatory reactions.

Receptor activator of NF-κB ligand (RANKL) as an osteoclast differentiation factor induces inflammatory reactions via production of thymic stromal lymphopoietin (TSLP). Epigallocatechin gallate (EGCG) is the major and the most active compound in green tea and has anti-inflammatory, anti-cancer, anti-oxidant, and neuroprotective effects. However, the effect and molecular mechanisms of EGCG are still unknown in RANKL-induced inflammatory reactions. Here we investigated the immuno-regulatory effects and its molecular mechanisms of epigallocatechin gallate (EGCG) in RANKL-stimulated human mast cell line, HMC-1 cells. In this study, EGCG prevented expression of PI3 Kinase and phosphorylation of mitogen-activated protein (MAP) Kinases in RANKL-stimulated HMC-1 cells. EGCG prevented caspase-1 activity and decreased transcriptional activity of nuclear factor (NF)-κB by suppressing inhibitory protein κBα phosphorylation in RANKL-stimulated HMC-1 cells. EGCG has been shown to prevent production and mRNA expression of TSLP, interleukin (IL)-1β, IL-6, and IL-8 by RANKL without cytotoxicity. Furthermore, EGCG prevented degranulation of mast cell in RANKL-stimulated HMC-1 cells. Overall, these results suggest that EGCG acts as a natural agent for preventing and treating RANKL-mediated inflammatory diseases by targeting PI3 Kinase, MAP Kinase, caspase-1, and NF-κB signaling cascade in mast cells.