Glaucocalyxin A (GLA) has various pharmacological effects like antioxidation, immune regulation, and antiatherosclerosis. Here, in this study, the effect and mechanism of GLA on mast cell degranulation were studied. The results of the anti-DNP
IgE-mediated passive cutaneous anaphylaxis (PCA) showed that GLA dramatically inhibited PCA in vivo, as evidenced by reduced
Evans blue extravasation and decreased ear thickness. In addition, GLA significantly reduced the release of
histamine and β-
hexosaminidase,
calcium influx,
cytokine (IL-4, TNF-α, IL-1β, IL-13, and IL-8) production in the RBL-2H3 (rat basophilic
leukemia cells), and RPMCs (peritoneal mast cells) in vitro. Moreover, we further investigated the regulatory mechanism of GLA on
antigen-induced mast cells by Western blot, which showed that GLA inhibited FcεRI-mediated signal transduction and invalidated the phosphorylation of Syk, Fyn, Lyn, Gab2, and PLC-γ1. In addition, GLA inhibited the recombinant mouse high mobility group
protein B1- (HMGB1-) induced mast cell degranulation through limiting nuclear translocation of NF-κBp65. Treatment of mast cells with siRNA-HMGB1 significantly inhibited
HMGB1 levels, as well as MyD88 and TLR4, decreased intracellular
calcium levels, and suppressed the release of β-
hexosaminidase. Meanwhile, GLA increased NrF2 and HO-1 levels by activating p38MAPK phosphorylation. Consequently, these data suggest that GLA regulates the NrF2/HO-1 signaling pathway through p38MAPK phosphorylation and inhibits
HMGB1/TLR4/NF-κB signaling pathway to reduce mast cell degranulation and allergic
inflammation. Our findings could be used as a promising therapeutic drug against allergic inflammatory disease.