Nepetin, a natural compound from Inulae flos, suppresses degranulation and eicosanoid generation through PLCγ1 and Akt signaling pathways in mast cells.

Nepetin derived from the flowers of Inula japonica, Inulae flos, has been reported to exert several biological activities, including anti-inflammatory responses. In this study, we evaluated the anti-allergic property of nepetin with its molecular mechanisms in bone marrow-derived mast cells (BMMC) and mice. In this in vitro study, we investigated the inhibitory effects of nepetin on degranulation and generation of leukotriene C₄ (LTC₄) and prostaglandin D₂ (PGD₂) in IgE/antigen (Ag)-stimulated BMMC. The effect of nepetin on passive cutaneous anaphylaxis (PCA) reaction was also studied in mice. Nepetin reduced degranulation and LTC₄ generation in BMMC. The IgE/Ag-mediated signaling pathway demonstrated that nepetin suppressed intracellular Ca²⁺ level and activation of PLCγ1 and cPLA₂. However, MAPKs were not affected by nepetin in BMMC. In addition, nepetin treatment reduced PGD₂ production and suppressed cyclooxygenase-2 protein expression via the inhibition of the Akt and nuclear factor-κB signaling pathways. With respect to the local allergic response in vivo, oral administration of nepetin suppressed mast cell-dependent PCA reaction in a dose-dependent manner. The results of this study suggest that nepetin might have an anti-allergic potential related to mast cell-mediated inflammatory diseases.