Oridonin Suppresses Mast Cell Degranulation and Alleviates Ovalbumin-Induced Allergic Rhinitis

Incidence of type I allergies, such as hay fever, is continuously increasing in developed countries, including Japan. Type I allergies are triggered by chemical mediators, such as histamine, which are released via immunoglobulin E (IgE)-mediated mast cell degranulation. Therefore, medications inhibiting the synthesis, release, and receptor binding of these mediators are commonly used to manage type I allergy symptoms. As self-care disease prevention practices are gaining attention worldwide, regular consumption of food and supplements containing safe components inhibiting mast cell degranulation is a potential strategy to prevent allergic attacks. Here, we aimed to assess the ability of phytochemicals derived from edible plants to inhibit mast cell degranulation using the β-hexosaminidase release assay and investigate their cytotoxicity and efficiency in alleviating allergic symptoms. We found that oridonin, a diterpenoid isolated from Isodon japonicus Hara, strongly inhibited β-hexosaminidase release from both the RBL-2H3 rat cell line and mouse bone marrow-derived mast cells stimulated with dinitrophenyl (DNP)-conjugated human serum albumin after sensitization with DNP-IgE. Oridonin also inhibited β-hexosaminidase release induced by the calcium ionophore, A23187, in both cell types. Notably, oridonin did not adversely affect cell survival at concentrations necessary to inhibit β-hexosaminidase release. In a mouse model of ovalbumin (OVA)-induced allergic rhinitis, intraperitoneal administration of oridonin significantly reduced the nasal rubbing caused by intranasal OVA administration without affecting the serum levels of OVA-specific IgE. Therefore, oridonin could be an effective daily intake component to alleviate allergic diseases by inhibiting mast cell degranulation.