DPP4 Inhibitor Sitagliptin Reduces Inflammatory Responses and Mast Cell Activation in Allergic Rhinitis

Introduction: DPP4 is thought to be involved in certain immune processes and plays an important role in allergic reactions in the lungs. The effect of the DPP4 inhibitor sitagliptin on the effector phase of allergic rhinitis (AR) in ovalbumin (OVA)-sensitized mice and on mast cell degranulation in vitro was assessed. Methods: The AR mouse model was established by intraperitoneal injection combined with OVA intranasal method. OVA was injected intraperitoneally 3 times for the first 2 weeks, and the mice were subsequently given DPP4 inhibitors by oral gavage, accompanied by an OVA intranasal challenge. The impacts of DPP4 inhibitors on DPP4 levels in mouse model were determined. Nasal mucosa tissue was collected for H&E staining and toluidine blue staining. Immunoglobulin E (IgE) levels and histamine levels were analyzed, and IL-4, IL-5, and IL-12 as well as IFN-γ levels were assessed. Following the treatment of dinitrophenol (DNP)-IgE or DNP-IgE plus sitagliptin in RBL-2H3 cells, β-hexosaminidase activity was analyzed and toluidine blue staining was performed. Results: DPP4 level was reduced in AR patients, as well as in AR mouse models. Nasal allergic symptoms such as sneezing and nose-scratching showed high frequency in OVA-induced mice. Sitagliptin treatment during the intranasal challenge of OVA decreased DPP4 levels, suppressed allergic symptoms, eosinophil infiltration, IgE levels, mast cell infiltration, as well as the levels of inflammatory cytokines. We further found that sitagliptin inhibited mast cell activation and histamine levels in vitro. Conclusion: Sitagliptin suppresses the effector phase of AR, and this mechanism is partly attributed to the suppression of inflammatory response and mast cell degranulation.