Bruceine D ameliorates the balance of Th1/Th2 in a mouse model of ovalbumin-induced allergic asthma via inhibiting the NOTCH pathway

Allergic asthma is a heterogeneous inflammatory disorder triggered by inhaled allergens, leading to airflow obstruction, bronchial inflammation, and airway hyperresponsiveness (AHR). T helper (Th) 2 cell-mediated immune response and airway inflammation are the key features of allergic asthma. Bruceine D (BD) is a bioactive compound extracted from the seeds of Brucea javanica. The present study aimed to investigate the effects of increased doses of BD on AHR, secretion of Th1-/Th2-associated cytokines, and inflammatory cell infiltration in ovalbumin (OVA)-induced allergic asthma mice. The results showed that BD reduced OVA-induced inflammatory cell infiltration and bronchial hyperresponsiveness into the peribronchial tissues and perivascular areas. Mice treated with BD also showed significantly decreased expressions of Th2-associated cytokines (i.e., interleukin (IL)-4, IL-5, and IL-13) and elevated production of Th1-associated cytokines (i.e., interferon gamma and IL-2) following OVA stimulation. BD treatment dose-dependently inhibited OVA-induced accumulation of inflammatory cells in asthmatic mice. Further analysis revealed that OVA exposure upregulated pulmonary expressions of NOTCH signaling receptors, a group of transmembrane proteins that communicate signals upon binding to transmembrane ligands expressed on adjacent cells, while BD treatment significantly abolished OVA-induced activation of the NOTCH pathway. In conclusion, BD protected mice against OVA-induced allergic asthma by reducing AHR and restoring the Th1/Th2 balance through the NOTCH signaling pathway. Our findings highlighted the potential of BD as a therapeutic agent for allergic asthma.