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Ethnopharmacological Relevance: Radix Bupleuri is the root of Bupleurum chinense DC. (BC) and a classic aromatic traditional Chinese medicine. The traditional pharmacological effects of Radix Bupleuri are alleviating bronchial spasms, dilating airways, and promoting the resolution of respiratory inflammation, thereby reducing asthma symptoms., Aim of the Study: Studies have demonstrated the efficacy of water extracts from BC in asthma treatment. However, the potential role of volatile oil, another active constituent in BC, remains unexplored with asthma. Notably, volatile oil is renowned for its ease of absorption and direct targeting of affected areas, offering distinct advantages in alleviating airway inflammation. This study aims to explain the anti-asthmatic mechanism of BC-oil through in vivo and in vitro pharmacological experiments., Materials and Methods: Firstly, the OVA-induced SD rat asthma model was utilized to evaluate the pharmacological effect of BC-oil by lung function monitoring, HE staining, flow cytometry, ELISA, and RT-qPCR. The anti-asthmatic mechanism was further analyzed by combining transcriptomic analysis of lung tissue from rat model and airway smooth muscle tissue from public database. Initially, GC-MS was used to analyze the components of BC-oil. The anti-asthmatic activity was evaluated in 16-HBE, RBL-2H3, and ASMC cells using CAMKII inhibitors to explore of the critical signal transduction regulated by BC-oil. Furthermore, molecular docking and calcium flow assay were utilized to screen and identify the active components from BC-oil., Results: Oral administration of BC-oil significantly enhanced pulmonary function in asthmatic SD rats by reducing airway resistance and elastic resistance. Additionally, BC-oil inhibited inflammatory cytokines, including serum IL-2, pulmonary Il1b, Tnf, and Cxcl13, demonstrating potent anti-inflammatory and immunomodulatory effects. In this study, we analyzed the significant role of OR2W3 in asthma using public transcriptomic data. Furthermore, we indicated that BC-oil regulated the expression of Olr1433 and GNAL in rat lung tissue. BC-oil reduced degranulation and inhibited gene expression of Il3 and Tnf in RBL-2H3 cells and suppressed gene expression of IL8 and TNF in 16-HBE cells. BC-oil also attenuated airway smooth muscle cell proliferation and expression of Acta2 and Ccnd1. Furthermore, BC-oil regulates asthma-related cellular processes by activating CAMKII. GC-MS analysis identified 11 components of BC-oil, and n-hexadecanoic acid, linoleic acid and oleic acid from BC-oil were identified to interact with OR2W3 by molecular docking. The calcium flow assay revealed linoleic acid as a significant activator of OR2W3 and indicated that BC-oil alleviated asthma through the ectopic olfactory signaling pathway., Conclusions: The mechanism of BC-oil in treating asthma through signal transduction of OR2W3 is revealed at the molecular and cellular levels., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Olfactory receptors are ectopically expressed in extra-nasal tissues. The gut is constantly exposed to high levels of odorants where ectopic olfactory receptors may play critical roles. Activation of ectopic olfactory receptor 544 (Olfr544) by azelaic acid (AzA), an Olfr544 ligand, reduces adiposity in mice fed a high-fat diet (HFD) by regulating fuel preference to fats. Herein, we investigated the novel function of Olfr544 in the gut. In GLUTag cells, AzA induces the cAMP-PKA-CREB signaling axis and increases the secretion of GLP-1, an enteroendocrine hormone with anti-obesity effects. In mice fed a HFD and orally administered AzA, GLP-1 plasma levels were elevated in mice. The induction of GLP-1 secretion was negated in cells with Olfr544 gene knockdown and in Olfr544-deficient mice. Gut microbiome analysis revealed that AzA increased the levels of Bacteroides acidifaciens and microbiota associated with antioxidant pathways. In fecal metabolomics analysis, the levels of succinate and trehalose, metabolites correlated with a lean phenotype, were elevated by AzA. The function of Olfr544 in gut inflammation, a key feature in obesity, was further investigated. In RNA sequencing analysis, AzA suppressed LPS-induced activation of inflammatory pathways and reduced TNF-α and IL-6 expression, thereby improving intestinal permeability. The effects of AzA on the gut metabolome, microbiome, and colon inflammation were abrogated in Olfr544-KO mice. These results collectively demonstrated that activation of Olfr544 by AzA in the gut exerts multiple effects by regulating GLP-1 secretion, gut microbiome and metabolites, and colonic inflammation in anti-obesogenic phenotypes and, thus, may be applied for obesity therapeutics.