Mechanism of electroacupuncture in the treatment of olfactory function in rats with allergic rhinitis based on TLR4/NLRP3/Caspase-1/GSDMD pyroptosis pathway

To observe the effect of electroacupuncture (EA) on olfactory function and the olfactory mucosa toll-like receptor 4 (TLR4)/NOD-like receptor thermal protein domain associated protein 3 (NLRP3)/Caspase-1/gasdermin D (GSDMD) signaling pathway in rats with allergic rhinitis (AR) and olfactory dysfunction (OD), so as to explore the mechanism of EA in improving olfactory function.

The AR rat model was established using the ovalbumin sensitization method. Rats with OD were screened using the buried food pellet test (BFPT) and randomly divided into a model group and an EA group, with 3 rats in each group. Three normal SD rats were taken as the control group. Rats of the EA group received EA at bilateral “Yingxiang” (LI20) for 10 min each time, once daily for 14 d. After EA intervention, nasal symptom scores were assessed in each group; BFPT was used to evaluate olfactory function; HE staining was used to observe the morphological changes of the olfactory mucosa; ELISA was used to detect serum contents of tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, and IL-18; immunohistochemistry was used to detect the positive expressions of TLR4, NLRP3, GSDMD, phosphorylated nuclear factor-κB (p-NF-κB) p65, Caspase-1, and olfactory marker protein (OMP) in the olfactory mucosa.

In the model group, the olfactory mucosal epithelium exhibited thinning with a reduced number of cell layers, mucosal cell necrosis and exfoliation, structural disruption, disorganized arrangement, and significant inflammatory cell infiltration. Compared with the control group, nasal symptom score was increased (P<0.01), olfactory function was decreased (P<0.01), serum levels of TNF-α, IL-1β, and IL-18 and the expressions of TLR4, NLRP3, GSDMD, p-NF-κB p65, and Caspase-1 in the olfactory mucosa were increased (P<0.01), while OMP expression was decreased (P<0.01) in the model group. After EA intervention, the EA group showed increased thickness of the olfactory epithelium and number of cell layers, reduced necrosis and shedding of mucosal cells and structural damage, and no significant inflammatory cell infiltration. Compared with the model group, the EA group showed a reduction in nasal symptom score (P<0.05), improvement in olfactory function (P<0.01), decreased serum contents of TNF-α, IL-1β, and IL-18, as well as reduced expressions of TLR4, NLRP3, GSDMD, p-NF-κB p65, and Caspase-1 in the olfactory mucosa (P<0.05, P<0.01), along with increased expression of OMP (P<0.01).

EA may improve olfactory function in AR rats with OD by inhibiting the release of inflammatory factors and regulating pyroptosis mediated by the TLR4/NLRP3/Caspase-1/GSDMD pathway.