Amygdalin Attenuates Airway Epithelium Apoptosis, Inflammation, and Epithelial-Mesenchymal Transition through Restraining the TLR4/NF-κB Signaling Pathway on LPS-Treated BEAS-2B Bronchial Epithelial Cells

Background: Cough-variant asthma (CVA) is a special type of asthma, solely manifesting with coughing. Studies suggest that airway inflammation is associated with CVA pathogenesis. Amygdalin is found to have an anti-inflammatory potential, while how it affects CVA remains unexplored. Methods: Cytotoxicity delivered by various concentrations of LPS and amygdalin on BEAS-2B cells was determined by Cell Counting Kit-8 assay. CVA in vitro models were established via LPS exposure on BEAS-2B cells which underwent amygdalin pretreatment. Cell apoptosis was determined by flow cytometry. Production of tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-8, and mucin 5AC (MUC5AC) in BEAS-2B cells was measured by ELISA and qRT-PCR. Expressions of TLR4, E-cadherin, N-cadherin, α-smooth muscle actin (SMA), vimentin, phosphorylated-p65 (p-p65), p65, phosphorylated-IκBα (p-IκBα), and IκBα in BEAS-2B cells were measured by qRT-PCR or Western blot. Results: LPS and high concentrations of amygdalin (over 600 μg/mL) decreased BEAS-2B cell toxicity. Exposure to LPS inhibited toxicity, enhanced apoptosis; and promoted production of TNF-α, IL-6, IL-8, and MUC5AC, increased the levels of N-Cadherin, α-SMA, vimentin, p-p65, and p-IκBα, and decreased the levels of E-cadherin and IκBα in BEAS-2B cells. Amygdalin pretreatment counteracted the effects of LPS on BEAS-2B cells. Overexpressing TLR4 reversed amygdalin-exerted effects in LPS-exposed BEAS-2B cells. Conclusion: Amygdalin attenuated airway epithelium apoptosis, inflammation and epithelial-mesenchymal transition through restraining the TLR4/NF-κB signaling pathway in CVA.