Systems pharmacology-based dissection of potential mechanisms of Exocarpium Citri Grandis for the treatment of chronic bronchitis

Exocarpium Citri Grandis (ECG), a precious traditional Chinese medicine (TCM), has been widely utilized to improve the symptoms of chronic bronchitis (CB) such as cough or sputum. However, its underlying pharmacological mechanisms remain unclear. To investigate the potential mechanisms of ECG for the treatment of CB, a comprehensive systems pharmacology strategy combining network pharmacology, molecular docking, molecular dynamics simulations, and molecular biology experiments in vitro was carried out. In this study, 46 potential targets of CB screened for 10 active ingredients of ECG were strongly linked to inflammatory responses, immune processes, and apoptosis. Molecular docking revealed that the active ingredients of ECG have high binding activity for MyD88, NF-κB p65, Caspase9, and Caspase3, respectively. Meanwhile, MD simulations confirmed that neohesperidin and naringenin have high stability and low binding free energy with NF-κB p65 and Caspase3 in the binding pocket. In the LPS-induced RAW264.7 cell inflammatory model, ECG markedly reduced the secretion of IL1β, IL6, TNF-α, and NO. Transcriptomics showed a total of 337 differential expression genes (DEGs) were screened after ECG treatment, of which 233 down-regulated DEGs were closely associated with the NF-κ B signaling pathway, the Toll-like receptor signaling pathway, the IL-17 signaling pathway, and the TNF signaling pathway. Further analysis results revealed that ECG significantly down-regulated the expression of TLR4, MyD88, NF-κB p65, NF-κB p-p65 (S536), p-IκBα (S36), COX2, ICAM1, and iNOS, and up-regulated the expression of IκBα, inhibited NF-κB p65 entry into the nucleus, thereby suppressing NF-κB signaling transduction. Furthermore, ECG also significantly up-regulated the expression of Bcl-2 and down-regulated the expression of Bax, Caspase3, Caspase8, and Caspase9, inhibiting apoptosis in a dose-dependent manner. Our study reveals the potential pharmacological mechanisms of ECG for the treatment of CB and provides a scientific basis for its clinical application.