Therapeutic Effect of Oridonin Against Inflammatory Bowel Disease Involves Inhibition of Intestinal Fibrosis via NF‐κB Pathway

Abstract

IntroductionIntestinal fibrosis and stricture formation are frequent complications of inflammatory bowel disease (IBD). In response to inflammatory stimuli, intestinal epithelial cells may undergo epithelial‐mesenchymal transition (EMT). EMT is a process by which epithelial cells acquire a mesenchymal‐like phenotype, resulting in intestinal fibrosis. Oridonin, a bioactive diterpenoid isolated from Rabdosia rubescens, was reported to have therapeutic effects for IBD. However, the cellular mechanism remains unclear. We hypothesize that oridonin attenuates inflammation‐related EMT and fibrogenesis in intestinal epithelial cells.MethodsIEC‐6 and IEC‐18 cells exposed to TNFα were pre‐treated with or without oridonin. Cellular proteins were analyzed with Western blot or immunofluorescence assay. Cytokine secretion was determined with ELISA.ResultsOridonin treatment suppressed TNFα‐induced NF‐κB activation evidenced by blocking TNFα‐induced NF‐κB p65 nuclear translocation and DNA binding activity. TNFα‐induced phosphorylation of IKKα/β and IκBα as well as total IκBα degradation were prevented by oridonin. TNFα‐stimulated secretion of pro‐inflammatory cytokine IL‐6 was inhibited by oridonin. Oridonin moderately up‐regulates endogenous E‐cadherin and down‐regulates Snail. The expression of extracellular matrix proteins fibronectin and laminin were increased by TNFα and suppressed by pre‐treatment with oridonin. For the first time, we demonstrated that TNFα dose‐dependently up‐regulated α‐smooth muscle actin (α‐SMA), a myofibroblast marker, in IEC‐6 cells. These results indicate that IEC‐6 cells underwent transition into mesenchymal cells after TNFα stimulation. Notably, oridonin inhibited TNFα‐stimulated α‐SMA, but not TGFβ1‐stimulated EMT‐related proteins.ConclusionThe protective effects of oridonin in intestinal epithelial cells may occur through suppression of the TNFα‐induced NF‐κB pathway and EMT‐related fibrogenesis.