Background: Inflammatory bowel disease (IBD) is a chronic, relapsing inflammatory disorders of the intestinal tract and the pathogenesis of IBD remains unclear. Heme oxygenase-1 (HO-1) is the rate-limiting enzyme and response to different inflammatory mediators and have protective effect in many inflammations. Oregonin has been known to exert anti-inflammatory and anti-oxidative effect and used for traditional oriental medicine. In this study, we have investigated whether oregonin have anti-inflammatory properties in intestinal epithelial cells and mouse model of colitis.
Methods: Caco-2 cells were stimulated with tert-butyl hydroperoxide (t-BH). Monolayer permeability was assessed by measuring the transepithelial electrical resistance and inulin flux. Colitis was induced in mice by intrarectal administration of trinitrobenzene sulfonic acid (TNBS). The mRNA levels were analyzed by real-time polymerase chain reaction (PCR). The protein expression of cyclooxygenase-2 (COX-2), intercellular adhesion molecule-1 (ICAM-1), nuclear factor kappa B (NF-κB), (ZO-1), claudin-1, HO-1, ERK1/2 and JNK were analyzed by Western blot. To silenced HO-1 expression, the cells were transfection with HO-1 siRNA.
Results: Oregonin administration improved the clinical parameters and tissue histological appearance. Oregonin prevented the t-BH-induced increase in permeability by inhibiting the reduction in zonula occludens-1 (ZO-1) and claudin-1 expression. Oregonin inhibit tumor necrosis factor (TNF)-α-induced COX-2 and ICAM-1 expression in the HT-29 cells, as well as NF-kB translocation. It is also induced HO-1 protein expression, whereas, the reduction of COX-2 expression by oregonin were reversed in HO-1 deficient cells. Additionally, pretreatment with ERK and JNK inhibitors also attenuate anti-inflammatory effect of HO-1 which was induced by oregonin. It indicates that HO-1 induction may be regulated by MAPK pathway. In addition, oregonin-induced HO-1 expression also exhibit protective activities in Caco2 cells. t-BH-induced ZO-1 and claudin-1 loss were reversed by oregonin pretreatment and due to oregonin-mediated HO-1 in ERK/JNK pathway.
Conclusions: In this study, we suggest that oregonin inhibits TNF-α induced inflammation and epithelial barrier disruption mediated by HO-1 induction. Thus, our results elucidated the oregonin-mediated HO-1 expression might contribute to the suppression of intestinal inflammation in intestinal epithelial cells, may be potential therapeutic agent for IBD.