The effects of Rheum emodin on LPS-induced HIF-1α and COX-2 expression in intestinal epithelial cells

Abstract

Objective To observe the level of hypoxia-inducible factor-1 alpha (HIF-1α) and its downstream target gene cyclooxygenase-2 (COX-2) in LPS-treated intestinal epithelial cells,and to explore the possible intervention targets of Rheum emodin.Methods Human intestinal epithelial cells were cultured in vitro treated with LPS to establish the experimental model.The protein level trends of HIF-1α and COX-2 were measured by Western blot in LPS dose-dependent and time-dependent manners.The protein level trends of HIF-1α,COX-2,Phospho-IκB-α and Phospho-NF-κB p65 were measured in LPS plus various concentrations of Rheum emodin treated groups.The expression of HIF-1α mRNA were detected by PCR after cells treated with LPS or LPS plus Rheum emodin,respectively.The effect of Rheum emodin on the proliferation of intestinal epithelial cells was measured by MTT assay in each group.Data were analyzed with ANOVA,and P ＜0.05 was considered significant.Results LPS induced the protein level of HIF-1α in a dose-dependent and a time-dependent manners.With increasing concentrations of LPS,the protein level of HIF-1α increased to the peak when cells were treated with LPS at 10-30mg/mL,and then gradually decreased (P ＜0.05).Firstly the protein level of HIF-1α reached the peak at 0.5 h after treatment,and then decreased to the lowest level at 4 h,and finally returned to a high level (P＜0.05).The protein level trend of COX-2 went a similar way to that of HIF-1α (P ＜0.05).Rheum emodin inhibited the protein levels of LPS-induced HIF-1α,COX-2,Phospho-IκB-α and Phospho-NF-κB p65 with a significant dose-effect relationship (P ＜ 0.05).The PCR showed Rheum emodin inhibited LPS-induced increasing expression of HIF-1α mRNA.MTT assay showed different concentrations of Rheum emodin (0 μmol/L,20 μmol/L,40 μmol/L,60 μmol/L,80 μmol/L) had no significant effect on cell proliferation (0.95 ± 0.02,0.89 ± 0.03,0.88 ± 0.04,0.91 ± 0.03,0.83 ± 0.03,P ＞ 0.05).Although Rheum emodin produced biological effect at this concentration range,and it had no toxicity to intestinal cells.Conclusions LPS induces HIF-1α/COX-2 signaling pathway in a time-dependent and a dose-dependent manners in intestinal epithelial cells.Rheum emodin blocks the hypoxia pathway of LPS/HIF-1α/COX-2 and the inflammatory pathway of LPS/IκB-α/NF-κB/COX-2,which may play a protective effect on intestinal epithelial cells. Key words: LPS; HIF-1α; Intestinal epithelial cell; Emodin; COX-2