Baicalin methyl ester prevents the LPS - induced mice intestinal barrier damage in vivo and in vitro via P65/TNF-α/MLCK/ZO-1 signal pathway

The effect of baicalin methyl ester (BME) on the regulation of mice intestinal barrier in the inflammatory response was studied in vivo and in vitro. Thirty six C57/BL mice were randomly divided into six groups (n = 6): control group; LPS group (LPS 3.5 mg/kg given intraperitoneal [ip] on day 7 of the study only), PBS group, and three BME groups (low: 50 mg/kg; medium: 100 mg/kg; high: 200 mg/kg) orally dosed with BME for 7d and LPS ip on day 7. All mice were sacrificed on day 8, and jejunum tissue collected for histopathology (H&E and PAS staining), protein expression of pro-inflammatory factors (TNF-α, IL-6, IL-8, IFN-γ) by ELISA, and intestinal tight junction proteins (ZO-1, occludin, claudin-1 and claudin-4) by Western Blot. Compared with the control group, LPS significantly increased the serum cytokines DAO (p < 0.01) and DLA (p < 0.01), upregulated the expression of pro-inflammatory factors, MLCK proteins (p <0.05) and increased the MLCK/ZO-1ratio (p <0.001). LPS also decreased the expression of claudin-4 (p < 0.01) in the jejunum and induced an inflammatory response damaging the jejunal mucosal barrier. Pretreatment with BME (100-200 mg/kg) significantly decreased the cytokines DAO (p < 0.05) and DLA (p < 0.01) in the serum, pro-inflammatory factors in the jejunum, significantly down-regulated the expression of MLCK (p <0.05) and the ratio of MLCK/ZO-1(p <0.001) but upregulated the expressions of ZO-1(p < 0.01), occludin (p < 0.05), claudin-1(p < 0.05) and claudin-4 (p < 0.05), and thereby restored the intestinal tissue structure, suggestive of alleviation of LPS-induced intestinal inflammation by BME. In vitro, MODE-K cells (derived from mice intestinal epithelium) were exposed to BME at 0 (control group-No LPS), 10, 20 and 40 μM BME for 24 h prior to LPS addition at 50 μg/mL for 2 h. LPS significantly increased the expression of pro-inflammatory factors, MLCK (p < 0.01) and the ratio of MLCK/ZO-1(p <0.001), decreased the expressions of ZO-1 (p < 0.05), occludin (p < 0.01), claudin-1 (p < 0.01) and claudin-4 (p < 0.01) in MODE-K cells compared with the control group. Compared with the LPS group, BME (10 - 40 μM) significantly decreased the expression of pro-inflammatory factors, MLCK (p < 0.05) and the ratio of MLCK/ZO-1(p <0.01) but increased the expressions of ZO-1(p < 0.01), occludin (p < 0.05) and claudin-4(p < 0.01) indicating an up-regulation of the expression of tight junction proteins by BME. On addition of extrinsic TNF-α plus LPS, the TNF- α level increased (p < 0.001) in MODE-K cells and the protein expression of MLCK (p < 0.01) was markedly up-regulated. Molecular docking predicted BME interacted with P65 by forming hydrogen bonds. IP-WB further confirmed that BME was directly bound to P65 protein in MODE-K cells. In conclusion, BME was able to restore the intestinal barrier through the P65 / TNF-α / MLCK / ZO-1 signaling pathway.