Adrenomedullin improves intestinal epithelial barrier function by downregulating myosin light chain phosphorylation in ulcerative colitis rats

Adrenomedullin (AM) is a pivotal endogenous vasoactive peptide, which can maintain epithelial barrier function in inflammatory bowel disease. Myosin light chain kinase (MLCK)-dependent phosphorylated myosin light chain kinase (p-MLC) is a key regulator of intestinal barrier function. The aim of the present study was to investigate the effect and mechanism of AM on the intestinal epithelial barrier in a rat model of ulcerative colitis (UC) induced by 2,4,6-trinitro-benzene-sulfonic acid (TNBS). A total of 21 male Sprague-Dawley rats were randomly divided into the following three groups and administered different agents for 7 days: The normal group (water and saline), model group (TNBS and saline) and the AM group (TNBS and AM; 1.0 mu g). The weight of rats was recorded every day. Serum tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) levels were detected using ELISA kits. Colon tissue was collected for the assessment of histological alterations. The protein expression of MLCK, p-MLC and zonula occludens-1 (ZO-1) was examined by western blot analysis. Intestinal epithelial tight junctions were examined using transmission electron microscopy. The results demonstrated that in colitis model rats, the expression of TNF-a, IL-6, MLCK and p-MLC significantly increased compared with normal rats. In addition, the expression of ZO-1 decreased (P< 0.05) and intestinal epithelial cell permeability increased. Following AM administration, TNF-a, IL-6, MLCK and p-MLC expression significantly decreased compared with the model rats, the expression of ZO-1 increased (P< 0.05) and intestinal epithelial cell permeability reduced. These data indicate a protective effect of AM on intestinal epithelial barrier dysfunction via suppression of inflammatory cytokines and downregulation of MLCK-p-MLC in TNBS-induced UC. In conclusion, AM/MLCK-p-MLC may be an important signaling pathway in the occurrence and development of UC.