Protection of rat intestinal epithelial cells from ischemia/reperfusion injury by (D-Ala2, D-Leu5)-enkephalin through inhibition of the MKK7-JNK signaling pathway

Previous studies have demonstrated that (D-Ala2, D-Leu5)-enkephalin (DADLE) protects rats from hepatic ischemia/reperfusion (I/R) injury. In the present study, DADLE was also observed to alleviate IR-induced intestinal epithelial cell injury in rats by inhibiting mitogen-activated protein kinase kinase 7 (MKK7)-c-Jun N-terminal kinase (JNK) pathway signaling. To investigate the protective effect of DADLE on hypoxia/reoxygenation injury in rat intestinal epithelial cells, rat intestinal epithelial cells were treated with different concentrations of DADLE, following which the cell survival rate was determined using a tetrazolium (MTT) colorimetric assay, and apoptosis was determined using flow cytometry. To confirm whether the protective effect of DADLE was due to its effect on MKK7-JNK signaling, the phosphorylation levels of MKK7 and JNK were analyzed using western blot analysis following treatment with different concentrations of DADLE. The results demonstrated that, following treatment with DADLE, the survival rate of the rat intestinal cells subjected to I/R-induced injury increased significantly and the apoptotic rate decreased in a concentration-dependent manner. In addition, the levels of phosphorylated MKK7 and JNK decreased in a concentration-dependent manner following treatment with DADLE. Silencing the gene expression of MKK7 using small interfering RNA prior to DADLE treatment resulted in a reduction in the protective effects of DADLE on the rat intestinal epithelial cells subjected to I/R injury. Collectively, the results of the present study demonstrated that the protective effects of DADLE in I/R injury in rat intestinal cells occurred through inhibition of the MKK7-JNK pathway.