Exendin-4 alleviates oxidative stress and liver fibrosis by activating Nrf2/HO-1 in streptozotocin-induced diabetic mice

To investigate the effects of exendin-4 on hepatic lipid metabolism, fibrosis and oxidative stress in mice with streptozotocin (STZ)-induced diabetes and explore the underlying mechanisms. C57BL/6J mice were fed with high-fat diet (HFD) for 4 weeks and received intraperitoneal injections of 120 mg/kg STZ to induce diabetes. After successful modeling, the mice were randomized into diabetic control group and exendin-4 treatment group (DM+E4), and in the latter group, the mice were given a daily dose of 1 nmol/kg of exendin-4 for 8 weeks. The changes in the body weight (BW) and random blood glucose (RBG) in the mice were recorded. The mRNA expressions of the genes related with liver lipid metabolism, fibrosis and oxidative stress were analyzed using RT-PCR, and the structural changes of the liver tissues were observed with HE, Sirius red and oil red O staining; the expressions of TGF-β1, Nrf2 and HO-1 proteins in the liver tissues were detected using Western blotting. The diabetic mice showed significantly higher RBG levels and BW with obvious lipid deposition, fibrosis and oxidative stress in the liver as compared with the normal control mice ( < 0.001). Exendin-4 treatment of the diabetic mice did not significantly lessened liver lipid deposition but obviously reduced the levels of RBG and TG ( < 0.05), lowered the expression levels of liver fibrosis-related genes TGF-β, -SMA and Col-Ⅰ ( < 0.05), increased the expression levels of the antioxidant genes Nrf2, HO-1 and GPX4 ( < 0.01), and enhanced the protein expressions of Nrf2 and HO-1 in the liver tissues ( < 0.01). Exendin-4 improves liver fibrosis and oxidative stress in diabetic mice by activating Nrf2/HO-1 pathway without significantly reducing liver lipid deposition.