Epigallocatechin Gallate Protects Diabetes Mellitus Rats Complicated with Cardiomyopathy through TGF-β1/JNK Signaling Pathway

Abstract

Background: Epigallocatechin gallate (EGCG) is the main component of rhubarb tannin, with antioxidant, anti-angiogenic, anti-cancer and antiviral activities. Diabetes mellitus (DM) is a high blood sugar and protein metabolism disorder syndrome, which is caused by absolute or relative factors, such as deficiency of insulin and oxidative stress. Diabetes cardiomyopathy (DCM) is one of the most frequent complications of DM.

Objective: This study aims to explore whether EGCG can improve diabetic complication, myocardial fibrosis, in diabetic rats with an intraperitoneal injection of streptozotocin (STZ) through the transforming growth factor β1 (TGF-β1)/C-Jun N -terminal kinase (JNK) signaling pathway.

Methods: 50 male SD rats were randomly divided into five groups, including the control group, model group, and EGCG drug groups (10 mg/kg, 20 mg/kg, 40 mg/kg), with 10 rats in each group. Rats, except for the control group, were intraperitoneally injected with STZ (65 mg/kg) to induce the diabetic rats model. EGCG drug groups were given distilled water according to the dose, while the control group and model group were given the same volume of distilled water for 12 weeks. The levels of glucose (GLU), triglyceride (TG), cholesterol (CHO), low-density lipoprotein (LDL), and high-density lipoprotein (HDL) in serum were detected by ELISA of all rats. Myocardial function was observed by HE, Masson staining and Sirius red staining in DCM rats. Immunohistochemistry was used to detect the expression of Collagen I (COL-I) and Collagen III (COL-III), and detect the degree of myocardial fibrosis of DM rats. Western blot was used to detect the expression of matrix metalloproteinases (MMPs), tissue inhibitor of matrix metalloproteinase (TIMPs), TGF-β1, JNK and p-JNK in the myocardium.

Results: Compared to the model group, the levels of GLU, TG, CHO, and LDL in serum were decreased while the level of HDL in serum was increased in EGCG groups rats; cardiac index and left ventricular mass index were decreased while heart function was improved in EGCG groups rats; the expressions of the COL-I and COL-III were decreased in EGCG groups, and the high dose group was the best; the expressions of TGF-β1, JNK, p-JNK, and TIMP-1 were down-regulated, and the expression of MMP-9 was up-regulated in EGCG groups.

Conclusion: The results demonstrated that EGCG could improve STZ-induced diabetic complication, i.e., myocardial fibrosis, in diabetic rats, and protect their heart through TGF-β1/JNK signaling pathway.

Keywords: EGCG; TGF-β1/JNK; diabetic cardiomyopathy; fibrosis; myocardium; signalling pathway.