The Mechanism Of Endothelin Receptor Antagonist Ameliorates Cardiac Fibrosis In Diabetic Mice

Background—Cardiac complication in diabetic patients remained high despite a very good control of blood glucose. In diabetic patients,the development of cardiac fibrosis have been associated with persistently high plasma endothelin-1 (ET-1) levels, which results from fibroblast recruitment and the deposition of extracellular matrix. Since dysfunction of endothelial cell, which is the main source of ET-1, is believed to have an important role in pathophysiology of diabetic complication The underlying mechanism, however, remains elusive. Here, we hypothesize that ET-1 might contribute to the development of cardiac fibrosis and cardiac dysfunction.Objective:To explore the potential protective effect of Bosentan in diabetic cardiac fibrosis.Methods:Male 6-week old C57BL/6 mice were fallen into 3 groups, Control group, diabetes mellitus (DM) group and DM-B group (diabeteswith bosentan group),15 in each group. Streptozotocin (STZ) was injected intraperitoneally accountingfor 70 mg/kg for single dose which was used to confirm that diabetes was induced in the mice, fasting blood glucose (FBG) wasmeasured at 0-,1-,2-week after STZ injection. The second day after STZ injection, mice in DM-B group underwent intragastricadministration of Bosentan (100 mg/kg) once a day after STZ injection for 24 weeks,mice in the rest of the two groups were injected with the same amount of saline lavage. Cardiac fibrosis was evaluated by morphometric analysis and electron microscopy. RT-PCR was applied to detect vascular endothelial growth factor (VEGF), transforming growth factor beta (TGF-3), connective tissue growth factor (CTGF),and the expression of RNA (mRNA) which was the messenger of collagen protein 1 (collagen-1). Cardiac systolic function was evaluated by echocardiography.Results:After 24 weeks of diabetic situation, FBG of DM mice was significantly higher than that of Control mice and was similar with that of DM-B mice (DM mice vs. control mice, P<0.001; DM-B vs. control mice, P<0.01; DM mice vs. DM-B mice, P>0.05). HE staining showed thatinflammatory cell infiltration, interstitial fibrosis and myocardial cell hypertrophy in mice heart, and the result was ameliorated by Bosentan.Pathological analysis with Masson's Trichrome stainingshowed significant fibrotic changes in diabetic myocardium, and the fibrosis was ameliorated by Bosentan. Electron microscopy study revealed a disruption of sarcomere, myofibril structure in myocardium and Mitochondrial damage of DM mice, which is partially prevented by Bosentan. VEGF and fibrotic genes (TGF-?, CTGF and Collagen-1) are associated with cardiac fibrosis. Compared with DM group, the cardiac VEGF mRNA level in DM-B group is significantly higher (P< 0.01),and the expression of fibrotic genes (TGF-?, CTGF and Collagen-1) is significantly lower (P< 0.01). Furthermore, cardiac systolic function (fractional shortening, FS) of DM and DM-B mice decreased after24weeks of diabetes (DM vs Control mice, P<0.001). However, the impairment of cardiac function(FS) was significantly ameliorated, even nearly normalized by Bosentan (DM-B vs Control mice, P>0.05).Conclusions:These findings indicate the potential usefulness of an ET receptor antagonist Bosentan in the amelioration of diabetic cardiac complications (myocardial fibrosis and cardiac dysfunction) without affecting blood glucose. This may provide a promising therapeutical strategy for diabetic heart disease.