EX-527 Prevents the Progression of High-Fat Diet-Induced Hepatic Steatosis and Fibrosis by Upregulating SIRT4 in Zucker Rats

Sirtuin (SIRT) is known to prevent nonalcoholic fatty liver disease (NAFLD); however, the role of SIRT4 in the progression of hepatic fibrosis remains unknown. We hypothesize that EX-527, a selective SIRT1 inhibitor, can inhibit the progression of high-fat diet (HFD)-induced hepatic fibrosis. We found that SIRT4 expression in the liver of NAFLD patients is significantly lower than that in normal subjects. In this study, EX-527 (5 µg/kg), administered to HFD rats twice a week for ten weeks, reduced the serum levels of triglyceride (TG), total cholesterol, alanine aminotransferase (ALT), and aspartate aminotransferase (AST) and attenuated hepatic fibrosis evidenced by Masson’s trichrome and hepatic fat by oil red-O staining. EX-527 upregulated SIRT2, SIRT3, and SIRT4 expression in the liver of HFD fed rats but downregulated transforming growth factor-β1 (TGF-β1) and α-smooth muscle actin (α-SMA) expression. It decreased proinflammatory cytokine production and hydroxyproline levels in the serum and SMAD4 expression and restored apoptotic protein (Bcl-2, Bax, and cleaved caspase-3) expression. These data propose a critical role for the SIRT4/SMAD4 axis in hepatic fibrogenesis. SIRT4 upregulation has the potential to counter HFD-induced lipid accumulation, inflammation, and fibrogenesis. We demonstrate that EX-527 is a promising candidate in inhibiting the progression of HFD-induced liver fibrosis.