Cilostazol inhibits insulin-stimulated expression of sterol regulatory binding protein-1c via inhibition of LXR and Sp1

Hepatic steatosis is common in obese individuals with hyperinsulinemia and is an important hepatic manifestation of metabolic syndrome. Sterol regulatory binding protein-1c (SREBP-1c) is a master regulator of lipogenic gene expression in the liver. Hyperinsulinemia induces transcription of SREBP-1c via activation of liver X receptor (LXR) and specificity protein 1 (Sp1). Cilostazol is an antiplatelet agent that prevents atherosclerosis and decreases serum triglyceride levels. However, little is known about the effects of cilostazol on hepatic lipogenesis. Here, we examined the role of cilostazol in the regulation of SREBP-1c transcription in the liver. The effects of cilostazol on the expression of SREBP-1c and its target genes in response to insulin or an LXR agonist (T0901317) were examined using real-time RT-PCR and western blot analysis on cultured hepatocytes. To investigate the effect of cilostazol on SREBP-1c at the transcriptional level, transient transfection reporter assays and electrophoretic mobility shift assays (EMSAs) were performed. Cilostazol inhibited insulin-induced and LXR-agonist-induced expression of SREBP-1c and its downstream targets, acetyl-CoA carboxylase and fatty acid synthase, in cultured hepatocytes. Cilostazol also inhibited activation of the SREBP-1c promoter by insulin, T0901317 and Sp1 in a luciferase reporter assay. EMSA analysis showed that cilostazol inhibits SREBP-1c expression by repressing the binding of LXR and Sp1 to the promoter region. These results indicate that cilostazol inhibits insulin-induced hepatic SREBP-1c expression via the inhibition of LXR and Sp1 activity and that cilostazol is a negative regulator of hepatic lipogenesis. The antiplatelet drug cilostazol, which is currently used to reduce leg pain caused by poor circulation, may help to ameliorate fatty liver disease in people with metabolic syndrome. A research team in South Korea, led by Keun-Gyu Park from Kyungpook National University School of Medicine and Mi-Kyung Kim from Keimyung University School of Medicine, exposed human and rodent liver cells to insulin or other factors that induce the expression of sterol regulatory binding protein-1c (SREBP-1c), a transcription factor that regulates many enzymes involved in lipid metabolism. After adding cilostazol, the researchers observed a drastic reduction in SREBP-1c levels. They showed that this effect resulted fromcilostazol blocking the activity of liver X receptor and specificity protein 1, two transcription factors implicated in converting the SREBP-1c precursor into its active form.