Epigallocatechin gallate suppresses hepatic cholesterol synthesis by targeting SREBP-2 through SIRT1/FOXO1 signaling pathway.

ABSTRACT

This study aims to explore the effect of epigallocatechin gallate (EGCG) on blood lipids, liver lipids, and cholesterol synthesis in hyperlipidemic rats. SREBP-2 transgenic rats were used to investigate the transcriptional level of SREBP-2 regulated by SIRT-1/FOXO1 and the molecular mechanism of rate-limiting enzyme HMGCR that affects cholesterol synthesis. Rat models of hyperlipidemia were established and administered EGCG. Cholesterol synthesis was observed. Enzyme linked immunosorbent assay was used to determine serum triglyceride (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), free fatty acid (FFA), superoxide dismutase (SOD), malondialdehyde (MDA), and T-AOC contents. Hematoxylin-eosin staining and oil red O staining were utilized to observe the histological changes in the liver. Biochemical method was applied to measure serum ALT and AST changes. Western blot assay and qRT-PCR were employed to detect the changes in SIRT1/FOXO1 pathway-related proteins, cholesterol synthesis-related genes, and SREBP-2. EGCG 50 mg/kg could obviously decrease the liver weight and liver coefficient, reduce serum TG, TC, LDL-C, and FFA levels (P < 0.05), and increase serum HDL-C levels in hyperlipidemic rats. EGCG could diminish hyperlipidemia-induced liver injury and reduce serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels. Oil red O staining results demonstrated that the number of red lipid droplets in hepatocytes reduced to varying degrees, especially high-dose EGCG. EGCG remarkably diminished MDA content in the liver with hypercholesterolemia and increased T-AOC and SOD activity. In the model group, SIRT1 expression increased, and FOXO1 expression decreased. EGCG activated SIRT1 and increased FOXO1 expression, whose expression trend was consistent with the fenofibrate group. HMGCR, FDPS, SS, and ABCA1 expression increased, and ACAT2 expression noticeably reduced in SREBP-2+/+ transgenic rats. EGCG could reverse the expression trend of each gene. Simultaneously, EGCG increased FOXO1 expression, and decrease SREBP-2 expression; however, no significant changes in these expression were found in SREBP-2-/- rats. EGCG can alleviate liver injury and oxidative stress in hyperlipidemic rats. EGCG can activate SIRT1, activate FOXO1 protein, regulate SREBP-2 protein, and inhibit hepatic cholesterol synthesis.