Biliary Surgery, Shengjing Hospital of China Medical University, Shenyang, 110004, People's Republic of China.
Mol Cell Biochem. 2018 Nov;448(1-2):175-185. doi: 10.1007/s11010-018-3324-x. Epub 2018 Feb 14.
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.
本研究旨在探讨表没食子儿茶素没食子酸酯（EGCG）对高脂血症大鼠血脂、肝脂和胆固醇合成的影响。利用 SREBP-2 转基因大鼠，探讨 SIRT-1/FOXO1 调节的 SREBP-2 转录水平及影响胆固醇合成的限速酶 HMGCR 的分子机制。建立高脂血症大鼠模型并给予 EGCG，观察胆固醇合成情况。采用酶联免疫吸附试验测定血清三酰甘油（TG）、总胆固醇（TC）、低密度脂蛋白胆固醇（LDL-C）、高密度脂蛋白胆固醇（HDL-C）、游离脂肪酸（FFA）、超氧化物歧化酶（SOD）、丙二醛（MDA）和总抗氧化能力（T-AOC）含量。采用苏木精-伊红（HE）染色和油红 O 染色观察肝组织的组织学变化。采用生化法检测血清丙氨酸氨基转移酶（ALT）和天门冬氨酸氨基转移酶（AST）的变化。采用 Western blot 法和 qRT-PCR 法检测 SIRT1/FOXO1 通路相关蛋白、胆固醇合成相关基因和 SREBP-2 的变化。EGCG 50mg/kg 可明显降低高脂血症大鼠的肝重和肝系数，降低血清 TG、TC、LDL-C 和 FFA 水平（P<0.05），升高血清 HDL-C 水平。EGCG 可减轻高脂血症引起的肝损伤，降低血清 ALT 和 AST 水平。油红 O 染色结果表明，肝细胞内红色脂质滴的数量均有不同程度减少，尤以高剂量 EGCG 组明显。EGCG 可显著降低高脂血症肝组织 MDA 含量，提高 T-AOC 和 SOD 活性。模型组 SIRT1 表达增加，FOXO1 表达减少。EGCG 激活 SIRT1，增加 FOXO1 表达，其表达趋势与非诺贝特组一致。SREBP-2 转基因大鼠 HMGCR、FDPS、SS 和 ABCA1 表达增加，ACAT2 表达明显降低，EGCG 可逆转各基因表达趋势。同时，EGCG 增加 FOXO1 表达，降低 SREBP-2 表达，但 SREBP-2 大鼠各基因表达未见明显变化。EGCG 可减轻高脂血症大鼠肝损伤和氧化应激。EGCG 可激活 SIRT1，激活 FOXO1 蛋白，调节 SREBP-2 蛋白，抑制肝内胆固醇合成。
