苦丁内酯型三萜皂苷对脂质代谢的调控作用及其靶向SREBP活化的机制研究

Hyperlipidemia is closely related to metabolic diseases, such as atherosclerosis, hypertension and type II diabetes, which are becoming worldwide problems. Sterol regulatory element-binding protein (SREBP) is major transcription factors activating the expression of genes involved in biosynthesis of cholesterol, fatty acid and triglyceride. We previously discovered that total triterpenoid saponins of Ilex latifoloside Thunb descreased the lipid and glucose contents in serum and tissues, and improved insulin resistance in the high-fat diet-fed C57BL/6 mice. Furthermore, we demonstrated the inhibitory effect of several kudinoside，isolated from Ilex latifoloside Thunb, on 3T3-L1adipocyte differentiation induced by insulin through suppression of SREBP activation. With the support of this fund, we will further isolate and identify more new compounds, and investigate their functions on lipid metabolism and the inhibitory activity of SREBP.The present study will provide more insights for developing the effective safety new drug for the treatment of hyperlipidemia.

高脂血症可诱发动脉粥样硬化、高血压、糖尿病、冠心病或其它心脑血管疾病，是一类常见多发症。现有的靶向降脂药物均为单一适应症的药物，疗效有限且副作用较大。故"单靶点、双靶向"的药物已成为降血脂药物研发的一个重要方向。脂质代谢过程受到多种蛋白的正负调控，其中，SREBP既能调控脂肪酸的合成又能调节胆固醇的合成，是脂质代谢的关键调节因子。在前期工作中，我们发现大叶冬青叶总皂苷部位具有显著的降血脂、降血糖、调节胰岛素抵抗和减轻肝脏细胞脂肪化的作用，并从中分离鉴定了一系列新型的苦丁内酯型三萜皂苷。活性结果显示，该类化合物可显著抑制3T3-L1细胞向脂肪细胞的分化，初步的机制研究提示该类成分作用的作用靶点可能为SREBP。本项目拟在前期工作基础上，进一步分离和富集大叶冬青叶中的苦丁内酯型三萜皂苷类化合物，并评价和研究其抑制调节脂质代谢的生物活性及作用机制，为研究和开发有效无毒的降血脂药物提供科学依据。

本项目通过建立油酸与棕榈酸混合诱导HepG2细胞甘油三酯聚集的体外筛选模型评价了大叶冬青三萜皂苷化合物的降脂活性。并通过体内外模型探讨了kudinoside A抑制HepG2细胞甘油三酯累积的作用机制。发现苦丁内酯型三萜皂苷的活性要强于其他类型的三萜皂苷。其中kudinoside A抑制甘油三酯在HepG2细胞的累积较明显。Kudinoside A促进PPARα基因的上调，抑制脂肪酸合成过程中相关基因FAS，SREBP-1c，SCD-1的表达。Kudinoside A上调AMPKα和ACC蛋白的磷酸化，降低SREBP-1c蛋白在细胞核的表达。AMPK激动剂AICAR与kudinoside A协同促进AMPKα的磷酸化，kudinoside A抑制AMPK抑制剂Compound C对AMPKα蛋白的去磷酸化。AICAR与kudinoside A能明显抑制SREBP-1c基因和蛋白水平的表达，表明kudinoside A的降脂作用通过AMPK信号通路。体内实验结果表明：kudinoside A能够明显降低NAFLD模型小鼠肝组织中甘油三酯及胆固醇的累积，改善体内脂质代谢。