College of Medicine, Xi'an Jiaotong University, Xi'an 710061, People's Republic of China.
J Ethnopharmacol. 2013 May 20;147(2):509-16. doi: 10.1016/j.jep.2013.03.057. Epub 2013 Mar 30.
Panax ginseng is a well-known traditional Chinese medicine and has been used for treatment of various diseases for more than four thousand years in Asia. Ginseng saponins or ginsenosides, the active constituents are reported to possess antidiabetic activity, but their antihyperglycemic mechanisms are not fully elucidated. In the present study, the mechanisms of action of ginsenoside Re were investigated in vitro models.
3T3-L1 cells were chosen as the model to investigate the molecular mechanisms of action of ginsenoside Re. Influence of ginsenoside Re on the adipogenesis was examined by determining TG levels in 3T3-L1 adipocytes by the method of TG oxidation enzyme. Glucose uptake in 3T3-L1 cells stimulated by insulin in the absence or presence of ginsenoside Re were quantified by measuring (3)H-2-deoxy-d-glucose levels. Cytokine proteins released into the medium including adiponectin and TNF-α were tested using respective ELISA kits. In addition, real time RT-PCR was conducted to investigate the expression changes of PPAR-γ and its responsive genes, ap2, adiponectin, IRS-1, GLUT4 and TNF-α. And western blot analysis was performed to determine the translocation of GLUT4. Finally, effects of ginsenoside Re on NO production in 3T3-L1 adipocytes and in macrophages were investigated through measurement of nitrite concentration by Griess reagent.
Ginsenoside Re induced adipogenesis of 3T3-L1 adipocytes by accumulating TG, increased glucose uptake and up-regulated PPAR-γ2, IRS-1, ap2 and adiponectin genes expressions. Meanwhile, Re also increased production and release of adiponectin. Although having no effects on GLUT4 gene expression, Re facilitated GLUT4 protein translocation to the membranes. In addition, Re inhibited the expression and release of TNF-α. Finally, Re did not show inhibitory effects on NO production both in 3T3-L1 cells stimulated by LPS, TNF-α and IFN-γ and in LPS-stimulated mouse peritoneal macrophages.
Ginsenoside Re exhibited the action of reducing insulin resistance through activation of PPAR-γ pathway by directly increasing the expressions of PPAR-γ2 and its responsive genes, adiponectin, IRS-1, ap2, inhibiting TNF-α production and facilitating the translocation of GLUT4 to promote glucose uptake and disposal in 3T3-L1 adipocytes.
人参是一种著名的中药，在亚洲，它已经被用于治疗各种疾病超过四千年。人参皂苷或人参皂甙，作为其活性成分，据报道具有抗糖尿病活性，但它们的降血糖机制尚未完全阐明。在本研究中，我们在体外模型中研究了人参皂甙 Re 的作用机制。
我们选择 3T3-L1 细胞作为模型，以研究人参皂甙 Re 的作用机制。通过 TG 氧化酶法测定 3T3-L1 脂肪细胞中的 TG 水平，研究人参皂甙 Re 对脂肪生成的影响。用（3）H-2-脱氧-d-葡萄糖测定法测定胰岛素刺激的 3T3-L1 细胞中的葡萄糖摄取量，并在有无人参皂甙 Re 的情况下进行定量。用各自的 ELISA 试剂盒检测细胞培养液中释放的细胞因子蛋白，包括脂联素和 TNF-α。此外，还进行实时 RT-PCR 以研究 PPAR-γ 及其反应基因，ap2、脂联素、IRS-1、GLUT4 和 TNF-α的表达变化。并通过 Western blot 分析确定 GLUT4 的易位。最后，通过测量亚硝酸盐浓度，用人参皂甙 Re 检测其对 3T3-L1 脂肪细胞和巨噬细胞中一氧化氮（NO）产生的影响。
人参皂甙 Re 通过积累 TG 诱导 3T3-L1 脂肪细胞的脂肪生成，增加葡萄糖摄取并上调 PPAR-γ2、IRS-1、ap2 和脂联素基因的表达。同时，Re 还增加了脂联素的产生和释放。虽然对 GLUT4 基因表达没有影响，但 Re 促进了 GLUT4 蛋白向膜的易位。此外，Re 抑制了 TNF-α 的表达和释放。最后，Re 对 LPS、TNF-α 和 IFN-γ 刺激的 3T3-L1 细胞和 LPS 刺激的小鼠腹腔巨噬细胞中 NO 的产生没有抑制作用。
人参皂甙 Re 通过直接增加 PPAR-γ2 及其反应基因、脂联素、IRS-1、ap2 的表达，抑制 TNF-α 的产生，促进 GLUT4 向膜的易位，从而促进葡萄糖的摄取和处理，发挥降低胰岛素抵抗的作用。
