Department of Pharmacology and Clinical Pharmacy, College of Pharmacy, Kyung Hee University, Seoul 130-701, Republic of Korea.
Biochem Pharmacol. 2013 May 1;85(9):1330-40. doi: 10.1016/j.bcp.2013.02.007. Epub 2013 Feb 19.
Non-alcoholic fatty liver disease (NAFLD) is emerging as the most common liver disease in industrialized countries. The discovery of food components that can ameliorate NAFLD is therefore of interest. Betulinic acid (BA) is a triterpenoid with many pharmacological activities, but the effect of BA on fatty liver is as yet unknown. To explore the possible anti-fatty liver effects and their underlying mechanisms, we used insulin-resistant HepG2 cells, primary rat hepatocytes and liver tissue from ICR mice fed a high-fat diet (HFD). Oil Red O staining revealed that BA significantly suppressed excessive triglyceride accumulation in HepG2 cells and in the livers of mice fed a HFD. Ca(+2)-calmodulin dependent protein kinase kinase (CAMKK) and AMP-activated protein kinase (AMPK) were both activated by BA treatment. In contrast, the protein levels of sterol regulatory element-binding protein 1 (SREBP1), mammalian target of rapamycin (mTOR) and S6 kinase (S6K) were all reduced when hepatocytes were treated with BA for up to 24h. We found that BA activates AMPK via phosphorylation, suppresses SREBP1 mRNA expression, nuclear translocation and repressed SREBP1 target gene expression in HepG2 cells and primary hepatocytes, leading to reduced lipogenesis and lipid accumulation. These effects were completely abolished in the presence of STO-609 (a CAMKK inhibitor) or compound C (an AMPK inhibitor), indicating that the BA-induced reduction in hepatic steatosis was mediated via the CAMKK-AMPK-SREBP1 signaling pathway. Taken together, our results suggest that BA effectively ameliorates intracellular lipid accumulation in liver cells and thus is a potential therapeutic agent for the prevention of fatty liver disease.
非酒精性脂肪性肝病（NAFLD）正在成为工业化国家最常见的肝脏疾病。因此，发现可以改善 NAFLD 的食物成分具有重要意义。白桦脂酸（BA）是一种具有多种药理活性的三萜类化合物，但 BA 对脂肪肝的影响尚不清楚。为了探索 BA 可能的抗脂肪肝作用及其潜在机制，我们使用胰岛素抵抗 HepG2 细胞、原代大鼠肝细胞和高脂饮食（HFD）喂养的 ICR 小鼠肝脏组织进行实验。油红 O 染色显示，BA 可显著抑制 HepG2 细胞和 HFD 喂养小鼠肝脏中甘油三酯的过度积累。BA 处理可激活钙调蛋白依赖性蛋白激酶激酶（CAMKK）和 AMP 激活的蛋白激酶（AMPK）。相比之下，BA 处理原代肝细胞长达 24 小时，固醇调节元件结合蛋白 1（SREBP1）、雷帕霉素哺乳动物靶蛋白（mTOR）和 S6 激酶（S6K）的蛋白水平均降低。我们发现，BA 通过磷酸化激活 AMPK，抑制 HepG2 细胞和原代肝细胞中 SREBP1 mRNA 表达、核易位以及 SREBP1 靶基因表达，从而减少脂肪生成和脂质积累。在存在 STO-609（CAMKK 抑制剂）或化合物 C（AMPK 抑制剂）的情况下，这些作用完全被阻断，表明 BA 诱导的肝脂肪变性减少是通过 CAMKK-AMPK-SREBP1 信号通路介导的。综上所述，我们的研究结果表明，BA 可有效改善肝细胞内的脂质积累，因此是预防脂肪肝疾病的潜在治疗药物。
