OBJECTIVE: Long-term treatment of olanzapine, the most widely-prescribed second-generation antipsychotic, remarkably increases the risk of non-alcoholic fatty liver disease (NAFLD), whereas the mechanism for olanzapine-induced NAFLD remains unknown. Excessive hepatic fat accumulation is the basis for the pathogenesis of NAFLD, which results from the disturbance of TG metabolism in the liver. Apolipoprotein A5 (ApoA5) is a key regulator for TG metabolism in vivo that promotes TG accumulation in hepatocytes, thereby resulting in the development of NAFLD. However, there are no data indicating the role of apoA5 in olanzapine-induced NAFLD. Therefore, this study aims to investigate the role of apoA5 in olanzapine-induced NAFLD.
METHODS: This study was carried out via animal studies, cell experiment, and ApoA5 gene knockdown experiment. Six-week-old male C57BL/6J mice were randomized into a control group, a low-dose group, and a high-dose group, which were treated by 10% DMSO, 3 mg/(kg·d) olanzapine, and 6 mg/(kg·d) olanzapine, respectively for 8 weeks. The lipid levels in plasma, liver function indexes, and expression levels of ApoA5 were detected. HepG2 cells were treated with 0.1% DMSO (control group), 25 μmol/L olanzapine (low-dose group), 50 μmol/L olanzapine (medium-dose group), and 100 μmol/L olanzapine (high-dose group) for 24 h. HepG2 cells pretreated with 100 μmol/L olanzapine were transfected with siRNA and scrambled siRNA (negative control), respectively. We observed the changes in lipid droplets within liver tissues and cells using oil red O staining and fat deposition in liver tissues using HE staining. The mRNA and protein levels of ApoA5 were determined by real-time PCR and Western blotting, respectively.
RESULTS: After intervention with 3 and 6 mg/(kg·d) olanzapine for 8 weeks, there was no significant difference in body weight among the 3 groups (P>0.05). Olanzapine dose-dependently increased the plasma TG, ALT and AST levels, and reduced plasma ApoA5 levels (all P<0.05), whereas there was no significant difference in plasma cholesterol (HDL-C, LDL-C, and TC) levels among the 3 groups (all P>0.05). Olanzapine dose-dependently up-regulated ApoA5 protein levels in liver tissues (all P<0.05), but there was no significant change in ApoA5 mRNA expression among groups (P>0.05). In the control group, the structure of liver tissues was intact, the morphology of liver cells was regular, and only a few scattered lipid droplets were found in the cells. In the olanzapine-treated group, there was a large amount of lipid deposition in hepatocytes, and cells were balloon-like and filled with lipid droplet vacuoles. The nucleus located at the edge of cell, and the number of lipid droplets was increased significantly, especially in the high-dose group. Likewise, when HepG2 cells were treated with olanzapine for 24 h, the number and size of lipid droplets were significantly elevated in a dose-dependent manner. Moreover, olanzapine dose-dependently up-regulated ApoA5 protein levels in HepG2 cells (all P<0.05), but there was no significant difference in ApoA5 mRNA expression among groups (P>0.05). Compared with the HepG2 cells transfected with scrambled siRNA, the number and size of lipid droplets in HepG2 cells transfected with ApoA5 siRNA were significantly reduced.
CONCLUSIONS: The short-term intervention of olanzapine does not significantly increase body weight of mice, but it can directly induce hypertriglyceridemia and NAFLD in mice. Olanzapine inhibits hepatic apoA5 secretion but does not affect hepatic apoA5 synthesis, resulting in the pathogenesis of NAFLD. Inhibition of apoA5 secretion plays a key role in the development of olanzapine-related NAFLD, which may serve as an intervention target for this disease.
目的: 奥氮平是最常用第2代抗精神病药,若长期服用会显著增加发生非酒精性脂肪性肝病(non-alcoholic fatty liver disease,NAFLD)的风险,但其发病机制不明。肝内脂肪过度沉积是NAFLD的病理基础,且与肝内TG代谢障碍密切相关。载脂蛋白A5(apolipoprotein A5,ApoA5)是体内TG代谢的关键调节因子,促进肝细胞内TG蓄积,参与NAFLD发病。然而,奥氮平是否通过ApoA5诱发NAFLD尚无报道。本研究探讨ApoA5是否参与奥氮平相关NAFLD的发病。方法: 从动物实验、细胞实验及ApoA5基因敲低实验3个层次上进行探讨。将6周龄雄性C57BL/6J小鼠随机分为对照组、低剂量组、高剂量组,分别给予10% DMSO、3 mg/(kg·d)奥氮平、6 mg/(kg·d)奥氮平。干预8周后,测定各组小鼠的血脂4项、肝转氨酶2项和ApoA5水平。HepG2细胞分为对照组、低剂量组、中剂量组、高剂量组,分别给予0.1% DMSO、25 μmol/L奥氮平、50 μmol/L奥氮平、100 μmol/L奥氮平干预24 h。对100 μmol/L奥氮平预处理的HepG2细胞分别转染ApoA5 siRNA或scrambled siRNA(阴性对照)。采用油红O染色观察肝组织和肝细胞中的脂滴;HE染色观察肝组织脂质沉积情况;实时PCR检测ApoA5 mRNA表达水平;蛋白质印迹法检测ApoA5蛋白质表达水平。结果: 3或6 mg/(kg·d)的奥氮平干预后,各组小鼠体重差异无统计学意义(P>0.05),血浆TG、ALT和AST水平呈剂量依赖性升高,血浆ApoA5水平呈剂量依赖性降低(均P<0.05);但各组小鼠血浆胆固醇(HDL-C、LDL-C、TC)水平差异均无统计学意义(均P>0.05)。肝组织中ApoA5蛋白质水平呈剂量依赖性升高(均P<0.05),但各组ApoA5 mRNA表达差异无统计学意义(P>0.05)。对照组小鼠肝组织结构完整,肝细胞形态规则,细胞内仅见少量散在脂滴;给予3或6 mg/(kg·d)奥氮平的小鼠肝细胞内可见大量脂肪沉积,细胞呈气球样变,充盈着大量的脂滴空泡,细胞核位于细胞边缘,红色脂滴数量明显增多,且高剂量组更明显。25、50、100 μmol/L的奥氮平干预HepG2细胞24 h后,细胞内脂滴数量明显增多和体积明显增大,且给药剂量越高变化越明显;细胞中ApoA5蛋白质水平呈剂量依赖性升高(P<0.05),但各组ApoA5 mRNA表达差异无统计学意义(P>0.05)。与转染scrambled siRNA的HepG2细胞相比,转染ApoA5 siRNA的HepG2细胞内脂滴的数量明显减少,体积明显缩小。结论: 奥氮平短期干预,虽不显著增加小鼠体重,但可直接诱发高TG血症和NAFLD;奥氮平通过抑制肝脏ApoA5分泌(但不影响肝脏ApoA5合成),诱导NAFLD发病,提示ApoA5分泌障碍是奥氮平相关NAFLD发病的关键机制及干预靶点。.