n-3多不饱和脂肪酸改善高同型半胱氨酸血症引起小鼠肝脏脂肪变性的机制研究

Nonalcoholic fatty liver disease (NAFLD) and Hyperhomocysteinemia (HHcy) both are major health problems worldwild, whose incidence are closely related to each other. The role of n-3 Polyunsaturated fatty acid (PUFA) in HHcy induced hepatic steatosis remains unclear. In the previous study, we demonstrated that Lipoxin A4 (LXA4) derived from arachidonic acid (AA) mediated HHcy induced hepatic steatosis. Our preliminary results showed that n-3 PUFA ameliorated High Methionine Diet (HMD)-induced hepatic lipid deposition. Targeted PUFA metabonomics revealed that n-3 PUFA markedly increased LXA5 content which derived from eicosapentaenoic acid (EPA). It suggests that n-3 PUFA may have protective effects on lipid accumulation by producing AA corresponding metabolites. Consequently, we hypothesize that n-3 PUFA will protect mice against HHcy-induced liver lipid accumulation by increasing hepatic LXA5 content, which competes with LXA4 for aryl hydrocarbon receptor (AHR) binding site and blocks the combination of AHR with AHR nuclear translocator (ARNT), inhibiting the activation of AHR signaling pathway. The current study was aimed to explore a novel theraputic target of HHcy-induced fatty liver.

非酒精性脂肪性肝脏疾病（NAFLD）与高同型半胱氨酸血症（HHcy）均为世界范围内的重要健康问题，二者发病密切相关。n-3多不饱和脂肪酸（n-3 PUFA）在HHcy引起脂肪肝疾病的作用尚未有报道。前期研究发现花生四烯酸代谢产物LXA4参与了HHcy诱导的肝脏脂肪变性。预实验结果显示，饮食添加n-3 PUFA可改善高蛋氨酸饮食（HMD）喂养引起的肝脏脂质沉积。PUFA靶向代谢组学发现，HMD添加n-3 PUFA后，二十碳五烯酸（EPA）对应代谢产物LXA5的含量显著增加，提示n-3 PUFA可能通过对应代谢产物发挥拮抗作用，进而改善肝脏脂质沉积。基于此，我们提出假说：n-3 PUFA可通过增加EPA代谢产物LXA5含量，拮抗LXA4与AHR结合，阻碍AHR与其伴侣蛋白（ARNT）结合，抑制AHR下游信号传导，减轻HHcy引起的肝脏脂肪变性，期望为HHcy引发NAFLD的临床治疗开辟新途径。

肝脏脂肪变性是非酒精性肝脏疾病(Non-alcoholic fatty liver disease, NAFLD）)的起始阶段，高同型半胱氨酸血症（Hyperhomocysteinemia, HHcy）是其重要危险因素。n-3多不饱和脂肪酸（n-3 Polyunsaturated fatty acid, n-3 PUFA）在HHcy引起的脂肪肝疾病中的作用尚未有报道。本项目研究显示，n-3 PUFA通过抑制HHcy诱导的Ahr激活相关脂肪酸摄取关键基因Cd36的表达，改善肝脏的脂肪变性。利用PUFA靶向代谢组学分析发现，n-3 PUFA明显增加了肝脏二十碳五烯酸代谢产物脂氧素A5（Lipoxin A5, LXA5）的含量。给予原代肝细胞LXA5处理，阻断了同型半胱氨酸（Homocysteine, Hcy）诱导的肝细胞Cd36表达和Ahr激活，减轻了肝细胞的脂质沉积。以上结果表明，n-3 PUFA可通过增加肝脏LXA5的含量，抑制HHcy引起的Ahr-Cd36信号路径的激活，改善肝脏的脂肪变性。另外，基于实验室前期研究发现，可溶性表氧化物水解酶（Soluble epoxide hydrolase，sEH）可降解环氧三烯酸和其他环氧脂肪酸，降低他们的心血管保护作用。但是，sEH是否参与HHcy诱导的肝脂肪变性尚不清楚。本项目研究发现HHcy在体内和体外均诱导了sEH表达和活性增加及肝细胞脂质积累。给予sEH抑制剂以配体依赖方式促进过氧物酶体（Peroxisome proliferator-activated receptor-α, PPAR-α）激活，增加PPAR-α靶基因的表达，促进肝脏的脂肪酸氧化，缓解HHcy诱导的肝脏脂肪变性。因此，sEH活性的增加是HHcy诱导的肝脂肪变性发病的关键决定因素，抑制sEH可能是治疗HHcy诱导的肝脂肪变性的有效方法。本项目的研究结果预期可为NAFLD的临床治疗开辟新的途径。在本项目的资助下，于Am J Physiol Gastrointest Liver Physiol., Hypertension, Cell Mol Gastroenterol Hepatol., Sci China Life Sci., Circ Res.上海大学学报等发表论文6篇。