胰高糖素样肽-1受体激动剂改善内皮功能和诱导内皮一氧化氮合成酶复偶联及其机制研究

Guanosine 5'-triphosphate cyclohydrolase -Ⅰ(GTPCH-Ⅰ) is the rate-limiting enzyme in tetrahydrobiopterin（BH4） synthesis. Endogenous NO is derived from L-argine in the catalysis of endothelial NO synthase （NOS）. BH4 is an essential cofactor for endothelial NOS (eNOS). It plays a role in the electron transfer during the production of NO . When BH4 levels are inadequate, eNOS is no longer coupled to L-arginine oxidation, which results in reactive oxygen species (ROS) rather than NO production, thereby inducing vascular endothelial dysfunction. Our previous study showed that homocysteine can significantly inhibited the expression of BH4 and induced eNOS out-coupling in endothelial cells. Moreover, the coronary endothelial function had been impaired significantly in hyperhomocysteinemic patients. Our study also showed that the level of eNOS detected by western blot was increased and the expression of ROS was decreased after treated with glucagon-like peptide-1 (GLP-1) receptor agonist. Hence, we suppose that GLP-1 receptor agonist can induce eNOS re-coupling through the mechanism of up-regulating GTPCH1 level, and inhibite the oxidation of BH4 in endothelial cells. In present study, we investigate whether GLP-1 receptor agonist could improve the expression of intracellular BH4 through upregulating GTPCH- Ⅰ, thus contributing to the re-coupling of eNOS in endothelial cells and apolipoprotein E knockout mice, respectively. These results will suggest that glucagon-like peptide-1 (GLP-1) receptor agonist might help protect endothelial function and against atherosclerosis by increasing level of BH4 and decreasing production of ROS through up-regulating the level of intracellular GTPCH-Ⅰ.

三磷酸鸟苷环化水解酶(GTPCH)Ⅰ是四氢生物蝶呤（BH4）合成的关键限速酶，BH4是内皮一氧化氮合酶（eNOS）的辅助因子。糖尿病等病理条件下，BH4水平下降促使eNOS脱偶联，导致内皮功能异常。胰高糖素样肽（GLP-1）可增强内皮eNOS的磷酸化、增加NO、发挥内皮保护作用。我们以往研究显示，同型半胱氨酸可抑制内皮BH4水平、诱导eNOS脱偶联，损害患者冠脉内皮功能。预实验显示，GLP-1受体激动剂可促进内皮细胞eNOS表达、抑制氧化应激、增加NO。我们假设,GLP-1受体激动剂可通过上调内皮GTPCH1水平、减少BH4氧化机制，引起eNOS复偶联。本研究分别在内皮细胞及apoE 敲除小鼠整体水平，探讨GLP-1受体激动剂能否通过上调血管内皮GTPCH1水平、增加BH4、抑制氧化应激、促使eNOS复偶联等机制，发挥血管内皮保护作用，并在临床水平进一步验证。