基于LXR、FXR调控胆固醇/胆汁酸代谢转运通路探讨广金钱草“利胆消石”的分子机制

Cholesterol gallstone disease (CGD) is one of the most common gastrointestinal diseases. However, its etiology has not yet been fully elucidated. Precipitation of excess cholesterol in the bile as solid crystals is a prerequisite for cholesterol gallstone formation.Cholesterol precipitation can occur as a result of the disorder of cholesterol/bile acid homeostasis.Nuclear receptors are ligand-activated transcriptional regulators of several key aspects of hepatic physiology and pathophysiology. As such, nuclear receptors control a large variety of metabolic processes including the cholesterol/bile acid homeostasis. Derangements of nuclear receptor regulation and genetic variants may contribute to the pathogenesis and progression of CGD. The nuclear receptors, liver X receptor (LXR) and farnesoid X receptor (FXR), have been implicated in the regulation of the rate-limiting enzymes involved in the metabolism of cholesterol/bile acids. Along with the regulation of cholesterol/bile acid metabolism, FXR/LXR is also involved, directly and indirectly, in several important transport of cholesterol/bile acid in vivo by modulating various transport proteins. The critical role of LXR/FXR in controlling cholesterol/bile acid homeostasis makes those receptors a potentially attractive target for the development of drug for the treatment of CGD. The Chinese herbal medicine Herba Desmodii has been used to treat the urinary tract infection, urinary calculi, hepatitis and gallstone diseases for thousand years, but its mechanism and material base did not clear yet. Therefore, the project hypothesize that Herba Desmodii improves CGD, inhibits hepatic cholesterol accumulation and increases bile acid synthesis via the activation of LXR/FXR signaling pathways in vitro and in vivo. To test this hypothesis, we determined the effects of Desmodii on serum and hepatic cholesterol accumulation in HFD-fed C57BL/6J mice. In addition, we characterized the molecular mechanisms underlying the effects of Desmodii in HepG2 hepatocytes and CRL-1790 enterocytes. The project is aim to find out the potential mechanism and material base of Herba Desmodii in preventing CGD, and to propose a new treatment target gene of CGD.

胆固醇结石病（CGD）是一种全球性、多发性、难愈性的胃肠道疾病，迄今病因仍未完全阐明。但大量研究已证明形成胆固醇结石的先决条件是肝脏胆固醇代谢异常所引起的胆汁胆固醇过饱和。而肝脏胆固醇代谢受体内多种核受体及其下游基因的紧密调控。广金钱草为传统治疗黄疽尿路结石中药，具清热祛湿、利尿通淋、利胆排石的功效，主要用于泌尿系结石、胆囊结石、黄疽型肝炎等病症。本项目组前期研究发现其黄酮类成分具有显著的利胆药理活性，但其作用机制与物质基础尚未明确。因此，本项目选择特异性活化核受体LXR、FXR调控胆固醇-胆汁酸代谢转运通路的研究角度，通过工具药广金钱草外源性激活LXR、FXR对其相关靶基因进行调控，恢复胆固醇与胆汁酸合成代谢和/或排泄，维持机体胆固醇/胆汁酸平衡，并找寻其药效物质基础，从而阐明中医药"利胆消石"功效的中医科学内涵，为CGD的治疗提供新的靶标和思路。

胆固醇结石病（CGD）是一种全球性、多发性、难愈性的胃肠道疾病，迄今病因仍未完全阐明。但大量研究已证明形成胆固醇结石的先决条件是肝脏胆固醇代谢异常所引起的胆汁胆固醇过饱和。而肝脏胆固醇代谢受体内多种核受体及其下游基因的紧密调控。广金钱草为传统治疗黄疽尿路结石中药，主要用于泌尿系结石、胆囊结石、黄疽型肝炎等病症。本项目组研究前期发现其黄酮类成分具有显著的利胆退黄药理活性，其作用机制可能与选择特异性活化核受体LXR、FXR调控胆固醇-胆汁酸代谢转运通路有关。因此项目组通过建立胆固醇结石小鼠模型，选择广金钱草为工具药，外源性激活lxr、fxr进而对其相关靶基因cyp7a1、bsep、mrp2、abcg5、abcg8、ibabp等进行调控。结果发现广金钱草可促进胆汁分泌，降低胆固醇结石形成率，降低胆汁CSI水平，升高血清中HDLC和TBA水平，升高血清中 cAMP 水平和 NO 的含量，降低血清 TG、TC、LDLC 浓度，调节脂质代谢，减轻氧化损害而发挥保肝利胆消石的药理作用。其分子机制可能一方面它能激活肝脏胆酸感受器 fxr 进而上调其靶基因bsep、mrp2 的表达水平，增加肝细胞膜上 bsep、mrp2 的转录，加速肝内过多的胆汁酸从肝细胞向胆小管的外排转运，恢复胆汁酸/胆固醇转化平衡；另一方面广金钱草可特异性活化lxr 调节相关靶基因abcg5/8 表达差异，降低 scp2 表达，促进肝脏胆固醇外排，避免胆固醇蓄积；同时降低 npc1l1 基因表达减少肠道对胆固醇的吸收，增加ibabp基因表达，促进肠道胆固醇的外排，改善肠道胆固醇的蓄积和过饱和状态，重新恢复胆固醇与胆汁酸合成代谢和/或排泄，维持了机体胆固醇/胆汁酸平衡。本项目以期揭示中医药“利胆消石”功效的中医科学内涵，为CGD的治疗提供新的靶标和思路，为广金钱草的开发和利用提供实验依据。