胆汁酸及其受体在非酒精性脂肪性肝病发病机制中的作用及药物治疗的研究进展

非酒精性脂肪性肝病(NAFLD)是以肝细胞内脂质蓄积为主要特征的肝脏代谢紊乱疾病,已成为全球范围内慢性肝病的主要病因。20%～30%的NAFLD会进展为非酒精性脂肪性肝炎(NASH), NASH的发展与多种代谢紊乱密切相关。胆汁酸及其受体功能在NASH的发病机制中起着重要作用,胆汁酸受体是治疗NASH重要的靶点。本文对胆汁酸及其受体在NAFLD和NASH发展中的作用,特别是关于法尼醇X受体(FXR)在不同组织(包括肝脏和肠道)中的功能的研究予以综述,介绍基于胆汁酸及其受体的NASH治疗药物的研究进展。     

妊娠期肝内胆汁淤积症中FXR调节胆汁酸代谢的分子机制研究进展

妊娠期肝内胆汁淤积症（ICP）病因及发病机制目前仍不清楚，近年来关于其分子机制方面的研究取得了较大的进展，确认了多种胆汁酸转运蛋白及其基因，并发现其中大部分为“胆汁酸感受器”——法尼醇受体（FXR）的靶基因，胆汁酸作用于FXR，通过上调或下调靶基因的转录水平降低胆汁酸，形成胆汁酸的自身反馈调节机制，保护肝细胞免受毒性胆汁酸成分的损伤。     

阻塞性黄疸患者血清载脂蛋白M与胆汁酸的相关性

<正>载脂蛋白M(apolipoprotein M,apo M)是1999年Xu等发现的一种载脂蛋白[1]。类法尼醇X核内受体(farnesoid X receptor,FXR)是一种胆汁酸(bile acid,BA)激活受体[2],在脂类代谢中起着重要的作用[3]。研究发现,BA可激活FXR,呈剂量依赖性下调HepG 2细胞和小鼠肝脏中apo M的表达[4-5]。血清中BA与apo M的关系尚未见文献报道。本研究旨在探讨健康人群血清apo M与总胆汁酸(total bile acid,TBA)的相关性,并分析TBA显著增高的阻塞性黄疸(obstructive jaundice,OJ)患者血清apo M的变化,以进一步探讨BA与apo M之间的关系。     

健康人和肝脏病患者血清胆汁酸浓度在一天内的波动

外周循环血胆汁酸浓度在一天中不断波动,其浓度的高低在任何时间都取决于输送至肝脏的胆汁酸的负荷及肝脏从血液中摄取胆汁酸的能力之间的平衡,而这种平衡又与下列因素有关,即餐后胆囊的收缩、肠道吸收胆汁酸的能力,流入肝脏的血量,以及胆汁酸和胆固醇的合成速度.在肝脏疾病时,由于摄取、结合和排泄胆汁酸发生障碍,所以肝脏消除胆汁酸的速度减慢.正常肝脏摄取和排泄胆汁酸的能力超过由肠道吸收进入门脉循环的负荷,因此,体循环胆汁酸水平低,且只在较小的范围内波动.     

胆汁酸测定在肝脏疾病中的应用

胆汁酸是存在于胆汁中的一类胆烷酸的总称，在肝细胞内以胆固醇为原料合成初级胆汁酸(胆母鸡及鹅脱氧胆酸)。在肠道内以初级胆酸为原料，在肠道菌酶的作用下形成次级胆酸(脱氧胆酸、石胆酸、熊脱氧胆酸等)。胆汁酸由肝细胞内的微粒体、线粒体、溶酶体合成，主要以结合的形式分泌到胆汁中，在胆汁中含量可达69％。胆汁进入肠腔后，在回肠和结肠，绝大部分胆汁酸被肝细胞所摄取，又因肠肝循环基本上属于闭锁式的．故外周血循环中胆汁酸的浓度较低。当肝胆有疾病时，循环血液中的胆汁酸含量即有不同程度的增加，故血清中总胆汁酸(TBA)可作为肝实质性损伤的灵敏诊断指标。综述如下。     

非诺贝特上调法尼醇X受体转录活性的研究

目的:探讨降脂药物非诺贝特激活法尼醇X受体FXR的机制。方法 :分离小鼠肝脏原代细胞,予非诺贝特处理,通过实时定量PCR检测FXR下游基因的表达情况,并通过荧光素酶双报告基因实验,分析非诺贝特对FXR下游基因调控的机制。结果:①非诺贝特处理可诱导FXR下游靶基因SHP和BSEP的表达,进而降低三酰甘油合成关键转录因子SREBP1c的表达。②非诺贝特能促进FXR上调SHP和BSEP启动子活性,而FXR配体结合区域及转录激活域缺失型则丧失该功能。结论:非诺贝特可能是潜在的FXR激动型配体,可通过激活FXR信号通路,降低三酰甘油合成基因的表达,从而抑制肝脏三酰甘油的沉积。     

肠道菌群代谢产物在自身免疫性疾病中的作用

肠道菌群及其代谢产物在维持宿主免疫稳态方面具有重要作用,肠道菌群紊乱及代谢产物异常与多种自身免疫疾病的发生发展密切相关。肠道菌群代谢产物中,短链脂肪酸、色氨酸及其衍生物、胆汁酸的研究最为广泛。本文将重点阐述肠道菌群代谢产物的形成途径、对免疫应答的影响及与自身免疫性疾病的关联等,解析其在自身免疫疾病中的作用。     

血清总胆汁酸测定在肝胆疾病中的应用

胆汁酸是胆汁中的主要成分，是在肝细胞有关酶的作用下，经一系列反应由胆固醇转化而来。肝胆系统与肠道处于正常状态时，胆汁酸的合成、分泌及肠肝循环处于动态平衡。当肝胆功能受损，这种动态平衡被打破，血中胆汁酸浓度随之变化。本文通过对151例肝胆病患者血中胆汁酸测定，并与常规检测谷丙转氨酶(alanine aminotrans terase，ALT)进行比较，以探讨其在肝胆疾病中的意义。     

法尼酯X受体FXR在乳腺浸润性导管癌中的表达

目的探讨法尼酯X受体(FXR)在乳腺浸润性导管癌组织中的表达。方法用免疫组织化学MaxVision法检测FXR、雌激素ER、孕激素PR在10例正常乳腺组织和34例乳腺浸润性导管癌组织中的表达。结果 FXR在正常乳腺组中阳性率100%,浸润性导管癌中阳性率55.88%。FXR蛋白表达与年龄、病理分级无明显关系(P>0.05),与淋巴结未转移组比较,有淋巴结转移组高表达FXR蛋白(P<0.05)。FXR蛋白与ER蛋白表达呈显著正相关(r=0.373,P<0.05);PR蛋白高表达时,虽FXR蛋白也高表达,但无相关性(r=0.206,P>0.05)。结论 FXR高表达可能促进乳腺癌淋巴结转移,FXR与ER雌激素表达呈显著正相关。     

法尼醇类受体基因在胆囊中的表达

目的:探讨法尼醇类受体基因(FXR)的表达与胆囊的关系。方法:采用含17000cDNA克隆的基因微矩阵,与2例正常胆囊之cDNA杂交,发现FXR基因信号后,进一步进行RT-PCR和测序验证。结果:基因芯片能够检测出FXR在正常胆囊中的表达,其平均灰度值为16.80。在进一步的RT-PCR实验中,扩增出FXR的特异性片段,为352碱基。该PCR片段经测序后,其结果在GENEBANK数据库经BLAST比对,证实其同源性与FXR一致。结论:FXR在胆囊中表达,提示该基因可能还有新的未知功能。     

Farnesoid X receptor deficiency in mice leads to increased intestinal epithelial cell proliferation and tumor development

Increased dietary fat consumption is associated with colon cancer development. The exact mechanism by which fat induces colon cancer is not clear, however, increased bile acid excretion in response to high-fat diet may promote colon carcinogenesis. The farnesoid X receptor (FXR) is a member of the nuclear receptor superfamily, and bile acids are endogenous ligands of FXR. FXR is highly expressed in the intestine and liver where FXR is essential for maintaining bile acid homeostasis. The role of FXR in intestine cancer development is not known. The current study evaluated the effects of FXR deficiency in mice on intestinal cell proliferation and cancer development. The results showed that FXR deficiency resulted in increased colon cell proliferation, which was accompanied by an up-regulation in the expression of genes involved in cell cycle progression and inflammation, including cyclin D1 and interleukin-6. Most importantly, FXR deficiency led to an increase in the size of small intestine adenocarcinomas in adenomatous polyposis coli mutant mice. Furthermore, after treatment with a colon carcinogen, azoxymethane, FXR deficiency increased the adenocarcinoma multiplicity and size in colon and rectum of C57BL/6 mice. Loss of FXR function also increased the intestinal lymphoid nodule numbers in the intestine. Taken together, the current study is the first to show that FXR deficiency promotes cell proliferation, inflammation, and tumorigenesis in the intestine, suggesting that activation of FXR by nonbile acid ligands may protect against intestinal carcinogenesis.     

Bile Acids Induce Cdx2 Expression Through the Farnesoid X Receptor in Gastric Epithelial Cells

Clinical and experimental studies showed that the reflux of bile into the stomach contributes to the induction of intestinal metaplasia of the stomach and gastric carcinogenesis. Caudal-type homeobox 2 (Cdx2) plays a key role in the exhibition of intestinal phenotypes by regulating the expression of intestine-specific genes such as goblet-specific gene mucin 2 (MUC2). We investigated the involvement of the farnesoid X receptor (FXR), a nuclear receptor for bile acids, in the chenodeoxycholic acid (CDCA)-induced expression of Cdx2 and MUC2 in normal rat gastric epithelial cells (RGM-1 cells). RGM-1 cells were treated with CDCA or GW4064, an FXR agonist, in the presence or absence of guggulsterone, an FXR antagonist. CDCA induced dose-dependent expression of Cdx2 and MUC2 at both the mRNA and protein levels. The maximum stimulation of Cdx2 and MUC2 mRNA induced by CDCA was observed at 3 h and by 6 h, respectively. GW4064 also induced expression of these molecules. The effects of CDCA and GW4064 on expression of Cdx2 and MUC2 were abolished by guggulsterone. These findings suggest that bile acids may induce gastric intestinal metaplasia and carcinogenesis through the FXR.     

Protective effects of 6-ethyl chenodeoxycholic acid, a farnesoid X receptor ligand, in estrogen-induced cholestasis

The farnesoid X receptor (FXR), an endogenous sensor for bile acids, regulates a program of genes involved in bile acid biosynthesis, conjugation, and transport. Cholestatic liver diseases are a group of immunologically and genetically mediated disorders in which accumulation of endogenous bile acids plays a role in the disease progression and symptoms. Here, we describe the effect of 6-ethyl chenodeoxycholic acid (6-ECDCA or INT-747), a semisynthetic bile acid derivative and potent FXR ligand, in a model of cholestasis induced by 5-day administration of 17alpha-ethynylestradiol (E(2)17alpha) to rats. The exposure of rat hepatocytes to 1 microM 6-ECDCA caused a 3- to 5-fold induction of small heterodimer partner (Shp) and bile salt export pump (bsep) mRNA and 70 to 80% reduction of cholesterol 7alpha-hydroxylase (cyp7a1), oxysterol 12beta-hydroxylase (cyp8b1), and Na(+)/taurocholate cotransporting peptide (ntcp). In vivo administration of 6-ECDCA protects against cholestasis induced by E(2)17alpha. Thus, 6-ECDCA reverted bile flow impairment induced by E(2)17alpha, reduced secretion of cholic acid and deoxycholic acid, but increased muricholic acid and chenodeoxycholic acid secretion. In vivo administration of 6-ECDCA increased liver expression of Shp, bsep, multidrug resistance-associated protein-2, and multidrug resistance protein-2, whereas it reduced cyp7a1 and cyp8b1 and ntcp mRNA. These changes were reproduced by GW4064, a synthetic FXR ligand. In conclusion, by demonstrating that 6-ECDCA protects against E(2)17alpha cholestasis, our data support the notion that development of potent FXR ligands might represent a new approach for the treatment of cholestatic disorders.     

法尼醇X受体、胆汁酸盐输出泵与胆汁淤积性疾病发病研究进展

正胆汁淤积(Cholestasis)是指多种原因引起胆汁分泌不畅或排泄障碍,不能正常流入十二指肠所导致的一系列继发病变。由于致病因素多样且内外因素交互影响,胆汁淤积的具体发病机制尚未完全清楚,但主要与胆汁分泌调节异常、胆汁酸转运蛋白表达量减少或活性下降,胆汁酸转运量降低、肝细胞膜脂质成分改变影响膜的流动性;Na+/K+-ATP酶活性降低抑制对胆汁酸摄取等因素密切相关。胆汁正常代谢需要肝脏及胆囊的所有结构和功能具有完整性,其中任何一个环节的缺失都有可能引起胆汁循环障碍,进而形成胆汁淤积,导致胆汁中胆汁酸盐等毒性物质潴留,引起不同程度的细胞损伤,释放细胞因子和炎症介质,诱发胆道系统的炎症反应和肝纤     

Intestinal farnesoid X receptor signaling promotes nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a major worldwide health problem. Recent studies suggest that the gut microbiota influences NAFLD pathogenesis. Here, a murine model of high-fat diet–induced (HFD-induced) NAFLD was used, and the effects of alterations in the gut microbiota on NAFLD were determined. Mice treated with antibiotics or tempol exhibited altered bile acid composition, with a notable increase in conjugated bile acid metabolites that inhibited intestinal farnesoid X receptor (FXR) signaling. Compared with control mice, animals with intestine-specific Fxr disruption had reduced hepatic triglyceride accumulation in response to a HFD. The decrease in hepatic triglyceride accumulation was mainly due to fewer circulating ceramides, which was in part the result of lower expression of ceramide synthesis genes. The reduction of ceramide levels in the ileum and serum in tempol- or antibiotic-treated mice fed a HFD resulted in downregulation of hepatic SREBP1C and decreased de novo lipogenesis. Administration of C16:0 ceramide to antibiotic-treated mice fed a HFD reversed hepatic steatosis. These studies demonstrate that inhibition of an intestinal FXR/ceramide axis mediates gut microbiota–associated NAFLD development, linking the microbiome, nuclear receptor signaling, and NAFLD. This work suggests that inhibition of intestinal FXR is a potential therapeutic target for NAFLD treatment.