法尼醇X受体激动剂的研究进展

法尼醇X受体(FXR)作为一种胆汁酸感受器,在体内发挥着重要作用,是治疗血脂异常和脂肪肝的重要靶点。近年来,FXR激动剂的研究由甾体类转向非甾体类化合物,人们通过高通量筛选也发现了许多结构新颖的FXR激动剂。本文对近年来FXR激动剂的研究进行综述。     

法呢醇X受体激动剂研究进展

法呢醇X受体（FXR）通过调节胆汁酸的合成、分泌和吸收来调节胆汁酸的代谢和稳态。法呢醇X受体激动剂有望成为治疗胆汁酸代谢相关疾病的新型药物。该文对近年来报道的法呢醇X受体激动剂进行简要综述。     

Probucol ameliorates hepatic stellate cell activation and autophagy is associated with farnesoid X receptor

Probucol has antioxidant effects and inhibits inflammation. Farnesoid X receptor (FXR) is a nuclear receptor that regulates autophagy, which is regarded as the key cause of the activation of hepatic stellate cell (HSC). In this study, the effects of probucol on HSC activation and autophagy in vitro and vivo and the role of FXR in this progress were investigated. Results showed that probucol ameliorated hepatic fibrosis and autophagy, and increased the expression of FXR in liver in a mouse model of fibrosis induced by CCl₄. And probucol could alleviate lipopolysaccharide-induced autophagy and HSC activation in vitro. In addition, probucol increased FXR expression, and the Z-guggulsterone, an antagonist of FXR, could block the effects of probucol on HSC activation and autophagy. Additionally, agonists of FXR could suppress LPS-induced autophagy and activation. These results suggest that probucol could ameliorate hepatic fibrosis, and inhibit HSC autophagy and activation, and these effects are associated with FXR.     

Interactions of the stereoisomers of alpha-hydroxytamoxifen with human hydroxysteroid sulfotransferase SULT2A1 and rat hydroxysteroid sulfotransferase STa.

Tamoxifen (TAM) is a nonsteroidal antiestrogenic drug that is widely used for the treatment of estrogen receptor-dependent breast cancer. An increased risk of endometrial cancer in some patients treated with TAM has been linked to the metabolic formation of alpha-hydroxytamoxifen (alpha-OHTAM) and its subsequent sulfation. Alpha-OHTAM has been found to be a substrate for rat and human hydroxysteroid sulfotransferases (STa and SULT2A1, respectively). Since stereochemistry plays an important role in the interactions of hydroxysteroid sulfotransferases with their substrates, we have now investigated the interactions of each of the stereoisomers of alpha-OHTAM with highly purified recombinant STa and SULT2A1. Methods for the preparation of the enantiomers of E- and Z-alpha-OHTAM were developed. When each of the four enantiomers was examined with rat STa, E-(+)-alpha-OHTAM was the only substrate for the enzyme, whereas E-(-)-alpha-OHTAM, Z-(+)-alpha-OHTAM, and Z-(-)-alpha-OHTAM were inhibitors of the sulfation of E-(+)-alpha-OHTAM catalyzed by STa. The dissociation constants for the alpha-OHTAM enantiomers indicated that they bound to STa with similar affinity, but only the E-(+)-enantiomer was a substrate. In contrast to the results obtained with rat hydroxysteroid sulfotransferase STa, all enantiomers of alpha-OHTAM were substrates for the human SULT2A1. Moreover, kcat/Km values with SULT2A1 were higher with the Z enantiomers than with the E enantiomers. As a result of the potential for interconversion of the E and Z geometric isomers upon metabolism, the sulfation of the Z isomers may be of greater concern in human tissues than has been previously assumed.     

法尼醇X受体激动剂奥贝胆酸

奥贝胆酸是一种治疗原发性胆汁性肝硬化和非酒精性脂肪肝的新型候选药物,由美国Intercept制药公司研发,其机制主要是通过激动法尼醇X受体,调节相关基因,影响胆汁酸的合成、分泌、转运和吸收。临床研究表明,对熊去氧胆酸不能完全耐受的患者,通过服用奥贝胆酸能够明显改善碱性磷酸酶和血清胆红素的水平,提示奥贝胆酸的临床效果可能优于现有药物熊去氧胆酸。将从奥贝胆酸的药物概况、相关背景、合成路线、药理作用、临床前及临床试验研究以及安全性评价方面进行简述。     

Identification of liver X receptor and farnesoid X receptor dual agonists from Tithonia diversifolia

Tithonia diversifolia is a novel herbal medicine exerting antihyperglycemic and hepatoprotective effects, but the molecular mechanism underlying these therapeutic effects remains unclear. Liver X receptor (LXR) and farnesoid X receptor (FXR) are members of nuclear receptor superfamily. Their agonists were demonstrated to exhibit antihyperglycemic and hepatoprotective effects. In this study, sesquiterpene lactones, tirotundin and tagitinin A, were isolated from the crude oil of T. diversifolia and evaluated for their activity against LXR and FXR by the transient transfection reporter and mammalian one-hybrid assays. Tirotundin and tagitinin A stimulated LXR-dependent rat CYP7A1, SREBP-1c, and ABCA1 gene promoter transactivation by approximately two-fold of vehicle effect at 10 μM. They also transrepressed LXR-dependent PEPCK gene promoter activation by approximately 50 % of vehicle effect at 10 μM. Additionally, they enhanced the transactivation of FXR-dependent SHP gene promoter by more than two-fold of vehicle effect at 10 μM. These results strongly indicated that tirotundin and tagitinin A acted as dual LXR/FXR agonists so T. diversifolia might exert therapeutic effects through LXR and FXR pathways.     

核受体FXR的配体及复合物结构研究进展

法尼醇X受体(FXR)属于核受体超家族,与代谢综合征的形成以及葡萄糖在体内的动态平衡等过程密切相关,是研发代谢疾病和抗糖尿病药物的重要靶标。近几年,FXR的激动剂、拮抗剂以及晶体结构等方面的研究有了较快的发展。本文综述了目前报道的不同类型的FXR配体及其构效关系,以及FXR复合物晶体结构的最新进展。     

Differential activation of the human farnesoid X receptor depends on the pattern of expressed isoforms and the bile acid pool composition

The farnesoid X receptor (FXR) is a key sensor in bile acid homeostasis. Although four human FXR isoforms have been identified, the physiological role of this diversity is poorly understood. Here we investigated their subcellular localization, agonist sensitivity and response of target genes. Measurement of mRNA revealed that liver predominantly expressed FXRα1(+/−), whereas FXRα2(+/−) were the most abundant isoforms in kidney and intestine. In all cases, the proportion of FXRα(1/2)(+) and FXRα(1/2)(−) isoforms, i.e., with and without a 12 bp insert, respectively, was approximately 50%. When FXR was expressed in liver and intestinal cells the magnitude of the response to GW4064 and bile acids differs among FXR isoforms. In both cell types the strongest response was that of FXRα1(−). Different efficacy of bile acids species to activate FXR was found. The four FXR isoforms shared the order of sensitivity to bile acids species. When in FXR-deficient cells FXR was transfected, unconjugated, but not taurine- and glycine-amidated bile acids, were able to activate FXR. In contrast, human hepatocytes and cell lines showing an endogenous expression of FXR were sensitive to both unconjugated and conjugated bile acids. This suggests that to activate FXR conjugated, but not unconjugated, bile acids require additional component(s) of the intracellular machinery not related with uptake processes, which are missing in some tumor cells. In conclusion, cell-specific pattern of FXR isoforms determine the overall tissue sensitivity to FXR agonists and may be involved in the differential response of FXR target genes to FXR activation.     

International Union of Pharmacology. LXII. The NR1H and NR1I receptors: constitutive androstane receptor, pregnene X receptor, farnesoid X receptor alpha, farnesoid X receptor beta, liver X receptor alpha, liver X receptor beta, and vitamin D receptor

The nuclear receptors of the NR1H and NR1I subgroups include the constitutive androstane receptor, pregnane X receptor, farnesoid X receptors, liver X receptors, and vitamin D receptor. The newly emerging functions of these related receptors are under the control of metabolic pathways, including metabolism of xenobiotics, bile acids, cholesterol, and calcium. This review summarizes results of structural, pharmacologic, and genetic studies of these receptors.     

Bile duct ligation differently regulates protein expressions of organic cation transporters in intestine,liver and kidney of rats through activation of farnesoid X receptor by cholate and bilirubin

Body is equipped with organic cation transporters (OCTs). These OCTs mediate drug transport and are also involved in some disease process. We aimed to investigate whether liver failure alters intestinal, hepatic and renal Oct expressions using bile duct ligation (BDL) rats. Pharmacokinetic analysis demonstrates that BDL decreases plasma metformin exposure, associated with decreased intestinal absorption and increased urinary excretion. Western blot shows that BDL significantly downregulates intestinal Oct2 and hepatic Oct1 but upregulates renal and hepatic Oct2. In vitro cell experiments show that chenodeoxycholic acid (CDCA), bilirubin and farnesoid X receptor (FXR) agonist GW4064 increase OCT2/Oct2 but decrease OCT1/Oct1, which are remarkably attenuated by glycine-β-muricholic acid and silencing FXR. Significantly lowered intestinal CDCA and increased plasma bilirubin levels contribute to different Octs regulation by BDL, which are confirmed using CDCA-treated and bilirubin-treated rats. A disease-based physiologically based pharmacokinetic model characterizing intestinal, hepatic and renal Octs was successfully developed to predict metformin pharmacokinetics in rats. In conclusion, BDL remarkably downregulates expressions of intestinal Oct2 and hepatic Oct1 protein while upregulates expressions of renal and hepatic Oct2 protein in rats, finally, decreasing plasma exposure and impairing hypoglycemic effects of metformin. BDL differently regulates Oct expressions via Fxr activation by CDCA and bilirubin.     

Importance of peri-interactions on the stereospecificity of rat hydroxysteroid sulfotransferase STa with 1-arylethanols

Hydroxysteroid (alcohol) sulfotransferases catalyze the sulfation of polycyclic aromatic hydrocarbons (PAHs) that contain benzylic hydroxyl functional groups. This metabolic reaction is often a critical step in the activation of a hydroxyalkyl-substituted PAH to form an electrophilic metabolite that is capable of forming covalent bonds at nucleophilic sites on DNA, RNA, and proteins. Since hydroxyalkyl-substituted PAHs are often metabolically formed by the stereoselective enzymatic hydroxylation of a benzylic position on an alkyl-substituted PAH, we have investigated the possibility that the sulfation of hydroxyalkyl aromatic hydrocarbons is also stereoselective. Homogeneous preparations of rat hepatic hydroxysteroid (alcohol) sulfotransferase STa were utilized to investigate the stereoselectivity of its catalytic function with the enantiomers of model 1-arylethanols. While only minimal stereoselectivity was observed for the catalytic efficiency of STa with the enantiomers of 1-(2-naphthyl)ethanol and 1-acenaphthenol, the enzyme was stereospecific for (R)-(+)-1-(1-naphthyl)ethanol, (R)-(+)-1-(1-pyrenyl)ethanol, and (R)-(+)-1-(9-phenanthryl)ethanol as substrates. Moreover, (S)-(-)-1-(1-naphthyl)ethanol, (S)-(-)-1-(1-pyrenyl)ethanol, and (S)-(-)- 1-(9-phenanthryl)ethanol were competitive inhibitors of STa. Structural and conformational analyses of these 1-arylethanols indicated that steric interactions between the substituents on the benzylic carbon and the hydrogen in the peri-position on the aromatic ring system were important determinants of the stereospecificity of the enzyme with these molecules. The findings presented here have implications for the more accurate prediction of the ability of hydroxyalkyl-substituted PAHs to be activated via metabolic formation of electrophilic sulfuric acid esters.