Structure-activity relationship of bile acids and bile acid analogs in regard to FXR activation

The farnesoid X receptor (FXR) is a bile acid-activated nuclear receptor that plays a major role in bile acid and cholesterol metabolism. To obtain an insight into the structure-activity relationships of FXR ligands, we investigated the functional roles of structural elements in the physiological ligands chenodeoxycholic acid [CDCA; (3α,7α)], cholic acid [CA; (3α,7α,12α)], deoxycholic acid [DCA; (3α,12α)], and lithocholic acid (3α) in regard to FXR activation in a cell-based FXR response element-driven luciferase assay and an in vitro coactivator association assay. Conversion of the carboxyl group of CDCA or CA to an alcohol did not greatly diminish their ability to activate FXR. In contrast, the 7β-epimers of the alcohols were inactive, indicating that the bile alcohols retained the ligand properties of the original bile acids and that the 7β-hydroxyl group diminished their FXR-activating effect. Similarly, hydroxyl epimers of DCA exhibited decreased activity compared with DCA, indicating a negative effect of 3β- or 12β-hydroxyl groups. Introduction of an alkyl group at the 7β- or 3β-position of CDCA resulted in diminished FXR activation in the following order of alkyl groups: 7-ethyl = 7-propyl > 3-methyl > 7-methyl.These results indicate that bulky substituents, whether hydroxyl groups or alkyl residues, at the β-position of cholanoids decrease their ability to activate FXR. The farnesoid X receptor (FXR) is a bile acid-activated nuclear receptor that plays a major role in bile acid and cholesterol metabolism. To obtain an insight into the structure-activity relationships of FXR ligands, we investigated the functional roles of structural elements in the physiological ligands chenodeoxycholic acid [CDCA; (3α,7α)], cholic acid [CA; (3α,7α,12α)], deoxycholic acid [DCA; (3α,12α)], and lithocholic acid (3α) in regard to FXR activation in a cell-based FXR response element-driven luciferase assay and an in vitro coactivator association assay. Conversion of the carboxyl group of CDCA or CA to an alcohol did not greatly diminish their ability to activate FXR. In contrast, the 7β-epimers of the alcohols were inactive, indicating that the bile alcohols retained the ligand properties of the original bile acids and that the 7β-hydroxyl group diminished their FXR-activating effect. Similarly, hydroxyl epimers of DCA exhibited decreased activity compared with DCA, indicating a negative effect of 3β- or 12β-hydroxyl groups. Introduction of an alkyl group at the 7β- or 3β-position of CDCA resulted in diminished FXR activation in the following order of alkyl groups: 7-ethyl = 7-propyl > 3-methyl > 7-methyl. These results indicate that bulky substituents, whether hydroxyl groups or alkyl residues, at the β-position of cholanoids decrease their ability to activate FXR. Bile acid biosynthesis is a major component of cholesterol homeostasis and represents an important pathway for the elimination of cholesterol from the body. Cholesterol 7α-hydroxylase (CYP7A1), a rate-limiting enzyme for bile acid formation, is negatively controlled by bile acids returning to the liver (1Pandak W.M. Vlahcevic Z.R. Heuman D.M. Redford K.S. Chiang J.Y. Hylemon P.B. Effects of different bile salts on steady-state mRNA levels and transcriptional activity of cholesterol 7α-hydroxylase.Hepatology. 1994; 19: 941-947Crossref PubMed Scopus (66) Google Scholar, 2Russell D.W. Setchell K.D. Bile acid biosynthesis.Biochemistry. 1992; 31: 4737-4749Crossref PubMed Scopus (646) Google Scholar, 3Stravitz R.T. Hylemon P.B. Heuman D.M. Hagey L.R. Schteingart C.D. Ton-Nu H.T. Hofmann A.F. Vlahcevic Z.R. Transcriptional regulation of cholesterol 7α-hydroxylase mRNA by conjugated bile acids in primary cultures of rat hepatocytes.J. Biol. Chem. 1993; 268: 13987-13993Abstract Full Text PDF PubMed Google Scholar). Recent studies have shown that this downregulation is mediated by the farnesoid X receptor (FXR), a nuclear receptor activated by several hydrophobic bile acids (4Chiang J.Y. Kimmel R. Weinberger C. Stroup D. Farnesoid X receptor responds to bile acids and represses cholesterol 7α-hydroxylase gene (CYP7A1) transcription.J. Biol. Chem. 2000; 275: 10918-10924Abstract Full Text Full Text PDF PubMed Scopus (250) Google Scholar, 5Makishima M. Okamoto A.Y. Repa J.J. Tu H. Learned R.M. Luk A. Hull M.V. Lustig K.D. Mangelsdorf D.J. Shan B. Identification of a nuclear receptor for bile acids.Science. 1999; 284: 1362-1365Crossref PubMed Scopus (2064) Google Scholar, 6Parks D.J. Blanchard S.G. Bledsoe R.K. Chandra G. Consler T.G. Kliewer S.A. Stimmel J.B. Willson T.M. Zavacki A.M. Moore D.D. Lehmann J.M. Bile acids: natural ligands for an orphan nuclear receptor.Science. 1999; 284: 1365-1368Crossref PubMed Scopus (1772) Google Scholar, 7Wang H. Chen J. Hollister K. Sowers L.C. Forman B.M. Endogenous bile acids are ligands for the nuclear receptor FXR/BAR.Mol. Cell. 1999; 3: 543-553Abstract Full Text Full Text PDF PubMed Scopus (1233) Google Scholar). Activation of FXR induces an orphan nuclear receptor, the small heterodimer partner (SHP), which forms a complex with liver receptor homolog-1 (LRH-1). Because LRH-1 is required for transcription of CYP7A1, increased SHP levels result in decreased CYP7A1 expression (8Goodwin B. Jones S.A. Price R.R. Watson M.A. McKee D.D. Moore L.B. Galardi C. Wilson J.G. Lewis M.C. Roth M.E. Maloney P.R. Willson T.M. Kliewer S.A. A regulatory cascade of the nuclear receptors FXR, SHP-1, and LRH-1 represses bile acid biosynthesis.Mol. Cell. 2000; 6: 517-526Abstract Full Text Full Text PDF PubMed Scopus (1453) Google Scholar, 9Lu T.T. Makishima M. Repa J.J. Schoonjans K. Kerr T.A. Auwerx J. Mangelsdorf D.J. Molecular basis for feedback regulation of bile acid synthesis by nuclear receptors.Mol. Cell. 2000; 6: 507-515Abstract Full Text Full Text PDF PubMed Scopus (1196) Google Scholar). Sterol 12α-hydroxylase (CYP8B1), which catalyzes the synthesis of cholic acid (CA), is also repressed by bile acids through an FXR-dependent mechanism (10Brendel C. Schoonjans K. Botrugno O.A. Treuter E. Auwerx J. The small heterodimer partner interacts with the liver X receptor α and represses its transcriptional activity.Mol. Endocrinol. 2002; 16: 2065-2076Crossref PubMed Scopus (165) Google Scholar, 11Castillo-Olivares A. Gil G. Suppression of sterol 12α-hydroxylase transcription by the short heterodimer partner: insights into the repression mechanism.Nucleic Acids Res. 2001; 29: 4035-4042Crossref PubMed Scopus (80) Google Scholar). In addition, FXR is expressed in the intestine, where bile acids are efficiently reabsorbed. The intestinal bile acid binding protein, a cytosolic bile acid transporter in ileal enterocytes, is induced by bile acids that activate FXR (12Kanda T. Foucand L. Nakamura Y. Niot I. Besnard P. Fujita M. Sakai Y. Hatakeyama K. Ono T. Fujii H. Regulation of expression of human intestinal bile acid-binding protein in Caco-2 cells.Biochem. J. 1998; 330: 261-265Crossref PubMed Scopus (84) Google Scholar). Thus, FXR is considered to play a critical role in cholesterol and bile acid metabolism. Several compounds not structurally related to bile acids have been shown to activate or antagonize FXR (13Howard W.R. Pospisil J.A. Njolito E. Noonan D.J. Catabolites of cholesterol synthesis pathways and forskolin as activators of the farnesoid X-activated nuclear receptor.Toxicol. Appl. Pharmacol. 2000; 163: 195-202Crossref PubMed Scopus (55) Google Scholar, 14Urizar N.L. Liverman A.B. Dodds D.T. Silva F.V. Ordentlich P. Yan Y. Gonzalez F.J. Heyman R.A. Mangelsdorf D.J. Moore D.D. A natural product that lowers cholesterol as an antagonist ligand for FXR.Science. 2002; 296: 1703-1706Crossref PubMed Scopus (423) Google Scholar, 15Zavacki A.M. Lehmann J.M. Seol W. Willson T.M. Kliewer S.A. Moore D.D. Activation of the orphan receptor RIP14 by retinoids.Proc. Natl. Acad. Sci. USA. 1997; 94: 7909-7914Crossref PubMed Scopus (87) Google Scholar). Although chenodeoxycholic acid (CDCA) is the most potent physiological ligand of FXR, its 7β-epimer, ursodeoxycholic acid (UDCA), does not activate FXR and has no effect on CYP7A1 in vivo (3Stravitz R.T. Hylemon P.B. Heuman D.M. Hagey L.R. Schteingart C.D. Ton-Nu H.T. Hofmann A.F. Vlahcevic Z.R. Transcriptional regulation of cholesterol 7α-hydroxylase mRNA by conjugated bile acids in primary cultures of rat hepatocytes.J. Biol. Chem. 1993; 268: 13987-13993Abstract Full Text PDF PubMed Google Scholar, 5Makishima M. Okamoto A.Y. Repa J.J. Tu H. Learned R.M. Luk A. Hull M.V. Lustig K.D. Mangelsdorf D.J. Shan B. Identification of a nuclear receptor for bile acids.Science. 1999; 284: 1362-1365Crossref PubMed Scopus (2064) Google Scholar, 6Parks D.J. Blanchard S.G. Bledsoe R.K. Chandra G. Consler T.G. Kliewer S.A. Stimmel J.B. Willson T.M. Zavacki A.M. Moore D.D. Lehmann J.M. Bile acids: natural ligands for an orphan nuclear receptor.Science. 1999; 284: 1365-1368Crossref PubMed Scopus (1772) Google Scholar). Thus, it is likely that the minor structural modifications of bile acid lead to significant changes in their ability to activate FXR. Enhancement of bile acid biosynthesis by releasing it from the negative feedback control is considered to be a strategy for developing hypocholesterolemic agents. Several bile acid analogs have already been developed as hypocholesterolemic agents (16Kim H.G. Une M. Hino A. Wada H. Yoshii M. Kuramoto T. Fujimura K. Bile acid sulfonate and 7-alkylated bile acid analogs: effect on intestinal absorption of taurocholate and cholesterol 7α-hydroxylase activity in cultured rat hepatocytes.Steroids. 2000; 65: 24-28Crossref PubMed Scopus (4) Google Scholar, 17Kim H.G. Une M. Kuramoto T. Noshiro M. Fujimura K. Hypocholesterolemic effect of bile acid sulfonate analogs in hamsters.Biol. Pharm. Bull. 2001; 24: 218-220Crossref PubMed Scopus (4) Google Scholar, 18Mikami T. Kihira K. Ikawa S. Yoshii M. Miki S. Mosbach E.H. Hoshita T. Metabolism of sulfonate analogs of ursodeoxycholic acid and their effects on biliary bile acid composition in hamsters.J. Lipid Res. 1993; 34: 429-435Abstract Full Text PDF PubMed Google Scholar, 19Une M. Yamanaga K. Mosbach E.H. Tsujimura K. Hoshita T. Metabolism of 7β-alkyl chenodeoxycholic acid analogs and their effect on cholesterol metabolism in hamsters.J. Lipid Res. 1990; 31: 1015-1021Abstract Full Text PDF PubMed Google Scholar), and elucidation of the structure-activity relationships of FXR ligands should provide a useful strategy for the development of new therapeutic agents. The present study focused on the relationship between the activity and structure of the nucleus or the side chain and was performed to elucidate the ability of naturally occurring bile acids, synthetic bile acid analogs, and bile alcohols (depicted in Fig. 1)to activate FXR in a cell-based luciferase assay and a coactivator association assay. The latter was a ligand sensor assay in vitro in which ligand-dependent recruitment of the steroid receptor coactivator-1 (SRC-1) to FXR was monitored by surface plasmon resonance (SPR) technology. Bile alcohols derived from bile acids were shown to exhibit ligand properties for FXR comparable to those of the original bile acids. In addition, introduction of a hydroxyl or alkyl substituent into the β-site of steroid nuclei decreased their ability to activate FXR, probably by diminishing binding affinity to the ligand binding domain (LBD) of FXR. CA, CDCA, deoxycholic acid (DCA), UDCA, and lithocholic acid (LCA) were commercial products. acid was from CA as G. S. of bile acids: synthesis of and bile Lipid Res. Full Text PDF PubMed Google Scholar). and acid were as M. Mosbach E.H. bile acid analogs: and Lipid Res. Full Text PDF PubMed Google Scholar, M. Yamanaga K. Mosbach E.H. S. Hoshita T. of bile acid analogs: 7-alkylated chenodeoxycholic PubMed Scopus Google Scholar). and were from the bile acids as K. Yoshii M. Okamoto A. Ikawa S. H. Hoshita T. of new bile and Lipid Res. 1990; 31: Full Text PDF PubMed Google Scholar). acid and and acids were by the H. P. K. J. of bile acids and the of acid from Biol. Chem. Full Text PDF PubMed Google Scholar). acid was from CDCA by with to the H. P. K. J. of bile acids and the of acid from Biol. Chem. Full Text PDF PubMed Google Scholar). To a of the in of was with a of The was at for with and with with The was with to and to The of acids was with and the were on a of and with The and were with in and in of the the acids acid nuclear resonance = and acid nuclear resonance = were from the of and in FXR was expressed in as a protein and on with FXR response luciferase was by of from the protein Zavacki A.M. Moore D.D. Identification of the binding and for the farnesoid X-activated Biol. Chem. 2000; 275: Full Text Full Text PDF PubMed Scopus Google and for and of the The expression and were by the human FXR and human X into expression were with of of and and of control with in were to bile acids at of to for were with the and the luciferase and were activity was to that of in The were performed a as Y. M. Y. T. K. K. and T. from human the nuclear receptor and the were and on of to of resonance and FXR with ligands for was the in a of and at of the the complex was with for an The were to the by of a of and and were by The of the in To to in were with from with CDCA has been shown to be the most potent natural ligand of FXR M. Okamoto A.Y. Repa J.J. Tu H. Learned R.M. Luk A. Hull M.V. Lustig K.D. Mangelsdorf D.J. Shan B. Identification of a nuclear receptor for bile acids.Science. 1999; 284: 1362-1365Crossref PubMed Scopus (2064) Google Scholar, 6Parks D.J. Blanchard S.G. Bledsoe R.K. Chandra G. Consler T.G. Kliewer S.A. Stimmel J.B. Willson T.M. Zavacki A.M. Moore D.D. Lehmann J.M. Bile acids: natural ligands for an orphan nuclear receptor.Science. 1999; 284: 1365-1368Crossref PubMed Scopus (1772) Google Scholar, 7Wang H. Chen J. Hollister K. Sowers L.C. Forman B.M. Endogenous bile acids are ligands for the nuclear receptor FXR/BAR.Mol. Cell. 1999; 3: 543-553Abstract Full Text Full Text PDF PubMed Scopus (1233) Google Scholar). investigated whether of the carboxyl group to an alcohol the ability of CDCA to activate FXR. In a assay an luciferase and human FXR and expression a bile alcohol derived from CDCA, exhibited activity comparable to that of CDCA in a coactivator association assay in potent between FXR and indicating that is a ligand for FXR. that and CDCA decreased the by and compared with the control indicating increased Thus, the that of the carboxyl group in CDCA to an alcohol its ability to activate and for farnesoid X receptor coactivator-1 induced by bile acids and bile acid cholic CDCA, chenodeoxycholic in a new CA, cholic CDCA, chenodeoxycholic CA was in assay CA has been shown to activate FXR in a cell-based assay the transporter is expressed D.J. Blanchard S.G. Bledsoe R.K. Chandra G. Consler T.G. Kliewer S.A. Stimmel J.B. Willson T.M. Zavacki A.M. Moore D.D. Lehmann J.M. Bile acids: natural ligands for an orphan nuclear receptor.Science. 1999; 284: 1365-1368Crossref PubMed Scopus (1772) Google Scholar, 7Wang H. Chen J. Hollister K. Sowers L.C. Forman B.M. Endogenous bile acids are ligands for the nuclear receptor FXR/BAR.Mol. Cell. 1999; 3: 543-553Abstract Full Text Full Text PDF PubMed Scopus (1233) Google Scholar). In contrast, a bile alcohol from CA, efficiently activated FXR indicating that the of the carboxyl group to an alcohol its into of the ability of CA to activate FXR. to be into by Although as as CA, was in the coactivator association assay the of CA to the association in vitro has been in a resonance assay M. Okamoto A.Y. Repa J.J. Tu H. Learned R.M. Luk A. Hull M.V. Lustig K.D. Mangelsdorf D.J. Shan B. Identification of a nuclear receptor for bile acids.Science. 1999; 284: 1362-1365Crossref PubMed Scopus (2064) Google Scholar, 6Parks D.J. Blanchard S.G. Bledsoe R.K. Chandra G. Consler T.G. Kliewer S.A. Stimmel J.B. Willson T.M. Zavacki A.M. Moore D.D. Lehmann J.M. Bile acids: natural ligands for an orphan nuclear receptor.Science. 1999; 284: 1365-1368Crossref PubMed Scopus (1772) Google Scholar). UDCA, a of CDCA, has been shown not to activate FXR M. Okamoto A.Y. Repa J.J. Tu H. Learned R.M. Luk A. Hull M.V. Lustig K.D. Mangelsdorf D.J. Shan B. Identification of a nuclear receptor for bile acids.Science. 1999; 284: 1362-1365Crossref PubMed Scopus (2064) Google Scholar, 6Parks D.J. Blanchard S.G. Bledsoe R.K. Chandra G. Consler T.G. Kliewer S.A. Stimmel J.B. Willson T.M. Zavacki A.M. Moore D.D. Lehmann J.M. Bile acids: natural ligands for an orphan nuclear receptor.Science. 1999; 284: 1365-1368Crossref PubMed Scopus (1772) Google Scholar, 7Wang H. Chen J. Hollister K. Sowers L.C. Forman B.M. Endogenous bile acids are ligands for the nuclear receptor FXR/BAR.Mol. Cell. 1999; 3: 543-553Abstract Full Text Full Text PDF PubMed Scopus (1233) Google Scholar). To the role of the 7β-hydroxyl group in the diminished ligand for FXR, we bile alcohols from and acid the of the of was as the original in the cell-based luciferase assay and the coactivator association assay in vitro Similarly, the of was in regard to FXR These that the of the hydroxyl group at the is critical for FXR of whether the side chain is an acid or an To elucidate the role of the of the hydroxyl groups at and in FXR we a of epimers of DCA by the cell-based luciferase assay. The and the of DCA the activity of DCA Similarly, the activity of the of for of the activity of Thus, of the 3β- 12β-hydroxyl groups in DCA and diminished their FXR-activating To insight into the diminishing effect of the 7β- or group on FXR we the effect of alkyl at the 7β- or 3β-position of shown in Fig. introduction of a group at the of CDCA decreased its ability to activate FXR by of that of The of a substituent or its activity and of that of CDCA, In contrast, at the of effect on its activity Introduction of a group at the in CDCA diminished the effect of CDCA by the activity of its was compared with that of CDCA The ability of CDCA to was by the introduction of an alkyl substituent at the or the of CDCA and the following order of groups to their ability to diminish the activity of 7-ethyl = 7-propyl > 3-methyl > this order was to the order for FXR in the luciferase assay Thus, the that alkyl at the 7β- or the 3β-position diminish the ability of CDCA to activate FXR. the that as FXR the no effect on the by CDCA The present study was to the relationship between the structural of bile acids and their FXR-activating by the structure of the physiological ligands CDCA, CA, DCA, and that bile bile alcohols exhibit and ligand properties in to FXR comparable to those of the original bile acids. alcohol is a potent of FXR that is as as CDCA in the cell-based luciferase assay and the coactivator association assay in vitro Similarly, from CA activated FXR in the cell-based luciferase assay The between the results from the cell-based assay and the in vitro coactivator association assay is it should be that CA was in the coactivator association assay in of the M. Okamoto A.Y. Repa J.J. Tu H. Learned R.M. Luk A. Hull M.V. Lustig K.D. Mangelsdorf D.J. Shan B. Identification of a nuclear receptor for bile acids.Science. 1999; 284: 1362-1365Crossref PubMed Scopus (2064) Google Scholar, 6Parks D.J. Blanchard S.G. Bledsoe R.K. Chandra G. Consler T.G. Kliewer S.A. Stimmel J.B. Willson T.M. Zavacki A.M. Moore D.D. Lehmann J.M. Bile acids: natural ligands for an orphan nuclear receptor.Science. 1999; 284: 1365-1368Crossref PubMed Scopus (1772) Google or in Fig. Because CA is of association in a cell-based assay the transporter is expressed M. T.T. W. H. R.M. Mangelsdorf D.J. receptor as an intestinal bile acid 2002; 296: PubMed Scopus Google Scholar), the activation of FXR by CA Thus, indicate that the of the carboxyl group of bile acids to an alcohol their binding affinity and activation of bile acids with or has been shown to have effect on FXR activation M. Okamoto A.Y. Repa J.J. Tu H. Learned R.M. Luk A. Hull M.V. Lustig K.D. Mangelsdorf D.J. Shan B. Identification of a nuclear receptor for bile acids.Science. 1999; 284: 1362-1365Crossref PubMed Scopus (2064) Google Scholar, 6Parks D.J. Blanchard S.G. Bledsoe R.K. Chandra G. Consler T.G. Kliewer S.A. Stimmel J.B. Willson T.M. Zavacki A.M. Moore D.D. Lehmann J.M. Bile acids: natural ligands for an orphan nuclear receptor.Science. 1999; 284: 1365-1368Crossref PubMed Scopus (1772) Google Scholar, 7Wang H. Chen J. Hollister K. Sowers L.C. Forman B.M. Endogenous bile acids are ligands for the nuclear receptor FXR/BAR.Mol. Cell. 1999; 3: 543-553Abstract Full Text Full Text PDF PubMed Scopus (1233) Google Scholar). on the results of the structure the at in conjugated and bile acids is to the with in the FXR S. J.M. R. Willson T.M. S. basis for bile acid binding and activation of the nuclear receptor Cell. Full Text Full Text PDF PubMed Scopus Google Scholar). The binding affinity of or also be through the of the at with In to and their alcohols derived from and were as as the original bile acids indicating that cholanoids with 7β-hydroxyl not activate FXR. on the that UDCA, the of CDCA, is M. Okamoto A.Y. Repa J.J. Tu H. Learned R.M. Luk A. Hull M.V. Lustig K.D. Mangelsdorf D.J. Shan B. Identification of a nuclear receptor for bile acids.Science. 1999; 284: 1362-1365Crossref PubMed Scopus (2064) Google Scholar, 6Parks D.J. Blanchard S.G. Bledsoe R.K. Chandra G. Consler T.G. Kliewer S.A. Stimmel J.B. Willson T.M. Zavacki A.M. Moore D.D. Lehmann J.M. Bile acids: natural ligands for an orphan nuclear receptor.Science. 1999; 284: 1365-1368Crossref PubMed Scopus (1772) Google Scholar, 7Wang H. Chen J. Hollister K. Sowers L.C. Forman B.M. Endogenous bile acids are ligands for the nuclear receptor FXR/BAR.Mol. Cell. 1999; 3: 543-553Abstract Full Text Full Text PDF PubMed Scopus (1233) Google Scholar), it has been that the of the hydroxyl group at in the steroid nucleus is critical for FXR also this also the of the of the hydroxyl group at the and The negative effect of 3β- or 12β-hydroxyl groups was shown in epimers of DCA and These results the that an of DCA the expression of mRNA (3Stravitz R.T. Hylemon P.B. Heuman D.M. Hagey L.R. Schteingart C.D. Ton-Nu H.T. Hofmann A.F. Vlahcevic Z.R. Transcriptional regulation of cholesterol 7α-hydroxylase mRNA by conjugated bile acids in primary cultures of rat hepatocytes.J. Biol. Chem. 1993; 268: 13987-13993Abstract Full Text PDF PubMed Google Scholar). in physiological activity and properties between CDCA and are by their hydrophobic and The 7β-hydroxyl group in the hydrophobic of the acid the with the the of Thus, it is that the decreased at the β-site results in the diminished ligand of in the present we that the introduction of a alkyl group at the decreased the ability of CDCA to activate FXR in the luciferase assay and to coactivator association to the of UDCA, the of the β-site of the steroid was increased by this the ability to activate FXR as a result of the was by and were a group was at the These indicate that to a bulky substituent in the or not a in the hydrophobic of the is the of the diminished ligand The of to with CDCA for coactivator recruitment that a bulky substituent at the or of CDCA its binding affinity for the FXR ligand binding A structural study that a 7β-hydroxyl group an ligand binding in the of coactivator association M. M.A. R. J.B. M.E. A.M. J.M. J.G. R.M. A and structural of the nuclear bile acid receptor Cell. Full Text Full Text PDF PubMed Scopus Google Scholar). Thus, it is likely that an alkyl substituent at the have a to decreased coactivator The decreased FXR activation by a mechanism for that CDCA represses activity in primary cultured rat efficiently does CDCA (16Kim H.G. Une M. Hino A. Wada H. Yoshii M. Kuramoto T. Fujimura K. Bile acid sulfonate and 7-alkylated bile acid analogs: effect on intestinal absorption of taurocholate and cholesterol 7α-hydroxylase activity in cultured rat hepatocytes.Steroids. 2000; 65: 24-28Crossref PubMed Scopus (4) Google Scholar). In to the negative effect of in CDCA, the introduction of a group at the of did not its is likely that the group at the is to the affinity to FXR, the group in CDCA forms with in the FXR S. J.M. R. Willson T.M. S. basis for bile acid binding and activation of the nuclear receptor Cell. Full Text Full Text PDF PubMed Scopus Google Scholar, M. M.A. R. J.B. M.E. A.M. J.M. J.G. R.M. A and structural of the nuclear bile acid receptor Cell. Full Text Full Text PDF PubMed Scopus Google Scholar). is that the decreased affinity by by the 7β-hydroxyl group is to the effect of the to be in to at the of CDCA, which to of FXR ligand R. S. E. C. G. Maloney P.R. A. D.J. Willson T.M. acid a potent and FXR with Chem. 2002; PubMed Scopus Google Scholar). Although the group in DCA and a negative acid exhibited activity comparable to that of CDCA which to that the group its A structure study with that the group of CDCA is not for FXR activation S. J.M. R. Willson T.M. S. basis for bile acid binding and activation of the nuclear receptor Cell. Full Text Full Text PDF PubMed Scopus Google Scholar). In this study that the steroid nucleus structure of bile acids was critical for FXR as an alkyl group or a hydroxyl group at the β-site of the steroid nucleus in bile acids, diminished ligand Conversion of the carboxyl groups of bile acids to alcohols did not ligand properties into These provide that be useful in the of new to acid was in by from the for and and by a from the cholic acid chenodeoxycholic acid cholesterol 7α-hydroxylase sterol 12α-hydroxylase deoxycholic acid farnesoid X receptor lithocholic acid liver receptor homolog-1 X receptor small heterodimer partner steroid receptor coactivator-1 acid ursodeoxycholic acid