Functional characterization of the semisynthetic bile acid derivative INT-767, a dual farnesoid X receptor and TGR5 agonist.

Two dedicated receptors for bile acids (BAs) have been identified, the nuclear hormone receptor farnesoid X receptor (FXR) and the G protein-coupled receptor TGR5, which represent attractive targets for the treatment of metabolic and chronic liver diseases. Previous work characterized 6α-ethyl-3α,7α-dihydroxy-5ß-cholan-24-oic acid (INT-747), a potent and selective FXR agonist, as well as 6α-ethyl-23(S)-methyl-3α,7α,12α-trihydroxy-5ß-cholan-24-oic acid (INT-777), a potent and selective TGR5 agonist. Here we characterize 6α-ethyl-3α,7α,23-trihydroxy-24-nor-5ß-cholan-23-sulfate sodium salt (INT-767), a novel semisynthetic 23-sulfate derivative of INT-747. INT-767 is a potent agonist for both FXR (mean EC(50), 30 nM by PerkinElmer AlphaScreen assay) and TGR5 (mean EC(50), 630 nM by time resolved-fluorescence resonance energy transfer), the first compound described so far to potently and selectively activate both BA receptors. INT-767 does not show cytotoxic effects in HepG2 cells, does not inhibit cytochrome P450 enzymes, is highly stable to phase I and II enzymatic modifications, and does not inhibit the human ether-a-go-go-related gene potassium channel. In line with its dual activity, INT-767 induces FXR-dependent lipid uptake by adipocytes, with the beneficial effect of shuttling lipids from central hepatic to peripheral fat storage, and promotes TGR5-dependent glucagon-like peptide-1 secretion by enteroendocrine cells, a validated target in the treatment of type 2 diabetes. Moreover, INT-767 treatment markedly decreases cholesterol and triglyceride levels in diabetic db/db mice and in mice rendered diabetic by streptozotocin administration. Collectively, these preclinical results indicate that INT-767 is a safe and effective modulator of FXR and TGR5-dependent pathways, suggesting potential clinical applications in the treatment of liver and metabolic diseases.

Nongenomic actions of bile acids. Synthesis and preliminary characterization of 23- and 6,23-alkyl-substituted bile acid derivatives as selective modulators for the G-protein coupled receptor TGR5.

23-Alkyl-substituted and 6,23-alkyl-disubstituted derivatives of chenodeoxycholic acid are identified as potent and selective agonists of TGR5, a G-protein coupled receptor for bile acids (BAs). In particular, we show that methylation at the C-23(S) position of natural BAs confers a marked selectivity for TGR5 over FXR, while the 6alpha-alkyl substitution increases the potency at both receptors. The present results allow for the first time a pharmacological differentiation of genomic versus nongenomic effects mediated by BA derivatives.

Back door modulation of the farnesoid X receptor: design, synthesis, and biological evaluation of a series of side chain modified chenodeoxycholic acid derivatives.

Carbamate derivatives of bile acids were synthesized with the aim of systematically exploring the potential for farnesoid X receptor (FXR) modulation endowed with occupancy of the receptor's back door, localized between loops H1-H2 and H4-H5. Since it was previously shown that bile acids bind to FXR by projecting the carboxylic tail opposite the transactivation function 2 (AF-2, helix 12), functionalization of the side chain is not expected to interfere directly with the orientation of H12 but can result in a more indirect way of receptor modulation. The newly synthesized compounds were extensively characterized for their ability to modulate FXR function in a variety of assays, including the cell-free fluorescence resonance energy transfer (FRET) assay and the cell-based luciferase transactivation assay, and displayed a broad range of activity from full agonism to partial antagonism. Docking studies clearly indicate that the side chain of the new derivatives fits in a so far unexploited receptor cavity localized near the "back door" of FXR. We thus demonstrate the possibility of achieving a broad FXR modulation without directly affecting the H12 orientation.

Bile acid derivatives as ligands of the farnesoid X receptor. Synthesis, evaluation, and structure-activity relationship of a series of body and side chain modified analogues of chenodeoxycholic acid.

The farnesoid X receptor (FXR) is activated by endogenous bile acids (BAs) and plays a variety of physiological roles related to modulation of gene transcription. In particular, FXR positively regulates the cholesterol catabolism while feedback inhibits the BA synthesis by repressing the expression of the CYP7A and CYP8B genes. We have previously shown that 6alpha-ethyl-CDCA (6ECDCA) is a potent and selective FXR agonist. In this paper we report an extensive structure-activity relationship for a series of synthetic bile acids. Our results indicate that the 6alpha position plays a fundamental role in determining affinity and that the side chain of BA is amenable to a variety of chemical modification. Although none of the new derivatives is more potent than 6ECDCA, we show here that a wide variability in efficacy, from full agonists to partial antagonists, can be obtained.

Novel stereoselective synthesis and chromatographic evaluation of E-guggulsterone.

A new stereoselective synthesis of E-guggulsterone is described starting from androsten-3,17-dione. Protection of the ring A enonic system, followed by regioselective Wittig reaction and C-16 oxidation, affords E-guggulsterone in good yields and high stereoselectivity, making this approach easily accessible and scalable. Moreover, an original normal-phase HPLC method enabling the fast quantitation of the guggulsterone isomeric purity, combined with the suitability for sampling procedures, is detailed. The relying upon the cellulose-based Chiralpak IB column and the chloroform as the "non-standard" component of the eluent mixture, allows to get profitably high chromatographic performances.

3alpha-6alpha-Dihydroxy-7alpha-fluoro-5beta-cholanoate (UPF-680), physicochemical and physiological properties of a new fluorinated bile acid that prevents 17alpha-ethynyl-estradiol-induced cholestasis in rats.

3alpha-6alpha-Dihydroxy-7alpha-fluoro-5beta-cholanoate (UPF-680), the 7alpha-fluorine analog of hyodeoxycholic acid (HDCA), was synthesized to improve bioavailability and stability of ursodeoxycholic acid (UDCA). Acute rat biliary fistula and chronic cholestasis induced by 17alpha-ethynyl-estradiol (17EE) models were used to study and compare the effects of UPF-680 (dose range 0.6-6.0 micromol/kg min) with UDCA on bile flow, biliary bicarbonate (HCO(3)(-)), lipid output, biliary bile acid composition, hepatic enzymes and organic anion pumps. In acute infusion, UPF-680 increased bile flow in a dose-related manner, by up to 40.9%. Biliary HCO(3)(-) output was similarly increased. Changes were observed in phospholipid secretion only at the highest doses. Treatment with UDCA and UPF-680 reversed chronic cholestasis induced by 17EE; in this model, UDCA had no effect on bile flow in contrast to UPF-680, which significantly increased bile flow. With acute administration of UPF-680, the biliary bile acid pool became enriched with unconjugated and conjugated UPF-680 (71.7%) at the expense of endogenous cholic acid and muricholic isomers. With chronic administration of UPF-680 or UDCA, the main biliary bile acids were tauro conjugates, but modification of biliary bile acid pool was greater with UPF-680. UPF-680 increased the mRNA for cytochrome P450 7A1 (CYP7A1) and cytochrome P450 8B (CYP8B). Both UDCA and UPF-680 increased the mRNA for Na(+) taurocholate co-transporting polypeptide (NCTP). In conclusion, UPF-680 prevented 17EE-induced cholestasis and enriched the biliary bile acid pool with less detergent and cytotoxic bile acids. This novel fluorinated bile acid may have potential in the treatment of cholestatic liver disease.

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.