As a cellular bile acid sensor, farnesoid X receptor (FXR) and the membrane G-coupled receptor (GPBAR1) participate in maintaining bile acid, lipid, and glucose homeostasis. To date, several selective and dual agonists have been developed as promising pharmacological approach to metabolic disorders, with most of them possessing an acidic conjugable function that might compromise their pharmacokinetic distribution. Here, guided by docking calculations, nonacidic 6-ethyl cholane derivatives have been prepared. In vitro pharmacological characterization resulted in the identification of bile acid receptor modulators with improved pharmacokinetic properties.
The nuclear bile acid receptor FXR (farnesoid X receptor) is one of the key factors that suppress bile acid biosynthesis in the liver. PGC-1α [PPARγ (peroxisome-proliferator-activated receptor γ) co-activator-1α] is known to control energy homoeostasis in adipose tissue, skeletal muscle and liver. We performed cell-based reporter assays using the expression system of a GAL4–FXR chimaera, the ligand-binding domain of FXR fused to the DNA-binding domain of yeast GAL4, to find the co-activators for FXR. We found that the transcriptional activation of a reporter plasmid by a GAL4–FXR chimaera was strongly enhanced by PGC-1α, in a ligand-dependent manner. Transcriptional activation of the SHP (small heterodimer partner) gene by the FXR–RXRα (retinoid X receptor α) heterodimer was also enhanced by PGC-1α in the presence of CDCA (chenodeoxycholic acid). Co-immunoprecipitation and pull-down studies using glutathione S-transferase–PGC-1α fusion proteins revealed that the ligand-binding domain of FXR binds PGC-1α in a ligand-influenced manner both in vivo and in vitro. Furthermore, our studies revealed that SHP represses its own transcription, and the addition of excess amounts of PGC-1α can overcome the inhibitory effect of SHP. These observations indicate that PGC-1α mediates the ligand-dependent activation of FXR and transcription of SHP gene.
Introduction of Nonacidic Side Chains on 6-Ethylcholane Scaffolds in the Identification of Potent Bile Acid Receptor Agonists with Improved Pharmacokinetic Properties