Microbially-conjugated Bile Salts Found in Human Bile Activate the Bile Salt Receptors TGR5 and FXR.

Background & AimsBile salts of hepatic and microbial origin mediate inter-organ crosstalk in the gut-liver axis. Here, we assessed whether the newly discovered class of microbial bile salt conjugates (MBSCs), activate the main host bile salt receptors (TGR5 and FXR) and enter the human systemic and enterohepatic circulation. Approach & ResultsN-amidates of (chenodeoxy)cholic acid and leucine, tyrosine and phenylalanine were synthesized. Receptor activation was studied in cell-free and cell-based assays. MBSCs were quantified in mesenteric and portal blood and bile of patients undergoing pancreatic surgery. MBSCs were activating ligands of TGR5 as evidenced by recruitment of Gs protein, activation of a cAMP-driven reporter, and diminution of LPS-induced cytokine release from macrophages. Intestine- and liver-enriched FXR isoforms were both activated by MBSCs, provided that a bile salt importer was present. Affinity of MBSCs for TGR5 and FXR was not superior to host-derived bile salt conjugates. Individual MBSCs were generally not detected (i.e. View larger version (25K): org.highwire.dtl.DTLVardef@72f57borg.highwire.dtl.DTLVardef@1526fe8org.highwire.dtl.DTLVardef@130fd89org.highwire.dtl.DTLVardef@155603f_HPS_FORMAT_FIGEXP M_FIG C_FIG Created with BioRender.com