Biology subjects

Schaap, F. G.

Publications and source records attributed to Schaap, F. G..

3 recordsLinked to original sources

bioRxiv2023

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. <2.5 nmol/L) in human mesenteric or portal blood, but Leu- and Phe-variants were readily measurable in bile, where MBSCs comprised up to 213 ppm of biliary bile salts. ConclusionsMBSCs activate the cell surface receptor TGR5 and the transcription factor FXR, and are substrates for intestinal (ASBT) and hepatic (NTCP) transporters. Their entry into the human circulation is, however, non-substantial. Given low systemic levels and surplus of other equipotent bile salt species, the studied MBSCs are unlikely to have an impact on enterohepatic TGR5/FXR signaling in humans. Origin and function of biliary MBSCs remain to be determined. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=106 SRC="FIGDIR/small/556292v1_ufig1.gif" ALT="Figure 1"> 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

molecular biology↗

bioRxiv2022

The FXR agonist obeticholic acid does not stimulate liver regeneration in hepatectomized mice.

BackgroundPostresectional liver failure (PLF) is a dreaded complication after partial hepatectomy (PH). Data from animal experiments indicate that endogenous ligands (i.e. bile salts) can stimulate liver regeneration and prevent liver injury after PH, via hepatic Fxr and the ileal Fxr-Fgf15 axis. AimTo investigate whether exogenous activation of the Fxr pathway with the semi-synthetic bile acid derivative obeticholic acid (OCA) could stimulate postresectional liver regeneration in mice. MethodsTwelve weeks old male C57BL6/J mice were pre-treated with OCA (10 mg/kg/day) or vehicle, and after 7 days subjected to 70% PH. Mice were sacrificed at 24, 48 and 72 hrs after PH, and liver injury, secretory function, and regenerative indices were assessed. In a second study, OCA pre-treated mice received oral sucrose supplementation in the postoperative trajectory, and a group of mice receiving intraperitoneal injection of FGF19 was included as a positive control group. Here, mice were sacrificed at 48 hours after PH. ResultsNo effect could be detected on liver mass recovery after PH, although responses of Cyp7a1, Cyp8b1 and other Fxr target genes implied general effectiveness of OCA treatment. OCA had no consistent effects on the number of Ki-67+ hepatocytes and mitotic figures around the peak of proliferation (i.e. 48 hrs) after PH, having no effect or increasing these regenerative indices in the consecutive experiments. Hepatic bile salt content, an important determinant of PH-induced liver regeneration, at this time point was not affected by OCA. After pretreatment of mice with FGF19, a reduced expression of ileal bile salt-regulated genes Fgf15 and Slc51b indicating FGF19-mediated repression of bile salt synthesis was seen, but this did not stimulate postresectional liver regeneration in mice. ConclusionDespite the activation of hepatic and ileal Fxr as shown by induction of target genes, treatment with OCA or FGF19 did not result in accelerated liver regeneration after PH and liver bile salt content was not influenced. We speculate that bile salt homeostasis and endogenous bile salt signaling is already optimal in unaffected livers for proper progression of regeneration after PH. It will be interesting to study the effects of Fxr agonism on liver regeneration after PH, and prevention of PLF in the context of compromised bile salt homeostasis/signaling prior to PH.

cell biology↗

bioRxiv2022

Development of a mouse model for postresectional liver failure.

BackgroundPostresectional liver failure (PLF) is a dreaded complication after extended liver resection. Post-operative hyperbilirubinemia suggests that impaired hepatobiliary transport with intrahepatic accumulation of harmful cholephiles plays an etiological role. Bile salts serve dual roles as signaling molecules engaged in liver regeneration after partial hepatectomy (PH) and biological detergents. AimIn this study we tested the hypothesis that excessive accumulation of bile salts in the regenerating liver results in PLF. MethodsTwelve weeks old male C57BL6/J mice were subjected to 70% PH and post-operatively challenged with a diet supplemented with cholic acid (CA, 0.5 or 1.0%; n=5-6 per group) or a control diet. After 48 hours mice were sacrificed, and liver injury, secretory function, and regenerative indices were assessed. ResultsMice fed a 1.0% CA diet displayed more pronounced weight loss following PH and had a deranged post-operative glucose course. Liver injury (aminotransferase elevations) and impaired hepatobiliary transport function (hyperbilirubinemia) were apparent in the group fed a 1.0% CA diet, but not in animals fed a 0.5% CA diet. No differences in liver mass recovery were observed among groups. However, the percentage of hepatocytes staining positive for the proliferation marker Ki-67 were reduced in mice receiving a 1.0% CA diet relative to animals fed a 0.5% CA diet. PH-induced expression of key factors involved in cell cycle progression (e.g. Foxm1b, Cdc25b) was abrogated in the 1.0% CA group. ConclusionA postresectional challenge with a 1.0% CA diet induces signs of liver injury and defective liver regeneration. A longer duration of the dietary challenge and/or secondary hits may further improve the model. Once validated, it can be used to evaluate pharmaceutical strategies to prevent or treat PLF.

cell biology↗