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

Abstract

Background. Postresectional 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. Aim. To 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. Methods. Twelve 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. Results. No 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 pre-treatment 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. Conclusion. Despite 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.