Localization of the therapeutic targets for endothelin receptor antagonists and sodium-glucose co-transporter 2 inhibitors in the chronic liver disease, primary sclerosing cholangitis.

INTRODUCTION: Primary sclerosing cholangitis (PSC) is a chronic liver disease of unknown cause contributing to cirrhosis and cancer but has no cure. PSC is characterized by inflammation within ductal fibrosis, progressive bile duct narrowing and loss, with damage to cholangiocytes (epithelial cells affecting bile production) and liver repair. ET-1, produced by cholangiocytes, contributes to fibrosis, vasoconstriction, and inflammation via ET(A) receptors. In patients, ET-1 and ET(A) gene expression are elevated and ET(A) antagonists reduce disease progression in PSC animal models. Ongoing clinical trials of portal hypertension in liver disease are testing the efficacy of a new treatment strategy combining ET(A)-selective antagonist zibotentan with SGLT2 inhibitor dapagliflozin. METHODS: To interrogate the potential of a comparable strategy in PSC we have initially compared the localization of ET receptors and SGLT2 transporter in human PSC liver. RESULTS: In ethically sourced healthy human liver, ET(A) immunofluorescence was primarily found in bile duct epithelial cells within the portal tract, smooth muscle of the central vein, with low levels in hepatocytes. SGLT2 immunofluorescence was mainly detected on bile duct epithelial cells and hepatocytes. ET(A) co-localized with smooth muscle cells in large arteries and veins, while ET(B) immunoreactivity was present in hepatocytes and endothelial cells. In the PSC vasculature, the pattern of expression of smooth muscle ET(A) receptors that mediate vasoconstriction was retained, consistent with the hypothesis that ET(A) selective antagonists would be beneficial in reducing portal hypertension. ET(B) receptors were principally localised on endothelial cells and would be expected to mediate beneficial vasodilation. In diseased areas, all three proteins localised to ductal reactions, reflecting the response of the liver to injury, involving cholangiocyte proliferation, promoting beneficial regeneration but also associated with fibrosis and inflammation. Both ET(A,) ET(B) and low levels of SGLT2 immunofluorescence localised to fibroblasts within the fibrous septa where bands of scar tissue can restrict hepatic blood flow, leading to cirrhosis. DISCUSSION: Both drug targets were retained in the key hallmarks of PSC pathology; ET(A) and SGLT2 staining within cholangiocytes undergoing ductal transformation and cells within the fibrotic septa, supporting the proposed benefit of combination treatment strategy.