Secretin receptor antagonist treatment reduces biliary damage and liver fibrosis in a mouse model of early stage primary biliary cholangitis (PBC), but not advanced PBC

Background: Early stage Primary Biliary Cholangitis (PBC) is evidenced by ductular reaction, but advanced PBC is characterized by ductopenia. Secretin (Sec) binds to its receptor (SR) to increase biliary mass (IBDM) and liver fibrosis. dnTGFbRII mice at 12 wk of age mimic early stage PBC, but at 34 wk mimic advanced PBC. We have shown that the Sec/SR axis is increased in early stage PBC, but reduced in advanced PBC in mouse models and human samples, and Sec treatment reduces biliary damage and liver fibrosis in the advanced PBC mouse model. We evaluated the therapeutic potential of SR antagonist treatment in dnTGFbRII mice, and Sec secretion and Sec/SR expression in human PBC. Methods: Male and female wild-type, dnTGFbRII 12 wk and dnTGFbRII 34 wk mice received control or SR antagonist (SCT 5-27, 10 mg/kg/day) for 1 wk. Portal inflammation, lymphocytic infiltration and liver necrosis were evaluated by H&E. IBDM and biliary proliferation were measured by CK-19 and Ki67 staining. Biliary apoptosis was measured by TUNEL staining. Biliary senescence was assessed by immunofluorescence (IF) for CCL2 or p16 co-stained with CK-19 (to image bile ducts). Liver fibrosis was assessed by qPCR for collagen-1a and a-SMA, and Sirius Red staining. Hepatic stellate cell (HSC) activation was shown by IF for Syp-9 (HSC marker). HSC senescence was shown by IF for CCL2 or p16 co-stained with desmin (to image HSCs). Human control, early and advanced PBC samples were obtained. Serum and bile Sec levels were measured by EIA. Biliary Sec/SR expression was shown by staining. Results: dnTGFbRII mice at 12 wk had increased liver damage, IBDM, biliary proliferation and senescence, liver fibrosis, HSC activation and Sec secretion, but decreased biliary apoptosis and HSC senescence. SCT 5-27 reversed these parameters, thereby ameliorating biliary damage and liver fibrosis. dnTGFbRII mice at 34 wk had increased liver damage, biliary apoptosis and senescence, liver fibrosis and HSC activation, but reduced IBDM, biliary proliferation, HSC senescence and Sec secretion. SCT 5-27 exacerbated these parameters, thereby increasing biliary damage and liver fibrosis. Human early stage PBC had enhanced Sec secretion and biliary Sec/SR expression; however, these parameters were reduced in human advanced PBC. Conclusion: Enhanced Sec/SR signaling increases biliary proliferation and liver fibrosis in early stage PBC, which are reduced by SCT 5-27. Loss of the Sec/ SR axis in advanced PBC contributes to ductopenia and liver fibrosis thereby exacerbating liver damage. However, SR antagonist treatment may be a beneficial therapeutic for early stage PBC patients.