UDCA treatment reverses biliary proliferation and hepatic fibrosis in Mdr2−/− mice and human PSC by decreasing mast cell infiltration and histamine release
Authors: Kennedy Lindsey Leann , Hargrove Laura , Demieville Jennifer , Meng Fanyin , Invernizzi Pietro , Alpini Gianfranco , Francis Heather 
Published: November 2023

BackgroundUrsodeoxycholic acid (UDCA) is used to treat biliary disorders but yields inconsistent effects on improving cholestatic injury. We have shown that during cholestatic injury, including the Mdr2−/− model of PSC, mast cells (MC) infiltrate the liver and release large amounts of histamine (HA) that promote hepatic fibrosis by increasing inflammation and hepatic stellate cell (HSC) activation. Previously, it was shown that UDCA decreases MC degranulation and HA release.AimTo determine the effects of UDCA treatment on MC infiltration, HA release and liver pathology in Mdr2−/− mice and human PSC samples.MethodsWild‐type (WT) and Mdr2−/− mice at 12 wks of age were fed a bile acid control diet or UDCA enriched diet (0.5% wt/wt for 7 days). Human samples were collected from control and PSC patients (84% early stage, 16% advanced stage) that were untreated or treated with UDCA (15 mg/kg/BW). MC infiltration was measured in mouse and human samples by immunofluorescence for FCɛR1 and chymase, and by qPCR for the expression of c‐kit, chymase and tryptase. Intrahepatic bile duct mass (IBDM) and cholangiocyte proliferation were evaluated by immunohistochemistry for CK‐19 and Ki67 in mouse livers. Hepatic fibrosis was detected by Masson's Trichrome and Sirius Red staining in liver sections and qPCR for α‐SMA, fibronectin, collagen‐type 1a and TGF‐β in total liver. HSC activation was measured by immunofluorescence and qPCR for SYP‐9. HA secretion was evaluated in mouse and human serum samples by EIA. In vitro, cultured MCs were treated with basal or UDCA (40 μM) prior to evaluation of HA secretion and MC marker (chymase and tryptase) expression. Expression of bile acid transporters (TGR5, OATP2, ASBT, FXRβ, NTCP and VDR) and were shown in cultured MCs by immunofluorescence. Cholangiocytes were co‐cultured with MCs treated with control or UDCA, and qPCR for fibrosis marker (α‐SMA, fibronectin and collagen‐type 1a) and proliferation by BrDU incorporation were evaluated.ResultsIn Mdr2−/− mice and human PSC, HA secretion and MC number increase, and MCs are found in close proximity to bile ducts; however, these parameters are decreased in Mdr2−/− mice and patients treated with UDCA. IBDM and cholangiocyte proliferation are increased in Mdr2−/− mice compared to WT; however, these parameters are decreased in Mdr2−/− mice fed UDCA. Hepatic fibrosis and HSC activation are increased in both Mdr2−/− mice and untreated human PSC. Treatment with UDCA decreases fibrosis and HSC activation in both Mdr2−/− mice and human PSC samples. In vitro, MCs express all bile acid transporters, and stimulation with UDCA decreases MC HA release and MC marker expression. Biliary fibrosis and proliferation is decreased in cholangiocytes co‐cultured with MCs pre‐treated with UDCA.ConclusionDuring PSC, MCs infiltrate the liver and promote biliary hyperplasia and hepatic fibrosis. UDCA acts on MCs to reduce HA secretion, thereby decreasing the hyperplastic/fibrotic reaction seen in PSC patients. Inhibition of MC infiltration may be an important therapeutic option for PSC patients.Support or Funding InformationPSC Partners Seeking a CureNIH DK108595VA Merit 11I01BX003031