Chronic Administration of Nicotine Increases Biliary Damage and Hepatic Fibrosis in Mdr2 Knockout (KO) Mice
Authors: O'Brien April , Ehrlich Laurent , Hall Chad , White Tori , Dostal David , Alpini Gianfranco , Glaser Shannon 
Published: November 2023

In chronic cholestatic liver diseases, cholangiocytes, through the products of their cellular activation, are suggested to be an important link between biliary injury and the subepithelial fibrosis that characterizes chronic hepatobiliary injury. The role of nicotine in the pathogenesis of primary sclerosing cholangitis (PSC) is unknown. We have shown that activation of the α7‐nicotine receptor (nAChR) with nicotine stimulates biliary proliferation that was associated with increased profibrotic gene expression by cholangiocytes and deposition of collagen in portal areas in normal mice. In addition, knockdown of α7‐nAChR prevents biliary hyperplasia and hepatic fibrosis during extrahepatic cholestasis induced by bile duct ligation. On the basis of this background, we AIM to evaluate the role of nicotine and α7‐nAChR in the regulation of biliary proliferation and hepatic fibrosis in Mdr2 KO mice that mimic some features of primary sclerosing cholangitis.

METHODS

Studies were performed in FVB (WT) and Mdr2 KO mice (12 wk of age). Mice were treated with control and nicotine (50 μM) drinking water for 2 wks. α7‐nAChR expression was evaluated in liver sections and isolated cholangiocytes by immunohistochemistry (IHC) and immunoblots, respectively. Liver enzyme serum levels were evaluated. Intrahepatic bile duct mass (IBDM) and biliary proliferation was evaluated by IHC for CK‐19 and PCNA, respectively, in liver sections, and by immunoblots in isolated cholangiocytes. Liver fibrosis was evaluated by Sirius red staining in liver sections, hydroxyproline content and qPCR for the profibrotic markers [collagen 1 (COL1A1), fibronectin (FN‐1), and αSMA] in isolated cholangiocytes and total liver samples.

RESULTS

As expected there was a significant increase in proliferation and hepatic fibrosis in WT mice treated with nicotine. There was a significant increase in biliary proliferation (PCNA) and IBDM (CK‐19) in Mdr2 KO mice treated with nicotine compared to WT treated with nicotine and Mdr2 KO mice receiving control water. There was also a significant increase in ALT, AST and AP levels in the serum in Mdr2 KO mice treated with nicotine compared to WT treated with nicotine. In addition to an increase in proliferation, there was also an increase in hepatic fibrosis by Sirius red staining, hydroxyproline content and a significant increase in COL1A1, FN‐1 and αSMA gene expression in Mdr2 KO mice treated with nicotine.

CONCLUSION

Chronic administration of nicotine stimulates proliferation and hepatic fibrosis in Mdr2 KO mouse model of cholestasis that mimics the features of human PSC. Modulation of the α7‐nAChR axis during extrahepatic cholestasis may represent a novel therapeutic approach for cholestatic liver diseases including PSC.

Support or Funding Information

This work was supported in part by a VA Merit Award (5I01BX002192) to Dr. Glaser from the United States (U.S.) Department of Veterans Affairs Biomedical Laboratory Research and Development Service. This material is the result of work supported with resources and the use of facilities at the Central Texas Veterans Health Care System, Temple, Texas. The views presented are those of the authors and do not necessarily represent the views of the Department of Veterans Affairs.