Background and Aim Hepatic fibrosis is marked by activation of hepatic stellate cells (HSCs). Cholestatic injury precedes liver fibrosis and cholangiocytes interact with HSCs promoting fibrosis. Mast cells (MCs) infiltrate following liver injury and release histamine increasing biliary proliferation. We evaluated if inhibition of MC-derived histamine decreases biliary proliferation and fibrosis. Methods WT and Mdr2−/− mice (9-11 weeks) were treated with cromolyn sodium for 1 week to block MC-derived histamine. Biliary mass and proliferation were evaluated by immunohistochemistry for CK-19 and Ki-67. Bile flow, bicarbonate excretion and total bile acids were measured in all mice. Fibrosis was evaluated by Sirius Red/Fast Green staining and by qPCR for α-SMA, fibronectin, collagen type 1a and TGF-β1. HSC activation was evaluated by qPCR in total liver and immunofluorescent staining in tissues for synaptophysin 9. Histamine serum secretion was measured by EIA. Mouse liver and human liver samples from control or PSC patients were evaluated for MC markers by qPCR and immunohistochemistry. In vitro, cultured MCs were transfected with HDC shRNA to decrease histamine secretion and subsequently co-cultured with cholangiocytes or HSCs prior to measuring fibrosis markers, proliferation and TGF-β1 secretion. Results Treatment with cromolyn sodium decreased biliary proliferation, fibrosis, histamine secretion, and bile flow in Mdr2−/− mice. PSC mice and patients have increased MCs. Knockdown of MC HDC decreased cholangiocyte and HSC proliferation/activation. Conclusion MCs are recruited to proliferating cholangiocytes and promote fibrosis. Inhibition of MC-derived histamine decreases fibrosis and regulation of MC mediators may be a therapeutic for PSC.

Activated mast cells (MCs) release histamine (HA) and MCs infiltrate the liver following bile duct ligation (BDL) increasing intrahepatic bile duct mass (IBDM) and fibrosis. We evaluated the effects of BDL in MC deficient mice. Methods: WT and KitW-sh mice were subjected to sham or BDL for up to 7 days and KitW-sh mice were injected with cultured mast cells or 1X PBS before collecting serum, liver blocks and cholangiocytes. Liver damage was assessed by H&E and ALT levels. IBDM was detected by CK-19 expression and proliferation by Ki-67 immunohistochemistry. Fibrosis was detected by immunohistochemistry, hydroxyproline content and by qPCR for fibrotic markers. Hepatic stellate cell (HSC) activation and TGF-β1 expression/secretion were evaluated. HDC and histamine receptor (HR) expression were detected by qPCR and HA secretion by EIA. To evaluate vascular cells, Von Willebrand (vWF) and VEGF-C expression were measured. In vitro, cultured HSCs were stimulated with cholangiocyte supernatants and α-SMA measured. Results: BDL-induced liver damage was reduced in the BDL KitW-sh mice, whereas injection of MCs did not mimic BDL-induced damage. In BDL KitW-sh mice, IBDM, proliferation, HSC activation/fibrosis and TGF-β1 expression/secretion were decreased. The HDC/HA/HR axis was ablated in sham and BDL KitW-sh mice. vWF and VEGF-C expression decreased in BDL KitW-sh mice. In KitW-sh mice injected with MCs, IBDM, proliferation, fibrosis and vascular cell activation increased. Stimulation with cholangiocyte supernatants from BDL WT or KitW-sh mice injected with MCs increased HSC activation, which decreased with supernatants from BDL KitW-sh mice. Conclusion: MCs promote hyperplasia, fibrosis and vascular cell activation. Knockout of MCs decreases BDL-induced damage. Modulation of MCs may be important in developing therapeutics for cholangiopathies.

Inhibition of H1/H2HR reverses PSC-associated damage and decreases CCA growth, angiogenesis, and EMT; because PSC patients are at risk of developing CCA, using HR blockers may be therapeutic for these diseases. (Hepatology 2018).

Non-alcoholic fatty liver disease (NAFLD) is a disease of increasing interest as its prevalence is on the rise. NAFLD has been linked to metabolic syndrome, which is becoming more common due to the Western diet. Since NAFLD can lead to cirrhosis and related complications including hepatocellular carcinoma, the increasing prevalence is concerning and medical therapy aimed at treating NAFLD is of great interest. Researchers studying the effects of medical therapy on NAFLD use dietary mouse models. The two main types of mouse model diets are the methionine- and choline-deficient (MCD) diet and Western-like Diet (WD). Although both induce NAFLD, the mechanisms are very different. We reviewed several studies conducted within the last 5 years that use MCD diet or WD mouse models in order to mimic this disease in a way most similar to humans. The MCD diet inconsistently induces NAFLD and fibrosis and doesn’t completely induce metabolic syndrome. Thus, the clinical significance of the MCD diet is questionable. In contrast, WD mouse models consisting of high fat, cholesterol, and a combination of high fructose corn syrup, sucrose, fructose or glucose not only lead to metabolic syndrome but also induce NAFLD with fibrosis making these choices most suitable for research.

Feeding a high-fat diet (HFD) coupled with sugar, mimicking a Western diet, causes fatty liver disease in mice. Histamine induces biliary proliferation and fibrosis and regulates leptin signaling. Wild-type (WT) and l-histidine decarboxylase (Hdc) mice were fed a control diet or an HFD coupled with a high fructose corn syrup equivalent. Hematoxylin and eosin and Oil Red O staining were performed to determine steatosis. Biliary mass and cholangiocyte proliferation were evaluated by immunohistochemistry. Senescence and fibrosis were measured by quantitative PCR and immunohistochemistry. Hepatic stellate cell activation was detected by immunofluorescence. Histamine and leptin levels were measured by enzyme immunoassay. Leptin receptor (Ob-R) was evaluated by quantitative PCR. The HDC/histamine/histamine receptor axis, ductular reaction, and biliary senescence were evaluated in patients with nonalcoholic fatty liver disease, nonalcoholic steatohepatitis, or end-stage liver disease. Hdc HFD mice had increased steatosis compared with WT HFD mice. WT HFD mice had increased biliary mass, biliary proliferation, senescence, fibrosis, and hepatic stellate cell activation, which were reduced in Hdc HFD mice. In Hdc HFD mice, serum leptin levels increased, whereas biliary Ob-R expression decreased. Nonalcoholic steatohepatitis patients had increased HDC/histamine/histamine receptor signaling. Hdc HFD mice are susceptible to obesity via dysregulated leptin/Ob-R signaling, whereas the lack of HDC protects from HFD-induced fibrosis and cholangiocyte damage. HDC/histamine/leptin signaling may be important in managing obesity-induced biliary damage.