S. Saccomanno

Glucagon-like peptide-1 receptor activation stimulates hepatic lipid oxidation and restores hepatic signalling alteration induced by a high-fat diet in nonalcoholic steatohepatitis.

Background/Aims: High‐fat dietary intake and low physical activity lead to insulin resistance, nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH). Recent studies have shown an effect of glucagon‐like peptide‐1 (GLP‐1) on hepatic glucose metabolism, although GLP‐1 receptors (GLP‐1r) have not been found in human livers. The aim of this study was to investigate the presence of hepatic GLP‐1r and the effect of exenatide, a GLP‐1 analogue, on hepatic signalling.

Dysbiosis contributes to fibrogenesis in the course of chronic liver injury in mice

Nonalcoholic fatty liver disease (NAFLD) may lead to hepatic fibrosis. Dietary habits affect gut microbiota composition, whereas endotoxins produced by Gram‐negative bacteria stimulate hepatic fibrogenesis. However, the mechanisms of action and the potential effect of microbiota in the liver are still unknown. Thus, we sought to analyze whether microbiota may interfere with liver fibrogenesis. Mice fed control (CTRL) or high‐fat diet (HFD) were subjected to either bile duct ligation (BDL) or CCl4 treatment. Previously gut‐sterilized mice were subjected to microbiota transplantation by oral gavage of cecum content obtained from donor CTRL‐ or HFD‐treated mice. Fibrosis, intestinal permeability, bacterial translocation, and serum endotoxemia were measured. Inflammasome components were evaluated in gut and liver. Microbiota composition (dysbiosis) was evaluated by Pyrosequencing. Fibrosis degree was increased in HFD+BDL versus CTRL+BDL mice, whereas no differences were observed between CTRL+CCl4 and HFD+CCl4 mice. Culture of mesenteric lymph nodes showed higher density of infection in HFD+BDL mice versus CTRL+BDL mice, suggesting higher bacterial translocation rate. Pyrosequencing revealed an increase in percentage of Gram‐negative versus Gram‐postive bacteria, a reduced ratio between Bacteroidetes and Firmicutes, as well as a dramatic increase of Gram‐negative Proteobacteria in HFD+BDL versus CTRL+BDL mice. Inflammasome expression was increased in liver of fibrotic mice, but significantly reduced in gut. Furthermore, microbiota transplantation revealed more liver damage in chimeric mice fed CTRL diet, but receiving the microbiota of HFD‐treated mice; liver damage was further enhanced by transplantation of selected Gram‐negative bacteria obtained from cecum content of HFD+BDL‐treated mice. Conclusions: Dietary habits, by increasing the percentage of intestinal Gram‐negative endotoxin producers, may accelerate liver fibrogenesis, introducing dysbiosis as a cofactor contributing to chronic liver injury in NAFLD. (Hepatology 2014;59:1738–1749)

Effect of pirfenidone on rat hepatic stellate cell proliferation and collagen production

BACKGROUND/AIMS Pirfenidone has been recently shown to reduce dimethynitrosamine-induced liver fibrosis in the rat, but no information are available on the effect of this drug on cultured hepatic stellate cells (HSC). METHODS HSC proliferation was evaluated by measuring bromodeoxyuridine incorporation; PDGF-receptor autophosphorylation, extracellular signal-regulated kinase (ERK1/2) and pp70(S6K) activation were evaluated by western blot; protein kinase C activation was evaluated by western blot and by ELISA; type I collagen accumulation and alpha1(I) procollagen mRNA expression were evaluated by ELISA and northern blot, respectively. RESULTS Pirfenidone significantly inhibited PDGF-induced HSC proliferation, starting at a concentration of 1 microM, with a maximal effect at 1000 microM, without affecting HSC viability and without inducing apoptosis. The inhibition of PDGF-induced HSC proliferation was associated neither with variations in PDGF-receptor autophosphorylation, or with ERK1/2 and pp70(S6K) activation. On the other hand, pirfenidone was able to inhibit PDGF-induced activation of the Na(+)/H(+) exchanger, which is involved in PDGF-induced HSC proliferation in HSC, with a maximal effect at 1000 microM and inhibited PDGF-induced protein kinase C activation. Pirfenidone 100 and 1000 microM inhibited type I collagen accumulation in the culture medium induced by transforming growth factor(beta1) by 54% and 92%, respectively, as well as TGF(beta1)-induced alpha1(I) procollagen mRNA expression. RESULTS Pirfenidone could be a new candidate for antifibrotic therapy in chronic liver diseases.

Early response of α2(I) collagen to acetaldehyde in human hepatic stellate cells is TGF-β independent†

Acetaldehyde is fibrogenic and induces the expression of type I collagen genes in hepatic stellate cells. Some of these acetaldehyde‐dependent events are mediated by H2O2 and thus establish a direct connection between oxidative stress and collagen upregulation. We localized to the −378 to −183 region of the α2(I) collagen (COL1A2) promoter an acetaldehyde‐responsive element (AcRE) functional in human hepatic stellate cells (HHSCs) and investigated molecular mechanisms whereby acetaldehyde stimulates and modulates its transcriptional activity. Because the AcRE co‐localized with a previously described transforming growth factor β (TGF‐β)1–responsive element, and both acetaldehyde and this cytokine induce their effects through H2O2, we investigated whether all fibrogenic actions of acetaldehyde were mediated by this cytokine. Here we show that acetaldehyde‐induced COL1A2 upregulation in HHSCs recognizes two distinct but overlapping early and late stages that last from 1 to 6 hours and from 6 to 24 hours, respectively. We present several lines of evidence to show that early acetaldehyde‐mediated events are independent of TGF‐β1. These include significant time‐course differences in the expression of COL1A2 and TGF‐β1 mRNAs and inability of neutralizing antibodies to TGF‐β1 to inhibit acetaldehyde‐dependent collagen gene transcription and Smad 3 phosphorylation. We also show that although acetaldehyde‐dependent upregulation of collagen was PI3K dependent, that of TGF‐β1 was PI3K independent. In conclusion, acetaldehyde‐dependent mechanisms involved in COL1A2 upregulation are similar, but not identical, to those of TGF‐β1. We suggest that early acetaldehyde‐dependent events induce the late expression of TGF‐β1 and create an H2O2‐dependent autocrine loop that may sustain and amplify the fibrogenic response of this alcohol metabolite. (HEPATOLOGY 2005;42:343–352.)

Leptin enhances cholangiocarcinoma cell growth

Cholangiocarcinoma is a strongly aggressive malignancy with a very poor prognosis. Effective therapeutic strategies are lacking because molecular mechanisms regulating cholangiocarcinoma cell growth are unknown. Furthermore, experimental in vivo animal models useful to study the pathophysiologic mechanisms of malignant cholangiocytes are lacking. Leptin, the hormone regulating caloric homeostasis, which is increased in obese patients, stimulates the growth of several cancers, such as hepatocellular carcinoma. The aim of this study was to define if leptin stimulates cholangiocarcinoma growth. We determined the expression of leptin receptors in normal and malignant human cholangiocytes. Effects on intrahepatic cholangiocarcinoma (HuH-28) cell proliferation, migration, and apoptosis of the in vitro exposure to leptin, together with the intracellular pathways, were then studied. Moreover, cholangiocarcinoma was experimentally induced in obese fa/fa Zucker rats, a genetically established animal species with faulty leptin receptors, and in their littermates by chronic feeding with thioacetamide, a potent carcinogen. After 24 weeks, the effect of leptin on cholangiocarcinoma development and growth was assessed. Normal and malignant human cholangiocytes express leptin receptors. Leptin increased the proliferation and the metastatic potential of cholangiocarcinoma cells in vitro through a signal transducers and activators of transcription 3-dependent activation of extracellular signal-regulated kinase 1/2. Leptin increased the growth and migration, and was antiapoptotic for cholangiocarcinoma cells. Moreover, the loss of leptin function reduced the development and the growth of cholangiocarcinoma. The experimental carcinogenesis model induced by thioacetamide administration is a valid and reproducible method to study cholangiocarcinoma pathobiology. Modulation of the leptin-mediated signal could be considered a valid tool for the prevention and treatment of cholangiocarcinoma.

Regulation of ERK/JNK/p70S6K in two rat models of liver injury and fibrosis

BACKGROUND/AIMS The regulation of three major intracellular signalling protein kinases was investigated in two models of liver injury leading to hepatic fibrosis, dimethylnitrosamine administration (DMN) and bile duct ligation (BDL). METHODS Extracellular signal-regulated kinases (ERK)1/2, c-Jun terminal kinase (JNK) and p70S6-kinase (p70(S6K)) were studied in vivo in the whole liver, in liver sections and in isolated hepatocytes, cholangiocytes and hepatic stellate cells (HSC). RESULTS In the whole liver, activation of these kinases occurred with a different kinetic pattern in both models of liver injury. By immunohistochemistry and Western blot in isolated cells, phosphorylated kinases were detected in proliferating cells (i.e. hepatocytes and cholangiocytes after DMN and BDL, respectively), in addition to stellate-like elements. ERK1/2, JNK and p70(S6K) activation was associated with hepatocytes proliferation after DMN, while JNK activation was not associated with cholangiocytes proliferation after BDL. In HSC isolated from injured livers, protein kinases were differentially activated after BDL and DMN. Kinases activation in HSC in vivo preceded cell proliferation and alpha-smooth muscle actin appearance, a marker of HSC transformation in myofibroblast-like cells, and collagen deposition. CONCLUSIONS Our findings indicate that these kinases are coordinately regulated during liver regeneration and suggest that their modulation could be considered as a future therapeutic approach in the management of liver damage.

Exendin-4, a Glucagon-Like Peptide 1 receptor agonist, protects cholangiocytes from apoptosis

Background and aims: Progression of chronic cholestatic disorders towards ductopenia results from the dysregulation of cholangiocyte survival, with cell death by apoptosis prevailing over compensatory proliferation. Currently, no therapy is available to sustain cholangiocyte survival in the course of those disorders. It was recently shown that cholangiocytes express the glucagon-like peptide-1 receptor (GLP-1R); its activation results in enhanced proliferative reaction to cholestasis. The GLP-1R selective agonist exendin-4 sustains pancreatic β cell proliferation and prevents cell death by apoptosis. Exendin-4 is now employed in humans as a novel therapy for diabetes. The aim of the present study was to verify whether exendin-4 is effective in preventing cholangiocyte apoptosis. Methods: In vitro, tests were carried out to determine if exendin-4 is able to prevent apoptosis of cholangiocytes isolated from normal rats induced by glycochenodeoxycholic acid (GCDCA); in vivo, animals subjected to 1 week of bile duct ligation and to a single intraperitoneal injection of CCl4 were treated with exendin-4 for 3 days. Results: Exendin-4 prevented GCDCA-induced Bax mitochondrial translocation, cytochrome c release and an increase in caspase 3 activity. Phosphatidylinositol 3-kinase, but not cAMP/protein kinase A or Ca2+/calmodulin-dependent protein kinase inhibitors, neutralised the effects of exendin-4. In vivo, exendin-4 administration prevented the increase in TUNEL (terminal deoxynucleotidyl transferase-mediated triphosphate end-labelling)-positive cholangiocytes and the loss of bile ducts observed in bile duct-ligated rats treated with CCl4. Conclusion: Exendin-4 prevents cholangiocyte apoptosis both in vitro and in vivo; such an effect is due to the ability of exendin-4 to counteract the activation of the mitochondrial pathway of apoptosis. These findings support the hypothesis that exendin-4 may be effective in slowing down the progression of cholangiopathies to ductopenia.

Intracellular pH regulation and Na+/H+ exchange activity in human hepatic stellate cells: effect of platelet-derived growth factor, insulin-like growth factor 1 and insulin

BACKGROUND/AIMS The Na+/H+ exchanger is involved in rat hepatic stellate cell (HSC) proliferation induced by platelet-derived growth factor (PDGF). We therefore evaluated in human HSC: (1) the mechanisms of intracellular pH regulation; (2) the relationship between Na+/H+ exchange activation and cell proliferation induced by PDGF, insulin-like growth factor 1 (IGF-1) and insulin. METHODS/RESULTS pH(i) regulation was mainly dependent on the activity of the Na+/H+ exchanger, which was evaluated by measuring pH(i) recovery from an acute acid load. PDGF (25 ng/ml) gradually increased the activity of the Na+/H+ exchanger which peaked at 18 h and remained stable until the 24th h. IGF-1 (10 nmol/l), but not insulin (100 nmol/l), slightly but significantly increased the activity of the Na+/H+ exchanger. Amiloride (100 micromol/l) and 20 micromol/l 5-N-ethyl-N-isopropyl-amiloride completely inhibited HSC proliferation (evaluated by measurement of bromodeoxyuridine incorporation) induced by PDGF and IGF-1, but did not affect proliferation of HSC induced by insulin. Finally, IGF-1 did not modify the activity of the Na+/Ca2+ exchanger. CONCLUSIONS The Na+/H+ exchanger is involved in HSC proliferation induced by PDGF and IGF-1, whereas the proliferative effect of insulin is mediated by intracellular pathways which are Na+/H+ exchange-independent.

Endoplasmic Reticulum stress induces hepatic stellate cell apoptosis and contributes to fibrosis resolution

Survival of hepatic stellate cells (HSCs) is a hallmark of liver fibrosis, while the induction of HSC apoptosis may induce recovery. Activated HSC are resistant to many pro‐apoptotic stimuli. To this issue, the role of Endoplasmic Reticulum (ER) stress in promoting apoptosis of HSCs and consequently fibrosis resolution is still debated.

Insulin resistance and necroinflammation drives ductular reaction and epithelial-mesenchymal transition in chronic hepatitis C

Objective To study the mechanism(s) linking insulin resistance (IR) to hepatic fibrosis and the role of the epithelial component in tissue repair and fibrosis in chronic hepatitis C (CHC). Design Prospective observational study. Setting Tertiary care academic centre. Patients 78 consecutive patients with CHC. Main outcome measures IR, calculated by the oral glucose insulin sensitivity during oral glucose tolerance test; necroinflammatory activity and fibrosis, defined according to Ishaks score; steatosis, graded as 0 (<5% of hepatocytes), 1 (5–33%), 2 (33–66%) and 3 (>66%). To evaluate the role of the epithelial component in tissue repair and fibrosis, the expansion of the ductular reaction (DR) was calculated by keratin-7 (CK7) morphometry. Nuclear expression of Snail, downregulation of E-cadherin and expression of fibroblast specific protein-1 (FSP1) and vimentin by CK7-positive cells were used as markers of epithelial-mesenchymal transition in DR elements. Results IR, the degree of necroinflammation and expansion of the DR (stratified as reactive ductular cells (RDCs), hepatic progenitor cells and intermediate hepatobiliary cells according to morphological criteria) were all associated with the stage of fibrosis. Nuclear Snail expression, E-cadherin downregulation and vimentin upregulation were observed in RDCs. By dual immunofluorescence for CK7 and FSP1, the number of RDCs undergoing epithelial-mesenchymal transition progressively increased together with the necroinflammatory score. By multivariate analysis, total inflammation and insulin resistance were the only factors significantly predicting the presence of advanced fibrosis (Ishak score ≥3) and the expansion of RDCs. Conclusion This study indicates that IR is associated with the degree of necroinflammatory injury in CHC and contributes to hepatic fibrosis by stimulating the expansion of RDCs that express epithelial-mesenchymal transition markers.