Blocking integrin α4β7-mediated CD4 T cell recruitment to the intestine and liver protects mice from western diet-induced non-alcoholic steatohepatitis

BACKGROUND & AIMS

The heterodimeric integrin receptor α₄β₇ regulates CD4 T cell recruitment to inflamed tissues, but its role in the pathogenesis of non-alcoholic steatohepatitis (NASH) is unknown. Herein, we examined the role of α₄β₇-mediated recruitment of CD4 T cells to the intestine and liver in NASH.

METHODS

Male littermate F11r^+/+ (control) and junctional adhesion molecule A knockout F11r^-/- mice were fed a normal diet or a western diet (WD) for 8 weeks. Liver and intestinal tissues were analyzed by histology, quantitative reverse transcription PCR (qRT-PCR), 16s rRNA sequencing and flow cytometry. Colonic mucosa-associated microbiota were analyzed using 16s rRNA sequencing. Liver biopsies from patients with NASH were analyzed by confocal imaging and qRT-PCR.

RESULTS

WD-fed knockout mice developed NASH and had increased hepatic and intestinal α₄β₇⁺ CD4 T cells relative to control mice who developed mild hepatic steatosis. The increase in α₄β₇⁺ CD4 T cells was associated with markedly higher expression of the α₄β₇ ligand mucosal addressin cell adhesion molecule 1 (MAdCAM-1) in the colonic mucosa and livers of WD-fed knockout mice. Elevated MAdCAM-1 expression correlated with increased mucosa-associated Proteobacteria in the WD-fed knockout mice. Antibiotics reduced MAdCAM-1 expression indicating that the diet-altered microbiota promoted colonic and hepatic MAdCAM-1 expression. α₄β₇ blockade in WD-fed knockout mice significantly decreased α₄β₇⁺ CD4 T cell recruitment to the intestine and liver, attenuated hepatic inflammation and fibrosis, and improved metabolic indices. MAdCAM-1 blockade also reduced hepatic inflammation and fibrosis in WD-fed knockout mice. Hepatic MAdCAM-1 expression was elevated in patients with NASH and correlated with higher expression of α₄ and β₇ integrins.

CONCLUSIONS

These findings establish α₄β₇/MAdCAM-1 as a critical axis regulating NASH development through colonic and hepatic CD4 T cell recruitment.

LAY SUMMARY

Non-alcoholic steatohepatitis (NASH) is an advanced and progressive form of non-alcoholic fatty liver disease (NAFLD), and despite its growing incidence no therapies currently exist to halt NAFLD progression. Herein, we show that blocking integrin receptor α₄β₇-mediated recruitment of CD4 T cells to the intestine and liver not only attenuates hepatic inflammation and fibrosis, but also improves metabolic derangements associated with NASH. These findings provide evidence for the potential therapeutic application of α₄β₇ antibody in the treatment of human NASH.

Western diet-induced increase in colonic bile acids compromises epithelial barrier in nonalcoholic steatohepatitis

There is compelling evidence implicating intestinal permeability in the pathogenesis of nonalcoholic steatohepatitis (NASH), but the underlying mechanisms remain poorly understood. Here we examined the role of bile acids (BA) in western diet (WD)-induced loss of colonic epithelial barrier (CEB) function in mice with a genetic impairment in intestinal epithelial barrier function, junctional adhesion molecule A knockout mice, F11r^-/- . WD-fed knockout mice developed severe NASH, which was associated with increased BA concentration in the cecum and loss of CEB function. Analysis of cecal BA composition revealed selective increases in primary unconjugated BAs in the WD-fed mice, which correlated with increased abundance of microbial taxa linked to BA metabolism. In vitro permeability assays revealed that chenodeoxycholic acid (CDCA), which was elevated in the cecum of WD-fed mice, increased paracellular permeability, while the BA-binding resin sevelamer hydrochloride protected against CDCA-induced loss of barrier function. Sequestration of intestinal BAs by in vivo delivery of sevelamer to WD-fed knockout mice attenuated colonic mucosal inflammation and improved CEB. Sevelamer also reduced hepatic inflammation and fibrosis, and improved metabolic derangements associated with NASH. Collectively, these findings highlight a hitherto unappreciated role for BAs in WD-induced impairment of the intestinal epithelial barrier in NASH.

Consensus guidelines: best practices for detection, assessment and management of suspected acute drug-induced liver injury occurring during clinical trials in adults with chronic cholestatic liver disease

BACKGROUND

Improved knowledge of the molecular pathophysiology and immunopathogenesis of cholestatic liver diseases in recent years has led to an increased interest in developing novel therapies. Patients with cholestatic liver disease often require different approaches to assessment and management of suspected drug-induced liver injury (DILI) compared to those with healthy livers and those with parenchymal liver diseases. At present, there are no regulatory guidelines or society position papers, that systematically address best practices pertaining to detection of DILI in these patients.

AIMS

To outline best practices for detection, assessment and management of suspected acute DILI during clinical trials in adults with the cholestatic liver diseases - Primary Biliary Cholangitis (PBC) and Primary Sclerosing Cholangitis (PSC).

METHODS

This is one of the several papers developed by the IQ DILI Initiative, which is comprised of members from 16 pharmaceutical companies, in collaboration with DILI experts from academia and regulatory agencies. The contents are the result of an extensive literature review, as well as in-depth discussions among industry, regulatory and academic DILI experts, to achieve consensus recommendations on DILI-related issues occurring during clinical trials for cholestatic liver diseases.

RESULTS

Recommended best practices are outlined pertaining to hepatic eligibility criteria, monitoring of liver tests, approach to a suspected DILI signal, and hepatic discontinuation rules.

CONCLUSIONS

This paper provides a framework for the approach to detection, assessment and management of suspected acute DILI occurring during clinical trials in adults with cholestatic liver disease.

Molecular Genetic and Immune Functional Responses Distinguish Bone Marrow Mesenchymal Stromal Cells from Hepatic Stellate Cells

Defining the immune physiology of culture-adapted mesenchymal stromal cells (MSCs) derived from distinct tissue compartments informs their potential utility as pharmaceuticals. Here, we have investigated the comparative immune plasticity of MSCs and hepatic stellate cells (HeSCs) isolated from human and murine bone marrow (BM) and liver, respectively. Although both BM-MSCs and HeSCs share mesenchymal phenotype and overall molecular genetic responses to inflammatory cues, HeSCs differ from BM-MSCs in a meaningful manner. We show that culture-adapted HeSCs express substantially higher levels of hepatocyte growth factor (HGF), matrix metalloproteinase-1, and chemokine (CC motif) ligand 2 (CCL2) than BM-MSCs. Both human BM-MSCs and HeSCs inhibit T-cell proliferation by a shared indoleamine 2,3-dioxygenase (IDO)-dependent mechanism. However, HeSCs are distinct from BM-MSCs by their significant differential expression of HGF, CCL2, IL-8, CCL11, and GMCSF when cocultured with and/or without activated peripheral blood mononuclear cells. We have investigated MSCs and HeSCs derived from murine systems to describe interspecies comparability. Murine BM-MSCs inhibit T-cell proliferation through inducible nitric oxide synthase (iNOS) but not IDO. However, murine HeSCs inhibit T-cell proliferation through a mechanism distinct from either IDO or iNOS. Altogether, these results suggest that although culture-adapted BM-MSCs and HeSCs display a similar phenotype, their secretome and immune plasticity are in part distinct likely mirroring their tissular origins. In addition, the discordance in immune biology between mouse and human sourced HeSC and BM-MSCs speaks to the importance of comparative biology when interrogating rodent systems for human translational insights. Stem Cells 2019;37:1075-1082.

Consensus: guidelines: best practices for detection, assessment and management of suspected acute drug-induced liver injury during clinical trials in patients with nonalcoholic steatohepatitis

BACKGROUND

The last decade has seen a rapid growth in the number of clinical trials enrolling patients with nonalcoholic fatty liver disease and nonalcoholic steatohepatitis (NASH). Due to the underlying chronic liver disease, patients with NASH often require different approaches to the assessment and management of suspected drug-induced liver injury (DILI) compared to patients with healthy livers. However, currently no regulatory guidelines or position papers systematically address best practices pertaining to DILI in NASH clinical trials.

AIMS

This publication focuses on best practices concerning the detection, monitoring, diagnosis and management of suspected acute DILI during clinical trials in patients with NASH.

METHODS

This is one of several papers developed by the IQ DILI Initiative, comprised of members from 15 pharmaceutical companies, in collaboration with DILI experts from academia and regulatory agencies. This paper is based on extensive literature review, and discussions between industry members with expertise in drug safety and DILI experts from outside industry to achieve consensus on common questions related to this topic.

RESULTS

Recommended best practices are outlined pertaining to hepatic inclusion and exclusion criteria, monitoring of liver tests, DILI detection, approach to a suspected DILI signal, causality assessment and hepatic discontinuation rules.

CONCLUSIONS

This paper provides a framework for the approach to assessment and management of suspected acute DILI during clinical trials in patients with NASH.

Adiponectin inhibits hepatic stellate cell activation by targeting the PTEN/AKT pathway

Adiponectin inhibits hepatic stellate cell (HSC) activation and subsequent development of liver fibrosis via multiple mechanisms. Phosphatase and tensin homolog deletion 10 (PTEN) plays a crucial role in suppression of HSC activation, but its regulation by adiponectin is not fully understood. Here, we investigated the effect of adiponectin on PTEN in LX-2 cells, a human cell line and examined the underlying molecular mechanisms involved in adiponectin-mediated upregulation of PTEN activity during fibrosis. PTEN expression was found to be significantly reduced in the livers of mice treated with CCl4, whereas its expression was rescued by adiponectin treatment. The DNA methylation proteins DNMT1, DNMT3A, and DNMT3B are all highly expressed in activated primary HSCs compared to quiescent HSCs, and thus represent additional regulatory targets during liver fibrogenesis. Expression of DNMT proteins was significantly induced in the presence of fibrotic stimuli; however, only DNMT3B expression was reduced in the presence of adiponectin. Adiponectin-induced suppression of DNMT3B was found to be mediated by enhanced miR-29b expression. Furthermore, PTEN expression was significantly increased by overexpression of miR-29b, whereas its expression was markedly reduced by a miR-29b inhibitor in LX-2 cells. These findings suggest that adiponectin-induced upregulation of miR-29b can suppress DNMT3B transcription in LX-2 cells, thus resulting in reduced methylation of PTEN CpG islands and ultimately suppressing the PI3K/AKT pathway. Together, these data suggest a possible new explanation for the inhibitory effect of adiponectin on HSC activation and liver fibrogenesis.

Dysregulation of junctional adhesion molecule-A contributes to ethanol-induced barrier disruption in intestinal epithelial cell monolayers

Alcohol consumption promotes loss of intestinal barrier function. However, mechanisms by which ethanol affects the tight junction (TJ), the cellular structure responsible for maintaining the gut epithelial barrier, are not well understood. Three classes of transmembrane proteins comprise TJs: occludin, claudins, and junctional adhesion molecules (JAMs). It has recently been postulated that JAM‐A (F11R), the most abundant JAM expressed in intestinal epithelium, regulates “leak” pathway flux, a paracellular route for the nonselective permeation of large solutes. Since transluminal flux of many gut‐derived antigens occurs through this pathway, we investigated the role of JAM‐A in ethanol‐induced disruption of the intestinal epithelial barrier. Using Caco‐2 and SK‐CO15 monolayers, we found that ethanol induced a dose‐ and time‐dependent decrease in JAM‐A protein expression to about 70% of baseline levels. Alcohol also reduced Ras‐related protein 2 (Rap2) activity, and enhanced myosin light chain kinase (MLCK) activity, changes consistent with impaired JAM‐A signaling. Stable overexpression and shRNA‐mediated knockdown of JAM‐A were employed to investigate the role of JAM‐A in paracellular‐mediated flux following alcohol exposure. The paracellular flux of 40‐kDa fluorescein isothiocynate (FITC)‐dextran following ethanol treatment was decreased by the overexpression of JAM‐A; conversely, flux was enhanced by JAM‐A knockdown. Thus, we conclude that ethanol‐mediated control of JAM‐A expression and function contributes to mechanisms by which this chemical induces intestinal epithelial leakiness.

Periostin promotes liver fibrogenesis by activating lysyl oxidase in hepatic stellate cells

Liver fibrosis arises from dysregulated wound healing due to persistent inflammatory hepatic injury. Periostin is a nonstructural extracellular matrix protein that promotes organ fibrosis in adults. Here, we sought to identify the molecular mechanisms in periostin-mediated hepatic fibrosis. Hepatic fibrosis in periostin^-/- mice was attenuated as evidenced by significantly reduced collagen fibril density and liver stiffness compared with those in WT controls. A single dose of carbon tetrachloride caused similar acute liver injury in periostin^-/- and WT littermates, and we did not detect significant differences in transaminases and major fibrosis-related hepatic gene expression between these two genotypes. Activated hepatic stellate cells (HSCs) are the major periostin-producing liver cell type. We found that in primary rat HSCs in vitro, periostin significantly increases the expression levels and activities of lysyl oxidase (LOX) and lysyl oxidase-like (LOXL) isoforms 1-3. Periostin also induced expression of intra- and extracellular collagen type 1 and fibronectin in HSCs. Interestingly, periostin stimulated phosphorylation of SMAD2/3, which was sustained despite short hairpin RNA-mediated knockdown of transforming growth factor β (TGFβ) receptor I and II, indicating that periostin-mediated SMAD2/3 phosphorylation is independent of TGFβ receptors. Moreover, periostin induced the phosphorylation of focal adhesion kinase (FAK) and AKT in HSCs. Notably, siRNA-mediated FAK knockdown failed to block periostin-induced SMAD2/3 phosphorylation. These results suggest that periostin promotes enhanced matrix stiffness in chronic liver disease by activating LOX and LOXL, independently of TGFβ receptors. Hence, targeting periostin may be of therapeutic benefit in combating hepatic fibrosis.

Loss of Junctional Adhesion Molecule A Promotes Severe Steatohepatitis in Mice on a Diet High in Saturated Fat, Fructose, and Cholesterol

BACKGROUND & AIMS

There is evidence from clinical studies that compromised intestinal epithelial permeability contributes to the development of nonalcoholic steatohepatitis (NASH), but the exact mechanisms are not clear. Mice with disruption of the gene (F11r) encoding junctional adhesion molecule A (JAM-A) have defects in intestinal epithelial permeability. We used these mice to study how disruption of the intestinal epithelial barrier contributes to NASH.

METHODS

Male C57BL/6 (control) or F11r(-/-) mice were fed a normal diet or a diet high in saturated fat, fructose, and cholesterol (HFCD) for 8 weeks. Liver and intestinal tissues were collected and analyzed by histology, quantitative reverse-transcription polymerase chain reaction, and flow cytometry. Intestinal epithelial permeability was assessed in mice by measuring permeability to fluorescently labeled dextran. The intestinal microbiota were analyzed using 16S ribosomal RNA sequencing. We also analyzed biopsy specimens from proximal colons of 30 patients with nonalcoholic fatty liver disease (NAFLD) and 19 subjects without NAFLD (controls) undergoing surveillance colonoscopy.

RESULTS

F11r(-/-) mice fed a HFCD, but not a normal diet, developed histologic and pathologic features of severe NASH including steatosis, lobular inflammation, hepatocellular ballooning, and fibrosis, whereas control mice fed a HFCD developed only modest steatosis. Interestingly, there were no differences in body weight, ratio of liver weight:body weight, or glucose homeostasis between control and F11r(-/-) mice fed a HFCD. In these mice, liver injury was associated with significant increases in mucosal inflammation, tight junction disruption, and intestinal epithelial permeability to bacterial endotoxins, compared with control mice or F11r(-/-) mice fed a normal diet. The HFCD led to a significant increase in inflammatory microbial taxa in F11r(-/-) mice, compared with control mice. Administration of oral antibiotics or sequestration of bacterial endotoxins with sevelamer hydrochloride reduced mucosal inflammation and restored normal liver histology in F11r(-/-) mice fed a HFCD. Protein and transcript levels of JAM-A were significantly lower in the intestinal mucosa of patients with NAFLD than without NAFLD; decreased expression of JAM-A correlated with increased mucosal inflammation.

CONCLUSIONS

Mice with defects in intestinal epithelial permeability develop more severe steatohepatitis after a HFCD than control mice, and colon tissues from patients with NAFLD have lower levels of JAM-A and higher levels of inflammation than subjects without NAFLD. These findings indicate that intestinal epithelial barrier function and microbial dysbiosis contribute to the development of NASH. Restoration of intestinal barrier integrity and manipulation of gut microbiota might be developed as therapeutic strategies for patients with NASH.

C/EBP homologous protein modulates liraglutide-mediated attenuation of non-alcoholic steatohepatitis

The CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP), a major transcriptional regulator of endoplasmic reticulum (ER) stress-mediated apoptosis, is implicated in lipotoxicity-induced ER stress and hepatocyte apoptosis in non-alcoholic fatty liver disease (NAFLD). We have previously demonstrated that the glucagon-like peptide-1 (GLP-1) agonist, liraglutide, protects steatotic hepatocytes from lipotoxicity-induced apoptosis by improved handling of free fatty acid (FFA)-induced ER stress. In the present study, we investigated whether CHOP is critical for GLP-1-mediated restoration of ER homeostasis and mitigation of hepatocyte apoptosis in a murine model of NASH (non-alcoholic steatohepatitis). Our data show that despite similar caloric intake, CHOP KO (CHOP(-/-)) mice fed a diet high in fat, fructose, and cholesterol (HFCD) for 16 weeks developed more severe histological features of NASH compared with wild-type (WT) controls. Severity of NASH in HFCD-fed CHOP(-/-) mice correlated with significant decrease in peroxisomal β-oxidation, and increased de novo lipogenesis and ER stress-mediated hepatocyte apoptosis. Four weeks of liraglutide treatment markedly attenuated steatohepatitis in HFCD-fed WT mice by improving insulin sensitivity, and suppressing de novo lipogenesis and ER stress-mediated hepatocyte apoptosis. However, in the absence of CHOP, liraglutide did not improve insulin sensitivity, nor suppress peroxisomal β-oxidation or ER stress-mediated hepatocyte apoptosis. Taken together, these data indicate that CHOP protects hepatocytes from HFCD-induced ER stress, and has a significant role in the mechanism of liraglutide-mediated protection against NASH pathogenesis.

Glial cell line-derived neurotrophic factor-induced mice liver defatting: A novel strategy to enable transplantation of steatotic livers

Moderate macrovesicular steatosis (>30%), which is present in almost 50% of livers considered for transplantation, increases the risk of primary graft dysfunction. Our previously published data showed that glial cell line-derived neurotrophic factor (GDNF) is protective against high-fat diet (HFD)-induced hepatic steatosis in mice. Hence, we hypothesized that perfusion of steatotic livers with GDNF may reduce liver fat content before transplantation. Livers from 8 weeks of regular diet (RD) and of HFD-fed mice were perfused ex vivo for 4 hours with either vehicle, GDNF, or a previously described defatting cocktail. The liver's residual fat was quantified colorimetrically using a triglyceride (TG) assay kit and by Oil Red O (ORO) and Nile red/Hoechst staining. Liver tissue injury was assessed by using a lactate dehydrogenase (LDH) activity assay. In vitro induction of lipolysis in HepG2 cells was assessed by measuring glycerol and free fatty acid release. ORO staining showed significantly more steatosis in livers from HFD-fed mice compared with RD-fed mice (P < 0.001). HFD livers perfused with GDNF had significantly less steatosis than those not perfused (P = 0.001) or perfused with vehicle (P < 0.05). GDNF is equally effective in steatotic liver defatting compared to the defatting cocktail; however, GDNF induces less liver damage than the defatting cocktail. These observations were consistent with data obtained from assessment of liver TG content. Assessment of liver injury revealed significant hepatocyte injury in livers perfused with the control defatting cocktail but no evidence of injury in livers perfused with either GDNF or vehicle. In vitro, GDNF reduced TG accumulation in HepG2 cells and stimulated increased TG lipolysis. In conclusion, GDNF can decrease mice liver fat content to an acceptable range and could be a potential defatting agent before liver transplantation.

Low-Dose Cadmium Causes Metabolic and Genetic Dysregulation Associated With Fatty Liver Disease in Mice

Cadmium (Cd) is present in food at low levels and accumulates in humans throughout life because it is not effectively excreted. Cd from smoking or occupational exposure shows adverse effects on health, but the mechanistic effect of Cd at low dietary intake levels is poorly studied. Epidemiology studies found that nonalcoholic fatty liver disease (NAFLD), common in U.S. adults, is associated with Cd burden. In cell studies, we found that environmental low-dose Cd oxidized proteins and stimulated inflammatory signaling. However, little is known about low-dose Cd effects on liver function and associated metabolic pathways in vivo. We investigated effects of low-level Cd exposure on liver gene transcripts, metabolites, and associated metabolic pathways and function after challenging mice with Cd (10 mg/l) by drinking water. Results showed liver Cd in treated mice was similar to adult humans without occupational or smoking exposures and 10-fold higher than control mouse values. Pathway analysis of significantly altered liver genes and metabolites mapped to functional pathways of lipid metabolism, cell death and mitochondrial oxidative phosphorylation. These are well-recognized pathways associated with NAFLD. Cd-treated mice had higher liver enzymes in plasma and a trend toward fat accumulation in liver. To verify low-dose Cd-induced stimulation of cell death pathways, phosphorylation of c-Jun N-terminal kinase (JNK) was examined in cultured hepatic cells. Consistent with mouse liver data, low-dose Cd stimulated JNK activation. Together, the results show that low-dose Cd exposure causes liver function changes consistent with a role in NAFLD and possibly also nonalcoholic steatohepatitis.

Hepatitis B Virus Reactivation During Successful Treatment of Hepatitis C Virus With Sofosbuvir and Simeprevir

Treatment of hepatitis C virus with potent, interferon-free, direct-acting antiviral regimens with no activity against hepatitis B virus (HBV) may increase the risk for HBV reactivation in coinfected patients. We present 2 cases of HBV reactivation during treatment with an all-oral regimen of simeprevir and sofosbuvir and discuss strategies to prevent HBV flare.

Hepatitis B Virus Reactivation During Successful Treatment of Hepatitis C Virus With Sofosbuvir and Simeprevir

Treatment of hepatitis C virus with potent, interferon-free, direct-acting antiviral regimens with no activity against hepatitis B virus (HBV) may increase the risk for HBV reactivation in coinfected patients. We present 2 cases of HBV reactivation during treatment with an all-oral regimen of simeprevir and sofosbuvir and discuss strategies to prevent HBV flare.

Adipocytokines and hepatic fibrosis

Obesity and metabolic syndrome pose significant risk for the progression of many types of chronic illness, including liver disease. Hormones released from adipocytes, adipocytokines, associated with obesity and metabolic syndrome, have been shown to control hepatic inflammation and fibrosis. Hepatic fibrosis is the final common pathway that can result in cirrhosis, and can ultimately require liver transplantation. Initially, two key adipocytokines, leptin and adiponectin, appeared to control many fundamental aspects of the cell and molecular biology related to hepatic fibrosis and its resolution. Leptin appears to act as a profibrogenic molecule, while adiponectin has strong-antifibrotic properties. In this review, we emphasize pertinent data associated with these and other recently discovered adipocytokines that may drive or halt the fibrogenic response in the liver.

Saturated fat and cholesterol are critical to inducing murine metabolic syndrome with robust nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the metabolic syndrome (MetS). Up to a third of NAFLD subjects are at risk for developing nonalcoholic steatohepatitis (NASH). Many rodent models fail to replicate both MetS and NASH. The purpose of this study was to develop a reliable mouse model of NASH and MetS using a diet containing cholesterol, saturated fat and carbohydrate that is reflective of Western diets of North Americans.

EXPERIMENTAL DESIGN

We used adult male C57BL/6 J 4- to 5-week-old mice and administered a solid diet containing 0.2% cholesterol, 45% of its calories from fat, with 30% of the fat in the form of partially hydrogenated vegetable oil. We also provided carbohydrate largely as high-fructose corn syrup equivalent in water. In a separate cohort, we gave the identical diet in the absence of cholesterol. Glucose and insulin tolerance testing was conducted throughout the feeding period. The feeding was conducted for 16 weeks, and the mice were sacrificed for histological analysis, markers of MetS, liver inflammation, circulating lipids, as well as liver staining for fibrosis and alpha smooth muscle actin (α-SMA).

RESULTS

We found that cholesterol significantly increased serum leptin, interleukin-6, liver weight and liver weight/body weight ratio, fibrosis and liver α-SMA.

CONCLUSIONS

Mice administered a diet accurately reflecting patterns associated with humans afflicted with MetS can reliably replicate features of MetS, NASH and significant liver fibrosis. The model we describe significantly reduces the time by several months for development of stage 3 hepatic fibrosis.

Antagonistic interaction between Wnt and Notch activity modulates the regenerative capacity of a zebrafish fibrotic liver model

In chronic liver failure patients with sustained fibrosis, excessive accumulation of extracellular matrix proteins substantially dampens the regenerative capacity of the hepatocytes, resulting in poor prognosis and high mortality. Currently, the mechanisms and the strategies of inducing endogenous cellular sources such as hepatic progenitor cells (HPCs) to regenerate hepatocytes in various contexts of fibrogenic stimuli remain elusive. Here we aim to understand the molecular and cellular mechanisms that mediate the effects of sustained fibrosis on hepatocyte regeneration using the zebrafish as a model. In the ethanol-induced fibrotic zebrafish model, we identified a subset of HPCs, responsive to Notch signaling, that retains its capacity to regenerate as hepatocytes. Discrete levels of Notch signaling modulate distinct cellular outcomes of these Notch-responsive HPCs in hepatocyte regeneration. Lower levels of Notch signaling promote amplification and subsequent differentiation of these cells into hepatocytes, while high levels of Notch signaling suppress these processes. To identify small molecules facilitating hepatocyte regeneration in the fibrotic liver, we performed chemical screens and identified a number of Wnt agonists and Notch antagonists. Further analyses demonstrated that these Wnt agonists are capable of attenuating Notch signaling by inducing Numb, a membrane-associated protein that inhibits Notch signaling. This suggests that the antagonistic interplay between Wnt and Notch signaling crucially affects hepatocyte regeneration in the fibrotic liver.

CONCLUSION

Our findings not only elucidate how signaling pathways and cell-cell communications direct the cellular response of HPCs to fibrogenic stimuli, but also identify novel potential therapeutic strategies for chronic liver disease.

Adiponectin agonist ADP355 attenuates CCl4-induced liver fibrosis in mice

Liver fibrosis is a growing global health problem characterized by excess deposition of fibrillar collagen, and activation of hepatic stellate cells (HSCs). Adiponectin is known to possess anti-fibrotic properties; however a high physiological concentration and multiple forms circulating in blood prohibit clinical use. Recently, an adiponectin-like small synthetic peptide agonist (ADP355: H-DAsn-Ile-Pro-Nva-Leu-Tyr-DSer-Phe-Ala-DSer-NH2) was synthesized for the treatment of murine breast cancer. The present study was designed to evaluate the efficacy of ADP355 as an anti-fibrotic agent in the in vivo carbon tetrachloride (CCl4)-induced liver fibrosis model. Liver fibrosis was induced in eight-week old male C57BL/6J mice by CCl4-gavage every other day for four weeks before injection of a nanoparticle-conjugated with ADP355 (nano-ADP355). Control gold nanoparticles and nano-ADP355 were administered by intraperitoneal injection for two weeks along with CCl4-gavage. All mice were sacrificed after 6 weeks, and serum and liver tissue were collected for biochemical, histopathologic and molecular analyses. Biochemical studies suggested ADP355 treatment attenuates liver fibrosis, determined by reduction of serum aspartate aminotransferase (AST), alanine aminotransferase ALT) and hydroxyproline. Histopathology revealed chronic CCl4-treatment results in significant fibrosis, while ADP355 treatment induced significantly reversed fibrosis. Key markers for fibrogenesis-α-smooth muscle actin (α-SMA), transforming growth factor-beta1 (TGF-β1), connective tissue growth factor (CTGF), and the tissue inhibitor of metalloproteinase I (TIMP1) were also markedly attenuated. Conversely, liver lysates from ADP355 treated mice increased phosphorylation of both endothelial nitric oxide synthase (eNOS) and AMPK while AKT phosphorylation was diminished. These findings suggest ADP355 is a potent anti-fibrotic agent that can be an effective intervention against liver fibrosis.

Adiponectin modulates focal adhesion disassembly in activated hepatic stellate cells: implication for reversing hepatic fibrosis

Previous evidence indicates that adiponectin possesses antifibrogenic activity in inhibiting liver fibrosis. Therapeutic strategies, however, are limited by adiponectin quaternary structure and effective concentrations in circulation. Here we postulate a novel molecular mechanism, whereby adiponectin targets focal adhesion kinase (FAK) activity and disrupts key features of the fibrogenic response. Adiponectin-null (Ad(-/-)) mice and wild-type littermates were exposed to either saline or carbon tetrachloride (CCl4) for 6 wk. CCl4-gavaged mice were also injected with attenuated adenoviral adiponectin (Ad-Adn) or Ad-LacZ for 2 wk. Hepatic stellate cells (HSCs) were treated with or without adiponectin to elucidate signal transduction mechanisms. In vivo delivery of Ad-Adn markedly attenuates CCl4-induced expression of key integrin proteins and markers of HSC activation: αv, β3, β1, α2(I) collagen, and α-smooth muscle actin. Confocal experiments of liver tissues demonstrated that adiponectin delivery also suppressed vinculin and p-FAK activity in activated HSCs. In vitro, adiponectin induced dephosphorylation of FAK, mediated by a physical association with activated tyrosine phosphatase, Shp2. Conversely, Shp2 knockdown by siRNA significantly attenuated adiponectin-induced FAK deactivation, and expression of TIMP1 and α2(I) collagen was abolished in the presence of adiponectin and si-FAK. Finally, we documented that either adiponectin or the synthetic peptide with adiponectin properties, ADP355, suppressed p-FAK in synthetic matrices with stiffness measurements of 9 and 15 kPa, assessed by immunofluorescent imaging and quantitation. The in vivo and in vitro data presented indicate that disassembly of focal adhesion complexes in HSCs is pivotal for hepatic fibrosis therapy, now that small adiponectin-like peptides are available.

Glial cell line-derived neurotrophic factor protects against high-fat diet-induced obesity

Obesity is a growing epidemic with limited effective treatments. The neurotrophic factor glial cell line-derived neurotrophic factor (GDNF) was recently shown to enhance β-cell mass and improve glucose control in rodents. Its role in obesity is, however, not well characterized. In this study, we investigated the ability of GDNF to protect against high-fat diet (HFD)-induced obesity. GDNF transgenic (Tg) mice that overexpress GDNF under the control of the glial fibrillary acidic protein promoter and wild-type (WT) littermates were maintained on a HFD or regular rodent diet for 11 wk, and weight gain, energy expenditure, and insulin sensitivity were monitored. Differentiated mouse brown adipocytes and 3T3-L1 white adipocytes were used to study the effects of GDNF in vitro. Tg mice resisted the HFD-induced weight gain, insulin resistance, dyslipidemia, hyperleptinemia, and hepatic steatosis seen in WT mice despite similar food intake and activity levels. They exhibited significantly (P<0.001) higher energy expenditure than WT mice and increased expression in skeletal muscle and brown adipose tissue of peroxisome proliferator activated receptor-α and β1- and β3-adrenergic receptor genes, which are associated with increased lipolysis and enhanced lipid β-oxidation. In vitro, GDNF enhanced β-adrenergic-mediated cAMP release in brown adipocytes and suppressed lipid accumulation in differentiated 3T3L-1 cells through a p38MAPK signaling pathway. Our studies demonstrate a novel role for GDNF in the regulation of high-fat diet-induced obesity through increased energy expenditure. They show that GDNF and its receptor agonists may be potential targets for the treatment or prevention of obesity.

The role of gastrointestinal hormones in hepatic lipid metabolism

Hepatocellular accumulation of free fatty acids (FFAs) in the form of triglycerides constitutes the metabolic basis for the development of nonalcoholic fatty liver disease (NAFLD). Recent data demonstrate that excess FFA hepatocyte storage is likely to lead to lipotoxicity and hepatocyte apoptosis. Hence, FFA-mediated hepatocyte injury is a key contributor to the pathogenesis of nonalcoholic steatohepatitis (NASH). Nonalcoholic steatohepatitis, obesity, type 2 diabetes, essential hypertension, and other common medical problems together comprise metabolic syndrome. Evidence suggests that peptide hormones from the L cells of the distal small intestine, which comprise the core of the enteroendocrine system (EES), play two key roles, serving either as incretins, or as mediators of appetite and satiety in the central nervous system. Recent data related to glucagon-like peptide-1 (GLP-1) and other known L-cell hormones have accumulated due to the increasing frequency of bariatric surgery, which increase delivery of bile salts to the hindgut. Bile acids are a key stimulus for the TGR5 receptor of the L cells. Enhanced bile-salt flow and subsequent EES stimulation may be central to elimination of hepatic steatosis following bariatric surgery. Although GLP-1 is a clinically relevant pharmacological analogue that drives pancreatic β-cell insulin output, GLP-1 analogues also have independent benefits via their effects on hepatocellular FFA metabolism. The authors also discuss recent data regarding the role of the major peptides released by the EES, which promote satiety and modulate energy homeostasis and utilization, as well as those that control fat absorption and intestinal permeability. Taken together, elucidating novel functions for EES-related peptides and pharmacologic development of peptide analogues offer potential far-ranging treatment for obesity-related human disease.

A renaissance in medical biochemistry - Hepatology and Endocrinology kick it up a Notch!

COMMENTARY ON: Inhibition of Notch signaling ameliorates insulin resistance in a FoxO1-dependent manner. Pajvani UB, Shawber CJ, Samuel VT, Birkenfeld AL, Shulman GI, Kitajewski J, Accili D. Nat Med. July 31, 2011;17(8):961–7. Copyright (2012). Abstract reprinted by permission from McMillan Publishers Ltd. http://www.ncbi.nlm.nih.gov/pubmed/21804540 Transcription factor FoxO1 promotes hepatic glucose production. Genetic inhibition of FoxO1 function prevents diabetes in experimental animal models, providing impetus to identify pharmacological approaches to modulate this function. Altered Notch signaling is evident in tumorigenesis, and Notch antagonists are in clinical testing for application in cancer. Here we report that FoxO1 and Notch coordinately regulate hepatic glucose metabolism. Combined haploinsufficiency of FoxO1 and Notch1 markedly raises insulin sensitivity in diet-induced insulin resistance, as does liver-specific knockout of the Notch transcriptional effector Rbp-Jκ. Conversely, Notch1 gain-of-function promotes insulin resistance in a FoxO1-dependent manner and induces glucose-6-phosphatase expression. Pharmacological blockade of Notch signaling with γ-secretase inhibitors raises insulin sensitivity after in vivo administration in lean mice and in obese, insulin-resistant mice. The data identify a heretofore unknown metabolic function of Notch and suggest that Notch inhibition is beneficial in diabetes treatment, in part by helping to offset excessive FoxO1-driven hepatic glucose production. AND Insulin regulates liver metabolism in vivo in the absence of hepatic Akt and Foxo1. Lu M, Wan M, Leavens KF, Chu Q, Monks BR, Fernandez S, Ahima RS, Ueki K, Kahn CR, Birnbaum MJ. Nat Med. February 19, 2012;18(3):388–95. Copyright (2012). Abstract reprinted by permission from McMillan Publishers Ltd. http://www.ncbi.nlm.nih.gov/pubmed/22344295 Considerable data support the idea that forkhead box O1 (Foxo1) drives the liver transcriptional program during fasting and is then inhibited by thymoma viral proto-oncogene 1 (Akt) after feeding. Here we show that mice with hepatic deletion of Akt1 and Akt2 were glucose intolerant, insulin resistant and defective in their transcriptional response to feeding in the liver. These defects were normalized with concomitant liver-specific deletion of Foxo1. Notably, in the absence of both Akt and Foxo1, mice adapted appropriately to both the fasted and fed state, and insulin suppressed hepatic glucose production normally. A gene expression analysis revealed that deletion of Akt in liver led to the constitutive activation of Foxo1-dependent gene expression, but again, concomitant ablation of Foxo1 restored postprandial regulation, preventing the inhibition of the metabolic response to nutrient intake caused by deletion of Akt. These results are inconsistent with the canonical model of hepatic metabolism in which Akt is an obligate intermediate for proper insulin signaling. Rather, they show that a major role of hepatic Akt is to restrain the activity of Foxo1 and that in the absence of Foxo1, Akt is largely dispensable for insulin- and nutrient-mediated hepatic metabolic regulation in vivo.

Glp-1 analog, liraglutide, ameliorates hepatic steatosis and cardiac hypertrophy in C57BL/6J mice fed a Western diet

The aims of this study were designed to determine whether liraglutide, a long-acting glucagon-like peptide, could reverse the adverse effects of a diet high in fat that also contained trans-fat and high-fructose corn syrup (ALIOS diet). Specifically, we examined whether treatment with liraglutide could reduce hepatic insulin resistance and steatosis as well as improve cardiac function. Male C57BL/6J mice were pair fed or fed ad libitum either standard chow or the ALIOS diet. After 8 wk the mice were further subdivided and received daily injections of either liraglutide or saline for 4 wk. Hyperinsulinemic-euglycemic clamp studies were performed after 6 wk, revealing hepatic insulin resistance. Glucose tolerance and insulin resistance tests were performed at 8 and 12 wk prior to and following liraglutide treatment. Liver pathology, cardiac measurements, blood chemistry, and RNA and protein analyses were performed. Clamp studies revealed hepatic insulin resistance after 6 wk of ALIOS diet. Liraglutide reduced visceral adiposity and liver weight (P < 0.001). As expected, liraglutide improved glucose and insulin tolerance. Liraglutide improved hypertension (P < 0.05) and reduced cardiac hypertrophy. Surprisingly, liver from liraglutide-treated mice had significantly higher levels of fatty acid binding protein, acyl-CoA oxidase II, very long-chain acyl-CoA dehydrogenase, and microsomal triglyceride transfer protein. We conclude that liraglutide reduces the harmful effects of an ALIOS diet by improving insulin sensitivity and by reducing lipid accumulation in liver through multiple mechanisms including, transport, and increase β-oxidation.

GLP-1 analogs reduce hepatocyte steatosis and improve survival by enhancing the unfolded protein response and promoting macroautophagy

Background

Nonalcoholic fatty liver disease (NAFLD) is a known outcome of hepatosteatosis. Free fatty acids (FFA) induce the unfolded protein response (UPR) or endoplasmic reticulum (ER) stress that may induce apoptosis. Recent data indicate ER stress to be a major player in the progression of fatty liver to more aggressive lesions. Autophagy on the other hand has been demonstrated to be protective against ER stress- induced cell death. We hypothesized that exendin-4 (GLP-1 analog) treatment of fat loaded hepatocytes can reduce steatosis by autophagy which leads to reduced ER stress-related hepatocyte apoptosis.

Methodology/Principal Findings

Primary human hepatocytes were loaded with saturated, cis- and trans-unsaturated fatty acids (palmitic, oleic and elaidic acid respectively). Steatosis, induced with all three fatty acids, was significantly resolved after exendin-4 treatment. Exendin-4 sustained levels of GRP78 expression in fat-loaded cells when compared to untreated fat-loaded cells alone. In contrast, CHOP (C/EBP homologous protein); the penultimate protein that leads to ER stress-related cell death was significantly decreased by exendin-4 in hepatocytes loaded with fatty acids. Finally, exendin-4 in fat loaded hepatocytes clearly promoted gene products associated with macroautophagy as measured by enhanced production of both Beclin-1 and LC3B-II, markers for autophagy; and visualized by transmission electron microscopy (TEM). Similar observations were made in mouse liver lysates after mice were fed with high fat high fructose diet and treated with a long acting GLP-1 receptor agonist, liraglutide.

Conclusions/Significance

GLP-1 proteins appear to protect hepatocytes from fatty acid-related death by prohibition of a dysfunctional ER stress response; and reduce fatty acid accumulation, by activation of both macro-and chaperone-mediated autophagy. These findings provide a novel role for GLP-1 proteins in halting the progression of more aggressive lesions from underlying steatosis in humans afflicted with NAFLD.

Adiponectin activation of AMPK disrupts leptin-mediated hepatic fibrosis via suppressors of cytokine signaling (SOCS-3)

Adiponectin is an adipocytokine that was recently shown to be anti-fibrogenic in hepatic fibrosis. Leptin, on the other hand, promotes hepatic fibrosis. The purpose of the present study was to elucidate a mechanism (or mechanisms) whereby adiponectin dampens leptin signaling in activated hepatic stellate cells (HSCs), and prevents excess extracellular matrix production. Activated HSCs, between passages 2 and 5, were cultured and exposed to recombinant human adiponectin and recombinant leptin. Immunoblot analysis for SOCS-3, TIMP-1, and the phosphorylated species of Stat3 and adenosine monophosphate-activated protein kinase (AMPK) were conducted. We also examined MMP-1 activity by immunosorbant fluorimetric analysis. In HSCs, adiponectin-induced phosphorylation of AMPK, and subsequently suppressed leptin-mediated Stat3 phosphorylation and SOCS-3 induction. Adiponectin also blocked leptin-stimulated secretion of TIMP-1, and significantly increased MMP-1 activity, in vitro. To extend this study, we treated adiponectin knockout mice (Ad-/-) daily with 5 mg/kg recombinant leptin and/or carbon tetrachloride (2 ml/kg) for 6 weeks. Post-necropsy analysis was performed to examine for inflammation, and histological changes in the Ad-/- and wild-type mice. There was no significant difference in inflammation, or aminotransferases, between mice receiving carbon tetrachloride and leptin versus carbon tetrachloride alone. As anticipated, the combination of leptin and CCl(4) enhanced hepatic fibrosis in both wild-type and Ad-/- mice, as estimated by amount of collagen in injured livers, but wild-type mice had significantly higher levels of SOCS-3 and significantly lower levels of TIMP-1 mRNA and protein than did adiponectin KO mice exposed to both CCl(4) and leptin. We therefore conclude that the protective effects of adiponectin against liver fibrosis require AMPK activation, and may occur through inhibition of the Jak-Stat signal transduction pathway.

Adiponectin modulates C-jun N-terminal kinase and mammalian target of rapamycin and inhibits hepatocellular carcinoma

BACKGROUND & AIMS

Epidemiological studies have shown that obesity is a risk factor for hepatocellular carcinoma (HCC). Lower adiponectin levels are associated with poor prognosis in obese HCC patients, hence it is plausible that adiponectin acts as a negative regulator of HCC. We investigated the effects of adiponectin on HCC development and its molecular mechanisms.

METHODS

Assays with Huh7 and HepG2 HCC cells were used to examine the signal transduction pathways involved in the protective functions of adiponectin in HCC. These studies were followed by in vivo approaches using HCC xenografts and tumor analysis. Results from in vitro and in vivo findings were corroborated using human HCC tissue microarray and analysis of clinicopathological characteristics.

RESULTS

Adiponectin increased apoptosis of HCC cells through activation of caspase-3. Adiponectin increased phosphorylation of c-Jun-N-terminal kinase (JNK) and inhibition of c-Jun-N-terminal kinase-phosphorylation inhibited adiponectin-induced apoptosis and caspase-3 activation. Adiponectin increased phosphorylation of 5'-adenosine monophosphate-activated protein kinase and tumor suppressor tuberous sclerosis complex 2 and inhibited mammalian target of rapamycin phosphorylation. Inhibition of 5'-adenosine monophosphate-activated protein kinase phosphorylation not only inhibited adiponectin-induced c-Jun-N-terminal kinase phosphorylation, but also blocked biological effects of adiponectin. Adiponectin substantially reduced liver tumorigenesis in nude mice. Importantly, analysis of adiponectin expression levels in tissue microarray of human HCC patients revealed an inverse correlation of adiponectin expression with tumor size.

CONCLUSIONS

Adiponectin protects against liver tumorigenesis; its reduced expression is associated with poor prognosis in obese patients with HCC.

Adiponectin antagonizes the oncogenic actions of leptin in hepatocellular carcinogenesis

Obesity is rapidly becoming a pandemic and is associated with increased carcinogenesis. Obese populations have higher circulating levels of leptin in contrast to low concentrations of adiponectin. Hence, it is important to evaluate the dynamic role between adiponectin and leptin in obesity-related carcinogenesis. Recently, we reported the oncogenic role of leptin including its potential to increase tumor invasiveness and migration of hepatocellular carcinoma (HCC) cells. In the present study we investigated whether adiponectin could antagonize the oncogenic actions of leptin in HCC. We employed HCC cell lines HepG2 and Huh7, the nude mice-xenograft model of HCC, and immunohistochemistry data from tissue-microarray to demonstrate the antagonistic role of adiponectin on the oncogenic actions of leptin. Adiponectin treatment inhibited leptin-induced cell proliferation of HCC cells. Using scratch-migration and electric cell-substrate impedance-sensing-based migration assays, we found that adiponectin inhibited leptin-induced migration of HCC cells. Adiponectin treatment effectively blocked leptin-induced invasion of HCC cells in Matrigel invasion assays. Although leptin inhibited apoptosis in HCC cells, we found that adiponectin treatment induced apoptosis even in the presence of leptin. Analysis of the underlying molecular mechanisms revealed that adiponectin treatment reduced leptin-induced Stat3 and Akt phosphorylation. Adiponectin also increased suppressor of cytokine signaling (SOCS3), a physiologic negative regulator of leptin signal transduction. Importantly, adiponectin significantly reduced leptin-induced tumor burden in nude mice. In HCC samples, leptin expression significantly correlated with HCC proliferation as evaluated by Ki-67, whereas adiponectin expression correlated significantly with increased disease-free survival and inversely with tumor size and local recurrence.

CONCLUSION

Collectively, these data demonstrate that adiponectin has the molecular potential to inhibit the oncogenic actions of leptin by blocking downstream effector molecules.

Glucagon-like peptide-1 receptor is present on human hepatocytes and has a direct role in decreasing hepatic steatosis in vitro by modulating elements of the insulin signaling pathway

Glucagon-like peptide 1 (GLP-1) is a naturally occurring peptide secreted by the L cells of the small intestine. GLP-1 functions as an incretin and stimulates glucose-mediated insulin production by pancreatic beta cells. In this study, we demonstrate that exendin-4/GLP-1 has a cognate receptor on human hepatocytes and that exendin-4 has a direct effect on the reduction of hepatic steatosis in the absence of insulin. Both glucagon-like peptide 1 receptor (GLP/R) messenger RNA and protein were detected on primary human hepatocytes, and receptor was internalized in the presence of GLP-1. Exendin-4 increased the phosphorylation of 3-phosphoinositide-dependent kinase-1 (PDK-1), AKT, and protein kinase C zeta (PKC-zeta) in HepG2 and Huh7 cells. Small interfering RNA against GLP-1R abolished the effects on PDK-1 and PKC-zeta. Treatment with exendin-4 quantitatively reduced triglyceride stores compared with control-treated cells.

CONCLUSION

This is the first report that the G protein-coupled receptor GLP-1R is present on human hepatocytes. Furthermore, it appears that exendin-4 has the same beneficial effects in vitro as those seen in our previously published in vivo study in ob/ob mice, directly reducing hepatocyte steatosis. Future use for human nonalcoholic fatty liver disease, either in combination with dietary manipulation or other pharmacotherapy, may be a significant advance in treatment of this common form of liver disease.

Bidirectional crosstalk between leptin and insulin-like growth factor-I signaling promotes invasion and migration of breast cancer cells via transactivation of epidermal growth factor receptor

Obesity is an independent risk factor for breast cancer, and obese breast cancer patients exhibit a higher risk for larger tumor burden and increased metastasis. Obesity, as associated with metabolic syndrome, results in an increase in circulating insulin-like growth factor (IGF), which acts as a mitogen. In addition, higher plasma level of adipocytokine leptin is associated with obesity. In the present study, we show that cotreatment with leptin and IGF-I significantly increases proliferation as well as invasion and migration of breast cancer cells. We found a novel bidirectional crosstalk between leptin and IGF-I signaling; IGF-I induced phosphorylation of leptin receptor (Ob-Rb) and leptin induced phosphorylation of IGF-I receptor (IGF-IR), whereas cotreatment induced synergistic phosphorylation and association of Ob-Rb and IGF-IR along with activation of downstream effectors, Akt and extracellular signal-regulated kinase. Leptin increased phosphorylation of IGF signaling molecules insulin-receptor substrate (IRS)-1 and IRS-2. Interestingly, we found that leptin and IGF-I cotreatment synergistically transactivated epidermal growth factor receptor (EGFR), depending on the proteolytic release of EGFR ligands, as the broad-spectrum matrix metalloproteinase inhibitor GM6001 could inhibit this effect. Using clinically relevant EGFR inhibitors, erlotinib and lapatinib, we found that inhibition of EGFR activation effectively inhibited leptin- and IGF-I-induced invasion and migration of breast cancer cells. Taken together, these data suggest a novel bidirectional crosstalk between leptin and IGF-I signaling that transactivates EGFR and promotes the metastatic properties as well as invasion and migration of breast cancer cells. Our findings indicate the possibility of using EGFR inhibitors erlotinib and lapatinib to counter the procancerous effects of leptin and IGF-I in breast cancers.

Model for end-stage liver disease score versus Child score in predicting the outcome of surgical procedures in patients with cirrhosis

AIM: To determine factors affecting the outcome of patients with cirrhosis undergoing surgery and to compare the capacities of the Child-Turcotte-Pugh (CTP) and model for end-stage liver disease (MELD) score to predict that outcome.

METHODS: We reviewed the charts of 195 patients with cirrhosis who underwent surgery at two teaching hospitals over a five-year period. The combined endpoint of death or hepatic decompensation was considered to be the primary endpoint.

RESULTS: Patients who reached the endpoint had a higher MELD score, a higher CTP score and were more likely to have undergone an urgent procedure. Among patients undergoing elective surgical procedures, no statistically significant difference was noted in the mean MELD (12.8 ± 3.9 vs 12.6 ± 4.7, P = 0.9) or in the mean CTP (7.6 ± 1.2 vs 7.7 ± 1.7, P = 0.8) between patients who reached the endpoint and those who did not. Both mean scores were higher in the patients reaching the endpoint in the case of urgent procedures (MELD: 22.4 ± 8.7 vs 15.2 ± 6.4, P = 0.0007; CTP: 9.9 ± 1.8 vs 8.5 ± 1.8, P = 0.008). The performances of the MELD and CTP scores in predicting the outcome of urgent surgery were only fair, without a significant difference between them (AUC = 0.755 ± 0.066 for MELD vs AUC = 0.696 ± 0.070 for CTP, P = 0.3).

CONCLUSION: The CTP and MELD scores performed equally, but only fairly in predicting the outcome of urgent surgical procedures. Larger studies are needed to better define the factors capable of predicting the outcome of elective surgical procedures in patients with cirrhosis.

Treatment of fibrosis in nonalcoholic fatty liver disease

Nonalcoholic steatohepatitis (NASH) is one of the most common liver disorders in North America. The mechanism of liver injury in NASH involves insulin resistance and oxidative stress as well as cytokine release. Therapeutic interventions aimed at enhancing insulin sensitivity or reducing oxidative stress have been studied. The role of peptide hormones secreted by adipose tissue--adipocytokines--in the potential pathogenesis of NASH is an area of intense research. As the function of adipokines in modulating hepatic inflammation and fibrosis is elucidated, the potential for novel treatment strategies in patients with NASH is likely to be realized.

leptin-induced growth stimulation of breast cancer cells involves recruitment of histone acetyltransferases and mediator complex to CYCLIN D1 promoter via activation of Stat3

Numerous epidemiological studies documented that obesity is a risk factor for breast cancer development in postmenopausal women. Leptin, the key player in the regulation of energy balance and body weight control also acts as a growth factor on certain organs in both normal and disease state. In this study, we analyzed the role of leptin and the molecular mechanism(s) underlying its action in breast cancer cells that express both short and long isoforms of leptin receptor. Leptin increased MCF7 cell population in the S-phase of the cell cycle along with a robust increase in CYCLIN D1 expression. Also, leptin induced Stat3-phosphorylation-dependent proliferation of MCF7 cells as blocking Stat3 phosphorylation with a specific inhibitor, AG490, abolished leptin-induced proliferation. Using deletion constructs of CYCLIN D1 promoter and chromatin immunoprecipitation assay, we show that leptin induced increase in CYCLIN D1 promoter activity is mediated through binding of activated Stat3 at the Stat binding sites and changes in histone acetylation and methylation. We also show specific involvement of coactivator molecules, histone acetyltransferase SRC1, and mediator complex in leptin-mediated regulation of CYCLIN D1 promoter. Importantly, silencing of SRC1 and Med1 abolished the leptin induced increase in CYCLIN D1 expression and MCF7 cell proliferation. Intriguingly, recruitment of both SRC1 and Med1 was dependent on phosphorylated Stat3 as AG490 treatment inhibited leptin-induced recruitment of these coactivators to CYCLIN D1 promoter. Our data suggest that CYCLIN D1 may be a target gene for leptin mediated growth stimulation of breast cancer cells and molecular mechanisms involve activated Stat3-mediated recruitment of distinct coactivator complexes.

Abnormal lipid and glucose metabolism in obesity: implications for nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease represents a spectrum of histopathologic abnormalities, the prevalence of which may be as high as 24% of the population of the United States. Nonalcoholic fatty liver disease will play a major role in the science and practice of gastroenterology in the near future. The fundamental derangement in nonalcoholic fatty liver disease is insulin resistance, a key component of the metabolic syndrome, which includes type 2 diabetes mellitus, hypertriglyceridemia, essential hypertension, low circulating high-density lipoprotein, and obesity. The natural history of fatty liver disease is not always benign, and causality for cirrhosis and chronic liver disease is well-founded in the literature. Treatment strategies are limited and, at present, are primarily focused on weight loss and use of insulin sensitizing agents, including the thiazolidenediones. Recent data clearly implicate hepatic insulin resistance as a culprit in accumulation of free fatty acids as triglycerides in hepatocytes. Hepatic insulin resistance is clearly exacerbated by systemic insulin resistance and impaired handling by skeletal muscle and adipose tissue of both glucose and free fatty acids. The key consequence of hepatic insulin resistance, impaired hepatocyte insulin signal transduction, results in adverse cellular and molecular changes exacerbating hepatocyte triglyceride storage. Cytokines secreted by white adipose tissue, adipokines, have emerged as key players in glucose and fat metabolism previously thought controlled largely by insulin. Modulation of adipokines may aid in further understanding of the pathophysiology and treatment of nonalcoholic fatty liver disease.

Concomitant activation of the JAK/STAT, PI3K/AKT, and ERK signaling is involved in leptin-mediated promotion of invasion and migration of hepatocellular carcinoma cells

Various epidemiologic studies have shown that obesity is associated with hepatocellular carcinoma. Leptin, the key player in the regulation of energy balance and body weight control, also acts as a growth factor on certain organs in both normal and disease states. It is plausible that leptin acts to promote hepatocellular carcinogenesis directly affecting malignant properties of liver cancer cells. However, a direct role for leptin in hepatocellular carcinoma has not been shown. In this study, we analyzed the role of leptin and the mechanism(s) underlying its action in hepatocellular carcinoma cells, which express both short and long isoforms of leptin receptors. Treatment with leptin resulted in increased proliferation of both HepG2 and Huh7 cells and involves activation of signal transducers and activators of transcription 3 (STAT3), AKT, and extracellular signal-regulated kinase (ERK) signaling pathways. Leptin-induced phosphorylation of ERK and AKT was dependent on Janus-activated kinase (JAK)/STAT activation. Intriguingly, we also found that leptin potently induces invasion of hepatocellular carcinoma cells in Matrigel invasion and electric cell-substrate impedance-sensing assays. Leptin-stimulated invasion was effectively blocked by pharmacologic inhibitors of JAK/STAT and, to a lesser extent, by ERK and phosphatidylinositol 3-kinase (PI3K) inhibition. Importantly, leptin also induced the migration of both HepG2 and Huh7 cells on fibronectin matrix. Inhibition of JAK/STAT, ERK, and PI3K activation using pharmacologic inhibitors effectively blocked leptin-induced migration of HepG2 and Huh7 cells. Taken together, these data indicate that leptin promotes hepatocellular carcinoma growth, invasiveness, and migration and implicate the JAK/STAT pathway as a critical mediator of leptin action. Our findings have potential clinical implications for hepatocellular carcinoma progression in obese patients.

Leptin increases tissue inhibitor of metalloproteinase I (TIMP-1) gene expression by a specificity protein 1/signal transducer and activator of transcription 3 mechanism

Leptin has properties of a profibrogenic cytokine. In liver, the activated hepatic stellate cell (HSC) is responsible for a net production of extracellular matrix. A key molecule synthesized is the tissue inhibitor of metalloproteinase I (TIMP-1), which acts to inhibit the activity of matrix metalloproteinases. The purpose of the present study was to determine how leptin, a gp130 cytokine, orchestrates the regulation of TIMP-1 gene activation and expression. Transient transfection of primary HSCs revealed that leptin significantly increased luciferase activity of a 229-bp TIMP-1 promoter construct (TIMP-1-229). An EMSA revealed that leptin enhanced specificity protein 1 (Sp1) binding. Site-directed mutagenesis for Sp1 reduced the enhancing effect of leptin on TIMP-1 transcriptional activation, and this effect was dose dependent on the number of Sp1 sites mutated. Chromatin immunoprecipitation revealed that leptin enhanced binding of Sp1; however, inhibition of signal transducer and activator of transcription (STAT) 3 phosphorylation by AG490 also blocked Sp1 phosphorylation and significantly reduced leptin-associated TIMP-1-229 promoter activity, indicating that one mechanism for leptin-increased transcriptional activity is via phosphorylation of Sp1 and subsequent promoter binding. Finally, we demonstrate that leptin also results in intranuclear pSTAT3 binding to Sp1. We propose a novel mechanism whereby leptin-mediated TIMP-1 transcription employs a Sp1/pSTAT3-dependent mechanism, one of which is a noncanonical association between Sp1 and pSTAT3. These data provide a new molecular mechanism whereby the adipocytokine leptin plays a role in complications of the metabolic syndrome.

Leptin promotes the proliferative response and invasiveness in human endometrial cancer cells by activating multiple signal-transduction pathways

An increase in the risk of cancer is one of the consequences of obesity. The predominant cancers associated with obesity have a hormonal basis and include breast, prostate, endometrium, colon and gall-bladder cancers. Leptin, the key player in the regulation of energy balance and body weight control also acts as a growth factor on certain organs in both normal and disease states. Therefore, it is plausible that leptin acts to promote cancer growth by acting as a mitogenic agent. However, a direct role for leptin in endometrial cancer has not been demonstrated. In this study, we analyzed the proliferative role of leptin and the mechanism(s) underlying this action in endometrial cancers which express both short and long isoforms of leptin receptors. Treatment with leptin resulted in increased proliferation of ECC1 and Ishikawa cells. The promotion of endometrial cancer cell proliferation by leptin involves activation of STAT3 and ERK2 signaling pathways. Moreover, leptin-induced phosphorylation of ERK2 and AKT was dependent on JAK/STAT activation. Therefore blocking its action at the JAK/STAT level could be a rational therapeutic strategy for endometrial carcinoma in obese patients. We also found that leptin potently induces invasion of endometrial cancer cells in a Matrigel invasion assay. Leptin-stimulated invasion was effectively blocked by pharmacological inhibitors of JAK/STAT (AG490) and phosphatidylinositol 3-kinase (LY294002). Taken together these data indicate that leptin promotes endometrial cancer growth and invasiveness and implicate the JAK/STAT and AKT pathways as critical mediators of leptin action. Our findings have potential clinical implications for endometrial cancer progression in obese patients.

An assessment of statin safety by hepatologists

The purpose of the Liver Expert Panel was to provide advice to the National Lipid Association's (NLA) Safety Task Force in response to specific questions concerning liver-associated risks of statin therapy. The panel was composed of academic hepatologists with clinical and research interests in nonalcoholic fatty liver disease, lipid metabolic disorders, and drug hepatotoxicity.