Fatty Liver Injury Research Articles

Status of hepatic DNA methylome predetermines and modulates the severity of non-alcoholic fatty liver injury in mice

BackgroundNonalcoholic fatty liver disease (NAFLD) is a major health problem and a leading cause of chronic liver disease in the United States and Western countries. In humans, genetic factors greatly influence individual susceptibility to NAFLD; nonetheless, the effect of inter-individual differences in the normal liver epigenome with regard to the susceptibility to NAFLD has not been determined.ResultsIn the present study, we investigated the association between the DNA methylation status in the livers of A/J and WSB/EiJ mice and the severity of NAFLD-associated liver injury. We demonstrate that A/J and WSB/EiJ mice, which are characterized by significant differences in the severity of liver injury induced by a choline- and folate-deficient (CFD) diet exhibit substantial differences in cytosine DNA methylation in their normal livers. Furthermore, feeding A/J and WSB/EiJ mice a CFD diet for 12 weeks resulted in different trends and changes in hepatic cytosine DNA methylation.ConclusionOur findings indicate a primary role of hepatic DNA methylation in the pathogenesis of NAFLD and suggest that individual variations in DNA methylation across the genome may be a factor determining and influencing the vulnerability to NAFLD.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2617-2) contains supplementary material, which is available to authorized users.

Ischemia-Reperfusion Injury in Fatty Liver Is Mediated by Activated NADPH Oxidase 2 in Rats.

Liver ischemia-reperfusion (I/R) injury is a severe complication of liver surgery, and steatosis is a risk factor for liver damage. Reactive oxygen species generated by nicotinamide adenine dinucleotide phosphate oxidase (NOX) contribute to liver dysfunction. Here we examined the role of NOX in I/R injury of fatty livers. Rats were fed a methionine and choline-deficient diet to induce a fatty liver. Rats then underwent surgically induced partial hepatic ischemia followed by reperfusion. The overall survival rate after I/R was lower in rats with fatty livers than with normal livers (P < 0.01). Necrotic area and the concentrations of 8-hydroxy-2'-deoxyguanosine (8-OHdG), TNFα, and IL-6 were higher in fatty liver tissue than in normal liver tissue (P < 0.01). The number of p47phox-positive cells was significantly higher in fatty liver tissue than in normal liver tissue after reperfusion and peaked 24 hours after reperfusion. The number of TLR-4 positive cells was significantly higher in fatty liver tissue than in normal liver tissue after reperfusion and peaked 4 and 24 hours after reperfusion coupled with a decreased number of high-mobility group box 1-positive hepatocytes. Apocynin significantly improved the survival rate, necrotic area, and concentrations of 8-hydroxy-2'-deoxyguanosine, TNFα, and IL-6 (P < 0.01). The protective effect of apocynin on fatty livers was greater than on normal livers. Ischemia-reperfusion injury was associated with increased high-mobility group box 1, TLR4, and NOX2. Inhibition of NOX activity improved oxidative stress and may prevent I/R injury in fatty liver.

Acute Injury in Natural Diet-Induced Fatty Livers - A Model for Therapy Development

Given the diabesity and metabolic syndrome epidemics, fatty liver disease is reaching epidemic proportions. Relatively indolent, this disease is often asymptomatic and the patient is often made aware of its presence only during a routine physical exam. Nevertheless, fatty livers are more susceptible to insult compared to their non-fatty counterparts and persons with fatty livers are at increased risk for morbidity and mortality following consumption of commonly used substances such as alcohol (EtOH) and acetaminophen (APAP). We have developed a rat model of natural diet-induced fatty liver disease and evaluated the effects of two commonly used substances viz. EtOH and APAP in this phenotype. High fat diet (HFD) fed animals exhibited steatosis, liver inflammation and liver fibrosis with an increase in serum aspartate aminotransferase. Bolus administration of EtOH, which was without effect on the livers from standard diet fed animals, had a profound and adverse impact on the HFD fatty liver. Similarly, APAP administration which was without effect on liver function tests in control animals, also provoked an increase in liver enzymes in HFD animals. Treatment with the poly(ADP-ribose) polymerase-1 inhibitor (PARP-1), veliparib, reduced the increase in liver function tests secondary to EtOH and APAP. This model forms the framework for identification of fatty liver disease biomarkers given that this disease is relatively asymptomatic but fraught with risk for acute injury. This model also forms the framework for evaluation of novel drugs for acute injury in fatty livers especially given that current strategies for management of acute liver failure in non-fatty livers are inadequate. Also, relevant patents related to the use of liver biomarkers as diagnostic are discussed. Keywords: Acetaminophen, acute, alcohol, fibrosis, injury, liver, steatosis.

Low-ω3 Fatty Acid and Soy Protein Attenuate Alcohol-Induced Fatty Liver and Injury by Regulating the Opposing Lipid Oxidation and Lipogenic Signaling Pathways.

Chronic ethanol-induced downregulation of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) and upregulation of peroxisome proliferator-activated receptor gamma coactivator 1-beta (PGC1β) affect hepatic lipid oxidation and lipogenesis, respectively, leading to fatty liver injury. Low-ω3 fatty acid (Low-ω3FA) that primarily regulates PGC1α and soy protein (SP) that seems to have its major regulatory effect on PGC1β were evaluated for their protective effects against ethanol-induced hepatosteatosis in rats fed with Lieber-deCarli control or ethanol liquid diets with high or low ω3FA fish oil and soy protein. Low-ω3FA and SP opposed the actions of chronic ethanol by reducing serum and liver lipids with concomitant decreased fatty liver. They also prevented the downregulation of hepatic Sirtuin 1 (SIRT1) and PGC1α and their target fatty acid oxidation pathway genes and attenuated the upregulation of hepatic PGC1β and sterol regulatory element-binding protein 1c (SREBP1c) and their target lipogenic pathway genes via the phosphorylation of 5′ adenosine monophosphate-activated protein kinase (AMPK). Thus, these two novel modulators attenuate ethanol-induced hepatosteatosis and consequent liver injury potentially by regulating the two opposing lipid oxidation and lipogenic pathways.

Protective effects ofCirsium setidensethanolic extracts against alcoholic fatty liver injury in rats

Purpose: In this study, we investigated the effects of Cirsium setidens ethanolic extract (CS) on the development of alcoholic fatty liver and associated injury. Methods: Sprague-Dawley male rats were fed either Lieber-DeCarli control (C) or ethanol (35.5% of total calories) liquid diet with 0 (E), 100 mg/kgBW CS (E+LCS), or 500 mg/kgBW CS (E+HCS) for 8 weeks. Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities as well as TG and cholesterol concentrations in the serum and liver tissues were measured by colorimetric assays. Liver histopathology was examined by Hematoxylin-eosin staining of the fixed liver tissues. Protein levels of phosphorylated-AMP activated protein kinase (p-AMPK), phosphorylated-acetyl CoA carboxylase (p-ACC), phosphorylated-nuclear factor kappa B (p-NFκB), and TNFα were measured by Western blot analyses. Results: Both doses of CS markedly suppressed alcohol-induced lipid droplets accumulation in the liver tissues and significantly inhibited alcohol-induced increases in activities of serum ALT and serum AST. Similarly, CS significantly reduced hepatic and serum TG concentrations. Compared to groups fed alcohol only, CS supplementation strongly increased hepatic levels of p-AMPK and p-ACC. Further, CS significantly inhibited alcoholinduced phosphorylation of NFκB, which was associated with reduced hepatic protein levels of TNFα. Conclusion: Our data demonstrated that CS has a protective effect against alcoholic liver injury, which was associated with activation of AMPK and inhibition of NFκB.

Hepatoprotective effect of licorice, the root of Glycyrrhiza uralensis Fischer, in alcohol-induced fatty liver disease.

BackgroundOur previous study suggested that licorice has anti-inflammatory activity in lipopolysaccharide-stimulated microglial cells and anti-oxidative activity in tert-butyl hydroperoxide–induced oxidative liver damage. In this study, we evaluated the effect of licorice on chronic alcohol-induced fatty liver injury mediated by inflammation and oxidative stress.MethodsRaw licorice was extracted, and quantitative and qualitative analysis of its components was performed by using LC–MS/MS. Mice were fed a liquid alcohol diet with or without licorice for 4 weeks.ResultsWe have standardized 70 % fermented ethanol extracted licorice and confirmed by LC-MS/MS as glycyrrhizic acid (GA), 15.77 ± 0.34 μg/mg; liquiritin (LQ), 14.55 ± 0.42 μg/mg; and liquiritigenin (LG), 1.34 ± 0.02 μg/mg, respectively. Alcohol consumption increased serum alanine aminotransferase and aspartate aminotransferase activities and the levels of triglycerides and tumor necrosis factor (TNF)-α. Lipid accumulation in the liver was also markedly induced, whereas the glutathione level was reduced. All these alcohol-induced changes were effectively inhibited by licorice treatment. In particular, the hepatic glutathione level was restored and alcohol-induced TNF-α production was significantly inhibited by licorice.ConclusionTaken together, our data suggests that protective effect of licorice against alcohol-induced liver injury may be attributed to its anti-inflammatory activity and enhancement of antioxidant defense.Electronic supplementary materialThe online version of this article (doi:10.1186/s12906-016-0997-0) contains supplementary material, which is available to authorized users.

Hepatocyte X-box binding protein 1 deficiency increases liver injury in mice fed a high-fat/sugar diet.

Fatty liver is associated with endoplasmic reticulum stress and activation of the hepatic unfolded protein response (UPR). Reduced hepatic expression of the UPR regulator X-box binding protein 1 spliced (XBP1s) is associated with human nonalcoholic steatohepatitis (NASH), and feeding mice a high-fat diet with fructose/sucrose causes progressive, fibrosing steatohepatitis. This study examines the role of XBP1 in nonalcoholic fatty liver injury and fatty acid-induced cell injury. Hepatocyte-specific Xbp1-deficient (Xbp1(-/-)) mice were fed a high-fat/sugar (HFS) diet for up to 16 wk. HFS-fed Xbp1(-/-) mice exhibited higher serum alanine aminotransferase levels compared with Xbp1(fl/fl) controls. RNA sequencing and Gene Ontogeny pathway analysis of hepatic mRNA revealed that apoptotic process, inflammatory response, and extracellular matrix structural constituent pathways had enhanced activation in HFS-fed Xbp1(-/-) mice. Liver histology demonstrated enhanced injury and fibrosis but less steatosis in the HFS-fed Xbp1(-/-) mice. Hepatic Col1a1 and Tgfβ1 gene expression, as well as Chop and phosphorylated JNK (p-JNK), were increased in Xbp1(-/-) compared with Xbp1(fl/fl) mice after HFS feeding. In vitro, stable XBP1-knockdown Huh7 cells (Huh7-KD) and scramble control cells (Huh7-SCR) were generated and treated with palmitic acid (PA) for 24 h. PA-treated Huh7-KD cells had increased cytotoxicity measured by lactate dehydrogenase release, apoptotic nuclei, and caspase3/7 activity assays compared with Huh7-SCR cells. CHOP and p-JNK expression was also increased in Huh7-KD cells following PA treatment. In conclusion, loss of XBP1 enhances injury in both in vivo and in vitro models of fatty liver injury. We speculate that hepatic XBP1 plays an important protective role in pathogenesis of NASH.

Dietary freshwater clam (Corbicula fluminea) extract suppresses accumulation of hepatic lipids and increases in serum cholesterol and aminotransferase activities induced by dietary chloretone in rats.

We investigated the ameliorative effect of freshwater clam extract (FCE) on fatty liver, hypercholesterolemia, and liver injury in rats exposed to chloretone. Furthermore, we examined the effects of major FCE components (fat and protein fractions) to determine the active components in FCE. Chloretone increased serum aminotransferase activities and led to hepatic lipid accumulation. Serum aminotransferase activities and hepatic lipid content were lower in rats fed total FCE or fat/protein fractions of FCE. Expression of fatty acid synthase and fatty acid desaturase genes was upregulated by chloretone. Total FCE and fat/protein fractions of FCE suppressed the increase in gene expression involved in fatty acid synthesis. Serum cholesterol levels increased twofold upon chloretone exposure. Total FCE or fat/protein fractions of FCE showed hypocholesterolemic effects in rats with hypercholesterolemia induced by chloretone. These suggest that FCE contains at least two active components against fatty liver, hypercholesterolemia, and liver injury in rats exposed to chloretone.

Altered gut–liver axis and hepatic adiponectin expression in OSAS: novel mediators of liver injury in paediatric non-alcoholic fatty liver

BackgroundMechanism(s) connecting obstructive sleep apnoea syndrome (OSAS) to liver injury in paediatric non-alcoholic fatty liver disease (NAFLD) are unknown. We hypothesised alterations in gut–liver axis and in the pool and...

Oligofructose protects against arsenic-induced liver injury in a model of environment/obesity interaction

Arsenic (As) tops the ATSDR list of hazardous environmental chemicals and is known to cause liver injury. Although the concentrations of As found in the US water supply are generally too low to directly damage the liver, subhepatotoxic doses of As sensitize the liver to experimental NAFLD. It is now suspected that GI microbiome dysbiosis plays an important role in development of NALFD. Importantly, arsenic has also been shown to alter the microbiome. The purpose of the current study was to test the hypothesis that the prebiotic oligofructose (OFC) protects against enhanced liver injury caused by As in experimental NAFLD. Male C57Bl6/J mice were fed low fat diet (LFD), high fat diet (HFD), or HFD containing oligofructose (OFC) during concomitant exposure to either tap water or As-containing water (4.9ppm as sodium arsenite) for 10weeks. HFD significantly increased body mass and caused fatty liver injury, as characterized by an increased liver weight-to-body weight ratio, histologic changes and transaminases. As observed previously, As enhanced HFD-induced liver damage, which was characterized by enhanced inflammation. OFC supplementation protected against the enhanced liver damage caused by As in the presence of HFD. Interestingly, arsenic, HFD and OFC all caused unique changes to the gut flora. These data support previous findings that low concentrations of As enhance liver damage caused by high fat diet. Furthermore, these results indicate that these effects of arsenic may be mediated, at least in part, by GI tract dysbiosis and that prebiotic supplementation may confer significant protective effects.

Serum fetuin-A and arginase-1 in human obesity model: Is there any interaction between inflammatory status and arginine metabolism?

Obesity is a major risk factor for many chronic metabolic diseases such as inflammation, insulin resistance (IR) and fatty liver injury. It was reported that obesity causes some variations on the serum levels of fetuin-A and is associated with arginine metabolism, especially arginase-1 levels. The aim of our study was to evaluate, the interaction and possible changes of these liver over produced proteins, fetuin-A and arginase-1 levels in obesity-related inflammatory status. Study groups were composed of individuals aged between 19 and 63 (n = 62). The control group included healthy subjects with BMI < 25, obese group included obese patients with BMI > 30 and with no other chronic disease. Biochemical markers were determined by an auto-analyzer. Adiponectin, fetuin-A, arginase-1, asymmetric dimethylarginine (ADMA), arginine, Hexanoyl-lysine (HEL) and leptin levels were measured with commercial ELISA immunoassay kits. Nitrite and nitrate were determined with colorimetric assay kit in serum samples. High sensitive C-reactive protein (hsCRP) levels and liver function enzymes activities were higher in the obese group in respect to the control group. Serum fetuin-A, arginase-1 and leptin levels were increased but adiponectin levels were decreased in obese subjects. Fetuin-A levels showed significant correlations with arginase-1 and HOMA-IR. Consequently, we carried out an investigation about higher serum fetuin-A and arginase-1 levels may have an important role in obesity and obesity-related liver damage.

Recent advances in the development of farnesoid X receptor agonists.

Farnesoid X receptors (FXRs) are nuclear hormone receptors expressed in high amounts in body tissues that participate in bilirubin metabolism including the liver, intestines, and kidneys. Bile acids (BAs) are the natural ligands of the FXRs. FXRs regulate the expression of the gene encoding for cholesterol 7 alpha-hydroxylase, which is the rate-limiting enzyme in BA synthesis. In addition, FXRs play a critical role in carbohydrate and lipid metabolism and regulation of insulin sensitivity. FXRs also modulate live growth and regeneration during liver injury. Preclinical studies have shown that FXR activation protects against cholestasis-induced liver injury. Moreover, FXR activation protects against fatty liver injury in animal models of nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH), and improved hyperlipidemia, glucose intolerance, and insulin sensitivity. Obeticholic acid (OCA), a 6α-ethyl derivative of the natural human BA chenodeoxycholic acid (CDCA) is the first-in-class selective FXR agonist that is ~100-fold more potent than CDCA. Preliminary human clinical trials have shown that OCA is safe and effective. In a phase II clinical trial, administration of OCA was well-tolerated, increased insulin sensitivity and reduced markers of liver inflammation and fibrosis in patients with type II diabetes mellitus and NAFLD. In two clinical trials of OCA in patients with primary biliary cirrhosis (PBC), a progressive cholestatic liver disease, OCA significantly reduced serum alkaline phosphatase (ALP) levels, an important disease marker that correlates well with clinical outcomes of patients with PBC. Together, these studies suggest that FXR agonists could potentially be used as therapeutic tools in patients suffering from nonalcoholic fatty and cholestatic liver diseases. Larger and Longer-term studies are currently ongoing.

Betaine supplementation prevents fatty liver induced by a high-fat diet: effects on one-carbon metabolism.

The purpose of this study was to examine the effects of betaine supplementation on the regulation of one-carbon metabolism and liver lipid accumulation induced by a high-fat diet in rats. Rats were fed one of three different liquid diets: control diet, high-fat diet and high-fat diet supplemented with betaine. The control and high-fat liquid diets contained, respectively, 35 and 71% of energy derived from fat. Betaine supplementation involved the addition of 1% (g/L) to the diet. After three weeks on the high-fat diet the rats had increased total liver fat concentration, liver triglycerides, liver TBARS and plasma TNF-α. The high-fat diet decreased the hepatic S-adenosylmethionine concentration and the S-adenosylmethionine/S-adenosylhomocysteine ratio compared to the control as well as altering the expression of genes involved in one-carbon metabolism. Betaine supplementation substantially increased the hepatic S-adenosylmethionine concentration (~fourfold) and prevented fatty liver and hepatic injury induced by the high-fat diet. It was accompanied by the normalization of the gene expression of BHMT, GNMT and MGAT, which code for key enzymes of one-carbon metabolism related to liver fat accumulation. In conclusion, the regulation of the expression of MGAT by betaine supplementation provides an additional and novel mechanism by which betaine supplementation regulates lipid metabolism and prevents accumulation of fat in the liver.

22‐S‐Hydroxycholesterol protects against ethanol‐induced liver injury by blocking the auto/paracrine activation of MCP‐1 mediated by LXRα

Chronic ethanol consumption causes hepatic steatosis and inflammation, which are associated with liver hypoxia. Monocyte chemoattractant protein‐1 (MCP‐1) is a hypoxia response factor that determines recruitment and activation of monocytes to the site of tissue injury. The level of MCP‐1 is elevated in the serum and liver of patients with alcoholic liver disease (ALD); however, the molecular details regarding the regulation of MCP‐1 expression are not yet understood completely. Here, we show the role of liver X receptor α (LXR α) in the regulation of MCP‐1 expression during the development of ethanol‐induced fatty liver injury, using an antagonist, 22‐S‐hydroxycholesterol (22‐S‐HC). First, administration of 22‐S‐HC attenuated the signs of liver injury with decreased levels of MCP‐1 and its receptor CCR2 in ethanol‐fed mice. Second, hypoxic conditions or treatment with the LXR α agonist GW3965 significantly induced the expression of MCP‐1, which was completely blocked by treatment with 22‐S‐HC or infection by shLXR α lentivirus in the primary hepatocytes. Third, over‐expression of LXR α or GW3965 treatment increased MCP‐1 promoter activity by increasing the binding of hypoxia‐inducible factor‐1α to the hypoxia response elements, together with LXR α. Finally, treatment with recombinant MCP‐1 increased the level of expression of LXR α and LXR α‐dependent lipid droplet accumulation in both hepatocytes and Kupffer cells. These data show that LXR α and its ligand‐induced up‐regulation of MCP‐1 and MCP‐1‐induced LXR α‐dependent lipogenesis play a key role in the autocrine and paracrine activation of MCP‐1 in the pathogenesis of alcoholic fatty liver disease, and that this activation may provide a promising new target for ALD therapy.Copyright © 2014 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

PPARα Agonist WY-14643 Induces SIRT1 Activity in Rat Fatty Liver Ischemia-Reperfusion Injury.

Ischemia-reperfusion injury (IRI) remains a frequent complication in surgery, especially in case of steatotic livers that present decreased tolerance towards IRI. Apart from its major role in metabolism, activation of peroxisome proliferator-activated receptor α (PPARα) has been related with positive effects on IRI. In addition, the deacetylase enzyme sirtuin 1 (SIRT1) has recently emerged as a promising target for preventing IRI, through its interaction with stress-related mechanisms, such as endoplasmic reticulum stress (ERS). Taking this into account, this study aims to explore whether PPARα agonist WY-14643 could protect steatotic livers against IRI through sirtuins and ERS signaling pathway. Obese Zucker rats were pretreated or not pretreated with WY-14643 (10 mg/kg intravenously) and then submitted to partial (70%) hepatic ischemia (1 hour) followed by 24 hours of reperfusion. Liver injury (ALT levels), lipid peroxidation (MDA), SIRT1 activity, and the protein expression of SIRT1 and SIRT3 and ERS parameters (IRE1α, peIF2, caspase 12, and CHOP) were evaluated. Treatment with WY-14643 reduced liver injury in fatty livers, enhanced SIRT1 activity, and prevented ERS. Together, our results indicated that PPARα agonist WY-14643 may exert its protective effect in fatty livers, at least in part, via SIRT1 induction and ERS prevention.

Innovative Pharmacological/Therapeutic Approaches against Hepatic Ischemia/Reperfusion Injury.

Prolonged oxygen deprivation corresponding to the ischemic period is observed during liver resection, transplantation, and trauma and subsequent oxygen restoration always leads to reperfusion injury. In particular, the ischemic period represents an inevitable event during conventional organ preservation before transplantation and the magnitude and severity of reperfusion injury depend on the time of liver preservation. Faced with the increasing shortage of donor organs for transplantation, there is renewed interest in marginal livers, such as those obtained from donation after circulatory death or fatty livers, which are particularly susceptible to ischemia/reperfusion (I/R) injury. The decreased tolerance towards I/R observed in fatty livers has not been fully elucidated yet, and underlying mechanisms appear different in lean and steatotic livers. The paper of A. Matsuda et al. proposed the use of activated protein C (APC), an anticoagulant, found to induce an initial attenuation of tissue damage by inhibiting inflammatory cell infiltration and sinusoidal endothelial injury in normal liver. Of interest, in steatotic mice livers, APC did not affect initial liver damage but attenuated late damage, suggesting the existence of an additional pathway to the anti-inflammatory cytoprotective effect of APC which may occur via activation of adenosine monophosphate-activated protein kinase (AMPK) phosphorylation. A further attempt to reduce the fatty liver susceptibility was reported by E. Pantazi et al. that used a peroxisome proliferator-activated receptor α (PPARα) agonist WY-14643. PPARα is a nuclear receptor highly expressed in liver and it functions as a lipid sensor. Treatment with WY-14643 reduced liver injury in fatty rat livers, enhanced the deacetylase enzyme sirtuin 1 (SIRT1), recently found to be a target for preventing I/R, and prevented endoplasmic reticulum stress. M. Bejaoui et al. investigated the use of polyethylene glycols (PEGs) that, besides their usefulness as oncotic agents in preservation solution, have been shown to protect against cold injury and ischemic damage. The intravenous PEG 35 administration by a unique dose protected steatotic rat liver grafts against the deleterious effects of cold storage and the subsequent reperfusion. The rationale for the intravenous administration of PEG 35 was to induce a pharmacological preconditioning effect; its protective mechanisms are related to preservation of mitochondria and the induction of protective cell signaling pathways (eNOS, Akt, and AMPK). An additional model of liver preconditioning by pharmacological induction of adenosine A2a receptor (A2aR) was reported by E. Alchera et al. The analysis of the molecular changes induced by A2aR stimulation revealed multiple mechanisms of liver cell protection that can be both immediate (early preconditioning) and delayed (late preconditioning). Note that the A2aR activation also protects against lipotoxicity by preventing lipoapoptosis in primary rat hepatocytes. Among the hepatic mechanisms involved in the development of I/R, mitochondrial dysfunction represents a crucial cellular event contributing to I/R injury. As reported by K. Go et al., the elimination of abnormal and dysfunction mitochondria by mitophagy appears to increase both the quality of the mitochondria and cell survival. Although the mechanisms underlying the onset and propagation of mitophagy remain elusive, this event represents an early adaptive response to facilitate cell survival during I/R. Articles published in this issue not only help to identify new pharmacological approaches for improving liver function during ischemia/reperfusion damage but also stimulate the identification of molecular mediators of hepatic injury. Mariapia Vairetti Hartmut Jaeschke Diethard Monbaliu Jae-Sung Kim Andrea Ferrigno

FGF21 treatment ameliorates alcoholic fatty liver through activation of AMPK-SIRT1 pathway.

Fibroblast growth factor 21 (FGF21), a recently identified member of the FGF superfamily, is mainly secreted from the liver and adipose tissues and plays an important role in improving metabolic syndrome and homeostasis. The aim of this study is to evaluate the role of FGF21 in alcoholic fatty liver disease (AFLD) and to determine if it has a therapeutic effect on AFLD. In this paper, we tested the effect of FGF21 on alcohol-induced liver injury in a murine model of chronic ethanol gavage and alcohol-treated HepG2 cells. Male KM mice received single dose of 5 g/kg ethanol gavage every day for 6 weeks, which induced significant fatty liver and liver injury. The alcohol-induced fatty liver cell model was achieved by adding ethanol into the medium of HepG2 cell cultures at a final concentration of 75 mM for 9 days. Results showed that treatment with recombinant FGF21 ameliorated alcoholic fatty liver and liver injury both in a murine model of chronic ethanol gavage and alcohol-treated HepG2 cells. In addition, FGF21 treatment down-regulated the hepatic expression of fatty acid synthetic key enzyme, activated hepatic AMPK-SIRT1 pathway and significantly down-regulated hepatic oxidative stress protein. Taken together, FGF21 corrects multiple metabolic parameters of AFLD in vitro and in vivo by activation of the AMPK-SIRT1 pathway.

Ketogenesis prevents diet-induced fatty liver injury and hyperglycemia.

Nonalcoholic fatty liver disease (NAFLD) spectrum disorders affect approximately 1 billion individuals worldwide. However, the drivers of progressive steatohepatitis remain incompletely defined. Ketogenesis can dispose of much of the fat that enters the liver, and dysfunction in this pathway could promote the development of NAFLD. Here, we evaluated mice lacking mitochondrial 3-hydroxymethylglutaryl CoA synthase (HMGCS2) to determine the role of ketogenesis in preventing diet-induced steatohepatitis. Antisense oligonucleotide-induced loss of HMGCS2 in chow-fed adult mice caused mild hyperglycemia, increased hepatic gluconeogenesis from pyruvate, and augmented production of hundreds of hepatic metabolites, a suite of which indicated activation of the de novo lipogenesis pathway. High-fat diet feeding of mice with insufficient ketogenesis resulted in extensive hepatocyte injury and inflammation, decreased glycemia, deranged hepatic TCA cycle intermediate concentrations, and impaired hepatic gluconeogenesis due to sequestration of free coenzyme A (CoASH). Supplementation of the CoASH precursors pantothenic acid and cysteine normalized TCA intermediates and gluconeogenesis in the livers of ketogenesis-insufficient animals. Together, these findings indicate that ketogenesis is a critical regulator of hepatic acyl-CoA metabolism, glucose metabolism, and TCA cycle function in the absorptive state and suggest that ketogenesis may modulate fatty liver disease.

The cytochrome P450 epoxygenase pathway regulates the hepatic inflammatory response in fatty liver disease.

Fatty liver disease is an emerging public health problem without effective therapies, and chronic hepatic inflammation is a key pathologic mediator in its progression. Cytochrome P450 (CYP) epoxygenases metabolize arachidonic acid to biologically active epoxyeicosatrienoic acids (EETs), which have potent anti-inflammatory effects. Although promoting the effects of EETs elicits anti-inflammatory and protective effects in the cardiovascular system, the contribution of CYP-derived EETs to the regulation of fatty liver disease-associated inflammation and injury is unknown. Using the atherogenic diet model of non-alcoholic fatty liver disease/non-alcoholic steatohepatitis (NAFLD/NASH), our studies demonstrated that induction of fatty liver disease significantly and preferentially suppresses hepatic CYP epoxygenase expression and activity, and both hepatic and circulating levels of EETs in mice. Furthermore, mice with targeted disruption of Ephx2 (the gene encoding soluble epoxide hydrolase) exhibited restored hepatic and circulating EET levels and a significantly attenuated induction of hepatic inflammation and injury. Collectively, these data suggest that suppression of hepatic CYP-mediated EET biosynthesis is an important pathological consequence of fatty liver disease-associated inflammation, and that the CYP epoxygenase pathway is a central regulator of the hepatic inflammatory response in NAFLD/NASH. Future studies investigating the utility of therapeutic strategies that promote the effects of CYP-derived EETs in NAFLD/NASH are warranted.

S3-3 - Oxysterols in the orchestra of liver cell metabolism

Non-alcoholic fatty liver disease (NAFLD) is a chronic hepatic disorder affecting up to 25% of the general population. Several intracellular events leading to NAFLD and progression to non-alcoholic steatohepatitis (NASH) have been identified, including lipid accumulation, mitochondrial dysfunction and oxidative stress. Emerging evidence has suggested the cooperation of both hepatic free fatty acids (FFAs) and cholesterol (FC) accumulation in NAFLD development. Oxysterols, oxidized derivatives of cholesterol were reported as activating ligands of Liver X Receptors. Interestingly, serum levels of agonist oxysterols such as 25-HC and 27-HC are significantly increased in NAFLD patients. By contrast, 22-s- HC is considered an antagonist ligand of LXRα. 22-s-Hc down-regulated expression of the FAS gene through an LXRE located in the promoter and abolished the effect of the synthetic LXRα agonist. In addition it has been reported that 22-s-HC attenuated hepatic steatogenesis in a mouse model of high-fat-induced fatty liver. Very recently, it has been demonstrated that the inhibition of LXRα by 22-s-HC dramatically represses steatosis and HIF-1 mediated activation of MCP-1 in ethanol-induced fatty liver injury in hepatocytes as well as in Kupferr cells. Our data demonstrated that High fat diet (HF) caused liver steatosis while an atherogenic diet (ATH) diet induced hepatocellular ballooning, but only the Ath+HF diet resulted in steatohepatitis with associated mitochondrial dysfunction and impaired mitochondriogenesis. We identified in the the oxysterol cholestane-3beta,5alpha,6beta-triol (Triol) the molecule able to impair mitochondrial respiration and mitochondriogenesis by down-regulation of PGC1-alpha, mTFA and NRF1 signal. It seems that the role of oxysterols in the pathogenesis of human diseases, particularly in fat induced injury, should take into account the possible disruption of the balance between activation and inhibition of LXR signalling. Development of LXRα that specifically control inflammation and hepatic lipogenesis may provide novel therapeutics that block the development and progression of NAFLD.