Identification of proteins to predict the molecular basis for the observed gender susceptibility in a rat model of alcoholic steatohepatitis by 2-D gel proteomics

The Role of Sex in Acute and Chronic Liver Damage

Acute and chronic hepatic damages are caused by xenobiotics or different diseases affecting the liver, characterized by different etiologies and pathological features. It has been demonstrated extensively that liver damage progresses differently in men and women, and some chronic liver diseases show a more favorable prognosis in women than in men. This review aims to update the most recent advances in the comprehension of the molecular basis of the sex difference observed in both acute and chronic liver damage. With this purpose, we report experimental studies on animal models and clinical observations investigating both acute liver failure, e.g., drug-induced liver injury (DILI), and chronic liver diseases, e.g., viral hepatitis, alcoholic liver disease (ALD), non-alcoholic fatty liver disease (NAFLD), autoimmune liver diseases, and hepatocellular carcinoma (HCC).

Isoliquiritigenin alleviates LPS/ D-GalN-induced acute liver failure by activating the PGC-1α/ Nrf2 pathway to reduce oxidative stress and inflammatory response

Acute liver failure (ALF) is a dramatic liver disease characterized by large areas of inflammation. However, there are no available effective targeted drugs for ALF treatment. In the study, serum biochemical index and H&E were used to explore the amelioration of the liver histopathological changes. The oxidative stress kits, quantitative real-time PCR, western blot, immunohistochemistry, immunofluorescence staining, reactive oxygen species (ROS), and siRNA were used to elucidate the mechanisms underlying isoliquiritigenin (ISL) protection. The results showed that ISL significantly improved the liver pathological changes. Furthermore, ISL reduced oxidative stress by altering the expression of PGC-1α, Nrf2, HO-1, NQO1, Keap1, GCLC, and GCLM in damaged hepatocytes. Moreover, the levels of inflammation-related genes including NLRP3 inflammasome, IL-1β, IL-6, TNF-α, iNOS, and Mip-2 were repressed by ISL. In addition, ISL alleviated LPS/D-GalN-induced hepatocytes apoptosis by increasing the Bcl-2/Bax ratio and suppressing the expression of cleaved caspase-3. Further in vivo and in vitro evidence proved the involvement of the PGC-1α/Nrf2 signaling pathway in ISL protection. In conclusion, ISL improves the ability of anti-oxidative stress, alleviates inflammatory reaction, apoptosis, and inhibits NLRP3 inflammasome to protect lipopolysaccharide/D-galactosamine (LPS/D-GalN)-induced ALF through activating the PGC-1α/Nrf2 pathway, which provides the possibility for the treatment of ALF.

Gender specific differences in the liver proteome of rats exposed to short term and low-concentration hexabromocyclododecane (HBCD)

The influence of short term (7-day) exposure of male rats to the brominated flame retardant hexabromocyclododecane (HBCD) was studied by investigation of the liver proteome, both in euthyroid and hypothyroid rats and by comparing results with general data on animal physiology and thyroid hormone, leptin, insulin and gonadotropin concentrations determined in parallel. Proteome analysis of liver tissue by two-dimensional fluorescence difference gel electrophoresis (2D-DIGE) revealed that only small protein pattern changes were induced by exposure in males, on just a few proteins with different functions and not involved in pathways in common. This is in contrast to previous findings in similarly exposed eu- and hypothyroid female rats, where general metabolic pathways had been shown to be affected. The largest gender-dependent effects concerned basal concentrations of liver proteins already in control and hypothyroid animals, involving mainly the pathways which were also differently affected by HBCD exposure. Among them were differences in lipid metabolism, which - upon exposure to HBCD - may also be the reason for the considerably higher ratio of γ-HBCD accumulated in white adipose tissue of exposed female rats compared to males. The results further elucidate the already suggested different sensitivity of genders towards HBCD exposure on the protein level, and confirm the need for undertaking toxicological animal experiments in both genders.

Proteomic analysis of mice fed methionine and choline deficient diet reveals marker proteins associated with steatohepatitis

The mechanisms underlying the progression of simple steatosis to steatohepatitis are yet to be elucidated. To identify the proteins involved in the development of liver tissue inflammation, we performed comparative proteomic analysis of non-alcoholic steatohepatitis (NASH). Mice fed a methionine and choline deficient diet (MCD) developed hepatic steatosis characterized by increased free fatty acid (FFA) and triglyceride levels as well as alpha-SMA. Two-dimensional proteomic analysis revealed that the change from the normal diet to the MCD diet affected the expressions of 50 proteins. The most-pronounced changes were observed in the expression of proteins involved in Met metabolism and oxidative stress, most of which were significantly downregulated in NASH model animals. Peroxiredoxin (Prx) is the most interesting among the modulated proteins identified in this study. In particular, cross-regulated Prx1 and Prx6 are likely to participate in cellular defense against the development of hepatitis. Thus, these Prx isoforms may be a useful new marker for early stage steatohepatitis. Moreover, curcumin treatment results in alleviation of the severity of hepatic inflammation in steatohepatitis. Notably, curcumin administration in MCD-fed mice dramatically reduced CYP2E1 as well as Prx1 expression, while upregulating Prx6 expression. These findings suggest that curcumin may have a protective role against MCD fed-induced oxidative stress.

Quantitative proteomic analysis of hepatocyte-secreted extracellular vesicles reveals candidate markers for liver toxicity

Extracellular vesicles have created great interest as possible source of biomarkers for different biological processes and diseases. Although the biological function of these vesicles is not fully understood, it is clear that they participate in the removal of unnecessary cellular material and act as carriers of various macromolecules and signals between the cells. In this report, we analyzed the proteome of extracellular vesicles secreted by primary hepatocytes. We used one- and two-dimensional liquid chromatography combined with data-independent mass spectrometry. Employing label-free quantitative proteomics, we detected significant changes in vesicle protein expression levels in this in vitro model after exposure to well-known liver toxins (galactosamine and Escherichia coli-derived lipopolysaccharide). The results allowed us to identify candidate markers for liver injury. We validated a number of these markers in vivo, providing the basis for the development of novel methods to evaluate drug toxicity. This report strongly supports the application of proteomics in the study of extracellular vesicles released by well-controlled in vitro cellular systems. Analysis of such systems should help to identify specific markers for various biological processes and pathological conditions.

BIOLOGICAL SIGNIFICANCE

Identification of low invasive candidate marker for hepatotoxicity. Support to apply proteomics in the study of extracellular vesicles released by well-controlled in vitro cellular systems to identify low invasive markers for diseases.

Multifactorial comparative proteomic study of cytochrome P450 2E1 function in chronic alcohol administration

With the use of iTRAQ technique, a multifactorial comparative proteomic study can be performed. In this study, to obtain an overview of ethanol, CYP2E1 and gender effects on liver injury and gain more insight into the underlying molecular mechanism, mouse liver proteomes were quantitatively analyzed using iTRAQ under eight conditions including mice of different genders, wild type versus CYP2E1 knockout, and normal versus alcohol diet. A series of statistical and bioinformatic analyses were explored to simplify and clarify multifactorial comparative proteomic data. First, with the Principle Component analysis, six proteins, CYP2E1, FAM25, CA3, BHMT, HIBADH and ECHS1, involved in oxidation reduction, energy and lipid metabolism and amino acid metabolism, were identified as the most differentially expressed gene products across all of the experimental conditions of our chronic alcoholism model. Second, hierarchical clustering analysis showed CYP2E1 knockout played a primary role in the overall differential protein expression compared with ethanol and gender factors. Furthermore, pair-wise multiple comparisons have revealed that the only significant expression difference lied in wild-type and CYP2E1 knockout mice both treated with ethanol. Third, K-mean clustering analysis indicated that the CYP2E1 knockout had the reverse effect on ethanol induced oxidative stress and lipid oxidation. More importantly, IPA analysis of proteomic data inferred that the gene expressions of two upstream regulators, NRF2 and PPARα, regulated by chronic alcohol feeding and CYP2E1 knockout, are involved in ethanol induced oxidative stress and lipid oxidation. The present study provides an effectively comprehensive data analysis strategy to compare multiple biological factors, contributing to biochemical effects of alcohol on the liver. The mass spectrometry proteomics data have been deposited to the ProteomeXchange with data set identifier of PXD000635.

Therapeutic reversal of chronic alcohol-related steatohepatitis with the ceramide inhibitor myriocin

Alcohol-related liver disease (ALD) is associated with steatohepatitis and insulin resistance. Insulin resistance impairs growth and disrupts lipid metabolism in hepatocytes. Dysregulated lipid metabolism promotes ceramide accumulation and oxidative stress, leading to lipotoxic states that activate endoplasmic reticulum (ER) stress pathways and worsen inflammation and insulin resistance. In a rat model of chronic alcohol feeding, we characterized the effects of a ceramide inhibitor, myriocin, on the histopathological and ultrastructural features of steatohepatitis, and the biochemical and molecular indices of hepatic steatosis, insulin resistance and ER stress. Myriocin reduced the severity of alcohol-related steatohepatitis including the abundance and sizes of lipid droplets and mitochondria, inflammation and architectural disruption of the ER. In addition, myriocin-mediated reductions in hepatic lipid and ceramide levels were associated with constitutive enhancement of insulin signalling through the insulin receptor and IRS-2, reduced hepatic oxidative stress and modulation of ER stress signalling mechanisms. In conclusion, ceramide accumulation in liver mediates tissue injury, insulin resistance and lipotoxicity in ALD. Reducing hepatic ceramide levels can help restore the structural and functional integrity of the liver in chronic ALD due to amelioration of insulin resistance and ER stress. However, additional measures are needed to protect the liver from alcohol-induced necroinflammatory responses vis-à-vis continued alcohol abuse.

Strategies to rescue steatotic livers before transplantation in clinical and experimental studies

The shortage of donor livers has led to an increased use of organs from expanded criteria donors. Included are livers with steatosis, a metabolic abnormality that increases the likelihood of graft complications post-transplantation. After a brief introduction on the etiology, pathophysiology, categories and experimental models of hepatic steatosis, we herein review the methods to rescue steatotic donor livers before transplantation applied in clinical and experimental studies. The methods span the spectrum of encouraging donor weight loss, employing drug therapy, heat shock preconditioning, ischemia preconditioning and selective anesthesia on donors, and the treatment on isolated grafts during preservation. These methods work at different stages of transplantation process, although share similar molecular mechanisms including lipid metabolism stimulation through enzymes or nuclear receptor e.g., peroxisomal proliferator-activated receptor, or anti-inflammation through suppressing cytokines e.g., tumor necrosis factor-α, or antioxidant therapies to alleviate oxidative stress. This similarity of molecular mechanisms implies possible future attempts to reinforce each approach by repeating the same treatment approach at several stages of procurement and preservation, as well as utilizing these alternative approaches in tandem.

Liver proteomics in progressive alcoholic steatosis

Fatty liver is an early stage of alcoholic and nonalcoholic liver disease (ALD and NALD) that progresses to steatohepatitis and other irreversible conditions. In this study, we identified proteins that were differentially expressed in the livers of rats fed 5% ethanol in a Lieber-DeCarli diet daily for 1 and 3 months by discovery proteomics (two-dimensional gel electrophoresis and mass spectrometry) and non-parametric modeling (Multivariate Adaptive Regression Splines). Hepatic fatty infiltration was significantly higher in ethanol-fed animals as compared to controls, and more pronounced at 3 months of ethanol feeding. Discovery proteomics identified changes in the expression of proteins involved in alcohol, lipid, and amino acid metabolism after ethanol feeding. At 1 and 3 months, 12 and 15 different proteins were differentially expressed. Of the identified proteins, down regulation of alcohol dehydrogenase (-1.6) at 1 month and up regulation of aldehyde dehydrogenase (2.1) at 3 months could be a protective/adaptive mechanism against ethanol toxicity. In addition, betaine-homocysteine S-methyltransferase 2 a protein responsible for methionine metabolism and previously implicated in fatty liver development was significantly up regulated (1.4) at ethanol-induced fatty liver stage (1 month) while peroxiredoxin-1 was down regulated (-1.5) at late fatty liver stage (3 months). Nonparametric analysis of the protein spots yielded fewer proteins and narrowed the list of possible markers and identified d-dopachrome tautomerase (-1.7, at 3 months) as a possible marker for ethanol-induced early steatohepatitis. The observed differential regulation of proteins have potential to serve as biomarker signature for the detection of steatosis and its progression to steatohepatitis once validated in plasma/serum.

A proteomic analysis of liver after ethanol binge in chronically ethanol treated rats

Background

Binge ethanol in rats after chronic ethanol exposure augments necrosis and steatosis in the liver. In this study, two-dimensional gel electrophoresis proteomic profiles of liver of control, chronic ethanol, control-binge, and chronic ethanol- binge were compared.

Results

The proteomic analysis identified changes in protein abundance among the groups. The levels of carbonic anhydrase 3 (CA3) were decreased after chronic ethanol and decreased further after chronic ethanol-binge. Ethanol binge alone in control rats had no effect on this protein suggesting its possible role in increased susceptibility to injury by binge after chonic ethanol treatment. A protein spot, in which both cytosolic isocitrate dehydrogenase (IDH1) and glutamine synthetase (GS) were identified, showed a small decrease after chronic ethanol binge but western blot demonstrated significant decrease only for glutamine synthetase in chronic ethanol treated rats. The level of gluathione S-transferase mu isoform (GSTM1) increased after chronic ethanol but was lower after chronic ethanol-binge compared to chronic ethanol treatment. The protein levels of the basic form of protein disulfide isomerase associated protein 3 (PDIA3) were significantly decreased and the acidic forms were increased after chronic ethanol- binge but not in chronic ethanol treated rats or ethanol binge in control rats. The significant changes in proteome profile in chronic ethanol binge were accompanied by a marked increase in liver injury as evidenced by enhanced steatosis, necrosis, increased 4-hydroxynonenal labeled proteins, CYP2E1 expression, and decreased histone H2AX phosphorylation.

Conclusions

Given the role of CA3, IDH1 and GST in oxidative stress; PDIA3 in protein quality control, apoptosis and DNA repair and decreased glutamine synthetase as a sensitive marker of pericentral liver injury this proteome study of chronic ethanol-binge rat model identifies these proteins for the first time as molecular targets with potential role in progression of liver injury by binge ethanol drinking.

Protective effects of ulinastatin on acute liver failure induced by lipopolysaccharide/D-galactosamine

BACKGROUND

Although treatment of acute liver failure has been improved significantly recently, the survival rate of acute liver failure is only 5-20%. Therefore, prevention and treatment of acute liver failure are still urgent issues in the field of liver disease.

AIMS

It has been demonstrated that ulinastatin could attenuate acute injury of internal organs from endotoxin. This study evaluates whether ulinastatin can prevent and/or attenuate acute liver failure induced by the combination of lipopolysaccharide and D-galactosamine (LPS/D-gal).

METHODS

Sprague-Dawley rats were employed to induce acute liver failure by injection of LPS/D-gal. The liver function, inflammatory factors, oxidative stress index, and hepatic histopathological alteration were examined in the rats with and without ulinastatin treatment.

RESULTS

In rats treated with LPS/D-gal, there were increases in the levels of ALT and AST in the serum and levels of malondialdehyde and inducible nitric oxide synthase in liver tissues. Moreover, the levels of antioxidants such as superoxide dismutase and glutathione peroxidase were reduced in the liver. Furthermore, inflammatory factors (TNF-alpha and IL-6) and apoptotic enzyme (caspase-3) were increased in the respective serum and liver of rats treated with LPS/D-gal. However, pre-treatment of ulinastatin significantly reversed all of these parameters in the rats that received LPS/D: -gal alone.

CONCLUSIONS

The finding in this study suggests that ulinastatin could be a potential agent for prevention and treatment of acute liver injury induced by LPS/D-gal.

Triangulated mal-signaling in Alzheimer's disease: roles of neurotoxic ceramides, ER stress, and insulin resistance reviewed

Ceramides are lipid signaling molecules that cause cytotoxicity and cell death mediated by insulin resistance, inflammation, and endoplasmic reticulum (ER) stress. However, insulin resistance dysregulates lipid metabolism, which promotes ceramide accumulation with attendant inflammation and ER stress. Herein, we discuss two major pathways, extrinsic and intrinsic, that converge and often overlap in propagating AD-type neurodegeneration via a triangulated mal-signaling network. First, we review evidence that systemic insulin resistance diseases linked to obesity, type 2 diabetes, and non-alcoholic steatohepatitis promote neurodegeneration. Mechanistically, we propose that toxic ceramides generated in extra-CNS tissues (e.g., liver) get released into peripheral blood, and subsequently transit across the blood-brain barrier into the brain where they induce brain insulin resistance, inflammation, and cell death (extrinsic pathway). Then we discuss the role of the intrinsic pathway of neurodegeneration which is mediated by endogenous or primary brain insulin/IGF resistance, and impairs neuronal and oligodendrocyte survival, energy metabolism, membrane integrity, cytoskeletal function, and AβPP-Aβ secretion. The end result is increased ER stress and ceramide generation, which exacerbate brain insulin resistance, cell death, myelin degeneration, and neuroinflammation. Altogether, the data suggest that the triangulated mal-signaling network mediated by toxic ceramides, ER stress, and insulin resistance should be targeted to disrupt positive feedback loops that drive the AD neurodegeneration cascade.

ERp57 is up-regulated in free fatty acids-induced steatotic L-02 cells and human nonalcoholic fatty livers

Pathogenesis of nonalcoholic fatty liver disease (NAFLD) is not clear. In this study we aimed to identify proteins involved in NAFLD development in free fatty acids (FFA)-induced hepatosteatotic cells and in human liver biopsies. Steatosis was induced by incubating a normal human hepatocyte-derived cell line L-02 with FFA. Differentially expressed proteins in the steatotic cells were analyzed by two-dimensional gel electrophoresis-based proteomics. Involvement of one of the up-regulated proteins in steatosis was characterized using the RNA interference approach with the steatotic cells. Protein expression levels in liver biopsies of patients with NAFLD were assessed by immunohistochemistry. Proteomic analysis of L-02 steatotic cells revealed the up-regulation of ERp57, a condition not previously implicated in NAFLD. Knockdown of ERp57 expression with siRNA significantly reduced fat accumulation in the steatotic cells. ERp57 expression was detected in 16 out of 17 patient biopsies and correlated with inflammation grades or fibrosis stages, while in 5 normal biopsies ERp57 expression was not detectable in hepatocytes. In conclusion, ERp57 was up-regulated in FFA-induced steatotic hepatic cells and in NAFLD patient livers and demonstrated steatotic properties in cultured cells. Further investigations are warranted to verify the involvement of ERp57 in NAFLD development.

Alcoholic liver injury: Influence of gender and hormones

This article discusses several subjects pertinent to a consideration of the role of gender and hormones in alcoholic liver injury (ALI). Beginning with an overview of factors involved in the pathogenesis of ALI, we review changes in sex hormone metabolism resulting from alcohol ingestion, summarize research that points to estrogen as a cofactor in ALI, consider evidence that gut injury is linked to liver injury in the setting of alcohol, and briefly review the limited evidence regarding sex hormones and gut barrier function. In both women and female animals, most studies reveal a propensity toward greater alcohol-induced liver injury due to female gender, although exact hormonal influences are not yet understood. Thus, women and their physicians should be alert to the dangers of excess alcohol consumption and the increased potential for liver injury in females.

Deficiency of glycine N-methyltransferase results in deterioration of cellular defense to stress in mouse liver

PURPOSE

Previously, we reported that glycine N-methyltransferase (GNMT) interacts with benzo[a]pyrene (BaP) and inhibits BaP-DNA adducts formation. In addition, Gnmt knockout (Gnmt(-/-)) mice developed chronic hepatitis and hepatocellular carcinoma (HCC). The aims of this study were to understand the gene expression profile of Gnmt(-/-) mice and to study the interaction between BaP and GNMT deficiency in vivo.

EXPERIMENTAL DESIGN

Gene expression profiles of Gnmt(-/-) mice were analyzed by 2-D PAGE and real-time PCR. Both wild-type and Gnmt(-/-) mice were challenged with BaP and sacrificed at the age of 13 months.

RESULTS

Compared with the wild-type mice, proteins involved in the anti-oxidation/detoxification response, glycolytic energy metabolism and one-carbon metabolism pathways were down-regulated significantly in Gnmt(-/-) mice. Malondialdehyde assay showed that lipid peroxidation was significantly increased in the Gnmt(-/-) mice liver. H(2)O(2) treatment demonstrated that the survival rate of HuH-7 cells overexpressing GNMT was significantly higher than the controls. BaP challenge experiments showed that 71.4% (5/7) of male and all (7/7) female Gnmt(-/-) mice developed HCC, while only 16.7% (1/6) of male and 20% (1/5) of female wild-type mice had HCC.

CONCLUSION AND CLINICAL RELEVANCE

GNMT regulates genes related to detoxification and anti-oxidation pathways. BaP is a liver cancer carcinogen especially during GNMT deficiency.