Fenofibrate, a peroxisome proliferator-activated receptor alpha agonist, reduces hepatic steatosis and lipid peroxidation in fatty liver Shionogi mice with hereditary fatty liver

Lipid-lowering agents inhibit hepatic steatosis in a non-alcoholic steatohepatitis-derived hepatocellular carcinoma mouse model

Non-alcoholic fatty liver disease (NAFLD) is associated with various metabolic disorders, and the therapeutic strategies for treating NAFLD and non-alcoholic steatohepatitis (NASH) have not been fully established. In the present study, we examined whether lipid-lowering agents inhibited the progression of NAFLD and tumorigenesis in a non-alcoholic steatohepatitis-derived hepatocellular carcinoma model mouse (STAM mice) generated by streptozotocin injection and a high-fat diet. Seven-week-old STAM mice were divided into groups fed a high-fat diet (Ctl) or a high-fat diet supplemented with ezetimibe (Ez), fenofibrate (Ff), rosuvastatin (Rs), ezetimibe plus fenofibrate (EF), or ezetimibe plus rosuvastatin (ER) for 4 weeks. At the end of the experiments, an oral glucose tolerance test, an insulin tolerance test, biochemical analyses using serum and liver, and a histological analysis of liver were performed in 11-week-old STAM mice. The lipid-lowering agents did not affect the body weight or the casual blood glucose levels in any of the groups. The serum triglyceride level was significantly decreased by Ff, Rs, and EF. Glucose tolerance was improved by Ez and Ff, but none of these agents improved insulin sensitivity. A histochemical analysis revealed that the lipid-lowering agents, with the exception of Rs, significantly inhibited the progression of hepatic steatosis. Nonetheless, no significant changes in the incidence of hepatic tumors were observed in any of the groups. Lipid-lowering agents inhibited the progression of hepatic steatosis without suppressing tumorigenesis in STAM mice. Our data has implications for the mechanism underlying steatosis-independent hepatic tumorigenesis in mice.

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.

Novel therapeutic targets for steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease in the Western hemisphere and is growing as an indication for liver transplantation. There are currently no approved therapies for NAFLD, especially its aggressive phenotype non-alcoholic steatohepatitis (NASH). However, there has been an explosion of information related to NASH that provides detailed data on the molecular pathogenesis of NASH and its progression to cirrhosis. The current review summarizes the pathophysiological rationale for the selection of specific targets for the treatment of NASH and provides an overview of the current strategies being used for the treatment of NASH and the pathophysiological rationale for the use of these strategies. Specifically, those targets that are being studied in both alcoholic and non-alcoholic steatohepatitis are also mentioned.

Comparative clinical study between the effect of fenofibrate alone and its combination with pentoxifylline on biochemical parameters and liver stiffness in patients with non-alcoholic fatty liver disease

BACKGROUND

Non-alcoholic fatty liver disease is a common health problem associated with increased liver and vascular specific complications.

AIM

The purpose of this study was to assess and compare the effect of fenofibrate alone or in combination with pentoxifylline on the measured biochemical parameters, inflammatory pathway and liver stiffness in patients with non-alcoholic fatty liver disease.

METHODS

The study design was randomized controlled trial. From July 2013 to June 2014, we recruited 90 non-alcoholic fatty liver patients from the Internal Medicine Department at Tanta University Hospital, Egypt. They were classified randomly into two groups to receive fenofibrate 300 mg daily or fenofibrate 300 mg daily plus pentoxifylline 1200 mg/day in three divided doses for 24 weeks. Fasting blood sample was obtained before and 24 weeks after treatment for biochemical analysis of liver and lipid panels, tumor necrosis factor-alpha, hyaluronic acid, transforming growth factor beta 1, fasting plasma insulin and fasting glucose. Liver stiffness measurement was carried out using fibro-scan. Data were statistically analyzed by paired and unpaired Student's t test.

RESULTS

The data obtained suggests that adding pentoxifylline to fenofibrate does not provide a beneficial effect on lipid panel, but has a beneficial effect on indirect biochemical markers of hepatic fibrosis, a direct marker linked to matrix deposition (hyaluronic acid), a cytokine/growth factor linked to liver fibrosis (transforming growth factor beta 1), the inflammatory pathway, insulin resistance and liver stiffness as compared to fenofibrate alone.

CONCLUSION

The combination pentoxifylline plus fenofibrate may represent a new therapeutic strategy for non-alcoholic fatty liver disease as it resulted in more beneficial effects on direct and indirect markers of liver fibrosis, liver stiffness, insulin resistance and inflammatory pathway implicated in NAFLD.

Kaempferol ameliorates symptoms of metabolic syndrome by regulating activities of liver X receptor-β

Kaempferol is a dietary flavonol previously shown to regulate cellular lipid and glucose metabolism. However, its molecular mechanisms of action and target proteins have remained elusive, probably due to the involvement of multiple proteins. This study investigated the molecular targets of kaempferol. Ligand binding of kaempferol to liver X receptors (LXRs) was quantified by time-resolved fluorescence resonance energy transfer and surface plasmon resonance analyses. Kaempferol directly binds to and induces the transactivation of LXRs, with stronger specificity for the β-subtype (EC50 = 0.33 μM). The oral administration of kaempferol in apolipoprotein-E-deficient mice (150 mg/day/kg body weight) significantly reduced plasma glucose and increased high-density lipoprotein cholesterol levels and insulin sensitivity compared with the vehicle-fed control. Kaempferol also reduced plasma triglyceride concentrations and did not cause liver steatosis, a common side effect of potent LXR activation. In immunoblotting analysis, kaempferol reduced the nuclear accumulation of sterol regulatory element-binding protein-1 (SREBP-1). Our results show that the suppression of SREBP-1 activity and the selectivity for LXR-β over LXR-α by kaempferol contribute to the reductions of plasma and hepatic triglyceride concentrations in mice fed kaempferol. They also suggest that kaempferol activates LXR-β and suppresses SREBP-1 to enhance symptoms in metabolic syndrome.

Fenofibrate treatment attenuated chronic endoplasmic reticulum stress in the liver of nonalcoholic fatty liver disease mice

Fenofibrate is widely used in clinical practice, but its influence on chronic endoplasmic reticulum (ER) stress induced by feeding a high-calorie and high-cholesterol diet (HCD) has still not been studied. We thus investigated its effects on the liver of the nonalcoholic fatty liver disease (NAFLD) mouse model. Male C57BL/6 mice fed an HCD for 3 months were treated with fenofibrate (HCD + FF, 40 mg/kg, once daily) via gavage for 4 weeks. Insulin sensitivity, serum lipid and inflammatory cytokines were measured. Liver tissues were procured for histological examination as well as analysis of hepatic triglyceride levels, distribution of inflammatory cytokines and genes involved in ER stress. Our results showed that chronic feeding of an HCD successfully induced an NAFLD model accompanied by inflammatory activation, apoptosis and severe ER stress in the liver. Fenofibrate administration significantly improved symptoms of NAFLD and decreased apoptosis, expression of inflammatory cytokines and genes involved in ER stress, such as inositol-requiring enzyme 1α (IRE1α), X-box binding protein 1 (XBP1) and JNK phosphorylation. Thus, our study suggests that fenofibrate protected against inflammatory injury and apoptosis, maybe alleviating ER stress through the IRE1α-XBP1-JNK pathway in the liver of NAFLD mice.

Potential approaches to ameliorate hepatic fat accumulation seen with MTP inhibition

Microsomal triglyceride transfer protein (MTP) is one of the promising targets for the therapy of dyslipidemia and MTP inhibition can lead to robust plasma low-density lipoprotein cholesterol (LDL-C) reduction. Lomitapide, a small-molecule MTP inhibitor, was recently approved by the US FDA as an additional treatment for homozygous familial hypercholesterolemia (hoFH). However, liver-related side effects, including hepatic fat accumulation and transaminase elevations, are the main safety concerns associated with MTP inhibitors. Here, we review recent knowledge on the mechanisms underlying liver toxicity of MTP inhibitors. The contribution of altered levels of intracellular triglycerides, cholesteryl esters, and free cholesterols toward cellular dysfunction is specifically addressed. On this basis, therapies targeted to attenuate cellular lipid accumulation, to reduce risk factors for non-alcoholic fatty liver disease (NAFLD) (i.e., insulin resistance and oxidative stress) and to specifically inhibit intestinal MTP may be useful for ameliorating liver damage induced by MTP inhibitors. In particular, weight loss through lifestyle interventions is expected to be the most effective and safest way to minimize the undesirable side effects. Specific dietary supplementation might also have protective effects against hepatosteatosis. Despite that, to date, few clinical data support these therapeutic options in MTP inhibition-related liver damage, such proposed approaches may be further explored in the future for their use in preventing unwanted effects of MTP inhibitors.

Ursolic acid improves lipid and glucose metabolism in high-fat-fed C57BL/6J mice by activating peroxisome proliferator-activated receptor alpha and hepatic autophagy

SCOPE

This study investigated metabolic effects of ursolic acid (UA), a peroxisome proliferation-activated receptor (PPAR)-α activator, in vivo.

METHODS AND RESULTS

High-fat diet (HFD)-fed C57BL/6J mice were orally administered UA (50 or 200 mg/kg body weight) for 8 wk. UA reduced liver and adipose tissue mass, adipocyte size, and plasma leptin concentrations, plasma triglyceride and low-density-lipoprotein cholesterol concentrations, while it elevated the high-density-lipoprotein cholesterol and adiponectin concentrations significantly compared with controls. UA induced the expression of PPARα and its responsive genes involved in fatty acid uptake and β-oxidation in the livers, whereas genes involved in lipogenesis, including sterol regulatory element-binding proteins-1c, were downregulated. UA administration improved glucose tolerance and insulin sensitivity significantly compared with the HFD-fed control livers. UA administration also activated hepatic autophagy as assessed by the expression of microtubule-associated protein 1A/1B-light chain 3 (LC3)-II and other key proteins in the autophagy pathway.

CONCLUSION

Our findings suggest that UA ameliorates lipid and glucose metabolism in HFD-fed mice primarily by the activation of PPARα and induction of the hepatic autophagy pathway. Thus, intake of UA in the diet or in an isolated form may ameliorate lipid and glucose metabolism.

SteatoNet: the first integrated human metabolic model with multi-layered regulation to investigate liver-associated pathologies

Current state-of-the-art mathematical models to investigate complex biological processes, in particular liver-associated pathologies, have limited expansiveness, flexibility, representation of integrated regulation and rely on the availability of detailed kinetic data. We generated the SteatoNet, a multi-pathway, multi-tissue model and in silico platform to investigate hepatic metabolism and its associated deregulations. SteatoNet is based on object-oriented modelling, an approach most commonly applied in automotive and process industries, whereby individual objects correspond to functional entities. Objects were compiled to feature two novel hepatic modelling aspects: the interaction of hepatic metabolic pathways with extra-hepatic tissues and the inclusion of transcriptional and post-transcriptional regulation. SteatoNet identification at normalised steady state circumvents the need for constraining kinetic parameters. Validation and identification of flux disturbances that have been proven experimentally in liver patients and animal models highlights the ability of SteatoNet to effectively describe biological behaviour. SteatoNet identifies crucial pathway branches (transport of glucose, lipids and ketone bodies) where changes in flux distribution drive the healthy liver towards hepatic steatosis, the primary stage of non-alcoholic fatty liver disease. Cholesterol metabolism and its transcription regulators are highlighted as novel steatosis factors. SteatoNet thus serves as an intuitive in silico platform to identify systemic changes associated with complex hepatic metabolic disorders.

Identification of master genes involved in liver key functions through transcriptomics and epigenomics of methyl donor deficiency in rat: relevance to nonalcoholic liver disease

SCOPE

Our study aims to investigate molecular events associated to methyl donor deficiency (MDD) by analyzing the transcriptome and the methylome of MDD rats in liver.

METHODS AND RESULTS

Twenty-one-day-old rats born to mothers fed either with a standard diet or a MDD diet during gestation and lactation were compared. From a total of 44 000 probes for 26 456 genes, we found two gene clusters in MDD rats whose expression levels had significant differences compared with controls: 3269 overexpressed (p < 0.0009) and 2841 underexpressed (p < 0.0004) genes. Modifications of DNA methylation were found in the promoter regions of 1032 genes out of 14 981 genes. Ontological analyses revealed that these genes are mainly involved in glucose and lipid metabolism, nervous system, coagulation, ER stress, and mitochondrial function.

CONCLUSION

Putative master genes exhibiting changes in both gene expression and DNA methylation are limited to 266 genes and are mainly involved in the renin-angiotensin system (n = 3), mitochondrion metabolism (n = 18), and phospholipid homeostasis (n = 3). Most of these master genes participate in nonalcoholic fatty liver disease. The adverse effects of MDD on the metabolic process indicate the beneficial impact of folate and vitamin B12, especially during the perinatal period.

The dipeptide H-Trp-Arg-OH (WR) Is a PPARα agonist and reduces hepatic lipid accumulation in lipid-loaded H4IIE cells

Dipeptides absorbed by the intestinal epithelium are delivered to circulation, but their metabolic roles are not yet clearly understood. We investigated the biological activities of a dietary dipeptide, H-Trp-Arg-OH (WR), on the regulation of peroxisome proliferator-activated receptor (PPAR) α activity. Reporter gene assays revealed that WR dose-dependently induced PPARα transactivation. Surface plasmon resonance experiments demonstrated that WR interacts directly with the PPARα ligand binding domain, and time-resolved fluorescence energy transfer analyses revealed recruitment of a co-activator peptide, fluorescein-PGC1α, to PPARα, confirming the direct binding of WR to PPARα and occurrence of conformational changes. WR induced cellular fatty acid uptake and the expression of PPARα response genes in fatty acid oxidation, thus reducing intracellular triglyceride accumulation in lipid-loaded hepatocytes. In conclusion, the dietary dipeptide WR activates PPARα and reduces hepatic lipid accumulation in lipid-loaded hepatocytes.

Icariin is a PPARα activator inducing lipid metabolic gene expression in mice

Icariin is effective in the treatment of hyperlipidemia. To understand the effect of icariin on lipid metabolism, effects of icariin on PPARα and its target genes were investigated. Mice were treated orally with icariin at doses of 0, 100, 200, and 400 mg/kg, or clofibrate (500 mg/kg) for five days. Liver total RNA was isolated and the expressions of PPARα and lipid metabolism genes were examined. PPARα and its marker genes Cyp4a10 and Cyp4a14 were induced 2-4 fold by icariin, and 4-8 fold by clofibrate. The fatty acid (FA) binding and co-activator proteins Fabp1, Fabp4 and Acsl1 were increased 2-fold. The mRNAs of mitochondrial FA β-oxidation enzymes (Cpt1a, Acat1, Acad1 and Hmgcs2) were increased 2-3 fold. The mRNAs of proximal β-oxidation enzymes (Acox1, Ech1, and Ehhadh) were also increased by icariin and clofibrate. The expression of mRNAs for sterol regulatory element-binding factor-1 (Srebf1) and FA synthetase (Fasn) were unaltered by icariin. The lipid lysis genes Lipe and Pnpla2 were increased by icariin and clofibrate. These results indicate that icariin is a novel PPARα agonist, activates lipid metabolism gene expressions in liver, which could be a basis for its lipid-lowering effects and its beneficial effects against diabetes.

Fenofibrate--a lipid-lowering drug--reduces voluntary alcohol drinking in rats

The administration of disulfiram raises blood acetaldehyde levels when ethanol is ingested, leading to an aversion to alcohol. This study was aimed at assessing the effect of fenofibrate on voluntary ethanol ingestion in rats. Fenofibrate reduces blood triglyceride levels by increasing fatty acid oxidation by liver peroxisomes, along with an increase in the activity of catalase, which can oxidize ethanol to acetaldehyde. UChB drinker rats were allowed to consume alcohol 10% v/v freely for 60 days, until consumption stabilized at around 7 g ethanol/kg/24 h. About 1-1.2 g ethanol/kg of this intake is consumed in the first 2 h of darkness of the circadian cycle. Fenofibrate subsequently administered (50 mg/kg/day by mouth [p.o.]) for 14 days led to a 60-70% (p < 0.001) reduction of 24-h ethanol consumption. When ethanol intake was determined within the first 2 h of darkness, the reduction was 85-90% (p < 0.001). We determined whether animals chronically allowed access to ethanol and subsequently treated with fenofibrate, would a) increase liver catalase activity, and b) increase blood acetaldehyde levels after a 24-h ethanol deprivation and the subsequent administration of 1 g ethanol/kg. The oral administration of 1 g ethanol/kg produced a rapid increase in blood (arterial) acetaldehyde in fenofibrate-treated animals versus controls also administered 1 g/kg ethanol (70 μM vs. 7 μM; p < 0.001). Liver catalase activity following fenofibrate treatment was increased 3-fold (p < 0.01). Other hepatic enzymes responsible for the metabolism of ethanol (alcohol dehydrogenase and aldehyde dehydrogenase) remained unchanged. No liver damage was induced, as measured by serum glutamic-pyruvic transaminase (GPT) activity. The effect of fenofibrate in reducing alcohol intake was fully reversible. Overall, in rats allowed chronic ethanol intake, by mouth (p.o.), fenofibrate administration increased liver catalase activity and reduced voluntary ethanol intake. The administration of 1 g ethanol/kg (p.o.) to these animals increased blood acetaldehyde levels in fenofibrate-treated animals, suggesting the possible basis for the reduction in ethanol intake.

Nonalcoholic Fatty liver disease: pathogenesis and therapeutics from a mitochondria-centric perspective

Nonalcoholic fatty liver disease (NAFLD) describes a spectrum of disorders characterized by the accumulation of triglycerides within the liver. The global prevalence of NAFLD has been increasing as the obesity epidemic shows no sign of relenting. Mitochondria play a central role in hepatic lipid metabolism and also are affected by upstream signaling pathways involved in hepatic metabolism. This review will focus on the role of mitochondria in the pathophysiology of NAFLD and touch on some of the therapeutic approaches targeting mitochondria as well as metabolically important signaling pathways. Mitochondria are able to adapt to lipid accumulation in hepatocytes by increasing rates of beta-oxidation; however increased substrate delivery to the mitochondrial electron transport chain (ETC) leads to increased reactive oxygen species (ROS) production and eventually ETC dysfunction. Decreased ETC function combined with increased rates of fatty acid beta-oxidation leads to the accumulation of incomplete products of beta-oxidation, which combined with increased levels of ROS contribute to insulin resistance. Several related signaling pathways, nuclear receptors, and transcription factors also regulate hepatic lipid metabolism, many of which are redox sensitive and regulated by ROS.

Molecular pathways in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a clinicopathological change characterized by the accumulation of triglycerides in hepatocytes and has frequently been associated with obesity, type 2 diabetes mellitus, hyperlipidemia, and insulin resistance. It is an increasingly recognized condition that has become the most common liver disorder in developed countries, affecting over one-third of the population and is associated with increased cardiovascular- and liver-related mortality. NAFLD is a spectrum of disorders, beginning as simple steatosis. In about 15% of all NAFLD cases, simple steatosis can evolve into non-alcoholic steatohepatitis, a medley of inflammation, hepatocellular injury, and fibrosis, often resulting in cirrhosis and even hepatocellular cancer. However, the molecular mechanism underlying NAFLD progression is not completely understood. Its pathogenesis has often been interpreted by the “double-hit” hypothesis. The primary insult or the “first hit” includes lipid accumulation in the liver, followed by a “second hit” in which proinflammatory mediators induce inflammation, hepatocellular injury, and fibrosis. Nowadays, a more complex model suggests that fatty acids (FAs) and their metabolites may be the true lipotoxic agents that contribute to NAFLD progression; a multiple parallel hits hypothesis has also been suggested. In NAFLD patients, insulin resistance leads to hepatic steatosis via multiple mechanisms. Despite the excess hepatic accumulation of FAs in NAFLD, it has been described that not only de novo FA synthesis is increased, but FAs are also taken up from the serum. Furthermore, a decrease in mitochondrial FA oxidation and secretion of very-low-density lipoproteins has been reported. This review discusses the molecular mechanisms that underlie the pathophysiological changes of hepatic lipid metabolism that contribute to NAFLD.

Upregulation of hepatic VLDLR via PPARα is required for the triglyceride-lowering effect of fenofibrate

The liver and the VLDL receptor (VLDLR) play major roles in TG and VLDL metabolism. However, the exact role of liver VLDLR is not well known because of the absence of or difficulty in detecting VLDLR in the liver. In this study, we demonstrate that fenofibrate, a PPARα agonist and widely used TG-lowering drug, markedly upregulated hepatic VLDLR, which is essential for lowering TG. This study also shows that the distinct regulatory roles of PPARα agonists on VLDLR in the liver and peripheral tissues including adipose tissues, heart, and skeletal muscles are due to the pattern of expression of PPARα. The in vivo portion of our study demonstrated that oral fenofibrate robustly increased liver VLDLR expression levels in hyperlipidemic and diabetic mice and significantly reduced the increase in serum TG observed in wt mice after feeding with high-fat diet (HFD) but not in Vldlr(-/-) mice or Pparα(-/-) mice. However, overexpression of mouse VLDLR in livers of Vldlr(-/-) mice significantly prevented the increase in serum TG induced by HFD. The in vitro portion of our study showed that fenofibrate upregulated VLDLR transcriptional activity through PPAR response element binding to the VLDLR promoter. The conclusions of our study provide a novel mechanism for the TG-lowering effects of fenofibrate in the treatment of dyslipidemia.

Modeling progressive non-alcoholic fatty liver disease in the laboratory mouse

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease in the world and its prevalence is rising. In the absence of disease progression, fatty liver poses minimal risk of detrimental health outcomes. However, advancement to non-alcoholic steatohepatitis (NASH) confers a markedly increased likelihood of developing severe liver pathologies, including fibrosis, cirrhosis, organ failure, and cancer. Although a substantial percentage of NAFLD patients develop NASH, the genetic and molecular mechanisms driving this progression are poorly understood, making it difficult to predict which patients will ultimately develop advanced liver disease. Deficiencies in mechanistic understanding preclude the identification of beneficial prognostic indicators and the development of effective therapies. Mouse models of progressive NAFLD serve as a complementary approach to the direct analysis of human patients. By providing an easily manipulated experimental system that can be rigorously controlled, they facilitate an improved understanding of disease development and progression. In this review, we discuss genetically- and chemically-induced models of NAFLD that progress to NASH, fibrosis, and liver cancer in the context of the major signaling pathways whose disruption has been implicated as a driving force for their development. Additionally, an overview of nutritional models of progressive NAFLD is provided.

The IGF2 mRNA binding protein p62/IGF2BP2-2 induces fatty acid elongation as a critical feature of steatosis

Liver-specific overexpression of the insulin-like growth factor 2 (IGF2) mRNA binding protein p62/IGF2BP2-2 induces a fatty liver, which highly expresses IGF2 Because IGF2 expression is elevated in patients with steatohepatitis, the aim of our study was to elucidate the role and interconnection of p62 and IGF2 in lipid metabolism. Expression of p62 and IGF2 highly correlated in human liver disease. p62 induced an elevated ratio of C18:C16 and increased fatty acid elongase 6 (ELOVL6) protein, the enzyme catalyzing the elongation of C16 to C18 fatty acids and promoting nonalcoholic steatohepatitis in mice and humans. The p62 overexpression induced the activation of the ELOVL6 transcriptional activator sterol regulatory element binding transcription factor 1 (SREBF1). Recombinant IGF2 induced the nuclear translocation of SREBF1 and a neutralizing IGF2 antibody reduced ELOVL6 and mature SREBF1 protein levels. Concordantly, p62 and IGF2 correlated with ELOVL6 in human livers. Decreased palmitoyl-CoA levels, as found in p62 transgenic livers, can explain the lipogenic action of ELOVL6. Accordingly, p62 represents an inducer of hepatic C18 fatty acid production via a SREBF1-dependent induction of ELOVL6. These findings underline the detrimental role of p62 in liver disease.

Rapid development of non-alcoholic steatohepatitis in Psammomys obesus (Israeli sand rat)

Background and Aims

A major impediment to establishing new treatments for non-alcoholic steatohepatitis is the lack of suitable animal models that accurately mimic the biochemical and metabolic characteristics of the disease. The aim of this study was to explore a unique polygenic animal model of metabolic disease as a model of non-alcoholic steatohepatitis by determining the effects of 2% dietary cholesterol supplementation on metabolic and liver endpoints in Psammomys obesus (Israeli sand rat).

Methods

P. obesus were provided ad libitum access to either a standard rodent diet (20% kcal/fat) or a standard rodent diet supplemented with 2% cholesterol (w/w) for 4 weeks. Histological sections of liver from animals on both diets were examined for key features of non-alcoholic steatohepatitis. The expression levels of key genes involved in hepatic lipid metabolism were measured by real-time PCR.

Results

P. obesus fed a cholesterol-supplemented diet exhibited profound hepatomegaly and steatosis, and higher plasma transaminase levels. Histological analysis identified extensive steatosis, inflammation, hepatocyte injury and fibrosis. Hepatic gene expression profiling revealed decreased expression of genes involved in delivery and uptake of lipids, and fatty acid and triglyceride synthesis, and increased expression of genes involved in very low density lipoprotein cholesterol synthesis, triglyceride and cholesterol export.

Conclusions

P. obesus rapidly develop non-alcoholic steatohepatitis when fed a cholesterol-supplemented diet that appears to be histologically and mechanistically similar to patients.

Novel effect of ezetimibe to inhibit the development of non-alcoholic fatty liver disease in Fatty Liver Shionogi mouse

AIM

Several studies using experimental non-alcoholic fatty liver disease (NAFLD) models have shown that ezetimibe, an inhibitor of cholesterol absorption mainly in the intestine, not only protects against diet-induced hyperlipidemia, but also attenuates liver steatosis. The aim of this study was to clarify whether ezetimibe inhibits the development of NAFLD and to elaborate the mechanism of ezetimibe to inhibit the development of NAFLD using Fatty Liver Shionogi (FLS) mice, a spontaneous model of NAFLD/non-alcoholic steatohepatitis.

METHODS

Male FLS mice at 20 weeks of age were divided into two groups (n = 7 in each group). Mice fed a normal laboratory chow, CRF-1 or CRF-1 containing 0.005% w/w ezetimibe (7 mg/kg per day) for 4 weeks. After 4-week treatment with ezetimibe, the livers of each group of mice were subjected to histological as well as molecular evaluation.

RESULTS

Ezetimibe administration for 4 weeks was associated with improvement of steatosis and fibrosis of the liver in normal diet-fed FLS mice. Ezetimibe reduced hepatic reactive oxygen species generation and prevented ubiquitination and protein degradation of microsomal triglyceride transfer protein (MTP), a key molecule for very low-density lipoprotein assembly and export, via downregulation of the protein expression of Skp2 and CDC20.

CONCLUSION

Ezetimibe not only reduced lipid synthesis in the liver, but also promoted lipid discharge from the liver by preventing post-translational degradation of MTP via a reduction of hepatic reactive oxygen species generation, leading to inhibition of the development of NAFLD.

Compound K modulates fatty acid-induced lipid droplet formation and expression of proteins involved in lipid metabolism in hepatocytes

BACKGROUND & AIMS

A key factor in the development of type 2 diabetes and non-alcoholic fatty liver disease (NAFLD) is hepatic steatosis. Incubation of human hepatic cells with free fatty acids (FFAs) causes accumulation of neutral lipids in lipid droplets (LDs) and serves as a model for hepatic steatosis. Ginsenosides, active constituents of ginsengs, have demonstrated beneficial effects in various pharmacological areas, including diabetes, however their effect on lipid accumulation in hepatocytes remains unclear. Here, we examine the effect of compound K (ComK), an active metabolite of ginsenosides, on the regulation of LD formation and on the expression of proteins involved in lipid homeostasis in hepatocytes.

METHODS

HuH7 cells were pretreated with ComK, followed by lipid loading with FFA. LDs were visualized using Oil Red O staining and immunohistochemistry for the LD-related protein PLIN2. Triglyceride levels were determined in isolated LDs. The expression of proteins involved in lipid homeostasis was examined by Western blotting.

RESULTS

Treatment with ComK significantly decreased LD formation in FFA-loaded HuH7 cells and increased phosphorylation levels of AMPK, and its substrate ACC. ComK also increased protein expression of peroxisome proliferator-activated receptor-α (PPAR-α) and acyl-CoA oxidase (ACOX1) together with elevated activity of a PPAR-α response element reporter construct. These effects were inhibited by the PPAR-α antagonist MK886.

CONCLUSIONS

ComK reduced LD formation and TG accumulation in FFA-loaded hepatocytes, in part by up-regulating AMPK activity and PPAR-α related pathways. These results suggest that ComK may have efficacy for the treatment of hepatic steatosis and associated diseases.

Effects of a Lactobacillus paracasei B21060 based synbiotic on steatosis, insulin signaling and toll-like receptor expression in rats fed a high-fat diet

Insulin resistance (IR) has been identified as crucial pathophysiological factor in the development and progression of non-alcoholic fatty liver disease (NAFLD). Although mounting evidence suggests that perturbation of gut microflora exacerbates the severity of chronic liver diseases, therapeutic approaches using synbiotic has remained overlooked. Here, we show that a synbiotic composed by Lactobacillus paracasei B21060 plus arabinogalactan and fructo-oligosaccharides lessens NAFLD progression in a rat model of high fat feeding. IR and steatosis were induced by administration of high fat diet (HFD) for 6 weeks. Steatosis and hepatic inflammation, Toll-like receptor (TLR) pattern, glucose tolerance, insulin signaling and gut permeability were studied. Liver inflammatory markers were down-regulated in rats receiving the synbiotic, along with an increased expression of nuclear peroxisome proliferator-activated receptors and expression of downstream target genes. The synbiotic improved many aspects of IR, such as fasting response, hormonal homeostasis and glycemic control. Indeed it prevented the impairment of hepatic insulin signaling, reducing the phosphorylation of insulin receptor substrate-1 in Ser 307 and down-regulating suppressor of cytokine signaling 3. Gene expression analysis revealed that in the liver the synbiotic reduced cytokines synthesis and restored the HFD-dysregulated TLR 2, 4 and 9 mRNAs toward a physiological level of expression. The synbiotic preserved gut barrier integrity and reduced the relative amount of Gram-negative Enterobacteriales and Escherichia coli in colonic mucosa. Overall, our data indicate that the L. paracasei B21060 based synbiotic is effective in reducing the severity of liver injury and IR associated with high fat intake, suggesting its possible therapeutic/preventive clinical utilization.

Current role of fenofibrate in the prevention and management of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a common health problem with a high mortality burden due to its liver- and vascular-specific complications. It is associated with obesity, high-fat diet as well as with type 2 diabetes mellitus (T2DM) and metabolic syndrome (MetS). Impaired hepatic fatty acid (FA) turnover together with insulin resistance are key players in NAFLD pathogenesis. Peroxisome proliferator-activated receptors (PPARs) are involved in lipid and glucose metabolic pathways. The novel concept is that the activation of the PPARα subunit may protect from liver steatosis. Fenofibrate, by activating PPARα, effectively improves the atherogenic lipid profile associated with T2DM and MetS. Experimental evidence suggested various protective effects of the drug against liver steatosis. Namely, fenofibrate-related PPARα activation may enhance the expression of genes promoting hepatic FA β-oxidation. Furthermore, fenofibrate reduces hepatic insulin resistance. It also inhibits the expression of inflammatory mediators involved in non-alcoholic steatohepatitis pathogenesis. These include tumor necrosis factor-α, intercellular cell adhesion molecule-1, vascular cell adhesion molecule-1 and monocyte chemoattractant protein-1. Consequently, fenofibrate can limit hepatic macrophage infiltration. Other liver-protective effects include decreased oxidative stress and improved liver microvasculature function. Experimental studies showed that fenofibrate can limit liver steatosis associated with high-fat diet, T2DM and obesity-related insulin resistance. Few studies showed that these benefits are also relevant even in the clinical setting. However, these have certain limitations. Namely, these were uncontrolled, their sample size was small, fenofibrate was used as a part of multifactorial approach, while histological data were absent. In this context, there is a need for large prospective studies, including proper control groups and full assessment of liver histology.

Fenofibrate does not affect burn-induced hepatic endoplasmic reticulum stress

BACKGROUND

Burn injury causes major metabolic derangements such as hypermetabolism, hyperlipidemia, and insulin resistance and is associated with liver damage, hepatomegaly, and hepatic endoplasmic reticulum (ER) stress. Although the physiological consequences of such derangements have been delineated, the underlying molecular mechanisms remain unknown. Previously, it was shown that fenofibrate improves patient outcome by attenuating postburn stress responses.

METHODS

Fenofibrate, a peroxisome proliferator-activated receptor alpha agonist, regulates liver lipid metabolism and has been used to treat hypertriglyceridemia and hypercholesterolemia for many years. The aim of the present study is to determine the effects of fenofibrate on burn-induced hepatic morphologic and metabolic changes. We randomized rats to sham, burn injury, and burn injury plus fenofibrate. Animals were sacrificed and livers were assessed at 24 or 48 h post burn.

RESULTS

Burn injury decreased albumin and increased alanine transaminase (P = 0.1 versus sham), indicating liver injury. Fenofibrate administration did not restore albumin or decrease alanine transaminase. In addition, ER stress was significantly increased after burn injury both with and without fenofibrate (P < 0.05 versus sham). Burn injury increased fatty acid metabolism gene expression (P < 0.05 versus sham), downstream of peroxisome proliferator-activated receptor alpha. Fenofibrate treatment increased fatty acid metabolism further, which reduced postburn hepatic steatosis (burn versus sham P < 0.05, burn + fenofibrate versus sham not significant).

CONCLUSIONS

Fenofibrate did not alleviate thermal injury-induced hepatic ER stress and dysfunction, but it reduced hepatic steatosis by modulating hepatic genes related to fat metabolism.

The FLS (fatty liver Shionogi) mouse reveals local expressions of lipocalin-2, CXCL1 and CXCL9 in the liver with non-alcoholic steatohepatitis

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) encompasses a wide spectrum of diseases, ranging from simple steatosis to nonalcoholic steatohepatitis (NASH), which carries a significant risk of progression to cirrhosis and hepatocellular carcinoma. Since NASH is a progressive but reversible condition, it is desirable to distinguish NASH from simple steatosis, and to treat NASH patients at an early stage. To establish appropriate diagnosis and therapy, the pathological mechanisms of the disease should be elucidated; however, these have not been fully clarified for both NASH and simple steatosis. This study aims to reveal the differences between simple steatosis and NASH.

METHODS

This study used fatty liver Shionogi (FLS) mice as a NASH model, for comparison with dd Shionogi (DS) mice as a model of simple steatosis. Genome-wide gene expression analysis was performed using Affymetrix GeneChip Mouse Genome 430 2.0 Array, which contains 45101 probe sets for known and predicted genes. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) and immunohistochemistry were used to investigate gene expression changes and protein localizations.

RESULTS

DNA microarray analysis of the liver transcriptomes and qRT-PCR of both types of mice revealed that LCN2, CXCL1 and CXCL9 mRNAs were overexpressed in FLS mouse livers. Immunohistochemistry showed that CXCL1 protein was mainly localized to steatotic hepatocytes. CXCL9 protein-expressing hepatocytes and sinusoidal endothelium were localized in some areas of inflammatory cell infiltration. Most interestingly, hepatocytes expressing LCN2, a kind of adipokine, were localized around almost all inflammatory cell clusters. Furthermore, there was a positive correlation between the number of LCN2-positive hepatocytes in the specimen and the number of inflammatory foci.

CONCLUSIONS

Overexpression and distinct localization of LCN2, CXCL1 and CXCL9 in the liver of fatty liver Shionogi mice suggest significant roles of these proteins in the pathogenesis of NASH.

Effects of sodium butyrate and its synthetic amide derivative on liver inflammation and glucose tolerance in an animal model of steatosis induced by high fat diet

Background & Aims

Nonalcoholic fatty liver disease (NAFLD) is the most common form of chronic liver disease. Insulin resistance (IR) appears to be critical in its pathogenesis. We evaluated the effects of sodium butyrate (butyrate) and its synthetic derivative N-(1-carbamoyl-2-phenyl-ethyl) butyramide (FBA) in a rat model of insulin resistance and steatosis induced by high-fat diet (HFD).

Methods

After weaning, young male Sprague-Dawley rats were divided into 4 groups receiving different diets for 6 weeks: 1. control group (standard diet); 2. HFD; 3. HFD plus butyrate (20 mg/kg/die) and 4. HFD plus FBA (42.5 mg/Kg/die, the equimolecular dose of butyrate). Liver tissues of the rats were analyzed by Western blot and real-time PCR. Insulin resistance, liver inflammation and Toll-like pattern modifications were determined.

Results

Evaluation of these two preparations of butyrate showed a reduction of liver steatosis and inflammation in HFD fed animals. The compounds showed a similar potency in the normalisation of several variables, such as transaminases, homeostasis model assessment for insulin resistance index, and glucose tolerance. Both treatments significantly reduced hepatic TNF-α expression and restored GLUTs and PPARs, either in liver or adipose tissue. Finally, FBA showed a higher potency in reducing pro-inflammatory parameters in the liver, via suppression of Toll-like receptors and NF-κB activation.

Conclusions

Our results demonstrated a protective effect of butyrate in limiting molecular events underlying the onset of IR and NAFLD, suggesting a potential clinical relevance for this substance. In particular, its derivative, FBA, could represent an alternative therapeutic option to sodium butyrate, sharing a comparable efficacy, but a better palatability and compliance.

Triterpenoid-Rich Fraction from Ilex hainanensis Merr. Attenuates Non-Alcoholic Fatty Liver Disease Induced by High Fat Diet in Rats

Non-alcoholic fatty liver disease (NAFLD) has become a major challenge to the healthcare system. This study was designed to evaluate the effect of the triterpenoid-rich fraction (TF) from Ilex hainanensis Merr. on NAFLD. Male Sprague-Dawley (SD) rats were fed a normal diet (control) or high fat diet (NAFLD model). After four weeks, the high fat diet group was orally administrated TF (250 mg/kg) for another two weeks. High fat diet fed rats displayed hyperlipidemia and a decline in liver function compared with control. However, administration with TF could effectively improve these symptoms, as demonstrated by decreasing the plasma levels of triglyceride (p <0.05), total cholesterol (p < 0.01), low-density lipoprotein cholesterol (p < 0.05), alanine transaminase (p < 0.05), aspartate aminotransferase (p < 0.01), liver index (p < 0.05) and insulin resistance index (p < 0.05) while increasing the high-density lipoprotein cholesterol (p < 0.05). Meanwhile, histopathological examination of livers also showed that TF could reduce the incidence of liver lesions induced by high fat diet. Furthermore, TF could alleviate oxidative stress and inflammation status indicated by the decline malondialdehyde and superoxide dismutase levels (p < 0.01, both) and levels of interleukin 6 and tumor necrosis factor-α (p < 0.05). In addition, immunohistochemistry showed TF evidently elevated the peroxisome proliferator-activated receptor (PPARα) expression (p < 0.01), while it diminished the Cytochrome P450 2E1 (CYP2E1) expression (p < 0.01) in liver. These results demonstrate that TF has potential ability to protect liver against NAFLD by regulating lipids metabolism and alleviating insulin resistance, inflammation and oxidative stress. This effect might be associated with regulating PPARα and CYP2E1 expression.

Rosiglitazone and bezafibrate modulate gene expression in a rat model of non-alcoholic fatty liver disease--a historical prospective

Background

Genetic factors implicated in the pathogenesis of non-alcoholic fatty liver disease are poorly understood. Our aim was to characterize three genes involved in a rat model of non-alcoholic fatty liver disease and investigate the effect of rosiglitazone and bezafibrate.

Method

Five rats were fed a chow diet (controls) and 18 a fructose-enriched diet (FED) for 5 weeks: 6 were administered rosiglitazone and 6 bezafibrate during the last 2 weeks and 6 were not treated at all. Livers were examined by reverse transcription-PCR for the genes encoding peroxisome proliferator-activated receptors (PPAR), PPAR-α, PPAR-γ, and Mn superoxide dismutase2 (Mn SOD2). Western blot was used for proteins levels.

Result

The FED rats showed a decrease in mRNA of MnSOD2, PPAR-α, and PPAR-γ (3, 3.5 fold, and 27%, respectively) (p<0.05). The 3 genes normalized in response to rosiglitazone and bezafibrate. The proteins of MnSOD2, PPAR-α and PPAR-γ in the FED rats decreased (2.5, 2, and 2.2, respectively) (p<0.05). Following administration of rosiglitazone, proteins of MnSOD2, PPAR-α and PPAR-γ in the FED rats increased (reaching 1.5-fold, a 20% increase and normalization, respectively), (p<0.05). Administration of bezafibrate to the FED rats restored the proteins of 3 genes to baseline.

Conclusion

A consistent reduction in hepatic expression of MnSOD2, PPAR-α and PPAR-γ in the FED rats compared with controls was observed. Administration of either rosiglitazone or bezafibrate to the FED rats restored these genes to a pre-morbid state.

Effect of V(IV)O(dipic-Cl)(H2O)2 on Lipid Metabolism Disorders in the Liver of STZ-Induced Diabetic Rats

Vanadium complexes are potent antidiabetic agents for therapeutical treatment of diabetes. In the present study, we investigated the hypolipidemic effect of V(IV)O(dipic-Cl)(H2O)2 (V4dipic-Cl) in liver of streptozotocin- (STZ-)-induced diabetic rats. We found that diabetic animals exhibited hepatic inflammatory infiltration and impaired liver function along with triglyceride (TG) accumulation in the liver. V4dipic-Cl treatment not only ameliorated liver pathological state but also reduced hepatic TG level. Moreover, the upregulation of fatty acid translocase (FAT/CD36) mRNA (4.0-fold) and protein (8.2-fold) levels in the liver of diabetic rats were significantly reversed after V4dipic-Cl treatment. However, no significant effects of V4dipic-Cl on the mRNA expression of fatty acid metabolism-related fatty acid bounding protein 1 (FABP1) and fatty acid transporter 5 (FATP5) were observed. These results suggest that the modification of lipid metabolism-related FAT/CD36 in the liver of diabetic rats is likely involved in the hypolipidemic effects of V4dipic-Cl.

Nordihydroguaiaretic acid improves metabolic dysregulation and aberrant hepatic lipid metabolism in mice by both PPARα-dependent and -independent pathways

Creosote bush-derived nordihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor, possesses antioxidant properties and functions as a potent antihyperlipidemic agent in rodent models. Here, we examined the effect of chronic NDGA treatment of ob/ob mice on plasma dyslipidemia, hepatic steatosis, and changes in hepatic gene expression. Feeding ob/ob mice a chow diet supplemented with either low (0.83 g/kg diet) or high-dose (2.5 g/kg diet) NDGA for 16 wk significantly improved plasma triglyceride (TG), inflammatory chemokine levels, hyperinsulinemia, insulin sensitivity, and glucose intolerance. NDGA treatment caused a marked reduction in liver weight and TG content, while enhancing rates of fatty acid oxidation. Microarray analysis of hepatic gene expression demonstrated that NDGA treatment altered genes for lipid metabolism, with genes involved in fatty acid catabolism most significantly increased. NDGA upregulated the mRNA and nuclear protein levels of peroxisome proliferator-activated receptor α (PPARα), and the activated (phosphorylated) form of AMP-activated kinase. NDGA increased PPARα promoter activity in AML12 hepatocytes and also prevented the fatty acid suppression of PPARα expression. In contrast, PPARα siRNA abrogated the stimulatory effect of NDGA on fatty acid catabolism. Likewise, no stimulatory effect of NDGA on hepatic fatty acid oxidation was observed in the livers of PPARα-deficient mice, but the ability of NDGA to reverse fatty liver conditions was unaffected. In conclusion, the beneficial actions of NDGA on dyslipidemia and hepatic steatosis in ob/ob mice are exerted primarily through enhanced fatty acid oxidation via PPARα-dependent pathways. However, PPARα-independent pathways also contribute to NDGA's action to ameliorate hepatic steatosis.

PPARs in Liver Diseases and Cancer: Epigenetic Regulation by MicroRNAs

Peroxisome-proliferator-activated receptors (PPARs) are ligand-activated nuclear receptors that exert in the liver a transcriptional activity regulating a whole spectrum of physiological functions, including cholesterol and bile acid homeostasis, lipid/glucose metabolism, inflammatory responses, regenerative mechanisms, and cell differentiation/proliferation. Dysregulations of the expression, or activity, of specific PPAR isoforms in the liver are therefore believed to represent critical mechanisms contributing to the development of hepatic metabolic diseases, disorders induced by hepatic viral infections, and hepatocellular adenoma and carcinoma. In this regard, specific PPAR agonists have proven to be useful to treat these metabolic diseases, but for cancer therapies, the use of PPAR agonists is still debated. Interestingly, in addition to previously described mechanisms regulating PPARs expression and activity, microRNAs are emerging as new important regulators of PPAR expression and activity in pathophysiological conditions and therefore may represent future therapeutic targets to treat hepatic metabolic disorders and cancers. Here, we reviewed the current knowledge about the general roles of the different PPAR isoforms in common chronic metabolic and infectious liver diseases, as well as in the development of hepatic cancers. Recent works highlighting the regulation of PPARs by microRNAs in both physiological and pathological situations with a focus on the liver are also discussed.

Fenofibrate decreases radiation sensitivity via peroxisome proliferator-activated receptor α-mediated superoxide dismutase induction in HeLa cells

Purpose

The fibrates are ligands for peroxisome proliferator-activated receptor (PPAR) α and used clinically as hypolipidemic drugs. The fibrates are known to cause peroxisome proliferation, enhance superoxide dismutase (SOD) expression and catalase activity. The antioxidant actions of the fibrates may modify radiation sensitivity. Here, we investigated the change of the radiation sensitivity in two cervix cancer cell lines in combination with fenofibrate (FF).

Materials and Methods

Activity and protein expression of SOD were measured according to the concentration of FF. The mRNA expressions were measured by using real time reverse-transcription polymerase chain reaction. Combined cytotoxic effect of FF and radiation was measured by using clonogenic assay.

Results

In HeLa cells total SOD activity was increased with increasing FF doses up to 30 µM. In the other hand, the catalase activity was increased a little. As with activity the protein expression of SOD1 and SOD2 was increased with increasing doses of FF. The mRNAs of SOD1, SOD2, PPARα and PPARγ were increased with increasing doses of FF. The reactive oxygen species (ROS) produced by radiation was decreased by preincubation with FF. The surviving fractions (SF) by combining FF and radiation was higher than those of radiation alone. In Me180 cells SOD and catalase activity were not increased with FF. Also, the mRNAs of SOD1, SOD2, and PPARα were not increased with FF. However, the mRNA of PPARγ was increased with FF.

Conclusion

FF can reduce radiation sensitivity by ROS scavenging via SOD induction in HeLa. SOD induction by FF is related with PPARα.

Additive effects of clofibric acid and pyruvate dehydrogenase kinase isoenzyme 4 (PDK4) deficiency on hepatic steatosis in mice fed a high saturated fat diet

Although improving glucose metabolism by inhibition of pyruvate dehydrogenase kinase 4 (PDK4) may prove beneficial in the treatment of type 2 diabetes or diet-induced obesity, it may have detrimental effects by inhibiting fatty acid oxidation. Peroxisome proliferator-activated receptor α (PPARα) agonists are often used to treat dyslipidemia in patients, especially in type 2 diabetes. Combinational treatment using a PDK4 inhibitor and PPARα agonists may prove beneficial. However, PPARα agonists may be less effective in the presence of a PDK4 inhibitor because PPARα agonists induce PDK4 expression. In the present study, the effects of clofibric acid, a PPARα agonist, on blood and liver lipids were determined in wild-type and PDK4 knockout mice fed a high-fat diet. As expected, treatment of wild-type mice with clofibric acid resulted in less body weight gain, smaller epididymal fat pads, greater insulin sensitivity, and lower levels of serum and liver triacylglycerol. Surprisingly, rather than decreasing the effectiveness of clofibric acid, PDK4 deficiency enhanced the beneficial effects of clofibric acid on hepatic steatosis, reduced blood glucose levels, and did not prevent the positive effects of clofibric acid on serum triacylglycerols and free fatty acids. The metabolic effects of clofibric acid are therefore independent of the induction of PDK4 expression. The additive beneficial effects on hepatic steatosis may be due to induction of increased capacity for fatty acid oxidation and partial uncoupling of oxidative phosphorylation by clofibric acid, and a reduction in the capacity for fatty acid synthesis as a result of PDK4 deficiency.

PPARα is down-regulated following liver transplantation in mice

BACKGROUND & AIMS

Graft dysfunction is one of the major complications after liver transplantation, but its precise mechanism remains unclear. Since steatotic liver grafts are susceptible to post-transplant dysfunction, and peroxisome proliferator-activated receptor (PPAR) α plays an important role in the maintenance of hepatic lipid homeostasis, we examined the role of PPARα in liver transplantation.

METHODS

Livers were harvested from Sv/129 wild-type (Ppara(+/+)) mice and PPARα-null (Ppara(-/-)) mice and transplanted orthotopically into syngeneic Ppara(+/+) mice.

RESULTS

Hepatocellular damage was unexpectedly milder in transplanted Ppara(-/-) livers compared with Ppara(+/+) ones. This was likely due to decreased lipid peroxides in the Ppara(-/-) livers, as revealed by the lower levels of fatty acid oxidation (FAO) enzymes, which are major sources of reactive oxygen species. Hepatic PPARα and its target genes, such as FAO enzymes and pyruvate dehydrogenase kinase 4, were strongly down-regulated after transplantation, which was associated with increases in hepatic tumor necrosis factor-α expression and nuclear factor-κB activity. Inhibiting post-transplant PPARα down-regulation by clofibrate treatment markedly augmented oxidative stress and hepatocellular injury.

CONCLUSIONS

Down-regulation of PPARα seemed to be an adaptive response to metabolic alterations following liver transplantation. These results provide novel information to the understanding of the pathogenesis of early post-transplant events.

Dyslipidemia in patients with nonalcoholic fatty liver disease

Patients with nonalcoholic fatty liver disease (NAFLD) often have dyslipidemia along with other features of metabolic syndrome such as obesity, diabetes mellitus, and hypertension. The dyslipidemia in NAFLD is characterized by increased serum triglycerides, increased small, dense low-density lipoprotein (LDL nontype A) particles, and low high-density lipoprotein (HDL) cholesterol. The pathogenesis of dyslipidemia in NAFLD is not well understood, but it is likely related to hepatic overproduction of the very low-density lipoprotein particles and dysregulated clearance of lipoproteins from the circulation. There is unequivocal evidence that cardiovascular disease is the most common cause of mortality in patients with NAFLD. Aggressive treatment of dyslipidemia plays a critical role in the overall management of patients with NAFLD. Statins are the first-line agents to treat high cholesterol and their dosage should be adjusted based on achieving therapeutic targets and tolerability. Although all statins appear to be effective in improving cholesterol levels in patients with NAFLD, there is more experience with atorvastatin in patients with NAFLD; furthermore, it is the only statin to date to show a reduced cardiovascular morbidity in patients with NAFLD. The risk for serious liver injury from statins is quite rare and patients with NAFLD are not at increased risk for statin hepatotoxicity. Omega-3 fatty acids are perhaps the first choice to treat hypertriglyceridemia because of their safety, tolerability, and efficacy in improving serum triglycerides, as well as their potential to improve liver disease.

Redox balance in the pathogenesis of nonalcoholic fatty liver disease: mechanisms and therapeutic opportunities

Nonalcoholic fatty liver disease (NAFLD) is currently the most common liver disease in the world. It encompasses a histological spectrum, ranging from simple, nonprogressive steatosis to nonalcoholic steatohepatitis (NASH), which may progress to cirrhosis and hepatocellular carcinoma. While liver-related complications are confined to NASH, emerging evidence suggests both simple steatosis and NASH predispose to type 2 diabetes and cardiovascular disease. The pathogenesis of NAFLD is currently unknown, but accumulating data suggest that oxidative stress and altered redox balance play a crucial role in the pathogenesis of steatosis, steatohepatitis, and fibrosis. We will examine intracellular mechanisms, including mitochondrial dysfunction and impaired oxidative free fatty acid metabolism, leading to reactive oxygen species generation; additionally, the potential pathogenetic role of extracellular sources of reactive oxygen species in NAFLD, including increased myeloperoxidase activity and oxidized low density lipoprotein accumulation, will be reviewed. We will discuss how these mechanisms converge to determine the whole pathophysiological spectrum of NAFLD, including hepatocyte triglyceride accumulation, hepatocyte apoptosis, hepatic inflammation, hepatic stellate cell activation, and fibrogenesis. Finally, available animal and human data on treatment opportunities with older and newer antioxidant will be presented.

Comprehensive analysis of PPARalpha-dependent regulation of hepatic lipid metabolism by expression profiling

PPARα is a ligand-activated transcription factor involved in the regulation of nutrient metabolism and inflammation. Although much is already known about the function of PPARα in hepatic lipid metabolism, many PPARα-dependent pathways and genes have yet to be discovered. In order to obtain an overview of PPARα-regulated genes relevant to lipid metabolism, and to probe for novel candidate PPARα target genes, livers from several animal studies in which PPARα was activated and/or disabled were analyzed by Affymetrix GeneChips. Numerous novel PPARα-regulated genes relevant to lipid metabolism were identified. Out of this set of genes, eight genes were singled out for study of PPARα-dependent regulation in mouse liver and in mouse, rat, and human primary hepatocytes, including thioredoxin interacting protein (Txnip), electron-transferring-flavoprotein β polypeptide (Etfb), electron-transferring-flavoprotein dehydrogenase (Etfdh), phosphatidylcholine transfer protein (Pctp), endothelial lipase (EL, Lipg), adipose triglyceride lipase (Pnpla2), hormone-sensitive lipase (HSL, Lipe), and monoglyceride lipase (Mgll). Using an in silico screening approach, one or more PPAR response elements (PPREs) were identified in each of these genes. Regulation of Pnpla2, Lipe, and Mgll, which are involved in triglyceride hydrolysis, was studied under conditions of elevated hepatic lipids. In wild-type mice fed a high fat diet, the decrease in hepatic lipids following treatment with the PPARα agonist Wy14643 was paralleled by significant up-regulation of Pnpla2, Lipe, and Mgll, suggesting that induction of triglyceride hydrolysis may contribute to the anti-steatotic role of PPARα. Our study illustrates the power of transcriptional profiling to uncover novel PPARα-regulated genes and pathways in liver.

PPARs, Obesity, and Inflammation

The worldwide prevalence of obesity and related metabolic disorders is rising rapidly, increasing the burden on our healthcare system. Obesity is often accompanied by excess fat storage in tissues other than adipose tissue, including liver and skeletal muscle, which may lead to local insulin resistance and may stimulate inflammation, as in steatohepatitis. In addition, obesity changes the morphology and composition of adipose tissue, leading to changes in protein production and secretion. Some of these secreted proteins, including several proinflammatory mediators, may be produced by macrophages resident in the adipose tissue. The changes in inflammatory status of adipose tissue and liver with obesity feed a growing recognition that obesity represents a state of chronic low-level inflammation. Various molecular mechanisms have been implicated in obesity-induced inflammation, some of which are modulated by the peroxisome proliferator-activated receptors (PPARs). PPARs are ligand-activated transcription factors involved in the regulation of numerous biological processes, including lipid and glucose metabolism, and overall energy homeostasis. Importantly, PPARs also modulate the inflammatory response, which makes them an interesting therapeutic target to mitigate obesity-induced inflammation and its consequences. This review will address the role of PPARs in obesity-induced inflammation specifically in adipose tissue, liver, and the vascular wall.

Peroxisome proliferator activated receptors and lipoprotein metabolism

Plasma lipoproteins are responsible for carrying triglycerides and cholesterol in the blood and ensuring their delivery to target organs. Regulation of lipoprotein metabolism takes place at numerous levels including via changes in gene transcription. An important group of transcription factors that mediates the effect of dietary fatty acids and certain drugs on plasma lipoproteins are the peroxisome proliferator activated receptors (PPARs). Three PPAR isotypes can be distinguished, all of which have a major role in regulating lipoprotein metabolism. PPARalpha is the molecular target for the fibrate class of drugs. Activation of PPARalpha in mice and humans markedly reduces hepatic triglyceride production and promotes plasma triglyceride clearance, leading to a clinically significant reduction in plasma triglyceride levels. In addition, plasma high-density lipoprotein (HDL)-cholesterol levels are increased upon PPARalpha activation in humans. PPARgamma is the molecular target for the thiazolidinedione class of drugs. Activation of PPARgamma in mice and human is generally associated with a modest increase in plasma HDL-cholesterol and a decrease in plasma triglycerides. The latter effect is caused by an increase in lipoprotein lipase-dependent plasma triglyceride clearance. Analogous to PPARalpha, activation of PPARbeta/delta leads to increased plasma HDL-cholesterol and decreased plasma triglyceride levels. In this paper, a fresh perspective on the relation between PPARs and lipoprotein metabolism is presented. The emphasis is on the physiological role of PPARs and the mechanisms underlying the effect of synthetic PPAR agonists on plasma lipoprotein levels.

Overweight induced by chronic risperidone exposure is correlated with overexpression of the SREBP-1c and FAS genes in mouse liver

Weight gain and metabolic disturbances, such as dyslipidemia and hyperglycaemia, are common side effects of most antipsychotic drugs, including risperidone. The aim of this study was to investigate the effects of chronic treatment with risperidone on body weight, fat accumulation, liver weight, and hepatic expression of key genes involved in lipid metabolism in female mice. We also addressed the mechanism of risperidone induction of metabolic side effects by exploring its effect on lipid and cholesterol metabolism in primary cultures of rat hepatocytes. Eleven weeks of treatment with long-acting risperidone (12.5 mpk/week) resulted in a significant weight gain associated with an increase of liver and adipose tissue weight. These effects were positively correlated with hepatic mRNA induction of two key genes involved in lipogenesis: sterol regulatory element binding protein-1c (SREBP-1c) and fatty acid synthase (FAS). Furthermore, in line with these in vivo results, risperidone elicited significant inductions of SREBP-1 maturation and FAS mRNA expression in primary cultures of rat hepatocytes associated with an increase of free fatty acid, triacylglycerol, and phospholipid synthesis as assessed by acetate incorporation. The current investigations underscore the usefulness of a mouse model to study the weight gain observed with risperidone treatment in humans. This study shows that risperidone induces similar effects in the liver (in vivo) and in hepatocyte cell cultures (in vitro) on the expression of key genes and/or proteins that control lipid metabolism. This suggests that risperidone could alter lipid metabolism in the liver and induce weight gain in a way that is partly independent of its action on the central nervous system.

Probiotics as an emerging therapeutic strategy to treat NAFLD: focus on molecular and biochemical mechanisms

Nonalcoholic fatty liver disease (NAFLD) is currently the most common liver disease worldwide, both in adults and in children. NAFLD is characterized by aberrant lipid storage in hepatocytes (hepatic steatosis) and inflammatory progression to nonalcoholic steatohepatitis. Evidences so far suggest that intrahepatic lipid accumulation does not always derive from obesity. Gut microbiota has been considered as a regulator of energy homeostasis and ectopic fat deposition, suggesting its implications in metabolic diseases. Probiotics are live microbial that alter the enteric microflora and have beneficial effects on human health. Although the molecular mechanisms of probiotics have not been completely elucidated yet, many of their effects have proved to be beneficial in NAFLD, including the modulation of the intestinal microbiota, an antibacterial substance production, an improved epithelial barrier function and a reduced intestinal inflammation. Given the close anatomical and functional correlation between the bowel and the liver, and the immunoregulatory effects elicited by probiotics, the aim of this review is to summarize today's knowledge about probiotics in NAFLD, focusing in particular on their molecular and biochemical mechanisms, as well as highlighting their efficacy as an emerging therapeutic strategy to treat this condition.

Bioinformatics-driven identification and examination of candidate genes for non-alcoholic fatty liver disease

Objective

Candidate genes for non-alcoholic fatty liver disease (NAFLD) identified by a bioinformatics approach were examined for variant associations to quantitative traits of NAFLD-related phenotypes.

Research Design and Methods

By integrating public database text mining, trans-organism protein-protein interaction transferal, and information on liver protein expression a protein-protein interaction network was constructed and from this a smaller isolated interactome was identified. Five genes from this interactome were selected for genetic analysis. Twenty-one tag single-nucleotide polymorphisms (SNPs) which captured all common variation in these genes were genotyped in 10,196 Danes, and analyzed for association with NAFLD-related quantitative traits, type 2 diabetes (T2D), central obesity, and WHO-defined metabolic syndrome (MetS).

Results

273 genes were included in the protein-protein interaction analysis and EHHADH, ECHS1, HADHA, HADHB, and ACADL were selected for further examination. A total of 10 nominal statistical significant associations (P<0.05) to quantitative metabolic traits were identified. Also, the case-control study showed associations between variation in the five genes and T2D, central obesity, and MetS, respectively. Bonferroni adjustments for multiple testing negated all associations.

Conclusions

Using a bioinformatics approach we identified five candidate genes for NAFLD. However, we failed to provide evidence of associations with major effects between SNPs in these five genes and NAFLD-related quantitative traits, T2D, central obesity, and MetS.

Comparison of dietary control and atorvastatin on high fat diet induced hepatic steatosis and hyperlipidemia in rats

Background

Treatment with atorvastatin (ATO) or dietary control has been demonstrated to benefit patients with non-alcoholic fatty liver disease (NAFLD) and hyperlipidemia. However, little is known on whether combination of dietary control and ATO treatment could enhance the therapeutic effect.

Methods

We employed a rat model of NAFLD to examine the therapeutic efficacy of dietary control and/or ATO treatment. Sprague-Dawley rats were fed with normal chow diet as normal controls or with high fat diet (HFD) for 12 weeks to establish NAFLD. The NAFLD rats were randomized and continually fed with HFD, with normal chow diet, with HFD and treated with 30 mg/kg of ATO or with normal chow diet and treated with the same dose of ATO for 8 weeks. Subsequently, the rats were sacrificed and the serum lipids, aminotranferase, hepatic lipids, and liver pathology were characterized. The relative levels of fatty acid synthesis and β-oxidation gene expression in hepatic tissues were measured by quantitative real-time polymerase chain reaction (qRT-PCR). Hepatic expression of hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase was determined by Western blot assay.

Results

While continual feeding with HFD deteriorated NAFLD and hyperlipidemia, treatment with dietary control, ATO or ATO with dietary control effectively improved serum and liver lipid metabolism and liver function. In comparison with ATO treatment, dietary control or combined with ATO treatment significantly reduced the liver weight and attenuated the HFD-induced hyperlipidemia and liver steatosis in rats. Compared to ATO treatment or dietary control, combination of ATO and dietary control significantly reduced the levels of serum total cholesterol and low density lipoprotein cholesterol (LDL-C). However, the combination therapy did not significantly improve triglyceride and free fatty acid metabolism, hepatic steatosis, and liver function, as compared with dietary control alone.

Conclusions

ATO treatment effectively improved NAFLD-related hyperlipidemia and inhibited liver steatosis, accompanied by modulating the expression of genes for regulating lipid metabolism. ATO enhanced the effect of dietary control on reducing the levels of serum total cholesterol and LDL-C, but not triglyceride, free fatty acid and hepatic steatosis in HFD-induced fatty liver and hyperlipidemia in rats.

Proteomic analysis of protein expression affected by peroxiredoxin V knock-down in hypoxic kidney

Peroxiredoxin V, an atypical thioredoxin peroxidase, is widely expressed in mammalian tissues. In addition, Prdx V is localized in mitochondria, peroxisome, cytosol, and the nucleus. Prdx V has been reported to protect a wide range of cellular environments as an antioxidant enzyme, and its dysfunctions may be implicated in several diseases, such as cancer, inflammation, and neurodegenerative disease. Identification and relative quantification of proteins affected by Prdx V may help identify novel signaling mechanisms that are important for oxidative stress response. However, the role of Prdx V in the modulation of hypoxia-related cellular response is not studied yet. To examine the function of endogenous Prdx V in hypoxic condition in vivo, we generated a transgenic mouse model with Prdx V siRNA expression controlled by U6 promoter. Of many tissues, the knockdown of Prdx V expression was displayed in the kidney, lung, and liver but not the spleen and skin. We conducted on the basis of nano-UPLC-MS(E) proteomic study to identify the Prdx V-affected protein networks in hypoxic kidneys. In this study, we identified protein networks associated with oxidative stress, fatty acid metabolism, and mitochondrial dysfunction. Our results indicated that Prdx V affected to regulation of kidney homeostasis under hypoxia stress.

Differential response to trichloroethylene-induced hepatosteatosis in wild-type and PPARalpha-humanized mice

BACKGROUND

Trichloroacetic acid, an oxidative metabolite of trichloroethylene (TRI), is a ligand of the peroxisome proliferator-activated receptor alpha (PPAR) alpha, which is involved in lipid homeostasis and anti-inflammation.

OBJECTIVE

We examined the role of mouse and human PPARalpha in TRI-induced hepatic steatosis and toxicity.

METHODS

Male wild-type (mPPARalpha), Pparalpha-null, and humanized PPARalpha (hPPARalpha) mice on an Sv/129 background were exposed via inhalation to 0, 1,000, and 2,000 ppm TRI for 8 hr/day for 7 days. We assessed TRI-induced steatosis or hepatic damage through biochemical and histopathological measurements.

RESULTS

Plasma alanine aminotransferase and aspartate aminotransferase activities increased in all mouse lines after exposure to 1,000 and 2,000 ppm TRI. Exposure induced hepatocyte necrosis and inflammatory cells in all mouse lines, but hepatic lipid accumulation was observed only in Pparalpha-null and hPPARalpha mice. No differences were observed in TRI-mediated induction of hepatic PPARalpha target genes except for a few genes that differed between mPPARalpha and hPPARalpha mice. However, TRI significantly increased expression of triglyceride (TG)-synthesizing enzymes, diacyl-glicerol acyltransferases, and PPARgamma in Pparalpha-null and hPPARalpha mice, which may account for the increased TG in their livers. TRI exposure elevated nuclear factor-kappa B (NFkappaB) p52 mRNA and protein in all mice regardless of PPARalpha genotype.

CONCLUSIONS

NFkappaB-p52 is a candidate molecular marker for inflammation caused by TRI, and PPARalpha may be involved in TRI-induced hepatosteatosis. However, human PPARalpha may afford only weak protection against TRI-mediated effects compared with mouse PPARalpha.