Serum fatty acid synthase concentration is increased in patients with hepatitis viral infection and may assist in the prediction of liver steatosis

Interplay between Lipid Metabolism, Lipid Droplets, and DNA Virus Infections

Lipid droplets (LDs) are cellular organelles rich in neutral lipids such as triglycerides and cholesterol esters that are coated by a phospholipid monolayer and associated proteins. LDs are known to play important roles in the storage and availability of lipids in the cell and to serve as a source of energy reserve for the cell. However, these structures have also been related to oxidative stress, reticular stress responses, and reduced antigen presentation to T cells. Importantly, LDs are also known to modulate viral infection by participating in virus replication and assembly. Here, we review and discuss the interplay between neutral lipid metabolism and LDs in the replication cycle of different DNA viruses, identifying potentially new molecular targets for the treatment of viral infections.

Nonalcoholic Fatty Liver Disease: Focus on New Biomarkers and Lifestyle Interventions

Nonalcoholic fatty liver disease (NAFLD) is considered a hepatic manifestation of metabolic syndrome, characterized from pathological changes in lipid and carbohydrate metabolism. Its main characteristics are excessive lipid accumulation and oxidative stress, which create a lipotoxic environment in hepatocytes leading to liver injury. Recently, many studies have focused on the identification of the genetic and epigenetic modifications that also contribute to NAFLD pathogenesis and their prognostic implications. The present review is aimed to discuss on cellular and metabolic alterations associated with NAFLD, which can be helpful to identify new noninvasive biomarkers. The identification of accumulated lipids in the cell membranes, as well as circulating cytokeratins and exosomes, provides new insights in understanding of NAFLD. This review also suggests that lifestyle modifications remain the main prevention and/or treatment for NAFLD.

Plasma Energy-Balance Metabolites Discriminate Asymptomatic Patients with Peripheral Artery Disease

Peripheral artery disease (PAD) is a common disease affecting 20-25% of population over 60 years old. Early diagnosis is difficult because symptoms only become evident in advanced stages of the disease. Inflammation, impaired metabolism, and mitochondrial dysfunction predispose to PAD, which is normally associated with other highly prevalent and related conditions, such as diabetes, dyslipidemia, and hypertension. We have measured energy-balance-associated metabolite concentrations in the plasma of PAD patients segregated by the severity of the disease and in plasma of healthy volunteers using a quantitative and targeted metabolomic approach. We found relevant associations between several metabolites (3-hydroxybutirate, aconitate, (iso)citrate, glutamate, and serine) with markers of oxidative stress and inflammation. Metabolomic profiling also revealed that (iso)citrate and glutamate are metabolites with high ability to discriminate between healthy participants and PAD patients without symptoms. Collectively, our data suggest that metabolomics provide significant information on the pathogenesis of PAD and useful biomarkers for the diagnosis and assessment of progression.

Fatty acid synthase (FASN) as a therapeutic target in breast cancer

INTRODUCTION

Ten years ago, we put forward the metabolo-oncogenic nature of fatty acid synthase (FASN) in breast cancer. Since the conception of this hypothesis, which provided a model to explain how FASN is intertwined with various signaling networks to cell-autonomously regulate breast cancer initiation and progression, FASN has received considerable attention as a therapeutic target. However, despite the ever-growing evidence demonstrating the involvement of FASN as part of the cancer-associated metabolic reprogramming, translation of the basic science-discovery aspects of FASN blockade to the clinical arena remains a challenge. Areas covered: Ten years later, we herein review the preclinical lessons learned from the pharmaceutical liabilities of the first generation of FASN inhibitors. We provide an updated view of the current development and clinical testing of next generation FASN-targeted drugs. We also discuss new clinico-molecular approaches that should help us to convert roadblocks into roadways that will propel forward our therapeutic understanding of FASN. Expert opinion: With the recent demonstration of target engagement and early signs of clinical activity with the first orally available, selective, potent and reversible FASN inhibitor, we can expect Big pharma to revitalize their interest in lipogenic enzymes as well-credentialed targets for oncology drug development in breast cancer.

Lipids and RNA virus replication

Most viruses rely heavily on their host machinery to successfully replicate their genome and produce new virus particles. Recently, the interaction of positive-strand RNA viruses with the lipid biosynthetic and transport machinery has been the subject of intense investigation. In this review, we will discuss the contribution of various host lipids and related proteins in RNA virus replication and maturation.

Pathogenesis and significance of hepatitis C virus steatosis: An update on survival strategy of a successful pathogen

Hepatitis C virus (HCV) is a successful pathogen on the grounds that it exploits its host’s metabolism to build up viral particles; moreover it favours its own survival by inducing chronic disease and the development of specific anatomic changes in the infected organ. Steatosis, therefore, is associated with HCV infection by necessity rather than by chance alone. Approximately 6% of HCV patients have steatohepatitis. Interestingly, HCV steatosis occurs in the setting of multiple metabolic abnormalities (hyperuricemia, reversible hypocholesterolemia, insulin resistance, arterial hypertension and expansion of visceral adipose tissue) collectively referred to as “hepatitis C-associated dysmetabolic syndrome” (HCADS). General, nonalcoholic fatty liver disease (NAFLD)-like, mechanisms of steatogenesis (including increased availability of lipogenic substrates and de novo lipogenesis; decreased oxidation of fatty substrates and export of fatty substrates) are shared by all HCV genotypes. However, genotype 3 seemingly amplifies such steatogenic molecular mechanisms reported to occur in NAFLD via more profound changes in microsomal triglyceride transfer protein; peroxisome proliferator-activated receptor alpha; sterol regulatory element-binding proteins and phosphatase and tensin homologue. HCV steatosis has a remarkable clinical impact in as much as it is an acknowledged risk factor for accelerated fibrogenesis; for impaired treatment response to interferon and ribavirin; and development of hepatocellular carcinoma. Recent data, moreover, suggest that HCV-steatosis contributes to premature atherogenesis via both direct and indirect mechanisms. In conclusion, HCV steatosis fulfills all expected requirements necessary to perpetuate the HCV life cycle. A better understanding of the physiology of HCADS will likely result in a more successful handling of disease with improved antiviral success rates.

Modulation of fatty acid synthase enzyme activity and expression during hepatitis C virus replication

The hepatitis C virus (HCV) induces alterations of host cells to facilitate its life cycle. Fatty acid synthase (FASN) is a multidomain enzyme that plays a key role in the biosynthesis of fatty acids and is upregulated during HCV infection. Herein, we applied activity-based protein profiling (ABPP) that allows for the identification of differentially active enzymes in complex proteomic samples, to study the changes in activity of FASN during HCV replication. For this purpose, we used an activity-based probe based on the FASN inhibitor Orlistat, and observed an increase in the activity of FASN in the presence of a subgenomic and a genomic HCV replicon as well as in chimeric SCID/Alb-uPA mice infected with HCV genotype 1a. To study the molecular basis for this increase in FASN activity, we overexpressed individual HCV proteins in Huh7 cells and observed increased expression and activity of FASN in the presence of core and NS4B, as measured by western blots and ABPP, respectively. Triglyceride levels were also elevated in accordance with FASN expression and activity. Lastly, immunofluorescence and ABPP imaging analyses demonstrated that while the abundance and activity of FASN increases significantly in the presence of HCV, its localization does not change. Together these data suggest that the HCV-induced production of fatty acids and neutral lipids is provided by an increase in FASN abundance and activity that is sufficient to allow HCV propagation without transporting FASN to the replication complexes.

Differential regulation of host genes including hepatic fatty acid synthase in HBV-transgenic mice

Hepatitis B virus (HBV) is the most common of the hepatitis viruses that cause chronic liver infections in humans, and it is considered to be a major global health problem. To gain a better understanding of HBV pathogenesis, and identify novel putative targets for anti-HBV therapy, this study was designed to elucidate the differential expression of host proteins in liver tissue from HBV-transgenic mice. Liver samples from two groups, (1) HBV-transgenic (Tg) mice, (2) corresponding background normal mice, wild-type (WT) mice, were collected and subjected to iTRAQ and mass spectrometry analysis. In total, 1950 unique proteins were identified, and 68 proteins were found to be differentially expressed in HBV-Tg mice as compared with that in WT mice. Several differentially expressed proteins were further validated by real-time quantitative RT-PCR, Western blot and immunohistochemical analysis. Furthermore, the association of HBV replication with fatty acid synthase (FASN), one of the highly expressed proteins in HBV-Tg mice, was verified. Silencing of FASN expression in HepG2.2.15 cells suppressed viral replication through the IFN signaling pathway, and some downstream antiviral effectors. The implicated role of FASN in HBV replication provides an opportunity to test existing compounds against FASN for adjuvant therapy and/or treatment of HBV replication.

Hepatitis C virus replication is modulated by the interaction of nonstructural protein NS5B and fatty acid synthase

Hepatitis C virus (HCV) nonstructural protein 5B (NS5B) is an RNA-dependent RNA polymerase (RdRp) that acts as a key player in the HCV replication complex. Understanding the interplay between the viral and cellular components of the HCV replication complex could provide new insight for prevention of the progression of HCV-associated hepatocellular carcinoma (HCC). In this study, the NS5B protein was used as the bait in a pulldown assay to screen for NS5B-interacting proteins that are present in Huh7 hepatoma cell lysates. After mass spectrophotometric analysis, fatty acid synthase (FASN) was found to interact with NS5B. Coimmunoprecipitation and double staining assays further confirmed the direct binding between NS5B and FASN. The domain of NS5B that interacts with FASN was also determined. Moreover, FASN was associated with detergent-resistant lipid rafts and colocalized with NS5B in active HCV replication complexes. In addition, overexpression of FASN enhanced HCV expression in Huh7/Rep-Feo cells, while transfection of FASN small interfering RNA (siRNA) or treatment with FASN-specific inhibitors decreased HCV replication and viral production. Notably, FASN directly increased HCV NS5B RdRp activity in vitro. These results together indicate that FASN interacts with NS5B and modulates HCV replication through a direct increase of NS5B RdRp activity. FASN may thereby serve as a target for the treatment of HCV infection and the prevention of HCV-associated HCC progression.

Lipoprotein receptors and lipid enzymes in hepatitis C virus entry and early steps of infection

Viruses are obligate intracellular agents that depend on host cells for successful propagation, hijacking cellular machineries to their own profit. The molecular interplay between host factors and invading viruses is a continuous coevolutionary process that determines viral host range and pathogenesis. The hepatitis C virus (HCV) is a strictly human pathogen, causing chronic liver injuries accompanied by lipid disorders. Upon infection, in addition to protein-protein and protein-RNA interactions usual for such a positive-strand RNA virus, HCV relies on protein-lipid interactions at multiple steps of its life cycle to establish persistent infection, making use of hepatic lipid pathways. This paper focuses on lipoproteins in HCV entry and on receptors and enzymes involved in lipid metabolism that HCV exploits to enter hepatocytes.

Metformin: a cheap and well-tolerated drug that provides benefits for viral infections

OBJECTIVES

Insulin resistance in viral infections is common. We have explored the effectiveness of metformin for alleviating insulin resistance in HIV-infected patients and assessed the relevance of the ataxia-telangiectasia mutated (ATM) rs11212617 variant in the clinical response with the rationale that metformin modulates cellular bioenergetics in an ATM-dependent process.

METHODS

HIV-infected patients (n = 385) were compared with controls recruited from the general population (n = 300) with respect to the genotype distribution of the ATM rs11212617 variant and its influence on selected metabolic and inflammatory variables. We also followed up a subset of male patients with HIV and hepatitis C virus (HCV) coinfection (n = 47) who were not receiving antiviral treatment and for whom metformin was prescribed for insulin resistance, which tends to have a higher incidence and severity in coinfected patients.

RESULTS

Among the HIV-infected patients, human cytomegalovirus (91.9%) and HCV (62.3%) coinfections were frequent. Selected metabolic and/or inflammatory variables were significantly altered in infected patients. Treatment with metformin in HIV and HCV coinfected patients was well tolerated and significantly increased the sensitivity of peripheral tissues to insulin. The minor allele (C) of the rs11212617 variant was associated with treatment success and may affect the course of insulin resistance in response to metformin (odds ratio 1.21; 95% confidence interval 1.07-1.39; P = 0.005). There were no differences between treated and untreated patients in viral loads or variables measuring immune defence, indicating that toxicity is unlikely.

CONCLUSIONS

We provide novel data suggesting that identification of the ATM rs11212617 variant may be important in assessing the glycaemic response to metformin treatment for insulin resistance in HIV-infected patients.

Increased serum levels of lipogenic enzymes in patients with severe liver steatosis

Background

Lipid metabolism is altered in subjects with liver steatosis. FAS is a key enzyme in de novo lipogenesis and both FAS gene expression and enzymatic activity are primarily regulated by metabolic signals in the liver. Lipoprotein lipase (LPL), the rate-limiting enzyme for the hydrolysis of core triglycerides, plays a pivotal role in lipid metabolism. This study aims to investigate if circulating levels of FAS and LPL could be clinically associated with liver steatosis.

Methods

In this work, we present data obtained from a subsample of 94 subjects with liver steatosis enrolled by NUTRIEPA study, a nutritional trial in subjects with liver steatosis. Serum levels of FAS protein and LPL activity were evaluated by ELISA test and by a fluorescent method, respectively. The diagnosis and the degree of liver steatosis were based on laboratory and ecographic measurements. Statistical methods included Kruskal-Wallis analysis of variance and Wilcoxon signed-rank test, where appropriate. The χ² test has been performed to analyse categorical variables.

Results

The subjects with severe steatosis had significantly higher serum levels of FAS protein and LPL activity compared to subjects with mild and moderate liver steatosis. Moreover, a positive trend in serum levels of FAS expression from lower to higher degree of steatosis was also detected.

Conclusions

We describe a relationship between human liver steatosis and elevated levels of circulating lipogenic enzymes. Increased serum levels of FAS expression and LPL activity could be considered a marker of severe liver steatosis.

Plant-derived polyphenols regulate expression of miRNA paralogs miR-103/107 and miR-122 and prevent diet-induced fatty liver disease in hyperlipidemic mice

BACKGROUND

MicroRNAs have the potential for clinical application. Probable modulation by plant-derived polyphenols might open preventive measures using simple dietary recommendations.

METHODS

We assessed the ability of continuous administration of high-dose polyphenols to modulate hepatic metabolism and microRNA expression in diet-induced fatty liver disease in commercially available hyperlipidemic mice using well-established and accepted procedures that included the development of new antibodies against modified quercetin.

RESULTS

Weight gain, liver steatosis, changes in the composition of liver tissue, and insulin resistance were all attenuated by the continuous administration of polyphenols. We also demonstrated that metabolites of polyphenols accumulate in immune cells and at the surface of hepatic lipid droplets indicating not only bioavailability but a direct likely action on liver cells. The addition of polyphenols also resulted in changes in the expression of miR-103, miR-107 and miR-122.

CONCLUSIONS

Polyphenols prevent fatty liver disease under these conditions. The differential expression of mRNAs and miRNAs was also associated with changes in lipid and glucose metabolism and with the activation of 5'-adenosine monophosphate-activated protein kinase, effects that are not necessarily connected. miRNAs function via different mechanisms and miRNA-mRNA interactions are difficult to ascertain with current knowledge. Further, cell models usually elicit contradictory results with those obtained in animal models.

GENERAL SIGNIFICANCE

Our data indicate that plant-derived polyphenols should be tested in humans as preventive rather than therapeutic agents in the regulation of hepatic fatty acid utilization. A multi-faceted mechanism of action is likely and the regulation of liver miRNA expression blaze new trails in further research.

Hepatitis B virus infection and fatty liver in the general population

BACKGROUND & AIMS

In animal studies, expression of hepatitis B virus (HBV) proteins causes hepatic steatosis. We aimed to study the prevalence of fatty liver in people with and without HBV infection in the general population.

METHODS

We performed a cross-sectional population study in Hong Kong Chinese. Intrahepatic triglyceride content (IHTG) was measured by proton-magnetic resonance spectroscopy.

RESULTS

One thousand and thirteen subjects (91 HBV patients and 922 controls) were recruited. The median IHTG was 1.3% (0.2-33.3) in HBV patients and 2.1% (0-44.2) in controls (p <0.001). Excluding subjects with significant alcohol consumption, the prevalence of nonalcoholic fatty liver disease was 13.5% (95% confidence interval [CI] 6.4%, 20.6%) in HBV patients and 28.3% (95% CI 25.3%, 31.2%) in controls (p=0.003). The fatty liver prevalence differed in HBV patients and controls aged 40-59 years but was similar in those aged 60 years or above. After adjusting for demographic and metabolic factors, HBV infection remained an independent factor associated with lower risk of fatty liver (adjusted odds ratio 0.42; 95% CI 0.20, 0.88; p=0.022). HBV patients also had a lower prevalence of metabolic syndrome (11.0% vs. 20.2%; p=0.034), but the difference was mainly attributed to lower triglyceride levels. Among HBV patients, viral genotypes, HBV DNA level and hepatitis B e antigen status were not associated with fatty liver.

CONCLUSIONS

HBV infection is associated with a lower prevalence of fatty liver, hypertriglyceridemia and metabolic syndrome. Viral replication may affect lipid metabolism and this warrants further studies.