Exposure to an environmentally relevant mixture of organochlorine compounds and polychlorinated biphenyls Promotes hepatic steatosis in male Ob/Ob mice

Hepatic steatosis is recognized as an independent risk factor for the development of cardiovascular disease. While obesity and type 2 diabetes are well-established risk factors in the development of hepatic steatosis, recent studies have revealed exposure to mixtures of persistent organic pollutants (POPs), which are environmental contaminants in various fatty foods, can promote steatosis. Thus, the present study was designed to determine if exposure to a defined mixture of prevalent polychlorinated biphenyls (PCBs) and organochlorine (OC) pesticides or their metabolites promote hepatic steatosis in a genetically induced model of type 2 diabetes, the leptin-deficient ob/ob mouse. Male C57BL/6J wild type (WT) or ob/ob mice were administered an environmentally relevant mixture of PCBs and OCs for 7 weeks via oral gavage. Exposure to POPs did not significantly alter fasting serum glucose or insulin levels. However, POPs exposure significantly increased hepatic triglyceride content in ob/ob animals, while decreasing serum triglyceride levels. This POPs-mediated increase in hepatic triglyceride content did not appear to be associated with significantly increased inflammation in either the liver or adipose. Exposure to POPs significantly induced the expression of cytochrome P450 3a11 in WT animals, yet the expression of this cytochrome was significantly downregulated in ob/ob animals regardless of POPs exposure. Taken together, the present data indicate exposure to an environmentally relevant mixture of both PCBs and OC pesticides in ob/ob mice promotes hepatic steatosis while decreasing hypertriglyceridemia, which demonstrates exposure to a defined mixture of POPs alters systemic lipid metabolism in a genetically induced model of obesity and type 2 diabetes. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1399-1411, 2017.

Alcohol-related changes in the intestinal microbiome influence neutrophil infiltration, inflammation and steatosis in early alcoholic hepatitis in mice

Background

Alcohol-induced intestinal dysbiosis disrupts homeostatic gut-liver axis function and is essential in the development of alcoholic liver disease. Here, we investigate changes in enteric microbiome composition in a model of early alcoholic steatohepatitis and dissect the pathogenic role of intestinal microbes in alcohol-induced liver pathology.

Materials and methods

Wild type mice received a 10-day diet that was either 5% alcohol-containing or an isocaloric control diet plus a single binge. 16S rDNA sequencing defined the bacterial communities in the cecum of alcohol- and pair-fed animals. Some mice were treated with an antibiotic cocktail prior to and throughout alcohol feeding. Liver neutrophils, cytokines and steatosis were evaluated.

Results

Acute-on-chronic alcohol administration induced shifts in various bacterial phyla in the cecum, including increased Actinobacteria and a reduction in Verrucomicrobia driven entirely by a reduction in the genus Akkermansia. Antibiotic treatment reduced the gut bacterial load and circulating bacterial wall component lipopolysaccharide (LPS). We found that bacterial load suppression prevented alcohol-related increases in the number of myeloperoxidase- (MPO) positive infiltrating neutrophils in the liver. Expression of liver mRNA tumor necrosis factor alpha (Tnfα), C-X-C motif chemokine ligand 1 (Cxcl1) and circulating protein monocyte chemoattractant protein-1 (MCP-1) were also reduced in antibiotic-treated alcohol-fed mice. Alcohol-induced hepatic steatosis measured by Oil-Red O staining was significantly reduced in antibiotic treated mice. Genes regulating lipid production and storage were also altered by alcohol and antibiotic treatment. Interestingly, antibiotic treatment did not protect from alcohol-induced increases in serum aminotransferases (ALT/AST).

Conclusions

Our data indicate that acute-on-chronic alcohol feeding alters the microflora at multiple taxonomic levels and identifies loss of Akkermansia as an early marker of alcohol-induced gut dysbiosis. We conclude that gut microbes influence liver inflammation, neutrophil infiltration and liver steatosis following alcohol consumption and these data further emphasize the role of the gut-liver axis in early alcoholic liver disease.

Deficiency of CKIP-1 aggravates high-fat diet-induced fatty liver in mice

Casein kinase 2 interacting protein-1(CKIP-1) is widely expressed in a variety of tissues and cells, and plays an important role in various critical cellular and physiological processes including cell growth, apoptosis, differentiation, cytoskeleton and bone formation. Here, we found: (1) CKIP-1 deficient mice exhibited increased body weight, liver weight, number and size of lipid droplets, and TG content comparing with WT mice after being exposed to high fat diet (HFD); (2) the levels of serum insulin, liver glycogen, phosphorylated C-Jun-N-terminal kinase-1 (pJNK1) and phosphorylated insulin receptor substrate -1(pIRS1) in CKIP-1^-/- mice were higher than those of WT mice; (3) CKIP-1 interacted with JNK1 in vitro. Our results indicate that CKIP-1 deficiency in mice aggravates HFD-induced fatty liver by upregulating JNK1 phosphorylation and further upregulating IRS-1 phosphorylation and RI.

Fatty liver and drugs: the two sides of the same coin

Drug-induced liver injury (DILI) is a common and underestimated cause of liver disease. Several drugs and other xenobiotics can be the cause of different clinicopathologic patterns of liver disease. Steatosis and steatohepatitis are rare but well-documented types of DILI. Over the past decades commonly used drugs like amiodarone, tamoxifen, irinotecan, methotrexate, valproic acid and glucocorticoids have been recognized to be associated with steatosis. Even though the pathophysiological pathways are still only partially understood, inhibition of mitochondrial beta-oxidation, reduced very low-density lipoprotein secretion, insulin resistance induction and increased de novo synthesis or increased liver uptake of fatty acids are considered the main pathogenic mechanisms through which drugs can lead to hepatic steatosis. On the other hand, fatty liver itself is a very common clinical condition, and there is a growing awareness of the potential risk factors for DILI due to the underlying metabolic condition itself.

Bisphenol a induces steatosis in HepaRG cells using a model of perinatal exposure

Human exposure to bisphenol A (BPA) could favor obesity and related metabolic disorders such as hepatic steatosis. Investigations in rodents have shown that these deleterious effects are observed not only when BPA is administered during the adult life but also with different protocols of perinatal exposure. Whether perinatal BPA exposure could pose a risk in human is currently unknown, and thus appropriate in vitro models could be important to tackle this major issue. Accordingly, we determined whether long-term BPA treatment could induce steatosis in human HepaRG cells by using a protocol mimicking perinatal exposure. To this end, the kinetics of expression of seven proteins differentially expressed during liver development was determined during a 4-week period of cell culture required for proliferation and differentiation. By analogy with data reported in rodents and humans, our results indicated that the period of cell culture around day 15 and day 18 after seeding could be considered as the "natal" period. Consequently, HepaRG cells were treated for 3 weeks with BPA (from 0.2 to 2000 nM), with a treatment starting during the proliferating period. BPA was able to induce steatosis with a nonmonotonic dose response profile, with significant effects on neutral lipids and triglycerides observed for the 2 nM concentration. However, the expression of many enzymes involved in lipid and carbohydrate homeostasis was unchanged in exposed HepaRG cells. The expression of other potential BPA targets and enzymes involved in BPA biotransformation was also determined, giving answers as well as new questions regarding the mechanisms of action of BPA. Hence, HepaRG cells provide a valuable model that can prove useful for the toxicological assessment of endocrine disruptors on hepatic metabolisms, in particular in the developing liver. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1024-1036, 2017.

Using In Vitro High-Throughput Screening Data for Predicting Benzo[k]Fluoranthene Human Health Hazards

Today there are more than 80,000 chemicals in commerce and the environment. The potential human health risks are unknown for the vast majority of these chemicals as they lack human health risk assessments, toxicity reference values, and risk screening values. We aim to use computational toxicology and quantitative high-throughput screening (qHTS) technologies to fill these data gaps, and begin to prioritize these chemicals for additional assessment. In this pilot, we demonstrate how we were able to identify that benzo[k]fluoranthene may induce DNA damage and steatosis using qHTS data and two separate adverse outcome pathways (AOPs). We also demonstrate how bootstrap natural spline-based meta-regression can be used to integrate data across multiple assay replicates to generate a concentration-response curve. We used this analysis to calculate an in vitro point of departure of 0.751 μM and risk-specific in vitro concentrations of 0.29 μM and 0.28 μM for 1:1,000 and 1:10,000 risk, respectively, for DNA damage. Based on the available evidence, and considering that only a single HSD17B4 assay is available, we have low overall confidence in the steatosis hazard identification. This case study suggests that coupling qHTS assays with AOPs and ontologies will facilitate hazard identification. Combining this with quantitative evidence integration methods, such as bootstrap meta-regression, may allow risk assessors to identify points of departure and risk-specific internal/in vitro concentrations. These results are sufficient to prioritize the chemicals; however, in the longer term we will need to estimate external doses for risk screening purposes, such as through margin of exposure methods.

Dietary Macronutrient Composition Directs ChREBP Isoform Expression and Glucose Metabolism in Mice

Carbohydrate response element binding protein (ChREBP) is a lipogenic transcription factor that is thought to be involved in the development of hepatic steatosis and insulin resistance. Increased ChREBP expression in liver results in increased hepatic steatosis, and the isoform ChREBPβ in adipose tissue can predict insulin sensitivity in obese humans. As ChREBP is activated by glucose, it was postulated that the composition of diet would regulate ChREBP isoform expression in metabolically relevant tissues.

We compared the effects of diets with high complex carbohydrate, high fat, or a normal chow on ChREBP expression and metabolic parameters in C57BL/6 mice. We found that diets high in fat decrease ChREBP expression in adipose tissue, but isocaloric diets high in carbohydrate have no effect. Interestingly, this decrease in adipose ChREBP was associated with increased inflammatory markers. In the same animals a high carbohydrate diet induced a robust increase in hepatic ChREBPβ expression (≈2-fold; p = 0.0002), but little detectable change in the more abundant ChREBPα transcript. This change was accompanied by increased expression of target genes liver pyruvate kinase (p<0.0001), acetyl-CoA carboxylase (p = 0.0191) and stearoyl-CoA desaturase-1 (p = 0.0045). This increase in ChREBP expression was associated with increased hepatic steatosis, despite no changes in body weight or body fat when compared to chow-fed mice. Unexpectedly, mice fed a high carbohydrate diet displayed enhanced sensitivity to exogenous insulin, despite having mild glucose intolerance and increased liver steatosis.

In summary, we have shown the composition of diet can selectively regulate ChREBP isoform expression in a tissue specific manner. Furthermore, we have shown a high complex carbohydrate diet selectively increases hepatic ChREBPβ expression, which associates with hepatic steatosis but not insulin resistance. In contrast, a high fat diet reduces adipose ChREBP, which associates with inflammation and insulin resistance.

Curcumin inhibits hyperlipidemia and hepatic fat accumulation in high-fructose-fed male Wistar rats

CONTEXT

Curcumin, an active principal of Curcuma longa Linn. (Zingiberaceae), has potent antioxidant and anti-inflammatory properties.

OBJECTIVES

This study investigated the effects of curcumin on hyperlipidemia and hepatic steatosis in high-fructose-fed Wistar rats.

MATERIALS AND METHODS

Forty male Wistar rats were divided into four groups with 10 rats in each. Two groups were fed with standard rodent diet and the other two with 60% high-fructose diet for 10 weeks. Curcumin (200 mg/kg body weight) was administered along with the diets simultaneously to each of the aforementioned diet groups. After 10 weeks of experiment, blood samples were collected from tail vein. Liver, adipose and epididymal tissues were collected after sacrifice of the animals and stored for further analyses.

RESULTS

Administration of curcumin reduced body weight (280.6 ± 7.4 g), liver weight (2.5 ± 0.2 g/100 g BW), adipose weight (1.4 ± 0.3 g/100 g BW), plasma levels of TAG (86.1 ± 13.5 mg/dL), VLDL-C (17.2 ± 2.7 mg/dL), lipid ratios and increased HDL-C (28.4 ± 4.5 mg/dL) in fructose-fed rats. Curcumin supplementation significantly lowered TAG content and decreased the protein expression of LXR-α (43%) and SREBP1c (59%) in the liver. Furthermore, curcumin suppressed the expression of lipogenic enzymes, ACLY (95%), ACC (50%) and FAS (77%) in rats fed with high-fructose diet. No significant change was found in the expression of PPAR-α.

DISCUSSION AND CONCLUSION

Curcumin prevented the high-fructose induced hyperlipidemia and hepatic steatosis.

Silymarin improved diet-induced liver damage and insulin resistance by decreasing inflammation in mice

CONTEXT

Silymarin is the main flavonoid extracted from milk thistle, which has been used to treat liver diseases.

OBJECTIVE

The in vivo effect of silymarin on HFD-induced insulin resistance and fatty liver in mice was studied.

MATERIALS AND METHODS

Male C57BL/6 mice were fed with high-fat diet (HFD) to induce obesity and insulin resistance and treated with 30, 60 mg/kg silymarin for 18 days. Food intake, body weight and the content/histology of epididymal fat and liver tissue were examined; the content of lipids, AST, ALT and inflammatory cytokines in serum were estimated.

RESULTS

Administration of silymarin caused bodyweight loss in diet induced obesity (DIO) mice (HFD group: 47.7 g, 60 mg/kg group: 43.0 g) while the food intake remain unchanged. Silymarin (60 mg/kg) significantly reduced the epididymal fat mass (from 1.75 g to 1.12 g). Elevated plasma lipids (TC 6.1 mM, TG 1.3 mM, LDL 1.2 mM) in DIO mice were all suppressed by silymarin (TC 4.5 mM, TG 0.89 mM, LDL 0.9 mM), as well as insulin (5.1 ng/ml in HFD group to 2.0 ng/ml (60 mg/kg silymarin). Examination of cytokine levels (TNF-α, IL-1β and IL-6) in each group proved that silymarin treatment significantly decreased inflammation in DIO mice. Finally, silymarin effectively protected liver from HFD-induced injury as evidenced by decreasing histological damage and reducing ALT and AST levels, as follows: ALT; 47.4 U/L in HFD group to 28.4 U/L (60 mg/kg silymarin); AST; 150.1 U/L in HFD group to 88.1 U/L (60 mg/kg silymarin) in serum.

DISCUSSION AND CONCLUSION

Our results suggested that silymarin-induced alleviation of inflammatory response could be a mechanism responsible for its benefits against liver damage and insulin resistance.

Microvesicular Steatosis Induced by a Short Chain Fatty Acid: Effects on Mitochondrial Function and Correlation with Gene Expression

Hepatotoxicity characterized by microvesicular steatosis (MVS) is characterized by an abnormal accumulation of numerous small cytoplasmic lipid droplets in hepatocytes. Fulminant or progressive cases of microvesicular steatosis may lead to liver failure and death. Experimentally, short-chain carboxylic acids are known to induce microvesicular steatosis. The identification of gene changes that correlate with MVS concomitant with biochemical and histological indices could provide a better understanding of how this toxicity occurs as well as biomarkers that could be used to avoid this toxicity in the future. Sprague—Dawley rats were dosed days with cyclopropane carboxylic acid (CPCA) a short-chain fatty acid that can induce microvesicular steatosis, and with butyrate, a short chain fatty acid that served as a negative control. CPCA initiated microvesicular steatosis while butyrate did not. In addition, CPCA inhibited beta-oxidation in a concentration-dependent manner in vitro and caused a reduction in mitochondrial respiration ex vivo; no inhibition was evident with butyrate. Microarray results showed that gene expression changes with CPCA resulted in regulation of genes involved in beta-oxidation, as well as other genes associated with mitochondrial function. Overall, these results support altered hepatic mitochondrial function as a mechanism of the toxicity induced by a short-chain fatty acid and may provide potential biomarkers for this toxicity.

Prolyl Oligopeptidase Inhibition Attenuates Steatosis in the L02 Human Liver Cell Line

Background

Prolyl oligopeptidase (POP) is a serine endopeptidase that is widely distributed in vivo, particularly in the liver. Significant changes in functional mitochondrial proteins involved with mitochondrial oxidoreductases/transporters and nucleic acid binding proteins were observed after POP inhibition in the liver, which suggested a role of POP in regulating liver energy metabolism. Steatosis in nonalcoholic fatty liver disease (NAFLD) is associated with disturbances in lipid and energy metabolism in hepatocytes. Here, we aimed to study the effect of POP on hepatocyte steatosis.

Methods

The human liver cell line L02 was used to investigate the biological effects of POP. An in vitro cell model of steatosis was successfully induced with oleic acid and palmitic acid. L02 cells were also subjected to S17092 (a POP inhibitor) at different concentrations for 24 or 48 h. Ac-SDKP levels and POP activity were measured to assess the rate of inhibition of POP by S17092. The POP gene and protein expression levels were detected using real-time PCR and Western blots, respectively. Oil red O staining was performed and the triglyceride levels in the L02 cells were also measured. Cell proliferation and apoptosis were detected using CCK-8 and flow cytometry, respectively. The expression of genes involved in lipid metabolism was detected using real-time PCR. The effects of POP inhibition on LC3B II were detected by Western blot.

Results

Compared with the control, the POP mRNA levels increased by approximately 30%, and the POP protein levels increased by almost 60% in the steatotic L02 cells. After S17092 (0.026~130 μM) incubation for 24 or 48 h, cell proliferation was significantly decreased in the free fatty acid (FFA)-treated cells at 26–130 μM; however, S17092 did not affect the proliferation of L02 cells after 24 h of incubation with S17092 at 0.026–65 μM without FFA treatment. S17092 treatment (13 and 26 μM) also elicited no significant effect on apoptosis in normal L02 cells, but FFA treatment increased cell apoptosis, which was attenuated by S17092 incubation. S17092 treatment inhibited intracellular POP activity and decreased the AcSDKP level at the concentration of 0.026–26 μM. After treatment with FFA for 24 h, oil red O staining revealed significant lipid accumulation in the cells in the model group compared with the controls; however, lipid accumulation was suppressed after the administration of S17092 (13 and 26 μM). Accordingly, the triglyceride levels in the FFA-treated cells were approximately 5-fold greater than those of the controls and were decreased by approximately 25% and 45% after the administration of S17092 at 13 and 26 μM, respectively. The mRNA levels of FASN, PPAR-γ, and SREBP-1c were higher in the FFA-treated cells than in the normal controls, and all of these levels were significantly inhibited in the presence of S17092 at both 13 and 26 μM. S17092 treatment did not affect LC3B II in the FFA-treated cells compared with FFA treatment alone.

Conclusion

The expression of POP increases with hepatocyte steatosis, and POP inhibitors can significantly reduce intracellular lipid accumulation, which might be related to the inhibition of genes involved in lipid synthesis.

ChREBP regulates fructose-induced glucose production independently of insulin signaling

Obese, insulin-resistant states are characterized by a paradoxical pathogenic condition in which the liver appears to be selectively insulin resistant. Specifically, insulin fails to suppress glucose production, yet successfully stimulates de novo lipogenesis. The mechanisms underlying this dysregulation remain controversial. Here, we hypothesized that carbohydrate-responsive element-binding protein (ChREBP), a transcriptional activator of glycolytic and lipogenic genes, plays a central role in this paradox. Administration of fructose increased hepatic hexose-phosphate levels, activated ChREBP, and caused glucose intolerance, hyperinsulinemia, hypertriglyceridemia, and hepatic steatosis in mice. Activation of ChREBP was required for the increased expression of glycolytic and lipogenic genes as well as glucose-6-phosphatase (G6pc) that was associated with the effects of fructose administration. We found that fructose-induced G6PC activity is a major determinant of hepatic glucose production and reduces hepatic glucose-6-phosphate levels to complete a homeostatic loop. Moreover, fructose activated ChREBP and induced G6pc in the absence of Foxo1a, indicating that carbohydrate-induced activation of ChREBP and G6PC dominates over the suppressive effects of insulin to enhance glucose production. This ChREBP/G6PC signaling axis is conserved in humans. Together, these findings support a carbohydrate-mediated, ChREBP-driven mechanism that contributes to hepatic insulin resistance.

Fatty liver disease induced by perfluorooctane sulfonate: Novel insight from transcriptome analysis

Perfluorooctane sulfonate (PFOS), a hepato-toxicant and potential non-genotoxic carcinogen, was widely used in industrial and commercial products. Recent studies have revealed the ubiquitous occurrence of PFOS in the environment and in humans worldwide. The widespread contamination of PFOS in human serum raised concerns about its long-term toxic effects and its potential risks to human health. Using fatty liver mutant foie gras (fgr(-/-))/transport protein particle complex 11 (trappc11(-/-)) and PFOS-exposed wild-type zebrafish embryos as the study model, together with RNA sequencing and comparative transcriptomic analysis, we identified 499 and 1414 differential expressed genes (DEGs) in PFOS-exposed wild-type and trappc11 mutant zebrafish, respectively. Also, the gene ontology analysis on common deregulated genes was found to be associated with different metabolic processes such as the carbohydrate metabolic process, glycerol ether metabolic process, mannose biosynthetic process, de novo' (Guanosine diphosphate) GDP-l-fucose biosynthetic process, GDP-mannose metabolic process and galactose metabolic process. Ingenuity Pathway Analysis further highlighted that these deregulated gene clusters are closely related to hepatitis, inflammation, fibrosis and cirrhosis of liver cells, suggesting that PFOS can cause liver pathogenesis and non-alcoholic fatty liver disease in zebrafish. The transcriptomic alterations revealed may serve as biomarkers for the hepatotoxic effect of PFOS.

Valproic Acid and Hepatic Steatosis: A Possible Link? About a Case Report

BACKGROUND

Valproic acid is a mood-stabilizing anticonvulsant. Hepatic injuries are among the occasionally observed adverse effects of this medication.

CASE PRESENTATION

We present the case of a 47-year-old man who had bipolar disorder for ten years and treated with valproic acid. He demonstrated elevated serum aminotransferases and ultrasonography revealed that hepatomegaly was suggestive of hepatic steatosis.

CONCLUSION

This case report stresses the importance of a complete drug history and the need for clinicians to be aware of the delayed onset of hepatic injuries.

Fatal lactic acidosis associated with highly active antiretroviral therapy in patients with advanced human immunodeficiency virus infection in Taiwan

Lactic acidosis (LA), a rare but life-threatening adverse effect associated with antiretroviral therapy, has been reported with an increasing frequency since the mid1990s. From June 1994 to June 2002, a total of six patients, four males and two females with a median age of 43 years (range, 30 to 74 years), had been diagnosed with LA. The estimated incidence of LA was 5.1 per 1000 patient-years (PYs) on highly active antiretroviral therapy (HAART) (95% confidence interval [95% CI], 4.5-5.5 per 1000 PYs) and 4.4 per 1000 PY on nucleoside analogues (NAs) (95% CI, 3.9-4.7 per 1000 PYs). Their median body mass index at diagnosis of LA was 17.6 kg/m2 (range 16.3 to 22.6 kg/m2). The median CD4+ lymphocyte count at the initial diagnosis of HIV infection and at the onset of LA was 38 cells/µL (range, 4 to 103 cells/µL) and 108 cells/µL (range, 79 to 224 cells/µL), respectively. The most common symptoms were nausea, vomiting, and dyspnoea. All of the patients had findings suggestive of NA-related mitochondrial toxicity, such as myositis, pancreatitis, fatty hepatitis, peripheral neuropathy or lipodystrophy. The prescribed NA related to LA were stavudine in six patients, lamivudine, five, and didanosine, one. Despite treatment, all patients died of persistent circulatory collapse following LA. The median duration from diagnosis to death was eight days (range, 4-17 days). Our report highlights that clinicians caring for patients with AIDS should be alerted to the potentially fatal LA associated with antiretroviral therapy when patients present with low body mass index, lipodystrophy, unexplained abdominal symptoms, dyspnoea, or elevated aminotransferases.

Role of Transcription Factors in Steatohepatitis and Hypertension after Ethanol: The Epicenter of Metabolism

Chronic alcohol consumption induces multi-organ damage, including alcoholic liver disease (ALD), pancreatitis and hypertension. Ethanol and ethanol metabolic products play a significant role in the manifestation of its toxicity. Ethanol metabolizes to acetaldehyde and produces reduced nicotinamide adenine dinucleotide (NADH) by cytosolic alcohol dehydrogenase. Ethanol metabolism mediated by cytochrome-P450 2E1 causes oxidative stress due to increased production of reactive oxygen species (ROS). Acetaldehyde, increased redox cellular state and ROS activate transcription factors, which in turn activate genes for lipid biosynthesis and offer protection of hepatocytes from alcohol toxicity. Sterol regulatory element binding proteins (SREBPs) and peroxisome proliferator activated-receptors (PPARs) are two key lipogenic transcription factors implicated in the development of fatty liver in alcoholic and non-alcoholic steatohepatitis. SREBP-1 is activated in the livers of chronic ethanol abusers. An increase in ROS activates nuclear factor erythroid-2-related factor-2 (Nrf2) and hypoxia inducible factor (HIF) to provide protection to hepatocytes from ethanol toxicity. Under ethanol exposure, due to increased gut permeability, there is release of gram-negative bacteria-derived lipopolysaccharide (LPS) from intestine causing activation of immune response. In addition, the metabolic product, acetaldehyde, modifies the proteins in hepatocyte, which become antigens inviting auto-immune response. LPS activates macrophages, especially the liver resident macrophages, Kupffer cells. These Kupffer cells and circulating macrophages secrete various cytokines. The level of tumor necrosis factor-α (TNFα), interleukin-1beta (IL-1β), IL-6, IL-8 and IL-12 have been found elevated among chronic alcoholics. In addition to elevation of these cytokines, the peripheral iron (Fe(2+)) is also mobilized. An increased level of hepatic iron has been observed among alcoholics. Increased ROS, IL-1β, acetaldehyde, and increased hepatic iron, all activate nuclear factor-kappa B (NF-κB) transcription factor. Resolution of increased reactive oxygen species requires increased expression of genes responsible for dismutation of increased ROS which is partially achieved by IL-6 mediated activation of signal transducers and activators of transcription 3 (STAT3). In addition to these transcription factors, activator protein-1 may also be activated in hepatocytes due to its association with resolution of increased ROS. These transcription factors are central to alcohol-mediated hepatotoxicity.

Bisphenol A Induces Fatty Liver by an Endocannabinoid-Mediated Positive Feedback Loop

The xenoestrogen bisphenol A (BPA) is a widespread plasticizer detectable within several ecosystems. BPA is considered a metabolic disruptor, affecting different organs; however, little is known about its mechanism of action in the liver, in which it triggers triglyceride accumulation. Adult zebrafish (Danio rerio) exposed to BPA developed hepatosteatosis, which was associated with an increase in the liver levels of the obesogenic endocannabinoids 2-arachidonoylglycerol and anandamide and a concomitant decrease in palmitoylethanolamide. These changes were associated with variations in the expression of key endocannabinoid catabolic and metabolic enzymes and an increase in the expression of the endocannabinoid receptor cnr1. Acute and chronic in vitro treatments with nano- and micromolar BPA doses showed increased anandamide levels in line with decreased activity of fatty acid amide hydrolase, the main anandamide hydrolytic enzyme, and induced triglyceride accumulation in HHL-5 cells in a CB1-dependent manner. We conclude that BPA is able to produce hepatosteatosis in zebrafish and human hepatocytes by up-regulating the endocannabinoid system.

Anthocyanin-rich extracts from blackberry, wild blueberry, strawberry, and chokeberry: antioxidant activity and inhibitory effect on oleic acid-induced hepatic steatosis in vitro

BACKGROUND

Limited information is available regarding the relationship between the chemical structures and inhibitory effects of anthocyanin (ACN) on triglyceride (TG) overaccumulation. Thus this study investigated the antioxidant activity and inhibitory effect of blackberry, wild blueberry, strawberry, and chokeberry ACN-rich extracts, with different structural characteristics, on oleic acid-induced hepatic steatosis in vitro. Four major ACNs from these berries, with different aglycones, namely cyanidin-3-glucoside (Cy-3-glu), delphinidin-3-glucoside, pelargonidin-3-glucoside, and malvidin-3-glucoside, were also investigated.

RESULTS

Blackberry ACN-rich extract exhibited the most significant inhibitory effect on TG clearance (30.5% ± 3.4%) and reactive oxygen species generation. TG clearance was significantly correlated with total phenolic content (r = 0.991, P < 0.05) and oxygen radical absorbance capacity value (r = 0.961, P < 0.05). Furthermore, Cy-3-glu showed the highest inhibitory effect on intracellular TG overaccumulation, with a maximum TG clearance of 61.3% at 40 µg mL(-1) .

CONCLUSION

Our findings suggest that the inhibitory effects of different ACNs on oleic acid-induced hepatic steatosis significantly vary. Cy-3-glu, which contains the ortho hydroxyl group in its B ring, possibly confers the protective effects of antioxidants and inhibits TG accumulation in HepG2 cells. © 2015 Society of Chemical Industry.

Uric acid regulates hepatic steatosis and insulin resistance through the NLRP3 inflammasome-dependent mechanism

BACKGROUND & AIMS

Hyperuricemia significantly increases risk of non-alcoholic fatty liver disease (NAFLD) and insulin resistance. However, the mechanisms responsible for this association are as yet unclear. This study aimed to investigate the effects and underlying mechanisms of uric acid on development of NAFLD and insulin resistance.

METHODS

We initially analyzed the impact of uric acid on the development of hepatic steatosis and insulin resistance in mice and in two cell models, HepG2 and L02. Subsequently, we studied the role of the NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome in uric acid-induced fat accumulation and insulin signaling impairment.

RESULTS

We found that uric acid directly induces hepatocyte fat accumulation, insulin resistance, and insulin signaling impairment both in vivo and in vitro. We also found that uric acid-induced NLRP3 inflammasome activation, whereas lowering uric acid by allopurinol inhibited NLRP3 inflammasome activation in a high fat diet mouse model of NAFLD. Moreover, knocking down NLRP3 expression significantly attenuated uric acid-induced fat accumulation both in HepG2 cells and L02 cells. Knocking down NLRP3 expression also rescued uric acid-induced insulin signaling impairment in both cell types.

CONCLUSIONS

Uric acid regulates hepatic steatosis and insulin resistance through the NLRP3 inflammasome. Uric acid may be a new therapeutic target for NAFLD and insulin resistance.

Steatohepatitis is developed by a diet high in fat, sucrose, and cholesterol without increasing iron concentration in rat liver

Iron overload to the liver is known to be a pathogenesis of nonalcoholic steatohepatitis through oxidative stress. High-fat diets have been reported to increase iron concentration in livers that developed steatohepatitis in experimental animals. However, the effect of high-fat diets on hepatic iron concentration is controversial. We hypothesized that a diet high in lard, cholesterol, and sucrose (Western diet) leads to the development of steatohepatitis without increasing hepatic iron concentration. Rats were given either a control or the Western diet for 12 weeks. The Western diet increased triacylglycerol concentration and oxidative stress markers such as the concentration of thiobarbituric acid reactive substances and messenger RNA (mRNA) expression of heme oxygenase-1 in the liver. The Western diet also increased the mRNA expression of macrophage-1 antigen, cluster of differentiation (CD) 45, and CD68 in the liver, and nuclear factor κB level in liver nuclear fraction, suggesting the development of hepatic inflammation. Histological observation also indicated fatty liver and hepatic inflammation in the rats given the Western diet. In contrast, the Western diet decreased iron concentration in the liver. These results clearly indicated that the diet high in lard, cholesterol, and sucrose induces steatohepatitis without increasing hepatic iron concentration.

Dietary Betaine Supplementation Increases Fgf21 Levels to Improve Glucose Homeostasis and Reduce Hepatic Lipid Accumulation in Mice

Identifying markers of human insulin resistance may permit development of new approaches for treatment and prevention of type 2 diabetes. To this end, we analyzed the fasting plasma metabolome in metabolically characterized human volunteers across a spectrum of insulin resistance. We demonstrate that plasma betaine levels are reduced in insulin-resistant humans and correlate closely with insulin sensitivity. Moreover, betaine administration to mice with diet-induced obesity prevents the development of impaired glucose homeostasis, reduces hepatic lipid accumulation, increases white adipose oxidative capacity, and enhances whole-body energy expenditure. In parallel with these beneficial metabolic effects, betaine supplementation robustly increased hepatic and circulating fibroblast growth factor (Fgf)21 levels. Betaine administration failed to improve glucose homeostasis and liver fat content in Fgf21(-/-) mice, demonstrating that Fgf21 is necessary for betaine's beneficial effects. Together, these data indicate that dietary betaine increases Fgf21 levels to improve metabolic health in mice and suggest that betaine supplementation merits further investigation as a supplement for treatment or prevention of type 2 diabetes in humans.

Metformin administration induces hepatotoxic effects in paraoxonase-1-deficient mice

Metformin is the first-line pharmacological treatment of diabetes. In these patients, metformin reduces body weight and decreases the risk of diabetes-related complications such as cardiovascular disease. However, whether metformin elicits beneficial effects on liver histology is a controversial issue and, as yet, there is no consensus. Paraoxonase-1 (PON1), an enzyme synthesized mainly by the liver, degrades lipid peroxides and reduces oxidative stress. PON1 activities are decreased in chronic liver diseases. We evaluated the effects of metformin in the liver of PON1-deficient mice which, untreated, present a mild degree of liver steatosis. Metformin administration aggravated inflammation in animals given a standard mouse chow and in those fed a high-fat diet. Also, it was associated with a higher degree of steatosis in animals fed a standard chow diet. This report is a cautionary note regarding the prescription of metformin for the treatment of diabetes in patients with concomitant liver impairment.

Prophylactic and abundant intake of α-lipoic acid causes hepatic steatosis and should be reconsidered in usage as an anti-aging drug

The majority of research has suggested that α-lipoic acid (ALA) is a potential therapeutic agent for chronic diseases associated with oxidative stress, including atherosclerosis, diabetes, and neurodegeneration. Therefore, a nutritional supplementation with ALA is recommended although the effects of a short- and long-term intake of ALA on central organs in healthy individuals are not studied in detail yet. Therefore, liver tissue of 4 and 74 weeks ALA-treated healthy C57BL6/J mice with respect to lipid metabolism was analyzed. In doing so, it was shown that short-term and long-term ALA treatment caused a marked increase of β-oxidation, as indicated by a significant rise of mRNA expression of fgf21, pparα, and its target genes, for example, acox1, cpt1α, and cpt2, as well as of Fgf21 plasma concentration. Glycolytic activity, as assessed by pklr1 mRNA expression and pyruvate kinase activity, was also found increased. In addition, it was shown that both short- and long-term ALA treatment increased cholesterol content, induced systemic triglyceridemia, and enhanced rxrα and lxrα mRNA expression. Despite the fact that short-term ALA intake reduced lipogenesis, as given by significant declines of fas and srebp1c mRNA expression, and that a long-term ALA intake induced a significant rise of these lipogenic genes, both treatment regimen caused fat accumulation. This, however, was more pronounced upon long-term ALA intake, leading to hepatic steatosis and liver injury, as indicated by increased inflammation and disruption of the general hepatic architecture. In summary, the prophylactic and abundant use of ALA under healthy conditions should be considered with caution.

Docosahexaenoic Acid Ameliorates Fructose-Induced Hepatic Steatosis Involving ER Stress Response in Primary Mouse Hepatocytes

The increase in fructose consumption is considered to be a risk factor for developing nonalcoholic fatty liver disease (NAFLD). We investigated the effects of docosahexaenoic acid (DHA) on hepatic lipid metabolism in fructose-treated primary mouse hepatocytes, and the changes of Endoplasmic reticulum (ER) stress pathways in response to DHA treatment. The hepatocytes were treated with fructose, DHA, fructose plus DHA, tunicamycin (TM) or fructose plus 4-phenylbutyric acid (PBA) for 24 h. Intracellular triglyceride (TG) accumulation was assessed by Oil Red O staining. The mRNA expression levels and protein levels related to lipid metabolism and ER stress response were determined by real-time PCR and Western blot. Fructose treatment led to obvious TG accumulation in primary hepatocytes through increasing expression of fatty acid synthase (FAS) and acetyl-CoA carboxylase (ACC), two key enzymes in hepatic de novo lipogenesis. DHA ameliorates fructose-induced TG accumulation by upregulating the expression of carnitine palmitoyltransferase 1A (CPT-1α) and acyl-CoA oxidase 1 (ACOX1). DHA treatment or pretreatment with the ER stress inhibitor PBA significantly decreased TG accumulation and reduced the expression of glucose-regulated protein 78 (GRP78), total inositol-requiring kinase 1 (IRE1α) and p-IRE1α. The present results suggest that DHA protects against high fructose-induced hepatocellular lipid accumulation. The current findings also suggest that alleviating the ER stress response seems to play a role in the prevention of fructose-induced hepatic steatosis by DHA.

Chronic Uridine Administration Induces Fatty Liver and Pre-Diabetic Conditions in Mice

Uridine is a pyrimidine nucleoside that exerts restorative functions in tissues under stress. Short-term co-administration of uridine with multiple unrelated drugs prevents drug-induced liver lipid accumulation. Uridine has the ability to modulate liver metabolism; however, the precise mechanism has not been delineated. In this study, long-term effects of uridine on liver metabolism were examined in both HepG2 cell cultures and C57BL/6J mice. We report that uridine administration was associated with O-GlcNAc modification of FOXO1, increased gluconeogenesis, reduced insulin signaling activity, and reduced expression of a liver-specific fatty acid binding protein FABP1. Long-term uridine feeding induced systemic glucose intolerance and severe liver lipid accumulation in mice. Our findings suggest that the therapeutic potentials of uridine should be designed for short-term acute administration.