Gene expression profiling in livers of mice after acute inhibition of beta-oxidation

A promising anti-tumor targeting on ERMMDs mediated abnormal lipid metabolism in tumor cells

The investigation of aberrations in lipid metabolism within tumor has become a burgeoning field of study that has garnered significant attention in recent years. Lipids can serve as a potent source of highly energetic fuel to support the rapid growth of neoplasia, in where the ER-mitochondrial membrane domains (ERMMDs) provide an interactive network for facilitating communication between ER and mitochondria as well as their intermembrane space and adjunctive proteins. In this review, we discuss fatty acids (FAs) anabolic and catabolic metabolism, as well as how CPT1A-VDAC-ACSL clusters on ERMMDs participate in FAs transport, with a major focus on ERMMDs mediated collaborative loop of FAO, Ca2+ transmission in TCA cycle and OXPHOS process. Here, we present a comprehensive perspective on the regulation of aberrant lipid metabolism through ERMMDs conducted tumor physiology might be a promising and potential target for tumor starvation therapy.

Lactobacillus rhamnosus NKU FL1-8 Isolated from Infant Feces Ameliorates the Alcoholic Liver Damage by Regulating the Gut Microbiota and Intestinal Barrier in C57BL/6J Mice

Alcoholic liver damage is caused by long-term or heavy drinking, and it may further progress into alcoholic liver diseases (ALD). Probiotic supplements have been suggested for the prevention or improvement of liver damage. This study was designed to consider the ameliorative effects of Lactobacillus rhamnosus NKU FL1-8 isolated from infant feces against alcoholic liver damage. The mice were gavaged with a 50% ethanol solution and treated with 109 CFU of L. rhamnosus NKU FL1-8 suspension. The factors for liver function, oxidative stress, inflammation, gut microbiota composition, and intestinal barrier integrity were measured. The results showed that L. rhamnosus NKU FL1-8 could decrease the levels of aspartate aminotransferase (AST) to 61% and alanine aminotransferase (ALT) to 50% compared with ethanol given by gavage. It could inhibit the expression level of malondialdehyde (MDA), increase superoxide dismutase (SOD), glutathione (GSH) to relieve oxidative stress, and down-regulate the cytokines to decrease hepatic inflammation. After treatment, the level of triglycerides was reduced, and the expression levels of adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) and the peroxisome proliferators-activated receptor-α (PPAR-α) pathway were up-regulated. Additionally, the 16S rRNA sequencing analysis showed that L. rhamnosus NKU FL1-8 increased the relative abundance of Lactobacillus, Ruminococcaceae, etc. At the same time, L. rhamnosus NKU FL1-8 could significantly reduce lipopolysaccharides (LPS) and enhance intestinal tight junction proteins. These results demonstrated that L. rhamnosus NKU FL1-8 could reduce the level of oxidative stress, fat accumulation, and liver inflammation caused by alcohol in the host. The underlying mechanism could be that L. rhamnosus NKU FL1-8 inhibits LPS by regulating the gut microbiota and repairing the intestinal barrier. Thereby, these findings support L. rhamnosus NKU FL1-8 as a potential functional food for the relief of ALD.

RNA-Seq Analysis Identifies Differentially Expressed Genes in the Longissimus dorsi of Wagyu and Chinese Red Steppe Cattle

Meat quality has a close relationship with fat and connective tissue; therefore, screening and identifying functional genes related to lipid metabolism is essential for the production of high-grade beef. The transcriptomes of the Longissimus dorsi muscle in Wagyu and Chinese Red Steppe cattle, breeds with significant differences in meat quality and intramuscular fat deposition, were analyzed using RNA-seq to screen for candidate genes associated with beef quality traits. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that the 388 differentially expressed genes (DEGs) were involved in biological processes such as short-chain fatty acid metabolism, regulation of fatty acid transport and the peroxisome proliferator-activated receptor (PPAR) signaling pathway. In addition, crystallin alpha B (CRYAB), ankyrin repeat domain 2 (ANKRD2), aldehyde dehydrogenase 9 family member A1 (ALDH9A1) and enoyl-CoA hydratase and 3-hydroxyacyl CoA dehydrogenase (EHHADH) were investigated for their effects on intracellular triglyceride and fatty acid content and their regulatory effects on genes in lipogenesis and fatty acid metabolism pathways. This study generated a dataset from transcriptome profiling of two cattle breeds, with differing capacities for fat-deposition in the muscle, and revealed molecular evidence that CRYAB, ANKRD2, ALDH9A1 and EHHADH are related to fat metabolism in bovine fetal fibroblasts (BFFs). The results provide potential functional genes for maker-assisted selection and molecular breeding to improve meat quality traits in beef cattle.

Genome-wide association study identifies quantitative trait loci regions involved in muscle acidic profile in Large White heavy pigs

The widespread use of genome-wide association studies resulted in the discovery of genomic regions associated with fatty acid (FA) composition in different porcine tissues, but little information exists about the genes involved in FA composition of meat obtained from heavy pigs selected for the production of Italian dry-cured hams. To this objective, we genotyped with a single nucleotide polymorphism (SNP) panel 795 Italian Large White heavy pigs to identify the markers and genomic regions associated with Semimembranosus muscle FA profile. Heritability estimates for intramuscular fat FA profile were of low-to-moderate magnitude, suggesting that these traits may be improved with genomic selection. On the whole, 45 SNPs were significantly associated with 14 FAs, and 4 of them (ALGA008109, ALGA0081097, CASI0010164 and SIRI0000267) were associated with more than 1 FA. The palmitoleic : palmitic and oleic : stearic ratios displayed the highest number of significant markers and the most significant associations (Bonferroni adjusted P < 5.00E-07). Of particular interest, the palmitoleic : palmitic ratio was strongly associated with markers located at 111 to 114 Mb on chromosome 14, in the same chromosomal region where Stearoyl-CoA desaturase Δ9 (SCD) gene is located. Several significant chromosomal regions were found; some of them harbour key genes playing pivotal roles in FA desaturation and elongation, such as SCD and some members of the Elongation of Very Long-Chain FA (ELOVL) gene family. The results suggest that the identification of causal mutations in these regions may provide a set of markers useful for selection schemes aimed at improving FA composition in pork products.

Mild Methylenetetrahydrofolate Reductase Deficiency Alters Inflammatory and Lipid Pathways in Liver

SCOPE

Dietary and genetic folate disturbances can lead to nonalcoholic fatty liver disease (NAFLD). A common variant in methylenetetrahydrofolate reductase (MTHFR 677C→T) causes mild MTHFR deficiency with lower 5-methyltetrahydrofolate for methylation reactions. The goal is to determine whether mild murine MTHFR deficiency contributes to NAFLD-related effects.

METHODS AND RESULTS

Wild-type and Mthfr^+/- mice, a model for the human variant, are fed control (CD) or high-fat (HFAT) diets for 8 weeks. On both diets, MTHFR deficiency results in decreased S-adenosylmethionine, increased S-adenosylhomocysteine, and decreased betaine with reduced methylation capacity, and changes in expression of several inflammatory or anti-inflammatory mediators (Saa1, Apoa1, and Pon1). On CD, MTHFR deficiency leads to microvesicular steatosis with expression changes in lipid regulators Xbp1s and Cyp7a1. The combination of MTHFR deficiency and HFAT exacerbates changes in inflammatory mediators and introduces additional effects on inflammation (Saa2) and lipid metabolism (Nr1h4, Srebf1c, Ppara, and Crot). These effects are consistent with increased expression of pro-inflammatory HDL precursors and greater lipid accumulation. MTHFR deficiency may enhance liver injury through alterations in methylation capacity, inflammatory response, and lipid metabolism.

CONCLUSION

Individuals with the MTHFR variant may be at increased risk for liver disease and related complications, particularly when consuming high-fat diets.

Tomato Juice Supplementation Influences the Gene Expression Related to Steatosis in Rats

The objective of this work was to identify the effect of tomato juice on the expression of genes and levels of metabolites related to steatosis in rats. Male Sprague Dawley rats (8 weeks-old) were grouped (6 rats/group) in four experimental groups: NA (normal diet and water), NL (normal diet and tomato juice), HA (high-fat diet and water), and HL (high-fat diet and tomato juice). After an intervention period of 5 weeks, rats were sacrificed and biochemical parameters, biomarkers of oxidative stress, liver metabolites, and gene expression were determined. Although the H diet provoked dislipemia related to steatosis, no changes in isoprostanes or liver malondialdehyde (MDA) were observed. Changes in the gene expression of the HA group were produced by the high consumption of fat, whereas the consumption of tomato juice had different effects, depending on the diet. In the NL group, the genes involved in β-oxidation were upregulated, and in groups NL and HL upregulation of CD36 and downregulation of APOB and LPL were observed. In addition, in the HL group the accumulation of lycopene upregulated the genes FXR and HNF4A, which have been suggested as preventive factors in relation to steatosis. Regarding the metabolomics study, intake of tomato juice stimulated the biosynthesis of glutathione and amino acids of the transulfurization pathway, increasing the levels of metabolites related to the antioxidant response.

Analysis of molecular mechanisms of 5-fluorouracil-induced steatosis and inflammation in vitro and in mice

Chemotherapy-associated steatohepatitis is attracting increasing attention because it heralds an increased risk of morbidity and mortality in patients undergoing surgery because of liver metastases. The aim of this study was to develop in vitro and in vivo models to analyze the pathogenesis of 5-fluorouracil (5-FU)-induced steatohepatitis.

Therefore, primary human hepatocytes and HepG2 hepatoma cells were incubated with 5-FU at non-toxic concentrations up to 24 h. Furthermore, hepatic tissue of C57BL/6N mice was analyzed 24 h after application of a single 5-FU dose (200 mg/kg body weight). In vitro, incubation with 5-FU induced a significant increase of hepatocellular triglyceride levels. This was paralleled by an impairment of mitochondrial function and a dose- and time-dependently increased expression of fatty acid acyl-CoA oxidase 1 (ACOX1), which catalyzes the initial step for peroxisomal β-oxidation. The latter is known to generate reactive oxygen species, and consequently, expression of the antioxidant enzyme heme oxygenase 1 (HMOX1) was significantly upregulated in 5-FU-treated cells, indicative for oxidative stress. Furthermore, 5-FU significantly induced c-Jun N-terminal kinase (JNK) activation and the expression of pro-inflammatory genes IL-8 and ICAM-1. Also in vivo, 5-FU significantly induced hepatic ACOX1 and HMOX1 expression as well as JNK-activation, pro-inflammatory gene expression and immune cell infiltration. In summary, we identified molecular mechanisms by which 5-FU induces hepatocellular lipid accumulation and inflammation. Our newly developed models can be used to gain further insight into the pathogenesis of 5-FU-induced steatohepatitis and to develop therapeutic strategies to inhibit its development and progression.

Dietary DHA/EPA ratio affected tissue fatty acid profiles, antioxidant capacity, hematological characteristics and expression of lipid-related genes but not growth in juvenile black seabream (Acanthopagrus schlegelii)

An 8-week feeding trial was conducted to investigate the effects of dietary docosahexaenoic to eicosapentaenoic acid ratio (DHA/EPA) on growth performance, fatty acid profiles, antioxidant capacity, hematological characteristics and expression of some lipid metabolism related genes of juvenile black seabream (Acanthopagrus schlegelii) of initial weight 9.47 ± 0.03 g. Five isonitrogenous and isolipidic diets (45% crude protein and 14% crude lipid) were formulated to contain graded DHA/EPA ratios of 0.65, 1.16, 1.60, 2.03 and 2.67. There were no differences in growth performance and feed utilization among treatments. Fish fed higher DHA/EPA ratios had higher malondialdehyde (MDA) contents in serum than lower ratios. Serum triacylglycerol (TAG) content was significantly higher in fish fed the lowest DHA/EPA ratio. Tissue fatty acid profiles reflected the diets despite down-regulation of LC-PUFA biosynthesis genes, fatty acyl desaturase 2 (fads2) and elongase of very long-chain fatty acids 5 (elovl5), by high DHA/EPA ratios. Expression of acetyl-CoA carboxylase alpha (accα) and carnitine palmitoyl transferase 1A (cpt1a) were up-regulated by high DHA/EPA ratio, whereas sterol regulatory element-binding protein-1 (srebp-1) and hormone-sensitive lipase (hsl) were down-regulated. Fatty acid synthase (fas), 6-phosphogluconate dehydrogenase (6pgd) and peroxisome proliferator-activated receptor alpha (pparα) showed highest expression in fish fed intermediate (1.16) DHA/EPA ratio. Overall, this study indicated that dietary DHA/EPA ratio affected fatty acid profiles and significantly influenced lipid metabolism including LC-PUFA biosynthesis and other anabolic and catabolic pathways, and also had impacts on antioxidant capacity and hematological characteristics.

Korean pine nut oil replacement decreases intestinal lipid uptake while improves hepatic lipid metabolism in mice

BACKGROUND/OBJECTIVES

Consumption of pine nut oil (PNO) was shown to reduce weight gain and attenuate hepatic steatosis in mice fed a high-fat diet (HFD). The aim of this study was to examine the effects of PNO on both intestinal and hepatic lipid metabolism in mice fed control or HFD.

MATERIALS/METHODS

Five-week-old C57BL/6 mice were fed control diets containing 10% energy fat from either Soybean Oil (SBO) or PNO, or HFD containing 15% energy fat from lard and 30% energy fat from SBO or PNO for 12 weeks. Expression of genes related to intestinal fatty acid (FA) uptake and channeling (Cd36, Fatp4, Acsl5, Acbp), intestinal chylomicron synthesis (Mtp, ApoB48, ApoA4), hepatic lipid uptake and channeling (Lrp1, Fatp5, Acsl1, Acbp), hepatic triacylglycerol (TAG) lipolysis and FA oxidation (Atgl, Cpt1a, Acadl, Ehhadh, Acaa1), as well as very low-density lipoprotein (VLDL) assembly (ApoB100) were determined by real-time PCR.

RESULTS

In intestine, significantly lower Cd36 mRNA expression (P < 0.05) and a tendency of lower ApoA4 mRNA levels (P = 0.07) was observed in PNO-fed mice, indicating that PNO consumption may decrease intestinal FA uptake and chylomicron assembly. PNO consumption tended to result in higher hepatic mRNA levels of Atgl (P = 0.08) and Cpt1a (P = 0.05). Significantly higher hepatic mRNA levels of Acadl and ApoB100 were detected in mice fed PNO diet (P < 0.05). These results suggest that PNO could increase hepatic TAG metabolism; mitochondrial fatty acid oxidation and VLDL assembly.

CONCLUSIONS

PNO replacement in the diet might function in prevention of excessive lipid uptake by intestine and improve hepatic lipid metabolism in both control diet and HFD fed mice.

Apigenin Ameliorates Dyslipidemia, Hepatic Steatosis and Insulin Resistance by Modulating Metabolic and Transcriptional Profiles in the Liver of High-Fat Diet-Induced Obese Mice

Several in vitro and in vivo studies have reported the anti-inflammatory, anti-diabetic and anti-obesity effects of the flavonoid apigenin. However, the long-term supplementary effects of low-dose apigenin on obesity are unclear. Therefore, we investigated the protective effects of apigenin against obesity and related metabolic disturbances by exploring the metabolic and transcriptional responses in high-fat diet (HFD)-induced obese mice. C57BL/6J mice were fed an HFD or apigenin (0.005%, w/w)-supplemented HFD for 16 weeks. In HFD-fed mice, apigenin lowered plasma levels of free fatty acid, total cholesterol, apolipoprotein B and hepatic dysfunction markers and ameliorated hepatic steatosis and hepatomegaly, without altering food intake and adiposity. These effects were partly attributed to upregulated expression of genes regulating fatty acid oxidation, tricarboxylic acid cycle, oxidative phosphorylation, electron transport chain and cholesterol homeostasis, downregulated expression of lipolytic and lipogenic genes and decreased activities of enzymes responsible for triglyceride and cholesterol ester synthesis in the liver. Moreover, apigenin lowered plasma levels of pro-inflammatory mediators and fasting blood glucose. The anti-hyperglycemic effect of apigenin appeared to be related to decreased insulin resistance, hyperinsulinemia and hepatic gluconeogenic enzymes activities. Thus, apigenin can ameliorate HFD-induced comorbidities via metabolic and transcriptional modulations in the liver.

The antiobesity factor WDTC1 suppresses adipogenesis via the CRL4WDTC1 E3 ligase

WDTC1/Adp encodes an evolutionarily conserved suppressor of lipid accumulation. While reduced WDTC1 expression is associated with obesity in mice and humans, its cellular function is unknown. Here, we demonstrate that WDTC1 is a component of a DDB1-CUL4-ROC1 (CRL4) E3 ligase. Using 3T3-L1 cell culture model of adipogenesis, we show that disrupting the interaction between WDTC1 and DDB1 leads to a loss of adipogenic suppression by WDTC1, increased triglyceride accumulation and adipogenic gene expression. We show that the CRL4(WDTC) (1) complex promotes histone H2AK119 monoubiquitylation, thus suggesting a role for this complex in transcriptional repression during adipogenesis. Our results identify a biochemical role for WDTC1 and extend the functional range of the CRL4 complex to the suppression of fat accumulation.

L-Carnitine Ameliorates Cancer Cachexia in Mice Partly via the Carnitine Palmitoyltransferase-Associated PPAR-γ Signaling Pathway

BACKGROUND

L-Carnitine has been demonstrated to ameliorate cachectic symptoms. In the present study, we sought to investigate the role of the peroxisome proliferator-activated receptor-γ (PPAR-γ) signaling pathway in the ameliorative effects of L-carnitine on cancer cachexia in a colon-26 tumor-bearing mouse model.

METHODS

The cachectic mice received L-carnitine (p.o.) or etomoxir (i.p.), or pioglitazone hydrochloride (p.o.) or GW9662 (i.p.). The physiological cachexia parameters, biochemical parameters, and serum cytokines were measured. The expression levels of representative molecules in the PPAR-γ signaling pathway were measured by using quantitative real-time polymerase chain reaction (qRT-PCR) or Western blot analysis.

RESULTS

Oral administration of L-carnitine at 9 mg/kg/day improved the cachexia parameters and biochemical parameters in cancer cachectic mice. The elevated serum concentrations of interleukin (IL)-6 and tumor necrosis factor-α (TNF-α) were decreased by L-carnitine. These ameliorative effects of L-carnitine were lessened by the carnitine palmitoyltransferase I (CPT I) inhibitor, etomoxir. The mRNA and protein expression levels of PPAR-α and PPAR-γ were decreased in the livers of cancer cachectic mice and increased after L-carnitine administration, which attenuated the increased mRNA expression levels of sterol-regulatory element-binding protein-1c (SREBP-1c) and fatty acid synthase (FAS). Similar to pioglitazone, L-carnitine augmented the phosphorylation of PPAR-γ and attenuated the expression levels of phospho-p65 and cyclooxygenase (COX)-2. Additionally, the above-mentioned effects of L-carnitine were reversed by GW9662.

CONCLUSION

L-Carnitine exerts its ameliorative effects in cancer cachexia in association with the PPAR-γ signaling pathway.

Ananas comosus L. Leaf Phenols and p-Coumaric Acid Regulate Liver Fat Metabolism by Upregulating CPT-1 Expression

In this study, we aimed to investigate the effect and action mechanisms of pineapple leaf phenols (PLPs) on liver fat metabolism in high-fat diet-fed mice. Results show that PLP significantly reduced abdominal fat and liver lipid accumulation in high-fat diet-fed mice. The effects of PLP were comparable with those of FB. Furthermore, at the protein level, PLP upregulated the expression of carnitine palmitoyltransferase 1 (CPT-1), whereas FB had no effects on CPT-1 compared with the HFD controls. Regarding mRNA expression, PLP mainly promoted the expression of CPT-1, PGC1a, UCP-1, and AMPK in the mitochondria, whereas FB mostly enhanced the expression of Ech1, Acox1, Acaa1, and Ehhadh in peroxisomes. PLP seemed to enhance fat metabolism in the mitochondria, whereas FB mainly exerted the effect in peroxisomes. In addition, p-coumaric acid (CA), one of the main components from PLP, significantly inhibited fat accumulation in oleic acid-induced HepG2 cells. CA also significantly upregulated CPT-1 mRNA and protein expressions in HepG2 cells. We, firstly, found that PLP enhanced liver fat metabolism by upregulating CPT-1 expression in the mitochondria and might be promising in treatment of fatty liver diseases as alternative natural products. CA may be one of the active components of PLP.

A simple transcriptomic signature able to predict drug-induced hepatic steatosis

It is estimated that only a few marketed drugs are able to directly induce liver steatosis. However, many other drugs may exacerbate or precipitate fatty liver in the presence of other risk factors or in patients prone to non-alcoholic fatty liver disease. On the other hand, current in vitro tests for drug-induced steatosis in preclinical research are scarce and not very sensitive or reproducible. In the present study, we have investigated the effect of well-characterized steatotic drugs on the expression profile of 47 transcription factors (TFs) in human hepatoma HepG2 cells and found that these drugs are able to up- and down-regulate a substantial number of these factors. Multivariate data analysis revealed a common TF signature for steatotic drugs, which consistently and significantly repressed FOXA1, HEX and SREBP1C in cultured cells. This signature was also observed in the livers of rats and in cultured human hepatocytes. Therefore, we selected these three TFs as predictive biomarkers for iatrogenic steatosis. With these biomarkers, a logistic regression analysis yielded a predictive model, which was able to correctly classify 92 % of drugs. The developed algorithm also predicted that ibuprofen, nifedipine and irinotecan are potential steatotic drugs, whereas troglitazone is not. In summary, this is a sensitive, specific and simple RT-PCR test that can be easily implemented in preclinical drug development to predict drug-induced steatosis. Our results also indicate that steatotic drugs affect expression of both common and specific subsets of TF and lipid metabolism genes, thus generating complex transcriptomic responses that cause or contribute to steatosis in hepatocytes.

Consumption of Ocimum sanctum L. and Citrus paradisi infusions modulates lipid metabolism and insulin resistance in obese rats

A high saturated fat and fructose diet leads to metabolic disorders through dysregulation of genes involved in lipid metabolism.

Cholesterol-secreting and statin-responsive hepatocytes from human ES and iPS cells to model hepatic involvement in cardiovascular health

Hepatocytes play a central and crucial role in cholesterol and lipid homeostasis, and their proper function is of key importance for cardiovascular health. In particular, hepatocytes (especially periportal hepatocytes) endogenously synthesize large amounts of cholesterol and secrete it into circulating blood via apolipoprotein particles. Cholesterol-secreting hepatocytes are also the clinically-relevant cells targeted by statin treatment in vivo. The study of cholesterol homeostasis is largely restricted to the use of animal models and immortalized cell lines that do not recapitulate those key aspects of normal human hepatocyte function that result from genetic variation of individuals within a population. Hepatocyte-like cells (HLCs) derived from human embryonic and induced pluripotent stem cells can provide a cell culture model for the study of cholesterol homeostasis, dyslipidemias, the action of statins and other pharmaceuticals important for cardiovascular health. We have analyzed expression of core components for cholesterol homeostasis in untreated human iPS cells and in response to pravastatin. Here we show the production of differentiated cells resembling periportal hepatocytes from human pluripotent stem cells. These cells express a broad range of apolipoproteins required for secretion and elimination of serum cholesterol, actively secrete cholesterol into the medium, and respond functionally to statin treatment by reduced cholesterol secretion. Our research shows that HLCs derived from human pluripotent cells provide a robust cell culture system for the investigation of the hepatic contribution to human cholesterol homeostasis at both cellular and molecular levels. Importantly, it permits for the first time to also functionally assess the impact of genetic polymorphisms on cholesterol homeostasis. Finally, the system will also be useful for mechanistic studies of heritable dyslipidemias, drug discovery, and investigation of modes of action of cholesterol-modulatory drugs.

Methyl donor deficiency impairs fatty acid oxidation through PGC-1α hypomethylation and decreased ER-α, ERR-α, and HNF-4α in the rat liver

BACKGROUND & AIMS

Folate and cobalamin are methyl donors needed for the synthesis of methionine, which is the precursor of S-adenosylmethionine, the substrate of methylation in epigenetic, and epigenomic pathways. Methyl donor deficiency produces liver steatosis and predisposes to metabolic syndrome. Whether impaired fatty acid oxidation contributes to this steatosis remains unknown.

METHODS

We evaluated the consequences of methyl donor deficient diet in liver of pups from dams subjected to deficiency during gestation and lactation.

RESULTS

The deprived rats had microvesicular steatosis, with increased triglycerides, decreased methionine synthase activity, S-adenosylmethionine, and S-adenosylmethionine/S-adenosylhomocysteine ratio. We observed no change in apoptosis markers, oxidant and reticulum stresses, and carnityl-palmitoyl transferase 1 activity, and a decreased expression of SREBP-1c. Impaired beta-oxidation of fatty acids and carnitine deficit were the predominant changes, with decreased free and total carnitines, increased C14:1/C16 acylcarnitine ratio, decrease of oxidation rate of palmitoyl-CoA and palmitoyl-L-carnitine and decrease of expression of novel organic cation transporter 1, acylCoA-dehydrogenase and trifunctional enzyme subunit alpha and decreased activity of complexes I and II. These changes were related to lower protein expression of ER-α, ERR-α and HNF-4α, and hypomethylation of PGC-1α co-activator that reduced its binding with PPAR-α, ERR-α, and HNF-4α.

CONCLUSIONS

The liver steatosis resulted predominantly from hypomethylation of PGC1-α, decreased binding with its partners and subsequent impaired mitochondrial fatty acid oxidation. This link between methyl donor deficiency and epigenomic deregulations of energy metabolism opens new insights into the pathogenesis of fatty liver disease, in particular, in relation to the fetal programming hypothesis.

[All signs of metabolic syndrome in the hypertensive ISIAH rats are associated with increased activity of transcription factors PPAR, LXR, PXR, and CAR in the liver]

It is known that the metabolic syndrome (MS), which includes hypertension, dislipidemia, glucose intolerance, and obesity leads to cardiovascular diseases. The MS risk is growing catastrophically. Molecular mechanisms allowing to understand the reason of integrated dysfunctions, taking place at MS cases, have remained almost unstudied. The chronical stress plays a crucial role in MS development; therefore in the present work a hypertensive rat strain with Inherited Stress-Induced Arterial Hypertension (ISIAH) was used as a model. It was shown that ISIAH rat strain as compared with the control WAG rat strain is characterized by increased content of triglyceride, VLDL and LDL cholesterols, a decreased content of HDL cholesterol, a high level of apolipoprotein B-100, and decreased level of apolipoprotein A-I. The ISIAH rats body weight was higher as compared with WAG rats; ISIAH rats blood glucose content was higher too. Thus, strain hypertension for ISIAH rat is accompanied by dislipidemia, increased glucose content, and increased body weight, representing a whole set of MS signs. Since at MS cases the systemic abnormalities in lipid and carbohydrate metabolism take place, the functional activity of transcription factors (TFs) participating in integral regulation of lipid and carbohydrate metabolism genes in liver was measured. PPAR, LXR, PXR, CAR DNA-binding activity was increased in ISIAH rats, suggesting involvement of these TFs in MS development. Integrated investigation of PPAR, LXR, PXR, CAR regulatory mechanisms, signal transduction and transcriptional targets will provide insights into the pathogenesis of MS and offer valuable information for designing of drugs for MS treatment.

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.

The mechanistic basis for the induction of hepatic steatosis by xenobiotics

INTRODUCTION

Hepatic steatosis is the histological observation of numerous lipid inclusions due to an excess accumulation of triacylglycerols. They are a concern with new therapeutic candidates because they signify altered lipid metabolism that can progress to more serious liver toxicity.

AREAS COVERED

This article is based on an article search using the PubMed database from 1987 to 2011 and confirms associations for several previously marketed drugs with four basic hepatocellular mechanisms. The article also describes how these mechanisms are controlled by master regulators of lipid metabolism, which include gene transcription factors, nuclear receptors, hormonal signaling, energy sensing proteins, endoplasmic reticulum stress signaling and certain key metabolic intermediates.

EXPERT OPINION

Drug-induced hepatic steatosis is typically not detectable by conventional means other than invasive histological examinations. By understanding the basic mechanisms, key regulators and energy signaling systems of the liver, the investigator is better equipped to avoid xenobiotics with steatogenic potential in the drug discovery or early development process. There are now a number of methods for detecting this potential, specifically gene expression or metabolomic profiling and pathway analysis or mechanism-based in vitro systems.

Reversal of mouse Acyl-CoA oxidase 1 (ACOX1) null phenotype by human ACOX1b isoform [corrected]

Disruption of the peroxisomal acyl-CoA oxidase 1 (Acox1) gene in the mouse results in the development of severe microvesicular hepatic steatosis and sustained activation of peroxisome proliferator-activated receptor-alpha (PPARalpha). These mice manifest spontaneous massive peroxisome proliferation in regenerating hepatocytes and eventually develop hepatocellular carcinomas. Human ACOX1, the first and rate-limiting enzyme of the peroxisomal beta-oxidation pathway, has two isoforms including ACOX1a and ACOX1b, transcribed from a single gene. As ACOX1a shows reduced activity toward palmitoyl-CoA as compared with ACOX1b, we used adenovirally driven ACOX1a and ACOX1b to investigate their efficacy in the reversal of hepatic phenotype in Acox1(-/-) mice. In this study, we show that human ACOX1b is markedly effective in reversing the ACOX1 null phenotype in the mouse. In addition, expression of human ACOX1b was found to restore the production of nervonic (24:1) acid and had a negative impact on the recruitment of coactivators to the PPARalpha-response unit, which suggests that nervonic acid might well be an endogenous PPARalpha antagonist, with nervonoyl-CoA probably being the active form of nervonic acid. In contrast, restoration of docosahexaenoic (22:6) acid level, a retinoid-X-receptor (RXRalpha) agonist, was dependent on the concomitant hepatic expression of both ACOX1a and ACOX1b isoforms. This is accompanied by a specific recruitment of RXRalpha and coactivators to the PPARalpha-response unit. The human ACOX1b isoform is more effective than the ACOX1a isoform in reversing the Acox1 null phenotype in the mouse. Substrate utilization differences between the two ACOX1 isoforms may explain the reason why ACOX1b is more effective in metabolizing PPARalpha ligands.

Regulatory enzymes of mitochondrial beta-oxidation as targets for treatment of the metabolic syndrome

Insulin sensitizers like metformin generally act through pathways triggered by adenosine monophosphate-activated protein kinase. Carnitine palmitoyltransferase 1 (CPT1) controls mitochondrial beta-oxidation and is inhibited by malonyl-CoA, the product of acetyl-CoA carboxylase (ACC). The adenosine monophosphate-activated protein kinase-ACC-CPT1 axis tightly regulates mitochondrial long-chain fatty acid oxidation. Evidence indicates that ACC2, the isoform located in close proximity to CPT1, is the major regulator of CPT1 activity. ACC2 as well as CPT1 are therefore potential targets to treat components of the metabolic syndrome such as obesity and insulin resistance. Reversible inhibitors of the liver isoform of CPT1, developed to prevent ketoacidosis and hyperglycemia, have been found to be associated with side effects like hepatic steatosis. However, stimulation of systemic CPT1 activity may be an attractive means to accelerate peripheral fatty acid oxidation and hence improve insulin sensitivity. Stimulation of CPT1 can be achieved by elimination or inhibition of ACC2 activity and through activating transcription factors like peroxisome proliferator-activated receptors and their protein partners. The latter leads to enhanced CPT1 gene expression. Recent developments are discussed, including a recently identified CPT1 isoform, i.e. CPT1C. This protein is highly expressed in the brain and may provide a target for new tools to prevent obesity.

Trans-10, cis-12-conjugated linoleic acid alters hepatic gene expression in a polygenic obese line of mice displaying hepatic lipidosis

The trans-10, cis-12 isomer of conjugated linoleic acid (CLA) causes a rapid reduction of body and adipose mass in mice. In addition to changes in adipose tissue, numerous studies have reported alterations in hepatic lipid metabolism. Livers of CLA-fed mice gain mass, partly due to lipid accumulation; however, the precise molecular mechanisms are unknown. To elucidate these mechanisms, we examined fatty acid composition and gene expression profiles of livers from a polygenic obese line of mice fed 1% trans-10, cis-12-CLA for 14 days. Analysis of gene expression data led to the identification of 1393 genes differentially expressed in the liver of CLA-fed male mice at a nominal P value of .01, and 775 were considered significant using a false discovery rate (FDR) threshold of .05. While surprisingly few genes in lipid metabolism were impacted, pathway analysis found that protein kinase A (PKA) and cyclic adenosine monophosphate (cAMP) pathways signaling pathways were affected by CLA treatment and 98 of the 775 genes were found to be regulated by hepatocyte nuclear factor 4alpha, a transcription factor important in controlling liver metabolic status.

Dynamic and differential regulation of proteins that coat lipid droplets in fatty liver dystrophic mice

Lipid droplet proteins (LDPs) coat the surface of triglyceride-rich lipid droplets and regulate their formation and lipolysis. We profiled hepatic LDP expression in fatty liver dystrophic (fld) mice, a unique model of neonatal hepatic steatosis that predictably resolves between postnatal day 14 (P14) and P17. Western blotting revealed that perilipin-2/ADRP and perilipin-5/OXPAT were markedly increased in steatotic fld liver but returned to normal by P17. However, the changes in perilipin-2 and perilipin-5 protein content in fld mice were exaggerated compared with relatively modest increases in corresponding mRNAs encoding these proteins, a phenomenon likely mediated by increased protein stability. Conversely, cell death-inducing DFFA-like effector (Cide) family genes were strongly induced at the level of mRNA expression in steatotic fld mouse liver. Surprisingly, levels of peroxisome proliferator-activated receptor gamma, which is known to regulate Cide expression, were unchanged in fld mice. However, sterol-regulatory element binding protein 1 (SREBP-1) was activated in fld liver and CideA was revealed as a new direct target gene of SREBP-1. In summary, LDP content is markedly increased in liver of fld mice. However, whereas perilipin-2 and perilipin-5 levels are primarily regulated posttranslationally, Cide family mRNA expression is induced, suggesting that these families of LDP are controlled at different regulatory checkpoints.

An increased flux through the glucose 6-phosphate pool in enterocytes delays glucose absorption in Fxr-/- mice

The farnesoid X receptor (FXR) is involved in regulation of bile acid and lipid metabolism. Recently, a role for FXR in control of glucose metabolism became evident. Because FXR is expressed along the length of the small intestine, we evaluated the potential role of FXR in glucose absorption and processing. During intravenous infusion of a trace amount of d-[6,6-(2)H(2)]glucose, a d-[U-(13)C]glucose-enriched oral glucose bolus was given, and glucose kinetics were determined in wild-type and Fxr(-/-) mice. Compared with wild-type mice, Fxr(-/-) mice showed a delayed plasma appearance of orally administered glucose. Multicompartmental kinetic modeling revealed that this delay was caused by an increased flux through the glucose 6-phosphate pool in enterocytes. Thus, our results show involvement of FXR in intestinal glucose absorption, representing a novel physiological function for this nuclear receptor.

Polymorphisms of MRP2 (ABCC2) are associated with susceptibility to nonalcoholic fatty liver disease

AIMS

We hypothesized that ABCC2 gene variants may contribute to susceptibility to nonalcoholic fatty liver disease (NAFLD). Additionally, we tested the hypothesis of a relation between gene variants and disease severity.

PATIENTS AND METHODS

The study involved 167 individuals: 109 consecutively presenting unrelated patients with features of NAFLD and different stages of disease severity, and a group of 58 healthy individuals. Four tag single-nucleotide polymorphisms (SNPs; rs717620 A/G, rs2756105 C/T, rs2002042 C/T and rs3740066 A/G) representing 46 polymorphic sites (r(2)>.8) were genotyped. Furthermore, two additional SNPs (rs17222723 A/T and rs8187710 G/A) were included.

RESULTS

On univariate analysis, after multiple comparison correction by permutation tests, there were significant differences observed in the allele frequencies of rs17222723 and rs8187710 between healthy individuals and NAFLD patients (empirical P=.037 and .035, respectively). Allelic odds ratios [95% confidence interval] for rs17222723 and rs8187710 were 2.80 [1.11-7.04] and 2.80 [1.11-7.04], respectively. When we tested the hypothesis of a relation between gene variants and the clinical and histological spectra of NAFLD by multinomial regression analysis, a significant association was observed with the same markers: rs17222723 (P=.0029) and rs8187710 (P=.015).

CONCLUSIONS

Our study suggests a potential role of ABCC2 in susceptibility to NAFLD and disease severity.

Statins in liver disease: a molehill, an iceberg, or neither?

A growing number of chronic liver disease patients, especially those with metabolic syndrome-associated nonalcoholic fatty liver disease or hepatitis C virus-associated dysmetabolic syndrome, will take statins to prevent cardiovascular disease. As a result, clinicians will weigh complex issues raised by the interaction of statins with liver metabolism in these disorders. In this article, we critically review data concerning statins and liver pathophysiology with an emphasis on nonalcoholic fatty liver disease and hepatitis C virus, while also touching on other chronic liver diseases. Basic research interests include statins' mechanism of action and their effects on cholesterol-related cell signaling pathways and angiogenesis. From the clinical standpoint, many chronic liver diseases increase cardiovascular risk and would undeniably benefit from sustained statin use. The false alarms and security accompanying aminotransferase monitoring, however, are disturbing in light of the scarcity of data on statins' long-term effects on liver histology. Although some actions of statins might eventually prove to be particularly useful in nonalcoholic steatohepatitis, hepatitis C virus, or hepatocellular carcinoma, others may prove harmful. The lack of definitive data makes a fully informed decision impossible. Research using histological endpoints is urgently needed to determine the indications and contraindications of this extraordinary class of agents in patients with chronic liver disease.

Fatty acids metabolic profile in high fat diet-induced non-alcoholic fatty liver disease in rats

AIM: To analyze fatty acid metabolic profile changes of fatty livers induced by a high fat diet and to determine it's role in non-alcoholic steatohepatitis (NASH).

METHODS: Sprague-Dawley rats were randomly divided into two groups: the control group (treated with normal diet, n = 7) and the model group (treated with high fat diet, n = 7). The rats were all killed at wk 16 to detect pathological changes in liver tissues. The metabolic profile changes of fatty acid in NASH and normal liver tissue samples were detected by ECF derivatization for GC/MS technology. Data were analyzed using SPSS 11.0 software package.

RESULTS: After a high fat diet for 16 wk, severe fatty livers (+++) were present in the high fat diet group with remarkable inflammation. A significant morphological difference was detected between the two groups. Total ion current (TIC) and principal component analysis (PCA) indicated that there were significantly different metabolic patterns in liver tissues between the two groups. Compared with the control group, all fatty acids were raised significantly except a 56% decrease in dodecanoic acid (P < 0.05). Octadecanoic acid, tetradecanoic acid, hexadecanoic acid, eicosanoic acid, 9-octadecenoic acid, 9, 12, 15-octadecatrienoic acid, 5, 8, 11, 14-eicosatetraenoic acid and 9, 12-octadecadienoic acid were raised 5.42, 4.10, 11.56, 5.86, 1.82 and 8.00, 2.44-folds, respectively. Moreover, ω-6/ω-3 polyunsaturated fatty acids (PUFAs) ratio was raised.

CONCLUSION: Our results suggest that there are significant fatty acids metabolic profile changes in NASH. Excessive fatty acids accumulation in hepatic cells, ω-6/ω-3 ratio imbalance and dudecanoic acid decrease may pay a crucial role in steatohepatitis and hepatic injury.

Inhibition of mitochondrial fatty acid oxidation in vivo only slightly suppresses gluconeogenesis but enhances clearance of glucose in mice

Mitochondrial fatty acid oxidation (mFAO) is considered to be essential for driving gluconeogenesis (GNG) during fasting. However, quantitative in vivo data on de novo synthesis of glucose-6-phosphate upon acute inhibition of mFAO are lacking. We assessed hepatic glucose metabolism in vivo after acute inhibition of mFAO by 30 mg kg(-1) 2-tetradecylglycidic acid (TDGA) in hypoketotic hypoglycemic male C57BL/6J mice by the infusion of [U-(13)C]glucose, [2-(13)C]glycerol, [1-(2)H]galactose, and paracetamol for 6 hours, which was followed by mass isotopomer distribution analysis in blood glucose and urinary paracetamol-glucuronide. During TDGA treatment, endogenous glucose production was unaffected (127 +/- 10 versus 118 +/- 7 micromol kg(-1) minute(-1), control versus TDGA, not significant), but the metabolic clearance rate of glucose was significantly enhanced (15.9 +/- 0.9 versus 26.3 +/- 1.1 mL kg(-1) minute(-1), control versus TDGA,P < 0.05). In comparison with control mice, de novo synthesis of glucose-6-phosphate (G6P) was slightly decreased in TDGA-treated mice (108 +/- 19 versus 85 +/- 6 micromol kg(-1) minute(-1), control versus TDGA, P < 0.05). Recycling of glucose was decreased upon TDGA treatment (26 +/- 14 versus 12 +/- 4 micromol kg(-1) minute(-1), control versus TDGA, P < 0.05). Hepatic messenger RNA (mRNA) levels of genes encoding enzymes involved in de novo G6P synthesis were unaltered, whereas glucose-6-phosphate hydrolase mRNA expressions were increased in TDGA-treated mice. Glucokinase and pyruvate kinase mRNA levels were significantly decreased, whereas pyruvate dehydrogenase kinase isozyme 4 expression was increased 30-fold; this suggested decreased glycolytic activity.

CONCLUSION

Acute pharmacological inhibition of mFAO using TDGA had no effect on endogenous glucose production and only a marginal effect on de novo G6P synthesis. Hence, fully active mFAO is not essential for maintenance of hepatic GNG in vivo in fasted mice.