De Novo Lipogenesis Research Articles

Regulation on Citrate Influx and Metabolism through Inhibiting SLC13A5 and ACLY: A Novel Mechanism Mediating the Therapeutic Effects of Curcumin on NAFLD.

Upregulated de novo lipogenesis (DNL) plays a pivotal role in the progress of the nonalcoholic fatty liver disease (NAFLD). Cytoplasmic citrate flux, mediated by plasma membrane citrate transporter (SLC13A5), mitochondrial citrate carrier (SLC25A1), and ATP-dependent citrate lyase (ACLY), determines the central carbon source for acetyl-CoA required in DNL. Curcumin, a widely accepted dietary polyphenol, can attenuate lipid accumulation in NAFLD. Here, we first investigated the lipid-lowering effect of curcumin against NAFLD in oleic and palmitic acid (OPA)-induced primary mouse hepatocytes and high-fat plus high-fructose diet (HFHFD)-induced mice. Curcumin profoundly attenuated OPA- or HFHFD-induced hyperlipidemia and aberrant hepatic lipid deposition via modulating the expression and function of SLC13A5 and ACLY. The possible mechanism of curcumin on the citrate pathway was investigated using HepG2 cells, HEK293T cells transfected with human SLC13A5, and recombinant human ACLY. In OPA-stimulated HepG2 cells, curcumin rectified the dysregulated expression of SLC13A5/ACLY possibly via the AMPK-mTOR signaling pathway. Besides, curcumin also functionally inhibited both citrate transport and metabolism mediated by SLC13A5 and ACLY, respectively. These findings confirm that curcumin improves the lipid accumulation in the liver by blocking citrate disposition and hence may be used to prevent NAFLD.

Losartan Prevents Hepatic Steatosis and Macrophage Polarization by Inhibiting HIF-1α in a Murine Model of NAFLD.

Hypoxia and hepatosteatosis microenvironments are fundamental traits of nonalcoholic fatty liver disease (NAFLD). Hypoxia-inducible factor-1α (HIF-1α) is a transcription factor that controls the cellular response to hypoxia and is activated in hepatocytes of patients with NAFLD, whereas the route and regulation of lipid droplets (LDs) and macrophage polarization related to systemic inflammation in NAFLD is unknown. Losartan is an angiotensin II receptor antagonist, that approved portal hypertension and related HIF-1α pathways in hepatic injury models. Here, we show that losartan in a murine model of NAFLD significantly decreased hepatic de novo lipogenesis (DNL) as well as suppressed lipid droplets (LDs), LD-associated proteins, perilipins (PLINs), and cell-death-inducing DNA-fragmentation-factor (DFF45)-like effector (CIDE) family in liver and epididymal white adipose tissues (EWAT) of ob/ob mice. Obesity-mediated macrophage M1 activation was also required for HIF-1α expression in the liver and EWAT of ob/ob mice. Administration of losartan significantly diminishes obesity-enhanced macrophage M1 activation and suppresses hepatosteatosis. Moreover, HIF-1α-mediated mitochondrial dysfunction was reversed in ob/ob mice treated with losartan. Together, the regulation of HIF-1α controls LDs protein expression and macrophage polarization, which highlights a potential target for losartan in NAFLD.

Defective insulin-stimulated GLUT4 translocation in brown adipocytes induces systemic glucose homeostasis dysregulation independent of thermogenesis in female mice

ObjectiveRecent studies indicate that brown adipose tissue, in addition to its role in thermogenesis, has a role in the regulation of whole-body metabolism. Here we characterize the metabolic effects of deleting Rab10, a protein key for insulin stimulation of glucose uptake into white adipocytes, solely from brown adipocytes. MethodsWe used a murine brown adipocyte cell line and stromal vascular fraction-derived in vitro differentiated brown adipocytes to study the role of Rab10 in insulin-stimulated GLUT4 translocation to the plasma membrane and insulin-stimulated glucose uptake. We generated a brown adipocyte-specific Rab10 knockout for in vivo studies of metabolism and thermoregulation. ResultsWe demonstrate that deletion of Rab10 from brown adipocytes results in a two-fold reduction of insulin-stimulated glucose transport by reducing translocation of the GLUT4 glucose transporter to the plasma membrane, an effect linked to whole-body glucose intolerance and insulin resistance in female mice. This effect on metabolism is independent of the thermogenic function of brown adipocytes, thereby revealing a metabolism-specific role for brown adipocytes in female mice. The reduced glucose uptake induced by Rab10 deletion disrupts ChREBP regulation of de novo lipogenesis (DNL) genes, providing a potential link between DNL in brown adipocytes and whole-body metabolic regulation in female mice. However, deletion of Rab10 from male mice does not induce systemic insulin resistance, although ChREBP regulation is disrupted. ConclusionsOur studies of Rab10 reveal the role of insulin-regulated glucose transport into brown adipocytes in whole-body metabolic homeostasis of female mice. Importantly, the contribution of brown adipocytes to whole-body metabolic regulation is independent of its role in thermogenesis. It is unclear whether the whole-body metabolic sexual dimorphism is because female mice are permissive to the effects of Rab10 deletion from brown adipocytes or because male mice are resistant to the effect.

A Narrative Review on the Role of AMPK on De Novo Lipogenesis in Non-Alcoholic Fatty Liver Disease: Evidence from Human Studies.

5′AMP-activated protein kinase (AMPK) is known as metabolic sensor in mammalian cells that becomes activated by an increasing adenosine monophosphate (AMP)/adenosine triphosphate (ATP) ratio. The heterotrimeric AMPK protein comprises three subunits, each of which has multiple phosphorylation sites, playing an important role in the regulation of essential molecular pathways. By phosphorylation of downstream proteins and modulation of gene transcription AMPK functions as a master switch of energy homeostasis in tissues with high metabolic turnover, such as the liver, skeletal muscle, and adipose tissue. Regulation of AMPK under conditions of chronic caloric oversupply emerged as substantial research target to get deeper insight into the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Evidence supporting the role of AMPK in NAFLD is mainly derived from preclinical cell culture and animal studies. Dysbalanced de novo lipogenesis has been identified as one of the key processes in NAFLD pathogenesis. Thus, the scope of this review is to provide an integrative overview of evidence, in particular from clinical studies and human samples, on the role of AMPK in the regulation of primarily de novo lipogenesis in human NAFLD.

Loss of Acot12 contributes to NAFLD independent of lipolysis of adipose tissue

In this study, we hypothesized that deregulation in the maintenance of the pool of coenzyme A (CoA) may play a crucial role in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). Specific deletion of Acot12 (Acot12−/−), the major acyl-CoA thioesterase, induced the accumulation of acetyl-CoA and resulted in the stimulation of de novo lipogenesis (DNL) and cholesterol biosynthesis in the liver. KEGG pathway analysis suggested PPARα signaling as the most significantly enriched pathway in Acot12−/− livers. Surprisingly, the exposure of Acot12−/− hepatocytes to fenofibrate significantly increased the accumulation of acetyl-CoA and resulted in the stimulation of cholesterol biosynthesis and DNL. Interaction analysis, including proximity-dependent biotin identification (BioID) analysis, suggested that ACOT12 may directly interact with vacuolar protein sorting-associated protein 33A (VPS33A) and play a role in vesicle-mediated cholesterol trafficking and the process of lysosomal degradation of cholesterol in hepatocytes. In summary, in this study, we found that ACOT12 deficiency is responsible for the pathogenesis of NAFLD through the accumulation of acetyl-CoA and the stimulation of DNL and cholesterol via activation of PPARα and inhibition of cholesterol trafficking.

Measurement of lipogenic flux by deuterium resolved mass spectrometry

De novo lipogenesis (DNL) is disrupted in a wide range of human disease. Thus, quantification of DNL may provide insight into mechanisms and guide interventions if it can be performed rapidly and noninvasively. DNL flux is commonly measured by 2H incorporation into fatty acids following deuterated water (2H2O) administration. However, the sensitivity of this approach is limited by the natural abundance of 13C, which masks detection of 2H by mass spectrometry. Here we report that high-resolution Orbitrap gas-chromatography mass-spectrometry resolves 2H and 13C fatty acid mass isotopomers, allowing DNL to be quantified using lower 2H2O doses and shorter experimental periods than previously possible. Serial measurements over 24-hrs in mice detects the nocturnal activation of DNL and matches a 3H-water method in mice with genetic activation of DNL. Most importantly, DNL is detected in overnight-fasted humans in less than an hour and is responsive to feeding during a 4-h study. Thus, 2H specific MS provides the ability to study DNL in settings that are currently impractical.

Agomelatine reduces circulating triacylglycerides and hepatic steatosis in fructose-treated rats

Agomelatine (AGO) is an antidepressant drug with agonistic activity at melatonin receptor 1 (MT1) and MT2 and with neutral antagonistic activity at serotonin receptor 5-HT2C. Although experimental studies show that melatonin reduces hypertriglyceridemia and hepatic steatosis induced by excessive fructose intake, no studies have tested if AGO exerts similar actions. To address this issue we have treated male Wistar rats with fructose (15% in the drinking water) and/or AGO (40 mg/kg/day) for two weeks. AGO reduced body weight gain, feeding efficiency and hepatic lipid levels without affecting caloric intake in fructose-treated rats. AGO has also decreased very low-density lipoprotein (VLDL) production and circulating TAG levels after an oral load with olive oil. Accordingly, treatment with AGO reduced the hepatic expression of fatty acid synthase (Fasn), a limiting step for hepatic de novo lipogenesis (DNLG). The expression of apolipoprotein B (Apob) and microsomal triglyceride transfer protein (Mttp) in the ileum, two crucial proteins for intestinal lipoprotein production, were also downregulated by treatment with AGO. Altogether, the present data show that AGO mimics the metabolic benefits of melatonin when used in fructose-treated rats. This study also suggests that it is relevant to evaluate the potential of AGO to treat metabolic disorders in future clinical trials.

New Insights on Hepatic De Novo Lipogenesis in Rat’s Fetus

ObjectivesAmong the macronutrients provided by the mothers to fetuses free fatty acids (FFA), particularly palmitic acid and glycerol cross the placental barrier in smaller proportions respect to glucose and amino acids, due to a minor placental permeability. It has already been suggested that during advanced gestation, fetal FA are mainly derived from de novo lipogenesis (DNL) in the fetal liver. Therefore, the aim of this study was to evaluate DNL metabolic biomarkers in fetuses of rat dams at gestational day (GD) 16, which represent the beginning of the third stage of gestation. Peculiarly, besides the usual lipid biomarkers of DNL, increase of PA and POA and the ratio PA/LA, we also evaluated whether C16:0 ceramide biosynthesis was enhanced by DNL thereby representing a novel biomarker of DNL. MethodsThe profile of FA and ceramides was measured by using LC-DAD and MS/MS in line in liver of rat dams sacrificed at GD16 and their fetuses. Differences between rat dams and their fetuses were determined by an Mann-Whitney unpaired test. ResultsOur results show that lipid metabolism in the liver of fetuses, when compared to those of their mother, was characterized by profound differences in the fatty acid profile, i.e., increased levels of the palmitic acid (16:0) (1.24 fold; p = 0.04) and its desaturase product palmitoleic acid (16:1-n7) (2.5 fold; p = 0.002) indicating an overactive DNL. Peculiarly, we found striking higher levels (30 fold; p = 0.02) in fetal liver respect to rat dams liver of C16:0 ceramide, while the other ceramides species didn’t increase significantly. ConclusionsOur data suggest that the 16:0 to form fetal C16:0 ceramide derives from DNL. C16:0 ceramide in adults is usually associated to impaired insulin signalling and energy homeostasis, and eventually to insulin resistance and type 2 diabetes. On the other hand, it has also been shown that C16:0 ceramide sustains lipogenesis, which may be functional to the increased fetal growth rate characteristic of the last gestational stage. Funding SourcesThis study was supported by grant from the Ministry of University and Research (MUR) - Proof of Concept 2018.

Rottlerin Suppresses Fat Accumulation by Inhibiting Adipogenesis and De Novo Lipogenesis in 3T3-L1 Adipocytes

ObjectivesRottlerin is isolated from Mallotus japonicus, a rich-in polyphenol. Rottlerin is a PKC delta inhibitor known for an uncoupler of oxidative phosphorylation and anti-neoplastic agent. However, the effect of anti-obesity is not conclusive. This study hypothesized that rottlerin inhibits lipid accumulation in adipocytes. Methods3T3-L1 cells were maintained with DMEM containing 10% BCS and 1% penicillin. The cells were seeded in a 6-well plate with a density of 8 × 104 followed by cultured for 4 days until reaching 120% confluency and incubated in a differentiation medium for 6 days. Rottlerin was incubated with differentiation media (0, 1, 2, and 4 μM). Cells were harvested after treatment for measurement of Oil Red O stating, immunoblotting, and RT-PCR. ResultsDifferentiated 3T3-L1 adipocytes were stained using the Oil Red O, which stains triglycerides into the red. Lipid accumulation was significantly inhibited in 4 μM of rottlerin (P < 0.001). In protein levels, PPARγ, an adipogenesis marker, was reduced dose-dependently decreased (P < 0.001), indicating lipid droplet formation reduced. FAS and SCD1 were diminished by rottlerin treated groups (all P < 0.001). ACC-pS79/ACC was increased by rottlerin (P = 0.02). In mRNA gene expressions, C/EBPα was reduced by rottlerin in a dose-dependent manner (P < 0.001), and PPARγ tend to be decreased by rottlerin (P = 0.06). FAS and SREBP1 were inhibited by rottlerin (P < 0.01). SCD1 was dramatically reduced by rottlerin (P < 0.001). ConclusionsWe found that rottlerin reduces lipid accumulation by inhibiting adipogenesis in differentiated 3T3-L1 adipocytes. This suggests that rottlerin is a potential nutraceutical for treating dyslipidemia, non-alcoholic fatty liver disease, and obesity. Funding SourcesThis work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (Ministry of Science and ICT; MSIT).

Discovery of analogues of non-β oxidizable long-chain dicarboxylic fatty acids as dual inhibitors of fatty acids and cholesterol synthesis: Efficacy of lead compound in hyperlipidemic hamsters reveals novel mechanism

Background and aimsCholesterol and triglycerides are risk factors for developing cardiovascular disease. Therefore, appropriate cells and assays are required to discover and develop dual cholesterol and fatty acid inhibitors. A predictive hyperlipidemic animal model is needed to evaluate mechanism of action of lead molecule for therapeutic indications. Methods and resultsPrimary hepatocytes from rat, hamster, rabbit, and humans were compared for suitability to screen compounds by de novo lipogenesis (DNL) using14C-acetate. Hyperlipidemic hamsters were used to evaluate efficacy and mode of action.In rat hepatocytes DNL assay, both the central moiety and carbon chain length influenced the potency of lipogenesis inhibition. In hyperlipidemic hamsters, ETC-1002 decreased plasma cholesterol and triglycerides by 41% and 49% at the 30 mg/kg dose. Concomitant decreases in non-esterified fatty acids (−34%) and increases in ketone bodies (20%) were associated with induction of hepatic CPT1-α. Reductions in proatherogenic VLDL-C and LDL-C (−71% and −64%) occurred partly through down-regulation of DGAT2 and up-regulation of LPL and PDK4. Activation of PLIN1 and PDK4 dampened adipogenesis and showed inverse correlation with adipose mass. Hepatic concentrations of cholesteryl ester and TG decreased by 67% and 64%, respectively. Body weight decreased with concomitant decreases in epididymal fat. Plasma and liver concentrations of ETC-1002 agreed with the observed dose–response efficacy. ConclusionsTaken together, ETC-1002 reduced proatherogenic lipoproteins, hepatic lipids and adipose tissues in hyperlipidemic hamsters via induction of LPL, CPT1-α, PDK4, and PLIN1, and downregulation of DGAT2. These characteristics may be useful in the treatment of fatty livers that causes non-alcoholic steatohepatitis.

Iron oxide nanoparticles aggravate hepatic steatosis and liver injury in nonalcoholic fatty liver disease through BMP-SMAD-mediated hepatic iron overload

Nonalcoholic fatty liver disease (NAFLD) is the leading hepatic manifestation of metabolic syndrome worldwide, and is clinically accompanied by iron overload. As the increasing application of iron oxide nanoparticles (IONPs) on the imaging and diagnosis in NAFLD, the potential hepatic effect and mechanism of IONPs on NAFLD should be well studied. Here, we demonstrate that carboxyl-modified (COOH-IONPs) and amino-coated IONPs (NH2-IONPs) exhibit no significant hepatic toxicity in normal mice at the clinical injection dose, but aggravate SREBP-1c-mediated de novo lipogenesis (DNL) in the livers of mice with NAFLD induced by high-fat diet (HFD) and in HepG2 cells incubated with oleic acid (OA), especially in those treated by the positive NH2-IONPs. In the present study, mice receiving IONPs for 7 day show mild iron overload in the liver and exhibit enhanced hepatic inflammation in NAFLD. The BMP-SMAD pathway is initiated by hepatic iron overload and is aggravated in NAFLD. In conclusion, BMP-SMAD-mediated hepatic iron overload aggravated lipid accumulation in the liver and hepatic inflammatory responses, implying that effective measures in addition to hepatic iron overload are needed for individuals at the risk of IONPs in NAFLD.

Geniposide and Chlorogenic Acid Combination Improves Non-Alcoholic Fatty Liver Disease Involving the Potent Suppression of Elevated Hepatic SCD-1.

Background: Non-alcoholic fatty liver disease (NAFLD), characterized by the excessive accumulation of hepatic triglycerides (TGs), has become a worldwide chronic liver disease. But efficient therapy keeps unsettled. Our previous works show that geniposide and chlorogenic acid combination (namely the GC combination), two active chemical components combined with a unique ratio (67.16:1), presents beneficial effects on high-fat diet-induced NAFLD rodent models. Notably, microarray highlighted the more than 5-fold down-regulated SCD-1 gene in the GC combination group. SCD-1 is an essential lipogenic protein for monounsaturated fatty acids’ biosynthesis and serves as a key regulatory enzyme in the last stage of hepatic de novo lipogenesis (DNL). Methods: NAFLD mice model was fed with 16 weeks high-fat diet (HFD). The pharmacological effects, primarily on hepatic TG, TC, FFA, and liver enzymes, et al. of the GC combination and two individual components were evaluated. Furthermore, hepatic SCD-1 expression was quantified with qRT-PCR, immunoblotting, and immunohistochemistry. Finally, the lentivirus-mediated over-expressed cell was carried out to confirm the GC combination’s influence on SCD-1. Results: The GC combination could significantly reduce hepatic TG, TC, and FFA in NAFLD rodents. Notably, the GC combination presented synergetic therapeutic effects, compared with two components, on normalizing murine hepatic lipid deposition and disordered liver enzymes (ALT and AST). Meanwhile, the robust SCD-1 induction induced by HFD and FFA in rodents and ALM-12 cells was profoundly blunted, and this potent suppression was recapitulated in lentivirus-mediated SCD-1 over-expressed cells. Conclusion: Taken together, our data prove that the GC combination shows a substantial and synergetic anti-lipogenesis effect in treating NAFLD, and these amelioration effects are highly associated with the potent suppressed hepatic SCD-1 and a blunted DNL process.

Short Term Glucagon‐Like Peptide‐1 Receptor Agonist Therapy Does Not Influence Hepatic De Novo Lipogenesis in Polycystic Ovary Syndrome

Background PCOS is common and associated with obesity and the metabolic syndrome. Adolescents with PCOS and obesity are more likely to have hepatic steatosis (HS) which portends worsening metabolic disease. Glucagon like peptide -1 receptor agonist (GLP1RA) therapy has been shown to reduce HS, but its influence on mechanisms such as decreasing of de novo lipogenesis (DNL) or free fatty acid (FFA) concentrations are unknown. Methods Adolescents with obesity and PCOS (N=22), half with HS, were enrolled. Participants underwent an overnight metabolic study followed by a morning oral sugar tolerance test (OSTT; 76-78 g glucose +25 g fructose), with half treated with an evening and morning dose of GLP1RA. Serum for fasting and post-OSTT hormones and metabolic markers was collected. DNL rates were measured fasting and during the OSTT using an overnight intravenous stable isotope 13C2 acetate infusion with measurements of incorporation of the tracer into VLDL-triglyceride palmitate. Hepatic fat was measured with MRI utilizing the Dixon method. Groups were compared via t-test or Mann-Whitney U. Metabolic curves between groups were compared via linear mixed effects models. Results TheGLP1RA (N=10, age 15.3 ± 2.2 years, BMI 34.9 ± 7.7 kg/m2, 50% HS) and control groups (N=12, age 16.0 ± 2.2, BMI 36.3 ± 5.7, 50% HS) were similar at baseline in terms of hormonal and metabolic measures, although the fasting serum TG were significantly higher in GLP1RA (126 [95,169] vs 87 [75,106] mg/dL). In GLP1RA, OSTT glucose curveswere significantly lower (p<0.001 overall), as were time points 20, 60, 75, 90, 105, 120, 135, 150, 180, and 210 minutes. Although the OSTT response curves between the groups were not different for FFA, insulin, glycerol or glucagon, fasting glucagon was lower, and insulin at 60 min and glycerol at 300 min were higher in GLP1RA. No significant group differences were found between measures of fractional DNL, although the GLP1RA group was non-significantly lower for every individual time point during fasting and post-OSTT. The absolute DNL level was similar between groups. Conclusions Two doses of GLP1RA treatment impacted fasting and OSTT glucose, insulin and glucagon responses. Glycerol and FFA concentrations did not change and there was a trend for lower fractional DNL. Further study after a longer duration of GLP1RA treatment is needed to determine if decreased DNL is associated with decreases in hepatic steatosis following GLP1RA therapy.

MED1 is a lipogenesis coactivator required for postnatal adipose expansion

MED1 often serves as a surrogate of the general transcription coactivator complex Mediator for identifying active enhancers. MED1 is required for phenotypic conversion of fibroblasts to adipocytes in vitro but its role in adipose development and expansion in vivo has not been reported. Here we show that MED1 is dispensable for adipose development in mice. Instead, MED1 is required for postnatal adipose expansion and the induction of de novo lipogenesis (DNL) genes after pups switch diet from high-fat maternal milk to carbohydrate-based chow. During adipogenesis, MED1 is dispensable for induction of lineage-determining transcription factors (TFs) PPARγ and C/EBPα but is required for lipid accumulation in the late phase of differentiation. Mechanistically, MED1 controls the induction of DNL genes by facilitating lipogenic TF ChREBP-dependent recruitment of Mediator to active enhancers. Together, our findings identify a cell- and gene-specific regulatory role of MED1 as a lipogenesis coactivator required for postnatal adipose expansion.

Expanding Roles of De Novo Lipogenesis in Breast Cancer.

In recent years, lipid metabolism has gained greater attention in several diseases including cancer. Dysregulation of fatty acid metabolism is a key component in breast cancer malignant transformation. In particular, de novo lipogenesis provides the substrate required by the proliferating tumor cells to maintain their membrane composition and energetic functions during enhanced growth. However, it appears that not all breast cancer subtypes depend on de novo lipogenesis for fatty acid replenishment. Indeed, while breast cancer luminal subtypes rely on de novo lipogenesis, the basal-like receptor-negative subtype overexpresses genes involved in the utilization of exogenous-derived fatty acids, in the synthesis of triacylglycerols and lipid droplets, and fatty acid oxidation. These metabolic differences are specifically associated with genomic and proteomic changes that can perturb lipogenic enzymes and related pathways. This behavior is further supported by the observation that breast cancer patients can be stratified according to their molecular profiles. Moreover, the discovery that extracellular vesicles act as a vehicle of metabolic enzymes and oncometabolites may provide the opportunity to noninvasively define tumor metabolic signature. Here, we focus on de novo lipogenesis and the specific differences exhibited by breast cancer subtypes and examine the functional contribution of lipogenic enzymes and associated transcription factors in the regulation of tumorigenic processes.

Relationship between de novo lipogenesis and serum sex hormone binding globulin in humans.

ObjectiveObesity and liver fat are associated with decreased levels of serum sex hormone binding globulin (SHBG). Laboratory studies suggest that hepatic de novo lipogenesis (DNL) is involved in the downregulation of SHBG synthesis. The aim of the present study was to address the role of DNL on serum SHBG in humans.DesignA cross‐sectional study examining the association between DNL, measured by stable isotopes, and serum SHBG, stratified by sex.ParticipantsHealthy men (n = 34) and women (n = 21) were combined from two cross‐sectional studies. Forty‐two per cent of participants had hepatic steatosis, and the majority were overweight (62%) or obese (27%).ResultsDNL was inversely associated with SHBG in women (β: −0.015, 95% CI: −0.030; 0.000), but not in men (β: 0.007, 95% CI: −0.005; 0.019) (p for interaction = .068). Adjustment for study population, age and body mass index did not materially change these results, although statistical significance was lost after adjustment for serum insulin.ConclusionsAn inverse association between DNL and SHBG may explain the decreased SHBG levels that are observed in obesity, at least in women.

N-3 PUFAs protect against adiposity and fatty liver by promoting browning in postnatally overfed male rats: a role for NRG4

Early-life nutrition plays an important role in regulating adult metabolism. This study evaluated the effects of early nutrition during the suckling and postweaning periods on expression of the adipocytokine Neuregulin 4 (Nrg4) and its relationship with nonalcoholic fatty liver disease (NAFLD) in adulthood. In vivo, male rats were adjusted to litter sizes of three (small litter, SL) or ten (normal litter, NL) on postnatal day 3. Pups were fed control chow (NL and SL groups) or a high-fat diet (NL-HF and SL-HF groups), and SL pups specifically were fed a fish oil diet rich in n-3 polyunsaturated fatty acids (n-3 PUFAs) (SL-FO group), from postnatal weeks 3 to 13. The results demonstrated that postnatal overnutrition increased weight, hepatic de novo lipogenesis (DNL) gene expression and NAFLD and decreased body temperature and Nrg4, Ucp1 and Pgc1a mRNA expression in adipose tissues in SL, SL-HF and NL-HF rats compared to NL rats in adulthood. The opposite trends were observed in SL-FO rats. Moreover, in vitro, recombinant NRG4 protein reduced lipid accumulation by inhibiting DNL gene expression in fatty HepG2 cells stimulated with sodium oleate. In HPAs, eicosapentaenoic acid (EPA) treatment elevated NRG4 production and caused adipocyte browning, and these effects were abrogated by PPARG antagonism. In conclusion, a postweaning n-3 PUFA diet enhanced Nrg4 expression in adipose tissues, associated with attenuation of NAFLD induced by SL rearing. Additionally, external NRG4 reduced lipogenesis in steatotic hepatocytes. Thus, white adipose tissue browning induced by n-3 PUFAs may promote NRG4 production through the PPARG pathway.

Pharmacologic inhibition of ketohexokinase prevents fructose-induced metabolic dysfunction

ObjectiveRecent studies suggest that excess dietary fructose contributes to metabolic dysfunction by promoting insulin resistance, de novo lipogenesis (DNL), and hepatic steatosis, thereby increasing the risk of obesity, type 2 diabetes (T2D), non-alcoholic steatohepatitis (NASH), and related comorbidities. Whether this metabolic dysfunction is driven by the excess dietary calories contained in fructose or whether fructose catabolism itself is uniquely pathogenic remains controversial. We sought to test whether a small molecule inhibitor of the primary fructose metabolizing enzyme ketohexokinase (KHK) can ameliorate the metabolic effects of fructose. MethodsThe KHK inhibitor PF-06835919 was used to block fructose metabolism in primary hepatocytes and Sprague Dawley rats fed either a high-fructose diet (30% fructose kcal/g) or a diet reflecting the average macronutrient dietary content of an American diet (AD) (7.5% fructose kcal/g). The effects of fructose consumption and KHK inhibition on hepatic steatosis, insulin resistance, and hyperlipidemia were evaluated, along with the activation of DNL and the enzymes that regulate lipid synthesis. A metabolomic analysis was performed to confirm KHK inhibition and understand metabolite changes in response to fructose metabolism in vitro and in vivo. Additionally, the effects of administering a single ascending dose of PF-06835919 on fructose metabolism markers in healthy human study participants were assessed in a randomized placebo-controlled phase 1 study. ResultsInhibition of KHK in rats prevented hyperinsulinemia and hypertriglyceridemia from fructose feeding. Supraphysiologic levels of dietary fructose were not necessary to cause metabolic dysfunction as rats fed the American diet developed hyperinsulinemia, hypertriglyceridemia, and hepatic steatosis, which were all reversed by KHK inhibition. Reversal of the metabolic effects of fructose coincided with reductions in DNL and inactivation of the lipogenic transcription factor carbohydrate response element-binding protein (ChREBP). We report that administering single oral doses of PF-06835919 was safe and well tolerated in healthy study participants and dose-dependently increased plasma fructose indicative of KHK inhibition. ConclusionsFructose consumption in rats promoted features of metabolic dysfunction seen in metabolic diseases such as T2D and NASH, including insulin resistance, hypertriglyceridemia, and hepatic steatosis, which were reversed by KHK inhibition.

High-fructose feeding does not induce steatosis or non-alcoholic fatty liver disease in pigs

Non-alcoholic fatty liver disease (NAFLD) is an increasingly prevalent condition that has been linked to high-fructose corn syrup consumption with induction of hepatic de novo lipogenesis (DNL) as the suggested central mechanism. Feeding diets very high in fructose (> 60%) rapidly induce several features of NAFLD in rodents, but similar diets have not yet been applied in larger animals, such as pigs. With the aim to develop a large animal NAFLD model, we analysed the effects of feeding a high-fructose (HF, 60% w/w) diet for four weeks to castrated male Danish Landrace-York-Duroc pigs. HF feeding upregulated expression of hepatic DNL proteins, but levels were low compared with adipose tissue. No steatosis or hepatocellular ballooning was seen on histopathological examination, and plasma levels of transaminases were similar between groups. Inflammatory infiltrates and the amount of connective tissue was slightly elevated in liver sections from fructose-fed pigs, which was corroborated by up-regulation of macrophage marker expression in liver homogenates. Supported by RNA-profiling, quantitative protein analysis, histopathological examination, and biochemistry, our data suggest that pigs, contrary to rodents and humans, are protected against fructose-induced steatosis by relying on adipose tissue rather than liver for DNL.

Glucocorticoid signaling and lipid metabolism disturbances in the liver of rats treated with 5α-dihydrotestosterone in an animal model of polycystic ovary syndrome.

Polycystic ovary syndrome (PCOS) is a complex reproductive disorder often associated with obesity, insulin resistance, and dyslipidemia. Hormonal changes in PCOS may also include altered glucocorticoid signaling. Our aim was to examine whether alterations in hepatic glucocorticoid signaling are associated with disturbances of glucose and lipid metabolism in animal model of PCOS. Female rats, 3 weeks old, were subcutaneously implanted with 5α-dihydrotestosterone (DHT) or placebo pellets for 90 days to induce PCOS. Expression of 11β-hydroxysteroid dehydrogenase 1 (11βHSD1) and A-ring reductases (5α and 5β), as well as intracellular distribution of glucocorticoid receptor (GR) and expression of its regulated genes were examined in the liver. Proteins of hepatic lipid and carbohydrate metabolism and markers of inflammation were also assessed. DHT treatment induced increase in body and liver mass, as well as in triglycerides and free fatty acids levels in plasma. Elevation of 11βHSD1 and reduction of 5α-reductase expression was observed together with increased hepatic corticosterone concentration and nuclear GR activation. Induced expression of Krüppel-like factor 15 and decreased expression of genes for proinflammatory cytokines and de novo lipogenesis (DNL) were detected in the liver of DHT-treated rats, while DNL regulators and proinflammatory markers were not changed. However, increased mRNA levels of stearoyl-CoA desaturase and apolipoprotein B were observed in DHT animals. DHT treatment stimulated hepatic glucocorticoid prereceptor metabolism through increased corticosterone availability which is associated with enhanced GR activation. This does not affect gluconeogenesis and DNL, but could be linked to stimulated triglyceride synthesis and hypertriglyceridemia.