Steatosis In High-fat Diet-fed Mice Research Articles

Madecassoside ameliorates hepatic steatosis in high-fat diet-fed mice through AMPK/autophagy-mediated suppression of ER stress

Hepatic endoplasmic reticulum (ER) stress is a contributing factor in the development of hepatic steatosis in obesity. Madecassoside (MA), a pentacyclic triterpene derived from Centella asiatica, is known for its anti-inflammatory properties in the treatment of skin wounds. However, the impact of MA on hepatic ER stress and lipid metabolism in experimental obesity models has not been investigated. In this study, we examined the effects of MA on primary hepatocytes treated with palmitate and the livers of mice fed a high-fat diet (HFD). Our findings demonstrated that MA treatment reduced lipogenic lipid accumulation, apoptosis, and ER stress in hepatocytes. Additionally, MA treatment increased the phosphorylation of AMP-activated protein kinase (AMPK) and markers of autophagy. Importantly, when AMPK was inhibited by small interfering RNA (siRNA) or autophagy was blocked by 3-methyladenine (3MA), the protective effects of MA against ER stress, lipogenic lipid deposition, and apoptosis in palmitate-treated hepatocytes were abolished. These results suggest that MA mitigates hepatic steatosis in obesity through an AMPK/autophagy-dependent pathway. The present study highlights the potential of MA as a promising therapeutic candidate for hepatic steatosis.

Type II Transmembrane Serine Proteases as Modulators in Adipose Tissue Phenotype and Function.

Adipose tissue is a crucial organ in energy metabolism and thermoregulation. Adipose tissue phenotype is controlled by various signaling mechanisms under pathophysiological conditions. Type II transmembrane serine proteases (TTSPs) are a group of trypsin-like enzymes anchoring on the cell surface. These proteases act in diverse tissues to regulate physiological processes, such as food digestion, salt-water balance, iron metabolism, epithelial integrity, and auditory nerve development. More recently, several members of the TTSP family, namely, hepsin, matriptase-2, and corin, have been shown to play a role in regulating lipid metabolism, adipose tissue phenotype, and thermogenesis, via direct growth factor activation or indirect hormonal mechanisms. In mice, hepsin deficiency increases adipose browning and protects from high-fat diet-induced hyperglycemia, hyperlipidemia, and obesity. Similarly, matriptase-2 deficiency increases fat lipolysis and reduces obesity and hepatic steatosis in high-fat diet-fed mice. In contrast, corin deficiency increases white adipose weights and cell sizes, suppresses adipocyte browning and thermogenic responses, and causes cold intolerance in mice. These findings highlight an important role of TTSPs in modifying cellular phenotype and function in adipose tissue. In this review, we provide a brief description about TTSPs and discuss recent findings regarding the role of hepsin, matriptase-2, and corin in regulating adipose tissue phenotype, energy metabolism, and thermogenic responses.

Patchouli alcohol ameliorates skeletal muscle insulin resistance and NAFLD via AMPK/SIRT1-mediated suppression of inflammation

Obesity-induced chronic low-grade inflammation and thus causes various metabolic diseases, such as insulin resistance and non-alcoholic fatty liver disease (NAFLD). Patchouli alcohol (PA), an active component extracted from patchouli, displayed anti-inflammatory effects on different cell types. However, the impact of PA on skeletal muscle insulin signaling and hepatic lipid metabolism remains unclear. This study aimed to investigate whether PA would affect insulin signaling impairment in myocytes and lipid metabolism in hepatocytes. Treatment with PA ameliorated palmitate-induced inflammation and aggravation of insulin signaling in C2C12 myocytes and lipid accumulation in HepG2 hepatocytes. Treatment of C2C12 myocytes and HepG2 cells with PA augmented AMP-activated protein kinase (AMPK) phosphorylation and Sirtuin 1 (SIRT1) expression in a dose-dependent manner. siRNA-mediated suppression of AMPK or SIRT1 mitigated the effects of PA on palmitate-induced inflammation and insulin resistance in C2C12 myocytes and lipid accumulation in HepG2 cells. Animal experiments demonstrated that PA administration increased AMPK phosphorylation and SIRT1 expression, and ameliorated inflammation, thereby attenuating skeletal muscle insulin resistance and hepatic steatosis in high-fat diet-fed mice. These results denote that PA alleviates skeletal muscle insulin resistance and hepatic steatosis through AMPK/SIRT1-dependent signaling. This study might provide a novel therapeutic approach for treating obesity-related insulin resistance and NAFLD.

Suppression of E4BP4 SUMOylation sensitize mice to HFD‐induced fatty liver disease by promoting lipid droplet formation

Background As the most common chronic liver disease, non-alcoholic fatty liver disease (NAFLD) affects 10-30% of the general population. Characterized by excessive lipid droplet formation in hepatocytes, fatty liver may progress to nonalcoholic steatohepatitis (NASH), eventually leading to cirrhosis and liver failure. Currently, there have been no effective therapeutic or preventive measures for NAFLD. Thus, there is an urgent need to identify hepatic mediators that promote lipid droplet accumulation as well as the underlying molecular mechanisms in the liver during the pathogenesis of NAFLD. We previously reported that E4 promoter-binding protein 4 (E4BP4) is an insulin-induced stabilizer of the lipogenic factor SREBP-1c and promotes the SREBP-1c-mediated lipogenesis in hepatocytes. Our most recent mass spectrometry data revealed that E4BP4 may undergo SUMOylation, a reversible post-translational modification that was shown to regulate E4BP4-dependent NK cell development. In this study, we set out to determine how hepatic E4BP4 regulates lipid droplet formation and liver steatosis a high-fat diet-induced NAFLD mouse model and investigate how E4BP4 SUMOylation impacts the process. Results Compared with E4bp4flox/flox mice, E4bp4 liver-specific KO (E4bp4-LKO) mice exhibit decreased lipid accumulation in the liver despite similar body weight after 12 weeks of high-fat diet feeding. Our microarray analysis showed a reduction in the expression of lipid droplet biding genes such as Cidea, Cidec (Fsp27), Plin4 in the liver of E4bp4-LKO mice. Restoring E4bp4 expression in E4bp4-LKO primary hepatocytes was sufficient to induce lipid droplet formation and Fsp27β expression, while overexpression of Fsp27β increased lipid droplets and triglycerides in E4bp4-LKO primary mouse hepatocytes and promoted lipid accumulation HFD-fed E4bp4-LKO mice. Meanwhile, we generated an E4BP4 mutant, namely E4BP4-5KR, which contains five lysine to arginine (5KR) substitutions in the five SUMOylation motifs. Our in vitro SUMOylation assay confirmed the SUMOylation of E4BP4-WT but not E4BP4-5KR mutant in the presence of E1/2, SUMO2/3, and ATP. We detected more lipid droplet formation in hepa1 cells transfected with E4bp4-5KR vs. E4bp4-WT. Lastly, the abundance of SUMOylated E4BP4 was reduced in the liver of high-fat diet-fed mice vs. regular chow-fed mice. Conclusion All together, our data demonstrated that E4bp4 drives lipid droplet formation and live steatosis in high-fat diet-fed mice likely through its regulation of lipid-droplet binding genes. Our study also highlights the critical role of deSUMOylation of hepatic E4BP4 in promoting NAFLD and suggests that E4BP4 SUMOylation in the liver could be targeted for treating NAFLD.

Effects of the Combination of Evogliptin and Leucine on Insulin Resistance and Hepatic Steatosis in High-Fat Diet-Fed Mice.

In this study, we aimed to investigate the effects of 8 weeks of treatment with a combination of evogliptin and leucine, a branched-chain amino acid, in mice with high-fat diet (HFD)-induced diabetes. Treatment with evogliptin alone or in combination with leucine reduced the body weight of the mice, compared to the case for those from the HFD control group. Long-term treatment with evogliptin alone or in combination with leucine resulted in a significant reduction in glucose intolerance; however, leucine alone did not affect postprandial glucose control, compared to the case for the mice from the HFD control group. Furthermore, the combination of evogliptin and leucine prevented HFD-induced insulin resistance, which was associated with improved homeostasis model assessment for insulin resistance, accompanied by markedly reduced liver fat deposition, hepatic triglyceride content, and plasma alanine aminotransferase levels. The combination of evogliptin and leucine increased the gene expression levels of hepatic peroxisome proliferator-activated receptor alpha, whereas those of the sterol regulatory element-binding protein 1 and stearoyl-CoA desaturase 1 were not altered, compared to the case in the HFD-fed mice (p<0.05). Thus, our results suggest that the combination of evogliptin and leucine may be beneficial for treating patients with type 2 diabetes and hepatic steatosis; however, further studies are needed to delineate the molecular mechanisms underlying the action of this combination.

Anti-hepatic steatosis activity of Sicyos angulatus extract in high-fat diet-fed mice and chemical profiling study using UHPLC-qTOF-MS/MS spectrometry

BackgroundNonalcoholic fatty liver disease (NAFLD) is a hepatic manifestation of metabolic syndrome. Recently, the inhibitory effects of flavone glycosides isolated from Sicyos angulatus extract on hepatic lipid accumulation in vitro were demonstrated. However, the effects of S. angulatus extract and its major flavonoid glycoside on in vivo hepatic steatosis induced by a high-fat diet have not yet been established. Hypothesis/PurposeThe aim of this study was to investigate the effects of S. angulatus extract and its major flavonoid glycoside, kaempferol 3-O-[α-l-rhamnopyranosyl-(1→6)]-β-d-glucopyranosyl-7-O-α-l-rhamnopyranoside, on hepatic steatosis in high-fat diet-fed mice, which serves as a model of NAFLD. In addition, attempts have been made to chemically profile the metabolites involved in the activity of the S. angulatus extract. MethodsC57BL/6 J mice were divided into vehicle, total extract of S. angulatus (SA; 50, 100 and 200 mg/kg) and major active component (20 mg/kg) groups. The mice were fed a high-fat diet (HFD) with or without S. angulatus extract or its major single compound for 10 weeks. Chemical identification was carried out using ultra-high-pressure liquid chromatography-quadrupole time-of-flight tandem mass spectrometry (UHPLC-qTOF-MS/MS) and then quantified by HPLC-DAD. ResultsAdministration of S. angulatus extract significantly lowered plasma ALT and AST levels in HFD-fed mice compared to those of the vehicle group. The hepatic lipid content, as evidenced by oil-red O staining and quantification, was significantly lower in the S. angulatus-administered group, and the effect was dose dependent. These beneficial effects of S. angulatus extract were related to the decreased expression of hepatic genes involved in fatty acid (ACC1, FAS and SCD1) and triglyceride (DGAT) synthesis. The expression levels of two key transcription factors regulating lipogenesis, SREBP-1c and PPARγ, were significantly suppressed in the liver by administration of S. angulatus extract with HFD. Treatment of the HFD-fed mice with the major compound isolated from S. angulatus extract resulted in improved liver function along with an anti-steatotic effect similar to the results seen with S. angulatus extract. For the standardization of the S. angulatus extract, 23 compounds were identified based on MS/MS fragmentation and UV spectroscopy. Quantitative analysis of the major compound showed that the major component was present in 15.35 ± 0.01 mg/g of total extract. ConclusionThese findings suggest that S. angulatus extract and its major component have the potential to improve liver function and hepatic steatosis in diet-induced obese mice.

Effects of lobeglitazone on insulin resistance and hepatic steatosis in high-fat diet-fed mice.

Lobeglitazone (Lobe) is a novel thiazolidinedione antidiabetic drug that reduces insulin resistance by activating peroxisome proliferator-activated receptor-gamma (PPARγ). However, the exact mechanisms of antidiabetic effects of Lobe have not been established in an animal model. The aim of this study was to evaluate the hypoglycemic effects of Lobe and investigate possible factors involved in Lobe-enhanced hepatic steatosis in high-fat diet (HFD)-fed mice. Mice were fed an HFD for 15 weeks. Lobe was administrated orally during the last 9 weeks. Lobe treatment significantly reduced insulin resistance and increased expression of hepatic glucose transporter 4 (GLUT4) and PPARs in HFD-fed mice. However, increased body weight and hepatic steatosis were not reduced by Lobe in these mice. Metabolomics fingerprinting showed that several lipogenesis-related hepatic and serum metabolites in HFD-fed mice had positive or negative correlations with Lobe administration. In particular, increased leptin levels during HFD were further increased by Lobe. HFD-induced signaling transducer and activator of transcription 3 (STAT3) phosphorylation in the hypothalamus was increased by Lobe. In addition, immunohistochemical analysis showed more proopiomelanocortin (POMC)-positive neurons in the hypothalamus of HFD-fed mice (with or without Lobe) compared with normal diet-fed mice. Despite improving leptin signaling in the hypothalamus and enhancing insulin sensitivity in HFD-fed mice, Lobe increased body weight and steatosis. Further research is necessary regarding other factors affecting Lobe-enhanced hepatic steatosis and hyperphagia.

Kefir alleviates obesity and hepatic steatosis in high-fat diet-fed mice by modulation of gut microbiota and mycobiota: targeted and untargeted community analysis with correlation of biomarkers

Kefir is a probiotic beverage containing over 50 species of lactic acid bacteria and yeast. In this study, the anti-obesity and anti-non-alcoholic fatty liver disease (NAFLD) effects of kefir were comprehensively addressed along with targeted and untargeted community analysis of the fecal microbiota in a high-fat diet (HFD)-induced obese mouse model. HFD-fed C57BL/6 mice were orally administrated either kefir or milk (control) once a day for 12 weeks, and body and organ weight, fecal microbiota and mycobiota, histopathology, blood cholesterol and cytokines and gene expressions were analyzed. Compared to the control, mice in the kefir group exhibited a significantly lower body weight (34.18 g vs. 40.24 g; p=0.00004) and histopathological liver lesion score (1.13 vs. 3.25; p=0.002). Remarkably, the kefir-fed mice also harbored more Lactobacillus/Lactococcus (7.01 vs. 6.32 log CFU/g), total yeast (6.07 vs. 5.01 log CFU/g) and Candida (5.56 vs. 3.88 log CFU/g). Kefir administration also up-regulated genes related to fatty acid oxidation, PPARα and AOX, in both the liver and adipose tissue (PPARα, 2.95- and 2.15-fold; AOX, 1.89- and 1.9-fold, respectively). The plasma concentration of IL-6, a proinflammatory marker, was significantly reduced following kefir consumption (50.39 pg/ml vs. 111.78 pg/ml; p=0.03). Strikingly, the populations of Lactobacillus/Lactococcus, total yeast and Candida were strongly correlated with PPARα gene expression in adipose and hepatic tissue (r=0.599, 0.580 and 0.562, respectively). These data suggest that kefir consumption modulates gut microbiota and mycobiota in HFD-fed mice, which prevents obesity and NAFLD via promoting fatty acid oxidation.

Oxyresveratrol Supplementation to C57bl/6 Mice Fed with a High-Fat Diet Ameliorates Obesity-Associated Symptoms.

Oxyresveratrol has been proven effective in inhibiting adipogenesis in a 3T3-L1 cell model. We investigated the preventive effect of oxyresveratrol supplementation on obesity development in high-fat diet-fed mice. Male C57bl/6 mice were randomly subjected to control (5% fat by weight, LF), high-fat (30% fat by weight, HF), and high-fat supplemented with 0.25% and 0.5% oxyresveratrol (OXY1 and OXY2, respectively) diet groups for eight weeks. Oxyresveratrol supplementation effectively alleviated obesity-associated symptoms such as insulin resistance, hyperglycemia, and hepatic steatosis in high-fat diet-fed mice. Compared to the high-fat diet group, oxyresveratrol supplementation suppressed expression of glucose-6-phosphatase, sterol regulatory element-binding proteins 1, fatty acid synthase and CCAAT/Enhancer-binding proteins α, and elevated AMP-activated protein kinase (α2-catalytic subunit) level in liver, upregulated insulin-dependent glucose transporter type 4 level in adipose tissue, and increased expression of insulin receptor substrate 1, insulin-dependent glucose transporter type 4, AMP-activated protein kinase α, peroxisome proliferator-activated receptor γ coactivator-1α, and sirtuin 1 in muscle to regulate lipid and glucose homeostasis in these tissues. This study demonstrated that oxyresveratrol supplementation effectively ameliorated obesity-associated symptoms in high-fat diet-fed mice, presumably attributed to mediating critical regulators involved in lipid and glucose homeostasis in liver, visceral fat, and muscle.

Myeloid-specific SIRT1 Deletion Aggravates Hepatic Inflammation and Steatosis in High-fat Diet-fed Mice.

Sirtuin 1 (SIRT1) is a mammalian NAD+-dependent protein deacetylase that regulates cellular metabolism and inflammatory response. The organ-specific deletion of SIRT1 induces local inflammation and insulin resistance in dietary and genetic obesity. Macrophage-mediated inflammation contributes to insulin resistance and metabolic syndrome, however, the macrophage-specific SIRT1 function in the context of obesity is largely unknown. C57/BL6 wild type (WT) or myeloid-specific SIRT1 knockout (KO) mice were fed a high-fat diet (HFD) or normal diet (ND) for 12 weeks. Metabolic parameters and markers of hepatic steatosis and inflammation in liver were compared in WT and KO mice. SIRT1 deletion enhanced HFD-induced changes on body and liver weight gain, and increased glucose and insulin resistance. In liver, SIRT1 deletion increased the acetylation, and enhanced HFD-induced nuclear translocation of nuclear factor kappa B (NF-κB), hepatic inflammation and macrophage infiltration. HFD-fed KO mice showed severe hepatic steatosis by activating lipogenic pathway through sterol regulatory element-binding protein 1 (SREBP-1), and hepatic fibrogenesis, as indicated by induction of connective tissue growth factor (CTGF), alpha-smooth muscle actin (α-SMA), and collagen secretion. Myeloid-specific deletion of SIRT1 stimulates obesity-induced inflammation and increases the risk of hepatic fibrosis. Targeted induction of macrophage SIRT1 may be a good therapy for alleviating inflammation-associated metabolic syndrome.