The role of the lipogenic pathway in the development of hepatic steatosis

Protective Effects of Alisma orientale Extract against Hepatic Steatosis via Inhibition of Endoplasmic Reticulum Stress

Endoplasmic reticulum (ER) stress is associated with the pathogenesis of hepatic steatosis. Alisma orientale Juzepzuk is a traditional medicinal herb for diuretics, diabetes, hepatitis, and inflammation. In this study, we investigated the protective effects of methanol extract of the tuber of Alisma orientale (MEAO) against ER stress-induced hepatic steatosis in vitro and in vivo. MEAO inhibited the tunicamycin-induced increase in luciferase activity of ER stress-reporter constructs containing ER stress response element and ATF6 response element. MEAO significantly inhibited tunicamycin-induced ER stress marker expression including GRP78, CHOP, and XBP-1 in tunicamycin-treated Human hepatocellular carcinoma (HepG2) cells and the livers of tunicamycin-injected mice. It also inhibited tunicamycin-induced accumulation of cellular triglyceride. Similar observations were made under physiological ER stress conditions such as in palmitate (PA)-treated HepG2 cells and the livers of high-fat diet (HFD)-induced obese mice. MEAO repressed hepatic lipogenic gene expression in PA-treated HepG2 cells and the livers of HFD obese mice. Furthermore, MEAO repressed very low-density lipoprotein receptor (VLDLR) expression and improved ApoB secretion in the livers of tunicamycin-injected mice or HFD obese mice as well as in tunicamycin or PA-treated HepG2 cells. Alismol, a guaiane-type sesquiterpenes in Alisma orientale, inhibited GRP78 expression in tunicamycin-treated HepG2 cells. In conclusion, MEAO attenuates ER stress and prevents hepatic steatosis pathogenesis via inhibition of expression of the hepatic lipogenic genes and VLDLR, and enhancement of ApoB secretion.

Endogenously elevated n-3 polyunsaturated fatty acids alleviate acute ethanol-induced liver steatosis

Effective means for the prevention of alcohol-induced liver disease, a global health problem, have yet to be developed. We evaluated whether the high endogenous levels of omega-3 polyunsaturated acids (n-3 PUFA) in fat-1 transgenic mice could protect them against acute ethanol-induced liver steatosis. We induced alcoholic liver steatosis in 9-week-old male heterozygous fat-1 mice and their wild-type (WT) male littermates through three oral gavages of 60% ethanol at 4.7 g/kg body weight. Hepatic lipid accumulation was significantly increased in both alcohol treatment groups, but by much less in the fat-1 group compared with the WT group. Fat-1 mice exhibited significantly lower levels of total hepatic/plasma TG and plasma alanine aminotransferase activity. Accordingly, hepatic expression of lipogenesis-related genes (e.g., SREBP-1c, FAS, and SCD-1) and plasma levels of inflammatory cytokines (e.g., IL-6, TNF-α, and MCP-1) were reduced in the fat-1 mice. Furthermore, decreased hepatic expression of cytochrome P450 2E1 (CYP2E1) and increased hepatic levels of PPAR-α and HO-1 were observed in the fat-1 mice, compared to the WT mice. These findings show that elevated tissue n-3 PUFA protect against acute ethanol-induced liver steatosis in fat-1 mice, possibly through the down-regulation of hepatic lipogenesis, inflammatory response, and oxidative stress.

Vigna nakashimae extract prevents hepatic steatosis in obese mice fed high-fat diets

Vigna species are important food resources and are traditionally used for the treatment of various diseases. In this study, we examined the inhibitory effects of Vigna nakashimae (VN) extract on high-fat diet (HFD)-induced hepatic steatosis and elucidated the molecular mechanisms. C57BL/6J mice were fed an HFD with or without VN extract for 16 weeks. VN extract decreased HFD-induced body weight, liver weight, hepatic lipid accumulation, and plasma alanine aminotransferase, and suppressed oxidative stress and inflammation associated with hepatitis. VN extract decreased plasma lipid levels and the expression of lipogenic genes in the livers of HFD-fed mice. VN extract significantly increased phosphorylation of adenosine monophosphate (AMP)-activated protein kinase (AMPK) and acetyl-CoA carboxylase, and expression of fatty acid oxidation genes in the liver of VN-treated HFD mice and HepG2 cells. Further, VN extract inhibited insulin or glucose-stimulated lipogenesis in HepG2 cells. In conclusion, VN extract prevents HFD-induced hepatic steatosis and lipotoxicity through AMPK activation.

Resveratrol prevents hepatic steatosis and endoplasmic reticulum stress and regulates the expression of genes involved in lipid metabolism, insulin resistance, and inflammation in rats

Previous research demonstrated that resveratrol possesses promising properties for preventing obesity. Endoplasmic reticulum (ER) stress was proposed to be involved in the pathophysiology of both obesity and hepatic steatosis. In the current study, we hypothesized that resveratrol could protect against high-fat diet (HFD)-induced hepatic steatosis and ER stress and regulate the expression of genes related to hepatic steatosis. Rats were fed either a control diet or a HFD for 12 weeks. After 4 weeks, HFD-fed rats were treated with either resveratrol or vehicle for 8 weeks. Body weight, serum metabolic parameters, hepatic histopathology, and hepatic ER stress markers were evaluated. Moreover, an RT2 Profiler Fatty Liver PCR Array was performed to investigate the mRNA expressions of 84 genes related to hepatic steatosis. Our work showed that resveratrol prevented dyslipidemia and hepatic steatosis induced by HFD. Resveratrol significantly decreased activating transcription factor 4, C/EBP-homologous protein and immunoglobulin binding protein levels, which were elevated by the HFD. Resveratrol also decreased PKR-like ER kinase phosphorylation, although it was not affected by the HFD. Furthermore, resveratrol increased the expression of peroxisome proliferator-activated receptor δ, while decreasing the expression of ATP citrate lyase, suppressor of cytokine signaling-3, and interleukin-1β. Our data suggest that resveratrol can prevent hepatic ER stress and regulate the expression of peroxisome proliferator-activated receptor δ, ATP citrate lyase, suppressor of cytokine signaling-3, tumor necrosis factor α, and interleukin-1β in diet-induced obese rats, and these effects likely contribute to resveratrol's protective function against excessive accumulation of fat in the liver.

Vitex agnus-castus L. (Verbenaceae) Improves the Liver Lipid Metabolism and Redox State of Ovariectomized Rats

Vitex agnus-castus (VAC) is a plant that has recently been used to treat the symptoms of menopause, by its actions on the central nervous system. However, little is known about its actions on disturbances in lipid metabolism and nonalcoholic fat liver disease (NAFLD), frequently associated with menopause. Ovariectomized (OVX) rats exhibit increased adiposity and NAFLD 13 weeks after ovary removal and were used as animal models of estrogen deficiency. The rats were treated with crude extract (CE) and a butanolic fraction of VAC (ButF) and displayed the beneficial effects of a reduction in the adiposity index and a complete reversion of NAFLD. NAFLD reversion was accompanied by a general improvement in the liver redox status. The activities of some antioxidant enzymes were restored and the mitochondrial hydrogen peroxide production was significantly reduced in animals treated with CE and the ButF. It can be concluded that the CE and ButF from Vitex agnus-castus were effective in preventing NAFLD and oxidative stress, which are frequent causes of abnormal liver functions in the postmenopausal period.

Effects of ferulic acid and γ-oryzanol on high-fat and high-fructose diet-induced metabolic syndrome in rats

BACKGROUND

The high morbidity of metabolic dysfunction diseases has heightened interest in seeking natural and safe compounds to maintain optimal health. γ-Oryzanol (OZ), the ferulic acid (FA) ester with phytosterols, mainly present in rice bran has been shown to improve markers of metabolic syndrome. This study investigates the effects of FA and OZ on alleviating high-fat and high-fructose diet (HFFD)-induced metabolic syndrome parameters.

METHODS

Male SD rats were fed with a regular rodent diet, HFFD, or HFFD supplemented with 0.05% FA or 0.16% OZ (equimolar concentrations) for 13 weeks. Food intake, organ indices, serum lipid profiles, glucose metabolism, insulin resistance (IR) index and cytokine levels were analyzed. The mechanisms were further investigated in oleic acid-stimulated HepG2 cells by analyzing triglyceride (TG) content and lipogenesis-related gene expressions.

RESULTS

In the in vivo study, FA and OZ exhibited similar effects in alleviating HFFD-induced obesity, hyperlipidemia, hyperglycemia, and IR. However, only OZ treatment significantly decreased liver index and hepatic TG content, lowered serum levels of C-reactive protein and IL-6, and increased serum concentration of adiponectin. In the in vitro assay, only OZ administration significantly inhibited intracellular TG accumulation and down-regulated expression of stearoyl coenzyme-A desaturase-1, which might facilitate OZ to enhance its hepatoprotective effect.

CONCLUSION

OZ is more effective than FA in inhibiting hepatic fat accumulation and inflammation. Thus, FA and OZ could be used as dietary supplements to alleviate the deleterious effects of HFFD.

Hepatitis C viral proteins perturb metabolic liver zonation

BACKGROUND & AIMS

The metabolic identity of a hepatocyte is determined by its position along the porto-centrilobular axis of a liver lobule. Altered patterns of metabolic liver zonation are associated with several pathologies. In hepatitis C, although only a minority of hepatocytes harbour the virus, the liver undergoes major systemic metabolic changes. We have investigated the HCV-driven mechanisms that allow the systemic loss of metabolic zonation.

METHODS

Transgenic mice with hepatocyte-targeted expression of all HCV proteins (FL-N/35 model) and needle biopsies from hepatitis C patients were studied with respect to patterns of lipid deposition in the context of metabolic zonation of the liver lobule.

RESULTS

We report that low levels of viral proteins are sufficient to drive striking alterations of hepatic metabolic zonation. In mice, a major lipogenic enzyme, fatty acid synthase, was redistributed from its normal periportal expression into the midzone of the lobule, coinciding with a highly specific midzone accumulation of lipids. Strikingly, alteration of zonation was not limited to lipogenic enzymes and appeared to be driven by systemic signalling via the Wnt/β-catenin pathway. Importantly, we show that similarly perturbed metabolic zonation appears to precede steatosis in early stages of human disease associated with HCV infection.

CONCLUSIONS

Our results rationalize systemic effects on liver metabolism, triggered by a minority of infected cells, thus opening new perspectives for the investigation of HCV-related pathologies.

Fatty acid changes help to better understand regression of nonalcoholic fatty liver disease

AIM: To investigate whether liver steatosis reduction due to a six-month dietary intervention results in significant changes in the concentrations of fatty acids.

METHODS: A group of 35 Caucasian individuals diagnosed with different levels of steatosis were prospectively enrolled in the present study. Analysis of the fatty acid profiles was performed according to changes in liver steatosis (liver steatosis reduction by one or two degrees) after a six-month dietary intervention. The diet helped reduce body mass in obese and overweight patients, and stabilize both glycemia and dyslipidemia. Fatty acids were extracted according to the Folch method and analyzed by gas chromatography.

RESULTS: This study showed significant changes in fatty acid profiles in patients who had reduced liver steatosis by one as well as two degrees. A reduction in liver steatosis by one degree caused a significant increase in the level of the n-3 family: eicosapentaenoic acid (P < 0.055), docosapentaenoic acid-C 22:5 (P < 0.05) and docosahexaenoic acid (P < 0.05). A reduction in liver steatosis by two degrees caused a significant decrease in serum palmitoleic acid-C 16:1 (P < 0.05).

CONCLUSION: Liver steatosis reduction is associated with changes in fatty acid profiles, and these changes may reflect an alteration in fatty acid synthesis and metabolism. These findings may help better understand regression of nonalcoholic fatty liver disease.

1-deoxynojirimycin isolated from Bacillus subtilis improves hepatic lipid metabolism and mitochondrial function in high-fat-fed mice

The aim of this study was to determine whether 1-deoxynojirimycin (DNJ) isolated from Bacillus subtilis MORI beneficially influences lipid metabolism and mitochondrial function in the liver of mice fed a high-fat diet in addition to the anti-obesity properties of DNJ. Male C57BL/6 mice (n = 29; 5 weeks old) were randomly assigned to three groups: normal control diet (CTL, n = 10), high-fat diet (HF, n = 10), and high-fat diet supplemented with DNJ (DNJ, n = 9). After 12 weeks, the HF group exhibited higher overall weight gain, of the liver, and of various fat pads than the CTL and DNJ groups did. The HF group also showed greater expression of C/EBPα and CD36 mRNA in the liver than that in the CTL and/or DNJ groups. In addition, mRNA expressions of AAC and FAS were lower, while mRNA expression of PGC-1β was higher in the liver of the DNJ group than that of the HF group. The hepatic expression of p-AMPK/AMPK was higher in the DNJ group than in the HF group. This study provides novel insight into the protective effect of DNJ supplementation against obesity-induced hepatic lipid abnormalities and mitochondrial dysfunction.

DLK1/PREF1 regulates nutrient metabolism and protects from steatosis

Nonalcoholic fatty liver disease (NAFLD) is associated with insulin resistance and obesity, as well as progressive liver dysfunction. Recent animal studies have underscored the importance of hepatic growth hormone (GH) signaling in the development of NAFLD. The imprinted Delta-like homolog 1 (Dlk1)/preadipocyte factor 1 (Pref1) gene encodes a complex protein producing both circulating and membrane-tethered isoforms whose expression dosage is functionally important because even modest elevation during embryogenesis causes lethality. DLK1 is up-regulated during embryogenesis, during suckling, and in the mother during pregnancy. We investigated the normal role for elevated DLK1 dosage by overexpressing Dlk1 from endogenous control elements. This increased DLK1 dosage caused improved glucose tolerance with no primary defect in adipose tissue expansion even under extreme metabolic stress. Rather, Dlk1 overexpression caused reduced fat stores, pituitary insulin-like growth factor 1 (IGF1) resistance, and a defect in feedback regulation of GH. Increased circulatory GH culminated in a switch in whole body fuel metabolism and a reduction in hepatic steatosis. We propose that the function of DLK1 is to shift the metabolic mode of the organism toward peripheral lipid oxidation and away from lipid storage, thus mediating important physiological adaptations associated with early life and with implications for metabolic disease resistance.

Induction of fatty liver by Coleus forskohlii extract through enhancement of de novo triglyceride synthesis in mice

Coleus forskohlii extract (CFE), an herbal ingredient, is used for weight-loss products. CFE's alleged efficacy is attributed to forskolin. However, CFE has been shown to induce fatty liver in mice, with components other than forskolin playing a part in this effect. The present study addressed the underlying mechanism of CFE-induced fatty liver by analyzing changes in CFE-treated mice of lipid concentrations and of the levels of mRNAs encoding enzymes and transcription factors known to be related to fatty liver. Mice were fed a diet containing 0, 0.3 and 1% CFE for 2 weeks. CFE at 1% clearly induced fatty liver, as demonstrated by histological examination and confirmed by increases in triglyceride concentrations in liver. However, treated mice did not exhibit elevation in plasma levels of non-esterified fatty acids. Comprehensive analysis of liver mRNA levels revealed accumulation of multiple transcripts, including mRNAs encoding enzymes acetyl-CoA carboxylase and long-chain elongase; transcription factor peroxisome proliferator-activated receptor gamma (PPARγ); and lipid-droplet-associated fat-specific protein 27 (Fsp27). These findings suggest that the de novo synthesis and accumulation of triglyceride in the liver, through the enhanced expression of specific lipogenic mRNAs, is a major underlying mechanism of fatty liver induction by CFE.

Differences in the prospective association between individual plasma phospholipid saturated fatty acids and incident type 2 diabetes: the EPIC-InterAct case-cohort study

BACKGROUND

Conflicting evidence exists regarding the association between saturated fatty acids (SFAs) and type 2 diabetes. In this longitudinal case-cohort study, we aimed to investigate the prospective associations between objectively measured individual plasma phospholipid SFAs and incident type 2 diabetes in EPIC-InterAct participants.

METHODS

The EPIC-InterAct case-cohort study includes 12,403 people with incident type 2 diabetes and a representative subcohort of 16,154 individuals who were selected from a cohort of 340.234 European participants with 3·99 million person-years of follow-up (the EPIC study). Incident type 2 diabetes was ascertained until Dec 31, 2007, by a review of several sources of evidence. Gas chromatography was used to measure the distribution of fatty acids in plasma phospholipids (mol%); samples from people with type 2 diabetes and subcohort participants were processed in a random order by centre, and laboratory staff were masked to participant characteristics. We estimated country-specific hazard ratios (HRs) for associations per SD of each SFA with incident type 2 diabetes using Prentice-weighted Cox regression, which is weighted for case-cohort sampling, and pooled our findings using random-effects meta-analysis.

FINDINGS

SFAs accounted for 46% of total plasma phospholipid fatty acids. In adjusted analyses, different individual SFAs were associated with incident type 2 diabetes in opposing directions. Even-chain SFAs that were measured (14:0 [myristic acid], 16:0 [palmitic acid], and 18:0 [stearic acid]) were positively associated with incident type 2 diabetes (HR [95% CI] per SD difference: myristic acid 1·15 [95% CI 1·09-1·22], palmitic acid 1·26 [1·15-1·37], and stearic acid 1·06 [1·00-1·13]). By contrast, measured odd-chain SFAs (15:0 [pentadecanoic acid] and 17:0 [heptadecanoic acid]) were inversely associated with incident type 2 diabetes (HR [95% CI] per 1 SD difference: 0·79 [0·73-0·85] for pentadecanoic acid and 0·67 [0·63-0·71] for heptadecanoic acid), as were measured longer-chain SFAs (20:0 [arachidic acid], 22:0 [behenic acid], 23:0 [tricosanoic acid], and 24:0 [lignoceric acid]), with HRs ranging from 0·72 to 0·81 (95% CIs ranging between 0·61 and 0·92). Our findings were robust to a range of sensitivity analyses.

INTERPRETATION

Different individual plasma phospholipid SFAs were associated with incident type 2 diabetes in opposite directions, which suggests that SFAs are not homogeneous in their effects. Our findings emphasise the importance of the recognition of subtypes of these fatty acids. An improved understanding of differences in sources of individual SFAs from dietary intake versus endogenous metabolism is needed.

FUNDING

EU FP6 programme, Medical Research Council Epidemiology Unit, Medical Research Council Human Nutrition Research, and Cambridge Lipidomics Biomarker Research Initiative.

Non-alcoholic fatty liver disease in obese adults: clinical aspects and current management strategies

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disorder whose prevalence is strongly linked to the current epidemic of obesity in many western countries. The prevalence of NAFLD is two to four times higher in populations with pre-existing metabolic comorbidities than in the general population. The diagnosis of primary NAFLD involves establishing the presence of hepatic steatosis or steatohepatitis by imaging or histology, along with establishing the non-alcoholic nature of the disease process and excluding competing aetiologies for hepatic steatosis. Among the indirect serum biomarkers, the NAFLD fibrosis score can help to identify patients with NAFLD and with higher likelihood of having fibrosis or cirrhosis. A liver biopsy should be considered in NAFLD patients at increased risk for steatohepatitis/advanced fibrosis and in cases where a liver biopsy is necessary to exclude co-existing chronic liver diseases and other aetiologies for hepatic steatosis. The treatment and management recommendations for obesity-associated NAFLD are aimed towards weight reduction. The currently available interventions employed to promote weight loss and improve the metabolic responses in NAFLD include lifestyle modification, pharmacotherapy and bariatric surgery.

Liver clock protein BMAL1 promotes de novo lipogenesis through insulin-mTORC2-AKT signaling

The clock protein BMAL1 (brain and muscle Arnt-like protein 1) participates in circadian regulation of lipid metabolism, but its contribution to insulin AKT-regulated hepatic lipid synthesis is unclear. Here we used both Bmal1(-/-) and acute liver-specific Bmal1-depleted mice to study the role of BMAL1 in refeeding-induced de novo lipogenesis in the liver. Both global deficiency and acute hepatic depletion of Bmal1 reduced lipogenic gene expression in the liver upon refeeding. Conversely, Bmal1 overexpression in mouse liver by adenovirus was sufficient to elevate the levels of mRNA of lipogenic enzymes. Bmal1(-/-) primary mouse hepatocytes displayed decreased levels of de novo lipogenesis and lipogenic enzymes, supporting the notion that BMAL1 regulates lipid synthesis in hepatocytes in a cell-autonomous manner. Both refed mouse liver and insulin-treated primary mouse hepatocytes showed impaired AKT activation in the case of either Bmal1 deficiency or Bmal1 depletion by adenoviral shRNA. Restoring AKT activity by a constitutively active mutant of AKT nearly normalized de novo lipogenesis in Bmal1(-/-) hepatocytes. Finally, Bmal1 deficiency or knockdown decreased the protein abundance of RICTOR, the key component of the mTORC2 complex, without affecting the gene expression of key factors of insulin signaling. Thus, our study uncovered a novel metabolic function of hepatic BMAL1 that promotes de novo lipogenesis via the insulin-mTORC2-AKT signaling during refeeding.

Identification of antihyperlipidemic constituents from the roots of Rubia yunnanensis Diels

ETHNOPHARMACOLOGICAL RELEVANCE

The roots of Rubia yunnanensis Diels (Rubiaceae) have been used as an alternative for Rubia cordifolia for the treatment of various diseases including cardiovascular disease and metabolic disease for a long history in traditional Chinese medicine. To evaluate antihyperlipidemic activity of the roots of Rubia. yunnanensis Diels and to identify active compounds from the active fraction.

MATERIAL AND METHODS

Antihyperlipidemic effects of extract and compounds of the roots of Rubia yunnanensis were studied in HepG2 cells and in vivo model in olive oil-loaded mice. The isolation of compounds was conducted using various chromatographic methods and the structures of the isolated compounds were elucidated by NMR and MS techniques.

RESULTS

Methanol extract and ethyl acetate fraction of Rubia yunnanensis potently decreased the triglycerides accumulation in HepG2 cells and the methanol extract of Rubia yunnanensis (125, 250 and 500 mg/kg) significantly inhibited the TG elevation in a dose dependent manner in olive oil-loaded mice. Through various chromatographic methods, twenty-three compounds (1-23) were isolated in which arborinane-type triterpenoids and a free anthraquinone potently inhibited TG levels in HepG2 cells.

CONCLUSION

Arborinane-type triterpenoids, especial rubiarbonone C (16) and an anthraquinone, 2-methyl-1, 3, 6-trihydroxy-9, 10-anthraquinone (MTHA) (22) were identified as the main active compounds responsible for antihyperlipidemic activity. Based on these findings, we proposed that the extract of Rubia yunnanensis and its active components, arborinane-type triterpenoids and the free anthraquinone might be beneficial in the treatment and prevention of hyperlipidemic disease.

Serum phospholipid omega-3 polyunsaturated fatty acids and insulin resistance in type 2 diabetes mellitus and non-alcoholic fatty liver disease

AIMS

To investigate the relationship between serum phospholipid omega-3 polyunsaturated fatty acids (ω-3 PUFAs) and insulin resistance (IR) in patients with type 2 diabetes mellitus (T2DM) and non-alcoholic fatty liver disease (NAFLD).

METHODS

51 patients with T2DM and NAFLD (T2DM+NAFLD group), 50 with T2DM alone (T2DM group), 45 with NAFLD alone (NAFLD group), and 42 healthy control subjects (NC group) were studied. Serum ω-3 PUFA profiles were analyzed by gas chromatography, and alanine aminotransferase (ALT), aspartate aminotransferase (AST), γ-glutamyltransferase (GGT), and serum lipid concentrations were measured. Insulin resistance was assessed by the homeostasis model assessment method (HOMA-IR).

RESULTS

HOMA-IR levels were higher in the T2DM+NAFLD group than in the T2DM, NAFLD and NC groups (p<0.05), as were ALT, AST, GGT, total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and triglyceride (TG) concentrations (p<0.05). Conversely, serum ω-3 PUFA levels were significantly lower in the T2DM+NAFLD group than in the other groups (p<0.05). The ω-3 PUFA level was negatively correlated with HOMA-IR, TC, LDL-C and TG.

CONCLUSIONS

Serum phospholipid ω-3 PUFA levels were significantly decreased in patients with T2DM and NAFLD, and were negatively related with insulin resistance. Thus, reduced ω-3 PUFAs may play an important role in the development of T2DM and NAFLD.

Exendin-4 Improves Nonalcoholic Fatty Liver Disease by Regulating Glucose Transporter 4 Expression in ob/ob Mice

Exendin-4 (Ex-4), a glucagon-like peptide-1 receptor (GLP-1R) agonist, has been known to reverse hepatic steatosis in ob/ob mice. Although many studies have evaluated molecular targets of Ex-4, its mechanism of action on hepatic steatosis and fibrosis has not fully been determined. In the liver, glucose transporter 4 (GLUT4) is mainly expressed in hepatocytes, endothelial cells and hepatic stellate cells (HSCs). In the present study, the effects of Ex-4 on GLUT4 expression were determined in the liver of ob/ob mice. Ob/ob mice were treated with Ex-4 for 10 weeks. Serum metabolic parameters, hepatic triglyceride levels, and liver tissues were evaluated for hepatic steatosis. The weights of the whole body and liver in ob/ob mice were reduced by long-term Ex-4 treatment. Serum metabolic parameters, hepatic steatosis, and hepatic fibrosis in ob/ob mice were reduced by Ex-4. Particularly, Ex-4 improved hepatic steatosis by enhancing GLUT4 via GLP-1R activation in ob/ob mice. Ex-4 treatment also inhibited hepatic fibrosis by decreasing expression of connective tissue growth factor in HSCs of ob/ob mice. Our data suggest that GLP-1 agonists exert a protective effect on hepatic steatosis and fibrosis in obesity and type 2 diabetes.

NHE1 deficiency in liver: implications for non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease NAFLD is closely associated with the dysregulation of lipid homeostasis. Diet-induced hepatic steatosis, which can initiate NAFLD progression, has been shown to be dramatically reduced in mice lacking the electroneutral Na(+)/H(+) exchanger NHE1 (Slc9a1). In this study, we investigated if NHE1 deficiency had effects in liver that could contribute to the apparent protection against aberrant lipid accumulation. RT-PCR and immunoblot analyses of wild-type and NHE1-null livers revealed an expression profile that strongly suggested attenuation of both de novo lipogenesis and hepatic stellate cell activation, which is implicated in liver fibrosis. This included upregulation of the farnesoid X receptor FXR, peroxisome proliferator-activated receptor PPARγ, its co-activator PGC1α, and sestrin 2, an antioxidant protein involved in hepatic metabolic homeostasis. Furthermore, expression levels of the pro-lipogenic liver X receptor LXRα, and acetyl CoA carboxylases 1 and 2 were downregulated. These changes were associated with evidence of reduced cellular stress, which persisted even upon exposure to a high-fat diet, and the better preservation of insulin signaling, as evidenced by protein kinase B/Akt phosphorylation (Ser473). These results indicate that NHE1 deficiency may protect against NAFLD pathogenesis, which is significant given the availability of highly specific NHE1 inhibitors.

Crude extracts from Lycium barbarum suppress SREBP-1c expression and prevent diet-induced fatty liver through AMPK activation

Lycium barbarum polysaccharide (LBP) is well known in traditional Chinese herbal medicine that, has beneficial effects. Previous study reported that LBP reduced blood glucose and serum lipids. However, the underlying LBP-regulating mechanisms remain largely unknown. The main purpose of this study was to investigate whether LBP prevented fatty liver through activation of adenosine monophosphate-activated protein kinase (AMPK) and suppression of sterol regulatory element-binding protein-1c (SREBP-1c). Male C57BL/6J mice were fed a low-fat diet, high-fat diet, or 100 mg/kg LBP-treatment diet for 24 weeks. HepG2 cells were treated with LBP in the presence of palmitic acid. In our study, LBP can improve body compositions and lipid metabolic profiles in high-fat diet-fed mice. Oil Red O staining in vivo and in vitro showed that LBP significantly reduced hepatic intracellular triacylglycerol accumulation. H&E staining also showed that LBP can attenuate liver steatosis. Hepatic genes expression profiles demonstrated that LBP can activate the phosphorylation of AMPK, suppress nuclear expression of SREBP-1c, and decrease protein and mRNA expression of lipogenic genes in vivo or in vitro. Moreover, LBP significantly elevated uncoupling protein-1 (UCP1) and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) expression of brown adipose tissue. In summary, LBP possesses a potential novel treatment in preventing diet-induced fatty liver.

Lipogenesis in cancer progression (review)

In normal tissues, energy-providing lipids come principally from circulating lipids. However, in growing tumors, energy supply is mainly provided by lipids coming from de novo synthesis. It is not surprising to see elevated expression of several lipogenic genes in tumors from different origins. The role of lipogenic genes in the establishment of the primary tumor has been clearly established. A large number of studies demonstrate a role of fatty acid synthase in the activation of cell cycle and inhibition of apoptosis in tumor cells. Other lipogenic genes such as the acetyl CoA carboxylase (ACC) and the stearoyl CoA desaturase 1 (SCD1) are highly expressed in primary tumors and also appear to play a role in their development. However, the role of lipogenesis in the metastatic process is less clear. In the present review, we aim to present the most recent evidences for the key role of lipogenic enzymes in the metastatic process and in epithelial to mesenchymal transition.

Hepatic glucose sensing and integrative pathways in the liver

The hepatic glucose-sensing system is a functional network of enzymes and transcription factors that is critical for the maintenance of energy homeostasis and systemic glycemia. Here we review the recent literature on its components and metabolic actions. Glucokinase (GCK) is generally considered as the initial postprandial glucose-sensing component, which acts as the gatekeeper for hepatic glucose metabolism and provides metabolites that activate the transcription factor carbohydrate response element binding protein (ChREBP). Recently, liver receptor homolog 1 (LRH-1) has emerged as an upstream regulator of the central GCK-ChREBP axis, with a critical role in the integration of hepatic intermediary metabolism in response to glucose. Evidence is also accumulating that O-linked β-N-acetylglucosaminylation (O-GlcNAcylation) and acetylation can act as glucose-sensitive modifications that may contribute to hepatic glucose sensing by targeting regulatory proteins and the epigenome. Further elucidation of the components and functional roles of the hepatic glucose-sensing system may contribute to the future treatment of liver diseases associated with deregulated glucose sensors.

Thyroid hormone analogues and derivatives: Actions in fatty liver

Fatty liver or nonalcoholic fatty liver disease (NAFLD), a problem of increasing clinical significance and prevalence worldwide, is associated with increased risk for the development of cirrhosis and hepatocellular carcinoma. Although several therapeutic approaches can be used in the context of NAFLD, dietary and physical activities are still the most frequently used strategies. Some pharmacological agents show promising results although no conclusions can be drawn from recent clinical trials. Thyroid hormones [THs; thyroxine (T4) and 3,3′,5-triiodo-L-thyronine (T3)] coordinate a diverse array of physiological events during development and lipid/energy homeostasis and have some potentially therapeutic actions which include inducing weight loss, and lowering plasma cholesterol levels and tissue adiposity. The thyroid hormones exert their physiological effects by binding to specific nuclear receptors [thyroid hormone receptors (TR)] of which the TRβ isoform is liver specific and has been considered a putative target for the treatment of dyslipidemia and fatty liver. In view of this, the aim of the review is (1) to provide an overview of the action of T3 on lipid metabolism with implications for liver steatosis and (2) to provide an update on the current knowledge concerning the administration of TRβ selective thyromimetics (GC-1 and MB07811), as well as of 3,5-diiodo-L-thyronine and its novel functional analogue TRC150094 in animal models of overweight and related disorders including primarily fatty liver.

Maternal high-fat diet consumption modulates hepatic lipid metabolism and microRNA-122 (miR-122) and microRNA-370 (miR-370) expression in offspring

Maternal consumption of a high-fat diet (HFD) during pregnancy and lactation is closely related to hepatic lipid accumulation, insulin resistance and increased serum cytokine levels in offspring and into their adulthood. MicroRNA (miRNA) have been implicated in cholesterol biosynthesis and fatty acid metabolism. We evaluated the modulation of hepatic fatty acid synthesis (de novo), β-oxidation pathways, and miRNA-122 (miR-122) and miRNA-370 (miR-370) expression in recently weaned offspring (day 28) of mouse dams fed a HFD (HFD-O) or a standard chow (SC-O) during pregnancy and lactation. Compared with SC-O mice, HFD-O mice weighed more, had a larger adipose tissue mass and were more intolerant to glucose and insulin (P< 0·05). HFD-O mice also presented more levels of serum cholesterol, TAG, NEFA and hepatic IκB kinase and c-Jun N-terminal kinase phosphorylation compared with SC-O mice (P< 0·05). Protein levels of fatty acid synthase, acetyl-CoA carboxylase and 3-hydroxy-3-methylglutaryl-CoA reductase were similar in HFD-O and SC-O mice, whereas expression levels of SCD1 mRNA and protein were more abundant in HFD-O mice than in SC-O mice (P< 0·05). Interestingly, mRNA expression levels of the β-oxidation-related genes ACADVL and CPT1 were decreased in HFD-O mice (P< 0·05). Furthermore, the expression of miR-122 was reduced but that of miR-370 was increased in HFD-O mice compared with that in SC-O mice (P< 0·05). Changes in hepatic lipid metabolism were accompanied by increased mRNA content of AGPAT1 and TAG deposition in HFD-O mice (P< 0·05). Taken together, the present results strongly suggest that maternal consumption of a HFD affects the early lipid metabolism of offspring by modulating the expression of hepatic β-oxidation-related genes and miRNA that can contribute to metabolic disturbances in adult life.

MTP -493G>T polymorphism and susceptibility to nonalcoholic fatty liver disease: a meta-analysis

Microsomal transfer protein (MTP), a lipid transfer protein localized in the endoplasmic reticulum of hepatocytes and enterocytes, plays an important role in the development of nonalcoholic fatty liver disease (NAFLD). Many existing studies have demonstrated that a common polymorphism (-493G>T, rs1800591 G>T) in the MTP gene may be implicated in the development and progression of NAFLD, but individually published results are inconclusive. This meta-analysis aimed to investigate whether MTP -493G>T polymorphism may be a potential risk factor for NAFLD. We searched CISCOM, CINAHL, Web of Science, PubMed, Google Scholar, EBSCO, Cochrane Library, and CBM databases from inception through October 1, 2013. Meta-analysis was performed using the STATA 12.0 software. Eleven clinical case-control studies with a total of 636 NAFLD cases and 918 healthy controls met the inclusion criteria. Our meta-analysis results revealed that MTP -493G>T polymorphism was strongly correlated with an increased risk of NAFLD. Subgroup analysis by ethnicity suggested that MTP -493G>T polymorphism might increase individuals' susceptibility to NAFLD among both Caucasian and non-Caucasian populations. No publication bias was observed in this meta-analysis. In short, the present meta-analysis indicates that MTP -493G>T polymorphisms may contribute to individuals' susceptibility to NAFLD. Thus, MTP -493G>T polymorphism may be a valuable and practical biomarker for early detection of NAFLD.

Modulation of hepatic steatosis by dietary fatty acids

Non-alcoholic fatty liver disease (NAFLD) describes a range of conditions caused by fat deposition within liver cells. Liver fat content reflects the equilibrium between several metabolic pathways involved in triglyceride synthesis and disposal, such as lipolysis in adipose tissue and de novo lipogenesis, triglyceride esterification, fatty acid oxidation and very-low-density lipoprotein synthesis/secretion in hepatic tissue. In particular, it has been demonstrated that hepatic de novo lipogenesis plays a significant role in NAFLD pathogenesis. It is widely known that the fatty acid composition of the diet influences hepatic lipogenesis along with other metabolic pathways. Therefore, dietary fat may not only be involved in the pathogenesis of hepatic steatosis, but may also prevent and/or reverse hepatic fat accumulation. In this review, major data from the literature about the role of some dietary fats as a potential cause of hepatic fat accumulation or as a potential treatment for NAFLD are described. Moreover, biochemical mechanisms responsible for an increase or decrease in hepatic lipid content are critically analyzed. It is noteworthy that both quantitative and qualitative aspects of dietary fat influence triglyceride deposition in the liver. A high-fat diet or the dietary administration of conjugated linoleic acids induced hepatic steatosis. In contrast, supplementation of the diet with krill oil or pine nut oil helped in the prevention and/or in the treatment of steatotic liver. Quite interesting is the “case” of olive oil, since several studies have often provided different and⁄or conflicting results in animal models.

Testosterone replacement ameliorates nonalcoholic fatty liver disease in castrated male rats

Nonalcoholic fatty liver disease is common in developed countries and is associated with obesity, metabolic syndrome, and type 2 diabetes. T deficiency is a risk factor for developing these metabolic deficiencies, but its role in hepatic steatosis has not been well studied. We investigated the effects of T on the pathogenesis of hepatic steatosis in rats fed a high-fat diet (HFD). Adult male rats were randomly placed into four groups and treated for 15 weeks: intact rats on regular chow diet (RCD), intact rats on liquid HFD (I+HFD), castrated rats on HFD (C+HFD), and castrated rats with T replacement on HFD (C+HFD+T). Fat contributed 71% energy to the HFD but only 16% of energy to the RCD. Serum T level was undetectable in castrated rats, and T replacement led to 2-fold higher mean serum T levels than in intact rats. C+HFD rats gained less weight but had higher percentage body fat than C+HFD+T. Severe micro- and macrovesicular fat accumulated in hepatocytes with multiple inflammatory foci in the livers of C+HFD. I+HFD and C+HFD+T hepatocytes demonstrated only mild to moderate microvesicular steatosis. T replacement attenuated HFD-induced hepatocyte apoptosis in castrated rats. Serum glucose and insulin levels were not increased with HFD in any group. Immunoblots showed that insulin-regulated proteins were not changed in any group. This study demonstrates that T deficiency may contribute to the severity of hepatic steatosis and T may play a protective role in hepatic steatosis and nonalcoholic fatty liver disease development without insulin resistance.

Dietary camphene attenuates hepatic steatosis and insulin resistance in mice

OBJECTIVE

The aim of this study was to investigate the protective effects of camphene on high-fat diet (HFD)-induced hepatic steatosis and insulin resistance in mice and to elucidate its mechanism of action.

DESIGN AND METHODS

Male C57BL/6N mice were fed with a normal diet, HFD (20% fat and 1% cholesterol of total diet), or HFD supplemented with 0.2% camphene (CPND) for 10 weeks.

RESULTS

Camphene alleviated the HFD-induced increases in liver weight and hepatic lipid levels in mice. Camphene also increased circulating adiponectin levels. To examine the direct effects of camphene on adiponectin secretion, 3T3-L1 adipocytes were incubated with camphene. Consistent with in vivo result, camphene increased adiponectin expression and secretion in 3T3-L1 adipocytes. In HFD-fed mice, camphene increased hepatic adiponectin receptor expression and AMP-activated protein kinase (AMPK) activation. Concordant with the activation of adiponectin-AMPK signaling, camphene increased hepatic expression of fatty acid oxidation-related genes and decreased those of lipogenesis-related genes in HFD-fed mice. Moreover, camphene increased insulin-signaling molecules activation and stimulated glucose transporter-2translocation to the plasma membrane in the liver.

CONCLUSIONS

These results suggest camphene prevents HFD-induced hepatic steatosis and insulin resistance in mice; furthermore, these protective effects are mediated via the activation of adiponectin-AMPK signaling.

Reduced hepatic aquaporin-9 and glycerol permeability are related to insulin resistance in non-alcoholic fatty liver disease

BACKGROUND/OBJECTIVES

Glycerol represents an important metabolite for the control of lipid accumulation and hepatic gluconeogenesis. We investigated whether hepatic expression and functionality of aquaporin-9 (AQP9), a channel mediating glycerol influx into hepatocytes, is impaired in non-alcoholic fatty liver disease (NAFLD) and steatohepatitis (NASH) in the context of insulin resistance.

SUBJECTS/METHODS

Liver biopsies were obtained from 66 morbid obese patients undergoing bariatric surgery (66% women, mean body mass index (BMI) 46.1±1.0 kg m(-2)) with available liver echography and pathology analysis of the biopsies in this cross-sectional study. Subjects were classified according to normoglycemia (NG), impaired glucose tolerance (IGT) or type 2 diabetes (T2D). Hepatic expression of AQP9 was analyzed by real-time PCR, western blotting and immunohistochemistry, while glycerol permeability (P(gly)) was measured by stopped-flow light scattering.

RESULTS

AQP9 was the most abundantly (P<0.0001) expressed aquaglyceroporin in human liver (AQP9>>>AQP3>AQP7>AQP10). Obese patients with T2D showed increased plasma glycerol as well as lower P(gly) and hepatic AQP9 expression. The prevalence of NAFLD and NASH in T2D patients was 100 and 65%, respectively. Interestingly, AQP9 expression was decreased in patients with NAFLD and NASH as compared with those without hepatosteatosis, in direct relation to the degree of steatosis and lobular inflammation, being further reduced in insulin-resistant individuals. The association of AQP9 with insulin sensitivity was independent of BMI and age. Consistent with these data, fasting insulin and C-reactive protein contributed independently to 33.1% of the hepatic AQP9 mRNA expression variance after controlling for the effects of age and BMI.

CONCLUSIONS

AQP9 downregulation together with the subsequent reduction in hepatic glycerol permeability in insulin-resistant states emerges as a compensatory mechanism whereby the liver counteracts further triacylglycerol accumulation within its parenchyma as well as reduces hepatic gluconeogenesis in patients with NAFLD.

Circadian rhythms in liver physiology and liver diseases

In mammals, circadian rhythms function to coordinate a diverse panel of physiological processes with environmental conditions such as food and light. As the driving force for circadian rhythmicity, the molecular clock is a self-sustained transcription-translational feedback loop system consisting of transcription factors, epigenetic modulators, kinases/phosphatases, and ubiquitin E3 ligases. The molecular clock exists not only in the suprachiasmatic nuclei of the hypothalamus but also in the peripheral tissues to regulate cellular and physiological function in a tissue-specific manner. The circadian clock system in the liver plays important roles in regulating metabolism and energy homeostasis. Clock gene mutant animals display impaired glucose and lipid metabolism and are susceptible to diet-induced obesity and metabolic dysfunction, providing strong evidence for the connection between the circadian clock and metabolic homeostasis. Circadian-controlled hepatic metabolism is partially achieved by controlling the expression and/or activity of key metabolic enzymes, transcription factors, signaling molecules, and transporters. Reciprocally, intracellular metabolites modulate the molecular clock activity in response to the energy status. Although still at the early stage, circadian clock dysfunction has been implicated in common chronic liver diseases. Circadian dysregulation of lipid metabolism, detoxification, reactive oxygen species (ROS) production, and cell-cycle control might contribute to the onset and progression of liver steatosis, fibrosis, and even carcinogenesis. In summary, these findings call for a comprehensive study of the function and mechanisms of hepatic circadian clock to gain better understanding of liver physiology and diseases.

Dietary walnut oil modulates liver steatosis in the obese Zucker rat

Purpose

Non-alcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the metabolic syndrome. We aimed to clarify the impact of dietary walnut oil versus animal fat on hepatic steatosis, representing the initial step of multistage pathogenesis of NAFLD, in Zucker obese rats.

Methods

Zucker lean ad libitum (a.l.), Zucker obese a.l. or Zucker obese pair fed (p.f.) to the lean received isocaloric diets containing 8 % walnut oil (W8), W14 or 14 % lard (L14) (n = 10/group). Body weight, clinical serology, liver weight, lipid content and fatty acid composition and hepatic lipid metabolism-related transcripts were evaluated.

Results

Compared to lean, Zucker obese a.l. and p.f. showed hepatic triacylglyceride (TAG) accumulation. In Zucker obese p.f., W14 compared to W8 and L14 reduced liver lipids, TAG as well as hepatic omega-6 (n-6)/n-3 ratio and SCD activity index [(C18:0 + C18:1)/C18:0 ratio] paralleled by decreased lipoprotein lipase mRNA in obese p.f. and elevated microsomal triglyceride transfer protein mRNA in lean and obese. Further, W14 elevated the fasting blood TAG and reduced cholesterol levels in obese.

Conclusions

In our model, consumption of W14 inhibited hepatic lipid accumulation along with modulated hepatic gene expression implicated in hepatic fatty acid influx or lipoprotein assembly. These results provide first indication that dietary lipids from walnut oil are modulators of hepatic steatosis as the initial step of progressive NAFLD pathogenesis.

Peculiarities of one-carbon metabolism in the strict carnivorous cat and the role in feline hepatic lipidosis

Research in various species has indicated that diets deficient in labile methyl groups (methionine, choline, betaine, folate) produce fatty liver and links to steatosis and metabolic syndrome, but also provides evidence of the importance of labile methyl group balance to maintain normal liver function. Cats, being obligate carnivores, rely on nutrients in animal tissues and have, due to evolutionary pressure, developed several physiological and metabolic adaptations, including a number of peculiarities in protein and fat metabolism. This has led to specific and unique nutritional requirements. Adult cats require more dietary protein than omnivorous species, maintain a consistently high rate of protein oxidation and gluconeogenesis and are unable to adapt to reduced protein intake. Furthermore, cats have a higher requirement for essential amino acids and essential fatty acids. Hastened use coupled with an inability to conserve certain amino acids, including methionine, cysteine, taurine and arginine, necessitates a higher dietary intake for cats compared to most other species. Cats also seemingly require higher amounts of several B-vitamins compared to other species and are predisposed to depletion during prolonged inappetance. This carnivorous uniqueness makes cats more susceptible to hepatic lipidosis.

Pleiotropic effects of rosuvastatin on the glucose metabolism and the subcutaneous and visceral adipose tissue behavior in C57Bl/6 mice

The aim of this study was to evaluate whether rosuvastatin (HMG-CoA reductase inhibitor) modulates the carbohydrate and lipid metabolism, the development of non-alcoholic fatty liver disease (NAFLD), and the increase in body mass in a model of diet-induced obesity. Male C57Bl/6 mice (3-months-old) were fed a high-fat diet (HF, 60% lipids) or the standard chow (SC, 10% lipids) for 15 weeks. The animals were then treated with 10 mg/kg/day (HF-R10 group), 20 mg/kg/day (HF-R20), or 40 mg/kg/day (HF-R40) of rosuvastatin for five weeks. The HF diet led to glucose intolerance, insulin resistance, weight gain, increased visceral adiposity with adipocyte hypertrophy, and hepatic steatosis (micro and macrovesicular). The rosuvastatin treatment decreased the adiposity and the adipocyte size in the HF-R10 and HF-R20 groups. In addition, rosuvastatin changed the pattern of fat distribution in the HF-R40 group because more fat was stored subcutaneously than in visceral depots. This redistribution improved the fasting glucose and the glucose intolerance. Rosuvastatin also improved the liver morphology and ultrastructure in a dose-dependent manner. In conclusion, rosuvastatin exerts pleiotropic effects through a dose-dependent improvement of glucose intolerance, insulin sensitivity and NAFLD and changes the fat distribution from visceral to subcutaneous fat depots in a mouse model of diet-induced obesity.

Piperine reverses high fat diet-induced hepatic steatosis and insulin resistance in mice

This study examined the effect of piperine on hepatic steatosis and insulin resistance induced in mice by feeding a high-fat diet (HFD) for 13 weeks and elucidated potential underlying molecular mechanisms. Administration of piperine (50 mg/kg body weight) to mice with HFD-induced hepatic steatosis resulted in a significant increase in plasma adiponectin levels. Also, elevated plasma concentrations of insulin and glucose and hepatic lipid levels induced by feeding a HFD were reversed in mice when they were administered piperine. However, piperine did not reduce body weight and other biochemical markers to an extent where they became equal to the levels found in the CD-fed mice. Piperine reversed HFD-induced down-regulation of adiponecitn-AMP-activated protein kinase (AMPK) signalling molecules which play an important role in mediating lipogenesis, fatty acid oxidation and insulin signalling in the livers of mice. The expressions of lipogenic target genes were decreased, whereas the expression of carnitine palmitoyltransferase 1 (CPT1) gene involved in fatty acid oxidation was increased in the livers of the Pin50 group. Piperine significantly decreased the phosphorylation of insulin receptor substrate-1 (IRS-1) compared with the HFD-fed mice. Administration of piperine appeared to reverse preexisting HFD-induced hepatic steatosis and insulin resistance, probably by activation of adiponectin-AMPK signalling in mice.

In vivo hepatic lipid quantification using MRS at 7 Tesla in a mouse model of glycogen storage disease type 1a

The assessment of liver lipid content and composition is needed in preclinical research to investigate steatosis and steatosis-related disorders. The purpose of this study was to quantify in vivo hepatic fatty acid content and composition using a method based on short echo time proton magnetic resonance spectroscopy (MRS) at 7 Tesla. A mouse model of glycogen storage disease type 1a with inducible liver-specific deletion of the glucose-6-phosphatase gene (L-G6pc(-/-)) mice and control mice were fed a standard diet or a high-fat/high-sucrose (HF/HS) diet for 9 months. In control mice, hepatic lipid content was found significantly higher with the HF/HS diet than with the standard diet. As expected, hepatic lipid content was already elevated in L-G6pc(-/-) mice fed a standard diet compared with control mice. L-G6pc(-/-) mice rapidly developed steatosis which was not modified by the HF/HS diet. On the standard diet, estimated amplitudes from olefinic protons were found significantly higher in L-G6pc(-/-) mice compared with that in control mice. L-G6pc(-/-) mice showed no noticeable polyunsaturation from diallylic protons. Total unsaturated fatty acid indexes measured by gas chromatography were in agreement with MRS measurements. These results showed the great potential of high magnetic field MRS to follow the diet impact and lipid alterations in mouse liver.

The endocannabinoid system in energy homeostasis and the etiopathology of metabolic disorders

Endocannabinoids and cannabinoid CB1 receptors are known to play a generalized role in energy homeostasis. However, clinical trials with the first generation of CB1 blockers, now discontinued due to psychiatric side effects, were originally designed to reduce food intake and body weight rather than the metabolic risk factors associated with obesity. In this review, we discuss how, in addition to promoting energy intake, endocannabinoids control lipid and glucose metabolism in several peripheral organs, particularly the liver and adipose tissue. Direct actions in skeletal muscle and pancreas are also emerging. This knowledge may help in the design of future therapies for the metabolic syndrome.

Qushi Huayu Decoction Inhibits Hepatic Lipid Accumulation by Activating AMP-Activated Protein Kinase In Vivo and In Vitro

Qushi Huayu Decoction (QHD), a Chinese herbal formula, has been proven effective on alleviating nonalcoholic fatty liver disease (NAFLD) in human and rats. The present study was conducted to investigate whether QHD could inhibit hepatic lipid accumulation by activating AMP-activated protein kinase (AMPK) in vivo and in vitro. Nonalcoholic fatty liver (NAFL) model was duplicated with high-fat diet in rats and with free fatty acid (FFA) in L02 cells. In in vivo experimental condition, QHD significantly decreased the accumulation of fatty droplets in livers, lowered low-density lipoprotein cholesterol (LDL-c), alanine aminotransferase (ALT), and aspartate aminotransferase (AST) levels in serum. Moreover, QHD supplementation reversed the HFD-induced decrease in the phosphorylation levels of AMPK and acetyl-CoA carboxylase (ACC) and decreased hepatic nuclear protein expression of sterol regulatory element-binding protein-1 (SREBP-1) and carbohydrate-responsive element-binding protein (ChREBP) in the liver. In in vitro, QHD-containing serum decreased the cellular TG content and alleviated the accumulation of fatty droplets in L02 cells. QHD supplementation reversed the FFA-induced decrease in the phosphorylation levels of AMPK and ACC and decreased the hepatic nuclear protein expression of SREBP-1 and ChREBP. Overall results suggest that QHD has significant effect on inhibiting hepatic lipid accumulation via AMPK pathway in vivo and in vitro.

Metformin and cancer

Type 2 diabetes mellitus is a rising cause of cardiovascular morbidity and mortality. A number of studies have also identified diabetic patients as having increased risk for the development of cancer. Metformin is a widely prescribed antidiabetic drug with an established efficacy coupled with a favorable safety profile and low cost. An increasing number of studies have associated metformin treatment with a decrease of cancer risk. Moreover, metformin has also been associated with improved outcomes in cancer patients. These possible pleiotropic effects of metformin may establish metformin as a cancer prevention and treatment option. However, any favorable effects of metformin on cancer are not always corroborated by clinical trials. Larger studies are expected to better investigate the possible antineoplastic effects of metformin.

Gene expression profile analysis of type 2 diabetic mouse liver

Liver plays a key role in glucose metabolism and homeostasis, and impaired hepatic glucose metabolism contributes to the development of type 2 diabetes. However, the precise gene expression profile of diabetic liver and its association with diabetes and related diseases are yet to be further elucidated. In this study, we detected the gene expression profile by high-throughput sequencing in 9-week-old normal and type 2 diabetic db/db mouse liver. Totally 12132 genes were detected, and 2627 genes were significantly changed in diabetic mouse liver. Biological process analysis showed that the upregulated genes in diabetic mouse liver were mainly enriched in metabolic processes. Surprisingly, the downregulated genes in diabetic mouse liver were mainly enriched in immune-related processes, although all the altered genes were still mainly enriched in metabolic processes. Similarly, KEGG pathway analysis showed that metabolic pathways were the major pathways altered in diabetic mouse liver, and downregulated genes were enriched in immune and cancer pathways. Analysis of the key enzyme genes in fatty acid and glucose metabolism showed that some key enzyme genes were significantly increased and none of the detected key enzyme genes were decreased. In addition, FunDo analysis showed that liver cancer and hepatitis were most likely to be associated with diabetes. Taken together, this study provides the digital gene expression profile of diabetic mouse liver, and demonstrates the main diabetes-associated hepatic biological processes, pathways, key enzyme genes in fatty acid and glucose metabolism and potential hepatic diseases.

Mecanismos da intoxicação do fígado de rato causada pelo gossipol

O fígado desempenha uma função central no metabolismo devido à sua interposição entre o trato digestivo e a circulação geral do organismo. Ele é também o principal órgão envolvido na biotransformação de substâncias exógenas (xenobióticos), com capacidade de converter compostos hidrofóbicos em hidrossolúveis, mais facilmente eliminados pelo organismo. O gossipol é uma substância fenólica tóxica presente na semente de algodão (Gossypium sp). Com o objetivo de estudar os mecanismos envolvidos na hepatotoxicidade do gossipol avaliou-se os seus efeitos no sistema antioxidante do fígado de ratos no que diz respeito ao estresse oxidativo e aspectos histopatológicos. Foram utilizados ratos machos da linhagem Wistar, separados em dois grupos, sendo que um recebeu óleo de canola (veículo, grupo Controle) e o outro recebeu gossipol na dosagem de 40 mg/kg de peso vivo do animal por 15 dias (grupo Tratado). O tratamento com gossipol promoveu alterações na atividade sérica das enzimas marcadoras de dano hepático e um significativo estresse oxidativo caracterizado pela diminuição nos níveis da glutationa reduzida (GSH) e consequente aumento da glutationa oxidada (GSSG), incluindo, ainda, danos à membrana plasmática e de organelas demonstrados pela peroxidação lipídica. O resultado da avaliação histopatológica demonstrou degeneração dos hepatócitos.

Involvement of SIRT1-AMPK signaling in the protective action of indole-3-carbinol against hepatic steatosis in mice fed a high-fat diet

This study addressed the effect of indole-3-carbinol (I3C) supplementation on hepatic steatosis in mice fed a high-fat diet (HFD) and clarified the underlying mechanism. Male C57BL/6N mice were divided into three groups: those who received a normal diet, those fed with HFD and those fed with 0.1% I3C-supplemented diet (I3CD). In the present study, an HFD supplemented with 0.1% I3C significantly decreased body and liver weight as well as plasma and hepatic lipid levels. The activation of the silent mating type information regulation 2 homolog 1 (SIRT1)-AMP-activated protein kinase (AMPK) signaling system by I3C correlated with decreased mRNA levels of sterol regulatory element-binding protein-1c-regulated lipogenic enzymes. In addition, I3C significantly reversed HFD-induced up-regulation of ER stress-mediated signaling molecules in the liver, which may have contributed to the protective effects of I3C against hepatic steatosis. Furthermore, HFD-induced up-regulations of inflammatory genes such as tumor necrosis factor α and interleukin 6 were significantly reversed by dietary I3C supplementation. Our study suggests that the protective action of I3C against hepatic steatosis is mediated, at least in part, through the up-regulation of a SIRT1-AMPK signaling system in the livers of HFD-fed mice. Further investigations revealed that alleviation of the ER stress response represented a critical mechanism underlying the beneficial effects of I3C on hepatic steatosis.

Oleic acid stimulates complete oxidation of fatty acids through protein kinase A-dependent activation of SIRT1-PGC1α complex

Fatty acids are essential components of the dynamic lipid metabolism in cells. Fatty acids can also signal to intracellular pathways to trigger a broad range of cellular responses. Oleic acid is an abundant monounsaturated omega-9 fatty acid that impinges on different biological processes, but the mechanisms of action are not completely understood. Here, we report that oleic acid stimulates the cAMP/protein kinase A pathway and activates the SIRT1-PGC1α transcriptional complex to modulate rates of fatty acid oxidation. In skeletal muscle cells, oleic acid treatment increased intracellular levels of cyclic adenosine monophosphate (cAMP) that turned on protein kinase A activity. This resulted in SIRT1 phosphorylation at Ser-434 and elevation of its catalytic deacetylase activity. A direct SIRT1 substrate is the transcriptional coactivator peroxisome proliferator-activated receptor γ coactivator 1-α (PGC1α), which became deacetylated and hyperactive after oleic acid treatment. Importantly, oleic acid, but not other long chain fatty acids such as palmitate, increased the expression of genes linked to fatty acid oxidation pathway in a SIRT1-PGC1α-dependent mechanism. As a result, oleic acid potently accelerated rates of complete fatty acid oxidation in skeletal muscle cells. These results illustrate how a single long chain fatty acid specifically controls lipid oxidation through a signaling/transcriptional pathway. Pharmacological manipulation of this lipid signaling pathway might provide therapeutic possibilities to treat metabolic diseases associated with lipid dysregulation.

Glucose intolerance and lipid metabolic adaptations in response to intrauterine and postnatal calorie restriction in male adult rats

Enhanced de novo lipogenesis (DNL), an adult hepatic adaption, is seen with high carbohydrate or low-fat diets. We hypothesized that ad libitum intake after prenatal calorie restriction will result in adult-onset glucose intolerance and enhanced DNL with modified lipid metabolic gene expression profile. Stable isotopes were used in 15-month-old adult male rat offspring exposed to prenatal (IUGR), pre- and postnatal (IPGR), or postnatal (PNGR) caloric restriction vs. controls (CON). IUGR vs. CON were heavier with hepatomegaly but unchanged visceral white adipose tissue (WAT), glucose intolerant with reduced glucose-stimulated insulin secretion (GSIS), pancreatic β-cell mass, and total glucose clearance rate but unsuppressed hepatic glucose production. Liver glucose transporter (Glut) 1 and DNL increased with decreased hepatic acetyl-CoA carboxylase (ACC) and fatty acid synthase but increased WAT fatty acid transport protein-1 and peroxisomal proliferator-activated receptor-γ, resistin, and visfatin gene expression. In contrast, PNGR and IPGR were lighter, had reduced visceral WAT, and were glucose tolerant with unchanged hepatic glucose production but with increased GSIS, β-cell mass, glucose clearance rate, and WAT insulin receptor. Hepatic Glut1 and DNL were also increased in lean IPGR and PNGR with increased hepatic ACC, phosphorylated ACC, and pAMPK and reduced WAT fatty acid transport protein-1, peroxisomal proliferator-activated receptor-γ, and ACCα. We conclude the following: 1) the heavy, glucose-intolerant and insulin-resistant IUGR adult phenotype is ameliorated by postnatal caloric restriction; 2) increased DNL paralleling hepatic Glut1 is a biomarker of exposure to early caloric restriction rather than the adult metabolic status; 3) hepatic lipid enzyme expression reflects GSIS rather than DNL; and 4) WAT gene expression reflects an obesogenic vs. lean phenotype.

Non-alcoholic fatty liver disease and insulin resistance: from bench to bedside

Non-alcoholic fatty liver disease (NAFLD) is now the most frequent chronic liver disease in the developed countries. There is also growing evidence from basic and clinical research that NAFLD has a strong relationship to insulin resistance, which is a key factor in the development of type 2 diabetes. The aim of this review is to summarize the recent important findings linking NAFLD and insulin resistance. Lipid accumulation, particularly of diacylglycerol, appears to be of major importance in this process. Mitochondrial dysfunction, through decreased mitochondrial biogenesis, increases oxidative stress, and ageing also plays an important role. Finally, endoplasmic reticulum stress and inflammation also probably contribute to the development of insulin resistance via mechanisms that are still not well understood. Clinical aspects of NAFLD, such as its diagnosis and management, are also investigated in this review.

Liver specific inactivation of carboxylesterase 3/triacylglycerol hydrolase decreases blood lipids without causing severe steatosis in mice

Carboxylesterase 3/triacylglycerol hydrolase (Ces3/TGH) participates in hepatic very low-density lipoprotein (VLDL) assembly and in adipose tissue basal lipolysis. Global ablation of Ces3/Tgh expression decreases serum triacylglycerol (TG) and nonesterified fatty acid levels and improves insulin sensitivity. To understand the tissue-specific role of Ces3/TGH in lipid and glucose homeostasis, we generated mice with a liver-specific deletion of Ces3/Tgh expression (L-TGH knockout [KO]). Elimination of hepatic Ces3/Tgh expression dramatically decreased plasma VLDL TG and VLDL cholesterol concentrations but only moderately increased liver TG levels in mice fed a standard chow diet. Significantly reduced plasma TG and cholesterol without hepatic steatosis were also observed in L-TGH KO mice challenged with a high-fat, high-cholesterol diet. L-TGH KO mice presented with increased plasma ketone bodies and hepatic fatty acid oxidation. Intrahepatic TG in L-TGH KO mice was stored in significantly smaller lipid droplets. Augmented hepatic TG levels in chow-fed L-TGH KO mice did not affect glucose tolerance or glucose production from hepatocytes, but impaired insulin tolerance was observed in female mice.

CONCLUSION

Our data suggest that ablation of hepatic Ces3/Tgh expression decreases plasma lipid levels without causing severe hepatic steatosis.

A very low carbohydrate ketogenic diet prevents the progression of hepatic steatosis caused by hyperglycemia in a juvenile obese mouse model

Objective:

To investigate whether the improvement in hyperglycemia by dietary control influences hyperglycemia-induced pathologies in tissues of juvenile obese (ob/ob) mice.

Design:

Five-week-old ob/ob mice were fed a very low carbohydrate ketogenic diet (KD) for 7 weeks. The blood glucose levels and body weight were monitored during this period. Biochemical parameters in the serum and tissue pathologies of the mice were analyzed at the end of the 7-week period.

Results:

The hyperglycemic phenotype of the ob/ob mice was improved by KD feeding for 7 weeks. Surprisingly, we found that KD feeding also drastically reduced the hepatic steatosis phenotype in ob/ob mice, while their obesity phenotype was unaltered. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis revealed that several proteins found in the liver of ob/ob mice fed a regular chow diet were undetectable after being fed KD. Liquid chromatography with tandem mass spectrometry (LC-MS/MS) MASCOT search and western blot analysis revealed that the proteins absent from the mice fed KD included fatty acid synthase (FAS) and acetyl-CoA carboxylase 1 (ACC1), which are key enzymes for lipogenesis in the liver. Fatty acid analysis supported the results because the ratio of C18:1, which is a major product of lipogenesis, was reduced by KD feeding. However, C18:2, which cannot be synthesized in mammalian cells but is present in the KD, was found to be a major component in the liver of KD-fed ob/ob mice.

Conclusion:

Hyperglycemia promotes hepatic steatosis via the lipogenic pathway in the liver of juvenile ob/ob mice. However, the development of steatosis is prevented by feeding KD owing to an improvement in hyperglycemia. We found that the progression of steatosis is reflected by the composition of fatty acids in the total lipids of the liver and serum.