Lower Hepatic Triglyceride Levels Research Articles

Effect of nanoformulated copper/zinc superoxide dismutase on chronic ethanol-induced alterations in liver and adipose tissue.

We previously reported that nanoformulated copper/zinc superoxide dismutase (Nano) attenuates non-alcoholic fatty liver disease and adipose tissue (AT) inflammation in obese animals. Here, we sought to determine whether Nano treatment attenuates alcohol-associated liver disease (AALD) and AT inflammation in alcohol-fed mice. We pre-treated E-47cells (HepG2 cells that over-express CYP2E1) with native- or nano-superoxide dismutase (SOD) for 6h, followed by treatment with ethanol and/or linoleic acid (LA), a free fatty acid. For invivo studies, male C57BL/6 mice were fed the Lieber-DeCarli control or ethanol liquid diet for 4 weeks. The mice received Nano once every 2 days during the last 2 weeks of ethanol feeding. Our invitro studies revealed that Nano pretreatment reduced LA+ethanol-induced oxidative stress in E-47cells. Our invivo experiments showed that ethanol-fed Nano-treated mice had 22% lower hepatic triglyceride levels than mice fed ethanol alone. Nano-treated ethanol-fed mice also had 2-fold lower levels of Cd68 and similarly reduced levels of Ccl2 and Mmp12 mRNAs, than in untreated ethanol-fed mice. We also noted that ethanol feeding caused a remarkable increase in hepatic and/or plasma MCP-1 and CCR2 protein, which was blunted in ethanol+Nano-treated animals. The hepatic content of SREBP-1c, a transcription factor that promotes lipogenesis, was higher in ethanol-fed mice than controls but was attenuated in ethanol+Nano-treated animals. Further, livers of ethanol+Nano-treated mice had significantly higher levels of phosphorylated adenosine monophosphate-activated protein kinase (AMPK) than both control and ethanol-fed mice. In AT, the levels of Il6 mRNA, a hepatoprotective cytokine, and that of Arg1, a marker of anti-inflammatory macrophages, were significantly increased in ethanol+Nano-treated mice compared with control mice. Our data indicate that Nano treatment attenuates ethanol-induced steatohepatitis and that this effect is associated with an apparent activation of AMPK signaling. Our data also suggest that Nano induces Arg1 and Il6 expression in AT, suggesting anti-inflammatory effects in this tissue.

Hepatocyte-specific clusterin overexpression attenuates diet-induced nonalcoholic steatohepatitis

Clusterin is a multifunctional glycoprotein that plays important roles and is up-regulated in liver diseases such as hepatitis and hepatocellular carcinoma. However, little is known about the significance of clusterin in the pathogenesis of non-alcoholic steatohepatitis (NASH). The aim of this study is to examine the role of clusterin in progression of steatohepatitis in mice fed a methionine and choline deficient (MCD) diet. We generated hepatocyte-specific clusterin overexpression (hCLU-tg) mice, and hCLU-tg mice showed lower levels of hepatic triglycerides, less infiltration of macrophages and reduction of TNF-α, activation of Nrf-2 than wild-type littermates fed the MCD diet. Also, sustained clusterin expression in liver ameliorated hepatic fibrogenesis by reducing the activation of hepatic stellate cells by MCD diet. Sustained expression of clusterin in liver functioned as a preconditioning stimulus and prevented MCD diet-induced severe steatohepatitis injury via Nrf2 activation. These results demonstrate a novel function of clusterin as an immune preconditioning regulator in various inflammatory diseases including steatohepatitis.

High-Fructose Intake Impairs the Hepatic Hypolipidemic Effects of a High-Fat Fish-Oil Diet in C57BL/6 Mice

Overnutrition of saturated fats and fructose is one of the major factors for the development of nonalcoholic fatty liver disease. Because omega-3 polyunsaturated fatty acids (n-3fa) have established lipid lowering properties, we tested the hypothesis that n-3fa prevents high-fat and fructose-induced fatty liver disease in mice. Male C57BL/6J mice were randomly assigned to one of the following diet groups for 14 weeks: normal diet (ND), high-fat lard-based diet (HFD), HFD with fructose (HFD+Fru), high-fat fish-oil diet (FOD), or FOD+Fru. Despite for the development of obesity and insulin resistance, FOD had 65.3% lower (P<0.001) hepatic triglyceride levels than HFD+Fru, which was blunted to a 38.5% difference (P=0.173) in FOD+Fru. The lower hepatic triglyceride levels were associated with a lower expression of lipogenic genes LXRα and FASN, as well as the expression of genes associated with fatty acid uptake and triglyceride synthesis, CD36 and SCD1, respectively. Conversely, the blunted hypotriglyceride effect of FOD+Fru was associated with a higher expression of CD36 and SCD1. During overnutrition, a diet rich in n-3fa may prevent the severity of hepatic steatosis; however, when juxtaposed with a diet high in fructose, the deleterious effects of overnutrition blunted the hypolipidemic effects of n-3fa.

Bile acids override steatosis in farnesoid X receptor deficient mice in a model of non-alcoholic steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) is one of the most common liver diseases, and the pathogenesis is still not well known. The farnesoid X receptor (FXR) is a member of the nuclear hormone receptor superfamily and plays an essential role in maintaining bile acid and lipid homeostasis. In this study, we study the role of FXR in the pathogenesis of NFALD. We found that FXR deficient (FXR−/−) mice fed methionine- and choline-deficient (MCD) diet had higher serum ALT and AST activities and lower hepatic triglyceride levels than wild-type (WT) mice fed MCD diet. Expression of genes involved in inflammation (VCAM-1) and fibrosis (α-SMA) was increased in FXR−/− mice fed MCD diet (FXR−/−/MCD) compared to WT mice fed MCD diet (WT/MCD). Although MCD diet significantly induced hepatic fibrosis in terms of liver histology, FXR−/−/MCD mice showed less degree of hepatic steatosis than WT/MCD mice. Moreover, FXR deficiency synergistically potentiated the elevation effects of MCD diet on serum and hepatic bile acids levels. The super-physiological concentrations of hepatic bile acids in FXR−/−/MCD mice inhibited the expression of genes involved in fatty acid uptake and triglyceride accumulation, which may be an explanation for less steatosis in FXR−/−/MCD mice in contrast to WT/MCD mice. These results suggest that hepatic bile acids accumulation could override simple steatosis in hepatic injury during the progression of NAFLD and further emphasize the role of FXR in maintaining hepatic bile acid homeostasis in liver disorders and in hepatic protection.

Role of brain stearoyl‐CoA desaturase‐1 in metabolism, obesity, and glucose homeostasis (605.2)

The high prevalence of obesity, coupled with its potential to develop into serious health issues including type II diabetes, insulin resistance and coronary artery disease, reveals it is a significant health problem. To investigate how excess adipose tissue manifests into these health issues, we have observed the effects of a disruption in stearoyl‐CoA desaturase 1 (SCD1), which is involved in the synthesis of endogenous monounsaturated fatty acids from saturated fatty acids. We have previously demonstrated that whole‐body deficiency of SCD1 in mice protects from high‐fat diet‐induced obesity, hepatic steatosis and insulin resistance. However, the tissue‐specific contribution of SCD1 to these phenotypes remains to be fully elucidated. In the current study, we investigated the role of brain SCD1 in mediating the metabolic consequences of a high‐fat diet (HFD). We fed nestin‐cre+;SCD1 flox/flox brain‐specific SCD1 knockout (BKO) mice a HFD for 18 weeks. We observed that both male and female BKO mice weighed significantly less than Lox controls. In addition, male BKO mice had lower hepatic triglyceride levels than Lox mice, and enhanced glucose tolerance relative to Lox mice. Overall, these results indicate brain SCD1 plays a role in HFD‐induced adiposity and glucose homeostasis.

Acute activation of central GLP-1 receptors enhances hepatic insulin action and insulin secretion in high-fat-fed, insulin resistant mice

Glucagon-like peptide-1 (GLP-1) receptor knockout (Glp1r(-/-)) mice exhibit impaired hepatic insulin action. High fat (HF)-fed Glp1r(-/-) mice exhibit improved, rather than the expected impaired, hepatic insulin action. This is due to decreased lipogenic gene expression and triglyceride accumulation. The present studies overcome these secondary adaptations by acutely modulating GLP-1R action in HF-fed wild-type mice. The central GLP-1R was targeted given its role as a regulator of hepatic insulin action. We hypothesized that acute inhibition of the central GLP-1R impairs hepatic insulin action beyond the effects of HF feeding. We further hypothesized that activation of the central GLP-1R improves hepatic insulin action in HF-fed mice. Insulin action was assessed in conscious, unrestrained mice using the hyperinsulinemic euglycemic clamp. Mice received intracerebroventricular (icv) infusions of artificial cerebrospinal fluid, GLP-1, or the GLP-1R antagonist exendin-9 (Ex-9) during the clamp. Intracerebroventricular Ex-9 impaired the suppression of hepatic glucose production by insulin, whereas icv GLP-1 improved it. Neither treatment affected tissue glucose uptake. Intracerebroventricular GLP-1 enhanced activation of hepatic Akt and suppressed hypothalamic AMP-activated protein kinase. Central GLP-1R activation resulted in lower hepatic triglyceride levels but did not affect muscle, white adipose tissue, or plasma triglyceride levels during hyperinsulinemia. In response to oral but not intravenous glucose challenges, activation of the central GLP-1R improved glucose tolerance. This was associated with higher insulin levels. Inhibition of the central GLP-1R had no effect on oral or intravenous glucose tolerance. These results show that inhibition of the central GLP-1R deteriorates hepatic insulin action in HF-fed mice but does not affect whole body glucose homeostasis. Contrasting this, activation of the central GLP-1R improves glucose homeostasis in HF-fed mice by increasing insulin levels and enhancing hepatic insulin action.

ApoB siRNA‐induced Liver Steatosis is Resistant to Clearance by the Loss of Fatty Acid Transport Protein 5 (Fatp5)

The association between hypercholesterolemia and elevated serum apolipoprotein B (APOB) has generated interest in APOB as a therapeutic target for patients at risk of developing cardiovascular disease. In the clinic, mipomersen, an antisense oligonucleotide (ASO) APOB inhibitor, was associated with a trend toward increased hepatic triglycerides, and liver steatosis remains a concern. We found that siRNA-mediated knockdown of ApoB led to elevated hepatic triglycerides and liver steatosis in mice engineered to exhibit a human-like lipid profile. Many genes required for fatty acid synthesis were reduced, suggesting that the observed elevation in hepatic triglycerides is maintained by the cell through fatty acid uptake as opposed to fatty acid synthesis. Fatty acid transport protein 5 (Fatp5/Slc27a5) is required for long chain fatty acid (LCFA) uptake and bile acid reconjugation by the liver. Fatp5 knockout mice exhibited lower levels of hepatic triglycerides due to decreased fatty acid uptake, and shRNA-mediated knockdown of Fatp5 protected mice from diet-induced liver steatosis. Here, we evaluated if siRNA-mediated knockdown of Fatp5 was sufficient to alleviate ApoB knockdown-induced steatosis. We determined that, although Fatp5 siRNA treatment was sufficient to increase the proportion of unconjugated bile acids 100-fold, consistent with FATP5's role in bile acid reconjugation, Fatp5 knockdown failed to influence the degree, zonal distribution, or composition of the hepatic triglycerides that accumulated following ApoB siRNA treatment.Electronic supplementary materialThe online version of this article (doi:10.1007/s11745-011-3596-3) contains supplementary material, which is available to authorized users.

Pharmacogenetic Evidence That Cd36Is a Key Determinant of the Metabolic Effects of Pioglitazone

Pioglitazone, like other thiazolidinediones, is an insulin-sensitizing agent that activates the peroxisome proliferator-activated receptor gamma and influences the expression of multiple genes involved in carbohydrate and lipid metabolism. However, it is unknown which of these many target genes play primary roles in determining the antidiabetic and hypolipidemic effects of thiazolidinediones. To specifically investigate the role of the Cd36 fatty acid transporter gene in the insulin-sensitizing actions of thiazolidinediones, we studied the metabolic effects of pioglitazone in spontaneously hypertensive rats (SHR) that harbor a deletion mutation in Cd36 in comparison to congenic and transgenic strains of SHR that express wild-type Cd36. In congenic and transgenic SHR with wild-type Cd36, administration of pioglitazone was associated with significantly lower circulating levels of fatty acids, triglycerides, and insulin as well as lower hepatic triglyceride levels and epididymal fat pad weights than in SHR harboring mutant Cd36. Additionally, insulin-stimulated glucose oxidation in isolated soleus muscle was significantly augmented in pioglitazone-fed rats with wild-type Cd36 versus those with mutant Cd36. The Cd36 genotype had no effect on pioglitazone-induced changes in blood pressure. These findings provide direct pharmacogenetic evidence that in the SHR model, Cd36 is a key determinant of the insulin-sensitizing actions of a thiazolidinedione ligand of peroxisome proliferator-activated receptor gamma.

Effects of tibolone and conventional hormone replacement therapies on arterial and hepatic cholesterol accumulation and on circulating endothelin-1, vascular cell adhesion molecule-1, and E-selectin in surgically menopausal monkeys.

Menopause and aging are associated with a marked increase in the incidence of coronary heart disease as well as reductions in circulating estrogen, progestogen, and androgen levels. The synthetic compound tibolone and its metabolites have estrogenic, progestogenic, and androgenic characteristics. In the present study, we compared the effects of tibolone, estrogen replacement therapy, and estrogen plus progestogen replacement therapy on arterial and hepatic lipid accumulation and on circulating soluble adhesion molecule and endothelin-1 concentrations in surgically postmenopausal cynomolgus monkeys. Animals were fed an atherogenic diet for 2 years while receiving either no hormone treatment (control, n = 31) or the following treatments at doses designed to mimic the human dose on a daily caloric intake basis: tibolone at 2.5 mg/day (HiTib, n = 31), tibolone at 0.625 mg/day (LoTib, n = 29), conjugated equine estrogens (CEE) alone at 0.625 mg/day (CEE, n = 29), or CEE plus continuous medroxyprogesterone acetate (MPA) at 2.5 mg MPA/day (CEE + MPA, n = 30). Relative to the control group, iliac artery total cholesterol content was not different in the HiTib, LoTib, and CEE + MPA groups but was significantly lower in the group receiving CEE only (P < 0.05). In contrast, hepatic free cholesterol content was reduced in all treatment groups [HiTib (P < 0.01), LoTib (P < 0.05), CEE (P < 0.01), and CEE + MPA (P < 0.05)], whereas hepatic total and esterified cholesterol content were reduced in the HiTib, CEE, and CEE + MPA groups (all P < 0.05). HiTib and CEE groups had lower hepatic triglyceride levels per milligram of protein (P < 0.05). Iliac arterial cholesterol content was highly correlated with hepatic cholesterol content and with previously published histomorphometrically determined coronary artery atherosclerosis, supporting the use of the iliac artery as a surrogate for the coronary artery in the monkey. Circulating levels of soluble vascular cell adhesion molecule-1 were significantly reduced in the HiTib (P < 0.02) and CEE (P < 0.05) groups, whereas soluble E-selectin was reduced in the CEE group only (P < 0.01). Plasma endothelin-1 was significantly reduced in the LoTib (P < 0.05), CEE (P < 0.01), and CEE + MPA (P < 0.01) groups. These results suggest that while tibolone caused marked depression of high-density lipoprotein cholesterol and a resultant twofold increase in the total plasma cholesterol/high-density lipoprotein cholesterol ratio, those effects did not result in exacerbation of iliac artery atherosclerosis, perhaps because of beneficial effects on vascular biology or hepatic metabolism.

In vivo triglyceride secretion and hepatic and plasma lipids in rats fed medium-chain triglycerides, tripelargonin, or corn oil

The relationship between in vivo triglyceride secretion and the concentrations of cholesterol and triglycerides in liver and plasma was studied in fasted, male Sprague Dawley rats (150–170 g) fed 16% fat diets containing 8–16% medium chain triglycerides (68% C 8:0 and 24% C 10:0), 14% tripelargonate (C 9:0), or corn oil. Plasma and liver cholesterol concentrations were 10–20% lower ( P < 0.05), and hepatic activity of 3-hydroxymethyl-3-glutaryl Coenzyme A reductase was 44–66% lower ( P < 0.05) with ingestion of 14% medium chain triglycerides or tripelargonin than corn oil. Liver triglyceride concentrations were 19–44% lower ( P < 0.01) with ingestion of 14% medium chain triglycerides or tripelargonin than corn oil. Using the Triton WR-1339 technique, the rate of triglyceride secretion (mg/min × 100 g body wt), plasma triglyceride pool size, and the fractional rate constant for triglyceride secretion were not significantly different among treatment groups. This suggests that a greater rate of triglyceride secretion is not the primary factor associated with lower hepatic triglyceride levels in rats fed medium chain triglycerides. In summary, 10–20% lower plasma and liver cholesterol concentrations were noted with ingestion of saturated, medium-chain-length fatty acid triglycerides containing 8, 9, or 10 carbons compared to corn oil.

Hepatic ATP and Triglyceride Levels in Choline-deficient Rats with and without Dietary Orotic Acid Supplementation

Hepatic ATP depletion is probably important in the pathogenesis of the experimental fatty livers produced by orotic acid and several other agents that inhibit hepatic lipoprotein production. Because choline deficiency also impairs lipoprotein production, we have investigated the role of ATP depletion in this condition. Rats fed a choline-deficient diet for 5 days had no change in hepatic ATP despite a 30-fold increase in triglycerides. Furthermore, adenine sulfate, an ATP precursor, failed to influence the degree of lipid accumulation when added to the diet. In contrast, adding 1% orotic acid to a choline-supplemented diet for 5 days produced a 50% fall in ATP along with a sevenfold increase in hepatic triglycerides, and 0.25% dietary adenine sulfate completely prevented both these effects. A previously reported protective effect of orotic acid in choline deficiency was confirmed by the fact that choline-deficient rats fed orotic acid had about 50% lower hepatic triglyceride levels than those not given this agent. Despite this, orotic acid lowered ATP in choline-deficient animals equally as well as in choline-supplemented animals. These results indicate that unlike the lipid accumulation induced by orotic acid, the fatty liver of choline deficiency is not related to hepatic ATP depletion. The paradoxical protective effect of orotic acid in choline deficiency appears to be independent of its influence on ATP.