Differential effects of fenofibrate or simvastatin treatment of rats on hepatic microsomal overt and latent diacylglycerol acyltransferase activities

Ethnicity based differences in statin use and hypercholesterolemia control among patients with premature coronary artery disease-results of I-PAD study

Background

Statins use is the most important treatment for high LDL cholesterol in patients with premature coronary artery disease (CAD). Previous reports have shown racial and gender differences in statin use in the general population, but this wasn't studied in premature CAD based on different ethnicities.

Methods and results

Our study includes 1917 men and women with confirmed diagnosis of premature CAD. Logistic regression model was used to evaluate the high LDL cholesterol control in the groups and the OR with 95% confidence interval (CI) was reported as the effect size. After adjustment for confounders, the odds of controlling LDL in women taking Lovastatin, Rosuvastatin, and Simvastatin were 0.27 (0.03, 0.45) lower in comparison with men. Also, in participant who took 3 types of statins, the odds of controlling LDL were significantly different between Lor and Arab compared with Fars ethnicity. After adjustment to all confounders (full model), the odds of controlling LDL were lower for Gilak in Lovastatin, Rosuvastatin, and Simvastatin by 0.64 (0.47, 0.75); 0.61 (0.43, 0.73); 0.63 (0.46, 0.74) respectively and higher for Arab in Lovastatin, Rosuvastatin, and Simvastatin by 4.63 (18.28, 0.73); 4.67 (17.47, 0.74); 4.55 (17.03, 0.71) respectively compared to Fars.

Conclusions

Major differences in different gender and ethnicities may have had led to disparities in statin use and LDL control. Awareness of the statins impact on high LDL cholesterol based on different ethnicities can help health decision-makers to close the observed gaps in statin use and control LDL to prevent CAD problems.

Metabolite Signature of Simvastatin Treatment Involves Multiple Metabolic Pathways

Statins inhibit the 3-hydroxy-3-methylglutaryl-CoA reductase enzyme and are the most widely used medication for hypercholesterolemia. Previous studies on the metabolite signature of simvastatin treatment have included only a small number of metabolites. We performed a high-throughput liquid chromatography–tandem mass spectroscopy profiling on the effects of simvastatin treatment on 1098 metabolite concentrations in the participants of the METSIM (Metabolic Syndrome In Men) study including 1332 participants with simvastatin treatment and 6200 participants without statin treatment. We found that simvastatin exerts profound pleiotropic effects on different metabolite pathways, affecting not only lipids, but also amino acids, peptides, nucleotides, carbohydrates, co-factors, vitamins, and xenobiotics. We identified 321 metabolites significantly associated with simvastatin treatment, and 313 of these metabolites were novel. Our study is the first comprehensive evaluation of the metabolic signature of simvastatin treatment in a large population-based study.

Beneficial Effect of Fenofibrate and Silymarin on Hepatic Steatosis and Gene Expression of Lipogenic and Cytochrome P450 Enzymes in Non-Obese Hereditary Hypertriglyceridemic Rats

The efficacy of fenofibrate in the treatment of hepatic steatosis has not been clearly demonstrated. In this study, we investigated the effects of fenofibrate and silymarin, administered as monotherapy and in combination to existing hepatic steatosis in a unique strain of hereditary hypertriglyceridemic rats (HHTg), a non-obese model of metabolic syndrome. HHTg rats were fed a standard diet without or with fenofibrate (100 mg/kg b.wt./day) or with silymarin (1%) or with a combination of fenofibrate with silymarin for four weeks. Fenofibrate alone and in combination with silymarin decreased serum and liver triglycerides and cholesterol and increased HDL cholesterol. These effects were associated with the decreased gene expression of enzymes involved in lipid synthesis and transport, while enzymes of lipid conversion were upregulated. The combination treatment had a beneficial effect on the gene expression of hepatic cytochrome P450 (CYP) enzymes. The expression of the CYP2E1 enzyme, which is source of hepatic reactive oxygen species, was reduced. In addition, fenofibrate-induced increased CYP4A1 expression was decreased, suggesting a reduction in the pro-inflammatory effects of fenofibrate. These results show high efficacy and mechanisms of action of the combination of fenofibrate with silymarin in treating hepatic steatosis and indicate the possibility of protection against disorders in which oxidative stress and inflammation are involved.

The beneficial effects of Lactobacillus brevis FZU0713-fermented Laminaria japonica on lipid metabolism and intestinal microbiota in hyperlipidemic rats fed with a high-fat diet

This study aimed to investigate the beneficial effects of the oral administration of Lactobacillus brevis FZU0713-fermented Laminaria japonica (FLJ) on lipid metabolism and intestinal microbiota in hyperlipidemic rats fed with a high-fat diet (HFD). The results demonstrated that the oral administration of FLJ significantly inhibited obesity and improved the serum and hepatic biochemical parameters in HFD-fed rats. Histopathological results also indicated that FLJ intervention could significantly reduce the accumulation of lipid droplets in the liver induced by HFD feeding. Furthermore, FLJ intervention up-regulated the fecal short-chain fatty acid (SCFA) levels (mainly acetate, propionate and isobutyrate) in HFD-fed rats. Intestinal microbiota profiling by 16S rRNA gene sequencing revealed that FLJ intervention increased the relative abundance of Akkermansia, Collinsella, Ruminococcaceae_UCG-013, Defluviitaleaceae_UCG-011, Intestinimonas, Actinomyces and Tyzzerella, but decreased the abundance of Flavonifractor, Collinsella, Sporosarcina and Lacticigenium. Based on Spearman's correlation, the fecal levels of TC, TG, acetic acid and butyric acid were positively correlated with the relative abundance of Akkermansia and Ruminococcaceae_NK4A214, but negatively correlated with the relative amount of Flavonifractor and Collinsella. The metabolic function of intestinal microbiota predicted by PICRUSt analysis of 16S rRNA gene sequences demonstrated that primary and secondary bile acid biosyntheses, fatty acid biosynthesis, taurine and hypotaurine metabolism, arachidonic acid metabolism, glycolysis/gluconeogenesis, etc. were significantly down-regulated after 8 weeks of FLJ intervention. Additionally, FLJ intervention significantly regulated the hepatic mRNA levels (including BSEP, CYP7A1, LDLR, HMGCR, CD36 and SREBP1-C) involved in lipid metabolism and bile acid homeostasis. In conclusion, these findings support the possibility that Laminaria japonica fermented with probiotic Lactobacillus has the potential to reduce the disturbance of lipid metabolism by regulating intestinal microflora and liver gene expression profiles, so it can be employed as a potential functional food to prevent hyperlipidemia.

Therapeutic advancement of simvastatin-loaded solid lipid nanoparticles (SV-SLNs) in treatment of hyperlipidemia and attenuating hepatotoxicity, myopathy and apoptosis: Comprehensive study

This study set out to optimize simvastatin (SV) in lipid nanoparticles (SLNs) to improve bioavailability, efficacy and alleviate adverse effects. Simvastatin-loaded solid lipid nanoparticles (SV-SLNs) were prepared by hot-melt ultrasonication method and optimized by box-Behnken experimental design. Sixty Wister albino rats were randomly assigned into six groups and treated daily for 16 weeks: control group, the group fed with 20 g of high-fat diet (HFD), group treated with vehicle (20 mg/kg, P.O.) for last four weeks, group treated with HFD and SV (20 mg/kg, P.O.) / or SV-SLNs (20 mg/kg/day, P.O.) / or SV-SLNs (5 mg/kg, P.O.) at last four weeks. Blood, liver tissues, and quadriceps muscles were collected for biochemical analysis, histological and immunohistochemical assays. The optimized SV-SLNS showed a particle-size 255.2 ± 7.7 nm, PDI 0.31 ± 0.09, Zeta-potential - 19.30 ± 3.25, and EE% 89.81 ± 2.1%. HFD showed severe changes in body weight liver functions, lipid profiles, atherogenic index (AIX), albumin, glucose, insulin level, alkaline phosphatase as well as muscle injury, oxidative stress biomarkers, and protein expression of caspase-3. Simvastatin treatment in animals feed with HFD showed a significant improvement of all tested parameters, but it was associated with hepatotoxicity, myopathy, and histological changes in quadriceps muscles. SV-SLNs exhibited a significant improvement of all biochemical, histological examinations, and immunohistochemical assays. SV-SLNs (5 mg/kg) treatment returns all measured parameters to control itself. These results represent that SV-SLNs is a promising candidate as a drug carrier for delivering SV with maximum efficacy and limited adverse reaction.

Ameliorative effects of autophagy inducer, simvastatin on alcohol-induced liver disease in a rat model

Alcoholic liver disease (ALD) encompasses a variety of liver injuries with various underlying mechanisms but still no effective treatment. So we aimed to monitor the influence of simvastatin on alcohol-induced liver injury and elucidate the underlying mechanisms of its cytoprotective effect. Thirty male albino rats were randomly divided into five equal groups. Group 1 (control): received a standard diet; group 2: received simvastatin (10 mg kg^-1  day ^-1 ) once a day orally for 8 weeks; group 3: received 20% ethanol (7.9 g kg ^-1  day ^-1 ) daily orally for 8 weeks; group 4: received 20% ethanol along with same simvastatin dose daily for 8 weeks; group 5: received 20% ethanol orally for 8 weeks then received the same simvastatin dose for the next 8 weeks. Serum alanine aminotransferase, aspartate aminotransferase, total cholesterol, triglycerides, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol were measured. Liver tissue malondialdehyde, reduced glutathione levels, and superoxide dismutase activity were estimated. B-cell lymphoma 2 and C/EBP homologous protein levels were evaluated by enzyme linked immunosorbent assay (ELISA). Light chain 3-II and peroxisome proliferation-activated receptor gamma messenger RNA expression was assessed by real-time polymerase chain reaction. Immunohistochemical staining was performed using anti-rat tumor necrosis factor-alpha antibody. Our results revealed that simvastatin treatment was able to ameliorate alcohol-induced liver damage; the improved biochemical data were confirmed by histopathological evaluation. Simvastatin being an autophagy inducer was able to prevent and reverse alcohol-induced liver changes via induction of autophagy, attenuation of oxidative stress, inflammation, and endoplasmic reticulum stress-induced apoptosis. Therefore, our findings suggest that treatment with simvastatin may be a useful approach in the management strategy of ALD.

The triglyceride synthesis enzymes DGAT1 and DGAT2 have distinct and overlapping functions in adipocytes

Mammals store metabolic energy as triacylglycerols (TGs) in adipose tissue. TG synthesis is catalyzed by the evolutionarily unrelated acyl-CoA:diacylglycerol acyltransferase (DGAT) enzymes DGAT1 and DGAT2, which catalyze the same reaction and account for nearly all TG synthesis. The reasons for their convergent evolution to synthesize TGs remain unclear. Mice lacking DGAT1 are viable with reduced fat stores of TGs, whereas DGAT2 KO mice die postnatally just after birth with >90% reduction of TGs, suggesting that DGAT2 is the predominant enzyme for TG storage. To better understand the functional differences between the DGATs, we studied mice fed chow or high-fat diets lacking either enzyme in adipose tissue. Unexpectedly, mice lacking DGAT2 in adipocytes have normal TG storage and glucose metabolism on regular or high-fat diets, indicating DGAT2 is not essential for fat storage. In contrast, mice lacking DGAT1 in adipocytes have normal TG storage on a chow diet but moderately decreased body fat accompanied by glucose intolerance when challenged with a high-fat diet. The latter changes were associated with the activation of ER stress pathways. We conclude that DGAT1 and DGAT2 can largely compensate for each other for TG storage but that DGAT1 uniquely has an important role in protecting the ER from the lipotoxic effects of high-fat diets.

Grifola frondosapolysaccharides ameliorate lipid metabolic disorders and gut microbiota dysbiosis in high-fat diet fed rats

G. frondosapolysaccharides have the potential to ameliorate lipid metabolic disorders in part through modulating gut microbiota and mRNA expression of genes involved in hepatic lipid and cholesterol metabolism.

Hepatic VLDL secretion: DGAT1 determines particle size but not particle number, which can be supported entirely by DGAT2

We investigated whether, in view of its activity being expressed on both aspects of the endoplasmic reticulum (ER; dual membrane topology), diacylglycerol acyltransferase 1 (DGAT1) plays a distinctive role in determining the triglyceride (TAG) content of VLDL particles secreted by the liver. Mice in which the DGAT1 gene was specifically ablated in hepatocytes (DGAT1-LKO mice) had the same number of VLDL particles (apoB concentration) in the plasma 1 h after Triton 1339 treatment, but these particles were approximately half the size of VLDL particles secreted by control mice and had a proportionately decreased content of TAG, with normal cholesterol and cholesteryl ester contents. Analyses of purified microsomal fractions prepared from 16 h fasted control and DAGT1-LKO mice showed that the TAG/protein ratio in the ER was significantly lower in the latter. Electron micrographs of these livers showed that those from DGAT1-LKO mice did not show the increased lipid content of the smooth ER shown by control livers. The effects of DGAT1- and DGAT2-specific inhibitors on apoB secretion by HepG2 cells showed that DGAT1 is not indispensable for apoB secretion and demonstrated redundancy in the ability of the two enzymes to support apoB secretion. Therefore, our findings show that DGAT1 is essential for the complete lipidation and maturation of VLDL particles within the lumen of the ER, consistent with its dual topology within the ER membrane. In the mouse, DGAT2 can support apoB secretion (particle number) even when TAG availability for full VLDL lipidation is restricted in the absence of DGAT1.

Effects of free omega-3 carboxylic acids and fenofibrate on liver fat content in patients with hypertriglyceridemia and non-alcoholic fatty liver disease: A double-blind, randomized, placebo-controlled study

BACKGROUND

Treatment with omega-3 fatty acids and fenofibrates reduces serum triglyceride levels, but few studies have compared the effect of these agents on liver fat.

OBJECTIVE

The aim of the EFFECT I trial (NCT02354976) was to determine the effects of free omega-3 carboxylic acids (OM-3CA) and fenofibrate on liver fat in overweight or obese individuals with non-alcoholic fatty liver disease and hypertriglyceridemia.

METHODS

Seventy-eight patients were randomized to receive oral doses of 4 g OM-3CA (n = 25), 200 mg fenofibrate (n = 27), or placebo (n = 26) for 12 weeks in a double-blind, parallel-group study. Liver proton density fat fraction (PDFF) and volume, pancreas volume, and adipose tissue volumes were assessed by magnetic resonance imaging.

RESULTS

Changes in liver PDFF at 12 weeks were not significantly different across treatment groups (relative changes from baseline: placebo, +4%; OM-3CA, -2%; and fenofibrate, +17%). The common PNPLA3 genetic polymorphism (I148M) did not significantly influence the effects of OM-3CA or fenofibrate on liver PDFF. Fenofibrate treatment significantly increased liver and pancreas volumes vs placebo treatment, and the changes in liver and pancreas volumes were positively correlated (rho 0.45, P = .02). Total liver fat volume increased significantly in patients using fenofibrate vs OM-3CA (+23% vs -3%, P = .04). Compared with OM-3CA, fenofibrate increased total liver fat and liver volume. Serum triglycerides decreased with OM-3CA (-26%, P = .02) and fenofibrate (-38%, P < .001) vs placebo. In contrast to OM-3CA, fenofibrate reduced plasma docosahexaenoic acid levels and increased plasma acetylcarnitine and butyrylcarnitine levels, estimated delta-9 desaturase activity and the concentration of urine F2-isoprostanes.

CONCLUSIONS

OM-3CA and fenofibrate reduced serum triglycerides but did not reduce liver fat. Fenofibrate increased total liver volume and total liver fat volume vs OM-3CA, indicating a complex effect of fenofibrate on human hepatic lipid metabolism.

Fish Oil Supplementation Alleviates the Altered Lipid Homeostasis in Blood, Liver, and Adipose Tissues in High-Fat Diet-Fed Rats

This study investigated the effects of dietary supplementation of fish oil on the signals of lipid metabolism involved in hepatic cholesterol and triglyceride influx and excretion in high-fat diet (HFD)-fed rats. Fish oil (FO) repressed body (HFD, 533 ± 18.2 g; HFD+FO, 488 ± 28.0 g, p < 0.05) and liver weights (HFD, 5.7 ± 0.6 g/100 g of body weight; HFD+FO, 4.8 ± 0.4 g/100 g of body weight, p < 0.05) in HFD-fed rats. Fish oil could also improve HFD-induced imbalance of lipid metabolism in blood, liver, and adipose tissues including the significant decreases in plasma and liver total cholesterol (TC) (plasma-HFD, 113 ± 33.6 mg/dL; HFD+FO, 50.0 ± 5.95 mg/dL, p < 0.05; liver-HFD, 102 ± 13.0 mg/g liver; [corrected] HFD+FO, 86.6 ± 7.81 mg/g liver, [corrected] p < 0.05), blood, liver, and adipose triglyceride (TG) (blood-HFD, 52.5 ± 20.4 mg/dL; HFD+FO, 29.8 ± 4.30 mg/dL, p < 0.05; liver-HFD, 56.2 ± 10.0 mg/g liver; [corrected] HFD+FO, 30.3 ± 5.28 mg/g liver, [corrected] p < 0.05; adipose-HFD, 614 ± 73.2 mg/g liver, [corrected] HFD+FO, 409 ± 334 mg/g of adipose tissue, [corrected] p < 0.05), and low density (HFD, 79.8 ± 40.9 mg/dL; HFD+FO, 16.6 ± 5.47 mg/dL, p < 0.05) and very-low-density (HFD, 49.7 ± 33.3 mg/dL; HFD+FO, 10.4 ± 3.45 mg/dL, p < 0.05) lipoprotein and the significant increases in fecal TC (HFD, 12.2 ± 0.67 mg/g feces; [corrected] HFD+FO, 16.3 ± 2.04 mg/g feces, [corrected] < 0.05) and TG (HFD, 2.09 ± 0.10 mg/g feces; [corrected] HFD+FO, 2.38 ± 0.22 mg/g feces, [corrected] p < 0.05) and lipoprotein lipase activity of adipose tissues (HFD, 16.6 ± 3.64 μM p-nitrophenol; HFD+FO, 24.5 ± 4.19 μM p-nitrophenol, p < 0.05). Moreover, fish oil significantly activated the protein expressions of hepatic lipid metabolism regulators (AMPKα and PPARα) and significantly regulated the lipid-transport-related signaling molecules (ApoE, MTTP, ApoB, Angptl4, ApoCIII, ACOX1, and SREBPF1) in blood or liver of HFD-fed rats. These results suggest that fish oil supplementation improves HFD-induced imbalance of lipid homeostasis in blood, liver, and adipose tissues in rats.

Amelioration of diet-induced steatohepatitis in mice following combined therapy with ASO-Fsp27 and fenofibrate

Nonalcoholic fatty liver disease (NAFLD) is the leading cause of chronic liver disease. NAFLD progresses from benign steatosis to steatohepatitis (NASH) to cirrhosis and is linked to hepatocellular carcinoma. No targeted treatment is currently approved for NAFLD/NASH. We previously showed that fat-specific protein 27 (FSP27), a lipid droplet-associated protein that controls triglyceride turnover in the hepatocyte, is required for fasting- and diet-induced triglyceride accumulation in the liver. However, silencing Fsp27 with antisense oligonucleotides (ASOs) did not improve hepatosteatosis in genetic nor nutritional mouse models of obesity. Herein, we tested the therapeutic potential of ASO-Fsp27 when used in combination with the PPARα agonist fenofibrate. C57BL/6 mice were fed a high-trans-fat, high-cholesterol, high-fructose diet for eight weeks to establish NASH, then kept on diet for six additional weeks while dosed with ASOs and fenofibrate, alone or in combination. Data show that ASO-Fsp27 and fenofibrate synergize to promote resistance to diet-induced obesity and hypertriglyceridemia and to reverse hepatic steatosis, inflammation, oxidative stress, and fibrosis. This multifactorial improvement of liver disease noted when combining both drugs suggests that a course of treatment that includes both reduced FSP27 activity and activation of PPARα could provide therapeutic benefit to patients with NAFLD/NASH.

The regulatory effects of fish oil and chitosan on hepatic lipogenic signals in high-fat diet-induced obese rats

The present study investigated the regulatory effects of fish oil and chitosan on the signals of hepatic lipid metabolism and the postulated mechanism in high-fat diet-induced obese rats. Diet supplementation of chitosan and fish oil efficiently suppressed the increased weights in body and livers of high-fat diet-fed rats. Supplementation of chitosan and fish oil significantly decreased the activities of hepatic lipid biosynthesis-related enzymes and efficiently regulated plasma lipoprotein homeostasis. Both chitosan and fish oil significantly ameliorated the alterations in the protein expressions of hepatic lipogenic transcription factors (LXRα and PPARα), and could also significantly regulate the downstream hepatic lipogenic genes (FAS, HMGCR, CYP7A1, FATP, FABP, AOX, and ABCA) expressions in high-fat diet-fed rats. These results suggest that both fish oil and chitosan exerts downregulative effects on hepatic lipid metabolism in high-fat diet-induced obese rats via the LXRα inhibition and PPARα activation, which further affect the expressions of hepatic lipogenesis-associated genes.

Osthole improves glucose and lipid metabolism via modulation of PPARα/γ-mediated target gene expression in liver, adipose tissue, and skeletal muscle in fatty liver rats

CONTEXT

Osthole may be a dual agonist of peroxisome proliferator-activated receptors (PPAR) α/γ and ameliorate the insulin resistance (IR), but its mechanisms are not yet understood completely.

OBJECTIVE

We investigated the effects of osthole on PPARα/γ-mediated target genes involved in glucose and lipid metabolism in liver, adipose tissue, and skeletal muscle in fatty liver and IR rats.

MATERIALS AND METHODS

The rat model was established by orally feeding high-fat and high-sucrose emulsion for 9 weeks. The experimental rats were treated with osthole 5-10 mg/kg by gavage after feeding the emulsion for 6 weeks, and were sacrificed 4 weeks after administration.

RESULTS

After treatment with osthole 5-10 mg/kg for 4 weeks, the lipid levels in serum and liver were decreased by 37.9-67.2% and 31.4-38.5% for triglyceride, 33.1-47.5% and 28.5-31.2% for free fatty acid, respectively, the fasting blood glucose, fasting serum insulin, and homeostasis model assessment of IR were also decreased by 17.2-22.7%, 25.9-26.7%, and 37.5-42.8%, respectively. Osthole treatment might simultaneously decrease the sterol regulatory element binding protein-1c, diacylglycerol acyltransferase, and fatty acid synthase mRNA expressions in liver and adipose tissue, and increase the carnitine palmitoyltransferase-1A mRNA expression in liver and glucose transporter-4 mRNA expression in skeletal muscle, especially in the osthole 10 mg/kg group (p < 0.01).

DISCUSSION AND CONCLUSION

Osthole can improve glucose and lipid metabolism in fatty liver and IR rats, and its mechanisms may be associated with synergic modulation of PPARα/γ-mediated target genes involved in glucose and lipid metabolism in liver, adipose tissue, and skeletal muscle.

Fenofibrate insulates diacylglycerol in lipid droplet/ER and preserves insulin signaling transduction in the liver of high fat fed mice

Hepatic steatosis is often associated with insulin resistance as a hallmark of the metabolic syndrome in the liver. The present study investigated the effects of PPARα activation induced by fenofibrate (FB) on the relationship of insulin resistance and hepatic steatosis in mice fed a high-fat (HF) diet, which increases lipid influx into the liver. Mice were fed HF diet to induce insulin resistance and hepatic steatosis with or without FB. FB activated PPARα and ameliorated HF diet-induced glucose intolerance and hepatic insulin resistance without altering either hepatic steatosis or inflammation signaling (JNK or IKK). Interestingly, FB treatment simultaneously increased fatty acid (FA) synthesis (50%) and oxidation (66%, both p<0.01) into intermediate lipid metabolites, suggesting a FA oxidation-synthesis cycling in operation. Associated with these effects, diacylglycerols (DAGs) were sequestered within the lipid droplet/ER compartment, thus reducing their deposition in the cellular membrane, which is known to impair insulin signal transduction. These findings suggest that the reduction in membrane DAGs (rather than total hepatic steatosis) may be critical for the protection by fenofibrate-induced PPARα activation against hepatic insulin resistance induced by dietary fat.

CIDEC/FSP27 is regulated by peroxisome proliferator-activated receptor alpha and plays a critical role in fasting- and diet-induced hepatosteatosis

The cell death-inducing DNA fragmentation factor alpha-like effector c (CIDEC; also known in rodents as FSP27 or fat-specific protein 27) is a lipid droplet-associated protein that promotes intracellular triglyceride (TAG) storage. CIDEC/Fsp27 is highly expressed in adipose tissue, but undetectable in normal liver. However, its hepatic expression rises during fasting or under genetic or diet-induced hepatosteatosis in both mice and patients. Herein, we demonstrate that CIDEC/Fsp27 is a direct transcriptional target of the nuclear receptor PPARα (peroxisome proliferator-activated receptor alpha) in both mouse and human hepatocytes, and that preventing Fsp27 induction accelerates PPARα-stimulated fatty acid oxidation. We show that adenoviral-mediated silencing of hepatic Fsp27 abolishes fasting-induced liver steatosis in the absence of changes in plasma lipids. Finally, we report that anti-Fsp27 short hairpin RNA and PPARα agonists synergize to ameliorate hepatosteatosis in mice fed a high fat diet.

CONCLUSIONS

Together, our data highlight the physiological importance of CIDEC/Fsp27 in TAG homeostasis under both physiological and pathological liver steatosis. Our results also suggest that patients taking fibrates likely have elevated levels of hepatic CIDEC, which may limit the efficient mobilization and catabolism of hepatic TAGs.

Urokinase-type plasminogen activator (uPA) stimulates triglyceride synthesis in Huh7 hepatoma cells via p38-dependent upregulation of DGAT2

OBJECTIVE

The liver is the central organ of fatty acid and triglyceride metabolism. Oxidation and synthesis of fatty acids and triglycerides is under the control of peroxisome-proliferator-activated receptors (PPAR) α. Impairment of these receptors' function contributes to the accumulation of triglycerides in the liver resulting in non-alcoholic fatty liver disease. Urokinase-type plasminogen activator (uPA) was shown to regulate gene expression in the liver involving PPARγ transcriptional activity. In this study we questioned whether uPA modulates triglyceride metabolism in the liver, and investigated the mechanisms involved in the observed processes.

METHODS AND RESULTS

Huh7 hepatoma cells were incubated with increasing concentrations of uPA for 24 h uPA dose-dependently increased the cellular triglyceride mass, and this effect resulted from increased de novo triglyceride synthesis mediated by the enzyme diglyceride acyltransferase 2 (DGAT2). Also, the amount of free fatty acids was highly up regulated by uPA through activation of the transcription factor SREBP-1. Chemical activation of PPARα further increased uPA-stimulated triglyceride synthesis, whereas inhibition of p38, an upstream activator of PPARα, completely abolished the stimulatory effect of uPA on both triglyceride synthesis and DGAT2 upregulation. The effect of uPA on triglyceride synthesis in Huh7 cells was mediated via binding to its receptor, the uPAR. In vivo studies in uPAR(-/-) mice demonstrated that no lipid droplets were observed in their livers compared to C57BL/6 mice and the triglyceride levels were significantly lower.

CONCLUSION

This study presents a new biological function of the uPA/uPAR system in the metabolism of triglycerides and might present a new target for an early therapeutic intervention for NAFLD.

High-level copy number gains of established and potential drug target genes in gastric cancer as a lead for treatment development and selection

PURPOSE

The overall survival rate of patients with advanced gastric cancer is poor. Therefore, there is an urgent need for new treatment options for these patients. The identification of drug target genes located on DNA regions exhibiting high-level copy number gains (CNG) may be an effective approach, as has e.g. previously been shown for HER2. The aim of the present study was to identify putative drug targets in patients with gastric cancer by applying this strategy.

METHODS

Genome-wide array comparative genomic hybridization (array CGH) data available from 183 primary gastric cancer samples were analyzed through Ingenuity Pathway Analysis (IPA) to assess whether any established or potential anticancer drug target genes showed high-level CNG, including focal amplifications.

RESULTS

A total of 147 high-level gained regions were identified in the gastric cancer samples, harboring 167 genes that had previously been annotated as drug target genes. Thirty (18 %) of these genes showed high-level gains in at least 2 % of the tumors. The identified drug target genes included those for drugs known to be active in advanced (gastric) cancer, targets for targeted therapies in clinical development, as well as targets for drugs currently used for other indications but of potential interest for anticancer treatment. In addition, 12 potential drug target genes were identified, including genes involved in growth factor signaling and cell cycle regulation.

CONCLUSION

The majority of gastric cancers carried one or more high-level CNGs or focal amplifications encompassing putative drug target genes. A number of the associated drugs are currently not being considered for treatment of gastric cancer. Based on these results we hypothesize that DNA copy number profiling may be a useful tool to identify new drug targets and to guide individualized treatment strategies in patients with gastric cancer.

The g0/g1 switch gene 2 is an important regulator of hepatic triglyceride metabolism

Nonalcoholic fatty liver disease is associated with obesity and insulin resistance. Factors that regulate the disposal of hepatic triglycerides contribute to the development of hepatic steatosis. G₀/G₁ switch gene 2 (G0S2) is a target of peroxisome proliferator-activated receptors and plays an important role in regulating lipolysis in adipocytes. Therefore, we investigated whether G0S2 plays a role in hepatic lipid metabolism. Adenovirus-mediated expression of G0S2 (Ad-G0S2) potently induced fatty liver in mice. The liver mass of Ad-G0S2-infected mice was markedly increased with excess triglyceride content compared to the control mice. G0S2 did not change cellular cholesterol levels in hepatocytes. G0S2 was found to be co-localized with adipose triglyceride lipase at the surface of lipid droplets. Hepatic G0S2 overexpression resulted in an increase in plasma Low-density lipoprotein (LDL)/Very-Low-density (VLDL) lipoprotein cholesterol level. Plasma High-density lipoprotein (HDL) cholesterol and ketone body levels were slightly decreased in Ad-G0S2 injected mice. G0S2 also increased the accumulation of neutral lipids in cultured HepG2 and L02 cells. However, G0S2 overexpression in the liver significantly improved glucose tolerance in mice. Livers expressing G0S2 exhibited increased 6-(N-(7-nitrobenz-2-oxa-1-3-diazol-4-yl) amino)-6-deoxyglucose uptake compared with livers transfected with control adenovirus. Taken together, our results provide evidence supporting an important role for G0S2 as a regulator of triglyceride content in the liver and suggest that G0S2 may be a molecular target for the treatment of insulin resistance and other obesity-related metabolic disorders.

Hepatic triacylglycerol synthesis and secretion: DGAT2 as the link between glycaemia and triglyceridaemia

lThe liver regulates both glycaemia and triglyceridaemia. Hyperglycaemia and hypertriglyceridaemia are both characteristic of (pre)diabetes. Recent observations on the specialised role of DGAT2 (diacylglycerol acyltransferase 2) in catalysing the de novo synthesis of triacylglycerols from newly synthesized fatty acids and nascent diacylglycerols identifies this enzyme as the link between the two. This places DGAT2 at the centre of carbohydrate-induced hypertriglyceridaemia and hepatic steatosis. This function is complemented, but not substituted for, by the ability of DGAT1 to rescue partial glycerides from complete hydrolysis. In peripheral tissues not normally considered to be lipogenic, synthesis of triacylglycerols may largely bypass DGAT2 except in hyperglycaemic/hyperinsulinaemic conditions, when induction of de novo fatty acid synthesis in these tissues may contribute towards increased triacylglycerol secretion (intestine) or insulin resistance (adipose tissue, and cardiac and skeletal muscle).

Diacylglycerol acyltransferase 2 acts upstream of diacylglycerol acyltransferase 1 and utilizes nascent diglycerides and de novo synthesized fatty acids in HepG2 cells

The two diacylglycerol acyltransferases, DGAT1 and DGAT2, are known to have non-redundant functions, in spite of catalysing the same reaction and being present in the same cell types. The basis for this distinctiveness, which is reflected in the very different phenotypes of Dgat1(-/-) and Dgat2(-/-) mice, has not been resolved. Using selective inhibitors of human DGAT1 and DGAT2 on HepG2 cells and gene silencing, we show that, although DGAT2 activity accounts for a modest fraction (< 20%) of overall cellular DGAT activity, inhibition of DGAT2 activity specifically inhibits (and is rate-limiting for) the incorporation of de novo synthesized fatty acids and of glycerol into cellular and secreted triglyceride to a much greater extent than it affects the incorporation of exogenously added oleate. By contrast, inhibition of DGAT1 affects equally the incorporation of glycerol and exogenous (preformed) oleate into cellular and secreted triacylglycerol (TAG). These data indicate that DGAT2 acts upstream of DGAT1, largely determines the rate of de novo synthesis of triglyceride, and uses nascent diacylglycerol and de novo synthesized fatty acids as substrates. By contrast, the data suggest that DGAT1 functions in the re-esterification of partial glycerides generated by intracellular lipolysis, using preformed (exogenous) fatty acids. Therefore, we describe distinct but synergistic roles of the two DGATs in an integrated pathway of TAG synthesis and secretion, with DGAT2 acting upstream of DGAT1.

The use of stable isotope-labeled glycerol and oleic acid to differentiate the hepatic functions of DGAT1 and -2

Diacylglycerol acyltransferase (DGAT) catalyzes the final step in triglyceride (TG) synthesis. There are two isoforms, DGAT1 and DGAT2, with distinct protein sequences and potentially different physiological functions. To date, the ability to determine clear functional differences between DGAT1 and DGAT2, especially with respect to hepatic TG synthesis, has been elusive. To dissect the roles of these two key enzymes, we pretreated HepG2 hepatoma cells with (13)C(3)-D(5)-glycerol or (13)C(18)-oleic acid, and profiled the major isotope-labeled TG species by liquid chromatography tandem mass spectrometry. Selective DGAT1 and DGAT2 inhibitors demonstrated that (13)C(3)-D(5)-glycerol-incorporated TG synthesis was mediated by DGAT2, not DGAT1. Conversely, (13)C(18)-oleoyl-incorporated TG synthesis was predominantly mediated by DGAT1. To trace hepatic TG synthesis and VLDL triglyceride (VLDL-TG) secretion in vivo, we administered D(5)-glycerol to mice and measured plasma levels of D(5)-glycerol-incorporated TG. Treatment with an antisense oligonucleotide (ASO) to DGAT2 led to a significant reduction in D(5)-glycerol incorporation into VLDL-TG. In contrast, the DGAT2 ASO had no effect on the incorporation of exogenously administered (13)C(18)-oleic acid into VLDL-TG. Thus, our results indicate that DGAT1 and DGAT2 mediate distinct hepatic functions: DGAT2 is primarily responsible for incorporating endogenously synthesized FAs into TG, whereas DGAT1 plays a greater role in esterifying exogenous FAs to glycerol.

Evidence that diacylglycerol acyltransferase 1 (DGAT1) has dual membrane topology in the endoplasmic reticulum of HepG2 cells

Triacylglycerol (TAG) synthesis and secretion are important functions of the liver that have major impacts on health, as overaccumulation of TAG within the liver (steatosis) or hypersecretion of TAG within very low density lipoproteins (VLDL) both have deleterious metabolic consequences. Two diacylglycerol acyltransferases (DGATs 1 and 2) can catalyze the final step in the synthesis of TAG from diacylglycerol, which has been suggested to play an important role in the transfer of the glyceride moiety across the endoplasmic reticular membrane for (re)synthesis of TAG on the lumenal aspect of the endoplasmic reticular (ER) membrane (Owen, M., Corstorphine, C. C., and Zammit, V. A. (1997) Biochem. J. 323, 17-21). Recent topographical studies suggested that the oligomeric enzyme DGAT1 is exclusively lumen facing (latent) in the ER membrane. By contrast, in the present study, using two specific inhibitors of human DGAT1, we present evidence that DGAT1 has a dual topology within the ER of HepG2 cells, with approximately equal DGAT1 activities exposed on the cytosolic and lumenal aspects of the ER membrane. This was confirmed by the observation of the loss of both overt (partial) and latent (total) DGAT activity in microsomes prepared from livers of Dgat1(-/-) mice. Conformational differences between DGAT1 molecules having the different topologies were indicated by the markedly disparate sensitivities of the overt DGAT1 to one of the inhibitors. These data suggest that DGAT1 belongs to the family of oligomeric membrane proteins that adopt a dual membrane topology.

Peroxisome proliferator activated receptors and lipoprotein metabolism

Plasma lipoproteins are responsible for carrying triglycerides and cholesterol in the blood and ensuring their delivery to target organs. Regulation of lipoprotein metabolism takes place at numerous levels including via changes in gene transcription. An important group of transcription factors that mediates the effect of dietary fatty acids and certain drugs on plasma lipoproteins are the peroxisome proliferator activated receptors (PPARs). Three PPAR isotypes can be distinguished, all of which have a major role in regulating lipoprotein metabolism. PPARalpha is the molecular target for the fibrate class of drugs. Activation of PPARalpha in mice and humans markedly reduces hepatic triglyceride production and promotes plasma triglyceride clearance, leading to a clinically significant reduction in plasma triglyceride levels. In addition, plasma high-density lipoprotein (HDL)-cholesterol levels are increased upon PPARalpha activation in humans. PPARgamma is the molecular target for the thiazolidinedione class of drugs. Activation of PPARgamma in mice and human is generally associated with a modest increase in plasma HDL-cholesterol and a decrease in plasma triglycerides. The latter effect is caused by an increase in lipoprotein lipase-dependent plasma triglyceride clearance. Analogous to PPARalpha, activation of PPARbeta/delta leads to increased plasma HDL-cholesterol and decreased plasma triglyceride levels. In this paper, a fresh perspective on the relation between PPARs and lipoprotein metabolism is presented. The emphasis is on the physiological role of PPARs and the mechanisms underlying the effect of synthetic PPAR agonists on plasma lipoprotein levels.

Osthol regulates hepatic PPAR alpha-mediated lipogenic gene expression in alcoholic fatty liver murine

Our previous studies found that osthol, an active constituent isolated from Cnidium monnieri (L.) Cusson (Apiaceae), could ameliorate the accumulation of lipids and decrease the lipid levels in serum and hepatic tissue in alcohol-induced fatty liver mice and rats. The objective of this study was to investigate its possible mechanism of the lipid-lowering effect. A mouse model with alcoholic fatty liver was induced by orally feeding 52% erguotou wine by gavage when they were simultaneously treated with osthol 10, 20, 40 mg/kg for 4 weeks. The BRL cells (rat hepatocyte line) were cultured and treated with osthol at 25, 50, 100, 200 microg/ml for 24h. The mRNA expressions of peroxisome proliferator-activated receptor (PPAR) alpha, diacylglycerol acyltransferase (DGAT), 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase and cholesterol 7 alpha-hydroxylase (CYP7A) in mouse hepatic tissue or cultured hepatocytes were determined by reverse transcription polymerase chain reaction (RT-PCR). After treatment with osthol, the PPAR alpha mRNA expression in mouse liver and cultured hepatocytes was increased in dose dependent manner, while its related target genes for mRNA expression, e.g., DGAT and HMG-CoA reductase, were decreased, the CYP7A was inversely increased. And osthol-regulated mRNA expressions of DGAT, HMG-CoA reductase and CYP7A in the cultured hepatocytes were abrogated after pretreatment with specific inhibitor of PPAR alpha, MK886. It was concluded that osthol might regulate the gene expressions of DGAT, HMG-CoA reductase and CYP7A via increasing the PPAR alpha mRNA expression.

Combination peroxisome proliferator-activated receptor gamma and alpha agonist treatment in Type 2 diabetes prevents the beneficial pioglitazone effect on liver fat content

AIMS

Peroxisome proliferator-activated receptor (PPAR)-gamma and PPAR-alpha agonists individually reduce intra-organ triglyceride content and improve insulin sensitivity. However, the precise effects of combined PPAR-gamma and PPAR-alpha therapy on intra-organ triglyceride content and insulin sensitivity in subjects with Type 2 diabetes have not yet been determined.

METHODS

Diet-controlled Type 2 subjects (n = 9) were studied before and after 16 weeks of combined PPAR-gamma [pioglitazone (PIO), 45 mg daily] and PPAR-alpha [bezafibrate (BEZA), modified release 400 mg daily] agonist therapy. Glucose metabolism and endogenous glucose production were measured following a standard liquid test meal. Liver and muscle triglyceride levels were measured by (1)H magnetic resonance spectroscopy.

RESULTS

Combined PIO and BEZA therapy reduced mean fasting (7.5 +/- 0.5 vs. 6.5 +/- 0.2 mmol/l, P = 0.04) and peak postprandial plasma glucose (15.3 +/- 1.1 vs. 11.7 +/- 0.6 mmol/l, P = 0.007). No significant change in hepatic or muscle triglyceride content was observed. Postprandial suppression of endogenous glucose production remained similar on both study days. Both subcutaneous and visceral fat content increased following therapy.

CONCLUSIONS

Combined PIO and BEZA therapy in Type 2 diabetes does not decrease intrahepatic triglyceride content or postprandial endogenous glucose production. This study demonstrates an unexpected adverse interaction of PPAR-alpha with PPAR-gamma agonist therapy.

Osthole regulates enzyme protein expression of CYP7A1 and DGAT2 via activation of PPARalpha/gamma in fat milk-induced fatty liver rats

Osthole (1), an active constituent isolated from Cnidium monnieri (L.) Cusson, has been used in the treatment of diseases for many years in clinical. The aim of this present study was to determine the effect of 1 on protein expression of PPARalpha/gamma and related target molecules such as CYP7A and DGAT protein expression in the liver of hyperlipidemic fatty liver (HFL) rats, and to investigate the possible mechanism of treating HFL.

Diacylglycerol acyltransferases: Potential roles as pharmacological targets

Triglyceride (TG) synthesis occurs in many cell-types, but only the adipocyte is specialised for TG storage. The increased incidence of obesity and its attendant pathologies have increased interest in pharmacological strategies aimed at inhibition of triglyceride synthesis. In the liver this would also appear to offer the advantages of the prevention of steatosis and/or dyslipidaemia. The two major enzymes that have DGAT activity appear to have specialised functions, that are most evident in triglyceride-secreting tissues. The presence of triglyceride in non-adipose cells can lead to (through lipolysis), or be a marker for, undesirable complications such as insulin resistance, or can be indicative of simultaneously high capacities for triglyceride synthesis, lipolysis and oxidation of fatty acids as in highly aerobic, trained muscle. Consequently, inhibition of triglyceride synthesis may not be a straightforward strategy, either in terms of its achievement pharmacologically or in its anticipated outcomes. The metabolic complexities of triglyceride synthesis, with particular reference to the diacylglycerol acyltransferases (DGATs) are considered in this short review.

Ferrylmyoglobin impairs secretion of VLDL triacylglycerols from stored intracellular pools: Involvement of lipid peroxidation

Ferrylmyoglobin (ferrylMb) may play a major role in vivo under certain pathological conditions. Preliminary experiments showed that ferrylmyoglobin induced a mild oxidative stress in rat hepatocytes, mainly reflected by early lipid peroxidation. One of the major functions of hepatocytes is the synthesis, secretion and distribution of lipids to other cells. The aim of this work was to examine whether ferrylMb affected the synthesis and secretion of triacylglycerols (TAG), and the possible involvement of lipid peroxidation on these effects. The heme protein completely impaired VLDL secretion, affecting both the lipid and apoB components of the lipoprotein particle. The incorporation of [(3)H]-oleate into newly synthesized diacylglycerol and TAG was not altered by ferrylMb. The co-treatment of cells with alpha-tocopherol prevented lipid peroxidation and concomitantly reverted VLDL TAG secretion to control values. Importantly, although ferrylMb dramatically blocked prelabeled TAG secretion, newly synthesized TAG secretion was not impaired. These data indicate that lipid peroxidation elicited by ferrylMb modulates the VLDL TAG secretion process, specifically affecting the stored intracellular TAG mobilization, rather than de novo synthesis. Apart from its potential role in vivo, ferrylmyoglobin constitutes a useful model for studying the interactions between lipid peroxidation and the specific TAG pool dependence for VLDL secretion.

Triglyceride accumulation by peroxisome proliferators in rat hepatocytes

Peroxisome proliferators (PxPs) induce peroxisomal beta-oxidation (Px-ox) in the liver of rodents and have a hypolipidemic function. To investigate hypolipidemic effect of PxPs, the relationship between TG fluctuation and Px-ox activity, as an indicator of the function of PxPs, was studied in primary cultured rat hepatocytes. Nafenopin (Nf) treatment of hepatocytes caused an increase in Px-ox activity in association with cellular TG accumulation in a time-dependent manner with a coefficient of r=0.918. This relationship between the activity and cellular TG were obtained using structurally diverse PxPs with a correlation coefficient of r=0.747. Treatment of the hypolipidemic drug, but non-PxP Pravastatin, decreased TG in the medium, but did not have the effects on cellular TG and Px-ox activity. The total amount of TG and diacylglycerol acyltransferase activity, the last enzyme in the TG de novo synthesis pathway, were not affected by Nf treatment. When hepatocytes were cultured with Brefeldin A, cellular TG was accumulated, the same as with Nf, however, Px-ox activity was not enhanced. Nf treatment markedly decreased the level of apolipoprotein B (apo B) in very low density lipoprotein (VLDL) fractions prepared from conditioned media and increased that of cellular apoB by Western blot analysis. Microsomal triglyceride transfer protein activity was not influenced by Nf. Together, with regards to TG lowering effect of PxPs, it is suggested that PxPs cause hepatocellular accumulation of TG without effects on TG biosynthesis and VLDL construction, and they might have inhibitory effect on VLDL secretion process.

Overexpression of rat long chain acyl-coa synthetase 1 alters fatty acid metabolism in rat primary hepatocytes

Long chain acyl-CoA synthetases (ACSL) activate fatty acids (FA) and provide substrates for both anabolic and catabolic pathways. We have hypothesized that each of the five ACSL isoforms partitions FA toward specific downstream pathways. Acsl1 mRNA is increased in cells under both lipogenic and oxidative conditions. To elucidate the role of ACSL1 in hepatic lipid metabolism, we overexpressed an Acsl1 adenovirus construct (Ad-Acsl1) in rat primary hepatocytes. Ad-ACSL1, located on the endoplasmic reticulum but not on mitochondria or plasma membrane, increased ACS specific activity 3.7-fold. With 100 or 750 mum [1-(14)C]oleate, Ad-Acsl1 increased oleate incorporation into diacylglycerol and phospholipids, particularly phosphatidylethanolamine and phosphatidylinositol, and decreased incorporation into cholesterol esters and secreted triacylglycerol. Ad-Acsl1 did not alter oleate incorporation into triacylglycerol, beta-oxidation products, or total amount of FA metabolized. In pulse-chase experiments to examine the effects of Ad-Acsl1 on lipid turnover, more labeled triacylglycerol and phospholipid, but less labeled diacylglycerol, remained in Ad-Acsl1 cells, suggesting that ACSL1 increased reacylation of hydrolyzed oleate derived from triacylglycerol and diacylglycerol. In addition, less hydrolyzed oleate was used for cholesterol ester synthesis and beta-oxidation. The increase in [1,2,3-(3)H]glycerol incorporation into diacylglycerol and phospholipid was similar to the increase with [(14)C]oleate labeling suggesting that ACSL1 increased de novo synthesis. Labeling Ad-Acsl1 cells with [(14)C]acetate increased triacylglycerol synthesis but did not channel endogenous FA away from cholesterol ester synthesis. Thus, consistent with the hypothesis that individual ACSLs partition FA, Ad-Acsl1 increased FA reacylation and channeled FA toward diacylglycerol and phospholipid synthesis and away from cholesterol ester synthesis.

Why do omega-3 fatty acids lower serum triglycerides?

PURPOSE OF REVIEW

Fish oils rich in n-3 fatty acids reduce serum triglyceride levels. This well known effect has been shown to be caused by decreased very low-density lipoprotein triglyceride secretion rates in kinetic studies in humans. Animal studies have explored the biochemical mechanisms underlying this effect. Triglyceride synthesis could be reduced by n-3 fatty acids in three general ways: reduced substrate (i.e. fatty acids) availability, which could be secondary to increase in beta-oxidation, decreased free fatty acids delivery to the liver, decreased hepatic fatty acids synthesis; increased phospholipid synthesis; or decreased activity of triglyceride-synthesizing enzymes (diacylgylcerol acyltranferase or phosphatidic acid phosphohydrolase).

RECENT FINDINGS

Rarely were experimental conditions used in rat studies physiologically relevant to the human situation in which 1.2% energy as n-3 fatty acids lowers serum triglyceride levels. Nevertheless, the most consistent effect of n-3 fatty acids feeding in rats is to decrease lipogenesis. Increased beta-oxidation was frequently, but not consistently, reported with similar numbers of studies reporting increased mitochondrial compared with peroxisomal oxidation. Inhibition of triglyceride-synthesizing enzymes was only occasionally noted.

SUMMARY

As the vast majority of studies fed unphysiologically high doses of n-3 fatty acids, these findings in rats must be considered tentative, and the mechanism by which n-3 fatty acids reduce triglyceride levels in humans remains speculative.

PPARalpha activation increases triglyceride mass and adipose differentiation-related protein in hepatocytes

Adipose differentiation-related protein (ADRP) is a lipid droplet-associated protein that is expressed in various tissues. In mice treated with the peroxisome proliferator-activated receptor alpha (PPARalpha) agonist Wy14,643 (Wy), hepatic mRNA and protein levels of ADRP as well as hepatic triglyceride content increased. Also in primary mouse hepatocytes, Wy increased ADRP expression and intracellular triglyceride mass. The triglyceride mass increased in spite of unchanged triglyceride biosynthesis and increased palmitic acid oxidation. However, Wy incubation decreased the secretion of newly synthesized triglycerides, whereas apolipoprotein B secretion increased. Thus, decreased availability of triglycerides for VLDL assembly could help to explain the cellular accumulation of triglycerides after Wy treatment. We hypothesized that this effect could be mediated by increased ADRP expression. Similar to PPARalpha activation, adenovirus-mediated ADRP overexpression in mouse hepatocytes enhanced cellular triglyceride mass and decreased the secretion of newly synthesized triglycerides. In ADRP-overexpressing cells, Wy incubation resulted in a further decrease in triglyceride secretion. This effect of Wy was not attributable to decreased cellular triglycerides after increased fatty acid oxidation because the triglyceride mass in Wy-treated ADRP-overexpressing cells was unchanged. In summary, PPARalpha activation prevents the availability of triglycerides for VLDL assembly and increases hepatic triglyceride content in part by increasing the expression of ADRP.

Prevention of diet-induced obesity by dietary isomerized hop extract containing isohumulones, in rodents

OBJECTIVE

Isomerized hop extract (IHE), which consists mainly of isohumulones and is required in the beer brewing process, was investigated for its effects on diet-induced obesity in two strains of mice.

DESIGN

C57BL/6N and KK-A(y) mice were fed a standard or high-fat diet containing IHE and their body and tissue weights were measured at various time points. Oral glucose tolerance tests (OGTT) and insulin tolerance tests (ITT) were carried out in high-fat diet-fed C57BL/6N mice. The effects of IHE on intestinal lipid absorption were examined in Wistar rats using a plasma triacylglycerol assay after oral administration of a lipid emulsion. Fecal lipid levels were also measured in these animals after they were fed a high-fat diet containing IHE for 15 days. The effects of IHE on pancreatic lipase activity and the expression of genes involved in hepatic lipid metabolism were also examined using an in vitro assay and quantitative RT-PCR, respectively.

RESULTS

Supplementation of high-fat-containing chow with IHE reduced body weight gain and improved glucose tolerance in our experimental mice. A reduction in body weight gain was also observed in C57BL/6N mice fed a standard diet containing IHE. Wistar rats fed a high-fat diet containing IHE showed reduced plasma triacylglycerol levels and an increase in their fecal lipid excretion. Similarly, their pancreatic lipase activity was inhibited and their elevation in plasma triacylglycerol levels seen after the oral administration of lipid emulsion was significantly suppressed. IHE-fed mice showed an increased expression in their lipid oxidation genes and a decreased expression in genes involved in triacylglycerol biosynthesis.

CONCLUSION

The inhibition of intestinal dietary fat absorption may be the mechanism by which IHE induces its weight-lowering effects in high-fat diet-fed mice. The modulatory effect of IHE on lipid metabolism may also, at least partly, be responsible for its beneficial effects on body weight gain. These results suggest that IHE may be helpful in humans in preventing diet-induced obesity and perhaps even metabolic syndrome, the latter of which is known to be associated with obesity.

Microarray analysis of early adipogenesis in C3H10T1/2 cells: cooperative inhibitory effects of growth factors and 2,3,7,8-tetrachlorodibenzo-p-dioxin

C3H10T1/2 mouse embryo fibroblasts differentiate into adipocytes when stimulated by a standard hormonal mixture (IDMB). 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), via the aryl hydrocarbon receptor (AhR), inhibits induction of the key adipogenic gene peroxisome proliferator-activated receptor gamma (PPARgamma) and subsequent adipogenesis. This TCDD-mediated inhibition requires activation of the extracellular signal-regulated kinase (ERK) pathway, which can be accomplished by serum, epidermal growth factor (EGF), or fibroblast growth factor (FGF). In the absence of serum or growth factors, IDMB induced adipogenesis without mitosis. Microarray analysis identified 200 genes that exhibited expression changes of at least twofold after 24 h of IDMB treatment. This time precedes most PPARgamma stimulation but follows the period of TCDD/ERK cooperation and periods of increased cell contraction and DNA synthesis. Functionally related gene clusters include genes associated with cell structure, triglyceride and cholesterol metabolism, oxidative regulation, and secreted proteins. In the absence of growth factors TCDD inhibited 30% of these IDMB responses without inhibiting the process of differentiation. A combination of EGF and TCDD that blocks differentiation cooperatively blocked a further 44 IDMB-responsive genes, most of which have functional links to differentiation, including PPARgamma. Cell cycle regulators that are stimulated by EGF were substantially inhibited by IDMB but these responses were unaffected by TCDD. By contrast, TCDD and EGF cooperatively reversed IDMB-induced changes in cell adhesion complexes immediately prior to increases in PPARgamma1 expression. Changes in adhesion-linked signaling may play a key role in TCDD affects on differentiation.

Increased Very Low Density Lipoprotein Secretion and Gonadal Fat Mass in Mice Overexpressing Liver DGAT1

Acyl-CoA:diacylglycerol acyltransferases (DGATs) catalyze the last step in triglyceride (TG) synthesis. The genes for two DGAT enzymes, DGAT1 and DGAT2, have been identified. To examine the roles of liver DGAT1 and DGAT2 in TG synthesis and very low density lipoprotein (VLDL) secretion, liver DGAT1- and DGAT2-overexpressing mice were created by adenovirus-mediated gene transfection. DGAT1-overexpressing mice had markedly increased DGAT activity in the presence of the permeabilizing agent alamethicin. This suggests that DGAT1 possesses latent DGAT activity on the lumen of the endoplasmic reticulum. DGAT1-overexpressing mice showed increased VLDL secretion, resulting in increased gonadal (epididymal or parametrial) fat mass but not subcutaneous fat mass. The VLDL-mediated increase in gonadal fat mass might be due to the 4-fold greater expression of the VLDL receptor protein in gonadal fat than in subcutaneous fat. DGAT2-overexpressing mice had increased liver TG content, but VLDL secretion was not affected. These results indicate that DGAT1 but not DGAT2 has a role in VLDL synthesis and that increased plasma VLDL concentrations may promote obesity, whereas increased DGAT2 activity has a role in steatosis.

Sexual dimorphism in lipid metabolic phenotype associated with old age in Sprague-Dawley rats

PURPOSE

Aged male rats show a decrease in liver PPARalpha. We aimed to determine if the sexual dimorphism in lipid metabolism observed in the PPARalpha-/- mouse is also present in senescent rats.

RESULTS

Eighteen-month old rats were obese and presented high plasma NEFA concentrations. Old male rats were more hypercholesterolemic and hyperleptinemic than females, presenting a higher content in hepatic triglycerides and cholesteryl esters, while 18-month old females were more hypertriglyceridemic than males. Although PPARalpha expression and binding activity was reduced in liver from old male and female rats, the mRNA for a PPARalpha target gene, such as CPT-I, was reduced in old males (-56%), while increased by 286% in old females. LXRalpha protein was increased, and its binding activity was decreased in livers of old males, while livers of old females showed an increase in DGAT1 (2.6-fold) and DGAT2 (4.9-fold) mRNA, with respect to 3-month old animals. The increases in DGAT1 and DGAT2 mRNAs matched in old females those of plasma (3.1-fold) and liver triglycerides (5.0-fold).

CONCLUSIONS

These features disclose a marked sexual dimorphism in lipid metabolism associated to old age in rats that can be partially attributed not only to an age-related decrease in liver PPARalpha expression, but also to changes in other hepatic transcription factors and enzymes, such as liver X receptor alpha (LXRalpha) and diacylglycerol acyltransferases (DGAT).

Rosuvastatin Reduces Plasma Lipids by Inhibiting VLDL Production and Enhancing Hepatobiliary Lipid Excretion in ApoE*3-Leiden Mice

The present study was designed to investigate the lipid-lowering properties and mechanisms of action of a new HMG-CoA reductase inhibitor, rosuvastatin, in female ApoE*3-Leiden transgenic mice. Mice received a high fat/cholesterol (HFC) diet containing either rosuvastatin (0 [control], 0.00125%, 0.0025%, or 0.005% [w/w]) or 0.05% (w/w) lovastatin. The highest dose of rosuvastatin reduced plasma cholesterol and triglyceride levels by 39% and 42%, respectively, compared with the HFC control. Lovastatin had no effect on plasma cholesterol and triglyceride levels. In ApoE*3-Leiden mice on a chow diet, rosuvastatin (0.005% [w/w]) decreased plasma cholesterol levels by 35% without having an effect on triglyceride levels. On a chow diet, expression of genes involved in cholesterol biosynthesis and uptake in the liver was increased by rosuvastatin. Further mechanistic studies in HFC-fed mice showed that rosuvastatin treatment resulted in decreased hepatic VLDL-triglyceride and VLDL-apolipoprotein B production. VLDL lipid composition remained unchanged, indicating a reduction in the number of VLDL particles secreted. Lipolytic activity and expression of genes involved in cholesterol and triglyceride synthesis and beta-oxidation of fatty acids in the liver were not affected by rosuvastatin treatment, and hepatic lipid content did not change. However, activity of hepatic diacylglycerol acyltransferase was significantly decreased by 25% after rosuvastatin treatment. Moreover, biliary excretion of cholesterol, phospholipids, and bile acids was increased during treatment. The results indicate that rosuvastatin treatment in ApoE*3-Leiden mice on a HFC diet leads to redistribution of cholesterol and triglycerides in the body, both by reduced hepatic VLDL production and triglyceride synthesis and by enhanced hepatobiliary removal of cholesterol, bile acids, and phospholipids, resulting in substantial reductions in plasma cholesterol and triglyceride levels.

Niacin noncompetitively inhibits DGAT2 but not DGAT1 activity in HepG2 cells

Niacin is a widely used lipid-regulating agent in dyslipidemic patients. Previously, we have shown that niacin inhibits triacylglycerol synthesis. In this report, using HepG2 cells, we have examined the effect of niacin on the mRNA expression and microsomal activity of diacylglycerol acyltransferase 1 and 2 (DGAT1 and DGAT2), the last committed but distinctly different enzymes for triglyceride synthesis. Addition of niacin to the DGAT assay reaction mixture dose-dependently (0-3 mM) inhibited DGAT activity by 35-50%, and the IC(50) was found to be 0.1 mM. Enzyme kinetic studies showed apparent K(m) values of 8.3 microM and 100 microM using [(14)C]oleoyl-CoA and sn-1,2-dioleoylglycerol as substrates, respectively. A decrease in apparent V(max) was observed with niacin, whereas the apparent K(m) remained constant. A Lineweaver-Burk plot of DGAT inhibition by niacin showed a noncompetitive type of inhibition. Niacin selectively inhibited DGAT2 but not DGAT1 activity. Niacin inhibited overt DGAT activity. Niacin had no effect on the expression of DGAT1 and DGAT2 mRNA. These data suggest that niacin directly and noncompetitively inhibits DGAT2 but not DGAT1, resulting in decreased triglyceride synthesis and hepatic atherogenic lipoprotein secretion, thus indicating a major target site for its mechanism of action.

Membrane transport of fatty acylcarnitine and free L-carnitine by rat liver microsomes

Recent studies have suggested that parts of the hepatic activities of diacylglycerol acyltransferase and acyl cholesterol acyltransferase are expressed in the lumen of the endoplasmic reticulum (ER). However the ER membrane is impermeable to the long-chain fatty acyl-CoA substrates of these enzymes. Liver microsomal vesicles that were shown to be at least 95% impermeable to palmitoyl-CoA were used to demonstrate the membrane transport of palmitoylcarnitine and free L-carnitine - processes that are necessary for an indirect route of provision of ER luminal fatty acyl-CoA through a luminal carnitine acyltransferase (CAT). Experimental conditions and precautions were established to permit measurement of the transport of [14C]palmitoylcarnitine into microsomes through the use of the luminal CAT and acyl-CoA:ethanol acyltransferase as a reporter system to detect formation of luminal [14C]palmitoyl-CoA. Rapid, unidirectional transport of free L-[3H]carnitine by microsomes was measured directly. This process, mediated either by a channel or a carrier, was inhibited by mersalyl but not by N-ethylmaleimide or sulfobetaine - properties that differentiate it from the mitochondrial inner membrane carnitine/acylcarnitine exchange carrier. These findings are relevant to the understanding of processes for the reassembly of triacylglycerols that lipidate very low density lipoprotein particles as part of a hepatic triacylglycerol lipolysis/re-esterification cycle.

The transport of triglycerides through the secretory pathway of hepatocytes is impaired in apolipoprotein E deficient mice

BACKGROUND/AIMS

Apolipoprotein E (apoE)-deficient mice develop hepatic steatosis and secrete reduced levels of VLDL-TG.

METHODS AND RESULTS

We examined the effects of apoE-deficiency on intracellular lipid homeostasis and secretion of triglycerides (TG). We show that intracellular TG turnover and activities of diacylglycerol acyltransferase (DGAT) and microsomal triglyceride transfer protein (MTP) are similar in Apoe(-/-) and wild type mice. In addition, apoB synthesis was not decreased in Apoe(-/-) cells. Thus, the accumulation of lipid in these cells is not attributable to perturbed TG turnover, apoB synthesis, and the activities of DGAT and MTP. Inhibition of MTP had a more profound impact on the secretion of VLDL-TG from wild type hepatocytes than Apoe(-/-) hepatocytes, indicating that MTP was more limiting for the production of VLDL-TG from wild type cells. In marked contrast to the MTP-deficient model of fatty liver, electron microscopy of lipid-stained liver sections of Apoe(-/-) mice revealed an accumulation of lipid in numerous small, putative ER-derived vesicles and in the cytosol. No abnormalities were observed in the Golgi of Apoe(-/-) mice.

CONCLUSIONS

These results suggest that the removal of lipids from the early or intermediary compartments of the secretory pathway of hepatocytes is impaired in Apoe(-/-) mice.

Regulation of triacylglycerol hydrolase expression by dietary fatty acids and peroxisomal proliferator-activated receptors

Triacylglycerol hydrolase (TGH) is an enzyme that catalyzes the lipolysis of intracellular stored triacylglycerol (TG). Peroxisomal proliferator-activated receptors (PPAR) regulate a multitude of genes involved in lipid homeostasis. Polyunsaturated fatty acids (PUFA) are PPAR ligands and fatty acids are produced via TGH activity, so we studied whether dietary fats and PPAR agonists could regulate TGH expression. In 3T3-L1 adipocytes, TGH expression was increased 10-fold upon differentiation, compared to pre-adipocytes. 3T3-L1 cells incubated with a PPARgamma agonist during the differentiation process resulted in a 5-fold increase in TGH expression compared to control cells. Evidence for direct regulation of TGH expression by PPARgamma could not be demonstrated as TGH expression was not affected by a 24-h incubation of mature 3T3-L1 adipocytes with the PPARgamma agonist. Feeding mice diets enriched in fatty acids for 3 weeks did not affect hepatic TGH expression, though a 3-week diet enriched in fatty acids and cholesterol increased hepatic TGH expression 2-fold. Two weeks of clofibrate feeding did not significantly affect hepatic TGH expression or microsomal lipolytic activities in wild-type or PPARalpha-null mice, indicating that PPARalpha does not regulate hepatic TGH expression. Therefore, TGH expression does not appear to be directly regulated by PPARs or fatty acids in the liver or adipocytes.

The role of acyl-CoA:diacylglycerol acyltransferase (DGAT) in energy metabolism

Acyl-CoA:diacylglycerol acyltransferase (DGAT, EC2.3.1.20), a key enzyme in triglyceride (TG) biosynthesis, not only participates in lipid metabolism but also influences metabolic pathways of other fuel molecules. Changes in the expression and/or activity levels of DGAT may lead to changes in systemic insulin sensitivity and energy homeostasis. The synthetic role of DGAT in adipose tissue, the liver, and the intestine, sites where endogenous levels of DGAT activity and TG synthesis are high, is relatively clear. Less clear is whether DGAT plays a mediating or preventive role in the development of ectopic lipotoxicity in tissues such as muscle and the pancreas, when their supply of free fatty acids (FFAs) exceeds their needs. Future studies with tissue-specific overexpression and/or knockout in these animal models would be expected to shed additional light on these issues.