In vivo absolute quantification of hepatic γ-ATP concentration in mice using 31 P MRS at 11.7 T.

Measurement of ATP concentrations and synthesis in humans indicated abnormal hepatic energy metabolism in obesity, non-alcoholic fatty liver disease (NAFLD) and Type 2 diabetes. Further mechanistic studies on energy metabolism require the detailed phenotyping of specific mouse models. Thus, this study aimed to establish and evaluate a robust and fast single voxel 31 P MRS method to quantify hepatic γ-ATP concentrations at 11.7 T in three mouse models with different insulin sensitivities and liver fat contents (72-week-old C57BL/6 control mice, 72-week-old insulin resistant sterol regulatory-element binding protein-1c overexpressing (SREBP-1c+ ) mice and 10-12-week-old prediabetic non-obese diabetic (NOD) mice). Absolute quantification was performed by employing an external reference and a matching replacement ATP phantom with 3D image selected in vivo spectroscopy 31 P MRS. This single voxel 31 P MRS method non-invasively quantified hepatic γ-ATP within 17 min and the repeatability tests provided a coefficient of variation of 7.8 ± 1.1%. The mean hepatic γ-ATP concentrations were markedly lower in SREBP-1c+ mice (1.14 ± 0.10 mM) than in C57BL/6 mice (2.15 ± 0.13 mM; p < 0.0002) and NOD mice (1.78 ± 0.13 mM; p < 0.006, one-way ANOVA test). In conclusion, this method allows us to rapidly and precisely measure hepatic γ-ATP concentrations, and thereby to non-invasively detect abnormal hepatic energy metabolism in mice with different degrees of insulin resistance and NAFLD. Thus, this 31 P MRS will also be useful for future mechanistic as well as therapeutic translational studies in other murine models.

Preventive Effect of Citrus aurantium Peel Extract on High-Fat Diet-Induced Non-alcoholic Fatty Liver in Mice.

Nonalcoholic fatty liver disease (NAFLD) is characterized by hepatic lipid accumulation, which is the most common form of chronic liver disease. Multiple clinical studies using natural compounds such as flavonoids have been conducted to treat NAFLD. In the present study, the pharmacological effect of Citrus aurantium L. (Rutaceae) peel extract (CAE), which contains over 27% of polymethoxyflavone nobiletin, on NAFLD was evaluated using a high-fat diet (HFD) animal model susceptible to developing NAFLD. C57BL/6 mice were fed an HFD (60% kcal of energy derived from fat) for 8 weeks to induce obesity. Obese mice were randomly allocated to four groups of eight mice each (HFD alone, HFD with silymarin, HFD with 50 mg/kg CAE, and HFD with 100 mg/kg CAE). After 8 weeks of treatment, all mice were euthanized, and plasma and liver tissues were analyzed biochemically and histopathologically. The results indicate that CAE treatment significantly reduced HFD-induced NAFLD, as shown by decreased serum lipid index and prevented liver histopathology. The expression of genes involved in lipid synthesis including free fatty acid (FFA), peroxisome-proliferator-activated receptor γ (PPAR-γ), sterol receptor element binding protein 1c (SREBP-1c), and fatty acid synthesis enzyme was suppressed by CAE treatment. Moreover, compared to untreated mice, CAE-treated HFD mice showed decreased pro-inflammatory cytokine expression. These results demonstrated that CAE prevented HFD-induced NAFLD by reducing plasma levels of triglyceride and cholesterol and de novo lipid synthesis.

Effect of Omega-3 Fatty Acid on STAMP2 Expression in the Heart and Kidney of 5/6 Nephrectomy Rat Model.

Six transmembrane protein of prostate 2 (STAMP2) is a critical modulator of inflammation and metabolism in adipose tissue. There are no data on the expression of STAMP2 in chronic kidney disease, which is an inflammatory disease related to metabolic disorders. This study aimed to investigate STAMP2 expression in the kidney and heart in 5/6 nephrectomy (Nx) rats, and the effect of omega-3 fatty acid (FA) on STAMP2 expression. Male Sprague Dawley rats were divided into three groups: sham control (0.9% saline), 5/6 Nx (0.9% saline), and 5/6 Nx treated with omega-3 FA (300 mg per kg per day by gastric gavage). The expression of STAMP2 in the kidney and heart were examined by western blotting. Serum creatinine levels were higher in 5/6 Nx rats than in controls. Compared with sham controls, the expression of IκB, NF-κB, NOX4, SREBP-1, and LXR were upregulated and STAMP2 and phosphorylated-AMPK expression were downregulated in the kidney and heart of 5/6 Nx rats. Omega-3 FA supplementation prevented these changes in biomarkers related to inflammation and metabolic lipid disorders. Omega 3-FA supplementation induced the upregulation of STAMP2 protein in 5/6 Nx rats, which was associated with an attenuation of inflammation- and metabolic disease-related markers.

Lipid accumulation stimulates the cap-independent translation of SREBP-1a mRNA by promoting hnRNP A1 binding to its 5'-UTR in a cellular model of hepatic steatosis.

Non-alcoholic fatty liver disease (NAFLD) is a chronic disease characterized by accumulation of lipid droplets in hepatocytes. Enhanced release of non-esterified fatty acids from adipose tissue accounts for a remarkable fraction of accumulated lipids. However, the de novo lipogenesis (DNL) is also implicated in the etiology of the NAFLD. Sterol Regulatory Element-Binding Protein-1 (SREBP-1) is a transcription factor modulating the expression of several lipogenic enzymes. In the present study, in order to investigate the effect of lipid droplet accumulation on DNL, we used a cellular model of steatosis represented by HepG2 cells cultured in a medium supplemented with free oleic and palmitic fatty acids (FFAs). We report that FFA supplementation induces the expression of genes coding for enzymes involved in the DNL as well as for the transcription factor SREBP-1a. The SREBP-1a mRNA translation, dependent on an internal ribosome entry site (IRES), and the SREBP-1a proteolytic cleavage are activated by FFAs. Furthermore, FFA treatment enhances the expression and the nucleus-cytosolic shuttling of hnRNP A1, a trans-activating factor of SREBP-1a IRES. The binding of hnRNP A1 to the SREBP-1a IRES is also increased upon FFA supplementation. The relocation of hnRNP A1 and the consequent increase of SREBP-1a translation are dependent on the p38 MAPK signal pathway, which is activated by FFAs. By RNA interference approach, we demonstrate that hnRNP A1 is implicated in the FFA-induced expression of SREBP-1a and of its target genes as well as in the lipid accumulation in cells.

Curcuma oil ameliorates insulin resistance & associated thrombotic complications in hamster & rat.

BACKGROUND & OBJECTIVES: Curcuma oil (C. oil) isolated from turmeric (Curcuma longa L.) has been shown to have neuro-protective, anti-cancer, antioxidant and anti-hyperlipidaemic effects in experimental animal models. However, its effect in insulin resistant animals remains unclear. The present study was carried out to investigate the disease modifying potential and underlying mechanisms of the C. oil in animal models of diet induced insulin resistance and associated thrombotic complications. METHODS: Male Golden Syrian hamsters on high fructose diet (HFr) for 12 wk were treated orally with vehicle, fenofibrate (30 mg/kg) or C. oil (300 mg/kg) in the last four weeks. Wistar rats fed HFr for 12 wk were treated orally with C. oil (300 mg/kg) in the last two weeks. To examine the protective effect of C. oil, blood glucose, serum insulin, platelet aggregation, thrombosis and inflammatory markers were assessed in these animals. RESULTS: Animals fed with HFr diet for 12 wk demonstrated hyperlipidaemia, hyperglycaemia, hyperinsulinaemia, alteration in insulin sensitivity indices, increased lipid peroxidation, inflammation, endothelial dysfunction, platelet free radical generation, tyrosine phosphorylation, aggregation, adhesion and intravascular thrombosis. Curcuma oil treatment for the last four weeks in hamsters ameliorated HFr-induced hyperlipidaemia, hyperglycaemia, insulin resistance, oxidative stress, inflammation, endothelial dysfunction, platelet activation, and thrombosis. In HFr fed hamsters, the effect of C. oil at 300 mg/kg [ ] was comparable with the standard drug fenofibrate. Curcuma oil treatment in the last two weeks in rats ameliorated HFr-induced hyperglycaemia and hyperinsulinaemia by modulating hepatic expression of sterol regulatory element binding protein 1c (SREBP-1c), peroxisome proliferator-activated receptor-gamma co-activator 1 (PGC-1)α and PGC-1ß genes known to be involved in lipid and glucose metabolism. INTERPRETATION & CONCLUSIONS: High fructose feeding to rats and hamsters led to the development of insulin resistance, hyperglycaemia, endothelial dysfunction and oxidative stress. C. oil prevented development of thrombotic complications associated with insulin resistance perhaps by modulating genes involved in lipid and glucose metabolism. Further studies are required to confirm these findings.

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.

Effect of dietary polyphenols from hop (Humulus lupulus L.) pomace on adipose tissue mass, fasting blood glucose, hemoglobin A1c, and plasma monocyte chemotactic protein-1 levels in OLETF rats.

Hop (Humulus lupulus L.) pomace contains procyanidin-rich polyphenols, which are large oligomeric compounds of catechin. We studied the effect of high dose (1%) of dietary hop pomace polyphenols (HPs) in Otsuka Long-EvansTokushima Fatty (OLETF) rats, an animal model of type 2 diabetes. By 70 days, the rats fed HPs tended to have a lower body weight and reduced mesenteric white adipose tissue weight than the rats fed a control diet. Triglyceride levels in both plasma and liver tended to be lower in the HPs-fed group than in the control group. Dietary HPs substantially suppressed the activities of hepatic fatty acid synthetase, glucose-6-phosphate dehydrogenase, and malic enzyme, through the suppression of SREBP1c mRNA expression in OLETF rats. Moreover, in the HPs-fed group, monocyte chemotactic protein-1 (MCP-1) expression and fasting blood glucose levels at 40 days, and hemoglobin A1c (HbA1c) levels at 70 days were significantly lower than those in the control group. Thus, dietary HPs may exert an ameliorative function on hepatic fatty acid metabolism, glucose metabolism, and inflammatory response accompanying the increase of the adipose tissue mass in OLETF rats.

Phthalate is associated with insulin resistance in adipose tissue of male rat: role of antioxidant vitamins.

Diethyl hexyl phthalate (DEHP) is a plasticizer, commonly used in a variety of products, including lubricants, perfumes, hairsprays and cosmetics, construction materials, wood finishers, adhesives, floorings and paints. DEHP is an endocrine disruptor and it has a continuum of influence on various organ systems in human beings and experimental animals. However, specific effects of DEHP on insulin signaling in adipose tissue are not known. Adult male albino rats of Wistar strain were divided into four groups. Control, DEHP treated (dissolved in olive oil at a dose of 10, and 100 mg/kg body weight, respectively, once daily through gastric intubations for 30 days) and DEHP + vitamin E (50 mg/kg body weight) and C (100 mg/kg body weight) dissolved in olive oil and distilled water, respectively, once daily through gastric intubations for 30 days. After the completion of treatment, adipose tissue was dissected out to assess various parameters. DEHP treatment escalated H(2)O(2) and hydroxyl radical levels as well as lipid peroxidation in the adipose tissue. DEHP impaired the expression of insulin signaling molecules and their phosphorelay pathways leading to diminish plasma membrane GLUT4 level and thus decreased glucose uptake and oxidation. Blood glucose level was elevated as a result of these changes. Supplementation of vitamins (C & E) prevented the DEHP-induced changes. It is concluded that DEHP-induced ROS and lipid peroxidation disrupts the insulin signal transduction in adipose tissue and favors glucose intolerance. Antioxidant vitamins have a protective role against the adverse effect of DEHP.

Green tea extract attenuates hepatic steatosis by decreasing adipose lipogenesis and enhancing hepatic antioxidant defenses in ob/ob mice.

Excess hepatic lipid accumulation and oxidative stress contribute to nonalcoholic fatty liver disease (NAFLD). Thus, we hypothesized that the hypolipidemic and antioxidant activities of green tea extract (GTE) would attenuate events leading to NAFLD. Obese mice (ob/ob; 5 weeks old, n=38) and their lean littermates (n=12) were fed 0%, 0.5% or 1% GTE for 6 weeks. Then, hepatic steatosis, oxidative stress and inflammatory markers were measured. Obese mice, compared to lean controls, had greater hepatic lipids and serum alanine aminotransferase (ALT). GTE at 1% lowered (P<.05) hepatic lipids and ALT in obese mice. The GTE-mediated attenuation in hepatic steatosis was accompanied by decreased mRNA expression of adipose sterol regulatory element-binding protein-1c, fatty acid synthase, stearoyl CoA desaturase-1, and hormone-sensitive lipase and decreased serum nonesterified fatty acid concentrations. Immunohistochemical data indicated that steatotic livers from obese mice had extensive accumulation of tumor necrosis factor-α (TNF-α), whereas GTE at 1% decreased hepatic TNF-α protein and inhibited adipose TNF-α mRNA expression. Hepatic total glutathione, malondialdehyde and Mn- and Cu/Zn-superoxide dismutase activities in obese mice fed GTE were normalized to the levels of lean littermates. Also, GTE increased hepatic catalase and glutathione peroxidase activities, and these activities were inversely correlated with ALT and liver lipids. Collectively, GTE mitigated NAFLD and hepatic injury in ob/ob mice by decreasing the release of fatty acids from adipose and inhibiting hepatic lipid peroxidation as well as restoring antioxidant defenses and decreasing inflammatory responses. These findings suggest that GTE may be used as an effective dietary strategy to mitigate obesity-triggered NAFLD.

Effect of Chinese prescription Kangen-karyu on lipid metabolism in type 2 diabetic db/db mice.

AIM OF THE STUDY: Chinese prescription Kangen-karyu is clinically used as a treatment for cardiovascular diseases, and we have reported the beneficial effects on chemically induced hyperlipidemic animal models. The present study was investigated to evaluate the hypolipidemic effect of Kangen-karyu in type 2 diabetic db/db mice which has not been explored yet. MATERIALS AND METHODS: Male db/db mice were divided into three groups, vehicle (control), Kangen-karyu 100, or 200 mg/kg body weight/day, and orally administered for 5 weeks every day. Age-matched non-diabetic m/m mice were used as a normal group. RESULTS: Serum triglyceride (TG) and total cholesterol levels in db/db mice were increased compared with those of m/m mice. However, the administration of Kangen-karyu reduced hyperlipidemia in db/db mice through a decline in the serum levels of TG and total cholesterol. The hepatic TG and total cholesterol levels of db/db mice were markedly higher than those of m/m mice, but these elevated lipid levels were significantly reduced by 200 mg/kg Kangen-karyu administration. Also, oil red O staining showed that the increased lipid deposition level in the liver of db/db control mice was improved by Kangen-karyu administration. The expression of sterol regulatory element-binding protein-1 in the liver of db/db mice was significantly down-regulated by the administration of Kangen-karyu at a dose of 200 mg/kg body weight. Kangen-karyu caused a slight elevation in the expression of peroxisome proliferator-activated receptor alpha in the liver of db/db mice. CONCLUSIONS: This study provides scientific evidence that Kangen-karyu improves hyperlipidemia and lipid deposition via the regulation of hepatic SREBP-1 expression in type 2 diabetic db/db mice.

Epigallocatechin-3-gallate improves nonalcoholic steatohepatitis model mice expressing nuclear sterol regulatory element binding protein-1c in adipose tissue.

We examined whether or not epigallocatechin-3-gallate (EGCG) improves liver injury of nonalcoholic steatohepatitis (NASH) model mice expressing nuclear sterol regulatory element-binding protein 1c (nSREBP-1c) in adipose tissue. nSREBP-1c transgenic C57BL6 mice aged 30 weeks were divided into group 1 (no treatment), group 2 (ascorbic acid alone), group 3 (ascorbic acid and 0.05% EGCG), and group 4 (ascorbic acid and 0.1% EGCG). At 42 weeks, we performed measurement of liver weight to body weight, biochemical assays, morphometry of liver specimens, immunohistochemistry for 8-hydro-2'-deoxyguanosine (8-OhdG), and Western blotting for insulin and TNF-alpha signalings. Ratio of liver weight to body weight in the high dose EGCG-treated group (group 4) was significantly lower than those of groups 1 and 2 (p<0.05 and <0.01, respectively). Blood ALT, glucose, total cholesterol, and triglyceride levels of group 4 were significantly low compared with those of the EGCG-non-treated group (groups 1 and 2) (p<0.05, respectively). The degrees of steatosis, inflammation, ballooning hepatocytes and Mallory-Denk bodies in group 4 significantly improved compared with those in other groups (p<0.05, respectively). The 8-OhdG immunolocalization in liver tissues of the group 4 obviously decreased compared with those of groups 2 and 3. For Western blotting, the expressions of insulin receptor substrate-1 (IRS-1) and phosphorylated IRS-1 (pIRS-1) in liver tissues of group 4 increased compared with those of groups 2 and 3. On the other hand, the expressions of pAkt, pIKKbeta and pNF-kappaB decreased compared with those of groups 2 and 3. From these results, EGCG reduces inflammation, insulin resistance and oxidative stress, and suppresses liver injury in nSREBP-1c transgenic mice.

Magnolia officinalis reverses alcoholic fatty liver by inhibiting the maturation of sterol regulatory element-binding protein-1c.

The generally accepted hypothesis for the pathogenesis of alcoholic liver disease (ALD) is the two-hit model, which proposes that fat accumulation in the liver increases the sensitivity of the liver to a second hit that leads to inflammatory liver cell damage. In this study we evaluated the effects of Magnolia officinalis (MO), which contains honokiol and magnolol as the primary pharmacological components, to eradicate fatty liver in rats fed an ethanol diet. In vitro studies showed that MO was able to protect RAW 264.7 cells from ethanol-induced production of tumor necrosis factor-alpha, reactive oxygen species, and superoxide anion radicals; the activation of NADPH oxidase; and subsequent cell death. We also investigated the therapeutic effects of MO on alcoholic fatty liver in Lieber-DeCarli ethanol diet-fed rats. MO treatment of the rats for the last 2 weeks of ethanol feeding completely reversed all the serum, hepatic parameters, and fatty liver changes. The increased maturation of sterol regulatory element-binding protein-1c in the liver by ethanol treatment was completely inhibited by treatment with MO. Therefore, MO may be a promising candidate for development as a therapeutic agent for ALD.

Cinnamon extract inhibits the postprandial overproduction of apolipoprotein B48-containing lipoproteins in fructose-fed animals.

We have reported previously that a cinnamon extract (CE), high in type A polyphenols, prevents fructose feeding-induced decreases in insulin sensitivity and suggested that improvements of insulin sensitivity by CE were attributable, in part, to enhanced insulin signaling. In this study, we examined the effects of CE on postprandial apolipoprotein (apo) B-48 increase in fructose-fed rats, and the secretion of apoB48 in freshly isolated intestinal enterocytes of fructose-fed hamsters. In an olive oil loading study, a water-soluble CE (Cinnulin PF, 50 mg/kg body weight, orally) decreased serum triglyceride (TG) levels and the over production of total- and TG-rich lipoprotein-apoB48. In ex vivo (35)S labeling study, significant decreases were also observed in apoB48 secretion into the media in enterocytes isolated from fructose-fed hamsters. We also investigated the molecular mechanisms of the effects of CE on the expression of genes of the insulin signaling pathway [insulin receptor (IR), IR substrate (IRS)1, IRS2 and Akt1], and lipoprotein metabolism [microsomal TG transfer protein (MTP), sterol regulatory element-binding protein (SREBP1c) in isolated primary enterocytes of fructose-fed hamsters, using quantitative real-time polymerase chain reaction. The CE reversed the expression of the impaired IR, IRS1, IRS2 and Akt1 mRNA levels and inhibited the overexpression of MTP and SREBP1c mRNA levels of enterocytes. Taken together, our data suggest that the postprandial hypertriglycerides and the overproduction of apoB48 can be acutely inhibited by a CE by a mechanism involving improvements of insulin sensitivity of intestinal enterocytes and regulation of MTP and SREBP1c levels. We present both in vivo and ex vivo evidence that a CE improves the postprandial overproduction of intestinal apoB48-containing lipoproteins by ameliorating intestinal insulin resistance and may be beneficial in the control of lipid metabolism.

Hepatic free fatty acids accumulate in experimental steatohepatitis: role of adaptive pathways.

BACKGROUND/AIMS: We determined the effects of dietary lipid composition on steatohepatitis development with particular attention to the nature of lipid molecules that accumulate in the liver and pathways of hepatic triglyceride synthesis. METHODS: Mice were fed methionine and choline deficient (MCD) diets supplemented with 20% fat as lard (saturated) or olive oil (monounsaturated), for 3 weeks. RESULTS: Irrespective of dietary lipid composition, MCD-fed mice developed steatosis, ballooning degeneration and lobular inflammation. MCD-feeding increased hepatic free fatty acid (FFA) levels 2-3-fold, as well as total triglyceride levels. Hepatic FFA composition was characterized by increased ratio of monounsaturated: saturated FFA. There were reduced nuclear levels of the lipogenic transcription factor sterol regulatory element binding protein-1 in MCD-fed mice, but no consistent reduction in fatty acid synthesis genes (acetyl-CoA carboxylase and fatty acid synthase). Consistent with pathways of hepatic triglyceride synthesis, expression of diacylglycerol acyltransferase-1 and -2 was increased, as were delta-5- and delta-6- fatty acid desaturase mRNA levels. CONCLUSIONS: In this nutritional model of steatohepatitis, accumulation of FFA occurs despite substantial suppression of lipogenesis and induction of triglyceride synthesis genes. Accumulation of FFA supports a lipotoxicity mechanism for liver injury in this form of fatty liver disease.

Calpain system regulates the differentiation of adult primitive mesenchymal ST-13 adipocytes.

The activity of calpain, a calcium-activated protease, is required during the mitotic clonal expansion phase of 3T3-L1 embryonic preadipocyte differentiation. Here we examined the role of calpain in the adipogenesis of ST-13 preadipocytes established from adult primitive mesenchymal cells, which do not require mitotic clonal expansion. After exposure to the calpain inhibitor, N-benzyloxycarbonyl-L-leucyl-L-leucinal or overexpression of calpastatin, a specific endogenous inhibitor of calpain, ST-13 preadipocytes acquired the adipocyte phenotype. Overexpression of calpastatin in ST-13 adipocytes stimulated the expression of adipocyte-specific CCAAT/enhancer-binding protein-alpha (C/EBPalpha), peroxisome proliferator-activated receptor (PPAR)-gamma, sterol regulatory element-binding protein 1, and the insulin signaling molecules, insulin receptor alpha, insulin-receptor substrates, and GLUT4. However, insulin-stimulated glucose uptake was reduced by approximately 52%. The addition of calpain to the nuclear fraction of ST-13 adipocytes resulted in the Ca(2+)-dependent degradation of PPARgamma and C/EBPalpha but not sterol regulatory element-binding protein 1. Exposing ST-13 adipocytes to A23187 also led to losses of endogenous PPARgamma and C/EBPalpha. Under both conditions, calpain inhibitors almost completely prevented C/EBPalpha cleavage but partially blocked the decrease of PPARgamma. Two ubiquitous forms of calpain, mu- and m-calpain, localized to the cytosol and the nucleus, whereas the activated form of mu- but not m-calpain was found in the nucleus. Finally, stable dominant-negative mu-calpain transfectants showed accelerated adipogenesis and increase in the levels of PPARgamma and C/EBPalpha during adipocyte program. These results support evidence that the calpain system is involved in regulating the differentiation of adult primitive mesenchymal ST-13 preadipocytes.

Regulation of retinal dehydrogenases and retinoic acid synthesis by cholesterol metabolites.

Retinoic acid (RA) constitutes the major active ingredient of vitamin A and is required for various biological processes. The tissue RA level is maintained through a cascade of metabolic reactions where retinal dehydrogenases (RALDHs) catalyze the terminal reaction of RA biosynthesis from retinal, a rate-limiting step. We showed that dietary supplement of cholesterol enhanced the expression of RALDH1 and 2 genes and the cellular RA content in vital organs such as brain, kidney, liver and heart. Consistently, the cholesterol-lowering agent (pravastatin sodium) downregulated the expression of RALDH1 and 2 genes in several organs especially the liver and in cultured liver cells. Further, cholesterol metabolites, predominantly the oxysterols, the natural ligands for liver X receptor (LXR), induced these genes via upregulation of sterol regulatory element binding protein-1c (SREBP-1c) that bound to the regulatory regions of these genes. Knockdown of LXRalpha/beta or SREBP-1c downregulated the expression of RALDH genes, which could be rescued by re-expressing SREBP-1c, suggesting SREBP-1c as a direct positive regulator for these genes. This study uncovered a novel crosstalk between cholesterol and RA biosynthesis.

Effect of docosahexaenoic acid and arachidonic acid on the expression of adipocyte determination and differentiation-dependent factor 1 in differentiating porcine adipocytes.

Adipocyte determination and differentiation-dependent factor 1 (ADD1) drives the expression of several lipogenic genes in mammals. Polyunsaturated fatty acids decrease ADD1 mRNA abundance in differentiating porcine adipocytes. The current study was designed to explore the mechanisms by which PUFA inhibit the expression of ADD1 in porcine adipocytes. Porcine preadipocytes were differentiated for 24 h with 0 or 100 microM of docosahexaenoic acid (DHA) and mixtures of different concentrations of antioxidants to investigate the effect of DHA and antioxidants on the ADD1 mRNA abundance. We found the relative mRNA abundance was decreased by the addition of 100 microM DHA to the medium for porcine differentiating adipocytes, and adding an antioxidant mixture to the medium prevented part of the decrease in ADD1 mRNA abundance. These data suggest that DHA decreased the steady-state transcription factor ADD1 mRNA through a mechanism related to fatty acid peroxidation. Indeed, adding 7.5 microM vitamin E (a natural antioxidant) also restored the concentrations of ADD1 and fatty acid synthase mRNA, which were decreased by DHA treatment; however, the DHA or the antioxidant treatment did not change the expression of antioxidation genes (superoxide dismutase 1 and glutathione peroxidase 1) in porcine stromal vascular cells. When supplemented with the eicosanoid synthesis pathway inhibitors, the inhibition of the expression of ADD1 by arachidonic acid was partially recovered. These results suggest that the mechanism by which PUFA decrease ADD1 mRNA is due to the metabolic product of eicosanoids and peroxidation of these PUFA.