Effects of fenofibrate on lipid metabolism in adipose tissue of rats

The effect of fenofibrate, a peroxisome proliferator-activated receptor alpha agonist, on body weight gain and on reduction of adipose tissue pads has been ascribed to increased fat catabolism in liver mainly through the induction of target enzymes involved in hepatic lipid metabolism. The aim of this study was to investigate whether peroxisome proliferator-activated receptor alpha activation also affects metabolic pathways in adipose tissue of rats treated with fenofibrate (100 mg/kg body weight) for 9 days. Fenofibrate lowered body weight gain and plasma triglyceride, total cholesterol, and high-density lipoprotein cholesterol but had no influence on food intake and on plasma glucose levels. The activity of lipoprotein lipase of treated animals decreased 50% in epididymal, 29% in retroperitoneal, and was not affected in the mesenteric fat pads. In this study, we show a 34% decrease in epididymal adipose tissue de novo lipogenesis by fenofibrate. The results demonstrate that insulin sensitivity of lipolysis is decreased in fenofibrate-treated rats which resulted in 30% higher rate of glycerol release when compared to the control group. These findings suggest that besides its effects on liver, fenofibrate exerts effects on lipid metabolism in adipose tissue which may contribute to decreasing adiposity.     

Dehydroepiandrosterone down-regulates the expression of peroxisome proliferator-activated receptor gamma in adipocytes

Dehydroepiandrosterone (DHEA) is expected to have a weight-reducing effect. In this study, we evaluated the effect of DHEA on genetically obese Otsuka Long Evans Fatty rats (OLETF) compared with Long-Evans Tokushima rats (LETO) as control. Feeding with 0.4% DHEA-containing food for 2 wk reduced the weight of sc, epididymal, and perirenal adipose tissue in association with decreased plasma leptin levels in OLETF. Adipose tissue from OLETF showed increased expression of peroxisome proliferator-activated receptor gamma (PPARgamma) protein, which was prevented by DHEA treatment. Further, we examined the effect of DHEA on PPARgamma in primary cultured adipocytes and monolayer adipocytes differentiated from rat preadipocytes. PPARgamma protein level was decreased in a time- and concentration-dependent manner, and DHEA significantly reduced mRNA levels of PPARgamma, adipocyte lipid-binding protein, and sterol regulatory element-binding protein, but not CCAAT/enhancer binding protein alpha. DHEA-sulfate also reduced the PPARgamma protein, but dexamethasone, testosterone, or androstenedione did not alter its expression. In addition, treatment with DHEA for 5 d reduced the triglyceride content in monolayer adipocytes. These results suggest that DHEA down-regulates adiposity through the reduction of PPARgamma in adipocytes.     

Fat-specific transgenic expression of resistin in the spontaneously hypertensive rat impairs fatty acid re-esterification

OBJECTIVE: To investigate the mechanism by which fat-specific transgenic expression of resistin affects fatty acid metabolism in the spontaneously hypertensive rat (SHR). DESIGN: Basal- and adrenaline-stimulated lipolysis, basal- and insulin-stimulated lipogenesis as well as the site (glycerol versus acyl moiety) of glucose incorporated into triglycerides were determined in adipose tissue isolated from SHR-Resistin transgenic and SHR control rats. RESULTS: A moderate expression of transgenic resistin in adipose tissue was associated with significant increase in the FFA/glycerol ratio during adrenaline-stimulated lipolysis in the SHR-Resistin transgenic rats (3.27+/-0.26) compared to SHR controls (2.11+/-0.10, P=0.0005). Transgenic SHR also exhibited a significant decrease in FFA re-esterification in adipose tissue (approximately by 23%). CONCLUSION: These findings raise the possibility that the prodiabetic effects of transgenic resistin may be partly mediated by increased FFA release from adipose tissue due to impaired FFA re-esterification in adipocytes.     

Adverse adipose phenotype and hyperinsulinemia in gravid mice deficient in placental growth factor

Pregnancy-induced metabolic changes are regulated by signals from an expanded adipose organ. Placental growth factor (PlGF), acting through vascular endothelial growth factor receptor-1, may be among those signals. There is a steep rise in circulating PlGF during normal pregnancy, which is repressed in gravidas who develop preeclampsia. PlGF-deficiency in mice impairs adipose vascularization and development. Here we studied young-adult PlGF-deficient (PlGF(-/-)) and wild-type mice on a high-fat diet in the nongravid state and at embryonic day (E) 13.5 or E18.5 of gestation. Litter size and weight were normal, but E18.5 placentas were smaller in PlGF(-/-) pregnancies. PlGF(-/-) mice showed altered intraadipose dynamics, with the following: 1) less blood vessels and fewer brown, uncoupling protein (UCP)-1-positive, adipocytes in white sc and perigonadal fat compartments and 2) white adipocyte hypertrophy. The mRNA expression of beta(3)-adrenergic receptors, peroxisome proliferator-activated receptor-gamma coactivator-1alpha, and UCP-1 was decreased accordingly. Moreover, PlGF(-/-) mice showed hyperinsulinemia. Pregnancy-associated changes were largely comparable in PlGF(-/-) and wild-type dams. They included expanded sc fat compartments and adipocyte hypertrophy, whereas adipose expression of key angiogenesis/adipogenesis (vascular endothelial growth factor receptor-1, peroxisome proliferator-activated receptor-gamma(2)) and thermogenesis (beta(3)-adrenergic receptors, peroxisome proliferator-activated receptor-gamma coactivator-1alpha, and UCP-1) genes was down-regulated; circulating insulin levels gradually increased during pregnancy. In conclusion, reduced adipose vascularization in PlGF(-/-) mice impairs adaptive thermogenesis in favor of energy storage, thereby promoting insulin resistance and hyperinsulinemia. Pregnancy adds to these changes by PlGF-independent mechanisms. Disturbed intraadipose dynamics is a novel mechanism to explain metabolic changes in late pregnancy in general and preeclamptic pregnancy in particular.     

Depot-specific regulation of perilipin by rosiglitazone in a diabetic animal model

Treatment with rosiglitazone, a potent peroxisome proliferator-activated receptor (PPAR) gamma agonist, results in lipid storage coupled with reduced release of free fatty acids into the circulation. Many studies have reported that PPAR-gamma agonists increase subcutaneous adiposity but have no effect on visceral fat mass. Perilipin, a family of phosphoproteins that coat intracellular lipid droplets in adipocytes, is essential for enlargement of lipid droplets. Recently, a functional PPAR-responsive element was identified within the murine perilipin gene. We hypothesized that the depot-specific regulation of perilipin by rosiglitazone may be associated with the fat-redistribution and insulin-sensitizing effects of rosiglitazone. After 6 weeks of rosiglitazone treatment in Otusuka Long-Evans Tokushima Fatty rats, an animal model of type 2 diabetes mellitus, we measured changes in adiposity, triglyceride content in liver and muscle, morphology of the pancreas, and perilipin messenger RNA and protein expression in adipose tissue. Rosiglitazone increased subcutaneous adiposity, decreased triglyceride content of liver and muscle, decreased plasma free fatty acids (2107 +/- 507 micromol/L in the placebo group vs 824 +/- 148 micromol/L in the rosiglitazone group; P < .05), and improved insulin resistance. The islets of placebo-treated rats showed hypertrophy and destruction, whereas the islets of rosiglitazone-treated rats showed hypertrophy, but the islet architecture remained intact. Perilipin messenger RNA and protein expression increased in subcutaneous fat, but did not change in visceral fat, after rosiglitazone treatment. In 3T3-L1 cells, rosiglitazone pretreatment decreased lipolysis and increased perilipin protein. In conclusion, increased perilipin expression in subcutaneous fat after rosiglitazone treatment is likely to be a mediator of reduced lipolysis, resulting in lipid storage in subcutaneous fat, fat redistribution, and insulin sensitization.     

Infliximab modifies mesenteric adipose tissue alterations and intestinal inflammation in rats with TNBS-induced colitis

Abstract Objective. Infliximab is a monoclonal anti-TNF-α antibody that is used therapeutically to treat Crohn's disease (CD). High levels of pro-inflammatory cytokines, especially TNF-α, have been observed in the gastrointestinal tract of CD patients and were associated with alterations in the mesenteric adipose tissue, which also contributed to the high levels of adipokine release. The authors used a rat model of colitis that produces mesenteric adipose tissue alterations that are associated with intestinal inflammation to study the effects that infliximab treatment has on adipokine production, morphological alterations in adipose tissue and intestinal inflammation. Material and methods. The ability of infliximab to neutralize rat TNF-α was evaluated in vitro using U937 cells. Colitis was induced by repeated intracolonic trinitrobenzene sulfonic acid instillations and was evaluated by macroscopic score, histopathological analysis, myeloperoxidase activity, TNF-α and IL-10 expression as well as iNOS (inducible NO synthase) expression and JNK phosphorylation in colon samples. The alterations in adipose tissue were assessed by TNF-α, IL-10, leptin, adiponectin and resistin levels as well as adipocyte size and peroxisome proliferator-activated receptor (PPAR)-γ expression. Results. Infliximab treatment controlled intestinal inflammation, which reduced lesions and neutrophil infiltration. Inflammatory markers, such as iNOS expression and JNK phosphorylation, were also reduced. In mesenteric adipose tissue, infliximab increased the production of IL-10 and resistin, which was associated with the restoration of adipocyte morphology and PPAR-γ expression. Conclusions. Our results suggest that infliximab could contribute to the control of intestinal inflammation by modifying adipokine production by mesenteric adipose tissue.     

The effects of thiazolidinedione treatment on the regulations of aquaglyceroporins and glycerol kinase in OLETF rats

Aquaporins (AQPs) that transport glycerol in addition to water are classified as aquaglyceroporins (AQP3, 7, 9). AQP7 in the adipose tissue and AQP9 in the liver may coordinately contribute to the increase in hepatic gluconeogenesis in states of insulin resistance. Thiazolidinedione (TZD) has been shown to increase adipose AQP7 and induce glycerol kinase (GlyK) which is nearly absent in adipocytes. In the present study, we analyzed both GlyK and AQP gene expression in adipose and hepatic tissues, and AQP3 in kidneys from Long-Evans Tokushima Otsuka (LETO), Otsuka Long-Evans Tokushima Fatty (OLETF), and rosiglitazone (RSG)-treated OLETF (RSG-OLETF) rats. We also evaluated AQP9 protein expression in cultured human hepatoma cells treated with oleic acid, Wy14643, or RSG. A 2-week RSG treatment increased AQP7 mRNA levels in the mesenteric fat, but not in the epididymal fat of OLETF rats. Rosiglitazone treatment markedly increased GlyK expression in both fat depots, with a greater increase in the mesenteric fat. The magnitudes of GlyK induction by RSG were greater than that of AQP7 in both adipose tissues (P < .05, each). AQP9 and GlyK levels in the liver were not affected by RSG treatment in OLETF rats. Oleic acid and Wy14643 upregulated AQP9 protein expression in cultured human hepatoma cells in a dose-dependent manner. AQP3 mRNA levels tended to increase in the outer medulla of the RSG-OLETF rats. These results indicate that in the adipose tissue TZD has an important role in the glycerol metabolic pathway through the regulation of AQP and GlyK, especially by GlyK induction. Free fatty acids may directly enhance glycerol availability in the liver via the upregulation of AQP9 levels. Renal AQP3 may be related to the fluid retention caused by TZD.     

Remodeling of white adipose tissue after retinoic acid administration in mice

A reduced brown adipose phenotype in white adipose tissue (WAT) may contribute to obesity and type 2 diabetes in humans. Retinoic acid, the carboxylic form of vitamin A, triggers in rodents a reduction of body weight and adiposity and an increased expression of uncoupling proteins in brown adipose tissue and skeletal muscle. In this study, we investigated possible remodeling effects of all-trans retinoic acid (ATRA) in WAT depots. Changes in the expression of genes related to thermogenesis and fatty acid oxidation and levels of phosphorylated retinoblastoma protein were analyzed in WAT depots of adult NMRI male mice acutely injected with ATRA or vehicle, together with biometric and blood parameters. Body fat loss after ATRA treatment was unaccompanied by any increase in circulating nonesterified fatty acids or ketone bodies and accompanied by increased rectal temperature. The treatment triggered an up-regulation of the mRNA levels of uncoupling proteins 1 and 2, peroxisome proliferator-activated receptor gamma coactivator-1alpha, peroxisome proliferator-activated receptor alpha, muscle- and liver-type carnitine palmitoyltransferase 1, and subunit II of cytochrome oxidase in different WAT depots. Levels of phosphorylated retinoblastoma protein in WAT depots were increased after ATRA treatment. Adipocyte size was reduced, and the number of multilocular adipocytes was increased in inguinal WAT of ATRA-treated mice. The results indicate that ATRA favors the acquisition of brown adipose tissue-like properties in WAT. Understanding the mechanisms and effectors involved in the remodeling of WAT can contribute to new avenues of prevention and treatment of obesity and type 2 diabetes.     

Metabolic remodeling in adipocytes promotes ciliary neurotrophic factor-mediated fat loss in obesity

Obesity is characterized by an expanded adipose tissue mass, and reversing obesity reduces the risk of insulin resistance and cardiovascular disease. Ciliary neurotrophic factor (CNTF) reverses obesity by promoting the preferential loss of white adipose tissue. We evaluated the cellular and molecular mechanisms by which CNTF regulates adiposity. Obese mice fed a high-fat diet were treated with saline or recombinant CNTF for 10 d, and adipose tissue was removed for analysis. Another group fed a high-fat diet was pair fed to CNTF mice. In separate experiments, 3T3-L1 adipocytes were treated with CNTF to examine metabolic responses and signaling. CNTF reduced adipose mass that resulted from reductions in adipocyte area and triglyceride content. CNTF treatment did not affect lipolysis but resulted in decreases in fat esterification and lipogenesis and enhanced fatty acid oxidation. The enhanced fat oxidation was associated with the expression of peroxisome proliferator-activated receptor coactivator-1alpha (PGC1alpha) and nuclear respiratory factor 1 and increases in oxidative phosphorylation subunits and mitochondrial biogenesis as determined by electron microscopy. Studies in cultured adipocytes revealed that CNTF activates p38 MAPK and AMP-activated protein kinase. Inhibiting p38 activation prevented the CNTF-induced increase in PGC1alpha but not AMP-activated protein kinase activation. Diminished food intake with pair feeding induced similar decreases in fat mass, but this was related to increased expression of uncoupling protein 1. We conclude that CNTF reprograms adipose tissue to promote mitochondrial biogenesis, enhancing oxidative capacity and reducing lipogenic capacity, thereby resulting in triglyceride loss.     

Postnatal testosterone exposure results in insulin resistance, enlarged mesenteric adipocytes, and an atherogenic lipid profile in adult female rats: comparisons with estradiol and dihydrotestosterone

Postnatal events contribute to features of the metabolic syndrome in adulthood. In this study, postnatally administered testosterone reduced insulin sensitivity and increased the mesenteric fat depot, the size of mesenteric adipocytes, serum levels of total cholesterol, low-density lipoprotein cholesterol, and triglycerides, and the atherogenic index in adult female rats. To assess the involvement of estrogen and androgen receptors in these programming effects, we compared testosterone-exposed rats to rats exposed to estradiol or dihydrotestosterone (DHT). Estradiol-treated rats had lower insulin sensitivity than testosterone-treated rats and, like those rats, had enlarged mesenteric adipocytes and increased triglyceride levels. DHT also reduced insulin sensitivity but did not mimic the other metabolic effects of testosterone. All treated rats were probably anovulatory, but only those treated with testosterone had reduced testosterone levels. This study confirms our previous finding that postnatal administration of testosterone reduces insulin sensitivity in adult female rats and shows that this effect is accompanied by unfavorable changes in mesenteric fat tissue and in serum lipid levels. The findings in the estradiol and DHT groups suggest that estrogen receptors exert stronger metabolic programming effects than androgen receptors. Thus, insults such as sex hormone exposure in early life may have long-lasting effects, thereby creating a predisposition to disturbances in insulin sensitivity, adipose tissue, and lipid profile in adulthood.     

Aging-associated changes in physical performance and energy metabolism in the senescence-accelerated mouse

The aim of the study was to clarify the aging-associated changes in physical performance and energy metabolism in senescence-accelerated prone mouse (SAMP1). The endurance of aged SAMP1 was significantly lower by 28% than the age-matched senescence-resistant mouse (SAMR1). Oxygen consumption and fat oxidation in aged SAMP1 were lower by 19% and 22%, respectively. Peroxisome proliferator-activated receptor-γ coactivator-1β and medium-chain acyl coenzyme A dehydrogenase messenger RNA expression was significantly lower in aged SAMP1. Aged SAMP1 exhibited higher plasma glucose, insulin, leptin, and lower adiponectin concentrations. Aged SAMP1 also had higher malondialdehyde levels in plasma and tissues and lower peroxisome proliferator-activated receptor-γ messenger RNA and protein levels in adipose tissue. These results indicate that physical performance and energy expenditure decrease earlier with aging in SAMP1, accompanied by decreased fatty acid catabolism in muscle and liver and increased inflammation and oxidative stress in adipose tissue. SAMP1 could thus be a useful accelerated functional depression model for studying physical performance and energy metabolism.     

Increased maternal nutrition stimulates peroxisome proliferator activated receptor-gamma, adiponectin, and leptin messenger ribonucleic acid expression in adipose tissue before birth

During fetal life, adipose tissue is predominantly comprised of brown or thermogenic adipocytes and there is a transition to white, lipid-storing adipocytes after birth concomitant with the onset of suckling. In pregnancies complicated by gestational diabetes, the fetus is hyperglycemic, has an increased fat mass, and is at increased risk of obesity in later life. In the present study, we have investigated the hypothesis that exposure to increased maternal nutrition during late gestation results in increased expression of genes that regulate adipogenesis and lipogenesis in perirenal fat in fetal sheep. Pregnant ewes were fed either at or approximately 55% above maintenance energy requirements during late pregnancy and quantitative RT-PCR was used to measure peroxisome proliferator-activated receptor gamma, lipoprotein lipase, glycerol-3-phosphate dehydrogenase, adiponectin, and leptin mRNA expression. We report that exposure to metabolic and hormonal signals of increased nutrition before birth results in an increase in the expression of the adipogenic factor, peroxisome proliferator-activated receptor gamma, and in lipoprotein lipase, adiponectin, and leptin mRNA expression in fetal perirenal fat. We propose that an increase in maternal, and hence fetal, nutrition results in a precocial increase in adipogenic, lipogenic, and adipokine gene expression in adipose tissue and that these changes may be important in the development of obesity in later life.