Assessment of diet-induced obese rats as an obesity model by comparative functional genomics

Objective: We applied a comparative functional genomics approach to evaluate whether diet‐induced obese (DIO) rats serve as an effective obesity model. Methods and Procedures: Gene‐expression profiles of epididymal fat from DIO and lean rats were generated using microarrays and compared with the published array data of obese and non‐obese human subcutaneous adipocytes. Results: Caloric intake and fuel efficiency were significantly higher in DIO rats, which resulted in increased body weight and adiposity. Circulating glucose, cholesterol, triglyceride, insulin, and leptin levels in DIO rats were significantly higher than those in the lean controls. DIO rats also exhibited impaired insulin sensitivity. A direct comparison of gene‐expression profiles from DIO and lean rats and those from obese and non‐obese humans revealed that global gene‐expression patterns in DIO rat fat resemble those of obese human adipocytes. Differentially expressed genes between obese and non‐obese subjects in both human and rat studies were identified and associated with biological pathways by mapping genes to Gene Ontology (GO) categories. Immune response–related genes and angiogenesis‐related genes exhibited significant upregulation in both obese humans and DIO rats when compared with non‐obese controls. However, genes in fatty acid metabolism and oxidation exhibited a broad downregulation only in obese human adipocytes but not in DIO rat epididymal fat. Discussion: Our study based on gene‐expression profiling suggested that DIO rats in general represent an appropriate obesity model. However, the discrepancies in gene‐expression alterations between DIO rats and obese humans, particularly in the metabolic pathways, may explain the limitations of using DIO rodent models in obesity research and drug discovery.     

Down-regulation of microsomal prostaglandin E2 synthase-1 in adipose tissue by high-fat feeding

Objective: Prostaglandin (PG)E₂ is a lipid mediator implicated in inflammatory diseases and in the regulation of lipolysis and adipocyte differentiation. This work was, thus, undertaken to study the regulation of the various PGE₂ synthases (PGESs) in obesity. Research Methods and Procedures: C57Bl/6 mice were subjected to a high‐fat or regular diet for 12 weeks. The levels of PGE₂ in white adipose tissue (WAT) of lean and obese mice were quantified by liquid chromatography‐mass spectrometry, and the change in expression of the three major PGES caused by diet‐induced obesity was characterized by Western blotting. Human preadipocytes and 3T3‐L1 cells were used to assess the expression of microsomal prostaglandin E₂ synthase‐1 (mPGES‐1) during adipogenesis. Results: mPGES‐1, mPGES‐2, and cytosolic PGES proteins were all detected in WAT of lean animals. mPGES‐1 was expressed at higher levels in WAT than in any other tissues examined and was more abundant (3‐ to 4‐fold) in epididymal (visceral) compared with inguinal (subcutaneous) WAT. Expression of mPGES‐1 was also detected in undifferentiated and differentiated 3T3‐L1 cells and in human primary subcutaneous preadipocytes at all stages of adipogenesis. The mPGES‐1 protein was substantially down‐regulated in epididymal and inguinal WAT of obese mice, whereas mPGES‐2 and cytosolic PGES remained relatively stable. Concordantly, the PGE₂ levels in obese inguinal WAT were significantly lower than those of lean animals. Discussion: These data suggest that mPGES‐1 is the major form of PGESs contributing to the synthesis of PGE₂ in WAT and that its down‐regulation might be involved in the alterations of lipolysis and adipogenesis associated with obesity.     

Antiobesity Effects of yerba maté Extract (Ilex paraguariensis) in High‐fat Diet–induced Obese Mice

Because the potential of yerba maté (Ilex paraguariensis) has been suggested in the management of obesity, the aim of the present study was to evaluate the effects of yerba maté extract on weight loss, obesity‐related biochemical parameters, and the regulation of adipose tissue gene expression in high‐fat diet–induced obesity in mice. Thirty animals were randomly assigned to three groups. The mice were introduced to standard or high‐fat diets. After 12 weeks on a high‐fat diet, mice were randomly assigned according to the treatment (water or yerba maté extract 1.0 g/kg). After treatment intervention, plasma concentrations of total cholesterol, high‐density lipoprotein cholesterol, triglyceride, low‐density lipoprotein (LDL) cholesterol, and glucose were evaluated. Adipose tissue was examined to determine the mRNA levels of several genes such as tumor necrosis factor‐α (TNF‐α), leptin, interleukin‐6 (IL‐6), C‐C motif chemokine ligand‐2 (CCL2), CCL receptor‐2 (CCR2), angiotensinogen, plasminogen activator inhibitor‐1 (PAI‐1), adiponectin, resistin, peroxisome proliferator‐activated receptor‐γ² (PPAR‐γ²), uncoupling protein‐1 (UCP1), and PPAR‐γ coactivator‐1α (PGC‐1α). The F4/80 levels were determined by immunoblotting. We found that obese mice treated with yerba maté exhibited marked attenuation of weight gain, adiposity, a decrease in epididymal fat‐pad weight, and restoration of the serum levels of cholesterol, triglycerides, LDL cholesterol, and glucose. The gene and protein expression levels were directly regulated by the high‐fat diet. After treatment with yerba maté extract, we observed a recovery of the expression levels. In conclusion, our data show that yerba maté extract has potent antiobesity activity in vivo. Additionally, we observed that the treatment had a modulatory effect on the expression of several genes related to obesity.     

Subcutaneous Fat Shows Higher Thyroid Hormone Receptor‐α1 Gene Expression Than Omental Fat

The aims of this work were to evaluate thyroid hormone receptor‐α (TRα), TRα1, and TRα2 mRNA gene expression and TRα1:TRα2 ratio, identified as candidate factors for explaining regional differences between human adipose tissue depots. TRα, TRα1, and TRα2 mRNA levels, and the gene expressions of arginine–serine‐rich, splicing factor 2 (SF2), heterogeneous nuclear ribonucleoprotein H1 (hnRNP H1), heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1), and Spot 14 (S14) were evaluated in 76 paired adipose tissue samples obtained from a population of 38 women who varied widely in terms of obesity and body fat distribution. Gene expression for these factors was also studied in stromal‐vascular cells (SVCs) and mature adipocytes (MAs) from eight paired fat depots. TRα gene and TRα1 mRNA expression were increased 1.46‐fold (P = 0.006) and 1.80‐fold (P < 0.0001), respectively, in subcutaneous (SC) vs. visceral fat. These differences in gene expression levels were most significant in the obese group, in which the TRα1:TRα2 ratio was 2.24‐fold (P < 0.0001) higher in SC vs. visceral fat. S14 gene expression was also increased by 2.42‐fold (P < 0.0001) and correlated significantly with TRα and TRα1 gene expression and with the TRα1:TRα2 ratio. In agreement with these findings, hnRNP A1:SF2 ratio was decreased by 1.39‐fold (P = 0.001). TRα and S14 levels were 2.1‐fold (P < 0.0001) and 112.4‐fold (P < 0.0001), respectively, higher in MAs than in SVCs from both fat depots. In summary, genes for TR‐α, their upstream regulators, and downstream effectors were differentially expressed in SC vs. omental (OM) adipose tissue. Our findings suggest that TRα1 could contribute to SC adipose tissue expandability in obese subjects.     

S‐Glutathionylation of hepatic and visceral adipose proteins decreases in obese rats

A number of clinical and biochemical studies demonstrate that obesity and insulin resistance are associated with increases in oxidative stress and inflammation. Paradoxically, insulin sensitivity can be enhanced by oxidative inactivation of cysteine residues of phosphatases, and inflammation can be reduced by S‐glutathionylation with formation of protein‐glutathione mixed disulfides (PSSG). Although oxidation of protein‐bound thiols (PSH) is increased in multiple diseases, it is not known whether there are changes in PSH oxidation species in obesity.

Objective:

In this work, the hypothesis that obesity is associated with decreased levels of proteins containing oxidized protein thiols was tested.

Design and Methods:

The tissue levels of protein sulfenic acids (PSOH) and PSSG in liver, visceral adipose tissue, and skeletal muscle derived from glucose intolerant, obese‐prone Sprague‐Dawley rats were examined.

Results:

The data in this study indicate that decreases in PSSG content occurred in liver (44%) and adipose (26%) but not skeletal muscle in obese rats that were fed a 45% fat‐calorie diet versus lean rats that were fed a 10% fat‐calorie diet. PSOH content did not change in the tissue between the two groups. The activity of the enzyme glutaredoxin (GLRX) responsible for reversal of PSSG formation did not change in muscle and liver between the two groups. However, levels of GLRX1 were elevated 70% in the adipose tissue of the obese, 45% fat calorie‐fed rats.

Conclusion:

These are the first data to link changes in S‐glutathionylation and GLRX1 to adipose tissue in the obese and demonstrate that redox changes in thiol status occur in adipose tissue as a result of obesity.     

Site specific changes of redox metabolism in adipose tissue of obese Zucker rats

Adipose tissues are differently involved in lipid metabolism and obesity according to their type and location. Increasing reports stress on the impact of redox metabolism on obesity and metabolic syndrome. The aim of this work is to investigate the site-specific redox metabolism in three different adipose tissues and its changes occurring in obesity. We analysed enzymatic and non-enzymatic parameters, and focused on the reduced/oxidized glutathione and coenzyme Q couples. In lean compared with obese non-diabetic Zucker rats, interscapular brown fat seems well protected against oxidative stress and epididymal adipose tissue shows a more reduced glutathione redox state, associated with a higher susceptibility to lipophilic oxidative stress than inguinal adipose tissue. Epididymal adipose tissue redox metabolism significantly differs from inguinal one by its limited redox metabolism adaptation. Our results demonstrate site-specific managements of reactive oxygen species metabolism in obese Zucker rats. These results are not consistent with the classic deciphering of inflammatory situation and produce a new conception of the redox parameters implication in the development of the metabolic syndrome.     

Extensive changes in innate immune gene expression in obese Göttingen minipigs do not lead to changes in concentrations of circulating cytokines and acute phase proteins

The usefulness of Göttingen minipigs as models for obesity and obesity‐related pathologies is well established. The low‐grade inflammation associated with obesity involves a range of innate immune factors; however, to our knowledge, the impact of obesity on innate immune factor expression has not been studied in Göttingen minipigs. Therefore, we studied the expression of innate immune genes in liver and adipose tissues as well as serum concentrations of cytokines and acute phase proteins in obese vs. lean Göttingen minipigs. In the liver, of 35 investigated genes, the expression of nine was significantly different in obese pigs (three up‐regulated, six down‐regulated). Of 33 genes in adipose tissues, obesity was associated with changed expression of 12 genes in the visceral adipose tissue (VAT) (three up‐regulated), 11 in the abdominal retroperitoneal adipose tissue (RPAT) (seven of these up‐regulated) and eight in the subcutaneous adipose tissue (SAT) from the neck (five of which were up‐regulated). Obesity‐associated expression changes were observed for three genes in all adipose tissues, namely chemokine (C‐C motif) ligand 3‐like 1 (up‐regulated), CD200 molecule (down‐regulated) and interleukin 1 receptor antagonist (up‐regulated) with interleukin 1 receptor antagonist being the most highly regulated gene in both VAT and RPAT. Looking at patterns of expression across the three types of adipose tissues, obesity was associated with an increased number of acute phase proteins differentially expressed between adipose tissues and a decreased tissue‐specific expression of cytokines and chemokines. In contrast to obese humans, no changes in serum concentrations of haptoglobin, C‐reactive protein, serum amyloid A, tumor necrosis factor‐α and interleukin 6 were found in obese Göttingen minipigs.     

Altered Kidney CYP2C and Cyclooxygenase‐2 Levels Are Associated with Obesity‐Related Albuminuria

Objective: To determine cytochrome P450 (CYP450) and cyclooxygenase (COX) expression and metabolite regulation and renal damage in the early stages of obesity‐related hypertension and diabetes. Research Methods and Procedures: Obese and lean Zucker rats at 10 to 12 weeks of age were studied. Blood pressure was measured in the conscious state using radiotelemetry. Blood glucose levels and body weight were measured periodically. Protein expression of CYP450 and COX enzymes in the kidney cortex, renal microvessels, and glomeruli was studied. The levels of CYP450 and COX metabolites in urine were measured, and urinary albumin excretion, an indicator of kidney damage, was measured. Results: Body weight and blood glucose averaged 432 ± 20 grams and 105 ± 5 mg/dl, respectively, in obese Zucker rats as compared with 320 ± 8 grams and 91 ± 5 mg/dl, respectively, in age‐matched 10‐ to 12‐week‐old lean Zucker rats. Renal microvascular CYP4A and COX‐2 protein levels were increased 2.3‐ and 17.0‐fold, respectively, in obese Zucker rats. The protein expression of CYP2C11 and CYP2C23 was decreased 2.0‐fold in renal microvessels isolated from obese Zucker rats when compared with lean Zucker rats. The urinary excretion rate of thromboxane B₂ was increased significantly in obese Zucker as compared with lean Zucker rats (22.0 ± 1.8 vs. 13.4 ± 1.0 ng/d). Urinary albumin excretion, an index of kidney damage, was increased in the obese Zucker rat at this early age. Discussion: These results suggest that increased CYP4A and COX‐2 protein levels and decreased CYP2C11 and CYP2C23 protein levels occur in association with microalbuminuria during the onset of obesity‐related hypertension and type 2 diabetes.     

Antiobesity Effects of Bifidobacterium breve Strain B-3 Supplementation in a Mouse Model with High-Fat Diet-Induced Obesity

The aim of the present study was to evaluate the anti-obesity activity of a probiotic bifidobacterial strain in a mouse model with obesity induced by a high-fat diet. The mice were fed a high-fat diet supplemented with Bifidobacterium breve B-3 at 10⁸ or 10⁹ CFU/d for 8 weeks. B. breve B-3 supplementation dose-dependently suppressed the accumulation of body weight and epididymal fat, and improved the serum levels of total cholesterol, fasting glucose and insulin. The bifidobacterial counts in the caecal contents and feces were significantly increased with the B. breve B-3 administration. The expression of genes related to fat metabolism and insulin sensitivity in the gut and epididymal fat tissue was up-regulated by this administration. These results suggest that the use of B. breve B-3 would be effective in reducing the risk of obesity.     

Macrophage-colony stimulating factor in obese adipose tissue: studies with heterozygous op/+ mice

Objective: We examined the gene expression of macrophage‐colony stimulating factor (M‐CSF) in mice with diet‐induced obesity and in genetically obese mice. We also examined the effect of decreased M‐CSF signaling on the susceptibility to obesity and macrophage recruitment into the adipose tissue of mice. Research Methods and Procedures: The adipose tissue from mice with diet‐induced obesity, obese KKA^y mice, and ob/ob obese mice was used for RNA preparation. Production of M‐CSF and monocyte chemoattractant protein‐1 (MCP‐1) was examined by quantitative real‐time polymerase chain reaction (PCR) and enzyme‐linked immunosorbent assay. The op/+ heterozygous mice, with decreased functional M‐CSF expression, were placed on a high‐fat diet or crossed with KKA^y mice to study the susceptibility to obesity. The gene expression of macrophage markers in adipose tissue was examined. Results: The expression of M‐CSF was not significantly changed in mice on a high‐fat diet or in either type of genetic obesity (KKA^y or ob/ob mice). No change in the degree of obesity or macrophage‐related gene expression (F4/80, CD68, and MCP‐1) in the adipose tissue was observed in op/+ mice compared with +/+ control mice, which were either treated with a high‐fat diet or crossed with KKA^y mice. Discussion: This study demonstrated that there was no significant change in the expression of M‐CSF in the adipose tissue from obese mice and only a minor phenotypic change, such as macrophage infiltration, in the adipose tissue from op/+ mice, suggesting that M‐CSF does not play a major role in macrophage recruitment in the adipose tissue of obese mice.     

The Effect of Low‐Intensity Exercise Training on Fat Metabolism of Obese Women

Objective: Previous studies have shown that fat metabolism is different in upper body (UB) and lower body (LB) obese women. The present study investigated whether the effect of low‐intensity exercise training on fat metabolism is different in UB and LB obese premenopausal women. Research Methods and Procedures: Twenty‐one healthy, premenopausal women with either LB obesity (waist‐to‐hip ratio of ≤0.79; n = 8) or UB obesity (waist‐to‐hip ratio of ≥0.85; n = 13) participated in the present study. The UB obese women were matched and randomly divided in an exercise training group (UB) and a nonexercising control group (UB‐C). Subjects in the UB and LB groups participated in a low‐intensity exercise training program (40% Vo ₂max) three times per week for 12 weeks. Before and after the intervention, measurements of fat metabolism at rest and during exercise, body composition, and maximal aerobic capacity were performed. Results: Exercise training did not change the respiratory exchange ratio at rest in the UB and LB groups. During exercise, relative fat oxidation increased in the UB group by 19% (p < 0.05), whereas no change in the LB and UB‐C groups was found. Plasma free fatty acid oxidation did not change by exercise training, and nonplasma fatty acid oxidation tended to increase in the UB group compared with the UB‐C group (p = 0.08). Discussion: Low‐intensity exercise training increased the contribution of fat oxidation to total energy expenditure during exercise but not at rest in UB obese women. Exercise training had no significant effect on fat metabolism in the LB obese women.     

Neuronal control of lipid metabolism by STR‐2 G protein‐coupled receptor promotes longevity in Caenorhabditis elegans

The G protein‐coupled receptor (GPCR) encoding family of genes constitutes more than 6% of genes in Caenorhabditis elegans genome. GPCRs control behavior, innate immunity, chemotaxis, and food search behavior. Here, we show that C. elegans longevity is regulated by a chemosensory GPCR STR‐2, expressed in AWC and ASI amphid sensory neurons. STR‐2 function is required at temperatures of 20°C and higher on standard Escherichia coli OP50 diet. Under these conditions, this neuronal receptor also controls health span parameters and lipid droplet (LD) homeostasis in the intestine. We show that STR‐2 regulates expression of delta‐9 desaturases, fat‐5, fat‐6 and fat‐7, and of diacylglycerol acyltransferase dgat‐2. Rescue of the STR‐2 function in either AWC and ASI, or ASI sensory neurons alone, restores expression of fat‐5, dgat‐2 and restores LD stores and longevity. Rescue of stored fat levels of GPCR mutant animals to wild‐type levels, with low concentration of glucose, rescues its lifespan phenotype. In all, we show that neuronal STR‐2 GPCR facilitates control of neutral lipid levels and longevity in C. elegans.     

Differential secretion of satiety hormones with progression of obesity in JCR:LA-corpulent rats

Objective: To characterize the gastrointestinal tract at the onset and in well‐established obesity. Methods and Procedures: Lean (+/?) and obese (cp/cp) male JCR:LA‐cp rats lacking a functional leptin receptor were killed at 3.5 weeks and 9 months of age and plasma concentrations of satiety hormones determined. The small intestine, colon, and stomach were measured, weighed, and mRNA levels of satiety genes quantified. Results: At the onset of obesity, obese rats had greater intestine, colon, and liver mass when adjusted for body weight compared to lean rats. Conversely, adult rats with established obesity had lower intestine and colon mass and length after adjustment for body weight. Early changes in gene expression included decreased ghrelin mRNA levels in stomach and increased peptide YY (PYY) mRNA levels in duodenum of young obese rats. After massive accumulation of adipose tissue had occurred, adult obese rats had increased proglucagon and ghrelin mRNA expression in the proximal intestine. In the distal small intestine, obese rats had lower proglucagon, ghrelin, and PYY mRNA levels. Finally, at the onset and in well‐established obesity, obese rats had higher plasma insulin, amylin, glucagon like peptide‐1 (GLP‐1), and PYY, a finding, with the exception of insulin, unique to this model. Plasma total ghrelin levels were significantly lower at the onset of obesity and established obesity compared to the lean rats. Discussion: Several defects are manifested in the obese gut early on in the disease before the accumulation of large excesses of body fat and represent potential targets for early intervention in obesity.