Larger anti-adipogenic effect of angiotensin II on omental preadipose cells of obese humans

Objective: The ability to form new adipose cells is important to adipose tissue physiology; however, the mechanisms controlling the recruitment of adipocyte progenitors are poorly understood. A role for locally generated angiotensin II in this process is currently proposed. Given that visceral adipose tissue reportedly expresses higher levels of angiotensinogen compared with other depots and the strong association of augmented visceral fat mass with the adverse consequences of obesity, we studied the role of angiotensin II in regulating adipogenic differentiation in omental fat of obese and non‐obese humans. Research Methods and Procedures: The angiotensin II effect on adipose cell formation was evaluated in human omental adipocyte progenitor cells that were stimulated to adipogenic differentiation in vitro. The adipogenic response was measured by the activity of the differentiation marker glycerol‐3‐phosphate dehydrogenase. Results: Angiotensin II reduced the adipogenic response of adipocyte progenitor cells, and the extent of the decrease correlated directly with the subjects’ BMI (p = 0.01, R² = 0.30). A 56.3 ± 3.4% and 44.5 ± 2.7% reduction of adipogenesis was found in obese and non‐obese donors’ cells, respectively (p < 0.01). The effect of angiotensin II was reversed by type 1 angiotensin receptor antagonist losartan. Discussion: A greater anti‐adipogenic response to angiotensin II in omental adipose progenitor cells from obese subjects opens a venue to understand the deregulation of visceral fat tissue cellularity that has been associated with severe functional abnormalities of the obese condition.     

Sensitivity of ob/ob Mice to Leptin‐Induced Adipose Tissue Apoptosis

Objective: ob/ob mice have increased sensitivity to many of leptin's effects. The primary objective of this experiment was to determine whether ob/ob mice demonstrated increased sensitivity to leptin‐induced adipose tissue apoptosis. Research Methods and Procedures: Fifteen‐week‐old female ob/ob and Ob/? mice received 0 (saline), 2.5, or 10 μg/d leptin for 14 days through subcutaneous (sc) osmotic minipumps. Food intake (FI), body temperature, physical activity, and body weight were measured daily. Body composition and weights and adipose tissue apoptosis (percentage DNA fragmentation) of inguinal, parametrial, and retroperitoneal fat pads were determined at the end of the study. Results: FI decreases were more pronounced in ob/ob. Leptin (10 μg/d) decreased total FI 71% in ob/ob and 34% in Ob/? (p < 0.05). Body weight was decreased by both doses of leptin in ob/ob (p < 0.01) but was unchanged in Ob/?. Leptin increased body temperature in ob/ob but not in Ob/?. Physical activity was increased 400% by 10 μg/d leptin in ob/ob (p < 0.01) but decreased 13% in Ob/? (p < 0.01). Body fat content of ob/ob was reduced by both leptin doses, whereas only 10 μg/d leptin decreased body fat in Ob/?. Fat pad weights were decreased similarly by leptin in both genotypes. However, apoptosis was increased by leptin in all three fat pads in ob/ob, whereas Ob/? showed significant increases only in retroperitoneal. Discussion: ob/ob mice had greater overall sensitivity to leptin. Although ob/ob mice appeared to be more sensitive than Ob/? mice to leptin‐induced adipose tissue apoptosis, there were differences among adipose depots in responsiveness to leptin‐induced apoptosis.     

Expression of Class III facilitative glucose transporter genes (GLUT-10 and GLUT-12) in mouse and human adipose tissues

We have examined whether GLUT-10 and GLUT-12, members of the Class III group of the recently expanded family of facilitative glucose transporters, are expressed in adipose tissues. The mouse GLUT-12 gene, located on chromosome 10, comprises at least five exons and encodes a 622 amino acid protein exhibiting 83% sequence identity and 91% sequence similarity to human GLUT-12. Expression of the GLUT-12 gene was evident in all the major mouse adipose tissue depots (epididymal, perirenal, mesenteric, omental, and subcutaneous white; interscapular brown). The GLUT-10 gene is also expressed in mouse adipose tissues and as with GLUT-12 expression occurred in the mature adipocytes as well as the stromal vascular cells. 3T3-L1 adipocytes express GLUT-10, but not GLUT-12, and expression of GLUT-12 was not induced by insulin or glucose. Both GLUT-10 and GLUT-12 expression was also found in human adipose tissue (subcutaneous and omental) and SGBS adipocytes. It is concluded that white fat expresses a wide range of facilitative glucose transporters.     

Influence of Dietary Conjugated Linoleic Acid and Fat Source on Body Fat and Apoptosis in Mice*

Objective: To determine whether altered dietary essential fatty acid (linoleic and arachidonic acid) concentrations alter sensitivity to conjugated linoleic acid (CLA)‐induced body fat loss or DNA fragmentation. Research Methods and Procedures: Mice were fed diets containing soy oil (control), coconut oil [essential fatty acid deficient (EFAD)], or fish oil (FO) for 42 days, and then diets were supplemented with a mixture of CLA isomers (0.5% of the diet) for 14 days. Body fat index, fat pad and liver weights, DNA fragmentation in adipose tissue, and fatty acid profiles of adipose tissue were determined. Results: The EFAD diet decreased (p < 0.05) linoleic and arachidonic acid in mouse adipose tissue but did not affect body fat. Dietary CLA caused a reduction (p < 0.05) in body fat. Mice fed the EFAD diet and then supplemented with CLA exhibited a greater reduction (p < 0.001) in body fat (20.21% vs. 6.94% in EFAD and EFAD + CLA‐fed mice, respectively) compared with mice fed soy oil. Dietary FO decreased linoleic acid and increased arachidonic acid in mouse adipose tissue. Mice fed FO or CLA were leaner (p < 0.05) than control mice. FO + CLA‐fed mice did not differ in body fat compared with FO‐fed mice. Adipose tissue apoptosis was increased (p < 0.001) in CLA‐supplemented mice and was not affected by fat source. Discussion: Reductions in linoleic acid concentration made mice more sensitive to CLA‐induced body fat loss only when arachidonic acid concentrations were also reduced. Dietary essential fatty acids did not affect CLA‐induced DNA fragmentation.     

Omental 11beta-hydroxysteroid dehydrogenase 1 correlates with fat cell size independently of obesity

Objectives: In ideopathic obesity, there is evidence that enhanced cortisol regeneration within abdominal subcutaneous adipose tissue may contribute to adiposity and metabolic disease. Whether the cortisol regenerating enzyme, 11β‐hydroxysteroid dehydrogenase type 1 (11βHSD1), or glucocorticoid receptor (GRα) levels are altered in other adipose depots remains uncertain. Our objective was to determine the association between 11βHSD1 and GRα mRNA levels in four distinct adipose depots and measures of obesity and the metabolic syndrome. Research Methods and Procedures: Adipose tissue biopsies were collected from subcutaneous (abdominal, thigh, gluteal) and intra‐abdominal (omental) adipose depots from 21 women. 11βHSD1 and GRα mRNA levels were measured by real‐time polymerase chain reaction. Body composition, fat distribution, fat cell size, and blood lipid, glucose, and insulin levels were measured. Results: 11βHSD1 mRNA was highest in abdominal subcutaneous (p < 0.001) and omental (p < 0.001) depots and was positively correlated with BMI and visceral adiposity in all depots. Omental 11βHSD1 correlated with percent body fat (R = 0.462, p < 0.05), fat cell size (R = 0.72, p < 0.001), and plasma triglycerides (R = 0.46, p < 0.05). Conversely, GRα mRNA was highest in omental fat (p < 0.001). GRα mRNA was negatively correlated with BMI in the abdominal subcutaneous (R = ?0.589, p < 0.05) and omental depots (R = ?0.627, p < 0.05). Omental GRα mRNA was inversely associated with visceral adiposity (R = ?0.507, p < 0.05), fat cell size (R = ?0.52, p < 0.01), and triglycerides (R = ?0.50, p < 0.05). Discussion: Obesity was associated with elevated 11βHSD1 mRNA in all adipose compartments. GRα mRNA is reduced in the omental depot with obesity. The novel correlation of 11βHSD1 with omental fat cell size, independent of obesity, suggests that intracellular cortisol regeneration is a strong predictor of hypertrophy in the omentum.     

Low resistin levels in adipose tissues and serum in high-fat fed mice and genetically obese mice: development of an ELISA system for quantification of resistin

Obesity is a major risk factor for insulin resistance. Resistin, an adipocyte-derived hormone-like molecule, is considered to serve as an important link between obesity and insulin resistance. However, the physiological role of resistin and the mechanism by which it neutralizes insulin action are still unclear. There are also conflicting reports that cast doubt on the cause of insulin resistance. In this study, we developed an enzyme-linked immunosorbent assay (ELISA) system for quantification of mouse resistin levels, analyzed in relation to insulin resistance. C57BL/6J mice fed high-fat diet compared with normal diet had low resistin levels (by 70%, P<0.01) in epididymal adipose tissues. Genetically obese mice, db/db and KK-A(y), had hyperinsulinemia and hyperglycemia but low resistin levels (decreases by 83 and 90%, both P<0.01) compared with C57/BL6J mice in epididymal adipose tissues. Serum resistin levels determined by Western blotting showed a similar pattern to those in adipose tissues. Resistin levels in adipose tissues correlated with serum adiponectin concentrations positively (r=0.49). Our results indicate that the novel ELISA system is suitable for measurement of resistin levels in adipose tissues. The results do not support a role for resistin in insulin resistance.     

mRNA Levels of the Insulin‐Signaling Molecule SORBS1 in the Adipose Depots of Nondiabetic Women

Objectives: The SORBS1 gene has been shown to be an important adaptor protein in the insulin‐signaling pathway in many molecular and cellular biology studies. However, its roles in humans either in health or disease are rarely explored. In this report, we measured the SORBS1 mRNA levels in human adipose tissues. Research Methods and Procedures: Adipose tissues of both the abdominal subcutaneous and omental depots were obtained from 62 nondiabetic women. The relative SORBS1 mRNA levels were quantified using real‐time polymerase chain reaction. Results: The relative SORBS1 mRNA levels from these two depots significantly correlated with each other (γ = 0.85, p = 0.0000). The relative SORBS1 mRNA levels in the omental depots were lower than those in the subcutaneous depots (p = 0.053 by two‐tailed test, p = 0.026 by one‐tailed paired Student's t test). The mean SORBS1 expression level in the omental depots was ～70% that in the subcutaneous depots. Moreover, the relative SORBS1 mRNA levels in the omental depots were significantly related to BMI using either correlation analysis (γ = ?0.41, p = 0.0008) or multivariate linear regression analysis (β = ?0.20 ± 0.09, p = 0.031) with adjustment for age, plasma glucose, serum insulin, triglyceride, and total cholesterol levels. Discussion: Our preliminary results indicate the depot‐specific differential expression of SORBS1 in relation to BMI. Further investigation of the functional significance of this phenomenon in human obesity is warranted.     

Upper and Lower Body Adipose Tissue Function: A Direct Comparison of Fat Mobilization in Humans

Objectives: Fat in the lower body is not associated with the same risk of cardiovascular disease as fat in the upper body. Is this explained by differences in the physiological functioning of the two depots? This study had two objectives: 1) to determine whether fat mobilization and blood flow differ between gluteal and abdominal adipose tissues in humans, and 2) to develop a new technique to assess gluteal adipose tissue function directly. Research Methods and Procedures: We performed detailed in vivo studies of adipose tissue function involving the assessment of fat mobilization by measurement of adipose tissue blood flows, arterio‐venous differences of metabolites across each depot, and gene expression in tissue biopsies in a small‐scale physiological study. Results: Gluteal adipose tissue has a lower blood flow (67% lower, p < 0.05) and lower hormone‐sensitive lipase rate of action (87% lower, p < 0.05) than abdominal adipose tissue. Lipoprotein lipase rate of action and mRNA expression are not different between the depots. This is the first demonstration of a novel technique to directly investigate gluteal adipose tissue metabolism. Discussion: Direct assessment of fasting adipose tissue metabolism in defined depots show that the buttock is metabolically “silent” in terms of fatty acid release compared with the abdomen.     

Characterization and comparison of adipose tissue‐derived cells from human subcutaneous and omental adipose tissues

Different fat depots contribute differently to disease and function. These differences may be due to the regional variation in cell types and inherent properties of fat cell progenitors. To address the differences of cell types in the adipose tissue from different depots, the phenotypes of freshly isolated adipose tissue‐derived cells (ATDCs) from subcutaneous (SC) and omental (OM) adipose tissues were compared using flow cytometry. Our results showed that CD31^?CD34⁺CD45^?CD90^‐CD105^?CD146⁺ population, containing vascular smooth muscle cells and pericytes, was specifically defined in the SC adipose tissue while no such population was observed in OM adipose tissue. On the other hand, CD31^?CD34⁺CD45^?CD90^?CD105^?CD146^? population, which is an undefined cell population, were found solely in OM adipose tissue. Overall, the SC adipose tissue contained more ATDCs than OM adipose tissue, while OM adipose tissue contained more blood‐derived cells. Regarding to the inherent properties of fat cell progenitors from the two depots, adipose‐derived stem cells (ADSCs) from SC had higher capacity to differentiate into both adipogenic and osteogenic lineages than those from OM, regardless of that the proliferation rates of ADSCs from both depots were similar. The higher differentiation capacity of ADSCs from SC adipose tissue suggests that SC tissue is more suitable cell source for regenerative medicine than OM adipose tissue. Copyright © 2009 John Wiley & Sons, Ltd.     

Extracellular superoxide dismutase in tissues from obese (ob/ob) mice

We have examined the protein content and gene expression of three superoxide dismutase (SOD) isoenzymes in eight tissues from obese ob/ob mice, particularly placing the focus on extracellular-SOD (EC-SOD) in the white adipose tissue (WAT). Obesity significantly increased EC-SOD level in liver, kidney, testis, gastrocnemius muscle, WAT, brown adipose tissue (BAT), and plasma, but significantly decreased the isoenzyme level in lung. Tumor necrosis factor-α and interleukin-1β contents in WAT were significantly higher in obese mice than in lean control mice. Immunohistochemically, both WAT and BAT from obese mice could be stained deeply with anti-mouse EC-SOD antibody compared with those from lean mice. Each primary culture per se almost time-dependently enhanced EC-SOD production, and overtly expressed its mRNA. The loss of heparin-binding affinity of EC-SOD type C with high affinity for heparin occurred in kidney of obese mice. These results suggest that the physiological importance of this SOD isoenzyme in WAT may be a compensatory adaptation to oxidative stress.     

Fatty acid binding protein expression in different human adipose tissue depots in relation to rates of lipolysis and insulin concentration in obese individuals

Two fatty acid binding proteins (FABPs) are expressed in adipose tissue, adipocyte lipid binding protein (ALBP) and keratinocyte lipid binding protein (KLBP). This study investigated FABP expression in visceral and subcutaneous human adipose tissue depots and associations with lipolytic differences between the depots and circulating insulin concentrations. ALBP and KLBP (protein and RNA) were quantified in subcutaneous and omental adipose tissue from obese individuals and expressed relative to actin. ALBP RNA and protein expression was significantly higher in subcutaneous compared to omental adipose tissue (both p < 0.05), whereas KLBP RNA and protein expression was no different between the two sites. There were significant inverse correlations between serum insulin concentrations and the ALBP/KLBP RNA ratio in both subcutaneous and omental adipose tissue (both p < 0.02). Basal rates of glycerol and fatty acid release measured in adipocytes isolated from subcutaneous and omental adipose tissue were significantly higher in the former (p 0.02). Therefore the relative ALBP/KLBP content of human adipose tissue is different in different adipose tissue depots and at the RNA level is related to the circulating insulin concentration, at least in obese subjects. The higher rates of basal lipolysis in adipocytes isolated from subcutaneous compared to omental adipose tissue might be related to the increased ALBP content of the former. Therefore adipose tissue FABPs are interesting candidates for investigation to further our understanding of the insulin resistance syndrome and regulation of lipolysis.     

Adipocyte cellularity in different adipose depots in bulls of seven Spanish breeds slaughtered at two body weights

The influence of body weight (BW) at slaughter and genotype on adipocyte size and number in the omental (OM), perirenal (PR), subcutaneous (SC) and intermuscular (IM) adipose tissues was studied in 168 bulls of Spain's local Asturiana, Avileña, Morucha, Parda Alpina, Pirenaica, Retinta, and Rubia Gallega cattle breeds. The young bulls were slaughtered at two BWs, 320 and 540 kg. The results obtained showed the higher amounts of lipids that accumulated between 320 and 540 kg BW (P < 0.001) to be ascribable primarily to adipose cell hypertrophy, i.e. larger adipocyte size, in the OM and PR depots (P < 0.001). In addition to hypertrophy, there was also an increase (P < 0.001) in the number of adipose cells, i.e. hyperplasia, in the SC and IM adipose depots. Significant differences were observed when comparing the different genotypes, with the Morucha, Retinta and Avileña breeds having the highest amount of adipose tissue and the largest adipocytes. The Asturiana and Rubia Gallega breeds had the lowest amount of adipose tissue and the smallest adipocytes. The Pirenaica and Parda Alpina breeds had intermediate values in between the two groups identified above. In short, the results were indicative of different lipid deposition patterns in the different breeds depending on the individual growth and maturation rates in each. Similar findings were made when comparing the different adipose tissue depots, with adipocyte hypertrophy being the main factor responsible for lipid accumulation in the OM and PR depots, as opposed to adipocyte hyperplasia in the SC and IM depots.     

Maternal Obesity in Sheep Increases Fatty Acid Synthesis,Upregulates Nutrient Transporters,and Increases Adiposity in Adult Male Offspring after a Feeding Challenge

Maternal obesity in women is increasing worldwide. The objective of this study was to evaluate differences in adipose tissue metabolism and function in adult male offspring from obese and control fed mothers subjected to an ad libitum feeding challenge. We developed a model in which obese ewes were fed 150% of feed provided for controls from 60 days before mating to term. All ewes were fed to requirements during lactation. After weaning, F1 male offspring were fed only to maintenance requirements until adulthood (control = 7, obese = 6), when they were fed ad libitum for 12 weeks with intake monitored. At the end of the feeding challenge offspring were given an intravenous glucose tolerance test (IVGTT), necropsied, and adipose tissue collected. During the feeding trial F1obese males consumed more (P < 0.01), gained more weight (P < 0.01) and became heavier (P < 0.05) than F1control males. During IVGTT, Obese F1 offspring were hyperglycemic and hypoinsulinemic (P < 0.01) compared to F1 control F1. At necropsy perirenal and omental adipose depots weights were 47% and 58% greater respectively and subcutaneous fat thickness 41% greater in F1obese vs F1control males (P < 0.05). Adipocyte diameters were greater (P ≤ 0.04) in perirenal, omental and subcutaneous adipose depots in F1obese males (11, 8 and 7% increase vs. control, respectively). When adipose tissue was incubated for 2 hrs with C-14 labeled acetate, subcutaneous, perirenal, and omental adipose tissue of F1 obese males exhibited greater incorporation (290, 83, and 90% increase vs. control, respectively P < 0.05) of acetate into lipids. Expression of fatty acid transporting, binding, and syntheses mRNA and protein was increased (P < 0.05) compared to F1 control offspring. Maternal obesity increased appetite and adiposity associated with increased adipocyte diameters and increased fatty acid synthesis in over-nourished adult male offspring.