Stearic acid content of abdominal adipose tissues in obese women

Objective:

Subcutaneous (SC) adipose tissue stearic acid (18:0) content and stearoyl-CoA desaturase-1 (SCD1)-mediated production of oleic acid (18:1) have been suggested to be altered in obesity. The objective of our study was to examine abdominal adipose tissue fatty acid content and SCD1 mRNA/protein level in women.

Subjects and methods:

Fatty acid content was determined by capillary gas chromatography in SC and omental (OM) fat tissues from two subgroups of 10 women with either small or large OM adipocytes. Samples from 10 additional women were used to measure SCD1 mRNA and protein expression, total extracellular signal-regulated kinase 1/2 (ERK1/2) and phosphorylated ERK1/2 protein as well as insulin receptor (IR) expression levels.

Results:

OM fat 18:0 content was significantly lower in women with large OM adipocytes compared with women who had similar adiposity, but small OM adipocytes (2.37±0.45 vs 2.75±0.30 mg per 100 g adipose tissue, respectively, P⩽0.05). OM fat 18:0 content was negatively related to the visceral adipose tissue area (r=−0.44, P=0.05) and serum triglyceride levels (r=−0.56, P<0.05), while SC fat 18:0 content was negatively correlated with total body fat mass (BFM) (r=−0.48, P<0.05) and fasting insulin concentration (r=−0.73, P<0.005). SC adipose tissue desaturation index (18:1/18:0), SCD1 expression and protein levels were positively correlated with BFM. Moreover, obese women were characterized by a reduced OM/SC ratio of SCD1 mRNA and protein levels. A similar pattern was observed for ERK1/2 and IR expression.

Conclusion:

The presence of large adipocytes and increased adipose mass in a given fat compartment is related to reduced 18:0 content and increased desaturation index in women, independently of dietary fat intake. The depot-specific difference in ERK1/2 expression and activation, as well as in SCD1 and IR expression in obese women is consistent with the hypothesis that they may predominantly develop SC fat, which could in turn help protect from metabolic disorders.     

Depot-specific messenger RNA expression of 11 beta-hydroxysteroid dehydrogenase type 1 and leptin in adipose tissue of children and adults

OBJECTIVE: To compare expression of messenger RNA (mRNA) coding for the cortisol regenerating enzyme 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1), and the adipocytokines leptin and resistin in paired biopsies of subcutaneous adipose tissue (SC) and omental adipose tissue (OM) from children. DESIGN: Paired biopsies (SC and OM) were obtained from 54 children (age 0.17-16 years, body mass index (BMI) 12.5-28.3 kg/m(2), BMI standard deviation score (SDS) -2.5-4.5) and 16 adults (age 27-79 years, BMI 19-46 kg/m(2)) undergoing open abdominal surgery. mRNA levels of 11beta-HSD1, leptin and resistin were measured using quantitative real-time polymerase chain reaction (PCR). RESULTS: 11beta-HSD1 mRNA level was higher in OM than in SC (P<0.05), whereas leptin mRNA was higher in SC than in OM (P<0.001). There was no difference in the resistin mRNA level between SC and OM. These results were consistent in children and adults. In children, 11beta-HSD1 mRNA in SC was positively associated with BMI SDS (P<0.05), whereas in OM it was positively associated with age (P<0.05). The association between 11beta-HSD1 expression and age remained significant after adjustment for BMI SDS and gender. Leptin mRNA was positively associated with BMI SDS (SC: P<0.001, OM: P<0.001) but not with age in children. In multiple regression analyses, including anthropometric variables and age, BMI SDS was independently associated with mRNA levels of 11beta-HSD1 (P<0.05) and leptin (P<0.001) in SC. When normal weight and overweight children were analyzed separately, 11beta-HSD1 mRNA levels were positively associated with leptin in OM in the overweight group (P<0.05). CONCLUSION: There are depot-specific differences in mRNA levels of 11beta-HSD1 and leptin in children and adults. The positive association of 11beta-HSD1 mRNA in OM with age may reflect a causal role in visceral fat accumulation during growth. Increasing 11beta-HSD1 and leptin mRNA in SC with increasing BMI SDS could suggest that the risk of metabolic consequences of obesity may be established early in life.     

Glucose transporter 4 and insulin receptor substrate-1 messenger RNA expression in omental and subcutaneous adipose tissue in women

Insulin receptor substrate-1 (IRS-1) and glucose transporter 4 (GLUT4) expression may provide an indirect reflection of the capacity of adipocytes to respond to insulin stimulation. We examined messenger RNA (mRNA) expression of these genes in omental and subcutaneous adipose tissue of women. Paired omental and subcutaneous adipose tissue samples were obtained from 36 women (age, 47 ± 5 years; body mass index, 28.0 ± 5.4 kg/m²) undergoing gynecologic surgeries. Total adiposity and visceral adiposity were assessed by dual-energy x-ray absorptiometry and computed tomography. The GLUT4 and IRS-1 mRNA expression levels were both significantly higher in subcutaneous compared with omental adipose tissue. A negative correlation was observed between body fat percentage and subcutaneous adipose tissue GLUT4 (r = −0.39, P < .05) and IRS-1 (r = −0.30, P < .08) mRNA abundance. However, in omental fat, only GLUT4 mRNA was inversely associated with body fat percentage (r = −0.53, P < .001). Moreover, the homeostasis model assessment of insulin resistance index was associated with mRNA expression of subcutaneous GLUT4 (r = −0.56, P < .001), subcutaneous IRS-1 (r = −0.51, P < .01), and omental GLUT4 (r = −0.54, P < .001), but not omental IRS-1. Interestingly, plasma adiponectin was only associated with subcutaneous GLUT4 (r = 0.48, P < .01) and IRS-1 (r = 0.48, P < .05) mRNA expression. The GLUT4 protein, unlike mRNA expression, was higher in omental than in subcutaneous adipose tissue. However, abdominal obesity-related differences in protein or mRNA expression were similar. Omental IRS-1 expression was low and unaffected by visceral obesity. In contrast, omental and subcutaneous GLUT4 as well as subcutaneous IRS-1 were reduced in visceral obesity. This divergent pattern of expression may reflect a lower capacity of omental adipose tissue to respond to insulin stimulation at all adiposity levels.     

Expression and activity of 20alpha-hydroxysteroid dehydrogenase (AKR1C1) in abdominal subcutaneous and omental adipose tissue in women

We examined the expression and activity of 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD) in abdominal adipose tissue in women. This recently characterized enzyme from the aldoketoreductase 1C family is responsible for the conversion of progesterone into 20alpha-hydroxyprogesterone. Abdominal sc (SC) and omental (OM) adipose tissue biopsies were obtained from a sample of 32 women aged 47.7 +/- 5.9 yr (body mass index 27.6 +/- 5.0 kg/m(2)) undergoing abdominal hysterectomies. Body composition and body fat distribution measurements were performed before the surgery by dual-energy x-ray absorptiometry and computed tomography, respectively. The expression of 20alpha-HSD was determined by real-time RT-PCR, and its activity was measured in whole-tissue homogenates. mRNA and activity of the enzyme were detected in both the SC and OM fat depots, the two measures being significantly higher in the SC compartment. Women characterized by a visceral adipose tissue area of 100 cm(2) or greater had an increased 20alpha-HSD conversion rate in their OM adipose tissue, compared with women without visceral obesity (13.99 +/- 2.07 vs. 7.92 +/- 0.83 fmol/microg protein per 24 h, P < 0.05). Accordingly, a positive correlation was found between OM adipose tissue 20alpha-HSD activity and computed tomography-measured visceral adipose tissue area (r = 0.36, P < 0.05). Significant positive correlations were also found between OM 20alpha-HSD activity and OM adipocyte diameter (r = 0.49, P < 0.05) and OM adipose tissue LPL activity (r = 0.36, P = 0.06). In conclusion, 20alpha-HSD activity and mRNA were detected in SC and OM adipose tissue in women, and OM 20alpha-hydroxylation of progesterone was highest in women with visceral obesity. Additional studies are required to establish whether local conversion of progesterone may impact on the metabolism and function of adipocytes located within the abdominal cavity.     

The relationship of visfatin/pre-B-cell colony-enhancing factor/nicotinamide phosphoribosyltransferase in adipose tissue with inflammation, insulin resistance, and plasma lipids

Visfatin/pre-B-cell colony-enhancing factor (PBEF)/nicotinamide phosphoribosyltransferase (Nampt) has been proposed as an insulin-mimicking adipocytokine predominantly secreted from visceral adipose tissue (VAT) and correlated with obesity. However, recent evidence challenged this proposal and instead suggested visfatin/PBEF/Nampt as a proinflammatory cytokine. The study aimed to examine whether visfatin/PBEF/Nampt was predominantly expressed in VAT and was correlated with obesity. The relationship of visfatin/PBEF/Nampt gene expression in adipose tissues with proinflammatory gene expression and metabolic phenotypes was also examined. The relative messenger RNA (mRNA) levels of visfatin/PBEF/Nampt, macrophage-specific marker CD68, and proinflammatory genes were measured in paired abdominal VAT and subcutaneous adipose tissues (SAT) and from 53 nondiabetic adults using quantitative real-time polymerase chain reaction. Fasting glucose, insulin, triglyceride, cholesterol, and uric acid levels were measured; and systemic insulin sensitivity was quantified with modified insulin suppression tests. There was no difference in visfatin/PBEF/Nampt mRNA levels between VAT and SAT, and neither was associated with measures of obesity. Visfatin/PBEF/Nampt mRNA levels were strongly correlated with proinflammatory gene expression including CD68 and tumor necrosis factor-α gene in both VAT and SAT. The VAT and SAT visfatin/PBEF/Nampt mRNA expressions were positively correlated with steady-state plasma glucose concentrations measured with modified insulin suppression tests, a direct measurement of systemic insulin resistance (r = 0.42, P = .03 and r = 0.44, P = .03, respectively). The VAT visfatin/PBEF/Nampt mRNA expression was also positively correlated with fasting triglyceride (r = 0.42, P = .002) and total cholesterol levels (r = 0.37, P = .009). Visfatin/PBEF/Nampt is not predominantly secreted from VAT and is not correlated with obesity. Our findings suggest that visfatin/PBEF/Nampt is a proinflammatory marker of adipose tissue associated with systemic insulin resistance and hyperlipidemia.     

Alterations in cyclic nucleotide phosphodiesterase activities in omental and subcutaneous adipose tissues in human obesity

Objective: To elucidate the activity and expression of cyclic nucleotide phosphodiesterase (PDE) families in omental (OM) and subcutaneous (SC) adipose tissue and adipocytes, and to study alterations in their activity in human obesity.Design: Cross-sectional, translational research study.Patients: In total, 25 obese and 9 non-obese subjects undergoing gastrointestinal surgery participated in the study.Results: Inverse correlations between PDE activities and body mass index (BMI) were seen in both SC and OM adipose tissue. Inverse correlations between total PDE and PDE3 activity and BMI were seen in OM adipocytes but not in SC adipocytes. In both SC and OM adipose tissue of obese patients, total PDE and PDE3 activities were decreased compared with the controls. In SC adipose tissue of Type 2 diabetes (T2D) patients, the PDE activity not inhibitable by PDE3 or PDE4 inhibitors (PDEn) was increased compared with obese non-diabetic patients. In addition to PDE3 and 4 isoforms, PDE7B, PDE9A and PDE10A proteins were also detected in adipose tissue or adipocytes.Conclusions: Multiple PDE families are present in human adipose tissue and their activities are differentially affected by obesity and T2D.     

17β-hydroxysteroid dehydrogenase type 2 activity,expression and cellular localization in abdominal adipose tissues from women

Context : 17β-hydroxysteroid dehydrogenase type 2 (17β-HSD2) may be involved in the local modulation of estradiol (E2) availability in adipose tissues. Objective: To assess the conversion of E2 into estrone (E1) as well as the expression of 17β-HSD2 and its localization in omental (OM) and subcutaneous (SC) adipose tissues obtained from women. Methods: Rates of ¹⁴C-E1 formation from ¹⁴C-E2 were measured in OM and SC adipose tissue homogenates from 29 women. Specific 17β-HSD2 inhibitor EM-919 was tested in OM and SC adipose tissue homogenates (n = 6). 17β-HSD2 mRNA expression was measured in whole OM and SC adipose tissues (n = 14). Cellular localization of the enzyme was examined using immunohistochemistry. Anthropometric measurements were obtained and body composition as well as body fat distribution were measured. Results: Significant ¹⁴C-E1 formation from ¹⁴C-E2 in OM and SC tissue homogenates was detected. The rate of ¹⁴C-E1 formation was significantly higher in OM than SC adipose tissue (p < .0001). The conversion of ¹⁴C-E2 to ¹⁴C-E1 was significantly inhibited by EM-919 in OM (p < .05) and SC (p < .05) adipose tissues. Significantly higher expression of 17β-HSD2 mRNA in OM versus SC fat was found (p = .03). 17β-HSD2 was localized in the vasculature of OM and SC tissues. Significant negative associations were detected between OM 17β-HSD2 activity and body mass index, WC, lean body mass as well as SC adipose tissue areas. Conclusion: 17β-HSD2 converts E2 to E1 in OM and SC adipose tissues of women. The activity of this enzyme decreases with increasing adiposity.     

Altered pattern of cannabinoid type 1 receptor expression in adipose tissue of dysmetabolic and overweight patients

In overweight patients (OW), the increased peripheral activity of the endocannabinoid system in visceral adipose tissue (VAT) may be mediated by cannabinoid type 1 (CB1) receptor expression. We determined whether CB1 receptor splice variants and messenger RNA (mRNA) levels in perirenal and subcutaneous adipose tissues are associated with obesity and metabolic syndrome (MetS). Gene expression with multiple-primers real-time polymerase chain reaction (TaqMan; Applied Biosystem, Weiterstadt, Germany) was performed to study VAT and paired subcutaneous adipose tissue (SAT) mRNA from 36 consecutive patients undergoing nephrectomy. Cannabinoid type 1A and CB1E mRNAs variants with the longer version of exon 4 were expressed. The CB1 expression in perirenal VAT significantly correlated with body mass index (BMI). Paired subcutaneous/perirenal samples from normal-weight patients (BMI <25 kg/m²) showed higher CB1 expression in SAT (P = .002), whereas in OW (BMI ≥25 kg/m²), the higher CB1 expression was in VAT (P = .038). In unpaired samples, SAT of normal-weight patients had significantly higher CB1 mRNA levels compared with SAT of OW, whereas higher CB1 expression (P = .009) was found in VAT of OW (n = 25). Overweight patients with increased visceral CB1 expression had higher waist circumference (P < .01), insulin (P < .01), and homeostasis model assessment index (P < .01). In addition, patients with the MetS (n = 22) showed higher CB1 expression in perirenal adipose tissues (P = .007). Visceral adipose CB1 expression correlated with BMI. Overweight patients and those with MetS showed a CB1 expression pattern supporting a CB1-mediated overactivity of the endocannabinoid system in human VAT.     

Characterisation of 11beta-hydroxysteroid dehydrogenase 1 in human orbital adipose tissue: a comparison with subcutaneous and omental fat

Glucocorticoids (GCs) have a profound effect on adipose biology increasing tissue mass causing central obesity. The pre-receptor regulation of GCs by 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) that activates cortisol from cortisone has been postulated as a fundamental mechanism underlying the metabolic syndrome mediating adipocyte hyperplasia and hypertrophy in the omental (OM) depot. Orbital adipose tissue (OF) is the site of intense inflammation and tissue remodelling in several orbital inflammatory disease states. In this study, we describe features of the GC metabolic pathways in normal human OF depot and compare it with subcutaneous (SC) and OM depots. Using an automated histological characterisation technique, OF adipocytes were found to be significantly smaller (parameters: area, maximum diameter and perimeter) than OM and SC adipocytes (P<0 x 001). Although immunohistochemical analyses demonstrated resident CD68+ cells in all three whole tissue adipose depots, OF CD68 mRNA and protein expression exceeded that of OM and SC (mRNA, P<0 x 05; protein, P<0 x 001). In addition, there was higher expression of glucocorticoid receptor (GR)alpha mRNA in the OF whole tissue depot (P<0 x 05). Conversely, 11beta-HSD1 mRNA together with the markers of late adipocyte differentiation (FABP4 and G3PDH) were significantly lower in OF. Primary cultures of OF preadipocytes demonstrated predominant 11beta-HSD1 oxo-reductase activity with minimal dehydrogenase activity. Orbital adipocytes are smaller, less differentiated, and express low levels of 11beta-HSD1 but abundant GRalpha compared with SC and OM. OF harbours a large CD68+ population. These characteristics define an orbital microenvironment that has the potential to respond to sight-threatening orbital inflammatory disease.     

Effects of weight loss and exercise on chemerin serum concentrations and adipose tissue expression in human obesity

Chemerin is a chemoattractant adipokine that regulates adipogenesis and may induce insulin resistance. Chemerin serum concentrations are elevated in obese, insulin-resistant, and inflammatory states in vivo. Here we investigate the role of omental (OM) and subcutaneous (SC) adipose tissue chemerin and CMKLR1 messenger RNA (mRNA) expression in human obesity. In addition, we test the hypothesis that changes in chemerin serum concentrations are primarily associated with reduced body fat mass in the context of 3 weight loss intervention studies. Chemerin serum concentration was measured in 740 individuals in a cross-sectional (n = 629) study including a subgroup (n = 161) for which OM and SC chemerin mRNA expression has been analyzed as well as in 3 interventions including 12 weeks of exercise (n = 60), 6 months of calorie-restricted diet (n = 19) studies, and 12 months after bariatric surgery (n = 32). Chemerin mRNA is significantly higher expressed in adipose tissue of patients with type 2 diabetes mellitus and correlates with circulating chemerin, body mass index (BMI), percentage body fat, C-reactive protein, homeostasis model assessment of insulin resistance, and glucose infusion rate in euglycemic-hyperinsulinemic clamps. CMKLR1 mRNA expression was not significantly different between the 2 fat depots. Obesity surgery-induced weight loss causes a significant reduction on both OM and SC chemerin expression. All interventions led to significantly reduced chemerin serum concentrations. Decreased chemerin serum concentrations significantly correlate with improved glucose infusion rate and reduced C-reactive protein levels independently of changes in BMI. Insulin resistance and inflammation are BMI-independent predictors of elevated chemerin serum concentrations. Reduced chemerin expression and serum concentration may contribute to improved insulin sensitivity and subclinical inflammation beyond significant weight loss.     

Expression of adrenomedullin in adipose tissue of lean and obese women

OBJECTIVE: Adrenomedullin (AM), a potent vasodilatator and antioxidative peptide, was shown recently to be expressed by adipose tissue. The aim of our study was to investigate the precise localization of AM within human adipose tissue, and to examine AM regulation in obesity. DESIGN: Subcutaneous (SC) and omental (OM) adipose tissues from 9 lean and 13 obese women were profiled for AM expression changes. Preadipocytes from human adipose tissue were isolated and differentiated under defined adipogenic conditions. METHODS: AM expression was analyzed by immunohistochemistry, in situ hybridization and quantitative RT-PCR. RESULTS: A strong AM expression was observed in vessel walls, stromal cell clusters and isolated stromal cells, some of them being CD 68 positive, whereas mature adipocytes were not labeled. Calcitonin receptor-like receptor and receptor activity-modifying proteins (RAMP) 2 and RAMP 3 were expressed in vessel walls. In vitro, preadipocytes of early differentiation stages spontaneously secreted AM. No difference in AM localization was found between SC and OM adipose tissue. AM levels in SC tissue did not differ between lean and obese subjects. By contrast, AM levels in OM tissue were significantly higher in obese as compared with lean women. Moreover, we found a positive relationship between OM AM and tumor necrosis factor alpha mRNA levels and AM-immunoreactive area in OM tissue followed the features of the metabolic syndrome. CONCLUSION: Stromal cells from human adipose tissue, including macrophages, produce AM. Its synthesis increased in the OM territory during obesity and paralleled the features of the metabolic syndrome. Therefore, AM should be considered as a new member of the adipokine family.     

Adipose triglyceride lipase expression in human adipose tissue and muscle. Role in insulin resistance and response to training and pioglitazone

Adipose triglyceride lipase (ATGL) catalyzes the first step in adipocyte and muscle triglyceride hydrolysis, and comparative gene identification-58 (CGI-58) is an essential cofactor. We studied the expression of ATGL and CGI-58 in human adipose and muscle and examined correlations with markers of muscle fatty acid oxidation. Nondiabetic volunteers were studied. Subjects with impaired glucose tolerance were treated with pioglitazone or metformin for 10 weeks. Subjects with normal glucose tolerance underwent a 12-week training program. We examined changes in ATGL and CGI-58 with obesity and insulin resistance, and effects of exercise and pioglitazone. Adipose triglyceride lipase messenger RNA (mRNA) expression showed no correlation with either body mass index or insulin sensitivity index in either adipose or muscle. However, adipose ATGL protein levels were inversely correlated with body mass index (r = −0.64, P < .02) and positively correlated with insulin sensitivity index (r = 0.67, P < .02). In muscle, ATGL mRNA demonstrated a strong positive relationship with carnitine palmitoyltransferase I mRNA (r = 0.82, P < .0001) and the adiponectin receptors AdipoR1 mRNA (r = 0.71, P < .0001) and AdipoR2 mRNA (r = 0.74, P < .0001). Muscle CGI-58 mRNA was inversely correlated with intramyocellular triglyceride in both type 1 (r = −0.35, P < .05) and type 2 (r = −0.40, P < .05) fibers. Exercise training resulted in increased muscle ATGL, and pioglitazone increased adipose ATGL by 31% (P < .05). Pioglitazone also increased ATGL in adipocytes. Adipose ATGL protein is decreased with insulin resistance and obesity; and muscle ATGL mRNA is associated with markers of fatty acid oxidation in muscle, as is CGI-58. The regulation of ATGL and CGI-58 has important implications for the control of lipotoxicity.     

Reduced adipsin expression in murine obesity: effect of age and treatment with the sympathomimetic-thermogenic drug mixture ephedrine and caffeine

Adipsin gene expression is greatly diminished in certain forms of genetic and acquired obesity. In the present study we evaluate the time course for the development of adipsin deficiency in obesity and its regulation by the sympathomimetic-thermogenic drug mixture ephedrine and caffeine. Previously, it was unknown whether adipsin deficiency occurred before or after the development of massive obesity. In the first series of experiments in which mice were treated with monosodium glutamate (MSG) for the first week of life, we demonstrate that adipsin deficiency occurs early in the development of MSG-induced obesity as evidenced by decreased circulating adipsin concentrations by 1 week of age and deficient adipsin mRNA levels in white adipose tissue (WAT) by 2 weeks. In db/db mice, diminished circulating adipsin was noted at 2 weeks of age. In both models, decreased adipsin gene expression precedes the development of marked obesity. Little is known about the factors which regulate adipsin gene expression in obesity. Common to the ob/ob, db/db and MSG models is diminished thermogenesis and sympathetic nervous system activity. In a second series of experiments we sought to determine whether adipsin deficiency in obesity could be corrected by treatment with ephedrine and caffeine (E+C), a sympathomimetic-thermogenic mixture previously shown to increase thermogenesis and reverse obesity in some models. In the present study, E+C treatment of MSG obese mice reversed obesity and markedly increased serum adipsin and adipsin mRNA levels in WAT and brown adipose tissue (BAT). In ob/ob mice, however, E+C treatment produced a negligible increase in adipsin mRNA levels in WAT and BAT as well as serum adipsin concentrations and this correlated with only a very small decrease in obesity. Thus, the ability of E+C to increase adipsin gene expression correlated with its ability to reverse obesity in these two models. Finally, the effect of E+C on adipsin gene expression may not be exerted directly on the fat cell since treatment of cultured 3T3-F442A adipocytes and isolated rat adipocytes in primary culture produced no effect on adipsin mRNA or secreted protein despite a lipolytic effect as measured by increased glycerol release. In summary, decreased adipsin gene expression occurs early in the development of MSG and db/db obesity and is markedly increased in the MSG model by the sympathomimetic-thermogenic drug mixture, E+C, which also reverses obesity. Elucidation of the factors responsible for these effects may enhance our understanding of fat cell gene regulation and obesity.     

Type I iodothyronine 5'-deiodinase mRNA and activity is increased in adipose tissue of obese subjects

Differentiation and metabolism of adipose tissue are modulated by thyroid hormones (THs), but relatively little is known about the metabolism of THs in this tissue. Expression of the genes for type I iodothyronine 5'-deiodinase (D1), leptin (LEP) and stearoyl-CoA desaturase 1 (SCD-1) was evaluated in omental (OM) and subcutaneous (SC) fat using a cohort of 70 humans. Activities of iodothyronine deiodinases (D1, D2 and D3) were assessed in a randomly selected subpopulation of 19 subjects. D1 expression was upregulated in both OM (P=0.011) and SC (P=0.003) fat of obese subjects. Concomitantly, OM (P=0.002) and SC (P=0.028) LEP expression were increased in obesity, associated with both D1 mRNA (r=0.315, P=0.014) and activity (r=0.647, P=0.023) and inversely related to SCD-1 (r=-0.266, P=0.034) expression in SC fat. Also D1 (but not D2 and D3) activity was increased in OM (～fourfold, P=0.010) and SC (～eightfold, P=0.004) fat of obese when compared with non-obese subjects and correlated in both OM (r=0.528, P=0.036) and SC (r=0.749, P=0.005) fat with body mass index. Our results document increased D1 gene expression and activity in adipose tissue of obese humans and suggest a role of 3,5,3'-triiodo-L-thyronine formed by D1 in response to leptin in the modulation of adipose tissue metabolism.     

The adipokine zinc‐α2‐glycoprotein (ZAG) is downregulated with fat mass expansion in obesity

Introduction Zinc‐α2‐glycoprotein (ZAG) is a novel adipokine, which may act locally to influence adipocyte metabolism. This study assessed the effect of increased adiposity on ZAG expression in adipose tissue in human subjects. The study also examined the association between ZAG and adiponectin expression in human adipose tissue, and whether ZAG modulates adiponectin secretion by human adipocytes. Methods Adipose tissue (visceral and subcutaneous) was collected from human subjects with a wide range of BMIs. Human Simpson‐Golabi‐Behmel syndrome (SGBS) adipocytes were used for in vitro studies. ZAG mRNA levels were quantified by real‐time PCR and protein by Western blotting. Results In human subjects, ZAG mRNA level was negatively correlated with BMI (r = ?0·61, P < 0·001, n = 23, visceral; r = ?0·6, P < 0·05, n = 14, subcutaneous) and fat mass (r = ?0·62, P < 0·01, visceral; r = ?0·6, P < 0·05, subcutaneous). Negative associations were also found between ZAG mRNA and insulin resistance parameters including plasma insulin (r = ?0·65, P < 0·001, visceral; r = ?0·55, P < 0·05, subcutaneous) and homeostasis model of insulin resistance (HOMA‐IR) (r = ?0·65, P < 0·001, visceral; r = ?0·52, P = 0·055, subcutaneous), and C reactive protein (CRP) (r = ?0·46, P < 0·05, visceral; r = ?0·53, P < 0·05, subcutaneous). However, ZAG mRNA was positively correlated with adiponectin (r = 0·5, P < 0·05, visceral; r = 0·82, P < 0·001, subcutaneous) but negatively associated with leptin mRNA (r = ?0·42, P < 0·05, visceral; r = ?0·54, P < 0·05, subcutaneous). ZAG secretion by differentiated human adipocytes was abundant. Addition of recombinant ZAG stimulated adiponectin release from human adipocytes. Conclusion ZAG gene expression in adipose tissue is downregulated with increased adiposity and circulating insulin. ZAG mRNA is positively correlated with adiponectin mRNA, and ZAG enhances adiponectin production by human adipocytes. We suggest that ZAG is linked to obesity and obesity‐related insulin resistance.     

Adipose tissue secretion of plasminogen activator inhibitor-1 in non-obese and obese individuals

Summary High plasma plasminogen activator inhibitor-1 (PAI-1) activity is a frequent finding in obesity, and both PAI-1 and obesity are risk factors for cardiovascular disease. To study the mechanisms underlying increased PAI-1 levels in obese individuals, gene expression and secretion of PAI-1 were measured in human abdominal subcutaneous adipose tissue. A total of 32 obese, otherwise healthy subjects and 10 never-obese healthy subjects with a body mass index (BMI) of 42.6 ± 1.2 and 24.3 ± 1.9 kg/m² (mean ± SEM), respectively, were investigated. Plasma PAI-1 activity, adipose tissue PAI-1 secretion and adipocyte PAI-1 mRNA levels were increased sevenfold (p < 0.0001), sixfold (p < 0.0001) and twofold (p < 0.05), respectively, in the obese group. There were clear associations between adipose tissue secretion of PAI-1 and PAI-1 mRNA levels on the one hand and fat cell volume on the other (r = 0.68, p < 0.0001 and r = 0.51, p < 0.01, respectively, in the obese group). PAI-1 mRNA levels were also related to the amount of PAI-1 secreted among obese individuals (r = 0.31, p = 0.09). It is concluded that adipose tissue secretes significant amounts of PAI-1, that PAI-1 secretion from adipose tissue is increased in obesity, and that PAI-1 secretion is related to the lipid content and cell volume of fat cells. Plasma PAI-1 activity is elevated in obesity, at least in part due to increased gene expression in adipocytes, which, in turn, enhances PAI-1 secretion from adipose tissue. [Diabetologia (1998) 41: 65–71] Received: 26 May 1997 and in revised form: 12 August 1997     

Modulation of angiogenesis during adipose tissue development in murine models of obesity

Development of vasculature and mRNA expression of 17 pro- or antiangiogenic factors were studied during adipose tissue development in nutritionally induced or genetically determined murine obesity models. Subcutaneous (SC) and gonadal (GON) fat pads were harvested from male C57Bl/6 mice kept on standard chow [standard fat diet (SFD)] or on high-fat diet for 0-15 wk and from male ob/ob mice kept on SFD. Ob/ob mice and C57Bl/6 mice on high-fat diet had significantly larger SC and GON fat pads, accompanied by significantly higher blood content, increased total blood vessel volume, and higher number of proliferating cells. mRNA and protein levels of angiopoietin (Ang)-1 were down-regulated, whereas those of thrombospondin-1 were up-regulated in developing adipose tissue in both obesity models. Ang-1 mRNA levels correlated negatively with adipose tissue weight in the early phase of nutritionally induced obesity as well as in genetically determined obesity. Placental growth factor and Ang-2 expression were increased in SC adipose tissue of ob/ob mice, and thrombospondin-2 was increased in both their SC and GON fat pads. mRNA levels of vascular endothelial growth factor (VEGF)-A isoforms VEGF-B, VEGF-C, VEGF receptor-1, -2, and -3, and neuropilin-1 were not markedly modulated by obesity. This modulation of angiogenic factors during development of adipose tissue supports their important functional role in obesity.     

The relationship between fat depot-specific preadipocyte differentiation and metabolic syndrome in obese women

Objective Obesity is strongly associated with metabolic syndrome, but not all obese individuals display a clustering of metabolic risk factors. Recent studies have shown that in vitro subcutaneous (SC)‐preadipocyte differentiation is negatively associated with obesity. These results suggest that impaired adipogenesis is an important factor linking obesity to metabolic disorders. We examined whether in vitro preadipocyte differentiation is associated with metabolic syndrome, independent of obesity. Design/patients/measurements Paired adipose tissue samples were obtained from the 13 nonobese women and the 65 obese women. The CD34⁺/CD31^? cells were isolated from the stromal‐vascular fraction of both SC and omental (OM) fat depots by immune magnetic separation, and the subset was cultured with a differentiation cocktail. Then, we analysed the relationship between the degree of preadipocyte differentiation and metabolic factors. Results Obese women without metabolic syndrome (n = 37) had significantly higher SC‐preadipocyte differentiation than equally obese women with metabolic syndrome (n = 28); however, OM‐preadipocyte differentiation was similar in both groups. SC‐preadipocyte differentiation was strongly correlated with triglycerides, HDL cholesterol, homoeostasis model assessment of insulin resistance and OM‐adipocyte size. However, OM‐preadipocyte differentiation was not correlated with any of these parameters. Conclusions This study identified that SC‐preadipocyte differentiation is associated with metabolic syndrome independent of obesity, whereas OM‐preadipocyte differentiation is not. These findings suggest that, in the setting of obesity, an enhanced adipogenic capacity of SC depots could be protective for metabolic syndrome. Our data underscores an interaction between adipose tissue homoeostasis and metabolic disorder.