Serum amyloid A: a marker of adiposity-induced low-grade inflammation but not of metabolic status

Objective: Adipocytes secrete a series of acute phase proteins including serum amyloid A (SAA); the link with metabolic status is unknown. We studied the variations of expression of the SAA gene in adipose and liver tissues and of SAA serum levels, as well as their relationships with metabolic features during weight loss. Research Methods and Procedures: Plasmatic variations of SAA, inflammatory markers (high sensitivity C‐reactive protein, interleukin‐6, fibrinogen, and orosomucoid), and adipokines (adiponectin, leptin) were studied in 60 morbidly obese patients before and after gastric surgery. For 10 subjects, SAA mRNA expression was measured at baseline in subcutaneous white adipose tissue (scWAT) and visceral white adipose tissue (vWAT) and in the liver. The evolution of SAA mRNA expression was also studied after surgery in scWAT. Results: SAA serum concentration displayed a significant reduction 3 months after surgery and remained stable beyond 6 months. mRNA expression of inducible SAA isoforms (SAA 1 and 2) in scWAT was higher than in vWAT (p = 0.01) and the liver (p < 0.01) and correlated significantly with BMI, SAA, and high sensitivity C‐reactive protein serum concentrations but not with metabolic markers (glucose, insulin, lipid parameters, adiponectin). SAA serum level and its variation during weight loss significantly correlated with adiposity markers (BMI and adipocyte volume, p < 0.01) and inflammatory markers but not with variations of metabolic parameters. The variations of SAA expression in scWAT after surgery correlated with changes in BMI and SAA protein serum levels (p < 0.05). Discussion: SAA can be considered as a marker of adiposity‐induced low‐grade inflammation but not of the metabolic status of obese subjects.     

Increased plasma levels of adipokines in preeclampsia: relationship to placenta and adipose tissue gene expression

Adipokines are predominantly secretory protein hormones from adipose tissue but may also originate in placenta and other organs. Cross-sectionally, we monitored maternal plasma concentration of adiponectin, resistin, and leptin and their mRNA expression in abdominal subcutaneous adipose tissue and placenta from preeclamptic (PE; n = 15) and healthy pregnant (HP; n = 23) women undergoing caesarean section. The study groups were similar in age and BMI, whereas HOMA-IR tended to be higher in the PE group. In fasting plasma samples, the PE group had higher concentrations of adiponectin (18.3 +/- 2.2 vs. 12.2 +/- 1.1 microg/ml, P = 0.011), resistin (5.68 +/- 0.41 vs. 4.65 +/- 0.32 ng/ml, P = 0.028), and leptin (34.4 +/- 3.2 vs. 22.7 +/- 2.1 ng/ml, P = 0.003) compared with the HP group. Adiponectin and leptin concentrations were still different between PE and HP after controlling for BMI and HOMA-IR, whereas resistin concentrations differed only after controlling for BMI but not HOMA-IR. We found similar mean mRNA levels of adiponectin, resistin, and leptin in abdominal subcutaneous adipose tissue in PE and HP women. When data were pooled from PE and HP women, resistin mRNA levels in adipose tissue also correlated with HOMA-IR (r = 0.470, P = 0.012) after controlling for BMI and pregnancy duration. Resistin mRNA levels in placenta were not significantly different between PE and HP, whereas leptin mRNA levels were higher in PE placenta compared with HP. Thus increased plasma concentrations of adiponectin and resistin in preeclampsia may not relate to altered expression levels in adipose tissue and placenta, whereas both plasma and placenta mRNA levels of leptin are increased in preeclampsia.     

Effect of Lifestyle Modification on Adipokine Levels in Obese Subjects with Insulin Resistance

Objective: To study the effect of weight loss in response to a lifestyle modification program on the circulating levels of adipose tissue derived cytokines (adipokines) in obese individuals with insulin resistance. Research Methods and Procedures: Twenty‐four insulin‐resistant obese subjects with varying degrees of glucose tolerance completed a 6‐month program consisting of combined hypocaloric diet and moderate physical activity. Adipokines [leptin, adiponectin, resistin, tumor necrosis factor‐α (TNF‐α), interleukin‐6 (IL‐6)] and highly sensitive C‐reactive protein were measured before and after the intervention. Insulin sensitivity index was evaluated by the frequently sampled intravenous glucose tolerance test. Results: Participants had a 6.9 ± 0.1 kg average weight loss, with a significant improvement in sensitivity index and reduction in plasma leptin (27.8 ± 3 vs. 23.6 ± 3 ng/mL, p = 0.01) and IL‐6 (2.75 ± 1.51 vs. 2.3 ± 0.91 pg/mL, p = 0.012). TNF‐α levels tended to decrease (2.3 ± 0.2 vs. 1.9 ± 0.1 pg/mL, p = 0.059). Adiponectin increased significantly only among diabetic subjects. The reductions in leptin were correlated with the decreases in BMI (r = 0.464, p < 0.05) and with changes in highly sensitive C‐reactive protein (r = 0.466, p < 0.05). Discussion: Weight reduction in obese individuals with insulin resistance was associated with a significant decrease in leptin and IL‐6 and a tendency toward a decrease in circulating TNF‐α, whereas adiponectin was increased only in diabetic subjects. Further studies are needed to elucidate the relationship between changes of adipokines and the health benefits of weight loss.     

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.     

Fat Depot‐specific Impact of Visceral Obesity on Adipocyte Adiponectin Release in Women

Our objective was to examine omental and subcutaneous adipocyte adiponectin release in women. We tested the hypothesis that adiponectin release would be reduced to a greater extent in omental than in subcutaneous adipocytes of women with visceral obesity. Omental and subcutaneous adipose tissue samples were obtained from 52 women undergoing abdominal hysterectomies (age: 47.1 ± 4.8 years; BMI: 26.7 ± 4.7 kg/m²). Adipocytes were isolated and their adiponectin release in the medium was measured over 2 h. Measures of body fat accumulation and distribution were obtained using dual‐energy X‐ray absorptiometry and computed tomography, respectively. Adiponectin release by omental and subcutaneous adipocytes was similar in lean individuals; however, in subsamples of obese or visceral obese women, adiponectin release by omental adipocytes was significantly reduced while that of subcutaneous adipocytes was not affected. Omental adipocyte adiponectin release was significantly and negatively correlated with total body fat mass (r = ?0.47, P < 0.01), visceral adipose tissue area (r = ?0.50, P < 0.01), omental adipocyte diameter (r = ?0.43, P < 0.01), triglyceride levels (r = ?0.32, P ≤ 0.05), cholesterol/high‐density lipoprotein (HDL)‐cholesterol (r = ?0.31, P ≤ 0.05), fasting glucose (r = ?0.39, P ≤ 0.01), fasting insulin (r = ?0.36, P ≤ 0.05), homeostasis model assessment index (r = ?0.39, P ≤ 0.01), and positively associated with HDL‐cholesterol concentrations (r = 0.33, P ≤ 0.05). Adiponectin release from subcutaneous cells was not associated with any measure of adiposity, lipid profile, or glucose homeostasis. In conclusion, compared to subcutaneous adipocyte adiponectin release, omental adipocyte adiponectin release is reduced to a greater extent in visceral obese women and better predicts obesity‐associated metabolic abnormalities.     

Adipokines,Ghrelin and Obesity‐Associated Insulin Resistance in Nondiabetic Patients with Acute Coronary Syndrome

Altered glucose metabolism negatively modulates outcome in acute coronary syndromes (ACS). Insulin resistance is commonly associated with increasing BMI in the general population and these associations may involve obesity‐related changes in circulating ghrelin and adipokines. We aimed at investigating interactions between BMI, insulin resistance and ACS and their associations with plasma ghrelin and adipokine concentrations. Homeostasis model assessment of insulin resistance (HOMA_IR)‐insulin resistance index, plasma adiponectin, leptin, total (T‐Ghrelin), acylated (Acyl‐Ghrelin), and desacylated ghrelin (Desacyl‐Ghrelin) were measured in 60 nondiabetic ACS patients and 44 subjects without ACS matched for age, sex, and BMI. Compared with non‐ACS, ACS patients had similar HOMA_IR and plasma adipokines, but lower T‐ and Desacyl‐Ghrelin and higher Acyl‐Ghrelin. Obesity (BMI > 30) was associated with higher HOMA_IR, lower adiponectin, and higher leptin (P < 0.05) similarly in ACS and non‐ACS subjects. In ACS (n = 60) HOMA_IR remained associated negatively with adiponectin and positively with leptin independently of BMI and c‐reactive protein (CRP) (P < 0.05). On the other hand, low T‐ and Desacyl‐Ghrelin with high Acyl‐Ghrelin characterized both obese and non‐obese ACS patients and were not associated with HOMA_IR. In conclusion, in ACS patients, obesity and obesity‐related changes in plasma leptin and adiponectin are associated with and likely contribute to negatively modulate insulin resistance. ACS per se does not however enhance the negative impact of obesity on insulin sensitivity. High acylated and low desacylated ghrelin characterize ACS patients independently of obesity, but are not associated with insulin sensitivity.     

Extension of coronary artery disease is associated with increased IL-6 and decreased adiponectin gene expression in epicardial adipose tissue

Epicardial adipose tissue (EAT) expresses lower levels of adiponectin in patients with CAD and higher levels of inflammatory mediators such as IL-6 and leptin than subcutaneous adipose tissue. This showed one important role of EAT in coronary artery disease. However, the relationship of EAT adiponectin and IL-6 levels to the extension of coronary artery disease has not hitherto been determined. We sought to determine whether the levels of adiponectin and interleukin-6 (IL-6) mRNA in epicardial adipose tissue are associated with the extension of coronary artery disease (CAD). Methods: Angiographic and hormones expression were evaluated from epicardial and subcutaneous adipose tissue. 92 patients (58 CAD, 34 non-CAD) who underwent cardiac surgery. Adiponectin and IL-6 mRNA levels were measured by real time RT-PCR in epicardial and subcutaneous adipose tissue (SAT) following angiographic evaluation of their coronary arteries. Results: We found that epicardial adipose tissue of CAD expressed lower levels of adiponectin mRNA and higher levels of IL-6 mRNA than that of non-CAD patients. As the number of injured arteries rose, adiponectin mRNA levels decreased (r = −0.402, p < 0.001) and IL-6 mRNA increased (r = 0.514, p < 0.001) in epicardial adipose tissue. Conclusions: The extension of CAD is significantly associated with the expression of adiponectin and IL-6 mRNA in EAT. These findings suggest that low adiponectin and high IL-6 expression by EAT may contribute to CAD extension.     

Relationship between Plasma Adiponectin Levels and Metabolic Risk Profiles in Taiwanese Children

Objective: Adiponectin, a novel adipokine with antiinflammatory and insulin‐sensitizing properties, has an important role in glucose metabolism and is negatively correlated with body fat amount in adults. The purpose of this study was to evaluate the association of plasma adiponectin level with metabolic risk profiles and insulin resistance status among Taiwanese children. Research Methods and Procedures: We enrolled 1248 children (608 boys and 640 girls) to ascertain their demographic, anthropometric, and cardiovascular risk factors distribution in Taipei. We measured plasma insulin, adiponectin, and leptin levels by radioimmunoassay (Linco Research Inc, St. Charles, MO). We calculated an insulin resistance index (IRI) using the Homeostasis Model Assessment model and also calculated an insulin resistance syndrome (IRS) summary score for each individual by adding the quartile ranks from the distribution of systolic blood pressure, serum triglyceride, high‐density lipoprotein‐cholesterol (HDL‐C) (inverse), and insulin levels. Results: In general, the boys had larger BMI, higher systolic blood pressure, serum total cholesterol, and triglyceride, and lower plasma leptin and adiponectin levels than girls. Plasma adiponectin levels were correlated negatively with BMI, leptin, insulin, IRI, and IRS summary score but positively correlated with HDL‐C in both boys and girls. In multivariate regression analyses, adiponectin was negatively associated with insulin (girls only), IRI (girls only), and IRS score, and positively associated with HDL‐C in both genders even after adjusting for age, BMI, plasma leptin level, and other potential confounders. Discussion: These data suggest that plasma adiponectin levels were negatively associated with metabolic risk profiles that may have played a protective role in the development of insulin resistance among Taiwanese school children.     

Deep subcutaneous adipose tissue: a distinct abdominal adipose depot

Objective: Abdominal visceral (VAT) and subcutaneous adipose tissue (SAT) display significant metabolic differences, with VAT showing a functional association to metabolic/cardiovascular disorders. A third abdominal adipose layer, derived by the division of SAT and identified as deep subcutaneous adipose tissue (dSAT), may play a significant and independent metabolic role. The aim of this study was to evaluate depot‐specific differences in the expression of proteins key to adipocyte metabolism in a lean population to establish a potential physiologic role for dSAT. Research Methods and Procedures: Adipocytes and preadipocytes were isolated from whole biopsies taken from superficial SAT (sSAT), dSAT, and VAT samples obtained from 10 healthy normal weight patients (7 women and 3 men), with a mean age of 56.4 ± 4.04 years and a mean BMI of 23.1 ± 0.5 kg/m². Samples were evaluated for depot‐specific differences in insulin sensitivity using adiponectin, glucose transport protein 4 (GLUT4), and resistin mRNA and protein expression, glucocorticoid metabolism by 11β‐hydroxysteroid dehydrogenase type‐1 (11β‐HSD1) expression, and alterations in the adipokines leptin and tumor necrosis factor‐α (TNF‐α). Results: Although no regional differences in expression were observed for adiponectin or TNF‐α, dSAT whole biopsies and adipocytes, while intermediary to both sSAT and VAT, reflected more of the VAT expression profile of 11β‐HSD1, leptin, and resistin. Only in the case of the intracellular pool of GLUT4 proteins in whole biopsies was an independent pattern of expression observed for dSAT. In an evaluation of the homeostatic model, dSAT 11β‐HSD1 protein (r = 0.9573, p = 0.0002) and TNF‐α mRNA (r = 0.8210, p = 0.0236) correlated positively to the homeostatic model. Discussion: Overall, dSAT seems to be a distinct abdominal adipose depot supporting an independent metabolic function that may have a potential role in the development of obesity‐associated complications.     

The Yellow Agouti Mutation Alters Some But Not All Responses to Diet and Exercise

Objective: Effects of ectopic expression of the agouti signaling protein were studied on responses to diet restriction and exercise in C57BL/6J (B6) mice and obese B6 mice congenic for the yellow agouti mutation [B6.Cg‐A^y (A^y)]. Research Methods and Procedures: Adult male A^y mice were either kept sedentary or exercised on a running wheel and fed ad libitum or diet restricted until weight matched to ad libitum‐fed B6 control mice. Body composition, plasma lipids, leptin, and adiponectin were measured. mRNA levels for leptin, adiponectin, lipoprotein lipase, and pyruvate dehydrogenase kinase 4 were measured in a visceral (epididymal) and a subcutaneous (femoral) fat depot by real‐time polymerase chain reaction. Results: Correlations among traits exhibited one of three patterns: similar lines for B6 and A^y mice, different slopes for B6 and A^y mice, and/or different intercepts for B6 and A^y mice. Correlations involving plasma leptin, mesenteric and epididymal adipose weights, or low‐density lipoprotein‐cholesterol were most likely to have different slopes and/or intercepts in B6 and A^y mice. mRNA levels for leptin, Acrp30, pyruvate dehydrogenase kinase 4, and lipoprotein lipase in epididymal adipose tissue were not correlated with corresponding levels in femoral adipose tissue. Discussion: The agouti protein interferes with leptin signaling at melanocortin receptors in the hypothalamus of A^y mice. Our results are consistent with the hypothesis that the melanocortin portion of the leptin‐signaling pathway mediates effects primarily on certain fat depots and on some, but not all, components of cholesterol homeostasis.     

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.     

Adipose tissue interleukin-18 mRNA and plasma interleukin-18: effect of obesity and exercise

Objectives: Obesity and a physically inactive lifestyle are associated with increased risk of developing insulin resistance. The hypothesis that obesity is associated with increased adipose tissue (AT) interleukin (IL)‐18 mRNA expression and that AT IL‐18 mRNA expression is related to insulin resistance was tested. Furthermore, we speculated that acute exercise and exercise training would regulate AT IL‐18 mRNA expression. Research Methods and Procedures: Non‐obese subjects with BMI < 30 kg/m² (women: n = 18; men; n = 11) and obese subjects with BMI >30 kg/m² (women: n = 6; men: n = 7) participated in the study. Blood samples and abdominal subcutaneous AT biopsies were obtained at rest, immediately after an acute exercise bout, and at 2 hours or 10 hours of recovery. After 8 weeks of exercise training of the obese group, sampling was repeated 48 hours after the last training session. Results: AT IL‐18 mRNA content and plasma IL‐18 concentration were higher (p < 0.05) in the obese group than in the non‐obese group. AT IL‐18 mRNA content and plasma IL‐18 concentration was positively correlated (p < 0.05) with insulin resistance. While acute exercise did not affect IL‐18 mRNA expression at the studied time‐points, exercise training reduced AT IL‐18 mRNA content by 20% in both sexes. Discussion: Because obesity and insulin resistance were associated with elevated AT IL‐18 mRNA and plasma IL‐18 levels, the training‐induced lowering of AT IL‐18 mRNA content may contribute to the beneficial effects of regular physical activity with improved insulin sensitivity.     

Sexual Dimorphism and Regulation of Resistin,Adiponectin, and Leptin Expression in the Mouse

Objective: To examine gender differences and hormonal regulation of resistin, adiponectin, and leptin. Research Methods and Procedures: Plasma levels were measured, and mRNA expression in perigonadal fat was quantified by RNase protection assays. Results: Plasma resistin declined with age despite an increase in adiposity in both genders. In male mice, plasma leptin increased, whereas adiponectin levels were constant. In females, both adiponectin and leptin levels increased with age. Resistin mRNA levels were significantly higher in female than male mice at all ages, whereas leptin and adiponectin mRNA levels were similar in fat from 6‐week‐old male and female mice, and sexual dimorphism was apparent only in the older mice, with higher levels apparent in females. Castration did not abolish gender differences in plasma levels or resistin, adiponectin, or leptin mRNAs. Castration of male mice did not significantly change adipokine mRNA levels or plasma levels of resistin or leptin; however, adiponectin was significantly increased. Dihydrotestosterone treatment had no effect on adipokine mRNA expression or resistin and adiponectin levels but increased leptin levels. In contrast, ovariectomy significantly increased resistin mRNA abundance and decreased leptin and adiponectin mRNAs. Plasma leptin levels were also increased by ovariectomy, whereas resistin and adiponectin levels were unchanged. Estrogen replacement significantly reduced resistin mRNA and increased leptin and adiponectin mRNA levels but had no effect on plasma adipokine levels. Discussion: The gender differences in adipokine mRNA expression and plasma levels were not ablated by castration and seem to be dependent on other factors in addition to gonadal steroids.     

High Local Concentrations and Effects on Differentiation Implicate Interleukin‐6 as a Paracrine Regulator

Objective: To examine the possibility that interleukin‐6 (IL‐6) can act as a paracrine regulator in adipose tissue by examining effects on adipogenic genes and measuring interstitial IL‐6 concentrations in situ. Research Methods and Procedures: Circulating and interstitial IL‐6 concentrations in abdominal and femoral adipose tissue were measured using the calibrated microdialysis technique in 20 healthy male subjects. The effects of adipose cell enlargement on gene expression and IL‐6 secretion were examined, as well as the effect of IL‐6 in vitro on gene expression of adiponectin and other markers of adipocyte differentiation. Results: The IL‐6 concentration in the interstitial fluid was ～100‐fold higher than that in plasma, suggesting that IL‐6 may be a paracrine regulator of adipose tissue. This was further supported by the finding that adding IL‐6 in vitro at similar concentrations down‐regulated the expression of adiponectin, aP2, and PPARγ‐2 in cultured human adipose tissue. In addition, gene expression and release of IL‐6, both in vivo and in vitro, correlated with adipose cell size. Discussion: These data suggest that IL‐6 may be a paracrine regulator of adipose tissue. Furthermore, increased adipose tissue production of IL‐6 after hypertrophic enlargement of the adipose cells may detrimentally affect systemic insulin action by inducing adipose tissue dysfunction with impaired differentiation of the pre‐adipocytes and/or adipocytes and lower adiponectin.