Maternal serum adiponectin multimers in patients with a small-for-gestational-age newborn

OBJECTIVE

Several mechanisms of disease have been implicated in the pathophysiology of small-for-gestational-age (SGA) including an anti-angiogenic state, and an exaggerated intravascular pro-inflammatory response. Adiponectin plays a role in a wide range of biological activities including those that have been implicated in the pathophysiology SGA. Thus, the aim of this study was to determine if third trimester adiponectin concentrations differed between women with normal weight infants and those with an SGA neonate.

STUDY DESIGN

This cross-sectional study included women with: 1) a normal pregnancy (n=234); and 2) an SGA neonate (n=78). SGA was defined as a birth weight below the 10th percentile for gestational age at birth. The study population was further stratified by first trimester body mass index (BMI) (normal weight <25 kg/m(2) vs. overweight/obese > or =25 kg/m(2)). Maternal serum adiponectin multimers [total, high-molecular-weight (HMW), medium-molecular-weight (MMW) and low-molecular-weight (LMW)] concentrations were determined by ELISA. Non-parametric statistics were used for analyses.

RESULTS

1) The median maternal serum concentrations of total, HMW and MMW adiponectin were significantly lower in patients with an SGA neonate than in those with normal pregnancies; 2) patients with an SGA neonate had a significantly lower median HMW/total adiponectin ratio and higher median MMW/total adiponectin and LMW/total adiponectin ratios than those with a normal pregnancy; 3) among patients with an SGA neonate, neither maternal serum concentrations of adiponectin multimers, nor their relative distribution differ between normal weight and overweight/obese patients.

CONCLUSION

1) Pregnancies complicated by an SGA neonate are characterized by a alterations in the maternal serum adiponectin multimers concentrations and their relative abundance; 2) the findings reported herein suggest that maternal adipose tissue may play a role, in the pathogenesis of SGA.

A pilot study of sampling subcutaneous adipose tissue to examine biomarkers of cancer risk

Examination of adipose tissue biology may provide important insight into mechanistic links for the observed association between higher body fat and risk of several types of cancer, in particular colorectal and breast cancer. We tested two different methods of obtaining adipose tissue from healthy individuals. Ten overweight or obese (body mass index, 25-40 kg/m(2)), postmenopausal women were recruited. Two subcutaneous abdominal adipose tissue samples were obtained per individual (i.e., right and left lower abdominal regions) using two distinct methods (method A: 14-gauge needle with incision, versus method B: 16-gauge needle without incision). Gene expression was examined at the mRNA level for leptin, adiponectin, aromatase, interleukin 6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha) in flash-frozen tissue, and at the protein level for leptin, adiponectin, IL-6, and TNF-alpha following short-term culture. Participants preferred biopsy method A and few participants reported any of the usual minor side effects. Gene expression was detectable for leptin, adiponectin, and aromatase, but was below detectable limits for IL-6 and TNF-alpha. For detectable genes, relative gene expression in adipose tissue obtained by methods A and B was similar for adiponectin (r = 0.64, P = 0.06) and leptin (r = 0.80, P = 0.01), but not for aromatase (r = 0.37,P = 0.34). Protein levels in tissue culture supernatant exhibited good intra-assay agreement [coefficient of variation (CV), 1-10%], with less agreement for intraindividual agreement (CV, 17-29%) and reproducibility, following one freeze-thaw cycle (CV, >14%). Subcutaneous adipose tissue biopsies from healthy, overweight individuals provide adequate amounts for RNA extraction, gene expression, and other assays of relevance to cancer prevention research.

Energy homoeostasis: The roles of adipose tissue-derived hormones, peptide YY and Ghrelin

This review discusses the physiology of the hormones leptin, adiponectin, resistin, peptide YY, and ghrelin and how each of these contributes to energy homoeostasis, weight regulation, and the pathogenesis of obesity. The relationship these hormones have with insulin and insulin resistance is also discussed, and the potential therapeutic use of each of these hormones is also considered.

Relation of adipose tissue to metabolic flexibility

Metabolic flexibility is the capacity for skeletal muscle to shift reliance between lipids and glucose during fasting or in response to insulin. We hypothesized that body fat, adipose tissue characteristics, e.g. larger adipocytes, presence of inflammatory gene markers and impaired suppression of non-esterified fatty acids (NEFAs) during insulin infusion might be related to metabolic flexibility. We measured changes in respiratory quotient (DeltaRQ) before and during euglycemic-hyperinsulinemic clamp in healthy young males. Body fat by DXA, laboratory measurements, abdominal subcutaneous adipose tissue biopsies and fat cell size (FCS) were obtained after an overnight fast. Gene expression for 17 adipose tissue genes related to lipid synthesis, uptake, oxidation and storage, lipolysis and inflammation were measured. Reduced metabolic flexibility was associated with higher body fat, larger FCS and impaired insulin suppression of NEFAs. Metabolic flexibility was associated with higher serum adiponectin levels. Lower adipose tissue gene expression for inflammation markers was associated with greater NEFA suppression by insulin and metabolic flexibility. Combined, these results indicate that body fat, larger adipocytes, failure of insulin to suppress NEFAs, decreased adiponectin levels and inflammation markers in adipose tissue are associated with decreased insulin-stimulated glucose uptake and oxidation, which is an important component of reduced metabolic flexibility.

Association between maternal seafood consumption before pregnancy and fetal growth: evidence for an association in overweight women. The EDEN mother-child cohort

Studies in countries with high seafood consumption have shown a benefit on fetal growth and child development. The objective of our study was to determine the association between seafood consumption in French pregnant women and fetal growth. Pregnant women included in the EDEN mother-child cohort study completed two food frequency questionnaires on their usual diet in the year before and during the last 3 months of pregnancy (n = 1805). Fetal circumferences were measured by ultrasound and anthropometry at birth. Variables were compared across tertiles of the mother's seafood consumption using multiple linear regression to adjust for confounding variables. Analyses were stratified by maternal overweight status because of an interaction between maternal seafood consumption and her body mass index (P < 0.01). There was no association between seafood intake and fetal growth in the whole sample of women. For overweight women (n = 464), higher consumption of seafood before pregnancy was associated with higher fetal biparietal and abdominal circumferences and anthropometric measures. From the lowest to the highest tertiles, mean birthweight was 167 g higher (P = 0.002). No significant association was found with consumption at the end of pregnancy. In conclusion, high seafood consumption before pregnancy is positively associated with fetal growth in overweight women.

Calorie restriction initiated at a young age activates the Akt/PKC zeta/lambda-Glut4 pathway in rat white adipose tissue in an insulin-independent manner

Calorie restriction (CR) may exert an anti-aging effect through a metabolic adaptation to limited energy intake. The present study investigated the effect of CR on insulin signaling in response to glucose load in the epididymal adipose tissue of male F344 rats at 7 and 22 months of age. Young and middle-aged rats were fed ad libitum (AL) or 30% CR diets for 4 months, underwent glucose tolerance tests and were sacrificed 15 min after an intraperitoneal glucose or saline injection to evaluate glucose-stimulated insulin response and subsequent activation of insulin signaling molecules in the adipose tissue. In the 7- and 22- month AL groups, glucose administration increased serum insulin levels and also increased phosphorylated (p) levels of the insulin receptor (IR), v-akt murine thymoma viral oncogene homolog (Akt), protein kinase C (PKC) zeta/lambda and the membrane fraction of glucose transporter 4 (mGlut4). In contrast, in the 7-month CR group, p-Akt, p-PKC zeta/lambda and mGlut4 levels were upregulated without glucose stimulation; the glucose load augmented the p-IR level but there was no additional activation of the downstream molecules. In the 22-month CR group, these unexpected findings were not observed. In summary, basal levels of insulin signaling molecules such as p-Akt, p-PKC zeta/lambda, and mGlut4 were significantly increased with a low insulin response in the 7-month CR group. The present results suggest the presence of an age-specific insulin-independent mechanism that is induced by CR to regulate energy metabolism in white adipose tissue.

Insulin resistance is associated with a modest increase in inflammation in subcutaneous adipose tissue of moderately obese women

AIMS/HYPOTHESIS

We have previously described differences in adipose cell size distribution and expression of genes related to adipocyte differentiation in subcutaneous abdominal fat obtained from insulin-sensitive (IS) and -resistant (IR) persons, matched for degree of moderate obesity. To determine whether other biological properties also differ between IR and IS obese individuals, we quantified markers of inflammatory activity in adipose tissue from overweight IR and IS individuals.

METHODS

Subcutaneous abdominal tissue was obtained from moderately obese women, divided into IR (n = 14) and IS (n = 19) subgroups by determining their steady-state plasma glucose (SSPG) concentrations during the insulin suppression test. Inflammatory activity was assessed by comparing expression of nine relevant genes and by immunohistochemical quantification of CD45- and CD68-containing cells.

RESULTS

SSPG concentrations were approximately threefold higher in IR than in IS individuals. Expression levels of CD68, EMR1, IL8, IL6 and MCP/CCL2 mRNAs were modestly but significantly increased (p < 0.05) in IR compared with IS participants. Results of immunohistochemical staining were consistent with gene expression data, demonstrating modest differences between IR and IS individuals. Crown-like structures, in which macrophages surround single adipocytes, were rarely seen in tissue from either subgroup.

CONCLUSIONS/INTERPRETATION

A modest increase in inflammatory activity was seen in subcutaneous adipose tissue from IR compared with equally obese IS individuals. Together with previous evidence of impaired adipose cell differentiation in IR vs equally obese individuals, it appears that at least two biological processes in subcutaneous adipose tissue characterize the insulin-resistant state independent of obesity per se.

Cellular retinol-binding protein type III is a PPARgamma target gene and plays a role in lipid metabolism

Cellular retinol-binding protein (CRBP) type III (CRBP-III) belongs to the family of intracellular lipid-binding proteins, which includes the adipocyte-binding protein aP2. In the cytosol, CRBP-III binds retinol, the precursor of retinyl ester and the active metabolite retinoic acid. The goal of the present work is to understand the regulation of CRBP-III expression and its role in lipid metabolism. Using EMSAs, luciferase reporter assays, and chromatin immunoprecipitation assays, we found that CRBP-III is a direct target of peroxisome proliferator-activated receptor-gamma (PPARgamma). Moreover, CRBP-III expression was induced in adipose tissue of mice after treatment with the PPARgamma agonist rosiglitazone. To examine a potential role of CRBP-III in regulating lipid metabolism in vivo, CRBP-III-deficient (C-III-KO) mice were maintained on a high-fat diet (HFD). Hepatic steatosis was decreased in HFD-fed C-III-KO compared with HFD-fed wild-type mice. These differences were partly explained by decreased serum free fatty acid levels and decreased free fatty acid efflux from adipose tissue of C-III-KO mice. In addition, the lack of CRBP-III was associated with reduced food intake, increased respiratory energy ratio, and altered body composition, with decreased adiposity and increased lean body mass. Furthermore, expression of genes involved in mitochondrial fatty acid oxidation in brown adipose tissue was increased in C-III-KO mice, and C-III-KO mice were more cold tolerant than wild-type mice fed an HFD. In summary, we demonstrate that CRBP-III is a PPARgamma target gene and plays a role in lipid and whole body energy metabolism.

Adipose inflammation, insulin resistance, and cardiovascular disease

Adiposity-associated inflammation and insulin resistance are strongly implicated in the development of type 2 diabetes and atherosclerotic cardiovascular disease. This article reviews the mechanisms of adipose inflammation, because these may represent therapeutic targets for insulin resistance and for prevention of metabolic and cardiovascular consequences of obesity. The initial insult in adipose inflammation and insulin resistance, mediated by macrophage recruitment and endogenous ligand activation of Toll-like receptors, is perpetuated through chemokine secretion, adipose retention of macrophages, and elaboration of pro-inflammatory adipocytokines. Activation of various kinases modulates adipocyte transcription factors, including peroxisome proliferator-activated receptor-gamma and NFkappaB, attenuating insulin signaling and increasing adipocytokine and free fatty acid secretion. Inflammation retards adipocyte differentiation and further exacerbates adipose dysfunction and inflammation. Paracrine and endocrine adipose inflammatory events induce a local and systemic inflammatory, insulin-resistant state promoting meta-bolic dyslipidemia, type 2 diabetes, and cardiovascular disease. Developing therapeutic strategies that target both adipose inflammation and insulin resistance may help to prevent type 2 diabetes and cardiovascular disease in the emerging epidemic of obesity.

Sarcopenic obesity: definition, cause and consequences

PURPOSE OF REVIEW

Older obese persons with decreased muscle mass or strength are at special risk for adverse outcomes. We discuss potential pathways to muscle impairment in obese individuals and the consequences that joint obesity and muscle impairment may have on health and disability. Tantamount to this discussion is whether low muscle mass or, rather, muscle weakness should be used for the definition.

RECENT FINDINGS

Excess energy intake, physical inactivity, low-grade inflammation, insulin resistance and changes in hormonal milieu may lead to the development of so-called 'sarcopenic obesity'. It was originally believed that the culprit of age-related muscle weakness was a reduction in muscle mass, but it is now clear that changes in muscle composition and quality are predominant. We propose that the risk of adverse outcomes, such as functional limitation and mortality, is better estimated by considering jointly obesity and muscle strength rather than obesity and muscle mass and the term 'sarcopenic obesity' should be revisited.

SUMMARY

Recognition of obese patients who have associated muscle problems is an essential goal for clinicians. Further research is needed to identify new target for prevention and cure of this important geriatric syndrome.

Why are we shaped differently, and why does it matter?

Body fat distribution is an important predictor of metabolic abnormalities in obese humans. Dysregulation of free fatty acid (FFA) release, especially from upper body subcutaneous adipose tissue, appears to contribute substantially to these metabolic disturbances. Why different individuals preferentially store fat in upper vs. lower body subcutaneous fat or subcutaneous vs. visceral fat is not completely understood. Current evidence suggests that defects in regional lipolysis are not the cause of net fat retention in larger fat depots. Regional variations in the storage of fatty acids, both meal derived and direct reuptake, and storage of circulating FFAs that may help to explain why some depots expand at the expense of others have been reported. We review the quantitative data on regional lipolysis, meal, and FFA storage in adults to provide an overview of fat balance differences in adults with different fat distribution patterns.

Interferon-gamma, a Th1 cytokine, regulates fat inflammation: a role for adaptive immunity in obesity

Adipose tissue (AT) can accumulate macrophages and secrete several inflammatory mediators. Despite its pivotal role in the progression of chronic inflammatory processes such as atherosclerosis, the adaptive role of immunity in obesity remains poorly explored. Visceral AT of diet-induced obese C57BL/6 mice had higher numbers of both CD4(+) and CD8(+) T cells than lean controls, monitored by flow cytometry. When stimulated in vitro, T cells from obese AT produced more interferon (IFN)gamma than those from controls. AT from obese animals also had more cells expressing I-A(b), a mouse class II histocompatibility marker implicated in antigen presentation, as determined by immunostaining. Differentiated 3T3-L1 cells stimulated with recombinant IFNgamma or T-helper 1-derived supernatant produced several chemokines and their mRNAs. Obese IFNgamma-deficient animals had significantly reduced AT expression of mRNA-encoding inflammatory genes such as tumor necrosis factor-alpha and monocyte chemoattractant protein-1, decreased AT inflammatory cell accumulation, and better glucose tolerance than control animals consuming the same diet. Obese mice doubly deficient for IFNgamma receptor and apolipoprotein (Apo)E on a mixed 129SvEv/C57BL/6 (129/B6) genetic background, despite exhibiting similar AT mRNA levels of tumor necrosis factor-alpha and monocyte chemoattractant protein-1 as 129/B6-ApoE(-/-) controls, had decreased expression of important T cell-related genes, such as IFNgamma-inducible protein-10 and I-A(b), and lower plasma triglycerides and glucose. These results indicate a role for T cells and IFNgamma, a prototypical T-helper 1 cytokine, in regulation of the inflammatory response that accompanies obesity.

Relationships between exercise-induced reductions in thigh intermuscular adipose tissue, changes in lipoprotein particle size, and visceral adiposity

Small LDL and HDL particle size are characteristic of a proatherogenic lipoprotein profile. Aerobic exercise increases these particle sizes. Although visceral adipose tissue (VAT) has been strongly linked with dyslipidemia, the importance of intermuscular adipose tissue (IMAT) to dyslipidemia and exercise responses is less well understood. We measured exercise-associated changes in thigh IMAT and VAT and examined their relationships with changes in LDL and HDL particle size. Sedentary, dyslipidemic, overweight subjects (n = 73) completed 8-9 mo of aerobic training. Linear regression models were used to compare the power of IMAT change and VAT change to predict lipoprotein size changes. In men alone (n = 40), IMAT change correlated inversely with both HDL size change (r = -0.42, P = 0.007) and LDL size change (r = -0.52, P < 0.001). That is, reduction of IMAT was associated with a shift toward larger, less atherogenic lipoprotein particles. No significant correlations were observed in women. After adding VAT change to the model, IMAT change was the only significant predictor of either HDL size change (P = 0.034 for IMAT vs. 0.162 for VAT) or LDL size change (P = 0.004 for IMAT vs. 0.189 for VAT) in men. In conclusion, in overweight dyslipidemic men, exercise-associated change in thigh IMAT was inversely correlated with both HDL and LDL size change and was more predictive of these lipoprotein changes than was change in VAT. Reducing IMAT through aerobic exercise may be functionally related to some improvements in atherogenic dyslipidemia in men.

Wdnm1-like, a new adipokine with a role in MMP-2 activation

White adipose tissue functions in energy storage and as an endocrine organ. DNA microarray analysis led us to identify Wdnm1-like, a distant member of the whey acidic protein/four-disulfide core (WAP/4-DSC) family, as a differentiation-dependent gene in white and brown adipogenesis. Wdnm1-like is a novel 6.8-kDa protein, and Western blot analysis reveals secretion into culture media. Wdnm1-like transcript is selectively expressed in adipose tissue and liver and is enriched approximately 500-fold in white adipose depots vs. brown. Cellular fractionation of WAT demonstrates Wdnm1-like transcript expression is restricted to the adipocyte population. Studies in 3T3-L1 preadipocytes, an in vitro model of white adipogenesis, indicate Wdnm1-like transcript increases within 6 h of adipogenic induction with an approximately 17,000-fold increase by day 7. Dramatic upregulation of Wdnm1-like also accompanies white adipogenesis of ScAP-23 preadipocytes and primary preadipocytes. TNF-alpha treatment of 3T3-L1 adipocytes increased Wdnm1-like transcript level 2.4-fold and was attenuated by pretreatment with the p38 MAP kinase inhibitor SB203580. A number of WAP/4-DSC family proteins function as protease inhibitors. This, taken with the role of extracellular remodeling in adipogenesis, led us to address effects of Wdnm1-like on matrix metalloproteinase (MMP) activity. Gelatin zymography of HT1080 fibrosarcoma cells transfected with a Wdnm1-like expression construct revealed markedly increased levels of active MMP-2. Our findings identify a new member of the adipocyte "secretome" that functions to enhance MMP-2 activity. We postulate that Wdnm1-like may play roles in remodeling of the extracellular milieu in adipogenesis, as well as in tumor microenvironments where adipocytes are key stromal components.

Effect of hypocaloric diet-induced weight loss in obese women on plasma apelin and adipose tissue expression of apelin and APJ

OBJECTIVE

Apelin is a novel adipokine acting on APJ receptor, regulated by insulin and tumor necrosis factor-alpha (TNF-alpha) in adipose tissue (AT). Plasma apelin levels are increased in obese hyperinsulinemic subjects. The aim was to investigate whether the hypocaloric diet associated with weight loss modifies the elevated plasma apelin levels and the expression of apelin and APJ receptor in AT in obese women.

DESIGN AND METHODS

Fasting plasma levels of apelin and TNF-alpha as well as mRNA levels of apelin and APJ in AT were measured before and after a 12-week hypocaloric weight-reducing diet in 20 obese women (body mass index (BMI) before diet 32.2+/-6.4 kg/m(2)). Twelve healthy women with a BMI of 20.7+/-0.6 kg/m(2) served as reference.

RESULTS

Plasma levels of apelin and TNF-alpha were higher in obese compared with lean controls. The hypocaloric diet resulted in a significant decrease of BMI to 29.8+/-6.3 kg/m(2), plasma insulin (8.16+/-0.73 to 6.58+/-0.66 mU/l), apelin (369+/-25 pg/ml to 257+/-12 pg/ml), TNF-alpha levels (0.66+/-0.04 pg/ml to 0.56+/-0.04 pg/ml), and AT mRNAs of apelin and APJ. In addition, changes in AT mRNA apelin were related to changes in AT mRNA APJ levels.

CONCLUSION

The hypocaloric diet associated with weight loss reduces the increased plasma and AT expression of apelin in obese women. This reduced apelin expression in AT could contribute to decreased circulating apelin levels.

Mineralocorticoid receptor blockade reverses obesity-related changes in expression of adiponectin, peroxisome proliferator-activated receptor-gamma, and proinflammatory adipokines

BACKGROUND

In obesity, decreases in adiponectin and increases in proinflammatory adipokines are associated with heart disease. Because adipocytes express mineralocorticoid receptor (MR) and MR blockade reduces cardiovascular inflammation and injury, we tested the hypothesis that MR blockade reduces inflammation and expression of proinflammatory cytokines in adipose tissue and increases adiponectin expression in adipose tissue and hearts of obese mice.

METHODS AND RESULTS

We determined the effect of MR blockade (eplerenone, 100 mg/kg per day for 16 weeks) on gene expression in retroperitoneal adipose and heart tissue from obese, diabetic db/db mice (n=8) compared with untreated obese, diabetic db/db mice (n=10) and lean, nondiabetic db/+ littermates (n=11). Expression of tumor necrosis factor-alpha, monocyte chemoattractant protein-1, plasminogen activator inhibitor type 1, and macrophage protein CD68 increased, and expression of adiponectin and peroxisome proliferator-activated receptor-gamma decreased in retroperitoneal adipose tissue from obese versus lean mice. In addition, adiponectin expression in heart was reduced in obese versus lean mice. MR blockade prevented these obesity-related changes in gene expression. Furthermore, treatment of undifferentiated preadipocytes with aldosterone (10(-8) mol/L for 24 hours) increased mRNA levels of tumor necrosis factor-alpha and monocyte chemoattractant protein-1 and reduced mRNA and protein levels of peroxisome proliferator-activated receptor-gamma and adiponectin, supporting a direct aldosterone effect on gene expression.

CONCLUSIONS

MR blockade reduced expression of proinflammatory and prothrombotic factors in adipose tissue and increased expression of adiponectin in heart and adipose tissue of obese, diabetic mice. These effects on adiponectin and adipokine gene expression may represent a novel mechanism for the cardioprotective effects of MR blockade.

High circulating levels of RBP4 and mRNA levels of aP2, PGC-1alpha and UCP-2 predict improvement in insulin sensitivity following pioglitazone treatment of drug-naïve type 2 diabetic subjects

CONTEXT

High levels of circulating retinol-binding protein 4 (RBP4) and baseline expression of adipogenic genes correlate with subsequent improvement in insulin sensitivity following Thiazolidinedione (TZD) treatment.

OBJECTIVE

The aim was to identify baseline characteristics and early changes related to TZD treatment that could predict a good treatment response.

DESIGN

Subjects were examined with oral glucose tolerance test, intravenous glucose tolerance test, hyperinsulinaemic euglycaemic clamp, body composition and standard blood sampling at baseline and after 4 and 12 weeks treatment. Subcutaneous adipose tissue biopsies were taken from the abdominal region at baseline, after 3 days and 4 weeks treatment to examine the gene expression profile.

SETTING

Research laboratory in a University hospital.

PARTICIPANTS

Ten newly diagnosed and previously untreated type 2 diabetic subjects were treated with pioglitazone for 3 months.

MAIN OUTCOME MEASURES

Baseline characteristics and early changes related to TZD treatment that could predict the response after 3 months.

RESULTS

Pioglitazone improved insulin sensitivity after 4 weeks combined with lower glucose and insulin levels without any change in BMI. It was accompanied by lower circulating resistin and plasminogen activator inhibitor-1 levels rapidly increased levels of circulating total and high molecular weight adiponectin as well as adiponectin and adipocyte fatty acid-binding protein (aP2) mRNA expression in the adipose tissue. High levels of circulating RBP4 at baseline and adipose tissue expression of aP2, proliferator-activated receptor-gamma coactivator 1 alpha (PGC-1alpha) and uncoupling protein 2 (UCP-2) predicted a good treatment response measured as improvement in insulin-stimulated whole-body glucose uptake after 3 months.

CONCLUSIONS

Circulating levels of RBP4 as an index of insulin sensitivity and mRNA levels of adipogenic genes correlate with the subsequent improvement in insulin sensitivity following TZD treatment.

Effect of beta-adrenergic stimulation on whole-body and abdominal subcutaneous adipose tissue lipolysis in lean and obese men

AIMS/HYPOTHESIS

Obesity is characterised by increased triacylglycerol storage in adipose tissue. There is in vitro evidence for a blunted beta-adrenergically mediated lipolytic response in abdominal subcutaneous adipose tissue (SAT) of obese individuals and evidence for this at the whole-body level in vivo. We hypothesised that the beta-adrenergically mediated effect on lipolysis in abdominal SAT is also impaired in vivo in obese humans.

METHODS

We investigated whole-body and abdominal SAT glycerol metabolism in vivo during 3 h and 6 h [2H5]glycerol infusions. Arterio-venous concentration differences were measured in 13 lean and ten obese men after an overnight fast and during intravenous infusion of the non-selective beta-adrenergic agonist isoprenaline [20 ng (kg fat free mass)(-1) min(-1)].

RESULTS

Lean and obese participants showed comparable fasting glycerol uptake by SAT (9.7+/-3.4 vs 9.3+/-2.5% of total release, p=0.92). Furthermore, obese participants showed an increased whole-body beta-adrenergically mediated lipolytic response versus lean participants. However, their fasting lipolysis was blunted [glycerol rate of appearance: 7.3+/-0.6 vs 13.1+/-0.9 micromol (kg fat mass)(-1) min(-1), p<0.01], as was the beta-adrenergically mediated lipolytic response per unit SAT [Delta total glycerol release: 140+/-71 vs 394+/-112 nmol (100 g tissue)(-1) min(-1), p<0.05] compared with lean participants. Net triacylglycerol flux tended to increase in obese compared with lean participants during beta-adrenergic stimulation [Delta net triacylglycerol flux: 75+/-32 vs 16+/-11 nmol (100 g tissue)(-1) min(-1), p=0.06].

CONCLUSIONS/INTERPRETATION

We demonstrated in vivo that beta-adrenergically mediated lipolytic response is impaired systematically and in abdominal SAT of obese versus lean men. This may be important in the development or maintenance of increased triacylglycerol stores and obesity.

Peripheral metabolic effects of endocannabinoids and cannabinoid receptor blockade

The endocannabinoid system consists of endogenous arachidonic acid derivates that activate cannabinoid receptors. The two most prominent endocannabinoids are anandamide and 2-arachidonoyl glycerol. In obesity, increased concentrations of circulating and tissue endocannabinoid levels have been described, suggesting increased activity of the endocannabinoid system. Increased availability of endocannabinoids in obesity may over-stimulate cannabinoid receptors. Blockade of cannabinoid type 1 (CB1) receptors was the only successful clinical development of an anti-obesity drug during the last decade. Whereas blockade of CB1 receptors acutely reduces food intake, the long-term effects on metabolic regulation are more likely mediated by peripheral actions in liver, skeletal muscle, adipose tissue, and the pancreas. Lipogenic effects of CB1 receptor signalling in liver and adipose tissue may contribute to regional adipose tissue expansion and insulin resistance in the fatty liver. The association of circulating 2-arachidonoyl glycerol levels with decreased insulin sensitivity strongly suggests further exploration of the role of endocannabinoid signalling for insulin sensitivity in skeletal muscle, liver, and adipose tissue. A few studies have suggested a specific role for the regulation of adiponectin secretion from adipocytes by endocannabinoids, but that has to be confirmed by more experiments. Also, the potential role of CB1 receptor blockade for the stimulation of energy expenditure needs to be studied in the future. Despite the current discussion of safety issues of cannabinoid receptor blockade, these findings open a new and exciting perspective on endocannabinoids as regulators of body weight and metabolism.

Fat tissue and long life

Studies over the last several years have revealed important roles of the body fat content, caloric intake and nutrition, insulin/IGF-1 signaling systems, and pathways involved in oxidative stress and control of protein acetylation on life span. Although the discovery of longevity genes supports the concept that life span is genetically determined, adipose tissue seems to be a pivotal organ in the aging process and in the determination of life span. Leanness and caloric restriction have been shown to increase longevity in organisms ranging from yeast to mammals. Increased longevity in mice with a fat-specific disruption of the insulin receptor gene (FIRKO) suggests that reduced adiposity, even in the presence of normal or increased food intake, leads to an extended life span. Reduced fat mass has an impact on longevity in a number of other model organisms. In Drosophila, a specific reduction in the fat body through overexpression of forkhead type transcription factor (dFOXO) extends life span. Sirtuin 1 (SIRT1), the mammalian ortholog of the life-extending yeast gene silent information regulator 2 (SIR2), was proposed to be involved in the molecular mechanisms linking life span to adipose tissue. Moreover, in the control of human aging and longevity, one of the striking physiological characteristics identified in centenarians is their greatly increased insulin sensitivity even compared with younger individuals. On the other hand, overweight and obesity seem to be associated with decreased life span in humans. In addition, it was recently shown that modifiable risk factors during the later years of life, including smoking, obesity, and hypertension, are associated not only with lower life expectancy, but also with poor health and function during older age. There is growing evidence that the effect of reduced adipose tissue mass on life span could be due to the prevention of obesity-related metabolic disorders including type 2 diabetes and atherosclerosis.

Gene expression of adiponectin receptors in human visceral and subcutaneous adipose tissue is related to insulin resistance and metabolic parameters and is altered in response to physical training

OBJECTIVE

Adiponectin receptors 1 and 2 (AdipoR1 and AdipoR2, respectively) mediate the effects of adiponectin on glucose and lipid metabolism in vivo. We examined whether AdipoR1 and/or AdipoR2 mRNA expression in human adipose tissue is fat-depot specific. We also studied whether their expression in visceral and subcutaneous fat depots is associated with metabolic parameters and whether their expression is regulated by intensive physical exercise.

RESEARCH DESIGN AND METHODS

We determined metabolic parameters and assessed AdipoR1 and AdipoR2 mRNA expression using quantitative real-time PCR in adipose tissue in an observational study of 153 subjects and an interventional study of 60 subjects (20 each with normal glucose tolerance, impaired glucose tolerance, and type 2 diabetes) before and after intensive physical training for 4 weeks.

RESULTS

AdipoR1 and AdipoR2 mRNA expression is not significantly different between omental and subcutaneous fat, but their expression is several-fold lower in adipose tissue than in muscle. AdipoR2 mRNA expression in visceral fat is highly correlated with its expression in subcutaneous fat. AdipoR2 mRNA expression in both visceral and subcutaneous fat is positively associated with circulating adiponectin and HDL levels but negatively associated with obesity as well as parameters of insulin resistance, glycemia, and other lipid levels before and after adjustment for fat mass. Physical training for 4 weeks resulted in increased AdipoR1 and AdipoR2 mRNA expression in subcutaneous fat.

CONCLUSIONS

AdipoR2 mRNA expression in fat is negatively associated with insulin resistance and metabolic parameters independently of obesity and may mediate the improvement of insulin resistance in response to exercise.

Scaling of human body composition to stature: new insights into body mass index

BACKGROUND

Although Quetelet first reported in 1835 that adult weight scales to the square of stature, limited or no information is available on how anatomical body compartments, including adipose tissue (AT), scale to height.

OBJECTIVE

We examined the critical underlying assumptions of adiposity-body mass index (BMI) relations and extended these analyses to major anatomical compartments: skeletal muscle (SM), bone, residual mass, weight (AT+SM+bone), AT-free mass, and organs (liver, brain).

DESIGN

This was a cross-sectional analysis of 2 body-composition databases: one including magnetic resonance imaging and dual-energy X-ray absorptiometry (DXA) estimates of evaluated components in adults (total n=411; organs=76) and the other a larger DXA database (n=1346) that included related estimates of fat, fat-free mass, and bone mineral mass.

RESULTS

Weight, primary lean components (SM, residual mass, AT-free mass, and fat-free mass), and liver scaled to height with powers of approximately 2 (all P<0.001); bone and bone mineral mass scaled to height with powers >2 (2.31-2.48), and the fraction of weight as bone mineral mass was significantly (P<0.001) correlated with height in women. AT scaled weakly to height with powers of approximately 2, and adiposity was independent of height. Brain mass scaled to height with a power of 0.83 (P=0.04) in men and nonsignificantly in women; the fraction of weight as brain was inversely related to height in women (P=0.002).

CONCLUSIONS

These observations suggest that short and tall subjects with equivalent BMIs have similar but not identical body composition, provide new insights into earlier BMI-related observations and thus establish a foundation for height-normalized indexes, and create an analytic framework for future studies.

Tissue engineering applications to vascular bypass graft development: the use of adipose-derived stem cells

The burgeoning field of vascular tissue engineering holds promise for the creation of a practical and successful small-diameter arterial bypass graft. Many creative combinations of autologous cells and scaffolds exist along with an equally long list of microenvironmental cues used to create a functional arterial conduit. This review outlines our work using abdominal wall fat as a source of autologous stem cells for vascular tissue engineering, focusing specifically on this stem cell's availability and potency to differentiate into endothelial-like cells. In a series of 49 patients undergoing elective peripheral vascular surgery, an abundant quantity of adult stem cells was harvested from fat obtained by liposuction. The efficacy of the isolation did not appear influenced by advanced age, obesity, renal failure, or vascular disease, although fat from diabetic patients yielded significantly less stem cells. In addition, these adipose-derived stem cells acquired several morphologic and molecular endothelial phenotypes when exposed to growth factors (endothelial cell growth supplement and vascular endothelial growth factor) and physiologic shear stress in vitro. Taken together, these studies suggest that fat appears to be a viable source of autologous stem cells for use in vascular tissue engineering.

Absence of an adipogenic effect of rosiglitazone on mature 3T3-L1 adipocytes: increase of lipid catabolism and reduction of adipokine expression

AIMS/HYPOTHESIS

The thiazolidinedione (TZD) rosiglitazone is a peroxisome proliferator-activated receptor-gamma agonist that induces adipocyte differentiation and, hence, lipid accumulation. This is in apparent contrast to the long-term glucose-lowering, insulin-sensitising effect of rosiglitazone. We tested whether the action of rosiglitazone involves specific effects on mature adipocytes, which are different from those on preadipocytes.

MATERIALS AND METHODS

Differentiated mature 3T3-L1 adipocytes were used as an in vitro model. Transcriptomics, proteomics and assays of metabolism were applied to assess the effect of rosiglitazone in different insulin and glucose conditions.

RESULTS

Rosiglitazone does not induce an increase, but rather a decrease in the lipid content of mature adipocytes. Analysis of transcriptome data, confirmed by quantitative RT-PCR and measurements of lipolysis, indicates that an altered energy metabolism may underlie this change. The pathway analysis shows a consistent picture dominated by lipid catabolism. In addition, we confirmed at both mRNA level and protein level that rosiglitazone represses adipokine expression and production, except for genes encoding adiponectin and apolipoprotein E. Moreover, transcriptome changes indicate that a general repression of genes encoding secreted proteins occurs.

CONCLUSIONS/INTERPRETATION

Our findings suggest that the change of adiposity as seen in vivo reflects a shift in balance between the different effects of TZDs on preadipocytes and on mature adipocytes, while the changes in circulating adipokine levels primarily result from an effect on mature adipocytes.

Approximation of total visceral adipose tissue with a single magnetic resonance image

BACKGROUND

A single axial image measured between the 4th and 5th lumbar vertebrae (L4-L5) is most frequently chosen to approximate total abdominal visceral adipose tissue (VAT) volume, but growing evidence suggests that this measurement site is not ideal.

OBJECTIVE

The objective was to determine the single magnetic resonance (MR) image that best approximates the total VAT volume in a biracial sample of healthy subjects.

DESIGN

We used contiguous abdominal MR images to measure VAT area and summed them to determine total VAT volume. The sample included 820 healthy men and women (n = 692 whites, 128 blacks) aged 18-88 y.

RESULTS

A range of MR images had equally high correlations with total VAT in each race and sex group. The image 6 cm above L4-L5 (L4-L5 + 6) was within the best equivalent range for all race and sex groups. The L4-L5 + 6 image crossed the L3 vertebra in 85% of subjects and crossed the L2-L3 intervertebral space or the L2 vertebra for 15% of subjects. Linear regression models indicated that the L4-L5 + 6 image explained 97% of the variance in total abdominal VAT volume, and additional covariates did not increase the R(2) value significantly. The L4-L5 image explained 83% of the variance in VAT volume, and the covariates accounted for an additional 7% of the variance. Rank-order values for VAT can change if total VAT volume is approximated by a single image area. Whereas 25% of subjects changed rank by >or=10% with the L4-L5 image, only 3% changed rank to that degree with the L4-L5 + 6 image.

CONCLUSIONS

A single MR image located approximately at the L3 vertebra can accurately estimate total VAT volume in blacks and whites of both sexes.

The effects of an individualized exercise intervention on body composition in breast cancer patients undergoing treatment

CONTEXT AND OBJECTIVE

Changes in metabolism have been reported in the majority of patients undergoing cancer treatment, and these are usually characterized by progressive change in body composition. The effects of aerobic exercise programs to combat the cancer and cancer treatment-related side effects, which include the negative changes in body composition, have been extensively reported in the literature. However, few resistance exercise intervention studies have hypothesized that breast cancer patients might benefit from this type of exercise. The purpose of this study was to determine whether exercise protocols that emphasize resistance training would change body composition and strength in breast cancer patients undergoing treatment.

DESIGN AND SETTING

Randomized controlled trial, at the Campus Recreation Center and Rocky Mountain Cancer Rehabilitation Institute of the University of Northern Colorado, and the North Colorado Medical Center.

METHODS

Twenty inactive breast cancer patients were randomly assigned to a 21-week exercise group (n = 10) or a control group (n = 10). The exercise group trained at low to moderate intensity for 60 minutes on two days/week. The primary outcome measurements included body composition (skinfold method) and muscle strength (one repetition maximum).

RESULTS

Significant differences in lean body mass, body fat and strength (p = 0.004, p = 0.004, p = 0.025, respectively) were observed between the groups at the end of the study.

CONCLUSION

The results suggest that exercise emphasizing resistance training promotes positive changes in body composition and strength in breast cancer patients undergoing treatment.

Immunogold localization of vitellogenin in the ovaries, hypopharyngeal glands and head fat bodies of honeybee workers, Apis mellifera

Vitellogenin is a yolk precursor protein in most oviparous females. In the advanced eusocial honeybee, Apis mellifera (Hymenoptera: Apidae), vitellogenin has recently attracted much interest as this protein, in addition to a classical function in oocyte development in the reproductive queen caste, has evolved functions in the facultatively sterile female worker caste not documented in other species. However, research on the spatial dynamics of vitellogenin in various tissues is not easily performed with available tools. Here we present an immunogold staining procedure that visualizes honeybee vitellogenin in resin embedded tissue. To establish the protocol, we used ovaries of worker bees from colonies with and without a queen. Under the first condition, vitellogenin is assumed not to be present in the workers' ovaries. Under the second condition, the ovaries of worker bees become vitellogenic, with abundant opportunities for detection of complex patterns of vitellogenin uptake and storage. By use of this experimental setup, the staining method is shown to be both sensitive and specific. To demonstrate the functional significance of the protocol, it was subsequently used to identify vitellogenin protein in the hypopharyngeal glands (brood food producing head glands) of nursing worker bees and in adjacent head fat body cells for the first time. Localization of vitellogenin in these tissues supports previously hypothesized roles of vitellogenin in social behavior. This protocol thus provides deeper insights into the functions of vitellogenin in the honeybee.

Neuron-like differentiation of adipose-derived stem cells from infant piglets in vitro

BACKGROUND/OBJECTIVE

Adipose-derived stem cells (ADSCs) are mesenchymal stem cells (MSCs) that can be extracted from adipose tissue and obtained by a less invasive method and in larger quantities compared with bone marrow-derived MSCs. The objective of this study was to harvest ADSCs from piglets and to explore their neuronal differentiation potential.

METHODS

Adipose tissue from piglet facial or abdominal fat was digested with collagenase type XI, followed by filter and centrifugation; the isolated adipose stromal cells were cultured in dishes. MSC markers were measured by flow cytometry; 2 to 5 passage cells were used for in vitro differentiation. Adipogenic, chondrogenic, osteogenic, and neuronal differentiation was induced by incubation of the ADSCs with different induction media.

RESULTS

ADSCs were easily expanded to beyond 15 passages, maintaining the undifferentiated state and exhibiting MSC characteristics and markers CD29, CD44, and CD90. ADSCs differentiated into other mesodermal cells including adipocytes, chondrocytes, and osteocytes. These cells were induced to differentiate into neuron-like cells as evidenced by neuronal morphology and the presence of neuronal markers including microtubule-associated protein 2, neuronal nuclear antigen, and beta-tubulin III.

CONCLUSIONS

ADSCs can be readily obtained from a small amount fat tissue and expanded in culture. Adipose tissue may be an alternative source of stem cell therapy for nervous system injury.

Gene expression variability in subcutaneous and omental adipose tissue of obese men

We investigated interindividual variability in gene expression in abdominal subcutaneous (SC) and omental (OM) adipose tissue of 10 massively obese men. Affymetrix human U133A microarrays were used to measure gene expression levels. A total of 6811 probesets generated significant signal in both depots in all samples. Interindividual variability in gene expression was rather low, with more than 90% of transcripts showing a coefficient of variation (CV) lower than 23.6% and 21.7% in OM and SC adipose tissues, respectively. The distributions of CV were similar between the two fat depots. A set of highly variable genes was identified for both tissues on the basis of a high CV and elevated gene expression level. Among the set of highly regulated genes, 18 transcripts were involved in lipid metabolism and 28 transcripts were involved in cell death for SC and OM samples, respectively. In conclusion, gene expression interindividual variability was rather low and globally similar between fat compartments, and the adipose tissue transcriptome appeared as relatively stable, although specific pathways were found to be highly variable in SC and OM depots.

Beta-adrenergic and atrial natriuretic peptide interactions on human cardiovascular and metabolic regulation

CONTEXT

Atrial natriuretic peptide (ANP) has well-known cardiovascular effects and modifies lipid and carbohydrate metabolism in humans.

OBJECTIVE

The objective of the study was to determine the metabolic and cardiovascular interaction of beta-adrenergic receptors and ANP.

DESIGN

This was a crossover study, conducted 2004-2005.

SETTING

The study was conducted at an academic clinical research center.

PATIENTS

PATIENTS included 10 healthy young male subjects (body mass index 24 +/- 1 kg/m2).

INTERVENTION

We infused iv incremental ANP doses (6.25, 12.5, and 25 ng/kg.min) with and without propranolol (0.20 mg/kg in divided doses followed by 0.033 mg/kg.h infusion). Metabolism was monitored through venous blood sampling, im, and sc microdialysis and indirect calorimetry. Cardiovascular changes were monitored by continuous electrocardiogram and beat-by-beat blood pressure recordings.

MAIN OUTCOME MEASURES

Venous nonesterified fatty acid, glycerol, glucose, and insulin; and microdialysate glucose, glycerol, lactate, and pyruvate were measured.

RESULTS

ANP increased heart rate dose dependently. beta-Adrenergic receptor blockade abolished the response. ANP elicited a dose-dependent increase in serum nonesterified fatty acid and glycerol concentrations. The response was not suppressed with propranolol. Venous glucose and insulin concentrations increased with ANP, both without or with propranolol. ANP induced lipid mobilization in sc adipose tissue. In skeletal muscle, microdialysate lactate increased, whereas the lactate to pyruvate ratio decreased, both with and without propranolol. Higher ANP doses increased lipid oxidation, whereas energy expenditure remained unchanged. Propranolol tended to attenuate the increase in lipid oxidation.

CONCLUSIONS

Selected cardiovascular ANP effects are at least partly mediated by beta-adrenergic receptor stimulation. ANP-induced changes in lipid mobilization and glycolysis are mediated by another mechanism, presumably stimulation of natriuretic peptide receptors, whereas substrate oxidation might be modulated through adrenergic mechanisms.

Molecular epidemiologic evidence for diabetogenic effects of dioxin exposure in U.S. Air force veterans of the Vietnam war

BACKGROUND

One of the outcomes positively associated with dioxin exposure in humans is type 2 diabetes.

OBJECTIVES

This study was conducted in order to find the molecular biological evidence for the diabetogenic action of dioxin in adipose samples from Vietnam veterans.

METHODS

We obtained 313 adipose tissue samples both from Vietnam veterans who were exposed to dioxin (Operation Ranch Hand) and from comparison veterans who served in Southeast Asia with no record of dioxin exposure. We conducted quantitative reverse-transcribed polymerase chain reaction studies on selected marker mRNAs from these samples.

RESULTS

We found the most sensitive and reliable molecular indicator of dioxin-induced diabetes to be the ratio of mRNA of glucose transporter 4 (GLUT4) and nuclear transcription factor kappa B (NFkappaB), a marker of inflammation. This ratio showed significant correlations to serum dioxin residues and to fasting glucose among those in the Ranch Hand group and, surprisingly, even in the comparison group, who have low levels of dioxin comparable to the general public. Such a correlation in the comparison group was particularly significant among those with known risk factors such as obesity and family history of diabetes.

CONCLUSIONS

These results show that the GLUT4:NFkappaB ratio is a reliable marker for the diabetogenic action of dioxin, particularly at very low exposure levels that are not much higher than those found in the general public, implying a need to address current exposure levels.

Inflammatory gene expression patterns revealed by DNA microarray analysis in TNF-alpha-treated SGBS human adipocytes

We report here the use of human inflammation arrays to study the inflammatory gene expression profile of TNF-alpha- treated human SGBS adipocytes. Human preadipocytes (SGBS) were induced to differentiate in primary culture, and adipocyte differentiation was confirmed, using Oil Red O staining. We treated the differentiated adipocytes with TNF-alpha, and RNA from differentiated adipocytes with or without TNF-alpha treatment was hybridized to MWG human inflammation arrays to compare expression profiles. Eleven genes were up- or down-regulated in TNF-alpha-treated adipocytes. As revealed by array analysis, among 6 up-regulated genes, only eotaxin-1, monocyte chemoattractant protein-1 (MCP-1), and vascular cell adhesion molecule 1 isoform a precursor (VCAM1) were confirmed by real-time polymerase chain reaction (PCR). Similarly, among 5 down-regulated genes, only IL-1 family member 5 (IL1F5), a disintegrin and metalloprotease with thrombospondin motifs-1 preproprotein (ADAMTS1), fibronectin 1 isoform 1 preprotein (FN1), and matrix metalloproteinase 15 preprotein (MMP15) were confirmed by real-time PCR. There was a substantial increase (50-fold) in eotaxin-1 in response to TNF-alpha. Taken together, we have identified several inflammatory molecules expressed in SGBS adipocytes and discovered molecular factors explaining the relationship between obesity and atherosclerosis, focusing on inflammatory cytokines expressed in the TNF-alpha-treated SGBS cells. Further investigation into the role of these up- or down-regulated cytokine genes during the pathological processes leading to the development of atherosclerosis is warranted.

Genes involved in obesity: Adipocytes, brain and microflora

The incidence of obesity and related metabolic disorders such as cardiovascular diseases and type 2 diabetes, are reaching worldwide epidemic proportions. It results from an imbalance between caloric intake and energy expenditure leading to excess energy storage, mostly due to genetic and environmental factors such as diet, food components and/or way of life. It is known since long that this balance is maintained to equilibrium by multiple mechanisms allowing the brain to sense the nutritional status of the body and adapt behavioral and metabolic responses to changes in fuel availability. In this review, we summarize selected aspects of the regulation of energy homeostasis, prevalently highlighting the complex relationships existing between the white adipose tissue, the central nervous system, the endogenous microbiota, and nutrition. We first describe how both the formation and functionality of adipose cells are strongly modulated by the diet before summarizing where and how the central nervous system integrates peripheral signals from the adipose tissue and/or the gastro-intestinal tract. Finally, after a short description of the intestinal commensal flora, rangingfrom its composition to its importance in immune surveillance, we enlarge the discussion on how nutrition modified this perfectly well-balanced ecosystem.

Use of a physiologically based pharmacokinetic model for rats to study the influence of body fat mass and induction of CYP1A2 on the pharmacokinetics of TCDD

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a highly lipophilic chemical that distributes into adipose tissue, especially at low doses. However, at high doses TCDD sequesters in liver because it induces cytochrome P450 1A2 (CYP1A2) that binds TCDD. A physiologically based pharmacokinetic (PBPK) model was developed that included an inducible elimination rate of TCDD in the Sprague-Dawley rat. Objectives of this work were to characterize the influence of induction of CYP1A2 and adipose tissue mass fraction on the terminal elimination half-life (t1/2) of TCDD using this PBPK model. When the model assumes a fixed elimination of TCDD, t1/2 increases with dose, due to hepatic sequestration. Because experimental data indicate that the t1/2 of TCDD decreases with dose, the model was modified to include an inducible elimination rate. The PBPK model was then used to compare the t1/2 after an increase of adipose tissue mass fraction from 6.9 to 70%. The model suggests that at low exposures, increasing adipose tissue mass increases the terminal t1/2. However, at higher exposures, as CYP1A2 is induced, the relationship between adipose tissue mass and t1/2 reaches a plateau. This demonstrates that an inducible elimination rate is needed in a PBPK model in order to describe the pharmacokinetics of TCDD. At low exposures these models are more sensitive to parameters related to partitioning into adipose tissue.

Effects of DGAT1 deficiency on energy and glucose metabolism are independent of adiponectin

Mice lacking acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1), an enzyme that catalyzes the terminal step in triacylglycerol synthesis, have enhanced insulin sensitivity and are protected from obesity, a result of increased energy expenditure. In these mice, factors derived from white adipose tissue (WAT) contribute to the systemic changes in metabolism. One such factor, adiponectin, increases fatty acid oxidation and enhances insulin sensitivity. To test the hypothesis that adiponectin is required for the altered energy and glucose metabolism in DGAT1-deficient mice, we generated adiponectin-deficient mice and introduced adiponectin deficiency into DGAT1-deficient mice by genetic crosses. Although adiponectin-deficient mice fed a high-fat diet were heavier, exhibited worse glucose tolerance, and had more hepatic triacylglycerol accumulation than wild-type controls, mice lacking both DGAT1 and adiponectin, like DGAT1-deficient mice, were protected from diet-induced obesity, glucose intolerance, and hepatic steatosis. These findings indicate that adiponectin is required for normal energy, glucose, and lipid metabolism but that the metabolic changes induced by DGAT1-deficient WAT are independent of adiponectin and are likely due to other WAT-derived factors. Our findings also suggest that the pharmacological inhibition of DGAT1 may be useful for treating human obesity and insulin resistance associated with low circulating adiponectin levels.

Long-term metabolic consequences of being born small for gestational age

During the last 15 years, a number of long-term health risks associated with reduced fetal growth have been identified, including cardiovascular diseases and the insulin-resistance syndrome or one of its components: hypertension, dyslipidemia, impaired glucose tolerance or Type 2 diabetes. A common feature of these conditions is the presence of high insulin levels, which are thought to play a pathogenic role. However, despite abundant data in the literature, it is still difficult to trace the pathway by which fetal events, environmental or not, may lead to the increased morbidity later in life. To explain this association, several hypotheses have been proposed pointing to the critical role of either a detrimental fetal environment or a genetic susceptibility, or indicating interaction of both. Clearly, not all subjects born small for gestational age are at the same risk of developing these complications. It appears that individuals at particular risk are those who were thin at birth and had a subsequent catch-up in body mass index, irrespective of the degree of adiposity in adulthood. It is suggested that this particular dynamic change in adiposity has a critical role in the development of long-term metabolic complications. Therefore, it is important to consider the relative impact of early postnatal events in relation to fetal growth to the diseases risk throughout life in forming health policy strategies towards eventual early interventions.

Obesity and the renin- angiotensin-aldosterone system

The renin-angiotensin-aldosterone system (RAAS) is a key regulator of cardiovascular function. RAAS activity is upregulated in obesity despite concurrent renal sodium retention, which is a hallmark and principle determinant of obesity-associated hypertension. The contribution of adipose tissue to increased angiotensinogen and aldosterone plasma levels in obesity is probably due to the secretion of angiotensinogen and, as yet, unidentified aldosterone secretagogues by adipocytes. Increased circulating renin activity, on the other hand, is probably due to increased sympathetic activity in the obese. Modest weight reduction significantly reduces RAAS activity by uncertain mechanisms. Pharmacological blockade of the RAAS yielded promising results, both with regard to cardiovascular function and metabolic complications of obesity. These studies suggest that the activated RAAS is a prime pharmacological target for reducing the cardiometabolic risk in obese patients.

Depot-specific regulation of glucose uptake and insulin sensitivity in HIV-lipodystrophy

Altered fat distribution is associated with insulin resistance in HIV, but little is known about regional glucose metabolism in fat and muscle depots in this patient population. The aim of the present study was to quantify regional fat, muscle, and whole body glucose disposal in HIV-infected men with lipoatrophy. Whole body glucose disposal was determined by hyperinsulinemic clamp technique (80 mU x m(-2) x min(-1)) in 6 HIV-infected men and 5 age/weight-matched healthy volunteers. Regional glucose uptake in muscle and subcutaneous (SAT) and visceral adipose tissue (VAT) was quantified in fasting and insulin-stimulated states using 2-deoxy-[18F]fluoro-D-glucose positron emission tomography. HIV-infected subjects with lipoatrophy had significantly increased glucose uptake into SAT (3.8 +/- 0.4 vs. 2.3 +/- 0.5 micromol x kg tissue(-1) x min(-1), P < 0.05) in the fasted state. Glucose uptake into VAT did not differ between groups. VAT area was inversely related with whole body glucose disposal, insulin sensitivity, and muscle glucose uptake during insulin stimulation. VAT area was highly predictive of whole body glucose disposal (r2 = 0.94, P < 0.0001). This may be mediated by adiponectin, which was significantly associated with VAT area (r = -0.75, P = 0.008), and whole body glucose disposal (r = 0.80, P = 0.003). This is the first study to directly demonstrate increased glucose uptake in subcutaneous fat of lipoatrophic patients, which may partially compensate for loss of SAT. Furthermore, we demonstrate a clear relationship between VAT and glucose metabolism in multiple fat and muscle depots, suggesting the critical importance of this depot in the regulation of glucose and highlighting the significant potential role of adiponectin in this process.

Role of adiponectin in the protective action of dietary saturated fat against alcoholic fatty liver in mice

The protective effect of dietary saturated fatty acids against the development of alcoholic liver disease has long been known, but the underlying mechanism is not completely understood. We examined the involvement of the adipocyte hormone adiponectin. Circulating adiponectin levels were significantly elevated by chronic ethanol administration to mice consuming a diet high in saturated fat. The increase in circulating adiponectin was associated with the activation a set of hepatic signaling pathways mediated through AMP-activated protein kinase, PPAR-alpha, and PPAR-gamma coactivator alpha, which in turn led to markedly increased rates of fatty acid oxidation, prevention of hepatic steatosis, and alleviation of liver enzyme changes. Furthermore, treatment of rat 3T3-L1 adipocytes with saturated fatty acids (palmitic or stearic acids) in the presence of ethanol increased secretion of adiponectin and enhanced activity of a mouse adiponectin promoter. In conclusion, the protective action of saturated fat against the development of alcoholic fatty liver in mice is partially mediated through induction of adiponectin. The present findings suggest a novel paradigm for dietary fatty acids in the pathogenesis of alcoholic liver disease and provide a promising therapeutic strategy-nutritional modulation of adiponectin-in treating human alcoholic fatty liver disease.

Microarray profiling of isolated abdominal subcutaneous adipocytes from obese vs non-obese Pima Indians: increased expression of inflammation-related genes

AIMS/HYPOTHESIS

Obesity increases the risk of developing major diseases such as diabetes and cardiovascular disease. Adipose tissue, particularly adipocytes, may play a major role in the development of obesity and its comorbidities. The aim of this study was to characterise, in adipocytes from obese people, the most differentially expressed genes that might be relevant to the development of obesity.

METHODS

We carried out microarray gene profiling of isolated abdominal subcutaneous adipocytes from 20 non-obese (BMI 25+/-3 kg/m2) and 19 obese (BMI 55+/-8 kg/m2) non-diabetic Pima Indians using Affymetrix HG-U95 GeneChip arrays. After data analyses, we measured the transcript levels of selected genes based on their biological functions and chromosomal positions using quantitative real-time PCR.

RESULTS

The most differentially expressed genes in adipocytes of obese individuals consisted of 433 upregulated and 244 downregulated genes. Of these, 410 genes could be classified into 20 functional Gene Ontology categories. The analyses indicated that the inflammation/immune response category was over-represented, and that most inflammation-related genes were upregulated in adipocytes of obese subjects. Quantitative real-time PCR confirmed the transcriptional upregulation of representative inflammation-related genes (CCL2 and CCL3) encoding the chemokines monocyte chemoattractant protein-1 and macrophage inflammatory protein 1alpha. The differential expression levels of eight positional candidate genes, including inflammation-related THY1 and C1QTNF5, were also confirmed. These genes are located on chromosome 11q22-q24, a region with linkage to obesity in the Pima Indians.

CONCLUSIONS/INTERPRETATION

This study provides evidence supporting the active role of mature adipocytes in obesity-related inflammation. It also provides potential candidate genes for susceptibility to obesity.

Increased expression of inflammation-related genes in cultured preadipocytes/stromal vascular cells from obese compared with non-obese Pima Indians

AIMS/HYPOTHESIS

The specific contributions made by the various cell types in adipose tissue to obesity, particularly obesity-related inflammation, need to be clarified. The aim of this study was to elucidate the potential role of adipocyte precursor cells (preadipocytes/stromal vascular cells [SVC]).

METHODS

We performed Affymetrix oligonucleotide microarray expression profiling of cultured abdominal subcutaneous preadipocytes/SVC isolated from the adipose tissue of 14 non-obese (BMI 25+/-4 kg/m2) and 14 obese (55+/-8 kg/m2) non-diabetic Pima Indian subjects. Quantitative real-time PCR (RT-PCR) was used to verify the differential expression of several genes in an independent group of subjects.

RESULTS

We identified 218 differentially expressed genes with p values less than 0.01. Microarray expression profiling revealed that the expression of inflammation-related genes was significantly upregulated in preadipocytes/SVC of obese individuals. Quantitative RT-PCR confirmed the upregulation of IL8, CTSS, ITGB2, HLA-DRA, CD53, PLA2G7 and MMP9 in preadipocytes/SVC of obese subjects.

CONCLUSIONS/INTERPRETATION

The upregulation of inflammation-related genes in preadipocytes/SVC of obese subjects may increase the recruitment of immune cells into adipose tissue and may also result in changes in the extracellular matrix (tissue remodelling) to accommodate adipose tissue expansion in obesity.

Adipose tissue in muscle: a novel depot similar in size to visceral adipose tissue

BACKGROUND

The manner in which fat depot volumes and distributions, particularly the adipose tissue (AT) between the muscles, vary by race is unknown.

OBJECTIVE

The objective was to quantify a previously unstudied and novel intermuscular AT (IMAT) depot and subcutaneous AT, visceral AT (VAT), and total-body skeletal muscle mass in healthy sedentary African American (AA), Asian, and white adults by whole-body magnetic resonance imaging. IMAT is the AT between muscles and within the boundary of the muscle fascia.

DESIGN

Analyses were conducted on 227 women [AA (n = 79): body mass index (BMI; in kg/m(2)), 29.0 +/- 5.5; age, 45.7 +/- 16.9 y; Asian (n = 38): BMI, 21.7 +/- 2.9; age, 47.2 +/- 19.9 y; whites (n = 110): BMI, 24.9 +/- 5.4; age, 43.7 +/- 16.2 y]) and 111 men [AA (n = 39): BMI, 25.6 +/- 3.2; age, 45.5 +/- 18.8 y; Asian (n = 13): BMI, 24.9 +/- 2.5; age, 45.6 +/- 25.0 y; white (n = 59): BMI, 25.8 +/- 3.8; age 44.5 +/- 16.3 y].

RESULTS

IMAT depots were not significantly different in size between race groups at low levels of adiposity; however, with increasing adiposity, AAs had a significantly greater increment in the proportion of total AT (TAT) than did the whites and Asians (58, 46, and 44 g IMAT/kg TAT, respectively; P = 0.001). VAT depots were not significantly different in size at low levels of adiposity but, with increasing adiposity, VAT accumulation was greater than IMAT accumulation in the Asians and whites; no significant differences were observed in AAs.

CONCLUSION

Race differences in AT distribution extend to IMAT, a depot that may influence race-ethnicity differences in dysglycemia.

Hepatic triglyceride content and its relation to body adiposity: a magnetic resonance imaging and proton magnetic resonance spectroscopy study

BACKGROUND

Hepatic steatosis is associated with obesity and type II diabetes. Proton magnetic resonance spectroscopy (1H MRS) is a non-invasive method for measurement of tissue fat content, including intrahepatocellular lipids (IHCL) and intramyocellular lipids (IMCL).

PATIENTS AND METHODS

We used 1H MRS and whole body magnetic resonance imaging (MRI) to assess the relationship between IHCL accumulation, total body adipose tissue (AT) content/distribution, and IMCL content in 11 subjects with biopsy proven hepatic steatosis and 23 normal volunteers.

RESULTS

IHCL signals were detectable in all subjects but were significantly greater in hepatic steatosis (geometric mean (GM) 11.5 (interquartile range (IQR) 7.0-39.0)) than in normal volunteers (GM 2.7 (IQR 0.7-9.3); p=0.02). In the study group as a whole, IHCL levels were significantly greater in overweight compared with lean subjects (body mass index (BMI) >25 kg/m2 (n=23): GM 7.7 (IQR 4.0-28.6) v BMI <25 kg/m2 (n=11): GM 1.3 (IQR 0.3-3.6; p=0.004)). There was a significant association between IHCL content and indices of overall obesity (expressed as a percentage of body weight) for total body fat (p=0.001), total subcutaneous AT (p=0.007), and central obesity (subcutaneous abdominal AT (p=0.001) and intra-abdominal AT (p=0.001)), after allowing for sex and age. No correlation between IHCL content and IMCL was observed. A significant correlation was observed between serum alanine aminotransferase and liver fat content (r=0.57, p=0.006).

CONCLUSIONS

Our results suggest that hepatic steatosis appears to be closely related to body adiposity, especially central obesity. MRS may be a useful method for monitoring IHCL in future interventional studies.

Weight loss increases 11beta-hydroxysteroid dehydrogenase type 1 expression in human adipose tissue

The global epidemic of obesity has heightened the need to understand the mechanisms that underpin its pathogenesis. Clinical observations in patients with Cushing's syndrome have highlighted the link between cortisol and central obesity. However, although circulating cortisol levels are normal or reduced in obesity, local regeneration of cortisol, from inactive cortisone, by 11beta-hydroxysteroid dehydrogenase type 1 (11betaHSD1) has been postulated as a pathogenic mechanism. Although levels of expression of 11betaHSD1 in adipose tissue in human obesity are debated in the literature, global inhibition of 11betaHSD1 improves insulin sensitivity. We have determined the effects of significant weight loss on cortisol metabolism and adipose tissue 11betaHSD1 expression after 10-wk ingestion of a very low calorie diet in 12 obese patients (six men and six women; body mass index, 35.9 +/- 0.9 kg/m2; mean +/- SE). All patients achieved significant weight loss (14.1 +/- 1.3% of initial body weight). Total fat mass fell from 41.8 +/- 1.9 to 32.0 +/- 1.7 kg (P < 0.0001). In addition, fat-free mass decreased (64.4 +/- 3.4 to 58.9 +/- 2.9 kg; P < 0.0001) and systolic blood pressure and total cholesterol also fell [systolic blood pressure, 135 +/- 5 to 121 +/- 5 mm Hg (P < 0.01); total cholesterol, 5.4 +/- 0.2 to 4.8 +/- 0.2 mmol/liter (P < 0.05)]. The serum cortisol/cortisone ratio increased after weight loss (P < 0.01). 11betaHSD1 mRNA expression in isolated adipocytes increased 3.4-fold (P < 0.05). Decreased 11betaHSD1 activity and expression in obesity may act as a compensatory mechanism to enhance insulin sensitivity through a reduction in tissue-specific cortisol concentrations. Inhibition of 11betaHSD1 may therefore be a novel, therapeutic strategy for insulin sensitization.

Polybrominated diphenyl ethers (PBDEs): new pollutants-old diseases

Polybrominated diphenyl ethers (PBDEs) are a class of recalcitrant and bioaccumulative halogenated compounds that have emerged as a major environmental pollutant. PBDEs are used as a flame-retardant and are found in consumer goods such as electrical equipment, construction materials, coatings, textiles and polyurethane foam (furniture padding). Similar in structure to polychlorinated biphenyls (PCBs), PBDEs resist degradation in the environment. Less brominated PBDEs like tetra-, penta- and hexa- demonstrate high affinity for lipids and can accumulate in the bodies of animals and humans. Breast milk from North American women contained much higher amounts of PBDEs than levels in breast milk from Swedish women, indicating that North American exposures to PBDEs may be particularly high. Evidence to date suggests that tetra- and penta-BDEs are likely to be the more toxic and bioaccumulative of the PBDE compounds, compared to octa- and deca-congeners. PBDEs are sold as mixtures, under names such as "pentabromodiphenyl ether" and "octabromodiphenyl ether." The pentabromo product is a mixture of tetra-BDEs and penta-BDEs in approximately equal amounts. Pentabromo consists of PBDEs that are believed to be the most toxic. This mixture has been banned by the European Union, but is still used in North America. The United States is the leading producer and user of pentabromo. In August 2003, the State of California passed a bill to phase out the use of penta- and octa-PBDE by 2008. The toxicology of PBDEs is not well understood, but PBDEs have been associated with tumors, neurodevelopmental toxicity and thyroid hormone imbalance. The neurotoxic effects of PBDEs are similar to those observed for PCBs. Children exposed to PBDEs are prone to subtle but measurable developmental problems. It is presumed that PBDEs are endocrine disruptors, but research in this area is scant. Further studies are imperative in a multitude of health and environmental disciplines to determine the adverse effects and mode of action of this widespread emerging pollutant on human health.

beta(3)-adrenoceptor regulation and relaxation responses in mouse ileum

1. This study examines the relationship between beta(3a)- and beta(3b)-adrenoceptor (AR) mRNA levels, beta(3)-AR binding and changes in ileum responses in mice treated with the beta(3)-AR agonist (R, R)-5-[2[[2-(3-chlorophenyl)-2-hydroxyethyl]-amino]-propyl]1, 3-benzodioxole-2,2-dicarboxylate (CL316243), or the beta(3)-AR antagonist 3-(2-ethylphenoxy)-1-[(1S)-1,2,3, 4-tetrahydronapth-1-ylamino]-2S-2-propanol oxalate (SR59230A), or dexamethasone or forskolin. 2. Levels of beta(3a)- and beta(3b)-AR mRNA and the maximum number of binding sites (B(max)) in ileum were unaffected following CL316243 treatment, although responses to CL316243 were reduced by 50% following 4 and 24 h treatment, indicating another desensitization mechanism not involving changes in receptor expression or number. beta(3a)-AR mRNA levels were reduced in both brown (BAT) and white adipose tissue (WAT) but beta(3b)-AR mRNA levels were significantly reduced only in WAT. Levels of beta(3a)- and beta(3b)-mRNA returned towards normal with continued treatment. 3. SR59230A treatment markedly increased beta(3)-AR mRN levels in ileum and BAT but not in WAT. The increase in beta(3)-AR mRNA levels in ileum was associated with increased B(max) levels in binding analysis and increased responses to CL316243, suggesting these as the cause of sensitization. 4. Treatment with forskolin (4 h) or dexamethasone (4 h) significantly reduced beta(3a)-AR mRNA levels in BAT and WAT but did not alter levels in ileum. Responses to CL316243 in ileum were unaffected by either treatment. 5. In summary, the beta(3)-AR is differently regulated in adipose tissue and ileum: Treatment with SR59230A increased beta(3)-AR number, mRNA and responsiveness in ileum, whereas treatment with CL316243 reduced responses without affecting beta(3)-AR number or mRNA levels.

Two compartments for insulin-stimulated exocytosis in 3T3-L1 adipocytes defined by endogenous ACRP30 and GLUT4

Insulin stimulates adipose cells both to secrete proteins and to translocate the GLUT4 glucose transporter from an intracellular compartment to the plasma membrane. We demonstrate that whereas insulin stimulation of 3T3-L1 adipocytes has no effect on secretion of the alpha3 chain of type VI collagen, secretion of the protein hormone adipocyte complement related protein of 30 kD (ACRP30) is markedly enhanced. Like GLUT4, regulated exocytosis of ACRP30 appears to require phosphatidylinositol-3-kinase activity, since insulin-stimulated ACRP30 secretion is blocked by pharmacologic inhibitors of this enzyme. Thus, 3T3-L1 adipocytes possess a regulated secretory compartment containing ACRP30. Whether GLUT4 recycles to such a compartment has been controversial. We present deconvolution immunofluorescence microscopy data demonstrating that the subcellular distributions of ACRP30 and GLUT4 are distinct and nonoverlapping; in contrast, those of GLUT4 and the transferrin receptor overlap. Together with supporting evidence that GLUT4 does not recycle to a secretory compartment via the trans-Golgi network, we conclude that there are at least two compartments that undergo insulin-stimulated exocytosis in 3T3-L1 adipocytes: one for ACRP30 secretion and one for GLUT4 translocation.

Alternative splicing generates two isoforms of the beta3-adrenoceptor which are differentially expressed in mouse tissues

The beta3-adrenoceptor (AR) differs from the beta1-AR and beta2-ARs in having introns within and downstream of the coding block. This study demonstrates two splice variants of the mouse beta3-AR which differ within the coding region. Reverse transcription/polymerase chain reaction with intron-spanning primers was used to demonstrate the splice variant of the mouse beta3-adrenoceptor. The novel beta3b-AR has 17 amino acids encoded by exon 2 (SSLLREPRHLYTCLGYP) which differ from the 13 in the known beta3a-AR (RFDGYEGARPFPT). Beta3b-AR mRNA is differentially expressed in mouse tissues, with levels relative to beta3a-AR mRNA highest in hypothalamus, cortex and white adipose tissue, and lower in ileum smooth muscle and brown adipose tissue.