Impaired insulin action in subcutaneous adipocytes from women with visceral obesity

Sex- and depot-specific differences in cellular insulin responsiveness during adipose expansion

BACKGROUND

Adipose tissue distribution, metabolism, and expansion capacity exhibit notable sex- and depot-specific differences. Herein, we monitored adipocyte traits related to insulin responsiveness and glucose transport during adipose expansion in visceral and subcutaneous fat from male and female mice.

MATERIALS AND METHODS

Adipocytes were isolated from perigonadal and inguinal adipose tissue of chow-fed female and male C57Bl6/J mice and assessed for adipocyte size distribution using a coulter counter; glucose uptake and cytosolic volume were measured using glucose tracer assays. GLUT1, GLUT4, and IRS-1 protein levels were assessed by western blot. Pharmacological inhibition (BAY876) of GLUT1 and GLUT4 was used to resolve their respective contribution to cellular glucose transport.

KEY FINDINGS

Independent of adiposity or sex, visceral adipocytes were larger and displayed higher glucose transport, cytosolic volume, and GLUT4 levelsthan subcutaneous adipocytes. GLUT1 content was higher in subcutaneous than visceral adipocytes in both sexes. Pharmacological inhibition confirmed that GLUT1 contributes to <10 % of adipocyte glucose uptake, while GLUT4 facilitates most of both basal and insulin-stimulated glucose uptake. Females showed significantly higher basal and insulin-stimulated glucose transport, higher cytosolic volume, and greater GLUT4 and IRS-1 protein levels than males in both adipose depots. Interestingly, insulin responsiveness was preserved in female subcutaneous adipocytes but deteriorated in subcutaneous male adipocytes during adipose expansion.

SIGNIFICANCE

The improved insulin responsiveness, increased glucose transport, and higher levels of GLUT4 and IRS-1 in adipocytes might protect females from the adverse systemic effects linked to obesity. Insulin responsiveness was preserved in female subcutaneous adipocytes during adipose tissue expansion, which could contribute to the reduced risk of females to develop systemic insulin resistance.

Short Sleep Duration Disrupts Glucose Metabolism: Can Exercise Turn Back the Clock?

Short sleep duration is prevalent in modern society and may be contributing to type 2 diabetes prevalence. This review will explore the effects of sleep restriction on glycemic control, the mechanisms causing insulin resistance, and whether exercise can offset changes in glycemic control. Chronic sleep restriction may also contribute to a decrease in physical activity leading to further health complications.

Adipocyte Phenotype Flexibility and Lipid Dysregulation

The prevalence of obesity and associated cardiometabolic diseases continues to rise, despite efforts to improve global health. The adipose tissue is now regarded as an endocrine organ since its multitude of secretions, lipids chief among them, regulate systemic functions. The loss of normal adipose tissue phenotypic flexibility, especially related to lipid homeostasis, appears to trigger cardiometabolic pathogenesis. The goal of this manuscript is to review lipid balance maintenance by the lean adipose tissue’s propensity for phenotype switching, obese adipose tissue’s narrower range of phenotype flexibility, and what initial factors account for the waning lipid regulatory capacity. Metabolic, hypoxic, and inflammatory factors contribute to the adipose tissue phenotype being made rigid. A better grasp of normal adipose tissue function provides the necessary context for recognizing the extent of obese adipose tissue dysfunction and gaining insight into how pathogenesis evolves.

Fat Cell Size: Measurement Methods, Pathophysiological Origins, and Relationships With Metabolic Dysregulations

The obesity pandemic increasingly causes morbidity and mortality from type 2 diabetes, cardiovascular diseases and many other chronic diseases. Fat cell size (FCS) predicts numerous obesity-related complications such as lipid dysmetabolism, ectopic fat accumulation, insulin resistance, and cardiovascular disorders. Nevertheless, the scarcity of systematic literature reviews on this subject is compounded by the use of different methods by which FCS measurements are determined and reported. In this paper, we provide a systematic review of the current literature on the relationship between adipocyte hypertrophy and obesity-related glucose and lipid dysmetabolism, ectopic fat accumulation, and cardiovascular disorders. We also review the numerous mechanistic origins of adipocyte hypertrophy and its relationship with metabolic dysregulation, including changes in adipogenesis, cell senescence, collagen deposition, systemic inflammation, adipokine secretion, and energy balance. To quantify the effect of different FCS measurement methods, we performed statistical analyses across published data while controlling for body mass index, age, and sex.

Sex differences in white adipose tissue expansion: emerging molecular mechanisms

The escalating prevalence of individuals becoming overweight and obese is a rapidly rising global health problem, placing an enormous burden on health and economic systems worldwide. Whilst obesity has well described lifestyle drivers, there is also a significant and poorly understood component that is regulated by genetics. Furthermore, there is clear evidence for sexual dimorphism in obesity, where overall risk, degree, subtype and potential complications arising from obesity all differ between males and females. The molecular mechanisms that dictate these sex differences remain mostly uncharacterised. Many studies have demonstrated that this dimorphism is unable to be solely explained by changes in hormones and their nuclear receptors alone, and instead manifests from coordinated and highly regulated gene networks, both during development and throughout life. As we acquire more knowledge in this area from approaches such as large-scale genomic association studies, the more we appreciate the true complexity and heterogeneity of obesity. Nevertheless, over the past two decades, researchers have made enormous progress in this field, and some consistent and robust mechanisms continue to be established. In this review, we will discuss some of the proposed mechanisms underlying sexual dimorphism in obesity, and discuss some of the key regulators that influence this phenomenon.

Age and Sex: Impact on adipose tissue metabolism and inflammation

Age associated chronic inflammation is a major contributor to diseases with advancing age. Adipose tissue function is at the nexus of processes contributing to age-related metabolic disease and mediating longevity. Hormonal fluctuations in aging potentially regulate age-associated visceral adiposity and metabolic dysfunction. Visceral adiposity in aging is linked to aberrant adipogenesis, insulin resistance, lipotoxicity and altered adipokine secretion. Age-related inflammatory phenomena depict sex differences in macrophage polarization, changes in T and B cell numbers, and types of dendritic cells. Sex differences are also observed in adipose tissue remodeling and cellular senescence suggesting a role for sex steroid hormones in the regulation of the adipose tissue microenvironment. It is crucial to investigate sex differences in aging clinical outcomes to identify and better understand physiology in at-risk individuals. Early interventions aimed at targets involved in adipose tissue adipogenesis, remodeling and inflammation in aging could facilitate a profound impact on health span and overcome age-related functional decline.

White Adipose Tissue Autophagy and Adipose-Liver Crosstalk Exacerbate Nonalcoholic Fatty Liver Disease in Mice

BACKGROUND & AIMS

Although nonalcoholic fatty liver disease (NAFLD) is closely associated with obesity, the role of adipose tissue in NAFLD is not well-understood. Because autophagy has been reported to be involved in the degradation of lipid droplets, we investigated the role of adipose tissue autophagy in the liver pathogenesis of NAFLD.

METHODS

C57BL/6J mice and adipocyte-specific Atg7-knockout mice (Adipoq-Atg7 KO mice) were fed a high-fat diet (HFD).

RESULTS

HFD feeding for up to 4 months increased both inguinal and epididymal white adipose tissue (iWAT and eWAT, respectively; the former represents subcutaneous fat, and the latter represents visceral fat) in mice. After HFD feeding, autophagy flux in both types of white adipose tissue was increased, and the levels of Rubicon, a negative autophagy regulator, were decreased, suggesting autophagy promotion. Adipoq-Atg7 KO mice exhibited suppressed autophagy in both iWAT and eWAT. Adipocyte-specific Atg7 KO enhanced HFD-induced iWAT hypertrophy. On the other hand, eWAT levels in Adipoq-Atg7 KO mice were increased after 1 month of HFD feeding but decreased after 4 months of HFD feeding compared with those in wild-type controls. Cleaved caspase 3 and JNK pathway protein expression in eWAT was increased without cytokine elevation in Adipoq-Atg7 KO mice fed an HFD compared with wild-type mice fed an HFD. Adipocyte-specific Atg7 KO decreased serum free fatty acid levels and ameliorated HFD-induced steatosis, liver inflammation, and fibrosis.

CONCLUSIONS

Autophagy was enhanced in the white adipose tissues of mice fed an HFD. Autophagy inhibition in white adipose tissues ameliorated the liver pathology of NAFLD via adipose-liver crosstalk.

The clinical impact of maternal weight on offspring health: lights and shadows in breast milk metabolome

INTRODUCTION

Pre-pregnancy overweight and obesity, depending on maternal nutrition and metabolic state, can influence fetal, neonatal and long-term offspring health, regarding cardio-metabolic, respiratory, immunological and cognitive outcomes. Thus, maternal weight can act, through mechanisms that are not full understood, on the physiology and metabolism of some fetal organs and tissues, to adapt themselves to the intrauterine environment and nutritional reserves. These effects could occur by modulating gene expression, neonatal microbiome, and through breastfeeding.

AREAS COVERED

In this paper, we investigated the potential effects of metabolites found altered in breast milk (BM) of overweight/obese mothers, through an extensive review of metabolomics studies, and the potential short- and long-term clinical effects in the offspring, especially regarding overweight, glucose homeostasis, insulin resistance, oxidative stress, infections, immune processes, and neurodevelopment.

EXPERT OPINION

Metabolomics seems the ideal tool to investigate BM variation depending on maternal or fetal/neonatal factors. In particular, BM metabolome alterations according to maternal conditions were recently pointed out in cases of gestational diabetes, preeclampsia, intrauterine growth restriction and maternal overweight/obesity. In our opinion, even if BM is the food of choice in neonatal nutrition, the deepest comprehension of its composition in overweight/obese mothers could allow targeted supplementation, to improve offspring health and metabolic homeostasis.

Sexual dimorphism in cardiometabolic health: the role of adipose tissue, muscle and liver

Obesity is associated with many adverse health effects, such as an increased cardiometabolic risk. Despite higher adiposity for a given BMI, premenopausal women are at lower risk of cardiometabolic disease than men of the same age. This cardiometabolic advantage in women seems to disappear after the menopause or when type 2 diabetes mellitus develops. Sexual dimorphism in substrate supply and utilization, deposition of excess lipids and mobilization of stored lipids in various key metabolic organs (such as adipose tissue, skeletal muscle and the liver) are associated with differences in tissue-specific insulin sensitivity and cardiometabolic risk profiles between men and women. Moreover, lifestyle-related factors and epigenetic and genetic mechanisms seem to affect metabolic complications and disease risk in a sex-specific manner. This Review provides insight into sexual dimorphism in adipose tissue distribution, adipose tissue, skeletal muscle and liver substrate metabolism and tissue-specific insulin sensitivity in humans, as well as the underlying mechanisms, and addresses the effect of these sex differences on cardiometabolic health. Additionally, this Review highlights the implications of sexual dimorphism in the pathophysiology of obesity-related cardiometabolic risk for the development of sex-specific prevention and treatment strategies.

Integration of molecular profiles in a longitudinal wellness profiling cohort

An important aspect of precision medicine is to probe the stability in molecular profiles among healthy individuals over time. Here, we sample a longitudinal wellness cohort with 100 healthy individuals and analyze blood molecular profiles including proteomics, transcriptomics, lipidomics, metabolomics, autoantibodies and immune cell profiling, complemented with gut microbiota composition and routine clinical chemistry. Overall, our results show high variation between individuals across different molecular readouts, while the intra-individual baseline variation is low. The analyses show that each individual has a unique and stable plasma protein profile throughout the study period and that many individuals also show distinct profiles with regards to the other omics datasets, with strong underlying connections between the blood proteome and the clinical chemistry parameters. In conclusion, the results support an individual-based definition of health and show that comprehensive omics profiling in a longitudinal manner is a path forward for precision medicine.

An important aspect of precision medicine is to probe the stability in molecular profiles among healthy individuals over time. Here, the authors sample a longitudinal wellness cohort and analyse blood molecular profiles as well as gut microbiota composition.

Impact of sex and age on metabolism, sympathetic activity, and hypertension

In this brief review, we summarize the current knowledge on the complex interplay between metabolism, sympathetic activity and hypertension with a focus on sex differences and changes with age in humans. Evidence suggests that in premenopausal women, sex hormones, particularly estrogen exerts a profound cardioprotective effect which may be associated with favorable metabolic profiles, as well as lower sympathetic activity and blood pressure at rest and any given physiological and environmental stimuli compared with men of a similar age. Along this line, premenopausal women seem to be generally protected from obesity-induced metabolic and cardiovascular complications. However, postmenopausal estrogen deprivation during midlife and older age has a detrimental impact on metabolism, may lead to adipose tissue redistribution from the subcutaneous to abdominal area, and augments sympathetic activity. All these changes could contribute significantly to the higher prevalence of hypertension and greater cardiometabolic risk in older women than older men. It is proposed that obesity-related hypertension has a neurogenic component which is characterized by sympathetic overactivity, but the impact of sex and age remains largely unknown. Understanding sex and age-specific differences in obesity and sympathetic neural control of blood pressure is important in the prevention and/or risk reduction of cardiometabolic disorders for both men and women.

The Human Breast Milk Metabolome in Overweight and Obese Mothers

Pre-pregnancy body mass index (BMI) is a major relevance factor, since maternal overweight and obesity can impair the pregnancy outcome and represent risk factors for several neonatal, childhood, and adult conditions, including excessive weight gain, cardiovascular disease, diabetes mellitus, and even behavioral disorders. Currently, breast milk (BM) composition in such category of mothers was not completely defined. In this field, metabolomics represents the ideal technology, able to detect the whole profile of low molecular weight molecules in BM. Limited information is available on human BM metabolites differences in overweight or obese compared to lean mothers. Analyzing all the metabolomics studies published on Medline in English language, this review evaluated the effects that 8 specific types of metabolites found altered by maternal overweight and obesity (nucleotide derivatives, 5-methylthioadenosine, sugar-alcohols, acylcarnitine and amino acids, polyamines, mono-and oligosaccharides, lipids) can exert on the risk of offspring obesity development and other potentially associated health outcomes and complications. However, metabolites variations in samples collected from overweight and obese mothers and the potentially correlated effects highlighted below still need further investigations and should be confirmed in future metabolomics studies on larger samples. Finally, the positive or negative influence of maternal overweight and obesity on the offspring, potentially exerted by breastfeeding, should be analyzed in close correlation with maternal age, genetic and environmental factors, including diet, and taking into account the interactions occurring between BM metabolites and lactobiome. The evaluation of all the factors affecting BM metabolites in overweight and obese mothers can lead to the comprehensive description of such biofluid and the related effects on breastfed subjects, potentially highlighting personalized needs of BM supplementation or short- and long-term prevention strategies to optimize offspring health.

Diurnal rhythms in the white adipose tissue transcriptome are disturbed in obese individuals with type 2 diabetes compared with lean control individuals

AIMS/HYPOTHESIS

Animal studies have indicated that disturbed diurnal rhythms of clock gene expression in adipose tissue can induce obesity and type 2 diabetes. The importance of the circadian timing system for energy metabolism is well established, but little is known about the diurnal regulation of (clock) gene expression in obese individuals with type 2 diabetes. In this study we aimed to identify key disturbances in the diurnal rhythms of the white adipose tissue transcriptome in obese individuals with type 2 diabetes.

METHODS

In a case-control design, we included six obese individuals with type 2 diabetes and six healthy, lean control individuals. All participants were provided with three identical meals per day for 3 days at zeitgeber time (ZT, with ZT 0:00 representing the time of lights on) 0:30, 6:00 and 11:30. Four sequential subcutaneous abdominal adipose tissue samples were obtained, on day 2 at ZT 15:30, and on day 3 at ZT 0:15, ZT 5:45 and ZT 11:15. Gene expression was measured using RNA sequencing.

RESULTS

The core clock genes showed reduced amplitude oscillations in the individuals with type 2 diabetes compared with the healthy control individuals. Moreover, in individuals with type 2 diabetes, only 1.8% (303 genes) of 16,818 expressed genes showed significant diurnal rhythmicity, compared with 8.4% (1421 genes) in healthy control individuals. Enrichment analysis revealed a loss of rhythm in individuals with type 2 diabetes of canonical metabolic pathways involved in the regulation of lipolysis. Enrichment analysis of genes with an altered mesor in individuals with type 2 diabetes showed decreased activity of the translation initiating pathway 'EIF2 signaling'. Individuals with type 2 diabetes showed a reduced diurnal rhythm in postprandial glucose concentrations.

CONCLUSIONS/INTERPRETATION

Diurnal clock and metabolic gene expression rhythms are decreased in subcutaneous adipose tissue of obese individuals with type 2 diabetes compared with lean control participants. Future investigation is needed to explore potential treatment targets as identified by our study, including clock enhancement and induction of EIF2 signalling.

DATA AVAILABILITY

The raw sequencing data and supplementary files for rhythmic expression analysis and Ingenuity Pathway Analysis have been deposited in NCBI Gene Expression Omnibus (GEO series accession number GSE104674).

Sex differences in metabolism and cardiometabolic disorders

PURPOSE OF REVIEW

Sex differences are pervasive in metabolic and cardiovascular traits, yet they have often been ignored in human and animal model research. Sex differences can arise from reversible hormonal effects, from irreversible organizational (developmental) processes, and from gene expression differences from the X and Y chromosomes. We briefly review our current understanding of the impact of these factors in metabolic traits and disorders, with an emphasis on the recent literature.

RECENT FINDINGS

Novel sex differences continue to be identified for metabolic and cardiovascular traits. For example, it is now clear that gut microbiota tend to differ between men and women, with potentially large implications for disease susceptibility. Also, tissue-specific gene regulation differs between men and women, contributing to differential metabolism. These new insights will open up personalized therapeutic avenues for cardiometabolic diseases.

SUMMARY

Sex differences in body fat distribution, glucose homeostasis, insulin signaling, ectopic fat accumulation, and lipid metabolism during normal growth and in response to hormonal or nutritional imbalance are mediated partly through sex hormones and the sex chromosome complement. Most of these differences are mediated in a tissue-specific manner. Important future goals are to better understand the interactions between genetic variation and sex differences, and to bring an understanding of sex differences into clinical practice.

Body composition and cardiometabolic health: the need for novel concepts

It seems reasonable that overweight and obesity should be defined based on body composition rather than indirect indices like BMI or waist circumference. The use of conventional parameters like fat mass or visceral fat is however of similar and limited value for disease risk prediction at the population level and does not contribute much beyond the use of simple BMI or waist circumference. This conundrum may be partly explained by using complex phenotypes (e.g., Metabolic Syndrome or whole body insulin resistance) rather than more disease-specific outcomes like liver- and muscle insulin resistance. In addition, there are multifactorial causes of similar body composition phenotypes that may add to explain the variance in metabolic consequences of these phenotypes. An intriguing hypothesis is that fat mass represents the metabolic load that interacts with fat-free mass that stands for metabolic capacity to determine disease risk. This concept has important implications for assessment of healthy growth and development and when it is challenged with weight gain in adults. Integration of body composition information at the whole body, organ-tissue and cellular level is not required to improve the diagnosis of obesity but facilitates a better understanding of the etiology of obesity-associated metabolic complications.

Inflammatory signatures distinguish metabolic health in African American women with obesity

Obesity-driven Type 2 diabetes (T2D) is a systemic inflammatory condition associated with cardiovascular disease. However, plasma cytokines and tissue inflammation that discriminate T2D risk in African American women with obese phenotypes are not well understood. We analyzed 64 circulating cytokines and chemokines in plasma of 120 African American women enrolled in the Black Women’s Health Study. We used regression analysis to identify cytokines and chemokines associated with obesity, co-morbid T2D and hypertension, and compared results to obese women without these co-morbidities, as well as to lean women without the co-morbidities. We then used hierarchical clustering to generate inflammation signatures by combining the effects of identified cytokines and chemokines and summarized the signatures using an inflammation score. The analyses revealed six distinct signatures of sixteen cytokines/chemokines (P = 0.05) that differed significantly by prevalence of T2D (P = 0.004), obesity (P = 0.0231) and overall inflammation score (P < E-12). Signatures were validated in two independent cohorts of African American women with obesity: thirty nine subjects with no metabolic complications or with T2D and hypertension; and thirteen breast reduction surgical patients. The signatures in the validation cohorts closely resembled the distributions in the discovery cohort. We find that blood-based cytokine profiles usefully associate inflammation with T2D risks in vulnerable subjects, and should be combined with metabolism and obesity counselling for personalized risk assessment.

Exercise differentially affects metabolic functions and white adipose tissue in female letrozole- and dihydrotestosterone-induced mouse models of polycystic ovary syndrome

Here we hypothesized that exercise in dihydrotestosterone (DHT) or letrozole (LET)-induced polycystic ovary syndrome mouse models improves impaired insulin and glucose metabolism, adipose tissue morphology, and expression of genes related to adipogenesis, lipid metabolism, Notch pathway and browning in inguinal and mesenteric fat. DHT-exposed mice had increased body weight, increased number of large mesenteric adipocytes. LET-exposed mice displayed increased body weight and fat mass, decreased insulin sensitivity, increased frequency of small adipocytes and increased expression of genes related to lipolysis in mesenteric fat. In both models, exercise decreased fat mass and inguinal and mesenteric adipose tissue expression of Notch pathway genes, and restored altered mesenteric adipocytes morphology. In conclusion, exercise restored mesenteric adipocytes morphology in DHT- and LET-exposed mice, and insulin sensitivity and mesenteric expression of lipolysis-related genes in LET-exposed mice. Benefits could be explained by downregulation of Notch, and modulation of browning and lipolysis pathways in the adipose tissue.

Kisspeptin-10 inhibits proliferation and regulates lipolysis and lipogenesis processes in 3T3-L1 cells and isolated rat adipocytes

INTRODUCTION

Kisspeptin, which is encoded by the KISS1 gene and acts via GPR54, plays a role in the regulation of reproductive functions. Expression of KISS1 and GRPR54 has been found in peripheral tissues, including adipose tissue, and was shown to be influenced by metabolic status.

PURPOSE

We hypothesized that kisspeptin could be involved in regulation of lipid metabolism in the mouse 3T3-L1 cell line and in isolated rat adipocytes.

METHODS

First, we characterized expression profiles of KISS1 and GPR54 mRNA and proteins in adipose cells isolated from male rats. Secondly, we studied the effects of kisspeptin-10 on cell proliferation and survival in 3T3-L1 cells. Thirdly, we assessed the rapid action of kisspeptin-10 on lipid metabolism and glucose uptake using 3T3-L1 cells and rat primary adipocytes. Finally, we examined the effects of kisspeptin-10 on the secretion of leptin and adiponectin in rat adipocytes.

RESULTS

We have found that: (1) KISS1 and GPR54 were expressed in mouse 3T3-L1 cells and isolated rat adipocytes; (2) kisspeptin-10: (i) inhibited cell proliferation, viability and adipogenesis in 3T3-L1 and decreased expression of PPAR-γ and CEBPβ-genes, which are involved in the differentiation processes and adipogenesis; (ii) increased lipolysis in 3T3-L1 cells and rat adipocytes by enhancing expression of periliphin and hormone-sensitive lipase; (iii) modulated glucose uptake and lipogenesis; (iv) stimulated leptin and decreased adiponectin secretion from rat adipocytes.

CONCLUSION

Kisspeptin-10 could play a role in the regulation of lipid metabolism in mouse 3T3-L1 cells and rat adipocytes.

Gene expression regional differences in human subcutaneous adipose tissue

BACKGROUND

Accumulation of visceral adipose tissue (VAT) is clearly associated with an increased risk of obesity-related diseases and all-cause mortality, whereas gluteal subcutaneous fat accumulation (g-SAT) is associated with a lower risk. The relative contribution, in term of cardiovascular risk, of abdominal subcutaneous adipose tissue (a-SAT) is still controversial with studies showing both a detrimental effect and a protective role. Animal and in vitro studies demonstrated that adipocytes from visceral and subcutaneous depots have distinct morphological, metabolic and functional characteristics. These regional differences have a key role in the pathogenesis of obesity-related diseases. There is recent evidence that differentiation between upper-body and lower-body adipose tissues might be under control of site-specific sets of developmental genes, such as Homebox (HOX) genes, a group of related genes that control the body plan of an embryo along the anterior-posterior axis. However, the possible heterogeneity between different subcutaneous regions has not been extensively investigated. Here we studied global mRNA expression in g-SAT and a-SAT with a microarray approach. RNA was isolated from g-SAT and a-SAT biopsy, from eight healthy subjects, and hybridized on RNA microarray chips in order to detect regional differences in gene expression.

RESULTS

A total of 131 genes are significantly and differently (>1.5 fold change, p < 0.05) expressed in a-SAT and g-SAT. Expression profiling reveals significant differences in expression of several HOX genes. Interestingly, two molecular signature of visceral adipocyte lineage, homebox genes HOXA5 and NR2F1, are up-regulated in a-SAT versus g-SAT by a 2.5 fold change.

CONCLUSIONS

Our study shows that g-SAT and a-SAT have distinct expression profiles. The finding of a different expression of HOX genes, fundamental during the embryo development, suggests an early regional differentiation of subcutaneous adipose depots. Moreover, the higher expression of HOXA5 and NR2F1, two molecular signatures of visceral adipocytes, in a-SAT suggests that this subcutaneous adipose depot could be more similar to VAT than g-SAT. Our data suggest that we should look at SAT as composed of distinct depots with possibly different impact in obesity associated metabolic complications.

Molecular implications of adenosine in obesity

Adenosine has broad activities in organisms due to the existence of multiple receptors, the differential adenosine concentrations necessary to activate these receptors and the presence of proteins able to synthetize, degrade or transport this nucleoside. All adenosine receptors have been reported to be involved in glucose homeostasis, inflammation, adipogenesis, insulin resistance, and thermogenesis, indicating that adenosine could participate in the process of obesity. Since adenosine seems to be associated with several effects, it is plausible that adenosine participates in the initiation and development of obesity or may function to prevent it. Thus, the purpose of this review was to explore the involvement of adenosine in adipogenesis, insulin resistance and thermogenesis, with the aim of understanding how adenosine could be used to avoid, treat or improve the metabolic state of obesity. Treatment with specific agonists and/or antagonists of adenosine receptors could reverse the obesity state, since adenosine receptors normalizes several mechanisms involved in obesity, such as lipolysis, insulin sensitivity and thermogenesis. Furthermore, obesity is a preventable state, and the specific activation of adenosine receptors could aid in the prevention of obesity. Nevertheless, for the treatment of obesity and its consequences, more studies and therapeutic strategies in addition to adenosine are necessary.

Cellular Mechanisms Driving Sex Differences in Adipose Tissue Biology and Body Shape in Humans and Mouse Models

Sex differences in adipose tissue distribution and the metabolic, endocrine, and immune functions of different anatomical fat depots have been described, but they are incompletely documented in the literature. It is becoming increasingly clear that adipose depots serve distinct functions in males and females and have specific physiological roles. However, the mechanisms that regulate the size and function of specific adipose tissues in men and women remain poorly understood. New insights from mouse models have advanced our understanding of depot differences in adipose growth and remodeling via the proliferation and differentiation of adipose progenitors that can expand adipocyte number in the tissue or simply replace dysfunctional older and larger adipocytes. A limited ability of a depot to expand or remodel can lead to excessive adipocyte hypertrophy, which is often correlated with metabolic dysfunction. However, the relationship of adipocyte size and function varies by depot and sex. For example, femoral adipose tissues of premenopausal women appear to have a greater capacity for adipose expansion via hyperplasia and hypertrophy; although larger, these gluteal-femoral adipocytes remain insulin sensitive. The microenvironment of specific depots, including the composition of the extracellular matrix and cellular composition, as well as cell-autonomous genetic differences, influences sex- and depot-dependent metabolic and growth properties. Although there are some species differences, studies of the molecular and physiological determinants of sex differences in adipocyte growth and function in humans and rodents are both needed for understanding sex differences in health and disease.

Relationships between Rodent White Adipose Fat Pads and Human White Adipose Fat Depots

The objective of this review was to compare and contrast the physiological and metabolic profiles of rodent white adipose fat pads with white adipose fat depots in humans. Human fat distribution and its metabolic consequences have received extensive attention, but much of what has been tested in translational research has relied heavily on rodents. Unfortunately, the validity of using rodent fat pads as a model of human adiposity has received less attention. There is a surprisingly lack of studies demonstrating an analogous relationship between rodent and human adiposity on obesity-related comorbidities. Therefore, we aimed to compare known similarities and disparities in terms of white adipose tissue (WAT) development and distribution, sexual dimorphism, weight loss, adipokine secretion, and aging. While the literature supports the notion that many similarities exist between rodents and humans, notable differences emerge related to fat deposition and function of WAT. Thus, further research is warranted to more carefully define the strengths and limitations of rodent WAT as a model for humans, with a particular emphasis on comparable fat depots, such as mesenteric fat.

Shaping fat distribution: New insights into the molecular determinants of depot- and sex-dependent adipose biology

OBJECTIVE

To review recent advances in understanding the cellular mechanisms that regulate fat distribution.

METHODS

In this review, new insights into depot and sex differences in the developmental origins and growth of adipose tissues as revealed by studies that use new methods, including lineage tracing, are highlighted.

RESULTS

Variations in fat distribution during normal growth and in response to alterations in nutritional or hormonal status are driven by intrinsic differences in cells found in each adipose depot. Adipose progenitor cells and preadipocytes in different anatomical adipose tissues derive from cell lineages that determine their capacity for proliferation and differentiation. As a result, rates of hypertrophy and hyperplasia during growth and remodeling vary among depots. The metabolic capacities of adipose cells are also determined by variations in the expression of key transcription factors and non-coding RNAs. These developmental events are influenced by sex chromosomes and hormonal and nutrient signals that determine the adipogenic, metabolic, and functional properties of each depot.

CONCLUSIONS

These new developments in the understanding of fat distribution provide a sound basis for understanding the association of body shape and health in men and women with and without obesity.

Obesity-related insulin resistance: implications for the surgical patient

In healthy surgical patients, preoperative fasting and major surgery induce development of insulin resistance (IR). IR can be present in up to 41% of obese patients without diabetes and this can rise in the postoperative period, leading to an increased risk of postoperative complications. Inflammation is implicated in the aetiology of IR. This review examines obesity-associated IR and its implications for the surgical patient. Searches of the Medline and Science Citation Index databases were performed using various key words in combinations with the Boolean operators AND, OR and NOT. Key journals, nutrition and metabolism textbooks and the reference lists of key articles were also hand searched. Adipose tissue has been identified as an active endocrine organ and the chemokines secreted as a result of macrophage infiltration have a role in the pathogenesis of IR. Visceral adipose tissue appears to be the most metabolically active, although results across studies are not consistent. Results from animal and human studies often provide conflicting results, which has rendered the pursuit of a common mechanistic pathway challenging. Obesity-associated IR appears, in part, to be related to inflammatory changes associated with increased adiposity. Postoperatively, the surgical patient is in a proinflammatory state, so this finding has important implications for the obese surgical patient.

Subcutaneous adipose tissue insulin resistance is associated with visceral adiposity in postmenopausal women

OBJECTIVE

Whole body and subcutaneous adipose tissue (SAT) insulin resistance association with regional fat mass (FM) was determined.

METHODS

Postmenopausal women (mean ± SD; age 56 ± 4 years, n = 25) who were overweight or obese (BMI 29.9 ± 5.1 kg/m(2) ) were studied. Whole body and regional FM were measured by dual-energy X-ray absorptiometry (DXA) and computed tomography (CT). Women were studied during basal and insulin-stimulated (3-stage euglycemic clamp) conditions. Whole-body lipolysis was assessed by [(2) H5 ]-glycerol rate of appearance and abdominal and femoral SAT lipolysis by interstitial glycerol (microdialysis).

RESULTS

Whole body insulin resistance in skeletal muscle (insulin-stimulated glucose disposal) and adipose tissue (insulin-suppressed lipolysis) were independently related to trunk FM (r = -0.336 and 0.484, respectively), but not leg FM (r = -0.142 and -0.148, respectively). Local antilipolytic insulin resistance in abdominal, but not femoral, SAT was positively related to trunk FM (r = 0.552) and visceral FM (r = 0.511) but not related to leg FM (r = -0.289). Whole body and abdominal, but not femoral, adipose tissue insulin sensitivity were strongly related to skeletal muscle insulin sensitivity (r = -0.727 and -0.674, respectively).

CONCLUSIONS

The association of SAT insulin sensitivity (lipolysis) with adiposity and skeletal muscle insulin sensitivity was specific to the abdominal region.

Fat mass localization alters fuel oxidation during exercise in normal weight women

PURPOSE

Abdominal and lower body fat mass tissues exhibit particular metabolic profiles at rest and during exercise. However, data are missing in normal weight women during exercise. The purpose of this study was to investigate the effect of low (LA/LB) and high (HA/LB) abdominal to lower body (A/LB) fat mass ratio on metabolic and hormonal responses during exercise in premenopausal normal weight women.

METHODS

After preliminary testing (V˙O2max and body composition assessment), substrate oxidation (RER, lipid, and carbohydrate oxidation rates), metabolic response (glycerol, free fatty acids, and glucose), and hormonal response (insulin, growth hormone, atrial natriuretic peptide, adrenaline, and noradrenaline) were determined during exercise (45 min at 65% of V˙O2max) in 21 premenopausal normal weight women (10 HA/LB women vs 11 LA/LB women).

RESULTS

Waist circumference was significantly higher in HA/LB women compared with LA/LB women (P < 0.01). No difference in other anthropometric characteristics, V˙O2max, and resting blood values was observed between the two groups. LA/LB subjects exhibited greater lipid oxidation rates compared with HA/LB women during exercise (P < 0.01). This occurred with lower plasma insulin (P < 0.05) and glucose (P < 0.05) concentrations and higher plasma free fatty acids (P < 0.05), glycerol (P < 0.05), growth hormone (P < 0.05), and atrial natriuretic peptide levels (P < 0.01) during exercise in the LA/LB group compared with the HA/LB group.

CONCLUSIONS

The present study demonstrated that LA/LB women exhibited an increase in whole-body lipid mobilization and use during exercise compared with HA/LB counterparts. This greater reliance on lipid as fuel metabolism during exercise could be explained by substrate availability and metabolic and hormonal responses. It appeared that LA/LB women exhibited greater metabolic flexibility during an exercise bout of 45 min at 65% of V˙O2max on cycle ergometer.

Obesity and its metabolic complications: the role of adipokines and the relationship between obesity, inflammation, insulin resistance, dyslipidemia and nonalcoholic fatty liver disease

Accumulating evidence indicates that obesity is closely associated with an increased risk of metabolic diseases such as insulin resistance, type 2 diabetes, dyslipidemia and nonalcoholic fatty liver disease. Obesity results from an imbalance between food intake and energy expenditure, which leads to an excessive accumulation of adipose tissue. Adipose tissue is now recognized not only as a main site of storage of excess energy derived from food intake but also as an endocrine organ. The expansion of adipose tissue produces a number of bioactive substances, known as adipocytokines or adipokines, which trigger chronic low-grade inflammation and interact with a range of processes in many different organs. Although the precise mechanisms are still unclear, dysregulated production or secretion of these adipokines caused by excess adipose tissue and adipose tissue dysfunction can contribute to the development of obesity-related metabolic diseases. In this review, we focus on the role of several adipokines associated with obesity and the potential impact on obesity-related metabolic diseases. Multiple lines evidence provides valuable insights into the roles of adipokines in the development of obesity and its metabolic complications. Further research is still required to fully understand the mechanisms underlying the metabolic actions of a few newly identified adipokines.

Interrelationships between changes in anthropometric variables and computed tomography indices of abdominal fat distribution in response to a 1-year physical activity–healthy eating lifestyle modification program in abdominally obese men

The objectives were to (i) measure the effects of a 1-year lifestyle modification program on body fat distribution/anthropometric variables; (ii) determine the interrelationships between changes in all these variables; and (iii) investigate whether there is a selective reduction in deep (DSAT) vs. superficial subcutaneous adipose tissue (SSAT) at the abdominal level following a 1-year lifestyle modification program. Anthropometric variables, body composition and abdominal and midthigh fat distribution were assessed at baseline and after 1 year in 109 sedentary, dyslipidemic and abdominally obese men. Reductions in anthropometric variables, skinfold thicknesses (except the trunk/extremity ratio) and fat mass as well as an increase in fat-free mass were observed after 1 year (p < 0.0001). Decreases in abdominal adipose tissue volumes were also noted (–23%, –26%, –18%, –19%, –17%, p < 0.0001 for total adipose tissue, visceral adipose tissue, subcutaneous adipose tissue, DSAT and SSAT, respectively). Adipose tissue areas at midthigh also decreased (–18%, –18%, –17%, p < 0.0001 for total, deep, and subcutaneous adipose tissue, respectively). A reduction (–9%, p < 0.0001) in low-attenuation muscle area and an increase (+1%, p < 0.05) in normal-attenuation muscle area were also observed. There was a positive relationship between changes in visceral adipose tissue and changes in DSAT (r = 0.65, p < 0.0001) or SSAT (r = 0.63, p < 0.0001). Although absolute changes in DSAT were greater than changes in SSAT, relative changes in both depots were similar, independent of changes in visceral adipose tissue. The 1-year lifestyle modification program therefore improved the body fat distribution pattern and midthigh muscle quality in abdominally obese men.

Free fatty acid flux in African-American and Caucasian adults--effect of sex and race

OBJECTIVE

Obesity, insulin resistance, and diabetes disproportionately affect African-American (AA) women. Abnormal adipose tissue free fatty acid (FFA) release is associated with these conditions. Resting energy expenditure (REE) and sex predict FFA release in Caucasians, but whether this is true in AA is unknown. The sex-specific relationships between FFA release, REE, and race was compared.

DESIGN AND METHODS

100 adults (47% AA, 50% male, age 32 ± 8 years [mean ± SD]) from three different centers underwent duplicate measures of FFA release ([U-13C] palmitate) and REE (indirect calorimetry). Body composition was determined by DXA and abdominal imaging.

RESULTS

AA participants had lower REE, but similar FFA concentrations and flux compared with Caucasian participants. The significant predictors of palmitate release were REE, sex, and race. REE and FFA flux were correlated in both sexes and both races. In a multiple linear regression analysis with palmitate flux as the dependent variable and REE, sex, race, total fat mass, fat-free mass, and insulin as independent variables, REE was the only independent predictor of FFA release in men. Both REE and race predicted palmitate flux in women.

CONCLUSIONS

FFA flux is related to REE, but the relationship differs in AA and Caucasian women.

Mesenchymal stem cells: a revolution in therapeutic strategies of age-related diseases

The great evolutionary biologist Theodosius Dobzhansky once said: "Nothing in biology makes sense except in the light of evolution". Aging is a complex biological phenomenon and the factors governing the process of aging and age-related diseases are only beginning to be understood, oxidative stress, telomere shortening in DNA components and genetic changes were shown to be the mainly regulating mechanisms during the recent decades. Although a considerable amount of both animal and clinical data that demonstrate the extensive and safe use of mesenchymal stromal cells (MSCs) is available, the precise summarization and identification of MSCs in age-related diseases remains a challenge. Along this line, this review discussed several typical age-related diseases for which MSCs have been proved to confer protection and put forward a hypothesis for the association among MSCs and age-related diseases from an evolutionary perspective. Above all, we hope further and more research efforts could be aroused to elucidate the role and mechanisms that MSCs involved in the age-related diseases.

Distinct developmental signatures of human abdominal and gluteal subcutaneous adipose tissue depots

CONTEXT

Fat distribution differs in men and women, but in both sexes, a predominantly gluteal-femoral compared with abdominal (central) fat distribution is associated with lower metabolic risk. Differences in cellular characteristics and metabolic functions of these depots have been described, but the molecular mechanisms involved are not understood.

OBJECTIVE

Our objective was to identify depot- and sex-dependent differences in gene expression in human abdominal and gluteal sc adipose tissues.

DESIGN AND METHODS

Abdominal and gluteal adipose tissue aspirates were obtained from 14 premenopausal women [age 27.5 ± 7.0 yr, body mass index (BMI) 27.3 ± 6.2 kg/m(2), and waist-to-hip ratio 0.82 ± 0.04] and 21 men (age 29.7±7.4 yr, BMI 27.2 ± 4.5 kg/m(2), and waist-to-hip ratio 0.91 ± 0.07) and transcriptomes were analyzed using Illumina microarrays. Expression of selected genes was determined in isolated adipocytes and stromal vascular fractions from each depot, and in in vitro cultures before and after adipogenic differentiation.

RESULTS

A total of 284 genes were differentially expressed between the abdominal and gluteal depot, either specifically in males (n = 66) or females (n = 159) or in both sexes (n = 59). Most notably, gene ontology and pathway analysis identified homeobox genes (HOXA2, HOXA3, HOXA4, HOXA5, HOXA9, HOXB7, HOXB8, HOXC8, and IRX2) that were down-regulated in the gluteal depot in both sexes (P = 2 × 10(-10)). Conversely, HOXA10 was up-regulated in gluteal tissue and HOXC13 was detected exclusively in this depot. These differences were independent of BMI, were present in both adipocytes and stromal vascular fractions of adipose tissue, and were retained throughout in vitro differentiation.

CONCLUSIONS

We conclude that developmentally programmed differences may contribute to the distinct phenotypic characteristics of peripheral fat.

Low-calorie diet induced weight loss may alter regulatory hormones and contribute to rebound visceral adiposity in obese persons with a family history of type-2 diabetes

PURPOSE

To examine potential detrimental long-term effects of acute diet-induced weight loss on visceral adiposity, insulin resistance, cortisol, and adipokines in obese individuals at risk for type-2 diabetes.

DATA SOURCES

Anthropometric measures (height, weight, waist circumference), self-report instruments, abdominal computed tomography (CT) scan, and blood samples (glucose, insulin, interleukin-6, leptin, adiponectin) were obtained from a convenience sample of 20 participants at baseline, after a 28-day low-calorie diet (800 kcal/day) intervention, and again 6 months later.

CONCLUSIONS

Fifteen of 20 participants completed the 28-day diet intervention and had a mean weight loss of 15 pounds. Comparison between baseline, postdiet, and 6-month data, demonstrated that although participants had significant improvements after the diet, they regained fat mass, particularly in the visceral area.

IMPLICATIONS FOR PRACTICE

Clinicians may need to revise recommendations for using low-calorie diets to achieve weight loss. Diet-induced weight cycling may contribute to dysregulation of metabolism and have long-term detrimental consequences for accumulation of visceral adipose tissue. The likelihood of success is low, with high dropout rates, and those patients who achieve weight loss are very likely to regain it. Thus, the perceived short-term benefits of calorie-restricted diets in this population likely do not outweigh the potential long-term detrimental effects.

Adipose tissue heterogeneity: implication of depot differences in adipose tissue for obesity complications

Obesity, defined as excess fat mass, increases risks for multiple metabolic diseases, such as type 2 diabetes, cardiovascular disease and several types of cancer. Over and above fat mass per se, the pattern of fat distribution, android or truncal as compared to gynoid or peripheral, has a profound influence on systemic metabolism and hence risk for metabolic diseases. Increases in upper body adipose tissue (visceral and abdominal subcutaneous) confer an independent risk, while the quantity of gluteofemoral adipose tissue is protective. Variations in the capacity of different depots to store and release fatty acids and to produce adipokines are important determinants of fat distribution and its metabolic consequences. Depot differences in cellular composition and physiology, including innervation and blood flow, likely influence their phenotypic properties. A number of lines of evidence also support the idea that adipocytes from different anatomical depots are intrinsically different as a result of genetic or developmental events. In this chapter, we will review the phenotypic characteristics of different adipose depots and mechanisms that link their depot-specific biology to metabolic complications in men and women.

Interleukin-1 beta: a potential link between stress and the development of visceral obesity

Background

A disproportionate amount of body fat within the abdominal cavity, otherwise known as visceral obesity, best predicts the negative health outcomes associated with high levels body fat. Growing evidence suggests that repeated activation of the stress response can favor visceral fat deposition and that visceral obesity may induce low-grade, systemic inflammation which is etiologically linked to the pathogenesis of obesity related diseases such as cardiovascular disease and type 2 diabetes. While the obesity epidemic has fueled considerable interest in these obesity-related inflammatory diseases, surprisingly little research is currently focused on understanding the functions of inflammatory proteins in healthy, non-obese white adipose tissue (WAT) and their possible role in modulating stress-induced shifts in body fat distribution.

Hypothesis

The current review presents evidence in support the novel hypothesis that stress-evoked interleukin-1 beta (IL-1β) signaling within subcutaneous adipose tissue, when repeatedly induced, contributes toward the development of visceral obesity. It is suggested that because acute stressor exposure differentially increases IL-1β levels within subcutaneous adipose relative to visceral adipose tissue in otherwise healthy, non-obese rats, repeated induction of this response may impair the ability of subcutaneous adipose tissue to uptake energy substrates, synthesize and retain triglycerides, and/or adapt to positive energy balance via hyperplasia. Consequently, circulating energy substrates may be disproportionately shunted to visceral adipose tissue for storage, thus driving the development of visceral obesity.

Conclusions

This review establishes the following key points: 1) body fat distribution outweighs the importance of total body fat when predicting obesity-related disease risk; 2) repeated exposure to stress can drive the development of visceral obesity independent of changes in body weight; 3) because of the heterogeneity of WAT composition and function, an accurate understanding of WAT responses requires sampling multiple WAT depots; 4) acute, non-pathogenic stressor exposure increases WAT IL-1β concentrations in a depot specific manner suggesting an adaptive, metabolic role for this cytokine; however, when repeated, stress-induced IL-1β in non-visceral WAT may result in functional impairments that drive the development of stress-induced visceral obesity.

Sex differences in human adipose tissues - the biology of pear shape

Women have more body fat than men, but in contrast to the deleterious metabolic consequences of the central obesity typical of men, the pear-shaped body fat distribution of many women is associated with lower cardiometabolic risk. To understand the mechanisms regulating adiposity and adipose tissue distribution in men and women, significant research attention has focused on comparing adipocyte morphological and metabolic properties, as well as the capacity of preadipocytes derived from different depots for proliferation and differentiation. Available evidence points to possible intrinsic, cell autonomous differences in preadipocytes and adipocytes, as well as modulatory roles for sex steroids, the microenvironment within each adipose tissue, and developmental factors. Gluteal-femoral adipose tissues of women may simply provide a safe lipid reservoir for excess energy, or they may directly regulate systemic metabolism via release of metabolic products or adipokines. We provide a brief overview of the relationship of fat distribution to metabolic health in men and women, and then focus on mechanisms underlying sex differences in adipose tissue biology.

Abdominal superficial subcutaneous fat: a putative distinct protective fat subdepot in type 2 diabetes

OBJECTIVE

Unlike visceral adipose tissue (VAT), the association between subcutaneous adipose tissue (SAT) and obesity-related morbidity is controversial. In patients with type 2 diabetes, we assessed whether this variability can be explained by a putative favorable, distinct association between abdominal superficial SAT (SSAT) (absolute amount or its proportion) and cardiometabolic parameters.

RESEARCH DESIGN AND METHODS

We performed abdominal magnetic resonance imaging (MRI) in 73 patients with diabetes (mean age 58 years, 83% were men) and cross-sectionally analyzed fat distribution at S1-L5, L5-L4, and L3-L2 levels. Patients completed food frequency questionnaires, and subgroups had 24-h ambulatory blood pressure monitoring and 24-h ambulatory electrocardiography.

RESULTS

Women had higher %SSAT (37 vs. 23% in men; P < 0.001) despite a similar mean waist circumference. Fasting plasma glucose (P = 0.046) and HbA(1c) (P = 0.006) were both lower with increased tertile of absolute SSAT. In regression models adjusted for age, waist circumference, and classes of medical treatments used in this patient population, increased %SSAT was significantly associated with decreased HbA(1c) (β = -0.317; P = 0.013), decreased daytime ambulatory blood pressure (β = -0.426; P = 0.008), and increased HDL cholesterol (β = 0.257; P = 0.042). In contrast, increased percent of deep SAT (DSAT) was associated with increased HbA(1c) (β = 0.266; P = 0.040) and poorer heart rate variability parameters (P = 0.030). Although total fat and energy intake were not correlated with fat tissue distribution, increased intake of trans fat tended to be associated with total SAT (r = 0.228; P = 0.05) and DSAT (r = 0.20; P = 0.093), but not with SSAT.

CONCLUSIONS

Abdominal SAT is composed of two subdepots that associate differently with cardiometabolic parameters. Higher absolute and relative distribution of fat in abdominal SSAT may signify beneficial cardiometabolic effects in patients with type 2 diabetes.

From PDE3B to the regulation of energy homeostasis

The incidence of obesity in the developed world is increasing at an alarming rate. Concurrent with the increase in the incidence of obesity is an increase in the incidence of type 2 diabetes. Cyclic AMP (cAMP) and cGMP are key second messengers in all cells; for example, when it comes to processes of relevance for the regulation of energy metabolism, cAMP is a key mediator in the regulation of lipolysis, glycogenolysis, gluconeogenesis and pancreatic β cell insulin secretion. PDE3B, one of several enzymes which hydrolyze cAMP and cGMP, is expressed in cells of importance for the regulation of energy homeostasis, including adipocytes, hepatocytes, hypothalamic cells and β cells. It has been shown, using PDE3 inhibitors and gene targeting approaches in cells and animals, that altered levels of PDE3B result in a number of changes in the regulation of glucose and lipid metabolism and in overall energy homeostasis. This article highlights the complexity involved in the regulation of PDE3B by hormones, and in the regulation of downstream metabolic effects by PDE3B in several interacting tissues.

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

Objective: To elucidate the activity and expression of cyclic nucleotide phosphodiesterase (PDE) families in omental (OM) and subcutaneous (SC) adipose tissue and adipocytes, and to study alterations in their activity in human obesity.

Design: Cross-sectional, translational research study.

Patients: In total, 25 obese and 9 non-obese subjects undergoing gastrointestinal surgery participated in the study.

Results: Inverse correlations between PDE activities and body mass index (BMI) were seen in both SC and OM adipose tissue. Inverse correlations between total PDE and PDE3 activity and BMI were seen in OM adipocytes but not in SC adipocytes. In both SC and OM adipose tissue of obese patients, total PDE and PDE3 activities were decreased compared with the controls. In SC adipose tissue of Type 2 diabetes (T2D) patients, the PDE activity not inhibitable by PDE3 or PDE4 inhibitors (PDEn) was increased compared with obese non-diabetic patients. In addition to PDE3 and 4 isoforms, PDE7B, PDE9A and PDE10A proteins were also detected in adipose tissue or adipocytes.

Conclusions: Multiple PDE families are present in human adipose tissue and their activities are differentially affected by obesity and T2D.

Anthropometric measurements and diabetes mellitus: clues to the "pathogenic" and "protective" potential of adipose tissue

BACKGROUND

Increased visceral adipose tissue (VAT) is "pathogenic" through adverse endocrine and immune contributions to metabolic diseases such as diabetes mellitus, hypertension, and dyslipidemia. Increased VAT increases waist circumference (WC), and WC is a recommended anthropometric measure of pathogenic adipose tissue distribution. Increased subcutaneous adipose tissue (SAT) is often described as "protective" against metabolic disease and frequently approximated by hip circumference (HC).

METHODS

The Study to Help Improve Early evaluation and management of risk factors Leading to Diabetes (SHIELD) evaluated a study sample weighted to reflect the U.S. adult population. Respondents diagnosed with type 2 diabetes mellitus (T2DM; n = 3825) and without T2DM (n = 13,327) self-reported their weight and height, WC, and HC.

RESULTS

T2DM men and women had a disproportionate increase in body mass index (BMI) and WC, with 30% of T2DM men and 40% of T2DM women having a WC within the highest quintile compared to the overall study population. Waist-to-hip ratio (WHR) appeared to be the best anthropometric predictor of T2DM. However, both T2DM men and women also had a disproportionate increase in HC, with 30% of T2DM men and 34% of T2DM women having a HC within the highest quintile, which was generally similar to the distribution of BMI and WHR.

CONCLUSIONS

This analysis suggests that: (1) An increase in adipose tissue generally increases the risk of T2DM; (2) central adiposity is more pathogenic than peripheral subcutaneous adiposity; and (3) SAT accumulation, as assessed by increased HC, does not always "protect" against metabolic diseases such as T2DM.

Glyceroneogenesis is inhibited through HIV protease inhibitor-induced inflammation in human subcutaneous but not visceral adipose tissue

Glyceroneogenesis, a metabolic pathway that participates during lipolysis in the recycling of free fatty acids to triglycerides into adipocytes, contributes to the lipid-buffering function of adipose tissue. We investigated whether glyceroneogenesis could be affected by human immunodeficiency virus (HIV) protease inhibitors (PIs) responsible or not for dyslipidemia in HIV-infected patients. We treated explants obtained from subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) depots from lean individuals. We observed that the dyslipidemic PIs nelfinavir, lopinavir and ritonavir, but not the lipid-neutral PI atazanavir, increased lipolysis and decreased glyceroneogenesis, leading to an increased release of fatty acids from SAT but not from VAT. At the same time, dyslipidemic PIs decreased the amount of perilipin and increased interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) secretion in SAT but not in VAT. Parthenolide, an inhibitor of the NFκB pathway, counteracted PI-induced increased inflammation and decreased glyceroneogenesis. IL-6 (100 ng) inhibited the activity of phosphoenolpyruvate carboxykinase, the key enzyme of glyceroneogenesis, in SAT but not in VAT. Our data show that dyslipidemic but not lipid-neutral PIs decreased glyceroneogenesis as a consequence of PI-induced increased inflammation in SAT that could have an affect on adipocytes and/or macrophages. These results add a new link between fat inflammation and increased fatty acids release and suggest a greater sensitivity of SAT than VAT to PI-induced inflammation.

Femoral adipose tissue may accumulate the fat that has been recycled as VLDL and nonesterified fatty acids

OBJECTIVE

Gluteo-femoral, in contrast to abdominal, fat accumulation appears protective against diabetes and cardiovascular disease. Our objective was to test the hypothesis that this reflects differences in the ability of the two depots to sequester fatty acids, with gluteo-femoral fat acting as a longer-term "sink."

RESEARCH DESIGN AND METHODS

A total of 12 healthy volunteers were studied after an overnight fast and after ingestion of a mixed meal. Blood samples were taken from veins draining subcutaneous femoral and abdominal fat and compared with arterialized blood samples. Stable isotope-labeled fatty acids were used to trace specific lipid fractions. In 36 subjects, adipose tissue blood flow in the two depots was monitored with (133)Xe.

RESULTS

Blood flow increased in response to the meal in both depots, and these responses were correlated (r(s) = 0.44, P < 0.01). Nonesterified fatty acid (NEFA) release was suppressed after the meal in both depots; it was lower in femoral fat than in abdominal fat (P < 0.01). Plasma triacylglycerol (TG) extraction by femoral fat was also lower than that by abdominal fat (P = 0.05). Isotopic tracers showed that the difference was in chylomicron-TG extraction. VLDL-TG extraction and direct NEFA uptake were similar in the two depots.

CONCLUSIONS

Femoral fat shows lower metabolic fluxes than subcutaneous abdominal fat, but differs in its relative preference for extracting fatty acids directly from the plasma NEFA and VLDL-TG pools compared with chylomicron-TG.

Resistance to the antilipolytic effect of insulin in adipocytes of African-American compared to Caucasian postmenopausal women

High fatty acid (FA) flux is associated with systemic insulin resistance, and African-American (AA) women tend to be more insulin resistant. We assessed possible depot and race difference in the antilipolytic effect of insulin in adipocytes isolated from abdominal (Abd) and gluteal (Glt) subcutaneous (sc) adipose tissue of overweight, postmenopausal AA and Caucasian (C) women. Percent body fat, fasting insulin, visceral adiposity, and adipocyte size was higher in AA women. Disinhibited lipolysis (presence of adenosine deaminase) per unit adipocyte surface area was similar in Abd and Glt and in AA and C. However, rates of 'basal' [submaximal phenylisopropyl adenosine (PIA)-suppressed] and insulin-suppressed lipolysis were higher in Abd of AA compared with C women even after adjustment for percent fat and visceral fat area. The race difference in rates of PIA- and insulin-suppressed lipolysis in AA were correlated with their hyperinsulinemia, but AA race, independent of fasting insulin, was associated with lower responsiveness (percent suppression) to submaximal insulin concentrations, although sensitivity (ED50) was not affected. Overall, these data are consistent with the hypothesis that decreased responsiveness of Abd adipocytes to antilipolytic effectors may contribute to higher FA availability and thereby to racial differences in insulin resistance.

Associations of the limb fat to trunk fat ratio with markers of cardiometabolic risk in elderly men and women

BACKGROUND

The ratio of limb fat to trunk fat (LF/TF) is associated with markers of cardiometabolic risk in elderly men and women. It is unknown if LF/TF is associated with cardiometabolic risk beyond that explained by LF and TF independently.

METHODS

Participants included abdominally obese men (n = 58) and women (n = 78) between 60 and 80 years of age. Regional adiposity was quantified using magnetic resonance imaging. Insulin resistance, fasting glucose, high-density lipoprotein (HDL) cholesterol, plasma triglycerides, and adiponectin were determined using standard procedures.

RESULTS

After control for potential confounders, TF was positively associated with fasting glucose, insulin resistance, and plasma triglycerides and negatively associated with HDL cholesterol and adiponectin (p < or = .05). These associations were strengthened after further control for LF (p < .05), with the exception of adiponectin in men (p > .05). After control for potential confounders, LF was negatively associated with adiponectin in men (p < .05) but not with any other marker of cardiometabolic risk (p > .05). After further control for TF, LF was negatively associated with plasma triglycerides and positively associated with HDL cholesterol in both genders combined (p < .05) and with adiponectin in women (p < .05) but not in men (p > .05). LF/TF was not associated with any marker of cardiometabolic risk after control for LF and TF.

CONCLUSION

These results suggest that it is the absolute, rather than relative, amounts of LF and TF that have the greatest influence on cardiometabolic risk in elderly men and women.

Is adiposopathy (sick fat) an endocrine disease?

OBJECTIVE

To review current consensus and controversy regarding whether obesity is a 'disease', examine the pathogenic potential of adipose tissue to promote metabolic disease and explore the merits of 'adiposopathy' and 'sick fat' as scientifically and clinically useful terms in defining when excessive body fat may represent a 'disease'.

METHODS

A group of clinicians and researchers, all with a background in endocrinology, assembled to evaluate the medical literature, as it pertains to the pathologic and pathogenic potential of adipose tissue, with an emphasis on metabolic diseases that are often promoted by excessive body weight.

RESULTS

The data support pathogenic adipose tissue as a disease. Challenges exist to convince many clinicians, patients, healthcare entities and the public that excessive body fat is often no less a 'disease' than the pathophysiological consequences related to anatomical abnormalities of other body tissues. 'Adiposopathy' has the potential to scientifically define adipose tissue anatomic and physiologic abnormalities, and their adverse consequences to patient health. Adiposopathy acknowledges that when positive caloric balance leads to adipocyte hypertrophy and visceral adiposity, then this may lead to pathogenic adipose tissue metabolic and immune responses that promote metabolic disease. From a patient perspective, explaining how excessive caloric intake might cause fat to become 'sick' also helps provide a rationale for patients to avoid weight gain. Adiposopathy also better justifies recommendations of weight loss as an effective therapeutic modality to improve metabolic disease in overweight and obese patients.

CONCLUSION

Adiposopathy (sick fat) is an endocrine disease.

Pathogenic potential of adipose tissue and metabolic consequences of adipocyte hypertrophy and increased visceral adiposity

When caloric intake exceeds caloric expenditure, the positive caloric balance and storage of energy in adipose tissue often causes adipocyte hypertrophy and visceral adipose tissue accumulation. These pathogenic anatomic abnormalities may incite metabolic and immune responses that promote Type 2 diabetes mellitus, hypertension and dyslipidemia. These are the most common metabolic diseases managed by clinicians and are all major cardiovascular disease risk factors. 'Disease' is traditionally characterized as anatomic and physiologic abnormalities of an organ or organ system that contributes to adverse health consequences. Using this definition, pathogenic adipose tissue is no less a disease than diseases of other body organs. This review describes the consequences of pathogenic fat cell hypertrophy and visceral adiposity, emphasizing the mechanistic contributions of genetic and environmental predispositions, adipogenesis, fat storage, free fatty acid metabolism, adipocyte factors and inflammation. Appreciating the full pathogenic potential of adipose tissue requires an integrated perspective, recognizing the importance of 'cross-talk' and interactions between adipose tissue and other body systems. Thus, the adverse metabolic consequences that accompany fat cell hypertrophy and visceral adiposity are best viewed as a pathologic partnership between the pathogenic potential adipose tissue and the inherited or acquired limitations and/or impairments of other body organs. A better understanding of the physiological and pathological interplay of pathogenic adipose tissue with other organs and organ systems may assist in developing better strategies in treating metabolic disease and reducing cardiovascular disease risk.

Endocannabinoid dysregulation in the pancreas and adipose tissue of mice fed with a high-fat diet

OBJECTIVE

In mice, endocannabinoids (ECs) modulate insulin release from pancreatic beta-cells and adipokine expression in adipocytes through cannabinoid receptors. Their pancreatic and adipose tissue levels are elevated during hyperglycemia and obesity, but the mechanisms underlying these alterations are not understood.

METHODS AND PROCEDURES

We assessed in mice fed for up to 14 weeks with a standard or high-fat diet (HFD): (i) the expression of cannabinoid receptors and EC biosynthesizing enzymes (N-acyl-phosphatidyl-ethanolamine-selective phospholipase D (NAPE-PLD) and DAGLalpha) and degrading enzymes (fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL)) in pancreatic and adipose tissue sections by immunohistochemical staining; (ii) the amounts, measured by liquid chromatography-mass spectrometry, of the ECs, 2-AG, and anandamide (AEA).

RESULTS

Although CB(1) receptors and biosynthetic enzymes were found mostly in alpha-cells, degrading enzymes were identified in beta-cells. Following HFD, staining for biosynthetic enzymes in beta-cells and lower staining for FAAH were observed together with an increase of EC pancreatic levels. While we observed no diet-induced change in the intensity of the staining of EC metabolic enzymes in the mesenteric visceral fat, a decrease in EC concentrations was accompanied by lower and higher staining of biosynthesizing enzymes and FAAH, respectively, in the subcutaneous fat. No change in cannabinoid receptor staining was observed following HFD in any of the analyzed tissues.

DISCUSSION

We provide unprecedented information on the distribution of EC metabolic enzymes in the pancreas and adipose organ, where their aberrant expression during hyperglycemia and obesity contribute to dysregulated EC levels.

Higher post-absorptive skeletal muscle LPL activity in African American vs. non-Hispanic White pre-menopausal women

OBJECTIVE

Higher post-absorptive post-heparin plasma lipoprotein lipase (LPL) activity has been reported in African Americans as compared to non-Hispanic whites but differences in tissue-specific LPL activity are unclear.

METHODS AND PROCEDURES

Post-absorptive skeletal muscle (SM)-LPL (vastus lateralis ) and subcutaneous abdominal adipose tissue (AT)-LPL activity was measured in overweight, sedentary African American females (n = 11) as well as in their non-Hispanic white counterparts (n = 6) during a period of controlled low fat (30%) diet (for 10 days) combined with physical activity (for days 8-10). Post-absorptive substrate utilization was measured on day 10; fasting blood levels and SM and AT biopsies were obtained on day 11.

RESULTS

African Americans had significantly greater post-absorptive SM-LPL activity (P = 0.04) when compared to non-Hispanic whites. There were no significant differences in post-absorptive AT-LPL activity, free fatty acids, and systemic fat oxidation or respiratory quotient between African American and white non-Hispanic women in this study (P > 0.2 for all).

DISCUSSION

During a controlled low fat (30%) diet post-absorptive vastus lateralis SM-LPL activity is higher in sedentary pre-menopausal African American as compared to non-Hispanic white women.