Preferential fat deposition in subcutaneous versus visceral depots is associated with insulin sensitivity

Noncanonical Wnt signaling promotes obesity-induced adipose tissue inflammation and metabolic dysfunction independent of adipose tissue expansion

Adipose tissue dysfunction plays a pivotal role in the development of insulin resistance in obese individuals. Cell culture studies and gain-of-function mouse models suggest that canonical Wnt proteins modulate adipose tissue expansion. However, no genetic evidence supports a role for endogenous Wnt proteins in adipose tissue dysfunction, and the role of noncanonical Wnt signaling remains largely unexplored. Here we provide evidence from human, mouse, and cell culture studies showing that Wnt5a-mediated, noncanonical Wnt signaling contributes to obesity-associated metabolic dysfunction by increasing adipose tissue inflammation. Wnt5a expression is significantly upregulated in human visceral fat compared with subcutaneous fat in obese individuals. In obese mice, Wnt5a ablation ameliorates insulin resistance, in parallel with reductions in adipose tissue inflammation. Conversely, Wnt5a overexpression in myeloid cells augments adipose tissue inflammation and leads to greater impairments in glucose homeostasis. Wnt5a ablation or overexpression did not affect fat mass or adipocyte size. Mechanistically, Wnt5a promotes the expression of proinflammatory cytokines by macrophages in a Jun NH2-terminal kinase-dependent manner, leading to defective insulin signaling in adipocytes. Exogenous interleukin-6 administration restores insulin resistance in obese Wnt5a-deficient mice, suggesting a central role for this cytokine in Wnt5a-mediated metabolic dysfunction. Taken together, these results demonstrate that noncanonical Wnt signaling contributes to obesity-induced insulin resistance independent of adipose tissue expansion.

Plexin D1 determines body fat distribution by regulating the type V collagen microenvironment in visceral adipose tissue

Genome-wide association studies have implicated PLEXIN D1 (PLXND1) in body fat distribution and type 2 diabetes. However, a role for PLXND1 in regional adiposity and insulin resistance is unknown. Here we use in vivo imaging and genetic analysis in zebrafish to show that Plxnd1 regulates body fat distribution and insulin sensitivity. Plxnd1 deficiency in zebrafish induced hyperplastic morphology in visceral adipose tissue (VAT) and reduced lipid storage. In contrast, subcutaneous adipose tissue (SAT) growth and morphology were unaffected, resulting in altered body fat distribution and a reduced VAT:SAT ratio in zebrafish. A VAT-specific role for Plxnd1 appeared conserved in humans, as PLXND1 mRNA was positively associated with hypertrophic morphology in VAT, but not SAT. In zebrafish plxnd1 mutants, the effect on VAT morphology and body fat distribution was dependent on induction of the extracellular matrix protein collagen type V alpha 1 (col5a1). Furthermore, after high-fat feeding, zebrafish plxnd1 mutant VAT was resistant to expansion, and excess lipid was disproportionately deposited in SAT, leading to an even greater exacerbation of altered body fat distribution. Plxnd1-deficient zebrafish were protected from high-fat-diet-induced insulin resistance, and human VAT PLXND1 mRNA was positively associated with type 2 diabetes, suggesting a conserved role for PLXND1 in insulin sensitivity. Together, our findings identify Plxnd1 as a novel regulator of VAT growth, body fat distribution, and insulin sensitivity in both zebrafish and humans.

Visceral obesity is associated with increased soluble CD163 concentration in men with type 2 diabetes mellitus

Monocyte/macrophage-specific soluble CD163 (sCD163) concentration is associated with insulin resistance and increases with deteriorating glycemic control independently of BMI. This led to the proposal of the hypothesis that obesity-associated white adipose tissue inflammation varies between individuals. The objective was to examine the effect of male overweight/obesity and type 2 diabetes mellitus (T2DM) on associations between adiposity parameters and sCD163. A total of 23 overweight/obese non-diabetic men, 16 overweight/obese men with T2DM, and a control group of 20 normal-weight healthy men were included. Body composition and regional body fat distribution were determined by whole-body dual X-ray absorptiometry scan and abdominal computed tomography (CT) scan. Serum sCD163 concentrations were determined by ELISA. Associations between adiposity parameters and sCD163 were investigated using multiple linear regression analysis. In the normal-weight healthy men, there was no significant association between adiposity parameters and sCD163, whereas in the overweight/obese non-diabetic men, measures of general and regional adiposity were positively associated with sCD163. In the overweight/obese men with T2DM, only visceral adipose tissue (VAT) and the ratio of VAT to abdominal subcutaneous adipose tissue (SAT), a measure of relative body fat distribution between VAT and SAT depots, were positively associated with sCD163. In a multivariate analysis, including VAT, upper-body SAT, and lower-body fat, adjusted for BMI and age, VAT remained a significant predictor of sCD163 in the overweight/obese T2DM men, but not in the overweight/obese non-diabetic men. Our results indicate that VAT inflammation is exaggerated in men with T2DM, and that propensity to store excess body fat viscerally is particularly detrimental in men with T2DM.

Main characteristics of metabolically obese normal weight and metabolically healthy obese phenotypes

In this review, the influence of fat depots on insulin resistance and the main characteristics of metabolically obese normal-weight and metabolically healthy obese phenotypes are discussed. Medline/PubMed and Science Direct were searched for articles related to the terms metabolically healthy obesity, metabolically obese normal weight, adipose tissue, and insulin resistance. Normal weight and obesity might be heterogeneous in regard to their effects. Fat distribution and lower insulin sensitivity are the main factors defining phenotypes within the same body mass index. Although these terms are interesting, controversies about them remain. Future studies exploring these phenotypes will help elucidate the roles of adiposity and/or insulin resistance in the development of metabolic alterations.

Identification of sex-specific thresholds for accumulation of visceral adipose tissue in adults

OBJECTIVE

The purpose of this study was to measure the linearity of visceral adipose tissue (VAT) accumulation with measures of total body adiposity to determine whether a threshold exists and to explore the association with cardiometabolic risk factors in adults.

METHODS

Using a cross-sectional design, data were obtained from 723 adults (324 females) age 19-47 years. Body mass index ranged from 15 to 52 kg/m(2) . Segmented linear regression was used to identify sex-specific percent body fat thresholds at which VAT slope changes. Linear regression measured the association of VAT mass, total fat mass, and subcutaneous fat with cardiometabolic risk factors above and below each threshold.

RESULTS

Adiposity thresholds were identified at 23.4% body fat in males and 38.3% body fat in females beyond which the slope of VAT per unit of percent body fat increased to strongly positive. Males and females above these adiposity thresholds had significant dyslipidemia (P<0.001), increased insulin resistance (P<0.001), and higher fat mass across all depots.

CONCLUSIONS

From these cross-sectional data, the following were inferred: the accumulation of VAT mass is not linear with increasing adiposity; increases in visceral accumulation above threshold are associated with decreased insulin sensitivity and cardiovascular risk in males and females independent of total body fat.

Fat quality and incident cardiovascular disease, all-cause mortality, and cancer mortality

CONTEXT

Cellular characteristics of fat quality have been associated with cardiometabolic risk and can be estimated by computed tomography (CT) attenuation.

OBJECTIVE

The aim was to determine the association between CT attenuation (measured in Hounsfield units [HU]) and clinical outcomes.

METHODS

This was a prospective community-based cohort study using data from the Framingham Heart Study (n = 3324, 48% women, mean age 51 years) and Cox proportional hazard models.

MAIN OUTCOMES

The primary outcomes of interest were incident cardiovascular disease (CVD) and all-cause mortality. The secondary outcomes of interest were incident cancer, non-CVD death, and cancer death.

RESULTS

There were 111 incident CVD events, 137 incident cancers, 85 deaths including 69 non-CVD deaths, and 45 cancer deaths in up to 23 047 person-years of follow-up. A 1-SD increment in visceral adipose tissue (VAT) HU was inversely associated with incident CVD in the age- and sex-adjusted model (hazard ratio [HR] 0.78, P = .02) but not after multivariable adjustment (HR 0.83, P = .11). VAT HU was directly associated with all-cause mortality (multivariable HR 1.40, P = .003), which maintained significance after additional adjustment for body mass index (HR 1.53, P < .001) and VAT volume (HR 1.99, P < .001). Non-CVD death remained significant in all 3 models, including after adjustment for VAT volume (HR 1.97, P < .001). VAT HU was also associated with cancer mortality (HR 1.93, P = .002). Similar results were obtained for sc adipose tissue HU.

CONCLUSIONS

Fat quality, as estimated by CT attenuation, is associated with all-cause mortality, non-CVD death, and cancer death. These associations highlight how indirect indices of fat quality can potentially add to a better understanding of obesity-related complications.

Molecular physiopathology of obesity-related diseases: multi-organ integration by GRK2

Obesity is a worldwide problem that has reached epidemic proportions both in developed and developing countries. The excessive accumulation of fat poses a risk to health since it favours the development of metabolic alterations including insulin resistance and tissue inflammation, which further contribute to the progress of the complex pathological scenario observed in the obese. In this review we put together the different outcomes of fat accumulation and insulin resistance in the main insulin-responsive tissues, and discuss the role of some of the key molecular routes that control disease progression both in an organ-specific and also in a more systemic manner. In particular, we focus on the importance of studying the integrated regulation of different organs and pathways that contribute to the global pathophysiology of this condition with a specific emphasis on the role of emerging key molecular nodes such as the G protein-coupled receptor kinase 2 (GRK2) signalling hub.

Role of FAT/CD36 in fatty acid sensing, energy, and glucose homeostasis regulation in DIO and DR rats

Hypothalamic fatty acid (FA) sensing neurons alter their activity utilizing the FA translocator/receptor, FAT/CD36. Depletion of ventromedial hypothalamus (VMH) CD36 with adeno-associated viral vector expressing CD36 shRNA (AAV CD36 shRNA) leads to redistribution of adipose stores and insulin resistance in outbred rats. This study assessed the requirement of VMH CD36-mediated FA sensing for the regulation of energy and glucose homeostasis in postnatal day 5 (P5) and P21 selectively bred diet-induced obese (DIO) and diet-resistant (DR) rats using VMH AAV CD36 shRNA injections. P5 CD36 depletion altered VMH neuronal FA sensing predominantly in DIO rats. After 10 wk on a 45% fat diet, DIO rats injected with VMH AAV CD36 shRNA at P21 ate more and gained more weight than DIO AAV controls, while DR AAV CD36 shRNA-injected rats gained less weight than DR AAV controls. VMH CD36 depletion increased inguinal fat pad weights and leptin levels in DIO and DR rats. Although DR AAV CD36 shRNA-injected rats became as obese as DIO AAV controls, only DIO control and CD36 depleted rats became insulin-resistant on a 45% fat diet. VMH CD36 depletion stunted linear growth in DIO and DR rats. DIO rats injected with AAV CD36 shRNA at P5 had increased fat mass, mostly due to a 45% increase in subcutaneous fat. They were also insulin-resistant with an associated 71% increase of liver triglycerides. These results demonstrate that VMH CD36-mediated FA sensing is a critical factor in the regulation of energy and glucose homeostasis and fat deposition in DIO and DR rats.

In vivo 2H2O administration reveals impaired triglyceride storage in adipose tissue of insulin-resistant humans

Indirect evidence suggests that impaired triglyceride storage in the subcutaneous fat depot contributes to the development of insulin resistance via lipotoxicity. We directly tested this hypothesis by measuring, in vivo, TG synthesis, de novo lipogenesis (DNL), adipocyte proliferation, and insulin suppression of lipolysis in subcutaneous adipose tissue of BMI-matched individuals classified as insulin resistant (IR) or insulin sensitive (IS). Nondiabetic, moderately obese subjects with BMI 25-35 kg/m(2), classified as IR or IS by the modified insulin suppression test, consumed deuterated water ((2)H2O) for 4 weeks. Deuterium incorporation into glycerol, palmitate, and DNA indicated TG synthesis, DNL, and adipocyte proliferation, respectively. Net TG synthesis and DNL in adipose cells were significantly lower in IR as compared with IS subjects, whereas adipocyte proliferation did not differ significantly. Plasma FFAs measured during an insulin suppression test were 2.5-fold higher in IR subjects, indicating resistance to insulin suppression of lipolysis. Adipose TG synthesis correlated directly with DNL but not with proliferation. These results provide direct in vivo evidence for impaired TG storage in subcutaneous adipose tissue of IR as compared with IS. Relative inability to store TG in the subcutaneous depot may represent a mechanism contributing to the development of insulin resistance in the setting of obesity.

Differential body composition effects of protease inhibitors recommended for initial treatment of HIV infection: a randomized clinical trial

BACKGROUND

It is unclear whether metabolic or body composition effects differ between protease inhibitor-based regimens recommended for initial treatment of human immunodeficiency virus (HIV) infection.

METHODS

ATADAR is a phase 4, open-label, multicenter, randomized clinical trial. Stable antiretroviral-naive HIV-infected adults were randomly assigned to atazanavir/ritonavir 300/100 mg or darunavir/ritonavir 800/100 mg in combination with tenofovir/emtricitabine daily. Predefined endpoints were treatment or virological failure, drug discontinuation due to adverse effects, and laboratory and body composition changes at 96 weeks.

RESULTS

At 96 weeks, 56 (62%) atazanavir/ritonavir and 62 (71%) darunavir/ritonavir patients remained free of treatment failure (estimated difference 8.2%; 95% confidence interval [CI], -.6 to 21.6) and 71 (79%) atazanavir/ritonavir and 75 (85%) darunavir/ritonavir patients remained free of virological failure (estimated difference 6.3%; 95% CI, -.5 to 17.6). Seven patients discontinued atazanavir/ritonavir and 5 discontinued darunavir/ritonavir due to adverse effects. Total and high-density lipoprotein cholesterol similarly increased in both arms, but there was a greater increase in triglycerides in the atazanavir/ritonavir arm. At 96 weeks, body fat (estimated difference 2862.2 gr; 95% CI, 726.7 to 4997.7; P = .0090), limb fat (estimated difference 1403.3 gr; 95% CI, 388.4 to 2418.2; P = .0071), and subcutaneous abdominal adipose tissue (estimated difference 28.4 cm(2); 95% CI, 1.9 to 55.0; P = .0362) increased more in the atazanavir/ritonavir arm than in darunavir/ritonavir arm. Body fat changes in the atazanavir/ritonavir arm were associated with higher insulin resistance.

CONCLUSIONS

We found no major differences between atazanavir/ritonavir and darunavir/ritonavir in efficacy, clinically relevant side effects, or plasma cholesterol fractions. However, atazanavir/ritonavir led to higher triglycerides and more total and subcutaneous fat than darunavir/ritonavir. Also, fat gains with atazanavir/ritonavir were associated with insulin resistance. Clinical Trials Registration. NCT01274780.

Ageing, adipose tissue, fatty acids and inflammation

A common feature of ageing is the alteration in tissue distribution and composition, with a shift in fat away from lower body and subcutaneous depots to visceral and ectopic sites. Redistribution of adipose tissue towards an ectopic site can have dramatic effects on metabolic function. In skeletal muscle, increased ectopic adiposity is linked to insulin resistance through lipid mediators such as ceramide or DAG, inhibiting the insulin receptor signalling pathway. Additionally, the risk of developing cardiovascular disease is increased with elevated visceral adipose distribution. In ageing, adipose tissue becomes dysfunctional, with the pathway of differentiation of preadipocytes to mature adipocytes becoming impaired; this results in dysfunctional adipocytes less able to store fat and subsequent fat redistribution to ectopic sites. Low grade systemic inflammation is commonly observed in ageing, and may drive the adipose tissue dysfunction, as proinflammatory cytokines are capable of inhibiting adipocyte differentiation. Beyond increased ectopic adiposity, the effect of impaired adipose tissue function is an elevation in systemic free fatty acids (FFA), a common feature of many metabolic disorders. Saturated fatty acids can be regarded as the most detrimental of FFA, being capable of inducing insulin resistance and inflammation through lipid mediators such as ceramide, which can increase risk of developing atherosclerosis. Elevated FFA, in particular saturated fatty acids, maybe a driving factor for both the increased insulin resistance, cardiovascular disease risk and inflammation in older adults.

Diabetes risk among overweight and obese metabolically healthy young adults

OBJECTIVE

To determine diabetes incidence over time among obese young adults without metabolic risk factors.

RESEARCH DESIGN AND METHODS

Incident diabetes during a median follow-up of 6.1 years was assessed among 33,939 young men (mean age 30.9 ± 5.2 years) of the Metabolic, Lifestyle and Nutrition Assessment in Young Adults cohort who were stratified for BMI and the number of metabolic abnormalities (based on the Adult Treatment Panel-III). Metabolically healthy (MH) obesity was defined as BMI ≥30 kg/m2 in the presence of normoglycemia, normal blood pressure, and normal levels of fasting triglyceride and HDL-cholesterol levels (n = 631).

RESULTS

A total of 734 new cases of diabetes were diagnosed during 210,282 person-years of follow-up. The incidence rate of diabetes among participants with no metabolic risk factors was 1.15, 2.10, and 4.34 cases per 1,000 person-years among lean, overweight, and obese participants, respectively. In a multivariable model adjusted for age, region of origin, family history of diabetes, physical activity, fasting plasma glucose, triglyceride level, HDL-cholesterol, systolic blood pressure, and white blood cell count, a higher diabetes risk was observed among MH-overweight (hazard ratio [HR] 1.89 [95% CI 1.25-2.86]; P < 0.001) and MH-obese (HR 3.88 [95% CI 1.94-7.77]; P < 0.001) compared with MH-normal weight subjects. There was no interaction between BMI and the number of metabolic abnormalities at enrollment in predicting diabetes risk.

CONCLUSIONS

Healthy metabolic profile and the absence of diabetes risk factors do not protect young adults from incident diabetes associated with overweight and obesity.

The altered mononuclear cell-derived cytokine response to glucose ingestion is not regulated by excess adiposity in polycystic ovary syndrome

CONTEXT

Excess adipose tissue is a source of inflammation. Polycystic ovary syndrome (PCOS) is a proinflammatory state and is often associated with excess abdominal adiposity (AA) alone and/or frank obesity.

OBJECTIVE

To determine the effect of glucose ingestion on cytokine release from mononuclear cells (MNC) in women with PCOS with and without excess AA and/or obesity.

DESIGN

A cross-sectional study.

SETTING

Academic medical center.

PATIENTS

Twenty-three women with PCOS (seven normal weight with normal AA, eight normal weight with excess AA, eight obese) and 24 ovulatory controls (eight normal weight with normal AA, eight normal weight with excess AA, eight obese).

INTERVENTION

Three-hour 75-g oral glucose tolerance test (OGTT).

MAIN OUTCOME MEASURES

Body composition was measured by dual energy x-ray absorptiometry. Insulin sensitivity was derived from the OGTT (ISOGTT). TNFα, IL-6, and IL-1β release was measured in supernatants of cultured MNC isolated from blood samples drawn while fasting and 2 hours after glucose ingestion.

RESULTS

Insulin sensitivity was lower in obese subjects regardless of PCOS status and in normal-weight women with PCOS compared with normal-weight controls regardless of body composition status. In response to glucose ingestion, MNC-derived TNFα, IL-6, and IL-1β release decreased in both normal-weight control groups but failed to suppress in either normal-weight PCOS group and in obese women regardless of PCOS status. For the combined groups, the cytokine responses were negatively correlated with insulin sensitivity and positively correlated with abdominal fat and androgens.

CONCLUSIONS

Women with PCOS fail to suppress MNC-derived cytokine release in response to glucose ingestion, and this response is independent of excess adiposity. Nevertheless, a similar response is also a feature of obesity per se. Circulating MNC and excess adipose tissue are separate and distinct sources of inflammation in this population.

The relationship of body mass and fat distribution with incident hypertension: observations from the Dallas Heart Study

BACKGROUND

Obesity has been linked to the development of hypertension, but whether total adiposity or site-specific fat accumulation underpins this relationship is unclear.

OBJECTIVES

This study sought to determine the relationship between adipose tissue distribution and incident hypertension.

METHODS

Normotensive participants enrolled in the Dallas Heart Study were followed for a median of 7 years for the development of hypertension (systolic blood pressure [SBP] ≥140 mm Hg, diastolic blood pressure ≥90 mm Hg, or initiation of blood pressure medications). Visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) was quantified by magnetic resonance imaging and proton-spectroscopic imaging, and lower body fat (LBF) was imaged by dual-energy x-ray absorptiometry. Multivariable relative risk regression was performed to test the association between individual fat depots and incident hypertension, adjusting for age, sex, race/ethnicity, diabetes, smoking, SBP, and body mass index (BMI).

RESULTS

Among 903 participants (median age, 40 years; 57% women; 60% nonwhite; median BMI 27.5 kg/m(2)), 230 (25%) developed incident hypertension. In multivariable analyses, higher BMI was significantly associated with incident hypertension (relative risk: 1.24; 95% confidence interval: 1.12 to 1.36, per 1-SD increase). However, when VAT, SAT, and LBF were added to the model, only VAT remained independently associated with incident hypertension (relative risk: 1.22; 95% confidence interval: 1.06 to 1.39, per 1-SD increase).

CONCLUSIONS

Increased visceral adiposity, but not total or subcutaneous adiposity, was robustly associated with incident hypertension. Additional studies will be needed to elucidate the mechanisms behind this association.

Intermuscular and intramuscular adipose tissues: Bad vs. good adipose tissues

Human studies of the influence of aging and other factors on intermuscular fat (INTMF) were reviewed. Intermuscular fat increased with weight loss, weight gain, or with no weight change with age in humans. An increase in INTMF represents a similar threat to type 2 diabetes and insulin resistance as does visceral adipose tissue (VAT). Studies of INTMF in animals covered topics such as quantitative deposition and genetic relationships with other fat depots. The relationship between leanness and higher proportions of INTMF fat in pigs was not observed in human studies and was not corroborated by other pig studies. In humans, changes in muscle mass, strength and quality are associated with INTMF accretion with aging. Gene expression profiling and intrinsic methylation differences in pigs demonstrated that INTMF and VAT are primarily associated with inflammatory and immune processes. It seems that in the pig and humans, INTMF and VAT share a similar pattern of distribution and a similar association of components dictating insulin sensitivity. Studies on intramuscular (IM) adipocyte development in meat animals were reviewed. Gene expression analysis and genetic analysis have identified candidate genes involved in IM adipocyte development. Intramuscular (IM) adipocyte development in human muscle is only seen during aging and some pathological circumstance. Several genetic links between human and meat animal adipogenesis have been identified. In pigs, the Lipin1 and Lipin 2 gene have strong genetic effects on IM accumulation. Lipin1 deficiency results in immature adipocyte development in human lipodystrophy. In humans, overexpression of Perilipin 2 (PLIN2) facilitates intramyocellular lipid accretion whereas in pigs PLIN2 gene expression is associated with IM deposition. Lipins and perilipins may influence intramuscular lipid regardless of species.

Adiposity distribution influences circulating adiponectin levels

Thirty percent of obese individuals are metabolically healthy and were noted to have increased peripheral obesity. Adipose tissue is the primary source of adiponectin, an adipokine with insulin-sensitizing and anti-inflammatory properties. Lower adiponectin levels are observed in individuals with obesity and those at risk for cardiovascular disease. Conversely, higher levels are noted in some obese individuals who are metabolically healthy. Our objective was to determine whether abdominal adiposity distribution, rather than body mass index (BMI) status, influences plasma adiponectin level. A total of 424 subjects (female, 255) of Northern European ancestry were recruited from "Take Off Pounds Sensibly" weight loss club members. Demographics, anthropometrics, and dual-emission x-ray absorptiometry of the whole body, and computed tomography scan of the abdomen were performed to obtain total body fat content and to quantify subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT), respectively. Laboratory measurements included fasting plasma glucose, insulin, lipid panel, and adiponectin. Age- and gender-adjusted correlation analyses showed that adiponectin levels were negatively correlated with BMI, waist circumference, triglycerides, total fat mass, and VAT. A positive correlation was noted with high-density lipoprotein cholesterol and fat-free mass (P < 0.05). SAT-to-VAT ratios were also significantly associated with adiponectin (r = 0.13, P = 0.001). Further, the best positive predictors for plasma adiponectin were found to be SAT-to-VAT ratios and gender by regression analyses (P < 0.01). Abdominal adiposity distribution is an important predictor of plasma adiponectin and obese individuals with higher SAT-to-VAT ratios may have higher adiponectin levels.

Pro- and anti-inflammatory cytokine gene expression in subcutaneous and visceral fat in severe obesity

BACKGROUND AND AIMS

Pro-inflammatory molecules produced by adipose tissue have been implicated in the risk of cardiovascular (CV) disease in obesity. We investigated the expression profile of 19 pro-inflammatory and seven anti-inflammatory genes in subcutaneous adipose tissue (SAT) and in visceral adipose tissue (VAT) in 44 severely obese individuals who underwent bariatric surgery.

METHODS AND RESULTS

SAT and VAT expressed an identical series of pro-inflammatory genes. Among these genes, 12 were significantly more expressed in SAT than in VAT while just one (IL18) was more expressed in VAT. The remaining genes were equally expressed. Among pro-inflammatory cytokines, both IL6 and IL8 were about 20 times more intensively expressed in SAT than in VAT. The expression of nine genes was highly associated in SAT and VAT. Only for three pro-inflammatory cytokines (IL8, IL18, SAA1) in SAT the gene expression in adipose tissue associated with the circulating levels of the corresponding gene products while no such an association was found as for VAT.

CONCLUSIONS

The expression of critical pro-inflammatory genes is substantially higher in SAT than in VAT in individuals with morbid obesity. The variability in circulating levels of pro-inflammatory cytokines is, in small part and just for three pro-inflammatory cytokines, explained by underlying gene expression in SAT but not in VAT. These results point to a compartment-specific adipose tissue contribution to inflammation in obesity and indicate that abdominal SAT contributes more than VAT to the pro-inflammatory milieu associated with severe obesity.

Investigation of relation between visceral and subcutaneous abdominal fat volumes and calcified aortic plaques via multislice computed tomography

OBJECTIVE

The present study investigated effect of subcutaneous fat volume and abdominal visceral fat volume on aortic atherosclerosis via multislice computed tomography.

MATERIALS AND METHODS

The present study comprised 424 subjects who underwent non-contrast-enhanced abdominal CT in our clinic between June 2012 and June 2013. Using dedicated software visceral fat volume was calculated for each individual and then subcutaneous fat volume was calculated by subtracting visceral fat volume from total fat volume. By dividing visceral fat volume/subcutaneous fat volume participants were assigned to three groups according to their mean visceral fat volume/subcutaneous fat volume: Group 1 consisted of subjects with visceral fat volume/subcutaneous fat volume lower than 0.48 (Group 1 < 0.48); Group 2 consisted of subjects with visceral fat volume/subcutaneous fat volume equal to or higher than 0.48 and lower than 0.69 (0.48 ≤ Group 2 < 0.69); and Group 3 consisted of subjects with visceral fat volume/subcutaneous fat volume equal to or higher than 0.69 (Group 3 ≥ 0.69).

RESULTS

The mean abdominal aortic calcium scores according to Agatston scoring (au) were 136.8 ± 418.7 au in Group 1, 179.9 ± 463 au in Group 2 and 212.2 ± 486.9 in Group 3, respectively.

CONCLUSIONS

We have demonstrated a significant correlation between visceral fat volume and abdominal aorta atherosclerosis, while there was absence of significant correlation between subcutaneous fat volume and abdominal atherosclerosis.

Predictors of insulin resistance in pediatric burn injury survivors 24 to 36 months postburn

Burn injury is a dramatic event with acute and chronic consequences including insulin resistance. However, factors associated with insulin resistance have not been previously investigated. The purpose of this study was to identify factors associated with long-term insulin resistance in pediatric burn injury survivors. The study sample consisted of 61 pediatric burn injury survivors 24 to 36 months after the burn injury, who underwent an oral glucose tolerance test. To assess insulin resistance, the authors calculated the area under the curve for glucose and insulin. The diagnostic criteria of the American Diabetes Association were used to define individuals with impaired glucose metabolism. Additional data collected include body composition, anthropometric measurements, burn characteristics, and demographic information. The data were analyzed using multivariate linear regression analysis. Approximately 12% of the patients met the criteria for impaired glucose metabolism. After adjusting for possible confounders, burn size, age, and body fat percentage were associated with the area under the curve for glucose (P < .05 for all). Time postburn and lean mass were inversely associated with the area under the curve for glucose (P < .05 for both). Similarly, older age predicted higher insulin area under the curve. The results indicate that a significant proportion of pediatric injury survivors suffer from glucose abnormalities 24 to 36 months postburn. Burn size, time postburn, age, lean mass, and adiposity are significant predictors of insulin resistance in pediatric burn injury survivors. Clinical evaluation and screening for abnormal glucose metabolism should be emphasized in patients with large burns, older age, and survivors with high body fat.

Association of fat density with subclinical atherosclerosis

Background

Ectopic fat density is associated with cardiovascular disease (CVD) risk factors above and beyond fat volume. Volumetric measures of ectopic fat have been associated with CVD risk factors and subclinical atherosclerosis. The aim of this study was to investigate the association between fat density and subclinical atherosclerosis.

Methods and Results

Participants were drawn from the Multi‐Detector Computed Tomography (MDCT) substudy of the Framingham Heart Study (n=3079; mean age, 50.1 years; 49.2% women). Fat density was indirectly estimated by computed tomography attenuation (Hounsfield Units [HU]) on abdominal scan slices. Visceral fat (VAT), subcutaneous fat (SAT), and pericardial fat HU and volumes were quantified using standard protocols; coronary and abdominal aortic calcium (CAC and AAC, respectively) were measured radiographically. Multivariable‐adjusted logistic regression models were used to evaluate the association between adipose tissue HU and the presence of CAC and AAC. Overall, 17.1% of the participants had elevated CAC (Agatston score [AS]>100), and 23.3% had elevated AAC (AS>age‐/sex‐specific cutoffs). Per 5‐unit decrement in VAT HU, the odds ratio (OR) for elevated CAC was 0.76 (95% confidence interval [CI], 0.65 to 0.89; P=0.0005), even after adjustment for body mass index or VAT volume. Results were similar for SAT HU. With decreasing VAT HU, we also observed an OR of 0.79 (95% CI, 0.67 to 0.92; P=0.004) for elevated AAC after multivariable adjustment. We found no significant associations between SAT HU and AAC. There was no significant association between pericardial fat HU and either CAC or AAC.

Conclusions

Lower VAT and SAT HU, indirect estimates of fat quality, are associated with a lower risk of subclinical atherosclerosis.

Sugar-sweetened beverage consumption is associated with abdominal fat partitioning in healthy adults

Abdominal adiposity, particularly visceral adipose tissue (VAT), is independently linked to the pathogenesis of diabetes and cardiovascular diseases. Emerging evidence suggests that greater intake of sugar-sweetened beverages (SSBs) may be associated with abnormal fat accumulation in VAT. We examined whether habitual SSB consumption and diet soda intakes are differentially associated with deposition of body fat. We conducted a cross-sectional analysis using previously collected data in 2596 middle-aged adults (1306 men and 1290 women) from the Framingham Heart Study Offspring and Third Generation cohorts. VAT and abdominal subcutaneous adipose tissue (SAT) were measured using multidetector computed tomography. Habitual intake of SSBs and diet soda was assessed by a validated food frequency questionnaire. We observed that SSB consumption was positively associated with VAT after adjustment for SAT and other potential confounders (P-trend < 0.001). We observed an inverse association between SSB consumption and SAT (P-trend = 0.04) that persisted after additional adjustment for VAT (P-trend < 0.001). Higher SSB consumption was positively associated with the VAT-to-SAT ratio (P-trend < 0.001). No significant association was found between diet soda consumption and either VAT or the VAT-to-SAT ratio, but diet soda was positively associated with SAT (P-trend < 0.001). Daily consumers of SSBs had a 10% higher absolute VAT volume and a 15% greater VAT-to-SAT ratio compared with nonconsumers, whereas consumption of diet soda was not associated with either volume or distribution of VAT.

Effect of tesamorelin on visceral fat and liver fat in HIV-infected patients with abdominal fat accumulation: a randomized clinical trial

IMPORTANCE

Among patients infected with human immunodeficiency virus (HIV), visceral adiposity is associated with metabolic dysregulation and ectopic fat accumulation. Tesamorelin, a growth hormone-releasing hormone analog, specifically targets visceral fat reduction but its effects on liver fat are unknown.

OBJECTIVE

To investigate the effect of tesamorelin on visceral and liver fat.

DESIGN, SETTING, AND PATIENTS

Double-blind, randomized, placebo-controlled trial conducted among 50 antiretroviral-treated HIV-infected men and women with abdominal fat accumulation at Massachusetts General Hospital in Boston. The first patient was enrolled on January 10, 2011; for the final patient, the 6-month study visit was completed on September 6, 2013.

INTERVENTIONS

Participants were randomized to receive tesamorelin, 2 mg (n=28), or placebo (n=22), subcutaneously daily for 6 months.

MAIN OUTCOMES AND MEASURES

Primary end points were changes in visceral adipose tissue and liver fat. Secondary end points included glucose levels and other metabolic end points.

RESULTS

Forty-eight patients received treatment with study drug. Tesamorelin significantly reduced visceral adipose tissue (mean change, -34 cm2 [95% CI, -53 to -15 cm2] with tesamorelin vs 8 cm2 [95% CI, -14 to 30 cm2] with placebo; treatment effect, -42 cm2 [95% CI, -71 to -14 cm2]; P = .005) and liver fat (median change in lipid to water percentage, -2.0% [interquartile range {IQR}, -6.4% to 0.1%] with tesamorelin vs 0.9% [IQR, -0.6% to 3.7%] with placebo; P = .003) over 6 months, for a net treatment effect of -2.9% in lipid to water percentage. Fasting glucose increased in the tesamorelin group at 2 weeks (mean change, 9 mg/dL [95% CI, 5-13 mg/dL] vs 2 mg/dL [95% CI, -3 to 8 mg/dL] in the placebo group; treatment effect, 7 mg/dL [95% CI, 1-14 mg/dL]; P = .03), but changes at 6 months in fasting glucose (mean change, 4 mg/dL [95% CI, -2 to 10 mg/dL] with tesamorelin vs 2 mg/dL [95% CI, -4 to 7 mg/dL] with placebo; treatment effect, 2 mg/dL [95% CI, -6 to 10 mg/dL]; P = .72 overall across time points) and 2-hour glucose (mean change, -1 mg/dL [95% CI, -18 to 15 mg/dL] vs -8 mg/dL [95% CI, -24 to 8 mg/dL], respectively; treatment effect, 7 mg/dL [95% CI, -16 to 29 mg/dL]; P = .53 overall across time points) were not significant.

CONCLUSIONS AND RELEVANCE

In this preliminary study of HIV-infected patients with abdominal fat accumulation, tesamorelin administered for 6 months was associated with reductions in visceral fat and additionally with modest reductions in liver fat. Further studies are needed to determine the clinical importance and long-term consequences of these findings.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT01263717.

Induction of adipocyte hyperplasia in subcutaneous fat depot alleviated type 2 diabetes symptoms in obese mice

OBJECTIVE

The role of subcutaneous adipose tissue (SAT) in the pathogenesis of type 2 diabetes is still under controversy. In this study, the metabolic effects of inducing adipocyte hyperplasia in SAT depots in obese mice were investigated.

METHODS

High fat diet was used to induce obesity and type 2 diabetes symptoms in C57BL6/J mice. To induce SAT expansion through hyperplasia, acellular adipogenic cocktails were injected around the SAT depots in high fat diet-induced obese mice.

RESULTS

Ten weeks after injections, significant neoadipogenesis was induced, which not only obviously expanded the volume of SATs but also significantly increased the adipocyte density within the whole SAT depots. Importantly, these mice exhibited improved glucose tolerance and insulin sensitivity (homeostatic model assessment) when compared to control group. Further studies suggested that these beneficial metabolic effects were associated with elevation of serum high-molecular-weight adiponectin level and reduction of ectopic lipid accumulation in liver.

CONCLUSIONS

These findings not only further supported the protective role of SAT in the pathogenesis of type 2 diabetes but also highlighted the importance of adipocyte hyperplasia in this protective effect.

Gender-assortative waist circumference in mother-daughter and father-son pairs, and its implications. An 11-year longitudinal study in children (EarlyBird 59)

BACKGROUND/OBJECTIVES

Body mass index (BMI) is reportedly gender assortative (mother-daughter, father-son) in contemporary children. We investigated the corresponding transmission of waist circumference (WC) and its implications.

METHODS

We measured parental WC at baseline and WC, height, weight and para-umbilical skin-fold (USF) annually in their offspring from 5 to 15 years (n = 223 trios). Parents were deemed normal metabolic risk (NR) or high risk (HR) according to World Health Organization (WHO) cut-points for WC (mothers 80 cm, fathers 94 cm). The residual from WC adjusted for BMI (WC|BMI ) was used as a surrogate for excess intra-abdominal fat, and its association with insulin resistance (HOMA2-IR) was sought.

RESULTS

WC and USF were both gender assortative, while WC|BMI was not. WC was greater by 1.62 cm (P < 0.05, confidence interval [CI]: 0.09-3.16) and USF by 0.37 cm (P < 0.01, CI: 0.19-0.56) among the daughters (but not the sons) of HR compared with those of NR mothers, and by 1.32 cm (P < 0.05, CI: 0.09-2.55) and 0.18 cm (P < 0.05, CI: 0.04-0.32), respectively in the corresponding father-son (but not father-daughter) pairings. No such differences could be demonstrated for WC|BMI . A standard deviation score 1(SDS) change in WC|BMI , independent of BMI, was associated with a 7.14% change in IR in girls (P < 0.01, CI: 1.76-12.80) and 8.02% in boys (P < 0.001, CI: 2.93-13.36), but there was no relationship between IR and USF.

CONCLUSION

The relationship of offspring WC to metabolic health and to parental size is complex. Subcutaneous abdominal fat is gender assortative but harmless, while intra-abdominal fat (its surrogate in this analysis) is unrelated to parental waist circumference, but metabolically harmful.

Metabolic health is a more important determinant for diabetes development than simple obesity: a 4-year retrospective longitudinal study

BACKGROUND

Recent studies report the importance of metabolic health beyond obesity. The aim of this study is to compare the risk for diabetes development according to different status of metabolic health and obesity over a median follow-up of 48.7 months.

METHODS

6,748 non-diabetic subjects (mean age 43 years) were divided into four groups according to the baseline metabolic health and obesity status: metabolically healthy non-obese (MHNO), metabolically healthy obese (MHO), metabolically unhealthy non-obese (MUHNO) and metabolically unhealthy obese (MUHO). Being metabolically healthy was defined by having less than 2 components among the 5 components, that is, high blood pressure, high fasting blood glucose, high triglyceride, low high-density lipoprotein cholesterol and being in the highest decile of homeostasis model assessment-insulin resistance (HOMA-IR) index. Obesity status was assessed by body mass index (BMI) higher than 25 kg/m2. The development of diabetes was assessed annually from self-questionnaire, fasting glucose and HbA1c.

RESULTS

At baseline, 45.3% of the subjects were MHNO, 11.3% were MHO, 21.7% were MUHNO, and 21.7% were MUHO. During a median follow-up of 48.7 months, 277 subject (4.1%) developed diabetes. The hazard ratio for diabetes development was 1.338 in MHO group (95% CI 0.67-2.672), 4.321 in MUHNO group (95% CI 2.702-6.910) and 5.994 in MUHO group (95% CI 3.561-10.085) when MHNO group was considered as the reference group. These results were similar after adjustment for the changes of the risk factors during the follow-up period.

CONCLUSION

The risk for future diabetes development was higher in metabolically unhealthy subgroups compared with those of metabolically healthy subjects regardless of obesity status.

MitoNEET-mediated effects on browning of white adipose tissue

MitoNEET is an outer mitochondrial membrane protein that, upon overexpression in white adipose tissue (WAT), exerts a positive impact on tissue expansion and whole-body lipid and carbohydrate homeostasis by altering mitochondrial matrix iron metabolism. Here we determine the key transcriptional events in subcutaneous WAT of mice in response to mitoNEET overexpression and a high-fat diet (HFD). Microarray analyses at key points during weight gain upon body-weight divergence with wild-type mice demonstrate that mitoNEET-enriched sWAT early on upregulates a browning signature program that limits WAT expansion in transgenic mice for a period of up to 12-weeks of HFD. This compensatory browning phenotype is subsequently lost, resulting in rapid WAT expansion and body-weight gain. Exposure to thermoneutral temperatures during HFD prompts weight gain significantly earlier. Similar WAT expansion is achieved upon infection with an adeno-associated virus expressing mitoNEET. Collectively, the mitoNEET enriched fat-pads feature a more vascularized, anti-inflammatory and less fibrotic environment.

Effects of eicosapentaenoic acid treatment on epicardial and abdominal visceral adipose tissue volumes in patients with coronary artery disease

AIM

Epicardial adipose tissue (EAT) is a pathogenic fat depot that may be associated with coronary atherosclerosis and cardiovascular events. Because eicosapentaenoic acid (EPA) has been reported to exert cardiovascular protective effects, we aimed to assess the effects of EPA on the volume of visceral adipose tissue, including EAT and abdominal visceral adipose tissue (AVAT), using multislice computed tomography (CT).

METHODS

In 30 patients with coronary artery diseases (9 women; mean age, 67.2 ± 5.4 years), EAT and AVAT volumes were compared between the control group (n=15, conventional therapy) and the EPA group (n=15, conventional therapy plus purified EPA 1800 mg/day) during a six-month period. EAT was defined as any pixel that had CT attenuation of -150 to -30 Hounsfield units (HU) within the pericardial sac.

RESULTS

After the six-month follow-up, the serum EPA level increased from 59.9 ± 18.8 to 177.2 ± 3.3 μg/mL in the EPA group (p<0.01), but no increase was noted in the control group. Similarly, the EPA/arachidonic acid (AA) ratio increased from 0.39 ± 0.12 to 1.22 ± 0.28 in the EPA group (p<0.01), with no significant increase in the control group. The AVAT and EAT volumes decreased in the EPA group but were unchanged in the control group (AVAT, -11.6 ± 17.0 vs. +8.8 ± 13.6 cm(2), p<0.01; EAT, -7.3 ± 8.3 vs. +8.7 ± 8.8 cm(3), p<0.01). Moreover, the change in the AVAT volume negatively correlated with the change in EPA (r=-0.58, p<0.01) and EPA/AA levels (r=-0.53, p<0.01). A similar negative correlation in these parameters was also observed for the EAT volume.

CONCLUSIONS

Oral intake of purified EPA appears to be associated with reductions in EAT and AVAT volumes.

Greater short-term weight loss in women 20-45 versus 55-65 years of age following bariatric surgery

BACKGROUND

Whether and how sex and age affect bariatric-surgery outcome is poorly understood. Estrogens regulate body composition in women and animals, and increase weight loss in a rodent model of gastric bypass, suggesting that premenopausal women may lose more weight following bariatric surgery.

METHODS

One thousand three hundred fifty-six female gastric-bypass or gastric-banding patients were retrospectively grouped as 20-45 years old (presumptively premenopausal; n = 1,199) and 55-65 years old (presumptively postmenopausal; n = 157). Mixed-model ANCOVA followed by Bonferroni-corrected t tests were used to categorically test the effect of age on percent excess body weight loss (%EBWL) at 1 and 2 years post-surgery, controlling for preoperative EBW and surgery type. Age effects were also tested dimensionally in all women and in 289 male patients.

RESULTS

Twenty- to forty-five-year-old women showed greater %EBWL 1 and 2 years post-surgery than 55-65-year-old women (p's < 0.0005). No age effect was detected in 20-25- vs. 30-35-, 30-35- vs. 40-45-, or 20-25- vs. 40-45-year-old women (p's > 0.2) This age effect was detected only after gastric banding, with 20-45-year-old women losing ∼7 kg more than 55-65-year-old women after 2 years. Dimensional analysis confirmed a significant inverse effect of age on bariatric surgery outcome in women, but did not detect any effect in men.

CONCLUSIONS

Results indicate that 55-65-year-old women lose less weight than 20-45-year-old women in the initial 2 years after bariatric surgery, especially gastric banding; this may be mediated by age- or menopause-associated changes in physical activity, energy expenditure, or energy intake.

The relationship between regional abdominal fat distribution and both insulin resistance and subclinical chronic inflammation in non-diabetic adults

OBJECTIVE

Obesity is associated with a high risk of insulin resistance (IR) and its metabolic complications. It is still debated that distributions of adipose tissue relate to an excess risk of IR and chronic inflammation in different race. This study was designed to examine the relation between insulin sensitivity, chronic inflammation and central fat distribution in non-diabetic volunteers in Taiwanese.

METHODS

There were 328 volunteers without family history of diabetes mellitus and with normal oral glucose tolerance test enrolled. Total body fat and abdominal fat were measured. Abdominal fat was categorized into intraperitoneal (IP), retroperitoneal (RP) and subcutaneous (SC) fat. The IR index was estimated by homeostatic model assessment. Five inflammatory markers: adiponectin, leptin, tumor necrosing factor-α (TNF-α), resistin and high sensitive CRP (hs-CRP) were measured.

RESULTS

IR was related to IP fat (r = 0.23, p < 0.001), but not RP fat, SC fat or total body fat. After correcting for age and sex, IP fat was the only significant predictor of IR (r2 = 58%, p = 0.001). Leptin showed the strongest relationship with all fat compartments (IP fat: r = 0.44, p = 0.001; RP fat: r = 0.36, p = 0.005, SC fat: r = 0.54, p < 0.001; total body fat: r = 0.61, p < 0.001). The hs-CRP and adiponectin were closely related both to IP (r = 0.29, p = 0.004; r = -0.20, p = 0.046, respectively) and total body fat (r = 0.29, p = 0.004; r = -0.29, p = 0.005, respectively), but not RP, or SC fat. TNF-α and resistin were not correlated to any fat compartment. After correcting for age and sex, leptin variance was mostly explained by SC fat (41.3%), followed by IP fat (33.6%) and RP fat (25.3%). The hs-CRP and adiponectin variance were mostly explained by IP fat (40% and 49% respectively).

CONCLUSIONS

IP fat is better predictors of IR and subclinical chronic inflammation in Taiwanese adults. A disproportionate accumulation of abdominal fat is associated with increased risk of cardiovascular diseases.

Impact of body composition during weight change on resting energy expenditure and homeostasis model assessment index in overweight nonsmoking adults

BACKGROUND

Weight change affects resting energy expenditure (REE) and metabolic risk factors. The impact of changes in individual body components on metabolism is unclear.

OBJECTIVE

We investigated changes in detailed body composition to assess their impacts on REE and insulin resistance.

DESIGN

Eighty-three healthy subjects [body mass index (BMI; in kg/m²) range: 20.2-46.8; 50% obese] were investigated at 2 occasions with weight changes between -11.2 and +6.5 kg (follow-up periods between 23.5 and 43.5 mo). Detailed body composition was measured by using the 4-component model and whole-body magnetic resonance imaging. REE, plasma thyroid hormone concentrations, and insulin resistance were measured by using standard methods.

RESULTS

Weight loss was associated with decreases in fat mass (FM) and fat-free mass (FFM) by 72.0% and 28.0%, respectively. A total of 87.9% of weight gain was attributed to FM. With weight loss, sizes of skeletal muscle, kidneys, heart, and all fat depots decreased. With weight gain, skeletal muscle, liver, kidney masses, and several adipose tissue depots increased except for visceral adipose tissue (VAT). After adjustments for FM and FFM, REE decreased with weight loss (by 0.22 MJ/d) and increased with weight gain (by 0.11 MJ/d). In a multiple stepwise regression analysis, changes in skeletal muscle, plasma triiodothyronine, and kidney masses explained 34.9%, 5.3%, and 4.5%, respectively, of the variance in changes in REE. A reduction in subcutaneous adipose tissue rather than VAT was associated with the improvement of insulin sensitivity with weight loss. Weight gain had no effect on insulin resistance.

CONCLUSION

Beyond a 2-compartment model, detailed changes in organ and tissue masses further add to explain changes in REE and insulin resistance.

Sex influences the effect of body mass index on the vascular response to angiotensin II in humans

OBJECTIVE

Sex influences the cardiorenal risk associated with body mass index (BMI). The role of the renin-angiotensin-aldosterone system in adiposity-mediated cardiorenal risk profiles in healthy, non-obese men and women was investigated.

METHODS

Systemic and renal hemodynamic responses to angiotensin-II (AngII) as a function of BMI, waist and hip circumference, waist-hip ratio, as well as fat and lean mass were measured in 18 men and 25 women in high-salt balance, stratified by BMI (<25 kg/m2 (ideal body weight (IBW)) vs. ≥25 kg/m2 overweight)).

RESULTS

In men (n = 7, BMI 23 ± 1 kg/m2) and women (n = 14, BMI 22 ± 2 kg/m2) of IBW, BMI was not associated with the systolic blood pressure (SBP) response to AngII. In contrast, overweight men (n = 11, 29 ± 2 kg/m2) demonstrated a progressively more blunted vasoconstrictor SBP response to AngII challenge as BMI increased (P = 0.007), even after adjustment for covariates. Women maintained the same relationship between BMI and the SBP response to AngII irrespective of weight status (P = 0.2, IBW vs. overweight women). Compared to BMI, other adiposity measures showed similar associations to systemic AngII responsiveness in men but not in women. Increasing BMI was associated with a blunted renovasoconstrictor response to AngII in all subjects, but was more pronounced in men.

CONCLUSION

Sex influences the effect of adiposity on vascular angiotensin-responsiveness.

Metabolic basis of ethnic differences in diabetes risk in overweight and obese youth

The global pandemic of childhood obesity has led to increased risk for prediabetes and type 2 diabetes mellitus (T2DM). Studies have shown decreased insulin sensitivity and/or secretion with increasing adiposity and consistently observed greater risk for T2DM in obese, non-Caucasian youth. In the current review we describe recent advances in understanding how obesity and metabolic status in children and adolescents confers various risk profiles for T2DM among Latinos, African Americans, Caucasians, Asians, and Native Americans. These possible determinants include ectopic fat distribution, adipose tissue inflammation and fibrosis, and elevated plasma levels of nonesterified free fatty acids. Future work should aim to elucidate the ethnic-specific pathophysiology of T2DM in order to develop and implement appropriate prevention and treatment strategies based on different ethnic profiles of diabetes risk.

Insulin resistance and beta-cell function in different ethnic groups in Kenya: the role of abdominal fat distribution

Little is known about the pathophysiology of diabetes in Africans. Thus, we assessed whether insulin resistance and beta-cell function differed by ethnicity in Kenya and whether differences were modified by abdominal fat distribution. A cross-sectional study in 1,087 rural Luo (n = 361), Kamba (n = 378), and Maasai (n = 348) was conducted. All participants had a standard 75-g oral glucose tolerance test (OGTT). Venous blood samples were collected at 0, 30, and 120 min. Serum insulin was analysed at 0 and 30 min. From the OGTT, we assessed the homoeostasis model assessment of insulin resistance by computer model, early phase insulin secretion, and disposition index (DI) dividing insulin secretion by insulin resistance. Abdominal subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) thickness were carried out by ultrasonography. Linear regression analyses were done to assess ethnic differences in insulin indices. The Maasai had 32 and 17% higher insulin resistance than the Luo and Kamba, respectively (p < 0.001). Early phase insulin secretion was 16% higher in the Maasai compared to the Luo (p < 0.001). DI was 12% (p = 0.002) and 10% (p = 0.015) lower in the Maasai compared to the Luo and Kamba, respectively. Adjustments of SAT (range 0.1-7.1 cm) and VAT (range 1.5-14.2 cm) largely explained these inter-group differences with the Maasai having the highest combined abdominal fat accumulation. The Maasai had the highest insulin resistance and secretion, but the lowest relative beta-cell function compared to the Luo and Kamba. These differences were primarily explained by abdominal fat distribution.

The association between cytokines and insulin sensitivity in Iraqi immigrants and native Swedes

OBJECTIVES

To investigate the associations between cytokines and insulin sensitivity in Swedish residents born in Iraq and Swedish residents born in Sweden.

DESIGN

Cross-sectional study.

SETTINGS

Iraqi and Swedish origin residents of Rosengård area of Malmö, aged 45-65 years, were randomly selected from the census register.

PARTICIPANTS/METHODS

194 (Iraqi, n=107; Swedish, n=87) participants agreed to participate in the study. Nineteen participants dropped out (Iraqi, n=11; Swedish, n=8). Participants who had already been diagnosed with type 2 diabetes mellitus (T2DM), those who could not participate in an oral glucose tolerance test and those who had a cold/fever at the time of blood sampling were excluded. In total, serum samples from 135 individuals of Swedish (n=62) and Iraqi (n=73) origin were included. Serum concentrations of a panel of 10 cytokines, comprising interleukin (IL)-1β, IL-2, IL-4, IL-5, IL-6, IL-10, IL-12 (p70), IL-13, interferon-γ and tumour necrosis factor-α were analysed by Luminex multiplex assay.

RESULTS

In the whole study population, levels of all tested cytokines were inversely associated with insulin sensitivity index (ISI), independent of age, sex, body mass index (BMI), sedentary lifestyle and family history of T2DM (p ≤ 0.05). Interestingly, stratification of the study population according to country of birth showed a significant inverse association between all tested cytokines and ISI in the Iraqi-born population (p ≤ 0.01). The association was independent of age, sex, BMI, sedentary lifestyle and family history of T2DM. In contrast, with the exception for IL-6 (p=0.05), no other tested cytokine was found to be significantly associated with ISI in the Swedish-born population (p≥0.05).

CONCLUSIONS

Our results show an association between cytokines and ISI in the Iraqi-born population but not in the Swedish-born population.

Routine clinical measures of adiposity as predictors of visceral fat in adolescence: a population-based magnetic resonance imaging study

Objective

Visceral fat (VF) increases cardiometabolic risk more than fat stored subcutaneously. Here, we investigated how well routine clinical measures of adiposity, namely body mass index (BMI) and waist circumference (waist), predict VF and subcutaneous fat (SF) in a large population-based sample of adolescents. As body-fat distribution differs between males and females, we performed these analyses separately in each sex.

Design and Methods

VF and SF were measured by magnetic resonance imaging in 1,002 adolescents (482 males, age 12–18 years). Relationships of BMI and waist with VF and SF were tested in multivariable analyses, which adjusted for potentially confounding effects of age and height.

Results

In both males and females, BMI and waist were highly correlated with VF and SF, and explained 55–76% of their total variance. When VF was adjusted for SF, however, BMI and waist explained, respectively, only 0% and 4% of VF variance in males, and 4% and 11% of VF variance in females. In contrast, when SF was adjusted for VF, BMI and waist explained, respectively, 36% and 21% of SF variance in males, and 48% and 23% of SF variance in females. These relationships were similar during early and late puberty.

Conclusions and Relevance

During adolescence, routine clinical measures of adiposity predict well SF but not VF. This holds for both sexes and throughout puberty. Further longitudinal studies are required to assess how well these measures predict changes of VF and SF over time. Given the clinical importance of VF, development of cost-effective imaging techniques and/or robust biomarkers of VF accumulation that would be suitable in everyday clinical practice is warranted.

Sex differences in insulin resistance and cardiovascular disease risk

CONTEXT

The possibility that differences in insulin sensitivity explain why women, especially younger women, have a lower cardiovascular disease (CVD) risk than men remains an unsettled issue.

OBJECTIVE

The objective of this study was to evaluate whether sex disparities in CVD risk are associated with differences in insulin resistance.

DESIGN/SETTING/PARTICIPANTS

This was a cross-sectional study of women (n = 468) and men (n = 354) who had the measurement of CVD risk factors and steady-state plasma glucose (SSPG) concentration (insulin resistance) using the insulin suppression test. The population was also divided by median age (51 y) to evaluate the effect of age on sex differences.

MAIN OUTCOME MEASURES/RESULTS

In general, the SSPG concentration was similar between sexes. At higher BMI (≥30 kg/m(2)), women had significantly lower SSPG concentration than men (sex × BMI interaction, P = .001). However, sex differences in CVD risk factors were not due to differences in SSPG but accentuated by a higher degree of insulin resistance in younger (age < 51 y) but not older (≥ 51 y) individuals. In younger individuals, women had significantly (P ≤ .007) lower diastolic blood pressure and fasting glucose and triglyceride concentration compared with men in SSPG tertile 3 (most insulin resistant) but not in tertile 1 (least insulin resistant). Older women had lower diastolic blood pressure compared with men, regardless of SSPG. High-density lipoprotein cholesterol remained higher in women, regardless of age or SSPG.

CONCLUSIONS

The female advantage is not due to a difference in insulin action but results from an attenuation of the relationship between insulin resistance and CVD risk, especially in younger individuals.

Ectopic fat and cardiometabolic and vascular risk

Given that the variation in how regional adipose tissue handles and stores excess dietary energy has substantial cardiometabolic implications, ectopic fat distribution might be an important predictor of cardiometabolic and vascular risk, in addition to overall obesity itself. Conceptually, ectopic fat depots may be divided into systemically acting fat depots and locally acting fat depots. Systemically acting fat depots include visceral fat, fat in the liver, muscle, or neck, and subcutaneous fat. Accumulation in the abdominal visceral area, compared with overall obesity, has an equally or more important role in the development of cardiometabolic risk. Fat depots in liver/muscle tissue cause adverse cardiometabolic effects by affecting energy metabolism. Fat depots in lower-body subcutaneous areas may be protective regarding cardiometabolic risk, by trapping remnant energy. Fat accumulation in the neck is a unique type of fat depot that may increase cardiovascular risk by increasing insulin resistance. Locally acting fat depots include pericardial fat, perivascular fat, and renal sinus fat. These fat depots have effects primarily on adjacent anatomic organs, directly via lipotoxicity and indirectly via cytokine secretion. Pericardial fat is associated with coronary atherosclerosis. Perivascular fat may play an independent role in adverse vascular biology, including arterial stiffness. Renal sinus fat is a unique fat depot that may confer additional cardiometabolic risk. Thus, ectopic fat depots may contribute to the understanding of the link between body composition and cardiometabolic risk. In this review, we focus on the role and clinical implications of ectopic fat depots in cardiometabolic and vascular risk.

Tracking adipogenesis during white adipose tissue development, expansion and regeneration

White adipose tissue displays high plasticity. We developed a system for the inducible, permanent labeling of mature adipocytes that we called the AdipoChaser mouse. We monitored adipogenesis during development, high-fat diet (HFD) feeding and cold exposure. During cold-induced 'browning' of subcutaneous fat, most 'beige' adipocytes stem from de novo-differentiated adipocytes. During HFD feeding, epididymal fat initiates adipogenesis after 4 weeks, whereas subcutaneous fat undergoes hypertrophy for a period of up to 12 weeks. Gonadal fat develops postnatally, whereas subcutaneous fat develops between embryonic days 14 and 18. Our results highlight the extensive differences in adipogenic potential in various fat depots.

Associations of visceral and abdominal subcutaneous adipose tissue with markers of cardiac and metabolic risk in obese adults

OBJECTIVE

Visceral (VAT) and abdominal subcutaneous (SAT) adipose tissues contribute to obesity but may have different metabolic and atherosclerosis risk profiles. We sought to determine the associations of abdominal VAT and SAT mass with markers of cardiac and metabolic risk in a large, multiethnic, population-based cohort of obese adults.

DESIGN AND METHODS

Among obese participants in the Dallas Heart Study, we examined the cross-sectional associations of abdominal VAT and SAT mass, assessed by magnetic resonance imaging (MRI) and indexed to body surface area (BSA), with circulating biomarkers of insulin resistance, dyslipidemia, and inflammation (n = 942); and with aortic plaque and liver fat by MRI and coronary calcium by computed tomography (n = 1200). Associations of VAT/BSA and SAT/BSA were examined after adjustment for age, sex, race, menopause, and body mass index.

RESULTS

In multivariable models, VAT significantly associated with the homeostasis model assessment of insulin resistance (HOMA-IR), lower adiponectin, smaller LDL and HDL particle size, larger VLDL size, and increased LDL and VLDL particle number (p < 0.001 for each). VAT also associated with prevalent diabetes, metabolic syndrome, hepatic steatosis, and aortic plaque (p < 0.001 for each). VAT independently associated with C-reactive protein but not with any other inflammatory biomarkers tested. In contrast, SAT associated with leptin and inflammatory biomarkers, but not with dyslipidemia or atherosclerosis. Associations between SAT and HOMA-IR were significant in univariable analyses but attenuated after multivariable adjustment.

CONCLUSION

VAT associated with an adverse metabolic, dyslipidemic, and atherogenic obesity phenotype. In contrast, SAT demonstrated a more benign phenotype, characterized by modest associations with inflammatory biomarkers and leptin, but no independent association with dyslipidemia, insulin resistance, or atherosclerosis in obese individuals. These findings suggest that abdominal fat distribution defines distinct obesity sub-phenotypes with heterogeneous metabolic and atherosclerosis risk.

Gene expression profiling in subcutaneous, visceral and epigastric adipose tissues of patients with extreme obesity

Objective

The goal of the present study was to identify differences in gene expression between SAT, VAT, and EAT depots in Class III severely obese individuals.

Design

Human subcutaneous (SAT) and visceral (VAT) adipose tissues exhibit differential gene expression profiles. There is little information, however, about the other proximal white adipose tissue, epigastric (EAT) in terms of its function and contribution to metabolism.

Subjects and Methods

Using RNA from adipose biospecimens obtained from Class III severely obese patients undergoing open Roux-en-Y gastric bypass surgery, we compared gene expression profiles between SAT, VAT, and EAT, using microarrays validated by real time quantitative PCR.

Results

The three depots were found to share 1,907 genes. VAT had the greatest number of genes [66] expressed exclusively in this depot, followed by SAT [23], and then EAT [14]. Moreover, VAT shared more genes with EAT [65] than with SAT [38]. Further analyses using ratios of SAT/EAT, VAT/EAT, and SAT/VAT, identified specific as well as overlapping networks and pathways of genes representing dermatological diseases, inflammation, cell cycle and growth, cancer, and development. Targeted analysis of genes playing a role in adipose tissue development and function, revealed that Peroxisome proliferator-activated receptor Gamma Coactivator 1-alpha (PGC1-α) that regulates the precursor of the hormone Irisin (FNCD5), were abundantly expressed in all three fat depots, along with fibroblast growth factors (FGF) FGF1, FGF7, and FGF10, whereas, FGF19 and FGF21 were undetectable.

Conclusions

These data indicate that EAT has more in common with VAT suggesting similar metabolic potential. The human epigastric adipose depot could play a significant functional role in metabolic diseases and should be further investigated.

A twenty-first century cancer epidemic caused by obesity: the involvement of insulin, diabetes, and insulin-like growth factors

Obesity has reached epidemic proportions in the developed world. The progression from obesity to diabetes mellitus type 2, via metabolic syndrome, is recognised, and the significant associated increase in the risk of major human cancers acknowledged. We review the molecular basis of the involvement of morbidly high concentrations of endogenous or therapeutic insulin and of insulin-like growth factors in the progression from obesity to diabetes and finally to cancer. Epidemiological and biochemical studies establish the role of insulin and hyperinsulinaemia in cancer risk and progression. Insulin-like growth factors, IGF-1 and IGF-2, secreted by visceral or mammary adipose tissue have significant paracrine and endocrine effects. These effects can be exacerbated by increased steroid hormone production. Structural studies elucidate how each of the three ligands, insulin, IGF-1, and IGF-2, interacts differently with isoforms A and B of the insulin receptor and with type I IGF receptor and explain how these protagonists contribute to diabetes-associated cancer. The above should inform appropriate treatment of cancers that arise in obese individuals and in those with diabetes mellitus type 2. Novel drugs that target the insulin and insulin-like growth factor signal transduction pathways are in clinical trial and should be effective if appropriate biomarker-informed patient stratification is implemented.

New insights into pancreatic cancer-induced paraneoplastic diabetes

Up to 85% of patients with pancreatic cancer have diabetes or hyperglycaemia, which frequently manifests as early as 2-3 years before a diagnosis of pancreatic cancer. Conversely, patients with new-onset diabetes have a 5-8-fold increased risk of being diagnosed with pancreatic cancer within 1-3 years of developing diabetes. Emerging evidence now indicates that pancreatic cancer causes diabetes. As in type 2 diabetes, β-cell dysfunction and peripheral insulin resistance are seen in pancreatic cancer-induced diabetes. However, unlike in patients with type 2 diabetes, glucose control worsens in patients with pancreatic cancer in the face of ongoing, often profound, weight loss. Diabetes and weight loss, which precede cachexia onset by several months, are paraneoplastic phenomena induced by pancreatic cancer. Although the pathogenesis of these pancreatic cancer-induced metabolic alterations is only beginning to be understood, these are likely mechanisms to promote the survival and growth of pancreatic cancer in a hostile and highly desmoplastic microenvironment. Interestingly, these metabolic changes could enable early diagnosis of pancreatic cancer, if they can be distinguished from the ones that occur in patients with type 2 diabetes. One such possible biomarker is adrenomedullin, which is a potential mediator of β-cell dysfunction in pancreatic cancer-induced diabetes.

Visceral and subcutaneous fat quality and cardiometabolic risk

OBJECTIVES

The aim of this study was to evaluate whether computed tomography (CT) attenuation, as a measure of fat quality, is associated with cardiometabolic risk factors above and beyond fat quantity.

BACKGROUND

Visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) are pathogenic fat depots associated with cardiometabolic risk. Adipose tissue attenuation in CT images is variable, similar to adipose tissue volume. However, whether the quality of abdominal fat attenuation is associated with cardiometabolic risk independent of the quantity is uncertain.

METHODS

Participants were drawn from the Framingham Heart Study CT substudy. The VAT and SAT volumes were acquired by semiquantitative assessment. Fat quality was measured by CT attenuation and recorded as mean Hounsfield unit (HU) within each fat depot. Sex-specific linear and logistic multivariable regression models were used to assess the association between standard deviation (SD) decrease in HU and each risk factor.

RESULTS

Lower CT attenuation of VAT and SAT was correlated with higher body mass index levels in both sexes. Risk factors were generally more adverse with decreasing HU values. For example, in women, per 1 SD decrease in VAT HU, the odds ratio (OR) was increased for hypertension (OR: 1.80), impaired fasting glucose (OR: 2.10), metabolic syndrome (OR: 3.65), and insulin resistance (OR: 3.36; all p < 0.0001). In models that further adjusted for VAT volume, impaired fasting glucose, metabolic syndrome, and insulin resistance remained significant. Trends were similar but less pronounced for SAT and for men. There was evidence of an interaction between HU and fat volume among both women and men.

CONCLUSIONS

Lower CT attenuation of VAT and SAT is associated with adverse cardiometabolic risk above and beyond total adipose tissue volume. Qualitative indices of abdominal fat depots may provide insight regarding cardiometabolic risk independent of fat quantity.

Adipose tissue angiogenesis: impact on obesity and type-2 diabetes

The growth and function of tissues are critically dependent on their vascularization. Adipose tissue is capable of expanding many-fold during adulthood, therefore requiring the formation of new vasculature to supply growing and proliferating adipocytes. The expansion of the vasculature in adipose tissue occurs through angiogenesis, where new blood vessels develop from those pre-existing within the tissue. Inappropriate angiogenesis may underlie adipose tissue dysfunction in obesity, which in turn increases type-2 diabetes risk. In addition, genetic and developmental factors involved in vascular patterning may define the size and expandability of diverse adipose tissue depots, which are also associated with type-2 diabetes risk. Moreover, the adipose tissue vasculature appears to be the niche for pre-adipocyte precursors, and factors that affect angiogenesis may directly impact the generation of new adipocytes. Here we review recent advances on the basic mechanisms of angiogenesis, and on the role of angiogenesis in adipose tissue development and obesity. A substantial amount of data points to a deficit in adipose tissue angiogenesis as a contributing factor to insulin resistance and metabolic disease in obesity. These emerging findings support the concept of the adipose tissue vasculature as a source of new targets for metabolic disease therapies. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.

Body fat distribution and insulin resistance

The burden of obesity has increased globally over the last few decades and its association with insulin resistance and related cardio-metabolic problems have adversely affected our ability to reduce population morbidity and mortality. Traditionally, adipose tissue in the visceral fat depot has been considered a major culprit in the development of insulin resistance. However, there is a growing body of evidence supporting the role of subcutaneous truncal/abdominal adipose tissue in the development of insulin resistance. There are significant differences in the functional characteristics of subcutaneous abdominal/truncal vs. intraabdominal vs. gluteo-femoral fat depots. More recently, mounting evidence has been supporting the role of adipose tissue function in the development of metabolic complications independent of adipose tissue volume or distribution. Decreased capacity for adipocyte differentiation and angiogenesis along with adipocyte hypertrophy can trigger a vicious cycle of inflammation leading to subcutaneous adipose tissue dysfunction and ectopic fat deposition. Therapeutic lifestyle change continues to be the most important intervention in clinical practice to improve adipose tissue function and avoid development of insulin resistance and related cardio-metabolic complications.

Gender-dependent associations of metabolite profiles and body fat distribution in a healthy population with central obesity: towards metabolomics diagnostics

Obesity is a risk factor for cardiovascular diseases and type 2 diabetes especially when the fat is accumulated to central depots. Novel biomarkers are crucial to develop diagnostics for obesity and related metabolic disorders. We evaluated the associations between metabolite profiles (136 lipid components, 12 lipoprotein subclasses, 17 low-molecular-weight metabolites, 12 clinical markers) and 28 phenotype parameters (including different body fat distribution parameters such as android (A), gynoid (G), abdominal visceral (VAT), subcutaneous (SAT) fat) in 215 plasma/serum samples from healthy overweight men (n=32) and women (n=83) with central obesity. (Partial) correlation analysis and partial least squares (PLS) regression analysis showed that only specific metabolites were associated to A:G ratio, VAT, and SAT, respectively. These association patterns were gender dependent. For example, insulin, cholesterol, VLDL, and certain triacylglycerols (TG 54:1-3) correlated to VAT in women, while in men VAT was associated with TG 50:1-5, TG 55:1, phosphatidylcholine (PC 32:0), and VLDL ((X)L). Moreover, multiple regression analysis revealed that waist circumference and total fat were sufficient to predict VAT and SAT in women. In contrast, only VAT but not SAT could be predicted in men and only when plasma metabolites were included, with PC 32:0 being most strongly associated with VAT. These findings collectively highlight the potential of metabolomics in obesity and that gender differences need to be taken into account for novel biomarker and diagnostic discovery for obesity and metabolic disorders.

Sex dimorphism and depot differences in adipose tissue function

Obesity, characterized by excessive adiposity, is a risk factor for many metabolic pathologies, such as type 2 diabetes mellitus (T2DM). Numerous studies have shown that adipose tissue distribution may be a greater predictor of metabolic health. Upper-body fat (visceral and subcutaneous abdominal) is commonly associated with the unfavorable complications of obesity, while lower-body fat (gluteal-femoral) may be protective. Current research investigations are focused on analyzing the metabolic properties of adipose tissue, in order to better understand the mechanisms that regulate fat distribution in both men and women. This review will highlight the adipose tissue depot- and sex-dependent differences in white adipose tissue function, including adipogenesis, adipose tissue developmental patterning, the storage and release of fatty acids, and secretory function. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.