Counterpoint: visceral adiposity is not causally related to insulin resistance

Novel Proteome Targets Marking Insulin Resistance in Metabolic Syndrome

CONTEXT/OBJECTIVE

In order to better understand which metabolic differences are related to insulin resistance in metabolic syndrome (MetSyn), we used hyperinsulinemic-euglycemic (HE) clamps in individuals with MetSyn and related peripheral insulin resistance to circulating biomarkers.

DESIGN/METHODS

In this cross-sectional study, HE-clamps were performed in treatment-naive men (n = 97) with MetSyn. Subjects were defined as insulin-resistant based on the rate of disappearance (Rd). Machine learning models and conventional statistics were used to identify biomarkers of insulin resistance. Findings were replicated in a cohort with n = 282 obese men and women with (n = 156) and without (n = 126) MetSyn. In addition to this, the relation between biomarkers and adipose tissue was assessed by nuclear magnetic resonance imaging.

RESULTS

Peripheral insulin resistance is marked by changes in proteins related to inflammatory processes such as IL-1 and TNF-receptor and superfamily members. These proteins can distinguish between insulin-resistant and insulin-sensitive individuals (AUC = 0.72 ± 0.10) with MetSyn. These proteins were also associated with IFG, liver fat (rho 0.36, p = 1.79 × 10-9) and visceral adipose tissue (rho = 0.35, p = 6.80 × 10-9). Interestingly, these proteins had the strongest association in the MetSyn subgroup compared to individuals without MetSyn.

CONCLUSIONS

MetSyn associated with insulin resistance is characterized by protein changes related to body fat content, insulin signaling and pro-inflammatory processes. These findings provide novel targets for intervention studies and should be the focus of future in vitro and in vivo studies.

The Expanding Problem of Regional Adiposity: Revisiting a 1985 Diabetes Classic by Ohlson et al

Body fat distribution is a predictor of metabolic health in obesity. In this Classics in Diabetes article, we revisit a 1985 Diabetes article by Swedish investigators Ohlson et al. This work was one of the first prospective population-based studies that established a relationship between abdominal adiposity and the risk for developing diabetes. Here, we discuss evolving concepts regarding the link between regional adiposity and diabetes and other chronic disorders. Moreover, we highlight fundamental questions that remain unresolved.

The Role of Olfactomedin 2 in the Adipose Tissue–Liver Axis and Its Implication in Obesity-Associated Nonalcoholic Fatty Liver Disease

This study’s objective was to assess the involvement of olfactomedin 2 (OLFM2), a secreted glycoprotein related to lipid metabolism regulation, in nonalcoholic fatty liver disease (NAFLD) mediated by the adipose-tissue–liver axis. OLFM2 mRNA expression was analyzed in subcutaneous (SAT) and visceral (VAT) adipose tissue by RT–qPCR. The cohort included women with normal weight (n = 16) or morbid obesity (MO, n = 60) who were subclassified into normal liver (n = 20), simple steatosis (n = 21), and nonalcoholic steatohepatitis (NASH, n = 19) groups. The results showed that OLFM2 expression in SAT was enhanced in MO individuals and in the presence of NAFLD. Specifically, OLFM2 expression in SAT was increased in mild and moderate degrees of steatosis in comparison to the absence of it. Moreover, OLFM2 expression in SAT was negatively correlated with interleukin-6 levels. On the other hand, OLFM2 expression in VAT decreased in the presence of NASH and exhibited a positive correlation with adiponectin levels. In conclusion, OLFM2 in SAT seems to be implicated in hepatic lipid accumulation. Additionally, since we previously suggested the possible implication of hepatic OLFM2 in NAFLD progression, now we propose a possible interaction between the liver and SAT, reinforcing the potential implication of this tissue in NAFLD development.

Superficial vs Deep Subcutaneous Adipose Tissue: Sex-Specific Associations With Hepatic Steatosis and Metabolic Traits

CONTEXT

Subcutaneous adipose tissue (SAT) is not homogeneous, as the fascia scarpa separates the deep SAT (dSAT) from the superficial SAT (sSAT).

OBJECTIVE

The aim of this study is to evaluate the sex-specific associations of sSAT and dSAT with hepatic steatosis and metabolic syndrome in overweight individuals.

METHODS

We recruited 285 individuals with a body mass index (BMI) greater than or equal to 27 and aged 55 to 81 years. Abdominal magnetic resonance imaging was performed around level L4 to L5 to measure visceral adipose tissue (VAT), dSAT, and sSAT volumes. The amount of hepatic fat was quantified by MR spectroscopy.

RESULTS

Men had significantly higher volumes of VAT (122.6 cm3 vs 98.7 cm3, P < .001) and had only half the volume of sSAT compared to women adjusted for BMI (50.3 cm3 in men vs 97.0 cm3 in women, P < .001). dSAT correlated significantly with hepatic fat content in univariate analysis (standardized β = .190, P < .05), while VAT correlated significantly with hepatic steatosis in a multivariate model, adjusted for age, alcohol use, and other abdominal fat compartments (standardized β = .184, P = .037). Moreover, dSAT in men correlated negatively with HDL cholesterol (standardized β = -0.165, P = .038) in multivariate analyses. In women with a BMI between 30 and 40, in a multivariate model adjusted for age, alcohol use, and other abdominal fat compartments, VAT correlated positively (standardized β = -.404, P = .003), and sSAT negatively (standardized β = -.300, P = .04) with hepatic fat content.

CONCLUSION

In men, dSAT is associated with hepatic steatosis and adverse metabolic traits, such as lower HDL cholesterol levels, whereas in women with obesity sSAT shows a beneficial relation with respect to hepatic fat content.

Diabetes in the Kokan region of India

BACKGROUND

BKL Walawalkar Hospital is situated near the village of Dervan in the Kokan region of the state of Maharashtra in India. A survey of 2200 surrounding villages showed 51.8% adults had body mass index (BMI) below <18.5 kg/m² and only 4.5% were overweight. A survey of 11521 adolescent girls from rural schools showed 64% prevalence of thinness. In the same region, government survey reported the prevalence of diabetes around 7%, and 70% prevalence of leanness. This reinforced the fact that the overall population of Kokan is lean. Hence, we decided to investigate body composition of diabetic people from our hospital clinic by carrying out a clinic-based case control study.

AIM

To study body composition of diabetics in a rural clinic of Kokan.

METHODS

In a case-control study, 168 type 2 diabetic patients (102 men) attending the outpatient department at a rural hospital and 144 non-diabetic controls (68 men) in the Chiplun area of the Kokan region were recruited. History of diabetes (age of onset, duration), anthropometric measurements (height, weight, waist and hip circumference) were recorded. Body composition was measured by bioimpedance using the TANITA analyzer.

RESULTS

More than 45% of diabetic subjects had a 1^st degree family history of diabetes, and more than 50% had macrovascular complications. The average BMI in diabetic subjects was 24.3 kg/m². According to World Health Organization standards, prevalence of underweight was 8% and that of normal BMI was around 50%. Underweight and normal diabetic subjects (men as well as women) had significantly lower body fat percentage, higher muscle mass percentage, lower visceral fat and lower basal metabolic rate when compared to their overweight counterparts.

CONCLUSION

The diabetic population in Kokan has near normal body composition, and BMI has considerable limitations in assessing body composition and it also lacks sensitivity for assessing risk for diabetes in this population. High prevalence of family history of diabetes may point towards genetic predisposition. Leanness is an inherent characteristic of this population and its metabolic significance needs further investigations with a larger sample size.

Elevated blood pressure and its predictors among secondary school students in Sarawak: a cross-sectional study

OBJECTIVES

Hypertension is a health issue affecting adolescents. Accumulating evidence affirms that elevated blood pressure begins in childhood and tracks into adulthood. This cross-sectional study was conducted to determine the prevalence of elevated blood pressure and its predictors among secondary school students in Sarawak, Malaysia.

METHODS

A total of 2,461 secondary school students aged 12-17 years from 19 schools in Sarawak participated in the study. Questionnaire was used to obtain socio-demographic data, parental history of hypertension, and self-reported physical activity. Anthropometric and blood pressure measurements were taken. Data was entered and analysed using SPSS version 23.0.

RESULTS

The prevalence of adolescents with elevated blood pressure, overweight, central obesity, and overfat were 30.1%, 24.3%, 13.5%, and 6.7%, respectively. Multivariate logistic regression demonstrated the predictors significantly associated with elevated blood pressure among respondents: overweight (adjusted odds ratio=3.144), being male (adjusted odds ratio=3.073), being Chinese (adjusted odds ratio=2.321) or Iban (adjusted odds ratio=1.578), central obesity (adjusted odds ratio=2.145), being overfat (adjusted odds ratio=1.885), and being an older adolescent (adjusted odds ratio=1.109). Parental history of hypertension, locality, and physical activity showed no significant associations.

CONCLUSION

The obesity epidemic must be tackled at community and school levels by health education and regulation of school canteen foods.

The "adipose tissue expandability" hypothesis: a potential mechanism for insulin resistance in obese youth

Obesity has become a major global health challenge of the 21st century, as it is associated with the onset of type 2 diabetes (T2D) and cardiovascular complications, even at a very early age in life. The root causes of pediatric obesity remain incompletely understood. The obesity epidemic together with the relationship of obesity to the growing population burden of chronic disease presents unprecedented research opportunities and challenges. Decades of obesity-related research funded by governments around the world have yielded many important discoveries about both etiological pathways and preventive or therapeutic interventions. Yet, there is a sense that the problem is outpacing these research efforts. Obesity poses a significant risk for the development of cardiovascular disease (CVD) , diabetes and certain cancers thereby shortening life expectancy. Nevertheless, many obese individuals do not develop any of these comorbidities. One hypothesis explaining this dilemma is that total body fat is not the culprit of adverse health in obesity rather the relative proportion of lipids in various fat depots is what determines the metabolic risk. In this review, we describe the role of altered fat partitioning in youth onset obesity and its relation to fatty liver and T2D during adolescence.

Dietary intake and cardiometabolic biomarkers in relation to insulin resistance and hypertension in a middle-aged and elderly population in Beijing, China

This study investigated the relationships of dietary intake and cardiometabolic biomarkers with insulin resistance and hypertension in rural middle-aged and elderly people in China. One hundred and eight middle-aged and elderly adults were recruited in Zhangfang village in May 2014. We measured blood pressure, anthropometric parameters, and biochemical indexes, including high-sensitivity C-reactive protein (hsCRP), soluble intercellular adhesion molecule-1 (sICAM-1), glucose, insulin, and blood lipids. Homeostasis model assessment of insulin resistance index (HOMA-IR) was assessed on the basis of fasting glucose and insulin. We recorded participant demographic characteristics, dietary intake, and lifestyle using questionnaires. Hypertensive participants had higher levels of triglycerides (TG), hsCRP, sICAM-1, body fat percentage (BF%), arm muscle circumference (AMC) and HOMA-IR than nonhypertensive individuals. Hypertensive participants had higher carbohydrate intake but lower intakes of protein and fat. Carbohydrate intake was positively correlated with hsCRP, sICAM-1, TG, BF%, and HOMA-IR, and was negatively correlated with AMC. Protein and fat intakes were negatively correlated with hsCRP and sICAM-1. Protein intake was also significantly negatively correlated with TG and HOMA-IR, and positively correlated with AMC. HOMA-IR was positively correlated with hsCRP, sICAM-1, TG and BF%, and negatively correlated with AMC. Multivariable linear regression indicated that TG, sICAM-1, and hsCRP were significantly associated with HOMA-IR. In conclusion, in a rural Chinese population, high intake of carbohydrate and low intake of fat and protein were associated with insulin resistance and hypertension, possibly by increasing inflammatory factors such as sICAM-1 and hsCRP, increasing BF% and increasing the level of plasma TG.

MicroRNA-17-92 cluster regulates pancreatic beta-cell proliferation and adaptation

MiR-17-92 cluster contributes to the regulation of mammalian development, aging and tumorigenesis. The functional roles of miR-17-92 in pancreatic beta-cells are largely unknown. In this study, we found that conditional deletion of miR-17-92 in mouse pancreatic beta-cells (miR-17-92βKO) significantly reduces glucose tolerance and the first phase of insulin secretion, despite normal ad libitum fed and fasting glucose levels. Proliferation is down-regulated in pancreatic beta-cells after deleting miR-17-92. MiR-17-92βKO mice show higher phosphatase and tensin homologue (PTEN) and lower phosphorylated AKT in islets. Under high fat diet challenge for 16 weeks, miR-17-92βKO mice lose compensation and exhibit higher glucose levels, and lower insulin secretion. Collectively, these data suggest that miR-17-92 is a critical contributor to molecular mechanisms regulating glucose-stimulated insulin secretion and pancreatic beta-cell adaptation under metabolic stress.

Nutrition Review: Diet and Nutrients in the Prevention and Treatment of Type 2 Diabetes

Lifestyle factors, including diet, are critical in the prevention and treatment of type 2 diabetes. Because weight gain increases diabetes risk, and even modest weight reduction reduces risk, weight management is paramount in lessening the occurrence and effects of diabetes. Weight loss interventions should include patient education, behavioral strategies, physical activity, energy intake deficits of 500 to 1000 kcal/day, and prevention of recidivism. Macronutrient distribution ranges of diets for diabetic patients follow those of the Dietary Reference Intakes, allowing for individualization according to a patient's metabolic responses, needs, and preferences. Nutrients to be limited include saturated fats, artificial trans fats, cholesterol, and sodium, whereas nutrients to be emphasized include monounsaturated fatty acids, omega-3 polyunsaturated fatty acids, fibers, antioxidants, and minerals, including potassium, magnesium, calcium, and chromium. Food sources are advised rather than supplements. Sugars can be isocalorically substituted for starches without detriments to glycemic control. Diets with low glycemic index or load may have modest benefits in managing type 2 diabetes. If a diabetic patient chooses to consume alcohol, he or she should do so in moderation. Foods advocated in type 2 diabetes are similar to those that are also beneficial in reducing risk for other chronic diseases.

The Associations Between Increasing Degrees of HOMA-IR and Measurements of Adiposity Among Euglycemic U.S. Adults

BACKGROUND

The purpose of this study was to examine the associations between increasing degrees of insulin resistance (using the homeostatic model assessment of insulin resistance [HOMA-IR]) and two measures of adiposity in a nationally representative sample of euglycemic U.S. adults.

MATERIALS AND METHODS

Sample included adult participants (≥ 20 years of age) [N = 1586 (body mass index, BMI model), N = 1577 (waist circumference, WC model)] from the 1999-2004 National Health and Nutrition Examination Survey (NHANES). HOMA-IR was categorized into quartiles. BMI and WC were examined continuously as the dependent variables.

RESULTS

Following adjustment for covariates, those with HOMA-IR values in the second, third, and fourth quartiles had significantly higher BMIs (P < 0.001) compared with subjects in the first quartile. In the model using WC, significantly higher WCs were found in subjects in the second, third, and fourth quartiles of HOMA-IR (P < 0.001) compared with those in the first quartile. A significant moderate correlation was found between HOMA-IR and BMI (R(2) = 0.4171, P < 0.001), as well as HOMA-IR and WC (R(2) = 0.4826, P < 0.001).

CONCLUSIONS

Having a higher HOMA-IR value is associated with higher BMI and WC values in euglycemic subjects.

AMPK/Mitochondria in Metabolic Diseases

The obtaining of nutrients is the most important task in our lives. Energy is central to life's evolutions; this was one of the aspect that induced the selection of the more adaptable and more energetically profitable species. Nowadays things have changed in our modern society. A high proportion of people has access to plenty amount of food and the obesity appear as one of the pathological characteristics of our society. Energy is obtained essentially in the mitochondria with the transfer of protons across the inner membrane that produce ATP. The exactly regulation of the synthesis and degradation of ATP (ATP ↔ ADP + phosphate) is essential to all form of life. This task is performed by the 5' adenosine monophosphate-activated protein kinase (AMPK). mtDNA is highly exposed to oxidative damage and could play a central role in human health and disease. This high potential rate of abnormalities is controlled by one of the most complex mechanism: the autophagy. AMPK appears to be the key cellular energy sensor involved in multiple cellular mechanisms and is essential to have a good metabolic homeostasis to face all the aggression and start the inflammatory reaction. Therefore its disturbances have been related with multiple diseases. Recent findings support the role of AMPK in inflammation and immunity such as Metabolic Syndrome, Obesity and Diabetes. All these Metabolic Disorders are considered pandemics and they need an adequate control and prevention. One important way to achieve it is deepen in the pathogenic mechanisms. Mitochondria and AMPK are the key elements through which it happen, their knowledge and research allow us to a better management. The discovery and use of drugs that can modulate them is imperative to improve our way of manage the metabolic disorders.

Lipid transport in cholecystokinin knockout mice

Cholecystokinin (CCK) is released in response to lipid feeding and regulates pancreatic digestive enzymes vital to the absorption of nutrients. Our previous reports demonstrated that cholecystokinin knockout (CCK-KO) mice fed for 10 weeks of HFD had reduced body fat mass, but comparable glucose uptake by white adipose tissues and skeletal muscles. We hypothesized that CCK is involved in energy homeostasis and lipid transport from the small intestine to tissues in response to acute treatment with dietary lipids. CCK-KO mice with comparable fat absorption had increased energy expenditure and were resistant to HFD-induced obesity. Using intraduodenal infusion of butter fat and intravenous infusion using Liposyn III, we determined the mechanism of lipid transport from the small intestine to deposition in lymph and adipocytes in CCK-KO mice. CCK-KO mice had delayed secretion of Apo B48-chylomicrons, lipid transport to the lymphatic system, and triglyceride (TG)-derived fatty acid uptake by epididymal fat in response to acute treatment of intraduodenal lipids. In contrast, CCK-KO mice had comparable TG clearance and lipid uptake by white adipocytes in response to TGs in chylomicron-like emulsion. Thus, we concluded that CCK is important for lipid transport and energy expenditure to control body weight in response to dietary lipid feeding.

The gut-adipose-liver axis in the metabolic syndrome

Obesity is associated with altered gut microbiota composition and impaired gut barrier function. These changes, together with interrelated mesenteric adipose tissue inflammation, result in increased release of pro-inflammatory cytokines, bacteria-derived factors, and lipids into the portal circulation, promoting the development of (hepatic) insulin resistance. Herein, the potential impact of obesity-related changes in gut and visceral adipose tissue biology on the development of insulin resistance and Type 2 diabetes is reviewed.

Short-term food restriction followed by controlled refeeding promotes gorging behavior, enhances fat deposition, and diminishes insulin sensitivity in mice

Rodents are commonly used in food restriction refeeding studies to investigate weight regain. Mice that are rationed food every 24 h may consume all allocated food in a short time (gorge) and therefore undergo a brief well-fed period followed by an extended fasted period until the next day's food allotment. These exaggerated metabolic states are not typical in mice fed ad libitum (nibbling). The aim of the current study was to elucidate the intraday and cumulative metabolic consequences of gorging (induced by food restriction) in mice during controlled refeeding. Accordingly, following a temporary food restriction, mice were fed rations similar to intakes of controls fed ad libitum. Temporary food restriction initiated gorging behavior that persisted during refeeding; consequently, metabolism-related measurements were obtained in the gorging mice during their daily fed and fasted metabolic states. Robust differences in adipose tissue lipogenic and inflammatory gene expression were found in the gorging mice by metabolic state (fed versus fasted). Additionally, despite a reduced cumulative food intake compared to mice fed ad libitum, restriction-induced gorging mice had increased intraabdominal fat accumulation, diminished hepatic and peripheral insulin sensitivity, and a gene expression profile favoring lipid deposition. Our findings highlight the intraday differences in gene expression in gorging mice before and after feeding that confound comparisons with mice fed ad libitum, or nibbling. The present study also provides evidence that weight regain following food restriction is associated with cumulative metabolic and behavioral abnormalities in mice.

Increase in visceral fat per se does not induce insulin resistance in the canine model

OBJECTIVES

To determine whether a selective increase of visceral adipose tissue content will result in insulin resistance.

METHODS

Sympathetic denervation of the omental fat was performed under general inhalant anesthesia by injecting 6-hydroxydopamine in the omental fat of lean mongrel dogs (n = 11). In the conscious animal, whole-body insulin sensitivity was assessed by the minimal model (SI ) and the euglycemic hyperinsulinemic clamp (SICLAMP ). Changes in abdominal fat were monitored by magnetic resonance. All assessments were determined before (Wk0) and 2 weeks (Wk2) after denervation. Data are medians (upper and lower interquartile).

RESULTS

Denervation of omental fat resulted in increased percentage (and content) of visceral fat [Wk0: 10.2% (8.5-11.4); Wk2: 12.4% (10.4-13.6); P < 0.01]. Abdominal subcutaneous fat remained unchanged. However, no changes were found in SI [Wk0: 4.7 (mU/l)(-1) min(-1) (3.1-8.8); Wk2: 5.3 (mU/l)(-1) min(-1) (4.5-7.2); P = 0.59] or SICLAMP [Wk0: 42.0 × 10(-4) dl kg(-1) min(-1) (mU/l)(-1) (41.0-51.0); Wk2: 40.0 × 10(-4) dl kg(-1) min(-1) (mU/l) (-1) (34.0-52.0); P = 0.67].

CONCLUSIONS

Despite a selective increase in visceral adiposity in dogs, insulin sensitivity in vivo did not change, which argues against the concept that accumulation of visceral adipose tissue contributes to insulin resistance.

Correlation of abdominal adiposity with components of metabolic syndrome, anthropometric parameters and Insulin resistance, in obese and non obese, diabetics and non diabetics: A cross sectional observational study. (Mysore Visceral Adiposity in Diabetes Study)

OBJECTIVES

To measure Visceral Fat (VF) and Subcutaneous Fat (SCF) by ultrasound, in obese and non-obese diabetics and obese and non-obese non diabetics, in a South Indian (Asian Indian) Population and correlate them with Body Mass Index (BMI), Waist Circumference (WC), components of metabolic syndrome and Insulin Resistance (IR).

RESEARCH DESIGN AND METHODS

This was a prospective observational study, 80 diabetics (40 obese and 40 non obese) and 80 non diabetics (40 obese and 40 non obese) a total of 160 subjects were enrolled, out of whom 153 completed the study. The subjects were evaluated with respect to BMI, WC, Blood Pressure (BP); Fasting Blood Sugar (FBS) Fasting Insulin levels (FIL), HbA1C and Lipid profile. The SCF and VF were measured by Ultrasonography.The results were statistically analyzed.

RESULTS

WC correlated significantly with VF in all the groups. Diabetics had more VF compared to non-diabetics. Insulin resistance was significant in all the groups; however diabetics had greater levels of IR, BMI, WC, VF and SCF had no correlation with IR and had no significant correlation with metabolic parameters.

CONCLUSIONS

In this study population, WC was found to be a useful surrogate measure of VF conforming to its well established applicability in other populations. Contrary to other studies elsewhere, SCF and VF were found to be poor indicators of Insulin Resistance. BMI, WC, VF and SCF were not useful in the prediction of metabolic syndrome. Ultrasound was found to be an easier and economic method of measuring abdominal adiposity and actual measurement of abdominal fat was more informative than anthropometric measurements.

Abdominal subcutaneous adipose tissue insulin resistance and lipolysis in patients with non-alcoholic steatohepatitis

BACKGROUND

Systemic insulin resistance (IR) is a primary feature in non-alcoholic steatohepatitis (NASH), however, there remain limited data on tissue-specific insulin sensitivity in vivo.

METHODS

We examined tissue-specific (adipose, muscle and liver) insulin sensitivity and inflammation in 16 European Caucasian patients with biopsy-confirmed NASH and in 15 healthy controls. All underwent a two-step hyperinsulinaemic euglycaemic clamp incorporating stable isotope measurements of carbohydrate and lipid metabolism with concomitant subcutaneous adipose tissue (SAT) microdialysis.

RESULTS

Hepatic and muscle insulin sensitivity were decreased in patients with NASH compared with controls, as demonstrated by reduced suppression of hepatic glucose production and glucose disposal (Gd) rates following insulin infusion. In addition, rates of lipolysis were higher in NASH patients with impaired insulin-mediated suppression of free fatty acid levels. At a tissue specific level, abdominal SAT in patients with NASH was severely insulin resistant, requiring >sixfold more insulin to cause ½-maximal suppression of glycerol release when compared with healthy controls. Furthermore, patients with NASH had significantly higher circulating levels of pro-inflammatory adipocytokines than controls.

CONCLUSION

NASH patients have profound IR in the liver, muscle and in particular adipose tissues. This study represents the first in vivo description of dysfunctional SAT in patients with NASH.

Sexual dimorphism in white and brown adipose tissue with obesity and inflammation

This article is part of a Special Issue "Energy Balance". Obesity and its associated comorbidities remain at epidemic levels globally and show no signs of abatement in either adult or child populations. White adipose tissue has long been established as an endocrine signalling organ possessing both metabolic and immune functions. This role can become dysregulated following excess adiposity caused by adipocyte hypertrophy and hyperplasia. In contrast, brown adipose tissue (BAT) is only present in comparatively small amounts in the body but can significantly impact on heat production, and thus could prevent excess white adiposity. Obesity and associated risk factors for adverse metabolic health are not only linked with enlarged fat mass but also are dependent on its anatomical deposition. In addition, numerous studies have revealed a disparity in white adipose tissue deposition prior to and during the development of obesity between the sexes. Females therefore tend to develop a greater abundance of femoral and gluteal subcutaneous fat whereas males exhibit more central adiposity. In females, lower body subcutaneous adipose tissue depots appear to possess a greater capacity for lipid storage, enhanced lipolytic flux and hyperplastic tissue remodelling compared to visceral adipocytes. These differences are acknowledged to contribute to the poorer metabolic and inflammatory profiles observed in males. Importantly, the converse outcomes between sexes disappear after the menopause, suggesting a role for sex hormones within the onset of metabolic complications with obesity. This review further considers how BAT impacts upon on the relationship between excess adiposity, gender, inflammation and endocrine signalling and could thus ultimately be a target to prevent obesity.

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.

Abdominal adipose tissue distribution on MRI and diabetes

RATIONALE AND OBJECTIVES

To introduce a simple magnetic resonance imaging (MRI) protocol for quantitative assessment of intraperitoneal, retroperitoneal, and subcutaneous adipose tissue (AT) and to compare AT distribution between diabetic and nondiabetic individuals.

MATERIALS AND METHODS

Thirty-eight consecutive male diabetic patients (group A) and 38 males (who matched for body mass index [BMI]) without metabolic syndrome (group B) underwent abdominal MRI with a three-dimensional spoiled gradient echo T1-weighted sequence. The amounts of intraperitoneal, retroperitoneal, and subcutaneous AT were calculated on a workstation, after manual anatomic segmentation and were correlated with 10 anthropometric measurements. Pearson product-moment correlation coefficients were used for correlation of AT volumes with anthropometric measurements, Wilcoxon test to compare AT measurements between automatic and manual technique used, and unpaired t test to compare volumes of AT compartments between group A and B.

RESULTS

Diabetic patients exhibited larger amount of intraperitoneal and retroperitoneal AT than normal individuals at all levels (t = 2.02,P < .05). Among anthropometric measurements, the waist circumference, BMI, and body fat percentage exhibited the best correlations with intraperitoneal and retroperitoneal AT (group A (r) = 0.88/0.78/0.0.69 and group B (r) = 0.91/0.87/0.81). The L2-L5 set of images was found to be the most representative of the amount of AT volumes.

CONCLUSIONS

Amount and distribution of AT can be accurately and easily assessed on MRI. Quantification of intraabdominal AT may promote the role of imaging in the study of metabolic syndrome.

A comprehensive review on metabolic syndrome

Metabolic syndrome is defined by a constellation of interconnected physiological, biochemical, clinical, and metabolic factors that directly increases the risk of cardiovascular disease, type 2 diabetes mellitus, and all cause mortality. Insulin resistance, visceral adiposity, atherogenic dyslipidemia, endothelial dysfunction, genetic susceptibility, elevated blood pressure, hypercoagulable state, and chronic stress are the several factors which constitute the syndrome. Chronic inflammation is known to be associated with visceral obesity and insulin resistance which is characterized by production of abnormal adipocytokines such as tumor necrosis factor α , interleukin-1 (IL-1), IL-6, leptin, and adiponectin. The interaction between components of the clinical phenotype of the syndrome with its biological phenotype (insulin resistance, dyslipidemia, etc.) contributes to the development of a proinflammatory state and further a chronic, subclinical vascular inflammation which modulates and results in atherosclerotic processes. Lifestyle modification remains the initial intervention of choice for such population. Modern lifestyle modification therapy combines specific recommendations on diet and exercise with behavioural strategies. Pharmacological treatment should be considered for those whose risk factors are not adequately reduced with lifestyle changes. This review provides summary of literature related to the syndrome's definition, epidemiology, underlying pathogenesis, and treatment approaches of each of the risk factors comprising metabolic syndrome.

The efficacy of probiotics for monosodium glutamate-induced obesity: dietology concerns and opportunities for prevention

Introduction

Obesity becomes endemic today. Monosodium glutamate was proved as obesogenic food additive. Probiotics are discussed to impact on obesity development.

Aims and objectives

The aim was to study the effects of probiotics on the development of monosodium glutamate (MSG)-induced obesity in rats.

Material and methods

We included 45 Wistar male rats and divided into three groups (n = 15). Newborn rats of group 1 (control) received subcutaneously 8 μl/g saline. Group 2 received 3 to 4 mg/g MSG subcutaneously on the second, fourth, sixth, eighth and tenth day of life. Within 4 months after birth, rats were on a standard diet. Group 3 received an aqueous solution of probiotics mixture (2:1:1 Lactobacillus casei IMVB-7280, Bifidobacterium animalis VKL, B. animalis VKB) at the dose of 5 × 10⁹ CFU/kg (50 mg/kg) intragastrically. Administration of probiotics was started at the age of 4 weeks just after weaning and continued for 3 months during 2-week courses. Group 2 received intragastrically 2.5 ml/kg water. Organometric and biochemical parameters in all groups of rats were analyzed over 4 months. The concentration of adiponectin was determined in serum, and leptin - in adipose tissue.

Results

Administration of MSG led to the development of obesity in rats; body weight had increased by 7.9% vs controls (p < 0.05); body length had increased by 5.4% (p < 0.05). Body mass index and Lee index and visceral fat mass had increased (p < 0.001). Under the neonatal injection of MSG, the concentration of total cholesterol, triglycerides, VLDL cholesterol and LDL cholesterol significantly increased (p < 0.001), in comparison with controls. Adipose-derived hormones changed in MSG obesity rats: adiponectin decreased by 58.8% (p < 0.01), and leptin concentration in adipose tissue had increased by 74.7% (p < 0.01). The probiotic therapy of rats from group 3 prevented obesity development. Parameters of rats treated with probiotic mixture did not differ from that in the control.

Conclusions

The introduction of MSG to newborn rats caused the obesity in adulthood. Periodic administration of probiotic mixture to rat injected with MSG neonatally resulted in recovery of lipid metabolism and prevention of the obesity development.

Visceral fat resection in humans: effect on insulin sensitivity, beta-cell function, adipokines, and inflammatory markers

OBJECTIVE

The visceral fat is linked to insulin resistance, the metabolic syndrome, type 2 diabetes and an increased cardiovascular risk, but it is not clear whether it has a causative role.

DESIGN AND METHODS

Surgical resection of this fat depot is a research model to address this issue. Twenty premenopausal women with metabolic syndrome and grade III obesity were randomized to undergo Roux-en-Y gastric bypass (RYGBP) either alone or combined with omentectomy. Insulin sensitivity (IS; euglycemic-hyperinsulinemic clamp), acute insulin response to glucose (AIR; intravenous glucose tolerance test), disposition index (DI = AIR × IS measured by clamp), lipid profile, adipokine profile (leptin, adiponectin, resistin, visfatin, interleukin-6, TNF-α, MCP-1), ultra-sensitive C-reactive protein (CRP), body composition, and abdominal fat echography were assessed prior to surgery and 1, 6, and 12 months post-surgery.

RESULTS

Omentectomy was associated with greater weight loss at all time points. IS improved similarly in both groups. Omentectomy was associated to lower CRP after 12 months, but it did not influence adipokines and other metabolic parameters. Among non-diabetic subjects, omentectomy was associated with a preservation of baseline AIR after 12 months (as opposed to deterioration in the control group) and a greater DI after 6 and 12 months.

CONCLUSION

Although omentectomy did not enhance the effect of RYGBP on insulin sensitivity and adipokines, it was associated with a preservation of insulin secretion, a greater weight loss, and lower CRP.

Waist circumference as measure of abdominal fat compartments

This study examines intercorrelations among waist circumference (WC), intraperitoneal fat (IPF), and subcutaneous abdominal fat (SAF) in ethnically diverse Dallas Heart Study consisting of 1538 women and 1212 men (50% Black). Correlations between fat depots and triglyceride or HOMA2-IR, biomarkers of metabolic syndrome, are also reported. Total abdominal fat (TAF), ASF, and IPF masses were measured by magnetic resonance imaging. The highest correlations with WC according to ethnicity and gender were noted for TAF (R (2) = 0.81 - 0.88) with progressively lower correlations with ASF (0.65-0.82) and IPF (0.29-0.85). The percentage of IPF relative to TAF was not significantly correlated with WC. For all WC categories, higher IPF/ASF ratios were associated with higher triglyceride levels. In contrast, differences in ratios had little or no association with HOMA2-IR. However, when all data were pooled, IPF was positively correlated with both triglyceride (r = 0.358 (men) and 0.363 (women)) and HOMA2-IR (r = 0.480 (men) and 0.517 (women)); after adjustment for ASF, IPF was still correlated with triglyceride (r = 0.353 (men) and 0.348 (women)) and HOMA2-IR (r = 0.290 (men) and 0.221 (women)). WC measures TAF reliably, but its association with IPF depends on IPF/ASF ratios that vary by gender and ethnicity.

Visceral fat and metabolic inflammation: the portal theory revisited

Abdominal (central) obesity strongly correlates with (hepatic) insulin resistance and type 2 diabetes. Among several hypotheses that have been formulated, the 'portal theory' proposes that the liver is directly exposed to increasing amounts of free fatty acids and pro-inflammatory factors released from visceral fat into the portal vein of obese patients, promoting the development of hepatic insulin resistance and liver steatosis. Thus, visceral obesity may be particularly hazardous in the pathogenesis of insulin resistance and type 2 diabetes. Herein, we will critically review existing evidence for a potential contribution of portally drained free fatty acids and/or cytokines to the development of hepatic insulin resistance.

Prevalence of obesity in children aged 6-12 years in Greece: nutritional behaviour and physical activity

INTRODUCTION

During the last two decades, obesity has proved to be one of the most important problems of public health, and it is considerably more frequent in developed countries, not only in adults, but in children, too. The aim of the current study is to evaluate the prevalence of overweight and obesity in children.

MATERIAL AND METHODS

Two thousand three hundred and seventy-four pupils in primary education were considered for the study (1206 boys and 1168 girls).

RESULTS

In the population-based study, the proportion of overweight children was 23.9%, of obese children 7.3%, and of those with central obesity 35.5%. The boys were obese in a higher percentage than the girls (9.2% vs. 5.3%, p < 0.05). The obesity rates were gradually reduced as the children were growing older. The nutritional habits which were identified to have a positive association with obesity were the following: skipping breakfast, not consuming fruits and vegetables, and consuming bread and soft drinks. Children's healthy nutrition in school was related to lower rates of generalised and central obesity, while the hours spent watching TV were positively associated with all types of obesity.

CONCLUSIONS

Results from the study suggest that a high proportion of children are overweight or obese. Therefore, it is important to adhere to a healthy lifestyle which emphasizes healthy food choices and habits, regular physical activity, and limiting screen time.

Tracing the fate of dietary fatty acids: metabolic studies of postprandial lipaemia in human subjects

Most postprandial studies have investigated the response of a single meal, yet the ingestion of sequential meals is more typical in a Western society. The aim of this review is to explain how natural and stable isotope tracers of fatty acids have been used to investigate the metabolism of dietary fat after single and multiple meals, with a focus on in vivo measurements of adipose tissue metabolism. When stable isotope tracers are combined with arteriovenous difference measurements, very specific measurements of metabolic flux across tissues can be made. We have found that adipose tissue is a net importer of dietary fat for 5 h following a single test meal and for most of the day during a typical three-meal eating pattern. When dietary fat is cleared from plasma, some fatty acids ‘spillover’ into the plasma and contribute up to 50% of postprandial plasma NEFA concentrations. Therefore, plasma NEFA concentrations after a meal reflect the balance between intracellular and extracellular lipolysis in adipose tissue. This balance is altered after the acute ingestion of fructose. The enzyme lipoprotein lipase is a key modulator of fatty acid flux in adipose tissue and its rate of action is severely diminished in obese men. In conclusion, in vivo studies of human metabolism can quantify the way that adipose tissue fatty acid trafficking modulates plasma lipid concentrations. This has implications for the flux of fatty acids to tissues that are susceptible to ectopic fat deposition such as the liver and muscle.

Depot-dependent effects of adipose tissue explants on co-cultured hepatocytes

We have developed an in vitro hepatocyte-adipose tissue explant (ATE) co-culture model enabling examination of the effect of visceral and subcutaneous adipose tissues on primary rat hepatocytes. Initial analyses of inflammatory marker genes were performed in fractionated epididymal or inguinal adipose tissues. Expressions of inflammation related genes (IL-6, TNF-α, COX-2) were higher in the inguinal than the epididymal ATE. Similarly, expressions of marker genes of macrophage and monocyte (MPEG-1, CD68, F4/80, CD64) were higher in the stromal vascular fraction (SVF) isolated from inguinal ATE than that from epididymal ATE. However, expressions of lipolysis related genes (ATGL, HSL, perilipin-1) were higher in the epididymal adipocytes than inguinal adipocytes. Moreover, secretion of IL-6 and PGE(2) was higher from inguinal ATEs than from epididymal ATEs. There was a trend that the total levels of IL-6, TNF-α and PGE(2) in the media from inguinal ATEs co-cultured with primary rat hepatocytes were higher than that in the media from epididymal ATEs co-cultured with hepatocytes, although the significant difference was only seen in PGE(2). Lipolysis, measured as glycerol release, was similar in the ATEs isolated from inguinal and epididymal adipose tissues when cultured alone, but the glycerol release was higher in the ATEs isolated from epididymal than from inguinal adipose tissue when co-cultured with hepatocytes. Compared to epididymal ATEs, the ATEs from inguinal adipose tissue elicited a stronger cytotoxic response and higher level of insulin resistance in the co-cultured hepatocytes. In conclusion, our results reveal depot-dependent effects of ATEs on co-cultured primary hepatocytes, which in part may be related to a more pronounced infiltration of stromal vascular cells (SVCs), particularly macrophages, in inguinal adipose tissue resulting in stronger responses in terms of hepatotoxicity and insulin-resistance.

Metabolic disruptions induced by reduced ambulatory activity in free-living humans

Physical inactivity likely plays a role in the development of insulin resistance and obesity; however, direct evidence is minimal and mechanisms of action remain unknown. Studying metabolic outcomes that occur after transitioning from higher to lower levels of physical activity is the best tool to answer these questions. Previous studies have successfully used more extreme models of inactivity, including bed rest, or the cessation of exercise in highly trained endurance athletes, to provide novel findings. However, these models do not accurately reflect the type of inactivity experienced by a large majority of the population. Recent studies have used a more applicable model in which active (∼10,000 steps/day), healthy young controls are asked to transition to an inactive lifestyle (∼1,500 steps/day) for a 14-day period. The transition to inactivity resulted in reduced insulin sensitivity and increased central adiposity. This review will discuss the outcomes of these studies, their implications for the cause/effect relationship between central adiposity and insulin resistance, and provide rationale for why inactivity induces these factors. In addition, the experimental challenges of directly linking acute responses to inactivity to chronic disease will also be discussed.

Metformin action on AMP-activated protein kinase: a translational research approach to understanding a potential new therapeutic target

Clinical studies in Type 2 diabetes mellitus have shown that the effects of metformin go beyond improving HbA(1c) and include reductions in cardiovascular endpoints. Metformin therapy has been widely used in the treatment of Type 2 diabetes for many years, yet the precise mode of action remains uncertain. It has recently been proposed that metformin-mediated stimulation of hepatic AMP-activated protein kinase (AMPK) underlies the hypoglycaemic effects of metformin. AMPK is a heterotrimeric enzyme that is expressed in many tissues and plays a central role in the regulation of energy homoeostasis. Furthermore, there is increasing evidence that AMPK is implicated in the pathophysiology of cardiovascular and metabolic diseases. The generation of more specific and potent activators of AMPK, however, could have additional metabolic and vascular benefits for patients with Type 2 diabetes.

Pro-inflammatory CD11c+CD206+ adipose tissue macrophages are associated with insulin resistance in human obesity

OBJECTIVE

Insulin resistance and other features of the metabolic syndrome have been causally linked to adipose tissue macrophages (ATMs) in mice with diet-induced obesity. We aimed to characterize macrophage phenotype and function in human subcutaneous and omental adipose tissue in relation to insulin resistance in obesity.

RESEARCH DESIGN AND METHODS

Adipose tissue was obtained from lean and obese women undergoing bariatric surgery. Metabolic markers were measured in fasting serum and ATMs characterized by immunohistology, flow cytometry, and tissue culture studies. RESULTS ATMs comprised CD11c(+)CD206(+) cells in "crown" aggregates and solitary CD11c(-)CD206(+) cells at adipocyte junctions. In obese women, CD11c(+) ATM density was greater in subcutaneous than omental adipose tissue and correlated with markers of insulin resistance. CD11c(+) ATMs were distinguished by high expression of integrins and antigen presentation molecules; interleukin (IL)-1beta, -6, -8, and -10; tumor necrosis factor-alpha; and CC chemokine ligand-3, indicative of an activated, proinflammatory state. In addition, CD11c(+) ATMs were enriched for mitochondria and for RNA transcripts encoding mitochondrial, proteasomal, and lysosomal proteins, fatty acid metabolism enzymes, and T-cell chemoattractants, whereas CD11c(-) ATMs were enriched for transcripts involved in tissue maintenance and repair. Tissue culture medium conditioned by CD11c(+) ATMs, but not CD11c(-) ATMs or other stromovascular cells, impaired insulin-stimulated glucose uptake by human adipocytes.

CONCLUSIONS

These findings identify proinflammatory CD11c(+) ATMs as markers of insulin resistance in human obesity. In addition, the machinery of CD11c(+) ATMs indicates they metabolize lipid and may initiate adaptive immune responses.

Gluteofemoral body fat as a determinant of metabolic health

Body fat distribution is an important metabolic and cardiovascular risk factor, because the proportion of abdominal to gluteofemoral body fat correlates with obesity-associated diseases and mortality. Here, we review the evidence and possible mechanisms that support a specific protective role of gluteofemoral body fat. Population studies show that an increased gluteofemoral fat mass is independently associated with a protective lipid and glucose profile, as well as a decrease in cardiovascular and metabolic risk. Studies of adipose tissue physiology in vitro and in vivo confirm distinct properties of the gluteofemoral fat depot with regards to lipolysis and fatty acid uptake: in day-to-day metabolism it appears to be more passive than the abdominal depot and it exerts its protective properties by long-term fatty acid storage. Further, a beneficial adipokine profile is associated with gluteofemoral fat. Leptin and adiponectin levels are positively associated with gluteofemoral fat while the level of inflammatory cytokines is negatively associated. Finally, loss of gluteofemoral fat, as observed in Cushing's syndrome and lipodystrophy is associated with an increased metabolic and cardiovascular risk. This underlines gluteofemoral fat's role as a determinant of health by the long-term entrapment of excess fatty acids, thus protecting from the adverse effects associated with ectopic fat deposition.

Visceral fat loss induced by a low-calorie diet: a direct comparison between women and men

AIM

No studies have assessed if changes in visceral adipose tissue (VAT) during weight loss differ between women and men with comparable amounts of VAT at baseline. The aim of this study was to assess if changes in VAT induced by a low-calorie diet (LCD) differ between women and men.

METHODS

In this post hoc analysis of an existing database, abdominal adipose tissue was evaluated before and after an 8-week LCD (800-1000 kcal/day) by a single-slice magnetic resonance scan performed at the abdominal level. Body composition was measured by dual X-ray energy absorptiometry.

RESULTS

Data from 111 obese subjects (85 women and 26 men) were available. Relative changes in VAT were found to be more pronounced in men [mean (95% CI): -32.6% (-38.7 to -26.6)] than in women [-21.9% (-25.0 to -18.8)] (p = 0.003) after correction for relative changes in fat mass (FM). When analysing only the data from a subgroup of 23 women and 23 men who were matched for similar visceral to abdominal subcutaneous fat ratio at baseline, these differences could not be observed anymore: the change in VAT was -33.7% (-38.7 to -28.7) in men and -26.8% (-31.8 to -21.8) in women (p = 0.07).

CONCLUSIONS

This study suggests that relative changes in VAT during a LCD may be greater in men than in women even after taking relative changes in FM into account. However, these differences disappear when properly matching the subjects for baseline amounts of VAT.

Treatment options for HIV-associated central fat accumulation

Central fat accumulation is increasingly recognized as a problem for patients with HIV infection. The term "lipodystrophy" has been used to describe collectively a constellation of body habitus changes and metabolic abnormalities commonly observed in HIV-infected patients, particularly since the advent of highly active antiretroviral therapy. Visceral fat accumulation can place patients at increased risk of coronary artery disease.Furthermore, body shape changes are a source of distress to patients that may compromise treatment adherence.Reduction of abdominal obesity can therefore be considered part of therapy in HIV-positive patients with visceral adipose tissue (VAT) accumulation. Currently, there are no drugs approved by the Food and Drug Administration for the treatment of HIV-associated central fat accumulation. Lifestyle modifications such as diet and exercise and switching antiretroviral therapies appear to be of limited value in reducing VAT. Metformin has shown some benefit in reducing VAT but at the expense of accelerating peripheral fat loss, and the thiazolidinediones have no effect on VAT. Similarly, testosterone does not appear to reduce VAT in these patients,and there are no data on anabolic steroids. Two large, randomized controlled trials have demonstrated the efficacy of recombinant human growth hormone (rhGH) in reducing visceral adipose tissue. There are also promising data regarding treatment with growth hormone releasing hormone (GHRH).

Adipose tissue fatty acid metabolism in insulin-resistant men

AIMS/HYPOTHESIS

Increased NEFA production and concentrations may underlie insulin resistance. We examined systemic and adipose tissue NEFA metabolism in insulin-resistant overweight men (BMI 25-35 kg/m2).

METHODS

In a cohort study we examined NEFA concentrations in men in the upper quartile of fasting insulin (n = 124) and in men with fasting insulin below the median (n = 159). In a metabolic study we examined NEFA metabolism in the fasting and postprandial states, in ten insulin-resistant men and ten controls.

RESULTS

In the cohort study, fasting NEFA concentrations were not significantly different between the two groups (median values: insulin-resistant men, 410 micromol/l; controls, 445 micromol/l). However, triacylglycerol concentrations differed markedly (1.84 vs 1.18 mmol/l respectively, p < 0.001). In the metabolic study, arterial NEFA concentrations again did not differ between groups, whereas triacylglycerol concentrations were significantly higher in insulin-resistant men. Systemic NEFA production and the release of NEFA from subcutaneous adipose tissue, expressed per unit of fat mass, were both reduced in insulin-resistant men compared with controls (fasting values by 32%, p = 0.02, and 44%, p = 0.04 respectively). 3-Hydroxybutyrate concentrations, an index of hepatic fat oxidation and ketogenesis, were lower (p = 0.03).

CONCLUSIONS/INTERPRETATION

Adipose tissue NEFA output is not increased (per unit weight of tissue) in insulin resistance. On the contrary, it appears to be suppressed by high fasting insulin concentrations. Alterations in triacylglycerol metabolism are more marked than those in NEFA metabolism and are indicative of altered metabolic partitioning of fatty acids (decreased oxidation, increased esterification) in the liver.

Renin-angiotensin system, natriuretic peptides, obesity, metabolic syndrome, and hypertension: an integrated view in humans

The obesity pandemic is closely related to hypertension and metabolic syndrome. Visceral adipose tissue plays a key role in the metabolic and cardiovascular complications of being overweight. The pathophysiological link between visceral adiposity and cardiometabolic complications focuses on insulin sensitivity, sympathetic nervous system, renin-angiotensin-aldosterone system (RAAS) and, only recently, on cardiac natriuretic peptide system (CNPS). RAAS and CNPS are endogenous antagonistic systems on sodium balance, cardiovascular system, and metabolism. The circulating RAAS is dysregulated in obese patients, and adipose tissue has a full local renin-angiotensin system that is active at local and systemic level. Adipocyte biology and metabolism are influenced by local renin-angiotensin system, with angiotensin II acting as a 'growth factor' for adipocytes. CNPS induces natriuresis and diuresis, reduces blood pressure, and, moreover, has powerful lipolytic and lipomobilizing activity in humans but not in rodents. In obesity, lower plasmatic natriuretic peptides levels with increasing BMI, waist circumference, and metabolic syndrome have been documented. Thus, reduced CNPS effects coupled with increased RAAS activity have a central role in obesity and its deadly complications. We propose herein an integrated view of the dysregulation of these two antagonistic systems in human obesity complicated with hypertension, metabolic syndrome, and increased cardiovascular risk.

Location, location, location

Intra-abdominal fat is an established risk factor for the metabolic syndrome. In this issue of Cell Metabolism, Tran et al. (2008) test the cell-autonomous and location-related properties of transplanted intra-abdominal and subcutaneous fat depots. While subcutaneous fat seems to confer metabolic benefits, species differences in adipose biology justify caution in interpreting the results.

Nutrition Review: Diet and Nutrients in the Prevention and Treatment of Type 2 Diabetes

Lifestyle factors, including diet, are critical in the prevention and treatment of type 2 diabetes. Because weight gain increases diabetes risk, and even modest weight reduction reduces risk, weight management is paramount in lessening the occurrence and effects of diabetes. Weight loss interventions should include patient education, behavioral strategies, physical activity, energy intake deficits of 500 to 1000 kcal/day, and prevention of recidivism. Macronutrient distribution ranges of diets for diabetic patients follow those of the Dietary Reference Intakes, allowing for individualization according to a patient's metabolic responses, needs, and preferences. Nutrients to be limited include saturated fats, artificial trans fats, cholesterol, and sodium, whereas nutrients to be emphasized include monounsaturated fatty acids, omega-3 polyunsaturated fatty acids, fibers, antioxidants, and minerals, including potassium, magnesium, calcium, and chromium. Food sources are advised rather than supplements. Sugars can be isocalorically substituted for starches without detriments to glycemic control. Diets with low glycemic index or load may have modest benefits in managing type 2 diabetes. If a diabetic patient chooses to consume alcohol, he or she should do so in moderation. Foods advocated in type 2 diabetes are similar to those that are also beneficial in reducing risk for other chronic diseases.

Body mass index and waist circumference in midchildhood and adverse cardiovascular disease risk clustering in adolescence

BACKGROUND

Body mass index (BMI) may not indicate the level of central adiposity associated with the clustering of cardiovascular disease (CVD) risk factors. Hence, it has been recommended that waist circumference be used as an alternative measure.

OBJECTIVE

The objective was to investigate whether waist circumference in midchildhood is more effective at predicting cardiovascular disease risk clustering in adolescence than is BMI.

DESIGN

Anthropometric measurements were made in 342 children aged 8 y. Seven years later, anthropometric measurements were made in 290 participants, and metabolic profiles were determined in 172 participants.

RESULTS

At 15 y, between 9.4% and 11.0% of adolescents were defined as having CVD risk clustering. Children who were overweight or obese at 8 y of age were 7 times (odds ratio: 6.9; 95% CI: 2.5, 19.0; P < 0.001) as likely to have CVD risk clustering in adolescence than were their peers who were not overweight or obese. Those with an increased waist circumference at 8 y were 4 times (3.6; 1.0, 12.9; P = 0.061) as likely to have CVD risk clustering in adolescence than were children with a smaller waist circumference. Neither BMI nor waist circumference were predictive of CVD risk clustering if adiposity was not included as a risk factor.

CONCLUSIONS

The association between measures of adiposity in midchildhood and later adverse CVD risk is a result of the tracking of adiposity status. Our results do not support the need to measure waist circumference in children, in addition to BMI, to identify those at increased risk of CVD risk factor clustering in adolescence.

Insulin resistance and body fat distribution in South Asian men compared to Caucasian men

OBJECTIVE

South Asians are susceptible to insulin resistance even without obesity. We examined the characteristics of body fat content, distribution and function in South Asian men and their relationships to insulin resistance compared to Caucasians.

RESEARCH DESIGN AND METHODS

Twenty-nine South Asian and 18 Caucasian non-diabetic men (age 27+/-3 and 27+/-3 years, respectively) underwent euglycemic-hyperinsulinemic clamp for insulin sensitivity, underwater weighing for total body fat, MRI of entire abdomen for intraperitoneal (IP) and subcutaneous abdominal (SA) fat and biopsy of SA fat for adipocyte size.

RESULTS

Compared to Caucasians, in spite of similar BMI, South Asians had higher total body fat (22+/-6 and 15+/-4% of body weight; p-value<0.0001), higher SA fat (3.5+/-1.9 and 2.2+/-1.3 kg, respectively; p-value = 0.004), but no differences in IP fat (1.0+/-0.5 and 1.0+/-0.7 kg, respectively; p-value = 0.4). SA adipocyte cell size was significantly higher in South Asians (3491+/-1393 and 1648+/-864 microm2; p-value = 0.0001) and was inversely correlated with both glucose disposal rate (r-value = -0.57; p-value = 0.0008) and plasma adiponectin concentrations (r-value = -0.71; p-value<0.0001). Adipocyte size differences persisted even when SA was matched between South Asians and Caucasians.

CONCLUSIONS

Insulin resistance in young South Asian men can be observed even without increase in IP fat mass and is related to large SA adipocytes size. Hence ethnic excess in insulin resistance in South Asians appears to be related more to excess truncal fat and dysfunctional adipose tissue than to excess visceral fat.

Metabolic inflexibility in skeletal muscle: a prelude to the cardiometabolic syndrome?

Peripheral insulin resistance, which is largely dependent on skeletal muscle, is closely linked to the development of the cardiometabolic syndrome. Metabolic flexibility is the capacity for skeletal muscle to acutely shift its reliance between lipids or glucose during fasting or postprandial conditions. Obese and insulin-resistant individuals display elevated intramuscular lipids, impaired vasculature function, decreased fatty add oxidation during fasting, and reduced postprandial glucose metabolism. Impairments in metabolic flexibility are linked to physical inactivity, excess energy intake and obesity, and genetic predisposition. Each of these factors precludes the development of insulin resistance and the cardiometabolic syndrome by mechanistic links that are not fully understood.

Triglyceride uptake and lipoprotein lipase-generated fatty acid spillover in the splanchnic bed of dogs

The action of lipoprotein lipase on triglyceride-rich lipoproteins generates fatty acids that are either transported into tissues or mix with circulating free fatty acids (FFAs) via a process known as spillover. In the present study, arterial, portal vein, and hepatic vein sampling catheters were surgically placed in nine mongrel dogs. The animals were subsequently studied after a 42-h fast during infusion of [14C]oleate and a lipid emulsion containing [3H]triolein; the emulsion was used as a surrogate for the study of chylomicron metabolism. More than one-half of splanchnic [3H]triglyceride uptake occurred in the liver, and substantial fractional spillover of [3H]oleate was observed in both liver and nonhepatic tissues (approximately 50% each). There was a significant correlation between FFA release from nonhepatic tissues (presumably visceral fat) and nonhepatic fractional spillover (R = 0.81, P < 0.01), consistent with a model in which the rate of intracellular lipolysis influences spillover by determining the direction of net fatty acid flow between the cell and the interstitium. There was a significant correlation between "true" and "net" splanchnic spillover (R = 0.84, P < 0.005), the latter representing calculation of spillover between arterial and hepatic venous blood without portal venous data. Metabolism of chylomicron triglycerides in visceral fat may be an important source of portal venous FFAs.

Genetics of the metabolic syndrome

The concept of a metabolic syndrome (MetS), a cluster of pre-clinical metabolic alterations commonly associated with obesity, is the object of much debate. Genetic studies have the potential to contribute to some of the key questions, including the true nature of the cluster of pre-clinical features and whether it is associated with human genetic variation. This review summarizes the evidence for the presence of familial aggregation for the individual components of MetS and their heritability levels. It also provides an overview of the studies that have dealt with candidate genes for MetS. Potential leads from genome-wide linkage scans are also discussed. The assumption is made that obesity, ectopic fat deposition and abnormal adipose tissue metabolism are responsible for alterations in lipid metabolism, which in turn generates the commonly observed pre-clinical shifts in glucose tolerance, lipids and lipoprotein profile, blood pressure, inflammatory markers, endothelial function, and a prothrombotic state. Progress in the understanding of the genetic basis of MetS should occur as soon as a consensus is reached on the true nature of MetS, its components and diagnostic criteria.

Physical Activity, Obesity Status, and Glycemic Control

PURPOSE

We aimed to evaluate the relationship of physical activity and obesity with glycemic control and insulin resistance.

METHODS

A randomized, population-based, cross-sectional health and nutrition survey was conducted in the province of Athens, Greece. Subjects included 1514 men and 1528 women without evidence of cardiovascular or other chronic disease. Participants were classified as inactive, minimally active, or health-enhancing physical activity (HEPA) active based on the International Physical Activity Questionnaire. Insulin sensitivity was assessed by the homeostatic model (HOMA), and overweight or obesity was assessed according to BMI (BMI >or= 25). Related social, biological, and lifestyle factors were also recorded and used as potential confounders.

RESULTS

Five hundred sixty-five (37.3%) men and 493 (32.3%) women were classified as physically active. From the 1058 (34.8%) subjects who were classified as active, 306 (10.1%) met the criteria for HEPA active, and the rest were minimally active. HEPA active and minimally active subjects smoked less and had lower BMI, waist, and waist-to-hip ratio. Lean and overweight or obese subjects with sedentary lifestyle had greater levels of glucose, insulin, and insulin resistance [corrected] However, overweight or obese volunteers with physical activity levels classified as HEPA had similar levels of glucose and insulin sensitivity, with lower insulin than lean inactive individuals. Linear regression analysis between HOMA and physical activity, taking into consideration several social and biological factors, showed that physical activity (MET x min x wk(-1)), age, BMI, and total energy intake are important predictors of HOMA, whereas other factors such as waist circumference did not reach statistical significance.

CONCLUSION

Our data show that physical activity is a significant factor on insulin sensitivity, whereas increased physical activity may ameliorate the well-known effects of obesity on insulin sensitivity.

Serum levels of C-peptide, IGFBP-1 and IGFBP-2 and endometrial cancer risk; Results from the European prospective investigation into cancer and nutrition

We conducted a case-control study nested within the European Prospective Investigation into Cancer and Nutrition, to examine the associations between prediagnostic serum concentrations of C-peptide, insulin-like growth factor binding protein (IGFBP)-1 and IGFBP-2, and endometrial cancer risk. Among pre- and post-menopausal women, who were not currently using exogenous hormones, 286 women developed incident endometrial cancer during an average 5.1 years follow-up. Using risk set sampling, 555 matched control subjects were selected. In conditional logistic regression models adjusted for matching factors only, endometrial cancer risk increased with increasing serum levels of C-peptide (relative risks (RR) for the top vs. bottom quartile = 2.13 [95% confidence interval (CI) 1.33-3.41], p(trend) = 0.001, and decreasing serum levels of IGFBP-2 (RR for the top vs. bottom quartile = 0.56 [95% CI 0.35-0.90], p(trend) = 0.03, but was not significantly associated with IGFBP-1 levels (RR for the top vs. bottom quartile = 0.76 [95% CI 0.47-1.21], p(trend) = 0.25). In BMI-adjusted models, only the C-peptide association remained marginally statistically significant (RR for the top vs. bottom quartile = 1.56 [95% CI 0.94-2.57], p(trend) = 0.05 for C-peptide; 0.84 [95% CI 0.50-1.40], p(trend) = 0.74 for IGFBP-2; and 1.08 [95% CI 0.65-1.78], p(trend) = 0.86 for IGFBP-1 levels). These associations were stronger among nonfasting women (< or =< or =6 hr since last meal; 63% of subjects) but were not evident among fasting women, although the interactions were not statistically significant. The C-peptide-risk association was substantially attenuated after adjustment for free estradiol in postmenopausal women (RR for the top vs. bottom quartile = 1.28 [95% CI 0.67-2.45], p(trend) = 0.42. Our results provide modest support to the hypothesis that hyperinsulinaemia is a risk factor for endometrial cancer.

Macrophage-conditioned medium inhibits the differentiation of 3T3-L1 and human abdominal preadipocytes

AIMS/HYPOTHESIS

In obesity, a limited adipogenic capacity may promote adipocyte hypertrophy and increase the risk of insulin resistance and type 2 diabetes. Recent data indicate that macrophages reside within adipose tissue in obese rodents and humans. We hypothesised that secreted macrophage factors may inhibit adipogenesis.

MATERIALS AND METHODS

Conditioned media from cultured murine J774 or human THP-1 macrophages were collected, and added to either murine 3T3-L1 preadipocytes or human abdominal stromal preadipocytes from subcutaneous or omental fat depots.

RESULTS

Macrophage-conditioned medium (MacCM) strongly inhibited 3T3-L1 adipogenesis. Dose-response studies with J774-MacCM revealed that 80 and 100% of J774-MacCM completely suppressed triacylglycerol accumulation as well as the induction of fatty acid synthase, peroxisome proliferator-activated receptor gamma, CCAAT/enhancer binding protein alpha, and adiponectin. Similar inhibitory effects on 3T3-L1 preadipocytes were observed with THP-1-MacCM. Differentiation of human abdominal subcutaneous stromal preadipocytes was moderately reduced (subcutaneous>omental) by J744-MacCM. In contrast, the differentiation of both subcutaneous and omental stromal preadipocytes was completely inhibited by THP-1-MacCM, as determined on the basis of morphology and triacylglycerol accumulation, as well as fatty acid synthase and adiponectin protein expression.

CONCLUSIONS/INTERPRETATION

Secreted macrophage products inhibit the differentiation of 3T3-L1 preadipocytes as well as human abdominal stromal preadipocytes.