Relationship of visceral adipose tissue to metabolic risk factors for coronary heart disease: is there a contribution of subcutaneous fat cell hypertrophy?

Age of obesity onset affects subcutaneous adipose tissue cellularity differently in the abdominal and femoral region

OBJECTIVE

We aimed to examine the effect of age of obesity onset, sex, and their interaction on abdominal and femoral subcutaneous adipose tissue (SAT) morphology (degree of adipocyte hyperplasia or hypertrophy).

METHODS

In this cross-sectional study, we isolated adipocytes via collagenase digestion from abdominal and femoral SAT biopsies taken from male and female adults with childhood-onset obesity (CO; n = 8 males, n = 16 females) or adult-onset obesity (AO; n = 8 males, n = 13 females). Regional body composition was measured with dual-energy x-ray absorptiometry and a single-slice abdominal computed tomography scan. Mean adipocyte size was measured in abdominal and femoral SAT and was used to quantify morphology in android and gynoid subcutaneous fat, respectively.

RESULTS

Abdominal SAT morphology was more hyperplastic in females with CO than females with AO (p = 0.004) but did not differ between males with CO and males with AO (p = 0.996). Conversely, femoral SAT morphology was more hypertrophic in males and females with CO than those with AO.

CONCLUSIONS

Age of obesity onset appears to affect SAT morphology differently in the abdominal and femoral regions of male and female adults. Our findings challenge the notion that SAT is uniformly hyperplastic in CO and hypertrophic in AO.

Impaired Remodeling of White Adipose Tissue in Obesity and Aging: From Defective Adipogenesis to Adipose Organ Dysfunction

The adipose organ adapts and responds to internal and environmental stimuli by remodeling both its cellular and extracellular components. Under conditions of energy surplus, the subcutaneous white adipose tissue (WAT) is capable of expanding through the enlargement of existing adipocytes (hypertrophy), followed by de novo adipogenesis (hyperplasia), which is impaired in hypertrophic obesity. However, an impaired hyperplastic response may result from various defects in adipogenesis, leading to different WAT features and metabolic consequences, as discussed here by reviewing the results of the studies in animal models with either overexpression or knockdown of the main molecular regulators of the two steps of the adipogenesis process. Moreover, impaired WAT remodeling with aging has been associated with various age-related conditions and reduced lifespan expectancy. Here, we delve into the latest advancements in comprehending the molecular and cellular processes underlying age-related changes in WAT function, their involvement in common aging pathologies, and their potential as therapeutic targets to influence both the health of elderly people and longevity. Overall, this review aims to encourage research on the mechanisms of WAT maladaptation common to conditions of both excessive and insufficient fat tissue. The goal is to devise adipocyte-targeted therapies that are effective against both obesity- and age-related disorders.

Obesity and the risk of cardiometabolic diseases

The prevalence of obesity has reached pandemic proportions, and now approximately 25% of adults in Westernized countries have obesity. Recognized as a major health concern, obesity is associated with multiple comorbidities, particularly cardiometabolic disorders. In this Review, we present obesity as an evolutionarily novel condition, summarize the epidemiological evidence on its detrimental cardiometabolic consequences and discuss the major mechanisms involved in the association between obesity and the risk of cardiometabolic diseases. We also examine the role of potential moderators of this association, with evidence for and against the so-called 'metabolically healthy obesity phenotype', the 'fatness but fitness' paradox or the 'obesity paradox'. Although maintenance of optimal cardiometabolic status should be a primary goal in individuals with obesity, losing body weight and, particularly, excess visceral adiposity seems to be necessary to minimize the risk of cardiometabolic diseases.

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

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

Assessing Obesity-Related Adipose Tissue Disease (OrAD) to Improve Precision Medicine for Patients Living With Obesity

Obesity is a heterogenous condition that affects the life and health of patients to different degrees and in different ways. Yet, most approaches to treat obesity are not currently prescribed, at least in a systematic manner, based on individual obesity sub-phenotypes or specifically-predicted health risks. Adipose tissue is one of the most evidently affected tissues in obesity. The degree of adipose tissue changes - "adiposopathy", or as we propose to relate to herein as Obesity-related Adipose tissue Disease (OrAD), correspond, at least cross-sectionally, to the extent of obesity-related complications inflicted on an individual patient. This potentially provides an opportunity to better personalize anti-obesity management by utilizing the information that can be retrieved by assessing OrAD. This review article will summarize current knowledge on histopathological OrAD features which, beyond cross-sectional analyses, had been shown to predict future obesity-related endpoints and/or the response to specific anti-obesity interventions. In particular, the review explores adipocyte cell size, adipose tissue inflammation, and fibrosis. Rather than highly-specialized methods, we emphasize standard pathology laboratory approaches to assess OrAD, which are readily-available in most clinical settings. We then discuss how OrAD assessment can be streamlined in the obesity/weight-management clinic. We propose that current studies provide sufficient evidence to inspire concerted efforts to better explore the possibility of predicting obesity related clinical endpoints and response to interventions by histological OrAD assessment, in the quest to improve precision medicine in obesity.

Impaired Adipogenesis and Dysfunctional Adipose Tissue in Human Hypertrophic Obesity

The subcutaneous adipose tissue (SAT) is the largest and best storage site for excess lipids. However, it has a limited ability to expand by recruiting and/or differentiating available precursor cells. When inadequate, this leads to a hypertrophic expansion of the cells with increased inflammation, insulin resistance, and a dysfunctional prolipolytic tissue. Epi-/genetic factors regulate SAT adipogenesis and genetic predisposition for type 2 diabetes is associated with markers of an impaired SAT adipogenesis and development of hypertrophic obesity also in nonobese individuals. We here review mechanisms for the adipose precursor cells to enter adipogenesis, emphasizing the role of bone morphogenetic protein-4 (BMP-4) and its endogenous antagonist gremlin-1, which is increased in hypertrophic SAT in humans. Gremlin-1 is a secreted and a likely important mechanism for the impaired SAT adipogenesis in hypertrophic obesity. Transiently increasing BMP-4 enhances adipogenic commitment of the precursor cells while maintained BMP-4 signaling during differentiation induces a beige/brown oxidative phenotype in both human and murine adipose cells. Adipose tissue growth and development also requires increased angiogenesis, and BMP-4, as a proangiogenic molecule, may also be an important feedback regulator of this. Hypertrophic obesity is also associated with increased lipolysis. Reduced lipid storage and increased release of FFA by hypertrophic SAT are important mechanisms for the accumulation of ectopic fat in the liver and other places promoting insulin resistance. Taken together, the limited expansion and storage capacity of SAT is a major driver of the obesity-associated metabolic complications.

MiR-122 marks the differences between subcutaneous and visceral adipose tissues and associates with the outcome of bariatric surgery

The physiological roles and clinical impacts of the differences between visceral fat (VF) and subcutaneous fat (SF) are unclear. The present study aimed to compare the miRNA signatures between visceral fat (VF) and subcutaneous fat (SF) and study their influences on outcomes of bariatric surgery. To study the microRNA signatures of the VF and SF in obesity, we performed paired microRNA arrays of the adipose tissues from 20 bariatric surgery patients. The microRNA analysis identified miR-122 as the most significant signature between VF and SF. The tissue distribution, functions, and influences on adipogensis of miR-122 were analysed by Northern blotting, microRNA mimics and inhibitors, and whole-genome microarray analysis. The outcomes of body weight changes after bariatric surgery were analysed and correlated with the miR-122 abundances. Northern blotting confirmed that miR-122 was highly expressed in VF and SF. Bioinformatics analysis of the microarray revealed that proliferator activator receptor-γ (PPAR-γ) signalling was critically affected by miR-122. The modulation of PPAR-γ by miR-122 was confirmed in murine adipocytes and human adipose tissues. Furthermore, the differentiation of preadipocytes was significantly influenced by miR-122. In obese patients receiving bariatric surgery, the ratio of VF and SF miR-122 abundance correlated with 6-month and 1-year % excess body weight loss. Our findings indicate that miR-122 is highly expressed in adipose tissue. The abundance of miR-122 affects PPAR-γ signalling and adipocytes differentiation in vitro and human adipose tissues. Higher miR-122 in VF may be associated with greater body weight loss after bariatric surgery.

Daily intake of Kaempferia parviflora extract decreases abdominal fat in overweight and preobese subjects: a randomized, double-blind, placebo-controlled clinical study

PURPOSE

Obesity is a serious problem, which is now a worldwide health problem. Kaempferia parviflora extract (KPE) exhibits anti-obesity effects in animals. However, as no clinical trials have evaluated the anti-obesity effects of KPE in humans, we examined the effects of KPE in reducing abdominal fat in overweight and preobese Japanese subjects.

MATERIALS AND METHODS

A 12-week, single-center, randomized, double-blind, placebo-controlled clinical trial was conducted. Seventy-six subjects (males and females aged 20 to <65 years) with a body mass index ≥24 and <30 kg/m² were randomly assigned into two groups. The subjects in each group ingested one capsule of placebo or active KPE (containing 150 mg of KPE) once daily for 12 weeks. The primary outcome was reduction in visceral fat area as determined by computed tomography scanning. The key secondary outcomes were reductions in subcutaneous fat area and total fat area. Subgroup analysis was also performed in healthy subjects without dyslipidemia, hypertension, or hyperglycemia. The safety of KPE ingestion was also evaluated.

RESULTS

Compared with the placebo group, the active KPE group exhibited significant reduction in abdominal fat area (visceral, subcutaneous, and total fat) and triglyceride levels after 12 weeks. Subgroup analyses demonstrated a significant reduction in abdominal fat area and triglyceride levels in healthy subjects compared with the placebo group after 12 weeks. Neither group exhibited adverse events related to the test foods or clinically relevant abnormal changes in physical, biochemical, or hematologic parameters, or in urinalysis results and medical interview.

CONCLUSION

Daily ingestion of KPE safely reduces body fat, particularly abdominal fat, in Japanese overweight and preobese subjects.

Matured hop extract reduces body fat in healthy overweight humans: a randomized, double-blind, placebo-controlled parallel group study

Background

Hops are the main components of beer that provide flavor and bitterness. Iso-α-acids, the bitter components of beer, have been reported to reduce body fat in humans, but the bitterness induced by effective doses of iso-α-acids precludes their acceptance as a nutrient. The matured hop bitter acids (MHBA) of oxidized hops appear to have a more pleasant bitterness compared to the sharper bitterness of iso-α-acids. While there has been little information concerning the identity of the MHBA compounds and their physiological effects, MHBA was recently found to be primarily composed of oxides derived from α-acids, and structurally similar to iso-α-acids. Here, we investigated the effects of matured hop extract (MHE) containing MHBA on reducing abdominal body fat in healthy subjects with a body mass index (BMI) of 25 to below 30 kg/m², classified as “obese level 1” in Japan or as “overweight” by the WHO.

Trial design

A randomized, double-blind, placebo-controlled parallel group study.

Methods

Two hundred subjects (male and female aged 20 to below 65 years with a BMI of 25 or more and less than 30 kg/m²) were randomly assigned to two groups. During a 12-week ingestion period, the subjects in each group ingested daily 350 mL of test-beverage, either containing MHE (with 35 mg MHBA), i.e. the namely active beverage, or a placebo beverage without MHE. The primary endpoint was reduction of the abdominal fat area as determined by CT scanning after continual ingestion of MHE for 12 weeks.

Results

Compared to the placebo group, a significant reduction was observed in the visceral fat area after 8 and 12 w, and in the total fat area after 12 w in the active group. There was also a concomitant decrease in body fat ratio in the active group compared to the placebo group. No adverse events related to the test beverages or clinically relevant abnormal changes in the circulatory, blood and urine parameters were observed in either group.

Conclusions

The present study suggests that continual ingestion of MHE safely reduces body fat, particularly the abdominal visceral fat of healthy overweight subjects.

Trial registration

UMIN-CTR UMIN000014185

Electronic supplementary material

The online version of this article (doi:10.1186/s12937-016-0144-2) contains supplementary material, which is available to authorized users.

Transgenic ω-3 PUFA enrichment alters morphology and gene expression profile in adipose tissue of obese mice: Potential role for protectins

OBJECTIVE

Dietary administration of ω-3 polyunsaturated fatty acids (PUFA) is often associated with altered adipose tissue (AT) morphology and/or function in obese mice. Yet, it is unclear whether this is an indirect consequence of reduced weight gain or results from direct actions of ω-3 PUFA. Here we studied the AT of high fat (HF)-fed fat-1 transgenic mice that convert endogenous ω-6 to ω-3 PUFA while maintaining equivalent fat accretion as their wild-type (WT) counterparts.

MATERIALS AND METHODS

Adipocyte size profiling, Affymetrix microarray pathway analysis, qPCR and protectin identification and analysis were performed in epididymal AT from hemizygous fat-1(+/-) mice and their wild type littermates that had been fed a HF diet for 8weeks from 6weeks of age.

RESULTS

Despite equivalent fat pad mass, we found that epididymal AT from HF-fed transgenic animals possesses fewer large and very large but more mid-size adipocytes compared to WT mice. In order to better understand the underlying mechanisms contributing to the observed alteration in adipocyte size we performed an Affymetrix microarray. Pathway analysis of these data highlighted adipogenesis, cholesterol biosynthesis, insulin signaling, prostaglandin synthesis/regulation and small ligand GPCRs as points where differentially expressed genes were significantly overrepresented. Observed changes were confirmed for four candidate genes: Cnr1, Cnr2, Faah and Pparg by qPCR. Finally we demonstrated that protectin DX is present in AT and that protectin DX and protectin D1 promote comparable PPARγ transcriptional activity.

CONCLUSIONS

These data provide unprecedented evidence that ω-3 PUFA coordinately regulate AT gene expression programs in a manner that is independent of restriction of weight gain or fat accrual and highlight an important influence of ω-3 PUFA on adipogenesis. Furthermore we provide primary evidence suggesting that protectins likely contribute to these effects via their influence on PPARγ.

Storage capacity of subcutaneous fat in Japanese adults

BACKGROUND

On the basis of our previous study, which examined the nonlinear relationship between visceral fat area (VFA) and percent regional fat mass in the trunk, we hypothesise the presence of some storage capacity of subcutaneous fat. This study aimed to examine the storage capacity of subcutaneous fat on the basis of subcutaneous fat area (SFA) and VFA in 791 Japanese adult males and 563 females.

METHODS

Regression analyses by using SFA as a dependent variable and VFA as an independent variable were performed for each group classified by visceral fat obesity (VO): VO (VFA ⩾ 100 cm(2)) and the no-VO (NVO) groups. To statistically identify an optimal critical point for subcutaneous fat accumulation, we changed the cutoff point for the VO group from 50-150 cm(2) in 10-cm(2) increments and confirmed the significance of the correlation between SFA and VFA for each obesity group, the statistical difference in correlations between NVO and VO groups, and the goodness of fit for the two regression lines using the standard error of estimation values. These analyses were conducted for each sex and age (<65 and ⩾ 65 years) group.

RESULTS

The critical point for subcutaneous fat accumulation appears at the following cutoff points of VFA: 130 cm(2) in <65-year-old males, 110 cm(2) in ⩾ 65-year-old males and 100 cm(2) in both female groups.

CONCLUSIONS

These results suggest the presence of some storage capacity of subcutaneous fat. As a further application, these findings may serve to improve the risk assessment of obesity-related diseases.

Three months of regular aerobic exercise in patients with obesity improve systemic subclinical inflammation without major influence on blood pressure and endocrine production of subcutaneous fat

The aim of our study was to explore the effects of regular aerobic exercise on anthropometric, biochemical and hormonal parameters and mRNA expression of selected factors involved in metabolic regulations in subcutaneous adipose tissue of patients with obesity. Fifteen obese women with arterial hypertension underwent a three-month exercise program consisting of 30 min of aerobic exercise 3 times a week. Fifteen healthy lean women with no intervention served as a control group. Obese group underwent anthropometric measurements, blood sampling, subcutaneous adipose tissue (SCAT) biopsy and 24-h blood pressure monitoring at baseline and after three months of exercise, while control group was examined only once. At baseline, obese group had increased SCAT expression of proinflammatory cytokines and adipokines relative to control group. Three months of regular exercise improved anthropometric parameters, decreased CRP, blood glucose and HOMA-IR, while having no significant effect on lipid profile and blood pressure. Gene expressions in SCAT were not affected by physical activity with the exception of increased aquaporin-3 mRNA expression. We conclude that three months of regular exercise decrease systemic subclinical inflammation with only minor influence on the blood pressure and the endocrine function of subcutaneous fat.

Bariatric endocrinology: principles of medical practice

Obesity, is a chronic, biological, preventable, and treatable disease. The accumulation of fat mass causes physical changes (adiposity), metabolic and hormonal changes due to adipose tissue dysfunction (adiposopathy), and psychological changes. Bariatric endocrinology was conceived from the need to address the neuro-endocrinological derangements that are associated with adiposopathy, and from the need to broaden the scope of the management of its complications. In addition to the well-established metabolic complications of overweight and obesity, adiposopathy leads to hyperinsulinemia, hyperleptinemia, hypoadiponectinemia, dysregulation of gut peptides including GLP-1 and ghrelin, the development of an inflammatory milieu, and the strong risk of vascular disease. Therapy for adiposopathy hinges on effectively lowering the ratio of orexigenic to anorexigenic signals reaching the the hypothalamus and other relevant brain regions, favoring a lower caloric intake. Adiposopathy, overweight and obesity should be treated indefinitely with the specific aims to reduce fat mass for the adiposity complications, and to normalize adipose tissue function for the adiposopathic complications. This paper defines the principles of medical practice in bariatric endocrinology-the treatment of overweight and obesity as means to treat adiposopathy and its accompanying metabolic and hormonal derangements.

Use of anthropometry for the prediction of regional body tissue distribution in adults: benefits and limitations in clinical practice

Regional body composition changes with aging. Some of the changes in composition are considered major risk factors for developing obesity related chronic diseases which in turn may lead to increased mortality in adults. The role of anthropometry is well recognized in the screening, diagnosis and follow-up of adults for risk classification, regardless of age. Regional body composition is influenced by a number of intrinsic and extrinsic factors. Therapeutic measures recommended to lower cardiovascular disease risk include lifestyle changes. The aim of this review is to systematically summarize studies that assessed the relationships between anthropometry and regional body composition. The potential benefits and limitations of anthropometry for use in clinical practice are presented and suggestions for future research given.

Endocrine effects of tobacco smoke exposure during lactation in weaned and adult male offspring

Children from pregnant smokers show more susceptibility to develop obesity in adult life. Previously, we failed to demonstrate a program for obesity in rat offspring only when the mothers were exposed to tobacco smoke during lactation. Here, we studied the short- and long-term effects of smoke exposure (SE) to both dams and their pups during lactation on endocrine and metabolic parameters. For this, we designed an experimental model where nursing rats and their pups were divided into two groups: SE group, exposed to smoke in a cigarette smoking machine (four times/day, from the third to the 21st day of lactation), and group, exposed to filtered air. Pups were killed at 21 and 180 days. At weaning, SE pups showed lower body weight (7%), length (5%), retroperitoneal fat mass (59%), visceral adipocyte area (60%), and higher subcutaneous adipocyte area (95%) with hypoinsulinemia (-29%), hyperthyroxinemia (59%), hypercorticosteronemia (60%), and higher adrenal catecholamine content (+58%). In adulthood, SE offspring showed higher food intake (+10%), body total fat mass (+50%), visceral fat mass (retroperitoneal: 55%; mesenteric: 67%; and epididymal: 55%), and lower subcutaneous adipocyte area (24%) with higher serum glucose (11%), leptin (85%), adiponectin (1.4-fold increase), total triiodothyronine (71%), free thyroxine (57%), TSH (36%), triglycerides (65%), VLDL cholesterol (+66%), and HDL cholesterol (91%) levels and lower corticosteronemia (41%) and adrenal catecholamine content (57%). Our present findings suggest that tobacco SE to both dams and their pups during lactation causes malnutrition in early life that programs for obesity and hormonal and metabolic disturbances in adulthood, only if the pups are submitted to the same smoke environment as the mother.

Obesity and type 2 diabetes: which patients are at risk?

An estimated 72.5 million American adults are obese, and the growing US obesity epidemic is responsible for substantial increase in morbidity and mortality, as well as increased health care costs. Obesity results from a combination of personal and societal factors, but is often viewed as a character flaw rather than a medical condition. This leads to stigma and discrimination towards obese individuals and decreases the likelihood of effective intervention. Conditions related to obesity are increasingly common, such as metabolic syndrome, impaired fasting glucose (IFG) and impaired glucose tolerance (IGT), all of which indicate high risk for type 2 diabetes (T2DM). This paper reviews the progression from obesity to diabetes, identifying physiological changes that occur along this path as well as opportunities for patient identification and disease prevention. Patients with prediabetes (defined as having IFG, IGT or both) and/or metabolic syndrome require interventions designed to preserve insulin sensitivity and β-cell function, both of which start to deteriorate prior to T2DM diagnosis. Lifestyle modification, including both healthy eating choices and increased physical activity, is essential for weight management and diabetes prevention. Although sustained weight loss is often considered by patients and physicians as being impossible to achieve, effective interventions do exist. Specifically, the Diabetes Prevention Program (DPP) and programs modelled along its parameters have shown repeated successes, even with long-term maintenance. Recent setbacks in the development of medications for weight loss further stress the importance of lifestyle management. By viewing obesity as a metabolic disorder rather than a personal weakness, we can work with patients to address this increasingly prevalent condition and improve long-term health outcomes.

Association of beta2-adrenergic receptor and insulin receptor substrate-1 polymorphisms with obesity in a Northern Indian population

BACKGROUND:

Imbalance in hormonal levels, regulated by host genetic factors, are known to be a major cause of obesity. Therefore, we aimed to evaluate association of genetic polymorphisms of β₂-adrenergic receptor (β₂-AR) and insulin receptor substrate-1 (IRS-1) with hormonal levels in northern Indian obese.

METHODS:

A total of 111 obese and 89 age matched non-obese subjects were studied after taking detailed clinical profile. Hormonal assays in serum/plasma for different hormones were done using IRMA and RIA kits. Genetic analysis of β₂-AR (-47 and -20, T to C) and IRS-1 (Arg972Gly) was done using PCR-RFLP.

STATISTICAL ANALYSIS:

Statistical analysis was performed by SPSS (version 11.5) software. All continuous variables were expressed as mean ± SD and tested by ANOVA test. Comparisons of categorical variables were assessed using X² tests or Fisher's exact test. P-value <0.05 was considered as significant.

RESULTS:

Analysis showed that obese subjects had significantly higher value of blood pressure (systolic), WHR, leptin insulin and glucagon and lower value of GH. In β₂-AR (-47) T/C and IRS-1 Gly972Arg gene polymorphisms we did not found significant differences in genotype or allele frequencies. Moreover, none of the studied hormonal or metabolic parameters showed any association with the gene polymorphisms.

CONCLUSIONS:

Study reveals no significant association of β₂-AR (-47 and -20, T to C) and IRS-1 Gly 972 Arg polymorphisms with obesity in northern Indians.

Subchronic treatment of rats with oxytocin results in improved adipocyte differentiation and increased gene expression of factors involved in adipogenesis

BACKGROUND AND PURPOSE

Treatment with thiazolidinediones, insulin-sensitizing drugs, enhances adipogenesis, which may result in unwanted increase in adiposity. Based on the suggested metabolic effects of oxytocin, the aims of the present study were to: (i) determine whether chronic treatment with oxytocin exerts positive effects on white adipose tissue growth without increasing adiposity; (ii) investigate possible mechanisms of action of oxytocin by measuring the level of gene expression of adipogenic factors; and (iii) test the hypothesis that oxytocin's effect on adipose tissue involves specific activation of eukaryotic elongation factor 2 (eEF2).

EXPERIMENTAL APPROACH

Adult rats were subcutaneously treated with oxytocin (3.6 µg·100 g⁻¹ body weight day⁻¹) via osmotic minipumps for 2 weeks. Adipocytes from epididymal adipose tissue were isolated and their size evaluated by light microscopy. Gene expression of adipogenic and angiogenic factors was determined by real-time PCR and dephosphorylation of eEF2 by immunoblotting.

KEY RESULTS

Oxytocin treatment decreased the diameter of adipocytes and increased the epididymal adipose tissue protein content without changing the adipose tissue mass. Increases in fatty acid binding protein, peroxisome proliferator-activated receptor γ, insulin-sensitive glucose transporter 4, leptin and CD31 mRNA levels were noted in the epididymal and/or retroperitoneal fat tissue of oxytocin-treated rats. Oxytocin enhanced the dephosphorylation of eEF2 in the epididymal adipose tissue.

CONCLUSIONS AND IMPLICATIONS

The present results demonstrate that subchronic treatment with oxytocin induces adipogenic and angiogenic effects and that the eEF2 signalling pathway is involved in these effects of oxytocin on adipose tissue in vivo. These findings are likely to motivate further research and indicate new approaches for modulating adipose tissue morphology and metabolism.

A pilot study of chromium picolinate for weight loss

BACKGROUND

Chromium is an essential trace element and nutritional supplement that has garnered interest for use as a weight loss aid.

OBJECTIVE

This trial assesses the effects of chromium picolinate supplementation, alone and combined with nutritional education, on weight loss in apparently healthy overweight adults.

DESIGN

This was a randomized, double-blind, placebo-controlled trial of 80 otherwise healthy, overweight adults assessed at baseline for central adiposity measured by computerized tomography. Subjects were randomly assigned to daily ingestion of 1000 microg of chromium picolinate or placebo for 24 weeks. All subjects received passive nutritional education at the 12-week point in both the intervention and control groups. Outcomes include weight, height, blood pressure, percent body fat, serum, and urinary biomarkers.

RESULTS

At baseline, both the chromium and placebo groups had similar mean body mass index (BMI) (chromium = 36 +/- 6.7 kg/m(2) versus placebo = 36.1 +/- 7.6 kg/m(2); p = 0.98). After 12 weeks, no change was seen in BMI in the intervention as compared to placebo (chromium = 0.3 +/- 0.8 kg/m(2) versus placebo = 0.0 +/- 0.4 kg/m(2); p = 0.07). No change was seen in BMI after 24 weeks in the intervention as compared to placebo (chromium = 0.1 +/- 0.2 kg/m(2) versus placebo = 0.0 +/- 0.5 kg/m(2); p = 0.81). Variation in central adiposity did not affect any outcome measures.

CONCLUSIONS

Supplementation of 1000 microg of chromium picolinate alone, and in combination with nutritional education, did not affect weight loss in this population of overweight adults. Response to chromium did not vary with central adiposity.

Apolipoprotein B/A-I ratio related to visceral but not to subcutaneous adipose tissue in elderly Swedes

OBJECTIVE

To investigate whether the amount of visceral (VAT) or subcutaneous adipose tissue (SAT) independently of the other can determine the apolipoprotein (apo)B/A-I ratio.

METHODS

VAT and SAT areas were assessed using magnetic resonance imaging in 247 randomly selected 70-year-old men and women who did not use lipid-lowering drugs. Their adipose tissue areas were compared to their apoB and apo A-I levels and to their apoB/A-I ratios.

RESULTS

The VAT area and the gender were significantly related to the apoB/A-I ratio whereas the SAT area was not. There was a positive relationship between the VAT area and the apoB/A-I ratio.

CONCLUSION

A positive relationship was established between the amount of VAT and the apoB/A-I ratio, whereas there was no relationship between the amount of SAT and the apoB/A-I ratio. This observation supports the notion that VAT is metabolically active.

The relationship of omental and subcutaneous adipocyte size to metabolic disease in severe obesity

Objective

Several studies have reported the existence of a subgroup of obese individuals with normal metabolic profiles. It remains unclear what factors are responsible for this phenomenon. We proposed that adipocyte size might be a key factor in the protection of metabolically healthy obese (MHO) individuals from the adverse effects of obesity.

Subjects

Thirty-five patients undergoing bariatric surgery were classified as MHO (n = 15) or metabolically unhealthy obese (MUO, n = 20) according to cut-off points adapted from the International Diabetes Federation definition of the metabolic syndrome. Median body mass index (BMI) was 48 (range 40–71).

Results

There was a moderate correlation between omental adipocyte size and subcutaneous adipocyte size (r = 0.59, p<0.05). The MHO group had significantly lower mean omental adipocyte size (80.9±10.9 µm) when compared with metabolically unhealthy patients (100.0±7.6 µm, p<0.0001). Mean subcutaneous adipocyte size was similar between the two groups (104.1±8.5 µm versus 107.9±7.1 µm). Omental, but not subcutaneous adipocyte size, correlated with the degree of insulin resistance as measured by HOMA-IR (r = 0.73, p<0.0005), as well as other metabolic parameters including triglyceride/HDL-cholesterol ratio and HbA1c. Twenty-eight patients consented to liver biopsy. Of these, 46% had steatohepatitis and fibrosis. Fifty percent (including all the MHO patients) had steatosis only. Both omental and subcutaneous adipocyte size were significantly associated with the degree of steatosis (r = 0.66, p<0.0001 and r = 0.63, p<0.005 respectively). However, only omental adipocyte size was an independent predictor of the presence or absence of fibrosis.

Conclusion

Metabolically healthy individuals are a distinct subgroup of the severely obese. Both subcutaneous and omental adipocyte size correlated positively with the degree of fatty liver, but only omental adipocyte size was related to metabolic health, and possibly progression from hepatic steatosis to fibrosis.

Body fat distribution, adipocyte size, and metabolic characteristics of nondiabetic adults

CONTEXT

It is unclear whether adipocyte size or body fat distribution is most strongly linked to the metabolic complications of obesity.

OBJECTIVE

Our objective was to test whether adipocyte size better predicts metabolic characteristics of obesity than body composition.

DESIGN, PARTICIPANTS, AND SETTING

We analyzed the relationship between metabolic and anthropometric data collected from 432 largely Caucasian research volunteers (264 women) participating in studies conducted in the Mayo General Clinical Research Center between 1995 and 2008.

MAIN OUTCOME MEASURES

Metabolic variables included fasting plasma glucose, insulin, and triglyceride concentrations. Anthropometric variables included body composition, fat distribution, and sc abdominal and femoral adipocyte size.

RESULTS

Using both univariate and multivariate regression analysis, fasting triglyceride in both men and women was best predicted by computed tomography of visceral fat area. Fasting insulin concentrations were best predicted by sc abdominal fat area in women (r(2) = 0.40; P < 0.01) and body mass index in men (r(2) = 0.53; P < 0.0001); adipocyte size did not contribute independently. In men, fasting glucose concentrations were predicted by femoral adipocyte size (partial r(2) = 0.07; P = 0.002), body mass index (partial r(2) = 0.03; P = 0.07), and age (partial r(2) = 0.02; P = 0.06). In women, fasting glucose was predicted by abdominal sc fat area (partial r(2) = 0.12; P < 0.0001) and age (partial r(2) = 0.03; P = 0.01).

CONCLUSIONS

Our hypothesis that adipocyte size is the best predictor of metabolic characteristics was not supported in this population. The alternative explanation is that fat mass and body fat distribution have more influence on metabolic responses than adipocyte size.

Is adiposopathy (sick fat) an endocrine disease?

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

Adiposopathy (sick fat) is an endocrine disease.

In vivo quantification of subcutaneous and visceral adiposity by micro-computed tomography in a small animal model

Accurate and precise techniques that identify the quantity and distribution of adipose tissue in vivo are critical for investigations of adipose development, obesity, or diabetes. Here, we tested whether in vivo micro-computed tomography (microCT) can be used to provide information on the distribution of total, subcutaneous and visceral fat volume in the mouse. Ninety C57BL/6J mice (weight range: 15.7-46.5 g) were microCT scanned in vivo at 5 months of age and subsequently sacrificed. Whole body fat volume (base of skull to distal tibia) derived from in vivo microCT was significantly (p<0.001) correlated with the ex vivo tissue weight of discrete perigonadal (R(2)=0.94), and subcutaneous (R(2)=0.91) fat pads. Restricting the analysis of tissue composition to the abdominal mid-section between L1 and L5 lumbar vertebrae did not alter the correlations between total adiposity and explanted fat pad weight. Segmentation allowed for the precise discrimination between visceral and subcutaneous fat as well as the quantification of adipose tissue within specific anatomical regions. Both the correlations between visceral fat pad weight and microCT determined visceral fat volume (R(2)=0.95, p<0.001) as well as subcutaneous fat pad weight and microCT determined subcutaneous fat volume (R(2)=0.91, p<0.001) were excellent. Data from these studies establish in vivo microCT as a non-invasive, quantitative tool that can provide an in vivo surrogate measure of total, visceral, and subcutaneous adiposity during longitudinal studies. Compared to current imaging techniques with similar capabilities, such as microMRI or the combination of DEXA with NMR, it may also be more cost-effective and offer higher spatial resolutions.

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

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

Subcutaneous adipocyte size and body fat distribution

BACKGROUND

Both body fat distribution and adipocyte size are associated with metabolic abnormalities.

OBJECTIVE

We defined the extent to which subcutaneous adipocyte size is related to regional fat mass and to the sizes of adipocytes in other subcutaneous depots independent of adiposity, age, and sex.

DESIGN

Data collected from 188 women and 133 men who were 18-50 y old and who had a body mass index (in kg/m2) of 18 to 50 were analyzed. The mean size of isolated subcutaneous abdominal, femoral, and gluteal adipocytes was measured by direct microscopy or by automated analysis of digital images. Visceral fat area was measured with computed tomography. Dual-energy X-ray absorptiometry was used to calculate adiposity.

RESULTS

Stepwise multiple regression analyses showed that abdominal adipocyte size was associated positively with visceral and subcutaneous abdominal fat areas and negatively with lower-body fat mass as a percentage of total-body fat, after control for sex and percentage body fat. Femoral adipocyte size was related to percentage body fat (P<0.0001), whereas gluteal adipocyte size was related to visceral fat area (P=0.002), which suggests that these 2 lower-body fat depots are distinct. Analyses of data from a subset of volunteers (n=99) for whom we had adipocyte size from all 3 depots showed that adipocyte size from 1 depot could be better predicted if adipocyte size from other depots were known.

CONCLUSIONS

Abdominal adipocyte size is related to body fat distribution. Adipocyte size in a person seems to be globally regulated by factors independent of variations in body fat distribution.

Effects of modified alternate-day fasting regimens on adipocyte size, triglyceride metabolism, and plasma adiponectin levels in mice

Calorie restriction (CR) affects adipocyte function and reduces body weight. However, the effects of alternate-day fasting (ADF) on adipose biology remain unclear. This study examined the effects of ADF and modified ADF regimens on adipocyte size, triglyceride (TG) metabolism, and adiponectin levels in relation to changes in body weight and adipose mass. Twenty-four male C57BL/6J mice were randomized for 4 weeks among 1) ADF-25% (25% CR on fast day, ad libitum on alternate day), 2) ADF-50% (50% CR on fast day), 3) ADF-100% (100% CR on fast day), and 4) control (ad libitum). The body weight of ADF-100% mice was lower than that of the other groups (P < 0.005) after treatment. Adipose tissue weights did not change. Inguinal and epididymal fat cells were 35-50% smaller (P < 0.01) than those of controls in ADF-50% and ADF-100% animals after treatment. Net lipolysis was augmented (P < 0.05) in ADF-100% mice, and the contribution from glyceroneogenesis to alpha-glycerol phosphate increased in ADF-50% and ADF-100% mice, whereas fractional and absolute de novo lipogenesis also increased in ADF-50% and ADF-100% animals, consistent with an alternating feast-fast milieu. Plasma adiponectin levels were not affected. In summary, modified ADF (ADF-50%) and complete ADF (ADF-100%) regimens modulate adipocyte function, despite there being no change in body weight or adipose tissue weight in the former group.

Peroxisome proliferator-activated receptors: Bridging metabolic syndrome with molecular nutrition

Over recent years, obesity rates and the onset of obesity-induced chronic diseases have risen dramatically. The more we learn about the physiological and morphological changes that occur during obesity, the more it is becoming clear that obesity-related disorders can be traced back to adipocyte hypertrophy and inflammation at white adipose tissue (WAT). To combat this problem, the body has developed a regulatory system specifically designed at mediating the systemic response to obesity, utilizing free fatty acids (FFAs) and their metabolites as nutrient messengers to signal adaptations from peripheral tissues. These messages are predominantly interceded through the peroxisome proliferator-activated receptors (PPARs), a family of ligand-induced transcription factors that serve as a net of lipid sensors throughout the body. Understanding how and why nutrients, nutrient derivatives and metabolites exert their physiological effects are the key goals in the study of molecular nutrition. By learning about the mechanisms and tissue-specific effects of endogenous PPAR ligands and expanding our knowledge of the body's integrated homeostatic system, we will significantly increase our odds of designing safe and effective preventive and therapeutic interventions that keep us one step ahead of obesity-related diseases.

Effects of resistance or aerobic exercises on metabolic parameters in obese women who are not on a diet

This longitudinal, controlled clinical study was conducted to compare the effects of resistance exercise (RE) and aerobic exercise (AE) on body mass index (BMI), weight, fat mass (FM), serum lipid profile, and insulin resistance in obese women who cannot adhere to energy-restricted diets. A total of 60 obese women with severe eating disorders were evaluated. Patients were randomly divided into 3 groups: control group with no exercise (n=20), group 1 with AE (n=20), and group 2 with RE (n=20). Demographic and anthropometric measurements were taken. Serum lipid fractions and fasting (FGlc) and postprandial glucose insulin (PGlc) levels were measured. Insulin resistance was calculated with use of homeostasis model assessment (HOMA-IR). Total body FM was measured by bioelectric impedance analysis. After 12 wk of exercise, significant decreases in BMI, waist and weight measurements, and FGlc, PGlc, triglyceride, and total cholesterol levels were noted in each of the study groups. Reduced low-density lipoprotein cholesterol level and FM and HOMA-IR measurements were observed only in group 1 (with AE). This study indicated that AE and RE training induces improvement in body fat composition and has a favorable metabolic effect in obese women with severe eating disorders.

The adipocyte life cycle hypothesis

The adipocyte life cycle hypothesis states that the metabolic properties of an adipocyte vary predictably during its life cycle: that as an adipocyte matures, it accumulates triacylglycerol (triglyceride) and becomes larger; that the rates of triacylglycerol synthesis and lipolysis are matched within adipocytes and that larger adipocytes, in general, have greater rates of triacylglycerol synthesis and, concurrently, greater rates of lipolysis and, therefore, larger adipocytes have greater rates of transmembrane fatty acid flux; and that the secretion of cytokines can also be related to adipocyte size with larger adipocytes having a more unfavourable profile of cytokine secretion than smaller adipocytes. Adipocyte location is an important modifier of this relationship and the favoured sites of adipocyte proliferation are a function of gender and the position within the life cycle of the organism at which proliferation occurs. The adipocyte life cycle hypothesis posits that the metabolic consequences of obesity depend on whether expansion of adipose tissue is achieved primarily by an increase in adipocyte number or adipocyte size. This hypothesis may explain a variety of previously unanswered clinical puzzles such as the vulnerability of many peoples from South East Asia to the adverse metabolic consequences of obesity.

Tissue leptin and plasma insulin are associated with lipoprotein lipase activity in severely obese patients

The development of metabolic complications of obesity has been associated with the existence of depot-specific differences in the biochemical properties of adipocytes. The aim of this study was to investigate, in severely obese men and women, both gender- and depot-related differences in lipoprotein lipase (LPL) expression and activity, as well as the involvement of endocrine and biometric factors and their dependence on gender and/or fat depot. Morbidly obese, nondiabetic, subjects (9 men and 22 women) aged 41.1+/-1.9 years, with a body mass index (BMI) of 54.7+/-1.7 kg/m(2) who had undergone abdominal surgery were studied. Both expression and activity of LPL and leptin expression were determined in adipose samples from subcutaneous and visceral fat depots. In both men and women, visceral fat showed higher LPL mRNA levels as well as lower ob mRNA levels and tissue leptin content than the subcutaneous one. In both subcutaneous and visceral adipose depots, women exhibited higher protein content, decreased fat cell size and lower LPL activity than men. The gender-related differences found in abdominal fat LPL activity could contribute to the increased risk for developing obesity-associated diseases shown by men, even in morbid obesity, in which the massive fat accumulation could mask these differences. Furthermore, the leptin content of fat depots as well as plasma insulin concentrations appear in our population as the main determinants of adipose tissue LPL activity, adjusted by gender, depot and BMI.

The metabolic syndrome in obese postmenopausal women: relationship to body composition, visceral fat, and inflammation

The purpose of this study was to investigate whether aerobic fitness, body composition, body fat distribution, and inflammation are different in obese postmenopausal women with and without the metabolic syndrome (MS), and whether the severity of MS is associated with these characteristics. Fifty-eight women (age, 59 +/- 1 yr; body mass index, 33.0 +/- 0.6 kg/m2)completed testing of maximal aerobic capacity, body composition (fat mass, lean mass, and percent body fat), body fat distribution (sc and visceral fat areas, and regional adipocyte sizes), and inflammation (C-reactive protein, IL-6, and TNF-alpha,and their soluble receptors). Lean mass (44.4 +/- 0.9 vs. 41.2 +/- 0.9 kg; P < 0.05), visceral fat area (180 +/- 10 vs. 135 +/- 7 cm2; P <0.001), and plasma soluble TNF receptor 1 (sTNFR1; 860 +/- 25 vs. 765 +/- 42 pg/ml; P < 0.05) were higher in women with the MS(n = 27) than in those without the MS (n = 31). The number of MS components was directly related to weight, body mass index, fat mass, lean mass, visceral fat area, and plasma sT-NFR1. We conclude that obese older women with the MS are characterized by high lean mass, high visceral fat, and elevated sTNFR1, and the severity of the MS is associated with body composition, visceral adiposity, and inflammation.

High local concentrations and effects on differentiation implicate interleukin-6 as a paracrine regulator

OBJECTIVE

To examine the possibility that interleukin-6 (IL-6) can act as a paracrine regulator in adipose tissue by examining effects on adipogenic genes and measuring interstitial IL-6 concentrations in situ.

RESEARCH METHODS AND PROCEDURES

Circulating and interstitial IL-6 concentrations in abdominal and femoral adipose tissue were measured using the calibrated microdialysis technique in 20 healthy male subjects. The effects of adipose cell enlargement on gene expression and IL-6 secretion were examined, as well as the effect of IL-6 in vitro on gene expression of adiponectin and other markers of adipocyte differentiation.

RESULTS

The IL-6 concentration in the interstitial fluid was approximately 100-fold higher than that in plasma, suggesting that IL-6 may be a paracrine regulator of adipose tissue. This was further supported by the finding that adding IL-6 in vitro at similar concentrations down-regulated the expression of adiponectin, aP2, and PPARgamma-2 in cultured human adipose tissue. In addition, gene expression and release of IL-6, both in vivo and in vitro, correlated with adipose cell size.

DISCUSSION

These data suggest that IL-6 may be a paracrine regulator of adipose tissue. Furthermore, increased adipose tissue production of IL-6 after hypertrophic enlargement of the adipose cells may detrimentally affect systemic insulin action by inducing adipose tissue dysfunction with impaired differentiation of the pre-adipocytes and/or adipocytes and lower adiponectin.

Racial differences in adipocyte size and relationship to the metabolic syndrome in obese women

OBJECTIVE

To determine whether racial differences exist in the relationship of the abnormalities defining the metabolic syndrome (MS) to regional adiposity and fat cell size (FCS) in obese postmenopausal women.

RESEARCH METHODS AND PROCEDURES

We determined the relationship of metabolic variables associated with the MS to regional body composition and abdominal (ABD) and gluteal (GLT) FCS in 25 white (CAU) and 25 African-American (AF-AMER) older women matched for age (58 +/- 5 years; mean +/- SD) and BMI (35 +/- 4 kg/m2).

RESULTS

MS was present in 36% of the AF-AMER and 57% of the CAU women. There were no differences in total body, trunk, gluteofemoral fat mass or regional FCS, but AF-AMER women had 22% lower visceral fat, 24% higher insulin, and 31% lower triglyceride levels than CAU women (p < 0.05). Multiple regression analysis with body fat, visceral ABD fat area, and FCS as independent variables showed that GLT FCS was independently correlated with 2-hour insulin (r = 0.56), triglyceride (r = 0.62), and high-density lipoprotein cholesterol (r = -0.72) levels in AF-AMER women but not in CAU women, where only systolic blood pressure correlated with subcutaneous ABD fat area (r = 0.57) (p < 0.05).

DISCUSSION

The associations between GLT FCS and metabolic dysfunction in obese AF-AMER but not CAU women suggest that central obesity is a less valid predictor of the MS in obese postmenopausal AF-AMER women than in CAU women and that GLT FCS may be a more sensitive indicator of risk for the MS in AF-AMER women.

Effect of increasing metabolic syndrome score on atherosclerotic risk profile and coronary artery disease angiographic severity

The metabolic syndrome (MS) is a frequent cause of coronary artery disease (CAD), and recently the National Cholesterol Education Program Adult Treatment Panel III suggested its diagnosis in the presence of 3 to 5 quantitatively defined markers. Because the consequences of the MS are likely related to the number and diversity of markers, we studied the relation between the number of markers-the MS score-and the degree of abdominal obesity, risk factor profile, and severity of CAD. One thousand one hundred eight subjects of a mostly white population with symptoms of CAD (793 men and 315 women; 58.1 +/- 9.8 years of age) were divided into 6 groups based on their MS scores. A low high-density lipoprotein cholesterol level was the most frequently observed marker, followed by increased blood pressure, triglycerides, waist circumference, and fasting glucose. As the MS score increased so did abdominal obesity, parameters of "nontraditional" dyslipidemia with surrogate markers of dense low-density lipoprotein and high-density lipoprotein particles, blood pressure, fasting glucose, insulin, and the homeostatic model assessment insulin resistance index. Similarly, an increasing MS score was significantly related to more severe coronary angiographic alterations and higher frequencies of unstable angina, myocardial infarction, percutaneous coronary intervention, and coronary artery bypass grafting. Therefore, the MS score provides a clinically useful index of MS severity and the associated atherosclerotic risk factor profile. It also correlates with the angiographic severity of CAD and its clinical complications.

A paradox resolved: the postprandial model of insulin resistance explains why gynoid adiposity appears to be protective

Although an increased visceral adipose mass is clearly linked to insulin resistance syndrome and increased vascular risk, some studies suggest that the ratio of visceral to subcutaneous fat (gynoid or abdominal) is a better correlate of insulin resistance. For example, the utility of waist-to-hip ratio as a risk factor illustrates this principle--and suggests that gynoid obesity may somehow be protective. The postprandial model of insulin resistance--the hypothesis that excessive postprandial free, fatty acid (FFA) flux plays a key role in the genesis of the insulin resistance syndrome--may help to rationalize this seemingly paradoxical observation. A high proportion of this FFA flux is derived, not from adipocytes, but from meal-derived fatty acids that adipocytes fail to store following chylomicron breakdown; insulin-resistant adipocytes are notably inefficient in regard to FFA storage. Hypertrophied visceral adipocytes are poorly insulin sensitive, whereas gynoid adipocytes tend to be highly insulin sensitive. After a fatty meal, the lipoprotein lipase (LPL) activities associated with the various depots--visceral and subcutaneous adipocytes, as well as skeletal muscle--effectively compete to hydrolyze chylomicra. When circulating triglycerides are broken down by muscle or by insulin-sensitive subcutaneous adipocytes, the evolved fatty acids are apt to be stored immediately--whereas the fatty acids produced by chylomicron breakdown in the visceral depot are much more prone to escape to the circulation and contribute to high postprandial FFA flux. Thus, the LPL activity of gynoid adipocytes provides protection from the potentially adverse metabolic consequences of fatty meals--and a large mass of gynoid adipocytes presumably is a marker for high LPL activity in this depot. The ability of the postprandial model of insulin resistance to rationalize the seeming protection afforded by gynoid obesity constitutes evidence that this model has validity.

Relationships in men of sex hormones, insulin, adiposity, and risk factors for myocardial infarction

That sex hormones, insulin, and obesity all correlate with the constellation of risk factors for myocardial infarction (MI) that has come to be known as "syndrome X," the "insulin-resistance syndrome," or the "metabolic syndrome" suggests that any one or more of them could underlie and link the risk factors to form the constellation. That sex hormones, insulin, and obesity also correlate with each other complicates their identification as an underlying link. To compare the likelihood of each being a link, we measured and determined the interrelationships of sex hormones, insulin, adiposity variables, and risk factors for MI in 80 apparently healthy men. Of the adiposity variables, visceral adipose tissue (VAT) correlated more strongly with the risk factors for MI than did body mass index (BMI), total adipose tissue (TAT), subcutaneous adipose tissue (SCAT), waist-to-hip ratio (WHR), and waist circumference (W). Controlling for VAT eliminated all of the other adiposity correlations that had been significant. VAT, therefore, was used as the measure of adiposity for further data analysis. VAT correlated more strongly with risk factors for MI than did sex hormones and insulin, and most of the correlations of sex hormones and insulin with risk factors for MI lost statistical significance after controlling for VAT. Testosterone and the ratio of estradiol-to-testosterone (E/T) correlated with insulin; on controlling for VAT, only the E/T-insulin correlation remained significant (r =.38, P <.001) and on multiple linear regression analysis, insulin was associated with estradiol (P =.01) and testosterone (P =.04) independently of VAT and age. In conclusion, (1) VAT in men may largely explain the correlations of sex hormones, insulin, and obesity with the risk factors for MI measured, (2) VAT may be the principal factor in men, independently of other measures of adiposity, that links risk factors for MI to form the constellation, and (3) estradiol may play a more important role in the sex hormone-insulin relationship in men than has generally been considered.

Incidence and clinical characteristics of the metabolic syndrome in patients with coronary artery disease

BACKGROUND AND OBJECTIVES

Several studies suggested that the insulin resistance-associated metabolic syndrome (MS) is a major risk factor for coronary artery disease (CAD), but the criteria to identify MS were only recently standardized by the National Cholesterol Education Program (NCEP) Adult Treatment Panel (ATP) III.

METHODS

We evaluated the incidence of the newly defined MS in patients with documented CAD and compared the characteristics of patients with and without this syndrome.

RESULTS

In a Canadian population with CAD (793 men and 315 women, age 58.1+/-9.8 years) 51% had MS. As compared to patients without the MS syndrome, these patients had significantly higher waist circumference, blood pressure levels and fasting glucose and triglyceride, but lower high-density lipoprotein (HDL)-cholesterol levels. Their homeostatic model assessment (HOMA) insulin resistance index was significantly higher, with indicators of highly atherogenic, small low-density lipoprotein (LDL) and HDL particles. Family history of diabetes and the use of hypoglycemic agents, beta-blockers and thiazides were more frequent, but physical exercise and alcohol consumption were less frequent in MS positive patients. Cumulative coronary stenosis score and the frequency of patients with >50% coronary artery narrowing were higher and there was a strong tendency for higher rates of previous myocardial infarction in MS positive patients.

CONCLUSIONS

In a CAD population documented in 1991-1992, 51% of participants had MS and in several respects a more advanced coronary disease than those without the syndrome. These results support the view of NCEP ATP III, that in CAD prevention, beyond lowering LDL-cholesterol levels, interventions concerning the constituents of MS should be important.

Clinical and pathophysiological consequences of abdominal adiposity and abdominal adipose tissue depots

OBJECTIVES

To highlight the clinical and metabolic correlates of abdominal obesity and various abdominal adipose tissue depots.

METHODS

We researched the topic using the search terms abdominal obesity, central obesity, visceral obesity, regional obesity, and subcutaneous adipose tissue from MEDLINE (National Library of Medicine, Bethesda, MD), PubMed (National Library of Medicine, Bethesda, MD), Current Contents (Institute for Scientific Information, Thomson Scientific, Philadelphia, PA), and using manual search for the cited references.

RESULTS

Abdominal obesity contributes significantly to the metabolic perturbations and cardiovascular risk in human beings. Abdominal adipose tissue depots (intraabdominal and subcutaneous [deep subcutaneous, posterior subcutaneous]) are metabolically active and appear to be important for the pathogenesis of insulin resistance, dyslipidemia, glucose intolerance, hypertension, hypercoagulable state, and cardiovascular risk. Adipocyte anatomy (size), physiology (growth, catecholamine sensitivity, lipolysis, insulin action), and biochemistry (leptin, plasminogen activator inhibitor-1, cytokines, renin-angiotensin system) are reported to be relatively site-specific, highlighting unique roles of regional adipose tissue depots.

CONCLUSIONS

Several physiological and metabolic parameters are site-specific in abdominal adipose tissue. The epidemiological, clinical, and prognostic significance and relative importance of the regional adipose tissue depots, however, remain to be ascertained.

Cross talk between adipose tissue cells: impact on pathophysiology

The metabolic functionality of adipose tissue is intimately dependent on local communication between various cell types. It influences not only the equilibrium between lipogenesis and lipolysis but also between hypertrophic and hyperplastic growth, thereby determining the role adipose tissue plays in the insulin resistance syndrome.

C-reactive protein is independently associated with total body fat, central fat, and insulin resistance in adult women

OBJECTIVE

To investigate whether C-reactive protein (CRP) concentrations are influenced by body composition, insulin resistance, and body fat distribution in healthy women.

DESIGN

Cross-sectional study of CRP plasma levels in adult women.

SUBJECTS

A total of 201 apparently healthy normal weight, overweight, and obese women, aged 18-60 y.

MEASUREMENTS

CRP plasma levels, several fatness and body fat distribution parameters (by bioimpedance analysis and anthropometry), and insulin resistance (HOMA(IR)), as calculated by homeostatic model assessment.

RESULTS

CRP was positively correlated with age, body mass index (BMI), waist, fasting glucose and insulin, HOMA(IR), fat-free mass (FFM) and fat mass (FM). After multivariate analyses, age, HOMA(IR), waist and FM maintained their independent association with CRP.

CONCLUSION

Our study has shown an independent relationship of central fat accumulation and insulin resistance with CRP plasma levels, thus suggesting that mild, chronic inflammation may be a further component of the metabolic syndrome and a mediator of the atherogenic profile of this syndrome.