Abdominal fat and insulin resistance in normal and overweight women: Direct measurements reveal a strong relationship in subjects at both low and high risk of NIDDM

Changes in risk factors for cardiovascular disease with body fat loss in obese women

BACKGROUND

Current guidelines for obesity management emphasize the improvements in health risks associated with weight losses of 5-10% initial weight. However, most of the data is derived from periods of acute weight loss and may not represent the true effect in the longer term or in obese but otherwise healthy individuals. This study examines the temporal changes in risk factors for cardiovascular disease with weight change over 52 weeks.

METHODS

In total, 57 overweight women (age 43.7 +/- 9.1 years, mean BMI of 31.7 kg/m2, range 27.2-38.5 kg/m2) with no other significant medical history, entered a milk-based, low-energy weight loss programme for 12 weeks and were then monitored without further intervention until 52 weeks. Weight, fat mass, fasting plasma insulin, lipids and blood pressure were measured at 0, 12, 24 and 52 weeks.

RESULTS

The mean weight change in sequential periods was -11.6% (p < 0.0001), +1.1% (p = 0.02) and +5.2% (p < 0.0001). The change from baseline to 1 year being -6.0% (p < 0.0001) an 11% (p < 0.0001) reduction in initial body fat mass. Initial weight loss (0-12 weeks) was positively correlated with greater longer term weight loss (0-52 weeks, r = 0.75, p < 0.0001) and not with weight regain (12-52 weeks, r = 0.14, p = 0.28). Despite significant improvements in insulin sensitivity, lipid profile and blood pressure (BP) with acute weight loss, in the group overall, only benefits in BP were maintained after 52 weeks. However, improvements in insulin sensitivity were sustained in those who maintained more than 5% weight loss, and those with higher baseline metabolic risk had greater benefits with weight loss. Change in waist circumference was better than BMI or fat mass in predicting improvements in metabolic risk in these obese women.

CONCLUSIONS

This study suggests, in otherwise apparently healthy obese women, the rationale of targeting individuals most likely to benefit from weight management. Most importantly it highlights the need to focus on achieving initial weight losses of greater than 10% to maintain longer term losses of at least 5% and the associated health benefits.

Altered myocellular and abdominal fat partitioning predict disturbance in insulin action in HIV protease inhibitor-related lipodystrophy

HIV protease inhibitor-related lipodystrophy is characterized by peripheral fat loss, hyperlipidemia, and insulin resistance. Increased availability of lipid to muscle may be one of the mechanisms that induce insulin resistance. Regional fat, intramyocellular lipid (by (1)H-magnetic resonance spectroscopy), serum lipids, and insulin-stimulated glucose disposal (by hyperinsulinemic-euglycemic clamp) were quantified in 10 men who had HIV-1 infection with moderate to severe lipodystrophy and a control group of 10 nonlipodystrophic men who had HIV-1 infection and were naïve to protease inhibitors to examine the effects of lipodystrophy on glucose and lipid metabolism. Lipodystrophic subjects showed lower insulin-stimulated glucose disposal than control subjects (P = 0.001) and had increased serum triglycerides (P = 0.03), less limb fat (P = 0.02), increased visceral fat as a proportion of total abdominal fat (P = 0.003), and increased intramyocellular lipid (1.90 +/- 0.15 vs. 1.23 +/- 0.16% of water resonance peak area; P = 0.007). In both groups combined, visceral fat related strongly to intramyocellular lipid (r = 0.83, P < 0.0001) and intramyocellular lipid related negatively to insulin-stimulated glucose disposal (r = -0.71, P = 0.0005). Fasting serum cholesterol and triglycerides related positively to intramyocellular lipid and visceral fat in lipodystrophic subjects only. The data indicate that lipodystrophy is associated with increased lipid content in muscle accompanying impaired insulin action. The results do not establish causation but emphasize the interrelationships among visceral fat, myocyte lipid, and insulin action.

No increase in the prevalence of known diabetes between 1986 and 1999 in subjects 25-64 years of age in northern Sweden

AIMS

A global increase in diabetes is predicted due to higher body weight and less physical activity. Over the period 1986-1999, the body mass index (BMI) of the adult population of northern Sweden increased from 25.3 to 26.2 and the prevalence of obesity (BMI > or = 30) from 11% to 15%, although this was more distal than central adiposity. Our hypothesis was that this would lead to a higher prevalence of diabetes.

METHODS

Four population surveys with new and independent cohorts of 2000 invited subjects, 25-64 years old, in 1986, 1990, 1994 and 1999. In the first three surveys an oral glucose tolerance test was carried out in 47%.

RESULTS

Over the time period 1986-1999 there was no increase in the prevalence of known diabetes. No trends were noted in the finding of previously undiagnosed diabetes or impaired glucose tolerance over the period 1986-1994, although the confidence intervals are wide. Fasting, but not post-load, glucose levels increased with 0.040 mmol/year (95% CI 0.026; 0.055) in men and 0.033 mmol/year (0.023; 0.044) in women.

CONCLUSION

In spite of a marked increase in BMI, we found no increased prevalence of known diabetes over a 13-year observation period, although our data cannot exclude minor increases in undiagnosed diabetes. The development of more distal than abdominal obesity, a diet with less saturated fat and lower glycaemic index and fewer regular smokers in the population may contribute to this. The effects of obesity may thus be attenuated by other secular trends in society and highlight potential ways of curbing the worldwide increase in diabetes.

Removal of visceral fat prevents insulin resistance and glucose intolerance of aging: an adipokine-mediated process?

Age-dependent changes in insulin action and body fat distribution are risk factors for the development of type 2 diabetes. To examine whether the accumulation of visceral fat (VF) could play a direct role in the pathophysiology of insulin resistance and type 2 diabetes, we monitored insulin action, glucose tolerance, and the expression of adipo-derived peptides after surgical removal of VF in aging (20-month-old) F344/Brown Norway (FBN) and in Zucker Diabetic Fatty (ZDF) rats. As expected, peripheral and hepatic insulin action were markedly impaired in aging FBN rats, and extraction of VF (accounting for approximately 18% of their total body fat) was sufficient to restore peripheral and hepatic insulin action to the levels of young rats. When examined at the mechanistic level, removal of VF in ZDF rats prevented the progressive decrease in insulin action and delayed the onset of diabetes, but VF extraction did not alter plasma free fatty acid levels. However, the expression of tumor necrosis factor-alpha and leptin in subcutaneous (SC) adipose tissue were markedly decreased after VF removal (by approximately three- and twofold, respectively). Finally, extracted VF retained approximately 15-fold higher resistin mRNA compared with SC fat. Our data suggest that insulin resistance and the development of diabetes can be significantly reduced in aging rats by preventing the age-dependent accumulation of VF. This study documents a cause-and-effect relationship between VF and major components of the metabolic syndrome.

Effect of rosiglitazone on insulin sensitivity and body composition in type 2 diabetic patients [corrected]

OBJECTIVE

To investigate the effects of rosiglitazone (RSG) on insulin sensitivity and regional adiposity (including intrahepatic fat) in patients with type 2 diabetes.

RESEARCH METHODS AND PROCEDURES

We examined the effect of RSG (8 mg/day, 2 divided doses) compared with placebo on insulin sensitivity and body composition in 33 type 2 diabetic patients. Measurements of insulin sensitivity (euglycemic hyperinsulinemic clamp), body fat (abdominal magnetic resonance imaging and DXA), and liver fat (magnetic resonance spectroscopy) were taken at baseline and repeated after 16 weeks of treatment.

RESULTS

There was a significant improvement in glycemic control (glycosylated hemoglobin -0.7 +/- 0.7%, p < or = 0.05) and an 86% increase in insulin sensitivity in the RSG group (glucose-disposal rate change from baseline: 17.5 +/- 14.5 micro mol glucose/min/kg free fat mass, p < 0.05), but no significant change in the placebo group compared with baseline. Total body weight and fat mass increased (p < or = 0.05) with RSG (2.1 +/- 2.0 kg and 1.4 +/- 1.6 kg, respectively) with 95% of the increase in adiposity occurring in nonabdominal regions. In the abdominal region, RSG increased subcutaneous fat area by 8% (25.0 +/- 28.7 cm(2), p = 0.02), did not alter intra-abdominal fat area, and reduced intrahepatic fat levels by 45% (-6.7 +/- 9.7%, concentration relative to water).

DISCUSSION

Our data indicate that RSG greatly improves insulin sensitivity in patients with type 2 diabetes and is associated with an increase in adiposity in subcutaneous but not visceral body regions.

Current concepts in insulin resistance, type 2 diabetes mellitus, and the metabolic syndrome

A clustering of risk factors, including elevated triglycerides, decreased high-density lipoprotein cholesterol, hyperinsulinemia, and hypertension often are observed in patients who are insulin resistant. Insulin resistance has been found to play a critical role in the development of cardiovascular disease, particularly in patients with type 2 diabetes. Patients with insulin resistance have an increase in small, dense low-density lipoprotein (LDL) cholesterol, which is more atherogenic than large, buoyant LDL cholesterol. In the context of insulin resistance, insulin has reduced effects on the phosphatidylinositol 3 kinase (PI3K) pathway, whereas mitogen-activated protein kinase activity is maintained. The result is an exaggeration of the mitogenic actions of insulin leading to vascular smooth muscle proliferation and elevated plasminogen activator inhibitor (PAI)-1. Notably, nitric oxide-mediated vasodilation also is impaired, further contributing to atherogenicity. In addition, hyperinsulinemia further contributes to cardiovascular risk by promoting thrombosis. Patients who are insulin resistant have decreased fibrinolysis, as indicated by increased levels of PAI-1. Studies have shown that enhancing insulin sensitivity with insulin sensitizers, such as thiazolidinediones, may improve insulin resistance and limit the development of adverse cardiovascular consequences.

Insulin resistance as the core defect in type 2 diabetes mellitus

Insulin resistance is a major contributor to the pathogenesis of type 2 diabetes and plays a key role in associated metabolic abnormalities, such as dyslipidemia and hypertension. Obesity, especially visceral adiposity, is negatively correlated with insulin sensitivity. The release of free fatty acids from adipocytes can block insulin-signaling pathways and lead to insulin resistance. In addition, recently identified adipocyte-specific chemical messengers, the adipocytokines, such as tumor necrosis factor-alpha, adiponectin, and resistin, appear to modulate the underlying insulin resistance. When insulin resistance is combined with beta-cell defects in glucose-stimulated insulin secretion, impaired glucose tolerance, hyperglycemia, or type 2 diabetes can result. The thiazolidinediones are potent peroxisome proliferator-activated receptor-gamma agonists and directly improve insulin resistance and glycemic control in patients with type 2 diabetes. Increasing evidence supports the early use of thiazolidinediones for preventing, delaying, or treating diabetes by improving insulin sensitivity and beta-cell insulin secretion.

Skeletal muscle triglyceride: marker or mediator of obesity-induced insulin resistance in type 2 diabetes mellitus?

The inability of insulin to stimulate glucose metabolism in skeletal muscle is a classic characteristic of type 2 diabetes, but this insulin resistance entails altered patterns of lipid metabolism as well. An association between intracellular triglyceride and insulin resistance has been well established in both human and animal studies of obesity-related insulin resistance and type 2 diabetes. Skeletal muscle's ability to select substrate for fuel metabolism, a metabolic flexibility, is also lost in insulin resistance, and defects in fatty acid metabolism during fasting or postabsorptive conditions likely play an important role in lipid oversupply to insulin-resistant muscle. These impairments appear to be at least indirectly centered on the ability of mitochondria to oxidize fatty acids, possibly through mediation of lipid metabolite levels such as ceramide or diacylglycerol, which are known to directly attenuate insulin signaling. Moreover, periodic use of muscle triglyceride by exercise may mediate the association between muscle triglyceride and insulin resistance. Thus, it appears that skeletal muscle triglyceride is perhaps a surrogate for other lipid species having a more direct effect on insulin action. Defining mechanisms by which dysregulation of fatty acid metabolism and persistent lipid oversupply alter insulin action may help to target more effective strategies to prevent or treat type 2 diabetes.

Effect of pioglitazone on abdominal fat distribution and insulin sensitivity in type 2 diabetic patients

We examined the effect of pioglitazone on abdominal fat distribution to elucidate the mechanisms via which pioglitazone improves insulin resistance in patients with type 2 diabetes mellitus. Thirteen type 2 diabetic patients (nine men and four women; age, 52 +/- 3 yr; body mass index, 29.0 +/- 1.1 kg/m(2)), who were being treated with a stable dose of sulfonylurea (n = 7) or with diet alone (n = 6), received pioglitazone (45 mg/d) for 16 wk. Before and after pioglitazone treatment, subjects underwent a 75-g oral glucose tolerance test (OGTT) and two-step euglycemic insulin clamp (insulin infusion rates, 40 and 160 mU/m(2).min) with [(3)H]glucose. Abdominal fat distribution was evaluated using magnetic resonance imaging at L4-5. After 16 wk of pioglitazone treatment, fasting plasma glucose (179 +/- 10 to 140 +/- 10 mg/dl; P < 0.01), mean plasma glucose during OGTT (295 +/- 13 to 233 +/- 14 mg/dl; P < 0.01), and hemoglobin A(1c) (8.6 +/- 0.4% to 7.2 +/- 0.5%; P < 0.01) decreased without a change in fasting or post-OGTT insulin levels. Fasting plasma FFA (674 +/- 38 to 569 +/- 31 microEq/liter; P < 0.05) and mean plasma FFA (539 +/- 20 to 396 +/- 29 microEq/liter; P < 0.01) during OGTT decreased after pioglitazone. In the postabsorptive state, hepatic insulin resistance [basal endogenous glucose production (EGP) x basal plasma insulin concentration] decreased from 41 +/- 7 to 25 +/- 3 mg/kg fat-free mass (FFM).min x microU/ml; P < 0.05) and suppression of EGP during the first insulin clamp step (1.1 +/- 0.1 to 0.6 +/- 0.2 mg/kg FFM.min; P < 0.05) improved after pioglitazone treatment. The total body glucose MCR during the first and second insulin clamp steps increased after pioglitazone treatment [first MCR, 3.5 +/- 0.5 to 4.4 +/- 0.4 ml/kg FFM.min (P < 0.05); second MCR, 8.7 +/- 1.0 to 11.3 +/- 1.1 ml/kg FFM(.)min (P < 0.01)]. The improvement in hepatic and peripheral tissue insulin sensitivity occurred despite increases in body weight (82 +/- 4 to 85 +/- 4 kg; P < 0.05) and fat mass (27 +/- 2 to 30 +/- 3 kg; P < 0.05). After pioglitazone treatment, sc fat area at L4-5 (301 +/- 44 to 342 +/- 44 cm(2); P < 0.01) increased, whereas visceral fat area at L4-5 (144 +/- 13 to 131 +/- 16 cm(2); P < 0.05) and the ratio of visceral to sc fat (0.59 +/- 0.08 to 0.44 +/- 0.06; P < 0.01) decreased. In the postabsorptive state hepatic insulin resistance (basal EGP x basal immunoreactive insulin) correlated positively with visceral fat area (r = 0.55; P < 0.01). The glucose MCRs during the first (r = -0.45; P < 0.05) and second (r = -0.44; P < 0.05) insulin clamp steps were negatively correlated with the visceral fat area. These results demonstrate that a shift of fat distribution from visceral to sc adipose depots after pioglitazone treatment is associated with improvements in hepatic and peripheral tissue sensitivity to insulin.

Upper abdominal obesity, insulin resistance and breast cancer risk

PURPOSE

A majority of prospective studies show breast cancer risk to be higher in obese postmenopausal women with upper abdominal adiposity than in those with overall adiposity. The evidence is more limited and inconsistent in the case of premenopausal women. The review examines evidence that aberrant insulin signalling may be involved in the promotion of mammary carcinogenesis. The aetiology and concomitants of abdominal visceral obesity are examined.

MECHANISMS

Clinical and experimental evidence suggests that the higher breast cancer risk associated with greater abdominal visceral obesity may be related to aberrant insulin signalling through the insulin receptor substrate 1 pathway, leading to insulin resistance, hyperinsulinaemia and increased concentrations of endogenous oestrogen and androgen. The putative role of aberrant insulin signalling in the promotion of mammary carcinogenesis may help to explain clinical relationships between breast cancer risk and age at menarche, pregnancies and onset of obesity.

CONCLUSION

Overall adiposity in women adversely affects breast cancer risk mainly by greater exposure of mammary epithelial tissue to endogenous oestrogen. Upper abdominal adiposity appears to involve an additional effect related to the presence of insulin resistance. Aetiological factors in the development of hyperinsulinaemic insulin resistance are still uncertain but may involve aberrant susceptibility genes in adipocyte insulin receptors or in the insulin receptor substrate 1 pathway. Epigenetic factors are also likely to contribute, including high free fatty acid levels and obesity. Dietary fatty acids, particularly polyunsaturated fatty acids, are known to regulate adipocyte differentiation through the nuclear peroxisome proliferator-activated receptor gamma, and may also have a role in insulin resistance. These aetiological factors are likely to be relevant to the high risk of postmenopausal breast cancer in industrialised Western populations.

Contributions of total and regional fat mass to risk for cardiovascular disease in older women

The aim of this study was to determine whether trunk fat mass, measured by dual-energy X-ray absorptiometry (DEXA), is predictive of insulin resistance and dyslipidemia, independently of arm and leg fat mass, in postmenopausal women. Total and regional body composition was measured by DEXA in 166 healthy, postmenopausal women (66 +/- 4 yr). Four primary markers of insulin resistance and dyslipidemia were assessed: 1) area under the curve for the insulin (INS(AUC)) response to an oral glucose tolerance test (OGTT), 2) product of the OGTT glucose and insulin areas (INS(AUC)xGLU(AUC)), 3) serum triglycerides (TG), and 4) high-density lipoprotein (HDL)-cholesterol. Trunk fat mass was the strongest independent predictor of each of the primary dependent variables. In multivariate regression models, trunk fat mass was associated with unfavorable levels of INS(AUC), INS(AUC)xGLU(AUC), TG, and HDL-C, whereas leg fat mass was favorably associated with each of these variables. Thus trunk fat is a strong independent predictor of insulin resistance and dyslipidemia in postmenopausal women, whereas leg fat appears to confer protective effects against metabolic dysfunction.

Effects of free fatty acids on insulin secretion in obesity

The prevalence of obesity in Western society has reached epidemic proportions and its aetiological role in the development of type 2 diabetes has made finding an effective treatment for the condition of crucial importance. Of the many consequences of obesity, derangements in glucose metabolism present one of the greatest problems to health. While the role of obesity in causing insulin resistance has received much attention, the effect of obesity on beta-cell failure and the consequent development of type 2 diabetes requires re-emphasis. In this review, the current understanding of the effects of elevated free-fatty acids on beta-cell function will be examined, including a discussion of potential mechanisms. In particular, dysregulation of biochemical pathways and alterations in key enzymes, proteins and hormones will be considered as grounds for the progression to a diabetic phenotype.

Body-image perceptions among urban Native American youth

OBJECTIVE

This study investigated body-image perceptions among Native American youth.

RESEARCH METHODS AND PROCEDURES

A modified and validated body-image measure for use with Native American youth was utilized in a cross-sectional assessment of 155 urban Native American youth attending an after-school program in Minneapolis, Minnesota. The youth (ages 5 to 18 years) expressed their perceptions of current and ideal body image, which allowed assessment of satisfaction or dissatisfaction. Body sizes perceived as healthy or most likely to develop diabetes were also communicated. Heights and weights were measured, and body mass index was calculated.

RESULTS

When asked to identify their ideal body figure, younger children selected thinner figures than adolescents, and overweight youth chose ideal figures similar to those of normal-weight youth. The mean body dissatisfaction of the youth was +/-0.99 and +/-1.49 body figures for boys and girls, respectively. Examination of the direction of body dissatisfaction revealed that 41% of the boys and 61% of the girls expressed a desire to be thinner. Those expressing the greatest dissatisfaction were overweight girls (>95th percentile). On a scale from one to eight, the median of the body image viewed as the healthiest was 4.0, whereas that most likely to develop diabetes was 8.0.

DISCUSSION

These results suggest that urban Native American youth are dissatisfied with their body size and that most acknowledge the diabetes risk associated with overweight, which implies that they may be receptive to obesity prevention measures.

A review of the literature of Bardet-Biedl disease and report of three cases associated with metabolic syndrome and diagnosed after the age of fifty

Bardet-Biedl syndrome (BBS) is a genetic autosomal-recessive disease (formerly grouped with Laurence-Moon-Biedl syndrome but considered today as a separate entity) characterized by abdominal obesity, mental retardation, dysphormic extremities (syndactyly, brachydactyly or polydactyly), retinal dystrophy or pigmentary retinopathy, hypogonadism or hypogenitalism (limited to male patients) and kidney structural abnormalities or functional impairment. The expression and severity of the various clinical BBS features show inter- and intrafamilial variability. This study focuses on three cases of familial BBS--two sisters and one brother (66, 64 and 51 years of age, respectively)--with the main cardinal findings of the disease plus a classic 'metabolic syndrome' (characterized by abdominal obesity, atherogenic dyslipidaemia, raised blood pressure, insulin resistance with or without glucose intolerance, and prothrombotic risk and proinflammatory states). One female patient (not affected by reproductive dysfunction) had three healthy offspring, while the other two patients were unmarried. Another severely affected brother died at 70 years of age; two other brothers are lean but affected by nephropathy, retinopathy, slight mental retardation, polydactyly, hypertension and thrombotic diseases, and had healthy offspring. BBS is a rather rare but severe syndrome that is often mis- or undiagnosed. Ophthalmologists, endocrinologists and nephrologists should be aware of BBS because of its adverse prognosis--early onset of blindness, associated findings of metabolic syndrome and increased vascular risk, and severe renal impairment (the most frequent cause of reduced survival and death early in life).

Calpain 3 gene expression in skeletal muscle is associated with body fat content and measures of insulin resistance

OBJECTIVE

To investigate whether skeletal muscle gene expression of calpain 3 is related to obesity and insulin resistance.

DESIGN

Cross-sectional studies in 27 non-diabetic human subjects and in Psammomys obesus, a polygenic animal model of obesity and type 2 diabetes.

MEASUREMENTS

Expression of CAPN3 in skeletal muscle was measured using Taqman fluorogenic PCR. In the human subjects, body composition was assessed by DEXA and insulin sensitivity was measured by euglycemic-hyperinsulinemic clamp. In Psammomys obesus, body composition was determined by carcass analysis, and substrate oxidation rates, physical activity and energy expenditure were measured by whole-body indirect calorimetry.

RESULTS

In human subjects, calpain 3 gene expression was negatively correlated with total (P = 0.022) and central abdominal fat mass (P = 0.034), and with blood glucose concentration in non-obese subjects (P = 0.017). In Psammomys obesus, calpain 3 gene expression was negatively correlated with circulating glucose (P = 0.013) and insulin (P = 0.034), and with body fat mass (P = 0.049). Indirect calorimetry revealed associations between calpain 3 gene expression and carbohydrate oxidation (P = 0.009) and energy expenditure (P = 0.013).

CONCLUSION/INTERPRETATION

Lower levels of expression of calpain 3 in skeletal muscle were associated with reduced carbohydrate oxidation and elevated circulating glucose and insulin concentrations, and also with increased body fat and in particular abdominal fat. Therefore, reduced expression of calpain 3 in both humans and Psammomys obesus was associated with phenotypes related to obesity and insulin resistance.

Regional intra-subject variability in abdominal adiposity limits usefulness of computed tomography

OBJECTIVE

Computed tomography (CT) and magnetic resonance imaging, the most accurate methods of abdominal fat measurement, have been applied using a number of protocols, ranging from single-slice area determination to multiple-slice volume calculation. The aim of this study was to assess the validity of single-slice CT for abdominal fat area measurement by estimating the intra-subject variability in abdominal fat areas and comparing the ranking of subjects across four contiguous abdominal levels.

RESEARCH METHODS AND PROCEDURES

Nineteen premenopausal women (age, 35.3 +/- 1.4 years; mean +/- SE) were studied. CT was used to measure intra-abdominal fat (IAF) area, percentage of total intra-abdominal area (%IAF), subcutaneous abdominal fat (SAF) area, and IAF/SAF at four adjacent cross-sectional lumbar levels (L2-L4). Intra-subject variability (percentage) was defined as SD/mean x 100. Total body fat was measured by DXA, which was further analyzed for central abdominal fat.

RESULTS

Mean body mass index was 24.9 +/- 1.0 kg/m(2). The average (range) intra-subject variability was 28% (8% to 61%) for IAF, 46% (19% to 124%) for %IAF, 26% (14% to 38%) for SAF area, and 19% (7% to 71%) for IAF/SAF. The pattern of this variability was not uniform between subjects, because their ranking by IAF area was markedly different at each CT level.

DISCUSSION

We demonstrated significant intra-subject variability in CT-measured adipose tissue areas across four predetermined sites. This resulted in a difference in the ordering of subjects by IAF at each of the four imaging sites, suggesting that the usefulness of single-slice CT in the assessment of abdominal adiposity in premenopausal women may be limited, particularly when performed for the purpose of making comparisons between subjects based on abdominal fat area.

The concurrent accumulation of intra-abdominal and subcutaneous fat explains the association between insulin resistance and plasma leptin concentrations : distinct metabolic effects of two fat compartments

Obesity is associated with insulin resistance, particularly when body fat has a central distribution. However, insulin resistance also frequently occurs in apparently lean individuals. It has been proposed that these lean insulin-resistant individuals have greater amounts of body fat than lean insulin-sensitive subjects. Alternatively, their body fat distribution may be different. Obesity is associated with elevated plasma leptin levels, but some studies have suggested that insulin sensitivity is an additional determinant of circulating leptin concentrations. To examine how body fat distribution contributes to insulin sensitivity and how these variables are related to leptin levels, we studied 174 individuals (73 men, 101 women), a priori classified as lean insulin-sensitive (LIS, n = 56), lean insulin-resistant (LIR, n = 61), and obese insulin-resistant (OIR, n = 57) based on their BMI and insulin sensitivity index (S(I)). Whereas the BMI of the two lean groups did not differ, the S(I) of the LIR subjects was less than half that of the LIS group. The subcutaneous and intra-abdominal fat areas, determined by computed tomography, were 45 and 70% greater in the LIR subjects (P < 0.001) and 2.5- and 3-fold greater in the OIR group, as compared with the LIS group. Fasting plasma leptin levels were moderately increased in LIR subjects (10.8 +/- 7.1 vs. 8.1 +/- 6.4 ng/ml in LIS subjects; P < 0.001) and doubled in OIR subjects (21.9 +/- 15.5 ng/ml; P < 0.001). Because of the confounding effect of body fat, we examined the relationships between adiposity, insulin sensitivity, and leptin concentrations by multiple regression analysis. Intra-abdominal fat was the best variable predicting insulin sensitivity in both genders and explained 54% of the variance in S(I). This inverse relationship was nonlinear (r = -0.688). On the other hand, in both genders, fasting leptin levels were strongly associated with subcutaneous fat area (r = 0.760) but not with intra-abdominal fat. In line with these analyses, when LIS and LIR subjects were matched for subcutaneous fat area, age, and gender, they had similar leptin levels, whereas their intra-abdominal fat and insulin sensitivity remained different. Thus, accumulation of intra-abdominal fat correlates with insulin resistance, whereas subcutaneous fat deposition correlates with circulating leptin levels. We conclude that the concurrent increase in these two metabolically distinct fat compartments is a major explanation for the association between insulin resistance and elevated circulating leptin concentrations in lean and obese subjects.

Lipid infusion impairs physiologic insulin-mediated capillary recruitment and muscle glucose uptake in vivo

Infusion of triglycerides and heparin causes insulin resistance in muscle. Because the vascular actions of insulin, particularly capillary recruitment, may contribute to the increase in glucose uptake by skeletal muscle, we investigated the effects of Intralipid/heparin infusion on the hemodynamic actions of insulin during clamp conditions. Saline or 10% Intralipid/heparin (33 U/ml) was infused into anesthetized rats at 20 microl/min for 6 h. At 4 h into the saline infusion, a 2-h hyperinsulinemic (3 mU. min(-1).kg(-1))-euglycemic clamp was conducted (Ins group). At 4 h into the lipid infusion, a 2-h saline control (Lip group) or 2-h hyperinsulinemic-euglycemic clamp (Lip + Ins group) was conducted. Arterial blood pressure, heart rate, femoral blood flow (FBF), hindleg vascular resistance, glucose infusion rate (GIR), hindleg glucose uptake (HGU), and muscle 2-deoxyglucose uptake (R'g) were measured. Capillary recruitment, as measured by metabolism of infused 1-methylxanthine (1-MX), was also assessed. When compared with either Lip or Lip + Ins, Ins had no effect on arterial blood pressure, heart rate, FBF, or vascular resistance but increased GIR, HGU, and R'g of soleus, plantaris, extensor digitorum longus, and gastrocnemius red muscles and hindlimb 1-MX metabolism. GIR, HGU, and R'g of soleus, plantaris, gastrocnemius red, and the combined muscles and 1-MX metabolism were less in Lip + Ins than in Ins rats. HGU correlated closely with hindleg capillary recruitment (r = 0.86, P < 0.001) but not total hindleg blood flow. In conclusion, acute elevation of plasma free fatty acids blocks insulin-mediated glucose uptake and capillary recruitment.

Adiposity, insulin and lipid metabolism in post-menopausal women

OBJECTIVE

To investigate relationships between body fat and its distribution and carbohydrate and lipid tolerance using statistical comparisons in post-menopausal women.

DESIGN

Sequential meal, postprandial study (600 min) which included a mixed standard breakfast (30 g fat) and lunch (44 g fat) given at 0 and 270 min, respectively, after an overnight fast.

SUBJECTS

Twenty-eight post-menopausal women with a diverse range of body weight (body mass index (BMI), mean 27.2, range 20.5-38.8 kg/m2) and abdominal fat deposition (waist, mean 86.4, range 63.5-124.0 cm). Women with BMI < 18 or > 37 kg/m2, age > 80 y and taking hormone replacement therapy (HRT) were excluded.

MEASUREMENTS

Anthropometric measurements were performed to assess total and regional fat deposits. The concentrations of plasma total cholesterol, high density lipoprotein (HDL) cholesterol, triacylglycerol (TAG), glucose, insulin (ins), non-esterified fatty acids (NEFA) and apolipoprotein (apo) B-48 were analysed in plasma collected at baseline (fasted state) and at 13 postprandial time points for a 600 min period.

RESULTS

Insulin concentrations in the fasted and fed state were significantly correlated with all measures of adiposity (BMI, waist, waist-hip ratio (W/H), waist-height ratio (W/Ht) and sum of skinfold thickness (SSk)). After controlling for BMI, waist remained significantly and positively associated with fasted insulin (r=0.559) with waist contributing 53% to the variability after multiple regression analysis. After controlling for waist, BMI remained significantly correlated with postprandial (IAUC) insulin (r=0.535) contributing 66% of the variability of this measurement. No association was found between any measures of adiposity and glucose concentrations, although insulin concentration in relation to glucose concentration (glucose-insulin ratio) was significantly negatively correlated with all measures of adiposity. A significant positive correlation was found between fasted TAG and BMI (r=0.416), waist (r=0.393) and Ssk (r=0.457) and postprandial (AUC) TAG with BMI (r=0.385) and Ssk (r=0.406). A significantly higher postprandial apolipoprotein (apo) B-48 response was observed in those women with high BMI (> 27 kg/m2). Fasting levels of NEFA were significantly and positively correlated with all measures of adiposity (except W/H). No association was found between cholesterol containing particles and any measure of adiposity.

CONCLUSION

Hyperinsulinaemia associated with increasing body fat and central fat distribution is associated with normal glucose but not TAG or NEFA concentrations in postmenopausal women.

Effect of 6-week course of glucagon-like peptide 1 on glycaemic control, insulin sensitivity, and beta-cell function in type 2 diabetes: a parallel-group study

BACKGROUND

Glucagon-like peptide 1 (GLP-1) has been proposed as a treatment for type 2 diabetes. We have investigated the long-term effects of continuous administration of this peptide hormone in a 6-week pilot study.

METHODS

20 patients with type 2 diabetes were alternately assigned continuous subcutaneous infusion of GLP-1 (n=10) or saline (n=10) for 6 weeks. Before (week 0) and at weeks 1 and 6, they underwent beta-cell function tests (hyperglycaemic clamps), 8 h profiles of plasma glucose, insulin, C-peptide, glucagon, and free fatty acids, and appetite and side-effect ratings on 100 mm visual analogue scales; at weeks 0 and 6 they also underwent dexascanning, measurement of insulin sensitivity (hyperinsulinaemic euglycaemic clamps), haemoglobin A(1c), and fructosamine. The primary endpoints were haemoglobin A(1c) concentration, 8-h profile of glucose concentration in plasma, and beta-cell function (defined as the first-phase response to glucose and the maximum insulin secretory capacity of the cell). Analyses were per protocol.

FINDINGS

One patient assigned saline was excluded because no veins were accessible. In the remaining nine patients in that group, no significant changes were observed except an increase in fructosamine concentration (p=0.0004). In the GLP-1 group, fasting and 8 h mean plasma glucose decreased by 4.3 mmol/L and 5.5 mmol/L (p<0.0001). Haemoglobin A(1c) decreased by 1.3% (p=0.003) and fructosamine fell to normal values (p=0.0002). Fasting and 8 h mean concentrations of free fatty acids decreased by 30% and 23% (p=0.0005 and 0.01, respectively). Gastric emptying was inhibited, bodyweight decreased by 1.9 kg, and appetite was reduced. Both insulin sensitivity and beta-cell function improved (p=0.003 and p=0.003, respectively). No important side-effects were seen.

INTERPRETATION

GLP-1 could be a new treatment for type 2 diabetes, though further investigation of the long-term effects of GLP-1 is needed.

Minor long-term changes in weight have beneficial effects on insulin sensitivity and beta-cell function in obese subjects

AIM

To evaluate the long-term effect of changes in body composition induced by weight loss on insulin sensitivity (SI), non-insulin mediated glucose disposal, glucose effectiveness (SG)and beta-cell function.

DESIGN

Glucose metabolism was evaluated before and after participation in a two-year weight loss trial of Orlistat vs. placebo, combined with an energy and fat restricted diet.

SUBJECTS

Twelve obese patients (11 women, 1 man), age 45.8 +/- 10.5 years, body weight (BW) 99.7 +/- 13.3 kg, BMI 35.3 +/- 2.8 kg/m(2).

MEASUREMENTS

At inclusion and 2 years later an oral glucose tolerance test (OGTT) and a frequently sampled intravenous glucose tolerance test (FSIGT) were performed. Body composition was estimated by a dual-energy X-ray absorptiometry (DXA) whole body scanning.

RESULTS

The patients obtained varying changes in BW ranging from a weight loss of 17.8 kg to a weight gain of 6.0 kg. Corresponding changes in fat mass (FM) varied from a 40% reduction to a19% increase. A significant decrease in both fasting (p = 0.038) and 2 h (p = 0.047) blood glucose at OGTT was found. The improvement in insulin sensitivity (SI) estimated by means of Bergmans Minimal Model, was significantly and linearly correlated to change in total FM (r = - 0.83,p = 0.0026). A multiple regression analysis showed that changes in truncal FM was the strongest predictor of change in S(I) explaining 67% of the variation. First phase insulin response (AIRg)remained unchanged whereas insulin disposition index increased significantly (p = 0.044). At inclusion five patients had impaired glucose tolerance of which four, who lost weight, were normalized at the retest 2 years later.

CONCLUSION

In obese subjects long-term minimal or moderate changes in weight were found to be linearly associated with changes in insulin sensitivity. In obese subjects with impaired glucose tolerance even a minor weight loss was able to normalize glucose tolerance.

Abdominal fat and birth size in healthy prepubertal children

BACKGROUND

Studies examining the foetal origins hypothesis suggest that small birth size may be a marker of foetal adaptations that programme future propensity to adult disease. We explore the hypothesis that birth size may relate to fat distribution in childhood and that fat distribution may be a link between birth size and adult disease.

OBJECTIVE

To investigate the relationship between birth size and abdominal fat, blood pressure, lipids, insulin and insulin:glucose ratio in prepubertal children.

DESIGN

Cross-sectional study, based on a birth cohort of consecutive full-term births.

SUBJECTS

Two hundred and fifty-five (137 females) healthy, 7- and 8-y-old children.

MEASUREMENTS

Body composition and abdominal fat was measured by dual energy X-ray absorptiometry. Lipid, glucose and insulin profiles were measured after an overnight fast and an automated BP monitor was used for blood pressure measurements.

RESULTS

There was a negative association between abdominal fat and birth weight s.d. score across a range of normal birth weights (beta=-0.18; 95% CI=-0.31 to -0.04, P=0.009) and a positive association with weight s.d. score at 7/8 y (beta=0.35; 95% CI=0.24 to 0.46, P<0.001). Children who were born with the lowest weight s.d. score and had the greatest weight s.d. score at 7/8 y had significantly more (P<0.001) abdominal fat, as a percentage of total fat (6.53+/-1.3%) than those who had the highest birth weight s.d. score and the lowest weight s.d. score at 7/8 y (4.14+/-0.5%). Similar results were seen if head circumference, but not ponderal index, was used as an indicator of birth size. Increased abdominal fat was associated with higher total cholesterol:HDL cholesterol, higher triglyceride concentration and increased diastolic blood pressure.

CONCLUSIONS

Birth weight independently predicted abdominal fat. Children with the highest amount of abdominal fat were those who tended to be born lighter and gained weight centiles. Increased abdominal fat was associated with precursor risk factors for ischaemic heart disease.

Short-term moderate weight loss and resistance training do not affect insulin-stimulated glucose disposal in postmenopausal women

OBJECTIVES

Moderate weight loss and exercise have been proposed as important tools in the treatment and prevention of type 2 diabetes. Therefore, we tested the hypothesis that short-term (4 weeks) moderate energy restriction (-750 kcal/day) would result in a significant increase in insulin-stimulated glucose disposal (40 mU x m(-2) x min(-1) hyperinsulinemic-euglycemic clamp) in moderately overweight postmenopausal women and that when combined with resistance training (RT) an even greater effect would be seen.

RESEARCH DESIGN AND METHODS

Older women were randomly assigned to energy restriction (WLoss group; n = 9) or energy restriction plus RT (RT + WLoss group; n = 10).

RESULTS

For the WLoss versus the RT + WLoss groups, changes in body weight (-3.0 +/- 0.2 kg vs. -3.2 +/- 0.3 kg), fat mass (FM) (-3.0 +/- 0.3 kg vs. -3.2 +/- 0.3 kg), and percent body fat (BF) (-2.1 +/- 0.4 vs. -2.4 +/- 0.3%) were not different between groups. Muscle mass (group-by-time interaction, P = 0.04) was preserved in RT + WLoss (0.40 +/- 0.40 kg) and reduced in WLoss (-0.64 +/- 0.18 kg). There were no changes in fat-free mass (FFM) and waist-to-hip ratio in either group. Whole body glucose disposal (WLoss 6.14 +/- 0.57 vs. 6.03 +/- 0.53, RT + WLoss 5.85 +/- 0.60 vs. 6.09 +/- 0.56 mg/kg of FFM/min) did not change in either group.

CONCLUSIONS

The results of this study demonstrate that short-term energy restriction resulting in moderate decreases in body weight (4.0 +/- 0.3%) and FM (8.2 +/- 0.7%) did not improve insulin-stimulated glucose disposal. The addition of RT to the hypoenergetic diet preserved muscle mass but provided no synergistic effect on insulin action. These results suggest that a greater change in body weight or FM may be necessary to observe a significant improvement in insulin action.

A role for protein phosphatase 2A-like activity, but not atypical protein kinase Czeta, in the inhibition of protein kinase B/Akt and glycogen synthesis by palmitate

We have shown previously that palmitate treatment of C2C12 skeletal muscle myotubes causes inhibition of the protein kinase B (PKB) pathway and hence reduces insulin-stimulated glycogen synthesis through the elevation of intracellular ceramide levels. Ceramide is known to activate both atypical protein kinase C (aPKC) zeta and protein phosphatase (PP) 2A, and each of these effectors has been reported to inhibit PKB. In the present study, palmitate pretreatment was found to elevate PP2A-like activity in myotubes and to prevent its inhibition by insulin. Incubation with the phosphatase inhibitor okadaic acid before insulin stimulation protected against the effect of the fatty acid on PKB phosphorylation. Palmitate was unable to inhibit PKB activity and glycogen synthesis in cells overexpressing the activated PKB mutant (T308D,S473D)-PKBalpha, which is unaffected by phosphatase. In contrast, PKB activity and glycogen synthesis were still inhibited by palmitate in cells overexpressing a membrane-targeted and, hence, activated PKB mutant that retains sensitivity to phosphatase. Although aPKC activity was also increased in palmitate-treated cells, overexpression of wild-type or kinase-dead aPKCzeta did not alter the inhibitory effects of the lipid on either stimulation of PKB or glycogen synthesis by insulin. We conclude that palmitate disrupts insulin signaling in C2C12 myotubes by promoting PP2A-like activity and, therefore, the dephosphorylation of PKB, which in turn reduces the stimulation of glycogen synthesis.

Independent influences of central fat and skeletal muscle lipids on insulin sensitivity

OBJECTIVE

Insulin resistance is closely associated with two disparate aspects of lipid storage: the intracellular lipid content of skeletal muscle and the magnitude of central adipose beds. Our aim was to determine their relative contribution to impaired insulin action.

RESEARCH METHODS AND PROCEDURES

Eighteen older (56 to 75 years of age) men were studied before elective knee surgery. Insulin sensitivity (M/Delta I) was determined by hyperinsulinemic-euglycemic clamp. Central abdominal fat (CF) was assessed by DXA. Skeletal muscle was excised at surgery and assayed for content of metabolically active long-chain acyl-CoA esters (LCAC).

RESULTS

Significant inverse relationships were observed between LCAC and M/Delta I (R(2) = 0.34, p = 0.01) and between CF and M/Delta I (R(2) = 0.38, p = 0.006), but not between CF and LCAC (R(2) = 0.0005, p = 0.93). In a multiple regression model (R(2) = 0.71, p < 0.0001), both CF (p = 0.0006) and LCAC (p = 0.0009) were independent statistical predictors of M/Delta I. Leptin levels correlated inversely with M/Delta I (R(2) = 0.60, p = 0.0002) and positively with central (R(2) = 0.41, p = 0.006) and total body fat (R(2) = 0.63, p = 0.0001).

DISCUSSION

The mechanisms by which altered lipid metabolism in skeletal muscle influences insulin action may not be related directly to those linking central fat and insulin sensitivity. In particular, it is unlikely that muscle accumulation of lipids directly derived from labile central fat depots is a principal contributor to peripheral insulin resistance. Instead, our results imply that circulating factors, other than nonesterified fatty acids or triglyceride, mediate between central fat depots and skeletal muscle tissue. Leptin was not exclusively associated with central fat, but other factors, secreted specifically from central fat cells, could modulate muscle insulin sensitivity.

Effects of clenbuterol on insulin resistance in conscious obese Zucker rats

The present study was conducted to determine the effect of chronic administration of the long-acting beta(2)-adrenergic agonist clenbuterol on rats that are genetically prone to insulin resistance and impaired glucose tolerance. Obese Zucker rats (fa/fa) were given 1 mg/kg of clenbuterol by oral intubation daily for 5 wk. Controls received an equivalent volume of water according to the same schedule. At the end of the treatment, rats were catheterized for euglycemic-hyperinsulinemic (15 mU insulin. kg(-1). min(-1)) clamping. Clenbuterol did not change body weight compared with the control group but caused a redistribution of body weight: leg muscle weights increased, and abdominal fat weight decreased. The glucose infusion rate needed to maintain euglycemia and the rate of glucose disappearance were greater in the clenbuterol-treated rats. Furthermore, plasma insulin levels were decreased, and the rate of glucose uptake into hindlimb muscles and abdominal fat was increased in the clenbuterol-treated rats. This increased rate of glucose uptake was accompanied by a parallel increase in the rate of glycogen synthesis. The increase in muscle glucose uptake could not be ascribed to an increase in the glucose transport protein GLUT-4 in clenbuterol-treated rats. We conclude that chronic clenbuterol treatment reduces the insulin resistance of the obese Zucker rat by increasing insulin-stimulated muscle and adipose tissue glucose uptake. The improvements noted may be related to the repartitioning of body weight between tissues.

Peroxisome proliferator-activated receptor (PPAR)-alpha activation lowers muscle lipids and improves insulin sensitivity in high fat-fed rats: comparison with PPAR-gamma activation

Peroxisome proliferator-activated receptor (PPAR)-alpha agonists lower circulating lipids, but the consequences for muscle lipid metabolism and insulin sensitivity are not clear. We investigated whether PPAR-alpha activation improves insulin sensitivity in insulin-resistant rats and compared the effects with PPAR-gamma activation. Three-week high fat-fed male Wistar rats were untreated or treated with the specific PPAR-alpha agonist WY14643 or the PPAR-gamma agonist pioglitazone (both 3 mg x kg(-1) x day(-1)) for the last 2 weeks of high-fat feeding. Like pioglitazone, WY14643 lowered basal plasma levels of glucose, triglycerides (-16% vs. untreated), and leptin (-52%), and also muscle triglyceride (-34%) and total long-chain acyl-CoAs (LCACoAs) (-41%) (P < 0.05). In contrast to pioglitazone, WY14643 substantially reduced visceral fat weight and total liver triglyceride content (P < 0.01) without increasing body weight gain. WY14643 and pioglitazone similarly enhanced whole-body insulin sensitivity (clamp glucose infusion rate increased 35 and 37% and glucose disposal 22 and 15%, respectively, vs. untreated). Both agents enhanced insulin-mediated muscle glucose metabolic index (Rg') and reduced muscle triglyceride and LCACoA accumulation (P < 0.05). Although pioglitazone had more potent effects than WY14643 on muscle insulin sensitization, this was associated with its greater effect to reduce muscle LCACoA accumulation. Overall insulin-mediated muscle Rg' was inversely correlated with the content of LCACoAs (r = -0.74, P = 0.001) and with plasma triglyceride levels (r = -0.77, P < 0.001). We conclude that even though WY14643 and pioglitazone, representing PPAR-alpha and PPAR-gamma activation, respectively, may alter muscle lipid supply by different mechanisms, both significantly improve muscle insulin action in the high fat-fed rat model of insulin resistance, and this effect is proportional to the degree to which they reduce muscle lipid accumulation.

Relationships of age, menopause and central obesity on cardiovascular disease risk factors in Chinese women

OBJECTIVE

To evaluate the inter-relationships of age- and menopause- related changes of general obesity and body fat distribution and their independent effects on cardiovascular risk factors.

DESIGN

Cross-sectional study.

SUBJECTS

One-hundred and thirty-six premenopausal and 193 postmenopausal Chinese women with body mass index (BMI) < 30 kg/m2.

MEASUREMENTS

Anthropometric surrogates of general obesity (BMI, total body fat percentage) and central obesity (waist-to-hip ratio, centrality index) were measured. Blood pressure, 75 g oral glucose tolerance test, glycosylated hemoglobin A1c and lipid profiles were also measured.

RESULTS

Significant correlation coefficients between age, general obesity, central obesity and cardiovascular disease risk factors were noted. Through the menopausal transition, the BMI and total body fat percentage were increased significantly. After adjustments for age and BMI, the postmenopausal women showed higher android fat percentage, centrality index, glycosylated hemoglobin A1c, serum concentrations of total cholesterol, low-density lipoprotein (LDL) cholesterol and atherogenic indices than the premenopausal women. In multiple stepwise regression models, age exerted independent effects on oral glucose tolerance test 2 h plasma glucose level, systolic and diastolic blood pressure, total cholesterol level, and LDL cholesterol. Menopause was an independent variable in relation to the changes of glycosylated hemoglobin A1c, total and LDL cholesterol levels, triglyceride levels and atherogenic indices. The centrality index was the major independent variable of all the cardiovascular disease risk factors, except total and LDL cholesterol level. However, the variation of total body fat percentage had no independent effect on any cardiovascular disease risk factors.

CONCLUSION

Through the aging and menopausal effects, women will increase total body fat content, favoring the central body fat distribution. Age, menopause and central obesity were all independent and significant factors to the cardiovascular disease risk factors in Chinese women.

Acute reversal of lipid-induced muscle insulin resistance is associated with rapid alteration in PKC-theta localization

Muscle insulin resistance in the chronic high-fat-fed rat is associated with increased membrane translocation and activation of the novel, lipid-responsive, protein kinase C (nPKC) isozymes PKC-theta and -epsilon. Surprisingly, fat-induced insulin resistance can be readily reversed by one high-glucose low-fat meal, but the underlying mechanism is unclear. Here, we have used this model to determine whether changes in the translocation of PKC-theta and -epsilon are associated with the acute reversal of insulin resistance. We measured cytosol and particulate PKC-alpha and nPKC-theta and -epsilon in muscle in control chow-fed Wistar rats (C) and 3-wk high-fat-fed rats with (HF-G) or without (HF-F) a single high-glucose meal. PKC-theta and -epsilon were translocated to the membrane in muscle of insulin-resistant HF-F rats. However, only membrane PKC-theta was reduced to the level of chow-fed controls when insulin resistance was reversed in HF-G rats [% PKC-theta at membrane, 23.0 +/- 4.4% (C); 39.7 +/- 3.4% (HF-F, P < 0.01 vs. C); 22.5 +/- 2.7% (HF-G, P < 0.01 vs. HF-F), by ANOVA]. We conclude that, although muscle localization of both PKC-epsilon and PKC-theta are influenced by chronic dietary lipid oversupply, PKC-epsilon and PKC-theta localization are differentially influenced by acute withdrawal of dietary lipid. These results provide further support for an association between PKC-theta muscle cellular localization and lipid-induced muscle insulin resistance and stress the labile nature of high-fat diet-induced insulin resistance in the rat.

Fat redistribution in indinavir-treated patients with HIV infection: A review of postmarketing cases

CONTEXT

Fat redistribution (FR) occurring alone or in association with hyperlipidemia has been associated with protease inhibitors (PI) and nucleoside reverse transcriptase inhibitors (NRTIs); however, the relationship between FR features, relationship of FR to hyperlipidemia, and pathogenesis of FR is unknown.

OBJECTIVE

To characterize the spectrum of FR, assess relationships among FR features, determine trends in occurrence of FR, and determine relationship of FR to hyperlipidemia.

DESIGN

Review of postmarketing indinavir reports of FR in Merck & Co. Inc.'s database.

SETTING AND PARTICIPANTS

282 reports of FR among HIV-positive patients taking indinavir submitted through the passive postmarketing system to Merck through February 23, 1998.

RESULTS

282 FR reports were compared across 3 groups: fat accumulation (FA) only, FA with peripheral wasting (FA with PW), and peripheral wasting only (PWO). Of 282 reports, 56% (159 of 282) had FA only, 22% (63 of 282) had FA with PW, and 21% (60 of 282) had PWO. The proportions of reports of PWO was higher in men, whereas the proportion of reports of FA was higher in women. Blood lipids were provided in 93 of 282 reports; were elevated in 69 of 93, and were normal in 24 of 93 reports. Proportions of hyperlipidemia and hypertriglyceridemia reports were significantly higher in the PWO group versus FA only group (p =.024 and.003, respectively) and versus FA with/without PW groups (p =.038 and.005, respectively). Weight gain was more frequently reported in those with FA (100%) or FA with PW (68%), whereas weight loss was usually reported in those with PWO (83%). In all, 98% of patients reporting FR on indinavir for whom a concomitant drug history was available were also taking lamivudine, stavudine, or both. A higher proportion of patients reporting PWO (34 of 60; 56.7%) versus FA (42 of 159; 26.4%) only took both lamivudine and stavudine.

CONCLUSIONS

Differences observed from analysis of cases in clinical features, gender, weight change, concomitant medications, and presence of hyperlipidemia among the three groups of FR cases reported to Merck suggests that PWO may be a distinct entity from other features of FR. The data suggest that certain antiretroviral combinations predispose HIV persons to development of FR.

Evaluation of waist circumference, waist-to-hip ratio, and the conicity index as screening tools for high trunk fat mass, as measured by dual-energy X-ray absorptiometry, in children aged 3-19 y

BACKGROUND

A central fat pattern has adverse health implications in both children and adults. Because adiposity tracks from childhood into adulthood, the ability of simple anthropometric techniques to correctly measure truncal adiposity in childhood needs to be assessed.

OBJECTIVES

We sought to assess the validity of waist circumference, waist-to-hip ratio (WHR), and the conicity index as indicators of trunk fat mass in children and adolescents.

DESIGN

Trunk fat mass (kg) was measured with dual-energy X-ray absorptiometry in 278 girls and 302 boys aged 3-19 y. Receiver operating characteristic (ROC) curves and areas under the curves (AUCs) for the ROCs were calculated to compare the relative abilities of the anthropometric measures to correctly identify children with high trunk fat mass (z score for our study population of > or =1).

RESULTS

The 80th percentile for waist circumference correctly identified 89% of girls and 87% of boys with high trunk fat mass (sensitivity) and 94% of girls and 92% of boys with low trunk fat mass (specificity). Waist circumference performed significantly better as an index of trunk fat mass than did WHR or the conicity index, as shown by the AUCs in girls and boys, respectively: waist circumference AUCs = 0.97 and 0.97, conicity index AUCs = 0.80 and 0.81, and WHR AUCs = 0.73 and 0.71. Our cutoffs for high trunk fat mass and high waist circumference are provided for both sexes for each year of age.

CONCLUSION

Waist circumference provides a simple yet effective measure of truncal adiposity in children and adolescents.

Android obesity at diagnosis and breast carcinoma survival: Evaluation of the effects of anthropometric variables at diagnosis, including body composition and body fat distribution and weight gain during life span,and survival from breast carcinoma

BACKGROUND

Although a large body of research exists concerning pathologic prognostic indicators of the rate of incidence and survival from breast carcinoma, to the authors' knowledge very few studies have examined the effects of anthropometric variables such as height, obesity, weight gain in adulthood, timing of weight gain, and body composition to survival, although these variables are related to the incidence rate.

METHODS

The survival status of 166 patients diagnosed with primary breast carcinoma and followed for at least 10 years was obtained from the Cancer Center's registry, and significant anthropometric and other known prognostic indicators regarding survival after diagnosis were determined by Cox proportional hazards analysis.

RESULTS

Eighty-three of 166 breast carcinoma patients (50%) with up to 10 years of follow-up died of disease. Android body fat distribution, as indicated by a higher suprailiac:thigh ratio, was a statistically significant (P < 0.0001) prognostic indicator for survival after controlling for stage of disease, with a hazards ratio of 2.6 (95% confidence interval [95% CI], 1.63-4.17). Adult weight gain, as indicated specifically by weight at age 30 years, was a statistically significant (P < 0.05) prognostic indicator for survival with a hazards ratio of 1.15 (95% CI, 1.0-1.28). In addition, the authors observed the Quatelet Index, a negatively significant (P < 0.01) prognostic indicator for survival with a hazards ratio of 0.92 (95% CI, 0.87-0.98). Other markers of general obesity such as weight at diagnosis, percent body fat, and body surface area were not significant markers influencing survival. Similarly, height; triceps, biceps; subscapular, suprailiac, abdominal, and thigh skinfolds; waist and hip circumferences; family history; and reproductive and hormonal variables at the time of diagnosis showed no apparent significant relation to survival.

CONCLUSIONS

The results of the current study provide some evidence that android body fat distribution at diagnosis and increased weight at age 30 years increases a woman's risk of dying of breast carcinoma.

Metabolic assessment of female chronic dieters with either normal or low resting energy expenditures

BACKGROUND

Chronic dieting syndrome can have negative physiologic and psychological consequences. Metabolic differences between female chronic dieters with normal and with low resting energy expenditures (REEs) have not been fully examined.

OBJECTIVE

To determine whether differences existed between 2 groups (n = 15/group) of female chronic dieters aged 21-49 y with either normal (>/=100% of predicted) and with low (</=85% of predicted) REEs based on the equation of Mifflin et al.

DESIGN

The sample was a nonrandomized convenience sample and the 2 groups were compared in an observational study design. Body composition, aerobic fitness, physical activity, glucose and insulin responses, leptin and thyroid hormone status, dietary intake, and dietary restraint were measured.

RESULTS

Both groups were similar with respect to age, height, weight, and body mass index. The normal-REE group had a higher lean body mass and insulin response to a test meal, higher thyroxine and reverse triiodothyronine concentrations, and lower dietary restraint. Within both groups, leptin decreased significantly from baseline to 2 h after an oral-glucose-tolerance test. The groups did not differ significantly with respect to dietary intake, aerobic fitness, or physical activity.

CONCLUSIONS

Differences in insulin response were associated with higher ratios of abdominal to gluteal body fat in the normal-REE group. Leptin response appears to be due to normal diurnal variations in leptin production rather than a direct response to food consumption. It appears that a normal REE does not necessarily predict positive metabolic health among chronic dieters.

Subdivisions of subcutaneous abdominal adipose tissue and insulin resistance

Whereas truncal (central) adiposity is strongly associated with the insulin resistant metabolic syndrome, it is uncertain whether this is accounted for principally by visceral adiposity (VAT). Several recent studies find as strong or stronger association between subcutaneous abdominal adiposity (SAT) and insulin resistance. To reexamine the issue of truncal adipose tissue depots, we performed cross-sectional abdominal computed tomography, and we undertook the novel approach of partitioning SAT into the plane superficial to the fascia within subcutaneous adipose tissue (superficial SAT) and that below this fascia (deep SAT), as well as measurement of VAT. Among 47 lean and obese glucose-tolerant men and women, insulin-stimulated glucose utilization, measured by euglycemic clamp, was strongly correlated with both VAT and deep SAT (r = -0.61 and -0.64, respectively; both P < 0.001), but not with superficial SAT (r = -0.29, not significant). Also, VAT and deep SAT followed a highly congruent pattern of associations with glucose and insulin area under the curve (75-g oral glucose tolerance test), mean arterial blood pressure, apoprotein-B, high-density lipoprotein cholesterol, and triglyceride. Superficial SAT had markedly weaker association with all these parameters and instead followed the pattern observed for thigh subcutaneous adiposity. We conclude that there are two functionally distinct compartments of adipose tissue within abdominal subcutaneous fat and that the deep SAT has a strong relation to insulin resistance.

Diabetic dyslipidaemia: current treatment recommendations

Insulin deficiency and hyperglycaemia in type 1 (insulin-dependent) diabetes mellitus produce lipid abnormalities, which can be corrected by appropriate insulin therapy. Diabetic nephropathy, which is the main risk factor for coronary heart disease (CHD) in type 1 diabetes, causes pro-atherosclerotic changes in lipid metabolism. Detection and treatment of elevated cholesterol levels is likely to be of benefit in these patients. Type 2 (noninsulin-dependent) diabetes mellitus is associated with abnormal lipid metabolism, even when glycaemic control is good and nephropathy absent. Elevated triglyceride levels, reduced high density lipoprotein (HDL) cholesterol and a preponderance of small, dense low density lipoprotein (LDL) particles are the key abnormalities that constitute diabetic dyslipidaemia. The prevalence of hypercholesterolaemia is the same as for the nondiabetic population, but the relative risk of CHD is greatly increased at every level of cholesterol. Based on effectiveness, tolerability and clinical trial results, treatment with HMG-CoA reductase inhibitors to lower LDL cholesterol is recommended as primary therapy. These agents are also moderately effective at reducing triglyceride and increasing HDL cholesterol levels. If hypertriglyceridaemia predominates, treatment with fibric acid derivatives is appropriate, although there is currently only limited clinical trial evidence that the risk of CHD will be reduced. In type 1 diabetes, but particularly in type 2 diabetes, lipid disorders are likely to contribute significantly to the increased risk of macrovascular complications. especially CHD. Management of the disordered lipid metabolism should be given a high priority in the clinical care of all patients with diabetes.

Depot-related and thiazolidinedione-responsive expression of uncoupling protein 2 (UCP2) in human adipocytes

OBJECTIVES

Uncoupling protein 2 (UCP2) is a recently described homologue of the uncoupling protein of brown adipocytes (UCP1), which is expressed at high levels in human white adipose tissue. Studies were undertaken (1) to establish whether the expression of UCP2 mRNA varies in a depot-related manner in isolated human adipocytes, (2) to determine whether thiazolidinedione exposure influences the expression of UCP2 mRNA in cultured human pre-adipocytes, and (3) to determine whether human UCP2 is targeted to mitochondria when transfected into mammalian cells.

SUBJECTS

Abdominal subcutaneous and omental adipose tissue biopsies were obtained from adult patients undergoing elective intra-abdominal surgical procedures.

MEASUREMENTS

A competitive reverse transcriptase-polymerase chain reaction (RT-PCR) was used to quantify UCP2 mRNA expression in human omental and subcutaneous adipocytes, and in cultured human preadipocytes differentiated in vitro using the thiazolidinedione, BRL49653. Chinese hamster ovary cells were transfected with a vector expressing human UCP2, and its cellular localization was determined by confocal immunofluorescence microscopy.

RESULTS

Adipocytes isolated from human omentum consistently expressed more UCP2 mRNA than did subcutaneous adipocytes from the same subjects (mean fold difference 2.92+/-0.44 P<0.001, n=11) with no effect of gender or body mass index being seen. BRL49653 treatment of subcutaneously, but not omentally, derived preadipocytes stimulated expression of UCP2 mRNA (5.1+/-1.1 fold). Transfected human UCP2 was detected exclusively in mitochondria of CHO cells.

CONCLUSIONS

Increased expression of UCP2 in human omental adipose tissue relative to subcutaneous adipose tissue is related to the expression levels in adipocytes per se, a finding which may relate to the particular functional attributes of this sub-population of adipocytes. Furthermore, BRL 49653 has site-specific effects of on the expression of UCP2 in human preadipocytes, a finding which may be relevant to the therapeutic effects of such compounds. Finally we present evidence for the mitochondrial localisation of human UCP2.

Fat distribution and health in obesity

Although independent associations of visceral fat with the insulin resistance syndrome were previously reported in obese women, the importance of truncal subcutaneous fat in this syndrome is controversial. The method by which the various fat depots are measured may be the reason for the underlying controversy. In the past five years, we have used various methods to measure visceral versus subcutaneous fat distribution in Caucasian (C) and African-American (AA) women and have related it to insulin sensitivity (SI) and to blood lipids, particularly fasting serum triglyceride levels (TG). Elevated TG levels in obese women were best predicted by an increased amount of visceral fat, whereas the amounts of truncal and peripheral subcutaneous fat did not have an impact on them. These results were confirmed, regardless of the method used to measure the fat depots. Insulin resistance (low SI) in obese women was predicted by both an increase of visceral and of upper-body (truncal) subcutaneous fat. However, measurements of the entire visceral and truncal subcutaneous fat volumes may be needed to confirm this latter association.

Thigh adipose tissue distribution is associated with insulin resistance in obesity and in type 2 diabetes mellitus

BACKGROUND

Adipose tissue (AT) content of the thigh is generally not considered to be associated with insulin resistance (IR), but it is unclear whether the distribution of AT in the thigh is a determinant of IR.

OBJECTIVE

We investigated whether subcompartments of AT within the thigh are determinants of IR.

DESIGN

Midthigh AT, muscle composition, and insulin sensitivity were compared in 11 obese patients with type 2 diabetes mellitus (DM); 40 obese, glucose-tolerant (GT) and 15 lean, GT volunteers; and 38 obese subjects who completed a weight-loss program. Midthigh AT area measured with computed tomography was partitioned into 3 components: subcutaneous AT (SCAT), AT beneath the fascia (SFAT), and AT infiltrating muscle groups (IMAT). Muscle attenuation characteristics were determined.

RESULTS

Obese DM and obese GT subjects had lower insulin sensitivity than lean GT subjects. SCAT was greater in obesity, yet did not correlate with insulin sensitivity. SFAT was approximately 8% of total thigh AT and correlated with insulin sensitivity. IMAT was highest in obese DM, and although it accounted for only approximately 3% of thigh AT, it was a strong correlate of insulin sensitivity. Mean attenuation was highest in lean subjects and was associated with higher insulin sensitivity. Weight loss reduced the amount of thigh AT, the proportion of thigh IMAT, and the amount of low-density thigh muscle.

CONCLUSIONS

SFAT and IMAT are markers of IR in obesity and DM although they are much smaller than SCAT, which does not predict IR. Muscle composition reflecting increased fat content is also associated with IR.

Relation of regional fat distribution to insulin sensitivity in postmenopausal women

OBJECTIVE

To examine the relation between insulin sensitivity and total and regional body fat in nonobese postmenopausal women.

DESIGN

Cross-sectional study.

SETTING

A clinical research center.

PATIENT(S)

Twenty-seven women in the early postmenopausal period, with a mean (+/-SD) age of 50.8 +/- 4.1 years, who had had their last menstrual period 6 months to 3 years before the study. None were taking hormone replacement therapy, and all had an FSH level of >35 mIU/mL, a body mass index of <30 kg/m2, and a waist circumference of <94 cm.

INTERVENTION(S)

Computed tomography scans at the L4-5 vertebral disk space, dual-photon x-ray absorptiometry scans, and euglycemic hyperinsulinemic clamps were performed.

MAIN OUTCOME MEASURE(S)

Intraabdominal fat, subcutaneous abdominal fat, sagittal diameter, total body fat, percent body fat, and insulin sensitivity.

RESULT(S)

The natural log of insulin sensitivity correlated significantly with intraabdominal fat (r = -.39), subcutaneous fat (r = -.43), and sagittal diameter (r = -.48). After adjusting for total fat, sagittal diameter remained significantly related to insulin sensitivity.

CONCLUSION(S)

Central abdominal fat is inversely and independently related to insulin sensitivity after adjusting for total fat in women in the early postmenopausal period. Efforts to reduce either subcutaneous abdominal fat or intraabdominal fat should be helpful in reducing the risk of noninsulin-dependent diabetes mellitus in postmenopausal women.

Interaction between aging and syndrome X: new insights on the pathophysiology of fat distribution

Increased fat mass (FM), and in particular a specific increase in visceral fat (VF), may account for the age-associated decrease in insulin action and the development of Syndrome X. Utilizing chronic caloric restriction (CR) with aging in a rodent model, we dissociated the effects of VF and FM, and demonstrated that the decrease in VF accumulation was sufficient to prevent the marked decrease in hepatic insulin action. This suggests that the typical increase in VF with aging, rather than aging per se, determines hepatic insulin resistance. To directly assess the role of VF, we studied rats after surgical removal of VF or sham operation. Surgical extraction of VF (which accounts for approximately 10% of total fat) improved hepatic insulin action by more than twofold. We studied the role of fat-derived peptides in the regulation of body composition and insulin action. While VF extraction resulted in decreased gene expression for leptin and TNF-alpha in the subcutaneous adipose, administration of leptin selectively decreased visceral fat (approximately 60%), and enhanced the action of insulin on inhibiting hepatic glucose production (approximately 80%). Thus, the cause-effect relationship between the age-related increase in VF and the decrease in hepatic insulin action may involve the failure of leptin to "cross talk" with other fat depots to regulate fat distribution.

The HISS story overview: a novel hepatic neurohumoral regulation of peripheral insulin sensitivity in health and diabetes

Data are reviewed that are consistent with the following working hypothesis that proposes a novel mechanism regulating insulin sensitivity, which when nonfunctional, leads to severe insulin resistance. Postprandial elevation in insulin levels activates a hepatic parasympathetic reflex release of a putative hepatic insulin-sensitizing substance (HISS), which activates glucose uptake at skeletal muscle. Insulin causes HISS release in fed but not fasted animals. The reflex is mediated by acetylcholine and involves release of nitric oxide in the liver. Interruption of the release of HISS is achieved by surgical denervation of the anterior hepatic nerve plexus, muscarinic receptor blockade, or nitric oxide synthase antagonism and leads to immediate severe insulin resistance. The nitric oxide donor, SIN-1, reverses L-NAME-induced insulin resistance. Denervation-induced insulin resistance is reversed by intraportal but not intravenous administration of acetylcholine or SIN-1. Liver disease is often associated with insulin resistance; the bile duct ligation model of liver disease results in parasympathetic neuropathy and insulin resistance that is reversed by intraportal acetylcholine. Possible relevance of this HISS-dependent control of insulin action to insulin resistance in diabetes, liver disease, and obesity is discussed.Key words: insulin resistance, parasympathetic nerves, liver, obesity, nitric oxide.

The use of anthropometric and dual-energy X-ray absorptiometry (DXA) measures to estimate total abdominal and abdominal visceral fat in men and women

OBJECTIVE

A single-slice computed tomography (CT) scan provides a criterion measure of total abdominal fat (TAF) and abdominal visceral fat (AVF), but this procedure is often prohibitive due to radiation exposure, cost, and accessibility. In the present study, the utility of anthropometric measures and estimates of trunk and abdominal fat mass by dual-energy X-ray absorptiometry (DXA) to predict CT measures of TAF and AVF (cross-sectional area, cm2) was assessed.

RESEARCH METHODS AND PROCEDURES

CT measures of abdominal fat (at the level of the L4-L5 inter-vertebral space), DXA scans, and anthropometric measures were obtained in 76 Caucasian adults ages 20-80 years.

RESULTS

Results demonstrated that abdominal sagittal diameter measured by anthropometry is an excellent predictor of sagittal diameter measured from a CT image (r=0.88 and 0.94; Total Error [TE]=4.1 and 3.1 cm, for men and women, respectively). In both men and women, waist circumference and abdominal sagittal diameter were the anthropometric measures most strongly associated with TAF (r=0.87 to 0.93; Standard Error of Estimate (SEE)=60.7 to 75.4 cm2) and AVF (r=0.84 to 0.93; SEE=0.7 to 30.0 cm2). The least predictive anthropometric measure of TAF or AVF was the commonly used waist-to-hip ratio (WHR). DXA estimates of trunk and abdominal fat mass were strongly associated with TAF (r=.94 to 0.97; SEE=36.9 to 50.9 cm2) and AVF (r=0.86 to 0.90; SEE=4.9 to 27.7 cm2).

DISCUSSION

The present results suggest that waist circumference and/or abdominal sagittal diameter are better predictors of TAF and AVF than the more commonly used WHR. DXA trunk fat and abdominal fat appear to be slightly better predictors of TAF but not AVF compared to these anthropometric measures. Thus DXA does not offer a significant advantage over anthropometry for estimation of AVF.

Obesity, hypertension, and vascular disease

Obesity, hypertension, and related metabolic and hemodynamic abnormalities contribute significantly to cardiovascular disease in westernized societies such as the United States. Both obesity and hypertension are more prevalent among minorities such as black and Hispanic populations. Obesity substantially increases the likelihood of hypertension, and weight reduction has been shown to be an effective hygienic measure in reducing blood pressure. There is accumulating evidence that central obesity, particularly obesity that is distributed in the paraomental (visceral) region, especially predisposes one to hypertension and related metabolic abnormalities that contribute cerebrovascular disease.

Restoration of reproductive potential by lifestyle modification in obese polycystic ovary syndrome: role of insulin sensitivity and luteinizing hormone

Weight reduction and exercise have been shown to help with menstrual disturbance and infertility in obese women with polycystic ovary syndrome. We studied the relationship between insulin sensitivity and ovulation patterns in 18 infertile anovulatory obese polycystic ovary syndrome (PCOS) women (NO) with normal glucose tolerance, aged between 22-39 yr with a body mass index of 27-45 kg/m2, before and after a 6-month diet and exercise program. This program promotes healthy lifestyle factors, but does not lead to rapid weight loss. The anthropometric, metabolic, and endocrine factors of these subjects were compared to those of 10 age- and weight-matched PCOS women with regular monthly ovulation (RO). Before lifestyle modification, the anovulatory subjects had greater central obesity than regular ovulators, as assessed by percent central fat (NO, 45.7 +/- 0.8%; RO, 42.2 +/- 1.6%; P < 0.05), higher glucose increment after glucose challenge (NO, 10.1 +/- 1.0 mmol/L; RO, 6.4 +/- 1.1 mmol/L; P < 0.02), lower insulin sensitivity index (NO, 1.2 +/- 0.2; RO, 2.8 +/- 0.6 micromol/kg x min/pmol/L; P < 0.005), higher plasma LH (NO, 8.9 +/- 0.9; RO, 4.6 +/- 0.9 IU/L; P < 0.005), and lower plasma sex hormone-binding globulin (NO, 18.0 +/- 2.5; RO, 27.8 +/- 5.7 nmol/L; P < 0.05]. Anovulatory subjects were classified as responders (R) to the intervention if they regained ovulation during the study. As a result of intervention, R showed an 11% reduction in central fat, a 71% improvement in insulin sensitivity index, a 33% fall in fasting insulin levels, and a 39% reduction in LH levels. None of these parameters changed significantly in nonresponders (NR). At the end of the study, R had lower fasting insulin (R, 13.6 +/- 1.7; NR, 23.0 +/- 3.5 mU/L) and LH levels (R, 5.0 +/- 1.7; NR, 7.4 +/- 1.4 IU/L), but similar androgen levels compared to NR. We conclude that lifestyle modification without rapid weight loss leads to a reduction of central fat and improved insulin sensitivity, which restores ovulation in overweight infertile women with PCOS. Lifestyle modification is the best initial management for obese women seeking to improve their reproductive function.