Adipocyte size, adipose tissue fibrosis, macrophage infiltration and disease risk are different in younger and older individuals with childhood versus adulthood onset obesity.

BACKGROUND: The timing of obesity onset and age have been shown to affect the risk of obesity-related comorbidities, although the impact of each of these factors on markers of adipose tissue function remains unclear. OBJECTIVE: The aim of this study was to determine whether differences in regional adipose tissue characteristics vary with age and age of obesity onset, and whether these differences are associated with the markers of cardiometabolic health. METHODS: Adipose tissue samples were obtained from 80 female bariatric surgery candidates who were classified by age of obesity onset and age into 4 groups: (1) younger adults (<40 y) with childhood-onset obesity (<18 y) (Child-Young); (2) younger adults with adulthood-onset obesity (>18 y) (Adult-Young); (3) older adults (>55 y) with childhood-onset obesity (Child-Old); and (4) older adults with adulthood-onset obesity (Adult-Old). Adipocyte diameter, adipose tissue fibrosis, and macrophage infiltration were determined in subcutaneous (SAT) and visceral adipose tissue (VAT). Clinical parameters were obtained from participants' medical records. RESULTS: Visceral adipocyte size in the Child-Young group was the smallest of all the groups. Age affected visceral infiltration of M1-like cells with greater percent of M1-like cells in the Adult-Old and Child-Old groups. Though not significant, a stepwise increase in M2-like macrophages in VAT was observed with Adult-Young having the smallest followed by Adult-Old, Child-Young, and Child-Old having the greatest percent of M2-like macrophages. Pericellular fibrosis accumulation in SAT and VAT varied with both age and onset, particularly in the Child-Old group, which had the lowest fibrosis levels. Markers of cardiometabolic health (fasting glucose, glycated hemoglobin, total, HDL- and LDL-cholesterol and triglyceride concentrations) were positively and well-associated with adipose tissue characteristics of the Child-Old group but not of the Adult-Young group. CONCLUSION: Older adults with childhood-onset obesity, who had the greatest duration of obesity exposure, were particularly vulnerable to the cardiometabolic effects associated with perturbations in adipose tissue characteristics. These results suggest that age and age of obesity onset may have independent and cumulative effects on obesity pathology.

Identification of the ectoenzyme CD38 as a marker of committed preadipocytes.

BACKGROUND/OBJECTIVES: Characterisation of the adipocyte cellular lineage is required for a better understanding of white adipose tissue homoeostasis and expansion. Although several studies have focused on the phenotype of the most immature adipocyte progenitors, very few tools exist to identify committed cells. In haematopoiesis, the CD38 ectoenzyme is largely used to delineate various stages of stem cell lineage commitment. We hypothesise that this marker could be used to identify committed preadipocytes. METHODS: Complementary strategies including flow cytometry, cell-sorting approaches, immunohistochemistry and primary cultures of murine adipose progenitors isolated from different fat pads of control or high-fat diet exposed C57BL/6 J mice were used to determine the molecular expression profile, proliferative and differentiation potentials of adipose progenitors expressing the CD38 molecule. RESULTS: We demonstrate here that a subpopulation of CD45- CD31- CD34+ adipose progenitors express the cell surface protein CD38. Using a cell-sorting approach, we found that native CD45- CD31- CD34+ CD38+ (CD38+) adipose cells expressed lower CD34 mRNA and protein levels and higher levels of adipogenic genes such as Pparg, aP2, Lpl and Cd36 than did the CD45- CD31- CD34+ CD38- (CD38-) population. When cultivated, CD38+ cells displayed reduced proliferative potential, assessed by BrdU incorporation and colony-forming unit assays, and greater adipogenic potential. In vitro, both CD38 mRNA and protein levels were increased during adipogenesis and CD38- cells converted into CD38+ cells when committed to the adipogenic differentiation programme. We also found that obesity development was associated with an increase in the number of CD38+ adipose progenitors, this effect being more pronounced in intra-abdominal than in subcutaneous fat, suggesting a higher rate of adipocyte commitment in visceral depots. CONCLUSIONS: Together, these data demonstrate that CD38 represents a new marker that identifies committed preadipocytes as CD45- CD31- CD34low CD38+ cells.

Relevance of omental pericellular adipose tissue collagen in the pathophysiology of human abdominal obesity and related cardiometabolic risk.

BACKGROUND: Adipose tissue fibrosis is a relatively new notion and its relationship with visceral obesity and cardiometabolic alterations remains unclear, particularly in moderate obesity. OBJECTIVE: Our objective was to examine if total and pericellular collagen accumulation are relevant for the pathophysiology of visceral obesity and related cardiometabolic risk. SUBJECTS AND METHODS: Surgical omental (OM) and subcutaneous (SC) fat samples were obtained in 56 women (age: 47.2±5.8 years; body mass index (BMI): 27.1±4.4 kg/m2). Body composition and fat distribution were measured by dual-energy X-ray absorptiometry and computed tomography, respectively. Total and pericellular collagen were measured using picrosirius red staining. CD68+ cells (total macrophages) and CD163+ cells (M2-macrophages) were identified using immunohistochemistry. RESULTS: We found that only pericellular collagen percentage, especially in OM fat, was associated with higher BMI, body fat mass and adipose tissue areas as well as lower radiologic attenuation of visceral adipose tissue and altered cardiometabolic risk variables. Strong correlations between peri-adipocyte collagen percentage and total or M2-macrophage percentages were observed in both depots. Total collagen percentage in either compartment was not related to adiposity, fat distribution or cardiometabolic risk. CONCLUSIONS: As opposed to whole tissue-based assessments of adipose tissue fibrosis, collagen deposition around the adipocyte, especially in the OM fat compartment is related to total and regional adiposity as well as altered cardiometabolic risk profile.

An explained variance-based genetic risk score associated with gestational diabetes antecedent and with progression to pre-diabetes and type 2 diabetes: a cohort study.

OBJECTIVE: To determine whether an explained-variance genetic risk score (GRS), with 36 single nucleotide polymorphisms (SNPs) previously associated with type 2 diabetes (T2D), is also associated with gestational diabetes mellitus (GDM), and with the progression to pre-diabetes and T2D among women with prior GDM. DESIGN: A cohort study. SETTING: Clinical investigation unit of Laval University, Quebec, Canada. POPULATION: A cohort of 214 women with prior GDM and 82 controls recruited between 2009 and 2012. METHODS: Associations between the GRS and GDM. MAIN OUTCOMES MEASURES: GDM and prevalence of pre-diabetes and T2D. RESULTS: Women with prior GDM had a higher GRS compared with controls (38.6 ± 3.9, 95% CI 38.1-39.1, versus 37.4 ± 3.2, 95% CI 36.7-38.1; P < 0.0001). In women with prior GDM, the explained-variance GRS was higher for pre-diabetic women compared with women who remained normoglucotolerant at testing (1.21 ± 0.18, 95% CI 1.18-1.23, versus 1.17 ± 0.15, 95% CI 1.13-1.20; P < 0.0001). Similarly, women with T2D had a higher explained-variance GRS compared with women with prior GDM who remained normoglucotolerant (1.20 ± 0.18, 95% CI 1.14-1.25, versus 1.17 ± 0.17, 95% CI 1.13-1.20; P < 0.0001). The predictive effects of the explained-variance GRS, age, and body mass index (BMI), or the additive effects of the three variables, were tested for pre-diabetes and T2D. We observed an area under the curve of 0.6269 (95% CI 0.5638-0.6901) for age and BMI, and adding the explained-variance GRS into the model increased the area to 0.6672 (95% CI 0.6064-0.7281) for the prediction of pre-diabetes. CONCLUSIONS: An explained-variance GRS is associated with both GDM and progression to pre-diabetes and T2D in women with prior GDM.

Predictors of body composition and body energy changes in response to chronic overfeeding.

OBJECTIVE: We have previously shown that 24 young lean men (12 pairs of identical twins) subjected to a standardized 353 MJ (84 000 kcal) overfeeding protocol over 100 days exhibited individual differences in body weight and composition gains. The mean (+s.d.) gains in fat mass (FM) and fat-free mass (FFM) were 5.4+1.9 kg and 2.7+1.5 kg for a total body energy (BE) gain of 221+75 MJ, representing 63% of the energy surplus consumed. We report here on the most important baseline correlates of these overfeeding-induced changes with the aim of identifying biomarkers of the response. RESULTS: Baseline maximal oxygen uptake per kg body mass was negatively correlated with gains in weight, FM and BE (all P<0.05). Enzyme activities indicative of skeletal muscle oxidative potential correlated with gains in FM and BE (all P<0.05). Baseline thyroid-stimulating hormone levels in response to thyrotropin-releasing hormone stimulation correlated positively with changes in FM-to-FFM ratio (P<0.05). Plasma concentrations of androstenediol sulfate, dehydroepiandrosterone and 17-hydroxy pregnenolone were negatively correlated with gains in FM and BE (0.01

A polymorphism of the interferon-gamma-inducible protein 30 gene is associated with hyperglycemia in severely obese individuals.

A previous expression profiling of visceral adipose tissue (VAT) revealed that the immune response gene interferon-gamma-inducible protein 30 (IFI30) gene was 1.72-fold more highly expressed in non-diabetic severely obese men with the metabolic syndrome as compared to those without. Given the importance of low-grade inflammation in obesity-related metabolic complications, we hypothesized that variants in the IFI30 gene are associated with cardiovascular disease (CVD) risk factors. A detailed genetic investigation was performed at the IFI30 locus by sequencing its promoter, exons and intron-exon junction boundaries using DNA of 25 severely obese men. Among the 21 sequence-derived single-nucleotide polymorphisms (SNPs), 5 tagged SNPs (covering 100% of the common SNPs identified) were genotyped in two independent samples of severely obese patients (total n = 1,283). Using a multistage experimental design, chi-square analyses and logistic regressions were performed to compare genotype frequencies and compute odds-ratios (OR) for low and high CVD risk groups (dyslipidemia, hyperglycemia/diabetes and hypertension). A significant association was observed with the non-synonymous SNP rs11554159 (p.R76Q), where GA individuals showed lower risk (OR = 0.67; P = 0.0009) for hyperglycemia/diabetes as compared to homozygotes for the major allele (GG). No association was observed between rs11554159 and VAT IFI30 mRNA levels (P = 0.81), and the expression levels were not correlated with fasting plasma glucose levels (P = 0.31) in 112 non-diabetic severely obese women. The localization of rs11554159 near the active site of IFI30 suggests a functional effect of this SNP. This study showed a novel association between rs11554159 (p.R76Q) polymorphism at the IFI30 locus and the risk of hyperglycemia/diabetes in severely obese individuals.

Human growth hormone receptor (GHR) expression in obesity: I. GHR mRNA expression in omental and subcutaneous adipose tissues of obese women.

OBJECTIVES: Growth hormone (GH)-deficient individuals display increased adiposity that can be effectively reduced by GH therapy because of GH's lipolytic effects. However, similar GH treatments of individuals with idiopathic obesity (not associated with an endocrinopathy/syndrome) have had little success. We hypothesized that this form of obesity may be associated with GH resistance at the level of the adipocyte because of reduced GH receptor (GHR) expression. SUBJECTS AND METHODS: We studied GHR expression in omental and subcutaneous fat tissues from a cohort of 55 women ranging from lean to obese by various adiposity parameters. mRNA levels of total GHR and the dominant-negative truncated GHR(1-279) (trGHR) form were assayed by quantitative reverse transcriptase-PCR. Associations between adiposity measures and GHR levels as well as trGHR/GHR ratios were analyzed. RESULTS: Total GHR mRNA expression was 2-3-fold lower in omental as well as subcutaneous adipose tissues of obese compared with lean women (P ≤ 0.05-0.001). Lean individuals expressed higher GHR mRNA levels in omental fat compared with subcutaneous (P ≤ 0.01); in obese women, this depot-specific difference was lost. Omental and subcutaneous adipose GHR mRNA levels displayed significant negative correlations with a spectrum of indicators of obesity while, in subcutaneous fat, there was a significantly higher trGHR/GHR ratio with increasing adiposity (P ≤ 0.05). CONCLUSION: These results support our hypothesis that, with obesity, there is lower GHR expression in the adipocyte, and suggest one possible explanation why GH supplementation is not an effective treatment for individuals with idiopathic obesity.

Plasma adiponectin concentration is strongly associated with VLDL-TG catabolism in postmenopausal women.

BACKGROUND AND AIMS: To investigate associations between plasma adiponectin concentration and very-low density lipoprotein-triglyceride (VLDL-TG) secretion and catabolism in postmenopausal women. METHODS AND RESULTS: This cross-sectional study included 30 postmenopausal women. Plasma adiponectin concentration was measured by ELISA. Insulin sensitivity was assessed by a 2-h euglycemic-hyperinsulinemic clamp. Fasting plasma glucose (FPG) and 2-hour plasma glucose (2hPG) were measured during an oral glucose tolerance test. The calculation of VLDL-TG fractional catabolic rate (FCR) and VLDL-TG total secretion rate (TSR) were based on the monoexponential decrease of TG-[²H5] glycerol values obtained following the administration of a ²H5-glycerol bolus. Plasma adiponectin concentration was negatively associated with VLDL-TG TSR (r=-0.50; p=0.005) and positively associated with VLDL-TG FCR (r=0.54; p<0.002). This latter association remained significant after further adjustments for insulin sensitivity, visceral adipose tissue, HDL-C, FPG and 2hPG concentrations. In a multivariate model including adiponectin, insulin sensitivity and 2hPG, plasma adiponectin level was the strongest correlate of VLDL-TG FCR. CONCLUSIONS: Elevated plasma adiponectin concentration is associated with a favourable VLDL-TG metabolism.

Hypertrophy and hyperplasia of abdominal adipose tissues in women.

OBJECTIVE: To examine the expression of selected transcription factors involved in adipogenesis and genes related to lipid metabolism in abdominal subcutaneous and omental fat tissue. RESEARCH DESIGN AND METHODS: We obtained subcutaneous and omental adipose tissue samples from 40 women undergoing abdominal hysterectomies (age: 47+/-5 years; BMI 27.9+/-5.3 kg/m(2)). We measured isolated adipocyte size and metabolism, and detailed measures of body fat accumulation and body fat distribution were obtained (dual-energy X-ray absorptiometry and computed tomography, respectively). RESULTS: Adipocyte size of both subcutaneous and omental fat were increased with higher body fat mass values, with similar regression slopes in each compartment. In contrast, with higher body fat mass values, fat accumulation was progressively higher in the subcutaneous than in the visceral fat compartment, suggesting hyperplasia in the subcutaneous fat compartment. Messenger RNA levels of CEBPalpha, PPARgamma2, SREBP1c and genes related to lipid metabolism (LPL, FABP4, DGAT1, DGAT2, PLIN and HSL) were significantly higher in subcutaneous than in omental fat tissue (P< or =0.001 for all). Only subcutaneous expression of these genes tracked with obesity levels as reflected by significant positive associations between subcutaneous fat CEBPalpha, SREBP1c and DGAT2 expression and total body fat mass (r=0.37, r=0.41, r=0.57, respectively, P< or =0,05), fat percentage (r=0.40, r=0.39, r=058, respectively, P< or =0,05) and subcutaneous adipose tissue area (r=0.36, r=0.38, r=0.58, respectively, P< or =0,05). Omental adipose tissue expression levels of these genes were not significantly related to adiposity measures. CONCLUSIONS: These results show that in obese women, hyperplasia is predominant in the subcutaneous fat depot, whereas fat cell hypertrophy is observed both in the omental and subcutaneous compartments.

Association of prenatal exposure to gestational diabetes with offspring body composition and regional body fat distribution.

The aim of this cohort study was to compare body composition and regional body fat distribution between children exposed (GDM+) or unexposed (GDM-) in utero to gestational diabetes mellitus (GDM) and to investigate the association with the glycaemic and the insulin profile. Data from 56 GDM+ and 30 GDM- were analysed. Height, weight and waist circumference were measured. Total and regional body composition was measured by dual-energy X-ray absorptiometry. Insulin, glucose and HbA1c were obtained from a fasting plasma sample, and the HOMA-IR index was calculated. anova was performed to compare adiposity measures between GDM+ and GDM-. Associations between the glycaemic and insulin profile and adiposity measures were studied using partial Pearson correlations. Mean age was 6.6 ± 2.3 years. Waist circumference, fat mass percentage, android fat mass, android fat mass percentage and android-to-gynoid fat mass ratio were higher among GDM+, and lean mass percentage was lower (P < 0.05). Among GDM+ children, body mass index (BMI) z score, waist circumference, fat mass percentage, android fat mass percentage and android-to-gynoid fat mass ratio were all positively correlated with HbA1C (r = 0.32-0.43, P < 0.05). Prenatal exposure to GDM is associated with increased total and abdominal adiposity. This increased adiposity observed among GDM+ children is associated with an altered glycaemic profile. This study is registered in the Clinical Trials.gov registry (NCT01340924).

A GWAS follow-up of obesity-related SNPs in SYPL2 reveals sex-specific association with hip circumference.

OBJECTIVE: A novel single-nucleotide polymorphism (SNP) associated with morbid obesity was recently identified by exome sequencing. The purpose of this study was to follow up this low-frequency coding SNP located within the SYPL2 locus and associated with body mass index in order to reveal novel associations with obesity-related traits. METHODS: The body mass index-associated SNP (rs62623713 A>G [chr1:109476817/hg19]) and two tagging SNPs within the SYPL2 locus, rs9661614 T>C (chr1:109479215) and rs485660 G>A (chr1:109480810), were genotyped in the obesity (n = 3,017) and the infogene (n = 676) cohorts, which were further combined, leading to a larger cohort of 3,693 individuals. Association testing was performed by general linear models in the obesity cohort and validated by joint analysis in the combined cohort. RESULTS: rs9661614 and rs485660 were significantly associated with hip circumference (HC) in the obesity cohort, with heterozygotes exhibiting a significantly lower HC. These results were validated by joint analysis for rs9661614 (false discovery rate [FDR]-corrected P = 7.5 × 10-4) and, to a lesser extent, for rs485660 (FDR corrected P = 3.9 × 10-2). The association with HC remained significant for rs9661614 when tested independently in women (FDR-corrected P = 1.7 × 10-2), but not for rs485660 (FDR-corrected P = 0.2). Both associations were absent in men. CONCLUSIONS: This study reveals strong evidence for a novel association between rs9661614 (T>C) and HC in women, which likely reflects a preferential association of SYPL2 to a gynoid profile of fat distribution. The study findings support a clinical significance of SYPL2 worth considering when assessing risk factors associated with obesity.

Hypertriglyceridemic waist: A marker of the atherogenic metabolic triad (hyperinsulinemia; hyperapolipoprotein B; small, dense LDL) in men?

BACKGROUND: The present study tested the hypothesis that simple variables, such as waist circumference and fasting plasma triglyceride (TG) concentrations, could be used as screening tools for the identification of men characterized by a metabolic triad of nontraditional risk factors (elevated insulin and apolipoprotein [apo] B and small, dense LDL particles). METHODS AND RESULTS: Results of the metabolic study (study 1) conducted on 185 healthy men indicate that a large proportion (>80%) of men with waist circumference values >/=90 cm and with elevated TG levels (>/=2.0 mmol/L) were characterized by the atherogenic metabolic triad. Validation of the model in an angiographic study (study 2) on a sample of 287 men with and without coronary artery disease (CAD) revealed that only men with both elevated waist and TG levels were at increased risk of CAD (odds ratio of 3.6, P<0.03) compared with men with low waist and TG levels. CONCLUSIONS: It is suggested that the simultaneous measurement and interpretation of waist circumference and fasting TG could be used as inexpensive screening tools to identify men characterized by the atherogenic metabolic triad (hyperinsulinemia, elevated apo B, small, dense LDL) and at high risk for CAD.

The apoB-100 gene EcoRI polymorphism influences the relationship between features of the insulin resistance syndrome and the hyper-apoB and dense LDL phenotype in men.

The aim of this study was to investigate whether the EcoRI polymorphism of the apolipoprotein B (apoB) gene influences the relationships between features of the insulin resistance syndrome and the dense LDL phenotype and apoB concentrations. A sample of 65 men was divided into two groups on the basis of the EcoRI genotype. Forty-four subjects were (+/+) homozygotes for the presence of the EcoRI restriction site that is associated with a glutamic acid at codon 4154. Twenty-one men were (+/-) heterozygotes for the absence of the restriction site resulting from a glutamic acid to a lysine substitution at codon 4154. In the (+/-) group, fasting plasma FFA levels were positively correlated with plasma apoB, LDL-apoB, and the LDL particle score that was calculated from the migration distances of LDL subspecies and their relative band intensities, reflecting the proportion of small dense LDL particles. However, these associations were not found among (+/+) subjects. The two genotypic groups were further divided into two subgroups on the basis of fasting FFA concentrations, and the LDL particle score and the LDL-apoB levels were compared. High FFA levels were associated with a higher proportion of small dense LDL particles, as reflected by a higher mean LDL particle score, irrespective of the genotype. However, the apoB-EcoRI polymorphism appeared to influence the association between high FFA levels and LDL-apoB concentrations because (+/-) heterozygotes with high FFA levels had higher LDL-apoB concentrations than (+/-) heterozygotes with low FFA levels. In addition, the integrated area under the curve of plasma insulin concentrations, measured in response to a 75-g oral glucose challenge, and the amount of visceral adipose tissue, measured by computed tomography, were positively associated with the LDL particle score only in (+/-) heterozygotes. When subjects were divided on the basis of insulin area (low vs. high) or visceral adipose tissue (low vs. high), (+/-) heterozygotes with high insulin area or with high levels of visceral adipose tissue had a higher mean LDL particle score than (+/-) heterozygotes with low insulin area or low visceral adipose tissue. However, among (+/+) homozygotes, low or high levels of insulin or visceral adipose tissue could not discriminate between men with large or small LDL particles. Therefore, (+/-) heterozygotes may be more susceptible to develop the dense LDL phenotype in presence of hyperinsulinemia and visceral obesity. Results of the present study suggest that the apoB-EcoRI polymorphism may exacerbate the alterations in the LDL particle (size and concentration) found among visceral obese-hyperinsulinemic men.

Impaired capacity to lose visceral adipose tissue during weight reduction in obese postmenopausal women with the Trp64Arg beta3-adrenoceptor gene variant.

Controversy exists regarding the association between the Trp64Arg variant of the beta3-adrenoceptor gene and visceral obesity. The cross-sectional nature of most studies, the modest effect of the variant, and sex or ethnic differences between groups have contributed to discrepancies among investigations. To overcome these confounding factors, we examined the effect of the Trp64Arg variant on total and visceral adipose tissue loss, insulin sensitivity, and cardiovascular disease risk factors in response to weight reduction in obese older women. A total of 24 women (age 57 +/- 4 years), including 1 Trp64Arg homozygote, 10 Trp64Arg heterozygotes, and 13 normal homozygotes, were admitted to a weight reduction program of 13 +/- 3 months, with weight and nutritional intake stabilization established before testing. Total and regional adiposity were measured with dual-energy X-ray absorptiometry and computed tomography, insulin sensitivity was measured by the hyperinsulinemic-euglycemic clamp technique, and a blood lipid profile was obtained. No baseline differences were noted in adiposity measurements, glucose disposal, and lipid profiles among carriers and noncarriers of the variant allele. In response to weight loss, carriers and noncarriers of the Trp64Arg allele had similar reductions in body weight (-16.4 +/- 5.0 vs. -14.1 +/- 6.2 kg, NS) and body fat (-10.0 +/- 5.2 vs. -11.5 +/- 3.9 kg, NS). However, loss of visceral adipose tissue was 43% lower in carriers of the Trp64Arg allele compared with noncarriers (-46 +/- 27 vs. -81 +/- 51 cm2, P = 0.05). Furthermore, there was less improvement in the total cholesterol-to-HDL cholesterol ratio (-0.18 +/- 0.54 vs. -0.72 +/- 0.56, P = 0.04) in carriers compared with noncarriers of the allele. Although glucose disposal improved in both groups, there was no difference in the magnitude of improvement between carriers and noncarriers of the variant allele. In conclusion, older obese women carrying the Trp64Arg beta3-adrenoceptor gene variant have an impaired capacity to lose visceral adipose tissue in response to prolonged caloric restriction. Despite these genetic differences in loss of intraabdominal adipose tissue, improvement in glucose disposal was similar between groups.

Obesity-related phenotypes and the beta3-adrenoceptor gene variant in postmenopausal women.

We examined the hypothesis that postmenopausal women with the beta3-adrenoceptor gene variant (Trp64Arg) have reduced total daily energy expenditure (TEE), altered free fatty acid kinetics, and increased intra-abdominal fat. A secondary objective was to examine whether the obese state masks the effect of the variant on resting metabolic rate (RMR). There were 23 obese heterozygous women with the genetic variant (age 58 +/- 6 years; BMI 36 +/- 7 kg/m2) who were compared with 19 homozygous obese women with the normal allele (age 56 +/- 4 years; BMI 36 +/- 3 kg/m2). Daily energy expenditure was determined from doubly labeled water and indirect calorimetry, lipolysis from infusion of [1-13C]palmitate, and body fat distribution from computed tomography. No significant differences were found in TEE, RMR, energy expenditure of physical activity, the thermic effect of a meal, fat oxidation as estimated by fasting and postprandial respiratory quotients (RQs), or rate of lipolysis. Similarly, no difference was found in visceral adipose tissue and abdominal subcutaneous fat areas. When RMR was compared between obese (n = 23) and never-obese women with the Trp64Arg variant (n = 16), we found a 317 kcal/day lower RMR in never-obese women after controlling for fat mass, fat-free mass, and age (P < 0.0017). These results do not support the hypothesis that already obese women with the Trp64Arg polymorphism of the beta3-adrenergic receptor gene have lower daily energy expenditure, altered lipolysis, and increased abdominal obesity. On the other hand, the lower RMR in never-obese women suggests that the obese state may mask a moderate effect of the Trp64Arg variant on energy expenditure. Although these results need to be confirmed in other populations, the obese state may have been a confounding factor in previous studies of the beta3-adrenoceptor Trp64Arg variant and energy expenditure.

Identification of an interactive effect of beta3- and alpha2b-adrenoceptor gene polymorphisms on fat mass in Caucasian women.

Several adrenoceptor subtypes are expressed in adipocytes, which together exert their influence on adipocyte metabolism. Therefore, we specifically examined the interactive effect of Trp64Arg (beta3) and Glu12/Glu9 (alpha2b) adrenoceptor (AR) polymorphisms on energy metabolism and body composition in healthy women with a wide range of body habitus. We genotyped 909 unrelated women (age 55 +/- 12 [mean +/- SD] years, range 19-87; body weight 88 +/- 22 kg, range 40-167; and BMI 33 +/- 8 kg/m2, range 16-64) for Trp64Arg beta3AR and Glu12/Glu9 alpha2bAR variants. We examined the independent effect of the Glu12/Glu9 alpha2bAR variant on body composition and energy balance, in a large cohort of Caucasian women (n = 909). A second goal was to examine the interaction effect of Glu12/Glu9 alpha2bAR and Trp64Arg beta3AR on the same phenotypes. The obesity-related phenotypes studied were as follows: body weight, BMI, fat mass, visceral fat, fat-free mass, resting metabolic rate (RMR), VO2max, leisure time physical activity, and daily energy intake. Body composition and body fat distribution were measured by dual-energy X-ray absorptiometry and radiographic imagery, VO2max by a treadmill test to exhaustion, and RMR by indirect calorimetry. An analysis of covariance indicated that in the entire cohort, there was no significant difference between Glu12/Glu9 alpha2bAR carriers and control subjects for any of the obesity-related phenotypes that were examined. However, we observed a significant interaction effect of the Trp64Arg and Glu12/Glu9 variants on fat mass (P = 0.009) and percent fat (P = 0.016). Age, height, body weight, BMI, fat-free mass, visceral fat, energy expenditure, respiratory quotient, physical fitness, and energy intake were not different among groups. Collectively, these findings support an interaction effect of the two adrenoceptor variants on body fatness in Caucasian women, although the physiological mechanism by which they exert this effect remains to be determined.

Sex hormone-binding globulin levels in middle-aged premenopausal women. Associations with visceral obesity and metabolic profile.

OBJECTIVE: Low sex hormone-binding globulin (SHBG) levels in women are associated not only with hyperinsulinemia, increased risk for cardiovascular disease, and type 2 diabetes but also with excess body fatness and abdominal obesity. We tested the hypothesis that an elevated total or intra-abdominal adipose tissue accumulation mediates the relationship between low SHBG levels and an altered metabolic profile. RESEARCH DESIGN AND METHODS: We measured body composition (dual-energy X-ray absorptiometry [DEXA]) and body fat distribution (computed tomography) in 52 middle-aged (46.7 +/- 0.4, mean +/- SEM) premenopausal women. Insulin and glucose responses to a 75-g oral glucose load and plasma lipid-lipoprotein levels were also measured. RESULTS: Low plasma SHBG concentrations were associated with increased total body fat mass (r = -0.41, P < 0.005) and subcutaneous abdominal (r = -0.39, P < 0.005) and intra-abdominal (r = -0.37, P < 0.008) adipose tissue area. Low SHBG was also associated with a greater insulin response to oral glucose (r = -0.40, P < 0.005), higher triglyceride levels (r = -0.29, P < 0.05), higher cholesterol/HDL cholesterol ratio (r = -0.51, P < 0.005), but lower HDL cholesterol concentrations (r = 0.65, P < 0.005). When matched for intra-abdominal fat or total fat mass, subjects with either low or high SHBG showed no difference in the insulin response to an oral glucose challenge. Statistical adjustment for differences in intra-abdominal adipose tissue accumulation or total body fat mass also eliminated the associations between SHBG levels and metabolic variables, with the exception of the association between SHBG and HDL cholesterol levels (r = 0.52, P < 0.005). CONCLUSIONS: Our results suggest that the previously reported relationship between low SHBG levels and increased metabolic disease risk in women is mediated, to a large extent, by concomitant variation in body fatness and intra-abdominal adipose tissue accumulation.

Relation of steroid hormones to glucose tolerance and plasma insulin levels in men. Importance of visceral adipose tissue.

OBJECTIVE: Low plasma testosterone levels are associated with hyperinsulinemia and glucose intolerance in men. However, it is unclear whether these abnormalities are related to the concomitant alteration in regional adipose tissue (AT) accumulation associated with reduced androgen levels. RESEARCH DESIGN AND METHODS: We measured plasma steroid levels in a sample of 79 men, ranging from lean to obese (aged 29-42 years), for whom an oral glucose tolerance test (OGTT), anthropometric and computed tomography (CT) measurements of body fatness, and AT distribution were performed. Sex hormone binding globulin (SHBG) and the following steroids were measured after extraction from plasma and chromatography: dehydroepiandrosterone, androstenedione, androst-5-ene-3 beta,17 beta-diol, testosterone, estrone, and estradiol (E2). RESULTS: Several significant negative correlations were found between adrenal C19 steroid precursors, testosterone, SHBG, and fasting insulin levels, as well as between plasma glucose and insulin concentrations measured during the OGTT (-0.25 < or = r < or = -0.35, 0.05 > or = P > or = 0.001). The best steroid correlate of plasma glucose and insulin homeostasis indexes was the E2: testosterone ratio (0.34 < or = r < or = 0.42, 0.005 > or = P > or = 0.001). However, after correction of steroid levels for either fat mass, body mass index (BMI), or visceral AT area, as measured by CT, no significant residual associations were noted between testosterone, adrenal C19 steroid, SHBG, and estrogen levels and indexes of plasma glucose-insulin homeostasis, although the positive association between the E2: testosterone ratio and glucose area remained significant after adjustment for total body fat mass and BMI. Furthermore, 15 pairs of obese subjects, matched for visceral AT area, showing either low or high levels of the steroids studied, did not differ in fasting insulin and postglucose plasma insulin levels or in glucose tolerance. CONCLUSIONS: These results suggest that the previously reported relationships between androgen levels and indexes of plasma glucose-insulin homeostasis are mediated, to a large extent, by concomitant alterations in levels of total body fat and visceral AT in men.

The dense LDL phenotype. Association with plasma lipoprotein levels, visceral obesity, and hyperinsulinemia in men.

OBJECTIVE: To investigate the potential relationship between the cluster of metabolic abnormalities found in visceral obesity and the small dense LDL phenotype. RESEARCH DESIGN AND METHODS: We have estimated LDL peak particle size by nondenaturing 2-16% gradient gel electrophoresis in a sample of 79 men. Glucose tolerance and fasting plasma insulin and lipoprotein levels were also measured. RESULTS: The LDL particle score, calculated from migration, distances and relative band intensities and reflecting the proportion of small dense LDL particles, was positively correlated with plasma triglyceride (TG) (r = 0.60, P < 0.0001) and negatively correlated with HDL cholesterol (r = -0.56, P < 0.0001) levels. Although the LDL particle score was not associated with variations in plasma LDL cholesterol or LDL apolipoprotein (apo) B concentrations, it was significantly correlated with the LDL apo B-to-LDL cholesterol ratio (r = 0.60, P < 0.0001). Fasting plasma insulin and visceral adipose tissue (AT) areas measured by computed tomography were weakly but significantly correlated with the LDL particle score (r = 0.23 and 0.29, respectively, P < 0.05). LDL peak particle size showed similar but inverse correlations with anthropometric and metabolic variables. Subjects classified as having small dense LDL particles (by comparing subjects in the highest tertile versus those in the lowest tertile of the LDL particle score distribution) were characterized by increased plasma TG, reduced HDL cholesterol, higher fasting insulin levels, and elevated visceral AT accumulation. However, multiple regression analyses revealed that visceral AT accumulation was not an independent predictor of the dense LDL phenotype after inclusion of TG and HDL cholesterol levels and lipoprotein ratios in the model. CONCLUSIONS: It thus appears that the high TG-low HDL cholesterol dyslipidemia frequently found in visceral obesity and in a hyperinsulinemic state is a strong correlate of the small dense LDL phenotype. Although associated with the dense LDL phenotype, visceral obesity and hyperinsulinemia were not independent predictors of an increased proportion of small dense LDL particles after controlling for TG and HDL cholesterol levels.

Age-related increase in visceral adipose tissue and body fat and the metabolic risk profile of premenopausal women.

OBJECTIVE: Age-related differences in body fat and, more specifically, in the accumulation of abdominal visceral adipose tissue (AT) were examined as potential covariates of the age-related difference in the metabolic profile predictive of cardiovascular disease (CVD) risk observed in young, as compared with middle-aged, premenopausal women. RESEARCH DESIGN AND METHODS: Body composition, AT distribution, plasma lipoprotein-lipid levels, glucose tolerance, and plasma insulin concentrations were assessed in a sample of 122 young women (27.4+/-7.5 years, mean +/- SD) and compared with a sample of 52 middle-aged premenopausal women (49.5+/-5.3 years) who still had a normal menstrual cycle. RESULTS: Middle-aged women were characterized by elevated levels of total abdominal and visceral AT and greater body fat mass and waist circumference, as well as by higher plasma levels of total cholesterol, LDL cholesterol, apolipoprotein (apo)B, and LDL-apoB compared with younger women. Furthermore, middle-aged women showed a greater glycemic response to a 75-g oral glucose load than young women (P < 0.01). In both young and middle-aged subjects, visceral AT accumulation was significantly correlated with plasma triglyceride, apoB, and LDL-apoB levels and with the cholesterol/HDL cholesterol ratio, as well as with plasma glucose, insulin, and C-peptide levels measured in the fasting state and after the oral glucose load, and negatively correlated with HDL cholesterol levels (-0.41 < or = r < or = 0.65, P < 0.05). When variables were adjusted for levels of visceral AT and fat mass, age-related differences that were initially found in plasma apoB and LDL-apoB levels, as well as in fasting glycemia and glucose tolerance, were eliminated. CONCLUSIONS: Results of the present study suggest that even before the onset of menopause there is an age-related deterioration in the metabolic risk profile and an increase in visceral AT deposition in middle-aged women compared with young control subjects. Furthermore, our results provide support for the notion that the age-related increase in visceral AT accumulation is a significant factor involved in the deterioration of the CVD risk profile noted in premenopausal women with age.