Adipose tissue morphology predicts improved insulin sensitivity following moderate or pronounced weight loss

BACKGROUND

Cross-sectional studies show that white adipose tissue hypertrophy (few, large adipocytes), in contrast to hyperplasia (many, small adipocytes), associates with insulin resistance and increased risk of developing type 2 diabetes. We investigated if baseline adipose cellularity could predict improvements in insulin sensitivity following weight loss.

METHODS

Plasma samples and subcutaneous abdominal adipose biopsies were examined in 100 overweight or obese individuals before and 10 weeks after a hypocaloric diet (7±3% weight loss) and in 61 obese subjects before and 2 years after gastric by-pass surgery (33±9% weight loss). The degree of adipose tissue hypertrophy or hyperplasia (termed the morphology value) in each individual was calculated on the basis of the relationship between fat cell volume and total fat mass. Insulin sensitivity was determined by homeostasis model assessment-estimated insulin resistance (HOMAIR).

RESULTS

In both cohorts at baseline, subjects with hypertrophy displayed significantly higher fasting plasma insulin and HOMAIR values than subjects with hyperplasia (P<0.0001), despite similar total fat mass. Plasma insulin and HOMAIR were normalized in both cohorts following weight loss. The improvement (delta insulin or delta HOMAIR) was more pronounced in individuals with hypertrophy, irrespective of whether adipose morphology was used as a continuous (P=0.0002-0.027) or nominal variable (P=0.002-0.047). Absolute adipocyte size associated (although weaker than morphology) with HOMAIR improvement only in the surgery cohort. Anthropometric measures at baseline (fat mass, body mass index, waist-to-hip ratio or waist circumference) showed no significant association with delta insulin or delta HOMAIR.

CONCLUSIONS

In contrast to anthropometric variables or fat cell size, subcutaneous adipose morphology predicts improvement in insulin sensitivity following both moderate and pronounced weight loss in overweight/obese subjects.

Visceral fat cell lipolysis and cardiovascular risk factors in obesity

Visceral fat accumulation relates to cardiovascular risk factors, but the underlying mechanisms are not well understood. We investigated the role of visceral adipocyte triglyceride breakdown (lipolysis) for several risk factors of cardiovascular disease. In 73 obese women, fat mass and distribution, blood pressure, blood samples for cardiometabolic risk factors, and whole-body insulin sensitivity were determined. A subcutaneous and a visceral fat biopsy were taken. Fat cell glycerol release after stimulation with a major lipolytic hormone, noradrenaline, was measured. In simple regression analysis, visceral fat cell lipolysis, but not subcutaneous adipocyte lipolysis was related to components of the metabolic syndrome. Moreover, subjects in the highest quartile of catecholamine-induced visceral lipolysis had higher levels of systolic blood pressure, estimated liver fat, plasma levels of glucose, insulin, cholesterol, LDL-cholesterol, triglycerides and apolipoprotein B and lower whole-body insulin sensitivity than those in the lowest quartile (p=0.0004-0.048). Among subjects with the metabolic syndrome, visceral fat cell lipolysis was 40% higher than in the remaining subjects (p=0.0052). Catecholamine-activated lipolysis in visceral but not subcutaneous fat cells is associated with cardiovascular risk factors in obesity.

Regional impact of adipose tissue morphology on the metabolic profile in morbid obesity

AIMS/HYPOTHESIS

The aim of this study was to determine whether the mean size of fat cells in either visceral or subcutaneous adipose tissue has an impact on the metabolic and inflammatory profiles in morbid obesity.

METHODS

In 80 morbidly obese women, mean visceral (omental) and subcutaneous fat cell sizes were related to in vivo markers of inflammation, glucose metabolism and lipid metabolism.

RESULTS

Visceral, but not subcutaneous, adipocyte size was significantly associated with plasma apolipoprotein B, total cholesterol, LDL-cholesterol and triacylglycerols (p ranging from 0.002 to 0.015, partial r ranging from 0.3 to 0.4). Subcutaneous, but not visceral, adipocyte size was significantly associated with plasma insulin and glucose, insulin-induced glucose disposal and insulin sensitivity (p ranging from 0.002 to 0.005, partial r ranging from -0.34 to 0.35). The associations were independent of age, BMI, body fat mass or body fat distribution. Adipose tissue hyperplasia (i.e. many small adipocytes) in both regions was significantly associated with better glucose, insulin and lipid profiles compared with adipose hypertrophy (i.e. few large adipocytes) in any or both regions (p ranging from <0.0001 to 0.04). Circulating inflammatory markers were not associated with fat cell size or corresponding gene expression in the fat cell regions examined.

CONCLUSIONS/INTERPRETATION

In morbidly obese women region-specific variations in mean adipocyte size are associated with metabolic complications but not systemic or adipose inflammation. Large fat cells in the visceral region are linked to dyslipidaemia, whereas large subcutaneous adipocytes are important for glucose and insulin abnormalities. Hyperplasia (many small adipocytes) in both adipose regions may be protective against lipid as well as glucose/insulin abnormalities in obesity.

Primary differences in lipolysis between human omental and subcutaneous adipose tissue observed using in vitro differentiated adipocytes

Catecholamine-induced lipolysis is elevated in omental as compared to subcutaneous adipocytes due to primary differences between the two cell types (i.e., they have different progenitor cells). Whether there is regional variation in atrial natriuretic peptide (ANP)-induced lipolysis is unknown. We studied whether beta-adrenoceptor signaling to lipolysis and ANP-induced lipolysis are involved in the primary differences in lipolysis. In vitro experiments on differentiated preadipocytes from human subcutaneous and omental adipose tissue were performed. The cells were kept in culture for a relative long duration, so any influence of local environment and circulation in the various adipose tissue depots could be excluded. Using beta1-, beta2-, and beta3-adenoceptor agonists, lipolysis was found to be significantly higher in omental as compared to subcutaneous differentiated preadipocytes. Forskolin and dibutyryl cAMP, which act at post-adrenoceptor levels, did not show any regional difference. There was no regional difference in ANP-induced lipolysis. Gene expression of beta1- and beta3-adrenoceptors was higher and beta2-adrenoceptor expression was lower in the omental cells. Omental fat cells have an increased beta-adrenoceptor-mediated lipolysis principally due to primary differences in the early event that couples beta-adrenoceptor subtypes to G-proteins. ANP-induced lipolysis is not subject to primary regional variation.

Impaired subcutaneous adipocyte lipogenesis is associated with systemic insulin resistance and increased apolipoprotein B/AI ratio in men and women

OBJECTIVES

To study the association between subcutaneous fat cell lipogenesis and components of the metabolic syndrome (systemic insulin resistance, dyslipidaemia and hypertension).

DESIGN AND SETTING

A university hospital-based cross-sectional study of 383 subjects (303 women and 80 men) with a wide range of BMI (18-53 kg m(-2)).

RESULTS

Strong negative correlations between in vitro fat cell lipogenesis (basal and after maximal insulin stimulation) and HOMA-IR were present in both genders (r = -0.42 to -0.56, P < 0.0001 and r = -0.37 to -0.44, P < 0.001, for women and men respectively). Insulin sensitivity measured using the insulin tolerance test (K(ITT)) was also correlated with adipocyte lipogenesis (r = 0.47-0.57, P < 0.0001, women, r = 0.52-0.70, P < 0.001, men). Plasma apolipoprotein B/AI-ratio negatively associated with fat cell lipogenesis in women (r = -0.41 to-0.51, P < 0.0001,) and men (r = -0.49 to -0.55, P < 0.0001). The negative relationship of fat cell lipogenesis with blood pressure was significant in women (r = -0.27 to -0.28, P < 0.0002,) but not in men (P = 0.08-0.09). All correlations remained significant after adjusting for differences in fat cell volume, body mass index, waist- to hip- ratio or age (P < 0.01).

CONCLUSIONS

Subcutaneous adipocyte lipogenesis is negatively associated with systemic insulin resistance, plasma apolipoprotein B/AI-ratio and blood pressure supporting the view that impaired fat cell function per se may contribute to the development of the metabolic syndrome.

Human adipose triglyceride lipase (PNPLA2) is not regulated by obesity and exhibits low in vitro triglyceride hydrolase activity

AIMS/HYPOTHESIS

The recent identification of murine adipose triglyceride lipase (ATGL, now known as patatin-like phospholipase domain containing 2 [PNPLA2]), gene product of Pnpla2, has questioned the unique role of hormone sensitive lipase (HSL, now known as LIPE), gene product of Lipe, in fat cell lipolysis. Here, we investigated human ATGL and HSL adipose tissue gene expression and in vitro lipase activity.

SUBJECTS, MATERIALS AND METHODS

Levels of mRNA in adipose tissue from healthy obese and non-obese subjects were measured and lipase activity and adipocyte lipolytic capacity determined. HSL and ATGL cDNAs were transfected into Cos-7 cells and the relative tri- and diglyceride hydrolase activities were measured.

RESULTS

Obesity was associated with a decreased subcutaneous and increased omental adipose tissue level of HSL mRNA. Subcutaneous HSL mRNA content was normalised upon weight reduction. In contrast, ATGL mRNA levels were unaffected by obesity and weight reduction. A high adipose tissue lipase activity was associated with increased maximal lipolysis and increased HSL, but not with ATGL mRNA levels. The in vitro triglyceride hydrolase activity of HSL was markedly higher than that of ATGL and contrary to HSL, ATGL was devoid of diglyceride hydrolase activity. The use of a selective HSL-inhibitor resulted in complete inhibition of HSL-mediated tri- and diglyceride hydrolase activity. The pH profile of human white adipose tissue triolein hydrolase activity was identical to that of HSL but differed from the ATGL profile.

CONCLUSIONS/INTERPRETATION

HSL, but not ATGL gene expression shows a regulation according to obesity status and is associated with increased adipose tissue lipase activity. Moreover, HSL has a higher capacity than ATGL to hydrolyse triglycerides in vitro.

The hormone-sensitive lipase C-60G promoter polymorphism is associated with increased waist circumference in normal-weight subjects

OBJECTIVE

Hormone-sensitive lipase (HSL) is a key enzyme in the mobilization of fatty acids from triglyceride stores in adipocytes. The aim of the present study was to investigate the role of the HSL gene promoter variant C-60G, a polymorphism which previously has been associated with reduced promoter activity in vitro, in obesity and type 2 diabetes.

DESIGN

We genotyped two materials consisting of obese subjects and non-obese controls, one material with offspring-parents trios, where the offspring was abdominally obese and one material with trios, where the offspring had type 2 diabetes or impaired glucose homeostasis. HSL promoter containing the HSL C-60G G-allele was generated and tested against a construct with the C-allele in HeLa cells and primary rat adipocytes. HSL mRNA levels were quantified in subcutaneous and visceral fat from 33 obese subjects.

RESULTS

We found that the common C-allele was associated with increased waist circumference and WHR in lean controls, but there was no difference in genotype frequency between obese and non-obese subjects. There was a significant increased transmission of C-alleles to the abdominally obese offspring but no increased transmission of C-alleles was observed to offspring with impaired glucose homeostasis. The G-allele showed reduced transcription in HeLa cells and primary rat adipocytes. HSL mRNA levels were significantly higher in subcutaneous compared to visceral fat from obese subjects.

CONCLUSION

The HSL C-60G polymorphism is associated with increased waist circumference in non-obese subjects.

Common neuropeptide Y2 receptor gene variant is protective against obesity among Swedish men

BACKGROUND

Gut hormones and their receptors are considered important in the control of feeding behavior. The gut hormone peptide-YY (PYY) has anorexic effects via the inhibitory neuropeptide Y2 receptor (Y2R) highly expressed in orexigenic NPY/AGRP neurons within the arcuate nucleus, a major integrator of appetite control in the hypothalamus.

DESIGN

Genetic case-control association study of single nucleotide polymorphisms (SNPs) in Y2R and PYY.

SUBJECTS

Swedish Caucasians comprising 148 lean, 129 overweight/obese and 226 morbidly obese men.

MEASUREMENTS

Genotypes of the common, silent and conserved SNP Y2R 585T>C and the common SNP PYY Arg72Thr, as well as various obesity-related clinical parameters.

RESULTS

Obese men had a lower allele and homozygosity frequency of the common allele 585T>C:T which was particularly evident comparing morbidly obese with lean men (P = 0.002), and analyzing dependence between continuous body mass index (BMI) and genotype (P = 0.002). In agreement, systolic blood pressure tended to be lower in those homozygous for allele T, which was not explained by the BMI - genotype dependence. We found no association to obesity for the PYY Arg72Thr polymorphism, which is located nearby the essential carboxy terminal.

CONCLUSION

A common and conserved variant of the PYY and NPY receptor Y2R is less prevalent among obese compared to among lean Swedish men. This suggests that the common Y2R variant is protective against obesity. Our findings further implicate Y2R in food intake regulation.

No difference in lipolysis or glucose transport of subcutaneous fat cells between moderate-fat and low-fat hypocaloric diets in obese women

The objective of the present study was to evaluate the effect of two different diets on lipolysis and lipogenesis in subcutaneous fat cells from obese women. In a ten-week nutritional intervention study, forty women were randomly assigned to a hypoenergetic-2,514 kJ (- 600 kcal/day) diet of either moderate-fat/moderate-carbohydrate or low-fat/high-carbohydrate content. Body weight was equally reduced by approximately 7.5 % in both diet groups (p = 0.58). A subcutaneous adipose tissue biopsy was obtained for subsequent measurement of triglyceride breakdown (lipolysis) using drugs active at different steps of the lipolytic signaling cascade, and lipid synthesis (glucose transport) before and after intervention. No difference was found between the two diet groups at the maximum rate of either lipolysis or adrenoceptor sensitivity (p-values: 0.14 - 0.97). Inhibition of lipolysis by insulin was also similar in both diet groups before and after intervention. Finally, insulin-stimulated glucose transport did not show any changes that could be attributed to the type of diet. In conclusion, our data suggest that macronutrient diet composition has no major influence on glucose transport or mobilization of triglycerides in human subcutaneous fat cells of obese women.

Prospective and controlled studies of the actions of insulin and catecholamine in fat cells of obese women following weight reduction

AIMS/HYPOTHESIS

Enlarged fat cells from obese subjects are characterised by insulin resistance and abnormal adrenergic regulation of lipolysis. The aim of the present study was to examine whether these aberrations return to normal following weight reduction.

MATERIALS AND METHODS

Obese women (n=25) were investigated before and 3+/-1 years (mean+/-SD) after steady-state weight reduction and compared with control women who were matched to the cases at re-examination in terms of age and BMI. Adipocyte volume, lipogenesis and lipolysis were determined in isolated subcutaneous fat cells following stimulation or inhibition at different steps of the lipolytic cascade.

RESULTS

Weight reduction decreased fat cell volume and basal and adrenergic-regulated lipolysis rates to values that were 20-40% lower than those in control women (p=0.0002-0.03), despite the fact that percentage body fat was almost identical in the two groups of women. Fat cell volume was directly proportional to lipolysis in obese subjects, both before and after weight reduction, and in control subjects. Insulin-induced antilipolysis and lipogenesis were completely normalised after weight reduction.

CONCLUSIONS/INTERPRETATION

Body-weight-reduced obese women had low basal and catecholamine-stimulated adipocyte lipolysis, presumably due to adipose tissue hyperplasia. This could make an important contribution to body weight gain following weight loss. Adipocyte insulin resistance is secondary to obesity.

Association study between chromosome 10q26.11 and obesity among Swedish men

OBJECTIVE

Proximal chromosome 10q26 was recently linked to waist/hip ratio in European and African-American families. The objective was to investigate whether genomic variation in chromosome 10q26.11 reflects variation in obesity-related clinical parameters in a Swedish population.

DESIGN

Genetic association study of single-nucleotide polymorphisms (SNPs) in chromosome 10q26.11 and obesity-related clinical parameters was performed. Obesity was defined as body mass index (BMI) > or = 30 kg/m2.

SUBJECTS

Swedish Caucasians comprising 276 obese and 480 nonobese men, 313 obese and 494 nonobese women, 177 obese and 163 nonobese patients with type 2 diabetes mellitus (T2DM), and 106 obese and 201 nonobese subjects with impaired glucose tolerance (IGT) patients.

MEASUREMENTS

Genotypes of 11 SNPs at chromosome 10q26.11, and various obesity-related clinical parameters.

RESULTS

Homozygosity of a common haplotype constructed by three SNPs, rs2185937, rs1797 and hCV1402327, covering an interval of 2.7 kb, was suggested to confer an increased risk for obesity of 1.5 among men (P = 0.043). The C allele frequency and homozygous genotype frequency of the rs1797 tended to be higher among obese compared to among nonobese men (P = 0.017 and 0.020, respectively). The distribution of BMI and diastolic blood pressure was higher among those with the C/C genotype (P = 0.022 and 0.0061, respectively). The obese and the nonobese groups were homogeneous over BMI subgroups with regard to rs1797 risk genotype distribution. There was no tendency for association between rs1797 and obesity among neither women nor T2DM nor IGT patients.

CONCLUSION

We show support for association between proximal chromosome 10q26.11 and obesity among Swedish men but not women through the analysis of a haplotype encompassing 2.7 kb.

β1-Adrenoceptor gene polymorphism predicts long-term changes in body weight

BACKGROUND

The genes controlling long-term weight changes are largely unknown. The beta1 (beta1)-adrenoceptor gene contains two nonsynonomous single nucleotide polymorphisms (SNPs), Ser49Gly and Gly389Arg, that both are functional in human cell lines.

DESIGN

We investigated the influence of these two SNPs on short- and long-term changes in body mass index (BMI) in a population-based cohort of 761 women who were examined during pregnancy in 1984-1985 and 15 y thereafter.

RESULTS

At entry, no genotype effect on BMI was found. After 15 y, the BMI of women carrying the Gly49-genotype (25.3+/-0.3 kg/m(2)) was higher (P<0.005) than that of Ser49-women (24.4+/-0.2 kg/m(2)). Also, the BMI-increase over 15 y was higher (P=0.018) in Gly49-women (3.3+/-0.2 kg/m(2)) than in Ser49-women (2.8+/-0.1 kg/m(2)). The odds ratio for being overweight after 15 y having the Gly49-genotype was 1.6 (confidence interval 1.1-2.3, P=0.01). No effect of SNP 389 alone on BMI was found but there was a genotype-genotype interaction. Those carrying the Gly49-Gly389 combination increased their BMI about 0.7 kg/m(2) more than other combinations (P=0.025). No genotype effect on BMI changes during pregnancy for either SNP was found.

CONCLUSION

Polymorphism of the beta1-adrenoceptor gene influences long-term weight gain and the incidence of adult-onset overweight in women.

Adipose tissue gene expression in obese subjects during low-fat and high-fat hypocaloric diets

AIMS/HYPOTHESIS

Adaptation to energy restriction is associated with changes in gene expression in adipose tissue. However, it is unknown to what extent these changes are dependent on the energy restriction as such or on the macronutrient composition of the diet.

METHODS

We determined the levels of transcripts for 38 genes that are expressed in adipose tissue and encode transcription factors, enzymes, transporters and receptors known to play critical roles in the regulation of adipogenesis, mitochondrial respiration, and lipid and carbohydrate metabolism. Two groups of 25 obese subjects following 10-week hypocaloric diet programmes with either 20-25 or 40-45% of total energy derived from fat were investigated. Levels of mRNA were measured by performing real-time RT-PCR on subcutaneous fat samples obtained from the subjects before and after the diets.

RESULTS

The two groups of subjects lost 7 kg over the duration of the diets. Ten genes were regulated by energy restriction; however, none of the genes showed a significantly different response to the diets. Levels of peroxisome proliferator-activated receptor gamma co-activator 1alpha mRNA were increased, while the expression of the genes encoding leptin, osteonectin, phosphodiesterase 3B, hormone-sensitive lipase, receptor A for natriuretic peptide, fatty acid translocase, lipoprotein lipase, uncoupling protein 2 and peroxisome proliferator-activated receptor gamma was decreased. Clustering analysis revealed new potential coregulation of genes. For example, the expression of the genes encoding the adiponectin receptors may be regulated by liver X receptor alpha.

CONCLUSIONS/INTERPRETATION

In accordance with the comparable loss of fat mass produced by the two diets, this study shows that energy restriction and/or weight loss rather than the ratio of fat: carbohydrate in a low-energy diet is of importance in modifying the expression of genes in the human adipose tissue.

A common polymorphism in the interleukin-6 gene promoter is associated with overweight

OBJECTIVE

Human body fat mass is to a large extent genetically determined, but little is known about the susceptibility genes for common obesity. Interleukin-6 (IL-6) suppresses body fat mass in rodents, and IL-6 treatment increases energy expenditure in both rodents and humans. The -174 G/C single-nucleotide polymorphism (SNP) in the IL-6 gene promoter is common in many populations, and -174 C-containing promoters have been found to be weaker enhancers of transcription. Moreover, a SNP at position -572 in the IL-6 promoter has recently been reported to affect transcription. The objective was to investigate the association between the IL-6 gene promoter SNPs and obesity.

DESIGN

Trans-sectional association study of IL-6 gene promoter SNPs and indices of obesity.

SUBJECTS

Two study populations, the larger one consisting of hypertensive individuals (mean age 57 y, 73% males, n=485) and the other consisting of 20 y younger nonobese healthy females (n=74).

MEASUREMENTS

Genotyping for the -174 IL-6 G/C and the -572 G/C SNPs, body mass index (BMI), serum leptin levels, serum IL-6 levels, C-reactive protein, fasting blood glucose and various blood lipids.

RESULTS

The common -174 C allele (f(C)=0.46), but not any -572 allele, was associated with higher BMI and higher serum leptin levels in both study populations. In the larger population, there were significant odds ratios for the association of CC (2.13) and GC (1.76) genotypes with overweight (BMI>25 kg/m(2)). Moreover, as the C allele was common, it accounted for a significant population-attributable risk of overweight (12%; CI 2-21%), although its average effect was modest in this sample.

CONCLUSION

Genetically determined individual differences in production of IL-6 may be relevant for the regulation of body fat mass.

Relationship between β-2 adrenoceptor gene haplotypes and adipocyte lipolysis in women

BACKGROUND AND AIMS

The beta(2)-adrenergic receptors are important for adipocyte lipolysis regulation by catecholamines in humans. The beta(2)-adrenoceptor gene is highly polymorphic. The role of these genetic variations for adipocyte lipolysis was investigated.

DESIGN AND METHODS

Six single-nucleotide polymorphisms (SNPs) in the promotor region and four SNPs in the coding region (leading to amino-acid substitution) of the beta(2)-adrenoceptor gene were determined in 141 overweight or obese, but otherwise healthy women. Lipolysis experiments were performed on isolated subcutaneous adipocytes.

RESULTS

Three homozygous haplotypes (6/6, 4/4 and 2/2) were found that differed about 500-fold in noradrenaline sensitivity or beta(2)-adrenoceptor sensitivity (6/6>2/2>4/4, P=0.01). The haplotypes also differed by 100% in maximum noradrenaline-induced lipolysis rates (6/6>2/2>4/4). However, there was no influence on beta(1)-, beta(3)- or alpha(2)A-adrenoceptor sensitivity. Heterozygosity at one or several SNPs in the haplotypes influenced the beta(2)-adrenoceptor sensitivity significantly.

CONCLUSION

Multiple SNPs in the beta(2)-adrenoceptor gene form several haplotypes that markedly influence beta(2)-receptor function- and catecholamine-induced lipolysis in fat cells. These haplotypes may be important genetic factors behind impaired lipolysis in obesity.

Evidence for an important role of perilipin in the regulation of human adipocyte lipolysis

AIMS/HYPOTHESIS

We investigated the role of the adipocyte-specific protein perilipin for lipolysis in humans.

METHODS

Perilipin protein content and lipolysis rates were measured in human subcutaneous fat cells of non-obese (n=10) and obese (n=117) women. Single nucleotide polymorphisms in the perilipin gene were examined in obese subjects.

RESULTS

Basal and noradrenaline-induced rates of lipolysis were two to fourfold increased (p<0.01) and perilipin protein content decreased 50% (p=0.005) in adipocytes of the obese women. In subjects matched for body mass index and fat-cell volume, a high rate of lipolysis was associated with a low adipocyte content of perilipin (p=0.01). Adipocyte content of perilipin was inversely correlated with the circulating concentrations of glycerol (r=0.62) and non-esterified fatty acids (n=0.49). A gene polymorphism (rs891460 A/G) in intron 6 was common. In AA subjects basal and noradrenaline induced lipolysis were 50 to 100% times more rapid (p</=0.01) and the adipocyte perilipin content was about 80% reduced (p=0.005) as compared to GG carriers. Intermediate values were found in AG carriers.

CONCLUSIONS/INTERPRETATION

Perilipin seems important for the regulation of lipolysis in human fat cells. Obesity and a polymorphism in the perilipin gene associate with decreased protein content of perilipin and increased basal (unstrained) and noradrenaline-induced lipolysis. Low perilipin content also associate with high in vivo lipolytic activity. Perilipin could be a factor behind impaired lipolysis in insulin-resistant conditions.

The hormone-sensitive lipase i6 gene polymorphism and body fat accumulation

BACKGROUND

The hormone sensitive lipase (HSL) catalyses the breakdown of adipose tissue triglycerides into free fatty acids. The objective of this study was to determine whether HSLi6 microsatellite allele 5 (A5) and/or homozygosity for this allele is associated with body fat in Swedes.

DESIGN

A large case-control study on gender-specific association for several body fat-related clinical parameters to HSLi6 A5, and to HSLi6 A5 homozygosity, comparing A5 with the other alleles in group. The subjects were 323 obese patients (85 males, 238 females) without other metabolic complication, and 301 nonobese healthy individuals (134 males, 167 females). They were analyzed for various body fat-related clinical parameters, and HSLi6 genotype.

RESULTS

Homozygosity for HSLi6 A5 was a risk factor for obesity, BMI > or = 30 kg m-2 (Odds ratio = 1.75, 95% CI 1.58-1.93) and body fat mass > 39.6% (Odds ratio = 1.89, 95% CI 1.60-2.23) in women. This genotype was also associated with increased diastolic blood pressure and triglyceride level among nonobese women, and with increased body fat mass and waist/hip ratio among nonobese men.

CONCLUSION

HSLi6 A5 homozygosity is a risk factor for body fat accumulation.

Glucocorticoid-regulated adipose tissue secretion of PAI-1, but not IL-6, TNFalpha or leptin in vivo

OBJECTIVE

Glucocorticoids are well-known regulators of adipose tissue metabolism and endocrine function. The aim of this study was to examine glucocorticoid effect on plasminogen activator inhibitor 1 (PAI-1), tumour necrosis factor alpha (TNFalpha), leptin and interleukin-6 (IL-6) adipose tissue secretion.

MATERIAL AND METHODS

Twelve healthy postmenopausal women with mean BMI of 28.9 kg/m(2) (+/- 0.8 SEM) received 25 mg prednisolone daily for 7 days. Before and after glucocorticoid treatment adipose tissue secretion of PAI-1, leptin, IL-6 and TNFalpha were measured, and adipocyte PAI-1 mRNA as well as anthropometrical and bio-chemical data were obtained.

RESULTS

Anthropometric measurements remained unaffected. Analyses of venous blood-samples showed a borderline increase of insulin levels (p = 0.062). PAI-1 secretion from adipose tissue increased (1.9 +/- 0.2 vs. 3.5 +/- 0.5 ng/g triglycerides, p = 0.012), but PAI-1 mRNA levels did not (0.19 +/- 0.02 vs. 0.21 +/- 0.04 arbitrary units after normalised to beta-actin, p = 0.51). There were no apparent differences in IL-6, TNFalpha or leptin secretion after glucocorticoid exposure.

CONCLUSION

This study shows an increased secretion of PAI-1, but not IL-6, TNFalpha or leptin, from abdominal adipose tissue after in vivo glucocorticoid treatment, which may be a finding of pathophysiological importance given the well-known effect of glucocorticoid excess on metabolic aberrations and cardiovascular morbidity.

Effects of obesity and weight loss on the expression of proteins involved in fatty acid metabolism in human adipose tissue

OBJECTIVE

Disturbances in adipocyte lipolysis in obesity may contribute to elevated circulating non-esterified fatty acid (NEFA) concentrations and insulin resistance. In experimental models, NEFA metabolism is influenced by adipocyte proteins such as adipocyte and keratinocyte lipid binding proteins (aP2/ALBP and mal1/KLBP) and fatty acid translocase (CD36). We investigated the effect of obesity and weight loss on the expression of these proteins in human subcutaneous adipose tissue.

STUDY DESIGN AND SUBJECTS

Subcutaneous adipose tissue was obtained from 12 obese (body mass index (BMI) 42.4+/-1.6 kg/m(2)) and 12 lean (23.4+/-0.6 kg/m(2)) subjects. The obese subjects underwent gastric banding and biopsies were taken again after 2 y following a significant weight reduction (BMI 32.8+/-1.4 kg/m(2)). Adipose tissue proteins were quantified by Western blotting.

RESULTS

Differential expression of ALBP, KLBP and CD36 was observed in lean and weight-reduced subjects compared with obese individuals. This resulted in a significantly lower ALBP/KLBP ratio in lean and weight-reduced individuals compared to obese subjects. Furthermore there was a significant influence of gender on this ratio. Moreover, the commonly used internal standard protein actin was expressed significantly higher in lean compared to obese individuals.

CONCLUSION

The relative content of ALBP and KLBP in human adipose tissue changes with obesity, weight loss and gender indicating differential regulation. Differing responses in the expression patterns of adipose tissue proteins capable of binding NEFAs in response to weight changes suggest a potential importance in the development of obesity-associated complications.

A polymorphism in the leptin promoter region (-2548 G/A) influences gene expression and adipose tissue secretion of leptin

There is a large inter-individual variation in circulating leptin concentrations at each level of body fat content. The reason for this is unknown. We investigated whether a polymorphism in the promoter region of the leptin gene (-2548G/A) influences gene transcription and leptin expression in 39 non-obese female subjects. Eleven subjects were homozygous for the AA genotype, 18 were heterozygous (GA) and 10 carried the GG genotype. AA subjects had higher levels of serum leptin than did GA/GG subjects (14.5 +/- 2.1 vs. 9.7 +/- 0.9 ng/ml, p = 0.02). Adipose tissue leptin secretion rate in AA subjects was twice as high as in GA/GG subjects: 1158 +/- 288 vs. 626 +/- 84 ng/2 h/10 (7) cells (p = 0.02). These differences were also statistically significant with leptin levels adjusted for body mass index (p = 0.03 - 0.04). Adipose tissue leptin mRNA levels were 60 % higher in AA subjects, as compared to GA/GG subjects, 74 +/- 10 vs. 46 +/- 4 amol/ micro g RNA (p = 0.01). EMSA revealed that nuclear extracts derived from both U937 cells and human adipocytes form a protein-DNA complex with the leptin -2548G/A polymorphic site and bind with higher affinity to the -2548A-site. In conclusion, a common polymorphism in the promoter of the human leptin gene (-2548G/A) influences leptin expression, possibly at the transcriptional level, and therefore also adipose secretion levels of the hormone.

The common -675 4G/5G polymorphism in the plasminogen activator inhibitor -1 gene is strongly associated with obesity

AIMS/HYPOTHESIS

Plasminogen activator inhibitor 1 (PAI-1) increases in several insulin-resistant conditions such as obesity. We tested the hypothesis that the PAI-1 gene might be a candidate for obesity and Type II (non-insulin-dependent) diabetes mellitus.

METHODS

We investigated the frequency of a common and functional -675 4G/5G promoter polymorphism in the PAI-1 gene in 188 lean, 70 overweight (BMI 25-30 kg/m(2)) and 247 obese otherwise healthy Scandinavian subjects.

RESULTS

The genotypic ( p = 0.002), or allelic ( p = 0.0004) distribution differed markedly between the three groups. Homozygosity for 4G was more common among obese people, whereas homozygosity for 5G was more common among lean subjects. Heterozygosity was evenly distributed. The lean and overweight groups did not differ in frequency distribution. The relative risk for being obese in comparison to being lean for 4G/4G was threefold higher ( p = 0.0003). Also, carriers of the 4G allele in the heterozygous or homozygous form were distributed differently between the three groups ( p = 0.006). The 4G carriers were more common among the obese than the lean group. The latter group did not differ from the overweight group. The relative risk of being obese in comparison with lean was twofold increased in 4G carriers ( p = 0.0015). Similar results were obtained in men and women.

CONCLUSION/INTERPRETATION

Thus, the common -675 4G/5G polymorphism in the PAI-1 gene is strongly linked to obesity and a markedly increased risk for obesity is associated with the 4G allele in its homozygous form.

Polymorphism in the Calpain 10 gene influences glucose metabolism in human fat cells

AIMS/HYPOTHESIS

A common G to A polymorphism ( UCSNP-43) in the Calpain 10 gene was recently found to be associated with Type II (non-insulin-dependent) diabetes mellitus and variations in post-absorptive and insulin stimulated glucose metabolism in vivo. We aimed to study the influence of Calpain 10 polymorphism on insulin action in fat cells.

METHODS

Calpain 10 polymorphism ( UCSNP-19, -43 or -63) were set in relation to lipolysis and lipogenesis in isolated subcutaneous adipocytes of 46 apparently healthy non-obese subjects.

RESULTS

For UCSNP-43 the G/G genotype had twofold higher basal and insulin stimulated rates as compared with AA/AG genotypes. However, there was no genotype effect on basal or insulin inhibited lipolysis rates in fat cells. The protein amount of GLUT 4 in adipocytes was not influenced by the polymorphism. Fat cells expressed mRNA for the Calpain 10 gene at a relatively high concentration, about 4 amol/microg RNA, which is similar to that of uncoupling protein-2. Neither a UCSNP-19 nor a UCSNP-63 polymorphism in the Calpain 10 gene was found to be associated with basal or insulin-induced adipocyte lipolysis and lipogenesis. None of the polymorphisms influenced body mass index or fasting plasma concentrations of insulin and glucose in 693 non-obese healthy subjects.

CONCLUSIONS/INTERPRETATION

The Calpain 10 gene could be involved in the regulation of glucose metabolism but not lipolysis in human fat cells, although it does not involve adipocyte GLUT-4 protein content. It is possible that the Calpain 10 gene predisposes to diabetes by influencing the glucose metabolism.

Depot-specific variation in protein-tyrosine phosphatase activities in human omental and subcutaneous adipose tissue: a potential contribution to differential insulin sensitivity

Compared with the sc depot, omental (om) adipose tissue is relatively resistant to the metabolic actions of insulin. Protein-tyrosine phosphatases (PTPases) modulate receptor kinase activation and signal transduction in insulin-sensitive tissues, and their activity is dependent on the reduced state of the cysteine thiol required for catalysis. Using a novel anaerobic technique to avoid air oxidation, we found that the mean endogenous PTPase activity was 2.1-fold higher in om compared with paired samples of sc adipose tissue (P < 0.003). The specific activity of PTP1B isolated under anaerobic conditions was also 41% higher in om adipose tissue (P < 0.001). Interestingly, the total PTPase activity from both adipose depots and the specific activity of PTP1B was increased by 42-71% after reduction in vitro with dithiothreitol, indicating that a major fraction of the cellular PTPase activity can be reactivated by sulfhydryl reduction. The mass of the insulin receptor beta-subunit and the PTPases PTP1B and leukocyte antigen related was not significantly different between the two adipose depots. These studies provide the first demonstration that endogenous PTPase activity, including PTP1B, is increased in om adipose tissue and may contribute to the relative insulin resistance of this fat depot. The finding that a substantial fraction of PTPase activity in human adipose tissue is present in a latent, oxidized form also suggests a potential means of in vivo regulation of these important cellular enzymes that modulate the insulin signaling cascade.

The Arg 389 Gly beta1-adrenergic receptor gene polymorphism and human fat cell lipolysis

BACKGROUND

The beta1-adrenoceptor is a candidate gene for obesity because of its role in catecholamine-induced energy homeostasis. A common Arg 389 Gly variant polymorphism has been shown in recombinant cells to influence its-coupling properties.

OBJECTIVE

To investigate the effect of the Arg 389 Gly beta1-adrenoceptor polymorphism on catecholamine-induced lipolysis in native human fat cells obtained by subcutaneous biopsy.

SUBJECTS

Two-hundred and ninety-eight apparently healthy male and female subjects with a wide variation in body mass index (BMI, 18-60 kg/m2).

MEASURES

The lipolytic sensitivities and maximum lipolytic action of noradrenaline and the selective adrenoceptor agonists dobutamine (beta1), terbutaline (beta2) and CGP 12177 (beta3) were determined in isolated subcutaneous adipocytes and related to beta-adrenoceptor radioligand binding parameters.

RESULTS

No differences in the sensitivity or maximum lipolytic capacity of the agonists were found between the genotypes. This was true both when all subjects were analyzed together and when subgroups (lean, obese, men, women) were analyzed separately. Radioligand binding to beta1- or beta2-adrenoceptors was also similar between genotypes. The polymorphism had no important influence on either BMI or the distribution of obese and non-obese subjects between the genotypes.

CONCLUSION

The distribution of the Arg 389 Gly polymorphism is similar in lean and obese subjects and has no apparent effect on the lipolytic response to beta-adrenergic stimulation in native human adipocytes. This suggests, despite the altered coupling properties reported in recombinant cells, that the Arg 386 Gly polymorphism has no important influence on human obesity.

Downregulation of uncoupling protein 2 mRNA in women treated with glucocorticoids

OBJECTIVE

Glucocorticoids are well-known regulators of energy turnover and adipose tissue metabolism. We investigated the effect of glucocorticoids on the expression of the human uncoupling protein 2 (UCP 2) gene, which has been implicated in energy expenditure.

DESIGN

Prednisolone (25 mg) was administered orally daily for 7 days. Subcutaneous adipose tissue UCP 2 mRNA was measured before and after treatment.

SUBJECTS

Eight healthy female subjects (age 52-63 y; body mass index 25-34 kg/m2).

RESULTS

No differences in body weight, waist-to-hip ratio or plasma-values of FFA or glucose were found after prednisolone treatment, as compared to pre-treatment values under these conditions. In contrast, plasma insulin levels were significantly increased by glucocorticoid administration, 54+/-6 before vs 70+/-12 (mean+/-sem) pmol/l after treatment (P=0.028). Furthermore, using RT-competitive-PCR, the UCP 2 mRNA level in abdominal subcutaneous adipose tissue was found to be down-regulated by half (6.3+/-0.4 vs 3.1+/-0.8 amol/microg RNA, P=0.012) after glucocorticoid treatment. No difference in expression levels of the reference gene 18SrRNA was observed before, as compared to after prednisolone exposure (249+/-11 vs 248+/-30 amol/microg RNA, P=0.87).

CONCLUSION

These data suggest that glucocorticoids may play a role in the regulation of UCP 2 mRNA expression in human adipose tissue in vivo.

A common hormone-sensitive lipase i6 gene polymorphism is associated with decreased human adipocyte lipolytic function

Hereditary factors may be involved in the pathogenesis of type 2 diabetes. A polymorphism in the hormone-sensitive lipase (HSL) gene (HSLi6) is associated with obesity and diabetes, although it is unknown whether the polymorphism is functional and thereby influences lipolysis. We genotyped 355 apparently healthy nonobese male and female subjects for the HSLi6 polymorphism. Allele 5 was found to be the most common allele (allele frequency 0.57). In 117 of the subjects, we measured abdominal subcutaneous fat cell lipolysis induced by drugs acting at various steps in the lipolytic cascade. The lipolysis rate induced by norepinephrine isoprenaline (acting on beta-adrenoceptors), forskolin (acting on adenylyl cyclase), and dibutyryl cyclic AMP (acting on HSL) were all decreased by approximately 50% in allele 5 homozygotes, as compared with noncarriers. Heterozygotes showed an intermediate lipolytic rate. The difference in lipolysis rate between genotypes was more pronounced in men than in women. We conclude that allele 5 of the HSLi6 polymorphism is associated with a marked decrease in the lipolytic rate of abdominal fat cells. This may in turn contribute to the development of obesity.

Fatty acid binding protein expression in different adipose tissue depots from lean and obese individuals

AIMS/HYPOTHESIS

This study investigated the expression of adipose tissue fatty acid binding proteins (FABPs) in subcutaneous and visceral human adipose tissue depots from lean and obese individuals.

METHODS

Adipocyte lipid binding protein (ALBP) and keratinocyte lipid binding protein (KLBP) expression was quantified by western blot in subcutaneous and omental adipose tissue from 20 obese and 9 lean individuals. RNA expression was quantified by Northern blot in the obese subjects.

RESULTS

In the obese subjects, ALBP protein and RNA expression was higher in subcutaneous compared with omental adipose tissue (increases of 31 +/- 14 % and 40 +/- 13 % respectively, both p < 0.05), whereas in the lean group, KLBP protein levels were 32 +/- 9 % lower in subcutaneous fat (p < 0.03). However, the ALBP/KLBP ratio was greater in subcutaneous compared to omental adipose tissue from both lean and obese subjects: increases of 187 +/- 71 % (p = 0.01) and 52 +/- 23 % (p = 0.17) respectively for the protein ratio, and 21 +/- 6 % for RNA (p = 0.01, obese individuals). In lean subjects, insulin concentrations correlated positively with the ALBP/KLBP protein ratio in both depots (both p < or = 0.03).

CONCLUSION/INTERPRETATION

There are regional differences in adipose tissue FABP expression, which could be influenced by obesity. However, the ALBP/KLBP ratio is greater in subcutaneous than visceral adipose tissue in lean as well as in obese subjects. Investigation of adipose tissue FABPs could further our understanding of the role of fatty acids in the insulin resistance syndrome.

Increased expression of eNOS protein in omental versus subcutaneous adipose tissue in obese human subjects

OBJECTIVE

To investigate the expression of eNOS and iNOS mRNA and protein in adipose tissue from subcutaneous (s.c.) and omental adipose tissue of obese subjects.

DESIGN

Subcutaneous and omental adipose tissue was obtained from subjects undergoing weight reduction surgery. Messenger RNA and protein levels were measured in tissue extracts and related to basal lipolysis, which was measured in isolated adipocytes from the same subjects.

SUBJECTS

Eight overweight but otherwise healthy male subjects (age 43.4+/-10.3 y, BMI 39+/-3.5 kg/m(2), mean+/-s.e.m.).

MEASUREMENTS

For mRNA detection a competitive reverse transcription polymerase chain reaction method was used while protein was detected by Western blot. Glycerol release was determined in isolated adipocytes using a standard luminometric assay.

RESULTS

Tissue mRNA levels for eNOS in s.c. tissue were 6098+/-1969 amol/mg RNA and in omental tissue 6987+/-2914 amol/mg RNA (mean+/-s.e.m., P=0.75). iNOS mRNA levels were substantially lower; in s.c. tissue 227+/-127 amol/mg RNA and in omental tissue 245+/-162 amol/mg RNA (P=0.8). In Western blot, eNOS protein levels in s.c. and omental tissue were 1.88+/-2.0 and 7.47+/-4.11 (OD/mm(2) 100 microg total protein, P=0.0063), respectively. iNOS protein was expressed at significantly lower levels and barely detectable in both s.c. and omental tissue. Basal rate of lipolysis was two times higher in s.c. compared to omental fat cells (P=0.028).

CONCLUSIONS

eNOS protein is markedly increased in omental compared to s.c. adipose tissue in human obese subjects, probably due to post-transcriptional mechanisms. Since basal lipolysis is much lower in omental vs s.c. adipose tissue it is possible that regionally increased NO production, primarily by eNOS, may be involved in the site difference of basal lipolysis in obese subjects.

A marked upregulation of uncoupling protein 2 gene expression in adipose tissue of hyperthyroid subjects

Recently, a family of uncoupling protein (UCP) genes has been discovered. The role of these genes is unknown, but it has been suggested that they are involved in regulating resting metabolic rate. In this study, we hypothesised that thyroid hormone status may influence the expression of UCP2 mRNA. The adipose tissue levels of UCP2 mRNA were measured in eight female subjects before and after treatment for thyrotoxicosis. All subjects in the hyperthyroid condition had markedly enhanced plasma levels of thyroxine (62.0 +/- 6.9 vs. 17.9 +/- 1.7, p = 0.012) and triiodothyronine (37.9 +/- 6.9 vs. 5.9 +/- 0.9, p = 0.012), accelerated heart rate (94 +/- 7 vs. 69 +/- 5, p = 0.012), decreased BMI (24.5 +/- 1.9 vs. 25.1 +/- 1.9, p = 0.025) and decreased percentage body fat (32.8 +/- 4.4 vs. 37.1 +/- 4.5, p = 0.018), as compared to the euthyroid state. Using RT-competitive-PCR, the UCP2 mRNA levels were found to be 2.5-fold upregulated in hyperthyroidism (10.4 +/- 1.7 vs. 4.2 +/- 1.3 amol/microg RNA, p = 0.012). In contrast, no difference in expression levels of the reference gene 18SrRNA was seen in the hyperthyroid versus the euthyroid state (317 +/- 49 vs. 279 +/- 25 amol/microg RNA, p = 0.48) but the difference in UCP2 mRNA levels between the hyper- and euthyroid state remained when UCP2 was related to 18SrRNA (p = 0.012). In conclusion, thyrotoxicosis markedly increases the expression of UCP2 mRNA in adipose tissue, which suggests a role for thyroid hormones in the regulation of this uncoupling protein in man.

Increased adipose angiotensinogen gene expression in human obesity

OBJECTIVE

Adipose angiotensinogen has been suggested as a stimulator of adipose tissue growth and development. Therefore, the association of subcutaneous adipose angiotensinogen gene expression with human obesity was studied.

RESEARCH METHODS AND PROCEDURES

The study group consisted of 17 men, undergoing either gastric banding for obesity or elective laparoscopic cholecystectomy (7 obese, 10 non-obese men; body mass index 22 to 51 kg/m2; age 26 to 68 years). Subcutaneous adipose angiotensinogen mRNA and 18S ribosomal RNA (reference gene) levels were measured using competitive quantitative reverse transcriptase-polymerase chain reaction.

RESULTS

Adipose angiotensinogen mRNA expression was about two times increased in obesity. The levels of 18S rRNA did not differ between the two groups. Body weight correlated independently and positively with adipose angiotensinogen mRNA expression after adjusting for differences in age and height.

DISCUSSION

Adipose angiotensinogen gene expression is elevated in obesity in men.

The association of human adipose angiotensinogen gene expression with abdominal fat distribution in obesity

OBJECTIVE

To investigate in obese subjects the relationship between angiotensinogen gene expression in the abdominal omental and subcutaneous adipose tissue on the one hand and body fat distribution as measured by waist-to-hip ratio (WHR) on the other hand and to compare angiotensinogen gene expression between the two adipose tissue regions.

SUBJECTS

Twenty obese subjects undergoing weight reduction surgery with adjustable gastric banding (12 men, eight women; WHR 0.89-1.09; body mass index (BMI) 29-51 kg/m2, age 26-54 y).

MEASUREMENTS

Omental and subcutaneous adipose angiotensinogen mRNA and 18S ribosomal RNA (reference gene) levels were measured by competitive quantitative reverse transcriptase-polymerase chain reaction.

RESULTS

Angiotensinogen mRNA levels were one-third higher in the omental than in the subcutaneous adipose tissue region (P=0.02). The 18S rRNA levels did not differ significantly between the two adipose tissue regions. WHR correlated positively and significantly with angiotensinogen mRNA in both the subcutaneous and the omental adipose tissue (r=0.5). This relationship was independent of age and BMI. However, WHR did not correlate with 18S rRNA in any of the adipose tissue regions.

CONCLUSION

The angiotensinogen gene in adipose tissue might be involved in the development of upper-body obesity.

Regional variation in plasminogen activator inhibitor-1 expression in adipose tissue from obese individuals

High plasma plasminogen activator inhibitor-1 (PAI-1) activity is a frequent finding in obesity and adipose tissue has recently been suggested to be a source of circulating PAI-1 in humans. In the present study, differences in adipose tissue gene expression and protein secretion rate of PAI-1 between subcutaneous and visceral adipose tissue was analysed in specimens obtained from 22 obese individuals. The secretion rate of PAI-1 was two-fold higher in subcutaneous adipose tissue than in visceral adipose tissue (292 +/- 50 vs 138 +/- 24 ng PAI-1/10(7) cells, P <0.05). In accordance with the secretion data, subcutaneous adipose tissue contained about three-fold higher levels of PAI-1 mRNA than visceral adipose tissue (2.43 +/- 0.37 vs 0.81 +/- 0.12 attomole PAI-1 mRNA/microg total RNA, P <0.00 ). PAI-1 secretion from subcutaneous but not from visceral adipose tissue correlated significantly with cell size (r = 0.43, P<0.05). In summary, subcutaneous adipose tissue secreted greater amounts of PAI-1 and had a higher PAI-1 gene expression than visceral adipose tissue from the same obese individuals. Bearing in mind that subcutaneous adipose tissue is the largest fat depot these finding may be important for the coagulation abnormalities associated with obesity.

Excessive fat accumulation is associated with the TNF alpha-308 G/A promoter polymorphism in women but not in men

AIMS/HYPOTHESIS

Tumour necrosis factor alpha (TNF alpha) is a candidate gene for the development of obesity, which in turn is a major risk factor for diabetes mellitus. The aim of our study was to investigate whether a previously known NcoI-sensitive polymorphism (-308 G/A) in the promoter region of the TNF alpha gene was related to body weight.

METHODS

Genotyping was done in 239 male and 342 female non-diabetic subjects with a marked variation in body mass index (BMI).

RESULTS

We found three genotypes; AA (n = 13), AG (n = 158) and GG (n = 410). When the material was divided according to sex, allele specific phenotypic differences were confined to women. The female subjects carrying the AA genotype were markedly more obese than both the AG and GG carriers (mean BMI = 41.4 vs 32.3 and 31.7 kg/m2, respectively, p = 0.02). The body fat content of female AA carriers was increased by one-third compared with AG/GG carriers (p = 0.02). We found no differences between genotypes with respect to waist-to-hip ratio, blood pressure or metabolic variables. Among obese female subjects (BMI > 27 kg/m2), we also found that the BMI and body fat content of AA carriers (n = 7) were also higher than for AG/GG carriers.

CONCLUSION/INTERPRETATION

The AA-variant at position -308 in the promoter region of the TNF alpha gene could be an important genetic factor behind excessive fat accumulation in women.

Mechanisms involved in the regulation of free fatty acid release from isolated human fat cells by acylation-stimulating protein and insulin

The effects of acylation-stimulating protein (ASP) and insulin on free fatty acid (FFA) release from isolated human fat cells and the signal transduction pathways to induce these effects were studied. ASP and insulin inhibited basal and norepinephrine-induced FFA release by stimulating fractional FFA re-esterification (both to the same extent) and by inhibiting FFA produced during lipolysis (ASP to a lesser extent than insulin). Protein kinase C inhibition influenced none of the effects of ASP or insulin. Phosphatidylinositol 3-kinase inhibition counteracted the effects of insulin but not of ASP. Phosphodiesterase 3 (PDE3) activity was stimulated by ASP and insulin, whereas PDE4 activity was slightly increased by ASP only. Selective PDE3 inhibition reversed the effects of both ASP and insulin on fractional FFA re-esterification and lipolysis. Selective PDE4 inhibition slightly counteracted the ASP but not the effect of insulin on fractional FFA re-esterification and did not prevent the action of ASP or insulin on lipolysis. Thus, ASP and insulin play a major role in regulating FFA release from fat cells as follows: insulin by stimulating fractional FFA re-esterification and inhibiting lipolysis and ASP mainly by stimulating fractional FFA re-esterification. For both ASP and insulin these effects on FFA release are mediated by PDE3, and for ASP PDE4 might also be involved. The signaling pathway preceding PDE is not known for ASP but involves phosphatidylinositol 3-kinase for insulin.

Adrenoceptor genes in human obesity

The genes causing obesity in rodent models have been characterized, but do not seem to be important for human obesity. Recently the putative association between obesity and polymorphism in human beta-adrenergic receptor genes have been studied intensely in the light of the important role of these receptors in the regulation of energy mobilization and utilization. A polymorphism (Trp64Arg) in the beta3-adrenergic receptor gene is associated with obesity (relative risk approximately 2) in some but not all investigations on Caucasian and Japanese populations. When expressed in artificial cell systems, the polymorphism is associated with alterations of the beta -adrenoceptor. The genetic allele variance influences also the native receptor function when measured in isolated human fat cells. The human beta2-adrenoceptor gene shows a high degree of polymorphism. The role of beta2-receptor gene polymorphism for obesity has so far only been investigaed in women. A Gln27Glu variant is markedly associated with obesity with a relative risk for obesity of approximately 7 and odds ratio of approximately 10. Women who are homozygous for 27Glu have approximately 20 kg higher fat mass than controls. Thus, polymorphism in genes coding for different beta-adrenoceptor subtypes may be important for the development of human obesity.

Reduced gene expression of UCP2 but not UCP3 in skeletal muscle of human obese subjects

Massive overweight is an increasing health problem and underlies several complications which in turn result in premature death. The mechanisms underlying the imbalance between energy intake and energy expenditure, that lead to obesity in humans, are still only partly understood. In rodents, heat generation and the burning of calories by the mitochondrial uncoupling protein 1 (UCP1) are important for metabolic control. However, UCP1 is exclusively expressed in brown fat which is only present in limited amounts in human adults. The recent characterization of two new uncoupling proteins, UCP2 and UCP3, may elucidate potentially important pathways for energy expenditure regulation in man. The aim of this study was to investigate whether obesity is accompanied by aberrations in UCP2 and UCP3 regulation. Expression of these two genes was examined using in situ hybridization in six lean and six obese, but otherwise healthy, men. The UCP2 expression was decreased by 28 % (p = 0.001) in the abdominal muscle of the obese subjects. No differences in UCP3 expression were observed between obese and control subjects, although there was great variation in the expression between subjects. In conclusion, these data suggest an impaired activity of the mitochondrial uncoupling protein UCP2, but probably not UCP3, in obese subjects. This may result in decreased energy expenditure and contribute to the development and maintenance of obesity.

Leptin secretion from subcutaneous and visceral adipose tissue in women

Upper body obesity is a risk factor for type 2 diabetes. Little is known about the regulation of body fat distribution, but leptin may be involved. This study examined the secretion of leptin in subcutaneous and omental fat tissue in 15 obese and 8 nonobese women. Leptin secretion rates were two to three times higher in subcutaneous than in omental fat tissue in both obese and nonobese women (P < 0.0001 and P < 0.001, respectively). There was a positive correlation between BMI and leptin secretion rates in both subcutaneous (r = 0.87, P < 0.0001) and omental (r = 0.74, P < 0.0001) fat tissue. Furthermore, leptin secretion rates in subcutaneous and omental fat tissue correlated well with serum leptin levels (r = 0.84, P < 0.0001 and r = 0.73, P = 0.001, respectively), although in multivariate analysis, the subcutaneous leptin secretion rate was the major regressor for serum leptin (F = 42). Subcutaneous fat cells were approximately 50% larger than omental fat cells, and there was a positive correlation between fat cell size and leptin secretion rate in both fat depots (r = 0.8, P < 0.01). Leptin (but not gamma-actin) mRNA levels were twofold higher in subcutaneous than in omental fat tissue (P < 0.05). Thus the subcutaneous fat depot is the major source of leptin in women owing to the combination of a mass effect (subcutaneous fat being the major depot) and a higher secretion rate in the subcutaneous than in the visceral region, which in turn could be due to increased cell size and leptin gene expression.

Variation in adrenergic regulation of lipolysis between omental and subcutaneous adipocytes from obese and non-obese men

Regional variations in adipocyte lipolysis between subcutaneous and visceral fat may be important for obesity complications. In the present study, we compared adrenergic regulation of lipolysis in omental and subcutaneous adipocytes from obese (n = 15) and non-obese (n = 14) male subjects. Waist-to-hip ratio, blood pressure, plasma insulin, and plasma triglycerides were increased in obesity. No regional differences in adrenoceptor lipolytic function were observed in non-obese subjects with the exception of a slight increase in noradrenaline sensitivity in omental adipocytes (P < 0.05), because of increased beta(1)-adrenoceptor sensitivity (P < 0.05). In the obese subjects, the rate of noradrenaline-induced glycerol release was 2-fold higher (P < 0.005) and the noradrenaline sensitivity was 3-fold higher (P < 0.05) in omental versus subcutaneous adipocytes. These findings were mainly due to a 50-fold increase in omental beta(3)-adrenoceptor sensitivity (P < 0.002) and to a smaller 6-fold increase in omental beta(1)-adrenoceptor sensitivity (P < 0.02), accompanied by increased beta(3)- as well as beta(1)-adrenoceptor lipolytic rates at approximately 50% receptor subtype occupancy by the agonist (P < 0.05). In conclusion, minor regional differences in adipocyte lipolytic response to catecholamines are present in non-obese males. In contrast, catecholamine-induced lipolysis is markedly increased in omental as compared to subcutaneous adipocytes in obese males, mainly due to an increase in beta(3)-adrenoceptor function of visceral fat cells, in combination with a smaller increase in beta(1)-adrenoceptor function.

The metabolic syndrome is related to beta 3-adrenoceptor sensitivity in visceral adipose tissue

The metabolic syndrome is a well-known risk for the development of cardiovascular disease. In the present study the possible importance of an altered visceral adipocyte beta-adrenoceptor function in this syndrome was investigated. In 65 subjects of both sexes undergoing elective surgery for non-malignant disorders, the metabolic syndrome phenotype and the lipolytic sensitivity for various beta-adrenoceptor subtype agonists in omental adipocytes were determined. The study group represented a wide range of abdominal adipose tissue distribution (waist-to-hip ratios 0.76-1.13), but was otherwise apparently healthy. The subjects were divided into three subgroups according to their waist-to-hip (WHR) ratios: 1) WHR < 0.92; 2) WHR 0.92-1.04; 3) WHR > 1.04. The subgroups demonstrated significant differences regarding body mass index, sagittal diameter, systolic and diastolic blood pressures, plasma concentrations of glucose, insulin, triglycerides and HDL-cholesterol (p = 0.005-0.0001). Furthermore, in omental adipocytes beta 3-adrenoceptor sensitivity, but not beta 1-and beta 2-adrenoceptor sensitivities, differed significantly between the WHR subgroups (p = 0.0001). beta 3-adrenoceptor sensitivity was also related to the other components of the metabolic syndrome, although a strong covariation between WHR and beta 3-adrenoceptor sensitivity vs blood pressure and the metabolic parameters was found. The present data provide evidence of a relationship between upperbody obesity and its associated metabolic complications and also, an increased visceral fat beta 3-adrenoceptor sensitivity. We suggest that the latter finding results in an augmented release of non-esterified fatty acids from the visceral fat depot to the portal venous system. This may in turn contribute to the development of the metabolic syndrome.

Effects of several putative beta 3-adrenoceptor agonists on lipolysis in human omental adipocytes

BACKGROUND

Atypical beta 3-adrenoceptor agonists have attained an increasing interest as potential drugs against obesity and diabetes. However, their pharmacological actions on the native, human beta 3-adrenoceptor are not well defined.

DESIGN

In the present study, the lipolytic effects of several putative beta 3-adrenoceptor agonists were investigated in human omental adipocytes.

RESULTS

CL 316 243 and CGP 12177 had selective partial beta 3-agonist effects (pD2 about 4 and 8, respectively); the latter drug is a beta 1-/beta 2-adrenoceptor blocker in addition to its beta 3-adrenoceptor agonist activity. BRL 37344 and SM 11044 were also partial agonists, but with significant beta 1- and/or beta 2-adrenoceptor agonist properties. Bucindolol, ZD 2079, ICI D7114 and SR 58611A were ineffective as lipolytic drugs. In addition, ICI D7114 was a non-selective beta 1-/beta 2-/beta 3-adrenoceptor antagonist in human adipocytes.

CONCLUSION

None of the beta 3-adrenoceptor agonists tested is an ideal drug for therapeutic use in man (i.e. regarded as a selective and full agonist with high receptor potency). Only CL 316 243 may have a potential therapeutic role, although the potency is very low. CGP 12177 is useful as a reference substance for human in vitro studies.

Systolic blood pressure is related to catecholamine sensitivity in subcutaneous abdominal fat cells

A relationship between abdominal obesity and hypertension is well established. In search for an early-onset defect in adipocyte function linking these two conditions, we compared catecholamine sensitivity in subcutaneous abdominal fat cells with 24-hour systolic, mean arterial and diastolic blood pressure in 16 healthy, normotensive subjects. Clear inter-individual variations in the adipocyte lipolytic adrenoceptor sensitivity (pD2) for noradrenaline were observed in dose-response experiments (i.e., about 4 log units). An inverse and independent correlation was found between the 24-hour systolic blood pressure and pD2 for noradrenaline (r = -0.67, p < 0.01). The mean arterial blood pressure was also negatively correlated to peripheral noradrenaline sensitivity (r = -0.58, p < 0.05). However, no significant relationship between the 24-hour diastolic blood pressure and pD2 for noradrenaline was demonstrated. In conclusion we suggest that catecholamine resistance in subcutaneous fat cells may be associated with autonomic dysfunction and impaired blood pressure regulation. This finding is supported by the fact that both noradrenaline sensitivity and 24-hour systolic blood pressure also are correlated to the individual orthostatic heart rate responses, reflecting the sympathetic nervous system tone (r = 0.61, p = 0.01 and r = -0.53, p = 0.03, respectively). The relationship between noradrenaline sensitivity and systolic blood pressure may be of importance in the early development of hypertension in man.

Determination of beta 3-adrenoceptor mediated lipolysis in human fat cells

The existence and relative importance of beta 3-adrenoceptors in man is still controversial. The aim of the present study was 1) to find further evidence for the existence of functional beta 3-adrenoceptors in human fat, and 2) to investigate factors that may influence this beta 3-adrenoceptor function. Fifty individuals were examined. Lipolysis mediated by the selective beta 3-adrenoceptor agonist CGP 12177 in omental fat cells correlated with the response in subcutaneous fat cells. However, lipolysis was more pronounced in omental as compared to subcutaneous adipocytes, the intrinsic activity for CGP 12177 was 41% and 33%, respectively, while dobutamine, terbutaline and norepinephrine were full agonists. Both the lipolytic response and the sensitivity to CGP 12177 correlated with the effects of norepinephrine in the omental fat cells (r2 = 0.68 and 0.50, respectively, p = 0.0001). The beta 3-adrenoceptor mediated lipolytic response did also correlate with the responses induced by beta 1- and beta 2-agonists and by postreceptor acting agents. The antagonistic properties (pA2) of the beta-adrenoceptor subtypes were also investigated. The pA2 for the selective beta 1- and beta 2-adrenoceptor antagonists versus CGP 12177-induced lipolysis were 2 to 3 log units lower than those for the beta 1-antagonist versus dobutamine or for the beta 2-antagonist versus terbutaline. Furthermore, bupranolol had a significantly better antagonistic effect (pA2 7.17, p < 0.001) on the CGP 12177-induced lipolysis than had the beta 1- and beta 2-adrenoceptor antagonists (pA2 6.26 and 6.05, respectively). These data clearly support the existence of a third human beta-adrenoceptor. Several factors may contribute to the contradictory beta 3-adrenoceptor results in man. The sensitivity of the different lipolytic systems vary considerably. Omental fat cells are preferable to subcutaneous cells for beta 3-adrenoceptor studies in man. The beta 3-responses are more attenuated in isolated fat cell preparations than in tissue fragments. Furthermore, as the beta 3-adrenoceptor activity correlates to the norepinephrine activity, more pronounced effects will be expected in catecholamine sensitive subjects. At present, the number of tools available for beta 3-adrenoceptor studies are limited, and the receptor is hard to study, why it is essential to perform beta 3-adrenoceptor studies under optimal conditions in order to obtain conclusive effects.

A pathogenic role of visceral fat beta 3-adrenoceptors in obesity

Increased release of free fatty acids (FFA) from visceral fat cells to the portal venous system may cause several metabolic disturbances in obesity. However, this hypothesis and the underlying mechanism remain to be demonstrated. In this study catecholamine-induced lipid mobilization through lipolysis in omental adipose tissue was investigated in vitro in 25 markedly obese subjects (body mass index range 35-56 kg/m2) undergoing weight reduction surgery and in 19 nonobese subjects (body mass index range 20-28 kg/m2) undergoing cholecystectomy. Release of FFA and glycerol, induced by norepinephrine or adrenergic receptor subtype-specific agonists, were determined in isolated omental fat cells. The obese subjects had higher fat cell volume, blood pressure, plasma insulin levels, blood glucose, plasma triglycerides, and plasma cholesterol than the controls. There was evidence of upper-body fat distribution in the obese group. The rate of FFA and glycerol response to norepinephrine was increased twofold in the cells of obese subjects; no significant reutilization of FFA during catecholamine-induced lipolysis was observed in any of the groups (glycerol/FFA ratio near 1:3). There were no differences in the lipolytic sensitivity to beta 3- or beta 2-adrenoceptor specific agonists between the two groups. However, beta 3-adrenoceptor sensitivity was approximately 50 times enhanced (P = 0.0001), and the coupling efficiency of these receptors was increased from 37 to 56% (P = 0.01) in obesity. Furthermore, the obese subjects demonstrated a sixfold lower alpha 2-adrenoceptor sensitivity (P = 0.04). beta 3-Adrenoceptor sensitivity, but not alpha 2-, beta 1-, or beta 2-adrenoceptor sensitivity, correlated with norepinephrine-induced lipolysis (r = -0.67, P = 0.0001) and fat cell volume (r = -0.71, P = 0.0001). In conclusion, catecholamine-induced rate of FFA mobilization from omental fat cells is accelerated due to elevated rate of lipolysis in obesity, mainly because of an increased beta 3-adrenoceptor function, but partly also because of a decreased alpha 2-adrenoceptor function. This promotes an increased release of FFA to the portal system, which may contribute to the parallel metabolic disturbances observed in upper-body obesity.