Regional differences in adrenoceptor binding and fat cell lipolysis in obese, postmenopausal women

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

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

Energy Metabolism Changes and Dysregulated Lipid Metabolism in Postmenopausal Women

Aging women experience hormonal changes, such as decreased estrogen and increased circulating androgen, due to natural or surgical menopause. These hormonal changes make postmenopausal women vulnerable to body composition changes, muscle loss, and abdominal obesity; with a sedentary lifestyle, these changes affect overall energy expenditure and basal metabolic rate. In addition, fat redistribution due to hormonal changes leads to changes in body shape. In particular, increased bone marrow-derived adipocytes due to estrogen loss contribute to increased visceral fat in postmenopausal women. Enhanced visceral fat lipolysis by adipose tissue lipoprotein lipase triggers the production of excessive free fatty acids, causing insulin resistance and metabolic diseases. Because genes involved in β-oxidation are downregulated by estradiol loss, excess free fatty acids produced by lipolysis of visceral fat cannot be used appropriately as an energy source through β-oxidation. Moreover, aged women show increased adipogenesis due to upregulated expression of genes related to fat accumulation. As a result, the catabolism of ATP production associated with β-oxidation decreases, and metabolism associated with lipid synthesis increases. This review describes the changes in energy metabolism and lipid metabolic abnormalities that are the background of weight gain in postmenopausal women.

The effects of mirabegron on obesity-induced inflammation and insulin resistance are associated with brown adipose tissue activation but not beiging in the subcutaneous white adipose tissue

Mirabegron is a selective β₃-adrenergic receptors agonist, which has been recently shown to improve metabolic health in rodents and humans. In this study, we investigated the effects of 2-week mirabegron treatment on the metabolic parameters of mice with a diet-induced obesity (DIO). C57BL/6JUnib mice were divided into control (CTR) and obese (OB) groups treated with vehicle, and an OB group treated with mirabegron (OB + MIRA). The obese groups were fed a high-fat diet for 12 weeks. Mirabegron (10 mg/kg/day) was administrated orally by gavage from weeks 10-12. After 2 weeks of mirabegron treatment, the energy expenditure was assessed with indirect calorimetry. Blood glucose, insulin, glycerol, free fatty acids (FFA), thiobarbituric acid reactive substance (TBAR), and tumour necrosis factor (TNF)-α levels were also assessed, and the HOMA index was determined. Liver tissue, brown adipose tissue (BAT), and inguinal white adipose tissue (iWAT) samples were collected for histological examination. The protein expressions of uncoupling protein 1 (UCP1) and mitochondrial transcription factor A (TFAM) were assessed using western blotting of the BAT and iWAT samples. In this study, mirabegron increased the energy expenditure and decreased adiposity in OB + MIRA. Increased UCP1 expression in BAT without changes in iWAT was also found. Mirabegron decreased circulating levels of FFA, glycerol, insulin, TNF-α, TBARS and HOMA index. DIO significantly increased the lipid deposits in the liver and BAT, but mirabegron partially reversed this change. Our findings indicate that treatment with mirabegron decreased inflammation and improved metabolism in obese mice. This effect was associated with increased BAT-mediated energy expenditure, but not iWAT beiging, which suggests that mirabegron might be useful for the treatment of obesity and diabetes.

Identification and characterization of adipose surface epitopes

Adipose tissue is a central regulator of metabolism and an important pharmacological target to treat the metabolic consequences of obesity, such as insulin resistance and dyslipidemia. Among the various cellular compartments, the adipocyte cell surface is especially appealing as a drug target as it contains various proteins that when activated or inhibited promote adipocyte health, change its endocrine function and eventually maintain or restore whole-body insulin sensitivity. In addition, cell surface proteins are readily accessible by various drug classes. However, targeting individual cell surface proteins in adipocytes has been difficult due to important functions of these proteins outside adipose tissue, raising various safety concerns. Thus, one of the biggest challenges is the lack of adipose selective surface proteins and/or targeting reagents. Here, we discuss several receptor families with an important function in adipogenesis and mature adipocytes to highlight the complexity at the cell surface and illustrate the problems with identifying adipose selective proteins. We then discuss that, while no unique adipocyte surface protein might exist, how splicing, posttranslational modifications as well as protein/protein interactions can create enormous diversity at the cell surface that vastly expands the space of potentially unique epitopes and how these selective epitopes can be identified and targeted.

The Effects of Small-Volume Liposuction Surgery of Subcutaneous Adipose Tissue in the Gluteal-Femoral Region on Selected Biochemical Parameters

Liposuction is becoming an increasingly common procedure of aesthetic surgery, that patients choose to shape the body. Apart from the risks associated with the surgery, one should also consider whether the reduction of adipose tissue can significantly affect the metabolism of lipids and carbohydrates and, indirectly, that of bone tissue. The aim of the presented study was to assess the effects of small-volume liposuction surgery in the gluteal-femoral region on the selected markers of carbohydrate, lipid, and bone metabolism. The study included 27 women (40.75 ± 13.67 years of age, BMI = 25.9 ± 4.13 kg/m2) subjected to the removal of 3.35 ± 0.994 L of adipose tissue to shape the body. Following the procedure, significant changes in the body composition and body adiposity indicators were observed in these women. A slight decrease in adiponectin, leptin, resistin and insulin levels and HOMA-IR value was found three months after the procedure. No changes in the lipid profile of the subjects were found. It can be concluded that the removal of a small volume of adipose tissue from the gluteal-femoral region has a slight but positive effect on carbohydrate and lipid metabolism, providing a decreased risk of developing insulin resistance.

Effects of a combined dietary, exercise and behavioral intervention and sympathetic system on body weight maintenance after intended weight loss: Results of a randomized controlled trial

BACKGROUND

Lifestyle based weight loss interventions are hampered by long-term inefficacy. Prediction of individuals successfully reducing body weight would be highly desirable. Although sympathetic activity is known to contribute to energy homeostasis, its predictive role in body weight maintenance has not yet been addressed.

OBJECTIVES

We investigated, whether weight regain could be modified by a weight maintenance intervention and analyzed the predictive role of weight loss-induced changes of the sympathetic system on long-term weight regain.

DESIGN

156 subjects (age > 18; BMI ≥ 27 kg/m²) participated in a 12-week weight reduction program. After weight loss (T0), 143 subjects (weight loss > 8%) were randomized to a 12-month lifestyle intervention or a control group. After 12 months (T12) no further intervention was performed until month 18 (T18). Weight regain at T18 (regain_BMI) was the primary outcome. Evaluation of systemic and tissue specific estimates of sympathetic system was a pre-defined secondary outcome.

RESULTS

BMI was reduced by 4.67 ± 1.47 kg/m² during the initial weight loss period. BMI maintained low in subjects of the intervention group until T12 (+0.07 ± 2.98 kg/m²; p = 0.58 compared to T0), while control subjects regained +0.98 ± 1.93 kg/m² (p < 0.001 compared to T0). The intervention group regained more weight than controls after ceasing the intervention (1.17 ± 1.34 vs. 0.57 ± 0.93 kg/m²) until T18. Consequently, BMI was not different at T18 (33.49 (32.64; 34.33) vs. 34.18 (33.61; 34.75) kg/m²; p=0.17). Weight loss-induced modification of urinary metanephrine excretion independently predicted regain_BMI (R² = 0.138; p < 0.05). The lifestyle intervention did not modify the course of urinary metanephrines after initial weight loss.

CONCLUSIONS

Our lifestyle intervention successfully maintained body weight during the intervention period. However, no long-term effect could be observed beyond the intervention period. Predictive sympathetic activity was not persistently modified by the intervention, which may partially explain the lack of long-term success of such interventions.

Inflammatory and cardiometabolic risk on obesity: role of environmental xenoestrogens

CONTEXT

Some chemicals used in consumer products or manufacturing (eg, plastics, pesticides) have estrogenic activities; these xenoestrogens (XEs) may affect immune responses and have recently emerged as a new risk factors for obesity and cardiovascular disease. However, the extent and impact on health of chronic exposure of the general population to XEs are still unknown.

OBJECTIVE

The objective of the study was to investigate the levels of XEs in plasma and adipose tissue (AT) depots in a sample of pre- and postmenopausal obese women undergoing bariatric surgery and their cardiometabolic impact in an obese state.

DESIGN AND PARTICIPANTS

We evaluated XE levels in plasma and visceral and subcutaneous AT samples of Portuguese obese (body mass index ≥ 35 kg/m(2)) women undergoing bariatric surgery. Association with metabolic parameters and 10-year cardiovascular disease risk was assessed, according to menopausal status (73 pre- and 48 postmenopausal). Levels of XEs were determined by gas chromatography with electron-capture detection. Anthropometric and biochemical data were collected prior to surgery. Adipocyte size was determined on tissue sections obtained during surgery.

RESULTS

Our data show that XEs are pervasive in this obese population. Distribution of individual and concentration of total XEs differed between plasma, visceral AT, and subcutaneous AT, and the pattern of accumulation was different between pre- and postmenopausal women. Significant associations between XE levels and metabolic and inflammatory parameters were found. In premenopausal women, XEs in plasma seem to be a predictor of 10-year cardiovascular disease risk.

CONCLUSIONS

Our findings point toward a different distribution of XE between plasma and AT in pre- and postmenopausal women, and reveal the association between XEs on the development of metabolic abnormalities in obese premenopausal women.

Preparation and differentiation of mesenchymal stem cells from ears of adult mice

External murine ears collected postmortem, as well as ear punches obtained during standard marking of live animals, are the source of mesenchymal stem cells, termed ear mesenchymal stem cells (EMSC). These cells provide an easily obtainable, primary culture model system for the study of lineage commitment and differentiation. EMSC are capable of differentiating into adipocytes, osteocytes, chondrocytes, and contractile myocytes. Facile adipogenic differentiation of EMSC provides an excellent model for the study of adipogenesis. In this chapter, methods for isolation, culture, and differentiation of EMSC are described.

Decrease of circulating SAA is correlated with reduction of abdominal SAA secretion during weight loss

OBJECTIVE

The study goal was to determine the effect of weight loss (WL) alone and with aerobic exercise (WL + AEX) on serum amyloid A (SAA) levels and adipose SAA secretion from gluteal and abdominal depots.

METHODS

Ninety-six overweight or obese postmenopausal women undertook a 6-month WL alone (n = 47) or with AEX training (n = 49) (6 months WL and WL + AEX are considered WL when groups were combined). Their serum SAA levels, body weight, and adipose SAA secretion ex vivo from gluteal and abdominal depot were measured before and after WL interventions.

RESULTS

The participants lost an average of 8% body weight with a 10% decrease of serum SAA. Serum SAA levels remained significantly correlated with body weight before and after WL. However, the changes of serum SAA level did not correlate with changes of body weight. The gluteal adipose tissue secreted ∼50% more SAA than the abdominal tissue, but the changes of abdominal, but not gluteal, SAA secretion correlated (R(2) = 0.19, p < 0.01) with those of serum SAA levels during WL.

CONCLUSIONS

No linear correlation between the decrease in systemic SAA and WL was found. There is a depot-dependent difference in adipose SAA secretion and abdominal SAA secretion, which may partially account for the systemic SAA reduction during WL.

Expression of inflammation-related genes in gluteal and abdominal subcutaneous adipose tissue during weight-reducing dietary intervention in obese women

Accumulation of adipose tissue in lower body lowers risk of cardiovascular and metabolic disorders. The molecular basis of this protective effect of gluteofemoral depot is not clear. The aim of this study was to compare the profile of expression of inflammation-related genes in subcutaneous gluteal (sGAT) and abdominal (sAAT) adipose tissue at baseline and in response to multiphase weight-reducing dietary intervention (DI). 14 premenopausal healthy obese women underwent a 6 months' DI consisting of 1 month very-low-calorie-diet (VLCD), subsequent 2 months' low-calorie-diet and 3 months' weight maintenance diet (WM). Paired samples of sGAT and sAAT were obtained before and at the end of VLCD and WM periods. mRNA expression of 17 genes (macrophage markers, cytokines) was measured using RT-qPCR on chip-platform. At baseline, there were no differences in gene expression of macrophage markers and cytokines between sGAT and sAAT. The dynamic changes induced by DI were similar in both depots for all genes except for three cytokines (IL6, IL10, CCL2) that differed in their response during weight maintenance phase. The results show that, in obese women, there are no major differences between sGAT and sAAT in expression of inflammation-related genes at baseline conditions and in response to the weight-reducing DI.

"Is obesity linked to aging?": adipose tissue and the role of telomeres

Obesity is a condition in which excess or abnormal fat accumulation may present with adverse effects on health and decreased life expectancy. Increased body weight and adipose tissue accumulation amplifies the risk of developing various age-related diseases, such as cardiovascular disease, type 2 diabetes mellitus, musculoskeletal disorders, respiratory diseases and certain types of cancer. This imbalance in body composition and body weight is now recognized as a state of increased oxidative stress and inflammation for the organism. Increasing oxidative stress and inflammation affect telomeres. Telomeres are specialized DNA-protein structures found at the ends of eukaryotic chromosomes and serve as markers of biological aging rate. They also play a critical role in maintaining genomic integrity and are involved in age-related metabolic dysfunction. Erosion of telomeres is hazardous to healthy cells, as it is a known mechanism of premature cellular senescence and loss of longevity. The association of telomeres and oxidative stress is evident in cultured somatic cells in vitro, where oxidative stress enhances the process of erosion with each cycle of replication. Shorter telomeres have been associated with increasing body mass index, increased adiposity, and more recently with increasing waist to hip ratio and visceral excess fat accumulation. Furthermore, many of the metabolic imbalances of obesity (e.g. glycemic, lipidemic, etc.) give rise to organ dysfunction in a way that resembles the accelerated aging process. This article is a non-systematic review of the evidence linking obesity and accelerated aging processes as they are regulated by telomeres.

Preferential reductions in intermuscular and visceral adipose tissue with exercise-induced weight loss compared with calorie restriction

Intermuscular adipose tissue (IMAT) and visceral adipose tissue (VAT) are associated with insulin resistance. We sought to determine whether exercise-induced weight loss (EX) results in greater reductions in IMAT and VAT compared with similar weight loss induced by calorie restriction (CR) and whether these changes are associated with improvements in glucoregulation. Sedentary men and women (50-60 yr; body mass index of 23.5-29.9 kg/m(2)) were randomized to 1 yr of CR (n = 17), EX (n = 16), or a control group (CON; n = 6). Bilateral thigh IMAT and VAT volumes were quantified using multi-slice magnetic resonance imaging. Insulin sensitivity index (ISI) was determined from oral glucose tolerance test glucose and insulin levels. Weight loss was comparable (P = 0.25) in the CR (-10.8 ± 1.4%) and EX groups (-8.3 ± 1.5%) and greater than in the control group (-2.0 ± 2.4%; P < 0.05). IMAT and VAT reductions were larger in the CR and EX groups than in the CON group (P ≤ 0.05). After controlling for differences in total fat mass change between the CR and EX groups, IMAT and VAT reductions were nearly twofold greater (P ≤ 0.05) in the EX group than in the CR group (IMAT: -45 ±5 vs. -25 ± 5 ml; VAT: -490 ± 64 vs. -267 ± 61 ml). In the EX group, the reductions in IMAT were correlated with increases in ISI (r = -0.71; P = 0.003), whereas in the CR group, VAT reductions were correlated with increases in ISI (r = -0.64; P = 0.006). In conclusion, calorie restriction and exercise-induced weight loss both decrease IMAT and VAT volumes. However, exercise appears to result in preferential reductions in these fat depots.

Impact of walking on adipose tissue lipoprotein lipase activity and expression in pre- and postmenopausal women

OBJECTIVE

The aim of this study was to examine regional variation in adipose tissue lipoprotein lipase (AT-LPL) activity and expression in pre-and postmenopausal women, before and after training, once differences in chronological age or obesity degree are taken into account.

METHODS

Sixteen late pre- and 14 early postmenopausal (49 +/- 2 vs. 52 +/- 2 years; p < 0.001) moderately obese women (body mass index 29-35 kg/m(2)) were subjected to a 16-week walking program (3 sessions/week of 45 min at 60% heart rate reserve). Abdominal and femoral AT-LPL activity and expression, fasting lipid-lipoprotein profile, body composition, and cardiorespiratory fitness (CRF) were measured before and after our intervention. Statistical analyses were performed using covariance analysis for age differences.

RESULTS

AT-LPL activity and expression, lipid-lipoprotein metabolism, body fatness, and CRF were similar at baseline, irrespective of the group considered. Slight reductions in plasma cholesterol and high-density lipoprotein (HDL) cholesterol levels, fat mass and waist girth reductions, CRF increases as well as femoral AT-LPL activity and expression decreases after our intervention were comparable, regardless of menopausal status (0.0001 < p < 0.05).

CONCLUSIONS

Lipid storage is decreased in the femoral depot after walking, regardless of menopausal status. Reduction in AT-LPL activity or expression does not lead to a more deleterious lipid-lipoprotein profile, despite the modest decrease noted in HDL cholesterol concentrations.

Treatment of cellulite: Part I. Pathophysiology

Cellulite is a topographic skin change that is nearly ubiquitous in postpubertal women. Treatment remains elusive. The various treatments currently available are only partially or temporarily effective. Newer therapeutic modalities continue to evolve without much understanding of the complex nature of cellulite. The successful treatment of cellulite will ultimately depend upon our understanding of the pathophysiology of cellulite adipose tissue. Part I of this two-part series on cellulite reviews how the concept and perception of cellulite has evolved over time and its proposed etiologies. The article also focuses on the physiology of human adipose tissue, particularly regarding cellulite.

Differential function of the alpha2A-adrenoceptor and Phosphodiesterase-3B in human adipocytes of different origin

OBJECTIVE

Human adipocytes can be obtained in vitro by differentiation of human preadipocytes or mesenchymal stem cells (hMSC). Although functionally similar to freshly isolated cells, no detailed comparison of the different cell types has been performed. The antilipolytic alpha2A-adrenoceptor (AR) and the cAMP-degrading enzyme Phosphodiesterase-3B (PDE3B) have been implicated in the fine-tuning of lipolysis but little is known regarding their role in human adipocytes nor whether their expression and/or function differs in fat cells from different precursors.

METHODS

The effects of alpha2A-AR and PDE3B inhibition in mature adipocytes was determined and compared to that in differentiated preadipocytes and hMSC-derived fat cells. Gene expression was determined by real-time PCR and protein expression by Western blot.

RESULTS

Noradrenaline (NA) stimulated lipolysis in preadipocytes and mature adipocytes but markedly reduced lipolysis in differentiated hMSC derived-adipocytes. This was due to a potent stimulation of alpha2A-AR since co-incubation with NA and the alpha2-AR-inhibitor yohimbine restored NA-induced lipolysis. The order of Yohimbine response was hMSC>preadipocytes>mature adipocytes. Although alpha2-AR mRNA expression was highest in mature adipocytes there was no difference in alpha2A-AR protein levels between the cell types. In contrast, Galphai2 mRNA and protein expression was significantly higher in MSC-derived adipocytes, suggesting that differences in the response to alpha2A-AR inhibition reside at the postreceptor level. Incubation with the cAMP-analog 8-bromo(8b) cAMP increased lipolysis in hMSC-derived fat cells while co-incubation with the PDE3-specific inhibitor OPC3911 did not alter the lipolytic effect. In contrast, OPC3911 increased 8bcAMP-induced lipolysis significantly in preadipocytes and mature adipocytes. The response to PDE3B inhibition was; mature adipocytes>preadipocytes>hMSC a finding that correlated significantly with both PDE3B mRNA expression and enzymatic activity.

CONCLUSION

Although differentiated adipocytes of different origins display similar functional characteristics there are important differences in the regulation of lipolysis with a marked alpha2A-AR and less pronounced PDE3B effect in fat cells from MSCs.

Insulin resistance--a common link between type 2 diabetes and cardiovascular disease

Evidence suggests that diabetes and cardiovascular disease (CVD) may share an underlying cause(s), a theory known as the 'common soil' hypothesis. Insulin resistance is central both to the progression from normal glucose tolerance to type 2 diabetes and to a constellation of cardiovascular risk factors known as the metabolic syndrome. These risk factors include visceral obesity and dyslipidaemia characterized by low levels of high-density lipoprotein cholesterol, hypertriglyceridaemia and raised small dense low-density lipoprotein particle levels. Changes in adipose tissue mass and metabolism may link insulin resistance and visceral obesity, a condition that is common in type 2 diabetes. Furthermore, weight reduction, increased physical activity, metformin and acarbose have been shown to reduce the development of type 2 diabetes in genetically predisposed subjects and may decrease the high cardiovascular risk of patients with diabetes. Some fatty acid derivatives can affect energy metabolism by activating peroxisome proliferator-activated receptors (PPARs), nuclear receptors that play a key role in energy homeostasis. These receptors represent an ideal therapeutic target for reducing cardiovascular risk, because they are involved in the regulation of both insulin action and lipid metabolism. In addition to lifestyle changes, PPARgamma agonists such as thiazolidinediones are frequently beneficial and have been shown to ameliorate insulin resistance, while activation of PPARalpha (e.g. by fibrates) can lead to improvements in free fatty acid oxidation and lipid profile, and a reduction in cardiovascular events. The development of agents with both PPARalpha and PPARgamma activity promises added benefits with amelioration of insulin resistance, delayed progression to and of type 2 diabetes and a reduction of CVD.

Abundance of two human preadipocyte subtypes with distinct capacities for replication, adipogenesis, and apoptosis varies among fat depots

Fat depots vary in function and size. The preadipocytes that fat cells develop from exhibit distinct regional characteristics that persist in culture. Human abdominal subcutaneous cultured preadipocytes undergo more extensive lipid accumulation, higher adipogenic transcription factor expression, and less TNF-alpha-induced apoptosis than omental preadipocytes. We found higher replicative potential in subcutaneous and mesenteric than in omental preadipocytes. In studies of colonies arising from single preadipocytes, two preadipocyte subtypes were found, one capable of more extensive replication, differentiation, and adipogenic transcription factor expression and less apoptosis in response to TNF-alpha than the other. The former was more abundant in subcutaneous and mesenteric than in omental preadipocyte populations, potentially contributing to regional variation in replication, differentiation, and apoptosis. Both subtypes were found in strains derived from single human preadipocytes stably expressing telomerase, confirming that both subtypes are of preadipocyte lineage. After subcloning of cells of either subtype, both subtypes were found, indicating that switching can occur between subtypes. Thus proportions of preadipocyte subtypes with distinct cell-dynamic properties vary among depots, potentially permitting tissue plasticity through subtype selection during development. Furthermore, mesenteric preadipocyte cell-dynamic characteristics are distinct from omental cells, indicating that visceral fat depots are not functionally uniform.

Porcine somatotropin alters body composition and the distribution of fat and lean tissue in the finisher gilt

The present study was designed to determine whether porcine somatotropin (pST) reduces whole animal and belly fat using dual energy X-ray absorptiometry and manual dissection. The study utilised 24 Large White × Landrace gilts selected at 16 weeks of age with an approximate liveweight of 80 kg and housed in individual pens. Gilts were stratified on liveweight into 8 blocks and 1 pig from each block was assigned to either 0, 5 or 10 mg per day of pST. Pigs were fed ad libitum a wheat-based diet containing 200 g crude protein, 10.2 g available lysine and 14.6 MJ DE/kg, to ensure that responses to pST were expressed. Feed intake and liveweight were measured on a weekly basis. An Hologic QDR4500A dual energy X-ray absorptiometer was used to determine lean, fat and ash composition of pigs initially and again 4 weeks later at the end of the experiment. After slaughter, the composition of the whole half carcass as well as the shoulder, ham, belly and loin primal cuts was determined with dual energy X-ray absorptiometry and verified with manual dissection. Daily pST treatment decreased feed intake (3440, 2710 and 2537 g/day for 0, 5 or 10 mg pST per day, respectively; P<0.001) and decreased feed conversion ratio (2.95, 2.18 and 2.03 g/g; P<0.001) even though there was no significant effect on daily gain. Pigs treated with pST deposited more lean tissue (620, 839 and 873 g/day; P<0.05) and less fat (384, 218 and 176 g/day; P<0.001) than control animals, but there was no effect of pST on ash deposition. As a consequence, pigs treated with 5 and 10 mg pST/day contained 5 and 9 kg less dissectible fat than control gilts, respectively. A dose dependent decrease in belly, loin, ham and shoulder fat was also observed, although the decrease in belly fat was more pronounced than for the whole carcass and other primal cuts. Overall, pST treatment has the potential to decrease carcass and especially belly fat in pigs and increase consumer acceptance of pork in markets that place a premium on carcass fat and lean yield in the belly region. The results determined with dual energy X-ray absorptiometry were confirmed by manual dissection.

Regulation of lipolysis and lipoprotein lipase after weight loss in obese, postmenopausal women

OBJECTIVE

To test the hypothesis that the greater beta-adrenoceptor (beta-AR)-stimulated lipolysis and sensitivity (half-maximal lipolytic response) in abdominal (ABD) adipocytes, greater gluteal (GLT) adipose tissue-lipoprotein lipase (AT-LPL) activity, and dyslipidemia associated with obesity in older women are modifiable by weight loss (WL) and are not due to menopause or aging.

RESEARCH METHODS AND PROCEDURES

The metabolic effects of 6 months of hypocaloric diet and low-intensity walking WL program on the regional regulation of in vitro lipolysis and AT-LPL activity in subcutaneous ABD and GLT adipocytes were measured in 34 obese (48.7 +/- 0.7% body fat, mean +/- SE) postmenopausal (59 +/- 1 years) white women.

RESULTS

The lipolytic responsiveness to the beta-AR agonist isoproterenol and basal lipolysis in the presence of 1 U/mL adenosine deaminase-uninhibited (lipolysis) were greater (p < 0.01) in ABD than GLT adipocytes before and after WL, but there were no regional differences in postreceptor (dibutyryl 3',5'-cyclic adenosine monophosphate)-stimulated lipolysis. beta-AR sensitivity was greater in ABD than GLT adipocytes before (p < 0.01) but not after WL. Regional AT-LPL did not change after WL, but the change in the activity of ABD (but not GLT) AT-LPL correlated with the baseline adenosine deaminase-uninhibited lipolysis (r = 0.38, p = 0.03). There were no relationships between the declines in plasma triglyceride or increases in high-density lipoprotein cholesterol associated with WL and the changes in regional fat cell metabolism.

DISCUSSION

Thus, despite improving lipoprotein lipid profiles in obese, postmenopausal women, WL does not affect the regulation of regional fat metabolism, and a greater tonic inhibition of basal lipolysis by endogenous adenosine may increase the activity of AT-LPL after WL and predispose older women to develop ABD adiposity.

Aerobic training improves exercise-induced lipolysis in SCAT and lipid utilization in overweight men

The aim of this study was to investigate whether endurance training improves lipid mobilization and oxidation in overweight subjects. Eleven young men (25.6 +/- 1.4 yr and body mass index 27.7 +/- 0.2) performed a 4-mo training program consisting of practicing aerobic exercise 5 days/wk. Before and after the training period, lipid oxidation was explored during a 60-min exercise at 50% of peak O2 consumption by use of indirect calorimetry. Lipid mobilization and antilipolytic alpha2-adrenoceptor effect were also studied using the microdialysis method in abdominal subcutaneous adipose tissue (SCAT). After training, plasma nonesterified fatty acid (NEFA) levels, at rest and during exercise, were significantly lower than before (P < 0.001). Lipolysis in SCAT was significantly higher after than before training. An antilipolytic alpha2-adrenoceptor effect in SCAT was underlined during exercise before training and disappeared after. The respiratory exchange ratio was lower after training, i.e., the percentage of lipid oxidation was higher only at rest. The amount of lipid oxidized was higher after training, at rest, and during exercise. Although exercise power was higher after training, the relative intensity was equivalent, as suggested by a similar increase in plasma catecholamine concentrations before and after training. In conclusion, 4-mo training in overweight men improved lipid mobilization through a decrease of antilipolytic alpha2-adrenoceptor effect in SCAT and lipid oxidation during moderate exercise. Training induced a decrease of blood NEFA, predicting better prevention of obesity.

Fatty acid mobilization from adipose tissue during exercise

By far the largest energy reserve in the human body is adipose tissue triglycerides, and these reserves are an important source of fuel during prolonged endurance exercise. To use this rich source of potential energy during exercise, adipose tissue triglycerides must first be hydrolyzed and the resultant fatty acids delivered to the working muscles. The aims of this review are to describe how exercise alters lipid mobilization from adipose tissue, to identify alternative sources of lipids and to discuss some of the key factors regulating fatty acid mobilization, uptake and oxidation during exercise. The impact of understanding factors involved in the coordinated regulation of lipid mobilization and oxidation during exercise goes far beyond its relevance for endurance exercise performance. A better understanding of the regulation of these processes will facilitate the development of more effective treatment modalities for obesity-related metabolic disorders.

Differences in adipose tissue metabolism between postmenopausal and perimenopausal women

Changes in adipose tissue metabolism may contribute to the changes in body fat distribution seen during the menopause transition. We compared in vitro abdominal and gluteal sc adipose tissue metabolism [basal and stimulated lipolysis and activity of adipose tissue lipoprotein lipase (AT-LPL)] in postmenopausal and perimenopausal women (n = 12/group), matched for race, body mass index (29.5 +/- 3.8 kg/m(2); mean +/- SD), and percentage body fat (42 +/- 6%). The postmenopausal women were older (54 +/- 3 vs. 48 +/- 3 yr; P < 0.01) and had higher FSH (55.5 +/- 26.4 vs. 16.6 +/- 22.5 IU/ml; P < 0.01) and lower estradiol (33.8 +/- 14.9 vs. 97.4 +/- 61.7 pmol/liter; P < 0.05) concentrations than the perimenopausal women. Despite similar fat cell size and beta-adrenergic receptor and postreceptor (dibutyryl-cAMP)-stimulated lipolysis, basal lipolysis was 77% lower in gluteal adipose cells from postmenopausal compared with perimenopausal women (P < 0.05). Within each group, AT-LPL activity in the gluteal region was significantly higher than in the abdominal region (P < 0.05). In addition, AT-LPL activity was significantly higher in the postmenopausal compared with perimenopausal women in both gluteal (4.9 +/- 3.6 vs. 2.0 +/- 1.4 nmol free fatty acid/g.min; P < 0.05) and abdominal (3.2 +/- 2.6 vs. 1.3 +/- 0.9 nmol free fatty acid/g.min; P < 0.05) adipose cells. The results of this study suggest that menopause status is associated with differences in adipose tissue metabolism in both the abdominal and gluteal fat depots. The lower lipolysis and higher AT-LPL activity in postmenopausal women may predispose them to gain body fat after menopause.

Gender effects on adrenergic receptor expression and lipolysis in white adipose tissue of rats

OBJECTIVE

To investigate the effects of short-term (15 days) cafeteria-diet feeding on the expression of alpha- and beta-adrenergic receptors (AR) and its association with lipolytic stimulation in isolated retroperitoneal white adipocytes.

RESEARCH METHODS AND PROCEDURES

Six female and 6 male Wistar rats (4 weeks old) were fed a cafeteria diet plus standard diet for 15 days. The remaining 12 age- and sex-matched rats received a standard diet only. White retroperitoneal adipose tissue was isolated and used for the determination of both alpha(2) and beta-AR expression and for in vitro studies of lipolytic activity.

RESULTS

In female control rats, we found higher lipolytic capacities located at the postreceptor level and a lower alpha(2)/beta(3)-AR ratio than male rats. Cafeteria-diet feeding for 15 days decreased lipolytic activity in both male and female rats and altered the alpha(2A)- and beta(3)-AR protein levels with an increase of alpha(2A)-AR in males and a beta(3)-AR decrease in females.

DISCUSSION

Our results indicate that a 15-day cafeteria-diet feeding induced an increase in the alpha(2)/beta(3)-AR balance and impaired adipose tissue lipolytic activity, which was higher in males and may contribute to the development of increased fat mass. The higher functionality of alpha(2)-AR, together with the minor role developed by beta(3)-AR and lower lipolytic capacities located at the postreceptor level in cafeteria-diet-fed male rats compared with female rats, may be responsible for the gender-dependent differences observed in this study.

Lack of alpha(2)-adrenergic antilipolytic effect during exercise in subcutaneous adipose tissue of trained men

The aim of this study was to investigate the involvement of the antilipolytic alpha(2)-adrenergic receptor pathway in the regulation of lipolysis during exercise in subcutaneous abdominal adipose tissue (SCAAT). Seven trained men and 15 untrained men were studied. With the use of microdialysis, the extracellular glycerol concentration was measured in SCAAT at rest and during 60 min of exercise at 50% of maximal oxygen consumption. One microdialysis probe was perfused with Ringer solution; the other was supplemented with phentolamine (alpha(2)-adrenergic receptor antagonist). No differences in baseline extracellular or plasma glycerol concentrations were found between the two groups. The exercise-induced extracellular and plasma glycerol increase was higher in trained compared with untrained subjects (P < 0.05). Addition of phentolamine to the perfusate enhanced the exercise-induced response of extracellular glycerol in untrained subjects but not in trained subjects. The exercise-induced increase in plasma norepinephrine and epinephrine concentrations and the decrease in plasma insulin were not different in the two groups. These in vivo findings demonstrate higher exercise-induced lipolysis in trained compared with untrained subjects and show that, in trained subjects, the alpha(2)-mediated antilipolytic action is not involved in the regulation of lipolysis in SCAAT during exercise.

Sex-dependent dietary obesity, induction of UCPs, and leptin expression in rat adipose tissues

OBJECTIVE

The aim of this study was to determine the sex-dependent differences in the response of key parameters involved in thermogenesis and control of body weight in brown adipose tissue (BAT) and white adipose tissue (WAT) in postcafeteria-fed rats, a model of dietary obesity.

RESEARCH METHODS AND PROCEDURES

BAT and WAT were obtained from male and female control and postcafeteria-fed Wistar rats. Postcafeteria-fed rats were initially fed with cafeteria diet from day 10 of life until day 110 (cafeteria period) and with standard chow diet from then until day 180 of life (postcafeteria period). Body mass and energy intake were evaluated. Biometric parameters were analyzed in interscapular BAT (IBAT). Levels of uncoupling protein 1 (UCP1), alpha(2)-adrenergic receptor (AR), and beta(3)-AR proteins and UCP1, UCP2, UCP3, beta(3)-AR, and leptin mRNAs, in IBAT or WAT, were studied by Western blot and Northern blot analyses, respectively.

RESULTS

Rats attained 59% (females) and 39% (males) increase in body weight at the end of the cafeteria period. During the postcafeteria period, the rats showed a loss of body weight, which was higher in females. Postcafeteria-fed female rats also presented higher activation of thermogenic parameters in IBAT, including UCP1, UCP2, and UCP3 mRNAs. Female control rats showed lower levels of both alpha 2 and beta(3)-ARs in BAT compared with male rats, but these levels in postcafeteria-fed female and male rats were the same, because males tended to down-regulate them. Levels of leptin mRNA in response to the postcafeteria state depended on gender and the specific WAT depot studied.

DISCUSSION

It is suggested that in postcafeteria-fed female rats, BAT thermogenic capacity becomes more efficiently activated than in males. Female rats also showed a bigger weight loss. The parallel regulation of the levels of UCP2 and UCP3 mRNAs, with respect to UCP1 mRNA, with higher activation in female postcafeteria-fed rats, suggests a possible role of both UCP2 and UCP3 in the regulation of energy expenditure and in the control of body weight. The distinct responses to overweight of alpha 2 and beta(3)-ARs--which were sex dependent--and leptin mRNA--which depended on both sex and WAT depot--also support the different response of thermogenesis-related parameters between overweight males and females.

Insulin-leptin-visceral fat relation during weight loss

INTRODUCTION

The relation between insulin-leptin-visceral fat axis during weight loss has not been studied previously.

AIMS

To evaluate the insulin, leptin, and abdominal adiposity relation during weight loss in patients with upper body obesity.

METHODOLOGY

Twenty volunteers (7 men, 13 women) with mean age 50.6+/-6.3 (SD) and upper body obesity (weight 105.4+/-12.3 kg, BMI 35.9+/-2.5 kg/m2) were recruited. Participants were enrolled in a one-arm clinical study using a calorie-deficient diet and an escalating dose regimen of sibutramine, starting with 5 mg daily and increasing in 5-mg increments to 20 mg per day. Body weight, insulin, leptin, glucose, lipids, abdominal computed tomography (CT), and total body electrical conductance (TOBEC) were measured serially at weeks 0, 4, 8, 12, and 24.

RESULTS

Eighteen patients completed the 6-month study: one man and one woman discontinued because of adverse events. With diet and sibutramine, body weight was significantly and continuously reduced throughout the 6-month study. There was a 16.0% (p = 0.0001) reduction in body weight (p < 0.001) and 22.5% (p = 0.0001) decrease in total body fat mass. Abdominal CT scans showed a 28.3% (p = 0.0001) reduction in total abdominal fat, a 26.0% (p = 0.0001) reduction in subcutaneous fat (p < 0.001), and a 31.0% (p = 0.0003) reduction in visceral fat (p < 0.001). There was a 32.0% (p = 0.0008) reduction in leptin levels and 37.9% (p = 0.0001) reduction in insulin levels between baseline and week 4, but no further significant reduction in leptin and insulin levels was observed for the duration of the study. There was a significant correlation between insulin and leptin concentrations throughout the study (p = 0.0001). Leptin was presented as a function of insulin measured at the same time. Significant associations between visceral abdominal fat, subcutaneous fat, and leptin were also observed.

CONCLUSION

In this study, we found that leptin and insulin were related in weight loss. The data suggest that insulin may act as a strong regulator of leptin secretion during weight loss and that circulating leptin levels can be predicted by insulin level. Using sibutramine in conjunction with hypocaloric diet reduced body weight and decreased fat mass significantly. Visceral and subcutaneous abdominal fat depots were shown to decrease. Whether sibutramine exerts any selective reduction of visceral abdominal fat as opposed to total body fat mass will require further clinical investigation.

Total and regional fat and serum cardiovascular disease risk factors in lean and obese children and adolescents

OBJECTIVE

This study was conducted to evaluate the association of total and central adiposity with serum cardiovascular disease (CVD) risk factors in lean and obese Portuguese children and adolescents.

RESEARCH METHODS AND PROCEDURES

A total of 87 girls (13.2 +/- 1.6 years old, 29.9 +/- 6.4% body fat [mean +/- SD]) and 72 boys (13.2 +/- 1.6 years old, 20.8 +/- 9.9% body fat) volunteered for the study. Whole-body composition and fat distribution, from DXA and anthropometry, and serum lipids, lipoproteins, and apolipoproteins were evaluated.

RESULTS

The sum of three trunk skinfolds (STS) was highly correlated with total trunk fat mass measured by DXA (p < 0.001). Body mass index, DXA-measured percentage of body fat, trunk fat mass, STS, and the waist-to-height ratio were generally found to be associated with triacylglycerol, the ratio of total cholesterol (TC) to high density lipoprotein-cholesterol (HDL-C), low density lipoprotein-cholesterol (LDL-C), and apolipoprotein B levels, (significant age-adjusted r between 0.16 and 0.27, p < 0.05). Body mass index, STS, and the waist circumference were also associated with HDL-C (p < 0.05), whereas no body composition variable significantly correlated with TC or apolipoproteins A-I. The STS was significantly correlated with HDL-C (p < 0.01), TC/HDL-C (p < 0.05), and apolipoproteins A-I (p < 0.05) independently of whole-body fatness. Obese subjects (n = 73) had higher TC, LDL-C, TC/HDL-C, and apolipoprotein B than did non-obese subjects (n = 86), and significant associations between central adiposity and some lipid variables (triacylglycerol and HDL-C) were found in obese children and adolescents that were not present in leaner individuals.

DISCUSSION

DXA- and anthropometry-based whole-body and central fat measures are associated with serum CVD risk factors in Portuguese boys and girls. Obese children and adolescents have a poorer lipid profile than do their leaner counterparts. Trunk skinfolds, which are easy to obtain even in large samples, predict CVD risk factors to the same extent as DXA-based variables, in some cases, independently of total fatness.

Expression of human alpha 2-adrenergic receptors in adipose tissue of beta 3-adrenergic receptor-deficient mice promotes diet-induced obesity

Catecholamines play an important role in controlling white adipose tissue function and development. beta- and alpha 2-adrenergic receptors (ARs) couple positively and negatively, respectively, to adenylyl cyclase and are co-expressed in human adipocytes. Previous studies have demonstrated increased adipocyte alpha 2/beta-AR balance in obesity, and it has been proposed that increased alpha 2-ARs in adipose tissue with or without decreased beta-ARs may contribute mechanistically to the development of increased fat mass. To critically test this hypothesis, adipocyte alpha 2/beta-AR balance was genetically manipulated in mice. Human alpha 2A-ARs were transgenically expressed in the adipose tissue of mice that were either homozygous (-/-) or heterozygous (+/-) for a disrupted beta 3-AR allele. Mice expressing alpha 2-ARs in fat, in the absence of beta 3-ARs (beta 3-AR -/- background), developed high fat diet-induced obesity. Strikingly, this effect was due entirely to adipocyte hyperplasia and required the presence of alpha2-ARs, the absence of beta 3-ARs, and a high fat diet. Of note, obese alpha 2-transgenic beta 3 -/- mice failed to develop insulin resistance, which may reflect the fact that expanded fat mass was due to adipocyte hyperplasia and not adipocyte hypertrophy. In summary, we have demonstrated that increased alpha 2/beta-AR balance in adipocytes promotes obesity by stimulating adipocyte hyperplasia. This study also demonstrates one way in which two genes (alpha 2 and beta 3-AR) and diet interact to influence fat mass.

The adoption of eating behaviors conducive to weight loss

Given the plethora of eating behavior techniques that obese individuals might adopt for weight loss, it is not likely that they could, or would be willing to, adopt all of them. Therefore, the purpose of this study was to identify the specific eating behaviors conducive to weight loss adopted during the behavioral treatment of obesity, and to distinguish those that were deemed beneficial from the ones that were not. Fifty obese (BMI 32+/-4 kg/m(2), mean+/-SD), postmenopausal women (60+/-6 years old) participated in a 6-month behavior modification, dietary, low-intensity walking weight loss program. For analysis, they were divided into two groups: "no weight loss" (<or=5 kg, n=18) versus "weight loss" (>5 kg, n=32). At pre- and posttreatment women completed the Eating Behavior Inventory (EBI) that measures specific strategies conducive to weight loss. Women who lost weight increased their total eating behavior score by 20% (p<0.001) and improved the adoption of 14 eating behaviors, which was more than twice that of the non-weight losers. Topping the list of most strongly adopted behaviors were carefully watching and recording the type and quantity of food consumed. Maintaining a weight graph and weighing daily also were important to these women. Neither group of women adopted potentially helpful eating behaviors such as leaving food uneaten, refusing food offered by others, or shopping from a list. In studies of obesity treatment, attendance at class sessions is one marker of program adherence. More definitively, implementing the EBI in clinical and research obesity treatment programs will provide its leaders with insight into whether participants adopt, ignore, or fight the essential behaviors that will facilitate success toward their personal weight loss goals.

Whole body and abdominal lipolytic sensitivity to epinephrine is suppressed in upper body obese women

We measured whole body and regional lipolytic and adipose tissue blood flow (ATBF) sensitivity to epinephrine in 8 lean [body mass index (BMI): 21 +/- 1 kg/m(2)] and 10 upper body obese (UBO) women (BMI: 38 +/- 1 kg/m(2); waist circumference >100 cm). All subjects underwent a four-stage epinephrine infusion (0.00125, 0.005, 0.0125, and 0.025 microgram. kg fat-free mass(-1). min(-1)) plus pancreatic hormonal clamp. Whole body free fatty acid (FFA) and glycerol rates of appearance (R(a)) in plasma were determined by stable isotope tracer methodology. Abdominal and femoral subcutaneous adipose tissue lipolytic activity was determined by microdialysis and (133)Xe clearance methods. Basal whole body FFA R(a) and glycerol R(a) were both greater (P < 0.05) in obese (449 +/- 31 and 220 +/- 12 micromol/min, respectively) compared with lean subjects (323 +/- 44 and 167 +/- 21 micromol/min, respectively). Epinephrine infusion significantly increased FFA R(a) and glycerol R(a) in lean (71 +/- 21 and 122 +/- 52%, respectively; P < 0.05) but not obese subjects (7 +/- 6 and 39 +/- 10%, respectively; P = not significant). In addition, lipolytic and ATBF sensitivity to epinephrine was blunted in abdominal but not femoral subcutaneous adipose tissue of obese compared with lean subjects. We conclude that whole body lipolytic sensitivity to epinephrine is blunted in women with UBO because of decreased sensitivity in upper body but not lower body subcutaneous adipose tissue.

Metabolic complications of obesity. Pathophysiologic considerations

Given a specific research interest in human fatty acid metabolism, this article focuses primarily on the evidence surrounding the hypothesis that dysregulation of the fuel release function of fat cells (lipolysis) is an important contributing factor to the health hazards of obesity.

Regional specificity of ASP binding in human adipose tissue

Obesity, in particular omental (OM) adiposity, is associated with diabetes and cardiovascular disease. Thus site-specific regulation of fat storage is important to understand. Acylation-stimulating protein (ASP) is a potent stimulator of glucose transport and triglyceride synthesis in adipocytes. In the present study, we characterized receptor binding of 125I-labeled ASP to human adipocyte plasma membranes from paired OM and subcutaneous (SC) sites in normal (N) and obese (O) male (M) and female (F) subjects (n = 24). Overall, specific binding of 125I-ASP was in the order of SC > OM and O > N (in SC tissue, particularly in F). Receptor affinity of 125I-ASP was higher [lower dissociation constant (Kd)] in SC than in OM (63.6 +/- 16.2 vs. 160.7 +/- 38.6 nM, P < 0.02), especially in F (37.0 +/- 11.1 F-N and 26.3 +/- 6.7 nM F-O) and lower (higher Kd) in male OM (291.8 +/- 116.8 M-N and 149.4 +/- 56.4 M-O). The greater binding and higher affinity of 125I-ASP binding to SC suggests that ASP may be an important factor in maintaining regional adipose tissue mass. Conversely, lower binding and receptor affinity in male OM adipose tissue may contribute to the fatty acid imbalance and metabolic complications associated with this syndrome, by reducing the efficiency of adipose fatty acid trapping by the ASP pathway.

Caloric restriction leads to regional specialisation of adipocyte function in the rat

The study analysed the responses of three metabolic parameters in five distinct adipose tissue depots to caloric restriction (4 weeks) in the rat. The aims were to evaluate whether specific adipose tissue depots were recruited for triacylglycerol (TAG) storage and/or mobilisation, and to determine to what extent specific adipose tissue depots exhibited preferences for the source of fatty acid (FA) for TAG storage. Caloric restriction led to a general enhancement of the response of lipoprotein lipase (LPL), FA synthesis and glucose utilisation to a meal. Effects were particularly marked in the parametrial, perirenal and interscapular depots compared with mesenteric and subcutaneous depots. There was no evidence that individual depots selectively expressed a preference for the pathways concerned with the generation of FA for storage (the exogenous (LPL) and the endogenous (synthesis) pathway). However, the temporal sequence of activation of these pathways differed in a manner consistent with a switch from preponderant use of FA produced via de novo synthesis during the very early phase of feeding towards later use of FA derived from circulating TAG. The overall excursions in insulin levels observed in the calorie-restricted rats were comparable to those found in free-feeding rats, but the magnitude and the rapidity of the individual metabolic responses of the adipocyte were augmented. The data are consistent with a general enhancement of insulin sensitivity and responsiveness in adipose tissue of calorie-restricted rats, together with adaptive regional specialisation of adipocyte function. These adaptations would be predicted to facilitate the immediate conservation of dietary nutrients by promoting their storage as the FA or glycerol moieties of adipose tissue TAG and thereby to ensure the regulated release of FA and glycerol from adipose tissue in accordance with the requirement for glucose conservation and/or production.