Control of lipolysis and its relevance to development of obesity in man

Effects of LED photobiomodulation therapy on the subcutaneous fatty tissue of obese individuals - histological and immunohistochemical analysis

Photobiomodulation therapy (PBMT) has become an adjuvant therapeutic possibility in body remodeling procedures. Given this scenario, this study was proposed with the aim of evaluating the effects of PBMT to Light Emitting Diode (LED) associating the red (630 nm) and infrared (850 nm) wavelengths in the subcutaneous fatty tissue. This controlled study of comparative intervention that evaluated a sample of subcutaneous fatty tissue from women with grade II obesity. The participants received the LED PBMT treatment with associated red and infrared wavelengths sequentially on the left side of the abdomen and the right side was considered as control, with the collection of biological material performed at the time of bariatric surgery. For histological and immunohistochemical evaluation, Caspase 3, Cleaved Caspase 3, CD68+, HSL and adipophilin markers were used. The participants showed positivity in the expression of Caspase 3 and Cleaved Caspase (p < .0001), CD68+ macrophages (p < .0001), HSL (p < .0001) and adipophilin (p < .0013) in the intervention sample when compared to the control. PBMT and LED associating red and infrared wavelengths were able to promote autophagic lipolysis induced by adipocyte cell apoptosis in the subcutaneous tissue of obese individuals.

Metabolic and Energy Imbalance in Dysglycemia-Based Chronic Disease

Metabolic flexibility is the ability to efficiently adapt metabolism based on nutrient availability and requirement that is essential to maintain homeostasis in times of either caloric excess or restriction and during the energy-demanding state. This regulation is orchestrated in multiple organ systems by the alliance of numerous metabolic pathways under the master control of the insulin-glucagon-sympathetic neuro-endocrine axis. This, in turn, regulates key metabolic enzymes and transcription factors, many of which interact closely with and culminate in the mitochondrial energy generation machinery. Metabolic flexibility is compromised due to the continuous mismatch between availability and intake of calorie-dense foods and reduced metabolic demand due to sedentary lifestyle and age-related metabolic slowdown. The resultant nutrient overload leads to mitochondrial trafficking of substrates manifesting as mitochondrial dysfunction characterized by ineffective substrate switching and incomplete substrate utilization. At the systemic level, the manifestation of metabolic inflexibility comprises reduced skeletal muscle glucose disposal rate, impaired suppression of hepatic gluconeogenesis and adipose tissue lipolysis manifesting as insulin resistance. This is compounded by impaired β-cell function and progressively reduced β-cell mass. A consequence of insulin resistance is the upregulation of the mitogen-activated protein kinase pathway leading to a pro-hypertensive, atherogenic, and thrombogenic environment. This is further aggravated by oxidative stress, advanced glycation end products, and inflammation, which potentiates the risk of micro- and macro-vascular complications. This review aims to elucidate underlying mechanisms mediating the onset of metabolic inflexibility operating at the main target organs and to understand the progression of metabolic diseases. This could potentially translate into a pharmacological tool that can manage multiple interlinked conditions of dysglycemia, hypertension, and dyslipidemia by restoring metabolic flexibility. We discuss the breadth and depth of metabolic flexibility and its impact on health and disease.

CREG1 heterozygous mice are susceptible to high fat diet-induced obesity and insulin resistance

Cellular repressor of E1A-stimulated genes 1 (CREG1) is a small glycoprotein whose physiological function is unknown. In cell culture studies, CREG1 promotes cellular differentiation and maturation. To elucidate its physiological functions, we deleted the Creg1 gene in mice and found that loss of CREG1 leads to early embryonic death, suggesting that it is essential for early development. In the analysis of Creg1 heterozygous mice, we unexpectedly observed that they developed obesity as they get older. In this study, we further studied this phenotype by feeding wild type (WT) and Creg1 heterozygote (Creg1^+/-) mice a high fat diet (HFD) for 16 weeks. Our data showed that Creg1^+/- mice exhibited a more prominent obesity phenotype with no change in food intake compared with WT controls when challenged with HFD. Creg1 haploinsufficiency also exacerbated HFD-induced liver steatosis, dyslipidemia and insulin resistance. In addition, HFD markedly increased pro-inflammatory cytokines in plasma and epididymal adipose tissue in Creg1^+/- mice as compared with WT controls. The activation level of NF-κB, a major regulator of inflammatory response, in epididymal adipose tissue was also elevated in parallel with the cytokines in Creg1^+/- mice. These pro-inflammatory responses elicited by CREG1 reduction were confirmed in 3T3-L1-derived adipocytes with CREG1 depletion by siRNA transfection. Given that adipose tissue inflammation has been shown to play a key role in obesity-induced insulin resistance and metabolic syndrome, our results suggest that Creg1 haploinsufficiency confers increased susceptibility of adipose tissue to inflammation, leading to aggravated obesity and insulin resistance when challenged with HFD. This study uncovered a novel function of CREG1 in metabolic disorders.

Serum amyloid A links endotoxaemia to weight gain and insulin resistance in mice

AIMS/HYPOTHESIS

Pre-adipocytes and adipocytes are responsive to the acute phase protein serum amyloid A (SAA). The combined effects triggered by SAA encompass an increase in pre-adipocyte proliferation, an induction of TNF-α and IL-6 release and a decrease in glucose uptake in mature adipocytes, strongly supporting a role for SAA in obesity and related comorbidities. This study addressed whether SAA depletion modulates weight gain and insulin resistance induced by a high-fat diet (HFD).

METHODS

Male Swiss Webster mice were fed an HFD for 10 weeks under an SAA-targeted antisense oligonucleotide (ASOSAA) treatment in order to evaluate the role of SAA in weight gain.

RESULTS

With ASOSAA treatment, mice receiving an HFD did not differ in energy intake when compared with their controls, but were prevented from gaining weight and developing insulin resistance. The phenotype was characterised by a lack of adipose tissue expansion, with low accumulation of epididymal, retroperitoneal and subcutaneous fat content and decreased inflammatory markers, such as SAA3 and toll-like receptor (TLR)-4 expression, as well as macrophage infiltration into the adipose tissue. Furthermore, a metabolic status similar to chow-fed mice counterparts could be observed, with equivalent levels of leptin, adiponectin, IGF-I, SAA, fasting glucose and insulin, and remarkable improvement in glucose and insulin tolerance test profiles. Surprisingly, the expected HFD-induced metabolic endotoxaemia was also prevented by the ASOSAA treatment.

CONCLUSIONS/INTERPRETATION

This study provides further evidence of the role of SAA in weight gain and insulin resistance. Moreover, we also suggest that beyond its proliferative and inflammatory effects, SAA is part of the lipopolysaccharide signalling pathway that links inflammation to obesity and insulin resistance.

Biological mechanisms that promote weight regain following weight loss in obese humans

Weight loss dieting remains the treatment of choice for the vast majority of obese individuals, despite the limited long-term success of behavioral weight loss interventions. The reasons for the near universal unsustainability of behavioral weight loss in [formerly] obese individuals have not been fully elucidated, relegating researchers to making educated guesses about how to improve obesity treatment, as opposed to developing interventions targeting the causes of weight regain. This article discusses research on several factors that may contribute to weight regain following weight loss achieved through behavioral interventions, including adipose cellularity, endocrine function, energy metabolism, neural responsivity, and addiction-like neural mechanisms. All of these mechanisms are engaged prior to weight loss, suggesting that these so called "anti-starvation" mechanisms are activated via reductions in energy intake, rather than depletion of energy stores. Evidence suggests that these mechanisms are not necessarily part of a homeostatic feedback system designed to regulate body weight, or even anti-starvation mechanisms per se. Although they may have evolved to prevent starvation, they appear to be more accurately described as anti-weight loss mechanisms, engaged with caloric restriction irrespective of the adequacy of energy stores. It is hypothesized that these factors may combine to create a biological disposition that fosters the maintenance of an elevated body weight and works to restore the highest sustained body weight, thus precluding the long-term success of behavioral weight loss. It may be necessary to develop interventions that attenuate these biological mechanisms in order to achieve long-term weight reduction in obese individuals.

Insulin Action in Rats Is Influenced by Amount and Composition of Dietary Fat

The chronic influence of dietary fat composition on obesity and insulin action is not well understood. We examined the effect of amount (20% vs 60% of total calories) and type (saturated vs polyunsaturated) of fat on insulin action and body composition in mature male rats. Six months of feeding a high fat (HF) diet led to obesity and impaired insulin action (determined by a euglycemic-hyperinsulinemic clamp), neither of which were reversed by a subsequent 6 months of feeding a low fat (LF) diet. Within HF fed rats, type of fat did not affect body composition or insulin action. Six months of feeding a low fat diet led to only a slight decline in insulin action, with no difference due to type of dietary fat. From 6-9 months, insulin action became more impaired in LF rats fed the saturated diet than in LF rats fed the polyunsaturated diet. By 12 months, all groups were obese and had a similar impairment in insulin action. The amount and type of fat in the diet did not influence the overall degree of impairment in insulin action but did affect the time course. Both feeding a high fat diet and feeding a low fat saturated diet accelerated the impairment in insulin action relative to rats fed a low fat polyunsaturated fat diet.

Sympathetic innervation does not contribute to glycerol release in ischemic flaps

BACKGROUND

Extracellular glycerol as detected by microdialysis has been used as a surrogate marker for (ischemic) tissue damage and cellular membrane breakdown in the monitoring of free microvascular musculocutaneous flaps. One confounding factor for glycerol as a marker of ischemic cell damage is the effect of lipolysis and associated glycerol release as induced by sympathetic signalling alone. We hypothesized that extracellular glycerol concentrations in a microvascular flap with sympathetic innervation would be confounded by intact innervation per se as compared to denervated flap. Clinical relevance is related to the use of both free and pedicled flaps in reconstructive surgery. We tested the hypothesis in an experimental model of microvascular musculocutaneal flaps.

METHODS

Twelve pigs were anesthetized and mechanically ventilated. Two identical rectus abdominis musculocutaneal flaps were raised for the investigation. In the A-flaps the adventitia of the artery and accompanying innervation was carefully stripped, while in the B-flaps it was left untouched. Flap ischemia was induced by clamping both vessels for 60 minutes. The ischemia was confirmed by measuring tissue oxygen pressure, while extracellular lactate to pyruvate ratio indicated the accompanying anaerobic metabolism locally.

RESULTS

Intramuscular and subcutaneal extracellular glycerol concentrations were measured by microdialysate analyzer. Contrary to our hypothesis, glycerol concentrations were comparable between the two ischemia groups at 60 minutes (p = 0.089, T-test).

CONCLUSIONS

In this experimental model of vascular flap ischemia, intact innervation of the flap did not confound ischemia detection by glycerol. Extrapolation of the results to clinical setting warrants further studies.

β-adrenoreceptor activation in brain, lung and adipose tissue, measured by microdialysis in pig

PURPOSE

The aim of this study is to investigate the effect of local activation of β-adrenoreceptor by Isoprenaline on metabolism in brain, fat and lung measured by microdialysis.

METHODS

We used 8 healthy pigs under general anaesthesia and placed microdialysis catheters in brain, fat, lung and artery. We performed a direct measurement of glucose, lactate, pyruvate and glycerol. The stimulation was performed by one-hour infusion of Isoprenaline, a β-adrenoreceptor agonist.

RESULTS

The infusion of isoprenaline did not affect the glucose in any tissue. The levels of lactate (p=0.008) and pyruvate (p=0.011) decreased significantly in lung after isoprenaline infusion. There was a significant increase in L/P ratio in fat tissue (p=0.001) while no significant changes could be found in brain (p=0.086) and lung (p=0.679). The most pronounced and significant change was observed in glycerol in fat (p<0.001) that increased by 95%.

CONCLUSION

The prominent increase in glycerol in fat proved to be a good measure of β-adrenoreceptor activation and a measure of lipolysis. This can be used to online monitor β-adrenoreceptor activation by glycerol measurement in patients.

Obesity and insulin resistance-related changes in the expression of lipogenic and lipolytic genes in morbidly obese subjects

BACKGROUND

The storage capacity of adipose tissue may be an important factor linking obesity, insulin resistance (IR), and associated morbidities. The aim of this study was to analyze the expression of lipogenic and lipolytic genes in adipose tissue and the influence of IR.

METHODS

We studied the mRNA expression of peroxisome proliferator-activated receptor-γ (PPARγ) and lipogenic and lipolytic enzymes in the visceral (VAT) and subcutaneous adipose tissue (SAT) from 23 morbidly obese patients (MO; 13 with low IR and ten with high IR) and from 15 healthy, lean controls.

RESULTS

In the VAT and SAT from the MO, we found an increased expression of PPARγ (p = 0.001 and p = 0.022, respectively), acyl-coenzyme A (CoA)/cholesterol acyltransferase (p < 0.001 and p < 0.001), aquaporin 7 (p < 0.001 and p = 0.003), and adipose triglyceride lipase (p < 0.001 and p < 0.001) and a reduced expression of acetyl-coenzyme A carboxylase (p = 0.004 and p < 0.001), independently of the state of IR. The expression of phosphoenolpyruvate carboxykinase and acyl-CoA synthetase, however, was significantly lower in the MO with high IR (p < 0.05). Glycerol kinase (p = 0.010), hormone-sensitive lipase (p < 0.001), and perilipin (p = 0.006) were only significantly increased in VAT. Acyl-CoA synthetase (p = 0.012) and fatty acid binding protein-4 (p = 0.003) were only significantly decreased in SAT. The expression of the genes studied was only greater in the SAT than the VAT in the controls.

CONCLUSION

Our results show an upregulation of genes facilitating triglyceride/fatty acid cycling and a reduction in the genes involved in de novo synthesis of fatty acids in morbid obesity. The expression of some of the genes studied seems to be related with the state of IR. VAT and SAT differ metabolically and also between controls and MO.

Resting metabolic rate after endurance exercise training

PURPOSE

1) To examine the effect of a 12-wk endurance exercise training program on RMR and 2) to provide insight into the mechanisms responsible for alterations in RMR that may occur after exercise training.

METHODS

Male participants (19-32 yr) in an exercise group (EX; n = 9) performed jogging and/or running 3-4 d x wk(-1), 25-40 min per session, at 60%-80% VO2max, whereas subjects in a control group (CON; n = 10) maintained their normal activity patterns. Body composition, VO2max, RMR, epinephrine, norepinephrine, total thyroxine, free thyroxine, insulin, free fatty acids, and glucose were measured before and after the intervention.

RESULTS

Training resulted in a significant increase in VO2max in EX (46.2 +/- 1.2 to 51.0 +/- 1.3 mL x kg(-1) x min(-1), P < 0.001). Absolute and relative values for RMR did not significantly change in EX after training. Mean values for epinephrine, norepinephrine, total thyroxine, insulin, and glucose did not significantly change in either group; however, free thyroxine decreased significantly after training in EX (P = 0.04). Training also resulted in a significant increase in free fatty acid concentration in EX (0.37 +/- 0.03 to 0.48 +/- 0.04 mmol x L(-1), P < 0.001). RMR in CON decreased significantly when expressed as an absolute value (P < 0.01) and relative to body weight (P < 0.01), fat-free mass (P < 0.01), and fat mass (P = 0.04).

CONCLUSIONS

The mechanism for the decrease in CON is unknown, but it may be related to seasonal variations in RMR. Training may have prevented a similar decline in RMR in EX and may be related to a training-induced increase in fat oxidation.

Glucose metabolism and diet predict changes in adiposity and fat distribution in weight-reduced women

Among obesity-prone individuals, metabolic state may interact with diet in determining body composition. We tested the hypotheses that, among 103 weight-reduced women over 1 year, (i) insulin sensitivity would be positively associated with change in %fat; (ii) this association would be modulated by dietary glycemic load (GL); and (iii) changes in fat distribution would be related to indexes of glucose metabolism. Insulin sensitivity, glucose effectiveness, fasting and postchallenge insulin and glucose, and glucose tolerance were assessed during intravenous glucose tolerance test (IVGTT). Changes in %fat and fat distribution were examined using dual-energy X-ray absorptiometry and computed tomography. Dietary GL was assessed on 67 women using food records. On average, women showed a +5.3 +/- 3.0% change in %fat over 1 year, with the magnitude of this change being greater in relatively insulin sensitive women (+6.0 +/- 0.4%, mean +/- s.e.m.) than in relatively insulin resistant women (+4.4 +/- 0.4 kg; P < 0.05). Women who were relatively insulin sensitive and who consumed a higher GL diet showed a +6.8 +/- 0.7% change in %fat, which was greater than those who were less insulin sensitive, regardless of diet (P < 0.05), but did not differ from women who were relatively insulin sensitive and who consumed a lower GL diet (P = 0.105). Changes in intra-abdominal and deep subcutaneous abdominal fat were inversely associated with the postchallenge decline in serum glucose. In conclusion, greater insulin sensitivity may predispose to adiposity among weight reduced women, an effect that may be ameliorated by a lower GL diet. The potential association between indexes of glucose disposal and changes in fat distribution warrants further study.

Metabolic effects of obesity: A review

With the many recent advances in the biomedical world, vast changes are taking place in our growing knowledge of the physiological aspects of almost all the tissues and organs of the human body. One of the most prevalent topics of discussion is the question of obesity and its effect on the metabolic changes in the human body. The original classical role of adipose tissue as an energy storage organ has been greatly modified. We now know that it is an endocrine organ, producing adipokines like leptin, adiponectin, visfatin, resistin, apelin, etc, which modulate metabolic processes in the body. Since obesity is associated with an increase in the adipose tissue mass, these hormones may be expected to be produced in increased concentrations and may thus have a significant impact on the macronutrient metabolism. Further, these adipokines may interact with long term energy modulators like insulin. Even though the scientific community has started unravelling the mysteries of the close linkage between obesity, its hormones and their physiological effects, a lot still remains to be discovered. The present discussion makes an attempt to trace the basic modern day concepts of the role of obesity in various metabolic processes.

Relationship of glucose regulation to changes in weight: a systematic review and guide to future research

Although weight gain and obesity are risk factors for poor glucose regulation, the relationship, if any, of glucose regulation to changes in weight is not well understood. The purpose of this study was to conduct a systematic review of research examining the relationship of glucose regulation to changes in weight in human-based studies and to provide guidelines for future research in this area. We searched electronic databases and reference sections of relevant articles, including both diabetic and non-diabetic populations, to locate all the literature published before February 2010, and then conducted a systematic review across studies to compare the research designs and findings. The 22 studies meeting our criteria for review generally supported the relationship of glucose regulation to changes in weight. Three studies reported that poor glucose regulation is associated with weight gain; 12 studies concluded that poor glucose regulation is associated with weight loss; 5 showed complex relationships depending on age, sex, or race/ethnicity; and 2 suggested no relationship. The diverse findings may imply that the direction (negative or positive) of the relationship may depend on specific conditions. More research focused on different subpopulations may provide more definitive information supplemental to the current preliminary findings. Recommendations regarding future research in this particular area are provided in the discussion.

Downregulation of adipose glutathione S-transferase A4 leads to increased protein carbonylation, oxidative stress, and mitochondrial dysfunction

OBJECTIVE

Peripheral insulin resistance is linked to an increase in reactive oxygen species (ROS), leading in part to the production of reactive lipid aldehydes that modify the side chains of protein amino acids in a reaction termed protein carbonylation. The primary enzymatic method for lipid aldehyde detoxification is via glutathione S-transferase A4 (GSTA4) dependent glutathionylation. The objective of this study was to evaluate the expression of GSTA4 and the role(s) of protein carbonylation in adipocyte function.

RESEARCH DESIGN AND METHODS

GSTA4-silenced 3T3-L1 adipocytes and GSTA4-null mice were evaluated for metabolic processes, mitochondrial function, and reactive oxygen species production. GSTA4 expression in human obesity was evaluated using microarray analysis.

RESULTS

GSTA4 expression is selectively downregulated in adipose tissue of obese insulin-resistant C57BL/6J mice and in human obesity-linked insulin resistance. Tumor necrosis factor-alpha treatment of 3T3-L1 adipocytes decreased GSTA4 expression, and silencing GSTA4 mRNA in cultured adipocytes resulted in increased protein carbonylation, increased mitochondrial ROS, dysfunctional state 3 respiration, and altered glucose transport and lipolysis. Mitochondrial function in adipocytes of lean or obese GSTA4-null mice was significantly compromised compared with wild-type controls and was accompanied by an increase in superoxide anion.

CONCLUSIONS

These results indicate that downregulation of GSTA4 in adipose tissue leads to increased protein carbonylation, ROS production, and mitochondrial dysfunction and may contribute to the development of insulin resistance and type 2 diabetes.

Insulin resistance, dyslipidemia, and metabolic syndrome in women with polycystic ovary syndrome

OBJECTIVE

To investigate the association of insulin resistance with dyslipidemia and metabolic syndrome (MBS) in women with polycystic ovary syndrome (PCOS).

METHODS

Fasting glucose (G), insulin (I), and lipid levels were measured in 50 infertile women with PCOS. A fasting G/I ratio of 4.5 or less (n=29) defined insulin resistance (IR).

RESULTS

The mean levels of total cholesterol (P<0.001), low-density lipoprotein (P=0.02), and triglycerides (P<0.001) were significantly higher and the mean levels of high-density lipoprotein were significantly lower (P<0.001) in the IR group. The prevalence of MBS (P=0.02) and obesity (P=0.04), hypertension (P=0.02), fasting hyperglycemia (P=0.03), low high-density lipoprotein levels (P=0.02), and hypertriglyceridemia (P=0.02) were also significantly higher in the IR group.

CONCLUSION

Insulin resistance is associated with dyslipidemia and MBS in women with PCOS. Lifestyle modification and insulin-sensitizing agents should be part of the management plan.

Association between serum amyloid A and obesity: a meta-analysis and systematic review

BACKGROUND

Emerging evidence indicates an association of the acute-phase protein serum amyloid A (SAA) with obesity. Here we review and summarize quantitatively the available data related to this association.

METHODS

PubMed was systematically searched using the terms "serum amyloid A" and "obesity." Eighty-one relevant studies between January 1966 and July 2009 were identified. Of these, only 11 cross-sectional studies and 10 prospective studies with successful interventions met our inclusion criteria for the meta-analysis. All analyses were conducted using the Comprehensive Meta-Analysis software. Literature pertaining to the relationship between SAA and other inflammatory markers, and the association between SAA and obesity-related disorders, such as cardiovascular diseases, atherosclerosis, diabetes, and insulin resistance was also reviewed.

RESULTS

A strong association between body mass index and SAA levels was found in the 11 cross-sectional studies. The overall correlation coefficient is 0.230 (95% CI 0.160-0.297, P < 0.0005). The ten prospective studies were subsequently analyzed, and the difference in SAA levels before and after weight loss, expressed as standardized mean difference was -0.480 (95% CI -0.678 to -0.283, P < 0.0005). We discuss some potential underlying mechanisms and clinical applications for reducing SAA levels in obesity.

Endoplasmic reticulum stress-induced apoptosis in the development of diabetes: is there a role for adipose tissue and liver?

Diabetes mellitus (DM) is a multifactorial chronic metabolic disease characterized by hyperglycaemia. Several different mechanisms have been implicated in the development of the disease, including endoplasmic reticulum (ER) stress. ER stress is increasingly acknowledged as an important mechanism in the development of DM, not only for β-cell loss but also for insulin resistance. Accumulating evidence suggests that ER stress-induced apoptosis may be an important mode of β-cell loss and therefore important in the development of diabetes. Recent data also suggest a role of ER stress-induced apoptosis in liver and adipose tissue in relation to diabetes, but more extensive studies on human adipocyte and hepatocyte (patho)physiology and ER stress are needed to identify the exact interactions between environmental signals, ER stress and apoptosis in these organs.

High lipolytic activity and dyslipidemia in a spontaneous hypertensive/NIH corpulent (SHR/N-cp) rat: a genetic model of obesity and type 2 diabetes mellitus

In order to better understand the link between obesity and type 2 diabetes, lipolysis and its adrenergic regulation was investigated in various adipose depots of obese adult females SHR/N-cp rats. Serum insulin, glucose, free fatty acids (FFA), triglycerides (TG) and glycerol were measured. Adipocytes were isolated from subcutaneous (SC), parametrial (PM) and retroperitoneal (RP) fat pads. Total cell number and size, basal lipolysis or stimulated by norepinephrine (NE) and BRL 37344 were measured in each depot. Obese rats were hyperinsulinemic and hyperglycemic, suggesting high insulin resistance. They presented a marked dyslipidemia, attested by increased serum FFA and TG levels. High serum glycerol levels also suggest a strong lipolytic rate. Obese rats showed an excessive development of all fat pads although a more pronounced effect was observed in the SC one. The cellularity of this depot was increased 8 fold when compared to lean rats, but these fat cells were only 1.5 to 2-fold larger. SC adipocytes showed a marked increase in their basal lipolytic activity but a lack of change in responsiveness to NE or BRL 37344. The association between high basal lipolysis and increased cellularity yields to a marked adipose cell lipolytic rate, especially from the SC region. SHR/N-cp rats were characterized by a hyperplasic type of obesity with an excessive development of the SC depot. The dyslipidemia, attested by an altered serum lipid profile could be attributed to excessive lipolysis that contributes to increased FFA levels, and to early development of insulin resistance through a lipotoxicity effect.

Cellulite: Is there a role for injectables?

BACKGROUND

Cellulite describes the cutaneous dimpling of the thighs, buttocks, and hips that is seen predominately in women. Current evidence suggests that structural differences in fat architecture between the sexes account for its appearance. Mesotherapy, a method of delivering medication locally with the use of numerous cutaneous injections, has recently become a popular method to purportedly treat the condition.

METHODS

An overview of cellulite and adipocyte physiology, with a literature review and appraisal of compounds commonly used in mesotherapy.

RESULTS

Experimental studies using individual mesotherapy ingredients for other conditions suggest a number of mechanisms, including lipolysis, disrupting connective tissue and augmenting circulation, which may theoretically improve cellulite. Peer-reviewed studies have not evaluated whether these effects translate clinically.

CONCLUSIONS

Until further studies are performed, patients considering mesotherapy for cellulite must be aware that the substances currently being injected to treat this cosmetically disturbing, but medically benign, condition have not been thoroughly evaluated for safety or efficacy.

Lipolysis and lipid mobilization in human adipose tissue

Triacylglycerol (TAG) stored in adipose tissue (AT) can be rapidly mobilized by the hydrolytic action of the three main lipases of the adipocyte. The non-esterified fatty acids (NEFA) released are used by other tissues during times of energy deprivation. Until recently hormone-sensitive lipase (HSL) was considered to be the key rate-limiting enzyme responsible for regulating TAG mobilization. A novel lipase named adipose triglyceride lipase/desnutrin (ATGL) has been identified as playing an important role in the control of fat cell lipolysis. Additionally perilipin and other proteins of the surface of the lipid droplets protecting or exposing the TAG core of the droplets to lipases are also potent regulators of lipolysis. Considerable progress has been made in understanding the mechanisms of activation of the various lipases. Lipolysis is under tight hormonal regulation. The best understood hormonal effects on AT lipolysis concern the opposing regulation by insulin and catecholamines. Heart-derived natriuretic peptides (i.e., stored in granules in the atrial and ventricle cardiomyocytes and exerting stimulating effects on diuresis and natriuresis) and numerous autocrine/paracrine factors originating from adipocytes and other cells of the stroma-vascular fraction may also participate in the regulation of lipolysis. Endocrine and autocrine/paracrine factors cooperate and lead to a fine regulation of lipolysis in adipocytes. Age, anatomical site, sex, genotype and species differences all play a part in the regulation of lipolysis. The manipulation of lipolysis has therapeutic potential in the metabolic disorders frequently associated with obesity and probably in several inborn errors of metabolism.

Regulation of lypolysis in white adipose tissues of lean and obese Zucker rats

Obese Zucker rat is often used as a model of genetic obesity to understand the mechanism of the development of obesity. In the present work, in order to better understand the regulation of lipolysis in the Zucker rat, the lipolytic activities of adipocytes isolated from different adipose depots of lean and obese Zucker rats, in the basal state or after catecholamine stimulation have been measured. The obese Zucker rat presents hyperinsulinemia without hyperglycemia and with elevated plasma free fatty acids, suggesting a dyslipidemia. Morphological studies of three adipose deposits show a marked hypertrophic and hyperplastic type of obesity, much pronounced in the subcutaneous depot. In the current study we show that the basal lipolytic rate is higher in adipocytes from each deposit of obese rats (when results are corrected for cell surface area). This finding, associated with the increase of all deposits, could contribute to the elevated plasma FFA observed. Investigation of the responsiveness of dibutyril cAMP (DBcAMP) points out that the defect in the NE responsiveness is essentially located at post-receptor level. Nevertheless, a receptor defect could not be excluded as suggested by a decrease of the beta-ARs observed in all deposits. Our study points out that the lipolytic resistance to catecholamines in adipose tissue of obese Zucker rats appears to counteract the increase in the lipolytic rate, in order to moderate the increase in plasma FFA levels that may contribute to the hyperinsulinemia observed, characteristic of an insulino-resistant state.

Lipolysis and insulin sensitivity at birth in infants who are large for gestational age

OBJECTIVE

In addition to neonatal hypoglycemia, infants who are born large for gestational age are at risk for developing obesity, cardiovascular disease, and diabetes later in life. The aim of this study was to investigate glucose production, lipolysis, and insulin sensitivity in infants who were born large for gestational age to mothers without diabetes. The effect of glucagon administration on production of energy substrates was also investigated.

METHODS

Ten healthy term infants who were born large for gestational age to mothers without diabetes were studied 16 +/- 8 hours postnatally after a 3-hour fast. Rates of glucose production and lipolysis were analyzed by gas chromatography-mass spectrometry following constant rate infusion of [6,6-(2)H2]glucose and [2-(13)C]glycerol. Insulin sensitivity was assessed by the Homeostasis Assessment Model. In 8 of the infants, the effect of an intravenous injection of 0.2 mg/kg glucagon was also analyzed.

RESULTS

Plasma glucose and glycerol averaged 3.8 +/- 0.5 mmol/L and 384 +/- 183 micromol/L, respectively. The glycerol production rate, reflecting lipolysis, was 12.7 +/- 2.9 micromol/kg per min. Mean rate of glucose production was 30.2 +/- 4.6 micromol/kg per min. Homeostasis Assessment Model insulin sensitivity corresponded to 82% +/- 19%, beta-cell function to 221% +/- 73%, and insulin resistance to 1.3 +/- 0.3. After glucagon administration, rate of glucose production increased by 13.3 +/- 8.3 micromol/kg per min and blood glucose by 1.4 +/- 0.5 mmol/L. Glycerol production decreased from 12.8 +/- 3.0 to 10.7 +/- 2.9 micromol/kg per min. Mean insulin concentration increased from 10.9 +/- 3.0 to 30.9 +/- 10.3 mU/L. There was a strong inverse correlation between the decrease in lipolysis and increase in insulin after glucagon administration.

CONCLUSIONS

Infants who are born large for gestational age show increased lipolysis and a propensity for decreased insulin sensitivity already at birth. The simultaneous increase in plasma insulin correlated strongly with the noted decrease in lipolysis, indicating an antilipolytic effect of insulin in these infants.

Nocturnal free fatty acids are uniquely elevated in the longitudinal development of diet-induced insulin resistance and hyperinsulinemia

Obesity is strongly associated with hyperinsulinemia and insulin resistance, both primary risk factors for type 2 diabetes. It has been thought that increased fasting free fatty acids (FFA) may be responsible for the development of insulin resistance during obesity, causing an increase in plasma glucose levels, which would then signal for compensatory hyperinsulinemia. But when obesity is induced by fat feeding in the dog model, there is development of insulin resistance and a marked increase in fasting insulin despite constant fasting FFA and glucose. We examined the 24-h plasma profiles of FFA, glucose, and other hormones to observe any potential longitudinal postprandial or nocturnal alterations that could lead to both insulin resistance and compensatory hyperinsulinemia induced by a high-fat diet in eight normal dogs. We found that after 6 wk of a high-fat, hypercaloric diet, there was development of significant insulin resistance and hyperinsulinemia as well as accumulation of both subcutaneous and visceral fat without a change in either fasting glucose or postprandial glucose. Moreover, although there was no change in fasting FFA, there was a highly significant increase in the nocturnal levels of FFA that occurred as a result of fat feeding. Thus enhanced nocturnal FFA, but not glucose, may be responsible for development of insulin resistance and fasting hyperinsulinemia in the fat-fed dog model.

Age-associated changes in fat metabolism in the rat and its relation to sympathetic activity

In this study, to determine if age associated changes in fat metabolism in skeletal muscle and liver were related with sympathetic activity, we measured sympathetic activity and palmitate oxidation rate, carnitine palmitoyltransferase-1 (CPT-1) activity, and triglyceride concentration in skeletal muscle and liver of rats at 8, 30 and 60 weeks of age. Body weight, intra-abdominal percent of fat mass, and plasma level of insulin, leptin, and triglyceride were all significantly increased with age. Tissue triglyceride concentration was increased with age in liver and skeletal muscle. The palmitate oxidation rate in liver and skeletal muscle was reduced with age in rats and inversely correlated with tissue triglyceride concentration. CPT-1 activity was not altered with age. Plasma catecholamine concentration and sympathetic activity, as measured by spectral analysis of heart rate variability, were increased with age. Plasma norepinephrine or epinephrine and tissue triglyceride had a positive correlation in liver and skeletal muscle. Plasma norepinephrine or epinephrine to tissue triglyceride ratio was similar according to age. In summary, in spite of increased sympathetic activity with age, the tissue triglyceride concentration was increased. Increased sympathetic activity may be the compensatory response and the reduced capacity of fatty acid oxidation is a main cause of obesity.

Acute-phase serum amyloid A: an inflammatory adipokine and potential link between obesity and its metabolic complications

BACKGROUND

Obesity is associated with low-grade chronic inflammation, and serum markers of inflammation are independent risk factors for cardiovascular disease (CVD). However, the molecular and cellular mechanisms that link obesity to chronic inflammation and CVD are poorly understood.

METHODS AND FINDINGS

Acute-phase serum amyloid A (A-SAA) mRNA levels, and A-SAA adipose secretion and serum levels were measured in obese and nonobese individuals, obese participants who underwent weight-loss, and persons treated with the insulin sensitizer rosiglitazone. Inflammation-eliciting activity of A-SAA was investigated in human adipose stromal vascular cells, coronary vascular endothelial cells and a murine monocyte cell line. We demonstrate that A-SAA was highly and selectively expressed in human adipocytes. Moreover, A-SAA mRNA levels and A-SAA secretion from adipose tissue were significantly correlated with body mass index (r = 0.47; p = 0.028 and r = 0.80; p = 0.0002, respectively). Serum A-SAA levels decreased significantly after weight loss in obese participants (p = 0.006), as well as in those treated with rosiglitazone (p = 0.033). The magnitude of the improvement in insulin sensitivity after weight loss was significantly correlated with decreases in serum A-SAA (r = -0.74; p = 0.034). SAA treatment of vascular endothelial cells and monocytes markedly increased the production of inflammatory cytokines, e.g., interleukin (IL)-6, IL-8, tumor necrosis factor alpha, and monocyte chemoattractant protein-1. In addition, SAA increased basal lipolysis in adipose tissue culture by 47%.

CONCLUSIONS

A-SAA is a proinflammatory and lipolytic adipokine in humans. The increased expression of A-SAA by adipocytes in obesity suggests that it may play a critical role in local and systemic inflammation and free fatty acid production and could be a direct link between obesity and its comorbidities, such as insulin resistance and atherosclerosis. Accordingly, improvements in systemic inflammation and insulin resistance with weight loss and rosiglitazone therapy may in part be mediated by decreases in adipocyte A-SAA production.

ICAM-1 and beta2 integrin deficiency impairs fat oxidation and insulin metabolism during fasting

Intercellular adhesion molecule 1 (ICAM-1) and beta2 integrins play critical roles in immune responses. ICAM-1 may also participate in regulation of energy balance because ICAM-1-deficient mice become obese on a high-fat diet. We show that mice deficient in these adhesion receptors are unable to respond to fasting by up-regulation of fatty acid oxidation. Normal mice, when fasted, exhibit reduced circulating neutrophil counts and increased ICAM-1 expression and neutrophil recruitment in liver. Mice lacking ICAM-1 or beta2 integrins fail to show these responses--instead they become hypoglycemic with steatotic livers. Fasting ICAM-1-deficient mice reduce insulin more slowly than wild-type mice. This produces fasting hyperinsulinemia that prevents activation of adenosine mono-phosphate (AMP)-activated protein kinase in muscles and liver, which results in decreased import of long chain fatty acids into mitochondria. Thus, we show a new role for immune cells and their adhesion receptors in regulating metabolic response to fasting.

Fat cells: afferent and efferent messages define new approaches to treat obesity

For a long time neural and endocrine messages were studied for their impact on adipocyte metabolism and control of storage/release of fatty acids. In fact, bidirectional communication exists between adipocytes and other tissues. Several molecules secreted from adipocytes are involved in fat cell signaling to other tissues. Adipocyte products could initiate antagonistic effects on target tissues. Fat cells produce peptides that can elicit insulin resistance, such as tumor necrosis factor-alpha and resistin, as well as hormones that can improve insulin resistance, such as leptin and adiponectin. Secretion of complement proteins, proinflammatory cytokines, procoagulant, and acute phase reactant proteins have also been observed in adipocytes. There is much to learn about how these signals function. It is unlikely that all the adipocyte's endocrine and paracrine signals have been identified. Putative pharmacological strategies aiming at modulation of afferent and efferent fat cell messages are reviewed and discussed.

Metabolism of lipids in human white adipocyte

Adipose tissue is considered as the body's largest storage organ for energy in the form of triacylglycerols, which are mobilized through lipolysis process, to provide fuel to other organs and to deliver substrates to liver for gluconeogenesis (glycerol) and lipoprotein synthesis (free fatty acids). The release of glycerol and free fatty acids from human adipose tissue is mainly dependent on hormone-sensitive lipase which is intensively regulated by hormones and agents, such as insulin (inhibition of lipolysis) and catecholamines (stimulation of lipolysis). A special attention is paid to the recently discovered perilipins which could regulate the activity of the lipase hormono-sensible. Most of the plasma triacylglycerols are provided by dietary lipids, secreted from the intestine in the form of chylomicron or from the liver in the form of VLDL. Released into circulation as non-esterified fatty acids by lipoprotein lipase, those are taken up by adipose tissue via specific plasma fatty acid transporters (CD36, FATP, FABPpm) and used for triacylglycerol synthesis. A small part of triacylglycerols is synthesized into adipocytes from carbohydrates (lipogenesis) but its regulation is still debated in human. Physiological factors such as dieting/fasting regulate all these metabolic pathways, which are also modified in pathological conditions e.g. obesity.

The insulin resistant subphenotype of polycystic ovary syndrome: clinical parameters and pathogenesis

OBJECTIVE

This study was undertaken to compare clinical and biochemical characteristics of the insulin resistant (IR) and non-IR subphenotypes of polycystic ovary syndrome (PCOS).

STUDY DESIGN

Infertile PCOS women were classified as IR (n=32) or non-IR (n=46) on the basis of fasting glucose and insulin levels. The incidence of acanthosis nigricans (AN), hirsutism, and ovulation in response to clomiphene citrate (CC) was compared between the 2 groups, along with serum levels of gonadotropins, and sex steroids. Blood samples from 28 PCOS patients and 8 controls were analyzed by enzymatic immunoassay for autophosphorylated insulin receptor (APIR) and total insulin receptor (TIR) content.

RESULTS

Insulin resistance was associated with obesity (odds ratio [OR]=3.5, P <.05), AN (OR=6.0, P <.05), hirsutism (OR=3.1, P <.05), and resistance to CC (OR=5.0, P <.05). Mean levels of LH, LH/FSH ratios, and testosterone were lower in women with IR (11.5 +/- 6.8 mIU/mL, 2.0 +/- 1.0, and 56.6 +/- 29.0 ng/dL, respectively) compared with women without IR (15.0 +/- 13.4 mIU/mL, 2.4 +/- 1.5, and 72.5 +/- 29.8 ng/dL, respectively) (P <.05). Mean APIR/TIR ratios in IR women were lower than in non-IR women (P <.05 at 100 nmol/L of insulin) and controls (P <.01 at 1, 10 and 100 nmol/L insulin).

CONCLUSION

Patients with IR are more likely to be obese and have AN, hirsutism, resistance to CC, and lower LH, LH/FSH ratios, and testosterone levels. Furthermore, IR patients appear to have defective autophosphorylation of the insulin receptor, a key element in insulin action, and a possible mechanism for IR in PCOS.

Lipase-selective Functional Domains of Perilipin A Differentially Regulate Constitutive and Protein Kinase A-stimulated Lipolysis

Perilipin (Peri) A is a lipid droplet-associated phosphoprotein that acts dually as a suppressor of basal (constitutive) lipolysis and as an enhancer of cyclic AMP-dependent protein kinase (PKA)-stimulated lipolysis by both hormone-sensitive lipase (HSL) and non-HSL(s). To identify domains of Peri A that mediate these multiple actions, we introduced adenoviruses expressing truncated or mutated Peri A and HSL into NIH 3T3 fibroblasts lacking endogenous perilipins and HSL but overexpressing acyl-CoA synthetase 1 and fatty acid transporter 1. We identified two lipase-selective functional domains: 1) Peri A (amino acids 1-300), which inhibits basal lipolysis and promotes PKA-stimulated lipolysis by HSL, and 2) Peri A (amino acids 301-517), which inhibits basal lipolysis by non-HSL and promotes PKA-stimulated lipolysis by both HSL and non-HSL. PKA site mutagenesis revealed that PKA-stimulated lipolysis by HSL requires phosphorylation of one or more sites within Peri 1-300 (Ser81, Ser222, and Ser276). PKA-stimulated lipolysis by non-HSL additionally requires phosphorylation of one or more PKA sites within Peri 301-517 (Ser433, Ser492, and Ser517). Peri 301-517 promoted PKA-stimulated lipolysis by HSL yet did not block HSL-mediated basal lipolysis, indicating that an additional region(s) within Peri 301-517 promotes hormone-stimulated lipolysis by HSL. These results suggest a model of Peri A function in which 1) lipase-specific "barrier" domains block basal lipolysis by HSL and non-HSL, 2) differential PKA site phosphorylation allows PKA-stimulated lipolysis by HSL and non-HSL, respectively, and 3) additional domains within Peri A further facilitate PKA-stimulated lipolysis, again with lipase selectivity.

High-insulinogenic nutrition--an etiologic factor for obesity and the metabolic syndrome?

This report postulates a critical role for the quantity and quality of dietary carbohydrate in the pathogenesis of obesity and the metabolic syndrome. Significant changes in human nutrition have occurred during the last 10,000 years, culminating in the current high-glycemic/high-insulinogenic nutrition. A high insulinogenic nutrition represents a chronic stimulus to the beta cells that may induce an adaptive hypertrophy and a progressive dysregulation of the cells, resulting in postprandial hyperinsulinemia, especially in genetically predisposed subjects. Significant evidence suggests that postprandial hyperinsulinemia promotes weight gain and the development of insulin resistance/metabolic syndrome. The hypothesis is able to explain the current epidemic of obesity and the metabolic syndrome in most industrialised countries, as well as some of the genetics of obesity, including the extreme high incidence of obesity and the metabolic syndrome in certain ethnic groups.

Seasonal variation in plasma catecholamines and adipose tissue lipolysis in adult female green sea turtles (Chelonia mydas)

We investigated three aspects of potential interrenal regulation of reproduction in female green sea turtles, Chelonia mydas. First, seasonal trends in plasma catecholamines were examined from female C. mydas at different stages of their reproductive cycles. Second, variation in catecholamine levels during a nesting season were analysed in relation to restraint time, and ecological variables such as nesting habitat, body size, and reproductive investment. Third, catecholamine and corticosterone (CORT) induced lipolysis was investigated with adipose tissue collected from gravid green turtles, using in vitro incubations. Plasma epinephrine (EPI) was lowest in non-vitellogenic (1.55 +/- 0.26 ng/ml) and post-breeding (1.57 +/- 0.22 ng/ml) females, and highest in courting females (2.87 +/- 0.28). Concentrations of norepinephrine (NE) and EPI were relatively constant throughout a nesting season, and not significantly related to restraint time, reproductive investment or nesting habitat. In vitro concentrations of CORT (>3 ng/ml) and NE (2 ng/ml) induced significant release of glycerol after 6h of incubation. Epinephrine tended to induce an antilipolytic affect at low concentrations (0.25 ng/ml) and a net lipolytic response at higher concentrations (>1 ng/ml). Our data suggest that EPI may play a role in regulating body condition during vitellogenesis, and maintaining energy stores during prolonged aphagia during courtship and nesting in female green sea turtles. Furthermore, we provide preliminary evidence that suggests that catecholamine production may be either down regulated or de-sensitised in gravid female C. mydas.

Expression of human hormone-sensitive lipase in white adipose tissue of transgenic mice increases lipase activity but does not enhance in vitro lipolysis

Hormone-sensitive lipase (HSL) catalyzes the hydrolysis of acylglycerols and cholesteryl esters (CEs). The enzyme is highly expressed in adipose tissues (ATs), where it is thought to play an important role in fat mobilization. The purpose of the present work was to study the effect of a physiological increase of HSL expression in vivo. Transgenic mice were produced with a 21 kb human genomic fragment encompassing the exons encoding the adipocyte form of HSL. hHSL mRNA was expressed at 3-fold higher levels than murine HSL mRNA in white adipocytes. Transgene expression was also observed in brown adipose tissue (BAT) and skeletal muscle. The human protein was detected in ATs of transgenic (Tg) mice. The hydrolytic activities against triacylglycerol (TG), diacylglycerol (DG) analog, and CE were increased in transgenic mouse AT. However, cAMP-inducible adipocyte lipolysis was lower in transgenic animals. In the B6CBA genetic background, transgenic mice up to 14 weeks of age showed lower body weight and fat mass. The phenotype was not observed in older animals and in mice fed a high-fat diet (HFD). In the OF1 genetic background, there was no difference in fat mass of mice fed ad libitum. However, transgenic mice became leaner than their wild-type (WT) littermates after a 4 day calorie restriction. The data show that overexpression of HSL, despite increased lipase activity, does not lead to enhanced lipolysis.

Growth hormone deficiency and vascular risk

The importance of growth hormone deficiency (GHD) in adult life has become more apparent over the last decade. As well as a distinct clinical syndrome there is a significant excess risk of cardiovascular disease. Although it is difficult to ascertain what part is played by the original pituitary disorder and the concomitant replacement hormonal therapies, there is clear evidence that GHD is associated with known cardiovascular risk factors such as body shape, lipid profile, insulin resistance, blood pressure, vessel wall morphology and haemostatic factors. Novel means of assessing vascular risk such as pulse wave velocity and flow-mediated dilatation can also estimate the risk without invasive procedures. The role of possible mediators of endothelial function such as nitric oxide and free radicals is being investigated further. Replacement of GH in GH-deficient patients leads to many effects on the above indices, some but not all of which are associated with reduced vascular risk. Long-term follow-up studies of morbidity and mortality are required for an accurate assessment of the beneficial effects of therapy.

Endocrine regulation of subcutaneous fat metabolism during cold exposure in humans

Increased oxidation of carbohydrates and free fatty acids is a well-known phenomenon during cold stress. Nevertheless, sources of the fuels used have not been fully clarified as yet. Thus, the aim of our study was to evaluate the effect of acute cold exposure on lipid and carbohydrate metabolism in human subcutaneous adipose tissue and to identify the possible regulatory mechanisms involved. Ten volunteers were exposed for 30 min to an ambient temperature of 4 degrees C. Interstitial metabolism was assessed with the aid of the microdialysis technique. Lipolysis intensity was evaluated from changes of glycerol concentration in plasma and in dialysate. Cold exposure induced a significant increase of glycerol concentration both in plasma (by 199 +/- 16%, p < 0.01) and in dialysate (by 308 +/- 58%, p < 0.001). No changes in glucose concentration were found whether in plasma or in the dialysate. Ethanol concentration in dialysate increased (148 +/- 15%, p < 0.01), indicating a slower blood flow in the subcutaneous region. Plasma concentrations of various gluco- and/or lipid-regulatory hormones remained unaffected by the cold exposure, except for norepinephrine, which rose about threefold (309 +/- 41%, p < 0.001). The data indicate an important role for subcutaneous adipose tissue in mobilization of free fatty acids during cold exposure. This process seems to be regulated by the sympathetic nervous system, whereas hormones involved in the regulation of lipid metabolism, such as epinephrine, insulin, cortisol, and growth hormone, may play a less significant role-at least under the conditions studied.

Assessment of skeletal muscle triglyceride content by (1)H nuclear magnetic resonance spectroscopy in lean and obese adolescents: relationships to insulin sensitivity, total body fat, and central adiposity

The metabolism and composition of skeletal muscle tissue is of special interest because it is a primary site of insulin action and plays a key role in the pathogenesis of insulin resistance. Intramyocellular (IMCL) triglyceride stores are an accessible form of energy that may decrease skeletal muscle glucose utilization, thereby contributing to impaired glucose metabolism. Because of the invasive nature of muscle biopsies, there is limited, if any, information about intramuscular lipid stores in children. The development of (1)H nuclear magnetic resonance (NMR) spectroscopy provides a unique noninvasive alternative method that differentiates intracellular fat from intercellular fat in muscle tissue. The present study was performed to determine whether IMCL and extramyocellular (EMCL) lipid contents are increased early in the development of juvenile obesity and to explore the relationships between IMCL and EMCL to in vivo insulin sensitivity, independently of total body fat and central adiposity in obese and nonobese adolescents. Eight nonobese (BMI 21 kg/m(2), age 11-16 years) and 14 obese (BMI 35 +/- 1.5 kg/m(2), age 11-15 years) adolescents underwent 1) (1)H-NMR spectroscopy to noninvasively quantify IMCL and EMCL triglyceride content of the soleus muscle, 2) a 2-h euglycemic-hyperinsulinemic clamp (40 mU.m(-2).min(-1)) to assess insulin sensitivity, 3) a dual-energy X-ray absorptiometry scan to measure total percent body fat, and 4) magnetic resonance imaging to measure abdominal fat distribution. Both the IMCL and EMCL content of the soleus muscle were significantly greater in the obese adolescents than in the lean control subjects. A strong inverse correlation was found between IMCL and insulin sensitivity, which persisted and became even stronger after controlling for percent total body fat and abdominal subcutaneous fat mass (partial correlation r = -0.73, P < 0.01) but not when adjusting for visceral fat (r = - 0.54, P < 0.08). In obese adolescents, increase in total body fat and central adiposity were accompanied by higher IMCL and EMCL lipid stores. The striking relationships between both IMCL and EMCL with insulin sensitivity in childhood suggest that these findings are not a consequence of aging but occur early in the natural course of obesity.

Modulation of hormone-sensitive lipase and protein kinase A-mediated lipolysis by perilipin A in an adenoviral reconstituted system

Perilipin (Peri) A is a phosphoprotein located at the surface of intracellular lipid droplets in adipocytes. Activation of cyclic AMP-dependent protein kinase (PKA) results in the phosphorylation of Peri A and hormone-sensitive lipase (HSL), the predominant lipase in adipocytes, with concurrent stimulation of adipocyte lipolysis. To investigate the relative contributions of Peri A and HSL in basal and PKA-mediated lipolysis, we utilized NIH 3T3 fibroblasts lacking Peri A and HSL but stably overexpressing acyl-CoA synthetase 1 (ACS1) and fatty acid transport protein 1 (FATP1). When incubated with exogenous fatty acids, ACS1/FATP1 cells accumulated 5 times more triacylglycerol (TG) as compared with NIH 3T3 fibroblasts. Adenoviral-mediated expression of Peri A in ACS1/FATP1 cells enhanced TG accumulation and inhibited lipolysis, whereas expression of HSL fused to green fluorescent protein (GFPHSL) reduced TG accumulation and enhanced lipolysis. Forskolin treatment induced Peri A hyperphosphorylation and abrogated the inhibitory effect of Peri A on lipolysis. Expression of a mutated Peri A Delta 3 (Ser to Ala substitutions at PKA consensus sites Ser-81, Ser-222, and Ser-276) reduced Peri A hyperphosphorylation and blocked constitutive and forskolin-stimulated lipolysis. Thus, perilipin expression and phosphorylation state are critical regulators of lipid storage and hydrolysis in ACS1/FATP1 cells.

Impact of polymorphisms of human beta-adrenergic receptor gene on changes in height during growth hormone treatment

The aim of this study was to investigate the occurrence of polymorphisms of the beta-adrenergic receptor gene in short children and to evaluate the possible influence of the polymorphisms on changes in height and obesity index in response to GH treatment. Of the 75 children enrolled in the study, 40 completed at least 5 years of GH treatment. The genotype distribution of the beta2 and 3-adrenergic receptor polymorphisms in the study population did not differ significantly from those reported in non-obese subjects. There were no significant differences in the SD score for height at any given time-point between the group with and without the Trp64Arg mutation of the beta3-adrenergic receptor gene. In relation to the Glyl6Arg polymorphism of the beta2-adrenergic receptor gene, the mean SD score for height increased significantly during GH treatment in children with Argl6Arg and Glyl6Arg. In those with Glyl6Gly, the score did not show any significant increase during all 5 years of GH treatment. In both the groups with and without the Trp64Arg mutation, the changes in obesity index did not reach statistical significance at any time-point. Only children with Glyl6Gly had a significantly higher baseline mean obesity index than those with Glyl6Arg. The index also decreased markedly from 21.9% to 5.8% in these children during the first 4 years of GH treatment. Thus, when the impact of the polymorphisms of these two receptor genes was studied simultaneously, it appeared that only the beta2-adrenergic receptor polymorphism had an important role to play in modulating the regulation of growth rate and energy expenditure in short children.

Hormone sensitive lipase expression and adipose tissue metabolism show gender difference in obese subjects after weight loss

OBJECTIVE

The effect of weight reduction on hormone sensitive lipase (HSL) and lipoprotein lipase (LPL) gene expression and their relationship with adipose tissue metabolism were studied in massively obese men and women.

SUBJECTS

Seventeen obese subjects (eight men, nine women) participated in the study (age 44+/-2 y, weight 145+/-8 kg, fat 40+/-2% of body mass, mean+/-s.e.m.), who were going through a gastric-banding operation for weight reduction.

MEASUREMENTS

HSL and LPL mRNA expressions were analyzed using the reverse transcription competitive polymerase chain reaction. Subcutaneous fat lipolysis was measured in vivo by microdialysis and in vitro in isolated subcutaneous abdominal adipocytes. Measurements were done before and after 1 y of weight reduction.

RESULTS

Significant reductions in weight (for men -20.3+/-2.5%, for women -18.3+/-2.1% (mean+/-s.e.m.) and fat mass (for men -27.6+/-7.9%, for women -21.8+/-3.9%) were observed in both genders. In women HSL mRNA expression decreased by 31% (P=0.008) and LPL expression increased slightly, but nonsignificantly (42%, P=0.110). These changes were not observed in men. In men, inhibition of lipolysis with alpha(2)-adrenergic and adenosine agonist was improved (P=0.001) in isolated adipocytes.

CONCLUSIONS

This study uncovers new differences between genders in adipocyte metabolism along with weight reduction. In women, the observed changes in HSL and LPL gene expression suggest that deposition of lipids into adipose tissue might be favored after weight reduction. In men, the results indicate improved responsiveness to inhibition in adipose tissue metabolism along with weight reduction.

Increase in plasma pollutant levels in response to weight loss in humans is related to in vitro subcutaneous adipocyte basal lipolysis

OBJECTIVE

To examine whether weight loss-induced changes in in vitro basal lipolysis of subcutaneous abdominal and femoral fat cells were related to those in plasma organochlorine levels.

DESIGN

A 15 week weight loss program induced by a moderate caloric restriction.

SUBJECTS

Seventeen men and 20 women (age 36-50 y, body fat 25-50%).

MEASUREMENTS

In vitro basal lipolysis of subcutaneous abdominal and femoral adipocytes and plasma levels of five polychlorinated biphenyl congeners (Aroclor 1260, PCBs 118, 138, 153 and 180) and three chlorinated pesticides (dichlorodiphenyl dichloroethene (p,p'-DDE), beta-hexachlorocyclohexane (beta-HCH) and hexachlorobenzene (HCB)) were measured before and after the weight reducing program.

RESULTS

Both genders showed a similar reduction in body weight (approximately 11 kg) in response to treatment, although men lost significantly more fat mass than women (mean+/-s.d., 9.4+/-4.1 vs 5.9+/-5 kg, respectively, P<0.05). Mean basal fat cell lipolysis did not vary before and after weight reduction, regardless of depots and genders. In response to weight loss, significant increases of all organochlorines investigated were observed in men, whereas only p,p'-DDE, Aroclor 1260, PCBs 153 and 180 significantly rose in women. In men, higher the increase in basal lipolysis of subcutaneous abdominal or femoral adipocytes, greater the rise in plasma levels of most pollutants (HCB, Aroclor 1260, PCBs 118, 138 and 153) was in response to weight loss (0.51<r<0.70, P<0.05). Similar positive correlations were also observed in women but only a few reached statistical significance (p,p'-DDE, PCBs 118 and 180).

CONCLUSION

The weight loss-induced increase in plasma pollutant levels is related to the rise in subcutaneous abdominal and femoral adipocyte basal lipolysis, especially in men.

Effects of acipimox on the lipolysis rate in subcutaneous adipose tissue of obese subjects

BACKGROUND

Acipimox is a hypolipidaemic agent reducing serum concentrations of triglycerides and non-esterified fatty acids. Acipimox may reduce triglyceride synthesis by decreasing non-esterified fatty acid availability from adipocytes, but this effect has yet to be demonstrated in vivo. Lipolysis after acipimox treatment was examined in subcutaneous adipose tissue of severely obese subjects with associated metabolic disorders.

METHODS

The microdialysis technique was performed in abdominal subcutaneous adipose tissue of eight hyperinsulinaemic subjects. After oral treatment with acipimox, glycerol concentration was determined as an index of lipolysis rate. Blood flow was assessed by the ethanol escape technique. The rates of release of glycerol from human adipose tissue maximally stimulated by norepinephrine were also investigated in the presence of acipimox. Eight weight- and age-matched subjects served as a control group.

RESULTS

Under acipimox treatment, basal glycerol release decreased in subcutaneous adipose tissue, whereas no effect was observed on blood flow. In stimulated adipose tissue acipimox showed no effect.

CONCLUSION

In the present study basal glycerol outflow from adipose tissue was inhibited by acipimox. The anti-lipolytic action of the agent may diminish elevated plasma concentrations of free fatty acids in subjects with severe obesity.

Exercise in weight management of obesity

Obesity is a chronic metabolic disorder associated with CVD and increased morbidity and mortality. When the BMI is > or = 30 kg/m2, mortality rates from all causes, and especially CVD, are increased by 50% to 100%. There is strong evidence that weight loss in overweight and obese individuals improves risk factors for diabetes and CVD. Additional evidence indicates that weight loss and the associated diuresis reduce blood pressure in both overweight hypertensive and nonhypertensive individuals, reduce serum TG levels, increase high-density lipoprotein cholesterol levels, and may produce some reduction in low-density lipoprotein cholesterol concentrations. Of interest, even if weight loss is minimal, obese individuals showing a good level of cardiorespiratory fitness are at reduced risk for cardiovascular mortality than lean but poorly fit subjects. Insulin and catecholamines have pronounced metabolic effects on human adipose tissue metabolism. Insulin stimulates LPL and inhibits HSL; the opposite is true for catecholamines. There is regional variation in adipocyte TG turnover favoring lipid mobilization in the visceral fat depots and lipid storage in the peripheral subcutaneous sites. The hormonal regulation of adipocyte TG turnover is altered in obesity and is most marked in central obesity. There is resistance to insulin stimulation of LPL; however, LPL activity in fasted obese subjects is increased and remains so following weight reduction. Catecholamine-induced lipolysis is enhanced in visceral fat but decreased in subcutaneous fat. Numerous adaptive responses take place with physical training. These adaptations result in a more efficient system for oxygen transfer to muscle, which is now able to better utilize the unlimited lipid stores instead of the limited carbohydrate reserves available. In addition, the reduced adipose tissue mass represents an important mechanical advantage, allowing better long-term work. Gender differences have been reported in the adaptation of adipose tissue metabolism to aerobic exercise training. Physical training helps counteract the permissive and affluent environment that predisposes reduced-obese subjects to regain weight. An exercise program using weight resistance modalities may also be included safely, and it improved program retention in a multidisciplinary weight management program that was designed for obese children. Thirty to 45 minutes of physical activity of moderate intensity, performed 3 to 5 days a week, should be encouraged. All adults should set a long-term goal to accumulate at least 30 minutes or more of moderate-intensity physical activity on most, and preferably all days. Public health interventions promoting walking are likely to be the most successful. Indeed, walking is unique because of its safety, accessibility, and popularity. It is noteworthy that there is a clear dissociation between the adaptation of cardiorespiratory fitness and the improvements in the metabolic risk profile that can be induced by endurance training programs. It appears that as long as the increase in energy expenditure is sufficient, low-intensity endurance exercise is likely to generate beneficial metabolic effects that would be essentially similar to those produced by high-intensity exercise. The clinician should therefore focus on the improvement of the metabolic profile rather than on weight loss alone. Realistic goals should be set between the clinician and the patient, with a weight loss of approximately of 0.5 to 1 pound per week. It should be kept in mind that since it generally takes years to become overweight or obese, a weight loss pattern of 0.5 or 1 pound per week will require time and perseverance to reach the proposed target. However, the use of physical activity as a method to lose weight seems inversely related to patients' age and BMI and directly related to the level of education. Thus, public health interventions helping these groups to become physically active remain a challenge and further emphasize the importance of the one-on-one interaction between the clinician/health care professional with the obese individual "at risk" of CVD. This notion is critical, as it has been shown that less than half of obese adults have reported being advised to lose weight under the guidance of health care professionals.

Amelioration of insulin resistance but not hyperinsulinemia in obese mice overexpressing GLUT4 selectively in skeletal muscle

The effects of gold-thioglucose (GTG) treatment were examined in mice overexpressing GLUT4 selectively in skeletal muscle (MLC-GLUT4 mice) and in age-matched controls. Groups of MLC-GLUT4 and control mice were injected with GTG or saline at 5 weeks of age. At 12 weeks following the injections, GTG-treated control mice exhibited a 35% increase in body weight versus saline-treated controls. Similarly, a 30% increase in body weight was observed in GTG-treated MLC-GLUT4 mice compared with saline-treated MLC-GLUT4 mice 12 weeks after the injections. In saline-treated lean MLC-GLUT4 and control mice, intraperitoneal injection of insulin decreased blood glucose in 1 hour by 63% and 38%, respectively. Insulin also decreased blood glucose by 40% in GTG-treated obese MLC-GLUT4 mice after 1 hour. However, insulin did not reduce blood glucose levels in GTG-treated obese control mice. The ability of insulin to clear blood glucose in GTG-treated obese MLC-GLUT4 mice is associated with increased skeletal muscle GLUT4 content and white adipose tissue (WAT) GLUT4 content as compared with GTG-treated obese controls. However, fasting blood glucose levels in GTG-treated obese MLC-GLUT4 and control mice were elevated by approximately 30% compared with saline-treated groups. Lastly, although GTG-treated obese MLC-GLUT4 mice exhibited improved glucose clearance in response to insulin, they nevertheless remained as hyperinsulinemic as GTG-treated obese control mice. These results suggest that genetic overexpression of GLUT4 in skeletal muscle may ameliorate the development of insulin resistance associated with obesity but cannot restore normal glucose and insulin levels.

Impact of polymorphisms of the human beta2-adrenoceptor gene on obesity in a French population

OBJECTIVE

To investigate the impact of two common polymorphisms in the human beta2-adrenoceptor gene (Gly16Arg and Gln27Glu substitutions) on obesity and anthropometric measurements as well as blood variables in a large sample of a French population.

DESIGN AND SUBJECTS

Within the framework of the WHO-MONICA project, a population study composed of 1195 subjects aged 35-64 y was randomly sampled from the electoral rolls of the Urban Community of Lille, in northern France. Subjects without any medical treatment (for hypercholesterolaemia, hypertension or diabetes mellitus) susceptible to interfere with body weight and biological variables were selected (n = 836, 419 men/417 women, age = 49.5+/-8.1 y, body mass index (BMI) = 25.7+/-4.4 kg/m2). Subjects with a body mass index > or = 30 kg/m2 were considered as obese (n = 119, age = 49.5+/-8.2 y, BMI = 33.9+/-3.3 kg/m2 range 30-44).

MEASUREMENTS

Genotyping was carried out with allele-specific oligonucleotides hybridization. Association between genotypes and various obesity markers (body weight, body mass index, waist and waist-to-hip ratio), lipid, glucose and insulin variables were studied.

RESULTS

The Gly16Arg and Gln27Glu polymorphisms were in complete linkage disequilibrium. Gln27Gln subjects had an increased risk of obesity (odds ratio (OR) = 1.77, 95% CI 1.19-2.62, P = 0.005). This effect was mainly detected in men (OR = 2.40, 95% CI 1.34-4.27, P = 0.003). Men bearing the Gln27Gln genotype had higher body weight, BMI, waist and hip circumferences and waist-to-hip ratio than others. Moreover, if Gln27Gln men carried in addition the Arg16 allele, the increase in body weight, BMI and waist-to-hip ratio was more important.

CONCLUSION

Our results suggest that genetic variability of the beta2-adrenoceptor gene is implicated in body weight regulation and in the onset of obesity in French men.

Metformin inhibits catecholamine-stimulated lipolysis in obese, hyperinsulinemic, hypertensive subjects in subcutaneous adipose tissue: an in situ microdialysis study

AIMS

Metformin has been reported to decrease the plasma concentrations of non-esterified fatty acids in Type 2 diabetic subjects. This study investigated the effects of metformin on basal and catecholamine-stimulated lipolysis in abdominal subcutaneous adipose tissue of obese, hyperinsulinaemic, hypertensive subjects.

METHODS

Fourteen subjects with severe obesity (12 female, twomale, age 35.4 +/- 4 years, body mass index 48.2 +/- 2 kg/m2, body fat mass 63.3 +/- 5 kg) were recruited. Glycerol and lactate concentrations were determined in the presence of metformin and after administration of catecholamines using microdialysis. Simultaneously, blood flow was assessed with the ethanol escape method.

RESULTS

Glycerol release was lowered by metformin during the 3-h experiment (P<0.01). The lipolytic activity of catecholamines was suppressed when adipose tissue was pre-treated with metformin (P<0.001). Lactate concentration increased after application of metformin (P<0.01) and catecholamines (P<0.001). Blood flow was decreased in the presence of adrenaline (P < 0.01), but this effect was abolished by metformin.

CONCLUSIONS

The present data demonstrate the effects of metformin on lipolysis in subcutaneous adipose tissue in vivo. In the large body fat mass of obese subjects, a reduction of lipolysis in adipose tissue may contribute to a decrease of VLDL synthesis in the liver resulting in a lowered plasma triglyceride concentration.

Regulation of body weight in humans

The mechanisms involved in body weight regulation in humans include genetic, physiological, and behavioral factors. Stability of body weight and body composition requires that energy intake matches energy expenditure and that nutrient balance is achieved. Human obesity is usually associated with high rates of energy expenditure. In adult individuals, protein and carbohydrate stores vary relatively little, whereas adipose tissue mass may change markedly. A feedback regulatory loop with three distinct steps has been recently identified in rodents: 1) a sensor that monitors the size of adipose tissue mass is represented by the amount of leptin synthesized by adipose cells (a protein encoded by the ob gene) which determines the plasma leptin levels; 2) hypothalamic centers, with specific leptin receptors, which receive and integrate the intensity of the signal; and 3) effector systems that influence the two determinants of energy balance, i.e., energy intake and energy expenditure. With the exception of a few very rare cases, the majority of obese human subjects have high plasma leptin levels that are related to the size of their adipose tissue mass. However, the expected regulatory responses (reduction in food intake and increase in energy expenditure) are not observed in obese individuals. Thus obese humans are resistant to the effect of endogenous leptin, despite unaltered hypothalamic leptin receptors. Whether defects in the leptin signaling cascade play a role in the development of human obesity is a field of great actual interest that needs further research. Present evidences suggest that genetic and environmental factors influence eating behavior of people prone to obesity and that diets that are high in fat or energy dense undermine body weight regulation by promoting an overconsumption of energy relative to need.

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

Visceral adipose tissue (VAT) accumulation is an important correlate of the metabolic complications found in obese patients. The aim of this study was to evaluate the respective contribution of VAT deposition versus subcutaneous abdominal or femoral fat cell hypertrophy as correlates of the metabolic risk profile in 69 men and 65 premenopausal women (aged 35+/-5 years) with a wide range of fatness (body mass index, 18 to 57 kg/m2). In both genders, VAT accumulation was positively correlated with fasting plasma insulin, triglyceride (TG), and low-density lipoprotein (LDL)-apolipoprotein B (apo B) levels and the cholesterol (CHOL)/high-density lipoprotein (HDL)-CHOL ratio (.24 < or = r < or = .71, P < .05). A similar pattern of positive relationships was found between subcutaneous abdominal fat cell weight and metabolic risk variables in men and women (.33 < or = r < or = .60, P < .01). Positive associations were also observed in women between femoral fat cell weight and fasting plasma insulin, TG, and CHOL levels and the CHOL/HDL-CHOL ratio (.29 < or = r < or = .42, P < .05). However, only plasma TG concentrations and the CHOL/HDL-CHOL ratio were positively correlated with femoral fat cell weight in men (r = .30, P < .05). To better investigate the relationships between the metabolic risk profile and hypertrophic subcutaneous obesity, individuals with small versus large subcutaneous abdominal adipocytes were matched according to VAT accumulation. Men with large abdominal fat cells displayed higher plasma TG and LDL-apo B levels compared with men characterized by small abdominal adipocytes (P < .05). Stepwise multiple regression analyses showed that subcutaneous abdominal fat cell weight was the best independent variable predicting plasma TG and LDL-apo B levels in men. No significant difference was found in the metabolic profile of subjects displaying small versus large femoral adipocytes. Taken together, these results suggest that for a given VAT deposition, the presence of hypertrophied subcutaneous abdominal adipocytes in men appears to be associated with further deterioration in the metabolic risk profile. On the other hand, the hypertrophy of femoral adipocytes does not further alter the metabolic complications generally related to obesity in both men and women.