Regional lipolytic responses to isoproterenol in women

Impact of human visceral and glutealfemoral adipose tissue transplant on glycemic control in a mouse model of diet-induced obesity

Regional distribution of adipose tissue is an important factor in conferring cardiometabolic risk and obesity-related morbidity. We tested the hypothesis that human visceral adipose tissue (VAT) impairs glucose homeostasis, whereas subcutaneous glutealfemoral adipose tissue (GFAT) protects against the development of impaired glucose homeostasis in mice. VAT and GFAT were collected from patients undergoing bariatric surgery and grafted onto the epididymal adipose tissue of weight- and age-matched severe, combined immunodeficient mice. SHAM mice underwent surgery without transplant of tissue. Mice were fed a high-fat diet after xenograft. Energy homeostasis, glucose metabolism, and insulin sensitivity were assessed 6 wk later. Xenograft of human adipose tissues was successful, as determined by histology, immunohistochemical evaluation of collagen deposition and angiogenesis, and maintenance of lipolytic function. Adipose tissue transplant did not affect energy expenditure, food intake, whole body substrate partitioning, or plasma free fatty acid, triglyceride, and insulin levels. Fasting blood glucose was significantly reduced in GFAT and VAT compared with SHAM, whereas glucose tolerance was improved only in mice transplanted with VAT compared with SHAM mice. This improvement was not associated with differences in whole body insulin sensitivity or plasma insulin between groups. Together, these data suggest that VAT improves glycemic control and GFAT does not protect against the development of high-fat diet-induced glucose intolerance. Hence, the intrinsic properties of VAT and GFAT do not necessarily explain the postulated negative and positive effects of these adipose tissue depots on metabolic health.

Sex Differences in Adipose Tissue Function

Regional adipose tissue distribution differs between men and women. Differences in the accumulation of adipose tissue as well as the regulation of secretion of a number of products from adipose tissue are under the control of sex steroids, which act through a wide variety of mechanisms, both direct and indirect, to tailor metabolism to the unique needs of each sex. A fuller understanding of sex-based differences in adipose tissue function may help with tailored strategies for disease prevention and treatment and provide insights into fundamental differences in the processes that regulate nutrient homeostasis and body weight.

In-vivo metabolic studies of regional adipose tissue

The accumulation of abdominal adipose tissue has long been associated with adverse cardiovascular outcomes. Paradoxically, increased gluteofemoral adipose tissue, which is predominantly subcutaneous fat, seems to play a protective role. There has been significant scientific interest in understanding how abdominal and gluteofemoral depots confer opposing metabolic risks. However, the study of regional adipose physiology in vivo remains challenging. We discuss some of the methodologies used. We focus specifically on the arteriovenous difference technique and present some insights into gluteofemoral adipose physiology.

The neuropeptide TLQP-21 opposes obesity via C3aR1-mediated enhancement of adrenergic-induced lipolysis

OBJECTIVES

Obesity is characterized by excessive fat mass and is associated with serious diseases such as type 2 diabetes. Targeting excess fat mass by sustained lipolysis has been a major challenge for anti-obesity therapies due to unwanted side effects. TLQP-21, a neuropeptide encoded by the pro-peptide VGF (non-acronymic), that binds the complement 3a receptor 1 (C3aR1) on the adipocyte membrane, is emerging as a novel modulator of adipocyte functions and a potential target for obesity-associated diseases. The molecular mechanism is still largely uncharacterized.

METHODS

We used a combination of pharmacological and genetic gain and loss of function approaches. 3T3-L1 and mature murine adipocytes were used for in vitro experiments. Chronic in vivo experiments were conducted on diet-induced obese wild type, β1, β2, β3-adrenergic receptor (AR) deficient and C3aR1 knockout mice. Acute in vivo lipolysis experiments were conducted on Sprague Dawley rats.

RESULTS

We demonstrated that TLQP-21 does not possess lipolytic properties per se. Rather, it enhances β-AR activation-induced lipolysis by a mechanism requiring Ca2+ mobilization and ERK activation of Hormone Sensitive Lipase (HSL). TLQP-21 acutely potentiated isoproterenol-induced lipolysis in vivo. Finally, chronic peripheral TLQP-21 treatment decreases body weight and fat mass in diet induced obese mice by a mechanism involving β-adrenergic and C3a receptor activation without associated adverse metabolic effects.

CONCLUSIONS

In conclusion, our data identify an alternative pathway modulating lipolysis that could be targeted to diminish fat mass in obesity without the side effects typically observed when using potent pro-lipolytic molecules.

Sex hormones and macronutrient metabolism

The biological differences between males and females are determined by a different set of genes and by a different reactivity to environmental stimuli, including the diet, in general. These differences are further emphasized and driven by the exposure to a different hormone flux throughout the life.

These differences have not been taken into appropriate consideration by the scientific community. Nutritional sciences are not immune from this “bias” and when nutritional needs are concerned, females are considered only when pregnant, lactating or when their hormonal profile is returning back to “normal,” i.e., to the male-like profile.

The authors highlight some of the most evident differences in aspects of biology that are associated with nutrition.

This review presents and describes available data addressing differences and similarities of the “reference man” vs. the “reference woman” in term of metabolic activity and nutritional needs. According to this assumption, available evidences of sex-associated differences of specific biochemical pathways involved in substrate metabolism are reported and discussed. The modulation by sexual hormones affecting glucose, amino acid and protein metabolism and the metabolization of nutritional fats and the distribution of fat depots, is considered targeting a tentative starting up background for a gender concerned nutritional science.

The Sexual Dimorphism of Lipid Kinetics in Humans

In addition to the obvious differences in body shape, there are substantial differences in lipid metabolism between men and women. These differences include how dietary fatty acids are handled, the secretion and clearance of very low-density lipoprotein-triglycerides, the release rates of free fatty acids (FFA) from adipose tissue relative to energy needs, and the removal of FFA from the circulation, including the storage of FFA into adipose tissue via the direct uptake process. We will review what is known about these processes and how they may contribute to the sexual dimorphism of body fat distribution.

Biology of upper-body and lower-body adipose tissue--link to whole-body phenotypes

The distribution of adipose tissue in the body has wide-ranging and reproducible associations with health and disease. Accumulation of adipose tissue in the upper body (abdominal obesity) is associated with the development of cardiovascular disease, insulin resistance, type 2 diabetes mellitus and even all-cause mortality. Conversely, accumulation of fat in the lower body (gluteofemoral obesity) shows opposite associations with cardiovascular disease and type 2 diabetes mellitus when adjusted for overall fat mass. The abdominal depots are characterized by rapid uptake of predominantly diet-derived fat and a high lipid turnover that is easily stimulated by adrenergic receptor activation. The lower-body fat stores have a reduced lipid turnover with a capacity to accommodate fat undergoing redistribution. Lower-body adipose tissue also seems to retain the capacity to recruit additional adipocytes as a result of weight gain and demonstrates fewer signs of inflammatory insult. New data suggest that the profound functional differences between the upper-body and lower-body tissues are controlled by site-specific sets of developmental genes, such as HOXA6, HOXA5, HOXA3, IRX2 and TBX5 in subcutaneous abdominal adipose tissue and HOTAIR, SHOX2 and HOXC11 in gluteofemoral adipose tissue, which are under epigenetic control. This Review discusses the developmental and functional differences between upper-body and lower-body fat depots and provides mechanistic insight into the disease-protective effects of lower-body fat.

Sex dimorphism and depot differences in adipose tissue function

Obesity, characterized by excessive adiposity, is a risk factor for many metabolic pathologies, such as type 2 diabetes mellitus (T2DM). Numerous studies have shown that adipose tissue distribution may be a greater predictor of metabolic health. Upper-body fat (visceral and subcutaneous abdominal) is commonly associated with the unfavorable complications of obesity, while lower-body fat (gluteal-femoral) may be protective. Current research investigations are focused on analyzing the metabolic properties of adipose tissue, in order to better understand the mechanisms that regulate fat distribution in both men and women. This review will highlight the adipose tissue depot- and sex-dependent differences in white adipose tissue function, including adipogenesis, adipose tissue developmental patterning, the storage and release of fatty acids, and secretory function. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.

Marked resistance of femoral adipose tissue blood flow and lipolysis to adrenaline in vivo

AIMS/HYPOTHESIS

Fatty acid entrapment in femoral adipose tissue has been proposed to prevent ectopic fat deposition and visceral fat accumulation, resulting in protection from insulin resistance. Our objective was to test the hypothesis of femoral, compared with abdominal, adipose tissue resistance to adrenergic stimulation in vivo as a possible mechanism.

METHODS

Regional fatty acid trafficking, along with the measurement of adipose tissue blood flow (ATBF) with (133)Xe washout, was studied with the arteriovenous difference technique and stable isotope tracers in healthy volunteers. Adrenergic agonists (isoprenaline, adrenaline [epinephrine]) were infused either locally by microinfusion or systemically. Local microinfusion of adrenoceptor antagonists (propranolol, phentolamine) was used to characterise specific adrenoceptor subtype effects in vivo.

RESULTS

Femoral adipose tissue NEFA release and ATBF were lower during adrenaline stimulation than in abdominal tissue (p < 0.001). Mechanistically, femoral adipose tissue displayed a dominant α-adrenergic response during adrenaline stimulation. The α-adrenoceptor blocker, phentolamine, resulted in the 'disinhibition' of the femoral ATBF response to adrenaline (p < 0.001).

CONCLUSIONS/INTERPRETATION

Fatty acids, once stored in femoral adipose tissue, are not readily released upon adrenergic stimulation. Femoral adipose tissue resistance to adrenaline may contribute to the prevention of ectopic fatty acid deposition.

Effects of weight gain and weight loss on regional fat distribution

BACKGROUND

Normal-weight adults gain lower-body fat via adipocyte hyperplasia and upper-body subcutaneous (UBSQ) fat via adipocyte hypertrophy.

OBJECTIVES

We investigated whether regional fat loss mirrors fat gain and whether the loss of lower-body fat is attributed to decreased adipocyte number or size.

DESIGN

We assessed UBSQ, lower-body, and visceral fat gains and losses in response to overfeeding and underfeeding in 23 normal-weight adults (15 men) by using dual-energy X-ray absorptiometry and abdominal computed tomography scans. Participants gained ∼5% of weight in 8 wk and lost ∼80% of gained fat in 8 wk. We measured abdominal subcutaneous and femoral adipocyte sizes and numbers after weight gain and loss.

RESULTS

Volunteers gained 3.1 ± 2.1 (mean ± SD) kg body fat with overfeeding and lost 2.4 ± 1.7 kg body fat with underfeeding. Although UBSQ and visceral fat gains were completely reversed after 8 wk of underfeeding, lower-body fat had not yet returned to baseline values. Abdominal and femoral adipocyte sizes, but not numbers, decreased with weight loss. Decreases in abdominal adipocyte size and UBSQ fat mass were correlated (ρ = 0.76, P = 0.001), as were decreases in femoral adipocyte size and lower-body fat (ρ = 0.49, P = 0.05).

CONCLUSIONS

UBSQ and visceral fat increase and decrease proportionately with a short-term weight gain and loss, whereas a gain of lower-body fat does not relate to the loss of lower-body fat. The loss of lower-body fat is attributed to a reduced fat cell size, but not number, which may result in long-term increases in fat cell numbers.

Catecholamine and insulin control of lipolysis in subcutaneous adipose tissue during long-term diet-induced weight loss in obese women

The aim of this study was to investigate the evolution of the adrenergic and insulin-mediated regulation of lipolysis during different phases of a 6-mo dietary intervention. Eight obese women underwent a 6-mo dietary intervention consisting of a 1-mo very low-calorie diet (VLCD) followed by a 2-mo low-calorie diet (LCD) and 3-mo weight maintenance (WM) diet. At each phase of the dietary intervention, microdialysis of subcutaneous adipose tissue (SCAT) was performed at rest and during a 3-h hyperinsulinemic euglycemic clamp. Responses of dialysate glycerol concentration (DGC) were determined at baseline and during local perfusions with adrenaline or adrenaline and phentolamine before and during the last 30 min of the clamp. Dietary intervention induced a body weight reduction and an improved insulin sensitivity. DGC progressively decreased during the clamp, and this decrease was similar during the different phases of the diet. The adrenaline-induced increase in DGC was higher at VLCD and LCD compared with baseline condition and returned to prediet levels at WM. In the probe with adrenaline and phentolamine, the increase in DGC was higher than that in the adrenaline probe at baseline and WM, but it was not different at VLCD and LCD. The results suggest that the responsiveness of SCAT to adrenaline-stimulated lipolysis increases during the calorie-restricted phases due to a reduction of the α(2)-adrenoceptor-mediated antilipolytic action of adrenaline. At WM, adrenaline-stimulated lipolysis returned to the prediet levels. Furthermore, no direct relationship between insulin sensitivity and the diet-induced changes in the regulation of lipolysis was found.

Splanchnic lipolysis in human obesity

Elevated FFA concentrations have been shown to reproduce some of the metabolic abnormalities of obesity. It has been hypothesized that visceral adipose tissue lipolysis releases excess FFAs into the portal vein, exposing the liver to higher FFA concentrations. We used isotope dilution/hepatic vein catheterization techniques to examine whether intra-abdominal fat contributes a greater portion of hepatic FFA delivery in visceral obesity. Obese women (n = 24) and men (n = 20) with a range of obesity phenotypes, taken together with healthy, lean women (n = 12) and men (n = 12), were studied. Systemic, splanchnic, and leg FFA kinetics were measured. The results showed that plasma FFA concentrations were approximately 20% greater in obese men and obese women. The contribution of splanchnic lipolysis to hepatic FFA delivery ranged from less than 10% to almost 50% and increased as a function of visceral fat in women (r = 0.49, P = 0.002) and in men (r = 0.52, P = 0.002); the slope of the relationship was greater in women than in men (P < 0.05). Leg and splanchnic tissues contributed a greater portion of systemic FFA release in obese men and women than in lean men and women. We conclude that the contribution of visceral adipose tissue lipolysis to hepatic FFA delivery increases with increasing visceral fat in humans and that this effect is greater in women than in men.

Effect of endurance training on lipid metabolism in women: a potential role for PPARalpha in the metabolic response to training

Endurance training increases fatty acid oxidation (FAO) and skeletal muscle oxidative capacity. However, the source of the additional fat and the mechanisms for increasing FAO capacity in muscle are not clear. We measured whole body and regional lipolytic activity and whole body and plasma FAO in six lean women during 90 min of bicycling exercise (50% pretraining peak O(2) consumption) before and after 12 wk of endurance training. We also assessed skeletal muscle content of peroxisome proliferator-activated receptor-alpha (PPARalpha) and its target proteins that regulate FAO [medium-chain and very long chain acyl-CoA dehydrogenase (MCAD and VLCAD)]. Despite a 25% increase in whole body FAO during exercise after training (P < 0.05), training did not alter regional adipose tissue lipolysis (abdominal: 0.56 +/- 0.26 and 0.57 +/- 0.10 micromol x 100 g(-1) x min(-1); femoral: 0.13 +/- 0.07 and 0.09 +/- 0.02 micromol x 100 g(-1) x min(-1)), whole body palmitate rate of appearance in plasma (168 +/- 18 and 150 +/- 25 micromol/min), and plasma FAO (554 +/- 61 and 601 +/- 45 micromol/min). However, training doubled the levels of muscle PPARalpha, MCAD, and VLCAD. We conclude that training increases the use of nonplasma fatty acids and may enhance skeletal muscle oxidative capacity by PPARalpha regulation of gene expression.

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.