Free fatty acid storage in human visceral and subcutaneous adipose tissue: role of adipocyte proteins

OBJECTIVE

Because direct adipose tissue free fatty acid (FFA) storage may contribute to body fat distribution, we measured FFA (palmitate) storage rates and fatty acid (FA) storage enzymes/proteins in omental and abdominal subcutaneous fat.

RESEARCH DESIGN AND METHODS

Elective surgery patients received a bolus of [1-¹⁴C]palmitate followed by omental and abdominal subcutaneous fat biopsies to measure direct FFA storage. Long chain acyl-CoA synthetase (ACS) and diacylglycerol acyltransferase activities, CD36, fatty acid-binding protein, and fatty acid transport protein 1 were measured.

RESULTS

Palmitate tracer storage (dpm/g adipose lipid) and calculated palmitate storage rates were greater in omental than abdominal subcutaneous fat in women (1.2 ± 0.8 vs. 0.7 ± 0.4 μmol ⋅ kg adipose lipid⁻¹ ⋅ min⁻¹, P = 0.005) and men (0.7 ± 0.2 vs. 0.2 ± 0.1, P < 0.001), and both were greater in women than men (P < 0.0001). Abdominal subcutaneous adipose tissue palmitate storage rates correlated with ACS activity (women: r = 0.66, P = 0.001; men: r = 0.70, P = 0.007); in men, CD36 was also independently related to palmitate storage rates. The content/activity of FA storage enzymes/proteins in omental fat was dramatically lower in those with more visceral fat. In women, only omental palmitate storage rates were correlated (r = 0.54, P = 0.03) with ACS activity.

CONCLUSIONS

Some adipocyte FA storage factors correlate with direct FFA storage, but sex differences in this process in visceral fat do not account for sex differences in visceral fatness. The reduced storage proteins in those with greater visceral fat suggest that the storage factors we measured are not a predominant cause of visceral adipose tissue accumulation.Excess visceral fat is associated with greater metabolic risk (1,2), whereas preferential lower body fat accumulation is not (3). The mechanisms by which some individuals gain fat in one depot at the expense of another are unknown, but surely relate to an imbalance between storage and release of fatty acids (FAs). The patterns of regional free FA (FFA) release suggest that lipolysis defects cannot explain adipose tissue distribution patterns (4–6). Likewise, meal fat storage patterns do not completely explain regional variations in adipose tissue accumulation (7–11).The direct FFA storage pathway, which is lipoprotein lipase (LPL) independent, exists in both animal (12) and human (13–15) adipose tissue in vivo. Furthermore, qualitative patterns of postabsorptive, direct adipose tissue FFA storage mirror that of body fat distribution (14). Direct FFA storage in men, but not women, is greater in the upper body than lower body subcutaneous fat, and women store FFA more efficiently in subcutaneous fat than men. Hannukainen et al. (16), using positron emission tomography scan technology, found that FFA storage rates are greater in visceral than subcutaneous fat in nonobese men, similar to what we observed in nonobese women (15).Because the direct FFA storage pathway seems to help determine body fat distribution, gaining insight into the adipocyte factors regulating FA incorporation into triacylglycerols may help explain depot differences in fat storage. Potential adipocyte specific rate-limiting steps include 1) facilitated FA transport across the plasma membrane, mediated by proteins such as CD36, plasma membrane-associated fatty acid-binding protein (FABP[pm]), and fatty acid transport protein 1 (FATP1); 2) acylation, which leads to activation/trapping of intracellular FAs, mediated by the activity of a number of fatty acyl-CoA synthetases (ACSs); and 3) the final step of triacylglycerol formation, mediated by diacylglycerol acyltransferase (DGAT).In this study, we measured direct FFA storage into visceral and abdominal subcutaneous adipose tissue using isotope tracer/adipose biopsy techniques. Our hypothesis was that men, typically having more visceral fat than women, would have greater direct FFA storage in omental than abdominal subcutaneous adipose tissue and greater direct omental FFA storage than women. We also measured factors related to the FA storage steps described above and studied their relation to direct FFA storage into adipocyte triglyceride. We hypothesized that depot differences in these factors would correlate with regional, sex-specific FFA storage differences. The results provide evidence for major between-depot and between-individual differences in the FA storage factors that relate to direct FFA storage.     

Pioglitazone attenuates lung injury by modulating adipose inflammation

Background

Pioglitazone modulates adipocyte differentiation and enhances adiponectin promoter activity to increase plasma adiponectin levels. We investigated the effects of pioglitazone on cecal ligation and puncture (CLP)-induced visceral-adipose-tissue inflammation and lung injury in mice.

Materials and methods

Eight-wk-old male mice were assigned to three groups: (1) a sham-operated control group, (2) a CLP group, and (3) a pioglitazone-treated CLP group. Pioglitazone (10 mg/kg) was injected intraperitoneally for 7 d. Serum, lung, and visceral adipose tissue were collected 24 h after surgery. Tumor necrosis factor α (TNF-α) levels in peritoneal lavage fluid were measured by an enzyme-linked immunosorbent assay, and TNF-α and interleukin 6 messenger RNA (mRNA) expression levels in visceral adipose tissue were quantified by real-time polymerase chain reaction. Lung tissue specimens were stained with hematoxylin-eosin, and the terminal deoxynucleotidyl transferase dUTP-mediated nick-end labeling method was used to evaluate tissue damage.

Results

TNF-α levels in peritoneal lavage fluid were significantly higher in the CLP group than in the sham group. TNF-α levels in the pioglitazone-treated CLP group were significantly lower than those in the CLP group. TNF-α and interleukin 6 mRNA expression levels of visceral adipose tissue were significantly higher in the CLP group than in the sham group. Pioglitazone treatment decreased the mRNA expression levels of these cytokines compared with the respective values in the CLP group. Histopathologic analysis of lung tissue revealed significantly increased numbers of terminal deoxynucleotidyl transferase dUTP-mediated nick-end labeling–positive cells in the CLP group compared with the sham group.

Conclusions

Pioglitazone effectively prevents lung injury caused by CLP-induced sepsis by maintaining the anti-inflammatory status of visceral adipose tissue.     

Subcutaneous adipose tissue characteristics and the risk of biochemical recurrence in men with high-risk prostate cancer

Purpose/objective(s)

To assess subcutaneous adipose tissue characteristics by computed tomography (CT) as potential imaging biomarkers predictive of biochemical recurrence in men with high-risk prostate cancer receiving radiotherapy (RT).

Angiogenesis associated with visceral and subcutaneous adipose tissue in severe human obesity

OBJECTIVE—The expansion of adipose tissue is linked to the development of its vasculature. However, the regulation of adipose tissue angiogenesis in humans has not been extensively studied. Our aim was to compare the angiogenesis associated with subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) from the same obese patients in an in vivo model.RESEARCH DESIGN AND METHODS—Adipose tissue samples from visceral (VAT) and subcutaneous (SAT) sites, obtained from 36 obese patients (mean BMI 46.5 kg/m²) during bariatric surgery, were layered on chick chorioallantoïc membrane (CAM).RESULTS—Both SAT and VAT expressed angiogenic factors without significant difference for vascular endothelial growth factor (VEGF) expression. Adipose tissue layered on CAM stimulated angiogenesis. Angiogenic stimulation was macroscopically detectable, with engulfment of the samples, in 39% and was evidenced by angiography in 59% of the samples. A connection between CAM and adipose tissue vessels was evidenced by immunohistochemistry, with recruitment of both avian and human endothelial cells. The angiogenic potency of adipose tissue was not related to its localization (with an angiogenic stimulation in 60% of SAT samples and 61% of VAT samples) or to adipocyte size or inflammatory infiltrate assessed in adipose samples before the graft on CAM. Stimulation of angiogenesis by adipose tissue was nearly abolished by bevacizumab, which specifically targets human VEGF.CONCLUSIONS—We have established a model to study the regulation of angiogenesis by human adipose tissue. This model highlighted the role of VEGF in angiogenesis in both SAT and VAT.Adipose tissue retains substantial plasticity in adulthood. Its mass can increase or decrease up to 10-fold throughout life. The prevalence of obesity has doubled over the last 20 years, and current pharmacotherapy is relatively ineffective in maintaining long-term weight loss (1). A better understanding of the development of adipose tissue is required to identify new therapeutic approaches to obesity.Angiogenesis and adipogenesis are linked functionally (2). During embryogenesis, the development of adipose tissue and its vascularization are temporally and spatially related (3). In animal models of genetic and induced obesity, the expansion of adipose tissue is associated with active angiogenesis, whereas inhibition of angiogenesis prevents adipose tissue development (4–6). Angiogenesis induced by adipose cells in animal models increases along with adipocyte differentiation (7–9), and conversely, angiogenic factors, such as vascular endothelial growth factor (VEGF), can modulate adipocyte differentiation (8). The cross-talk between adipocytes and endothelial cells involves numerous paracrine factors associated with angiogenesis and/or adipose tissue differentiation. It also involves direct cell-to-cell interactions, and it should be noted that human adipose tissue–derived stem cells can differentiate into either adipocyte or endothelial cells (10–12).Numerous studies have shown that adipose tissue can stimulate angiogenesis in physiological models, such as the chick chorioallantoïc membrane (CAM) and the rabbit cornea (7,13,14), or in pathophysiological models, such as wound healing and revascularization of ischemic tissues (2,11,12,15–17). Adipose tissue produces several factors involved in angiogenesis, and local or circulating levels of tumor necrosis factor-α (TNF-α), VEGF, plasminogen activator inhibitor-1 (PAI-1), and angiopoïetin-2 are increased in animal and human obesity (2,18–20). Conversely, factors involved in adipocyte regulation, such as leptin, adiponectin, visfatin, or peroxisome proliferator–activated receptor γ (PPARγ), for example (2,3,8,21–24), also regulate angiogenesis.However, there have been few studies of the mechanisms of stimulation of adipose tissue angiogenesis in obesity. The characteristics of adipose tissue that could influence angiogenesis in humans, such as whether the tissue is of subcutaneous or visceral origin, the presence of infiltrating macrophages, and the profile of expression of angiogenic factors are still unknown. Very few studies (8,24,25) have tried to inhibit angiogenic factors to identify their role in adipose tissue angiogenesis.Our main objectives were to compare the angiogenic potency of subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) from obese patients and to assess whether the characteristics of adipose tissue and the phenotype of the patients influence angiogenesis associated with adipose tissue.     

Cortisol release from adipose tissue by 11beta-hydroxysteroid dehydrogenase type 1 in humans

OBJECTIVE—11β-Hydroxysteroid dehydrogenase type 1 (11β-HSD1) regenerates cortisol from cortisone. 11β-HSD1 mRNA and activity are increased in vitro in subcutaneous adipose tissue from obese patients. Inhibition of 11β-HSD1 is a promising therapeutic approach in type 2 diabetes. However, release of cortisol by 11β-HSD1 from adipose tissue and its effect on portal vein cortisol concentrations have not been quantified in vivo.RESEARCH DESIGN AND METHODS—Six healthy men underwent 9,11,12,12-[²H]₄-cortisol infusions with simultaneous sampling of arterialized and superficial epigastric vein blood sampling. Four men with stable chronic liver disease and a transjugular intrahepatic porto-systemic shunt in situ underwent tracer infusion with simultaneous sampling from the portal vein, hepatic vein, and an arterialized peripheral vein.RESULTS—Significant cortisol and 9,12,12-[²H]₃-cortisol release were observed from subcutaneous adipose tissue (15.0 [95% CI 0.4–29.5] and 8.7 [0.2–17.2] pmol · min⁻¹ · 100 g⁻¹ adipose tissue, respectively). Splanchnic release of cortisol and 9,12,12-[²H]₃-cortisol (13.5 [3.6–23.5] and 8.0 [2.6–13.5] nmol/min, respectively) was accounted for entirely by the liver; release of cortisol from visceral tissues into portal vein was not detected.CONCLUSIONS—Cortisol is released from subcutaneous adipose tissue by 11β-HSD1 in humans, and increased enzyme expression in obesity is likely to increase local glucocorticoid signaling and contribute to whole-body cortisol regeneration. However, visceral adipose 11β-HSD1 activity is insufficient to increase portal vein cortisol concentrations and hence to influence intrahepatic glucocorticoid signaling.Cortisol has potent effects in adipose tissue, influencing insulin sensitivity, fatty acid metabolism, adipocyte differentiation, adipokine expression, and body fat distribution (1). Adrenal secretion of cortisol is controlled by the hypothalamic-pituitary-adrenal axis; however, recent evidence suggests that cortisol is also generated from inert cortisone within adipose tissue by the enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) (2,3). Conversion of cortisone to cortisol occurs in vitro in human adipocytes cultured from visceral and subcutaneous adipose depots (4) and in vivo during infusion of [³H]₂-cortisone into subcutaneous adipose tissue by microdialysis (5). In obesity, 11β-HSD1 mRNA and activity are increased in subcutaneous adipose tissue biopsies (6) and either increased or unchanged in visceral adipose tissue (rev. in 7). 11β-HSD1 inhibitors are being developed to lower intracellular cortisol concentrations in adipose tissue and liver in type 2 diabetes and obesity, with promising preclinical and early clinical results (8).In addition to influencing intra-adipose cortisol concentrations, it has been suggested that cortisol release into the portal vein from visceral adipose tissue contributes to hepatic insulin resistance associated with central obesity (4). Transgenic overexpression of 11β-HSD1 in adipose tissue in mice results in a two- to threefold increase in portal vein glucocorticoid concentrations without altering systemic levels (9). However, the extent to which cortisol generated by 11β-HSD1 is released into the portal or systemic circulation from visceral or subcutaneous adipose tissue, respectively, in humans is unknown. In arteriovenous samples across subcutaneous adipose tissue, cortisol concentrations do not change, although there is net removal of cortisone (10,11). Similarly, sampling from portal or omental veins during intra-abdominal surgery has not revealed higher cortisol concentrations than in arterial blood (12,13).Measuring cortisol concentrations in arterial and venous samples may not detect cortisol release by 11β-HSD1 if cortisol is also removed by other enzymes. This occurs, for example, in the liver, where cortisol concentrations are lower in hepatic vein than in arterial blood (14). A tracer technique is required to detect cortisol production in the liver in the face of additional cortisol clearance. We devised a stable isotope deuterated tracer—9,11,12,12-[²H]₄-cortisol (d4-cortisol)—for this purpose (15). During d4-cortisol infusion, there is removal of the 11α-²H by 11β-HSD type 2 to form d3-cortisone, which is then regenerated to d3-cortisol by 11β-HSD1 (Fig. 1). The dilution of d4-cortisol by d3-cortisol therefore indicates 11β-HSD1 reductase activity and is independent of removal of both d4-cortisol and d3-cortisol by other enzymes. In tissues in which there is no source of cortisol production other than by 11β-HSD1, the dilution of d4-cortisol by cortisol also indicates 11β-HSD1 activity. Using this technique, we and others have quantified substantial cortisol release into the hepatic vein by 11β-HSD1 in the splanchnic circulation (visceral organs plus liver) (16,17). Moreover, by extrapolating from the rate of cortisol release into hepatic vein during first-pass liver metabolism of an oral dose of cortisone, we estimated that a substantial proportion of splanchnic cortisol production occurs in visceral tissues and liver (16). However, direct cannulation of veins draining adipose tissue depots during tracer cortisol infusion has not been reported, and portal vein sampling has only been performed in dogs in which cortisol release by visceral tissues was undetectable (18).Open in a separate windowFIG. 1.Quantifying cortisol production using deuterated cortisol. d4-Cortisol is converted mainly in the kidney to d3-cortisone, with the loss of the deuterium on C₁₁. The d3-cortisone is then reduced by 11β-HSD1, predominantly in the liver and adipose tissue, with the addition of an unlabeled hydrogen to form d3-cortisol. Differences between d3-cortisol and d4-cortisol metabolism therefore reflect 11β-HSD1 reductase activity.Here, we report results of deuterated cortisol infusions with selective venous cannulation to measure arteriovenous differences across subcutaneous adipose tissue and visceral tissues, to quantify cortisol release by 11β-HSD1 from adipose tissue for the first time in humans.     

Storage rates of circulating free fatty acid into adipose tissue during eating or walking in humans

We measured subcutaneous adipose tissue free fatty acid (FFA) storage rates in postprandial and walking conditions to better understand the contributions of this pathway to body fat distribution. Palmitate tracers were infused intravenously and fat biopsies collected to measure palmitate storage in upper- (UBSQ) and lower-body subcutaneous (LBSQ) fat in 41 (17 men) and 40 (16 men) volunteers under postprandial and under postabsorptive walking conditions, respectively. Postprandial palmitate storage was greater in women than men in UBSQ (0.50 ± 0.25 vs. 0.33 ± 0.37 μmol ⋅ kg fat⁻¹ ⋅ min⁻¹; P = 0.007) and LBSQ fat (0.37 ± 0.25 vs. 0.22 ± 0.20 μmol ⋅ kg fat⁻¹ ⋅ min⁻¹; P = 0.005); storage rates were significantly greater in UBSQ than LBSQ fat in both sexes. During walking, UBSQ palmitate storage did not differ between sexes, whereas LBSQ storage was greater in women than men (0.40 ± 0.22 vs. 0.25 ± 0.15 μmol ⋅ kg fat⁻¹ ⋅ min⁻¹; P = 0.01). In women only, walking palmitate storage was significantly greater in LBSQ than UBSQ fat. Adipocyte CD36 and diacylglycerol acyltransferase (DGAT) correlated with LBSQ palmitate storage in the postprandial and walking condition, respectively. We conclude that UBSQ fat is the preferred postprandial FFA storage depot for both sexes, whereas walking favors storage in LBSQ fat in women. Transmembrane transport (CD36) and esterification into triglycerides (DGAT) may be rate-limiting steps for LBSQ FFA storage during feeding and exercise.Adipose tissue buffers the daily flux of fatty acids in circulation (1). The major fuel functions of adipose tissue are storage of dietary fatty acids postprandially and release of free fatty acids (FFAs) in the postabsorptive state and during physical activity. Despite active lipolysis, adipose tissue directly takes up and stores circulating FFAs in postabsorptive humans (2–4). Although lesser in magnitude than dietary fat storage, the regional patterns of direct FFA storage in the postabsorptive state match the well-known sex-specific body fat distribution (5), whereas dietary fatty acid storage does not (6). Specifically, postabsorptive, direct FFA storage favors redistribution of FFAs to lower-body subcutaneous fat (LBSQ) in women and to upper-body subcutaneous (UBSQ) fat in men (5).The FFA storage pathway has been easier to detect in the postprandial state, due to net fat storage in adipose tissue combined with suppressed lipolysis (7,8). In a mixed group of women and men, no regional differences were observed in postprandial FFA uptake between abdominal and femoral subcutaneous fat (8). It is unknown whether there are sex differences in regional FFA storage rates in subcutaneous fat postprandially. If there is preferential FFA storage in one fat depot over another in either sex, this would suggest that postprandial FFA storage can contribute to sex-specific regulation of body fat distribution.The other major condition that alters adipose tissue fatty acid balance is physical activity. During physical activity, adipose tissue lipolysis increases its supply of FFAs to systemic circulation and working muscles. Whether circulating FFAs can be taken up and stored in adipose tissue via the direct pathway under conditions of stimulated lipolysis is unknown.In the current study, we quantitatively measured FFA storage in subcutaneous fat in humans during feeding or walking to assess the potential contribution of this pathway to regulating body fat distribution in adults. Furthermore, we attempted to identify regulatory factors that may play a role in FFA storage by examining three proteins/enzymes involved in adipocyte FFA storage (collectively termed FFA storage factors): CD36, which is implicated in the transmembrane transport of FFAs (9), acyl-CoA synthetase (ACS) activity, which is involved in rapid activation of imported FFAs (10,11), and diacylglycerol acyltransferase (DGAT) activity, which catalyzes the final, committed step in triglyceride (TG) synthesis, the conversion of diacylglycerol to TGs (12). Lastly, we investigated whether obesity downregulates FFA storage in adipose tissue under postprandial and walking conditions, as it does for postabsorptive lipolysis and dietary fat storage (13–16).     

Glucose-Dependent Insulinotropic Polypeptide May Enhance Fatty Acid Re-esterification in Subcutaneous Abdominal Adipose Tissue in Lean Humans

OBJECTIVE

Glucose-dependent insulinotropic polypeptide (GIP) has been implicated in lipid metabolism in animals. In humans, however, there is no clear evidence of GIP effecting lipid metabolism. The present experiments were performed in order to elucidate the effects of GIP on regional adipose tissue metabolism.

RESEARCH DESIGN AND METHODS

Eight healthy subjects were studied on four different occasions. Abdominal subcutaneous adipose tissue metabolism was assessed by measuring arterio-venous concentration differences and regional adipose tissue blood flow during GIP (1.5 pmol/kg/min) or saline infused intravenously alone or in combination with a hyperinsulinemic-hyperglycemic (HI-HG) clamp.

RESULTS

During GIP and HI-HG clamp, abdominal subcutaneous adipose tissue blood flow, hydrolysis of circulating triacylglycerol (TAG) (P = 0.009), and glucose uptake (P = 0.03) increased significantly while free fatty acid (FFA) output (P = 0.04) and FFA/glycerol release ratio (P = 0.02) decreased compared with saline and HI-HG clamp.

CONCLUSIONS

In conclusion, GIP in combination with hyperinsulinemia and slight hyperglycemia increased adipose tissue blood flow, glucose uptake, and FFA re-esterification, thus resulting in increased TAG deposition in abdominal subcutaneous adipose tissue.Several animal studies support the idea that glucose-dependent insulinotropic polypeptide (GIP) may play a direct role in lipid metabolism, which could be to ensure efficient deposition of dietary fat in body stores in times of plenty (1,2). GIP enhances insulin release during a meal and because insulin is a major hormonal regulator of lipogenesis, a component of GIP''s action on fat metabolism is probably indirect (3–5). However, there is no clear evidence of a GIP effect on lipid metabolism in humans. We recently studied the effect of GIP on the removal rates of plasma triacylglycerol (TAG) and on free fatty acid (FFA) concentrations, which were increased after either a mixed meal or infusion of Intralipid and insulin (6). Under these experimental conditions, we were not able to demonstrate any effects of GIP on the removal rates of either chylomicron-TAG or Intralipid TAG concentrations. However, we found evidence for enhanced FFA re-esterification under conditions with combined high plasma GIP and insulin concentrations. Based on these findings, we hypothesized that GIP per se plays a role in the regulation of adipose tissue re-esterification of FFA, a process that is of central importance in adipose tissue handling of fatty acids (7,8). Therefore, the aim of the present study was to elucidate the effects of GIP alone or in combination with hyperinsulinemia and hyperglycemia on regional adipose tissue metabolism.     

Insulin and Metformin Regulate Circulating and Adipose Tissue Chemerin

OBJECTIVE

To assess chemerin levels and regulation in sera and adipose tissue from women with polycystic ovary syndrome (PCOS) and matched control subjects.

RESEARCH DESIGN AND METHODS

Real-time RT-PCR and Western blotting were used to assess mRNA and protein expression of chemerin. Serum chemerin was measured by enzyme-linked immunosorbent assay. We investigated the in vivo effects of insulin on serum chemerin levels via a prolonged insulin-glucose infusion. Ex vivo effects of insulin, metformin, and steroid hormones on adipose tissue chemerin protein production and secretion into conditioned media were assessed by Western blotting and enzyme-linked immunosorbent assay, respectively.

RESULTS

Serum chemerin, subcutaneous, and omental adipose tissue chemerin were significantly higher in women with PCOS (n = 14; P < 0.05, P < 0.01). Hyperinsulinemic induction in human subjects significantly increased serum chemerin levels (n = 6; P < 0.05, P < 0.01). In adipose tissue explants, insulin significantly increased (n = 6; P < 0.05, P < 0.01) whereas metformin significantly decreased (n = 6; P < 0.05, P < 0.01) chemerin protein production and secretion into conditioned media, respectively. After 6 months of metformin treatment, there was a significant decrease in serum chemerin (n = 21; P < 0.01). Importantly, changes in homeostasis model assessment–insulin resistance were predictive of changes in serum chemerin (P = 0.046).

CONCLUSIONS

Serum and adipose tissue chemerin levels are increased in women with PCOS and are upregulated by insulin. Metformin treatment decreases serum chemerin in these women.Polycystic ovary syndrome (PCOS), a common endocrinopathy affecting 5–10% of women in the reproductive age, is characterized by menstrual dysfunction and hyperandrogenism and is associated with insulin resistance and pancreatic β-cell dysfunction, impaired glucose tolerance (IGT), type 2 diabetes, dyslipidemia, and visceral obesity (1,2). The consequent hyperinsulinemia is more prevalent in lean and obese women with PCOS when compared with age- and weight-matched normal women (3).The metabolic syndrome is associated with excessive accumulation of central body fat. As well as its role in energy storage, adipose tissue produces several hormones and cytokines termed ‘adipokines’ that have widespread effects on carbohydrate and lipid metabolism. They appear to play an important role in the pathogenesis of insulin resistance, diabetes, and atherosclerosis (4). Furthermore, it is apparent that accumulation of visceral adipose tissue poses a greater cardiometabolic risk than subcutaneous adipose tissue (5) as removal of visceral rather than subcutaneous adipose tissue has been shown to improve insulin sensitivity (6). Moreover, differences in gene expression of adipocyte-secreted molecules (adipokines) suggest that there are inherent adipose tissue depot–specific differences in the endocrine function of adipose tissue. In relation to this, we have published data on the increased levels of vaspin in women with PCOS (7); vaspin is a recently described adipokine mainly formed in human visceral adipose tissue that has insulin-sensitizing effects (8).Recently, Bozaoglu et al. (9) reported chemerin as a novel adipokine, circulating levels of which significantly correlated with BMI, circulating triglycerides, and blood pressure, features of the metabolic syndrome. In addition, chemerin or chemerin receptor knockdown impaired differentiation of 3T3-L1 cells and attenuated the expression of adipocyte genes involved in glucose and lipid homeostasis (10).With the aforementioned in mind and the fact that there is no literature with regards to chemerin in human adipose tissue and its regulation, in study 1, we assessed circulating chemerin as well as mRNA expression and protein levels of chemerin in subcutaneous and omental adipose tissue depots in women with PCOS against age, BMI, and waist-to-hip ratio (WHR) in matched control subjects. Furthermore, we studied the in vivo (study 2) and ex vivo effects of insulin on circulating chemerin levels via a prolonged insulin-glucose infusion in humans and primary adipose tissue explant cultures, respectively. In study 3 we studied the effects of metformin therapy, widely used in the treatment of PCOS in women, on circulating chemerin levels in tandem with associated changes to clinical, hormonal, and metabolic parameters in the same cohort of PCOS in women. Additionally, we studied the ex vivo effects of metformin and steroid hormones in human primary adipose tissue explants.     

Cellularity and Adipogenic Profile of the Abdominal Subcutaneous Adipose Tissue From Obese Adolescents: Association With Insulin Resistance and Hepatic Steatosis

OBJECTIVE

We explored whether the distribution of adipose cell size, the estimated total number of adipose cells, and the expression of adipogenic genes in subcutaneous adipose tissue are linked to the phenotype of high visceral and low subcutaneous fat depots in obese adolescents.

RESEARCH DESIGN AND METHODS

A total of 38 adolescents with similar degrees of obesity agreed to have a subcutaneous periumbilical adipose tissue biopsy, in addition to metabolic (oral glucose tolerance test and hyperinsulinemic euglycemic clamp) and imaging studies (MRI, DEXA, ¹H-NMR). Subcutaneous periumbilical adipose cell-size distribution and the estimated total number of subcutaneous adipose cells were obtained from tissue biopsy samples fixed in osmium tetroxide and analyzed by Beckman Coulter Multisizer. The adipogenic capacity was measured by Affymetrix GeneChip and quantitative RT-PCR.

RESULTS

Subjects were divided into two groups: high versus low ratio of visceral to visceral + subcutaneous fat (VAT/[VAT+SAT]). The cell-size distribution curves were significantly different between the high and low VAT/(VAT+SAT) groups, even after adjusting for age, sex, and ethnicity (MANOVA P = 0.035). Surprisingly, the fraction of large adipocytes was significantly lower (P < 0.01) in the group with high VAT/(VAT+SAT), along with the estimated total number of large adipose cells (P < 0.05), while the mean diameter was increased (P < 0.01). From the microarray analyses emerged a lower expression of lipogenesis/adipogenesis markers (sterol regulatory element binding protein-1, acetyl-CoA carboxylase, fatty acid synthase) in the group with high VAT/(VAT+SAT), which was confirmed by RT-PCR.

CONCLUSIONS

A reduced lipo-/adipogenic capacity, fraction, and estimated number of large subcutaneous adipocytes may contribute to the abnormal distribution of abdominal fat and hepatic steatosis, as well as to insulin resistance in obese adolescents.White adipose tissue (WAT) plays a critical role in obesity-related metabolic dysfunctions. Danforth (1) and Shulman (2) raised the hypothesis that inadequate subcutaneous fat stores result in lipid overflow into visceral fat and other nonadipose tissues, which was elegantly explored by Ravussin and Smith (3). Sethi and Vidal-Puig proposed that impaired subcutaneous WAT expandability might cause obesity-associated insulin resistance (4). In adults, increased fat cell size, a marker of impaired adipogenesis, was reported to be related to insulin resistance and predicts the development of type 2 diabetes (5). Recent studies by McLaughlin et al. (6) reported in adults that an increase in the proportion of small adipocytes, but not increased fat cell size, and an impaired expression of markers for adipogenesis are related to insulin resistance. Little is known about adipocyte size and adipogenic capacity during adolescence, a time when the expansion of WAT results from combined adipocyte hypertrophy and hyperplasia. In contrast, adult adipocytes exhibit a remarkably constant turnover (7). Recently, we described a group of obese adolescents presenting with a reduced subcutaneous abdominal fat depot, increased visceral fat, hepatic steatosis, and marked insulin resistance (8). Building on these findings, we asked the following question: is the adipogenic capacity of the abdominal subcutaneous fat depot in obese adolescents associated with a decreased proportion of large adipose cells and reduced expression of genes regulating adipocyte differentiation? We hypothesized that, in some obese adolescents, the lack of expandability of the subcutaneous abdominal fat might be linked to adipocyte size, its adipogenic expression, and the fat accumulation in liver and muscle. To test this hypothesis, we used metabolic and imaging techniques, together with direct measurements of adipocyte size and gene expression, in two groups of obese adolescents with marked differences in the proportion of visceral to subcutaneous abdominal fat.     

Adiponectin inhibits lipolysis in mouse adipocytes

OBJECTIVE

Adiponectin is an adipocyte-derived hormone that sensitizes insulin and improves energy metabolism in tissues. This study was designed to investigate the direct regulatory effects of adiponectin on lipid metabolism in adipocytes.

RESEARCH DESIGN AND METHODS

Basal and hormone-stimulated lipolysis were comparatively analyzed using white adipose tissues or primary adipocytes from adiponectin gene knockout and control mice. To further study the underlying mechanisms through which adiponectin suppresses lipolysis, cultured 3T3-L1 adipocytes and adenovirus-mediated gene transduction were used.

RESULTS

Significantly increased lipolysis was observed in both adiponectin gene knockout mice and primary adipocytes from these mice. Hormone-stimulated glycerol release was inhibited in adiponectin-treated adipocytes. Adiponectin suppressed hormone-sensitive lipase activation without altering adipose triglyceride lipase and CGI-58 expression in adipocytes. Moreover, adiponectin reduced protein levels of the type 2 regulatory subunit RIIα of protein kinase A by reducing its protein stability. Ectopic expression of RIIα abolished the inhibitory effects of adiponectin on lipolysis in adipocytes.

CONCLUSIONS

This study demonstrates that adiponectin inhibits lipolysis in adipocytes and reveals a novel function of adiponectin in lipid metabolism in adipocytes.White adipose tissue (WAT) mass is mainly determined by adipocyte number and size. It is logical to assume that increase of adipocyte number and size expands adipose tissue mass and results in obesity. However, a study demonstrated that adipocyte populations are determined during the first 2 decades of life and are stable in adults (1), suggesting that lipid storage should play a key role in adult obesity. Lipid storage is dynamic and mainly controlled by two opposing processes: lipogenesis and lipolysis.Adiponectin is an adipocyte-secreted hormone that enhances insulin sensitivity. Adiponectin gene expression and blood levels are decreased in obese adults and animal models (2). Adiponectin transgenic female FVB mice exhibit increased body weight and fat tissue mass (3). Furthermore, modestly increasing serum adiponectin completely rescued the diabetic phenotype in ob/ob mice with significant expansion of adipose tissue (4). These studies suggest that adiponectin may regulate lipid metabolism in adipocytes through a direct or indirect mechanism.We describe a novel function of adiponectin in lipid metabolism in adipocytes. Our results show that adiponectin inhibits lipolysis by suppressing protein kinase A (PKA)–mediated hormone-sensitive lipase (HSL) activation. In addition, adiponectin reduces the PKA RIIα regulatory subunit protein level by increasing its protein degradation in adipocytes.     

Effects of sleeve gastrectomy in high fat diet-induced obese mice: respective role of reduced caloric intake,white adipose tissue inflammation and changes in adipose tissue and ectopic fat depots

Background

Sleeve gastrectomy (SG) has become a popular bariatric procedure. The mechanisms responsible for weight loss and improvement of metabolic disturbances have still not been completely elucidated. We investigated the effect of SG on body weight, adipose tissue depots, glucose tolerance, and liver steatosis independent of reduced caloric intake in high-fat-diet-induced obese mice.

Methods

C57BI/6 J mice fed a high fat diet (45 %) for 33 weeks were divided into three groups: sleeve gastrectomy (SG, 13 mice), sham-operated ad libitum fed (SALF, 13 mice) and sham-operated pair fed (PFS, 13 mice). The animals were humanely killed 23 days after surgery.

Results

In SG mice, food intake was reduced transiently, but weight loss was significant and persistent compared to controls (SG vs. PFS, P < 0.05; PFS vs. SALF, P < 0.05). SG mice showed improved glucose tolerance and lower levels of liver steatosis compared with controls (area under the curve, SG vs. PFS, P < 0.01; PFS vs. SALF, P < 0.05) (liver steatosis, SG vs. PFS, P < 0.05; PFS vs. SALF, P < 0.01). This was associated with a decrease in the ratios of the weight of pancreas, epididymal and inguinal adipose tissues to body weight, and an increase in the ratio of brown adipose tissue weight to body weight. Epididymal adipose tissue was also infiltrated by fewer activated T cells and by more anti-inflammatory regulatory T cells. Serum levels of fasting acyl ghrelin were still significantly decreased 3 weeks after surgery in SG mice compared to PFS mice (P < 0.05).

Conclusions

Reduced white adipose tissue inflammation, modification of adipose tissue development (brown vs. white adipose tissue), and ectopic fat are potential mechanisms that may account for the reduced caloric intake independent effects of SG.     

Adipose-derived stem cells enhance tissue regeneration of gastrotomy closure

Background

The aim of this study was to examine whether transplantation of adipose-derived stem cells (ADSCs) improves healing of a gastrotomy closure in rats. In digestive surgery, anastomotic leakage is a serious postoperative complication and anastomotic stenosis may reduce quality of life. Recent studies have suggested that ADSCs play material roles in intestinal healing, acceleration of angiogenesis, and reduction of fibrosis, and treatment with ADSCs may improve healing.

Materials and methods

ADSCs were isolated from intra-abdominal white adipose tissue of 40 male Wistar rats (weight 300 g) in four groups (n = 10 each). Gastrotomy closures were prepared surgically in all rats. Controls were treated with phosphate-buffered saline injection and sacrificed 7 d (group 1) or 28 d (group 3) after the surgery. Other animals were treated with locally autotransplanted ADSCs (labeled by CM-DiI) and sacrificed 7 d (group 2) or 28 d (group 4) after the surgery. Histopathologic features were evaluated in the four groups.

Results

Injection of ADSCs significantly enhanced angiogenesis and collagen deposition after 7 d, indicating improved healing of the gastrotomy closure. In contrast, ADSC transplantation significantly reduced collagen deposition after 28 d. The bursting pressure was higher in the transplant groups after 7 d.

Conclusions

ADSCs enhance tissue regeneration in gastrotomy closures by accelerating angiogenesis and fibrosis in the early healing period. In the late period, ADSCs prevent excessive fibrosis and assist in regeneration of tissues that closely resemble the native structure. These results suggest that therapy with transplanted ADSCs might improve postoperative complications in digestive surgery.     

The impact of race on outcomes following emergency surgery: an American College of Surgeons National Surgical Quality Improvement Program assessment

Background

Despite significant evolutions in health care, outcome discrepancies exist among demographic cohorts. We sought to determine the impact of race on emergency surgery outcomes.

Methods

This is a retrospective review of the American College of Surgeons National Surgical Quality Improvement Program database (2005 through 2009) for all patients aged ≥16 years undergoing emergency abdominal surgery. Primary outcomes included morbidity and mortality.

Results

We identified 75,280 patients (mean age 48.2 ± 19.9 years, 51.7% female; 79% white, 9.9% black, 5.0% Hispanic, 3.7% Asian, 1.3% American Indian or Alaskan, .2% Pacific Islander). Annual rates of emergency operations ranged from 7.3% to 8.5% (P = .22). The overall complication (18.6%) and mortality rate (4.6%) was highest in the black population (24.3%, 5.3%) followed by whites (18.7%, 4.6%), with the lowest rate in Hispanic (11.7%, 1.8%) and Pacific Islander populations (10.2%, 1.8%; P < .001). Compared with whites, blacks had a 1.25-fold (1.17 to 1.34; P < .001) increased risk of complications, but similar mortality (P = .168). When combining minorities, overall complications were 1.059-fold (1.004 to 1.12; P = .034) higher, however, mortality was reduced 1.7-fold (1.07 to 1.34; P = .001).

Conclusions

Following emergency abdominal surgery, minority race is independently associated with increased complications and reduced mortality.     

Similar VLDL-TG storage in visceral and subcutaneous fat in obese and lean women

OBJECTIVE

Excess visceral fat accumulation is associated with the metabolic disturbances of obesity. Differential lipid redistribution through lipoproteins may affect body fat distribution. This is the first study to investigate VLDL-triglyceride (VLDL-TG) storage in visceral fat.

RESEARCH DESIGN AND METHODS

Nine upper-body obese (UBO; waist circumference >88 cm) and six lean (waist circumference <80 cm) women scheduled for elective tubal ligation surgery were studied. VLDL-TG storage in visceral, upper-body subcutaneous (UBSQ), and lower-body subcutaneous (LBSQ) fat were measured with [9,10-³H]-triolein–labeled VLDL.

RESULTS

VLDL-TG storage in visceral fat accounted for only ∼0.8% of VLDL-TG turnover in UBO and lean women, respectively. A significantly larger proportion of VLDL-TG turnover was stored in UBSQ (∼5%) and LBSQ (∼4%) fat. The VLDL-TG fractional storage was similar in UBO and lean women for all regional depots. VLDL-TG fractional storage and VLDL-TG concentration were correlated in UBO women in UBSQ fat (r = 0.68, P = 0.04), whereas an inverse association was observed for lean women in visceral (r = −0.89, P = 0.02) and LBSQ (r = −0.87, P = 0.02) fat.

CONCLUSIONS

VLDL-TG storage efficiency is similar in all regional fat depots, and trafficking of VLDL-TG into different adipose tissue depots is similar in UBO and lean women. Postabsorptive VLDL-TG storage is unlikely to be of major importance in the development of preferential upper-body fat distribution in obese women.Upper-body obesity, especially when associated with visceral fat accumulation, is related to the development of metabolic abnormalities, such as insulin resistance, type 2 diabetes, and dyslipidemia (1,2). In contrast, lower-body obesity does not exhibit these abnormalities (3,4). The mechanism behind the development of these different obesity phenotypes remains unclear (5,6). Studies have not provided clear evidence to suggest that differences in regional lipolysis promote the development of differences in adipose tissue distribution (6–8). Moreover, studies of meal fat storage and direct plasma free fatty acid (FFA) storage have failed to demonstrate definite differences, with reports showing greater (9,10) and similar (6,11) storage in visceral compared with subcutaneous adipose tissue in lean and obese men and women.Differences between chylomicron and VLDL-triglyceride (VLDL-TG) uptake in different regional adipose tissues (12) underscore that studies of VLDL-TG storage are warranted. By using an ex vivo–labeled VLDL-TG tracer, we recently reported that VLDL-TG adipose tissue fatty acid storage was similar in upper-body subcutaneous (UBSQ) and lower-body subcutaneous (LBSQ) fat in lean and obese women (13) and in obese and type 2 diabetic men (14). Thus far, no studies have investigated VLDL-TG fatty acid storage in visceral adipose tissue.The aim of this study was to test the hypothesis that VLDL-TG fatty acid storage is greater in visceral adipose tissue compared with LBSQ and UBSQ adipose tissue. We wanted to test this hypothesis in both upper-body obese (UBO) and lean women. A secondary aim was to assess whether the storage pattern differed between UBO and lean women.     

Outcomes of Renal Transplantation in Patients With Major Lower Limb Amputation

Introduction

The impact of severe peripheral vascular disease on graft survival in patients undergoing renal transplantation is poorly defined. The aim of our study is to establish outcomes in renal transplant recipients who have severe peripheral vascular disease necessitating major lower limb amputation.

Methods

Data for patients undergoing renal transplantation from January 2001–December 2010 was extracted from a regional transplantation database. Patients undergoing lower limb amputation pre- and post-transplantation were identified and outcome measures including delayed graft function, biopsy-proven acute rejection, serum creatinine level at 1 year, and graft loss and recipient survival at 1 year and long-term were compared with patients who did not undergo amputation. Student t and Pearson's chi-squared tests were used to compare patients with and without amputation and Kaplan-Meier curves were used for survival analysis. A P value < .05 is considered statistically significant.

Results

A total of 762 patients underwent renal transplantation. Four (0.5%) patients had an amputation before transplantation and 16 (2.1%) underwent amputation after transplantation. Serum creatinine levels at 1 year were significantly higher in patients who had amputation after transplantation (308.5 ± 60.8 μmol/l vs 177.6 ± 6.4 μmol/l; P = .03). During longer follow-up (mean: 2053.1 ± 58.3 days), patients who underwent amputation after transplantation had a higher rate of graft loss (P < .01) and higher death rate (P < .01).

Conclusion

The requirement for amputation after renal transplantation is associated with poor long-term graft and patient survival and higher serum creatinine levels at 1 year. Patients at increased risk of severe peripheral vascular disease should be identified and measures taken to reduce the long-term risk.