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

OBJECTIVE: Disturbances in adipocyte lipolysis in obesity may contribute to elevated circulating non-esterified fatty acid (NEFA) concentrations and insulin resistance. In experimental models, NEFA metabolism is influenced by adipocyte proteins such as adipocyte and keratinocyte lipid binding proteins (aP2/ALBP and mal1/KLBP) and fatty acid translocase (CD36). We investigated the effect of obesity and weight loss on the expression of these proteins in human subcutaneous adipose tissue. STUDY DESIGN AND SUBJECTS: Subcutaneous adipose tissue was obtained from 12 obese (body mass index (BMI) 42.4+/-1.6 kg/m(2)) and 12 lean (23.4+/-0.6 kg/m(2)) subjects. The obese subjects underwent gastric banding and biopsies were taken again after 2 y following a significant weight reduction (BMI 32.8+/-1.4 kg/m(2)). Adipose tissue proteins were quantified by Western blotting. RESULTS: Differential expression of ALBP, KLBP and CD36 was observed in lean and weight-reduced subjects compared with obese individuals. This resulted in a significantly lower ALBP/KLBP ratio in lean and weight-reduced individuals compared to obese subjects. Furthermore there was a significant influence of gender on this ratio. Moreover, the commonly used internal standard protein actin was expressed significantly higher in lean compared to obese individuals. CONCLUSION: The relative content of ALBP and KLBP in human adipose tissue changes with obesity, weight loss and gender indicating differential regulation. Differing responses in the expression patterns of adipose tissue proteins capable of binding NEFAs in response to weight changes suggest a potential importance in the development of obesity-associated complications.     

Glucose uptake and insulin action in human adipose tissue--influence of BMI, anatomical depot and body fat distribution.

OBJECTIVE: To examine and compare in vitro basal and insulin-stimulated glucose uptake in human omental and subcutaneous adipose tissue derived from lean, overweight or obese individuals, and in those with central or peripheral obesity. DESIGN: In vitro study of basal and insulin-stimulated 2-deoxyglucose uptake in human omental and subcutaneous adipose tissue explants derived from patients undergoing elective abdominal surgery. SUBJECTS: Fourteen lean (average age 47 y, average body mass index (BMI) 22 kg/m(2)), 12 overweight (average age 51 y, average BMI 27 kg/m(2)), and 15 obese subjects (average age 45 y, average BMI 39 kg/m(2)). Ten peripherally obese (average age 43 y, average WHR 0.76) and 17 centrally obese (average age 50 y, average waist-to-hip ratio (WHR) 0.92). MEASUREMENTS: Fatness and fat distribution parameters (by anthropometry), basal and insulin stimulated [(3)H]-2-deoxyglucose uptake in omental and subcutaneous adipose tissue explants. RESULTS: In adipose tissue from lean subjects transport of 2-deoxyglucose over basal was stimulated approximately two-fold by insulin. In contrast, 2-deoxyglucose transport in adipose tissue of obese or overweight subjects was not responsive to insulin. Following incubation with 100-nM insulin for 35 min, insulin-stimulated 2-deoxyglucose transport was significantly lower in both omental and subcutaneous adipose tissue of obese and overweight compared to lean subjects. Basal 2-deoxyglucose uptake was also significantly reduced in omental and subcutaneous tissue in obese compared to lean subjects. Depot-specific differences in 2-deoxyglucose uptake were also seen. Overall 2-deoxyglucose uptake was greater in omental than subcutaneous adipose tissue but this was due to increased basal levels rather than increased insulin action. The reduction in insulin-stimulated 2-deoxyglucose uptake seen in overweight and obese subjects was relatively similar in both depots. However, insulin responsive 2-deoxyglucose transport was significantly lower in the omental adipose tissue of subjects with central obesity, as compared to that of subjects with peripheral obesity. No difference in insulin induced 2-deoxyglucose transport was observed in the subcutaneous adipose tissue explants of subjects with either central or peripheral obesity. CONCLUSION: In lean individuals insulin responsiveness of omental and subcutaneous adipose tissue was similar, but basal glucose uptake was significantly higher in omental adipose tissue. Adipose tissue obtained from overweight as well as obese individuals is insulin resistant. This insulin resistance occurs at a lower BMI than previously expected and is not adipose-depot specific. However, in obese subjects with a central distribution of adiposity insulin resistance occurs at the site of omental adipose tissue, in contrast to those with peripheral obesity.     

The fatty acid transporter FAT/CD36 is upregulated in subcutaneous and visceral adipose tissues in human obesity and type 2 diabetes

BACKGROUND: Long-chain fatty acids (LCFAs) cross the plasma membrane via a protein-mediated mechanism involving one or more LCFA-binding proteins. Among these, FAT/CD36 has been identified as key LCFA transporter in the heart and skeletal muscle, where it is regulated acutely and chronically by insulin. In skeletal muscle, FAT/CD36 expression and/or subcellular distribution is altered in obesity and type 2 diabetes. There is limited information as to whether the expression of this protein is also altered in subcutaneous and/or visceral adipose tissue depots in human obesity or type 2 diabetes. OBJECTIVES: To compare (a) the expression of FAT/CD36 in subcutaneous and visceral adipose tissue depots in lean, overweight, and obese individuals and in type 2 diabetics, (b) to determine whether the protein expression of FAT/CD36 in these depots is associated with the severity of insulin resistance (type 2 diabetes>obese>overweight/lean) and (c) whether FAT/CD36 protein expression in these adipose tissue depots is associated with alterations in circulating substrates and hormones. SUBJECTS: Subjects who were undergoing abdominal surgery and who were lean (n=10; three men, seven women), overweight (n=10; three men, seven women) or obese (n=7; one man, six women), or who had been diagnosed with type 2 diabetes (n=5; one man, four women) participated in this study. MEASUREMENTS: Subcutaneous and visceral adipose tissue samples, as well as blood samples, were obtained from the subjects while under general anesthesia. Adipose tissue samples were analyzed for FAT/CD36 using Western blotting. Serum samples were analyzed for glucose, insulin, FFA and leptin. BMI was also calculated. RESULTS: Subcutaneous adipose tissue FAT/CD36 expression was upregulated by +58, +76 and +150% in overweight, obese and type 2 diabetics, respectively. Relative to subcutaneous adipose tissue, visceral adipose tissue FAT/CD36 expression was upregulated in lean (+52%) and overweight subjects (+30%). In contrast, in obese subjects and type 2 diabetics, no difference in FAT/CD36 protein expression was observed between their subcutaneous and visceral adipose tissue depots (P>0.05). The subcutaneous adipose tissue FAT/CD36 expression (R=0.85) and the visceral adipose tissue FAT/CD36 expression (R=0.77) were associated with alteration in BMI and circulating glucose and insulin. CONCLUSIONS: Subcutaneous adipose tissue FAT/CD36 expression is upregulated in obesity and type 2 diabetes. As FAT/CD36 expression is not different in lean, overweight and obese subjects, and was only increased in type 2 diabetics, it appears that visceral adipose tissue FAT/CD36 may respond in a less dynamic manner to metabolic disturbances than subcutaneous adipose tissue FAT/CD36.     

Regional variation in adipose tissue insulin action and GLUT4 glucose transporter expression in severely obese premenopausal women

Summary Insulin action and GLUT4 expression were examined in adipose tissue of severely obese premenopausal women undergoing gastrointestinal surgery. Fat samples were taken from three different anatomical regions: the subcutaneous abdominal site, the round ligament (deep abdominal properitoneal fat), and the greater omentum (deep abdominal intraperitoneal fat). The stimulatory effect of insulin on glucose transport and the ability of the hormone to inhibit lipolysis were determined in adipocytes isolated from these three adipose depots. Insulin stimulated glucose transport 2–3 times over basal rates in all adipocytes. However, round ligament adipose cells showed a significantly greater responsiveness to insulin when compared to subcutaneous and omental adipocytes. Round ligament fat cells also displayed the greatest sensitivity and maximal antilipolytic response to insulin. We also investigated whether regional differences in fat cell insulin-stimulated glucose transport were linked to a differential expression of the GLUT4 glucose transporter. GLUT4 protein content in total membranes was 5 and 2.2 times greater in round ligament adipose tissue than in subcutaneous and omental fat depots, respectively. Moreover, GLUT4 mRNA levels were 2.1 and 3 times higher in round ligament than in subcutaneous or omental adipose tissues, respectively. Adipose tissue GLUT4 protein content was strongly and negatively associated (r = –0.79 to –0.89, p < 0.01) with the waist-to-hip ratio but not with total adiposity. In conclusion, these results demonstrate the existence of site differences in adipose tissue insulin action in morbidly obese women. The greater insulin effect on glucose transport in round ligament adipocytes was associated with a higher expression of GLUT4 when compared to subcutaneous abdominal and omental fat cells. Moreover, despite the regional variation in GLUT4 expression, an increased proportion of abdominal fat was found to be associated with lower levels of GLUT4 in all adipose regions investigated. [Diabetologia (1997) 40: 590–598] Received: 8 October 1996 and in revised form: 28 January 1997     

Defective regulation of phosphatidylinositol-3-kinase gene expression in skeletal muscle and adipose tissue of non-insulin-dependent diabetes mellitus patients

Summary We investigated the regulation of the mRNA expression of the insulin receptor, insulin receptor substrate-1 (IRS-1) and p85α-phosphatidylinositol-3-kinase (PI-3K), three major actors of insulin action, in skeletal muscle from 10 healthy lean volunteers, 13 obese patients with Type II (non-insulin-dependent) diabetes mellitus and 7 non-diabetic obese subjects. The in vivo regulation by insulin was studied using a 3-h euglycaemic, hyperinsulinaemic clamp. There were no differences in the basal concentrations of the three mRNAs in skeletal muscle between groups. Insulin infusion produced a twofold reduction in insulin receptor substrate-1 mRNA expression in the three groups (p < 0.02). In contrast, insulin increased p85α-phosphatidylinositol-3-kinase mRNA expression in muscle from non-diabetic subjects ( + 98 ± 22 % in lean and + 127 ± 16 % in obese, p < 0.02) but this effect was totally impaired in Type II diabetic patients ( + 5 ± 12 %, NS). A similar defect in insulin action on p85α-phosphatidylinositol-3-kinase mRNA expression was observed in abdominal subcutaneous adipose tissue ( + 138 ± 25 %, p < 0.01 in lean and + 46 ± 14 %, p < 0.02 in obese and + 29 ± 11 %, NS in Type II diabetic patients). The lack of action of insulin on p85α-phosphatidylinositol-3-kinase mRNA in diabetic subjects was probably not due to a deleterious effect of hyperglycaemia since improvement of the glycaemic control for 10 days did not restore the response in muscle or in adipose tissue. This study provides evidence for a defect in the regulation by insulin of PI-3K gene expression in Type II diabetic patients, thus reinforcing the concept that alterations at the gene expression might be involved in the pathogeny of Type II diabetes. [Diabetologia (1999) 42: 358–364] Received: 26 August 1998 and in revised form: 23 October 1998     

Endothelial nitric oxide synthase content in adipose tissue from obese and lean African American and white American women

It has been demonstrated that the enzyme endothelial nitric oxide synthase (eNOS) is present in adipose tissue, resulting in nitric oxide production and subsequent inhibition of lipolysis. A higher eNOS content has also been reported in the subcutaneous abdominal adipose tissue of obese than in that of lean white men. Furthermore, a lower lipolytic rate in obese than in lean women and a lower lipolytic rate in African American (AA) than in white American (WA) women have been demonstrated. The purpose of this study was to determine if eNOS protein content is higher in the subcutaneous and omental adipose tissues of obese than in those of lean women and if eNOS protein content is higher in the subcutaneous and omental adipose tissues of AA than in those of WA women. Whole tissue homogenates were prepared from frozen omental and subcutaneous adipose tissue samples obtained from lean and obese and AA and WA elective abdominal surgery patients and were analyzed for eNOS protein content using enzyme-linked immunosorbent assay. The adipose tissue eNOS protein content was approximately 40% higher in obese than in lean individuals (omental, 326.9 +/- 40.5 pg/mL lean and 445.3 +/- 38.0 pg/mL obese; subcutaneous, 246.8 +/- 20.8 pg/mL lean and 343.1 +/- 19.0 pg/mL obese; P < .05). There was no difference between the races for eNOS protein content in omental adipose tissue. In subcutaneous adipose tissue, there was a higher eNOS content in obese (417.1 +/- 78.9 pg/mg total protein) than in lean (216.7 +/- 29.9 pg/mg total protein) (P < .05) WA women, but there was no difference in subcutaneous adipose eNOS content between obese and lean AA women (250.7 +/- 47.4 and 294.1 +/- 42.2 pg/mg total protein, respectively). The higher eNOS content in the adipose tissue of obese than in that of lean WA women in the fasted state may contribute to the reduced lipolytic activity in WA women; however, eNOS protein content probably does not contribute to differences in lipolytic rates between AA and WA women.     

DPP-IV inhibition enhances the antilipolytic action of NPY in human adipose tissue

Context: Dipeptidyl peptidase IV (DPP‐IV) inactivates the incretin hormone glucagon‐like peptide. It can also affect the orexigenic hormone neuropeptide Y (NPY_1–36) which is truncated by DPP‐IV to NPY_3–36, as a consequence NPY’s affinity changes from receptor Y1, which mediates the antilipolytic function of NPY, to other NPY receptors. Little is known whether DPP‐IV inhibitors for the treatment of type 2 diabetic (T2DM) patients could influence these pathways. Aims: To investigate the in vitro effects of NPY with DPP‐IV inhibition in isolated abdominal subcutaneous (AbdSc) adipocytes on fat metabolism, and assessment of NPY receptor and DPP‐IV expression in adipose tissue (AT). Methods: Ex vivo human AT was taken from women undergoing elective surgery (body mass index: 27.5 (mean ± s.d.) ± 5 kg/m², age: 43.7 ± 10 years, n = 36). Isolated AbdSc adipocytes were treated with human recombinant (rh)NPY (1–100 nM) with and without DPP‐IV inhibitor (1 M); glycerol release and tissue distribution of DPP‐IV, Y1 and Y5 messenger RNA (mRNA) were measured and compared between lean and obese subjects. Results and conclusion: rhNPY reduced glycerol release, an effect that was further enhanced by co‐incubation with a DPP‐IV inhibitor [control: 224 (mean ± s.e.) ± 37 μmol/l; NPY, 100 nM: 161 ± 27 μmol/l**; NPY 100 nM/DPP‐IV inhibitor, 1 M: 127 ± 14 μmol/l**; **p < 0.01, n = 14]. DPP‐IV was expressed in AbdSc AT and omental AT with relative DPP‐IV mRNA expression lower in AbdSc AT taken from obese [77 ± 6 signal units (SU)] vs. lean subjects (186 ± 29 SU*, n = 10). Y1 was predominantly expressed in fat and present in all fat depots but higher in obese subjects, particularly the AbdSc AT‐depot (obese: 1944 ± 111 SU vs. lean: 711 ± 112 SU**, n = 10). NPY appears to be regulated by AT‐derived DPP‐IV. DPP‐IV inhibitors augment the antilipolytic effect of NPY in AT. Further studies are required to show whether this explains the lack of weight loss in T2DM patients treated with DPP‐IV inhibitors.     

Expression of fatty-acid-handling proteins in human adipose tissue in relation to obesity and insulin resistance

Aims/hypothesis Protein-mediated trans-membrane and intracellular fatty acid trafficking are becoming increasingly recognised as biochemically and physiologically important concepts. Obesity and insulin resistance are polygenic disorders, heavily influenced by environmental and life-style factors, and are virtually always associated with disturbed fatty acid metabolism in adipose and other tissues. The aim of this study was to investigate mRNA expression levels of fatty-acid-handling proteins in adipose tissue in relation to markers of genetic and acquired obesity and insulin resistance.Methods We quantified mRNA expression of subcutaneous adipose tissue fatty-acid-handling proteins (ALBP, KLBP, FATP1, FATP4, CD36, ACS1) in 17 monozygotic twin-pairs with a range of intra-pair differences () in BMI and detailed measures of obesity and insulin resistance, allowing influences of genetic and non-genetic factors to be distinguished.Results In acquired obesity FATP4 expression was up-regulated independently of genetic background (FATP4 versus BMI; r=0.50, p=0.04; FATP4 versus body fat; r=0.59, p=0.01). Similarly, CD36 and FATP1 expression correlated with acquired differences in HDL cholesterol and non-esterified fatty acid concentrations respectively. Moreover, FATP4 and CD36 expression levels correlated with measures of obesity and insulin resistance that are influenced by both genetic and non-genetic factors (FATP4 versus BMI: r=0.53, p=0.0001; FATP4 versus body fat: r=0.51, p=0.002; FATP4 versus homeostasis model assessment [HOMA]: r=0.49, p=0.001; CD36 versus BMI: r=0.50, p=0.02; CD36 versus body fat: r=0.63, p=0.001; CD36 versus HOMA: r=0.34, p=0.06).Conclusions/interpretation These findings indicate that expression of specific adipose tissue fatty-acid-handling proteins is related to obesity and insulin resistance, and that, in particular, FATP4 plays a role in acquired obesity. Our results suggest that facilitated fatty acid trafficking is a physiologically and pathologically relevant phenomenon in man.Abbreviations ACS acyl-CoA synthase - ALBP adipocyte lipid-binding protein - FABP fatty-acid-binding protein - FATP fatty acid transport protein - HOMA homeostasis model assessment - KLBP keratinocyte lipid-binding protein - MZ monozygotic - TBP TATA-box binding protein - TG triglycerideThis revised version was published online in June 2004 with corrections to title and author addresses.     

Committed subcutaneous preadipocytes are reduced in human obesity

Aims/hypothesis The aim of this study was to test whether the availability of committed preadipocytes in abdominal and femoral subcutaneous adipose tissue varies with obesity and body fat distribution. Methods Body composition, fat cell size, committed preadipocytes and macrophages were measured in subcutaneous abdominal and femoral adipose depots of 17 lean, 16 upper-body-obese (UBO) and 13 lower-body-obese (LBO) women. Preadipocytes and macrophages were identified by simultaneous staining with the respective markers aP2 and CD68. In a subset of samples we measured preadipocyte proliferation, differentiation and susceptibility to apoptosis. Results Abdominal adipocytes were smaller in lean than in obese women. Committed preadipocytes represented a greater fraction of stromovascular cells in lean than in obese women but were similar between UBO and LBO women (abdomen: ∼30 ± 3 vs ∼17 ± 2%; thigh: ∼30 ± 3 vs ∼17 ± 2%). Preliminary data suggested that preadipocyte kinetics were similar in LBO and lean women, whereas preadipocytes of UBO women differentiated less and were more susceptible to apoptotic stimuli. The fraction of stromovascular cells that were macrophages was greater in both depots in obese women (UBO and LBO) than in normal-weight women, but the difference was not statistically significant. Conclusions/interpretation The proportion of subcutaneous adipose tissue stromovascular cells that are committed preadipocytes is reduced with obesity. This could be due to greater recruitment of preadipocytes to adipogenesis or greater preadipocyte apoptosis, depending upon the obesity phenotype. These data are consistent with the concept that body fat distribution may be regulated partly through differences in adipogenesis.