OBJECTIVELipotoxicity and ectopic fat deposition reduce insulin signaling. It is not clear whether excess fat deposition in nonadipose tissue arises from excessive fatty acid delivery from adipose tissue or from impaired adipose tissue storage of ingested fat.RESEARCH DESIGN AND METHODSTo investigate this we used a whole-body integrative physiological approach with multiple and simultaneous stable-isotope fatty acid tracers to assess delivery and transport of endogenous and exogenous fatty acid in adipose tissue over a diurnal cycle in lean (n = 9) and abdominally obese men (n = 10).RESULTSAbdominally obese men had substantially (2.5-fold) greater adipose tissue mass than lean control subjects, but the rates of delivery of nonesterified fatty acids (NEFA) were downregulated, resulting in normal systemic NEFA concentrations over a 24-h period. However, adipose tissue fat storage after meals was substantially depressed in the obese men. This was especially so for chylomicron-derived fatty acids, representing the direct storage pathway for dietary fat. Adipose tissue from the obese men showed a transcriptional signature consistent with this impaired fat storage function.CONCLUSIONSEnlargement of adipose tissue mass leads to an appropriate downregulation of systemic NEFA delivery with maintained plasma NEFA concentrations. However the implicit reduction in adipose tissue fatty acid uptake goes beyond this and shows a maladaptive response with a severely impaired pathway for direct dietary fat storage. This adipose tissue response to obesity may provide the pathophysiological basis for ectopic fat deposition and lipotoxicity.

Aims/hypothesis The aim of this study was to explore whether fat cell size in human subcutaneous and omental adipose tissue is independently related to insulin action and adipokine levels. Materials and methods Fat cells were prepared from abdominal subcutaneous biopsies obtained from 49 type 2 diabetic and 83 non-diabetic subjects and from omental biopsies obtained from 37 non-diabetic subjects. Cell size and insulin action on glucose uptake capacity in vitro were assessed in isolated fat cells. Insulin sensitivity in vivo was assessed with euglycaemic-hyperinsulinaemic clamps. Fasting blood samples were collected and adipokines and NEFA were measured. Results Negative correlations were found between subcutaneous fat cell size and insulin sensitivity assessed as M-value during clamp and as insulin action on glucose uptake in fat cells in vitro. This was seen in non-diabetic subjects after including age, sex and BMI in the analyses. No such relationship was found in type 2 diabetic subjects. In both groups, subcutaneous fat cell size correlated positively and independently with plasma levels of leptin but not to any of the other assessed adipokines. In nondiabetic subjects, omental fat cell size was independently and negatively correlated with insulin action in subcutaneous, but not omental, fat cells in vitro.Conclusions/interpretation Fat cell enlargement is associated with insulin resistance in non-diabetic individuals independently of BMI. This was not seen in type 2 diabetic subjects, suggesting that after development of type 2 diabetes other factors, not related to fat cell size, become more important for the modulation of insulin resistance.

Human adipose tissue has a significant potential to up-regulate fat storage during a normal day that goes beyond increased lipoprotein lipase activation. The adaptation toward increasing fat storage may provide an explanation for the beneficial properties of normal amounts of adipose tissue.

Visceral adiposity is associated with insulin resistance and type 2 diabetes. This study explores the metabolic differences between s.c. and visceral fat depots with respect to effects in vitro of glucocorticoids and insulin on glucose uptake. Adipocytes from human s.c. and omental fat depots were obtained during abdominal surgery in 18 nondiabetic subjects. Cells were isolated, and metabolic studies were performed directly after the biopsies and after a culture period of 24 h with or without dexamethasone. After washing, basal and insulin-stimulated [14C]glucose uptake as well as cellular content of insulin signaling proteins and glucose transporter 4 (GLUT4) was assessed. Omental adipocytes had an approximately 2-fold higher rate of insulin-stimulated glucose uptake compared with s.c. adipocytes (P < 0.01). Dexamethasone treatment markedly inhibited (by approximately 50%; P < 0.05) both basal and insulin-stimulated glucose uptake in omental adipocytes but had no consistent effect in s.c. adipocytes. The cellular content of insulin receptor substrate 1 and phosphatidylinositol 3-kinase did not differ significantly between the depots, but the expression of protein kinase B (PKB) tended to be increased in omental compared with s.c. adipocytes (P = 0.09). Dexamethasone treatment decreased the expression of insulin receptor substrate 1 (by approximately 40%; P < 0.05) and PKB (by approximately 20%; P < 0.05) in omental but not in s.c. adipocytes. In contrast, dexamethasone pretreatment had no effect on insulin-stimulated Ser473 phosphorylation of PKB. GLUT4 expression was approximately 4-fold higher in omental than s.c. adipocytes (P < 0.05). Dexamethasone treatment did not alter the expression of GLUT4. In conclusion, human omental adipocytes display approximately 2-fold higher glucose uptake rate compared with s.c. adipocytes, and this could be explained by a higher GLUT4 expression. A marked suppression is exerted by glucocorticoids on glucose uptake and on the expression of insulin signaling proteins in omental but not in s.c. adipocytes. These findings may be of relevance for the interaction between endogenous glucocorticoids and visceral fat in the development of insulin resistance.

During short term fasting, lipoprotein lipase (LPL) activity in rat adipose tissue is rapidly down-regulated. This down-regulation occurs on a posttranslational level; it is not accompanied by changes in LPL mRNA or protein levels. The LPL activity can be restored within 4 h by refeeding. Previously, we showed that during fasting there is a shift in the distribution of lipase protein toward an inactive form with low heparin affinity. To study the nature of the regulatory mechanism, we determined the in vivo turnover of LPL activity, protein mass, and mRNA in rat adipose tissue. When protein synthesis was inhibited with cycloheximide, LPL activity and protein mass decreased rapidly and in parallel with half-lives of around 2 h, and the effect of refeeding was blocked. This indicates that maintaining high levels of LPL activity requires continuous synthesis of new enzyme protein. When transcription was inhibited by actinomycin, LPL mRNA decreased with half-lives of 13.3 and 16.8 h in the fed and fasted states, respectively, demonstrating slow turnover of the LPL transcript. Surprisingly, when actinomycin was given to fed rats, LPL activity was not down-regulated during fasting, indicating that actinomycin interferes with the transcription of a gene that blocks the activation of newly synthesized LPL protein. When actinomycin was given to fasted rats, LPL activity increased 4-fold within 6 h, even in the absence of refeeding. The same effect was seen with ␣-amanitin, another inhibitor of transcription. The response to actinomycin was much less pronounced in aging rats, which are obese and insulin-resistant. These data suggest a default state where LPL protein is synthesized on a relatively stable mRNA and is processed into its active form. During fasting, a gene is switched on whose product prevents the enzyme from becoming active even though synthesis of LPL protein continues unabated. Lipoprotein lipase (LPL)1 plays an important physiological role in regulating the release of fatty acids from triglyceriderich lipoproteins (1-4). The enzyme is synthesized in several extrahepatic tissues, but the highest activities are found in tissues that oxidize (e.g. heart and red skeletal muscle) or store (e.g. adipose tissue) fatty acids. After glycosylation, dimerization, and activation in the endoplasmic reticulum, the enzyme is secreted, transported through the extracellular matrix, and anchored to heparan sulfate proteoglycans on the intraluminal surface of nearby capillaries (3, 4). LPL is regulated at the level of gene expression in several physiological states: during fetal and early postnatal life, the enzyme is present in the liver but is then suppressed (5); in the mammary gland, the enzyme is switched on during lactation (6); in macrophages, it is switched on when the cells are activated (7); and in brown adipose tissue, the enzyme is switched on during cold adaptation (8). In white adipose tissue, LPL activity changes during the day according to the nutritional state. This appears to be mediated by posttranscripti...

Background: We aimed to investigate the associations between circulating endostatin and the different aspects of renal dysfunction, namely, estimated (cystatin C) glomerular filtration rate (GFR) and urine albumin-creatinine ratio (ACR). Methods: Two independent longitudinal community-based cohorts of elderly. ULSAM, n = 786 men; age 78 years; median GFR 74 ml/min/1.73 m²; median ACR 0.80 mg/mmol); and PIVUS, n = 815; age 75 years; 51% women; median GFR; 67 ml/min/1.73 m²; median ACR 1.39 mg/mmol. Cross-sectional associations between the endostatin levels and GFR as well as ACR, and longitudinal association between endostatin at baseline and incident CKD (defined as GFR <60 ml/min/1.73 m²) were assessed. Results: In cross-sectional regression analyses adjusting for age, gender, inflammation, and cardiovascular risk factors, serum endostatin was negatively associated with GFR (ULSAM: B-coefficient per SD increase -0.51, 95% CI (-0.57, -0.45), p < 0.001; PIVUS -0.47, 95% CI (-0.54, -0.41), p < 0.001) and positively associated with ACR (ULSAM: B-coefficient per SD increase 0.24, 95% CI (0.15, 0.32), p < 0.001; PIVUS 0.13, 95% CI (0.06-0.20), p < 0.001) in both cohorts. Moreover, in longitudinal multivariable analyses, higher endostatin levels were associated with increased risk for incident CKD defined as GFR <60 ml/min/1.73 m² at re-investigations in both ULSAM (odds ratio per SD increase of endostatin 1.39 (95% CI 1.01-1.90) and PIVUS 1.68 (95% CI 1.36-2.07)). Conclusions: Higher circulatingendostatin is associated with lower GFR and higher albuminuria and independently predicts incident CKD in elderly subjects. Further studies are warranted to investigate the underlying mechanisms linking endostatin to kidney pathology, and to evaluate the clinical relevance of our findings. i 2014 S. Karger AG, Basel

Abstract-Our aim is to study associations between circulating endostatin, hypertension duration, and hypertensive target-organ damage. Long-term hypertension induces cardiovascular and renal remodeling. Circulating endostatin, a biologically active derivate of collagen XVIII, has been suggested to be a relevant marker for extracellular matrix turnover and remodeling in various diseases. However, the role of endostatin in hypertension and hypertensive targetorgan damage is unclear. Serum endostatin was measured in 2 independent community-based cohorts: the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS; women 51%; n=812; mean age, 75 years) and the Uppsala Longitudinal Study of Adult Men (ULSAM; n=785; mean age, 77.6 years). Retrospective data on blood pressure measurements and antihypertensive medication (PIVUS >5 years, ULSAM >27 years), and cross-sectional data on echocardiographic left ventricular mass, endothelial function (endothelium-dependent vasodilation assessed by the invasive forearm model), and urinary albumin/creatinine ratio were available. In PIVUS, participants with ≥5 years of history of hypertension portrayed 0.42 SD (95% confidence interval, 0.23-0.61; P<0.001) higher serum endostatin, compared with that of normotensives. This association was replicated in ULSAM, in which participants with 27 years hypertension duration had the highest endostatin (0.57 SD higher; 95% confidence interval, 0.35-0.80; P<0.001).In addition, higher endostatin was associated with higher left ventricular mass, worsened endothelial function, and higher urinary albumin/creatinine ratio (P<0.03 for all) in participants with prevalent hypertension. Circulating endostatin is associated with the duration of hypertension, and vascular, myocardial, and renal indices of hypertensive target-organ damage.

The purpose of this investigation was to explore interactions between adrenergic stimulation, glucocorticoids, and insulin on the lipolytic rate in isolated human adipocytes from subcutaneous and omental fat depots, and to address possible sex differences. Fat biopsies were obtained from 48 nondiabetic subjects undergoing elective abdominal surgery. Lipolysis rate was measured as glycerol release from isolated cells and proteins involved in lipolysis regulation were assessed by immunoblots. Fasting blood samples were obtained and metabolic and inflammatory variables were analyzed. In women, the rate of 8-bromo-cAMP- and isoprenaline-stimulated lipolysis was approximately 2- and 1.5-fold higher, respectively, in subcutaneous compared to omental adipocytes, whereas there was no difference between the two depots in men. Dexamethasone treatment increased the ability of 8-bromo-cAMP to stimulate lipolysis in the subcutaneous depot in women, but had no consistent effects in fat cells from men. Protein kinase A, Perilipin A, and hormone sensitive lipase content in adipocytes was not affected by adipose depot, sex, or glucocorticoid treatment. In conclusion, catecholamine and glucocorticoid regulation of lipolysis in isolated human adipocytes differs between adipose tissue depots and also between sexes. These findings may be of relevance for the interaction between endogenous stress hormones and adipose tissue function in visceral adiposity and the metabolic syndrome.