| 1. |
- Arvidsson, E, et al.
(författare)
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Effects of different hypocaloric diets on protein secretion from adipose tissue of obese women
- 2004
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 53:8, s. 1966-1971
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Tidskriftsartikel (refereegranskat)abstract
- Little is known about common factors (e.g., macronutrients and energy supply) regulating the protein secretory function of adipose tissue. We therefore compared the effects of randomly assigned 10-week hypoenergetic (−600 kcal/day) diets with moderate-fat/moderate-carbohydrate or low-fat/high-carbohydrate content on circulating levels and production of proteins (using radioimmunoassays and enzyme-linked immunosorbent assays) from subcutaneous adipose tissue in 40 obese but otherwise healthy women. Similar results were obtained by the two diets. Body weight decreased by ∼7.5%. The secretion rate of leptin decreased by ∼40%, as did that of tumor necrosis factor-α (TNF-α), and interleukin (IL)-6 and -8 decreased by 25–30%, whereas the secretion of plasminogen activator inhibitor 1 (PAI-1) and adiponectin did not show any changes. Regarding mRNA expression (by real-time PCR), only that of leptin and IL-6 decreased significantly. Circulating levels of leptin and PAI-1 decreased by 30 and 40%, respectively, but there were only minor changes in circulating TNF-α, IL-6, or adiponectin. In conclusion, moderate caloric restriction but not macronutrient composition influences the production and secretion of adipose tissue–derived proteins during weight reduction, leptin being the most sensitive and adiponectin and PAI-1 the least sensitive.
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| 2. |
- Bolinder, J, et al.
(författare)
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Rates of skeletal muscle and adipose tissue glycerol release in nonobese and obese subjects
- 2000
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 49:5, s. 797-802
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Tidskriftsartikel (refereegranskat)abstract
- Skeletal muscle and adipose tissue lipolysis rates were quantitatively compared in 12 healthy nonobese and 14 insulin-resistant obese subjects for 3.5 h after an oral glucose load using microdialysis measurements of interstitial glycerol concentrations and determinations of local blood flow with 133Xe clearance in the gastrocnemius muscle and in abdominal subcutaneous adipose tissue. Together with measurements of arterialized venous plasma glycerol, the absolute rates of glycerol mobilization were estimated. In the basal state, skeletal muscle and adipose tissue glycerol levels were 50% higher (P < 0.05-0.01) and adipose tissue blood flow (ATBF) and muscle blood flow (MBF) rates were 30-40% lower (P < 0.02-0.05) in obese versus nonobese subjects. After glucose ingestion, adipose tissue glycerol levels were rapidly and transiently reduced, whereas in muscle, a progressive and less pronounced fall in glycerol levels was evident. MBF remained unchanged in both study groups, whereas ATBF increased more markedly (P < 0.01) in the nonobese versus obese subjects after the oral glucose load. The fasting rates of glycerol release per unit of tissue weight from skeletal muscle were between 20 and 25% of that from adipose tissue in both groups. After glucose ingestion, the rates of glycerol release from skeletal muscle and from adipose tissue were almost identical in nonobese and obese subjects. However, the kinetic patterns differed markedly between tissues; in adipose tissue, the rate of glycerol mobilization was suppressed by 25-30% (P < 0.05) after glucose ingestion, whereas no significant reduction was registered in skeletal muscle. We conclude that significant amounts of glycerol are released from skeletal muscle, which suggests that muscle lipolysis provides an important endogenous energy source in humans. In response to glucose ingestion, the regulation of skeletal muscle glycerol release differs from that in adipose tissue; although the rate of glycerol release from adipose tissue is clearly suppressed, the rate of glycerol mobilization from skeletal muscle remains unaltered. In quantitative terms, the rate of glycerol release per unit of tissue weight in adipose tissue and in skeletal muscle is similar in nonobese and obese subjects in both the postabsorptive state and after glucose ingestion.
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| 3. |
- Ek, I, et al.
(författare)
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A unique defect in the regulation of visceral fat cell lipolysis in the polycystic ovary syndrome as an early link to insulin resistance
- 2002
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Ingår i: Diabetes. - : American Diabetes Association. - 1939-327X .- 0012-1797. ; 51:2, s. 484-492
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Tidskriftsartikel (refereegranskat)abstract
- The etiology of polycystic ovary syndrome (PCOS) is unknown. However, PCOS has a strong resemblance to the insulin resistance (metabolic) syndrome, where an increased rate of visceral fat cell lipolysis is believed to play a pathophysiological role. We hypothesized that primary defects in visceral lipolysis might also exist in PCOS. Ten young, nonobese, and otherwise healthy PCOS women were compared with 13 matched control women. In vitro lipolysis regulation and stoichiometric properties of the final step in lipolysis activation, namely the protein kinase A (PKA)-hormone sensitive lipase (HSL) complex, were investigated in isolated visceral (i.e., omental) fat cells. Body fat distribution and circulating levels of insulin, glucose, and lipids were normal in PCOS women. However, in vivo insulin sensitivity was slightly decreased (P = 0.03). Catecholamine-induced adipocyte lipolysis was markedly (i.e., about twofold) increased in PCOS women due to changes at the postreceptor level, although there was no change in the antilipolytic properties of visceral fat cells. Western blot analyses of visceral adipose tissue showed twofold increased levels of the catalytic and the regulatory la components of PKA. In contrast, the regulatory RIIbeta component of PKA was almost 50% decreased in visceral adipose tissue in PCOS women. Recent studies on genetically modified mice have shown that a similar transition in the regulatory PKA units induces an increased lipolytic response to catecholamines. Further analysis showed that the level of HSL-short, an enzymatically inactive splice form of HSL, was decreased in PCOS (P < 0.01). The altered lipolysis in PCOS is different from that observed in visceral fat cells in the insulin resistance syndrome that occurs at the level of adrenergic receptors. We concluded that increased catecholamine-induced lipolysis in visceral fat cells may be due to unique alterations in the stoichiometric properties of the adipose PKA-HSL holoenzymes. This could be an early and possibly primary lipolysis defect in PCOS.
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| 4. |
- Hagstrom-Toft, E, et al.
(författare)
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Evidence for a major role of skeletal muscle lipolysis in the regulation of lipid oxidation during caloric restriction in vivo
- 2001
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 50:7, s. 1604-1611
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Tidskriftsartikel (refereegranskat)abstract
- A lipolytic process in skeletal muscle has recently been demonstrated. However, the physiological importance of this process is unknown. We investigated the role of skeletal muscle lipolysis for lipid utilization during caloric restriction in eight obese women before and after 11 days of very low–calorie diet (VLCD) (2.2 MJ per day). Subjects were studied with indirect calorimetry and microdialysis of skeletal muscle and adipose tissue in order to analyze substrate utilization and glycerol (lipolysis index) in connection with a two-step euglycemic-hyperinsulinemic (12 and 80 mU/m2 · min) clamp. Local blood flow rates in the two tissues were determined with 133Xe-clearance. Circulating free fatty acids and glycerol decreased to a similar extent during insulin infusion before and during VLCD, and there was a less marked insulin-induced reduction in lipid oxidation during VLCD. Adipose tissue glycerol release was hampered by insulin infusion to the same extent (∼40%) before and during VLCD. Skeletal muscle glycerol release was not influenced by insulin before VLCD. However, during VLCD insulin caused a marked (fivefold) (P < 0.01) increase in skeletal muscle glycerol release. The effect was accompanied by a fourfold stimulation of skeletal muscle blood flow (P < 0.01). We propose that, during short-term caloric restriction, the reduced ability of insulin to inhibit lipids, despite a preserved antilipolytic effect of the hormone in adipose tissue, is caused by an augmented mobilization of fat from skeletal muscle, and that a physiological role of muscle lipolysis provides a local source of fatty acids.
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| 5. |
- Hagstrom-Toft, E, et al.
(författare)
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Marked heterogeneity of human skeletal muscle lipolysis at rest
- 2002
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 51:12, s. 3376-3383
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Tidskriftsartikel (refereegranskat)abstract
- In this study, variations in lipolysis among different muscle groups were examined by measuring local net glycerol release in vivo in healthy, normal-weight subjects (n = 11) during rested, postabsorptive conditions. Microdialysis of the gastrocnemius, deltoid, and vastus lateralis muscle regions revealed that extracellular glycerol concentrations of these three muscle regions were 84.7 ± 6.7, 59.7 + 7.3, and 56.4 ± 7.5 μmol/l, respectively, and the arterial plasma glycerol concentration was 44.8 ± 2.3 μmol/l (P = 0.0003–0.006, gastrocnemius vs. others). Local tissue blood flow, as measured by Xe clearance, did not differ among the regions. Net glycerol release was significantly higher in gastrocnemius muscle than in the two other regions. There were no regional differences in glycerol uptake when studied during glycerol infusion. Gastrocnemius muscle showed a dominance of type 1 fibers (70%), whereas the vastus lateralis muscle had equal distribution of fiber types (P = 0.02). No differences in intramuscular triaclyceride content, perimuscular fat, or the adipocyte-specific protein perilipin were observed among the muscle regions. Triglyceride turnover in the gastrocnemius muscle was 3.3 + 1.4% over 24 h, which is about 10 times more rapid than the turnover rate in subcutaneous adipose tissue (P < 0.01). Thus there were marked differences in lipolytic activity among skeletal muscle groups at rest, possibly reflecting variations in fiber type.
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| 6. |
- Hoffstedt, J, et al.
(författare)
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A common hormone-sensitive lipase i6 gene polymorphism is associated with decreased human adipocyte lipolytic function
- 2001
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 50:10, s. 2410-2413
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Tidskriftsartikel (refereegranskat)abstract
- Hereditary factors may be involved in the pathogenesis of type 2 diabetes. A polymorphism in the hormone-sensitive lipase (HSL) gene (HSLi6) is associated with obesity and diabetes, although it is unknown whether the polymorphism is functional and thereby influences lipolysis. We genotyped 355 apparently healthy nonobese male and female subjects for the HSLi6 polymorphism. Allele 5 was found to be the most common allele (allele frequency 0.57). In 117 of the subjects, we measured abdominal subcutaneous fat cell lipolysis induced by drugs acting at various steps in the lipolytic cascade. The lipolysis rate induced by norepinephrine isoprenaline (acting on β-adrenoceptors), forskolin (acting on adenylyl cyclase), and dibutyryl cyclic AMP (acting on HSL) were all decreased by ∼50% in allele 5 homozygotes, as compared with noncarriers. Heterozygotes showed an intermediate lipolytic rate. The difference in lipolysis rate between genotypes was more pronounced in men than in women. We conclude that allele 5 of the HSLi6 polymorphism is associated with a marked decrease in the lipolytic rate of abdominal fat cells. This may in turn contribute to the development of obesity.
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| 7. |
- Lofgren, P, et al.
(författare)
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Secretion of tumor necrosis factor-alpha shows a strong relationship to insulin-stimulated glucose transport in human adipose tissue
- 2000
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 49:5, s. 688-692
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Tidskriftsartikel (refereegranskat)abstract
- Some animal models suggest that tumor necrosis factor (TNF)-alpha is a key component in obesity-linked insulin resistance because it inhibits insulin receptor signaling and glucose transport in insulin-sensitive tissues. However, in vivo data in humans have given conflicting results regarding the relationship between circulating TNF-alpha levels and insulin sensitivity. In the present study, the potential local role of TNF-alpha on insulin action in human subcutaneous adipose tissue was studied in 42 obese women (BMI 39+/-10 kg/m2). We found a strong inverse correlation between adipose TNF-alpha secretion and maximum insulin-stimulated glucose transport in adipocytes that was independent of fat cell volume, age, and BMI (P < 0.001, r = 0.58). As much as one-third of the variation in insulin-stimulated glucose transport could be accounted for by variations in TNF-alpha secretion. There was no significant correlation (r = 0.11) between secretion of adipose plasminogen activator inhibitor 1 and glucose transport. Furthermore, subcutaneous adipose tissue of 4 obese women (BMI 40+/-4) incubated with TNF-A for 24 h showed a one-third concentration-dependent inhibition of insulin-stimulated glucose transport (P < 0.01). In conclusion, adipose TNF-alpha may be an important specific and local factor in adipose tissue that influences the ability of insulin to stimulate glucose transport in human fat cells, at least in obese women.
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| 8. |
- Ryden, M, et al.
(författare)
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Effect of the (C825T) Gbeta(3) polymorphism on adrenoceptor-mediated lipolysis in human fat cells
- 2002
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 51:5, s. 1601-1608
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Tidskriftsartikel (refereegranskat)abstract
- A common Gβ3 gene polymorphism (C825T) influences G protein receptor-mediated signal transduction. We investigated whether this polymorphism influences lipolysis in isolated subcutaneous fat cells from 114 healthy obese subjects. The Gβ3 protein content was markedly decreased in adipocytes of TT carriers, but the alternatively spliced short form of Gβ3 previously shown in platelets of 825T carriers was not detected. Fat cells of TT carriers showed a significant 10-fold decrease in the half-maximum effective concentration of agonists selective for lipolytic β1- and β2-adrenoceptors as well as for the antilipolytic α2A-adrenoceptor. In TT carriers, maximum β-adrenoceptor agonist-stimulated lipolysis was decreased, but the maximum antilipolytic effect of α2-adrenoceptors was less marked. Norepinephrine induced adipocyte lipolysis and circulating fasting levels of free fatty acids and glycerol were reduced by half in TT carriers. The polymorphism did not influence the adipocyte content of α2A-adrenoceptors, β2-adrenoceptors, Gαi, or Gαs. In conclusion, the C825T variant of Gβ3 influences lipolysis. Adipocytes of TT carriers have a lower Gβ3 protein content and a decreased function of native Gs- as well as Gi-coupled adrenoceptors, which reduces the lipolytic effect of catecholamines. These data differ from those obtained in other cell systems that have shown increased expression of an alternative spliced Gβ3 variant and enhanced G protein signaling in 825T carriers, indicating that the polymorphism has cell type-specific effects that may be of importance for type 2 diabetes and other insulin-resistant conditions.
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| 9. |
- van Harmelen, V, et al.
(författare)
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Increased lipolysis and decreased leptin production by human omental as compared with subcutaneous preadipocytes
- 2002
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 51:7, s. 2029-2036
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Tidskriftsartikel (refereegranskat)abstract
- Site differences in adipose tissue function may have implications for insulin-resistant conditions. In mature adipose tissue, subcutaneous adipocytes have higher leptin secretion, similar tumor necrosis factor (TNF)-α secretion, and lower catecholamine-stimulated lipolysis as compared with omental adipocytes. In this study, lipolysis and leptin and TNF-α secretion were compared between human omental and subcutaneous preadipocytes. After 16 days of incubation in a minimal differentiation medium, leptin mRNA and secretion were found to be two to eight times higher in subcutaneous than omental preadipocytes (P < 0.05). On the other hand, norepinephrine-induced lipolysis was about two times higher in the omental than in the subcutaneous preadipocytes, whereas basal lipolysis did not differ between the two regions. TNF-α secretion was marginally but significantly higher in the omental than in the subcutaneous preadipocytes. Preadipocyte differentiation was equal in both regions and was augmented to the same extent by different thiazolidinediones (rosiglitazone, pioglitazone, or troglitazone) in the two depots. In the presence of rosiglitazone, leptin secretion remained about three times higher and norepinephrine-induced lipolysis about six times lower in subcutaneous as compared with omental preadipocytes (P < 0.05), whereas TNF-α secretion and basal lipolysis were similar in preadipocytes from the two regions. These findings remained unaltered even if rosiglitazone was removed from the medium. However, leptin mRNA showed no regional differences in rosiglitazone-treated cells. Thus, regional differences in adipocyte leptin secretion as well as in norepinephrine-induced lipolysis are marked and present during different stages of preadipocyte differentiation and seem to be determined by intrinsic (i.e., primary) factors.
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| 10. |
- Winzell, M S, et al.
(författare)
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The expression of hormone-sensitive lipase in clonal beta-cells and rat islets is induced by long-term exposure to high glucose
- 2001
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Ingår i: Diabetes. - : American Diabetes Association. - 1939-327X .- 0012-1797. ; 50:10, s. 2225-2230
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Tidskriftsartikel (refereegranskat)abstract
- Hormone-sensitive lipase (HSL) is expressed and enzymatically active in beta-cells and has been proposed to be involved in the generation of the lipid-derived signal that seems to be necessary for glucose-stimulated insulin secretion. In this study, we investigated whether the expression of HSL in INS-1 cells and in rat islets is affected by exposure to high glucose concentrations. Incubation of INS-1 cells in 25 mmol/l glucose for 16 and 32 h induced HSL protein expression twofold, whereas no effect was observed after 4 and 8 h of incubation. The HSL activity, defined as the diglyceride lipase activity inhibited by anti-rat HSL antibodies, constituted approximately 25% of total diglyceride lipase activity and was induced to a similar extent as HSL protein levels. The glucose effect at 16 h on HSL protein expression level was confirmed in freshly isolated rat islets. Exposure of INS-1 cells to different glucose concentrations for 16 h showed that the inductive effect on HSL protein levels was maximum at 20 mmol/l glucose (2- to 2.5-fold). Northern blot analysis demonstrated a more than threefold elevation of HSL mRNA levels. The induction was blocked by actinomycin D, and the half-life of the transcript seemed to be unchanged by high glucose, suggesting a transcriptional nature of the glucose effect on HSL gene expression. The nonmetabolizable glucose analog 2-deoxyglucose, which has no mitogenic effect, induced HSL approximately 1.3-fold, whereas mannose was similar to glucose, stimulating HSL expression 1.7- to 2-fold. The results suggest that HSL is involved in the beta-cell responses to hyperglycemia and also in generating the lipid signal that is needed in stimulus-secretion coupling.
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