| 1. |
- Arner, Peter, et al.
(author)
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Dynamics of human adipose lipid turnover in health and metabolic disease
- 2011
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In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 478:7367, s. 110-113
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Journal article (peer-reviewed)abstract
- Adipose tissue mass is determined by the storage and removal of triglycerides in adipocytes(1). Little is known, however, about adipose lipid turnover in humans in health and pathology. To study this in vivo, here we determined lipid age by measuring (14)C derived from above ground nuclear bomb tests in adipocyte lipids. We report that during the average ten-year lifespan of human adipocytes, triglycerides are renewed six times. Lipid age is independent of adipocyte size, is very stable across a wide range of adult ages and does not differ between genders. Adipocyte lipid turnover, however, is strongly related to conditions with disturbed lipid metabolism. In obesity, triglyceride removal rate (lipolysis followed by oxidation) is decreased and the amount of triglycerides stored each year is increased. In contrast, both lipid removal and storage rates are decreased in non-obese patients diagnosed with the most common hereditary form of dyslipidaemia, familial combined hyperlipidaemia. Lipid removal rate is positively correlated with the capacity of adipocytes to break down triglycerides, as assessed through lipolysis, and is inversely related to insulin resistance. Our data support a mechanism in which adipocyte lipid storage and removal have different roles in health and pathology. High storage but low triglyceride removal promotes fat tissue accumulation and obesity. Reduction of both triglyceride storage and removal decreases lipid shunting through adipose tissue and thus promotes dyslipidaemia. We identify adipocyte lipid turnover as a novel target for prevention and treatment of metabolic disease.
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| 2. |
- Bickerton, A. S. T., et al.
(author)
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Adipose tissue fatty acid metabolism in insulin-resistant men
- 2008
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In: Diabetologia. - : Springer Science and Business Media LLC. - 1432-0428 .- 0012-186X. ; 51:8, s. 1466-1474
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Journal article (peer-reviewed)abstract
- Aims/hypothesis Increased NEFA production and concentrations may underlie insulin resistance. We examined systemic and adipose tissue NEFA metabolism in insulin-resistant overweight men (BM1 25-35 kg/m(2)). Methods In a cohort study we examined NEFA concentrations in men in the upper quartile of fasting insulin (n = 124) and in men with fasting insulin below the median (n 159). In a metabolic study we examined NEFA metabolism in the fasting and postprandial states, in ten insulin-resistant men and ten controls. Results In the cohort study, fasting NEFA concentrations were not significantly different between the two groups (median values: insulin-resistant men, 410 mu mol/l; controls, 445 2 mu mol/l). However, triacylglycerol concentrations differed markedly (1.84 vs 1.18 mmol/l respectively, p<0.001). In the metabolic study, arterial NEFA concentrations again did not differ between groups, whereas triacylglycerol concentrations were significantly higher in insulin-resistant men. Systemic NEFA production and the release of NEFA from subcutaneous adipose tissue, expressed per unit of fat mass, were both reduced in insulin-resistant men compared with controls (fasting values by 32%, p=0.02, and 44%, p=0.04 respectively). 3-Hydroxybutyrate concentrations, an index of hepatic fat oxidation and ketogenesis, were lower (p=0.03). Conclusions/interpretation Adipose tissue NEFA output is not increased (per unit weight of tissue) in insulin resistance. On the contrary, it appears to be suppressed by high fasting insulin concentrations. Alterations in triacylglycerol metabolism are more marked than those in NEFA metabolism. and are indicative of altered metabolic partitioning of fatty acids (decreased oxidation, increased esterification) in the liver.
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| 3. |
- Fernandez, Celine, et al.
(author)
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Altered Desaturation and Elongation of Fatty Acids in Hormone-Sensitive Lipase Null Mice
- 2011
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In: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 6:6
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Journal article (peer-reviewed)abstract
- Background: Hormone-sensitive lipase (HSL) is expressed predominantly in adipose tissue, where it plays an important role in catecholamine-stimulated hydrolysis of stored lipids, thus mobilizing fatty acids. HSL exhibits broad substrate specificity and besides acylglycerides it hydrolyzes cholesteryl esters, retinyl esters and lipoidal esters. Despite its role in fatty acid mobilization, HSL null mice have been shown to be resistant to diet-induced obesity. The aim of this study was to define lipid profiles in plasma, white adipose tissue (WAT) and liver of HSL null mice, in order to better understand the role of this multifunctional enzyme. Methodology/ Principal Findings: This study used global and targeted lipidomics and expression profiling to reveal changed lipid profiles in WAT, liver and plasma as well as altered expression of desaturases and elongases in WAT and liver of HSL null mice on high fat diet. Decreased mRNA levels of stearoyl-CoA desaturase 1 and 2 in WAT were consistent with a lowered ratio of 16:1n7/16:0 and 18:1n9/18:0 in WAT and plasma. In WAT, increased ratio of 18:0/16:0 could be linked to elevated mRNA levels of the Elovl1 elongase. Conclusions: This study illustrates the importance of HSL for normal lipid metabolism in response to a high fat diet. HSL deficiency greatly influences the expression of elongases and desaturases, resulting in altered lipid profiles in WAT, liver and plasma. Finally, altered proportions of palmitoleate, a recently-suggested lipokine, in tissue and plasma of HSL null mice, could be an important factor mediating and contributing to the changed lipid profile, and possibly also to the decreased insulin sensitivity seen in HSL null mice.
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| 4. |
- Fernandez, Celine, et al.
(author)
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Disturbed cholesterol homeostasis in hormone-sensitive lipase-null mice.
- 2008
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In: American journal of physiology. Endocrinology and metabolism. - : American Physiological Society. - 0193-1849 .- 1522-1555. ; 295:4
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Journal article (peer-reviewed)abstract
- Transcriptomics analysis revealed that genes involved in hepatic de novo cholesterol synthesis were downregulated in fed HSL-null mice that had been on a high-fat diet (HFD) for 6 mo. This finding prompted a further analysis of cholesterol metabolism in HSL-null mice, which was performed in fed and 16-h-fasted mice on a normal chow diet (ND) or HFD regimen. Plasma cholesterol was elevated in HSL-null mice, in all tested conditions, as a result of cholesterol enrichment of HDL and VLDL. Hepatic esterified cholesterol content and ATP-binding cassette transporter A1 (ABCA1) mRNA and protein levels were increased in HSL-null mice regardless of the dietary regimen. Unsaturated fatty acid composition of hepatic triglycerides was modified in fasted HSL-null mice on ND and HFD. The increased ABCA1 expression had no major effect on cholesterol efflux from HSL-null mouse hepatocytes. Taken together, the results of this study suggest that HSL plays a critical role in the hydrolysis of cytosolic cholesteryl esters and that increased levels of hepatic cholesteryl esters, due to lack of action of HSL in the liver, are the main mechanism underlying the imbalance in cholesterol metabolism in HSL-null mice.
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| 5. |
- Marinou, Kyriakoula, et al.
(author)
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Young women partition fatty acids towards ketone body production rather than VLDL-TAG synthesis, compared with young men.
- 2011
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In: The British journal of nutrition. - 1475-2662 .- 0007-1145. ; 105:6, s. 857-65
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Journal article (peer-reviewed)abstract
- Before the menopause, women are relatively protected against CVD compared with men. The reasons for this sex difference are not completely understood, but hepatic fatty acid metabolism may play a role. The present study aimed to investigate the utilisation of plasma NEFA by the liver and to determine whether they are partitioned differently into ketone bodies and VLDL-TAG in healthy, lean young men and women. Volunteers were studied during a prolonged overnight fast (12-19 h) using an intravenous infusion of [U-¹³C]palmitate. After 12 h fasting, the women had a more advantageous metabolic profile with lower plasma glucose (P < 0·05) and TAG (P < 0·05) but higher plasma NEFA (P < 0·05) concentrations. Plasma 3-hydroxybutyrate (3-OHB) concentrations rose more in women than in men, and the transfer of ¹³C from [U-¹³C]palmitate to plasma [¹³C]3-OHB reached a plateau 6-7 h after the start of the infusion in women but was still increasing at 6 h in men. This implies a slower 3-OHB production rate and/or dilution by other precursor pools in men. In women, the high isotopic enrichment of plasma 3-OHB suggested that systemic plasma fatty acids were the major source of 3-OHB production. However, in men, this was not observed during the course of the study (P < 0·01). There were no sex differences for the incorporation of ¹³C into VLDL1- or VLDL2-TAG. The ability of young women to partition fatty acids towards ketone body production rather than VLDL-TAG may contribute to their more advantageous metabolic profile compared with young men.
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| 6. |
- Miller, Norman E., et al.
(author)
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Secretion of adipokines by human adipose tissue in vivo : partitioning between capillary and lymphatic transport
- 2011
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In: American Journal of Physiology. Endocrinology and Metabolism. - Bethesda, Md. : American Physiological Society. - 0193-1849 .- 1522-1555. ; 301:4, s. E659-E667
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Journal article (peer-reviewed)abstract
- Peptides secreted by adipose tissue (adipokines) may enter blood via capillaries or lymph. The relative importance of these pathways for a given adipokine might influence its biological effects. Because this has not been studied in any species, we measured the concentrations of seven adipokines and eight nonsecreted proteins in afferent peripheral lymph and venous plasma from 12 healthy men. Data for nonsecreted proteins were used to derive indices of microvascular permeability, which in conjunction with the molecular radii of the adipokines were used to estimate the amounts leaving the tissue via capillaries. Transport rates via lymph were estimated from the lymph adipokine concentrations and lymph flow rates and total transport (secretion) as the sum of this and capillary transport. Concentrations of nonsecreted proteins were always lower in lymph than in plasma. With the exception of adiponectin, adipokine concentrations were always higher in lymph (P < 0.01). Leptin and MCP-1 were secreted at the highest rates (means: 43 mu g/h or 2.7 nmol/h and 32 mu g/h or 2.4 nmol/h, respectively). IL-6 and MCP-1 secretion rates varied greatly between subjects. The proportion of an adipokine transported via lymph was directly related to its molecular radius (r(s) = +0.94, P = 0.025, n = 6), increasing from 14 to 100% as the radius increased from 1.18 (IL-8) to 3.24 nm (TNF alpha). We conclude that the lymph/capillary partitioning of adipokines is a function of molecular size, which may affect both their regional and systemic effects in vivo. This finding may have implications for the physiology of peptides secreted by other tissues.
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| 7. |
- Mostad, Ingrid L, et al.
(author)
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Addition of n-3 fatty acids to a 4-hour lipid infusion does not affect insulin sensitivity, insulin secretion, or markers of oxidative stress in subjects with type 2 diabetes mellitus
- 2009
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In: Metabolism. - : Elsevier BV. - 0026-0495 .- 1532-8600. ; 58:12, s. 1753-1761
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Journal article (peer-reviewed)abstract
- Fatty acids (FA) can impair glucose metabolism to a varying degree depending on time of exposure and also of type of FA. Here we tested for acute effects of marine n-3 FA on insulin sensitivity, insulin secretion, energy metabolism, and oxidative stress. This was a randomized, double-blind, crossover study in 11 subjects with type 2 diabetes mellitus. A 4-hour lipid infusion (Intralipid [Fresenius Kabi, Halden, Norway], total of 384 mL) was compared with a similar lipid infusion partly replaced by Omegaven (Fresenius Kabi) that contributed a median of 0.1 g fish oil per kilogram body weight, amounting to 0.04 g/kg of marine n-3 FA. Insulin sensitivity was assessed by isoglycemic hyperinsulinemic clamps; insulin secretion (measured after the clamps), by C-peptide glucagon tests; and energy metabolism, by indirect calorimetry. Infusion of Omegaven increased the proportion of n-3 FA in plasma nonesterified fatty acids (NEFA) compared with Intralipid alone (20:5n-3: median, 1.5% [interquartile range, 0.6%] vs -0.2% [0.2%], P = .001; 22:6n-3: 0.8% [0.4%] vs -0.7% [0.2%], P = .001). However, glucose utilization was not affected; neither was insulin secretion or total energy production (P = .966, .210, and .423, respectively, for the differences between the lipid clamps). Omegaven tended to lower oxidation of fat (P = .062) compared with Intralipid only, correlating with the rise in individual n-3 NEFA (r = 0.627, P = .039). The effects of clamping on phospholipid FA composition, leptin, adiponectin, or F(2)-isoprostane concentrations were not affected by Omegaven. Enrichment of NEFA with n-3 FA during a 4-hour infusion of Intralipid failed to affect insulin sensitivity, insulin secretion, or markers of oxidative stress in subjects with type 2 diabetes mellitus.
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| 8. |
- Risérus, Ulf, et al.
(author)
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Activation of peroxisome proliferator-activated receptor (PPAR)delta promotes reversal of multiple metabolic abnormalities, reduces oxidative stress, and increases fatty acid oxidation in moderately obese men
- 2008
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In: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 57:2, s. 332-339
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Journal article (peer-reviewed)abstract
- OBJECTIEVE-Pharmacological use of peroxisome proliferator-activated receptor (PPAR)delta agonists and transgenic overexpression of PPAR delta in mice suggest amelioration of features of the metabolic syndrome through enhanced fat oxidation in skeletal muscle. We hypothesize a similar mechanism operates in humans. RESEARCH DESIGN AND METHODS-The PPAR delta agonist (10 mg o.d. GW501516), a comparator PPAR alpha agonist (20 mu g o.d. GW590735)), and placebo were given in a double-blind, randomized, three-parallel group, 2-week study to six healthy moderately overweight subjects in each group. Metabolic evaluation was made before and after treatment including liver fat quantification, fasting blood samples, a 6-h meal tolerance test with stable isotope fatty acids, skeletal muscle biopsy for gene expression, and urinary isoprostanes for global oxidative stress. RESULTS-Treatment with GW501516 showed statistically significant reductions in fasting plasma triglycerides (-30%), apolipoprotein B (-26%), LDL cholesterol (-23%), and insulin (-11%), whereas HDL cholesterol was unchanged. A 20% reduction in liver fat content (P < 0.05) and 30% reduction in urinary isoprostanes (P = 0.01) were also observed. Except for a lowering of triglycerides (-30%, P < 0.05), none of these changes were observed in response to GW590735. The relative proportion of exhaled CO, directly originating from the fat content of the meal was increased (P < 0.05) in response to GW501516, and skeletal muscle expression of carnitine palmitoyl-transferase 1b (CPT1b) was also significantly increased. CONCLUSIONS-The PPAR delta agonist GW501516 reverses multiple abnormalities associated with the metabolic syndrome without increasing oxidative stress. The effect is probably caused by increased fat oxidation in skeletal muscle.
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| 9. |
- Risérus, Ulf, 0067-
(author)
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Conjugated linoleic acid and the metabolic syndrome : Clinical and metabolic studies with special reference to insulin resistance, oxidative stress and inflammation
- 2002
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Doctoral thesis (other academic/artistic)abstract
- The aim of this thesis was to investigate the metabolic effects of conjugated linoleic acid (CLA) in middle-aged men with the metabolic syndrome, a high-risk group for type 2 diabetes. CLA is a group of fatty acid isomers with antiobesity and antidiabetogenic effects in animals, and CLA is therefore used as a supplement in humans. The t10c12CLA isomer seems to mediate these actions, but effects in humans are unknown. In two randomized, double-blind, controlled studies, abdominally obese men were randomized to a t10c12CLA concentrate, an isomer mixture (CLA) or placebo in a dose of ~ 1 % of energy intake. Insulin sensitivity (euglycemic clamp), sagittal abdominal diameter, lipid peroxidation (isoprostanes), plasma inflammation markers (C-reactive protein, TNFa, IL-6), serum IGF-1 and leptin were assessed before and after 1-3 months. CLA had no favorable metabolic effects, despite a slight decrease in sagittal abdominal diameter. In contrast, CLA elevated lipid peroxidation and reduced HDL cholesterol. Unexpectedly, t10c12CLA caused isomer-specific insulin resistance, dyslipidemia, oxidative stress and signs of inflammation, independent of hyperglycemia. Interestingly, induced insulin resistance was related to oxidative stress, and plasma tocopherol levels were related to increased oxidative stress indicating a compensatory mechanism. There are important differences between humans and animals in metabolic response to CLA. In contrast to the hypothesis, t10c12CLA emerged as a unique model of induced metabolic syndrome. Commercial CLA have no beneficial effects in prediabetic men. In contrast, the t10c12CLA content (~40%) in CLA supplements might be diabetogenic and proatherogenic in predisposed subjects. In conclusion, this study reveals clinically relevant isomer-specific insulin resistance of CLA in prediabetic men, possibly via a free-radical linked mechanism. The results provide new physiological insights of the role of specific fatty acids as potent modulators of insulin resistance and inflammation in man with relevance for type 2 diabetes and cardiovascular disease.
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| 10. |
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