| 1. |
- Arner, Peter, et al.
(författare)
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Dynamics of human adipose lipid turnover in health and metabolic disease
- 2011
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 478:7367, s. 110-113
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Adipose tissue fatty acid metabolism in insulin-resistant men
- 2008
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Ingår i: Diabetologia. - : Springer Science and Business Media LLC. - 1432-0428 .- 0012-186X. ; 51:8, s. 1466-1474
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Tidskriftsartikel (refereegranskat)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. |
- Marinou, Kyriakoula, et al.
(författare)
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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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Ingår i: The British journal of nutrition. - 1475-2662 .- 0007-1145. ; 105:6, s. 857-65
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Tidskriftsartikel (refereegranskat)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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| 4. |
- Miller, Norman E., et al.
(författare)
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Secretion of adipokines by human adipose tissue in vivo : partitioning between capillary and lymphatic transport
- 2011
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Ingår i: 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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Tidskriftsartikel (refereegranskat)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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| 5. |
- Mostad, Ingrid L, et al.
(författare)
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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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Ingår i: Metabolism. - : Elsevier BV. - 0026-0495 .- 1532-8600. ; 58:12, s. 1753-1761
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Risérus, Ulf, et al.
(författare)
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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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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 57:2, s. 332-339
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Tidskriftsartikel (refereegranskat)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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| 7. |
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| 8. |
- Ruge, Toralph, et al.
(författare)
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Fasted to fed trafficking of fatty acids in human adipose tissue reveals a novel regulatory step for enhanced fat storage.
- 2009
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Ingår i: The Journal of clinical endocrinology and metabolism. - : The Endocrine Society. - 1945-7197 .- 0021-972X.
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Tidskriftsartikel (refereegranskat)abstract
- Context: Absence or excess of adipose tissue are both associated with metabolic complications implying the importance of well-functioning adipose tissue present in normal amounts. Adipose tissue sequesters dietary fat and thus protects other tissues from excess fat exposure, especially following meals. Objective: Use of an integrative physiological technique to quantify trafficking of fatty acids (FA) in adipose tissue over a 24-h period. Methods: Adipose tissue FA handling was studied in response to three meals in eight healthy men by the combination of arterio-venous blood sampling, tissue blood flow, and specific labelling of FA tracing of exogenous and endogenous fat by stable isotope methodology. Results: The efficiency of adipose tissue FA uptake increased robustly with each meal. Chylomicron-triglyceride (TG) was the dominating source of FA. Adipose tissue fractional extraction of chylomicron-TG increased from 21+/-4 to 47+/-8% (p=0.03) between the first and last meal. Although adipose tissue lipoprotein lipase (LPL) action increased with time (2-fold), there was an even greater increase in FA re-esterification (3-fold), which led to a reduced spillover of chylomicron-derived FA, from 77+/-15 to 34+/-7% (p=0.04) comparing the end of the first and the third meal period. Increased uptake of VLDL-derived FA was observed, but spillover of VLDL-derived FA was only seen in the fasting state. Conclusion: Human adipose tissue has a significant potential to up-regulate fat storage during a normal day that goes beyond increased LPL activation. The adaptation towards increasing fat storage may provide an explanation for the beneficial properties of normal amounts of adipose tissue.
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| 9. |
- Westerbacka, Jukka, et al.
(författare)
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Splanchnic balance of free fatty acids, endocannabinoids, and lipids in subjects with nonalcoholic fatty liver disease
- 2010
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Ingår i: Gastroenterology. - : Saunders Elsevier. - 0016-5085 .- 1528-0012. ; 139:6, s. 1961-1971.e1
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND & AIMS: Animal studies suggest that endocannabinoids could contribute to the development of nonalcoholic fatty liver disease (NAFLD). In addition, NAFLD has been shown to be associated with multiple changes in lipid concentrations in liver biopsies. There are no data on splanchnic free fatty acid (FFA), glycerol, ketone body, endocannabinoid, and lipid fluxes in vivo in subjects with NAFLD.METHODS: We performed hepatic venous catheterization studies in combination with [(2)H(2)]palmitate infusion in the fasting state and during a low-dose insulin infusion in 9 subjects with various degrees of hepatic steatosis as determined using liver biopsy. Splanchnic balance of endocannabinoids and individual lipids was determined using ultra performance liquid chromatography coupled to mass spectrometry.RESULTS: Concentrations of the endocannabinoid 2-arachidonoylglycerol were higher in arterialized (91 ± 33 μg/L basally) than in hepatic venous (51 ± 19 μg/L; P < .05) plasma. Fasting arterial (r = 0.72; P = .031) and hepatic venous (r = 0.70; P = .037) concentrations of 2-arachidonoylglycerol were related positively to liver fat content. Analysis of fluxes of 85 different triglycerides showed that the fatty liver overproduces saturated triglycerides. In the plasma FFA fraction in the basal state, the relative amounts of palmitoleate and linoleate were lower and those of stearate and oleate were higher in the hepatic vein than in the artery. Absolute concentrations of all nontriglyceride lipids were comparable in arterialized venous plasma and the hepatic vein both in the basal and insulin-stimulated states.CONCLUSIONS: The human fatty liver takes up 2-arachidonoylglycerol and overproduces triacylglycerols containing saturated fatty acids, which might reflect increased de novo lipogenesis.
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