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Risikesan J, Heebøll S, Kumarathas I, Søndergaard E, Johansen RF, Ringgaard S, Aagaard NK, Sandahl TD, Villadsen GE, Gormsen LC, Frystyk J, Jensen MD, Grønbæk H, Nielsen S. Similar insulin regulation of splanchnic FFA and VLDL-TG in men with nonalcoholic hepatic steatosis and steatohepatitis. J Lipid Res 2024; 65:100580. [PMID: 38901559 PMCID: PMC11301221 DOI: 10.1016/j.jlr.2024.100580] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2023] [Revised: 06/10/2024] [Accepted: 06/14/2024] [Indexed: 06/22/2024] Open
Abstract
This study aimed to determine whether obese men with nonalcoholic fatty liver disease (NAFLD) display differences between those with simple steatosis versus steatohepatitis (NASH) in splanchnic and hepatic FFA and VLDL-triglycerides (VLDL-TG) balances. The study involved 17 obese men with biopsy-proven NAFLD (9 with NASH and 8 with simple steatosis). We used hepatic vein catheterization in combination with [3H]palmitate and [14C]VLDL-TG tracers to measure splanchnic palmitate and VLDL-TG uptake and release rates during basal and hyperinsulinemic conditions. Indocyanine green was used to measure splanchnic plasma flow. Splanchnic palmitate uptake was similar in the two groups and significantly reduced during hyperinsulinemia (NASH: 62 (48-77) versus 38 (18-58) μmol/min; simple steatosis: 62 (46-78) versus 45 (25-65) μmol/min, mean (95% CI), basal versus clamp periods, respectively, P = 0.02 time-effect). Splanchnic palmitate release was also comparable between groups and nonsignificantly diminished during hyperinsulinemia. The percent palmitate delivered to the liver originating from visceral adipose tissue lipolysis was similar and unchanged by hyperinsulinemia. Splanchnic uptake and release of VLDL-TG were similar between groups. Hyperinsulinemia suppressed VLDL-TG release (P <0.05 time-effect) in both groups. Insulin-mediated glucose disposal was similar in the two groups (P = 0.54). Obese men with NASH and simple steatosis have similar splanchnic uptake and release of FFA and VLDL-TG and a similar proportion of FFA from visceral adipose tissue lipolysis delivered to the liver. These results demonstrate that the splanchnic balances of FFA and VLDL-TG do not differ between obese men with NASH and those with simple steatosis.
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Affiliation(s)
| | - Sara Heebøll
- Steno Diabetes Center Aarhus, Aarhus University Hospital (AUH), Aarhus, Denmark; Department of Endocrinology and Internal Medicine, AUH, Aarhus, Denmark
| | | | - Esben Søndergaard
- Steno Diabetes Center Aarhus, Aarhus University Hospital (AUH), Aarhus, Denmark
| | - Rakel F Johansen
- Steno Diabetes Center Aarhus, Aarhus University Hospital (AUH), Aarhus, Denmark
| | | | - Niels K Aagaard
- Department of Hepatology and Gastroenterology, AUH, Aarhus, Denmark; Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
| | - Thomas D Sandahl
- Department of Hepatology and Gastroenterology, AUH, Aarhus, Denmark; Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
| | - Gerda E Villadsen
- Department of Hepatology and Gastroenterology, AUH, Aarhus, Denmark; Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
| | - Lars C Gormsen
- Department of Clinical Medicine, Aarhus University, Aarhus, Denmark; Department of Nuclear Medicine and PET Centre, AUH, Aarhus, Denmark
| | - Jan Frystyk
- Department of Endocrinology, Odense University Hospital, Odense, Denmark
| | | | - Henning Grønbæk
- Department of Hepatology and Gastroenterology, AUH, Aarhus, Denmark; Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
| | - Søren Nielsen
- Steno Diabetes Center Aarhus, Aarhus University Hospital (AUH), Aarhus, Denmark; Department of Clinical Medicine, Aarhus University, Aarhus, Denmark.
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Heebøll S, Risikesan J, Ringgaard S, Kumarathas I, Sandahl TD, Grønbæk H, Søndergaard E, Nielsen S. Impaired Glucagon-Mediated Suppression of VLDL-Triglyceride Secretion in Individuals With Metabolic Dysfunction-Associated Fatty Liver Disease (MAFLD). Diabetes 2022; 71:2402-2411. [PMID: 36001750 PMCID: PMC9630084 DOI: 10.2337/db22-0313] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/04/2022] [Accepted: 08/22/2022] [Indexed: 01/25/2023]
Abstract
Individuals with metabolic dysfunction-associated fatty liver disease (MAFLD) have elevated plasma lipids as well as glucagon, although glucagon suppresses hepatic VLDL-triglyceride (TG) secretion. We hypothesize that the sensitivity to glucagon in hepatic lipid metabolism is impaired in MAFLD. We recruited 11 subjects with severe MAFLD (MAFLD+), 10 with mild MAFLD (MAFLD-), and 7 overweight control (CON) subjects. We performed a pancreatic clamp with a somatostatin analog (octreotide) to suppress endogenous hormone production, combined with infusion of low-dose glucagon (0.65 ng/kg/min, t = 0-270 min, LowGlucagon), followed by high-dose glucagon (1.5 ng/kg/min, t = 270-450 min, HighGlucagon). VLDL-TG and glucose tracers were used to evaluate VLDL-TG kinetics and endogenous glucose production (EGP). HighGlucagon suppressed VLDL-TG secretion compared with LowGlucagon. This suppression was markedly attenuated in MAFLD subjects compared with CON subjects (MAFLD+: 13% ± [SEM] 5%; MAFLD-: 10% ± 3%; CON: 36% ± 7%, P < 0.01), with no difference between MAFLD groups. VLDL-TG concentration and VLDL-TG oxidation rate increased between LowGlucagon and HighGlucagon in MAFLD+ subjects compared with CON subjects. EGP transiently increased during HighGlucagon without any difference between the three groups. Individuals with MAFLD have a reduced sensitivity to glucagon in the hepatic TG metabolism, which could contribute to the dyslipidemia seen in MAFLD patients. ClinicalTrials.gov: NCT04042142.
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Affiliation(s)
- Sara Heebøll
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
- Steno Diabetes Center Aarhus, Aarhus University Hospital, Aarhus, Denmark
- Corresponding author: Sara Heebøll,
| | - Jeyanthini Risikesan
- Steno Diabetes Center Aarhus, Aarhus University Hospital, Aarhus, Denmark
- Department of Internal Medicine, Regional Hospital Viborg, Viborg, Denmark
| | - Steffen Ringgaard
- Magnetic Resonance Research Centre, Aarhus University, Aarhus, Denmark
| | - Indumathi Kumarathas
- Steno Diabetes Center Aarhus, Aarhus University Hospital, Aarhus, Denmark
- Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
| | - Thomas D. Sandahl
- Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
- Department of Hepatology and Gastroenterology, Aarhus University Hospital, Aarhus, Denmark
| | - Henning Grønbæk
- Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
- Department of Hepatology and Gastroenterology, Aarhus University Hospital, Aarhus, Denmark
| | - Esben Søndergaard
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
- Steno Diabetes Center Aarhus, Aarhus University Hospital, Aarhus, Denmark
- Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
| | - Søren Nielsen
- Steno Diabetes Center Aarhus, Aarhus University Hospital, Aarhus, Denmark
- Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
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Risikesan J, Nellemann B, Christensen B, Jørgensen JOL, Nielsen S. No effect of 10 weeks erythropoietin treatment on lipid oxidation in healthy men. Endocr Connect 2020; 9:1148-1155. [PMID: 33112835 PMCID: PMC7774772 DOI: 10.1530/ec-20-0305] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/18/2020] [Accepted: 10/13/2020] [Indexed: 11/21/2022]
Abstract
Studies indicate that erythropoietin (EPO) has effect on lipid and energy metabolism; however, the impact of EPO on lipid oxidation in vivo has not been well documented. Here, we evaluate whether long-term erythropoiesis-stimulating agent (ESA) treatment affects the oxidation of plasma very low-density lipoprotein triglycerides (VLDL-TG) fatty acids (FA), plasma free fatty acids (FFA) and non-plasma (residual) FA in healthy, young, sedentary men. Infusion of [1-14C]VLDL-TG and [9,10-3H]palmitate was used in combination with indirect calorimetry to assess resting lipid fuel utilization and kinetics, and resting energy expenditure (REE) before and after 10 weeks of ESA exposure compared with placebo. REE increased significantly during ESA compared with placebo (P = 0.023, RM-ANOVA). Oxidation rates of VLDL-TG FA, FFA, and residual FA remained unchanged during ESA compared with placebo. The relative contribution of the lipid stores was greatest for FFA (47.1%) and the total lipid oxidation rate and was not significantly different between ESA and placebo-treated subjects. We conclude that long-term ESA treatment of healthy young men increases REE but does not alter the oxidation rates of plasma and non-plasma FA sources.
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Affiliation(s)
- Jeyanthini Risikesan
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
| | - Birgitte Nellemann
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
- Department of Rheumatology, Diakonhjemmet Hospital, Oslo, Norway
| | - Britt Christensen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
| | | | - Søren Nielsen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
- Steno Diabetes Center Aarhus, Aarhus University Hospital, Aarhus, Denmark
- Correspondence should be addressed to S Nielsen:
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Gormsen LC, Søndergaard E, Christensen NL, Jakobsen S, Nielsen EHT, Munk OL, Tolbod LP, Jessen N, Nielsen S. Metformin does not affect postabsorptive hepatic free fatty acid uptake, oxidation or resecretion in humans: A 3-month placebo-controlled clinical trial in patients with type 2 diabetes and healthy controls. Diabetes Obes Metab 2018; 20:1435-1444. [PMID: 29405635 DOI: 10.1111/dom.13244] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/07/2017] [Revised: 01/22/2018] [Accepted: 02/01/2018] [Indexed: 12/31/2022]
Abstract
AIMS To explore whether the pre-clinical findings that metformin improves lipid metabolism, possibly through modulation of intrahepatic partitioning of fatty acids towards oxidation and away from re-esterification and resecretion as triglycerides (TGs), can be translated to a human setting. MATERIALS AND METHODS We performed a 3-month randomized, placebo-controlled, parallel-group clinical trial in patients with type 2 diabetes (T2D; n = 24) and healthy controls (n = 12). Patients with T2D received either placebo (placebo group) or 1000 mg metformin twice daily (metformin group), while healthy subjects were all treated with metformin (control group). Hepatic fatty acid metabolism was measured by [11 C]palmitate positron-emission tomography, hepatic TG secretion and peripheral oxidation by ex vivo labelled [1-14 C]VLDL-TG and VLDL particle size by TG/apolipoprotein B ratio. Body composition was assessed by dual-energy X-ray and whole-body lipid oxidation by indirect calorimetry. RESULTS Metformin treatment for 3 months produced the anticipated decrease in fasting plasma glucose (FPG) in the metformin group (FPG 7.9 ± 1.8 mM [study day 1] vs 6.4 ± 1.1 mM [study day 2]), whereas patients in the placebo group and healthy controls had similar FPG levels before and after the trial (mixed model group vs time interaction; P = .003); however, contrary to our hypothesis, metformin treatment did not affect hepatic lipid metabolism or peripheral oxidation. CONCLUSION The observed beneficial effects on lipid metabolism during metformin treatment in humans appear to be secondary to long-term alterations in body composition or glucose homeostasis.
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Affiliation(s)
- Lars C Gormsen
- Department of Nuclear Medicine and PET Centre, Aarhus University Hospital, Aarhus C, Denmark
| | - Esben Søndergaard
- Department of Endocrinology, Aarhus University Hospital, Aarhus C, Denmark
| | - Nana L Christensen
- Department of Nuclear Medicine and PET Centre, Aarhus University Hospital, Aarhus C, Denmark
| | - Steen Jakobsen
- Department of Nuclear Medicine and PET Centre, Aarhus University Hospital, Aarhus C, Denmark
| | - Erik H T Nielsen
- Department of Nuclear Medicine and PET Centre, Aarhus University Hospital, Aarhus C, Denmark
| | - Ole L Munk
- Department of Nuclear Medicine and PET Centre, Aarhus University Hospital, Aarhus C, Denmark
| | - Lars P Tolbod
- Department of Nuclear Medicine and PET Centre, Aarhus University Hospital, Aarhus C, Denmark
| | - Niels Jessen
- Department of Clinical Pharmacology, Aarhus University Hospital, Aarhus C, Denmark
- Department of Biomedicine, Aarhus University, Aarhus C, Denmark
| | - Søren Nielsen
- Department of Endocrinology, Aarhus University Hospital, Aarhus C, Denmark
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Søndergaard E, Nielsen S. VLDL triglyceride accumulation in skeletal muscle and adipose tissue in type 2 diabetes. Curr Opin Lipidol 2018; 29:42-47. [PMID: 29135689 DOI: 10.1097/mol.0000000000000471] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
PURPOSE OF REVIEW Insulin resistance is closely linked to accumulation of lipid outside adipose tissue (ectopic fat storage). VLDL particles transport lipids from the liver to peripheral tissues. However, whether abnormalities in VLDL-triglyceride storage in muscle and adipose tissue exist in type 2 diabetes has previously been unknown, primarily because of methodological difficulties. Here, we review recent research on VLDL-triglyceride storage. RECENT FINDINGS In a recent study, men with type 2 diabetes had increased skeletal muscle VLDL-triglyceride storage compared to weight-matched nondiabetic men, potentially leading to intramyocellular triglyceride accumulation. In contrast, studies of adipose tissue VLDL-triglyceride storage have shown similar storage capacity in men with and without diabetes, both in the postabsorptive and the postprandial period. In the initial submission, studies have failed to show associations between lipoprotein lipase activity, considered the rate-limiting step in storage of lipids from lipoproteins, and VLDL-TG storage in both muscle and adipose tissue. SUMMARY Differences in muscle VLDL-triglyceride storage may lead to ectopic fat storage and contribute to the development of type 2 diabetes, whereas the ability to store VLDL-triglyceride in adipose tissue is preserved in type 2 diabetes.
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Affiliation(s)
- Esben Søndergaard
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus C
- Danish Diabetes Academy, Odense University Hospital, Odense C, Denmark
| | - Søren Nielsen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus C
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Søndergaard E, Johansen RF, Jensen MD, Nielsen S. Postprandial VLDL-TG metabolism in type 2 diabetes. Metabolism 2017; 75:25-35. [PMID: 28964326 DOI: 10.1016/j.metabol.2017.07.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Revised: 06/26/2017] [Accepted: 07/05/2017] [Indexed: 01/22/2023]
Abstract
BACKGROUND Type 2 diabetes is associated with excess postprandial lipemia due to accumulation of chylomicrons and VLDL particles. This is a risk factor for development of cardiovascular disease. However, whether the excess lipemia is associated with an impaired suppression of VLDL-TG secretion and/or reduced clearance into adipose tissue is unknown. OBJECTIVE We measured the postprandial VLDL-TG secretion, clearance and adipose tissue storage to test the hypothesis that impaired postprandial suppression of VLDL-TG secretion, combined with impaired VLDL-TG storage in adipose tissue, is associated with excess postprandial lipemia. DESIGN We studied 11 men with type 2 diabetes and 10 weight-matched non-diabetic men using ex-vivo labeled VLDL-TG tracers during an oral high-fat mixed-meal tolerance test to measure postprandial VLDL-TG secretion, clearance and storage. In addition, adipose tissue biopsies were analyzed for LPL activity and cellular storage factors. RESULTS Men with type 2 diabetes had greater postprandial VLDL-TG concentration compared to non-diabetic men. However, postprandial VLDL-TG secretion rate was similar in the two groups with equal suppression of VLDL-TG secretion rate (≈50%) and clearance rate. In addition, postprandial VLDL-TG storage was similar in the two groups in both upper body and lower body subcutaneous adipose tissue. CONCLUSIONS Despite greater postprandial VLDL-TG concentration, men with type 2 diabetes have similar postprandial suppression of VLDL-TG secretion and a similar ability to store VLDL-TG in adipose tissue compared to non-diabetic men. This may indicate that abnormalities in postprandial VLDL-TG metabolism are a consequence of obesity/insulin resistance more than a result of type 2 diabetes per se.
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Affiliation(s)
- Esben Søndergaard
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Nørrebrogade 44, 8000 Aarhus C, Denmark; Danish Diabetes Academy, Odense University Hospital, Kløvervænget 10, Entrance 112, 3rd floor, 5000 Odense C, Denmark; Endocrine Research Unit, Mayo Clinic, 1216 2nd St SW, Rochester, MN 55902, USA.
| | - Rakel Fuglsang Johansen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Nørrebrogade 44, 8000 Aarhus C, Denmark
| | - Michael D Jensen
- Endocrine Research Unit, Mayo Clinic, 1216 2nd St SW, Rochester, MN 55902, USA
| | - Søren Nielsen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Nørrebrogade 44, 8000 Aarhus C, Denmark
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Søndergaard E, Andersen IR, Sørensen LP, Gormsen LC, Nielsen S. Lipoprotein lipase activity does not predict very low-density lipoprotein-triglyceride fatty acid oxidation during exercise. Scand J Med Sci Sports 2017; 27:474-481. [PMID: 28207959 DOI: 10.1111/sms.12859] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/13/2017] [Indexed: 11/30/2022]
Abstract
Exercise lowers plasma triglyceride levels, but the physiological mechanisms remain not fully elucidated. Lipoprotein lipase (LPL) is a key enzyme in facilitating fatty acid uptake from lipoproteins. As exercise increases the efficiency of very low-density lipoprotein-triglyceride (VLDL-TG) oxidation, we hypothesized that muscle LPL activity would be a rate-limiting step and predict VLDL-TG Fatty acids oxidation during exercise. Sixteen healthy, lean subjects (eight men and eight women) were examined before and during an acute exercise bout (90 minutes at 50% of VO2-max). Heparin-releasable LPL activity was measured in muscle and adipose tissue biopsies. Breath 14 CO2 was measured after a primed-constant infusion of ex vivo labeled [14 C]-triolein VLDL-TG. Fractional VLDL-TG storage was measured in adipose tissue biopsies. Exercise did not affect muscle LPL activity (P=.30). No association was observed between muscle LPL activity and VLDL-TG oxidation, neither in the basal state (P=.17) nor during exercise (P=.83). Exercise did not affect upper body or lower body adipose tissue LPL activity (both P=.92). The basal adipose tissue fractional VLDL-TG storage (abdominal.13%±9%; femoral 17%±10% (P=.18)) was not associated with upper body (P=.56) or lower body (P=.44) subcutaneous adipose tissue LPL activity. Muscle LPL activity does not predict VLDL-TG oxidation during rest or exercise. In addition, adipose tissue LPL activity was not associated with VLDL-TG storage during rest. This suggests that LPL activity is present in excess of what is required to facilitate lipid uptake for oxidation during both rest and exercise.
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Affiliation(s)
- E Søndergaard
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark.,The Danish Diabetes Academy, Odense, Denmark
| | - I R Andersen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
| | - L P Sørensen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
| | - L C Gormsen
- Department of Nuclear Medicine and PET center, Aarhus University Hospital, Aarhus, Denmark
| | - S Nielsen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
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Andersen IR, Søndergaard E, Sørensen LP, Nellemann B, Gormsen LC, Jensen MD, Nielsen S. Increased VLDL-TG Fatty Acid Storage in Skeletal Muscle in Men With Type 2 Diabetes. J Clin Endocrinol Metab 2017; 102:831-839. [PMID: 27898284 DOI: 10.1210/jc.2016-2979] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/15/2016] [Accepted: 11/28/2016] [Indexed: 12/19/2022]
Abstract
CONTEXT Lipoprotein lipase (LPL) activity is considered the rate-limiting step of very-low-density-lipoprotein triglycerides (VLDL-TG) tissue storage, and has been suggested to relate to the development of obesity as well as insulin resistance and type 2 diabetes. OBJECTIVE The objective of the study was to assess the relationship between the quantitative storage of VLDL-TG fatty acids and LPL activity and other storage factors in muscle and adipose tissue. In addition, we examine whether such relations were influenced by type 2 diabetes. DESIGN We recruited 23 men (12 with type 2 diabetes, 11 nondiabetic) matched for age and body mass index. Postabsorptive VLDL-TG muscle and subcutaneous adipose tissue (abdominal and leg) quantitative storage was measured using tissue biopsies in combination with a primed-constant infusion of ex vivo triolein labeled [1-14C]VLDL-TG and a bolus infusion of ex vivo triolein labeled [9,10-3H]VLDL-TG. Biopsies were analyzed for LPL activity and cellular storage factors. RESULTS VLDL-TG storage rate was significantly greater in men with type 2 diabetes compared with nondiabetic men in muscle tissue (P = 0.02). We found no significant relationship between VLDL-TG storage rate and LPL activity or other storage factors in muscle or adipose tissue. However, LPL activity correlated with fractional VLDL-TG storage in abdominal fat (P = 0.04). CONCLUSIONS Men with type 2 diabetes have increased VLDL-TG storage in muscle tissue, potentially contributing to increased intramyocellular triglyceride and ectopic lipid deposition. Neither muscle nor adipose tissue storage rates were related to LPL activity. This argues against LPL as a rate-limiting step in the postabsorptive quantitative storage of VLDL-TG.
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Affiliation(s)
| | - Esben Søndergaard
- Departments of Endocrinology and Internal Medicine and
- Endocrine Research Unit, Mayo Clinic, Rochester, Minnesota 55905; and
- Danish Diabetes Academy, 5000 Odense, Denmark
| | | | | | - Lars C Gormsen
- Department of Nuclear Medicine and PET Center, Aarhus University Hospital, 8000 Aarhus, Denmark
| | - Michael D Jensen
- Endocrine Research Unit, Mayo Clinic, Rochester, Minnesota 55905; and
| | - Søren Nielsen
- Departments of Endocrinology and Internal Medicine and
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Johansen RF, Søndergaard E, Sørensen LP, Jurik AG, Christiansen JS, Nielsen S. Basal and insulin-regulated VLDL1 and VLDL2 kinetics in men with type 2 diabetes. Diabetologia 2016; 59:833-43. [PMID: 26781548 DOI: 10.1007/s00125-015-3856-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/26/2015] [Accepted: 12/08/2015] [Indexed: 12/12/2022]
Abstract
AIMS/HYPOTHESIS Hypertriacylglycerolaemia is a hallmark of diabetic dyslipidaemia with increased concentrations of triacylglycerol (TG)-rich VLDL1 particles. However, whether VLDL1 secretion or removal is abnormal in type 2 diabetes remains unclear. The aim of this study was to compare basal and insulin-mediated VLDL1- and VLDL2-TG kinetics in men with type 2 diabetes and healthy men using a novel direct VLDL1- and VLDL2-TG labelling method. METHODS Twelve men with type 2 diabetes and 12 healthy men matched for age and BMI were recruited. VLDL1- and VLDL2-TG turnover were measured during a 4 h basal period and a 3.5 h hyperinsulinaemic clamp period using a primed-constant infusion of ex vivo labelled VLDL1-TG and VLDL2-TG. RESULTS Basal VLDL1-TG and VLDL2-TG secretion rates were similar in men with diabetes and healthy men. During hyperinsulinaemia, VLDL1-TG secretion rates were suppressed significantly in both groups, whereas no suppression of VLDL2-TG secretion rate was observed. VLDL1-TG to VLDL2-TG transfer rate was not significantly different from zero in both groups, while VLDL1-TG fatty acid oxidation rate was substantial, with a contribution to total energy expenditure of approximately 15% during postabsorptive conditions. VLDL1 and VLDL2 particle size (TG/apolipoprotein B [apoB] ratio) and apoB-100 concentration were unaltered by hyperinsulinaemia in men with type 2 diabetes, but significantly reduced in healthy men. CONCLUSIONS/INTERPRETATION Insulin inhibits VLDL1-TG secretion rate similarly in age- and BMI-matched men with type 2 diabetes and healthy men, while VLDL2-TG secretion is unaltered by hyperinsulinaemia. However, VLDL1- and VLDL2-apoB levels are not lowered by hyperinsulinaemia in men with type 2 diabetes, which is indicative of a diminished hepatic response to insulin. TRIAL REGISTRATION ClinicalTrials.gov NCT01564550.
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Affiliation(s)
- Rakel F Johansen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Nørrebrogade 44, 8000, Aarhus C, Denmark.
| | - Esben Søndergaard
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Nørrebrogade 44, 8000, Aarhus C, Denmark
- The Danish Diabetes Academy, Odense, Denmark
| | - Lars Peter Sørensen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Nørrebrogade 44, 8000, Aarhus C, Denmark
| | - Anne Grethe Jurik
- Department of Radiology, Aarhus University Hospital, Aarhus, Denmark
| | - Jens S Christiansen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Nørrebrogade 44, 8000, Aarhus C, Denmark
| | - Søren Nielsen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Nørrebrogade 44, 8000, Aarhus C, Denmark
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Søndergaard E, Nellemann B, Sørensen LP, Christensen B, Gormsen LC, Nielsen S. Lean body mass, not FFA, predicts VLDL-TG secretion rate in healthy men. Obesity (Silver Spring) 2015; 23:1379-85. [PMID: 26052691 DOI: 10.1002/oby.21108] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/02/2014] [Accepted: 03/10/2015] [Indexed: 11/09/2022]
Abstract
OBJECTIVE Triglyceride is a risk factor for cardiovascular disease. However, the impact of body composition and free fatty acid (FFA) levels on very-low-density-lipoprotein triglyceride (VLDL-TG) secretion remains controversial. The aim was to identify predictors of VLDL-TG secretion in a data set compiled from seven previously published studies. METHODS VLDL-TG kinetics was studied in 96 healthy men covering a wide span in body composition. A primed-constant infusion of ex vivo labeled [1-(14)C]-triolein VLDL-TG was used. Body composition was determined by dual X-ray absorptiometry and computed tomography scanning. Energy expenditure was measured by indirect calorimetry. Palmitate flux was measured by a [9,10-(3)H]-palmitate infusion. RESULTS VLDL-TG secretion rate correlated significantly with body mass index (BMI), lean body mass (LBM), total fat mass, resting energy expenditure (REE), and insulin. A trend toward an inverse relationship between VLDL-TG secretion rate and FFA concentration was observed. In mixed model linear regression analysis, VLDL-TG secretion rate was positively associated with LBM (P = 0.03), and VLDL-TG clearance rate was inversely related to total fat mass (P < 0.01). CONCLUSIONS LBM is a predictor of VLDL-TG secretion in healthy men, whereas FFA availability is not associated with VLDL-TG secretion. The work suggests reporting VLDL-TG secretion rates normalized for LBM when comparing subjects with differences in body composition.
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Affiliation(s)
- Esben Søndergaard
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
- Danish Diabetes Academy, Odense, Denmark
| | - Birgitte Nellemann
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
| | - Lars Peter Sørensen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
| | - Britt Christensen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
| | | | - Søren Nielsen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
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Johansen RF, Søndergaard E, Sørensen LP, Nellemann B, Christiansen JS, Nielsen S. Isolated hyperglycaemia does not increase VLDL-triacylglycerol secretion in type 1 diabetic men. Diabetologia 2015; 58:355-62. [PMID: 25385409 DOI: 10.1007/s00125-014-3422-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/11/2014] [Accepted: 09/26/2014] [Indexed: 12/31/2022]
Abstract
AIMS/HYPOTHESIS In type 1 diabetes, abnormalities of both glucose and lipoprotein metabolism are seen. The relationship between these factors is not understood, but studies indicate that hyperglycaemia may increase hepatic VLDL-triacylglycerol (VLDL-TG) secretion and reduce VLDL-TG fatty acid oxidation, which could lead to the development of dyslipidaemia. The aim of this study was to determine the isolated effect of hyperglycaemia on VLDL-TG and NEFA kinetics in men with type 1 diabetes. METHODS VLDL-TG and palmitate kinetics were measured in eight men with type 1 diabetes using ex vivo labelled VLDL-TG and palmitate tracers. A 2.5 h basal period (plasma glucose 5 mmol/l) was followed by a 4 h hyperglycaemic period (plasma glucose 16 mmol/l). Steady-state VLDL-TG kinetics (VLDL-TG secretion, clearance and oxidation rates) were assessed by an isotope dilution technique using an intravenous primed-constant infusion of ex vivo labelled [1-(14)C]VLDL-TG in combination with sampling of blood and expired air. Palmitate turnover was measured using [9,10-(3)H]palmitate. RESULTS The VLDL-TG secretion rate (36.0 ± 9.6 vs 30.8 ± 6.1 μmol/min, NS) and clearance rate (209 ± 30.4 vs 197 ± 41.7 ml/min, NS) were unchanged during the basal and hyperglycaemic periods, resulting in unchanged VLDL-TG concentrations (0.25 ± 0.11 μmol/l vs 0.28 ± 0.10 μmol/l, NS). In addition, VLDL-TG fatty acid oxidation and palmitate flux were not changed during hyperglycaemia. CONCLUSIONS/INTERPRETATION Four hours of acute hyperglycaemia (16 mmol/l) without a concomitant increase in insulin does not alter VLDL-TG and NEFA kinetics in men with type 1 diabetes. CLINICAL TRIAL REGISTRY NUMBER NCT01178957.
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Affiliation(s)
- Rakel F Johansen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Nørrebrogade 44, 8000, Aarhus C, Denmark,
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12
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Nellemann B, Christensen B, Vissing K, Thams L, Sieljacks P, Larsen MS, Jørgensen JOL, Nielsen S. Ten weeks of aerobic training does not result in persistent changes in VLDL triglyceride turnover or oxidation in healthy men. Eur J Endocrinol 2014; 171:603-13. [PMID: 25117466 DOI: 10.1530/eje-14-0333] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
OBJECTIVE Very low density lipoprotein triglyceride (VLDL-TG) and free fatty acids (FFA) constitute a substantial proportion of human energy supply both at rest and during exercise. Exercise acutely decreases VLDL-TG concentration, and VLDL-TG clearance is increased after an exercise bout. However, the effects of long-term training are not clear. DESIGN The aim was to investigate long-term effects of training by direct assessments of VLDL-TG and palmitate kinetics and oxidation in healthy lean men (n=9) at rest, before and after a 10-week training program, compared with a non-training control group (n=9). METHODS VLDL-TG kinetics were assessed by a primed constant infusion of [1-14C]VLDL-TG, and VLDL-TG oxidation by specific activity (14CO2) in expired air. The metabolic study days were placed 60-72 h after the last exercise bout. RESULTS Palmitate kinetics and oxidation were assessed by a 2 h constant infusion of [9,10-(3)H]palmitate. In the training group (n=9), maximal oxygen uptake increased significantly by ≈20% (P<0.05), and the insulin sensitivity (assessed by the hyperinsulinemic-euglycemic clamp) improved significantly (P<0.05). Despite these metabolic improvements, no changes were observed in VLDL-TG secretion, clearance, or oxidation or in palmitate kinetics. CONCLUSION We conclude that 10 weeks of exercise training did not induce changes in VLDL-TG and palmitate kinetics in healthy lean men.
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Affiliation(s)
- Birgitte Nellemann
- Department of Endocrinology and Internal MedicineAarhus University Hospital, Nørrebrogade 44, 8000 Aarhus C, DenmarkSection of Sports ScienceDepartment of Public Health, Aarhus University, Aarhus, Denmark
| | - Britt Christensen
- Department of Endocrinology and Internal MedicineAarhus University Hospital, Nørrebrogade 44, 8000 Aarhus C, DenmarkSection of Sports ScienceDepartment of Public Health, Aarhus University, Aarhus, Denmark
| | - Kristian Vissing
- Department of Endocrinology and Internal MedicineAarhus University Hospital, Nørrebrogade 44, 8000 Aarhus C, DenmarkSection of Sports ScienceDepartment of Public Health, Aarhus University, Aarhus, Denmark
| | - Line Thams
- Department of Endocrinology and Internal MedicineAarhus University Hospital, Nørrebrogade 44, 8000 Aarhus C, DenmarkSection of Sports ScienceDepartment of Public Health, Aarhus University, Aarhus, Denmark
| | - Peter Sieljacks
- Department of Endocrinology and Internal MedicineAarhus University Hospital, Nørrebrogade 44, 8000 Aarhus C, DenmarkSection of Sports ScienceDepartment of Public Health, Aarhus University, Aarhus, Denmark
| | - Mads Sørensen Larsen
- Department of Endocrinology and Internal MedicineAarhus University Hospital, Nørrebrogade 44, 8000 Aarhus C, DenmarkSection of Sports ScienceDepartment of Public Health, Aarhus University, Aarhus, Denmark
| | - Jens Otto Lunde Jørgensen
- Department of Endocrinology and Internal MedicineAarhus University Hospital, Nørrebrogade 44, 8000 Aarhus C, DenmarkSection of Sports ScienceDepartment of Public Health, Aarhus University, Aarhus, Denmark
| | - Søren Nielsen
- Department of Endocrinology and Internal MedicineAarhus University Hospital, Nørrebrogade 44, 8000 Aarhus C, DenmarkSection of Sports ScienceDepartment of Public Health, Aarhus University, Aarhus, Denmark
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13
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Nellemann B, Søndergaard E, Jensen J, Pedersen SB, Jessen N, Jørgensen JOL, Nielsen S. Kinetics and utilization of lipid sources during acute exercise and acipimox. Am J Physiol Endocrinol Metab 2014; 307:E199-208. [PMID: 24895285 DOI: 10.1152/ajpendo.00043.2014] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Overweight is associated with abnormalities of lipid metabolism, many of which are reversed by exercise. We investigated the impact of experimental antilipolysis and acute exercise on lipid kinetics and oxidation from VLDL-TG, plasma FFA, and "residual lipids" in overweight men (n = 8) using VLDL-TG and palmitate tracers in combination with muscle biopsies in a randomized, placebo-controlled design. Participants received placebo or acipimox on each study day (4 h of rest, 90 min of exercise at 50% V(O(2 max))). Exercise suppressed VLDL-TG secretion significantly during placebo but not acipimox (placebo-rest: 64.2 ± 9.4; placebo-exercise: 48.3 ± 8.0; acipimox-rest: 55.2 ± 13.4; acipimox-exercise: 52.0 ± 10.9). Resting oxidation of VLDL-TG FA and FFA was significantly reduced during acipimox compared with placebo, whereas "residual lipid oxidation" increased significantly [VLDL-TG oxidation (placebo: 18 ± 3 kcal/h; acipimox: 11 ± 2 kcal/h), FFA oxidation (placebo: 14 ± 2 kcal/h; acipimox: 4 ± 0.5 kcal/h), and residual lipid oxidation (placebo: 3 ± 5 kcal/h; acipimox: 14 ± 5 kcal/h)]. Additionally, during exercise on both placebo and acipimox, oxidation of VLDL-TG and FFA increased, but the relative contribution to total lipid oxidation diminished, except for FFA, which remained unchanged during acipimox. Residual lipid oxidation increased significantly during exercise in both absolute and relative terms. Changes in selected cellular enzymes and proteins provided no explanations for kinetic changes. In conclusion, suppressed FFA availability blunts the effect of exercise on VLDL-TG secretion and modifies the contribution of lipid sources for oxidation.
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Affiliation(s)
- Birgitte Nellemann
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark; Department of Physical Performance, Norwegian School of Sport Sciences, Oslo, Norway; and
| | - Esben Søndergaard
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
| | - Jørgen Jensen
- Department of Physical Performance, Norwegian School of Sport Sciences, Oslo, Norway; and
| | - Steen Bønløkke Pedersen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
| | - Niels Jessen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark; Research Laboratory for Biochemical Pathology, Institute for Clinical Medicine, Aarhus University Hospital, Aarhus, Denmark
| | | | - Søren Nielsen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark;
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14
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Bush NC, Triay JM, Gathaiya NW, Hames KC, Jensen MD. Contribution of very low-density lipoprotein triglyceride fatty acids to postabsorptive free fatty acid flux in obese humans. Metabolism 2014; 63:137-40. [PMID: 24140092 PMCID: PMC3859725 DOI: 10.1016/j.metabol.2013.09.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/15/2013] [Revised: 09/06/2013] [Accepted: 09/13/2013] [Indexed: 11/23/2022]
Abstract
OBJECTIVE In the fasting state, plasma free fatty acids (FFA) are thought to derive almost exclusively from adipose tissue lipolysis. However, there are mixed reports as to whether the spillover of fatty acids (FA) from very low-density lipoprotein triglyceride (VLDL-TG) hydrolysis contributes significantly to the plasma FFA pool. Because substantial VLDL-TG fatty acid spillover into the plasma FFA pool would profoundly impact the interpretation of isotope dilution measures of FFA flux, we investigated the contribution of VLDL-TG spillover to plasma FFA appearance. MATERIALS/METHODS Eighteen obese adults (15 women) participated in these studies. Each volunteer received a primed, continuous infusion of their own ex-vivo labeled ([1-(14)C]triolein) VLDL-TG and a continuous infusion of [U-(13)C]oleate (8 nmol · kg fat free mass(-1) · min(-1)) to measure VLDL-TG and FFA rate of appearance (Ra), respectively. The presence of (14)C-oleate in the plasma FFA-oleate pool was used to calculate the contribution of spillover from VLDL-TG-oleate to the plasma FFA-oleate Ra. RESULTS The spillover rate of VLDL-TG-oleate into plasma FFA-oleate was 6 ± 2 μmol/min (7% ± 2% of [(14)C]oleate from VLDL-TG) and FFA-oleate flux was 240 ± 61 μmol/min. Thus, only 3% ± 1% of total plasma FFA-oleate appearance could be accounted for by VLDL-TG spillover. CONCLUSION The contribution of VLDL-TG spillover to the total plasma FFA pool is negligible and will not materially affect the interpretation of FFA flux measures as an index of adipose tissue lipolysis.
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Affiliation(s)
- Nikki C Bush
- Endocrine Research Unit, Mayo Clinic, Rochester, MN 55905, USA
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15
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Høst C, Gormsen LC, Christensen B, Jessen N, Hougaard DM, Christiansen JS, Pedersen SB, Jensen MD, Nielsen S, Gravholt CH. Independent effects of testosterone on lipid oxidation and VLDL-TG production: a randomized, double-blind, placebo-controlled, crossover study. Diabetes 2013. [PMID: 23193189 PMCID: PMC3636625 DOI: 10.2337/db12-0440] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Low testosterone (T) levels in men have been shown to predict development of the metabolic syndrome, but the effects of T on lipid metabolism are incompletely understood. In a randomized, double-blind, placebo-controlled, crossover study, 12 healthy, young males received gonadotropin-releasing hormone agonist treatment 1 month prior to 3 of 4 trial days to induce castrate levels of T. On trial days, T gel was applied to the body containing either high or low physiological T dose or placebo. On the 4th trial day, participants constituted their own eugonadal controls. Each study comprised a 5-h basal period and a 3-h hyperinsulinemic-euglycemic clamp. Short-term hypogonadism did not affect VLDL triglyceride (TG) secretion, nor did it affect VLDL-TG concentrations. It was, however, characterized by lower total lipid oxidation. In addition, acute rescue with high physiological T increased VLDL-TG secretion during both basal and clamp conditions. These data show that T can act through fast nongenomic pathways in the liver. In addition, the early hypogonadal state is characterized by decreased total lipid oxidation, but whether these changes represent early hypogonadal metabolic dysfunction warrants further investigations. T is not a major determinant of resting VLDL-TG kinetics in men.
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Affiliation(s)
- Christian Høst
- Department of Endocrinology and Internal Medicine and the Medical Research Laboratories, Clinical Institute, Aarhus University Hospital, Aarhus, Denmark.
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16
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Søndergaard E, Sørensen LP, Rahbek I, Gormsen LC, Christiansen JS, Nielsen S. Postprandial VLDL-triacylglycerol secretion is not suppressed in obese type 2 diabetic men. Diabetologia 2012; 55:2733-2740. [PMID: 22752024 DOI: 10.1007/s00125-012-2624-z] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/03/2012] [Accepted: 06/06/2012] [Indexed: 10/28/2022]
Abstract
AIMS/HYPOTHESIS Type 2 diabetes is characterised by insulin resistance and increased post-absorptive secretion of VLDL-triacylglycerol (VLDL-TAG). Whether postprandial suppression of endogenous VLDL-TAG secretion is abnormal--a finding that would link hyperlipidaemia and type 2 diabetes--remains unclear. METHODS Eight type 2 diabetic men and eight healthy men were studied before and after a fat-free test meal (40% of resting energy expenditure). VLDL-TAG kinetics were assessed using a primed-constant infusion of ex vivo labelled [1-(14)C]triolein VLDL-TAG using non-steady-state calculations. RESULTS Type 2 diabetic men had a higher basal VLDL-TAG secretion rate and concentration than healthy men (mean ± SD secretion rate 137 ± 61 vs 78 ± 30 μmol/min, respectively [p = 0.03]; median concentration 1.03 [range 0.58-1.75] vs 0.33 [0.13-1.14] mmol/l, respectively [p < 0.01]). Postprandially, the VLDL-TAG secretion rate decreased in healthy men (p < 0.01), but remained unchanged in diabetic men (p = 0.47). The VLDL-TAG concentration increased in diabetic men and decreased in healthy men postprandially (p < 0.05). The difference in VLDL-TAG secretion rate between the two groups approached significance (p = 0.06) and the relative change in VLDL-TAG secretion rate was significantly different (p = 0.01) between the two groups. Basal VLDL-TAG clearance was significantly lower in diabetic men (diabetic men 133 [49-390] ml/min; healthy controls 215 [137-933] ml/min [p < 0.05]). After meal ingestion, clearance decreased in healthy men (p = 0.03), but was unchanged in diabetic men (p = 0.58). CONCLUSIONS/INTERPRETATION Obese type 2 diabetic men have impaired postprandial suppression of VLDL-TAG secretion compared with lean healthy men, contributing to their postprandial lipaemia and hypertriacylglycerolaemia.
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Affiliation(s)
- E Søndergaard
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Nørrebrogade 44, 8000, Aarhus C, Denmark.
| | - L P Sørensen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Nørrebrogade 44, 8000, Aarhus C, Denmark
| | - I Rahbek
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Nørrebrogade 44, 8000, Aarhus C, Denmark
| | - L C Gormsen
- Department of Clinical Physiology and Nuclear Medicine, Aarhus University Hospital, Aarhus, Denmark
| | - J S Christiansen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Nørrebrogade 44, 8000, Aarhus C, Denmark
| | - S Nielsen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Nørrebrogade 44, 8000, Aarhus C, Denmark
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Abstract
PURPOSE OF REVIEW Plasma free fatty acids (FFA) are major substrates for hepatic VLDL-triglycerides (VLDL-TG) production. In addition, it is a common belief that VLDL-TG production is a substrate driven process primarily determined by systemic FFA delivery. This review summarizes recent research of our understanding of the regulation of VLDL-TG production. RECENT FINDINGS Recent studies have shown that increasing FFA flux is not inevitably associated with increased VLDL-TG production. Exercise induced increase in FFA flux resulting in unchanged VLDL-TG production in lean patients as well as in obese patients with increased hepatic fat despite exercise reduced hepatic fat content. With respect to the other inseparable conditions of insulin resistance and hyperinsulinemia, recent studies demonstrate that increased hepatic VLDL-TG production precedes the insulin resistance-associated impairment of the regulation of hepatic glucose production, whereas isolated chronic hyperinsulinemia (insulinoma) was not associated with increased VLDL-TG production. Insulin has been shown to have acute potent temporary suppressing effect on VLDL-TG production and new data demonstrates that increased glucagon reduces VLDL-TG production. Finally, recent studies indicate that sex hormones, oestrogen and testosterone, have no or very modest impact on VLDL-TG production. SUMMARY Regulation of hepatic VLDL-TG production involves interplay between systemic FFA delivery, hormonal, and nutritional factors that act in concert with hepatic fatty acid handling to regulate short-term and long-term VLDL-TG production. The results of recent studies underscore that our current understanding of these relationships is complex and needs further research.
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Affiliation(s)
- Søren Nielsen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
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18
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Søndergaard E, Gormsen LC, Nellemann B, Jensen MD, Nielsen S. Body composition determines direct FFA storage pattern in overweight women. Am J Physiol Endocrinol Metab 2012; 302:E1599-604. [PMID: 22510710 DOI: 10.1152/ajpendo.00015.2012] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Direct FFA storage in adipose tissue is a recently appreciated pathway for postabsorptive lipid storage. We evaluated the effect of body fat distribution on direct FFA storage in women with different obesity phenotypes. Twenty-eight women [10 upper body overweight/obese (UBO; WHR >0.85, BMI >28 kg/m(2)), 11 lower body overweight/obese (LBO; WHR <0.80, BMI >28 kg/m(2)), and 7 lean (BMI <25 kg/m(2))] received an intravenous bolus dose of [9,10-(3)H]palmitate- and [1-(14)C]triolein-labeled VLDL tracer followed by upper body subcutaneous (UBSQ) and lower body subcutaneous (LBSQ) fat biopsies. Regional fat mass was assessed by combining DEXA and CT scanning. We report greater fractional storage of FFA in UBSQ fat in UBO women compared with lean women (P < 0.01). The LBO women had greater storage per 10(6) fat cells in LBSQ adipocytes compared with UBSQ adipocytes (P = 0.04), whereas the other groups had comparable storage in UBSQ and LBSQ adipocytes. Fractional FFA storage was significantly associated with fractional VLDL-TG storage in both UBSQ (P < 0.01) and LBSQ (P = 0.03) adipose tissue. In conclusion, UBO women store a greater proportion of FFA in the UBSQ depot compared with lean women. In addition, LBO women store FFA more efficiently in LBSQ fat cells compared with UBSQ fat cells, which may play a role in development of their LBO phenotype. Finally, direct FFA storage and VLDL-TG fatty acid storage are correlated, indicating they may share a common rate-limiting pathway for fatty acid storage in adipose tissue.
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Affiliation(s)
- E Søndergaard
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Denmark
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Søndergaard E, Nellemann B, Sørensen LP, Gormsen LC, Christiansen JS, Ernst E, Dueholm M, Nielsen S. Similar VLDL-TG storage in visceral and subcutaneous fat in obese and lean women. Diabetes 2011; 60:2787-91. [PMID: 21911742 PMCID: PMC3198059 DOI: 10.2337/db11-0604] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE Excess visceral fat accumulation is associated with the metabolic disturbances of obesity. Differential lipid redistribution through lipoproteins may affect body fat distribution. This is the first study to investigate VLDL-triglyceride (VLDL-TG) storage in visceral fat. RESEARCH DESIGN AND METHODS Nine upper-body obese (UBO; waist circumference >88 cm) and six lean (waist circumference <80 cm) women scheduled for elective tubal ligation surgery were studied. VLDL-TG storage in visceral, upper-body subcutaneous (UBSQ), and lower-body subcutaneous (LBSQ) fat were measured with [9,10-(3)H]-triolein-labeled VLDL. RESULTS VLDL-TG storage in visceral fat accounted for only ~0.8% of VLDL-TG turnover in UBO and lean women, respectively. A significantly larger proportion of VLDL-TG turnover was stored in UBSQ (~5%) and LBSQ (~4%) fat. The VLDL-TG fractional storage was similar in UBO and lean women for all regional depots. VLDL-TG fractional storage and VLDL-TG concentration were correlated in UBO women in UBSQ fat (r = 0.68, P = 0.04), whereas an inverse association was observed for lean women in visceral (r = -0.89, P = 0.02) and LBSQ (r = -0.87, P = 0.02) fat. CONCLUSIONS VLDL-TG storage efficiency is similar in all regional fat depots, and trafficking of VLDL-TG into different adipose tissue depots is similar in UBO and lean women. Postabsorptive VLDL-TG storage is unlikely to be of major importance in the development of preferential upper-body fat distribution in obese women.
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Affiliation(s)
- Esben Søndergaard
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
| | - Birgitte Nellemann
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
| | - Lars P. Sørensen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
| | - Lars C. Gormsen
- Department of Clinical Physiology and Nuclear Medicine, Aarhus University Hospital, Aarhus, Denmark
| | - Jens S. Christiansen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
| | - Erik Ernst
- Department of Gynecology and Obstetrics, Aarhus University Hospital, Aarhus, Denmark
| | - Margit Dueholm
- Department of Gynecology and Obstetrics, Aarhus University Hospital, Aarhus, Denmark
| | - Søren Nielsen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
- Corresponding author: Søren Nielsen,
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Sørensen LP, Søndergaard E, Nellemann B, Christiansen JS, Gormsen LC, Nielsen S. Increased VLDL-triglyceride secretion precedes impaired control of endogenous glucose production in obese, normoglycemic men. Diabetes 2011; 60:2257-64. [PMID: 21810597 PMCID: PMC3161323 DOI: 10.2337/db11-0040] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
OBJECTIVE To assess basal and insulin-mediated VLDL-triglyceride (TG) kinetics and the relationship between VLDL-TG secretion and hepatic insulin resistance assessed by endogenous glucose production (EGP) in obese and lean men. RESEARCH DESIGN AND METHODS A total of 12 normoglycemic, obese (waist-to-hip ratio >0.9, BMI >30 kg/m(2)) and 12 lean (BMI 20-25 kg/m(2)) age-matched men were included. Ex vivo-labeled [1-(14)C]VLDL-TGs and [3-(3)H]glucose were infused postabsorptively and during a hyperinsulinemic-euglycemic clamp to determine VLDL-TG kinetics and EGP. Body composition was determined by dual X-ray absorptiometry and computed tomography scanning. Energy expenditure and substrate oxidation rates were measured by indirect calorimetry. RESULTS Basal VLDL-TG secretion rates were increased in obese compared with lean men (1.25 ± 0.34 vs. 0.86 ± 0.34 μmol/kg fat-free mass [FFM]/min; P = 0.011), whereas there was no difference in clearance rates (150 ± 56 vs. 162 ± 77 mL/min; P = NS), resulting in greater VLDL-TG concentrations (0.74 ± 0.40 vs. 0.38 ± 0.20 mmol/L; P = 0.011). The absolute insulin-mediated suppression of VLDL-TG secretion was similar in the groups. However, the percentage reduction (-36 ± 18 vs. -54 ± 10%; P = 0.008) and achieved VLDL-TG secretion rates (0.76 ± 0.20 vs. 0.41 ± 0.19 μmol/kg FFM/min; P < 0.001) were impaired in obese men. Furthermore, clearance rates decreased significantly in obese men, but there was no significant change in lean men (-17 ± 18 vs. 7 ± 20%; P = 0.007), resulting in less percentage reduction of VLDL-TG concentrations in obese men (-22 ± 20 vs. -56 ± 11%; P < 0.001). Insulin-suppressed EGP was similar (0.4 [0.0-0.8] vs. 0.1 [0.0-1.2] mg/kg FFM/min (median [range]); P = NS), and the percentage reduction was equivalent (-80% [57-98] vs. -98% [49-100], P = NS). Insulin-mediated glucose disposal was significantly reduced in obese men. CONCLUSIONS Basal VLDL-TG secretion rates are increased in normoglycemic but insulin-resistant, obese men, resulting in hypertriglyceridemia. Insulin-mediated suppression of EGP is preserved in obese men, whereas suppression of VLDL-TG secretion is less pronounced in obese men. Compared with EGP, the inability to achieve suppression of VLDL-TG secretions to a level similar to control subjects during hyperinsulinemia seems to be an early manifestation in male obesity.
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Affiliation(s)
- Lars P. Sørensen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
| | - Esben Søndergaard
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
| | - Birgitte Nellemann
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
| | - Jens S. Christiansen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
| | - Lars C. Gormsen
- Department of Nuclear Medicine, Aarhus University Hospital, Aarhus, Denmark
| | - Søren Nielsen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
- Corresponding author: Søren Nielsen,
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Sondergaard E, Rahbek I, Sørensen LP, Christiansen JS, Gormsen LC, Jensen MD, Nielsen S. Effects of exercise on VLDL-triglyceride oxidation and turnover. Am J Physiol Endocrinol Metab 2011; 300:E939-44. [PMID: 21386064 PMCID: PMC3279302 DOI: 10.1152/ajpendo.00031.2011] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Lipids are important substrates for oxidation at rest and during exercise. Aerobic exercise mediates a delayed onset decrease in total and VLDL-triglyceride (TG) plasma concentration. However, the acute effects of exercise on VLDL-TG oxidation and turnover remain unclear. Here, we studied the acute effects of 90 min of moderate-intensity exercise in healthy women and men. VLDL-TG kinetics were assessed using a primed constant infusion of ex vivo labeled [1-(14)C]triolein VLDL-TG. Fractional VLDL-TG-derived fatty acid oxidation was measured from (14)CO(2) specific activity in expired air. VLDL-TG concentration was unaltered during exercise and early recovery, whereas non-VLDL-TG concentration decreased significantly.VLDL-TG secretion rate decreased significantly during exercise and remained suppressed during recovery. Total VLDL-TG oxidation rate was unaffected by exercise. However, the contribution of VLDL-TG oxidation to total energy expenditure fell from 14 ± 9% at rest to 3 ± 4% during exercise. We conclude that VLDL-TG fatty acids are quantitatively important oxidative substrates under basal postabsorptive conditions but remain unaffected during 90-min moderate-intensity exercise and, thus, become relatively less important during exercise. Lower VLDL secretion rate during exercise may contribute to the decrease in TG concentrations during and after exercise.
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Affiliation(s)
- Esben Sondergaard
- Dept. of Endocrinology and Internal Medicine, Aarhus Univ. Hospital, Norrebrogade 44, DK-8000 Aarhus C, Denmark
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Sørensen LP, Andersen IR, Søndergaard E, Gormsen LC, Schmitz O, Christiansen JS, Nielsen S. Basal and insulin mediated VLDL-triglyceride kinetics in type 2 diabetic men. Diabetes 2011; 60:88-96. [PMID: 20858686 PMCID: PMC3012201 DOI: 10.2337/db10-0564] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
OBJECTIVE Increased very-low-density lipoprotein triglycerides (VLDL-TG) concentration is a central feature of diabetic dyslipidemia. The objective was to compare basal and insulin mediated VLDL-TG kinetics, oxidation, and adipose tissue storage in type 2 diabetic and healthy (nondiabetic) men. RESEARCH DESIGN AND METHODS Eleven type 2 diabetic and 11 healthy men, matched for BMI and age, were included. Ex vivo-labeled VLDL-TG tracers, blood and breath samples, fat biopsies, indirect calorimetry, and body composition measures were applied to determine VLDL-TG kinetics, VLDL-TG fatty acids (FA) oxidation, and storage in regional adipose tissue before and during a hyperinsulinemic euglycaemic clamp. RESULTS VLDL-TG secretion was significantly greater in diabetic compared with healthy men (basal: 86.9 [31.0] vs. 61.9 [30.0] μmol/min, P = 0.03; clamp: 60.0 [26.2] vs. 34.2 [17.9] μmol · min⁻¹, P = 0.01). The insulin mediated suppression of VLDL-TG secretion was significant in both groups. VLDL-TG clearance was lower in diabetic men (basal: 84.6 [32.7] vs. 115.4 [44.3] ml · min⁻¹, P = 0.08; clamp: 76.3 [30.6] vs. 119.0 [50.2] ml · min⁻¹, P = 0.03). During hyperinsulinemia fractional VLDL-TG FA oxidation was comparable, but in percentage of energy expenditure (EE), significantly higher in diabetic men. Basal VLDL-TG storage was similar, but significantly greater in abdominal compared with leg fat. CONCLUSIONS Increased VLDL-TG in type 2 diabetic men is caused by greater VLDL-TG secretion and less so by lower VLDL-TG clearance. The ability of hyperinsulinemia to suppress VLDL-TG secretion appears preserved. During hyperinsulinemia VLDL-TG FA oxidation is significantly increased in proportion of EE in type 2 diabetic men. Greater basal abdominal VLDL-TG storage may help explain the accumulation of upper-body fat in insulin-resistant individuals.
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Affiliation(s)
- Lars P. Sørensen
- Department of Endocrinology and Internal Medicine, University Hospital, Aarhus, Denmark
| | - Iben R. Andersen
- Department of Endocrinology and Internal Medicine, University Hospital, Aarhus, Denmark
| | - Esben Søndergaard
- Department of Endocrinology and Internal Medicine, University Hospital, Aarhus, Denmark
| | - Lars C. Gormsen
- Department of Nuclear Medicine, University Hospital, Aarhus, Denmark
| | - Ole Schmitz
- Department of Clinical Pharmacology, University of Aarhus, Aarhus, Denmark
| | - Jens S. Christiansen
- Department of Endocrinology and Internal Medicine, University Hospital, Aarhus, Denmark
| | - Søren Nielsen
- Department of Endocrinology and Internal Medicine, University Hospital, Aarhus, Denmark
- Corresponding author: Søren Nielsen,
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23
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Gormsen LC, Høst C, Hjerrild BE, Gravholt CH, Nielsen S. Acute estrogen exposure does not affect basal very low-density lipoprotein-triglyceride production or oxidation in postmenopausal women. Eur J Endocrinol 2010; 163:421-6. [PMID: 20566588 DOI: 10.1530/eje-10-0551] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
CONTEXT Long-term hormone replacement therapy (HRT) with estradiol (E(2)) is associated with an altered lipid profile including unfavorable increases in triglyceride (TG) concentrations and augmented hepatic very low-density lipoprotein (VLDL)-TG production. There are indications that this effect of estrogens may be immediate. OBJECTIVE To study the in vivo effect of a single dose of E(2) on VLDL-TG kinetics and oxidation in humans. METHODS Eight healthy, postmenopausal women were given a single dose of either placebo or E(2) (4 mg) orally. VLDL-TG kinetics was assessed by a 240-min primed-continuous infusion of ex vivo labeled [1-(14)C]triolein-labeled VLDL. Fractional and absolute VLDL-TG oxidation was determined by hyamin trapping of exhaled (14)C label. Indirect calorimetry provided measurements of lipid oxidation. RESULTS Administration of 4 mg of E(2) orally rapidly increased plasma E(2) concentrations from below detection threshold to premenopausal levels. Free fatty acids (FFA) and TG concentrations were unaltered. No immediate effect was observed on either VLDL-TG production (placebo versus E(2)): 20.0+/-12.4 vs 24.1+/-10.7 micromol/min, P=0.33; VLDL-TG oxidation: 12.3+/-10.9 vs 12.6+/-5.6 micromol/min, P=0.93); or VLDL-TG clearance rates: 51.4+/-16.8 vs 64.9+/-28.8 ml/min, P=0.34). CONCLUSIONS Short-term E(2) elevation does not affect VLDL-TG production, oxidation, or clearance in humans. We therefore propose that HRT-associated dyslipidemia has a gradual rather than immediate onset.
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Affiliation(s)
- Lars C Gormsen
- Medical Department M (Endocrinology and Diabetes), Aarhus University Hospital, DK-8000 Aarhus, Denmark.
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24
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Nellemann B, Gormsen LC, Christiansen JS, Jensen MD, Nielsen S. Postabsorptive VLDL-TG fatty acid storage in adipose tissue in lean and obese women. Obesity (Silver Spring) 2010; 18:1304-11. [PMID: 19875996 PMCID: PMC2893248 DOI: 10.1038/oby.2009.370] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Adipose tissue lipoprotein lipase (LPL) is a necessary enzyme for storage of very-low-density lipoprotein-triglyceride (VLDL-TG), but whether it is a rate-determining step is unknown. To test this hypothesis we included 10 upper-body obese (UBO), 11 lower-body obese (LBO), and 8 lean women. We infused ex vivo-labeled VLDL-(14)C-TG and then performed adipose tissue biopsies to understand the relationship between VLDL-TG storage and LPL activity in femoral and upper-body subcutaneous fat. Both fractional tracer storage and rate of storage of the VLDL-TG tracer were evaluated. VLDL-TG storage was also examined as a function of regional adipose tissue blood flow (ATBF), insulin, VLDL-TG turnover, regional fat mass, fat-free mass (FFM), and fat cell size. LPL activity per adipocyte was significantly greater in obese than lean women but not significantly different per gram lipid. Both VLDL-TG fractional tracer storage per kg lipid and VLDL-TG storage rate per kg lipid were similar in abdominal and femoral fat in all three groups and were not significantly different between groups. Multiple regression analysis identified FFM and femoral fat mass as significant independent predictors of VLDL-TG fractional tracer storage and insulin as a significant predictor of VLDL-TG fatty acid storage rate. LPL activity, ATBF, and VLDL-TG turnover did not predict VLDL-TG storage. We conclude that lower FFM and greater plasma insulin are associated with greater VLDL-TG deposition in abdominal subcutaneous and femoral fat. Greater femoral fat mass signals greater femoral VLDL-TG storage. We suggest that the differences in VLDL-TG storage in abdominal and femoral fat that occur with progressive obesity are regulated through mechanisms other than LPL activity.
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25
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Sørensen LP, Gormsen LC, Nielsen S. VLDL-TG kinetics: a dual isotope study for quantifying VLDL-TG pool size, production rates, and fractional oxidation in humans. Am J Physiol Endocrinol Metab 2009; 297:E1324-30. [PMID: 19773577 DOI: 10.1152/ajpendo.00366.2009] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Very-low-density lipoproteins (VLDLs) are large, complex particles containing both surface proteins (e.g., ApoB100) and core lipids, e.g., cholesterol and triglycerides (TG). Whereas ApoB100 kinetics have been thoroughly studied, accurate measurement of VLDL-TG kinetics have proven difficult due to either complex mathematics or laborious procedures. The present study was therefore designed to measure VLDL-TG kinetics by dual isotope ex vivo labeled VLDL-TG tracers and well-established kinetics equations (bolus injection or the primed continuous infusion). Ten healthy Caucasian men [age, 23 +/- 3 yr old (mean +/- SD); body mass index, 24.7 +/- 1.3 kg/m(2)] were included in the study. VLDL-TG rate of appearance (Ra) was measured using a dual-tracer technique ([9,10-(3)H]-labeled VLDL-TG and [1-(14)C]-labeled VLDL-TG) to allow comparison of various bolus decay curve fits with the Ra obtained by the primed continuous infusion (PCI; considered the gold standard). In addition, VLDL-TG fatty acid oxidation was measured as (14)CO(2) in exhaled breath, using the hyamine trapping technique. Following a bolus injection, tracer decay was better described by a biexponential than a monoexponential fit (r(2) = 0.99 +/- 0.01 vs. 0.97 +/- 0.04, respectively, P = 0.01). VLDL-TG Ra calculated using the PCI correlated significantly with the biexponential fit (rho = 0.62, P < 0.05), whereas this was not the case for the monoexponential fit (rho = -0.18, P = not significant). VLDL-TG Ra using the best fit of the bolus injection method (biexponential) was less than values obtained by the constant infusion technique [biexponential, 34.3 (range, 27.1-69.6) vs. PCI, 44.4 (range, 33.0-72.7), P < 0.05]. Fractional oxidation of VLDL-TG was 37.2 +/- 8.8% at 240 min corresponding to 198.8 +/- 55.9 kcal/day or 10.6 +/- 3.3% of resting energy expenditure (REE). Our data demonstrate that VLDL-TG Ra measured by a biexponential fit to a bolus decay curve correlates well with VLDL-TG Ra measured by a primed continuous infusion, and therefore that a "second" peripheral VLDL-TG compartment with rapid exchange of TG exists. VLDL-TG volume of distribution is therefore greater than previously anticipated. Finally our data supports that VLDL-TG contributes quantitatively to REE.
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Affiliation(s)
- Lars P Sørensen
- Medical Department M, Aarhus University Hospital, Aarhus, Denmark
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26
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Magkos F, Mittendorfer B. Stable isotope-labeled tracers for the investigation of fatty acid and triglyceride metabolism in humans in vivo. ACTA ACUST UNITED AC 2009; 4:215-230. [PMID: 20161007 DOI: 10.2217/clp.09.9] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Understanding lipid metabolism and its regulation requires information on the rates at which lipids are produced within the body, absorbed (dietary lipids) into the body, transported within the body, and utilized by various tissues. This article focuses on the use of stable isotope-labeled tracers for the quantitative evaluation of major pathways of fatty acid and triglyceride metabolism in humans in vivo. Adipose tissue lipolysis and free fatty acid appearance in plasma, fatty acid tissue uptake and oxidation, and hepatic very low-density lipoprotein triglyceride secretion are among the metabolic pathways that can be studied by using stable isotope labeled tracers, and will be discussed in detail. The methodology has been in use for many years and is constantly being refined. A variety of tracers and analytical approaches are available and can be used; knowing the advantages, assumptions, and limitations of each is essential for the planning of studies and the interpretation of data, which can provide unique insights into human lipid metabolism.
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Affiliation(s)
- Faidon Magkos
- Center for Human Nutrition, Washington University School of Medicine, St. Louis, MO, USA
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27
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Gormsen LC, Nellemann B, Sørensen LP, Jensen MD, Christiansen JS, Nielsen S. Impact of body composition on very-low-density lipoprotein-triglycerides kinetics. Am J Physiol Endocrinol Metab 2009; 296:E165-73. [PMID: 18984851 DOI: 10.1152/ajpendo.90675.2008] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Upper body obese (UBO) subjects have greater cardiovascular disease risk than lower body obese (LBO) or lean subjects. Obesity is also associated with hypertriglyceridemia that may involve greater production and impaired removal of very-low-density lipoprotein (VLDL)-triglycerides (TG). In these studies, we assessed the impact of body composition on basal VLDL-TG production, VLDL-TG oxidation, and VLDL-TG storage. VLDL-TG kinetics were assessed in 10 UBO, 10 LBO, and 10 lean women using a bolus injection of [1-(14)C]VLDL-TG. VLDL-TG oxidation was measured by (14)CO(2) production (hyamine trapping) and VLDL-TG adipose tissue storage by fat biopsies. Insulin sensititvity was assessed by the hyperinsulinemic-euglycemic clamp technique and body composition by dual X-ray absorptiometry in combination with computed tomography. Hepatic VLDL-TG production was significantly greater in UBO than in lean women [(mumol/min) UBO: 64.8 (SD 40.0) vs. LBO: 42.5 (SD 25.6) vs. lean: 31.8 (SD 13.3), P = 0.04], whereas VLDL-TG oxidation was similar in the three groups and averaged 20% of resting energy expenditure [(mumol/min) UBO: 38.3 (SD 26.5) vs. LBO: 23.5 (SD 13.5) vs. lean: 21.1 (SD 9.7), P = 0.09]. In UBO women, more VLDL-TG was deposited in upper body subcutaneous fat [VLDL-TG redeposition in abdominal adipose tissue (mumol/min): UBO: 5.0 (SD 2.9) vs. LBO: 4.0 (SD 3.2) vs. lean: 1.3 (SD 1.0), ANOVA P = 0.01]; in LBO women, more VLDL-TG was deposited in femoral fat [VLDL-TG redeposition in femoral adipose tissue (mumol/min): UBO: 5.1 (SD 3.1) vs. LBO: 5.8 (SD 4.3) vs. lean: 2.3 (SD 1.5), ANOVA P = 0.04]. Only a small proportion of VLDL-TG (8-16%) was partitioned into redeposition in either group. We found that elevated VLDL-TG production without concomitant increased clearance via oxidation and adipose tissue redeposition contributes to hypertriglyceridemia in UBO women.
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Affiliation(s)
- Lars C Gormsen
- Dept. of Nuclear Medicine, Aarhus Univ. Hospital, DK-8000 Aarhus C, Denmark.
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28
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Nelson RH, Basu R, Johnson CM, Rizza RA, Miles JM. Splanchnic spillover of extracellular lipase-generated fatty acids in overweight and obese humans. Diabetes 2007; 56:2878-84. [PMID: 17881612 DOI: 10.2337/db07-0812] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
OBJECTIVE Triglyceride-rich lipoproteins, primarily chylomicrons, can contribute to plasma free fatty acid (FFA) concentrations via spillover of fatty acids during intravascular hydrolysis into the venous effluent of some tissues. The present study was undertaken to determine whether spillover occurs in the splanchnic bed of humans. RESEARCH DESIGN AND METHODS Arterial and hepatic venous blood was sampled in postabsorptive (n = 6; study A) and postprandial (n = 5; study B) obese humans during infusion of carbon-labeled ((14)C or (13)C) oleate and (3)H triolein, the latter incorporated into a lipid emulsion as a surrogate for chylomicrons. Spillover was determined by measuring production of (3)H oleate. RESULTS Splanchnic spillover was higher than nonsplanchnic systemic spillover in both study A (60 +/- 7 vs. 24 +/- 6%; P < 0.01) and study B (54 +/- 3 vs. 16 +/- 5%; P < 0.005). Because portal vein sampling is not feasible in humans, assumptions regarding actual spillover in nonhepatic splanchnic tissues were required for the spillover calculation. A mathematical model was developed and demonstrated that nonhepatic splanchnic spillover rates in study A and study B of 69 and 80%, respectively, provided the best fit with the data. There was preferential splanchnic uptake of triglyceride fatty acids compared with FFAs in study B (fractional extraction 61 +/- 3 vs. 33 +/- 2%; P < 0.005). CONCLUSIONS These data confirm previous studies indicating that the transport of FFAs and triglyceride fatty acids are partitioned in tissues and indicate that splanchnic spillover from triglyceride-rich lipoproteins may be a significant source of both portal venous and systemic FFAs.
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Affiliation(s)
- Robert H Nelson
- Endocrine Research Unit, Division of Endocrinology, Metabolism, Diabetes and Nutrition, Mayo Clinic, 200 First St. SW, Rochester, MN 55905, USA
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29
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Nelson RH, Edgerton DS, Basu R, Roesner JC, Cherrington AD, Miles JM. Triglyceride uptake and lipoprotein lipase-generated fatty acid spillover in the splanchnic bed of dogs. Diabetes 2007; 56:1850-5. [PMID: 17416801 DOI: 10.2337/db06-1657] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The action of lipoprotein lipase on triglyceride-rich lipoproteins generates fatty acids that are either transported into tissues or mix with circulating free fatty acids (FFAs) via a process known as spillover. In the present study, arterial, portal vein, and hepatic vein sampling catheters were surgically placed in nine mongrel dogs. The animals were subsequently studied after a 42-h fast during infusion of [14C]oleate and a lipid emulsion containing [3H]triolein; the emulsion was used as a surrogate for the study of chylomicron metabolism. More than one-half of splanchnic [3H]triglyceride uptake occurred in the liver, and substantial fractional spillover of [3H]oleate was observed in both liver and nonhepatic tissues (approximately 50% each). There was a significant correlation between FFA release from nonhepatic tissues (presumably visceral fat) and nonhepatic fractional spillover (R = 0.81, P < 0.01), consistent with a model in which the rate of intracellular lipolysis influences spillover by determining the direction of net fatty acid flow between the cell and the interstitium. There was a significant correlation between "true" and "net" splanchnic spillover (R = 0.84, P < 0.005), the latter representing calculation of spillover between arterial and hepatic venous blood without portal venous data. Metabolism of chylomicron triglycerides in visceral fat may be an important source of portal venous FFAs.
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Affiliation(s)
- Robert H Nelson
- Endocrine Research Unit, Mayo Clinic, 200 First St. SW, Rochester, MN 55905, USA
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30
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Krag MB, Gormsen LC, Guo Z, Christiansen JS, Jensen MD, Nielsen S, Jørgensen JOL. Growth hormone-induced insulin resistance is associated with increased intramyocellular triglyceride content but unaltered VLDL-triglyceride kinetics. Am J Physiol Endocrinol Metab 2007; 292:E920-7. [PMID: 17132823 DOI: 10.1152/ajpendo.00374.2006] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The ability of growth hormone (GH) to stimulate lipolysis and cause insulin resistance in skeletal muscle may be causally linked, but the mechanisms remain obscure. We investigated the impact of GH on the turnover of FFA and VLDL-TG, intramuscular triglyceride content (IMTG), and insulin sensitivity (euglycemic clamp) in nine healthy men in a randomized double-blind placebo-controlled crossover study after 8 days treatment with (A) Placebo+Placebo, (B) GH (2 mg daily)+Placebo, and (C) GH (2 mg daily)+Acipimox (250 mgx3 daily). In the basal state, GH (B) increased FFA levels (P<0.05), palmitate turnover (P<0.05), and lipid oxidation (P=0.05), but VLDL-TG kinetics were unaffected. Administration of acipimox (C) suppressed basal lipolysis but did not influence VLDL-TG kinetics. In the basal state, IMTG content increased after GH (B; P=0.03). Insulin resistance was induced by GH irrespective of concomitant acipimox (P<0.001). The turnover of FFA and VLDL-TG was suppressed by hyperinsulinemia during placebo and GH, whereas coadministration of acipimox induced a rebound increase FFA turnover and VLDL-TG clearance. We conclude that these results show that GH-induced insulin resistance is associated with increased IMTG and unaltered VLDL-TG kinetics; we hypothesize that fat oxidation in muscle tissue is an important primary effect of GH and that circulating FFA rather than VLDL-TG constitute the major source for this process; and the role of IMTG in the development of GH-induced insulin resistance merits future research.
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Affiliation(s)
- Morten B Krag
- Medical Department M, Endocrinology and Diabetes, Aarhus University Hospital, DK-8000 Aarhus C, Denmark
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31
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Nelson RH, Prasad A, Lerman A, Miles JM. Myocardial uptake of circulating triglycerides in nondiabetic patients with heart disease. Diabetes 2007; 56:527-30. [PMID: 17259402 DOI: 10.2337/db06-1552] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Animal studies indicate that oversupply of fatty acids derived from the action of cardiac lipoprotein lipase (LPL) on plasma lipoproteins may contribute to myocardial dysfunction. However, the contribution of circulating triglycerides to myocardial fatty acid supply in humans is not known. Six postabsorptive nondiabetic subjects who were scheduled for diagnostic coronary angiography were studied. (14)C oleate and a lipid emulsion labeled with (3)H triolein were infused to assess myocardial uptake of free fatty acids (FFAs) and triglycerides, as well as myocardial spillover of LPL-generated fatty acids. Six paired blood samples were taken from the femoral artery and the coronary sinus. Coronary sinus concentrations of unlabeled triglycerides were slightly, but not significantly, lower than arterial (P = 0.12), whereas labeled triglyceride concentrations were significantly lower in the coronary sinus than in the artery (P < 0.05; extraction fraction congruent with 11%). Triglycerides and FFAs accounted for approximately 17% and approximately 83%, respectively, of myocardial fatty acid uptake. Systemic and myocardial fractional spillover of LPL-generated fatty acids was 49.0 +/- 7% and 34.7 +/- 13%, respectively. The myocardium was a minor contributor to systemic triglyceride uptake ( approximately 3%) and a trivial contributor to systemic FFA production ( approximately 0.5%). These results indicate that circulating triglycerides may be a significant source of fatty acids for myocardial respiration.
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Affiliation(s)
- Robert H Nelson
- Endocrine Research Unit, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA
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Gormsen LC, Jensen MD, Schmitz O, Møller N, Christiansen JS, Nielsen S. Energy expenditure, insulin, and VLDL-triglyceride production in humans. J Lipid Res 2006; 47:2325-32. [PMID: 16849776 DOI: 10.1194/jlr.m600175-jlr200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Hypertriglyceridemia is considered a cardiovascular risk factor in diabetic and nondiabetic subjects. In this study, we aimed to determine potential regulators of very low density lipoprotein-triglyceride (TG) production. VLDL-TG kinetics were measured in 13 men and 12 women [body mass index [mean (range)]: 24.8 (20.2-35.6) kg/m(2)]. VLDL-TG production was assessed from the plasma decay of a bolus injection of ex vivo labeled VLDL particles ([1-(14)C]triolein-VLDL-TG). Similar VLDL-TG production (micromol/min) was found in men and women. VLDL-TG production was not significantly correlated with palmitate flux ([9,10-(3)H]palmitate) (r = 0.09, P = 0.67) or palmitate concentration (r = -0.29, P = 0.2) but was correlated significantly with fasting insulin concentration (r = 0.46, P < 0.05) and resting energy expenditure (REE) (r = 0.45, P < 0.05). The latter correlation improved when adjusted for sex. The best multivariate model with VLDL-TG production as the dependent variable and REE, body composition, hormones, and substrate levels as independent variables included fasting insulin (P = 0.02) and REE (P = 0.02) (r(2) = 0.32, P < 0.001). We conclude that VLDL kinetics are similar in men and women and that REE and plasma insulin are significant independent predictors of VLDL-TG production. FFA availability and body fat distribution are unrelated to VLDL production. We suggest that REE plays a greater role in VLDL-TG production than previously anticipated. REE and insulin should be taken into account when VLDL-TG production comparisons between groups are made.
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Affiliation(s)
- Lars C Gormsen
- Medical Department M (Endocrinology and Diabetes), Aarhus University Hospital, DK-8000 Aarhus, Denmark
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