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Laupsa-Borge J, Grytten E, Bohov P, Bjørndal B, Strand E, Skorve J, Nordrehaug JE, Berge RK, Rostrup E, Mellgren G, Dankel SN, Nygård OK. Sex-specific responses in glucose-insulin homeostasis and lipoprotein-lipid components after high-dose supplementation with marine n-3 PUFAs in abdominal obesity: a randomized double-blind crossover study. Front Nutr 2023; 10:1020678. [PMID: 37404855 PMCID: PMC10315503 DOI: 10.3389/fnut.2023.1020678] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2022] [Accepted: 06/01/2023] [Indexed: 07/06/2023] Open
Abstract
Background Clinical studies on effects of marine-derived omega-3 (n-3) polyunsaturated fatty acids (PUFAs), mainly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), and the plant-derived omega-6 (n-6) PUFA linoleic acid (LA) on lipoprotein-lipid components and glucose-insulin homeostasis have shown conflicting results, which may partly be explained by differential responses in females and males. However, we have lacked data on sexual dimorphism in the response of cardiometabolic risk markers following increased consumption of n-3 or n-6 PUFAs. Objective To explore sex-specific responses after n-3 (EPA + DHA) or n-6 (LA) PUFA supplementation on circulating lipoprotein subfractions, standard lipids, apolipoproteins, fatty acids in red blood cell membranes, and markers of glycemic control/insulin sensitivity among people with abdominal obesity. Methods This was a randomized double-blind crossover study with two 7-week intervention periods separated by a 9-week washout phase. Females (n = 16) were supplemented with 3 g/d of EPA + DHA (fish oil) or 15 g/d of LA (safflower oil), while males (n = 23) received a dose of 4 g/d of EPA + DHA or 20 g/d of LA. In fasting blood samples, we measured lipoprotein particle subclasses, standard lipids, apolipoproteins, fatty acid profiles, and markers of glycemic control/insulin sensitivity. Results The between-sex difference in relative change scores was significant after n-3 for total high-density lipoproteins (females/males: -11%*/-3.3%, p = 0.036; *: significant within-sex change), high-density lipoprotein particle size (+2.1%*/-0.1%, p = 0.045), and arachidonic acid (-8.3%*/-12%*, p = 0.012), and after n-6 for total (+37%*/+2.1%, p = 0.041) and small very-low-density lipoproteins (+97%*/+14%, p = 0.021), and lipoprotein (a) (-16%*/+0.1%, p = 0.028). Circulating markers of glucose-insulin homeostasis differed significantly after n-3 for glucose (females/males: -2.1%/+3.9%*, p = 0.029), insulin (-31%*/+16%, p < 0.001), insulin C-peptide (-12%*/+13%*, p = 0.001), homeostasis model assessment of insulin resistance index 2 (-12%*/+14%*, p = 0.001) and insulin sensitivity index 2 (+14%*/-12%*, p = 0.001), and quantitative insulin sensitivity check index (+4.9%*/-3.4%*, p < 0.001). Conclusion We found sex-specific responses after high-dose n-3 (but not n-6) supplementation in circulating markers of glycemic control/insulin sensitivity, which improved in females but worsened in males. This may partly be related to the sex differences we observed in several components of the lipoprotein-lipid profile following the n-3 intervention. Clinical trial registration https://clinicaltrials.gov/, identifier [NCT02647333].
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Affiliation(s)
- Johnny Laupsa-Borge
- Hormone Laboratory, Department of Medical Biochemistry and Pharmacology, Haukeland University Hospital, Bergen, Norway
- Mohn Nutrition Research Laboratory, Department of Clinical Science, University of Bergen, Bergen, Norway
| | - Elise Grytten
- Hormone Laboratory, Department of Medical Biochemistry and Pharmacology, Haukeland University Hospital, Bergen, Norway
- Mohn Nutrition Research Laboratory, Department of Clinical Science, University of Bergen, Bergen, Norway
| | - Pavol Bohov
- Department of Clinical Science, University of Bergen, Bergen, Norway
| | - Bodil Bjørndal
- Department of Clinical Science, University of Bergen, Bergen, Norway
| | - Elin Strand
- Department of Clinical Science, University of Bergen, Bergen, Norway
| | - Jon Skorve
- Department of Clinical Science, University of Bergen, Bergen, Norway
| | - Jan Erik Nordrehaug
- Department of Clinical Science, University of Bergen, Bergen, Norway
- Department of Heart Disease, Haukeland University Hospital, Bergen, Norway
| | - Rolf K. Berge
- Department of Clinical Science, University of Bergen, Bergen, Norway
| | - Espen Rostrup
- Department of Heart Disease, Haukeland University Hospital, Bergen, Norway
| | - Gunnar Mellgren
- Hormone Laboratory, Department of Medical Biochemistry and Pharmacology, Haukeland University Hospital, Bergen, Norway
- Mohn Nutrition Research Laboratory, Department of Clinical Science, University of Bergen, Bergen, Norway
- Mohn Research Center for Diabetes Precision Medicine, Department of Clinical Science, University of Bergen, Bergen, Norway
| | - Simon N. Dankel
- Hormone Laboratory, Department of Medical Biochemistry and Pharmacology, Haukeland University Hospital, Bergen, Norway
- Mohn Nutrition Research Laboratory, Department of Clinical Science, University of Bergen, Bergen, Norway
- Mohn Research Center for Diabetes Precision Medicine, Department of Clinical Science, University of Bergen, Bergen, Norway
| | - Ottar K. Nygård
- Mohn Nutrition Research Laboratory, Department of Clinical Science, University of Bergen, Bergen, Norway
- Department of Heart Disease, Haukeland University Hospital, Bergen, Norway
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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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Dietary walnut oil modulates liver steatosis in the obese Zucker rat. Eur J Nutr 2013; 53:645-60. [PMID: 23942585 PMCID: PMC3925294 DOI: 10.1007/s00394-013-0573-z] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2013] [Accepted: 07/31/2013] [Indexed: 02/06/2023]
Abstract
Purpose Non-alcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the metabolic syndrome. We aimed to clarify the impact of dietary walnut oil versus animal fat on hepatic steatosis, representing the initial step of multistage pathogenesis of NAFLD, in Zucker obese rats. Methods Zucker lean ad libitum (a.l.), Zucker obese a.l. or Zucker obese pair fed (p.f.) to the lean received isocaloric diets containing 8 % walnut oil (W8), W14 or 14 % lard (L14) (n = 10/group). Body weight, clinical serology, liver weight, lipid content and fatty acid composition and hepatic lipid metabolism-related transcripts were evaluated. Results Compared to lean, Zucker obese a.l. and p.f. showed hepatic triacylglyceride (TAG) accumulation. In Zucker obese p.f., W14 compared to W8 and L14 reduced liver lipids, TAG as well as hepatic omega-6 (n-6)/n-3 ratio and SCD activity index [(C18:0 + C18:1)/C18:0 ratio] paralleled by decreased lipoprotein lipase mRNA in obese p.f. and elevated microsomal triglyceride transfer protein mRNA in lean and obese. Further, W14 elevated the fasting blood TAG and reduced cholesterol levels in obese. Conclusions In our model, consumption of W14 inhibited hepatic lipid accumulation along with modulated hepatic gene expression implicated in hepatic fatty acid influx or lipoprotein assembly. These results provide first indication that dietary lipids from walnut oil are modulators of hepatic steatosis as the initial step of progressive NAFLD pathogenesis.
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The opposite effects of high-sucrose and high-fat diet on Fatty Acid oxidation and very low density lipoprotein secretion in rat model of metabolic syndrome. J Nutr Metab 2012; 2012:757205. [PMID: 23125921 PMCID: PMC3483727 DOI: 10.1155/2012/757205] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2012] [Revised: 09/14/2012] [Accepted: 09/20/2012] [Indexed: 01/22/2023] Open
Abstract
Aims. To determine the effect of two different diets (high-sucrose (HS) and high-fat (HF)) on the main metabolic pathways potentially contributing to the development of steatosis: (1) activity of the liver lysosomal and heparin-releasable lipases; (2) fatty acid (FFA) oxidation; (3) FFA synthesis de novo; (4) VLDL output in vivo in a rat model of metabolic syndrome (MetS), hereditary hypertriglyceridemic (HHTg) rats fed HS or HF diets. Results. Both diets resulted in triacylglycerol (TAG) accumulation in the liver (HF > HS). The intracellular TAG lipolysis by lysosomal lipase was increased in both groups and positively correlated with the liver TAG content. Diet type significantly affected partitioning of intracellular TAG-derived fatty acids among FFA-utilizing metabolic pathways as HS feeding accentuated VLDL secretion and downregulated FFA oxidation while the HF diet had an entirely opposite effect. FFA de novo synthesis from glucose was significantly enhanced in the HS group (fed ≫ fasted) while being completely eradicated in the HF group. Conclusions. We found that in rats prone to the development of MetS associated diseases dietary-induced steatosis is not simply a result of impaired TAG degradation but that it depends on other mechanisms (elevated FFA synthesis or attenuated VLDL secretion) that are specific according to diet composition.
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Stat5a increases lactation of dairy cow mammary gland epithelial cells cultured in vitro. In Vitro Cell Dev Biol Anim 2012; 48:554-61. [DOI: 10.1007/s11626-012-9545-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2012] [Accepted: 08/16/2012] [Indexed: 10/27/2022]
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Abstract
PURPOSE OF REVIEW A strong positive correlation between plasma apolipoprotein (apo) C-III and triglyceride concentrations has been invariably observed in human and animal studies. The hypertriglyceridemic effect of apo C-III has been conventionally explained by its extracellular roles in inhibiting lipolysis catalysed by lipoprotein lipase and attenuating triglyceride-rich lipoprotein clearance through receptor-dependent and/or independent mechanisms. However, recent experimental evidence suggests that apo C-III may also play an intracellular role in promoting hepatic triglyceride-rich lipoprotein production. RECENT FINDINGS Kinetic studies with humans and genetically modified mice have shown that apo C-III is linked with increased production of triglyceride-rich lipoproteins, such as very-low-density lipoprotein 1 (VLDL1). Mutational studies on human apo C-III variants (originally identified in humans with hypotriglyceridemia or hyperalphalipoproteinemia) provide the structure-function analysis of human apo C-III, demonstrating that loss-of-function mutations within human apo C-III impair the assembly and secretion of triglyceride-rich VLDL1 under lipid-rich conditions. SUMMARY The current review summarizes recent experimental evidence for an intrahepatic role of human apo C-III in promoting mobilization and utilization of triglyceride during VLDL1 assembly/secretion. Understanding mechanisms by which hepatic apo C-III expression is regulated under insulin resistance and diabetic conditions will lead to better and more rational strategies for the prevention and treatment of diabetic hypertriglyceridemia that is closely related to premature atherosclerosis.
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Affiliation(s)
- Zemin Yao
- Department of Biochemistry, Microbiology and Immunology, Ottawa Institute of Systems Biology, University of Ottawa, Ottawa, Ontario, Canada
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Charkoudian LK, Farrell BP, Khosla C. Natural product inhibitors of glucose-6-phosphate translocase. MEDCHEMCOMM 2012. [DOI: 10.1039/c2md20008b] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
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Wu K, Cappel D, Martinez M, Stafford JM. Impaired-inactivation of FoxO1 contributes to glucose-mediated increases in serum very low-density lipoprotein. Endocrinology 2010; 151:3566-76. [PMID: 20501667 PMCID: PMC2940519 DOI: 10.1210/en.2010-0204] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
For patients with diabetes, insulin resistance and hyperglycemia both contribute to increased serum triglyceride in the form of very low-density lipoprotein (VLDL). Our objective was to define the insulin conditions in which hyperglycemia promotes increased serum VLDL in vivo. We performed hyperglycemic-hyperinsulinemic clamp studies and hyperglycemic-hypoinsulinemic clamp studies in rats, with metabolic tracers for glucose flux and de novo fatty acid synthesis. When blood glucose was clamped at hyperglycemia (17 mm) for 2 h under hyperinsulinemic conditions (4 mU/kg . min), serum VLDL levels were not increased compared with baseline. We speculated that hyperinsulinemia minimized glucose-mediated VLDL changes and performed hyperglycemic-hypoinsulinemic clamp studies in which insulin was clamped near fasting levels with somatostatin (17 mm blood glucose, 0.25 mU/kg . min insulin). Under low-insulin conditions, serum VLDL levels were increased 4.7-fold after hyperglycemia, and forkhead box O1 (FoxO1) was not excluded from the nucleus of liver cells. We tested the extent that impaired inactivation of FoxO1 by insulin was sufficient for glucose to promote increased serum VLDL. We found that, when the ability of insulin to inactivate FoxO1 is blocked after adenoviral delivery of constitutively active FoxO1, glucose increased serum VLDL triglyceride when given both by ip glucose tolerance testing (3.5-fold increase) and by a hyperglycemic clamp (4.6-fold). Under both experimental conditions in which insulin signaling to FoxO1 was impaired, we found increased activation of carbohydrate response element binding protein. These data suggest that glucose more potently promotes increased serum VLDL when insulin action is impaired, with either low insulin levels or disrupted downstream signaling to the transcription factor FoxO1.
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Affiliation(s)
- Ke Wu
- Wuhan University, Wuhan, Hubei, China
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9
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Kotokorpi P, Ellis E, Parini P, Nilsson LM, Strom S, Steffensen KR, Gustafsson JA, Mode A. Physiological differences between human and rat primary hepatocytes in response to liver X receptor activation by 3-[3-[N-(2-chloro-3-trifluoromethylbenzyl)-(2,2-diphenylethyl)amino]propyloxy]phenylacetic acid hydrochloride (GW3965). Mol Pharmacol 2007; 72:947-55. [PMID: 17628011 DOI: 10.1124/mol.107.037358] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The liver is central to the maintenance of glucose and lipid homeostasis, and liver X receptors (LXRs) are key regulators of expression of the genes involved. So far, effects of activation of LXR in human hepatocytes have not been well characterized. Here we show that treatment of primary human hepatocytes with the synthetic LXR ligand 3-[3-[N-(2-chloro-3-trifluoromethylbenzyl)-(2,2-diphenylethyl)amino]propyloxy]phenylacetic acid hydrochloride (GW3965) results in reduced output of bile acids and very low density lipoprotein triglycerides and induced expression of adipose differentiation-related protein accompanied by increased lipid storage. Genome wide-expression profiling identified novel human LXR target genes in the glycolytic and lipogenic pathways and indicated that LXR activation reduced hepatic insulin sensitivity. Comparative experiments showed significant differences in the response to GW3965 between human and rat hepatocytes, raising the question as to how well rodent models reflect the human situation. In summary, the risk of hepatic steatosis upon pharmaceutical targeting of LXR may be a particularly serious consequence in humans.
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Affiliation(s)
- Pia Kotokorpi
- Dept of Biosciences and Nutrition, Karolinska Institutet, Novum, S-141 57 Huddinge, Sweden
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Adiels M, Taskinen MR, Packard C, Caslake MJ, Soro-Paavonen A, Westerbacka J, Vehkavaara S, Häkkinen A, Olofsson SO, Yki-Järvinen H, Borén J. Overproduction of large VLDL particles is driven by increased liver fat content in man. Diabetologia 2006; 49:755-65. [PMID: 16463046 DOI: 10.1007/s00125-005-0125-z] [Citation(s) in RCA: 456] [Impact Index Per Article: 25.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/05/2005] [Accepted: 10/18/2005] [Indexed: 01/14/2023]
Abstract
AIMS/HYPOTHESIS We determined whether hepatic fat content and plasma adiponectin concentration regulate VLDL(1) production. METHODS A multicompartment model was used to simultaneously determine the kinetic parameters of triglycerides (TGs) and apolipoprotein B (ApoB) in VLDL(1) and VLDL(2) after a bolus of [(2)H(3)]leucine and [(2)H(5)]glycerol in ten men with type 2 diabetes and in 18 non-diabetic men. Liver fat content was determined by proton spectroscopy and intra-abdominal fat content by MRI. RESULTS Univariate regression analysis showed that liver fat content, intra-abdominal fat volume, plasma glucose, insulin and HOMA-IR (homeostasis model assessment of insulin resistance) correlated with VLDL(1) TG and ApoB production. However, only liver fat and plasma glucose were significant in multiple regression models, emphasising the critical role of substrate fluxes and lipid availability in the liver as the driving force for overproduction of VLDL(1) in subjects with type 2 diabetes. Despite negative correlations with fasting TG levels, liver fat content, and VLDL(1) TG and ApoB pool sizes, adiponectin was not linked to VLDL(1) TG or ApoB production and thus was not a predictor of VLDL(1) production. However, adiponectin correlated negatively with the removal rates of VLDL(1) TG and ApoB. CONCLUSIONS/INTERPRETATION We propose that the metabolic effect of insulin resistance, partly mediated by depressed plasma adiponectin levels, increases fatty acid flux from adipose tissue to the liver and induces the accumulation of fat in the liver. Elevated plasma glucose can further increase hepatic fat content through multiple pathways, resulting in overproduction of VLDL(1) particles and leading to the characteristic dyslipidaemia associated with type 2 diabetes.
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Affiliation(s)
- M Adiels
- Wallenberg Laboratory, Gothenburg University, Gothenburg, Sweden
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Härndahl L, Schmoll D, Herling AW, Agius L. The role of glucose 6-phosphate in mediating the effects of glucokinase overexpression on hepatic glucose metabolism. FEBS J 2006; 273:336-46. [PMID: 16403021 DOI: 10.1111/j.1742-4658.2005.05067.x] [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: 12/01/2022]
Abstract
Pharmacological activation or overexpression of glucokinase in hepatocytes stimulates glucose phosphorylation, glycolysis and glycogen synthesis. We used an inhibitor of glucose 6-phosphate (Glc6P) hydrolysis, namely the chlorogenic derivative, 1-[2-(4-chloro-phenyl)-cyclopropylmethoxy]-3, 4-dihydroxy-5-(3-imidazo[4,5-b]pyridin-1-yl-3-phenyl-acryloyloxy)-cyclohexanecarboxylic acid (also known as S4048), to determine the contribution of Glc6P concentration, as distinct from glucokinase protein or activity, to the control of glycolysis and glycogen synthesis by glucokinase overexpression. The validity of S4048 for testing the role of Glc6P was supported by its lack of effect on glucokinase binding and its nuclear/cytoplasmic distribution. The stimulation of glycolysis by glucokinase overexpression correlated strongly with glucose phosphorylation, whereas glycogen synthesis correlated strongly with Glc6P concentration. Metabolic control analysis was used to determine the sensitivity of glycogenic flux to glucokinase or Glc6P at varying glucose concentrations (5-20 mm). The concentration control coefficient of glucokinase on Glc6P (1.4-1.7) was relatively independent of glucose concentration, whereas the flux control coefficients of Glc6P (2.4-1.0) and glucokinase (3.7-1.8) on glycogen synthesis decreased with glucose concentration. The high sensitivity of glycogenic flux to Glc6P at low glucose concentration is consistent with covalent modification by Glc6P of both phosphorylase and glycogen synthase. The high control strength of glucokinase on glycogenic flux is explained by its concentration control coefficient on Glc6P and the high control strength of Glc6P on glycogen synthesis. It is suggested that the regulatory strength of pharmacological glucokinase activators on glycogen metabolism can be predicted from their effect on the Glc6P content.
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Affiliation(s)
- Linda Härndahl
- School of Clinical Medical Sciences-Diabetes, The University of Newcastle upon Tyne, Medical School, Newcastle upon Tyne, UK
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Cho HJ, Kang HC, Ju YC, Lee HS, Kim HS, Park HJ. Augmentation of Ca2+-Induced Microsomal Triglyceride Transfer Protein Activity by Glucose Supply Enhances Hypertriglyceridemia in Vivo. Biol Pharm Bull 2006; 29:889-95. [PMID: 16651714 DOI: 10.1248/bpb.29.889] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have investigated possible roles of intra-glucose supply on microsomal triglyceride (TG) transfer protein (MTP) in the secretion of TG-rich very low-density lipoprotein (VLDL) from the liver. Due to the activation of MTP, TG and apolipoprotein B (apoB) in the liver are assembled into VLDL and then the VLDL is transferred into the blood stream. High MTP activity can increase the release of VLDL into the blood stream, and this would lead high levels of TG and apoB in the blood. High MTP activity was found when the liver (or hepatocytes) contained a high level of total Ca2+ as a response of glucose administration. However, the MTP activity was reduced in response to the calmodulin antagonist N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide (W-7, Ki=25 microM), the intracellular Ca2+ chelator BAPTA-AM, and the extracellular Ca2+ chelator EDTA. These suggested that there might be a very close relationship between high MTP activity and high Ca2+ level in the liver by glucose administration. Glucose-derived hyperglycemic condition resulted from those elevations of TG and total cholesterol in the liver. This hyperglycemic phenomenon may be associated with the increase of TG and apoB levels in blood. The possibility for the regulation of VLDL formation in the liver and, further, those related circulatory diseases due to the excess of VLDL in the blood stream by controlling MTP activity in association with Ca2+ was investigated.
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Affiliation(s)
- Hyun-Jeong Cho
- Department of Biomedical Laboratory Science, College of Biomedical Science and Engineering, and Regional Research Center, Inje University, Gimhae, Gyungnam, Korea
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Dolinsky VW, Douglas DN, Lehner R, Vance DE. Regulation of the enzymes of hepatic microsomal triacylglycerol lipolysis and re-esterification by the glucocorticoid dexamethasone. Biochem J 2004; 378:967-74. [PMID: 14662008 PMCID: PMC1224021 DOI: 10.1042/bj20031320] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2003] [Revised: 12/08/2003] [Accepted: 12/09/2003] [Indexed: 12/25/2022]
Abstract
Hepatic VLDL (very-low-density lipoprotein) assembly is a complex process that is largely regulated by the provision of lipid for apolipoprotein B assembly. Intracellular stored TAG (triacylglycerol) undergoes an initial lipolysis followed by re-esterification of the lipolytic products to form TAG prior to their incorporation into a VLDL particle. TGH (TAG hydrolase) is a lipase that hydrolyses intracellular TAG within the hepatocyte. We have utilized both dexamethasone-injected mouse and primary hepatocyte models to address whether stimulation of TAG biosynthesis by the synthetic glucocorticoid, dexamethasone, altered hepatic lipolysis and re-esterification and the provision of stored TAG for lipoprotein secretion. Dexamethasone treatment resulted in decreased TGH expression, primarily due to a dexamethasone-induced decrease in TGH mRNA stability. The expression and activities of diacylglycerol acyltransferases 1 and 2 were stimulated by dexamethasone. The combination of reduced intracellular TAG lipolysis and increased TAG biosynthesis contributed to the accumulation of TAG within the livers of dexamethasone-injected mice. The rate of hepatic TAG secretion in dexamethasonetreated mice was maintained at similar levels as in control mice. Our data demonstrate that stimulation of de novo TAG synthesis by dexamethasone increased the proportion of secreted TAG that was derived from de novo sources, while the utilization of stored TAG for secretion was reduced. The results show that, during markedly increased TAG synthesis, some TAGs are diverted from the cytosolic storage pool and are utilized directly for VLDL assembly within the endoplasmic reticulum lumen.
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Affiliation(s)
- Vernon W Dolinsky
- Department of Biochemistry and CIHR Group on the Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, Alberta, Canada T6G 2S2
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Schonfeld G, Patterson BW, Yablonskiy DA, Tanoli TSK, Averna M, Elias N, Yue P, Ackerman J. Fatty liver in familial hypobetalipoproteinemia: triglyceride assembly into VLDL particles is affected by the extent of hepatic steatosis. J Lipid Res 2003; 44:470-8. [PMID: 12562873 DOI: 10.1194/jlr.m200342-jlr200] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Familial hypobetalipoproteinemia (FHBL) subjects may develop fatty liver. Liver fat was assessed in 21 FHBL with six different apolipoprotein B (apoB) truncations (apoB-4 to apoB-89) and 14 controls by magnetic resonance spectroscopy (MRS). Liver fat percentages were 16.7 +/- 11.5 and 3.3 +/- 2.9 (mean +/- SD) (P = 0.001). Liver fat percentage was positively correlated with body mass index, waist circumference, and areas under the insulin curves of 2 h glucose tolerance tests, suggesting that obesity may affect the severity of liver fat accumulation in both groups. Despite 5-fold differences in liver fat percentage, mean values for obesity and insulin indexes were similar. Thus, for similar degrees of obesity, FHBL subjects have more hepatic fat. VLDL-triglyceride (TG)-fatty acids arise from plasma and nonplasma sources (liver and splanchnic tissues). To assess the relative contributions of each, [2H2]palmitate was infused over 12 h in 13 FHBL subjects and 11 controls. Isotopic enrichment of plasma free palmitate and VLDL-TG-palmitate was determined by mass spectrometry. Non-plasma sources contributed 51 +/- 15% in FHBL and 37 +/- 13% in controls (P = 0.02). Correlations of liver fat percentage and percent VLDL-TG-palmitate from liver were r = 0.89 (P = 0.0001) for FHBL subjects and r = 0.69 (P = 0.01) for controls. Thus, apoB truncation-producing mutations result in fatty liver and in altered assembly of VLDL-TG.
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Affiliation(s)
- Gustav Schonfeld
- Department of Internal Medicine, Washington University, St. Louis, MO, USA.
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Elam MB, Wilcox HG, Cagen LM, Deng X, Raghow R, Kumar P, Heimberg M, Russell JC. Increased hepatic VLDL secretion, lipogenesis, and SREBP-1 expression in the corpulent JCR:LA-cp rat. J Lipid Res 2001. [DOI: 10.1016/s0022-2275(20)31533-9] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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Bandsma RH, Wiegman CH, Herling AW, Burger HJ, ter Harmsel A, Meijer AJ, Romijn JA, Reijngoud DJ, Kuipers F. Acute inhibition of glucose-6-phosphate translocator activity leads to increased de novo lipogenesis and development of hepatic steatosis without affecting VLDL production in rats. Diabetes 2001; 50:2591-7. [PMID: 11679439 DOI: 10.2337/diabetes.50.11.2591] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Glucose-6-phosphatase (G6Pase) is a key enzyme in hepatic glucose metabolism. Altered G6Pase activity in glycogen storage disease and diabetic states is associated with disturbances in lipid metabolism. We studied the effects of acute inhibition of G6Pase activity on hepatic lipid metabolism in nonanesthetized rats. Rats were infused with an inhibitor of the glucose-6-phosphate (G6P) translocator (S4048, 30 mg. kg(-1). h(-1)) for 8 h. Simultaneously, [1-(13)C]acetate was administered for determination of de novo lipogenesis and fractional cholesterol synthesis rates by mass isotopomer distribution analysis. In a separate group of rats, Triton WR 1339 was injected for determination of hepatic VLDL-triglyceride production. S4048 infusion significantly decreased plasma glucose (-11%) and insulin (-48%) levels and increased hepatic G6P (201%) and glycogen (182%) contents. Hepatic triglyceride contents increased from 5.8 +/- 1.4 micromol/g liver in controls to 20.6 +/- 5.5 micromol/g liver in S4048-treated animals. De novo lipogenesis was increased >10-fold in S4048-treated rats, without changes in cholesterol synthesis rates. Hepatic mRNA levels of acetyl-CoA carboxylase and fatty acid synthase were markedly induced. Plasma triglyceride levels increased fourfold, but no differences in plasma cholesterol levels were seen. Surprisingly, hepatic VLDL-triglyceride secretion was not increased in S4048-treated rats. These studies demonstrate that inhibition of the G6Pase system leads to acute stimulation of fat synthesis and development of hepatic steatosis, without affecting hepatic cholesterol synthesis and VLDL secretion. The results emphasize the strong interactions that exist between hepatic carbohydrate and fat metabolism.
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Affiliation(s)
- R H Bandsma
- Groningen University Institute for Drug Exploration, Center for Liver, Digestive and Metabolic Diseases, Department of Pediatrics, Academic Hospital Groningen, Groningen, the Netherlands.
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Secretion of hepatocyte apoB is inhibited by the flavonoids, naringenin and hesperetin, via reduced activity and expression of ACAT2 and MTP. J Lipid Res 2001. [DOI: 10.1016/s0022-2275(20)31634-5] [Citation(s) in RCA: 171] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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Gibbons GF, Islam K, Pease RJ. Mobilisation of triacylglycerol stores. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1483:37-57. [PMID: 10601694 DOI: 10.1016/s1388-1981(99)00182-1] [Citation(s) in RCA: 202] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Triacylglycerol (TAG) is an energy dense substance which is stored by several body tissues, principally adipose tissue and the liver. Utilisation of stored TAG as an energy source requires its mobilisation from these depots and transfer into the blood plasma. The means by which TAG is mobilised differs in adipose tissue and liver although the regulation of lipid metabolism in each of these organs is interdependent and synchronised in an integrated manner. This review deals principally with the mechanism of hepatic TAG mobilisation since this is a rapidly expanding area of research and may have important implications for the regulation of plasma very-low-density lipoprotein metabolism. TAG mobilisation plays an important role in fuel selection in non-hepatic tissues such as cardiac muscle and pancreatic islets and these aspects are also reviewed briefly. Finally, studies of certain rare inherited disorders of neutral lipid storage and mobilisation may provide useful information about the normal enzymology of TAG mobilisation in healthy tissues.
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Affiliation(s)
- G F Gibbons
- Metabolic Research Laboratory, Oxford Lipid Metabolism Group, University of Oxford, Radcliffe Infirmary, Woodstock Road, Oxford, UK.
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Bülow J, Simonsen L, Wiggins D, Humphreys SM, Frayn KN, Powell D, Gibbons GF. Co-ordination of hepatic and adipose tissue lipid metabolism after oral glucose. J Lipid Res 1999. [DOI: 10.1016/s0022-2275(20)32427-5] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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