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Beukhof CM, Massolt ET, Visser TJ, Korevaar TIM, Medici M, de Herder WW, Roeters van Lennep JE, Mulder MT, de Rijke YB, Reiners C, Verburg FA, Peeters RP. Effects of Thyrotropin on Peripheral Thyroid Hormone Metabolism and Serum Lipids. Thyroid 2018; 28:168-174. [PMID: 29316865 DOI: 10.1089/thy.2017.0330] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
BACKGROUND Subclinical hypothyroidism is associated with dyslipidemia and atherosclerosis. Whether these effects are in part mediated via direct effects of thyrotropin (TSH) on peripheral thyroid hormone (TH) metabolism and/or concentrations of serum lipids is not clear. OBJECTIVE This study examined whether TSH has direct effects on peripheral TH metabolism and serum lipids. METHODS Eighty-two patients with differentiated thyroid cancer were retrospectively analyzed. All patients had undergone total thyroidectomy and 131I remnant ablation. During follow-up, two successive injections of recombinant human TSH (rhTSH) were administered to patients on a stable dose of levothyroxine. In all patients, TSH, thyroxine (T4), free T4 (fT4), triiodothyronine (T3), reverse T3 (rT3), total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, apolipoprotein B, lipoprotein(a), and triglyceride levels were measured immediately before the first and approximately 72 hours after the second injection of rhTSH. RESULTS After rhTSH stimulation, T3 values decreased (from 1.91 to 1.81 nmol/L; p < 0.001). T4, fT4, and rT3 did not change. After rhTSH, median apolipoprotein B increased from 0.90 to 0.92 g/L (p = 0.03), lipoprotein(a) from 0.21 to 0.24 g/L (p < 0.001), and triglycerides from 1.98 to 2.50 mmol/L (p < 0.001). Serum high-density lipoprotein cholesterol decreased from 0.98 to 0.81 mmol/L (p < 0.001). Multiple regression analysis showed that the changes in lipids were most closely associated with the decrease in T3 levels. CONCLUSIONS TSH has direct effects on peripheral TH metabolism by decreasing T3 levels in levothyroxine-treated thyroidectomized patients. This decrease in T3 levels is accompanied by unfavorable changes in serum lipids.
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Affiliation(s)
- Carolien M Beukhof
- 1 Department of Internal Medicine, Academic Center for Thyroid Diseases, University Medical Center , Rotterdam, The Netherlands
| | - Elske T Massolt
- 1 Department of Internal Medicine, Academic Center for Thyroid Diseases, University Medical Center , Rotterdam, The Netherlands
| | - Theo J Visser
- 1 Department of Internal Medicine, Academic Center for Thyroid Diseases, University Medical Center , Rotterdam, The Netherlands
| | - Tim I M Korevaar
- 1 Department of Internal Medicine, Academic Center for Thyroid Diseases, University Medical Center , Rotterdam, The Netherlands
| | - Marco Medici
- 1 Department of Internal Medicine, Academic Center for Thyroid Diseases, University Medical Center , Rotterdam, The Netherlands
| | - Wouter W de Herder
- 1 Department of Internal Medicine, Academic Center for Thyroid Diseases, University Medical Center , Rotterdam, The Netherlands
| | | | - Monique T Mulder
- 2 Department of Vascular Medicine, University Medical Center , Rotterdam, The Netherlands
| | - Yolanda B de Rijke
- 1 Department of Internal Medicine, Academic Center for Thyroid Diseases, University Medical Center , Rotterdam, The Netherlands
- 3 Department of Clinical Chemistry, Erasmus MC, University Medical Center , Rotterdam, The Netherlands
| | - Christoph Reiners
- 4 Department of Nuclear Medicine, University Hospital Wuerzburg , Wuerzburg, Germany
| | - Frederik A Verburg
- 4 Department of Nuclear Medicine, University Hospital Wuerzburg , Wuerzburg, Germany
- 5 Department of Nuclear Medicine, University Hospital Marburg , Marburg, Germany
| | - Robin P Peeters
- 1 Department of Internal Medicine, Academic Center for Thyroid Diseases, University Medical Center , Rotterdam, The Netherlands
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Abstract
Nearly 50 years ago, I set out to investigate the clinical problem of hypoglycemia in children with illnesses that limited their food intake. My goal was to gather accurate and precise measurable data. At the time, I wasn't interested in nutrition as a discipline defined in its more general or popular sense. To address the specific problem that interested me required development of entirely new methods based on stable, nonradioactive tracers that satisfied the conditions of accuracy and precision. At the time, I had no inclination of the various theoretical and practical problems that would have to be solved to achieve this goal. Some are briefly described here. Nor did I have the slightest idea that developing the field would result in a fundamental change in how human clinical investigation was conducted, with the eventual replacement of radiotracers with stable isotopically labeled ones, even for adult clinical investigation. Additionally, I had no inclination that the original questions would open avenues to much broader questions of practical nutritional relevance. Moreover, only much later as the editor of The American Journal of Clinical Nutrition did I appreciate the policy implications of how nutritional data are presented in the scientific literature. At least in part, less accurate and precise measurements and less than full transparency in reporting nutritional data have resulted in widespread debate about the public policy recommendations and guidelines that are the intended result of collecting the data in the first place. This article provides a personal recollection (with all the known faults of self-reporting and retrospective memory) of the journey that starts with measurement certainty and ends with policy uncertainty.
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Affiliation(s)
- Dennis M Bier
- USDA/ARS Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, Texas 77030;
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3
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Daurio NA, Wang SP, Chen Y, Zhou H, McLaren DG, Roddy TP, Johns DG, Milot D, Kasumov T, Erion MD, Kelley DE, Previs SF. Enhancing Studies of Pharmacodynamic Mechanisms via Measurements of Metabolic Flux: Fundamental Concepts and Guiding Principles for Using Stable Isotope Tracers. J Pharmacol Exp Ther 2017; 363:80-91. [DOI: 10.1124/jpet.117.241091] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2017] [Accepted: 06/14/2017] [Indexed: 11/22/2022] Open
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SRM-based measurements of proprotein convertase subtilisin/kexin type 9 and lipoprotein(a) kinetics in nonhuman primate serum. Bioanalysis 2016; 8:2551-2563. [DOI: 10.4155/bio-2016-0146] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Aim: PCSK9 and Lp(a) have been identified as potential biomarkers for cardiovascular disease. The ability to measure protein turnover rates will provide insights into the dynamic properties of these proteins and lead to better understanding of their biological roles. We aimed to implement the stable isotope-labeled tracers ([2H3]-leucine) and develop a novel LC-selected reaction monitoring (SRM) mass spectrometry (MS) method to study the kinetics of PCSK9 and Lp(a). Results: A sensitive method using immunoaffinity enrichment coupled with LC-SRM MS was developed to measure the production and degradation rates of PCSK9 and Lp(a) in naive nonhuman primate serum. Comparable results were obtained from two different routes of tracer administration. Conclusion: Immunoaffinity enrichment coupled with LC-SRM MS demonstrated success in in vivo kinetic measurements of proteins with relatively slow turnover rate (Lp[a]) or low abundance (PCSK9) in serum.
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Thaxton CS, Rink JS, Naha PC, Cormode DP. Lipoproteins and lipoprotein mimetics for imaging and drug delivery. Adv Drug Deliv Rev 2016; 106:116-131. [PMID: 27133387 PMCID: PMC5086317 DOI: 10.1016/j.addr.2016.04.020] [Citation(s) in RCA: 100] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2016] [Revised: 04/02/2016] [Accepted: 04/19/2016] [Indexed: 12/22/2022]
Abstract
Lipoproteins are a set of natural nanoparticles whose main role is the transport of fats within the body. While much work has been done to develop synthetic nanocarriers to deliver drugs or contrast media, natural nanoparticles such as lipoproteins represent appealing alternatives. Lipoproteins are biocompatible, biodegradable, non-immunogenic and are naturally targeted to some disease sites. Lipoproteins can be modified to act as contrast agents in many ways, such as by insertion of gold cores to provide contrast for computed tomography. They can be loaded with drugs, nucleic acids, photosensitizers or boron to act as therapeutics. Attachment of ligands can re-route lipoproteins to new targets. These attributes render lipoproteins attractive and versatile delivery vehicles. In this review we will provide background on lipoproteins, then survey their roles as contrast agents, in drug and nucleic acid delivery, as well as in photodynamic therapy and boron neutron capture therapy.
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Affiliation(s)
- C Shad Thaxton
- Department of Urology, Northwestern University, Chicago, IL, USA; Simpson Querrey Institute for Bionanotechnology, Northwestern University, Chicago, IL, USA; International Institute for Nanotechnology, Northwestern University, Chicago, IL, USA; Robert H. Lurie Comprehensive Cancer Center, Northwestern University, Chicago, IL, USA
| | - Jonathan S Rink
- Department of Urology, Northwestern University, Chicago, IL, USA; Simpson Querrey Institute for Bionanotechnology, Northwestern University, Chicago, IL, USA
| | - Pratap C Naha
- Department of Radiology, University of Pennsylvania, 3400 Spruce St, 1 Silverstein, Philadelphia, PA 19104, USA
| | - David P Cormode
- Department of Radiology, University of Pennsylvania, 3400 Spruce St, 1 Silverstein, Philadelphia, PA 19104, USA; Department of Bioengineering, University of Pennsylvania, 3400 Spruce St, 1 Silverstein, Philadelphia, PA 19104, USA; Department of Cardiology, University of Pennsylvania, 3400 Spruce St, 1 Silverstein, Philadelphia, PA 19104, USA.
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Hooper AJ, Robertson K, Champain D, Hua J, Song S, Parhofer KG, Barrett PHR, van Bockxmeer FM, Burnett JR. Lipoprotein metabolism in an apoB-80 familial hypobetalipoproteinemia heterozygote. Clin Biochem 2016; 49:720-722. [DOI: 10.1016/j.clinbiochem.2016.02.008] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2016] [Revised: 02/17/2016] [Accepted: 02/19/2016] [Indexed: 11/30/2022]
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7
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Maternal and newborn infants amino acid concentrations in obese women born themselves with normal and small for gestational age birth weight. J Dev Orig Health Dis 2016; 6:278-84. [PMID: 26126860 DOI: 10.1017/s2040174415001117] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
This study was undertaken to compare amino acid concentrations in maternal and newborn infants' serum in normal pregnancy and two groups of obese women who were born themselves with normal and small for gestational age (SGA) birth weight. Maternal cholesterol, lipoproteins concentrations and maternal and infants amino acid concentrations were evaluated at the time of delivery in 28 normal pregnancies, 46 obese pregnant women with normal birth weight (Ob-AGA group) and 44 obese pregnant women born themselves SGA (Ob-SGA group). Mean birth weight of newborn infants in Ob-SGA group was significantly less than in normal and Ob-AGA groups. Cholesterol and lipoproteins were significantly elevated in obese women (more prominent in Ob-SGA group). Most amino acid concentrations and fetal-maternal amino acid gradients were significantly lower in Ob-SGA group. These data suggest significant changes in placental amino acid transport/synthetic function in obese women who were born themselves SGA.
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Pan L, Segrest JP. Computational studies of plasma lipoprotein lipids. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:2401-2420. [PMID: 26969087 DOI: 10.1016/j.bbamem.2016.03.010] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2016] [Revised: 03/03/2016] [Accepted: 03/04/2016] [Indexed: 12/27/2022]
Abstract
Plasma lipoproteins are macromolecular assemblies of proteins and lipids found in the blood. The lipid components of lipoproteins are amphipathic lipids such as phospholipids (PLs), and unesterified cholesterols (UCs) and hydrophobic lipids such as cholesteryl esters (CEs) and triglycerides (TGs). Since lipoproteins are soft matter supramolecular assemblies easily deformable by thermal fluctuations and they also exist in varying densities and protein/lipid components, a detailed understanding of their structure/function is experimentally difficult. Molecular dynamics (MD) simulation has emerged as a particularly promising way to explore the structure and dynamics of lipoproteins. The purpose of this review is to survey the current status of computational studies of the lipid components of the lipoproteins. Computational studies aim to explore three levels of complexity for the 3-dimensional structural dynamics of lipoproteins at various metabolic stages: (i) lipoprotein particles consist of protein with minimal lipid; (ii) lipoprotein particles consist of PL-rich discoidal bilayer-like lipid particles; (iii) mature circulating lipoprotein particles consist of CE-rich or TG-rich spheroidal lipid-droplet-like particles. Due to energy barriers involved in conversion between these species, other biomolecules also participate in lipoprotein biological assembly. For example: (i) lipid-poor apolipoprotein A-I (apoA-I) interacts with ATP-binding cassette transporter A1 (ABCA1) to produce nascent discoidal high density lipoprotein (dHDL) particles; (ii) lecithin-cholesterol acyltransferase (LCAT) mediates the conversion of UC to CE in dHDL, driving spheroidal HDL (sHDL) formation; (iii) transfer proteins, cholesterol ester transfer protein (CETP) and phospholipid transfer protein (PLTP), transfer both CE and TG and PL, respectively, between lipoprotein particles. Computational studies have the potential to explore different lipoprotein particles at each metabolic stage in atomistic detail. This review discusses the current status of computational methods including all-atom MD (AAMD), coarse-grain MD (CGMD), and MD-simulated annealing (MDSA) and their applications in lipoprotein structural dynamics and biological assemblies. Results from MD simulations are discussed and compared across studies in order to identify key findings, controversies, issues and future directions. This article is part of a Special Issue entitled: Biosimulations edited by Ilpo Vattulainen and Tomasz Róg.
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Affiliation(s)
- Lurong Pan
- Division of Gerontology, Geriatrics, & Palliative Care, School of Medicine, University of Alabama at Birmingham, Birmingham, AL 35294, United States
| | - Jere P Segrest
- Division of Gerontology, Geriatrics, & Palliative Care, School of Medicine, University of Alabama at Birmingham, Birmingham, AL 35294, United States.
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9
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Hooper AJ, Heeks L, Robertson K, Champain D, Hua J, Song S, Parhofer KG, Barrett PHR, van Bockxmeer FM, Burnett JR. Lipoprotein Metabolism in APOB L343V Familial Hypobetalipoproteinemia. J Clin Endocrinol Metab 2015; 100:E1484-90. [PMID: 26323024 DOI: 10.1210/jc.2015-2731] [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] [Indexed: 02/13/2023]
Abstract
CONTEXT Familial hypobetalipoproteinemia (FHBL) is a codominant disorder of lipoprotein metabolism characterized by decreased plasma concentrations of low-density lipoprotein (LDL)-cholesterol and apolipoprotein B (apoB). OBJECTIVE The objective was to examine the effect of heterozygous APOB L343V FHBL on postprandial triglyceride-rich lipoprotein (TRL) and fasting lipoprotein metabolism. METHODS Plasma incremental area under the curve apoB-48 and apoB-48 kinetics were determined after ingestion of a standardized oral fat load using compartmental modeling. Very low-density lipoprotein (VLDL)-, intermediate-density lipoprotein (IDL)-, and LDL-apoB kinetics were determined in the fasting state using stable isotope methods and compartmental modeling. RESULTS The postprandial incremental area under the curve (0-10 h) in FHBL subjects (n = 3) was lower for large TRL-triglyceride (-77%; P < .0001), small TRL-cholesterol (-83%; P < .001), small TRL-triglyceride (-88%; P < .001), and for plasma triglyceride (-70%; P < .01) and apoB (-63%; P < .0001) compared with controls. Compartmental analysis showed that apoB-48 production was lower (-91%; P < .05) compared with controls. VLDL-apoB concentrations in FHBL subjects (n = 2) were lower by more than 75% compared with healthy, normolipidemic control subjects (P < .01). The VLDL-apoB fractional catabolic rate (FCR) was more than 5-fold higher in the FHBL subjects (P = .07). ApoB production rates and IDL- and LDL-apoB FCRs were not different between FHBL subjects and controls. CONCLUSIONS We conclude that when compared to controls, APOB L343V FHBL heterozygotes show lower TRL production with normal postprandial TRL particle clearance. In contrast, VLDL-apoB production was normal, whereas the FCR was higher in heterozygotes compared with lean control subjects. These mechanisms account for the marked hypolipidemic state observed in these FHBL subjects.
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MESH Headings
- Adult
- Amino Acid Substitution
- Apolipoprotein B-48/blood
- Apolipoprotein B-48/metabolism
- Apolipoproteins B/blood
- Apolipoproteins B/genetics
- Apolipoproteins B/metabolism
- Diet, High-Fat/adverse effects
- Down-Regulation
- Female
- Heterozygote
- Humans
- Hypobetalipoproteinemia, Familial, Apolipoprotein B/blood
- Hypobetalipoproteinemia, Familial, Apolipoprotein B/genetics
- Hypobetalipoproteinemia, Familial, Apolipoprotein B/metabolism
- Lipoproteins/blood
- Lipoproteins/metabolism
- Lipoproteins, IDL/blood
- Lipoproteins, IDL/metabolism
- Lipoproteins, VLDL/blood
- Lipoproteins, VLDL/metabolism
- Male
- Meals
- Middle Aged
- Models, Biological
- Mutation
- Postprandial Period
- Triglycerides/blood
- Triglycerides/metabolism
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Affiliation(s)
- Amanda J Hooper
- Department of Clinical Biochemistry (A.J.H., L.H., K.R., F.M.v.B., J.R.B.), PathWest Laboratory Medicine WA, Royal Perth Hospital, Perth WA 6000, Australia; School of Medicine and Pharmacology (A.J.H., D.C., P.H.R.B., J.R.B.), and School of Pathology and Laboratory Medicine (A.J.H., K.R.), University of Western Australia, Crawley WA 6009, Australia; Department of Radiology (J.H., S.S.), Royal Perth Hospital, Perth WA 6000, Australia; Medical Department II (K.G.P.), Grosshadern, University of Munich, 81377 Munich, Germany; and School of Surgery (F.M.v.B.), University of Western Australia, Crawley WA 6009, Australia
| | - Liesl Heeks
- Department of Clinical Biochemistry (A.J.H., L.H., K.R., F.M.v.B., J.R.B.), PathWest Laboratory Medicine WA, Royal Perth Hospital, Perth WA 6000, Australia; School of Medicine and Pharmacology (A.J.H., D.C., P.H.R.B., J.R.B.), and School of Pathology and Laboratory Medicine (A.J.H., K.R.), University of Western Australia, Crawley WA 6009, Australia; Department of Radiology (J.H., S.S.), Royal Perth Hospital, Perth WA 6000, Australia; Medical Department II (K.G.P.), Grosshadern, University of Munich, 81377 Munich, Germany; and School of Surgery (F.M.v.B.), University of Western Australia, Crawley WA 6009, Australia
| | - Ken Robertson
- Department of Clinical Biochemistry (A.J.H., L.H., K.R., F.M.v.B., J.R.B.), PathWest Laboratory Medicine WA, Royal Perth Hospital, Perth WA 6000, Australia; School of Medicine and Pharmacology (A.J.H., D.C., P.H.R.B., J.R.B.), and School of Pathology and Laboratory Medicine (A.J.H., K.R.), University of Western Australia, Crawley WA 6009, Australia; Department of Radiology (J.H., S.S.), Royal Perth Hospital, Perth WA 6000, Australia; Medical Department II (K.G.P.), Grosshadern, University of Munich, 81377 Munich, Germany; and School of Surgery (F.M.v.B.), University of Western Australia, Crawley WA 6009, Australia
| | - Danie Champain
- Department of Clinical Biochemistry (A.J.H., L.H., K.R., F.M.v.B., J.R.B.), PathWest Laboratory Medicine WA, Royal Perth Hospital, Perth WA 6000, Australia; School of Medicine and Pharmacology (A.J.H., D.C., P.H.R.B., J.R.B.), and School of Pathology and Laboratory Medicine (A.J.H., K.R.), University of Western Australia, Crawley WA 6009, Australia; Department of Radiology (J.H., S.S.), Royal Perth Hospital, Perth WA 6000, Australia; Medical Department II (K.G.P.), Grosshadern, University of Munich, 81377 Munich, Germany; and School of Surgery (F.M.v.B.), University of Western Australia, Crawley WA 6009, Australia
| | - Jianmin Hua
- Department of Clinical Biochemistry (A.J.H., L.H., K.R., F.M.v.B., J.R.B.), PathWest Laboratory Medicine WA, Royal Perth Hospital, Perth WA 6000, Australia; School of Medicine and Pharmacology (A.J.H., D.C., P.H.R.B., J.R.B.), and School of Pathology and Laboratory Medicine (A.J.H., K.R.), University of Western Australia, Crawley WA 6009, Australia; Department of Radiology (J.H., S.S.), Royal Perth Hospital, Perth WA 6000, Australia; Medical Department II (K.G.P.), Grosshadern, University of Munich, 81377 Munich, Germany; and School of Surgery (F.M.v.B.), University of Western Australia, Crawley WA 6009, Australia
| | - Swithin Song
- Department of Clinical Biochemistry (A.J.H., L.H., K.R., F.M.v.B., J.R.B.), PathWest Laboratory Medicine WA, Royal Perth Hospital, Perth WA 6000, Australia; School of Medicine and Pharmacology (A.J.H., D.C., P.H.R.B., J.R.B.), and School of Pathology and Laboratory Medicine (A.J.H., K.R.), University of Western Australia, Crawley WA 6009, Australia; Department of Radiology (J.H., S.S.), Royal Perth Hospital, Perth WA 6000, Australia; Medical Department II (K.G.P.), Grosshadern, University of Munich, 81377 Munich, Germany; and School of Surgery (F.M.v.B.), University of Western Australia, Crawley WA 6009, Australia
| | - Klaus G Parhofer
- Department of Clinical Biochemistry (A.J.H., L.H., K.R., F.M.v.B., J.R.B.), PathWest Laboratory Medicine WA, Royal Perth Hospital, Perth WA 6000, Australia; School of Medicine and Pharmacology (A.J.H., D.C., P.H.R.B., J.R.B.), and School of Pathology and Laboratory Medicine (A.J.H., K.R.), University of Western Australia, Crawley WA 6009, Australia; Department of Radiology (J.H., S.S.), Royal Perth Hospital, Perth WA 6000, Australia; Medical Department II (K.G.P.), Grosshadern, University of Munich, 81377 Munich, Germany; and School of Surgery (F.M.v.B.), University of Western Australia, Crawley WA 6009, Australia
| | - P Hugh R Barrett
- Department of Clinical Biochemistry (A.J.H., L.H., K.R., F.M.v.B., J.R.B.), PathWest Laboratory Medicine WA, Royal Perth Hospital, Perth WA 6000, Australia; School of Medicine and Pharmacology (A.J.H., D.C., P.H.R.B., J.R.B.), and School of Pathology and Laboratory Medicine (A.J.H., K.R.), University of Western Australia, Crawley WA 6009, Australia; Department of Radiology (J.H., S.S.), Royal Perth Hospital, Perth WA 6000, Australia; Medical Department II (K.G.P.), Grosshadern, University of Munich, 81377 Munich, Germany; and School of Surgery (F.M.v.B.), University of Western Australia, Crawley WA 6009, Australia
| | - Frank M van Bockxmeer
- Department of Clinical Biochemistry (A.J.H., L.H., K.R., F.M.v.B., J.R.B.), PathWest Laboratory Medicine WA, Royal Perth Hospital, Perth WA 6000, Australia; School of Medicine and Pharmacology (A.J.H., D.C., P.H.R.B., J.R.B.), and School of Pathology and Laboratory Medicine (A.J.H., K.R.), University of Western Australia, Crawley WA 6009, Australia; Department of Radiology (J.H., S.S.), Royal Perth Hospital, Perth WA 6000, Australia; Medical Department II (K.G.P.), Grosshadern, University of Munich, 81377 Munich, Germany; and School of Surgery (F.M.v.B.), University of Western Australia, Crawley WA 6009, Australia
| | - John R Burnett
- Department of Clinical Biochemistry (A.J.H., L.H., K.R., F.M.v.B., J.R.B.), PathWest Laboratory Medicine WA, Royal Perth Hospital, Perth WA 6000, Australia; School of Medicine and Pharmacology (A.J.H., D.C., P.H.R.B., J.R.B.), and School of Pathology and Laboratory Medicine (A.J.H., K.R.), University of Western Australia, Crawley WA 6009, Australia; Department of Radiology (J.H., S.S.), Royal Perth Hospital, Perth WA 6000, Australia; Medical Department II (K.G.P.), Grosshadern, University of Munich, 81377 Munich, Germany; and School of Surgery (F.M.v.B.), University of Western Australia, Crawley WA 6009, Australia
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Umpleby AM. HORMONE MEASUREMENT GUIDELINES: Tracing lipid metabolism: the value of stable isotopes. J Endocrinol 2015; 226:G1-10. [PMID: 26047888 DOI: 10.1530/joe-14-0610] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 06/04/2015] [Indexed: 01/14/2023]
Abstract
Labelling molecules with stable isotopes to create tracers has become a gold-standard method to study the metabolism of lipids and lipoproteins in humans. There are a range of techniques which use stable isotopes to measure fatty acid flux and oxidation, hepatic fatty synthesis, cholesterol absorption and synthesis and lipoprotein metabolism in humans. Stable isotope tracers are safe to use, enabling repeated studies to be undertaken and allowing studies to be undertaken in children and pregnant women. This review provides details of the most appropriate tracers to use, the techniques which have been developed and validated for measuring different aspects of lipid metabolism and some of the limitations of the methodology.
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Affiliation(s)
- A Margot Umpleby
- Diabetes and Metabolic MedicineFaculty of Health and Metabolic Sciences, University of Surrey, Leggett Building, Daphne Jackson Road, Manor Park, Guildford GU2 7WG, UK
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Vergès B, Duvillard L, Lagrost L, Vachoux C, Garret C, Bouyer K, Courtney M, Pomié C, Burcelin R. Changes in lipoprotein kinetics associated with type 2 diabetes affect the distribution of lipopolysaccharides among lipoproteins. J Clin Endocrinol Metab 2014; 99:E1245-53. [PMID: 24694333 DOI: 10.1210/jc.2013-3463] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
CONTEXT Lipopolysaccharides (LPSs) are inflammatory components of the outer membrane of Gram-negative bacteria and, in plasma, are mostly associated with lipoproteins. This association is thought to promote their catabolism while reducing their proinflammatory effects. OBJECTIVES Our aim was to determine the impact of lipoprotein kinetics on plasma LPS distribution and how it may affect patients with type 2 diabetes mellitus (T2DM). DESIGN We performed a kinetic study in 30 individuals (16 T2DM patients, 14 controls) and analyzed the impact of changes in lipoprotein kinetics on LPS distribution among lipoproteins. RESULTS Plasma LPS levels in T2DM patients were not different from those in controls, but LPS distribution in the two groups was different. Patients with T2DM had higher LPS-very low-density lipoprotein (VLDL; 31% ± 7% vs 22% ± 11%, P = .002), LPS-high-density lipoprotein (HDL; 29% ± 9% vs 19% ± 10%, P = .015), free (nonlipoprotein bound) LPS (10% ± 4% vs 7% ± 4%, P = .043) and lower LPS-low-density lipoprotein (LDL; 30% ± 13% vs 52% ± 16%, P = .001). In multivariable analysis, VLDL-LPS was associated with HDL-LPS (P < .0001); LDL-LPS was associated with VLDL-LPS (P = .004), and VLDL apolipoprotein (apo) B100 catabolism (P = .002); HDL-LPS was associated with free LPS (P < .0001) and VLDL-LPS (P = .033); free LPS was associated with HDL-LPS (P < .0001). In a patient featuring a dramatic decrease in VLDL catabolism due to apoA-V mutation, LDL-LPS was severely decreased (0.044 EU/mL vs 0.788 EU/mL in controls). The difference between T2DM patients and controls for LDL-LPS fraction was no longer significant after controlling for VLDL apoB100 total fractional catabolic rate. CONCLUSIONS Our data suggest that in humans, free LPS transfers first to HDL and then to VLDL, whereas the LPS-bound LDL fraction is mainly derived from VLDL catabolism; the latter may hence represent a LPS catabolic pathway. T2DM patients show lower LDL-LPS secondary to reduced VLDL catabolism, which may represent an impaired catabolic pathway.
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Affiliation(s)
- Bruno Vergès
- Department of Endocrinology-Diabetology (B.V.), University-Hospital, and INSERM CRI 866 (B.V., L.D., L.L.), Medicine University, 21000 Dijon, France; INSERM Unité 1048 (C.V., C.G., C.P., R.B.), Institut de Recherche sur les Maladies Métaboliques et Cardiovasculaires de Rangueil (I2MC), 31432 Toulouse, France; and VAIOMER SAS (K.B., M.C.), 31670 Labège, France
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12
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Lassman ME, McAvoy T, Lee AYH, Chappell D, Wong O, Zhou H, Reyes-Soffer G, Ginsberg HN, Millar JS, Rader DJ, Gutstein DE, Laterza O. Practical immunoaffinity-enrichment LC-MS for measuring protein kinetics of low-abundance proteins. Clin Chem 2014; 60:1217-24. [PMID: 24751376 DOI: 10.1373/clinchem.2014.222455] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
BACKGROUND For a more complete understanding of pharmacodynamic, metabolic, and pathophysiologic effects, protein kinetics, such as production rate and fractional catabolic rate, can offer substantially more information than protein concentration alone. Kinetic experiments with stable isotope tracers typically require laborious sample preparation and are most often used for studying abundant proteins. Here we describe a practical methodology for measuring isotope enrichment into low-abundance proteins that uses an automated procedure and immunoaffinity enrichment (IA) with LC-MS. Low-abundance plasma proteins cholesteryl ester transfer protein (CETP) and proprotein convertase subtilisin/kexin type 9 (PCSK9) were studied as examples. METHODS Human participants (n = 39) were infused with [(2)H(3)]leucine, and blood samples were collected at multiple time points. Sample preparation and analysis were automated and multiplexed to increase throughput. Proteins were concentrated from plasma by use of IA and digested with trypsin to yield proteotypic peptides that were analyzed by microflow chromatography-mass spectrometry to measure isotope enrichment. RESULTS The IA procedure was optimized to provide the greatest signal intensity. Use of a gel-free method increased throughput while increasing the signal. The intra- and interassay CVs were <15% at all isotope enrichment levels studied. More than 1400 samples were analyzed in <3 weeks without the need for instrument stoppages or user interventions. CONCLUSIONS The use of automated gel-free methods to multiplex the measurement of isotope enrichment was applied to the low-abundance proteins CETP and PCSK9.
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Affiliation(s)
| | | | | | | | | | | | | | - Henry N Ginsberg
- Molecular Biomarkers and Diagnostics, Molecular Biomarkers-PPDM, and Clinical Pharmacology, Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Whitehouse Station, NJ; Columbia University Medical Center, New York, NY; Division of Translational Medicine and Human Genetics, University of Pennsylvania, Philadelphia, PA
| | - John S Millar
- Division of Translational Medicine and Human Genetics, University of Pennsylvania, Philadelphia, PA
| | - Daniel J Rader
- Division of Translational Medicine and Human Genetics, University of Pennsylvania, Philadelphia, PA
| | - David E Gutstein
- Clinical Pharmacology, Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Whitehouse Station, NJ
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13
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Lindenbach BD, Rice CM. The ins and outs of hepatitis C virus entry and assembly. Nat Rev Microbiol 2013; 11:688-700. [PMID: 24018384 DOI: 10.1038/nrmicro3098] [Citation(s) in RCA: 275] [Impact Index Per Article: 25.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Hepatitis C virus, a major human pathogen, produces infectious virus particles with several unique features, such as an ability to interact with serum lipoproteins, a dizzyingly complicated process of virus entry, and a pathway of virus assembly and release that is closely linked to lipoprotein secretion. Here, we review these unique features, with an emphasis on recent discoveries concerning virus particle structure, virus entry and virus particle assembly and release.
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Affiliation(s)
- Brett D Lindenbach
- Department of Microbial Pathogenesis, Yale University, New Haven, Connecticut 06536, USA
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14
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Zhou H, Castro-Perez J, Lassman ME, Thomas T, Li W, McLaughlin T, Dan X, Jumes P, Wagner JA, Gutstein DE, Hubbard BK, Rader DJ, Millar JS, Ginsberg HN, Reyes-Soffer G, Cleary M, Previs SF, Roddy TP. Measurement of apo(a) kinetics in human subjects using a microfluidic device with tandem mass spectrometry. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2013; 27:1294-302. [PMID: 23681806 PMCID: PMC4944116 DOI: 10.1002/rcm.6572] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2013] [Revised: 02/20/2013] [Accepted: 03/14/2013] [Indexed: 05/15/2023]
Abstract
RATIONALE Apolipoprotein(a) [apo(a)] is the defining protein component of lipoprotein(a) [Lp(a)], an independent risk factor for cardiovascular disease. The regulation of Lp(a) levels in blood is poorly understood in part due to technical challenges in measuring Lp(a) kinetics. Improvements in the ability to readily and reliably measure the kinetics of apo(a) using a stable isotope labeled tracer is expected to facilitate studies of the role of Lp(a) in cardiovascular disease. Since investigators typically determine the isotopic labeling of protein-bound amino acids following acid-catalyzed hydrolysis of a protein of interest [e.g., apo(a)], studies of protein synthesis require extensive protein purification which limits throughput and often requires large sample volumes. We aimed to develop a rapid and efficient method for studying apo(a) kinetics that is suitable for use in studies involving human subjects. METHODS Microfluidic device and tandem mass spectrometry were used to quantify the incorporation of [(2)H3]-leucine tracer into protein-derived peptides. RESULTS We demonstrated that it is feasible to quantify the incorporation of [(2)H3]-leucine tracer into a proteolytic peptide from the non-kringle repeat region of apo(a) in human subjects. Specific attention was directed toward optimizing the multiple reaction monitoring (MRM) transitions, mass spectrometer settings, and chromatography (i.e., critical parameters that affect the sensitivity and reproducibility of isotopic enrichment measurements). The results demonstrated significant advantages with the use of a microfluidic device technology for studying apo(a) kinetics, including enhanced sensitivity relative to conventional micro-flow chromatography, a virtually drift-free elution profile, and a stable and robust electrospray. CONCLUSIONS The technological advances described herein enabled the implementation of a novel method for studying the kinetics of apo(a) in human subjects infused with [(2)H3]-leucine.
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Affiliation(s)
- Haihong Zhou
- Molecular Biomarkers-PPDM, Merck Sharp & Dohme Corp., Whitehouse Station, NJ, USA
| | - Jose Castro-Perez
- Molecular Biomarkers-PPDM, Merck Sharp & Dohme Corp., Whitehouse Station, NJ, USA
| | - Michael E. Lassman
- Clinical Development Laboratory, Merck Sharp & Dohme Corp., Whitehouse Station, NJ, USA
| | | | - Wenyu Li
- Molecular Biomarkers-PPDM, Merck Sharp & Dohme Corp., Whitehouse Station, NJ, USA
| | - Theresa McLaughlin
- Molecular Biomarkers-PPDM, Merck Sharp & Dohme Corp., Whitehouse Station, NJ, USA
| | - Xie Dan
- Molecular Biomarkers-PPDM, Merck Sharp & Dohme Corp., Whitehouse Station, NJ, USA
| | - Patricia Jumes
- Clinical Pharmacology, Merck Sharp & Dohme Corp., Whitehouse Station, NJ, USA
| | - John A. Wagner
- Clinical Pharmacology, Merck Sharp & Dohme Corp., Whitehouse Station, NJ, USA
| | - David E. Gutstein
- Clinical Pharmacology, Merck Sharp & Dohme Corp., Whitehouse Station, NJ, USA
| | - Brian K. Hubbard
- Molecular Biomarkers-PPDM, Merck Sharp & Dohme Corp., Whitehouse Station, NJ, USA
| | - Daniel J. Rader
- Division of Translational Medicine and Human Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - John S. Millar
- Division of Translational Medicine and Human Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | | | | | - Michele Cleary
- Molecular Biomarkers-PPDM, Merck Sharp & Dohme Corp., Whitehouse Station, NJ, USA
| | - Stephen F. Previs
- Molecular Biomarkers-PPDM, Merck Sharp & Dohme Corp., Whitehouse Station, NJ, USA
- Correspondence to: S. F. Previs, Molecular Biomarkers, Merck Sharp & Dohme Corp., 2015 Galloping Hill Road, Kenilworth, NJ 07033, USA.
| | - Thomas P. Roddy
- Molecular Biomarkers-PPDM, Merck Sharp & Dohme Corp., Whitehouse Station, NJ, USA
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15
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Vergès B, Duvillard L, Brindisi MC, Gautier E, Krempf M, Costet P, Cariou B. Lack of association between plasma PCSK9 and LDL-apoB100 catabolism in patients with uncontrolled type 2 diabetes. Atherosclerosis 2011; 219:342-8. [DOI: 10.1016/j.atherosclerosis.2011.07.098] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/12/2011] [Revised: 07/04/2011] [Accepted: 07/14/2011] [Indexed: 11/26/2022]
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16
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Matthan NR, Jalbert SM, Barrett PHR, Dolnikowski GG, Schaefer EJ, Lichtenstein AH. Gender-specific differences in the kinetics of nonfasting TRL, IDL, and LDL apolipoprotein B-100 in men and premenopausal women. Arterioscler Thromb Vasc Biol 2008; 28:1838-43. [PMID: 18658047 PMCID: PMC2872098 DOI: 10.1161/atvbaha.108.163931] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE To investigate mechanisms underlying gender differences in serum lipoprotein concentrations, the kinetic behavior of apoB-100 was assessed. METHODS AND RESULTS Twenty subjects (<50 years; 12 men and 8 premenopausal women) were provided a Western diet for 4 to 6 weeks, after which the kinetics of apoB-100 in triglyceride-rich, intermediate-density, and low-density lipoprotein (TRL, IDL, and LDL) were determined in the fed state. Nonfasting plasma TC, LDL-C, and triglyceride concentrations were 23%, 34%, and 57% lower, respectively, in the women compared with men. Plasma TRL and LDL apoB 100 pool sizes were lower by 40% and 30%, respectively. These differences were accounted for by higher TRL and LDL apoB 100 fractional catabolic rates (FCR), rather than differences in production rates (PR). Plasma TRL-C and LDL-C were positively correlated with TRL and LDL apoB 100 concentrations and pool size, and negatively correlated with TRL and LDL apoB 100 FCR (women: r=-0.59, P<0.01 and r=-0.54, P<0.04, and men: r=-0.43, P<0.05 and r=-0.44, P<0.05). No significant associations were observed between plasma TRL-C and LDL-C and PR. CONCLUSIONS These data suggest the mechanism for lower TRL-C and LDL-C concentrations in women was determined predominantly by higher TRL and LDL FCR rather than lower PR. This could explain, in part, the lower CVD risk in premenopausal women relative to men.
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Affiliation(s)
- Nirupa R Matthan
- Cardiovascular Nutrition Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA 02111, USA.
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17
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Fouillet H, Juillet B, Bos C, Mariotti F, Gaudichon C, Benamouzig R, Tomé D. Urea-nitrogen production and salvage are modulated by protein intake in fed humans: results of an oral stable-isotope-tracer protocol and compartmental modeling. Am J Clin Nutr 2008; 87:1702-14. [PMID: 18541559 DOI: 10.1093/ajcn/87.6.1702] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND The influence of protein source on postprandial urea kinetics is poorly understood, despite its nutritional significance with respect to nitrogen homeostasis. Furthermore, traditional tracer infusion studies underestimate acute postprandial change in urea kinetics. OBJECTIVE We investigated postprandial, non-steady state urea kinetics and their modulation by qualitative and quantitative factors of protein intake by the combined use of robust clinical data on nitrogen postprandial distribution and mathematical modeling. DESIGN In healthy subjects standardized to a normal protein intake for 7 d, dietary and total nitrogen kinetics were measured for 8 h in plasma proteins, body, and urinary urea after the ingestion of a (15)N-labeled milk (n = 8), soy (n = 8), or wheat (n = 8) protein meal. In subjects who received the soy protein meal, these postprandial measurements were repeated after a further 7-d adaptation to a high protein intake. A 4-compartment model was developed to calculate from these data the postprandial kinetics of production, urinary excretion, and intestinal hydrolysis of urea nitrogen from both dietary and endogenous sources. RESULTS Urinary urea excretion was not influenced by the protein source in the meal but was influenced by the protein level in the diet. By contrast, urea production and hydrolysis were higher when ingesting plant versus animal protein, together with a higher efficiency of urea hydrolysis (50-60% versus 25% of the urea produced being hydrolyzed, respectively). CONCLUSIONS We conclude that urea hydrolysis is an acute nitrogen-sparing mechanism that can counterbalance a postprandial higher urea production, and the efficiency of this recycling is higher when the usual protein intake is lower.
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Affiliation(s)
- Hélène Fouillet
- INRA, CNRH-IdF, UMR914 Nutrition Physiology and Ingestive Behavior, F-75005 Paris, France.
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18
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Ng TWK, Watts GF, Barrett PHR, Rye KA, Chan DC. Effect of weight loss on LDL and HDL kinetics in the metabolic syndrome: associations with changes in plasma retinol-binding protein-4 and adiponectin levels. Diabetes Care 2007; 30:2945-50. [PMID: 17686833 DOI: 10.2337/dc07-0768] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
OBJECTIVE The purpose of this study was to examine the effect of weight loss on LDL and HDL kinetics and plasma retinol-binding protein-4 (RBP-4) and adiponectin levels in men with the metabolic syndrome. RESEARCH DESIGN AND METHODS LDL apolipoprotein (apo)B-100 and HDL apoA-I kinetics were studied in 35 obese men with the metabolic syndrome at the start and end of a 16-week intervention trial of a hypocaloric, low-fat diet (n = 20) versus a weight maintenance diet (n = 15) using a stable isotope technique and multicompartmental modeling. RESULTS Consumption of the low-fat diet produced significant reductions (P < 0.01) in BMI, abdominal fat compartments, and homeostasis model assessment score compared with weight maintenance. These were associated with a significant increase in adiponectin and a fall in plasma RBP-4, triglycerides, LDL cholesterol, and LDL apoB-100 concentration (P < 0.05). Weight loss significantly increased the catabolism of LDL apoB-100 (+27%, P < 0.05) but did not affect production; it also decreased both the catabolic (-13%) and production (-13%) rates of HDL apoA-I (P < 0.05), thereby not altering plasma HDL apoA-I or HDL cholesterol concentrations. VLDL apoB-100 production fell significantly with weight loss (P < 0.05). The increase in LDL catabolism was inversely correlated with the fall in RBP-4 (r = -0.54, P < 0.05) and the decrease in HDL catabolism with the rise in adiponectin (r = -0.56, P < 0.01). CONCLUSIONS In obese men with metabolic syndrome, weight loss with a low-fat diet decreases the plasma LDL apoB-100 concentration by increasing the catabolism of LDL apoB-100; weight loss also delays the catabolism of HDL apoA-I with a concomitant reduction in the secretion of HDL apoA-I. These effects of weight loss could partly involve changes in RBP-4 and adiponectin levels.
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Affiliation(s)
- Theodore W K Ng
- School of Medicine and Pharmacology, Metabolic Research Centre, University of Western Australia, New South Wales, Australia
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19
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Ramakrishnan R. Alternative equations for whole-body protein synthesis and for fractional synthetic rates of proteins. Metabolism 2007; 56:1550-60. [PMID: 17950107 PMCID: PMC2435311 DOI: 10.1016/j.metabol.2007.06.023] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/13/2007] [Accepted: 06/29/2007] [Indexed: 12/01/2022]
Abstract
In a constant infusion study of a mass isotope of leucine, two alternative equations are commonly available to calculate amino acid oxidation rate and, thence, whole-body protein synthesis. One, developed by Matthews et al (Am J Physiol Endocrinol Metab. 1980;238:E473-E479), is shown here to require assuming a tracee steady state (TSS), namely, that tracee (unlabeled) amino acid concentrations and fluxes (rates of oxidation and incorporation into protein) are unaltered compared with the preinfusion state. The other, developed by Garlick and coworkers (Melville et al, Metabolism 1989;38:248-255), stems from a protein steady state (PSS) assumption, namely, that protein synthesis is unaffected by the tracer infusion. We derive here a simple expression for the relative difference in whole-body protein synthesis computed from the two assumptions, and a simple test of the validity of TSS in the form of an equality that must be satisfied by plasma measurements at all times. We also propose two experiments to discriminate between the two assumptions. Theoretical reasons and experimental evidence from the literature are offered to support PSS. The two assumptions result in different expressions for fractional synthetic rates (FSRs) of individual or organ proteins-TSS requires the use of tracer-to-tracee ratios and PSS the use of enrichments. An expression is derived here for the relative difference in FSR with TSS vs PSS. For both whole-body synthesis and for FSR, the TSS assumption consistently results in an underestimate, the relative bias roughly equal to the precursor amino acid enrichment.
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Affiliation(s)
- Rajasekhar Ramakrishnan
- Department of Pediatrics, Columbia University College of Physicians and Surgeons, New York NY 10032, USA.
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20
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Lamon-Fava S, Diffenderfer MR, Barrett PHR, Buchsbaum A, Matthan NR, Lichtenstein AH, Dolnikowski GG, Horvath K, Asztalos BF, Zago V, Schaefer EJ. Effects of different doses of atorvastatin on human apolipoprotein B-100, B-48, and A-I metabolism. J Lipid Res 2007; 48:1746-53. [PMID: 17526934 DOI: 10.1194/jlr.m700067-jlr200] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Nine hypercholesterolemic and hypertriglyceridemic subjects were enrolled in a randomized, placebo-controlled, double-blind, crossover study to test the effect of atorvastatin 20 mg/day and 80 mg/day on the kinetics of apolipoprotein B-100 (apoB-100) in triglyceride-rich lipoprotein (TRL), intermediate density lipoprotein (IDL), and LDL, of apoB-48 in TRL, and of apoA-I in HDL. Compared with placebo, atorvastatin 20 mg/day was associated with significant reductions in TRL, IDL, and LDL apoB-100 pool size as a result of significant increases in fractional catabolic rate (FCR) without changes in production rate (PR). Compared with the 20 mg/day dose, atorvastatin 80 mg/day caused a further significant reduction in the LDL apoB-100 pool size as a result of a further increase in FCR. ApoB-48 pool size was reduced significantly by both atorvastatin doses, and this reduction was associated with nonsignificant increases in FCR. The lathosterol-campesterol ratio was decreased by atorvastatin treatment, and changes in this ratio were inversely correlated with changes in TRL apoB-100 and apoB-48 PR. No significant effect on apoA-I kinetics was observed at either dose of atorvastatin. Our data indicate that atorvastatin reduces apoB-100- and apoB-48-containing lipoproteins by increasing their catabolism and has a dose-dependent effect on LDL apoB-100 kinetics. Atorvastatin-mediated changes in cholesterol homeostasis may contribute to apoB PR regulation.
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Affiliation(s)
- Stefania Lamon-Fava
- Lipid Metabolism Laboratory, Jean Mayer United States Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, Boston, MA, USA.
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August E, Parker KH, Barahona M. A dynamical model of lipoprotein metabolism. Bull Math Biol 2007; 69:1233-54. [PMID: 17334872 DOI: 10.1007/s11538-006-9132-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2005] [Accepted: 03/29/2006] [Indexed: 11/30/2022]
Abstract
We present a dynamical model of lipoprotein metabolism derived by combining a cascading process in the blood stream and cellular level regulatory dynamics. We analyse the existence and stability of equilibria and show that this low-dimensional, nonlinear model exhibits bistability between a low and a high cholesterol state. A sensitivity analysis indicates that the intracellular concentration of cholesterol is robust to parametric variations while the plasma cholesterol can vary widely. We show how the dynamical response to time-dependent inputs can be used to diagnose the state of the system. We also establish the connection between parameters in the system and medical and genetic conditions.
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Affiliation(s)
- E August
- Department of Bioengineering, Imperial College London, South Kensington Campus, London, United Kingdom
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22
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Tremblay AJ, Lamarche B, Ruel IL, Hogue JC, Deshaies Y, Gagné C, Couture P. Effects of fenofibrate on apolipoprotein kinetics in patients with coexisting dysbetalipoproteinemia and heterozygous familial hypercholesterolemia. Atherosclerosis 2006; 188:203-12. [PMID: 16337207 DOI: 10.1016/j.atherosclerosis.2005.10.037] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/13/2005] [Revised: 10/06/2005] [Accepted: 10/22/2005] [Indexed: 02/03/2023]
Abstract
Dysbetalipoproteinemia (dysb) and familial hypercholesterolemia (FH) are two genetic disorders giving rise to severe disturbances of lipid homeostasis and premature atherosclerosis. The co-occurrence of both metabolic abnormalities is very rare and is estimated to affect 1 individual per 2,500,000 in the general population. However, the relative contribution of these two dyslipidemias to the combined lipoprotein phenotype is unknown. The two objectives of this study were (1) to compare the in vivo kinetics of triglyceride-rich lipoprotein (TRL) apolipoprotein (apo) B48, VLDL, IDL and LDL apo B100 as well as plasma apo A-l labelled with a stable isotope (l-(5,5,5-D3) leucine) in two subjects presenting both heterozygous FH and dysbetalipoproteinemia (FH+/dysb+), in six FH heterozygotes and in five normolipidemic controls, and (2) to examine the impact of a 6-week treatment with micronized fenofibrate 200 mg/d on apolipoprotein kinetics in FH+/dysb+. As compared with FH heterozygotes and controls, the two FH+/dysb+ subjects showed elevated TRL apo B48 and VLDL, IDL apo B100 pool sizes (PS) mainly due to lower fractional catabolic rates (FCR). Moreover, as compared with FH heterozygotes, FH+/dysb+ subjects presented lower LDL apo B100 PS due to a higher FCR. Pool size, FCR and production rate (PR) of apo A-l were higher in FH+/dysb+ subjects than in FH heterozygotes. In FH+/dysb+ subjects, fenofibrate treatment was associated with a decreased TRL apo B48 PS (-52 and -61%), VLDL apo B100 (-61 and -63%) and IDL apo B100 (-37 and -16%) and an increased FCR of TRL apo B48 (10 and 67%), VLDL apo B100 (123 and 57%) and IDL apo B100 (29 and 10%). Fenofibrate also increased LDL apo B100 PS (3 and 57%) due to an increase in PR (80 and 26%) but had divergent effects on LDL apo B100 FCR. These results indicate that the coexistence of dysbetalipoproteinemia and heterozygous FH results in a mixed lipoprotein phenotype that is intermediate between the two pure phenotypes and that fenofibrate treatment partially reverses lipoprotein abnormalities, mostly through changes in PR and FCR of apo B48- and B100-containing lipoproteins.
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Ramakrishnan R. Studying apolipoprotein turnover with stable isotope tracers: correct analysis is by modeling enrichments. J Lipid Res 2006; 47:2738-53. [PMID: 16951401 PMCID: PMC3276318 DOI: 10.1194/jlr.m600302-jlr200] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Lipoprotein kinetic parameters are determined from mass spectrometry data after administering mass isotopes of amino acids, which label proteins endogenously. The standard procedure is to model the isotopic content of the labeled precursor amino acid and of proteins of interest as tracer-to-tracee ratio (TTR). It is shown here that even though the administered tracer alters amino acid mass and turnover, apolipoprotein synthesis is unaltered and hence the apolipoprotein system is in a steady state, with the total (labeled plus unlabeled) masses and fluxes remaining constant. The correct model formulation for apolipoprotein kinetics is shown to be in terms of tracer enrichment, not of TTR. The needed mathematical equations are derived. A theoretical error analysis is carried out to calculate the magnitude of error in published results using TTR modeling. It is shown that TTR modeling leads to a consistent underestimation of the fractional synthetic rate. In constant-infusion studies, the bias error percent is shown to equal approximately the plateau enrichment, generally <10%. It is shown that, in bolus studies, the underestimation error can be larger. Thus, for mass isotope studies with endogenous tracers, apolipoproteins are in a steady state and the data should be fitted by modeling enrichments.
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Affiliation(s)
- Rajasekhar Ramakrishnan
- Department of Pediatrics, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA.
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24
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Barrett PHR, Chan DC, Watts GF. Thematic review series: Patient-Oriented Research. Design and analysis of lipoprotein tracer kinetics studies in humans. J Lipid Res 2006; 47:1607-19. [PMID: 16728729 DOI: 10.1194/jlr.r600017-jlr200] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Lipoprotein tracer kinetics studies have for many years provided new and important knowledge of the metabolism of lipoproteins. Our understanding of kinetics defects in lipoprotein metabolism has resulted from the use of tracer kinetics studies and mathematical modeling. This review discusses all aspects of the performance of kinetics studies, including the development of hypotheses, experimental design, statistical considerations, tracer administration and sampling schedule, and the development of compartmental models for the interpretation of tracer data. In addition to providing insight into new metabolic pathways, such models provide quantitative information on the effect of interventions on lipoprotein metabolism. Compartment models are useful tools to describe experimental data but can also be used to aid in experimental design and hypothesis generation. The SAAM II program provides an easy-to-use interface with which to develop and test compartmental models against experimental models. The development of a model requires that certain checks be performed to ensure that the model describes the experimental data and that the model parameters can be estimated with precision. In addition to methodologic aspects, several compartment models of apoprotein and lipid metabolism are reviewed.
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Affiliation(s)
- P Hugh R Barrett
- Metabolic Research Centre, School of Medicine and Pharmacology, University of Western Australia, Perth, Australia.
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25
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Parhofer KG, Barrett PHR. Thematic review series: patient-oriented research. What we have learned about VLDL and LDL metabolism from human kinetics studies. J Lipid Res 2006; 47:1620-30. [PMID: 16720894 DOI: 10.1194/jlr.r600013-jlr200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Lipoprotein metabolism is the result of a complex network of many individual components. Abnormal lipoprotein concentrations can result from changes in the production, conversion, or catabolism of lipoprotein particles. Studies in hypolipoproteinemia and hyperlipoproteinemia have elucidated the processes that control VLDL secretion as well as VLDL and LDL catabolism. Here, we review the current knowledge regarding apolipoprotein B (apoB) metabolism, focusing on selected clinically relevant conditions. In hypobetalipoproteinemia attributable to truncations in apoB, the rate of secretion is closely linked to the length of apoB. On the other hand, in patients with the metabolic syndrome, it appears that substrate, in the form of free fatty acids, coupled to the state of insulin resistance can induce hypersecretion of VLDL-apoB. Studies in patients with familial hypercholesterolemia, familial defective apoB, and mutant forms of proprotein convertase subtilisin/kexin type 9 show that mutations in the LDL receptor, the ligand for the receptor, or an intracellular chaperone for the receptor are the most important determinants in regulating LDL catabolism. This review also demonstrates the variance of results within similar, or even the same, phenotypic conditions. This underscores the sensitivity of metabolic studies to methodological aspects and thus the importance of the inclusion of adequate controls in studies.
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Briand F, Magot T, Krempf M, Nguyen P, Ouguerram K. Effects of atorvastatin on high-density lipoprotein apolipoprotein A-I metabolism in dogs. Eur J Clin Invest 2006; 36:224-30. [PMID: 16620283 DOI: 10.1111/j.1365-2362.2006.01622.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND The mechanisms involved in the decline of high-density lipoprotein (HDL) levels at a higher dose of atorvastatin have not yet been elucidated. We investigated the effects of atorvastatin on HDL-apolipoprotein (apo) A-I metabolism in dogs, a species lacking cholesteryl ester transfer protein activity. MATERIALS AND METHODS Seven ovariectomized normolipidaemic female Beagle dogs underwent a primed constant infusion of [5,5,5-(2)H(3)] leucine to determine HDL-apo A-I kinetics before and after atorvastatin treatment (5 mg kg(-1) d(-1) for 6 weeks). Plasma lipoprotein profiles, activity of HDL-modifying enzymes involved in reverse cholesterol transport and hepatic scavenger receptor class B type I (SR-BI) expression were also studied. RESULTS Atorvastatin treatment decreased HDL-cholesterol levels (3.56 +/- 0.24 vs. 2.64 +/- 0.15 mmol L(-1), P < 0.05). HDL-triglycerides were not affected. HDL-phospholipids levels were decreased (4.28 +/- 0.13 vs. 3.29 +/- 0.13 mmol L(-1), P < 0.05), as well as phospholipids transfer protein (PLTP) activity (0.83 +/- 0.05 vs. 0.60 +/- 0.05 pmol microL(-1) min(-1), P < 0.05). Activity of lecithin: cholesterol acyl transferase (LCAT), hepatic lipase (HL) and SR-BI expression did not change. HDL-apo A-I absolute production rate (APR) was higher after treatment (twofold, P < 0.05) as well as fractional catabolic rate (FCR) (threefold, P < 0.05). This resulted in lower HDL-apo A-I levels (2.36 +/- 0.03 vs. 1.55 +/- 0.04 g l(-1), P < 0.05). Plasma lipoprotein profiles showed a decrease in large HDL(1) levels, with lower apo A-I and higher apo E levels in this subfraction. CONCLUSIONS Although a high dose of atorvastatin up-regulated HDL-apo A-I production, this drug also increased HDL-apo A-I FCR in dogs. This effect could be explained by a higher uptake of apo E-enriched HDL(1) by hepatic lipoprotein receptors.
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Affiliation(s)
- F Briand
- Centre de Recherche en Nutrition Humaine, INSERM U539, CHU Nantes, France
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Dinkel RE, Barrett PHR, Demant T, Parhofer KG. In-vivo metabolism of VLDL-apolipoprotein-B, -CIII and -E in normolipidemic subjects. Nutr Metab Cardiovasc Dis 2006; 16:215-221. [PMID: 16580589 DOI: 10.1016/j.numecd.2005.06.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/13/2005] [Revised: 06/08/2005] [Accepted: 06/14/2005] [Indexed: 10/25/2022]
Abstract
BACKGROUND AND AIM ApoE and apoC-III are important components of lipoprotein metabolism. While the function of both apoproteins is relatively well understood, little is known about the in vivo metabolism of these proteins, partly because of the lack of a standardized method to isolate these apoproteins in large sample numbers. METHODS AND RESULTS We developed a new reverse phase HPLC method (acetonitril/phosphate gradient; Aquapore RP-300, 7 microm, 220 x 4.6 mm) to isolate a number of different apoproteins, including apoC-III and apoE from VLDL. This method was then used in a study which aimed at determining VLDL-apoE-3 and VLDL-apoC-III metabolism. In addition VLDL-apoB and LDL-apoB metabolism was determined. Endogenous labeling with d(3)-leucine, mass spectrometry and multicompartmental modeling was used in 6 normolipidemic healthy male subjects. Tracer/tracee ratios of free plasma leucine, VLDL-apoE, -apoC-III, -apoB, and LDL-apoB leucine were determined over 60 h following a bolus of d(3)-leucine (5 mg kg(-1)). In all subjects sufficient apoC-III could be isolated by reverse phase HPLC to derive metabolic parameters, while apoE metabolic parameters could only be determined if apoE plasma concentration was 0.75 mg dl(-1) or higher. Compared to VLDL-apoB (FCR 10.4 +/- 3.3 d(-1), production 17.8 +/- 4.5 mg kg(-1) d(-1)), VLDL-apoE-3 (FCR 1.03 +/- 0.11 d(-1), production 0.50 +/- 0.29 mg kg(-1) d(-1)) and VLDL-apoC-III (FCR 1.67 +/- 1.22 d(-1), production 0.44 +/- 0.24 mg kg(-1) d(-1)) parameters were much lower. This indicates that apoE-3 and apoC-III recirculate in plasma and that only a small fraction of apoE and apoC-III on VLDL is newly synthesized. CONCLUSIONS We conclude that HPLC methodology can be used to isolate VLDL-apoC-III and apoE for metabolic studies and that the metabolic fate of apoC-III and apoE is different from that of apoB because both apoproteins recycle through the VLDL fraction.
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Affiliation(s)
- Regina E Dinkel
- Department of Internal Medicine II, Grosshadern, Ludwig-Maximilians University, Munich, Germany
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28
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Christ ER, Cummings MH, Stolinski M, Jackson N, Lumb PJ, Wierzbicki AS, Sönksen PH, Russell-Jones DL, Umpleby AM. Low-density lipoprotein apolipoprotein B100 turnover in hypopituitary patients with GH deficiency: a stable isotope study. Eur J Endocrinol 2006; 154:459-66. [PMID: 16498060 DOI: 10.1530/eje.1.02105] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
BACKGROUND Epidemiological studies suggest that hypopituitary patients have an increased risk for cardiovascular mortality. The dyslipidaemia associated with this condition is often characterised by an increase in total cholesterol (TC) and low-density lipoprotein (LDL) cholesterol (LDL-C) and may contribute to these findings. The underlying mechanisms are not fully elucidated. MATERIALS AND METHODS LDL apolipoprotein B (apoB) production rate and metabolic clearance rate were measured in seven patients with hypopituitarism (including GH deficiency) under stable conventional replacement therapy (three males and four females; age 40-16.1 years; body mass index 29.0-6.1 kg/m(2) (means +/- s.d.)) and seven age-, gender- and body mass index-matched control subjects with an infusion of 1-(13)C-leucine. Fasting lipid profile and lipid composition of LDL were also measured. RESULTS Fasting TC, triglycerides (TG), high-density lipoprotein-C, LDL-C and free fatty acid concentrations were not different between hypopituitary patients and control subjects. LDL-TG (P < 0.006) and LDL-TG/LDL apoB ratio (P < 0.02) were significantly increased in hypopituitary patients. LDL apoB pool size was not statistically different between patients and control subjects. In the hypopituitary patients, LDL apoB metabolic clearance rate (P < 0.05) and LDL apoB production rate (P < 0.02) were lower than in the control subjects. CONCLUSIONS The present results suggest that LDL apoB turnover and LDL composition is altered in hypopituitary patients. Whether these findings explain the increased risk for cardiovascular disease in hypopituitary patients remains to be established.
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Affiliation(s)
- Emanuel R Christ
- Department of Endocrinology and Diabetology, University Hospital of Bern, Switzerland
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Ruel IL, Couture P, Cohn JS, Lamarche B. Plasma metabolism of apoB-containing lipoproteins in patients with hepatic lipase deficiency. Atherosclerosis 2005; 180:355-66. [PMID: 15910863 DOI: 10.1016/j.atherosclerosis.2004.12.014] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/23/2004] [Accepted: 12/08/2004] [Indexed: 11/20/2022]
Abstract
The metabolism of apoB-containing lipoproteins was investigated in the fasted state in three complete and three partial hepatic lipase (HL)-deficient subjects as well as in seven normotriglyceridemic (NTG) and two hypertriglyceridemic (HTG) controls using a 12 h primed-constant infusion of L-[5,5,5-D(3)]-leucine. Two males with complete HL deficiency had increased plasma pool sizes of VLDL and IDL apoB-100 due to substantial reductions in fractional catabolic rate (FCR) of VLDL and IDL apoB-100 compared with both NTG and HTG controls. Reductions in LDL apoB-100 production rate (PR) were also observed in these two patients compared with NTG and HTG controls. Complete HL deficiency in the female proband was associated with normal VLDL apoB-100 kinetics, while plasma IDL apoB-100 pool size was increased by 124% due to an 82% decrease in the FCR of IDL apoB-100. The FCR and PR of LDL apoB-100 were reduced by 64 and 51%, respectively, in the proband compared with sex-matched controls. Partial HL-deficient patients were characterized by apoB-containing lipoprotein metabolism similar to that of controls. These results indicate that complete HL deficiency is associated with a potentially atherogenic apoB-containing lipoprotein metabolism that can be modulated considerably by secondary factors such as gender and abdominal obesity.
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Affiliation(s)
- Isabelle L Ruel
- Institute on Nutraceuticals and Functional Foods, Pavillon INAF, Local 2742, 2440 Hochelaga Blvd., Laval University, Que., Canada G1K 7P4
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Jenner JL, Seman LJ, Millar JS, Lamon-Fava S, Welty FK, Dolnikowski GG, Marcovina SM, Lichtenstein AH, Barrett PHR, deLuca C, Schaefer EJ. The metabolism of apolipoproteins (a) and B-100 within plasma lipoprotein (a) in human beings. Metabolism 2005; 54:361-9. [PMID: 15736114 DOI: 10.1016/j.metabol.2004.10.001] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
The metabolism of apolipoproteins (apo) (a) and B-100 within plasma lipoprotein (a) [Lp(a)] was examined in the fed state in 23 subjects aged 41 to 79 years who received a primed-constant infusion of [5,5,5-2H3] leucine over 15 hours. Lipoprotein (a) was isolated from the whole plasma using a lectin affinity-based method. Apolipoprotein (a) and apoB-100 were separated by gel electrophoresis, and tracer enrichment of each apolipoprotein was measured using gas chromatography/mass spectrometry. Data were fit to a multicompartmental model to determine fractional catabolic rates (FCRs) and secretion rates (SRs). The FCRs of apo(a) and apoB-100 (mean +/- SEM) within plasma Lp(a) were significantly different (0.220 +/- 0.030 pool/d and 0.416 +/- 0.040 pool/d, respectively; P < .001). Apolipoprotein (a) SR (0.50 +/- 0.08 mg/[kg per d]) was significantly lower than that of apoB-100 SR (1.53 +/- 0.22 mg/[kg per d]; P < .001) of Lp(a). Plasma concentrations of Lp(a) were correlated significantly with both apo(a) SR and apoB-100 SR (r = 0.837 and r = 0.789, respectively; P < .001) and negatively with apo(a) FCR and Lp(a) apoB-100 FCR (r = -0.547 and r = -0.717, respectively; P < .01). These data implicate different metabolic fates for apo(a) and apoB-100 within Lp(a) in the fed state. We therefore hypothesize that apo(a) does not remain covalently linked to a single apoB-100 lipoprotein but that it rather reassociates at least once with another apoB-100 particle, probably newly synthesized, during its plasma metabolism.
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Affiliation(s)
- Jennifer L Jenner
- Lipid Metabolism Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA 02111, USA
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Chan DC, Barrett PHR, Watts GF. Lipoprotein transport in the metabolic syndrome: methodological aspects of stable isotope kinetic studies. Clin Sci (Lond) 2004; 107:221-32. [PMID: 15225121 DOI: 10.1042/cs20040108] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2004] [Revised: 05/19/2004] [Accepted: 06/30/2004] [Indexed: 11/17/2022]
Abstract
The metabolic syndrome encapsulates visceral obesity, insulin resistance, diabetes, hypertension and dyslipidaemia. Dyslipidaemia is a cardinal feature of the metabolic syndrome that accelerates the risk of cardiovascular disease. It is usually characterized by high plasma concentrations of triacylglycerol (triglyceride)-rich and apoB (apolipoprotein B)-containing lipoproteins, with depressed concentrations of HDL (high-density lipoprotein). However, lipoprotein metabolism is complex and abnormal plasma concentrations can result from alterations in the rates of production and/or catabolism of these lipoprotein particles. Our in vivo understanding of kinetic defects in lipoprotein metabolism in the metabolic syndrome has been achieved chiefly by ongoing developments in the use of stable isotope tracers and mathematical modelling. This review deals with the methodological aspects of stable isotope kinetic studies. The design of in vivo turnover studies requires considerations related to stable isotope tracer administration, duration of sampling protocol and interpretation of tracer data, all of which are critically dependent on the kinetic properties of the lipoproteins under investigation. Such models provide novel insight that further understanding of metabolic disorders and effects of treatments. Future investigations of the pathophysiology and therapy of the dyslipoproteinaemia of the metabolic syndrome will require the development of novel kinetic methodologies. Specifically, new stable isotope techniques are required for investigating in vivo the turnover of the HDL subpopulation of particles, as well as the cellular efflux of cholesterol into the extracellular space and its subsequent transport in plasma and metabolic fate in the liver.
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Affiliation(s)
- Dick C Chan
- Lipoprotein Research Unit, School of Medicine and Pharmacology, University of Western Australia, Perth, WA 6847
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32
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Bailhache E, Briand F, Nguyen P, Krempf M, Magot T, Ouguerram K. Metabolism of cholesterol ester of apolipoprotein B100-containing lipoproteins in dogs: evidence for disregarding cholesterol ester transfer. Eur J Clin Invest 2004; 34:527-34. [PMID: 15305886 DOI: 10.1111/j.1365-2362.2004.01387.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
BACKGROUND It has been shown that dogs exhibit no cholesterol ester transfer protein (CETP) activity in vitro, in contrast to humans. The aim of our study was to determine modalities of in vivo plasma cholesterol ester turnover in this species, using a kinetic approach with stable isotopes. MATERIALS AND METHODS Kinetics of very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) were studied in seven adult male Beagle dogs using a dual isotope approach through endogenous labelling of both their cholesterol moiety and their protein moiety. A primed constant infusion of both [1,2(13)C]acetate and [5,5,5-2H3]leucine enabled us to obtain measurable deuterium enrichments by gas chromatography-mass spectrometry for plasma leucine and apoB100, as well as measurable 13C enrichment by gas chromatography-combustion-isotopic ratio mass spectrometry for unesterified cholesterol and cholesterol ester in the VLDL and LDL. Two identical multicompartmental models (SAAM II) were used together for the analysis of tracer kinetics' data of proteins and cholesterol. RESULTS Characterization of the apoB100-containing lipoprotein cholesterol ester model allowed determination of kinetic parameters of VLDL and LDL cholesterol ester metabolism. We succeeded in modelling VLDL and LDL cholesterol ester metabolism and apoB100 metabolism simultaneously. Fractional catabolic rate (FCR) of apoB100 and CE had the same values. Introducing cholesterol ester transfer between lipoproteins in the model did not significantly improve the fit. Total VLDL FCR was 2.97 +/- 01.47 h(-1). Approximately one-quarter corresponded to the direct removal of VLDL (0.81 +/- 00.34 h(-1)) and the remaining three-quarters corresponded to the fraction of VLDL converted to LDL, which represented a conversion of VLDL into LDL of 2.16 +/- 01.16 h(-1). Low-density lipoproteins were produced exclusively from VLDL conversion and were then removed (0.031 +/- 0.004 h(-1)) from plasma. CONCLUSION These kinetic data showed that VLDL cholesterol ester and LDL cholesterol ester metabolism followed VLDL and LDL apoB100 metabolism, and that consequently there is no in vivo transfer of cholesterol ester in dogs.
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Affiliation(s)
- E Bailhache
- Centre de Recherche en Nutrition Humaine, INSERM U539, CHU Nantes, France
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Schwartz CC, VandenBroek JM, Cooper PS. Lipoprotein cholesteryl ester production, transfer, and output in vivo in humans. J Lipid Res 2004; 45:1594-607. [PMID: 15145983 DOI: 10.1194/jlr.m300511-jlr200] [Citation(s) in RCA: 195] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Our aim was to identify and quantify the major in vivo pathways of lipoprotein cholesteryl ester transport in humans. Normal (n = 7), bile fistula (n = 5), and familial hypercholesterolemia (FH; n = 1) subjects were studied. Each received isotopic free cholesterol in HDL, LDL, or particulate form, along with another isotope of free or esterified cholesterol or mevalonic acid. VLDL, intermediate density lipoprotein (IDL), LDL, HDL, blood cells, and bile were collected for up to 6 days for analysis of radioactivity and mass of free and esterified cholesterol. These raw data were subjected to compartmental analysis using the SAAM program. Results in all groups corroborated net transport of free cholesterol to the liver from HDL, shown previously in fistula subjects. New findings revealed that 70% of ester was produced from free cholesterol in HDL and 30% from free cholesterol in LDL, IDL, and VLDL. No evidence was found for tissue-produced ester in plasma. There was net transfer of cholesteryl ester to VLDL and IDL from HDL and considerable exchange between LDL and HDL. Irreversible ester output was from VLDL, IDL, and LDL, but very little was from HDL, suggesting that selective and holoparticle uptakes of HDL ester are minor pathways in humans. It follows that 1) they contribute little to reverse transport, 2) very high HDL would not result from defects thereof, and 3) the clinical benefit of high HDL is likely explained by other mechanisms. Reverse transport in the subjects with bile fistula and FH was facilitated by ester output to the liver from VLDL plus IDL.
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Affiliation(s)
- Charles C Schwartz
- Department of Medicine, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA 23298, USA.
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34
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Tremblay AJ, Lamarche B, Ruel IL, Hogue JC, Bergeron J, Gagné C, Couture P. Increased production of VLDL apoB-100 in subjects with familial hypercholesterolemia carrying the same null LDL receptor gene mutation. J Lipid Res 2004; 45:866-72. [PMID: 14967814 DOI: 10.1194/jlr.m300448-jlr200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Early radiokinetic studies revealed that the classical metabolic defect in patients with familial hypercholesterolemia (FH) is hypocatabolism of LDL due to decreased LDL receptor activity. However, recent studies have suggested that hepatic oversecretion of apolipoprotein B-100 (apoB-100)-containing lipoproteins could also contribute to the markedly elevated plasma concentrations of LDL-cholesterol found in FH. The aim of this study was to examine the kinetics of apoB-100 labeled with a stable isotope (l-[5,5,5-D(3)] leucine) in five normolipidemic controls and in seven well-characterized FH subjects that included six FH heterozygotes and one FH homozygote carrying the same null LDL receptor gene mutation. As compared with controls, the VLDL apoB-100 production rate was increased by 50% in the FH heterozygotes and by 109% in the FH homozygote. Furthermore, FH subjects had significantly higher LDL apoB-100 pool size and lower LDL apoB-100 fractional catabolic rate than controls. These results indicate that the elevation of plasma LDL-cholesterol found in FH is attributable to both decreased clearance of LDL and increased hepatic production of apoB-100-containing lipoproteins.
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Frank N, Sojka JE, Patterson BW, Wood KV, Bonham CC, Latour MA. Effect of hypothyroidism on kinetics of metabolism of very-low-density lipoprotein in mares. Am J Vet Res 2003; 64:1052-8. [PMID: 12926601 DOI: 10.2460/ajvr.2003.64.1052] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
OBJECTIVE To compare kinetics of the metabolism of very-low-density lipoprotein (VLDL) apolipoprotein B (apoB) before and after thyroidectomy in mares. ANIMALS 5 healthy adult mares. PROCEDURE Thyroidectomy was performed in euthyroid mares. Kinetics of VLDL apoB metabolism were measured before and after thyroidectomy by use of a bolus IV injection of 5,5,5-2H3 (98%) leucine (5 mg/kg) and subsequent isolation of labeled amino acid from plasma and VLDL. Labeled leucine was quantified by use of gas chromatography-mass spectrometry. Production rate (PR), delay time, and fractional catabolic rate (FCR) were calculated for the 2 forms of equine VLDL, apoB-48 VLDL, and apoB-100 VLDL. Plasma lipid concentrations were measured, and VLDL composition was determined. RESULTS Physical appearance of horses was not altered by thyroidectomy. Significantly lower mean blood concentrations of thyroid hormones and non-esterified fatty acids were detected following thyroidectomy. Mean percentage of free cholesterol in VLDL was significantly higher after thyroidectomy. Mean plasma VLDL concentration or kinetics of apoB-48 or apoB-100 were not significantly altered by thyroidectomy. Mean +/- SEM PR was significantly lower (8.70 +/- 1.61 mg/kg/d) and mean delay time significantly longer (1.58 +/- 0.12 hours) for apoB-48 VLDL in euthyroid mares, compared with values for thyroidectomized mares (16.15 +/- 2.24 mg/kg/d and 0.93 +/- 0.10 hours, respectively). CONCLUSIONS AND CLINICAL RELEVANCE Hypothyroidism did not significantly alter plasma VLDL concentrations or kinetics of VLDL apoB metabolism. Metabolism of apoB-48 VLDL differed significantly from that of apoB-100 VLDL in euthyroid mares.
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Affiliation(s)
- Nicholas Frank
- Department of Veterinary Clinical Sciences, School of Veterinary Medicine, School of Agriculture, Purdue University, West Lafayette, IN 47907-1248, USA
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Kearney T, de Gallegos CN, Proudler A, Parker K, Anayaoku V, Bannister P, Venkatesan S, Johnston DG. Effects of short- and long-term growth hormone replacement on lipoprotein composition and on very-low-density lipoprotein and low-density lipoprotein apolipoprotein B100 kinetics in growth hormone-deficient hypopituitary subjects. Metabolism 2003; 52:50-9. [PMID: 12524662 DOI: 10.1053/meta.2003.50061] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
In this study, we concurrently examined the effects of 8 and 40 weeks of growth hormone replacement (GHR) on lipids, lipoprotein composition, low-density lipoprotein (LDL) size, very-low-density lipoprotein (VLDL) apolipoprotein (apo)B kinetics and LDL apoB kinetics. Eight weeks of GHR did not alter lipid profiles. Forty weeks of GHR increased high-density lipoprotein-cholesterol (HDL-C) concentration (P =.01), nonsignificantly reduced LDL-C (P =.06), and reduced the HDL/LDL-C ratio (P =.04). Forty weeks of GHR increased HDL free cholesterol (P =.03), total cholesterol (P =.01), and cholesterol ester (P <.01) concentrations. No other significant changes in VLDL, LDL, or HDL composition or LDL size were noted at any time. Eight weeks of GHR reduced VLDL apoB absolute secretion rate (ASR, P =.03), with nonsignificant reductions in fractional secretion rate (FSR, P =.09) and pool size (P =.09). After 40 weeks of GHR, the VLDL apoB ASR, FSR, and pool size were not significantly different from baseline. Forty weeks of GHR increased both LDL apoB FSR (P =.02) and LDL apoB ASR (P =.04), with a small decrease in pool size. Thus, GHR may have important antiatherogenic effects; HDL-C increased, LDL-C was nonsignificantly reduced, the total/HDL-C ratio was reduced, VLDL apoB production was reduced, and LDL apoB turnover was increased.
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Affiliation(s)
- Tara Kearney
- Department of Metabolic Medicine, St. Mary's Hospital Campus, London, UK
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37
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Burnett JR, Barrett PHR. Apolipoprotein B metabolism: tracer kinetics, models, and metabolic studies. Crit Rev Clin Lab Sci 2002; 39:89-137. [PMID: 12014529 DOI: 10.1080/10408360208951113] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The study of apolipoprotein (apo) B metabolism is central to our understanding of lipoprotein metabolism. However, the assembly and secretion of apoB-containing lipoproteins is a complex process. Specialized techniques, developed and applied to in vitro and in vivo studies of apoB metabolism, have provided insights into the mechanisms involved in the regulation of this process. Moreover, these studies have important implications for understanding both the pathophysiology as well as the therapeutic options for the dyslipidemias. The purpose of this review is to examine the role of apoB in lipoprotein metabolism and to explore the applications of kinetic analysis and multicompartmental modeling to the study of apoB metabolism. New developments and significant advances over the last decade are discussed.
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Affiliation(s)
- John R Burnett
- Department of Core Clinical Pathology and Biochemistry, Royal Perth Hospital, University of Western Australia, Australia.
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38
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Oxazolinone derivative of leucine for GC-MS: a sensitive and robust method for stable isotope kinetic studies of lipoproteins. J Lipid Res 2002. [DOI: 10.1016/s0022-2275(20)30177-2] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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39
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Use of stable isotopically labeled tracers to measure very low density lipoprotein-triglyceride turnover. J Lipid Res 2002. [DOI: 10.1016/s0022-2275(20)30164-4] [Citation(s) in RCA: 104] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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40
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Christ ER, Carroll PV, Albany E, Umpleby AM, Lumb PJ, Wierzbicki AS, Simpson HL, Sönksen PH, Russell-Ones DL. Normal VLDL metabolism despite altered lipoprotein composition in type 1 diabetes mellitus. Clin Endocrinol (Oxf) 2001; 55:777-87. [PMID: 11895220 DOI: 10.1046/j.1365-2265.2001.01407.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
OBJECTIVES Patients with type 1 diabetes are at increased risk of cardiovascular disease, which may be related to abnormal lipid metabolism. Secretion and clearance of VLDL apolipoprotein B100 (apoB) are important determinants of plasma lipid concentrations and are known to be influenced by hormones, including insulin and growth hormone. PATIENTS This study examined overnight VLDL apoB metabolism and VLDL composition in six lean patients with type 1 diabetes during euglycaemia (controlled by a varying insulin infusion) and in six age-, sex- and BMI-matched control subjects. METHODS VLDL apoB kinetics were determined using a primed constant 1-13C leucine infusion, and VLDL apoB enrichment was measured by gas-chromatography mass-spectrometry. Fasting lipid profile, IGF-I, IGFBP-3, overnight GH profiles and free insulin concentrations were also assessed. RESULTS Fasting concentrations of triglycerides (TG), total cholesterol (TC), HDL-cholesterol (HDL-C) and LDL-cholesterol (LDL-C) were similar in both groups. The VLDL apoB secretion and metabolic clearance rates were not significantly different between the two groups, but the VLDL-TGNLDL apoB and the VLDL-CNLDL apoB ratios were significantly increased in those with diabetes (P < 0.02 and P < 0.03, respectively). Total IGF-I concentrations were similar between the two groups; however, the GH area under the curve and free insulin concentrations were increased in patients with type 1 diabetes (GH: diabetes: 94.8 +/- 15.1 vs. controls: 45.6 +/- 10-6, mU/L/h, P < 0.04; free insulin: diabetes: 78.4 +/- 5.0 vs. controls: 28.3 +/- 3.26, pmol/l, P < 0.001). IGFBP-3 concentrations were lower in diabetic patients (diabetes: 2,454.2 +/- 68.7 vs. controls: 3,219.4 +/- 76.4, ng/ml, P < 0.001). In the control group overnight GH secretion correlated negatively with fasting TC (P < 0.01) and LDL-C (P < 0.03) concentrations, whereas free insulin concentrations correlated positively with fasting TG concentrations (P < 0.009). No significant correlations were found in the patients with diabetes. CONCLUSION This study suggests that in euglycaemic conditions patients with type 1 diabetes mellitus have normal VLDL apoB kinetics but altered VLDL composition. The altered VLDL composition may be associated with accelerated atherogenesis. We speculate that the disrupted hormonal balance and, in particular, the increased GH secretion might be responsible for the compositional changes of VLDL particles in type 1 diabetes mellitus.
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Affiliation(s)
- E R Christ
- Department of Medicine, King's College London, St Thomas's Hospital, UK.
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41
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Hoogeveen RC, Ballantyne CM, Pownall HJ, Opekun AR, Hachey DL, Jaffe JS, Oppermann S, Kahan BD, Morrisett JD. Effect of sirolimus on the metabolism of apoB100- containing lipoproteins in renal transplant patients. Transplantation 2001; 72:1244-50. [PMID: 11602850 DOI: 10.1097/00007890-200110150-00011] [Citation(s) in RCA: 107] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
BACKGROUND Sirolimus (Rapamune, rapamycin, RAPA) is a potent immunosuppressive drug that has reduced the rate of acute rejection episodes by more than 40% in phase III trials when added to an immunosuppression regimen of cyclosporine (CsA) and prednisone. However, RAPA treatment tends to increase lipid levels, particularly among patients with pre-existing hyperlipidemia. METHODS To identify the metabolic pathway(s) leading to RAPA-mediated hyperlipidemia, five patients with renal transplants maintained on CsA+/-prednisone+/- azathioprine (AZA) were studied before and after 6 weeks of treatment with RAPA (off RAPA and on RAPA, respectively). Each study patient was infused with a single bolus of [2H4]-lysine to derive metabolic parameters for apoB100-containing lipoproteins by using kinetic analysis based upon quantitation of isotopic enrichment by gas chromatography-mass spectrometry. RESULTS Serial lipid measurements revealed that four patients displayed increased plasma triglyceride levels after RAPA treatment, which coincided with significantly higher plasma VLDL-apoB100 concentrations (21.7+/-12.1 mg/dl off RAPA vs. 38.7+/-14.8 mg/dl on RAPA, mean+/-SD, P<0.05). Kinetic analysis showed that the RAPA-induced increase in VLDL-apoB100 concentrations was due to a significant reduction in the fractional catabolic rate (FCR) of very low-density lipoprotein (VLDL) apoB100 (0.83+/-0.65 off RAPA vs. 0.24+/-0.10 on RAPA, mean+/-SD, P<0.05), rather than an enhanced VLDL-apoB100 synthesis. In one patient, RAPA treatment induced hypercholesterolemia but not hypertriglyceridemia. This hypercholesterolemia was due to elevated low-density lipoprotein (LDL) cholesterol levels, which coincided with a decreased FCR of LDL-apoB100. Heparin-induced lipoprotein lipase activity was significantly lower in the immunosuppressed hyperlipidemic patients than in normolipidemic controls. However, RAPA treatment did not significantly alter basal lipoprotein lipase activity in renal transplant patients in this study. CONCLUSIONS This study indicates that for renal transplant patients in whom RAPA treatment induces hyperlipidemia, this effect is the result of reduced catabolism of apoB100-containing lipoproteins.
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Affiliation(s)
- R C Hoogeveen
- Department of Medicine, Baylor College of Medicine, Brown-Fondren Bldg, A601, 6565 Fannin Street, Houston, TX 77030, USA
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42
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Sun Z, Welty FK, Dolnikowski GG, Lichtenstein AH, Schaefer EJ. Effects of a National Cholesterol Education Program Step II Diet on apolipoprotein A-IV metabolism within triacylglycerol-rich lipoproteins and plasma. Am J Clin Nutr 2001; 74:308-14. [PMID: 11522553 DOI: 10.1093/ajcn/74.3.308] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND Apolipoprotein (apo) A-IV is a major component of triacylglycerol-rich lipoprotein (TRL) apolipoproteins. OBJECTIVE We investigated the effects of dietary saturated fat and cholesterol restriction on the metabolism of TRL and plasma apo A-IV. DESIGN We assessed TRL and plasma apo A-IV kinetics in 16 and 4 subjects, respectively, consuming an average US (baseline) diet for 6 wk and a National Cholesterol Education Program Step II diet for 24 wk, respectively. At the end of each diet period, all subjects received a primed, constant infusion of deuterated leucine for 15 h with hourly feeding. Ratios of stable-isotope tracer to tracee were measured by using gas chromatography-mass spectrometry, and kinetic data were modeled by using SAAM II. RESULTS Mean apo A-IV concentrations during the isotope infusion period were 6.9 +/- 2.6 mg/L in TRL and 2.2 +/- 3.2 mg/L in plasma with the baseline diet; these values were 37.7% (P < 0.001) and 19.4% (P < 0.01) lower with the Step II diet. Similar changes were observed in the fasting state between the 2 diets. The mean apo A-IV secretion rate decreased significantly from baseline by 59.6% in TRLs and by 40.2% in plasma. Significant correlations were observed between TRL apo A-IV concentrations and the secretion rate (r = 0.94, P < 0.001) and between TRL apo A-IV pool size and TRL-cholesterol concentrations (r = 0.48, P < 0.01). CONCLUSIONS Our data indicate that the National Cholesterol Education Program Step II diet significantly decreases TRL and plasma apo A-IV concentrations compared with the average US diet and that this decrease is due to a decreased secretion rate.
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Affiliation(s)
- Z Sun
- Lipid Metabolism Laboratory and the Mass Spectrometry Laboratory, Jean Mayer US Department of Agriculture Human Nutrition Research Center on Aging, Tufts University, Boston, MA 02111, USA
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43
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Ahlman B, Charlton M, Fu A, Berg C, O'Brien P, Nair KS. Insulin's effect on synthesis rates of liver proteins. A swine model comparing various precursors of protein synthesis. Diabetes 2001; 50:947-54. [PMID: 11334437 DOI: 10.2337/diabetes.50.5.947] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Insulin's effect on the synthesis of liver proteins remains to be fully defined. Previous studies using various surrogate measures of amino acyl-tRNA have reported variable results of insulin's effect on liver protein synthesis. We determined the effect of insulin with or without amino acid supplementation on the synthesis rates of liver proteins (tissue, albumin, and fibrinogen) using L-[1-13C]Leu as a tracer in 24 male miniature swine. In addition, we compared the isotopic enrichment of different precursors of liver proteins with that of amino acyl-tRNA using L-[1-13C]Leu and L-[15N]Phe as tracers. Although liver tissue fluid enrichment of [13C]Leu and [15N]Phe and that of plasma [13C]ketoisocaproatic acid (KIC) were very similar to that of tRNA, plasma isotopic enrichment of both Leu and Phe were substantially higher (P < 0.01) and VLDL apolipoprotein-B100 enrichment was lower (P < 0.01) than the respective amino acyl-tRNA enrichment. Plasma KIC enrichment most accurately predicted leucyl-tRNA enrichment, whereas plasma Leu enrichment was best correlated with that of tRNA. Neither insulin alone nor insulin plus amino acid infusion had an effect on liver tissue protein synthesis. In contrast, insulin alone decreased the albumin synthesis rate, and insulin with amino acids maintained the albumin synthesis rate. Insulin with or without amino acids inhibited the fibrinogen synthesis rate. These results, based on synthetic rates using amino acyl-tRNA, were consistent with those obtained using KIC or tissue fluid Leu or Phe as precursor pools. These studies demonstrated that plasma KIC enrichment is a convenient and reliable surrogate measure of leucyl-tRNA in liver. We also concluded that insulin has differential effects on the synthesis rates of liver proteins. Whereas insulin with or without amino acid supplement has no acute effect on the synthesis of liver tissue protein, insulin has a substantial inhibitory effect on fibrinogen synthesis. In contrast, insulin administration along with amino supplement is necessary to maintain albumin synthesis rate.
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Affiliation(s)
- B Ahlman
- Endocrine Research Unit, Division of Endocrinology and Metabolism, Mayo Clinic and Foundation, Rochester, Minnesota 55905, USA
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44
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Zanetti M, Barazzoni R, Garibotto G, Davanzo G, Gabelli C, Kiwanuka E, Piccoli A, Tosolini M, Tessari P. Plasma protein synthesis in patients with low-grade nephrotic proteinuria. Am J Physiol Endocrinol Metab 2001; 280:E591-7. [PMID: 11254466 DOI: 10.1152/ajpendo.2001.280.4.e591] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Overt nephrotic syndrome is characterized by albumin and fibrinogen hyperproduction and reduced very low density lipoprotein apolipoprotein B-100 (VLDL apoB-100) clearance. Whether similar changes also occur in low-grade proteinuria is not known. Thus we measured albumin, fibrinogen, and VLDL apoB-100 kinetics in six patients with modest proteinuria and normal creatinine clearance (P) and in ten control subjects (C) by leucine tracer infusion and precursor-product relationships. In P, plasma albumin concentration was decreased (P < 0.003), whereas concentrations of fibrinogen and VLDL apoB-100 were increased (P < 0.001). In P, albumin fractional secretion rate (FSR) was increased (P < 0.01), fibrinogen FSR was normal, and VLDL apoB-100 FSR was decreased (P < 0.03). As a result, in P, absolute secretion rates (ASR) of albumin and fibrinogen were increased (P < 0.03), whereas VLDL apoB-100 ASR was normal. Albumin FSR was inversely correlated to oncotic pressure in P but not in C. These findings suggest that low-grade nephrotic proteinuria is characterized by simultaneous multiple alterations in turnover rates of albumin, fibrinogen, and VLDL apoB-100. Their pathogenesis, however, appears to be multifactorial.
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Affiliation(s)
- M Zanetti
- Departments of Metabolic Diseases and Internal Medicine, University of Padova, 35128 Padua, Italy
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Maugeais C, Ouguerram K, Frénais R, Maugère P, Charbonnel B, Magot T, Krempf M. Effect of low-density lipoprotein apheresis on kinetics of apolipoprotein B in heterozygous familial hypercholesterolemia. J Clin Endocrinol Metab 2001; 86:1679-86. [PMID: 11297603 DOI: 10.1210/jcem.86.4.7428] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The acute reduction of low-density lipoprotein (LDL) cholesterol obtained by LDL-apheresis allows the role of the high level of circulating LDL on lipoprotein metabolism in heterozygous familial hypercholesterolemia (heterozygous FH) to be addressed. We studied apolipoprotein B (apoB) kinetics in five heterozygous FH patients before and the day after an apheresis treatment using endogenous labeling with [(2)H(3)]leucine. Compared with younger control subjects, heterozygous FH patients before apheresis showed a significant decrease in the fractional catabolic rate of LDL (0.24 +/- 0.08 vs. 0.65 +/- 0.22 day(-1); P < 0.01), and LDL production was increased in heterozygous FH patients (18.9 +/- 7.0 vs. 9.9 +/- 4.2 mg/kg.day; P < 0.05). The modeling of postapheresis apoB kinetics was performed using a nonsteady state condition, taking into account the changing pool size of very low density lipoprotein (VLDL), intermediate density lipoprotein, and LDL apoB. The postapheresis kinetic parameters did not show statistical differences compared with preapheresis parameters in heterozygous FH patients; however, a trend for increases in fractional catabolic rate of LDL (0.24 +/- 0.08 vs. 0.35 +/- 0.09 day(-1); P = 0.067) and the production of VLDL (13.7 +/- 8.3 vs. 21.9 +/- 1.6 mg/kg.day; P = 0.076) was observed. These results suggested that the marked decrease in plasma LDL obtained a short time after LDL-apheresis is able to stimulate LDL receptor activity and VLDL production in heterozygous FH.
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Affiliation(s)
- C Maugeais
- Centre de Recherche en Nutrition Humaine, Hôtel Dieu, 44093 Nantes Cedex 01, France
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Kroon AA, van't Hof MA, Demacker PN, Stalenhoef AF. The rebound of lipoproteins after LDL-apheresis. Kinetics and estimation of mean lipoprotein levels. Atherosclerosis 2000; 152:519-26. [PMID: 10998482 DOI: 10.1016/s0021-9150(00)00371-3] [Citation(s) in RCA: 125] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
We studied the rebound of lipoproteins in 20 hypercholesterolemic men [mean total cholesterol (TC) levels 9.6+/-1.8 mmol/l] after LDL-apheresis (LA) to determine the rate of recovery and the change in cholesterol synthesis, and to find a uniform estimation for time-averaged levels. After 10-20 months on biweekly LA using dextran sulfate cellulose columns and concomitant simvastatin administration, time-averaged levels (+/-SD) measured by integration of the area under the curve were as follows: TC 4.4+/-1.0 mmol/l, LDL cholesterol (LDL-C) 2.5+/-1.0 mmol/l, apolipoprotein B (apo B) 1. 3+/-0.3 g/l, triglycerides (TG) 1.7+/-0.7 mmol/l, HDL-C 1.1+/-0.2 mmol/l, and lipoprotein(a) [Lp(a)] 53.7+/-49.4 mg/dl. Mean acute reductions in TC, LDL-C, apo B, Lp(a), and TG were 61, 77, 75, 76, and 62%, respectively. HDL-C levels were not influenced. Median recovery half times for TC, LDL-C, apo B, and Lp(a) were 3.0, 4.0, 2. 3, and 3.5 days, respectively. The rebound of Lp(a) was identical to LDL-C, in 12 and 13 days post-treatment, respectively, whereas apo B and TC returned to pre-treatment levels in 7.5 and 10 days, respectively, due to the fast rebound of VLDL particles. Notwithstanding these differences, time-averaged levels (C(AVG)) could be estimated uniformly for the four latter parameters with the formula: C(AVG)=C(MIN)+0.73(C(MAX)-C(MIN)), where C(MAX) and C(MIN) are the immediate pre- and post-treatment levels. During long-term treatment the whole-body cholesterol synthesis was increased as measured by the ratio lathosterol to cholesterol of 3.24+/-1.49 mmol/mmol, whereas no further transient increase in the recovery period after LA was found. In conclusion, long-term LA and simvastatin therapy induced acute and chronic changes in lipids and lipoproteins showing the feasibility of biweekly treatment. It was shown that time-averaged levels, as a measure for the effective plasma levels, can be accurately estimated from pre- and post-treatment levels only.
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Affiliation(s)
- A A Kroon
- Division of General Internal Medicine, Department of Medicine, 541 AIG, University Hospital Nijmegen, PO Box 9101, 6500 HB, Nijmegen, The Netherlands
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47
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Acute effects of low density lipoprotein apheresis on metabolic parameters of apolipoprotein B. J Lipid Res 2000. [DOI: 10.1016/s0022-2275(20)31992-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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Abstract
Amino acid precursors labelled with stable isotopes have been successfully used to explore the metabolism of the apolipoproteins of HDL. Some methodological and mathematical modelling problems remain, mainly related to amino acid recycling in a plasma protein such as apolipoprotein A-I with a long residence time (the reciprocal of the fractional catabolic rate) of 4-5 days. Apolipoprotein A-I, apolipoprotein E, and apolipoprotein A-IV in triglyceride-rich lipoproteins (containing chylomicrons, VLDL, and remnants) exhibit more complex kinetics. The small amounts of apolipoprotein A-I and of apolipoprotein A-IV in the triglyceride-rich lipoproteins have a residence time similar to that of the apolipoprotein A-I of HDL. In contrast, the apolipoprotein E in triglyceride-rich lipoproteins has been found to have an average residence time of 0.11 days. Diets low in saturated fat and cholesterol, which lower HDL levels, do so by decreasing the secretion of apolipoprotein A-I, with apolipoprotein A-II kinetics unaffected. Individuals with impaired glucose tolerance have a decreased residence time of apolipoprotein A-I but no change in secretion rate or in apolipoprotein A-II kinetics. This suggests a link between insulin resistance and the risk of atherosclerosis. In heterozygous familial hypercholesterolemia, both the fractional catabolic rate and the secretion rate of apolipoprotein A-I are increased, resulting in no change in the plasma level. Stable isotope studies have strengthened the evidence that triglyceride enrichment of HDL increases its catabolism Laboratory.
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Affiliation(s)
- J B Marsh
- Jean Mayer US Department of Agriculture, Human Nutrition Research Center on Aging at Tufts University, Boston, MA 02111, USA.
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Chrisoulidou A, Kousta E, Venkatesan S, Gray R, Bannister PA, Gallagher JJ, Lawrence N, Johnston DG. Effects of growth hormone treatment on very-low density lipoprotein apolipoprotein B100 turnover in adult hypopituitarism. Metabolism 2000; 49:563-6. [PMID: 10831163 DOI: 10.1016/s0026-0495(00)80028-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Adult hypopituitarism is associated with hyperlipidemia, mainly due to an increase of very-low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) levels. Recent studies have shown that such patients exhibit increased hepatic secretion of VLDL apolipoprotein B100 (VLDL apo B100). To examine the effects of growth hormone (GH) replacement on VLDL apo B100 turnover, 13 GH-deficient hypopituitary patients (8 women and 5 men; aged 47 +/- 3 years, mean +/- SEM; body mass index [BMI], 30 +/- 2 kg/m2) entered a double-blind placebo-controlled study for 6 months (GH 0.125 IU/kg/wk for 4 weeks, and then 0.25 IU/kg/wk). GH was subsequently used in all patients for a further 6 months. A 6-hour [1-13C] leucine infusion was administered at baseline and at 6 months. The secretion rate of VLDL apo B100 was derived by kinetic analysis following quantitation of isotopic enrichment by gas chromatography/mass spectrometry. The GH-treated group (6 patients) demonstrated a similar fractional secretion rate (FSR) for VLDL apo B100 at 0 and 6 months. The pool size and absolute secretion rate (ASR) also were unaffected significantly by GH therapy. No significant changes were observed in the placebo group (7 patients). Treatment with GH for 6 months caused an increase in the high-density lipoprotein (HDL) cholesterol concentration (13 patients, 1.27 +/- 0.13 v 1.16 +/- 0.10 mmol/L, respectively, P = .05), whereas total cholesterol and triglyceride concentrations did not change. Nonesterified fatty acids (NEFAs) increased during GH therapy (471 +/- 43 micromol/L at 6 months v 349 +/- 49 micromol/L at baseline, P < .0005). The data suggest that GH does not affect VLDL apo B100 turnover in a significant way.
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Affiliation(s)
- A Chrisoulidou
- Section of Endocrinology and Metabolic Medicine, Imperial College School of Medicine, St Mary's Hospital, London, UK
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50
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Elias N, Patterson BW, Schonfeld G. In vivo metabolism of ApoB, ApoA-I, and VLDL triglycerides in a form of hypobetalipoproteinemia not linked to the ApoB gene. Arterioscler Thromb Vasc Biol 2000; 20:1309-15. [PMID: 10807747 DOI: 10.1161/01.atv.20.5.1309] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Familial hypobetalipoproteinemia (FHBL) is an autosomal codominant disorder that may result from different mutations in the apolipoprotein B (apoB) gene or chromosome 2. However, linkage of FHBL to the apoB gene was ruled out in 2 kindreds reported to date, and the genetic and metabolic bases for FHBL remain unknown. One of the reported kindreds is our 40-member F kindred, in which we found linkage of FHBL to a novel susceptibility region on chromosome 3p21. 1-2. In addition to having low apoB levels, some, but not all, of the affected subjects in the F kindred also had low levels of high density lipoprotein (HDL) cholesterol and apoA-I. Our aim was to define the metabolic bases of the disorder in the F kindred. Therefore, we studied the in vivo kinetics of apoB and apoA-I and very low density lipoprotein (VLDL) triglycerides in 4 affected subjects and 5 normolipidemic relatives. Deuterated leucine and deuterated glycerol were used to label the apolipoproteins and triglycerides, respectively. Compartmental modeling was used to obtain the kinetic parameters. Affected subjects had (1) normal fractional catabolic rates (FCRs) for VLDL apoB, (2) increased FCRs for low density lipoprotein (LDL) apoB (0.050+/-0.009 versus 0. 030+/-0.006 pools per hour for normal subjects, P=0.005), and (3) decreased production rates of VLDL apoB (11.4+/-1.7 versus 25.6+/-4. 9 mg. kg(-1). d(-1), P=0.003), LDL apoB (7.8+/-1.3 versus 12.7+/-3.7 mg. kg(-1). d(-1), P=0.04), and VLDL triglycerides (8.2+/-4.5 versus 19.6+/-10.8 58 micromol. kg(-1). h(-1), P=0.09). These data differ from those obtained in previously studied FHBL heterozygotes bearing apoB-2 and apoB-9, 2 very short truncations of apoB. Low HDL cholesterol and apoA-I levels were caused by higher apoA-I FCRs (0. 035+/-0.005 versus 0.018+/-0.005 pools per hour in controls, P<0.01) without significant decrease in apoA-I production rates (18.7+/-2.7 versus 22.8+/-5.6 mg. kg(-1). d(-1)). In conclusion, decreased secretion of apoB-containing lipoproteins and hypercatabolism of LDL account for low apoB and cholesterol levels in this novel form of FHBL.
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Affiliation(s)
- N Elias
- Division of Atherosclerosis, Department of Internal Medicine, Washington University School of Medicine, St Louis, MO, USA
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