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Sips FLP, Tiemann CA, Oosterveer MH, Groen AK, Hilbers PAJ, van Riel NAW. A computational model for the analysis of lipoprotein distributions in the mouse: translating FPLC profiles to lipoprotein metabolism. PLoS Comput Biol 2014; 10:e1003579. [PMID: 24784354 PMCID: PMC4006703 DOI: 10.1371/journal.pcbi.1003579] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2013] [Accepted: 03/11/2014] [Indexed: 12/27/2022] Open
Abstract
Disturbances of lipoprotein metabolism are recognized as indicators of cardiometabolic disease risk. Lipoprotein size and composition, measured in a lipoprotein profile, are considered to be disease risk markers. However, the measured profile is a collective result of complex metabolic interactions, which complicates the identification of changes in metabolism. In this study we aim to develop a method which quantitatively relates murine lipoprotein size, composition and concentration to the molecular mechanisms underlying lipoprotein metabolism. We introduce a computational framework which incorporates a novel kinetic model of murine lipoprotein metabolism. The model is applied to compute a distribution of plasma lipoproteins, which is then related to experimental lipoprotein profiles through the generation of an in silico lipoprotein profile. The model was first applied to profiles obtained from wild-type C57Bl/6J mice. The results provided insight into the interplay of lipoprotein production, remodelling and catabolism. Moreover, the concentration and metabolism of unmeasured lipoprotein components could be determined. The model was validated through the prediction of lipoprotein profiles of several transgenic mouse models commonly used in cardiovascular research. Finally, the framework was employed for longitudinal analysis of the profiles of C57Bl/6J mice following a pharmaceutical intervention with a liver X receptor (LXR) agonist. The multifaceted regulatory response to the administration of the compound is incompletely understood. The results explain the characteristic changes of the observed lipoprotein profile in terms of the underlying metabolic perturbation and resultant modifications of lipid fluxes in the body. The Murine Lipoprotein Profiler (MuLiP) presented here is thus a valuable tool to assess the metabolic origin of altered murine lipoprotein profiles and can be applied in preclinical research performed in mice for analysis of lipid fluxes and lipoprotein composition.
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Affiliation(s)
- Fianne L P Sips
- Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands; Netherlands Consortium for Systems Biology, University of Amsterdam, Amsterdam, The Netherlands
| | - Christian A Tiemann
- Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands; Netherlands Consortium for Systems Biology, University of Amsterdam, Amsterdam, The Netherlands
| | - Maaike H Oosterveer
- Department of Pediatrics, University Groningen, University Medical Center Groningen, Groningen, The Netherlands
| | - Albert K Groen
- Netherlands Consortium for Systems Biology, University of Amsterdam, Amsterdam, The Netherlands; Department of Pediatrics, University Groningen, University Medical Center Groningen, Groningen, The Netherlands; Department of Laboratory Medicine, University Groningen, University Medical Center Groningen, Groningen, The Netherlands
| | - Peter A J Hilbers
- Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands; Netherlands Consortium for Systems Biology, University of Amsterdam, Amsterdam, The Netherlands
| | - Natal A W van Riel
- Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands; Netherlands Consortium for Systems Biology, University of Amsterdam, Amsterdam, The Netherlands
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2
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Pang J, Chan DC, Hamilton SJ, Tenneti VS, Watts GF, Barrett PHR. Effect of Niacin on High-Density Lipoprotein Apolipoprotein A-I Kinetics in Statin-Treated Patients With Type 2 Diabetes Mellitus. Arterioscler Thromb Vasc Biol 2014; 34:427-32. [DOI: 10.1161/atvbaha.113.302019] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Objective—
To investigate the effect of extended-release (ER) niacin on the metabolism of high-density lipoprotein (HDL) apolipoprotein A-I (apoA-I) in men with type 2 diabetes mellitus on a background of optimal statin therapy.
Approach and Results—
Twelve men with type 2 diabetes mellitus were recruited for a randomized, crossover design trial. Patients were randomized to rosuvastatin or rosuvastatin plus ER niacin for 12 weeks and then crossed over to the alternate therapy after a 3-week washout period. Metabolic studies were performed at the end of each treatment period. HDL apoA-I kinetics were measured after a standardized liquid mixed meal and a bolus injection of d3-leucine for 96 hours. Compartmental analysis was used to model the data. ER niacin significantly decreased plasma triglyceride, plasma cholesterol, non-HDL cholesterol, low-density lipoprotein cholesterol, and apoB (all
P
<0.05) and significantly increased HDL cholesterol and apoA-I concentrations (
P
<0.005 and
P
<0.05, respectively). ER niacin also significantly increased HDL apoA-I pool size (6088±292 versus 5675±305 mg;
P
<0.001), and this was attributed to a lower HDL apoA-I fractional catabolic rate (0.33±0.01 versus 0.37±0.02 pools/d;
P
<0.005), with no significant changes in HDL apoA-I production (20.93±0.63 versus 21.72±0.85 mg/kg per day;
P
=0.28).
Conclusions—
ER niacin increases HDL apoA-I concentration in statin-treated subjects with type 2 diabetes mellitus by lowering apoA-I fractional catabolic rate. The effect on HDL metabolism was independent of the reduction in plasma triglyceride with ER niacin treatment. Whether this finding applies to other dyslipidemic populations remains to be investigated.
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Affiliation(s)
- Jing Pang
- From the Metabolic Research Centre, School of Medicine and Pharmacology (J.P., D.C.C., S.J.H., V.S.T., G.F.W., P.H.R.B.), Combined Universities Centre for Rural Health (S.J.H.), and Faculty of Engineering, Computing and Mathematics (P.H.R.B), University of Western Australia, Perth, Australia
| | - Dick C. Chan
- From the Metabolic Research Centre, School of Medicine and Pharmacology (J.P., D.C.C., S.J.H., V.S.T., G.F.W., P.H.R.B.), Combined Universities Centre for Rural Health (S.J.H.), and Faculty of Engineering, Computing and Mathematics (P.H.R.B), University of Western Australia, Perth, Australia
| | - Sandra J. Hamilton
- From the Metabolic Research Centre, School of Medicine and Pharmacology (J.P., D.C.C., S.J.H., V.S.T., G.F.W., P.H.R.B.), Combined Universities Centre for Rural Health (S.J.H.), and Faculty of Engineering, Computing and Mathematics (P.H.R.B), University of Western Australia, Perth, Australia
| | - Vijay S. Tenneti
- From the Metabolic Research Centre, School of Medicine and Pharmacology (J.P., D.C.C., S.J.H., V.S.T., G.F.W., P.H.R.B.), Combined Universities Centre for Rural Health (S.J.H.), and Faculty of Engineering, Computing and Mathematics (P.H.R.B), University of Western Australia, Perth, Australia
| | - Gerald F. Watts
- From the Metabolic Research Centre, School of Medicine and Pharmacology (J.P., D.C.C., S.J.H., V.S.T., G.F.W., P.H.R.B.), Combined Universities Centre for Rural Health (S.J.H.), and Faculty of Engineering, Computing and Mathematics (P.H.R.B), University of Western Australia, Perth, Australia
| | - P. Hugh. R. Barrett
- From the Metabolic Research Centre, School of Medicine and Pharmacology (J.P., D.C.C., S.J.H., V.S.T., G.F.W., P.H.R.B.), Combined Universities Centre for Rural Health (S.J.H.), and Faculty of Engineering, Computing and Mathematics (P.H.R.B), University of Western Australia, Perth, Australia
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3
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Development of a method to measure preβHDL and αHDL apoA-I enrichment for stable isotopic studies of HDL kinetics. Lipids 2012; 47:1011-8. [PMID: 22886353 DOI: 10.1007/s11745-012-3703-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2012] [Accepted: 07/12/2012] [Indexed: 10/28/2022]
Abstract
Our understanding of HDL metabolism would be enhanced by the measurement of the kinetics of preβHDL, the nascent form of HDL, since elevated levels have been reported in patients with coronary artery disease. Stable isotope methodology is an established technique that has enabled the determination of the kinetics (production and catabolism) of total HDL apoA-I in vivo. The development of separation procedures to obtain a preβHDL fraction, the isotopic enrichment of which could then be measured, would enable further understanding of the pathways in vivo for determining the fate of preβHDL and the formation of αHDL. A method was developed and optimised to separate and measure preβHDL and αHDL apoA-I enrichment. Agarose gel electrophoresis was first used to separate lipoprotein subclasses, and then a 4-10 % discontinuous SDS-PAGE used to isolate apoA-I. Measures of preβHDL enrichment in six healthy subjects were undertaken following an infusion of L-[1-¹³C-leucine]. After isolation of preβ and αHDL, the isotopic enrichment of apoA-I for each fraction was measured by gas chromatography-mass spectrometry. PreβHDL apoA-I enrichment was measured with a CV of 0.51 % and αHDL apoA-I with a CV of 0.34 %. The fractional catabolic rate (FCR) of preβHDL apoA-I was significantly higher than the FCR of αHDL apoA-I (p < 0.005). This methodology can be used to selectively isolate preβ and αHDL apoA-I for the measurement of apoA-I isotopic enrichment for kinetics studies of HDL subclass metabolism in a research setting.
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4
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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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5
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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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6
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Chétiveaux M, Ouguerram K, Zair Y, Maugère P, Falconi I, Nazih H, Krempf M. New model for kinetic studies of HDL metabolism in humans. Eur J Clin Invest 2004; 34:262-7. [PMID: 15086357 DOI: 10.1111/j.1365-2362.2004.01322.x] [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] [Indexed: 11/29/2022]
Abstract
BACKGROUND The aim of the study was to develop a new model for kinetic studies of Apolipoprotein A-I of HDL (Apo A-I-HDL) labelled with stable isotope by using HDL subclasses isolated with fast protein liquid chromatography (FPLC). MATERIALS AND METHODS Apo A-I-HDL kinetics were studied by infusing [5.5.5-(2)H(3)]-leucine for 14 h in six healthy subjects. Prebeta(1) and alphaHDL were separated by FPLC and total HDL by ultracentrifugation (HDL-UC). RESULTS The tracer-to-tracee ratios were higher in prebeta(1) HDL than in HDL-UC or alphaHDL. Leucine enrichments found in HDL-UC were higher compared with alphaHDL, suggesting that HDL-UC were composed of a mixture of Apo A-I-alphaHDL and Apo A-I-prebeta(1) HDL. Kinetic analysis of data obtained from FPLC was achieved using a multicompartmental model, including a conversion between prebeta(1) and alphaHDL compartments. The production rate of prebeta(1) HDL was 7.72 +/- 2.86 mg kg(-1) d(-1) (mean +/- SD). Prebeta(1) HDL were converted to alphaHDL at a rate of 96.24 +/- 42.99 pool d(-1), and the synthesis rate of prebeta(1) HDL from alphaHDL was 10-fold slower: 7.09 +/- 4.51 pool d(-1). Apo A-I-FCR of HDL-UC was estimated using a one-compartment model (0.165 +/- 0.074 pool d(-1)), and was higher but not significantly compared with FCR of Apo A-I-alphaHDL (0.112 +/- 0.026 pool d(-1)) calculated with the new model. CONCLUSIONS This study reports for the first time a model involving enrichments of Apo A-I in prebeta(1) and alphaHDL which allowed the measure of Apo A-I cycling within HDL fraction and will aid better understanding of kinetics of HDL in humans.
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7
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Zhang B, Shimoji E, Tanaka H, Saku K. Evaluation of apolipoprotein A-I kinetics in rabbits in vivo using in situ and exogenous radioiodination methods. Lipids 2003; 38:209-18. [PMID: 12784860 DOI: 10.1007/s11745-003-1053-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
The kinetics of in vivo clearance of apolipoprotein (apo) A-I radioiodinated by the iodine monochloride (ICI) method of McFarlane [McFarlane, A.S. (1958) Efficient Trace-Labelling of Proteins with Iodine, Nature 182, 53] as modified by Bilheimer and co-workers [Bilheimer, D.W., Eisenberg, S., and Levy, R.I. (1972) The Metabolism of Very Low Density Lipoprotein Proteins. I. Preliminary in vitro and in vivo Observations, Biochim. Biophys. Acta 260, 212-221] and by using the IODO Beads Iodination Reagent were evaluated in rabbits. Both human apoA-I and rabbit HDL radioiodinated by the IODO Beads Iodination Reagent were cleared faster from plasma of rabbits than those radiolabeled by the ICI method. However, the different radiolabeling procedures in the ICI method, i.e., apoA-I radiolabeled either exogenously or in situ as a part of intact HDL, were not associated with a significant difference in the in vivo kinetics of apoA-I in rabbits if apoA-I was prepared by the guanidine HCI method and used fresh. 125I-ApoA-I subjected to delipidation and lyophilization was cleared only slightly faster from the plasma of rabbits than fresh 125I-apoA-I. We also found that apoA-I separated by the guanidine HCI method and used fresh was cleared faster from the plasma of rabbits when it was injected as free apoA-I without adding serum albumin or after in vitro incubation with rabbit HDL than when injected after reassociation with rabbit plasma. We conclude that the ICI method is a more appropriate radioiodination method for studying the in vivo kinetics of HDL than the IODO Beads Iodination Reagent and that the in vitro incubation conditions before injection are important factors that affect the in vivo kinetics of apo A-I.
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Affiliation(s)
- Bo Zhang
- Department of Cardiology, Fukuoka University School of Medicine, Fukuoka 814-0180, Japan
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8
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Barrett PHR, Watts GF. Kinetic studies of lipoprotein metabolism in the metabolic syndrome including effects of nutritional interventions. Curr Opin Lipidol 2003; 14:61-8. [PMID: 12544663 DOI: 10.1097/00041433-200302000-00011] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Nutritional interventions may favourably regulate dyslipoproteinemia and, hence, decrease cardiovascular disease risk. Lipoprotein kinetic studies afford a powerful approach to understanding and defining the mechanisms by which such interventions modulate lipoprotein metabolism. Stable isotope tracers and compartment models are now commonly employed for such studies. We review the recent application of tracer methodologies to the study of dyslipoproteinemia in the metabolic syndrome. We also focus on the effects of nutritional intervention studies that have addressed the effects of weight loss, n-3 fatty acids, plant sterols and alcohol on very low density lipoprotein, LDL and HDL metabolism. The potential for statin treatment as an adjunct to dietary modification is also discussed. New tracer methodologies are discussed, specifically those referring to reverse cholesterol transport. The nutritional interventions discussed in this review are readily transferable into clinical preventive practice. The potential benefits to be gained by weight loss and fish oil supplementation in the metabolic syndrome extend beyond their specific and positive effects on lipoprotein metabolism. Furthermore, recent developments in tracer methodologies afford new tools for probing the in-vivo pathways of lipoprotein metabolism in future studies.
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Affiliation(s)
- P Hugh R Barrett
- Lipoprotein Research Unit, Department of Medicine, University of Western Australia, Perth, Western Australia
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9
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Pont F, Duvillard L, Florentin E, Gambert P, Vergès B. High-density lipoprotein apolipoprotein A-I kinetics in obese insulin resistant patients. An in vivo stable isotope study. Int J Obes (Lond) 2002; 26:1151-8. [PMID: 12187390 DOI: 10.1038/sj.ijo.0802070] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/23/2001] [Revised: 04/17/2002] [Accepted: 04/22/2002] [Indexed: 11/08/2022]
Abstract
AIMS/HYPOTHESIS Mechanisms responsible for the decreased high-density lipoprotein (HDL) cholesterol level associated with insulin resistance in obese patients are not clearly understood. To determine the influence of insulin resistance at an early stage on HDL metabolism, we performed a stable isotope kinetic study of apolipoprotein (apo) A-I, in five obese insulin resistant women with normal fasting triglycerides and without impaired glucose tolerance, and in five age-matched control women. METHODS Each subject received a 16 h constant infusion of L-[1-(13)C]leucine at 0.7 mg/kg/h following a primed bolus of 0.7 mg/kg. RESULTS ApoA-I fractional catabolic rate (FCR) was significantly increased in insulin-resistant women compared to controls (0.316+/-0.056 vs 0.210+/-0.040 per day, P<0.01), indicating a significant 50% increase of apoA-I catabolism, leading to an important reduction of plasma apoA-I residence time (3.25+/-0.59 vs 4.92+/-1.11, P<0.01). ApoA-I production rate tended to be higher in insulin resistant women than in controls (364+/-77 vs 258+/-60 mg/l/day, P=0.13), but the difference was not statistically significant. ApoA-I FCR was correlated with triglycerides during the fed state (r=0.69; P=0.026) and HDL triglycerides-esterified cholesterol ratio (r=0.73; P=0.016), suggesting that alteration of apoA-I metabolism in insulin resistance may be partly related to HDL enrichment in triglycerides. CONCLUSIONS Our kinetic study shows that patients, at an early stage of insulin resistance (without impaired glucose tolerance nor fasting hypertriglyceridaemia), already have a significant alteration of apoA-I metabolism (increased apoA-I catabolism), which is consistent with the increased risk of atherosclerosis in this population.
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Affiliation(s)
- F Pont
- Laboratoire de Biochimie des Lipoprotéines, INSERM U 498, Faculté de Médecine, Dijon, France
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10
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Barrett PH, Watts GF. HDL kinetics, fish oils and diabetes. Atherosclerosis 2001; 159:243-4. [PMID: 11689229 DOI: 10.1016/s0021-9150(01)00690-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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11
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Dietary n-3 polyunsaturated fat increases the fractional catabolic rate of medium-sized HDL particles in African green monkeys. J Lipid Res 2001. [DOI: 10.1016/s0022-2275(20)30279-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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12
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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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13
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Duvillard L, Pont F, Florentin E, Gambert P, Vergès B. Inefficiency of insulin therapy to correct apolipoprotein A-I metabolic abnormalities in non-insulin-dependent diabetes mellitus. Atherosclerosis 2000; 152:229-37. [PMID: 10996359 DOI: 10.1016/s0021-9150(99)00473-6] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Non-insulin-dependent diabetes mellitus (NIDDM) is associated with low high density lipoprotein (HDL) cholesterol and apoA-I, related to an increased apoA-I fractional catabolic rate. This stable isotope kinetic experiment, using L-[1-(13)C] leucine, was designed to study the effect of insulin therapy on HDL apoA-I and A-II metabolism in poorly controlled NIDDM patients. A kinetic study was performed in five control subjects and in six NIDDM patients before and two months after the introduction of insulin therapy. ApoA-I and A-II were modelled using a monoexponential function. Insulin treatment was able to correct neither the low HDL apoA-I concentration observed in NIDDM patients (1.14+/-0.19 vs. 1.16+/-0. 12 g l(-1) (controls: 1.33+/-0.14)), nor the HDL apoA-I hypercatabolism (0.39+/-0.11 vs. 0.34+/-0.05 pool d(-1), (controls: 0.23+/-0.01, P< 0.01)). HDL apoA-I production rate was increased in NIDDM patients compared to control subjects and was not modified by insulin (0.45+/-0.12 vs. 0.39+/-0.08 g d(-1) l(-1), (controls: 0. 31+/-0.04, P< 0.05)). HDL apoA-II kinetic parameters were initially not significantly different between NIDDM patients and control subjects, and were not modified by insulin. The decreased insulin sensitivity, assessed by the insulin suppressive test, was not modified by insulin therapy in NIDDM patients. HDL apoA-I fractional catabolic rate was significantly correlated to HDL triglyceride/cholesteryl ester and triglyceride/protein ratios, which were significantly higher in NIDDM patients than in controls and were not modified by insulin therapy. The persistence of insulin resistance and of high neutral lipid exchanges between triglyceride rich lipoproteins and HDL in insulin-treated NIDDM patients probably explain the inefficiency of insulin therapy to correct HDL apoA-I metabolic abnormalities.
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Affiliation(s)
- L Duvillard
- INSERM U 498-Métabolisme des lipoprotéines humaines et interactions vasculaires, Faculté de Médecine, 21033, Dijon, France.
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14
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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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15
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Braschi S, Neville TA, Maugeais C, Ramsamy TA, Seymour R, Sparks DL. Role of the kidney in regulating the metabolism of HDL in rabbits: evidence that iodination alters the catabolism of apolipoprotein A-I by the kidney. Biochemistry 2000; 39:5441-9. [PMID: 10820016 DOI: 10.1021/bi9919504] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
To evaluate the factors that regulate HDL catabolism in vivo, we have measured the clearance of human apoA-I from rabbit plasma by following the isotopic decay of (125)I-apoA-I and the clearance of unlabeled apoA-I using a radioimmunometric assay (RIA). We show that the clearance of unlabeled apoA-I is 3-fold slower than that of (125)I-apoA-I. The mass clearance of iodinated apoA-I, as determined by RIA, is superimposable with the isotopic clearance of (125)I-apoA-I. The data demonstrate that iodination of tyrosine residues alters the apoA-I molecule in a manner that promotes an accelerated catabolism. The clearance from rabbit plasma of unmodified apoA-I on HDL(3) and a reconstituted HDL particle (LpA-I) were very similar and about 3-4-fold slower than that for (125)I-apoA-I on the lipoproteins. Therefore, HDL turnover in the rabbit is much slower than that estimated from tracer kinetic studies. To determine the role of the kidney in HDL metabolism, the kinetics of unmodified apoA-I and LpA-I were reevaluated in animals after a unilateral nephrectomy. Removal of one kidney was associated with a 40-50% reduction in creatinine clearance rates and a 34% decrease in the clearance rate of unlabeled apoA-I and LpA-I particles. In contrast, the clearance of (125)I-labeled molecules was much less affected by the removal of a kidney; FCR for (125)I-LpA-I was reduced by <10%. The data show that the kidneys are responsible for most (70%) of the catabolism of apoA-I and HDL in vivo, while (125)I-labeled apoA-I and HDL are rapidly catabolized by different tissues. Thus, the kidney is the major site for HDL catabolism in vivo. Modification of tyrosine residues on apoA-I may increase its plasma clearance rate by enhancing extra-renal degradation pathways.
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Affiliation(s)
- S Braschi
- Lipoproteins and Atherosclerosis Research Group, University of Ottawa Heart Institute, 40 Ruskin Street, Ottawa, Ontario, K1Y 4W7, Canada
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16
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Beghin L, Capps N, Duhal N, Davies J, Staels B, Luc G. Metabolism of apolipoproteins AI and AII in a patient with paradoxical reduction in high-density lipoprotein due to ciprofibrate. Ann Clin Biochem 1999; 36 ( Pt 4):523-5. [PMID: 10456219 DOI: 10.1177/000456329903600420] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Affiliation(s)
- L Beghin
- Dept of Atherosclerosis, INSERM U 325, Institut Pasteur de Lille, France
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17
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Schmidt HH, Haas RE, Remaley A, Genschel J, Strassburg CP, Büttner C, Manns MP. In vivo kinetics as a sensitive method for testing physiologically intact human recombinant apolipoprotein A-I: comparison of three different expression systems. Clin Chim Acta 1997; 268:41-60. [PMID: 9495570 DOI: 10.1016/s0009-8981(97)00155-1] [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: 02/06/2023]
Abstract
In order to assess the structural and functional integrity of recombinant human apoA-I, we expressed apoA-I using three different expression systems: Baculovirus transfected Spodoptera frugiperda (Sf9) cells, stably transfected Chinese hamster ovary (CHO) cells, and transformed Escherichia coli (E. coli). Purified apoA-I from the three expression systems was radioiodinated and their catabolism was compared in normolipemic rabbits. The kinetic turnover studies of radiolabelled apoA-I in normolipemic rabbits revealed that highly purified recombinant apoA-I had an identical decay curve compared to native apoA-I, regardless whether it was purified from Sf9 cells, CHO cells, or E. coli. We also determined the association of the three recombinant apoA-I forms with both rabbit and human HDL. All three recombinant apoA-I forms were associated with HDL2 and HDL3 after injection into the rabbits and after incubation with human serum using both a Superose 6 column separation system and density gradient ultracentrifugation. The addition of the pro-segment or the addition of methionine at the amino-terminal end of apoA-I did not alter its metabolism and association to HDL. In conclusion, all studied expression systems are capable of producing high levels of physiologically intact recombinant human apoA-I. The aminoterminal addition of the prosegment of apoA-I or methionine did not alter the in vivo metabolism of apoA-I or its association to HDL.
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Affiliation(s)
- H H Schmidt
- Department of Gastroenterology and Hepatology, Medizinische Hochschule Hannover, Germany
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18
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Maugeais C, Braschi S, Ouguerram K, Maugeais P, Mahot P, Jacotot B, Darmaun D, Magot T, Krempf M. Lipoprotein kinetics in patients with analbuminemia. Evidence for the role of serum albumin in controlling lipoprotein metabolism. Arterioscler Thromb Vasc Biol 1997; 17:1369-75. [PMID: 9261269 DOI: 10.1161/01.atv.17.7.1369] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
In vitro data suggested that albumin is a key factor controlling apolipoprotein (apo) synthesis by hepatocytes. Studies in analbuminemic rats have shown an increase in secretion of apoB-containing lipoprotein from the liver. We studied the kinetic aspects of apoB- and apoAI-containing lipoprotein metabolism in two sisters with analbuminemia using a constant 14-hour infusion of leucine labeled with stable isotopes. Compared with control subjects, total cholesterol was higher in the two patients (432 and 461 versus 155 +/- 14 mg/dL), as was apoB (257 and 230 versus 72 +/- 7 mg/dL). Triglycerides were slightly increased (134 and 105 versus 89 +/- 9 mg/dL), whereas apoAI was lower (109 and 105 versus 124 +/- 6 mg/dL). VLDL-apoB production was higher, as was the production of IDL-apoB and LDL-apoB (32.8 and 36.0 versus 24.8 +/- 5.9, 32.1 and 27.2 versus 16.4 +/- 2.3, and 14.1 and 17.6 versus 10.3 +/- 1.2 mg.kg-1.d-1, respectively). The fractional catabolic rate of all the apoB-containing lipoproteins was decreased (0.23 and 0.37 versus 0.48 +/- 0.05, 0.27 and 0.28 versus 0.62 +/- 0.08, and 0.012 and 0.009 versus 0.022 +/- 0.002.h-1, respectively). A similar mechanism could explain the dyslipidemia observed in other conditions associated with low albumin levels, such as nephrotic syndrome.
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Affiliation(s)
- C Maugeais
- Centre de Recherche en Nutrition Humaine, Hôpital G. & R. Laĕnnec, Nantes, France
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19
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Fisher WR, Venkatakrishnan V, Fisher ES, Stacpoole PW, Zech LA. The 3H-leucine tracer: its use in kinetic studies of plasma lipoproteins. Metabolism 1997; 46:333-42. [PMID: 9054478 DOI: 10.1016/s0026-0495(97)90262-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
3H-leucine administered as a bolus has been widely used as a tracer in kinetic investigations of protein synthesis and secretion. After intravenous injection, plasma specific radioactivity decays over several orders of magnitude during the first half-day, followed by a slow decay lasting a number of weeks that results from recycling of the leucine tracer as proteins are degraded and 3H-leucine reenters the plasma pool. In studies in which kinetic data are analyzed by mathematical compartmental modeling, plasma leucine activity is generally used as a forcing function to drive the input of 3H-leucine into the protein synthesis pathway. 3H-leucine is an excellent tracer during the initial hours of rapidly decreasing plasma activity; thereafter, reincorporation of recycled tracer into new protein synthesis obscures the tracer data from proteins with slower turnover rates. Thus, for proteins such as plasma albumin and apolipoprotein (apo) A-I, this tracer is unsatisfactory for measuring fractional catabolic (FCR) and turnover rates. By contrast, the kinetics of plasma very-low-density lipoprotein (VLDL)-apoB, a protein with a residence time of approximately 5 hours, are readily measured, since kinetic parameters of this protein can be determined by the time plasma leucine recycling becomes established. However, measurement of VLDL-apoB specific radioactivity extending up to 2 weeks provides further data on the kinetic tail of VLDL-apoB. Were plasma leucine a direct precursor for the leucine in VLDL-apoB, the kinetics of the plasma tracer should determine the kinetics of the protein. However, this is not the case, and the deviations from linearity are interpreted in terms of (1) the dilution of plasma leucine in the liver by unlabeled dietary leucine; (2) the recycling of hepatocellular leucine from proteins within the liver, where recycled cellular leucine does not equilibrate with plasma leucine; and (3) a "hump" in the kinetic data of VLDL-apoB, which we interpret to reflect recycling or retention of a portion of the apoB protein within the hepatocyte, with its subsequent secretion. Because hepatocellular tRNA is the immediate precursor for synthesis of these secretory proteins, its kinetics should be used as the forcing function to drive the modeling of this system. The VLDL-apoB tail contains the information needed to modify the plasma leucine data, to provide an appropriate forcing function when using 3H-leucine as a tracer of apolipoprotein metabolism. This correction is essential when using 3H-leucine as a tracer for measuring low-density lipoprotein (LDL)-apoB kinetics. The 3H-leucine tracer also highlights the importance of recognizing the difference between plasma and system residence times, the latter including the time the tracer resides within exchanging extravascular pools. The inability to determine these fractional exchange coefficients for apoA-I and albumin explains the failure of this tracer in kinetic studies of these proteins. For apoB-containing lipoproteins, plasma residence times are generally determined, and these measurements can be made satisfactorily with 3H-leucine.
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Affiliation(s)
- W R Fisher
- Department of Medicine, University of Florida, Gainesville 32610-0226, USA
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Nanjee MN, Crouse JR, King JM, Hovorka R, Rees SE, Carson ER, Morgenthaler JJ, Lerch P, Miller NE. Effects of intravenous infusion of lipid-free apo A-I in humans. Arterioscler Thromb Vasc Biol 1996; 16:1203-14. [PMID: 8792776 DOI: 10.1161/01.atv.16.9.1203] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Apolipoprotein (apo) A-I is the principal protein component of the plasma high density lipoproteins (HDLs). Tissue culture studies have suggested that lipid-free apo A-I may, by recruiting phospholipids (PLs) and unesterified cholesterol from cell membranes, initiate reverse cholesterol transport and provide a nidus for the formation, via lipid-poor, pre-beta-migrating HDLs, of spheroidal alpha-migrating HDLs. Apo A-I has also been shown to inhibit hepatic lipase (HL) and lipoprotein lipase (LPL) in vitro. To further study its functions and fate in vivo, we gave lipid-free apo A-I intravenously on a total of 32 occasions to six men with low HDL cholesterol (30 to 38 mg/dL) by bolus injection (25 mg/kg) and/or by infusion over 5 hours (1.25, 2.5, 5.0, and 10.0 mg.kg-1.h-1). The procedure was well tolerated: there were no clinical, biochemical, or hematologic changes, and there was no evidence of allergic, immunologic, or acute-phase responses. The 5-hour infusions increased plasma total apo A-I concentration in a dose-related manner by 10 to 50 mg/dL after which it decreased, with a half-life of 15 to 54 hours. Coinfusion of Intralipid reduced the clearance rate. The apparent volume of distribution exceeded the known extracellular space in humans, suggesting extensive first-pass clearance by one or more organs. No apo A-I appeared in the urine. Increases in apo A-I mass were confined to the pre-beta region on crossed immunoelectrophoresis of plasma and to HDL-size particles on size exclusion chromatography. Increases were recorded in HDL PL, but not in HDL unesterified or esterified cholesterol. Increases also occurred in LDL PL and in very low density lipoprotein cholesterol, triglycerides, and PL but not in plasma total apo B concentration. These results can all be explained by combined inhibition of HL and LPL activities. Owing to the effects that this would have had on HDL metabolism, no conclusions can be drawn from these data about the role of lipid-free apo A-I in the removal of PL and cholesterol from peripheral tissues in humans. The kinetic data suggest that the fractional catabolic rate of lipid-free apo A-I exceeds that of spheroidal HDLs and is reduced in the presence of surplus PL.
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Affiliation(s)
- M N Nanjee
- Department of Cardiovascular Biochemistry, St Bartholomew's Hospital Medical College, London, UK
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Ikewaki K, Zech LA, Brewer H, Rader DJ. ApoA-II kinetics in humans using endogenous labeling with stable isotopes: slower turnover of apoA-II compared with the exogenous radiotracer method. J Lipid Res 1996. [DOI: 10.1016/s0022-2275(20)37626-4] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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