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Quintão ECR. Plasma Non-cholesterol Sterols as Markers of Cholesterol Synthesis and Intestinal Absorption: A Critical Review. Curr Pharm Des 2020; 26:5152-5162. [PMID: 32744960 DOI: 10.2174/1381612826666200730220230] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2020] [Accepted: 07/01/2020] [Indexed: 11/22/2022]
Abstract
Plasma concentrations of phytosterols and non-cholesterol sterol precursors of cholesterol synthesis have been used as markers of intestinal cholesterol absorption and synthesis in inherited and secondary dyslipidemias and in population-based investigations to evaluate the risk for cardiovascular disease, respectively. The method aims at replacing initial research procedures such as the use of stable isotopes associated with fecal steroid balance, which are limited by the high cost and tedious procedures. However, we show in this review that numerous results obtained with serum sterol measurements are contradictory. In this regard, the following points are discussed: 1) how phytosterols relate to atherosclerosis considering that defects in biliary output or in the transport of phytosterols from the intestinal mucosa back into the intestinal lumen provide increased content of phytosterols and other sterols in plasma and tissues, thus not allowing to conclude that their presence in arteries and atheromas represents the etiology of atherosclerosis; 2) serum non-cholesterol sterols as markers of cholesterol synthesis and absorption, such as cholestanol, present discrepant results, rendering them often inadequate to identify cases of coronary artery disease as well as alterations in the whole body cholesterol metabolism; 3) such methods of measurement of cholesterol metabolism are confounded by factors like diabetes mellitus, body weight and other pathologies including considerable hereditary hyperlipidemias biological variabilities that influence the efficiency of synthesis and intestinal absorption of cholesterol.
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Li Y, Wei CH, Green MH, Ross AC. Dietary Iron Repletion Stimulates Hepatic Mobilization of Vitamin A in Previously Iron-Deficient Rats as Determined by Model-Based Compartmental Analysis. J Nutr 2020; 150:1982-1988. [PMID: 32297934 PMCID: PMC7443722 DOI: 10.1093/jn/nxaa098] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2019] [Revised: 01/24/2020] [Accepted: 03/19/2020] [Indexed: 01/26/2023] Open
Abstract
BACKGROUND Iron deficiency can result in hyporetinolemia and hepatic vitamin A (VA) sequestration. OBJECTIVES We used model-based compartmental analysis to determine the impact of iron repletion on VA metabolism and kinetics in iron-deficient rats. METHODS At weaning, Sprague-Dawley rats were assigned to either a VA-marginal diet (0.35 mg retinol equivalent/kg) with adequate iron (35 ppm, control group [CN]) or reduced iron (3 ppm, iron-deficient group [ID-]), with an equivalent average body weight for each group. After 5 wk, n = 4 rats from each group were euthanized for baseline measurements of VA and iron indices, and the remaining rats (n = 6 CN, n = 10 ID-) received an intravenous injection of 3H-labeled retinol in an emulsion as tracer to initiate the kinetic study. On day 21 after dosing, half of the ID- rats were switched to the CN diet to initiate iron repletion, referred to as the iron-repletion group (ID+). From the time of dosing, 34 serial blood samples were collected from each rat over a 92-d time course. Plasma tracer and tissue tracee data were fitted to 6- and 4-compartment models, respectively, to analyze the kinetic behavior of VA in all groups. RESULTS Our mathematical model indicated that ID- rats exhibited a nearly 6-fold decrease in liver VA secretion and >4-fold reduction in whole-body VA utilization, compared with CN rats, whereas these perturbed kinetic behaviors were notably corrected in ID+ rats, close to those from the CN group. CONCLUSIONS Iron repletion can remove the inhibitory effect that iron deficiency exerts on hepatic mobilization of VA and restore retinol kinetic parameters to values similar to that of never-deficient CN rats. Together with improvements in iron and VA indices, our results suggest that restoration of an iron-adequate diet is sufficient to improve VA kinetics after a previous state of iron deficiency.
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Affiliation(s)
- Yaqi Li
- Department of Nutritional Sciences, The Pennsylvania State University, University Park, PA, USA
| | - Cheng-Hsin Wei
- Molecular Pharmacology Program and Cancer Research Technology Program, Frederick National Laboratory for Cancer Research, Frederick, MD, USA
| | - Michael H Green
- Department of Nutritional Sciences, The Pennsylvania State University, University Park, PA, USA
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3
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Cholesterol metabolism in mice models of genetic hypercholesterolemia. J Physiol Biochem 2020; 76:437-443. [DOI: 10.1007/s13105-020-00753-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2020] [Accepted: 06/11/2020] [Indexed: 12/28/2022]
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4
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Zhang T, Chen J, Tang X, Luo Q, Xu D, Yu B. Interaction between adipocytes and high-density lipoprotein:new insights into the mechanism of obesity-induced dyslipidemia and atherosclerosis. Lipids Health Dis 2019; 18:223. [PMID: 31842884 PMCID: PMC6913018 DOI: 10.1186/s12944-019-1170-9] [Citation(s) in RCA: 66] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2019] [Accepted: 12/09/2019] [Indexed: 12/19/2022] Open
Abstract
Obesity is the most common nutritional disorder worldwide and is associated with dyslipidemia and atherosclerotic cardiovascular disease. The hallmark of dyslipidemia in obesity is low high density lipoprotein (HDL) cholesterol (HDL-C) levels. Moreover, the quality of HDL is also changed in the obese setting. However, there are still some disputes on the explanations for this phenomenon. There is increasing evidence that adipose tissue, as an energy storage tissue, participates in several metabolism activities, such as hormone secretion and cholesterol efflux. It can influence overall reverse cholesterol transport and plasma HDL-C level. In obesity individuals, the changes in morphology and function of adipose tissue affect plasma HDL-C levels and HDL function, thus, adipose tissue should be the main target for the treatment of HDL metabolism in obesity. In this review, we will summarize the cross-talk between adipocytes and HDL related to cardiovascular disease and focus on the new insights of the potential mechanism underlying obesity and HDL dysfunction.
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Affiliation(s)
- Tianhua Zhang
- Department of Cardiovascular Medicine, the Second Xiangya Hospital, Central South University, Changsha, Hunan, 410011, People's Republic of China
| | - Jin Chen
- Department of Cardiovascular Medicine, the Second Xiangya Hospital, Central South University, Changsha, Hunan, 410011, People's Republic of China
| | - Xiaoyu Tang
- Department of Cardiovascular Medicine, the Second Xiangya Hospital, Central South University, Changsha, Hunan, 410011, People's Republic of China
| | - Qin Luo
- Department of Cardiovascular Medicine, the Second Xiangya Hospital, Central South University, Changsha, Hunan, 410011, People's Republic of China
| | - Danyan Xu
- Department of Cardiovascular Medicine, the Second Xiangya Hospital, Central South University, Changsha, Hunan, 410011, People's Republic of China
| | - Bilian Yu
- Department of Cardiovascular Medicine, the Second Xiangya Hospital, Central South University, Changsha, Hunan, 410011, People's Republic of China.
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5
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Lin X, Racette SB, Ma L, Wallendorf M, Dávila-Román VG, Ostlund RE. Endogenous Cholesterol Excretion Is Negatively Associated With Carotid Intima-Media Thickness in Humans. Arterioscler Thromb Vasc Biol 2017; 37:2364-2369. [PMID: 28982667 DOI: 10.1161/atvbaha.117.310081] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2017] [Accepted: 09/21/2017] [Indexed: 01/11/2023]
Abstract
OBJECTIVE Epidemiological studies strongly suggest that lipid factors independent of low-density lipoprotein cholesterol contribute significantly to cardiovascular disease risk. Because circulating lipoproteins comprise only a small fraction of total body cholesterol, the mobilization and excretion of cholesterol from plasma and tissue pools may be an important determinant of cardiovascular disease risk. Our hypothesis is that fecal excretion of endogenous cholesterol is protective against atherosclerosis. APPROACH AND RESULTS Cholesterol metabolism and carotid intima-media thickness were quantitated in 86 nondiabetic adults. Plasma cholesterol was labeled by intravenous infusion of cholesterol-d7 solubilized in a lipid emulsion and dietary cholesterol by cholesterol-d5 and the nonabsorbable stool marker sitostanol-d4. Plasma and stool samples were collected while subjects consumed a cholesterol- and phytosterol-controlled metabolic kitchen diet and were analyzed by mass spectrometry. Carotid intima-media thickness was negatively correlated with fecal excretion of endogenous cholesterol (r=-0.426; P<0.0001), total cholesterol (r=-0.472; P≤0.0001), and daily percent excretion of cholesterol from the rapidly mixing cholesterol pool (r=-0.343; P=0.0012) and was positively correlated with percent cholesterol absorption (r=+0.279; P=0.0092). In a linear regression model controlling for age, sex, systolic blood pressure, hemoglobin A1c, low-density lipoprotein, high-density lipoprotein cholesterol, and statin drug use, fecal excretion of endogenous cholesterol remained significant (P=0.0008). CONCLUSIONS Excretion of endogenous cholesterol is strongly, independently, and negatively associated with carotid intima-media thickness. The reverse cholesterol transport pathway comprising the intestine and the rapidly mixing plasma, and tissue cholesterol pool could be an unrecognized determinant of cardiovascular disease risk not reflected in circulating lipoproteins. Further work is needed to relate measures of reverse cholesterol transport to atherosclerotic disease. CLINICAL TRIAL REGISTRATION URL: http://www.clinicaltrials.gov. Unique identifier: NCT01603758.
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Affiliation(s)
- Xiaobo Lin
- From the Division of Endocrinology, Metabolism, and Lipid Research, Department of Medicine (X.L., S.B.R., L.M., R.E.O.), Program in Physical Therapy (S.B.R.), Division of Biostatistics (M.W.), and Cardiovascular Imaging and Clinical Research Core Laboratory, Cardiovascular Division, Department of Medicine (V.G.D.-R.), Washington University School of Medicine, St. Louis, MO
| | - Susan B Racette
- From the Division of Endocrinology, Metabolism, and Lipid Research, Department of Medicine (X.L., S.B.R., L.M., R.E.O.), Program in Physical Therapy (S.B.R.), Division of Biostatistics (M.W.), and Cardiovascular Imaging and Clinical Research Core Laboratory, Cardiovascular Division, Department of Medicine (V.G.D.-R.), Washington University School of Medicine, St. Louis, MO
| | - Lina Ma
- From the Division of Endocrinology, Metabolism, and Lipid Research, Department of Medicine (X.L., S.B.R., L.M., R.E.O.), Program in Physical Therapy (S.B.R.), Division of Biostatistics (M.W.), and Cardiovascular Imaging and Clinical Research Core Laboratory, Cardiovascular Division, Department of Medicine (V.G.D.-R.), Washington University School of Medicine, St. Louis, MO
| | - Michael Wallendorf
- From the Division of Endocrinology, Metabolism, and Lipid Research, Department of Medicine (X.L., S.B.R., L.M., R.E.O.), Program in Physical Therapy (S.B.R.), Division of Biostatistics (M.W.), and Cardiovascular Imaging and Clinical Research Core Laboratory, Cardiovascular Division, Department of Medicine (V.G.D.-R.), Washington University School of Medicine, St. Louis, MO
| | - Victor G Dávila-Román
- From the Division of Endocrinology, Metabolism, and Lipid Research, Department of Medicine (X.L., S.B.R., L.M., R.E.O.), Program in Physical Therapy (S.B.R.), Division of Biostatistics (M.W.), and Cardiovascular Imaging and Clinical Research Core Laboratory, Cardiovascular Division, Department of Medicine (V.G.D.-R.), Washington University School of Medicine, St. Louis, MO
| | - Richard E Ostlund
- From the Division of Endocrinology, Metabolism, and Lipid Research, Department of Medicine (X.L., S.B.R., L.M., R.E.O.), Program in Physical Therapy (S.B.R.), Division of Biostatistics (M.W.), and Cardiovascular Imaging and Clinical Research Core Laboratory, Cardiovascular Division, Department of Medicine (V.G.D.-R.), Washington University School of Medicine, St. Louis, MO.
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The Interpretation of Cholesterol Balance Derived Synthesis Data and Surrogate Noncholesterol Plasma Markers for Cholesterol Synthesis under Lipid Lowering Therapies. CHOLESTEROL 2017; 2017:5046294. [PMID: 28321334 PMCID: PMC5340945 DOI: 10.1155/2017/5046294] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/16/2016] [Revised: 12/21/2016] [Accepted: 01/26/2017] [Indexed: 12/12/2022]
Abstract
The cholesterol balance procedure allows the calculation of cholesterol synthesis based on the assumption that loss of endogenous cholesterol via fecal excretion and bile acid synthesis is compensated by de novo synthesis. Under ezetimibe therapy hepatic cholesterol is diminished which can be compensated by hepatic de novo synthesis and hepatic extraction of plasma cholesterol. The plasma lathosterol concentration corrected for total cholesterol concentration (R_Lath) as a marker of de novo cholesterol synthesis is increased during ezetimibe treatment but unchanged under treatment with ezetimibe and simvastatin. Cholesterol balance derived synthesis data increase during both therapies. We hypothesize the following. (1) The cholesterol balance data must be applied to the hepatobiliary cholesterol pool. (2) The calculated cholesterol synthesis value is the sum of hepatic de novo synthesis and the net plasma-liver cholesterol exchange rate. (3) The reduced rate of biliary cholesterol absorption is the major trigger for the regulation of hepatic cholesterol metabolism under ezetimibe treatment. Supportive experimental and literature data are presented that describe changes of cholesterol fluxes under ezetimibe, statin, and combined treatments in omnivores and vegans, link plasma R_Lath to liver function, and define hepatic de novo synthesis as target for regulation of synthesis. An ezetimibe dependent direct hepatic drug effect cannot be excluded.
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Holleboom AG, Jakulj L, Franssen R, Decaris J, Vergeer M, Koetsveld J, Luchoomun J, Glass A, Hellerstein MK, Kastelein JJP, Hovingh GK, Kuivenhoven JA, Groen AK, Turner SM, Stroes ESG. In vivo tissue cholesterol efflux is reduced in carriers of a mutation in APOA1. J Lipid Res 2013; 54:1964-71. [PMID: 23650622 DOI: 10.1194/jlr.p028449] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Atheroprotection by high density lipoprotein (HDL) is considered to be mediated through reverse cholesterol transport (RCT) from peripheral tissues. We investigated in vivo cholesterol fluxes through the RCT pathway in patients with low plasma high density lipoprotein cholesterol (HDL-c) due to mutations in APOA1. Seven carriers of the L202P mutation in APOA1 (mean HDL-c: 20 ± 19 mg/dl) and seven unaffected controls (mean HDL-c: 54 ± 11 mg/dl, P < 0.0001) received a 20 h infusion of (13)C2-cholesterol ((13)C-C). Enrichment of plasma and erythrocyte free cholesterol and plasma cholesterol esters was measured. With a three-compartment SAAM-II model, tissue cholesterol efflux (TCE) was calculated. TCE was reduced by 19% in carriers (4.6 ± 0.8 mg/kg/h versus 5.7 ± 0.7 mg/kg/h in controls, P = 0.02). Fecal (13)C recovery and sterol excretion 7 days postinfusion did not differ significantly between carriers and controls: 21.3 ± 20% versus 13.3 ± 6.3% (P = 0.33), and 2,015 ± 1,431 mg/day versus 1456 ± 404 mg/day (P = 0.43), respectively. TCE is reduced in carriers of mutations in APOA1, suggesting that HDL contributes to efflux of tissue cholesterol in humans. The residual TCE and unaffected fecal sterol excretion in our severely affected carriers suggest, however, that non-HDL pathways contribute to RCT significantly.
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Affiliation(s)
- Adriaan G Holleboom
- Department of Vascular Medicine, Academic Medical Center, Amsterdam, The Netherlands
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8
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Wallentin L, Angelin B, Einarsson K, Leijd B. Lecithin: Cholesterol Acyl Transfer Rate in Plasma and its Relations to Lipoprotein Concentrations and to Kinetics of Bile Acids and Triglycerides in Hyperlipoproteinemic Subjects. Scandinavian Journal of Clinical and Laboratory Investigation 2011. [DOI: 10.1080/00365517809104908] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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9
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Prattes S, Hörl G, Hammer A, Blaschitz A, Graier WF, Sattler W, Zechner R, Steyrer E. Intracellular distribution and mobilization of unesterified cholesterol in adipocytes: triglyceride droplets are surrounded by cholesterol-rich ER-like surface layer structures. J Cell Sci 2000; 113 ( Pt 17):2977-89. [PMID: 10934037 DOI: 10.1242/jcs.113.17.2977] [Citation(s) in RCA: 117] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In addition to their central role in triglyceride storage, fat cells are a primary depot of unesterified cholesterol (FC) in the body. In comparison, peripheral cells contain very little FC. This difference in adipocytes versus peripheral tissues is inconsistent with the current theory of cholesterol homeostasis. Attempting to resolve this discrepancy, we examined intracellular storage sites of FC in murine 3T3-F442A adipocytes. Using the cholesterol-binding antibiotic, filipin, in combination with high resolution fluorescence microscopy, intense fluorescent staining characteristically decorated the periphery of triglyceride droplets (TGD) as well as the plasma membrane (PM) of fat cells. Filipin-staining was not visible inside the lipid droplets. Purification of TGD by subcellular fractionation demonstrated that the rise in total FC content of adipocytes upon differentiation was attributable to an increase in TGD-FC, which contributed up to one third of the total cellular FC. The protein component of purified TGD from cultured adipocytes as well as from murine adipocytes obtained from fresh tissues contained the lumenal endoplasmic reticulum (ER) immunoglobulin binding protein (BiP) and the integral ER membrane protein calnexin. Efflux experiments using the extracellular FC acceptors (β)-cyclodextrin or apolipoprotein A-I demonstrated that TGD-associated FC was releasable from TGD. Whereas FC efflux from adipocytes was unaffected in the presence of brefeldin A or monensin, the secretion of a control protein, lipoprotein lipase, was effectively reduced. In summary, our findings identify the TGD surface layer as primary intracellular storage site for FC within adipocytes. We suggest that the structural role of ER-resident proteins in this adipocyte TGD envelope has been previously neglected. Our findings support the suggestion that an ER-like structure, albeit of modified lipid composition, constitutes the lipid droplets' surface layer. Finally, the efflux process of FC from adipocytes upon extracellular stimulation with (beta)-cyclodextrin provides evidence for an energy-dependent intracellular trafficking route between the TGD-FC pool and the PM-FC sites which is distinct from the secretory pathway of proteins.
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Affiliation(s)
- S Prattes
- Department of Medical Biochemistry and Medical Molecular Biology, University of Graz, Austria
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10
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Fisher WR, Zech LA, Stacpoole PW. ApoB metabolism in familial hypercholesterolemia. Inconsistencies with the LDL receptor paradigm. ARTERIOSCLEROSIS AND THROMBOSIS : A JOURNAL OF VASCULAR BIOLOGY 1994; 14:501-10. [PMID: 8148348 DOI: 10.1161/01.atv.14.4.501] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The biology of the low-density lipoprotein (LDL) receptor has been examined in detail, and a paradigm for LDL metabolism has evolved from comparative studies of cholesterol metabolism in a variety of cells cultured from normal individuals and subjects with familial hypercholesterolemia (FH). Cultured cells from patients with homozygous FH lack a functional LDL receptor and show diminished LDL clearance, induction of the enzyme hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase, increased cholesterol synthesis, decreased cholesterol ester production, and depleted cholesterol ester stores. The observed decrease in the fractional catabolic rate (FCR) of LDL is attributed to the mutated LDL receptor gene. However, in the experimental animal model of this disease, the Watanabe heritable hyperlipidemic (WHHL) rabbit, cholesterol ester stores are increased, while hepatic cholesterol synthesis is decreased. Furthermore, in humans HMG-CoA reductase is suppressed, and the LDL apolipoprotein (apo) B production rate is increased in patients with FH. These findings raise questions about the adequacy of the paradigm in understanding hepatic cholesterol metabolism in vivo. In humans, apoB metabolism is believed to be principally determined by the liver, where apoB is both synthesized and catabolized. Assuming the neutral lipid content of the liver is the major determinant of apoB metabolism, we postulated that the changes in apoB metabolism in FH are predictable when based on the assumption of an increase in hepatic cholesterol and cholesterol ester content, as observed both in the WHHL rabbit and in humans. We examined this hypothesis in vivo in patients with heterozygous FH by using tracer kinetic methodology and have used similar data from normal and hypertriglyceridemic (HTG) subjects as controls. Whereas normal and HTG subjects secrete apoB primarily as large, triglyceride-enriched very-low-density lipoprotein (VLDL), heterozygous FH patients have an absolute decrease in apoB production and secrete almost 40% of apoB as smaller intermediate-density lipoprotein (IDL)/LDL. In normal humans, about half of secreted apoB is catabolized rather than being converted to LDL. In HTG subjects two thirds of apoB follows this same route, by which VLDL remnants remaining after triglyceride hydrolysis are largely returned to the liver. In contrast, in FH subjects secreted apoB is fully converted to LDL. Thus, although total apoB secretion is reduced in FH subjects, total LDL production is greater than in either normal or HTG subjects. Under basal conditions the elevated LDL in heterozygous FH is due to both decreased LDL receptor-mediated catabolism and increased LDL production. However, the number of LDL receptors actually expressed is suppressed below the number of potentially functional receptors.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- W R Fisher
- Department of Medicine (Endocrinology and Metabolism), University of Florida, College of Medicine, Gainesville 32610
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11
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Ostlund RE. A minimal model for human whole body cholesterol metabolism. THE AMERICAN JOURNAL OF PHYSIOLOGY 1993; 265:E513-20. [PMID: 8214059 DOI: 10.1152/ajpendo.1993.265.3.e513] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Important work by others has shown that human whole body cholesterol metabolism can be described by a three-compartment model computed from plasma cholesterol specific activity after an intravenous infusion of labeled cholesterol. However, some parameters of that model cannot be estimated precisely [coefficient of variation (CV) 15-19% after 40 wk of follow-up], making its use in routine clinical investigation difficult. On the other hand, a simpler two-compartment model can be calculated with excellent precision from only 10 wk of data (CV 2-8%), but its parameters are inaccurate (for example, the size of the central pool is overestimated by 20%, and the rate constant for fractional excretion of cholesterol from the body is underestimated by 15%). Thus both three-compartment and two-compartment models of cholesterol turnover have important limitations. An alternative is provided by a minimal model that takes advantage of the increased precision expected in the solution of models with fewer parameters. A three-compartment structure is used, but only four (rather than 6 or more) parameters are calculated: the mass of the rapidly mixing central cholesterol compartment, the fractional rate of cholesterol elimination from the body, and the average forward and reverse rate constants for cholesterol transfer between the rapid compartment and both slower compartments. Each of these parameters can be determined unambiguously (without the need to use a minimum or maximum estimate), accurately (mean values within 2% of theory), and with precision (CV 3-13%).(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- R E Ostlund
- Metabolism Division, Washington University School of Medicine, St. Louis, Missouri 63110
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12
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Schwartz CC, Zech LA, VandenBroek JM, Cooper PS. Cholesterol kinetics in subjects with bile fistula. Positive relationship between size of the bile acid precursor pool and bile acid synthetic rate. J Clin Invest 1993; 91:923-38. [PMID: 8450070 PMCID: PMC288045 DOI: 10.1172/jci116314] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Our aim was to identify and quantitate cholesterol pools and transport pathways in blood and liver. By studying bile fistula subjects, using several types of isotopic preparations, simultaneous labeling of separate cholesterol pools and sampling all components of blood and bile at frequent intervals, we developed a comprehensive multicompartmental model for cholesterol within the rapidly miscible pool. Data in six components (bile acids, esterified cholesterol in whole plasma, and free cholesterol in blood cells, bile, alpha lipoproteins, and beta lipoproteins) were modeled simultaneously with the SAAM program. The analysis revealed extensive exchange of free cholesterol between HDL and liver, blood cells, and other tissues. There was net free cholesterol transport from HDL to the liver in most subjects. The major organ that removed esterified cholesterol from blood was the liver. A large portion (4,211 mumol) of total hepatic cholesterol comprised a pool that turned over rapidly (t1/2 of 72 min) by exchanging mainly with plasma HDL and was the major source of bile acids and biliary cholesterol. Only 6% of hepatic newly synthesized cholesterol was used directly for bile acid synthesis: the analysis showed that 94% of newly synthesized cholesterol was partitioned into the large hepatic pool (putative plasma membrane free cholesterol) which exchanged rapidly with plasma lipoproteins. Bile acid synthetic rate correlated directly with the size of the large hepatic pool. In conclusion, hepatic and blood cholesterol pools and transports have been quantitated. HDL plays a central role in free cholesterol exchange/transport between all tissues and plasma. In humans, the metabolically active pool comprises a large portion of total hepatic cholesterol that, in part, regulates bile acid synthesis.
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Affiliation(s)
- C C Schwartz
- Department of Medicine, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298
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13
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Neese RA, Faix D, Kletke C, Wu K, Wang AC, Shackleton CH, Hellerstein MK. Measurement of endogenous synthesis of plasma cholesterol in rats and humans using MIDA. THE AMERICAN JOURNAL OF PHYSIOLOGY 1993; 264:E136-47. [PMID: 8430782 DOI: 10.1152/ajpendo.1993.264.1.e136] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We used the mass isotopomer distribution analysis (MIDA) technique to measure endogenous synthesis of plasma cholesterol in vivo in rats and normal human subjects. Sodium [1-13C]- or [2-13C]acetate was infused, and plasma free cholesterol was analyzed by gas chromatography-mass spectrometry. Frequencies of mass isotopomers M0-M4 (mass-to-charge ratio 368-372) were quantified. The enrichment of the true precursor for cholesterol synthesis (acetyl-coenzyme A in contributing tissues) was determined using the MIDA method. This technique remains mathematically valid even if more than one tissue contributes to circulating free cholesterol. The fractional contribution (f) from endogenous synthesis to free cholesterol in normal women (n = 5) was 2.48 +/- 0.39% after 7 h in the postabsorptive state and 1.27 +/- 0.41% after 8 h of refeeding. In ad libitum-fed rats (n = 12), f was 2.89 +/- 0.44% after 12 h, whereas administration of recombinant tumor necrosis factor increased this value fourfold. Next, the rate constant (k) for removal of labeled free cholesterol from plasma was calculated. Higher masses (M2-M4) were followed to avoid the problem of persistent label incorporation. During the 60 h after cessation of [13C]acetate infusions, k was 0.02490 +/- 0.00298/h in humans. Using these values of k and f, absolute cholesterogenesis was 568 +/- 55 mg/day in normal women (follicular menstrual phase), similar to prior estimates based on whole body sterol balances. Women also exhibited a diurnal variation for endogenous cholesterol synthesis (34.6 +/- 5.4 mg/h nighttime vs. 15.9 +/- 5.2 mg/h daytime) consistent with current knowledge about rhythms in cholesterogenesis. Checks on the model were internally consistent (e.g., comparisons among different isotopomers for calculating precursor enrichment). We conclude that fractional and absolute endogenous cholesterol synthesis can be measured using stable isotopes in vivo by the MIDA technique.
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Affiliation(s)
- R A Neese
- Department of Nutritional Sciences, University of California, Berkeley 94720
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14
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Goldberg IJ, Holleran S, Ramakrishnan R, Adams M, Palmer RH, Dell RB, Goodman DS. Lack of effect of lovastatin therapy on the parameters of whole-body cholesterol metabolism. J Clin Invest 1990; 86:801-8. [PMID: 2394831 PMCID: PMC296795 DOI: 10.1172/jci114777] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
UNLABELLED The effects of lovastatin therapy on the parameters of body cholesterol metabolism were explored in nine hypercholesterolemic patients. Long-term cholesterol turnover studies were performed before therapy, and were repeated after 15 mo of lovastatin therapy (40 mg/d) while continuing on therapy. The major question addressed was whether a reduction in plasma cholesterol level with lovastatin would be associated with a reduction in the whole-body production rate of cholesterol or with the sizes of exchangeable body cholesterol pools as determined by the three-pool model of cholesterol turnover. The mean plasma cholesterol level decreased 19.4% (from 294 to 237 mg/dl), and low-density lipoprotein cholesterol decreased 23.8% (from 210 to 159 mg/dl) with lovastatin therapy. Changes in high-density lipoprotein cholesterol level were not significant. The cholesterol production rate did not change significantly with therapy (1.09 +/- 0.10 [mean +/- S.D.] vs. 1.17 +/- 0.09 g/d). By comparison, colestipol and niacin treatment in three other subjects more than doubled the cholesterol production rate (1.14 +/- 0.28 vs. 2.42 +/- 0.34 g/d). Thus, hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase inhibition by lovastatin at the therapeutic dose used here did not change the steady-state rate of whole-body cholesterol synthesis. Despite the changes in plasma cholesterol levels, no significant changes were seen in the values of M1, of M3 or of Mtot, the sizes of the pools of rapidly, of slowly, and of total body exchangeable cholesterol. CONCLUSION lovastatin therapy to lower plasma cholesterol does not lead to corresponding reductions in body cholesterol pools or to a reduction in the rate of whole-body cholesterol synthesis. In the new steady state that exists during long-term lovastatin therapy, along with increased expression of the genes for HMG-CoA reductase and the LDL receptor, the body compensates for the effects of the drug so that cholesterol production rate and tissue pool sizes are not changed from pretreatment values.
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Affiliation(s)
- I J Goldberg
- Department of Medicine, Columbia University, New York 10032
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15
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Green MH, Green JB. Experimental and kinetic methods for studying vitamin A dynamics in vivo. Methods Enzymol 1990; 190:304-17. [PMID: 2087182 DOI: 10.1016/0076-6879(90)90035-y] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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16
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Johnson JA, Beitz DC, Jacobson NL. Effects of dietary beef and soy protein on tissue composition and low density lipoprotein uptake in young pigs. J Nutr 1989; 119:696-705. [PMID: 2723817 DOI: 10.1093/jn/119.5.696] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
To study effects of dietary protein source on plasma cholesterol homeostasis, six littermate pairs of 8-wk-old, castrated male pigs were assigned randomly to high fat diets containing either lean beef or soy protein isolate, with beef tallow as the major fat source in both diets. Diets were fed for 6 wk, with blood samples taken weekly and analyzed for lipid composition. At 6 wk, each pig was injected with [3H]cholesterol- and [14C]sucrose-labeled low density lipoproteins, and serial blood samples were taken. Pigs were then killed, and several tissues were sampled. Results show that dietary beef or soy protein, when fed with beef tallow as a fat source, has differential effects on rates of uptake of intact LDL by heart, M. sartorius muscle and subcutaneous adipose tissue, and on rates of uptake of LDL cholesterol by net free cholesterol exchange in subcutaneous and perirenal adipose tissues. Dietary protein source affected the composition of only two tissues analyzed. Pigs fed the beef-based diet had greater lipid concentrations in M. sartorius muscle, whereas pigs fed the soy protein-based diet had greater lipid concentrations in heart. Source of dietary protein did not influence in vivo kinetics of LDL cholesterol removal from blood plasma.
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Affiliation(s)
- J A Johnson
- Department of Biochemistry-Biophysics, Iowa State University, Ames 50011
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17
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Palmer RH, Nichols AV, Dell RB, Ramakrishnan R, Lindgren FT, Gong EL, Blum CB, Goodman DS. Lack of relationship in humans of the parameters of body cholesterol metabolism with plasma levels of subfractions of HDL or LDL, or with apoE isoform phenotype. J Lipid Res 1988. [DOI: 10.1016/s0022-2275(20)38810-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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18
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Weisweiler P. Simvastatin and bezafibrate: effects on serum lipoproteins and lecithin: cholesterol acyltransferase activity in familial hypercholesterolaemia. Eur J Clin Pharmacol 1988; 35:579-83. [PMID: 3234467 DOI: 10.1007/bf00637592] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Sixteen subjects with familial hypercholesterolaemia were randomly assigned to treatment with simvastatin 20-40 mg/day (an inhibitor of 3-hydroxy-3-methylglutaryl CoA reductase) or with bezafibrate 600 mg/day (a clofibrate analogue) for 12 weeks. Both drugs produced significant reductions in serum and LDL cholesterol; mean percentage fall -30.5% and -38.1% (simvastatin) and -17.8% and -20.6% (bezafibrate), respectively. Both drugs also caused a decrease in VLDL cholesterol, while only bezafibrate decreased the serum and VLDL triglyceride levels and increased HDL cholesterol and serum apolipoprotein A-I and A-II levels. Serum apolipoprotein B fell by 33.3% (simvastatin) and 15.7% (bezafibrate). Simvastatin and bezafibrate produced significant increases in the mean fractional esterification rate of LCAT, by +124.1% and +20.6%, respectively. Thus simvastatin was clearly more effective than bezafibrate in lowering LDL by enhancing its turnover, but bezafibrate had specific effects on VLDL and HDL that might be favourable in combined treatment regimens.
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Affiliation(s)
- P Weisweiler
- MRM-Metabolic Research Munich, Federal Republic of Germany
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19
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Miller NE. On the associations of body cholesterol pool size with age, HDL cholesterol and plasma total cholesterol concentration in humans. Atherosclerosis 1987; 67:163-72. [PMID: 3675711 DOI: 10.1016/0021-9150(87)90276-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Data from 17 subjects, in whom cholesterol kinetics had been measured by two-pool analysis of medium-term plasma cholesterol specific activity-time curves, were examined by multiple linear regression to explore the determinants of the size of the slowly exchanging cholesterol pool (MBmin) in humans. Pool size was independently and positively related to body weight (regression coefficient, 0.94 g per kg; P = 0.05) and age (1.77 g per year; P = 0.02). After allowance for these effects, MBmin retained a significant negative association with the plasma high density lipoprotein (HDL) cholesterol concentration (-0.56 g per mg/dl; P = 0.03), but was unrelated to plasma total cholesterol. This result is consistent with published data on the composition of those human tissues whose cholesterol is known to be largely a component of the slowly exchanging pool. It differs, however, from that of a recent study of cholesterol turnover [Blum et al, J. Lipid Res., 1985; 26: 1079-1088] in which pool size, measured by three-pool analysis of long-term decay curves, was unrelated to HDL and directly related to plasma total cholesterol. On the basis of other published data, it is considered that this discrepancy is unlikely to be a consequence of the difference between our respective studies in the duration and method of analysis of the specific activity decay curves. Differences in the variances of HDL cholesterol and plasma total cholesterol concentration that were examined, and in the biochemical-genetic factors underlying these variances, provide a more likely explanation. The overall weight of evidence favours the view that the pool of slowly exchangeable cholesterol in many human tissues expands during ageing at a rate which is increased in the presence of severe hypercholesterolemia, and which under some, but not all, circumstances also varies inversely with HDL cholesterol. The critical components of HDL metabolism which affect this process remain to be identified.
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Affiliation(s)
- N E Miller
- Department of Chemical Pathology and Metabolic Disorders, St. Thomas' Campus, United Medical School, Guy's Thomas' Hospital, London, U.K
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20
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Dilman VM, Revskoy SY, Golubev AG. Neuroendocrine-ontogenetic mechanism of aging: toward an integrated theory of aging. INTERNATIONAL REVIEW OF NEUROBIOLOGY 1986; 28:89-156. [PMID: 3542876 DOI: 10.1016/s0074-7742(08)60107-5] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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21
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Abstract
In humans, clofibrate increases the degree of bile cholesterol saturation and predisposes patients to cholesterol gallstone formation. To determine if this activity extends to the related hypolipidemic agent fenofibrate, duodenal bile lipid composition was studied in 15 subjects before they participated in a double-blind study of that drug. Eight subjects were studied again on fenofibrate and six on placebo; five placebo patients were also studied later on open-label fenofibrate. The results were similar in the double-blind and open-label studies, and changes in bile lipid composition were comparable to those seen in studies of clofibrate. Fenofibrate caused a significant decrease in the molar percentage of bile acids and increases in the molar percentage of phospholipids and cholesterol. The changes in bile acids and phospholipids had opposing effects on the cholesterol-holding capacity of bile. A statistically significant increase in the cholesterol saturation index was only apparent when all fenofibrate bile analyses were compared with all untreated bile analyses. The results demonstrated that fenofibrate has clear effects on bile lipid composition that may be associated with an increased propensity for gallstone formation, and when fenofibrate is used, patients should be monitored for this possibility.
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22
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Relationship of the parameters of body cholesterol metabolism with plasma levels of HDL cholesterol and the major HDL apoproteins. J Lipid Res 1985. [DOI: 10.1016/s0022-2275(20)34281-4] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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23
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24
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25
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Goodman DS, Deckelbaum RJ, Palmer RH, Dell RB, Ramakrishnan R, Delpre G, Beigel Y, Cooper M. Cholesterol turnover and metabolism in two patients with abetalipoproteinemia. J Lipid Res 1983. [DOI: 10.1016/s0022-2275(20)37859-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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26
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Predictive equations about whole body cholesterol metabolism in human beings. Nutr Rev 1983; 41:239-40. [PMID: 6355919 DOI: 10.1111/j.1753-4887.1983.tb07185.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
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27
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Maranhão RC, Quintão EC. Long term steroid metabolism balance studies in subjects on cholesterol-free and cholesterol-rich diets: comparison between normal and hypercholesterolemic individuals. J Lipid Res 1983. [DOI: 10.1016/s0022-2275(20)38010-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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28
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Ramakrishnan R, Dell RB, Goodman DS. On determining the extent of side-pool synthesis in a three-pool model for whole body cholesterol kinetics. J Lipid Res 1981; 22:1174-80. [PMID: 7320627 PMCID: PMC3277742] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Whole body cholesterol turnover is well described by a three-pool model. This model has eight unknown parameters: three masses, three synthesis rates, and two intercompartmental exchange rates. Only six parameters can be estimated by fitting the model to the plasma specific radioactivity-time curve which results from the intravenous injection of labeled cholesterol. Additional information is obtained if a precursor of cholesterol, labeled with a different isotope, is also injected. Equations are derived to enable the calculation of all eight model parameters from the two sum-of-exponentials equations that are fitted to the two tracer curves. The characteristics of a satisfactory precursor are discussed.
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29
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Ramakrishnan R, Dell RB, Goodman DS. On determining the extent of side-pool synthesis in a three-pool model for whole body cholesterol kinetics. J Lipid Res 1981. [DOI: 10.1016/s0022-2275(20)37309-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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30
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Miettinen TA. Effects of hypolipidemic drugs on bile acid metabolism in man. ADVANCES IN LIPID RESEARCH 1981; 18:65-97. [PMID: 6275661 DOI: 10.1016/b978-0-12-024918-3.50008-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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31
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Pohjanpalo H, Kekki M, Wahlström B. Estimation, resolution and solvability of linear compartmental models: cholesterol metabolism in man. INTERNATIONAL JOURNAL OF BIO-MEDICAL COMPUTING 1980; 11:397-413. [PMID: 7450916 DOI: 10.1016/0020-7101(80)90055-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
The paper presents a method to test metabolic linear multicompartment models for their mathematical solvability and their power of resolution with respect to individual parameters. The method can be seen as a means of predicting not only the model theoretical identifiability but also the expected quality of estimation before undertaking any actual serial experiments. The compartmental model of human cholesterol metabolism is taken as a demonstrative problem. The analysis shows that it is possible with tracer techniques to measure the cholesterol turnover, the cholesterol fluxes between exchangeable cholesterol pools, the cholesterol masses in individual pools, and the endogenous cholesterol synthesis in individual pools if certain conditions are met. In any complex kinetic situation, performance of a systematic model analysis is recommended before embarking on large-scale experimentation.
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32
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Goodman DS, Smith FR, Seplowitz AH, Ramakrishnan R, Dell RB. Prediction of the parameters of whole body cholesterol metabolism in humans. J Lipid Res 1980. [DOI: 10.1016/s0022-2275(20)34798-2] [Citation(s) in RCA: 79] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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33
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Nestel PJ, Miller NE. Cholesterol kinetics and faecal steroid excretion in subjects with primary hyperalphalipoproteinaemia. Atherosclerosis 1980; 36:127-34. [PMID: 7387772 DOI: 10.1016/0021-9150(80)90206-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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34
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TALL ALANR, SMALL DONALDM. Body Cholesterol Removal: Role of Plasma High-Density Lipoproteins1 1Supported by National Health Service Grants HL 18673, HL 07291, and HL 22682, and a Grant-In-Aid from the American Heart Association (316–3070–2286). ACTA ACUST UNITED AC 1980. [DOI: 10.1016/b978-0-12-024917-6.50007-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/18/2023]
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35
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Sodhi HS, Kudchodkar J, Mason DT. Cholesterol metabolism in clinical hyperlipidemias. ADVANCES IN LIPID RESEARCH 1980; 17:107-53. [PMID: 6992525 DOI: 10.1016/b978-0-12-024917-6.50009-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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36
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Ahlberg J, Angelin B, Björkhem I, Einarsson K, Leijd B. Hepatic cholesterol metabolism in normo- and hyperlipidemic patients with cholesterol gallstones. J Lipid Res 1979. [DOI: 10.1016/s0022-2275(20)40656-x] [Citation(s) in RCA: 36] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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37
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Wallentin L. Lecithin: cholestrol acyl transfer rate and high density lipoproteins in plasma during dietary and cholestyramine treatment of type IIa hyperlipoproteinaemia. Eur J Clin Invest 1978; 8:383-9. [PMID: 217692 DOI: 10.1111/j.1365-2362.1978.tb00869.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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38
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Wallentin L. Lecithin:cholesterol acyl transfer rate and high density lipoproteins in plasma during dietary and clofibrate treatment of hypertriglyceridemic subjects. Atherosclerosis 1978; 31:41-52. [PMID: 213085 DOI: 10.1016/0021-9150(78)90035-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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39
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Schwartz CC, Berman M, Vlahcevic ZR, Halloran LG, Gregory DH, Swell L. Multicompartmental analysis of cholesterol metabolism in man. Characterization of the hepatic bile acid and biliary cholesterol precursor sites. J Clin Invest 1978; 61:408-23. [PMID: 621281 PMCID: PMC372552 DOI: 10.1172/jci108952] [Citation(s) in RCA: 158] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The present report has presented the first clear evidence in man for the existence of specific hepatic cholesterol precursor sites associated with the formation and secretion of bile acids and biliary cholesterol. These hepatic compartments derive virtually all their cholesterol from newly synthesized and lipoprotein free cholesterol. The model which is presented was formulated on current concepts of cholesterol metabolism in man and is concerned, at this initial stage, with the elucidation of the bile acid and biliary cholesterol compartments. The complexity of cholesterol metabolism in man necessitated an initial approach that would minimize the number of inputs of cholesterol into the system, allow for the sampling of several cholesterol compartments, and permit the simultaneous labeling of newly synthesized cholesterol and preformed cholesterol. To achieve these objectives, we studied the patient with a total bile fistula. Six patients were administered simultaneously pulse injections of labeled mevalonic acid and [(14)C]cholesterol. The qualitative features of the specific activity time course curves after labeled mevalonic acid revealed no precursor-product relationship between bile acid, biliary cholesterol, and plasma free cholesterol. The peak specific activity of the bile acids was reached in approximately 100 min and was higher than the biliary cholesterol, which was higher than the plasma free cholesterol. The plasma free cholesterol specific activity became higher than the other lipids after 12 h and remained higher throughout the period of study. Similar related observations were made with [(14)C]cholesterol. The data were then subjected to simulation analysis and modeling using the SAAM-27 computer program. Computer least-square fits of the data were obtained after the model was evolved. During the model development, the least number of compartments and transport pathways were introduced consistent with a good fit of the data. Of particular importance was the constraint that the model fit the data obtained from both [(14)C]cholesterol and labeled mevalonic acid. The same parameter values were used to fit the data from both tracers. The fluxes arrived at in the model indicate that 31% and 20%, respectively, of the cholesterol input into the bile acid and biliary cholesterol precursor sites were derived directly from the newly synthesized hepatic cholesterol. The remainder had its origin predominantly from lipoprotein free cholesterol. Plasma esterified cholesterol (as free) made a small contribution (11%) to the bile acid compartment. Similarly, 10% of the biliary cholesterol arose from an unknown hepatic site. The present report has provided the basis for a new procedure for studying in vivo cholesterol metabolism in man. Examination of the derived cholesterol flux rates between the compartments suggests the presence of an important mechanism regulating the partitioning of lipoprotein free cholesterol between the bile acid and biliary cholesterol precursor sites. Aberrations in the proportioning of precursor cholesterol between these sites could be a causative factor precipitating the excessive secretion of biliary cholesterol and the production of lithogenic bile.
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Sodhi HS, Kudchodkar BJ, Clifford C, Borhani N, Mason DT. A reappraisal of the mechanisms of hypocholesterolemic action of therapeutic agents. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1978; 109:331-45. [PMID: 364950 DOI: 10.1007/978-1-4684-0967-3_19] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The most commonly used methods to study the mechanisms of hypocholesterolemic action of therapeutic agents generally determine the turnover of total (exchangeable) cholesterol pools in the body. This approach is based on the view that whatever increases the total load of cholesterol in the body will increase the levels of plasma cholesterol, and vice versa. Despite the importance of this assumption it has never been tested, and there is no evidence to indicate that it is valid under all conditions. This "overload" hypothesis dates from the times before the importance of plasma lipoproteins was recognized and their role in the transport of lipids was well understood. However, it is becoming increasingly clear that the levels of plasma cholesterol are determined more directly by the "transport" of cholesterol into and out of plasma compartment by lipoproteins than by the synthesis, absorption and elimination of cholesterol from the total body pools. Any effects that the latter parameters of cholesterol metabolism have on the levels of plasma cholesterol must be mediated through changes in synthesis and the subsequent metabolism of plasma lipoproteins. In other words, in any equation relating changes in the levels of plasma cholesterol to the changes in synthesis, absorption and elimination of cholesterol from the body pools we must consider the "transport" of cholesterol by lipoproteins and their metabolism.
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41
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Imawari M, Goodman DS. Immunological and immunoassay studies of the binding protein for vitamin D and its metabolites in human serum. J Clin Invest 1977; 59:432-42. [PMID: 402385 PMCID: PMC333379 DOI: 10.1172/jci108657] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
This study reports the development of a specific and sensitive radioimmunoassay and a simple and accurate radial immunodiffusion (RID) assay for the human serum-binding protein for vitamin D and its metabolites (DBP). These immunoassays employed a monospecific antiserum that was prepared in rabbits against human DBP. The radioimmunoassay effectively measured DBP in amounts of 1-10 ng, whereas the RID assay measured DBP accurately in amounts of 0.2-0.8 mug. The results obtained with the two immunoassays on the same samples of serum agreed well with each other. Using the RID assay, the mean (+/- SD) serum DBP concentration observed in 35 normal persons was 422 +/- 27 micrograms/ml. Generally similar levels were observed in 66 hyperlipidemic subjects. In molar terms, the mean DBP concentration (approximately 8 microgramsM) was of the order of 50 times the usual serum level of 25-hydroxyvitamin D (25-OH-D) plus vitamin D. Thus, most of plasma DBP circulates as apo-DBP, not containing a bound molecule of 25-OH-D or of vitamin D. DBP and 25-OH-D concentrations were measured in a limited number of patients with hypercalcemia, mild hypocalcemia, and markedly elevated serum 25-OH-D levels due to oral vitamin D supplementation. It was found that major changes can occur in the serum levels of 25-OH-D and of calcium with very little or no associated changes occurring in the serum concentration of DBP, The results suggest that neither serum 25-OH-D nor serum calcium plays an important role in the regulation of the metabolism of DBP. Data were obtained that confirmed and extended an earlier report on the identity of the group-specific component (Gc) protein in plasma with the plasma vitamin D-binding protein. On immunodiffusion against whole serum, the line formed with the anti-DBP antiserum showed a complete reaction-of-identity with the line formed with commercial antiserum against Gc protein. Furthermore, serum that had been depleted of DBP by treatment with Sepharose containing covalently coupled antibodies against DBP was found to be depleted also of immunoreactivity against anti-GC protein antiserum. In addition, the properties of the purified DBP preparation agreed closely with those previously reported by others for Gc protein. Finally, a comparative immunology study showed that sera from several different mammalian orders showed some immunoreactivity against the antihuman DBP antiserum. Thus, proteins immunologically similar to human DBP are present in sera from a number of mammalian species and orders.
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Krause BR, Hartman AD. Relationship between cell size, plasma cholesterol and rat adipocyte cholesterol storage. BIOCHIMICA ET BIOPHYSICA ACTA 1976; 450:197-205. [PMID: 990299 DOI: 10.1016/0005-2760(76)90091-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Plasma cholesterol and cholesterol storage/10(6) adipocytes were determined in the epididymal, perirenal, subcutaneous, and mesenteric fat depots of the fasted male rat. Adipocyte cholesterol increased exponentially as functions of mean cell diameter, body weight, and cell size (mug triacylglycerol/cell) in all depots examined, whereas plasma cholesterol was best described as a parabolic function of body weight. In all but the mesenteric depot, expression of storage as a ratio of cellular cholesterol:triacylglycerol was also described as a parabolic function of body weight, resulting in curves parallel to the cholesterol-body weight relationship. It is suggested that (1) adipose tissue cholesterol storage is most rapid after adipocyte number becomes fixed, (2) the level of cholesterol in the plasma may be a major determinant of fat cell cholesterol storage, especially in subcutaneous cells from adult animals in which cell size is constant but cholesterol storage continues to increase, and (3) the effect of plasma cholesterol is less pronounced in mesenteric adipocytes.
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44
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Cholesterol metabolism in groups of rhesus monkeys with high or low response of serum cholesterol to an atherogenic diet. J Lipid Res 1976. [DOI: 10.1016/s0022-2275(20)41739-0] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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