Nonuniform radiolabeling of VLDL apolipoprotein B: implications for the analysis of studies of the kinetics of the metabolism of lipoproteins containing apolipoprotein B - PubMed (original) (raw)
. 1990 Jun;31(6):1031-42.
Affiliations
- PMID: 2373953
- PMCID: PMC3275143
Nonuniform radiolabeling of VLDL apolipoprotein B: implications for the analysis of studies of the kinetics of the metabolism of lipoproteins containing apolipoprotein B
R Ramakrishnan et al. J Lipid Res. 1990 Jun.
Abstract
Radiolabeling of whole lipoproteins or individual apolipoproteins has been an essential tool for the determination of the kinetics of apolipoprotein metabolism in vivo. Mathematical analysis of specific radioactivity (SA) or total radioactivity data has demonstrated the existence of significant complexity in the plasma decay curves of several apolipoproteins. Results obtained during development of methods to study the metabolism of apolipoprotein B (apoB) in very low density lipoprotein (VLDL) subclasses isolated according to flotation (Sf) rates from whole radiolabeled (d less than 1.006 g/ml) VLDL suggested nonuniform radiolabeling of apoB in the three Sf subclasses being studied. We therefore determined apoB SA in VLDL Sf subclasses in ten hypertriglyceridemic and five normal subjects. After radioiodination of apoB in whole VLDL, different apoB SA were found in Sf 400-100, Sf 100-60, and Sf 60-20. The pattern of labeling was quite variable among subjects. On average, apoB SA in the VLDL tracer was greatest in Sf 400-100, and least in Sf 60-20. Nonuniform labeling could also be demonstrated in five studies in which samples were obtained 3 min after intravenous injection of the tracer into subjects with a wide range of plasma triglycerides. Nonuniform labeling of apoB in whole VLDL was also demonstrated in two of the subjects by isolating subclasses of their VLDL that did not bind to an anti-apolipoprotein E immunoaffinity column. These results indicate that the usual assumption of homogeneous labeling of apoB may be erroneous. We have derived a simple mathematical formula to study the consequences of this assumption in estimating kinetic parameters. It is shown that an erroneous assumption of homogeneous tracer labeling may significantly underestimate or overestimate the true production rate, even in a simple two-pool model. Identification of labeling characteristics and incorporation of this information into the mathematical analysis of the plasma radioactivity data can improve the accuracy of the analysis as well as the sensitivity of compartmental models generated by such data.
Figures
Fig. 1
Distribution of radioactivity in a 2–16% polyacrylamide gel. Aliquots of whole VLDL, Sf 400–100, Sf 100–60, and Sf 60–20 were subjected to the TMU method, the resulting apoB pellets were resolubilized, and the solubilized material was electrophoresed. The gels were cut into lanes, each lane was divided into 2- to 3-mm slices, and the radioactivity was determined in a gamma counter. There was a single peak of radioactivity for each sample in the first two slices and there were no significant differences in the remaining slices among the samples.
Fig. 2
ApoB SA in VLDL subfractions for the first 60 min after a bolus injection of radiolabeled whole VLDL. Lines are drawn freehand to provide visual continuity; A, subject 12; B, subject 13.
Fig. 3
A general n-pool model for the turnover of VLDL apoB. Mv is the total mass of apoB in VLDL, mi is the mass fraction in the i-th pool; ui is the initial SA in the i-th pool; R0i is the apoB flux out of the i-th pool, converted to IDL and/or LDL or removed from plasma. The dashed lines among the pools indicate possible fluxes (in any direction). The dashed box surrounds pools that are intravascular and are included in the measurement of whole VLDL SA. In this case, all VLDL pools are circulating and intravascular, by assumption.
Fig. 4
An n-pool model for the turnover of VLDL apoB, similar to that in Fig. 3, but flux out of VLDL is from only one pool, the n-th pqol.
Fig. 5
A two-pool cascade model for the turnover of VLDL apoB. Here, m1 is the mass fraction in the first pool; m2 (= 1 − m1) is the mass fraction in the second pool; u1 and u2 are initial SA in the two pools; R01 is the flux out of pool 1, which may be removed from plasma or converted to IDL and/or LDL; R02 is the corresponding flux out of pool 2.
Fig. 6
The ratio of the calculated production rate, under the uniform labeling assumption, to the true production rate, as a function of the ratio of specific activities in the two pools of the model shown in Fig. 5; A, the case with 30% of the total mass in pool 2; B, 50%; C, 70%. In each panel, the curves numbered 1–6 correspond to six different values of R02Rv0 (the fraction of total flux that exits from pool 2 ) −0.1, 0.3, 0.5, 0.7, 0.9, and 1.0, respectively. The highlighted regions correspond to the range of specific activity ratios that we have observed.
Similar articles
- Metabolism of apolipoprotein B in large triglyceride-rich very low density lipoproteins of normal and hypertriglyceridemic subjects.
Packard CJ, Munro A, Lorimer AR, Gotto AM, Shepherd J. Packard CJ, et al. J Clin Invest. 1984 Dec;74(6):2178-92. doi: 10.1172/JCI111644. J Clin Invest. 1984. PMID: 6511922 Free PMC article. - The 3H-leucine tracer: its use in kinetic studies of plasma lipoproteins.
Fisher WR, Venkatakrishnan V, Fisher ES, Stacpoole PW, Zech LA. Fisher WR, et al. Metabolism. 1997 Mar;46(3):333-42. doi: 10.1016/s0026-0495(97)90262-6. Metabolism. 1997. PMID: 9054478 - Thematic review series: patient-oriented research. What we have learned about VLDL and LDL metabolism from human kinetics studies.
Parhofer KG, Barrett PH. Parhofer KG, et al. J Lipid Res. 2006 Aug;47(8):1620-30. doi: 10.1194/jlr.R600013-JLR200. Epub 2006 May 23. J Lipid Res. 2006. PMID: 16720894 Review. - De novo production of low density lipoproteins: fact or fancy.
Shames DM, Havel RJ. Shames DM, et al. J Lipid Res. 1991 Jul;32(7):1099-112. J Lipid Res. 1991. PMID: 1940634 Review.
Cited by
- Niosomal formulation of mefenamic acid for enhanced cancer targeting; preparation, characterization and biodistribution study using radiolabeling technique.
Shewaiter MA, Selim AA, Rashed HM, Moustafa YM, Gad S. Shewaiter MA, et al. J Cancer Res Clin Oncol. 2023 Dec;149(20):18065-18080. doi: 10.1007/s00432-023-05482-8. Epub 2023 Nov 20. J Cancer Res Clin Oncol. 2023. PMID: 37982828 Free PMC article. - Lipoprotein kinetics in the metabolic syndrome: pathophysiological and therapeutic lessons from stable isotope studies.
Chan DC, Barrett PH, Watts GF. Chan DC, et al. Clin Biochem Rev. 2004 Feb;25(1):31-48. Clin Biochem Rev. 2004. PMID: 18516204 Free PMC article. - Delayed catabolism of apoB-48 lipoproteins due to decreased heparan sulfate proteoglycan production in diabetic mice.
Ebara T, Conde K, Kako Y, Liu Y, Xu Y, Ramakrishnan R, Goldberg IJ, Shachter NS. Ebara T, et al. J Clin Invest. 2000 Jun;105(12):1807-18. doi: 10.1172/JCI8283. J Clin Invest. 2000. PMID: 10862796 Free PMC article. - Lipoprotein (a) metabolism estimated by nonsteady-state kinetics.
Parhofer KG, Demant T, Ritter MM, Geiss HC, Donner M, Schwandt P. Parhofer KG, et al. Lipids. 1999 Apr;34(4):325-35. doi: 10.1007/s11745-999-0370-z. Lipids. 1999. PMID: 10443965
References
- Janus ED, Nicoll A, Wootton R, Turner PR, Magill PJ, Lewis B. Quantitative studies of very low density lipoprotein: conversion to low density lipoprotein in normal controls and primary hyperlipidaemic states and the role of direct secretion of low density lipoprotein in heterozygous familial hypercholesterolaemia. Eur J Clin Invest. 1980;10:149–159. - PubMed
- Fisher WR, Zech LA, Bardalaye P, Warmke G, Berman M. The metabolism of apolipoprotein B in subjects with hypertriglyceridemia and polydisperse LDL. J Lipid Res. 1980;21:760–774. - PubMed
- Chait A, Albers JJ, Brunzell JD. Very low density lipoprotein overproduction in genetic forms of hypertriglyceridemia. Eur J Clin Invest. 1980;10:17–22. - PubMed
Publication types
MeSH terms
Substances
Grants and funding
- RR-645/RR/NCRR NIH HHS/United States
- HL-36000/HL/NHLBI NIH HHS/United States
- T32 HL007343/HL/NHLBI NIH HHS/United States
- T32 HL007343-21/HL/NHLBI NIH HHS/United States
- HL-21006/HL/NHLBI NIH HHS/United States
LinkOut - more resources
Full Text Sources
Medical
Miscellaneous