scholarly journals A study of the chylomicron metabolism in WHHL rabbits after fat loading. Discrepancy between results based on measurement of apoprotein B-48 or retinyl palmitate

1992 ◽  
Vol 285 (2) ◽  
pp. 641-646 ◽  
Author(s):  
P N M Demacker ◽  
P J van Heijst ◽  
A F H Stalenhoef
Keyword(s):  
New Zealand ◽  
Strong Correlation ◽  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Retinyl Palmitate ◽  
Receptor Activity ◽  
Low Density ◽  
Apoprotein B ◽  
Chylomicron Metabolism

We studied the metabolism of chylomicrons in homozygous Watanabe heritable hyperlipidaemic (WHHL) rabbits and in cholesterol-fed or normally fed New Zealand White (NZW) rabbits by measuring the concentrations of apoprotein B-48 and of retinyl palmitate in their serum after feeding fat plus this vitamin according to two different protocols. Compared with NZW controls, retinyl palmitate accumulated in both hyperlipidaemic groups under study, not only in the d less than 1.019 fraction but also in the low-density lipoprotein (LDL) fraction. A strong correlation was found between the retinyl palmitate concentration in either the d less than 1.019 fraction or the LDL fraction of the WHHL rabbits and the concentrations of cholesterol and triacylglycerols in these fractions. This suggests that retinyl palmitate is exchanged rapidly between exogenous and endogenous lipoproteins. This is supported by the lack of a correlation between the retinyl palmitate concentrations and the intensity of the apoprotein B-48 band in the respective d less than 1.019 fractions or LDL fractions; in most fractions, in which large amounts of retinyl palmitate were present, the intensity of the apoprotein B-48 band was not increased compared with the fasting concentrations. Assuming that retinyl palmitate is a marker for the transfer of exogenous lipids, the results of our experiments indicate that the removal of exogenous lipids is delayed by complexing to endogenously synthesized lipoproteins. However, the clearance of apoprotein B-48 is normal and thus independent of the LDL-receptor activity.

scholarly journals Addition of a mannose-6-phosphate-containing oligosaccharide alters cellular processing of low density lipoprotein by parental and LDL-receptor-defective Chinese hamster ovary cells

1984 ◽  
Vol 68 (1) ◽  
pp. 183-194
Author(s):  
A.M. Leichtner ◽  
M. Krieger
Keyword(s):  
Chinese Hamster Ovary ◽  
Cho Cells ◽  
Low Density Lipoprotein ◽  
Chinese Hamster ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Receptor Activity ◽  
Low Density ◽  
Cellular Processing ◽  
Mannose 6 Phosphate

Low density lipoprotein (LDL) was chemically modified by the addition of omega-(6-phospho)-tetra(alpha 1–3)mannosyl-(alpha 1–2)mannose (M56P), a phosphorylated oligosaccharide containing a terminal mannose 6-phosphate residue. Uptake and degradation of this modified LDL (M56P-LDL) by Chinese hamster ovary (CHO) cells occurred via the lysosomal enzyme (mannose 6-phosphate) receptor pathway. Cellular processing of M56P-LDL was saturable, specific for the mannose 6-phosphate marker, and occurred with approximately threefold higher affinity than that of native LDL by the LDL receptor pathway. Mannose 6-phosphate receptor activity, as measured by degradation of M56P-LDL, was ninefold lower than the LDL receptor activity. Degradation of M56P-LDL was more sensitive to inhibition by the lysosomotropic agent chloroquine than was degradation of LDL, suggesting differences in the intracellular processing of mannose 6-phosphate-bearing ligands and LDL. Previously isolated CHO cell lines defective in LDL receptor activity resembled parental CHO cells in their ability to process M56P-LDL. The potential use of M56P-LDL in the isolation of cells with pleiotropic mutations affecting receptor-mediated endocytosis is discussed.

Heritability of the Low Density Lipoprotein Receptor Activity of Human Blood Mononuclear Cells: Studies in Normolipidaemic Adult Male Twins

1982 ◽  
Vol 62 (4) ◽  
pp. 397-401 ◽  
Author(s):  
M. Weight ◽  
C. Cortese ◽  
U. Sule N. E. Miller ◽  
B. Lewis
Keyword(s):  
Adult Male ◽  
Mononuclear Cells ◽  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Monozygotic Twins ◽  
Density Lipoprotein ◽  
Correlation Coefficients ◽  
Receptor Activity ◽  
Low Density ◽  
Blood Mononuclear Cells

1. The concordance of low density lipoprotein (LDL) receptor activity of blood mononuclear cells was examined in 26 pairs of monozygotic and 17 pairs of dizygotic normolipidaemic young adult male twins. 2. Receptor activity was quantified as the degradation of 125I-labelled LDL during a 6 h incubation, after derepression of the cells for 72 h in lipoprotein-deficient medium. 3. The total variance of receptor activity was similar in the two groups of twins. In contrast, within-pair variance was five times greater in dizygotic twins than in monozygotic twins (P < 0.001). 4. Estimates of heritability, mostly based on the intra-class correlation coefficients (monozygotic, r = 0.83; dizygotic, r = 0.39), ranged from 0.72 to 1.05. 5. These results suggest that the maximal LDL receptor activity of peripheral cells in normolipidaemic subjects is largely genetically determined.

scholarly journals Uptake of retinyl ester in HL-60 cells via the low-density-lipoprotein-receptor pathway

1989 ◽  
Vol 257 (1) ◽  
pp. 239-244 ◽  
Author(s):  
K O Wathne ◽  
B Carlander ◽  
K R Norum ◽  
R Blomhoff
Keyword(s):  
Low Density Lipoprotein ◽  
Cholesterol Acyltransferase ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Retinyl Palmitate ◽  
Low Density ◽  
Acyltransferase Activity ◽  
Retinyl Ester ◽  
Leukaemic Cells ◽  
Chylomicron Remnants

Newly absorbed retinol is transported in association with chylomicrons and their remnants. In addition, after intake of high doses of retinol, significant amounts are also found in low-density lipoprotein (LDL). As both chylomicron remnants and LDL may be taken up by cells via the LDL receptor, and retinoids inhibit proliferation of some leukaemic cells, we have studied the uptake of retinol in leukaemic cells via the LDL-receptor pathway. HL-60 cells contain saturable binding sites for LDL. The binding of LDL to its receptor has a dissociation constant of about 3.2 x 10(-9) M, and the number of receptors per cell was calculated to be about 2700. Uptake of 125I-LDL by HL-60 cells was increased 2-fold by preincubating the cells with mevinolin. The presence of specific receptors for LDL on HL-60 cells was further confirmed by the finding that exogenous LDL cholesterol was able to up-regulate the ACAT (acyl-CoA: cholesterol acyltransferase) activity of HL-60 cells. We then tested the uptake of retinyl ester in leukaemic cells via the LDL-receptor pathway. HL-60 cells were incubated with LDL or chylomicron remnants labelled with [3H]retinyl palmitate. Uptake of retinyl ester associated with both LDL and chylomicron remnants was observed. Furthermore, the presence of excess LDL decreased the uptake by 75-100%, supporting the hypothesis that the uptake of retinyl ester occurred via the LDL receptor in HL-60 cells.

Lack of Correlation between the Maximum Low-Density Lipoprotein (Ldl) Receptor Activity of Blood Lymphocytes and Plasma LDL Concentration in Normal Men

1983 ◽  
Vol 65 (1) ◽  
pp. 95-98 ◽  
Author(s):  
C. Cortese ◽  
P. R. Turner ◽  
C. B. Marenah ◽  
U. Sule ◽  
S. Price ◽  
...  
Keyword(s):  
Ldl Cholesterol ◽  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Receptor Activity ◽  
Cholesterol Concentration ◽  
Low Density ◽  
Blood Lymphocytes ◽  
Wide Range

1. Measurements were made of the maximal low-density lipoprotein (LDL) receptor activities of blood lymphocytes from 81 healthy men with a wide range of plasma LDL cholesterol concentrations (1.45-7.55 mmol/l). 2. Receptor activity was quantified by measuring the degradation of 125I-labelled LDL (10 μg of protein/ml) to trichloroacetic acid-soluble material during a 6 h incubation, after derepression of the lymphocytes for 72 h in lipoprotein-deficient medium. 3. No significant correlation existed between LDL receptor activity in vitro and plasma LDL cholesterol concentration in vivo (r = −0.08).

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