scholarly journals Exogenous cholesterol transport in rabbit plasma lipoproteins

1973 ◽  
Vol 134 (2) ◽  
pp. 531-537 ◽  
Author(s):  
L. L. Rudel ◽  
J. M. Felts ◽  
M. D. Morris
Keyword(s):  
Free Cholesterol ◽  
Specific Radioactivity ◽  
Plasma Lipoproteins ◽  
Cholesterol Transport ◽  
Low Density ◽  
Cholesteryl Esters ◽  
Exogenous Cholesterol ◽  
Rate Of Increase ◽  
Chylomicron Metabolism

1. The appearance of exogenous cholesterol in free cholesterol and ester cholesterol of plasma chylomicra, very-low-density (VLD), low-density (LD) and high-density (HD) lipoproteins was studied in unanaesthetized rabbits after ingestion of a meal containing 5% fat and 0.08% [3H]cholesterol. 2. The specific radioactivity of ester cholesterol of VLD lipoproteins reached the highest value of any lipoprotein fraction and for each lipoprotein it increased at a faster rate and reached a higher maximum than that of free cholesterol; the maximum in VLD lipoproteins occurred later than in chylomicra. 3. The pattern of appearance of exogenous cholesterol in chylomicra and VLD lipoproteins of plasma was similar to the pattern previously observed in lymph. The specific radioactivity of ester cholesterol in plasma VLD lipoproteins was higher than that in chylomicra in spite of a larger pool size and dilution of cholesteryl esters from VLD lipoproteins produced by the liver. These results support the concept that during absorption the major portion of exogenous cholesterol is transported in VLD lipoproteins as ester cholesterol. 4. The specific radioactivity of ester cholesterol of chylomicra and VLD lipoproteins increased at a faster rate than that of LD and HD lipoproteins. However, the rate of increase and the absolute values of the specific radioactivity in LD and HD lipoproteins were identical. Since cholesteryl esters are thought not to exchange between lipoproteins, this observation supports the hypothesis that a result of VLD lipoprotein and chylomicron metabolism is the formation of LD and HD lipoproteins. 5. Results in vivo showed that the free cholesterol of individual plasma lipoproteins does not equilibrate within a period of 24h.

scholarly journals An alternative procedure for incorporating radiolabelled cholesteryl ester into human plasma lipoproteins in vitro

1985 ◽  
Vol 226 (1) ◽  
pp. 319-322 ◽  
Author(s):  
D C K Roberts ◽  
N E Miller ◽  
S G L Price ◽  
D Crook ◽  
C Cortese ◽  
...  
Keyword(s):  
Cholesteryl Ester ◽  
Human Plasma ◽  
Specific Radioactivity ◽  
Density Lipoprotein ◽  
Plasma Lipoproteins ◽  
Cholesteryl Esters ◽  
Simple Method ◽  
High Specific Radioactivity

A simple method has been developed for labelling human plasma lipoproteins to high specific radioactivity with radioactive cholesteryl esters in vitro. After isolation by preparative ultracentrifugation, the selected lipoprotein was incubated for 30 min at 4 degrees C in human serum (d greater than 1.215) that had been prelabelled with [4-14C]cholesteryl oleate or [1,2-3H]cholesteryl linoleate, and was then re-isolated by ultracentrifugation. All major lipoprotein classes were labelled by the procedure. Specific radioactivities of up to 18 d.p.m. pmol-1 (46 d.p.m. ng-1) were achieved. When radiolabelled high-density lipoprotein was infused intravenously, the radioactive cholesteryl ester behaved in vivo indistinguishably from endogenous cholesteryl esters produced by the lecithin (phosphatidylcholine): cholesterol acyltransferase reaction.

scholarly journals Cholesterol is required for secretion of very-low-density lipoprotein by rat liver

1989 ◽  
Vol 258 (3) ◽  
pp. 807-816 ◽  
Author(s):  
B Khan ◽  
H G Wilcox ◽  
M Heimberg
Keyword(s):  
Free Cholesterol ◽  
Low Density Lipoprotein ◽  
Specific Radioactivity ◽  
Density Lipoprotein ◽  
Male Rats ◽  
Cholesterol Concentration ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Cholesteryl Esters ◽  
Metabolic Pool

To study potential effects of hepatic cholesterol concentration on secretion of very-low-density lipoprotein (VLDL) by the liver, male rats were fed on unsupplemented chow, chow with lovastatin (0.1%), or chow with lovastatin (0.1%) and cholesterol (0.1%) for 1 week. Livers were isolated from these animals and perfused in vitro, with a medium containing [2-14C]acetate, bovine serum albumin and glucose in Krebs-Henseleit buffer, and with an oleate-albumin complex. With lovastatin feeding, the hepatic concentrations of cholesteryl esters and triacylglycerols before perfusion were decreased, although free cholesterol was unchanged. However, hepatic secretion of all the VLDL lipids was decreased dramatically by treatment with lovastatin. Although total secretion of VLDL triacylglycerol, phospholipid, cholesterol and cholesteryl esters was decreased, the decrease in triacylglycerol was greater than that in free cholesterol or cholesteryl esters, resulting in secretion of a VLDL particle enriched in sterols relative to triacylglycerol. In separate studies, the uptake of VLDL by livers from control animals or animals treated with lovastatin was measured. Uptake of VLDL was estimated by disappearance of VLDL labelled with [1-14C]oleate in the triacylglycerol moiety, and was observed to be similar in both groups. During perfusion, triacylglycerol accumulated to a greater extent in livers from lovastatin-fed rats than in control animals. The depressed output of VLDL triacylglycerols and the increase in triacylglycerol in the livers from lovastatin-treated animals was indicative of a limitation in the rate of VLDL secretion. Addition of cholesterol (either free cholesterol or human low-density lipoprotein) to the medium perfusing livers from lovastatin-fed rats, or addition of cholesterol to the diet of lovastatin-fed rats, increased the hepatic concentration of cholesteryl esters and the output of VLDL lipids. The concentration of cholesteryl esters in the liver was correlated with the secretion of VLDL by the liver. These data suggest that cholesterol is an obligate component of the VLDL required for its secretion. It is additionally suggested that cholesteryl esters are in rapid equilibrium with a small pool of free cholesterol which comprises a putative metabolic pool available and necessary for the formation and secretion of the VLDL. Furthermore, the specific radioactivity (d.p.m./mumol) of the secreted VLDL free cholesterol was much greater than that of hepatic free cholesterol, suggesting that the putative hepatic metabolic pool is only a minor fraction of total hepatic free cholesterol.

scholarly journals Rabbit and rat C-reactive proteins bind apolipoprotein B-containing lipoproteins.

1984 ◽  
Vol 159 (2) ◽  
pp. 604-616 ◽  
Author(s):  
I F Rowe ◽  
A K Soutar ◽  
I M Trayner ◽  
M L Baltz ◽  
F C de Beer ◽  
...  
Keyword(s):  
Acute Phase ◽  
Apolipoprotein B ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Plasma Lipoproteins ◽  
Free Form ◽  
Low Density ◽  
Serum Samples ◽  
Acute Phase Serum

Immobilized rabbit and rat C-reactive protein (CRP) were found to selectively bind apolipoprotein B (apoB)-containing lipoproteins (low density lipoprotein, LDL and very low density lipoprotein, VLDL) from whole serum in a manner similar to that previously reported with human CRP. In acute phase human serum the CRP is in a free form, not complexed with lipoprotein or any other macromolecular ligand, and in acute phase serum from most rabbits fed on a normal diet the rabbit CRP was also free. However, in acute phase serum or heparinized plasma from hypercholesterolemic rabbits part or all of the CRP was found by gel filtration and immunoelectrophoretic techniques to be complexed with beta-VLDL, an abnormal apoB-containing plasma lipoprotein present in these animals. The presence of extent in different serum samples of CRP complexed with lipoprotein correlated closely with the serum apoB concentration. The formation of complexes between native, unaggregated rabbit CRP in solution and apoB-containing lipoproteins was readily demonstrable experimentally both with the isolated proteins and in whole serum. In all cases these interactions were calcium-dependent and inhibitable by free phosphoryl choline. The present findings extend earlier work in man and the rabbit and indicate that among the C-reactive proteins from different species, which are structurally highly conserved, the capacity for selective binding to apoB-containing plasma lipoproteins is also a constant feature. These interactions may therefore be related to the in vivo function of CRP in all species and this function may in turn be relevant to pathological conditions, such as atherosclerosis, in which lipoproteins are important.

scholarly journals Morphological characterization of the cholesteryl ester cycle in cultured mouse macrophage foam cells.

1983 ◽  
Vol 97 (4) ◽  
pp. 1156-1168 ◽  
Author(s):  
D J McGookey ◽  
R G Anderson
Keyword(s):  
Cholesteryl Ester ◽  
Lipase Activity ◽  
Lipid Droplets ◽  
Free Cholesterol ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
The Body ◽  
Cyclic Process ◽  
Low Density ◽  
Cholesteryl Esters

Mouse peritoneal macrophages can be induced to accumulate cholesteryl esters by incubating them in the presence of acetylated low density lipoprotein. The cholesteryl esters are sequestered in neutral lipid droplets that remain in the cell even when the acetylated low density lipoprotein is removed from the culture media. Previous biochemical studies have determined that the cholesterol component of cholesteryl ester droplets constantly turns over with a half time of 24 h by a cyclic process of de-esterification and re-esterification. We have used morphologic techniques to determine the spatial relationship of cholesteryl ester, free cholesterol, and lipase activity during normal turnover and when turnover is disrupted. Lipid droplets were surrounded by numerous 7.5-10.0-nm filaments; moreover, at focal sites on the margin of each droplet there were whorles of concentrically arranged membrane that penetrated the matrix. Histochemically detectable lipase activity was associated with these stacks of membrane. Using filipin as a light and electron microscopic probe for free cholesterol, we determined that a pool of free cholesterol was associated with each lipid droplet. Following incubation in the presence of the exogenous cholesterol acceptor, high density lipoprotein, the cholesteryl ester droplets disappeared and were replaced with lipid droplets of a different lipid composition. Inhibition of cholesterol esterification caused cholesteryl ester droplets to disappear and free cholesterol to accumulate in numerous myelin-like structures in the body of the cell.

scholarly journals Macrophages Create an Acidic Extracellular Hydrolytic Compartment to Digest Aggregated Lipoproteins

2009 ◽  
Vol 20 (23) ◽  
pp. 4932-4940 ◽  
Author(s):  
Abigail S. Haka ◽  
Inna Grosheva ◽  
Ethan Chiang ◽  
Adina R. Buxbaum ◽  
Barbara A. Baird ◽  
...  
Keyword(s):  
Free Cholesterol ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Low Density Lipoproteins ◽  
Critical Event ◽  
Low Density ◽  
Acid Hydrolases ◽  
Detailed Understanding ◽  
Physical Features

A critical event in atherogenesis is the interaction of macrophages with subendothelial lipoproteins. Although most studies model this interaction by incubating macrophages with monomeric lipoproteins, macrophages in vivo encounter lipoproteins that are aggregated. The physical features of the lipoproteins require distinctive mechanisms for their uptake. We show that macrophages create an extracellular, acidic, hydrolytic compartment to carry out digestion of aggregated low-density lipoproteins. We demonstrate delivery of lysosomal contents to these specialized compartments and their acidification by vacuolar ATPase, enabling aggregate catabolism by lysosomal acid hydrolases. We observe transient sealing of portions of the compartments, allowing formation of an “extracellular” proton gradient. An increase in free cholesterol is observed in aggregates contained in these compartments. Thus, cholesteryl ester hydrolysis can occur extracellularly in a specialized compartment, a lysosomal synapse, during the interaction of macrophages with aggregated low-density lipoprotein. A detailed understanding of these processes is essential for developing strategies to prevent atherosclerosis.

scholarly journals Physicochemical transfer of [3H]cholesterol from plasma lipoproteins to cultured human fibroblasts

1985 ◽  
Vol 228 (1) ◽  
pp. 219-225 ◽  
Author(s):  
B B Lundberg ◽  
L A Suominen
Keyword(s):  
Free Cholesterol ◽  
Water Solubility ◽  
Low Density Lipoprotein ◽  
Human Fibroblasts ◽  
Density Lipoprotein ◽  
Plasma Lipoproteins ◽  
Lung Fibroblasts ◽  
Cell Protein ◽  
Low Density ◽  
Free System

The transfer of free cholesterol from [3H]cholesterol-labelled plasma lipoproteins to cultured human lung fibroblasts was studied in a serum-free medium. The uptake of [3H]cholesterol depended upon time of incubation, concentration of lipoprotein in the medium, and temperature. Modified (reduced and methylated) low-density lipoprotein (LDL), which did not enter the cells by the receptor pathway, gave a somewhat lower transfer rate than unmodified LDL, but if the transfer values for native LDL were corrected for the receptor-mediated uptake of cholesterol the difference was eliminated. The initial rates of transfer of [3H]cholesterol from LDL and high-density lipoprotein (HDL) were of the same order of magnitude (0.67 +/- 0.05 and 0.75 +/- 0.06 nmol of cholesterol/h per mg of cell protein, respectively) while that from very-low-density lipoprotein (VLDL) was much lower (0.23 +/- 0.02 nmol of cholesterol/h per mg) (means +/- S.D., n = 5). The activation energy for transfer of cholesterol from reduced, methylated LDL to fibroblasts was determined to be 57.5 kJ/mol. If albumin was added to the incubation medium the transfer of [3H]cholesterol was enhanced, while that of [14C]dipalmitoyl phosphatidylcholine was decreased compared with the protein-free system. The results demonstrate that, in spite of its low water solubility, free cholesterol can move from lipoproteins to cellular membranes, probably by aqueous diffusion. We propose that physicochemical transfer of free cholesterol may be a significant mechanism for net uptake of the sterol into the artery during atherogenesis.

scholarly journals Reverse cholesterol transport in the isolated perfused rat spleen

1990 ◽  
Vol 268 (2) ◽  
pp. 499-505 ◽  
Author(s):  
M A Mindham ◽  
P A Mayes ◽  
N E Miller
Keyword(s):  
Whole Blood ◽  
Chemical Potential ◽  
Specific Radioactivity ◽  
Density Lipoprotein ◽  
Potential Gradient ◽  
Cholesterol Transport ◽  
Unesterified Cholesterol ◽  
Chemical Potential Gradient ◽  
High Specific Radioactivity

1. A method has been developed which enables the rat spleen to be loaded in vivo with [3H]cholesterol to a high specific radioactivity using cholesterol-labelled erythrocytes. The erythrocytes were shown to be rapidly degraded by the spleen and not released intact during subsequent perfusion. 2. When labelled spleens were perfused with whole blood or serum, lipoproteins in the high-density lipoprotein (HDL) range were shown to be the principal lipoprotein vehicles for the removal of cholesterol, the specific radioactivity of cholesterol being much greater in the HDL fractions than in other lipoproteins, particularly in the d 1.175-1.210 fraction. 3. The formation of [3H]cholesteryl ester was restricted to the major HDL fractions. 4. Experiments utilizing individual HDL fractions added to a basal perfusate indicated that HDL1 (d 1.050-1.085) was of less importance in the removal of cholesterol from the spleen than HDL subfractions of higher density. Also, a decrease in density of the lipoproteins was observed during perfusion, concurrent with uptake of cholesterol, especially in the d 1.085-1.125 subfraction. 5. When [3H]cholesterol-labelled spleens were perfused with whole blood, about half of the radioactivity released was detected in erythrocytes, indicating a rapid exchange or transport of cholesterol. Thus erythrocytes could play an important role in the transfer of unesterified cholesterol when the chemical potential gradient is favourable.

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