Uptake of cholesterol from the very low density lipoprotein or its remnants by the perfused rat liver

1981 ◽  
Vol 59 (6) ◽  
pp. 447-453 ◽  
Author(s):  
Simon-Pierre Noël ◽  
David Rubinstein
Keyword(s):  
Rat Liver ◽  
Lipid Composition ◽  
Low Density Lipoprotein ◽  
Liver Perfusion ◽  
Density Lipoprotein ◽  
Hepatic Uptake ◽  
Low Density ◽  
Perfused Liver ◽  
Very Low Density Lipoproteins

[3H]Cholesterol labelled very low density lipoproteins ([3H]chol-VLDL) were prepared to study the hepatic uptake of cholesterol associated with VLDL and its remnants in the perfused liver system. [3H]Chol-VLDL was incubated with rat postheparin plasma to produce labelled remnants in vitro. The degree of lipolysis of [3H]chol-VLDL depended on the ratio of triacylglycerols to lipase in the incubation medium. Therefore, the produced remnant of d < 1.019 g∙mL−1 had a variable lipid composition depending on the degree of lipolysis. [3H]Chol-VLDL or its remnants were added to liver perfusate and the radioactivity remaining in the perfusate was measured. The kinetic disappearance of [3H]chol-VLDL and its remnants in the perfused liver system indicated that remnant of d < 1.019 g∙mL−1 was taken up by the liver faster than the original VLDL preparation (t1/2 of 8 min vs. 51 min). Appearance of the label in bile during the perfusion was significantly faster when livers were perfused with [3H]chol-VLDL remnants as opposed to uncatabolized [3H]chol-VLDL.The results indicate that first of all, VLDL remnants produced in vitro and reisolated at density less than 1.019 g∙mL−1 do not have a fixed lipid composition but a rather variable one depending on the degree of lipolysis. Secondly, the rat liver may preferentially recognize this VLDL remnant of d < 1.019 g∙mL−1 and take it up more readily than uncatabolized VLDL. Finally when equimolar amount of cholesterol from VLDL or VLDL remnants are circulated in the liver perfusion, the VLDL remnants convey a significantly greater mass of cholesterol to the bile.

scholarly journals Altered hepatic catabolism of low-density lipoprotein subjected to lipid peroxidation in vitro

1994 ◽  
Vol 297 (3) ◽  
pp. 573-579 ◽  
Author(s):  
W L Stone ◽  
M Heimberg ◽  
R L Scott ◽  
I LeClair ◽  
H G Wilcox
Keyword(s):  
Lipid Peroxidation ◽  
Rat Liver ◽  
Low Density Lipoprotein ◽  
Liver Perfusion ◽  
Density Lipoprotein ◽  
Low Density ◽  
Perfusion System ◽  
Oxidatively Modified ◽  
Generating System

Recent evidence suggests that oxidatively modified forms of low-density lipoprotein (LDL) may be particularly atherogenic. In this investigation, the catabolism of human LDL modified by lipid peroxidation in vitro was studied with a recirculating rat liver perfusion system. A dual-labelling technique was used that permitted native LDL and modified LDL to be studied simultaneously in the liver perfusion system. Native human LDL was found to have a fractional catabolic rate (FCR) of 1.00 +/- 0.21%/h, in agreement with other investigators. Subjecting LDL to oxidation for 12 h in the presence of 30 microM FeEDTA did not significantly affect its FCR. LDL treated with a superoxide-generating system (xanthine oxidase, hypoxanthine, O2) in the presence of 30 microM FeEDTA did, however, show a significant increase in FCR (3.23 +/- 0.19%/h). The hepatic uptakes of native LDL and LDL oxidized with FeEDTA+O2 were similar, but both were significantly lower than the hepatic uptake of LDL treated with the superoxide-radical-generating system. The proteolysis of LDL with pancreatin did not influence either its susceptibility to oxidation or its FCR. LDL oxidation resulted in the preferential loss of alpha-tocopherol rather than gamma-tocopherol. These data indicate that the rat liver effectively catabolizes LDL oxidatively modified by treatment with the superoxide-generating system. Furthermore, our results suggest that only very low plasma levels of highly oxidized LDL could be found under conditions in vivo. The liver may therefore play a major role in protecting the arterial vasculature from highly atherogenic forms of LDL.

The disappearance rate of human versus rat intermediate density lipoproteins from rat liver perfusion

1991 ◽  
Vol 69 (8) ◽  
pp. 537-543 ◽  
Author(s):  
Robert Dupras ◽  
Louise Brissette ◽  
Paul D. Roach ◽  
Sylvain Begin ◽  
André Tremblay ◽  
...  
Keyword(s):  
Liver Perfusion ◽  
Density Lipoprotein ◽  
Low Density Lipoproteins ◽  
Low Density ◽  
Disappearance Rate ◽  
Very Low Density Lipoproteins ◽  
Rat Liver Perfusion ◽  
Heparin Plasma ◽  
Intermediate Density

The aim of this work was to compare the disappearance rate of human and rat intermediate density lipoproteins (IDL) using the rat liver perfusion system. Human and rat IDL were produced in vitro by incubating human or rat very low density lipoproteins (VLDL) with either rat post-heparin plasma (method I) or a resolubilized isopropanol precipitate of rat post-heparin plasma (method II). With both methods, the degree of triacylglycerol lipolysis was approximately 55%. The different preparations of IDL were labelled with 125I and added to perfusates of rat livers. The disappearance rates of 125I-labelled IDL were monitored by measuring the radioactivity associated with apolipoprotein (apo) B in the perfusate during a 15-min period. Both human and rat IDL prepared with method I had an increased apoE to apoC ratio as compared with their native counterparts. Furthermore, human IDL had a significantly higher apoE to apoC ratio than rat IDL. However, when IDL were produced in the absence of exchangeable apolipoproteins (method II), no change in the apoE to apoC ratios was observed for the transformation of VLDL to IDL and the ratios were similar for human and rat IDL. Despite these differences, human IDL were always removed at a lower rate than rat IDL. The only striking difference between the two types of IDL made by method II was that the apoB100 to apoB48 ratio was considerably higher in human than in rat IDL. These results suggest that the apoB100 to apoB48 ratio is likely to be responsible for the observed differences in liver uptake between rat and human IDL.Key words: very low density lipoproteins, intermediate density lipoproteins, low density lipoproteins, hepatic lipoprotein receptors, intermediate density lipoprotein uptake, in vitro lipolysis, very low density lipoprotein remnants, apolipoproteins.

scholarly journals Very-low-density-lipoprotein secretion by isolated hepatocytes of fat-fed rats

1981 ◽  
Vol 198 (2) ◽  
pp. 373-377 ◽  
Author(s):  
A D Kalopissis ◽  
S Griglio ◽  
M I Malewiak ◽  
R Rozen ◽  
X L Liepvre
Keyword(s):  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Isolated Hepatocytes ◽  
Low Density Lipoproteins ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Very Low Density Lipoproteins ◽  
Lipoprotein Secretion ◽  
Fat Feeding

The very-low-density-lipoprotein secretion rate of isolated hepatocytes obtained from rats fed a high-fat diet was half that of cells from control animals. In fat-fed rats, the initial cellular uptake of [l-14C]oleate in vitro was decreased by 25%, its esterification to triacylglycerols and phospholipids by 50% and its incorporation into very-low-density-lipoprotein triacylglycerols by 70%. Exogenous oleate was not the main precursor of very-low-density lipoproteins in these animals. Lipogenesis, a minor source of very-low-density lipoproteins with the control diet in our experimental conditions, was inhibited by 84% after fat-feeding. A short-term inhibition of lipogenesis in vitro did not result in a decrease in very-low-density-lipoprotein secretion rate. The results suggest that fat-feeding decreased availability of exogenous as well as endogenous fatty acids for synthesis of very-low-density lipoproteins.

scholarly journals High-density lipoprotein subpopulations as substrates for the transfer of cholesteryl esters to very-low-density lipoproteins

1990 ◽  
Vol 270 (2) ◽  
pp. 441-449 ◽  
Author(s):  
M A Lasunción ◽  
A Iglesias ◽  
N Skottová ◽  
E Orozco ◽  
E Herrera
Keyword(s):  
High Density Lipoprotein ◽  
Low Density Lipoprotein ◽  
Specific Radioactivity ◽  
Density Lipoprotein ◽  
Cholesteryl Oleate ◽  
High Density ◽  
Low Density ◽  
Very Low Density Lipoproteins ◽  
Apoprotein Composition

1. Human total HDL (high-density lipoprotein), HDL2 and HDL3 were labelled in vitro by incubation with lipoprotein-deficient serum (LPDS) which contained either [3H]cholesteryl oleate or [14C]cholesterol under different conditions. The lipoproteins were then subfractionated by heparin-Sepharose column chromatography, and three subfractions (A, B and C) were successively eluted from each preparation of HDL, HDL2 and HDL3. When the labelling was done at 37 degrees C for 17 h, the subfractions were homogeneously labelled with [3H]cholesteryl oleate. However, when it was performed for only 30 min at 4 degrees C, the subfractions showed marked differences in the 3H specific radioactivity, which was much higher in the C fractions than in the others. 2. 3H-labelled HDL2 and HDL3 subfractions behaved differently under the precipitant action of heparin-Mn2+; fraction C (the richest in apolipoprotein E) produced the largest amount of radioactive and chemical precipitate. More 3H radioactivity, but not the cholesterol, was precipitated from HDL2 or HDL3 by the reagent, demonstrating that 3H-labelled HDL2 and HDL3 behave like their fraction C, which becomes labelled to the highest specific radioactivity despite having the smallest mass. 3. The incubation of 3H-labelled HDL subfractions with human LPDS and very-low-density lipoprotein (VLDL) at 37 degrees C increased the quantity of 3H radioactivity that was precipitated, in proportion to the amount of VLDL present in the media. These changes were attributable to the action of cholesterol ester transfer protein, since they did not occur at 4 degrees C or when human LPDS was replaced with rat LPDS. 4. Kinetics of the transfer of HDL [3H]cholesteryl oleate to VLDL showed a greater apparent Vmax for fractions A than for fractions B from either HDL2 or HDL3, whereas the apparent Km values were very similar, which suggest that this transfer process is influenced by the apoprotein composition of the donor lipoprotein.

scholarly journals The metabolic conversion of very-low-density lipoprotein into low-density lipoprotein by the extrahepatic tissues of the rat

1979 ◽  
Vol 178 (2) ◽  
pp. 455-466 ◽  
Author(s):  
B S Suri ◽  
M E Targ ◽  
D S Robinson
Keyword(s):  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Quantitative Information ◽  
Low Density Lipoproteins ◽  
High Density Lipoproteins ◽  
Low Density ◽  
Very Low Density Lipoproteins ◽  
Apo B ◽  
Extrahepatic Tissues

1. The work reported was designed to provide quantitative information about the capacity of the extrahepatic tissues of the rat to degrade injected VLD lipoproteins (very-low-density lipoproteins, d less than 1.006) to LD lipoproteins (low-density lipoproteins, d 1.006–1.063) and to study the fate of the different VLD-lipoprotein apoproteins during the degradative process. 2. Rat liver VLD lipoproteins, radioactively labelled in their protein moieties, were produced by the perfusion of the organ and were either injected into the circulation of the supradiaphragmatic rats or incubated in rat plasma at 37 degrees C. At a time (75 min) when approx. 90% of the triacylglycerol of the VLD lipoproteins had been hydrolysed the supradiaphragmatic rats were bled and VLD lipoproteins, LD lipoproteins and HD lipoproteins (high-density lipoproteins, d 1.063–1.21) were separated from their plasma and from the plasma incubated in vitro. The apoproteins of each of the lipoprotein classes were resolved by gel-filtration chromatography into three main fractions, designated peaks I, II and III. 3. Incubation of the liver VLD lipoproteins in plasma in vitro led to the transfer of about 30% of the total protein radioactivity to the HD lipoproteins. The transfer mainly involved the peak-II (arginine-rich and/or apo A-I) and peak-III (apo C) proteins. There was also a small transfer of radioactivity (about 5% of the total) to the LD lipoproteins. 4. Injection of the liver VLD lipoproteins into the circulation of the supradiaphragmatic rat resulted in the transfer of about 15% of the total VLD-lipoprotein radioactivity to the LD lipoproteins. The transfer involved mainly the peak-I (apo B) proteins and accounted for about 20% of the total apo B protein radioactivity of the injected VLD lipoproteins. When the endogenous plasma VLD lipoprotein was taken into account the transfer of apo B protein was about 35%. 5. The transfer of peak-II protein radioactivity from the VLD to the HD lipoproteins was greater in the plasma of the supradiaphragmatic rat than in the incubated plasma suggesting that there was a net transfer of peak-II apoproteins during the VLD lipoprotein degradation. The transfer of peak-III protein radioactivity was not greater in the plasma of the supradiaphragmatic rat, but there was a loss of this radioactivity from the circulation.

scholarly journals A study of the interrelationship between the triacylglycerol and protein components of very-low-density lipoproteins using the perfused rat liver

1975 ◽  
Vol 150 (3) ◽  
pp. 315-321 ◽  
Author(s):  
S J Petersburg ◽  
A Madeley ◽  
D S Robinson
Keyword(s):  
Rat Liver ◽  
Low Density Lipoprotein ◽  
Polyacrylamide Gel Electrophoresis ◽  
Density Lipoprotein ◽  
Protein Release ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Perfused Rat Liver ◽  
Very Low Density Lipoproteins ◽  
Protein Components

High and low rates of very-low-density-lipoprotein triacylglycerol release from the perfused rat liver were achieved by using livers taken respectively from animals that had been given fructose for 48h or from animals that had been starved for 18h. 2. The higher rates of very-low-density-lipoprotein triacylglycerol release by the livers of the fructose-fed rats were associated with higher rates of very-low-density-lipoprotein protein release. 3. When the livers were perfused in the presence of [3H]leucine, radioactivity was incorporated into the very-low-density-lipoprotein apoproteins. The higher rates of very-low-density-lipoprotein triacylgycerol and protein release by the livers of fructose-fed rats were associated with a greater total incorporation of radioactivity into those apoproteins that entered the running gel during polyacrylamide-gel electrophoresis. However, the distribution of radioactivity among the various apoproteins was not significantly changed by the dietary treatments used.

scholarly journals Characterization of binding sites for acetylated low density lipoprotein in the rat liver in vivo and in vitro.

1985 ◽  
Vol 4 (5) ◽  
pp. 1157-1162 ◽  
Author(s):  
H.A. Dresel ◽  
E. Friedrich ◽  
D.P. Via ◽  
G. Schettler ◽  
H. Sinn
Keyword(s):  
Rat Liver ◽  
Binding Sites ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Low Density
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