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 Stimulation of triacylglycerol synthesis in rat adipocytes by plasma very-low-density lipoproteins

1978 ◽  
Vol 176 (1) ◽  
pp. 169-174 ◽  
Author(s):  
P Thomopoulos ◽  
M Berthelier ◽  
D Lagrange ◽  
M J Chapman ◽  
M H Laudat
Keyword(s):  
Fatty Acids ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Low Density Lipoproteins ◽  
High Density Lipoproteins ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Very Low Density Lipoproteins ◽  
Rat Adipocytes ◽  
Triacylglycerol Synthesis

The effect of human plasma lipoproteins on lipogenesis from glucose has been studied in isolated rat adipocytes. The very-low-density lipoproteins increased lipogenesis specifically, whereas low-density lipoproteins and high-density lipoproteins were without effect. Such stimulation could be reproduced with partially delipidated very-low-density lipoproteins. Nod-esterified fatty acids and glycerol were also without effect. Pretreatment of the adipocytes with trypsin did not alter the effect of very-low-density lipoprotein. The presence of Ca2+ was required for the full activation of lipogenesis. The synthesis of acylglycerol fatty acids and of acylglycerol glycerol were equally increased. The effect of very-low-density lipoprotein was not additive to that of insulin. It is suggested that very-low-density lipoprotein may directly stimulate lipogenesis in fat-cells, particularly in states when the lipoproteins are present at high concentration in the circulation.

Insufficient accuracy and specificity of polyanion precipitation methods for quantifying low-density lipoproteins

1990 ◽  
Vol 36 (12) ◽  
pp. 2109-2113 ◽  
Author(s):  
R Siekmeier ◽  
W März ◽  
W Gross
Keyword(s):  
Fatty Acids ◽  
Dextran Sulfate ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Low Density Lipoproteins ◽  
High Density Lipoproteins ◽  
Low Density ◽  
Very Low Density Lipoproteins ◽  
Nonesterified Fatty Acids ◽  
High Concentrations

Abstract Recently, polyanion precipitation assays for low-density lipoprotein (LDL)-cholesterol have been found to underestimate their analyte in normolipidemic samples (Siekmeier et al., Clin Chim Acta 1988;177:221-30). Therefore, accuracy, specificity, and interference by nonesterified fatty acids have been studied for three precipitants (obtained by heparin, dextran sulfate, or polyvinyl sulfate precipitation). At normal concentrations of LDL, precipitation is incomplete, whereas it is nearly quantitative at high concentrations of LDL. The polyvinyl sulfate reagent markedly responds to variations in the amount of non-LDL protein present in the precipitation mixture. In the dextran sulfate and the polyvinyl sulfate method, but not in the heparin method, the percentages of LDL precipitated notably increase as the concentration of the polyanion compound is decreased. In either assay, very-low-density lipoproteins, but not high-density lipoproteins, are significantly coprecipitated (dextran sulfate 28%, polyvinyl sulfate and heparin 66%) in a concentration-independent fashion. Increased concentrations of nonesterified fatty acids markedly interfere with the dextran sulfate and polyvinyl sulfate assay, but do not much affect results with the heparin reagent.

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.

Atherogenic Lipoprotein Subfractions and Carotid Atherosclerosis in Menopausal Women

Angiology ◽  
2017 ◽  
Vol 69 (8) ◽  
pp. 666-671 ◽  
Author(s):  
Arcangelo Iannuzzi ◽  
Marco Gentile ◽  
Gabriella Iannuzzo ◽  
Giuseppe Covetti ◽  
Camilla Panico ◽  
...  
Keyword(s):  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Intima Media Thickness ◽  
Carotid Intima Media Thickness ◽  
Low Density Lipoproteins ◽  
High Density Lipoproteins ◽  
Low Density ◽  
Very Low Density Lipoproteins ◽  
Lipoprotein Subfractions ◽  
Carotid Plaques

The aim of the study was to evaluate the relationship between cholesterol contained in very-low-density lipoproteins (VLDL-C), intermediate-density lipoproteins (IDL-C), low-density lipoproteins, high-density lipoproteins, and carotid intima–media thickness (cIMT) and carotid plaques in 228 postmenopausal women (63.1 ± 8.2 years) who participated in the ATENA Project and underwent clinical, biochemical (including the assay of lipoproteins using the Lipoprint system), and carotid ultrasound tests. Very-low-density lipoprotein cholesterol had a statistically significant linear association with cIMT ( P < .001), which remained significant after adjustment for age, smoking, systolic blood pressure, glucose, and body mass index ( r2 = .20, P < .05). Higher concentrations of IDL-C and cholesterol contained in triglyceride-rich lipoproteins (TRL-C, ie, VLDL-C + IDL-C) were associated with plaques in the common carotid (tertile III/tertile I: odds ratio [OR] = 2.52, 95% confidence interval [CI] = 1.21-5.32, P < .02; OR = 2.30, 95% CI = 1.05-5.01, P < .05, respectively), after adjustment for main cardiovascular risk factors. In conclusion, high concentrations of VLDL-C and TRL-C are independently associated with the presence of carotid plaques. Their assay represents a useful tool for improving our knowledge on the role of different classes of lipoproteins in atherosclerosis.

Transfer of newly made triglyceride from hepatocytes to preexisting extracellular very low density lipoproteins

1987 ◽  
Vol 65 (3) ◽  
pp. 337-343
Author(s):  
Gen Yoshino ◽  
George Steiner
Keyword(s):  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Liver Cells ◽  
Low Density Lipoproteins ◽  
In Vivo Studies ◽  
Low Density ◽  
Very Low Density Lipoproteins ◽  
Apoprotein B

Previous in vivo studies suggested a new model to describe the metabolism of very low density lipoproteins (VLDL). It was hypothesized that some of the lipoprotein triglyceride was transferred directly from hepatocytes and intestinal mucosal cells into preexisting extracellular VLDL particles. These studies employ an in vitro system to test this hypothesis. Isolated rat liver cells containing newly made radioactive triglyceride were prepared. These cells were incubated in medium to which exogenous VLDL had or had not been added. The presence of extracellular VLDL (rat or human) stimulated the transfer of labeled triglyceride out of the liver cells. This triglyceride was recovered in the medium's VLDL (as determined by its density and its precipitability by MnCl2–heparin or by anti-apoprotein B). Although these studies focussed on VLDL, preliminary data showed that similar triglyceride transfer occurred in the presence of the other apoprotein B containing lipoprotein, low density lipoprotein (LDL). However, in the presence of equivalent amounts of LDL, this triglyceride transfer was less than that seen in the presence of exogenous VLDL. Furthermore, the increased triglyceride released in the presence of LDL occurred entirely in the d < 1.006 fraction of the medium. That released in the presence of VLDL was recovered in the d > 1.006 fraction. Hence, we conclude that the transfer of the newly made triglyceride was from the cell to the extracellular lipoprotein that had been added to the medium. The transfer of triglyceride to VLDL did not depend on the synthesis and release of new VLDL particles because it was not accompanied by a change in the production of [14C]leucine VLDL protein, it was not blocked by chloroquine, and the LDL induced triglyceride release occurred into the d > 1.006 fraction. This transfer did not depend on the previously described triglyceride-transfer factor. The present in vitro studies support the model suggested by our earlier in vivo studies. The VLDL particle does not appear to be metabolized as a complete intact unit. Rather, some of its major lipid component, triglyceride, can move directly into and out of already existing extracellular lipoproteins.

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.

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