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.

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 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 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.

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.

scholarly journals Catabolism of human very low density lipoproteins in vitro: a fluorescent phospholipid method for monitoring lipolysis.

1981 ◽  
Vol 22 (2) ◽  
pp. 382-386
Author(s):  
M R Taskinen ◽  
J D Johnson ◽  
M L Kashyap ◽  
K Shirai ◽  
C J Glueck ◽  
...  
Keyword(s):  
Low Density Lipoproteins ◽  
Low Density ◽  
Very Low Density Lipoproteins

scholarly journals Sirtuin 3 Restores Synthesis and Secretion of Very Low-Density Lipoproteins in Cow Hepatocytes Challenged with Nonesterified Fatty Acids In Vitro

2021 ◽  
Vol 8 (7) ◽  
pp. 121
Author(s):  
Dongmei Xing ◽  
Baogen Wang ◽  
Hong Lu ◽  
Tao Peng ◽  
Jianming Su ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Dairy Cows ◽  
Low Density Lipoproteins ◽  
Mrna Abundance ◽  
Low Density ◽  
Sirtuin 3 ◽  
Very Low Density Lipoproteins ◽  
Nonesterified Fatty Acids ◽  
Tag Accumulation

Fatty liver is closely associated with elevated concentrations of nonesterified fatty acids (NEFA) and a low level of very low-density lipoproteins (VLDL) in blood of dairy cows. High NEFA inhibit the VLDL synthesis and assembly, and cause hepatic triacylglycerol (TAG) deposition. Sirtuin 3 (SIRT3), a mitochondrial deacetylase, antagonizes NEFA-induced TAG accumulation through modulating expressions of fatty acid synthesis and oxidation genes in cow hepatocytes. However, the role of SIRT3 in the VLDL synthesis and assembly was largely unknown. Here we aimed to test whether SIRT3 would recover the synthesis and assembly of VLDL in cow hepatocytes induced by high NEFA. Primary cow hepatocytes were isolated from 3 Holstein cows. Hepatocytes were infected with SIRT3 overexpression adenovirus (Ad-SIRT3), SIRT3-short interfering (si) RNA, or first infected with Ad-SIRT3 and then incubated with 1.0 mM NEFA (Ad-SIRT3 + NEFA). Expressions of key genes in VLDL synthesis and the VLDL contents in cell culture supernatants were measured. SIRT3 overexpression significantly increased the mRNA abundance of microsomal triglyceride transfer protein (MTP), apolipoprotein B100 (ApoB100) and ApoE (p < 0.01), and raised VLDL contents in the supernatants (p < 0.01). However, SIRT3 silencing displayed a reverse effect in comparison to SIRT3 overexpression. Compared with NEFA treatment alone, the Ad-SIRT3 + NEFA significantly upregulated the mRNA abundance of MTP, ApoB100 and ApoE (p < 0.01), and increased VLDL contents in the supernatants (p < 0.01). Our data demonstrated that SIRT3 restored the synthesis and assembly of VLDL in cow hepatocytes challenged with NEFA, providing an in vitro basis for further investigations testing its feasibility against hepatic TAG accumulation in dairy cows during the perinatal period.

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