Characterization of the binding of human low-density lipoprotein to cultured rat hepatocytes

1987 ◽  
Vol 15 (2) ◽  
pp. 253-254 ◽  
Author(s):  
ANDREW M. SALTER ◽  
JANICE SAXTON ◽  
DAVID N. BRINDLEY
Keyword(s):  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Rat Hepatocytes ◽  
Low Density ◽  
Cultured Rat Hepatocytes

scholarly journals Lysophosphatidylcholine metabolism and lipoprotein secretion by cultured rat hepatocytes deficient in choline

1989 ◽  
Vol 260 (1) ◽  
pp. 207-214 ◽  
Author(s):  
B S Robinson ◽  
Z Yao ◽  
D J Baisted ◽  
D E Vance
Keyword(s):  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Rat Hepatocytes ◽  
Cellular Protein ◽  
Low Density Lipoproteins ◽  
Low Density ◽  
Very Low Density Lipoproteins ◽  
Phosphatidylcholine Biosynthesis ◽  
Cultured Rat Hepatocytes ◽  
Phosphatidylcholine Synthesis

The metabolism of lysophosphatidylcholine was studied in cultured rat hepatocytes deficient in choline and methionine. Even though the cells were defective in phosphatidylcholine biosynthesis, the albumin-stimulated release of lysophosphatidylcholine (1.9 nmol/h per mg of cellular protein) was similar to that in hepatocytes supplemented with choline. Albumin also stimulated (1.4-fold) the release of phosphatidylcholine from the deficient cells. The extra phosphatidylcholine and lysophosphatidylcholine in the medium were largely recovered in the albumin fraction (density greater than 1.18 g/ml), suggesting that albumin released these lipids from hepatocytes because of binding to this protein. The secretion of glycerophosphocholine was decreased by about 40% by the addition of albumin. When choline-deficient hepatocytes were supplemented with lysophosphatidylcholine, it was transported into the cells and mainly acylated to form phosphatidylcholine, which increased in mass by 30-35% in the first 4 h of incubation. Lysophosphatidylcholine was shown to be as effective as choline in restoring the secretion of very-low-density lipoproteins to normal amounts, as judged by the secretion of triacylglycerol, phosphatidylcholine and the apolipoproteins associated with very-low-density lipoproteins. Thus phosphatidylcholine synthesis via reacylation of lysophosphatidylcholine, via the CDP-choline pathway or via methylation of phosphatidylethanolamine, will satisfy the requirements for secretion of very-low-density lipoprotein from hepatocytes.

scholarly journals Calcium-antagonists inhibit secretion of very-low-density lipoprotein from cultured rat hepatocytes

1987 ◽  
Vol 247 (2) ◽  
pp. 433-439 ◽  
Author(s):  
J O Nossen ◽  
A C Rustan ◽  
C A Drevon
Keyword(s):  
Calcium Antagonists ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Rat Hepatocytes ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Maximal Effect ◽  
Dependent Manner ◽  
Triacylglycerol Synthesis ◽  
Cultured Rat Hepatocytes

The effects of different calcium-antagonists on secretion of very-low-density lipoprotein (VLDL) from cultured rat hepatocytes were examined. Verapamil (an inhibitor of voltage-dependent calcium channels) and EGTA (a calcium chelator) decreased VLDL-triacylglycerol secretion in a concentration-dependent manner, with maximum inhibition (about 90%) at 0.2 mM-verapamil and 5 mM-EGTA. Inorganic calcium-antagonists such as lanthanum, nickel, cobalt and manganese decreased secretion of VLDL-triacylglycerol by 55-95%, whereas the calcium-agonist barium did not affect secretion. Inhibition of VLDL-triacylglycerol secretion appeared within 30 min, without inhibition of triacylglycerol synthesis. Pulse-chase experiments revealed that verapamil and cobalt inhibited the secretory pathway itself. Cobalt showed a concentration-dependent inhibition of VLDL-triacylglycerol secretion, with maximal effect at 8 mM. Although inhibition by cobalt was not completely reversible, Trypan Blue exclusion and lactate dehydrogenase leakage indicated that the hepatocytes were not injured by cobalt or any of the other calcium-antagonists tested. Inhibition of protein synthesis by cycloheximide did not affect triacylglycerol secretion (up to 2 h), and the observed effects were therefore probably not due to impaired production of apolipoproteins. Taken together, these results suggest that calcium is important for secretion of VLDL particles.

scholarly journals Unaltered catabolism of desialylated low-density lipoprotein in the pig and in cultured rat hepatocytes

1979 ◽  
Vol 180 (3) ◽  
pp. 647-654 ◽  
Author(s):  
A D Attie ◽  
D B Weinstein ◽  
H H Freeze ◽  
R C Pittman ◽  
D Steinberg
Keyword(s):  
Sialic Acid ◽  
Clostridium Perfringens ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Rat Hepatocytes ◽  
Low Density Lipoproteins ◽  
Low Density ◽  
Rapid Clearance ◽  
Cultured Rat Hepatocytes ◽  
Extrahepatic Tissues

Removal of the terminal sialic acid residues from many serum glycoproteins results in exposure of their penultimate galactose residues and rapid clearance from circulation by the liver. Low-density lipoprotein is a glycoprotein containing 21 galactose and 9 sialic acid residues per particle. Studies in this laboratory and others have shown that both the liver and extrahepatic tissues contribute to the degradation of low-density lipoprotein. This study was undertaken to determine whether desialylation of pig low-density lipoprotein alters its removal from circulation. Low-density lipoprotein was incubated at 37 degrees C with an agarose-bound neuraminidase, proteinase-free, from Clostridium perfringens. After 18 h at pH 5.0, 70% of the sialic acid residues were removed. The desialylated 131I-labelled and native 125I-labelled low-density lipoproteins were simultaneously injected into a pig, and their disappearance from plasma was followed for 96 h. The turnovers of the two were identical. In contrast, neuraminidase-treated fetuin was cleared about 200-fold faster than native fetuin. Studies were also performed in cultured rat hepatocytes. Rates of degradation of native and neuraminidase-treated low-density lipoprotein were similar, whereas asialo-fetuin was degraded at six to ten times the rate of native fetuin. Thus desialylation does not appear to alter low-density-lipoprotein catabolism by hepatic or extrahepatic cells.

scholarly journals Glycosylation of apolipoproteins by cultured rat hepatocytes. Effect of tunicamycin on lipoprotein secretion

1981 ◽  
Vol 200 (2) ◽  
pp. 409-414 ◽  
Author(s):  
J Bell-Quint ◽  
T Forte ◽  
P Graham
Keyword(s):  
Low Density Lipoprotein ◽  
Specific Inhibitor ◽  
Density Lipoprotein ◽  
Rat Hepatocytes ◽  
High Density ◽  
Protein Glycosylation ◽  
High Density Lipoproteins ◽  
Low Density ◽  
Apolipoprotein C ◽  
Cultured Rat Hepatocytes

Cultured rat hepatocytes were used to measure hepatic synthesis of rat plasma glycoproteins. [3H]Glucosamine was progressively incorporated into the protein of hepatocyte culture media very-low-density lipoprotein, low-density lipoprotein, high-density lipoprotein and the p greater than 1.21 g/ml fraction after 3.5 and 6.5 h incubation. Apolipoproteins B, E and C, as well as transferrin, were identified as glycoproteins. The association of radioactivity with apolipoprotein C of hepatocyte very-low-density and high-density lipoproteins suggests that apolipoprotein C-III-3, the only C apoglycoprotein in the rat, is synthesized de novo by the hepatocytes. Treatment of hepatocytes with tunicamycin, a specific inhibitor of protein glycosylation, resulted in a substantial decrease in [3H]glucosamine incorporation into hepatocyte very-low-density, low-density and high-density lipoproteins and p greater than 1.21 g/ml protein, but had little or no effect on secretion. In the rat, hepatic secretion of lipoproteins and transferrin does not appear to be dependent on prior protein glycosylation.

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