scholarly journals Processing of acetylated human low-density lipoprotein by parenchymal and non-parenchymal liver cells. Involvement of calmodulin?

1982 ◽  
Vol 208 (2) ◽  
pp. 493-503 ◽  
Author(s):  
Theo J. C. Van Berkel ◽  
Jan F. Nagelkerke ◽  
Leen Harkes ◽  
Johan K. Kruijt
Keyword(s):  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Liver Cells ◽  
Cell Protein ◽  
Low Density ◽  
Calmodulin Inhibitors ◽  
Parenchymal Liver ◽  
Modified Lipoproteins ◽  
Parenchymal Cells

1. Modified lipoproteins have been implicated to play a significant role in the pathogenesis of atherosclerosis. In view of this we studied the fate and mechanism of uptake in vivo of acetylated human low-density lipoprotein (acetyl-LDL). Injected intravenously into rats, acetyl-LDL is rapidly cleared from the blood. At 10min after intravenous injection, 83% of the injected dose is recovered in liver. Separation of the liver into a parenchymal and non-parenchymal cell fraction indicates that the non-parenchymal cells contain a 30–50-fold higher amount of radioactivity per mg of cell protein than the parenchymal cells. 2. When incubated in vitro, freshly isolated non-parenchymal cells show a cell-association of acetyl-LDL that is 13-fold higher per mg of cell protein than with parenchymal cells, and the degradation of acetyl-LDL is 50-fold higher. The degradation of acetyl-LDL by both cell types is blocked by chloroquine (10–50μm) and NH4Cl (10mm), indicating that it occurs in the lysosomes. Competition experiments indicate the presence of a specific acetyl-LDL receptor and degradation pathway, which is different from that for native LDL. 3. Degradation of acetyl-LDL by non-parenchymal cells is completely blocked by trifluoperazine, penfluridol and chlorpromazine with a relative effectivity that corresponds to their effectivity as calmodulin inhibitors. The high-affinity degradation of human LDL is also blocked by trifluoperazine (100μm). The inhibition of the processing of acetyl-LDL occurs at a site after the binding-internalization process and before intralysosomal degradation. It is suggested that calmodulin, or a target with a similar sensitivity to calmodulin inhibitors, is involved in the transport of the endocytosed acetyl-LDL to or into the lysosomes. 4. It is concluded that the liver, and in particular non-parenchymal liver cells, are in vivo the major site for acetyl-LDL uptake. This efficient uptake and degradation mechanism for acetyl-LDL in the liver might form in vivo the major protection system against the potential pathogenic action of modified lipoproteins.

scholarly journals Quantitative role of parenchymal and non-parenchymal liver cells in the uptake of [14C]sucrose-labelled low-density lipoprotein in vivo

1984 ◽  
Vol 224 (1) ◽  
pp. 21-27 ◽  
Author(s):  
L Harkes ◽  
J C Van Berkel
Keyword(s):  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Cell Types ◽  
Liver Cells ◽  
Low Density ◽  
Apo B ◽  
Parenchymal Liver ◽  
Ldl Uptake ◽  
Parenchymal Cells

In order to assess the relative importance of the receptor for low-density lipoprotein (LDL) (apo-B,E receptor) in the various liver cell types for the catabolism of lipoproteins in vivo, human LDL was labelled with [14C]sucrose. Up to 4.5h after intravenous injection, [14C]sucrose becomes associated with liver almost linearly with time. During this time the liver is responsible for 70-80% of the removal of LDL from blood. A comparison of the uptake of [14C]sucrose-labelled LDL and reductive-methylated [14C]sucrose-labelled LDL ([14C]sucrose-labelled Me-LDL) by the liver shows that methylation leads to a 65% decrease of the LDL uptake. This indicated that 65% of the LDL uptake by liver is mediated by a specific apo-B,E receptor. Parenchymal and non-parenchymal liver cells were isolated at various times after intravenous injection of [14C]sucrose-labelled LDL and [14C]sucrose-labelled Me-LDL. Non-parenchymal liver cells accumulate at least 60 times as much [14C]sucrose-labelled LDL than do parenchymal cells accumulate at least 60 times as much [14C]sucrose-labelled LDL than do parenchymal cells when expressed per mg of cell protein. This factor is independent of the time after injection of LDL. Taking into account the relative protein contribution of the various liver cell types to the total liver, it can be calculated that non-parenchymal cells are responsible for 71% of the total liver uptake of [14C]sucrose-labelled LDL. A comparison of the cellular uptake of [14C]sucrose-labelled LDL and [14C]sucrose-labelled Me-LDL after 4.5h circulation indicates that 79% of the uptake of LDL by non-parenchymal cells is receptor-dependent. With parenchymal cells no significant difference in uptake between [14C]sucrose-labelled LDL and [14C]sucrose-labelled Me-LDL was found. A further separation of the nonparenchymal cells into Kupffer and endothelial cells by centrifugal elutriation shows that within the non-parenchymal-cell preparation solely the Kupffer cells are responsible for the receptor-dependent uptake of LDL. It is concluded that in rats the Kupffer cell is the main cell type responsible for the receptor-dependent catabolism of lipoproteins containing only apolipoprotein B.

scholarly journals Characterization of the low-density-lipoprotein-receptor-independent interaction of β-very-low-density lipoprotein with rat and human parenchymal liver cells in vitro

1992 ◽  
Vol 282 (1) ◽  
pp. 41-48 ◽  
Author(s):  
R De Water ◽  
J A A M Kamps ◽  
M C M Van Dijk ◽  
E A M J Hessels ◽  
J Kuiper ◽  
...  
Keyword(s):  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Liver Cells ◽  
Recognition Site ◽  
Low Density ◽  
Hep G2 ◽  
Hep G2 Cells ◽  
Parenchymal Liver ◽  
Parenchymal Cells

beta-Migrating very-low-density lipoprotein (beta-VLDL) is a cholesteryl-ester-enriched lipoprotein which under normal conditions is rapidly cleared by parenchymal liver cells. In this study the characteristics of the interaction of beta-VLDL with rat parenchymal cells, Hep G2 cells and human parenchymal cells are evaluated. The binding of beta-VLDL to these cells follows saturation kinetics (Bmax. respectively 117, 106 and 103 ng of beta-VLDL apoliprotein/mg of cell protein), with a relatively high affinity (Kd respectively for beta-VLDL of 10.7, 5.1 and 8.4 micrograms/ml). Competition studies of unlabelled beta-VLDL, low-density lipoprotein (LDL) or acetylated LDL with the binding of radiolabelled beta-VLDL indicate that a LDL-receptor-independent, Ca(2+)-independent, specific recognition site for beta-VLDL is present on rat and human parenchymal cells, whereas with Hep G2 cells or mouse macrophages beta-VLDL recognition is performed by the LDL receptor. The binding of beta-VLDL to Hep G2 cells was down-regulated by 89% by prolonged exposure to beta-VLDL, whereas for human parenchymal and rat parenchymal cells down-regulation of 44% and 20% respectively was observed. Studies with antibodies against the LDL receptor support the presence of a LDL-receptor-independent specific beta-VLDL recognition site on rat and human parenchymal cells. It is concluded that a LDL-receptor-independent recognition site for beta-VLDL is present on rat and human parenchymal liver cells. The presence of a LDL-receptor-independent recognition site on human parenchymal cells may mediate in vivo the uptake of beta-VLDL during consumption of a cholesterol-rich diet, when LDL receptors are down-regulated, thus protecting against the extrahepatic accumulation of the atherogenic beta-VLDL constituents.

scholarly journals Recognition of lactoferrin and aminopeptidase M-modified lactoferrin by the liver: involvement of proteoglycans and the remnant receptor

1996 ◽  
Vol 313 (1) ◽  
pp. 289-295 ◽  
Author(s):  
Gijsbertus J. ZIERE ◽  
J. Kar KRUIJT ◽  
Martin K. BIJSTERBOSCH ◽  
Theo J. C. van BERKEL
Keyword(s):  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Liver Cells ◽  
Recognition Site ◽  
Low Density ◽  
Liver Uptake ◽  
Aminopeptidase M ◽  
Parenchymal Liver ◽  
Parenchymal Cells ◽  
Initial Binding

1. Lactoferrin and aminopeptidase M-modified lactoferrin (APM-lactoferrin; which lacks its 14 N-terminal amino acids) inhibit the liver uptake of lipoprotein remnants. In the present study, the role of proteoglycans in the initial interaction of β-migrating very-low-density lipoprotein (β-VLDL), native and APM-lactoferrin with isolated rat parenchymal liver cells was investigated. Treatment of the cells with chondroitinase lowered the Kd of lactoferrin binding (from 10 to 2.4 μM), and the number of sites/cell (from 20×106 to 7×106), while heparinase treatment did not affect the binding. The binding characteristics of APM-lactoferrin and β-VLDL were not altered by treatment of the cells with chondroitinase or heparinase. It is concluded that proteoglycans are not involved in the initial binding of APM-lactoferrin and β-VLDL to parenchymal cells, while chondroitin sulphate proteoglycans are mainly responsible for the massive, low-affinity binding of native lactoferrin. 2. The binding of lactoferrin, APM-lactoferrin and β-VLDL to parenchymal liver cells was not influenced by the glutathione S-transferase-receptor-associated protein (GST-RAP) (97.2±4.0%, 95.5±3.7% and 98.5% of the control binding), while the binding of α2-macroglobulin was fully blocked at 10 μg/ml GST-RAP (1.8±0.5% of the control binding). Since GST-RAP blocks the binding of all the known ligands to the low-density lipoprotein (LDL)-receptor-related protein (LRP), it is concluded that LRP is not the initial primary recognition site for lactoferrin, APM-lactoferrin and β-VLDL on parenchymal liver cells. 3. We showed earlier that APM-lactoferrin, as compared with lactoferrin, is a more effective inhibitor of the liver uptake of lipoprotein remnants (49.4±4.0% versus 80.8±4.8% of the control at 500 μg/ml respectively). We found in the present study that β-VLDL is able to inhibit the binding of APM-lactoferrin to parenchymal liver cells significantly (74.9±3.3% of the control; P < 0.002), while the lactoferrin binding was unaffected. It is concluded that a still unidentified specific recognition site (the putative remnant receptor) is responsible for the initial binding of remnants to parenchymal cells and it is suggested that the partial cross-competition between APM-lactoferrin and β-VLDL may be of further help in the elucidation of the molecular nature of this recognition site.

scholarly journals Uptake and degradation of human low-density lipoprotein by human liver parenchymal and Kupffer cells in culture

1991 ◽  
Vol 276 (1) ◽  
pp. 135-140 ◽  
Author(s):  
J A A M Kamps ◽  
J K Kruijt ◽  
J Kuiper ◽  
T J C Van Berkel
Keyword(s):  
Kupffer Cells ◽  
Human Liver ◽  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Cell Types ◽  
Liver Cells ◽  
Cell Protein ◽  
Parenchymal Liver ◽  
Parenchymal Cells

The association with and degradation by cultured human parenchymal liver cells and human Kupffer cells of human low-density lipoprotein (LDL) was investigated in order to define, for the human situation, the relative abilities of the various liver cell types to interact with LDL. With both human parenchymal liver cells and Kupffer cells the association of LDL with the cells followed saturation kinetics which were coupled to LDL degradation. The association of LDL (per mg of cell protein) to both cell types was comparable, but the association with human Kupffer cells was much more efficiently coupled to degradation than was the case in parenchymal cells. The capacity of human Kupffer cells to degrade LDL was consequently 18-fold higher (per mg of cell protein) than that of the human parenchymal liver cells. Competition studies showed that unlabelled LDL competed efficiently with the cell association and degradation of 125I-labelled LDL with both parenchymal and Kupffer cells, while unlabelled acetyl-LDL was ineffective. The degradation of LDL by parenchymal and Kupffer cells was blocked by chloroquine and NH4Cl, indicating that it occurs in the lysosomes. Binding and degradation of LDL by human liver parenchymal cells and human Kupffer cells appeared to be completely calcium-dependent. It is concluded that the association and degradation of LDL by human Kupffer and parenchymal liver cells proceeds through the specific LDL receptor, whereas the association of LDL to Kupffer cells is more efficiently coupled to degradation. The presence of the highly active LDL receptor on human Kupffer cells might contribute significantly to LDL catabolism by human liver, especially under conditions whereby the LDL receptor on parenchymal cells is down-regulated.

scholarly journals Uptake of lactosylated low-density lipoprotein by galactose-specific receptors in rat liver

1990 ◽  
Vol 270 (1) ◽  
pp. 233-239 ◽  
Author(s):  
M K Bijsterbosch ◽  
T J C Van Berkel
Keyword(s):  
Kupffer Cells ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Hepatic Uptake ◽  
Cell Protein ◽  
Low Density ◽  
Liver Uptake ◽  
Main Site ◽  
Specific Uptake ◽  
Parenchymal Cells

The liver contains two types of galactose receptors, specific for Kupffer and parenchymal cells respectively. These receptors are only expressed in the liver, and therefore are attractive targets for the specific delivery of drugs. We provided low-density lipoprotein (LDL), a particle with a diameter of 23 nm in which a variety of drugs can be incorporated, with terminal galactose residues by lactosylation. Radioiodinated LDL, lactosylated to various extents (60-400 mol of lactose/ mol of LDL), was injected into rats. The plasma clearance and hepatic uptake of radioactivity were correlated with the extent of lactosylation. Highly lactosylated LDL (greater than 300 lactose/LDL) is completely cleared from the blood by liver within 10 min. Pre-injection with N-acetylgalactosamine blocks liver uptake, which indicates that the hepatic recognition sites are galactose-specific. The hepatic uptake occurs mainly by parenchymal and Kupffer cells. At a low degree of lactosylation, approx. 60 lactose/LDL, the specific uptake (ng/mg of cell protein) is 28 times higher in Kupffer cells than in parenchymal cells. However, because of their much larger mass, parenchymal cells are the main site of uptake. At high degrees of lactosylation (greater than 300 lactose/LDL), the specific uptake in Kupffer cells is 70-95 times that in parenchymal cells. Under these conditions, Kupffer cells are, despite their much smaller mass, the main site of uptake. Thus not only the size but also the surface density of galactose on lactosylated LDL is important for the balance of uptake between Kupffer and parenchymal cells. This knowledge should allow us to design particulate galactose-bearing carriers for the rapid transport of various drugs to either parenchymal cells or Kupffer cells.

Sign in / Sign up

Export Citation Format

Share Document