scholarly journals Effect of apolipoproteins E and C-III on the interaction of chylomicrons with parenchymal and non-parenchymal cells from rat liver

1983 ◽  
Vol 216 (1) ◽  
pp. 71-80 ◽  
Author(s):  
T J C Van Berkel ◽  
J K Kruijt ◽  
L M Scheek ◽  
P H E Groot
Keyword(s):  
Liver Cells ◽  
Temperature Dependent ◽  
Oestrogen Treatment ◽  
Parenchymal Liver ◽  
Apo E ◽  
Cell Association ◽  
Parenchymal Cells ◽  
Apolipoproteins E

[3H]Triacylglycerol-labelled chylomicrons were isolated from intestinal lymph, obtained from rats made hypolipidaemic by treatment with pharmacological amounts of 17 alpha-ethynyloestradiol. Oestrogen treatment results in a large reduction in the content of apolipoproteins (apo) E and C of lymph chylomicrons. Upon incubation in vitro with freshly isolated parenchymal and non-parenchymal cells the apo E-, apo C-poor chylomicrons became readily cell-associated. With increasing chylomicron concentrations this cell-association was saturable and half-maximal cell-association was achieved at about 0.55 mg of triacylglycerol/ml. The cell-association was time- and temperature-dependent. A more than 90% inhibition of the cell-association of the [3H]triacylglycerol moiety was observed with both parenchymal and non-parenchymal cells when pure apo C-III (12.6 micrograms/mg of triacylglycerol) was incorporated into the chylomicrons. These data indicate that apo E-, apo C-poor chylomicrons are bound to both parenchymal and non-parenchymal liver cells at a high-affinity site of limited capacity and that binding to this site is strongly inhibited by apo C-III. With apo C-III-enriched chylomicrons simultaneous determination of the cell-association of the 125I-apo C-III and the [3H]triacylglycerol moiety indicated that more 125I-apo C-III becomes associated to the cells than expected on the basis of [3H]triacylglycerol radioactivity measurements. It is suggested that upon cell-association of apo C-III its binding to the chylomicron particles is lost. Consequently the occupation of the cellular recognition site by apo C-III prevents further chylomicron binding and thus leads to a decrease of the cell-association level of the [3H]triacylglycerol moiety. Apo E enrichment of the chylomicrons led to an increased cell-association rate with parenchymal cells and to a marked increase of the cell-association level with non-parenchymal cells. The cell-association of the apo E radioactivity followed closely the [3H]triacylglycerol radioactivity, indicating that the particle-apo E complex is bound as a unity. The apo E effects were opposed by apo C-III. With apo E-, apo C-III-enriched chylomicrons more 125I-apo E became associated with the cells than could be expected on the basis of the [3H]triacylglycerol measurements. It is concluded that apo C-III can weaken the interaction of apo E with the chylomicrons leading to the cell-association of free apo E. It appears that subtle changes in the apo E and/or apo C-III content of chylomicrons can influence the interaction with both parenchymal and non-parenchymal liver cells.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Recognition of chylomicron remnants and β-migrating very-low-density lipoproteins by the remnant receptor of parenchymal liver cells is distinct from the liver α2-macroglobulin-recognition site

1991 ◽  
Vol 279 (3) ◽  
pp. 863-870 ◽  
Author(s):  
M C M van Dijk ◽  
G J Ziere ◽  
W Boers ◽  
C Linthorst ◽  
M K Bijsterbosch ◽  
...  
Keyword(s):  
Parenchymal Cell ◽  
Liver Cells ◽  
Recognition Site ◽  
Low Density ◽  
Parenchymal Liver ◽  
Cell Association ◽  
Parenchymal Cells ◽  
Chylomicron Remnants

The uptake in vivo of chylomicrons and beta-migrating very-low-density lipoprotein (beta-VLDL) by rat liver, which is primarily carried out by parenchymal cells, is inhibited, 5 min after injection, to respectively 35 and 8% of the control values after preinjection of lactoferrin. The decrease in the uptake of lipoproteins by the liver caused by lactoferrin is a specific inhibition of uptake by parenchymal cells. Competition studies in vitro demonstrate that chylomicron remnants and beta-VLDL compete for the same recognition site on parenchymal cells. Data obtained in vivo together with the competition studies performed in vitro indicate that chylomicron remnants and beta-VLDL interact specifically with the same remnant receptor. Hepatic uptake of 125I-labelled-alpha 2-macroglobulin in vivo, mediated equally by parenchymal and endothelial cells, is not decreased by preinjection of lactoferrin and no effect on the parenchymal-cell-mediated uptake is found. In vitro, alpha 2-macroglobulin and chylomicron remnants or beta-VLDL show no cross-competition. Culturing of parenchymal cells for 24-48 h leads to a decrease in the cell association of alpha 2-macroglobulin to 26% of the initial value, while the cell association of beta-VLDL with the remnant receptor is not influenced. It is concluded that beta-VLDL and chylomicron remnants are recognized by a specific remnant receptor on parenchymal liver cells, while uptake of alpha 2-macroglobulin by liver is carried out by a specific receptor system (presumably involving the LDL-receptor-related protein) which shows properties that are distinct from those of the remnant receptor.

scholarly journals Characterization of the interaction both in vitro and in vivo of tissue-type plasminogen activator (t-PA) with rat liver cells. Effects of monoclonal antibodies to t-PA

1992 ◽  
Vol 284 (2) ◽  
pp. 545-550 ◽  
Author(s):  
M Otter ◽  
J Kuiper ◽  
R Bos ◽  
D C Rijken ◽  
T J van Berkel
Keyword(s):  
Endothelial Cells ◽  
Mannose Receptor ◽  
Liver Cells ◽  
Tissue Type ◽  
Tissue Type Plasminogen Activator ◽  
Type Plasminogen Activator ◽  
Liver Endothelial Cells ◽  
Parenchymal Cells

The interaction of 125I-labelled tissue-type plasminogen activator (125I-t-PA) with freshly isolated rat parenchymal and endothelial liver cells was studied. Binding experiments at 4 degrees C with parenchymal cells and endothelial liver cells indicated the presence of 68,000 and 44,000 high-affinity t-PA-binding sites, with an apparent Kd of 3.5 and 4 nM respectively. Association of 125I-t-PA with parenchymal cells was Ca(2+)-dependent and was not influenced by asialofetuin, a known ligand for the galactose receptor. Association of 125I-t-PA with liver endothelial cells was Ca(2+)-dependent and mannose-specific, since ovalbumin (a mannose-terminated glycoprotein) inhibited the cell association of t-PA. Association of 125I-t-PA with liver endothelial cells was inhibited by anti-(human mannose receptor) antiserum. Anti-(galactose receptor) IgG had no effect on 125I-t-PA association with either cell type. Degradation of 125I-t-PA at 37 degrees C by both cell types was inhibited by chloroquine or NH4Cl, indicating that t-PA is degraded lysosomally. in vitro experiments with three monoclonal antibodies (MAbs) demonstrated that anti-t-PA MAb 1-3-1 specifically decreased association of 125I-t-PA with the endothelial cells, and anti-t-PA Mab 7-8-4 inhibited association with the parenchymal cells. Results of competition experiments in rats in vivo with these antibodies were in agreement with findings in vitro. Both antibodies decreased the liver uptake of 125I-t-PA, while a combination of the two antibodies was even more effective in reducing the liver association of 125I-t-PA and increasing its plasma half-life. We conclude from these data that clearance of t-PA by the liver is regulated by at least two pathways, one on parenchymal cells (not galactose/mannose-mediated) and another on liver endothelial cells (mediated by a mannose receptor). Results with the MAbs imply that two distinct sites on the t-PA molecule are involved in binding to parenchymal cells and liver endothelial cells.

Uptake and Degradation of Tissue Plasminogen Activator in Rat Liver

1988 ◽  
Vol 59 (03) ◽  
pp. 474-479 ◽  
Author(s):  
Monica Einarsson ◽  
Bård Smedsrød ◽  
Håkan Pertoft
Keyword(s):  
Endothelial Cells ◽  
Plasminogen Activator ◽  
Tissue Plasminogen Activator ◽  
Rat Liver ◽  
Liver Cells ◽  
Terminal Phase ◽  
Tissue Plasminogen ◽  
Liver Endothelial Cells ◽  
Parenchymal Cells

SummaryThe mechanism of uptake of tissue plasminogen activator (tPA) in rat liver was studied. Radio-iodinated tPA was removed from the circulation after intravenous administration in a biphasic mode. The initial half life, t1/2(α), and the terminal phase, t1/2(β), were determined to be 0.5 min and 7.5 min, resp. Separation of the liver cells by collagenase perfusion and density centrifugation, revealed that the uptake per cell was two to three times higher in the non-parenchymal cells than in the parenchymal cells.Endocytosis of fluorescein isothiocyanate-labelled or 125I-labelled tPA was studied in pure cultures of liver cells in vitro. Liver endothelial cells and parenchymal cells took up and degraded tPA. Endocytosis was more efficient in liver endothelial cells than in parenchymal cells, and was almost absent in Kupffer cells.Competitivb inhibition experiments showing that excess unlabelled tPA could compete with the uptake and degradation of 125I-tPA, suggested that liver endothelial cells and parenchymal cells interact with the activator in a specific manner. Endocytosis of trace amounts of 125I-tPA in cultures of liver endothelial cells and parenchymal cells was inhibited by 50% in the presence of 19 nM unlabelled tPA. Agents that interfere with one or several steps of the endocytic machinery inhibited uptake and degradation of 125I-tPA in both cell types.These findings suggest that 1) liver endothelial cells and parenchymal cells are responsible for the rapid hepatic clearance of intravenously administered tPA; 2) the activator is taken up in these cells by specific endocytosis, and 3) endocytosed tPA is transported to the lysosomes where it is degraded.

scholarly journals Hepatic lipase is localized at the parenchymal cell microvilli in rat liver

1997 ◽  
Vol 321 (2) ◽  
pp. 425-430 ◽  
Author(s):  
Belinda BREEDVELD ◽  
Kees SCHOONDERWOERD ◽  
Adrie J. M. VERHOEVEN ◽  
Rob WILLEMSEN ◽  
Hans JANSEN
Keyword(s):  
Endothelial Cells ◽  
Rat Liver ◽  
Kupffer Cells ◽  
Binding Capacity ◽  
Hepatic Lipase ◽  
Parenchymal Cell ◽  
Liver Cells ◽  
Minor Amount ◽  
Parenchymal Liver ◽  
Parenchymal Cells

Hepatic lipase (HL) is thought to be located at the vascular endothelium in the liver. However, it has also been implicated in the binding and internalization of chylomicron remnants in the parenchymal cells. In view of this apparent discrepancy between localization and function, we re-investigated the localization of HL in rat liver using biochemical and immunohistochemical techniques. The binding of HL to endothelial cells was studied in primary cultures of rat liver endothelial cells. Endothelial cells bound HL in a saturable manner with high affinity. However, the binding capacity accounted for at most 1% of the total HL activity present in the whole liver. These results contrasted with earlier studies, in which non-parenchymal cell (NPC) preparations had been found to bind HL with a high capacity. To study HL binding to the different components of the NPC preparations, we separated endothelial cells, Kupffer cells and blebs by counterflow elutriation. Kupffer cells and endothelial cells showed a relatively low HL-binding capacity. In contrast, the blebs, representing parenchymal-cell-derived material, had a high HL-binding capacity (33 m-units/mg of protein) and accounted for more than 80% of the total HL binding in the NPC preparation. In contrast with endothelial and Kupffer cells, the HL-binding capacity of parenchymal cells could account for almost all the HL activity found in the whole liver. These data strongly suggest that HL binding occurs at parenchymal liver cells. To confirm this conclusion in situ, we studied HL localization by immunocytochemical techniques. Using immunofluorescence, we confirmed the sinusoidal localization of HL. Immunoelectron microscopy demonstrated that virtually all HL was located at the microvilli of parenchymal liver cells, with a minor amount at the endothelium. We conclude that, in rat liver, HL is localized at the microvilli of parenchymal cells.

scholarly journals Carrier-Mediated Delivery of 9-(2-Phosphonylmethoxyethyl)Adenine to Parenchymal Liver Cells: a Novel Therapeutic Approach for Hepatitis B

2000 ◽  
Vol 44 (3) ◽  
pp. 477-483 ◽  
Author(s):  
Remco L. A. de Vrueh ◽  
Erik T. Rump ◽  
Erika van de Bilt ◽  
Richard van Veghel ◽  
Jan Balzarini ◽  
...  
Keyword(s):  
Hepatitis B ◽  
Lithocholic Acid ◽  
Hepatic Uptake ◽  
Liver Cells ◽  
Asialoglycoprotein Receptor ◽  
Parenchymal Liver ◽  
Lipophilic Prodrug ◽  
Acid Labile

ABSTRACT Our aim is to selectively deliver 9-(2-phosphonylmethoxyethyl)adenine (PMEA) to parenchymal liver cells, the primary site of hepatitis B virus (HBV) infection. Selective delivery is necessary because PMEA, which is effective against HBV in vitro, is hardly taken up by the liver in vivo. Lactosylated reconstituted high-density lipoprotein (LacNeoHDL), a lipid particle that is specifically internalized by parenchymal liver cells via the asialoglycoprotein receptor, was used as the carrier. PMEA could be incorporated into the lipid moiety of LacNeoHDL by attaching, via an acid-labile bond, lithocholic acid-3α-oleate to the drug. The uptake of the lipophilic prodrug (PMEA-LO) by the liver was substantially increased after incorporation into LacNeoHDL. Thirty minutes after injection of [3H]PMEA-LO-loaded LacNeoHDL into rats, the liver contained 68.9% ± 7.7% of the dose (free [3H]PMEA, <5%). Concomitantly, the uptake by the kidney was reduced to <2% of the dose (free [3H]PMEA, >45%). The hepatic uptake of PMEA-LO-loaded LacNeoHDL occurred mainly by parenchymal cells (88.5% ± 8.2% of the hepatic uptake). Moreover, asialofetuin inhibited the liver association by >75%, indicating uptake via the asialoglycoprotein receptor. The acid-labile linkage in PMEA-LO, designed to release PMEA during lysosomal processing of the prodrug-loaded carrier, was stable at physiological pH but was hydrolyzed at lysosomal pH (half-life, 60 to 70 min). Finally, subcellular fractionation indicates that the released PMEA is translocated to the cytosol, where it is converted into its active diphosphorylated metabolite. In conclusion, lipophilic modification and incorporation of PMEA into LacNeoHDL improves the biological fate of the drug and may lead to an enhanced therapeutic efficacy against chronic hepatitis 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 Management of listeriosis.

1997 ◽  
Vol 10 (2) ◽  
pp. 345-357 ◽  
Author(s):  
H Hof ◽  
T Nichterlein ◽  
M Kretschmar
Keyword(s):  
Bacterial Species ◽  
Extracellular Fluid ◽  
Systemic Infection ◽  
Immunocompromised Host ◽  
Host Cells ◽  
Drug Of Choice ◽  
Alternative Measures ◽  
Parenchymal Cells

Determination of the MIC in vitro is often used as the basis for predicting the clinical efficacy of antibiotics. Listeriae are uniformly susceptible in vitro to most common antibiotics except cephalosporins and fosfomycin. However, the clinical outcome is poor. This is partially because listeriae are refractory to the bactericidal mechanisms of many antibiotics, especially to ampicillin-amoxicillin, which still is regarded as the drug of choice. A true synergism can be achieved by adding gentamicin. Another point is that listeriae are able to reside and multiply within host cells, e.g., macrophages, hepatocytes, and neurons, where they are protected from antibiotics in the extracellular fluid. Only a few agents penetrate, accumulate, and reach the cytosol of host cells, where the listeriae are found. Furthermore, certain host cells may exclude antibiotics from any intracellular compartment. Thus, determination of the antibacterial efficacy of a drug against listeriae in cell cultures may be a better approximation of potential therapeutic value. Certain host cells may have acquired the property of excluding certain antibiotics, for example macrolides, from intracellular spaces, which might explain therapeutic failures of antibiotic therapy in spite of low MICs. Animal models do not completely imitate human listeriosis, which is characterized by meningitis, encephalitis, soft tissue and parenchymal infections, and bacteremia. Meningitis produced in rabbits is a hyperacute disease, whereby most listeriae lie extracellularly, fairly accessible to antibiotics that can cross the blood-cerebrospinal fluid barrier. In the murine model of systemic infection, Listeria monocytogenes is located mainly within macrophages and parenchymal cells of the spleen and liver, hardly accessible to certain drugs, such as ampicillin and gentimicin. The therapeutic efficacy of drugs clearly depends on the model used. Thus, for example, the combination of ampicillin with gentamicin acts synergistically in the rabbit meningitis model but not in the mouse model. Since conventional antimicrobial therapy with antibiotics is not satisfactory, particularly in the immunocompromised host (about 30% of patients with listeriosis die in spite of a rational choice of antibiotics), other possibilities must be considered for therapy as well as prevention. Indeed, listeriae are highly susceptible to several endogenous antibiotics, such as defensins. Bacteriocins produced by related bacterial species, e.g., lactobacilli and enterococci, are rapidly bactericidal. However, unfortunately, the use of such alternative measures along with immunization and immunmodulation is not yet feasible.

scholarly journals Uptake of mannose-terminated glycoproteins in isolated rat liver cells. Evidence for receptor-mediated endocytosis in hepatocytes

1984 ◽  
Vol 223 (1) ◽  
pp. 151-160 ◽  
Author(s):  
H Tolleshaug ◽  
T Berg ◽  
R Blomhoff
Keyword(s):  
Binding Capacity ◽  
Liver Cells ◽  
Receptor Mediated Endocytosis ◽  
Parenchymal Liver ◽  
Yeast Invertase ◽  
Rat Liver Cells ◽  
Specific Uptake ◽  
Parenchymal Cells ◽  
Ribonuclease B

Even though most of the hepatic binding capacity for mannose-terminated glycoproteins has previously been shown to reside in the hepatocytes (not in the non-parenchymal cells), detailed evidence for the specific uptake of mannose-terminated ligands has been lacking. In the present studies, yeast invertase, a large glycoprotein (Mr 270 000) containing about 50% mannose, was shown to be taken up into hepatocytes by receptor-mediated endocytosis. The uptake was saturable and could be specifically inhibited by mannosides or by a Ca2+ chelator. The asialo-glycoprotein receptor was not involved. The low-Mr (13 000) ligand ribonuclease B, which contains a single high-mannose glycan, was not taken up by hepatocytes; however, it was taken up as fast as invertase by non-parenchymal liver cells. After injection of 131I-invertase into a rat in vivo, about one-half of the labelled protein was recovered in the hepatocytes. On a per-cell basis, each endothelial cell contained 3-4 times as much radioactivity as did the hepatocytes. On fractionation of hepatocytes in sucrose gradients, invertase showed a different intracellular distribution from that of asialo-fetuin, in that invertase moved much faster into that region of the gradient where the lysosomes were recovered. This indicates that invertase and asialo-fetuin are not transported intracellularly by identical mechanisms.

scholarly journals Uptake and degradation of filamentous actin and vitamin D-binding protein in the rat

1991 ◽  
Vol 274 (1) ◽  
pp. 237-241 ◽  
Author(s):  
S Dueland ◽  
M S Nenseter ◽  
C A Drevon
Keyword(s):  
Vitamin D ◽  
Binding Protein ◽  
Total Radioactivity ◽  
Liver Cells ◽  
Tissue Uptake ◽  
Rapid Rate ◽  
Vitamin D Binding Protein ◽  
Filamentous Actin ◽  
Parenchymal Liver

Tissue uptake and degradation of 125I-tyramine-cellobiose-labelled filamentous actin, vitamin D-binding protein (DBP) and actin-DBP complex were studied in the rat. Actin and actin-DBP complex were cleared from plasma at a faster rate than was DBP. About 40% of injected actin was recovered in the liver between 10 and 30 min after administration. Of the total radioactivity recovered in the liver, about 35% and 40% was detected in parenchymal and endothelial cells respectively when labelled actin or DBP-actin complex was injected intravenously. When labelled DBP alone was injected, approx. 55% of the radioactivity recovered in liver was in the Kupffer cells. These results suggest that actin is targeting the DBP-actin complex to the endothelial and parenchymal liver cells. Filamentous actin was also taken up in large amounts and at a rapid rate in parenchymal as well as non-parenchymal liver cells in vitro. Our data indicate that the rat has a mechanism to clear actin and the DBP-actin complex from plasma and that both parenchymal and non-parenchymal liver cells are involved in this process.

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