scholarly journals Role of the scavenger receptor in the uptake of methylamine-activated α2-macroglobulin by rat liver

1992 ◽  
Vol 287 (2) ◽  
pp. 447-455 ◽  
Author(s):  
M C M van Dijk ◽  
W Boers ◽  
C Linthorst ◽  
T J C van Berkel
Keyword(s):  
Endothelial Cells ◽  
Rat Liver ◽  
Kupffer Cells ◽  
Proteolytic Enzymes ◽  
Scavenger Receptor ◽  
Liver Cells ◽  
Cell Protein ◽  
Liver Uptake ◽  
Inosinic Acid ◽  
Parenchymal Cells

Alpha 2-Macroglobulin (alpha 2M) requires activation by small nucleophiles (e.g. methylamine; giving alpha 2M-Me) or proteolytic enzymes (e.g. trypsin; giving alpha 2M-Tr) in order to be rapidly removed from the circulation by the liver. Separation of rat liver cells into parenchymal, endothelial and Kupffer cells at 10 min after injection indicates that liver uptake of alpha 2M-Me is shared between parenchymal and endothelial cells, with relative contributions of 51.3% and 48.3% respectively of total liver-associated radioactivity. In contrast, alpha 2M-Tr is almost exclusively taken up by the parenchymal cells (90.1% of liver-associated radioactivity). A preinjection of 5 mg of poly(inosinic acid) decreased liver uptake of alpha 2M-Me to 39.9% of the control value, while it had no effect on liver uptake of alpha 2M-Tr. It appears that poly(inosinic acid) specifically reduces the uptake of alpha 2M-Me in vivo by endothelial cells, leaving uptake by parenchymal cells unaffected. In vitro studies with isolated liver cells indicate that the association of alpha 2M-Me with endothelial cells is 21-fold higher per mg of cell protein than with parenchymal cells. The capacity of endothelial cells to degrade alpha 2M-Me appears to be 46 times higher than that of parenchymal cells. Competition studies show that poly(inosinic acid) or acetylated low-density lipoprotein effectively competes with the association of alpha 2M-Me with endothelial and Kupffer cells, but association with parenchymal cells is unaffected. It is suggested that activation of alpha 2M by methylamine induces a charge distribution on the protein which triggers specific uptake by the scavenger receptor on endothelial cells. It is concluded that the uptake of alpha 2M-Me by the scavenger receptor might function as an additional system for the uptake of activated alpha 2M.

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.

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 The uptake and metabolism of chylomicron-remnant lipids by rat liver parenchymal and non-parenchymal cells in vitro

1985 ◽  
Vol 232 (2) ◽  
pp. 395-401 ◽  
Author(s):  
P M Lippiello ◽  
P J Sisson ◽  
M Waite
Keyword(s):  
Endothelial Cells ◽  
Rat Liver ◽  
Kupffer Cells ◽  
Liver Cell ◽  
Cholesterol Ester ◽  
Cell Types ◽  
Chylomicron Remnant ◽  
Parenchymal Cells ◽  
Uptake And Metabolism

The uptake and metabolism of chylomicron-remnant lipids by individual liver cell types was examined by incubating remnants with monolayer cultures of hepatocytes, Kupffer cells, and endothelial cells from rat liver. Remnants were prepared in vitro from radiolabelled mesenteric-lymph chylomicra, utilizing either purified lipoprotein lipase from bovine milk, or plasma isolated from heparinized rats. The resulting particles contained [3H]phosphatidylcholine and cholesterol, and [14C]oleate in the acylglycerol, phospholipid, fatty-acid and cholesterol-ester fractions. The capacities of the three cell types for uptake of both [3H]lipids and [14C]lipids were determined to be, on a per-cell basis, in the order: Kupffer greater than hepatocytes greater than endothelial. The relative proportions of [3H]phospholipid and total [3H]cholesterol taken up by hepatocytes and non-parenchymal cells remained constant with time. The uptake of [14C]oleoyl lipids by all three cell types was slightly greater than that of the total [3H]cholesterol and [3H]phospholipid components. There was evidence of cholesterol-ester hydrolysis and turnover of [14C]oleate in the phospholipid fraction in hepatocytes and Kupffer cells, but not endothelial cells, over the first 2 h. With both remnant preparations, these observations indicate that significant differences exist between the three major liver cell types with respect to the uptake and metabolism of remnant lipid components.

Release of osmolytes induced by phagocytosis and hormones in rat liver

2000 ◽  
Vol 278 (2) ◽  
pp. G227-G233 ◽  
Author(s):  
Matthias Wettstein ◽  
Thorsten Peters-Regehr ◽  
Ralf Kubitz ◽  
Richard Fischer ◽  
Claudia Holneicher ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Cell Volume ◽  
Rat Liver ◽  
Kupffer Cells ◽  
Hepatic Stellate Cells ◽  
Stellate Cells ◽  
Receptor Expression ◽  
Sinusoidal Endothelial Cells ◽  
Fluorescence Measurements ◽  
Parenchymal Cells

Betaine, taurine, and inositol participate as osmolytes in liver cell volume homeostasis and interfere with cell function. In this study we investigated whether osmolytes are also released from the intact liver independent of osmolarity changes. In the perfused rat liver, phagocytosis of carbon particles led to a four- to fivefold stimulation of taurine efflux into the effluent perfusate above basal release rates. This taurine release was inhibited by 70–80% by the anion exchange inhibitor DIDS or by pretreatment of the rats with gadolinium chloride. Administration of vasopressin, cAMP, extracellular ATP, and glucagon also increased release of betaine and/or taurine, whereas insulin, extracellular UTP, and adenosine were without effect. In isolated liver cells, it was shown that parenchymal cells and sinusoidal endothelial cells, but not Kupffer cells and hepatic stellate cells, release osmolytes upon hormone stimulation. This may be caused by a lack of hormone receptor expression in these cells, because single-cell fluorescence measurements revealed an increase of intracellular calcium concentration in response to vasopressin and glucagon in parenchymal cells and sinusoidal endothelial cells but not in Kupffer cells and hepatic stellate cells. The data show that Kupffer cells release osmolytes during phagocytosis via DIDS-sensitive anion channels. This mechanism may be used to compensate for the increase in cell volume induced by the ingestion of phagocytosable material. The physiological significance of hormone-induced osmolyte release remains to be evaluated.

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.

scholarly journals Liver endothelium and not hepatocytes or Kupffer cells have transferrin receptors

Blood ◽  
1984 ◽  
Vol 63 (2) ◽  
pp. 270-276
Author(s):  
R Soda ◽  
M Tavassoli
Keyword(s):  
Endothelial Cells ◽  
Rat Liver ◽  
Kupffer Cells ◽  
Liver Cell ◽  
Cell Suspensions ◽  
Transferrin Receptors ◽  
Visual Probe ◽  
Covalently Linked ◽  
Parenchymal Cells

Using a visual probe, consisting of latex minibeads covalently linked to transferrin (TF), we found that, in rat liver cell suspensions, transferrin receptors were limited to endothelial cells. Neither hepatocytes nor Kupffer cells contained an appreciable number of TF receptors. Specificity of this reaction was demonstrated by preincubation with non-derivatized TF, which inhibited the binding. This was further confirmed by fractionation of liver cell suspensions on metrizamide gradients. The uptake of either the visual probe or 125I- labeled TF was again limited to the endothelium-rich fraction. Transferrin bound to endothelial membrane was internalized at 37 degrees C, but not at 4 degrees C, via a coated pit system. Again, hepatocytes and Kupffer cells did not internalize the probe. The findings suggest that iron may be first taken up by liver endothelium and then transmitted to parenchymal cells. These results emphasize the generally unappreciated role of endothelium in the transport across the tissue-blood barrier.

scholarly journals New Scavenger Receptor-Like Receptors for the Binding of Lipopolysaccharide to Liver Endothelial and Kupffer Cells

1998 ◽  
Vol 66 (11) ◽  
pp. 5107-5112 ◽  
Author(s):  
Marijke van Oosten ◽  
Erika van de Bilt ◽  
Theo J. C. van Berkel ◽  
Johan Kuiper
Keyword(s):  
Endothelial Cells ◽  
Kupffer Cells ◽  
Binding Sites ◽  
Oxidized Ldl ◽  
Scavenger Receptor ◽  
Scavenger Receptors ◽  
Liver Endothelial Cells ◽  
Parenchymal Cells

ABSTRACT Lipopolysaccharide (LPS) is cleared from the blood mainly by the liver. The Kupffer cells are primarily responsible for this clearance; liver endothelial and parenchymal cells contribute to a lesser extent. Although several binding sites have been described, only CD14 is known to be involved in LPS signalling. Among the other LPS binding sites that have been identified are scavenger receptors. Scavenger receptor class A (SR-A) types I and II are expressed in the liver on endothelial cells and Kupffer cells, and a 95-kDa receptor, identified as macrosialin, is expressed on Kupffer cells. In this study, we examined the role of scavenger receptors in the binding of LPS by the liver in vivo and in vitro. Fucoidin, a scavenger receptor ligand, significantly reduced the clearance of 125I-LPS from the serum and decreased the liver uptake of 125I-LPS about 40%. Within the liver, the in vivo binding of 125I-LPS to Kupffer and liver endothelial cells was decreased 72 and 71%, respectively, while the binding of 125I-LPS to liver parenchymal cells increased 34% upon fucoidin preinjection. Poly(I) inhibited the binding of 125I-LPS to Kupffer and endothelial cells in vitro 73 and 78%, respectively, while poly(A) had no effect. LPS inhibited the binding of acetylated low-density lipoprotein (acLDL) to Kupffer and liver endothelial cells 40 and 55%, respectively, and the binding of oxidized LDL (oxLDL) to Kupffer and liver endothelial cells 65 and 61%, respectively. oxLDL and acLDL did not significantly inhibit the binding of LPS to these cells. We conclude that on both endothelial cells and Kupffer cells, LPS binds mainly to scavenger receptors, but SR-A and macrosialin contribute to a limited extent to the binding of LPS.

scholarly journals Liver endothelium and not hepatocytes or Kupffer cells have transferrin receptors

Blood ◽  
1984 ◽  
Vol 63 (2) ◽  
pp. 270-276 ◽  
Author(s):  
R Soda ◽  
M Tavassoli
Keyword(s):  
Endothelial Cells ◽  
Rat Liver ◽  
Kupffer Cells ◽  
Liver Cell ◽  
Cell Suspensions ◽  
Transferrin Receptors ◽  
Visual Probe ◽  
Covalently Linked ◽  
Parenchymal Cells

Abstract Using a visual probe, consisting of latex minibeads covalently linked to transferrin (TF), we found that, in rat liver cell suspensions, transferrin receptors were limited to endothelial cells. Neither hepatocytes nor Kupffer cells contained an appreciable number of TF receptors. Specificity of this reaction was demonstrated by preincubation with non-derivatized TF, which inhibited the binding. This was further confirmed by fractionation of liver cell suspensions on metrizamide gradients. The uptake of either the visual probe or 125I- labeled TF was again limited to the endothelium-rich fraction. Transferrin bound to endothelial membrane was internalized at 37 degrees C, but not at 4 degrees C, via a coated pit system. Again, hepatocytes and Kupffer cells did not internalize the probe. The findings suggest that iron may be first taken up by liver endothelium and then transmitted to parenchymal cells. These results emphasize the generally unappreciated role of endothelium in the transport across the tissue-blood barrier.

scholarly journals Cadmium metabolism by rat liver endothelial and Kupffer cells

1984 ◽  
Vol 221 (3) ◽  
pp. 631-636 ◽  
Author(s):  
T J Caperna ◽  
M L Failla
Keyword(s):  
Endothelial Cells ◽  
Rat Liver ◽  
Kupffer Cells ◽  
Metal Binding ◽  
Metal Salt ◽  
Extracellular Medium ◽  
Competitive Binding Assay ◽  
Monolayer Cultures ◽  
Parenchymal Cells

The metabolism of cadmium was investigated in Wistar-rat liver non-parenchymal cells. Kupffer and endothelial cells, the major cell populations lining the sinusoidal tracts, were isolated by collagenase dispersion and purified by centrifugal elutriation. At 20 h after subcutaneous injection of the metal salt (1.5 mg of Cd/kg body weight), endothelial cells accumulated 2-fold higher concentrations of Cd than did Kupffer or parenchymal cells. Most of the Cd in non-parenchymal cells was associated with cytosolic metallothionein (MT), the low-Mr heavy-metal-binding protein(s). When MT was quantified in cytosols from cells isolated from control rats by a 203Hg competitive-binding assay, low levels were found to be present in Kupffer, endothelial and parenchymal cells. Cd injection significantly increased MT levels in all three cell types. The induction of MT synthesis was investigated in vitro by using primary monolayer cultures. The incorporation of [35S]cysteine into MT increased 47% over constitutive levels in endothelial-cell cultures after the addition of 0.8 microM-Cd2+ to the medium for 10 h. MT synthesis in Kupffer cells was not observed. The lack of MT synthesis by monolayer cultures of Kupffer cells in vitro was associated with a decreased capacity of these cells to accumulate heavy metals from the extracellular medium. This apparent decreased ability to transport metals did not reflect a general defect in either cellular function or metabolic activity, since isolated Kupffer cells incorporated [3H]leucine into protein at rates comparable with those shown by liver parenchymal cells and readily phagocytosed particles.

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