Phagocytic properties of hepatic endothelial cells and splenic macrophages compensating for a decreased phagocytic function of Kupffer cells in the chronically ethanol-fed rats

The balance of phagocytic function among Kupffer cells, hepatic endothelial cells and splenic macrophages in the chronically ethanol-fed rats has been investigated. Clearance of latex particles in the blood was measured to estimate the function of the reticuloendothelial system. Phagocytosis of latex particles by Kupffer cells, hepatic endothelial cells or splenic macrophages in vivo was measured by counting the number of ingested particles in a cell after isolation of hepatic nonparenchymal cells or spleen cells following injection of different amounts of latex particles. Latex particle clearance was suppressed in the ethanol-fed rats, demonstrating a decreased phagocytic capacity of the reticuloendothelial system. Markedly decreased phagocytic function was found in 40% of Kupffer cells of the chronically ethanol-fed rats. In contrast, the number of latex particles in hepatic endothelial cells and in splenic macrophages was increased after injection of a triggering dose of latex particles. From these results it may be concluded that an increased phagocytosis of hepatic endothelial cells and splenic macrophages could compensate for the decreased phagocytic function of Kupffer cells.     

A scanning electron microscopic study of the rat liver sinusoid

The surface ultrastructure of Kupffer cells in the rat liver has been studied by scanning electron microscopy (SEM). The results demonstrate that Kupffer cells are both significantly different and clearly distinct from endothelial cells. Kupffer cells have neither pores (and/or "sieve plates") nor fenestrations, all of which are present in endothelial cells. They possess a stellate shape, and only indirectly, with slender and irregular evaginations, contribute to the lining of the sinusoidal wall. Furthermore, the luminal surface in some areas contains a large population of short microvilli, microphicae and invaginations. These elements form a kind of microlabyrinth which may correpond to the "worm-like" structures described by transmission electron microscopy (TEM). In the present study, transition forms between endothelial and Kupffer cells were never found. On the contrary, considering the highly fenestrated nature of the endothelial cells, the Kupffer cells may, by ameboid movements, easily cross the overlapping barrier of the sinusoid and protrude into the lumen. Thus, acting as activated macrophages, the Kupffer cells might function to prevent the entrance of foreign material into the tissues of the liver through the fragile and highly fenestrated endothelium. Finally, the topographical reconstruction of the sinusoid by correlated SEM and TEM studies demonstrates the Kupffer cells, with their protruding cytoplasm and ability to extend into the lumen of the sinusoid, may actually change the caliber of the vessel, and thus function as a "sphincter" which causes a temporary arrest of the blood flow when the diameter of the sinusoidal lumen is reduced.     

Uptake of lithium carmine by sinusoidal endothelial and Kupffer cells of the rat liver: new insights into the classical vital staining and the reticulo-endothelial system

Sinusoidal cells in the rat liver were studied in vivo and in vitro using the original vital staining with lithium carmine, which has contributed much to the development of the concept of the reticulo-endothelial system. Immunohistochemical and electron-microscopic studies revealed that the dye-incorporating cells were sinusoidal endothelial cells, Kupffer cells, and monocytes. The endothelial cells took up much more dye than did the Kupffer cells and bulged largely into the sinusoidal lumen. Electron microscopy revealed that small particles of lithium carmine were associated with coated vesicles of endothelial cells and ruffled membranes of Kupffer cells. In the endothelial cells, these particles were present in various concentrations within vacuolated structures and condensed in the lysosomes forming large aggregates of lithium carmine lumps. These lumps showed crystalline structures, within which the size of the individual particle was up to 30 nm in width and 50 nm in length. A few endothelial cells containing abundant dye underwent degeneration, and some were taken up by Kupffer cells. Liver endothelial cells isolated from lithium carmine-administered rats endocytosed fluorescence-labeled collagen. Isolated endothelial cells from normal rat liver, when cultured with lithium carmine, did not take up any dye, and their endocytosis of formaldehyde-treated albumin was inhibited dose-dependently. We conclude that in the liver, endothelial cells, but not Kupffer cells, predominantly take up lithium carmine. Furthermore, we propose the existence of a generalized cell system based on its vital staining capacity.     

Isolation and characterization of Kupffer and endothelial cells from the rat liver

Non-parenchymal cell suspensions were prepared from rat livers by three different methods based on a collagenase, a pronase and a combined collagenase-pronase treatment. The highest yield of Kupffer and endothelial cells was obtained with the pronase treatment. Attempts were made for a further purification of these cells by Metrizamide density gradient centrifugation after preferentially loading lysosomal structures in Kupffer cells with Triton WR 1339, Jectofer^®, Neosilvol^®, Zymosan or colloidal carbon. After loading with Triton WR 1339 or Jectofer^®, highly purified endothelial cell suspensions were obtained, but the final Kupffer cell preparations were contaminated with about 20% of endothelial cells. Kupffer and endothelial cells purified in this way showed an altered ultrastructure and contained increased activities of the lysosomal enzymes acid phosphatase, arylsulphatase B and cathepsin D. As an alternative procedure for the purification of Kupffer and endothelial cells, a method based on centrifugal elutriation was employed. With this procedure, highly purified preparations of Kupffer or endothelial cells with a well preserved ultrastructure were obtained. Compared with endothelial cells, purified Kupffer cells had a three times higher cathepsin D activity, whereas the arylsulphatase B activity was three times higher in endothelial cells. The high cathepsin D activity in Kupffer cells could be nearly completely inhibited by the specific cathepsin D inhibitor pepstatin, which excludes a possible contribution to this activity by proteases endocytosed during the isolation of the cells.     

BETA-glucuronidase and chloroacetate-esterase staining discriminates rat liver sinusoidal endothelial cells from Kupffer cells in primary culture

Beta-glucuronidase and N-AS-D-chloroacetate esterase cytochemistry have been applied to rat liver sinusoidal endothelial cells and Kupffer cells. Both staining procedures allowed a clear-cut differentiation of either cell type. Kupffer cells which had been stained with beta-glucuronidase showed a positive reaction, whereas sinusoidal endothelial cells were completely negative. If the chloroacetate reaction was used, the former stained diffusely while the latter showed a characteristic granular staining pattern. Identity and purity of sinusoidal endothelial cells and Kupffer cells was validated by transmission and scanning electron microscopy as well as by the pattern of released eicosanoids which is characteristic for either cell type. These two staining techniques are a valuable addition to the peroxidase reaction commonly applied for differentiation.     

Hormonal control of glycogenolysis in parenchymal liver cells by Kupffer and endothelial liver cells

Conditioned media of isolated Kupffer and endothelial liver cells were added to incubations of parenchymal liver cells, in order to test whether secretory products of Kupffer and endothelial liver cells could influence parenchymal liver cell metabolism. With Kupffer cell medium an average stimulation of glucose production by parenchymal liver cells of 140% was obtained, while endothelial liver cell medium stimulated with an average of 127%. The separation of the secretory products of Kupffer and endothelial liver cells in a low and a high molecular weight fraction indicated that the active factor(s) had a low molecular weight. Media, obtained from aspirin-pretreated Kupffer and endothelial liver cells, had no effect on the glucose production by parenchymal liver cells. Because aspirin blocks prostaglandin synthesis, it was tested if prostaglandins could be responsible for the effect of media on parenchymal liver cells. It was found that prostaglandin (PG) E1, E2, and D2 all stimulated the glucose production by parenchymal liver cells, PGD2 being the most potent. Kupffer and endothelial liver cell media as well as prostaglandins E1, E2, and D2 stimulated the activity of phosphorylase, the regulatory enzyme in glycogenolysis. The data indicate that prostaglandins, present in media from Kupffer and endothelial liver cells, may stimulate glycogenolysis in parenchymal liver cells. This implies that products of Kupffer and endothelial liver cells may play a role in the regulation of glucose homeostasis by the liver.     

Beta-glucuronidase and chloroacetate-esterase staining discriminates rat liver sinusoidal endothelial cells from Kupffer cells in primary culture

Beta-glucuronidase and N-AS-D-chloroacetate esterase cytochemistry have been applied to rat liver sinusoidal endothelial cells and Kupffer cells. Both staining procedures allowed a clear-cut differentiation of either cell type. Kupffer cells which had been stained with beta-glucuronidase showed a positive reaction, whereas sinusoidal endothelial cells were completely negative. If the chloroacetate reaction was used, the former stained diffusely while the latter showed a characteristic granular staining pattern. Identity and purity of sinusoidal endothelial cells and Kupffer cells was validated by transmission and scanning electron microscopy as well as by the pattern of released eicosanoids which is characteristic for either cell type. These two staining techniques are a valuable addition to the peroxidase reaction commonly applied for differentiation.     

Fluid phase endocytosis of [125I]iodixanol in rat liver parenchymal, endothelial and Kupffer cells

Endocytosis of [125I]iodixanol was studied in vivo and in vitro in rat liver cells to determine fluid phase endocytic activity in different liver cells (hepatocytes, Kupffer cells and endothelial cells). The Kupffer cells were more active in the uptake of [l25I]iodixanol than parenchymal cells or endothelial cells. Inhibition of endocytic uptake via clathrin-coated pits (by potassium depletion and hypertonic medium) reduced uptake of [125I]iodixanol much more in Kupffer cells and endothelial cells than in hepatocytes. To gain further information about the importance of clathrin-mediated fluid phase endocytosis, the expression of proteins known to be components of the endocytic machinery was investigated. Using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting, endothelial cells and Kupffer cells were found to express approximately fourfold more rab4, rab5 and rab7 than parenchymal cells, while clathrin was expressed at a higher level in endothelial cells than in Kupffer cells and hepatocytes. Using electron microscopy it was shown that liver endothelial cells contained approximately twice as many coated pits per membrane unit than the parenchymal and Kupffer cells, thus confirming the immunoblotting results concerning clathrin expression. Electron microscopy on isolated liver cells following fluid phase uptake of horseradish peroxidase (HRP) showed that HRP-containing organelles had a different morphology in the different cell types: In the liver endothelial cells HRP was in small, tubular endosomes, while in Kupffer cells HRP was mainly found in larger structures, reminiscent of macropinosomes. Parenchymal cells contained HRP in small vacuolar endosomes with a punctuated distribution. In conclusion, we find that the Kupffer cells and the endothelial cells have a higher pinocytic activity than the hepatocytes. The hepatocytes do, however, account for most of the total hepatic uptake. The fluid phase endocytosis in liver endothelial cells depends mainly on clathrin-mediated endocytosis, while the parenchymal cells have additional clathrin-independent mechanisms that may play an important role in the uptake of plasma membrane components. In the Kupffer cells the major uptake of fluid phase markers seems to take place via a macropinocytic mechanism.     

Peroxidase-positive endothelial cells in sinusoids of the mouse liver

The cytochemical localization of endogenous peroxidase activity in sinus lining cells of mouse liver has been investigated. Kupffer cells, as identified by their exclusive ability to phagocytize large (0.8 micron) latex particles, exhibited strong peroxidase activity in nuclear envelope and endoplasmic reticulum. In addition, weak to moderate peroxidase activity was found in 57% of all endothelial cells. The enzyme in endothelial cells was also localized in nuclear envelope and endoplasmic reticulum, with a negative reaction in the Golgi apparatus. These observations indicate that peroxidase staining, as a marker for identification of Kupffer cells in mouse liver, is only of limited value and should be used in conjunction with other methods (e.g., latex phagocytosis).     

Glucagon receptors in endothelial and Kupffer cells of mouse liver

To determine whether hepatic sinusoidal cells contain glucagon receptors and, if so, to study the significance of the receptors in the cells, binding of [125I]-glucagon to nonparenchymal cells (mainly endothelial cells and Kupffer cells) isolated from mouse liver was examined by quantitative autoradiography and biochemical methods. Furthermore, the pathway of intracellular transport of colloidal gold-labeled glucagon (AuG) was examined in vivo. Autoradiographic and biochemical results demonstrated many glucagon receptors in both endothelial cells and Kupffer cells, and more receptors being present in endothelial cells than in Kupffer cells. In vivo, endothelial cells internalized AuG particles into coated vesicles via coated pits and transported the particles to endosomes, lysosomes, and abluminal plasma membrane. Therefore, receptor-mediated transcytosis of AuG occurs in endothelial cells. The number of particles present on the abluminal plasma membrane was constant if the amount of injected AuG increased. Therefore, the magnitude of receptor-mediated transcytosis of AuG appears to be regulated by endothelial cells. Kupffer cells internalized the ligand into cytoplasmic tubular structures via plasma membrane invaginations and transported the ligand exclusively to endosomes and lysosomes, suggesting that the ligand is degraded by Kupffer cells.     

Localization of cathepsin D in rat liver

Summary Light and electron microscopic localization of cathepsin D in rat liver was investigated by post-embedding immunoenzyme and protein A-gold techniques. By light microscopy, cytoplasmic granules of parenchymal cells and Kupffer cells were stained for cathepsin D. Weak staining was also noted in sinusoidal endothelial cells. In the parenchymal cells many of positive granules located around bile canaliculi. In the Kupffer cells and the endothelial cells, diffuse staining was noted in the cytoplasm in addition to granular staining. By electron microscopy, gold particles representing the antigenic sites for cathepsin D were seen in typical secondary lysosomes and some multivesicular bodies of the parenchymal cells and Kupffer cells. The lysosomes of the endothelial cells and fat-storing cells were weakly labeled. Quantitative analysis of the labeling density in the lysosomes of these three types of cells demonstrated that the lysosomes of parenchymal cells and Kupffer cells are main containers of cathepsin D in rat liver. The results suggest that cathepsin D functions in the intracellular digestive system of parenchymal cells and Kupffer cells but not so much in that of the endothelial cells.     

Changes in intracellular calcium induced by acute hypothermia in parenchymal, endothelial, and Kupffer cells of the rat liver.

Disturbances in intracellular calcium have been implicated in liver graft damage after cold preservation and warm reperfusion. Despite improvements noted with the use of calcium channel blockers, such as nisoldipine, the exact nature and cellular basis of the presumed changes in intracellular calcium as well as the actual target of these blockers remain unclear. Isolated rat parenchymal, endothelial, and Kupffer cells were cultured and changes in intracellular calcium measured in vitro after acute hypothermia (5-8 degrees C) by fluorescence imaging using FURA-2. Between 50 and 80% of parenchymal, endothelial, and Kupffer cells exhibited significant increases in baseline calcium that were gradual and sustained for the duration of acute hypothermia. Removal of extracellular calcium completely abolished the positive response of hepatocytes and diminished the proportion of responding endothelial and Kupffer cells. The calcium channel blocker nisoldipine (1 microM) slightly diminished the proportion of positive responders in parenchymal but not in endothelial or Kupffer cells. However, nisoldipine did not modify the amplitude of the calcium rise in responding cells of all types. Acute hypothermia causes calcium influx into a majority of parenchymal, endothelial, and Kupffer cells. Nisoldipine does not effectively prevent these changes in intracellular calcium. Pathways of calcium entry resistant to the drug or other than voltage-dependent calcium channels may thus be involved.     

Measurement and activity of cytosolic deoxyribonucleoside-activated nucleotidase in various cell types from rat liver and spleen

The enzyme activity was measured in hepatocytes, Kupffer cells, endothelial cells and spleen cells. Hepatocytes showed proportionality between enzyme activity and cytosol concentration, but with Kupffer cells, endothelial cells and spleen cells the specific activity decreased with decreasing cytosol concentration when the amount of cytosol protein in 250 microliters incubation mixture was below 80, 60 and 20 micrograms, respectively. The specific activities in hepatocytes, Kupffer cells, endothelial cells and spleen cells were 2, 16, 18 and 115 nmol/min per mg of cytosol protein, respectively.     

Localization of cathepsin D in rat liver. Immunocytochemical study using post-embedding immunoenzyme and protein A-gold techniques

Light and electron microscopic localization of cathepsin D in rat liver was investigated by post-embedding immunoenzyme and protein A-gold techniques. By light microscopy, cytoplasmic granules of parenchymal cells and Kupffer cells were stained for cathepsin D. Weak staining was also noted in sinusoidal endothelial cells. In the parenchymal cells many of positive granules located around bile canaliculi. In the Kupffer cells and the endothelial cells, diffuse staining was noted in the cytoplasm in addition to granular staining. By electron microscopy, gold particles representing the antigenic sites for cathepsin D were seen in typical secondary lysosomes and some multivesicular bodies of the parenchymal cells and Kupffer cells. The lysosomes of the endothelial cells and fat-storing cells were weakly labeled. Quantitative analysis of the labeling density in the lysosomes of these three types of cells demonstrated that the lysosomes of parenchymal cells and Kupffer cells are main containers of cathepsin D in rat liver. The results suggest that cathepsin D functions in the intracellular digestive system of parenchymal cells and Kupffer cells but not so much in that of the endothelial cells.     

Formaldehyde treated albumin contains monomeric and polymeric forms that are differently cleared by endothelial and Kupffer cells of the liver: evidence for scavenger receptor heterogeneity.

Formaldehyde treated albumin (F-HSA) was found to consist of a monomeric and a polymeric fraction. Both fractions were primarily endocytosed by rat liver sinusoidal cells. However, immunohistochemical staining of endocytosed material showed that the relative contribution of the endothelial and Kupffer cells in uptake of the monomer and the polymer differed significantly, with the monomer mainly having an endothelial cell- and the polymer predominantly having a Kupffer cell pattern of distribution. To directly confirm these heterogeneous patterns, we injected in vivo the 125I-labeled F-HSA fractions and isolated the endothelial and Kupffer cells by centrifugal elutriation. 73.7% of the monomeric F-HSA was found in endothelial cells and only 14.9% was found in Kupffer cells. In contrast, the polymeric F-HSA (1500 kD) was mainly endocytosed by Kupffer cells (71%), whereas the endothelial cells contributed only for 24% in hepatic uptake. In vivo studies and isolated perfused rat liver experiments showed that endocytosis of both monomer and polymer was inhibited by co-administration of polyinosinic acid, a well known inhibitor for scavenger receptors, indicating that these receptors on endothelial and Kupffer cells are mainly involved in this uptake process.     

Uridine catabolism in Kupffer cells, endothelial cells, and hepatocytes

Kupffer cells, endothelial cells, and hepatocytes were separated by centrifugal elutriation. The rate of uracil formation from [2-14C]uridine, the first step in uridine catabolism, was monitored in suspensions of the three different liver cell types. Kupffer cells demonstrated the highest rate of uridine phosphorolysis. 15 min after the addition of the nucleoside the label in uracil amounted to 51%, 13%, and 19% of total radioactivity in the medium of Kupffer cells, endothelial cells, and hepatocytes, respectively. If corrected for Kupffer cell contamination, hepatocyte suspensions demonstrated similar activities as endothelial cells. In contrast to non-parenchymal cells, hepatocytes continuously cleared uracil from the incubation medium. The lack of uracil consumption by Kupffer cells and endothelial cells points to uracil as the end-product of uridine catabolism in these cells. Kupffer cells and endothelial cells did not produce radioactive CO2 upon incubation in the presence of [2-14C]uridine. Hepatocytes, however, were able to degrade uridine into CO2, beta-alanine, and ammonia as demonstrated by active formation of volatile radioactivity from the labeled nucleoside. There was almost no detectable formation of thymine from thymidine or of cytosine, uracil, or uridine from cytidine by any of the different cell types tested. These results are in line with low thymidine phosphorolysis and cytidine deamination in rat liver. Our studies suggest a co-operation of Kupffer cells, endothelial cells, and hepatocytes in the breakdown of uridine from portal vein blood with uridine phosphorolysis predominantly occurring in Kupffer cells and with uracil catabolism restricted to parenchymal liver cells.     

The role of lysosomal enzymes in protein degradation in different types of rat liver cells

Highly purified suspensions of parenchymal, endothelial and Kupffer cells were prepared from the rat liver. The respective roles of these cell classes in the degradation of proteins was investigated by analysing the cellular distribution of two lysomal proteases. The specific arginine naphthylamidase activity was 2 times higher in Kupffer cells compared with the nearly equal activities in endothelial and parenchymal cells. The specific activity of the important endopeptidase cathepsin D in endothelial and Kupffer cells was about 12 and 36 times higher, respectively, than the activity in parenchymal cells. These results are in agreement with an important role of Kupffer and endothelial cells in the degradation of proteins and protein containing material of exogenous origin.     

The interaction of ceruloplasmin with Kupffer cells

The binding and uptake of ceruloplasmin was studied with rat liver cells using gold-labeled probes. Ceruloplasmins from either rat or sheep were used, in which different molecular conformations had been induced according to established biochemical criteria. The native protein from either species could bind not only to the endothelium, but also to Kupffer cells, at variance with previous findings. The proteins which had been converted to the conformation typical of stored molecules--which can be considered aged, but not denatured, according to standard activity and spectroscopic assays--were bound by endothelium irrespective of species, while only rat ceruloplasmin was able to bind to rat Kupffer cells. Internalization of sheep ceruloplasmin occurred with either endothelium or Kupffer cells. This property was lost with isolated suspended Kupffer cells. These findings suggest the presence of receptors for ceruloplasmin on Kupffer cells which are different from those present on endothelial cells.     

Separation of Kupffer and endothelial cells of the rat liver by centrifugal elutriation

Isolated non-parenchymal cells from rat liver were separated by centrifugal elutriation into two fractions consisting of structurally intact Kupffer and endothelial cells with purities of 91 and 95%, respectively. Purified Kupffer and endothelial cells showed nearly equal specific activities for the lysosomal enzyme acid phosphatase, whereas the specific activity of cathepsin D was about 3 times higher in Kupffer cells. It was calculated that a significant amount of the cathepsin D activity in the liver is present in the Kupffer cells.