The binding and processing of mannose-bovine serum albumin derivatives by rabbit alveolar macrophages. Effect of the sugar density

Red blood cell mannoses as phagocytic ligands mediating both sickle cell anaemia and malaria resistance

In both sickle cell disease and malaria, red blood cells (RBCs) are phagocytosed in the spleen, but receptor-ligand pairs mediating uptake have not been identified. Here, we report that patches of high mannose N-glycans (Man_5-9GlcNAc₂), expressed on diseased or oxidized RBC surfaces, bind the mannose receptor (CD206) on phagocytes to mediate clearance. We find that extravascular hemolysis in sickle cell disease correlates with high mannose glycan levels on RBCs. Furthermore, Plasmodium falciparum-infected RBCs expose surface mannose N-glycans, which occur at significantly higher levels on infected RBCs from sickle cell trait subjects compared to those lacking hemoglobin S. The glycans are associated with high molecular weight complexes and protease-resistant, lower molecular weight fragments containing spectrin. Recognition of surface N-linked high mannose glycans as a response to cellular stress is a molecular mechanism common to both the pathogenesis of sickle cell disease and resistance to severe malaria in sickle cell trait.

Mannan-coated gelatin nanoparticles for sustained and targeted delivery of didanosine: in vitro and in vivo evaluation

Macrophages of the reticuloendothelial system and brain act as major reservoir for HIV because of their long term survival after HIV infection and ability to spread virus particles to bystander CD4 positive lymphocyte cells. The objective of the present study was to investigate mannan-coated nanoparticles for macrophage targeting of didanosine. Different didanosine loaded nanoparticles were prepared using the double desolvation technique and were characterized in vitro, ex vivo and in vivo. Results of the ex vivo cellular uptake study indicated 5-fold higher uptake of didanosine from the mannan-coated nanoparticles formulation (62.5 +/- 5.4%) by the macrophages in comparison with didanosine solution in phosphate buffer saline (PBS, pH 7.4) (12.1 +/- 2.3%). The better cellular uptake from the nanoparticles formulation was further confirmed by fluorescence microscopy using hydrophilic 6-carboxyfluorescein as a marker. Results of the quantitative biodistribution study showed 1.7, 12.6 and 12.4 times higher localization of didanosine in the spleen, lymph nodes and brain, respectively, after administration of mannan-coated nanoparticles compared to that after injection of didanosine solution in PBS (pH 7.4). Results of the present study showed that the mannan-coated nanoparticles targeted didanosine to the macrophage by mannosyl receptor mediated endocytosis.

Development of cell-specific targeting systems for drugs and genes

Cell-specific targeting systems for drugs and genes have been developed by using glycosylated macromolecule as a vehicle that can be selectively recognized by carbohydrate receptors. Pharmacokinetic analyses of the tissue distribution of glycosylated proteins came to the conclusion that the surface density of the sugar moiety on the protein derivative largely determines the binding affinity for the receptors and plasma lectin. Many glycosylated delivery systems have been developed and their usefulness investigated in various settings. Galactosylated polymers, when properly designed, were found to be effective in delivering prostaglandin E1 and other low-molecular-weight drugs selectively to hepatocytes. In addition, glycosylated superoxide dismutase and catalase were successfully developed with minimal loss of enzymatic activity. A simultaneous targeting of these two enzymes to liver nonparenchymal cells significantly prevented hepatic ischemia/reperfusion injury. On the other hand, galactosylated catalase, a derivative selectively delivered to hepatocytes, effectively inhibited hepatic metastasis of colon carcinoma cells in mice. Finally, hepatocyte-targeted in vivo gene transfer was achieved by synthesizing a multi-functional carrier molecule, which condenses plasmid DNA, delivering DNA to hepatocytes through recognition by asialoglycoprotein receptors, and releasing DNA from endosomes/lysosomes into cytoplasm.

Tissue and intrahepatic distribution and subcellular localization of a mannosylated lipoplex after intravenous administration in mice

We have previously reported that, unlike a lipoplex and mannosylated (Man) lipoplex underwent gene transfer to liver nonparenchymal cells (NPC) that possess mannose receptors after intravenous administration in mice. In this study, the tissue, intrahepatic distribution, and subcellular localization of the lipoplex after intravenous administration were investigated. DC-Chol liposome was selected as a cationic liposomes. After administration of lipoplex and Man lipoplex, the high gene expression was observed in the lung and liver, respectively. After administration of [32P]Man lipoplex, about 80% of [32P]plasmid DNA (pDNA) was accumulated in the liver. As for the intrahepatic distribution, the NPC/parenchymal cells (PC) ratio of [32P]Man lipoplex was 9.64, whereas the NPC/PC ratio of [32P]lipoplex was 1.93. The radioactivity in the cytosolic fraction of liver homogenate of [111In]Man lipoplex was two-fold higher than that of [111In]lipoplex, indicating that Man liposomes facilitate the release of pDNA into the cytosolic space. However, a rapid sorting of the radioactivity from endosomes to lysosomes was observed with the [111In]Man lipoplex. Also, amplification of pDNA by PCR suggested that the Man lipoplex is more rapidly degraded within the intracellular vesicles than the lipoplex. These results suggested that modulation of its intracellular sorting could improve the transfection efficiency of Man lipoplex.

CD4-independent infection of astrocytes by human immunodeficiency virus type 1: requirement for the human mannose receptor

Human immunodeficiency virus type 1 (HIV-1) infection occurs in the central nervous system and causes a variety of neurobehavioral and neuropathological disorders. Both microglia, the residential macrophages in the brain, and astrocytes are susceptible to HIV-1 infection. Unlike microglia that express and utilize CD4 and chemokine coreceptors CCR5 and CCR3 for HIV-1 infection, astrocytes fail to express CD4. Astrocytes express several chemokine coreceptors; however, the involvement of these receptors in astrocyte HIV-1 infection appears to be insignificant. In the present study using an expression cloning strategy, the cDNA for the human mannose receptor (hMR) was found to be essential for CD4-independent HIV-1 infectivity. Ectopic expression of functional hMR rendered U87.MG astrocytic cells susceptible to HIV-1 infection, whereas anti-hMR serum and hMR-specific siRNA blocked HIV-1 infection in human primary astrocytes. In agreement with these findings, hMR bound to HIV-1 virions via the abundant and highly mannosylated sugar moieties of HIV-1 envelope glycoprotein gp120 in a Ca(2+)-dependent fashion. Moreover, hMR-mediated HIV-1 infection was dependent upon endocytic trafficking as assessed by transmission electron microscopy, as well as inhibition of viral entry by endosomo- and lysosomotropic drugs. Taken together, these results demonstrate the direct involvement of hMR in HIV-1 infection of astrocytes and suggest that HIV-1 interaction with hMR plays an important role in HIV-1 neuropathogenesis.

Inhibition of liver metastasis by targeting of immunomodulators using mannosylated liposome carriers

Mannosylated liposomes were prepared by incorporating cholesten-5-yloxy-N-(4-((1-imino-2-beta-D-thiomannosylethyl)amino)butyl)formamide (Man-C4-Chol) into small unilamellar liposomes consisting of cholesterol and distearoyl phosphatidylcholine (DSPC). The biodistribution of liposomes labeled with [3H]cholesteryl hexadecyl ether was examined in mice. The rate and extent of the hepatic uptake of those [3H]liposomes increased proportionally on increasing the mixing ratio of Man-C4-Chol. Their hepatic uptake was reduced by increasing the administered dose due to the limited number of mannose receptors. The liver uptake of [3H]Man-liposomes was preferentially mediated by liver non-parenchymal cells (NPC) and significantly inhibited by co-injection with an excess of Man-BSA, indicating the involvement of a mannose receptor-mediated mechanism in the hepatic uptake of Man-liposomes. Muramyl dipeptide (MDP), an immunomodulator, was also incorporated into the liposomes and its inhibitory effect in an experimental liver metastasis model was examined. In contrast to free MDP treatment, which showed little effect on the inhibition of metastasis, liposomal MDP significantly reduced the number of metastatic colonies in the liver. Active targeting of MDP to liver NPC by Man-liposomes resulted in more effective inhibition than delivery of MDP by liposomes without mannose. Treatment with MDP/Man-liposomes further increased the survival of the tumor-bearing mice. These results suggest that Man-liposomes are effective carriers for targeted delivery of bioactive compounds to liver NPC.

In vivo recognition of mannosylated proteins by hepatic mannose receptors and mannan-binding protein

In vivo recognition of mannosylated proteins by hepatic mannose receptors and serum mannan-binding protein (MBP) was investigated in mice. After intravenous administration, all three different (111)In-mannosylated proteins were taken up mainly by liver, and uptake was saturated with increasing doses. (111)In-Man-superoxide dismutases and (111)In-Man(12)- and (111)In-Man(16)-BSA had simple dose-dependent pharmacokinetic profiles, whereas other derivatives ((111)In-Man(25)-, -Man(35)-, and -Man(46)-BSA and (111)In-Man-IgGs) showed slow hepatic uptake at <1 mg/kg. Purified MBP experiments in vitro indicated that these derivatives bind to MBP in serum after injection, which interferes with their hepatic uptake. To quantitatively evaluate these recognition properties in vivo, a pharmacokinetic model-based analysis was performed for (111)In-Man-BSAs, estimating some parameters, including the Michaelis-Menten constant of the hepatic uptake and the dissociation constant of MBP, which correlate to the affinity of Man-BSAs for mannose receptors and MBP, respectively. The dissociation constant of Man-BSA and MBP decreased dramatically with increasing density of mannose, but the Michaelis-Menten constant of hepatic uptake of Man-BSA was not so sensitive to the change in density. This suggests that the in vivo recognition of MBP has a stronger cluster effect than that of mannose receptors. Differences obtained here are due to the unique arrangement of carbohydrate recognition domains on each mannose-specific lectin available for mannosylated ligand recognition.

Involvement of the mannose receptor in infection of macrophages by influenza virus

Influenza viruses A/PR/8/34 (PR8; H1N1), A/Aichi/68 X-31 (HKx31; H3N2), and A/Beijing/89 X-109 (BJx109; H3N2) show marked differences in their ability to infect murine macrophages, including resident alveolar and peritoneal macrophages as well as the macrophage-derived cell line J774. The hierarchy in infectivity of the viruses (PR8 < HKx31 < BJx109) resembles that of their reactivity with mannose-binding lectins of the collectin family. Since the macrophage mannose receptor recognizes the same spectrum of monosaccharides as the collectins do, we investigated the possible involvement of this receptor in infection of macrophages by influenza virus. In competitive binding studies, the binding of (125)I-labeled mannosylated bovine serum albumin to macrophages was inhibited by the purified hemagglutinin and neuraminidase (HANA) glycoproteins of influenza virus but not by HANA that had been treated with periodate to oxidize its oligosaccharide side chains. The inhibitory activity of HANA from the three strains of virus differed markedly and correlated with the infectivity of each virus for macrophages. Infection of macrophages, but not MDCK cells, by influenza virus was inhibited by yeast mannan. A variant line of J774 cells, J774E, which expresses elevated levels of the mannose receptor, was more readily infected than J774, and the sensitivity of J774E cells to infection was greatly reduced by culture in the presence of D-mannose, which down-modulated mannose receptor expression. Together, the data implicate the mannose receptor as a major endocytic receptor in the infectious entry of influenza virus, and perhaps other enveloped viruses, into murine macrophages.

Pharmacokinetic evaluation of mannosylated bovine serum albumin as a liver cell-specific carrier: quantitative comparison with other hepatotropic ligands

To assess the feasibility of mannosylated macromolecules as a liver-specific carrier system, hepatic uptake characteristics of mannosylated bovine serum albumin (Man-BSA) were pharmacokinetically investigated. After intravenous injection, 111In-Man18-BSA accumulated in the liver up to 70% of dose at 2h; the endothelial cells and Kupffer cells contributed about 66% and 21% of the uptake, respectively. In single-pass perfusion experiments using rat liver at varying inflow concentrations (0.1-2.0 microg/ml), 111In-Man18-BSA and 111In-Man33-BSA were continuously extracted by the liver and their extraction ratios decreased with the increasing inflow concentrations. The outflow curves of each 111In-Man-BSA at three concentrations were simultaneously fitted to a pharmacokinetic model including a binding to the cell surface and an internalization, by using a nonlinear regression program MULTI(RUNGE). The binding constant augmented with the increase in the number of mannose per BSA, whereas the internalization rate constant was quite comparable for both derivatives. The pharmacokinetic analysis has demonstrated that the uptake process of 111In-Man-BSA is characterized to possess fewer binding sites and a greater internalization rate in comparison with other liver-specific carriers such as galactosylated, succinylated and cationized BSAs. These results will provide useful information in designing drug targeting systems to the liver nonparenchymal cells via mannose receptors.

A Comparison of the Pharmacological Properties of Carbohydrate Remodeled Recombinant and Placental-Derived β-Glucocerebrosidase: Implications for Clinical Efficacy in Treatment of Gaucher Disease

The objective of these studies was to characterize the macrophage mannose receptor binding and pharmacological properties of carbohydrate remodeled human placental-derived and recombinant β-glucocerebrosidase (pGCR and rGCR, respectively). These are similar but not identical molecules that were developed as enzyme replacement therapies for Gaucher disease. Both undergo oligosaccharide remodeling during purification to expose terminal mannose sugar residues. Competitive binding data indicated carbohydrate remodeling improved targeting to mannose receptors over native enzyme by two orders of magnitude. Mannose receptor dissociation constants (Kd) for pGCR and rGCR were each 13 nmol/L. At 37°C, 95% of the total macrophage binding was mannose receptor specific. In vivo, pGCR and rGCR were cleared from circulation by a saturable pathway. The serum half-life (t1/2) was 3 minutes when less than saturable amounts were injected intravenously (IV) into mice. Twenty minutes postdose, β-glucocerebrosidase activity increased over endogenous levels in all tissues examined. Fifty percent of the injected activity was recovered. Ninety-five percent of recovered activity was in the liver. Parenchymal cells (PC), Kupffer cells (KC), and liver endothelium cells (LEC) were responsible for 75%, 22%, and 3%, respectively, of the hepatocellular uptake of rGCR and for 76%, 11%, and 12%, respectively, of the hepatocellular uptake of pGCR. Both molecules had poor stability in LEC and relatively long terminal half-lives in PC (t1/2 = 2 days) and KC (t1/2 = 3 days).

A Comparison of the Pharmacological Properties of Carbohydrate Remodeled Recombinant and Placental-Derived β-Glucocerebrosidase: Implications for Clinical Efficacy in Treatment of Gaucher Disease

The objective of these studies was to characterize the macrophage mannose receptor binding and pharmacological properties of carbohydrate remodeled human placental-derived and recombinant β-glucocerebrosidase (pGCR and rGCR, respectively). These are similar but not identical molecules that were developed as enzyme replacement therapies for Gaucher disease. Both undergo oligosaccharide remodeling during purification to expose terminal mannose sugar residues. Competitive binding data indicated carbohydrate remodeling improved targeting to mannose receptors over native enzyme by two orders of magnitude. Mannose receptor dissociation constants (Kd) for pGCR and rGCR were each 13 nmol/L. At 37°C, 95% of the total macrophage binding was mannose receptor specific. In vivo, pGCR and rGCR were cleared from circulation by a saturable pathway. The serum half-life (t1/2) was 3 minutes when less than saturable amounts were injected intravenously (IV) into mice. Twenty minutes postdose, β-glucocerebrosidase activity increased over endogenous levels in all tissues examined. Fifty percent of the injected activity was recovered. Ninety-five percent of recovered activity was in the liver. Parenchymal cells (PC), Kupffer cells (KC), and liver endothelium cells (LEC) were responsible for 75%, 22%, and 3%, respectively, of the hepatocellular uptake of rGCR and for 76%, 11%, and 12%, respectively, of the hepatocellular uptake of pGCR. Both molecules had poor stability in LEC and relatively long terminal half-lives in PC (t1/2 = 2 days) and KC (t1/2 = 3 days).

Antagonists of the mannose receptor and the LDL receptor-related protein dramatically delay the clearance of tissue plasminogen activator

BACKGROUND

Clinical application of tissue plasminogen activator (TPA) as a fibrinolytic agent is complicated by its rapid clearance from the bloodstream, which is caused by TPA liver uptake. The mannose receptor on endothelial liver cells and the LDL receptor-related protein (LRP) on parenchymal liver cells were reported to contribute to liver uptake.

METHODS AND RESULTS

In this study, we addressed whether TPA clearance can be delayed by inhibiting receptor-mediated endocytosis of TPA. A series of cluster mannosides was synthesized, and their affinity for the mannose receptor was determined. A cluster mannoside carrying six mannose groups (M6L5) displayed a subnanomolar affinity for the mannose receptor (Ki = 0.41 +/- 0.09 nmol/L). Preinjection of M6L5 (1.2 mg/kg) reduced the clearance of 125I-TPA in rats by 60% because of specific inhibition of the endothelial cell uptake. The low toxicity of M6L5, combined with its accessible synthesis and high specificity for the mannose receptor, makes it a promising agent to improve the pharmacokinetics of TPA. Blockade of LRP by 39-kD receptor-associated protein (GST-RAP) also inhibited TPA clearance by 60%. Finally, combined preinjection of M6L5 and GST-RAP almost completely abolished reduced liver uptake of TPA and delayed its clearance by a factor of 10.

CONCLUSIONS

It can be concluded that (1) the mannose receptor and LRP appear to be the sole major receptors responsible for TPA clearance and (2) therapeutic levels of TPA can be maintained for a prolonged time span by coadministration of the aforementioned receptor antagonists.

Lysine-based cluster mannosides that inhibit ligand binding to the human mannose receptor at nanomolar concentration

In search of synthetic high affinity ligands for the mannose receptor, we synthesized a series of lysine-based oligomannosides containing two (M2L) to six (M6L5) terminal alpha-D-mannose groups that are connected with the backbone by flexible elongated spacers (16 A). The synthesized cluster mannosides were all able to displace binding of biotinylated ribonuclease B and tissue-type plasminogen activator to isolated human mannose receptor. The affinity of these cluster mannosides for the mannose receptor was continuously enhanced from 18-23 microM to 0.5-2.6 nM, with mannose valencies increasing from two to six. On average, expansion of the cluster mannoside with an additional alpha-D-mannose group resulted in a 10-fold increase in its affinity for the mannose receptor. M3L2 to M6L5 displayed negative cooperative inhibition of ligand binding to the mannose receptor, suggesting that binding of these mannosides involves multiple binding sites. The nanomolar affinity of the most potent ligand, the hexamannoside M6L5 makes it the most potent synthetic cluster mannoside for the mannose receptor yet developed. As a result of its high affinity and accessible synthesis, M6L5 not only is a powerful tool to study the mechanism of ligand binding by the mannose receptor, but it is also a promising targeting device to accomplish cell-specific delivery of genes and drugs to liver endothelial cells or macrophages in bone marrow, lungs, spleen, and atherosclerotic plaques.

Mannose receptor dependent uptake of ricin A1 and A2 chains by macrophages

The ricin A chain, the toxic subunit of ricin, consists of two forms which differ in sugar content. The major component A1 contains one high mannose chain while the minor component A2 contains an additional high mannose chain. Endocytosis of this toxin occurs in macrophages via the mannose receptor. To study the role of the sugar residues in ricin A chain cytotoxicity, we have purified the two forms by ion-exchange chromatography. The uptake of A1 and A2 by a macrophage cell line was concentration and time dependent. The total amount of A2 internalized was approximately twice the amount of A1, indicating a higher affinity of A2 for the mannose receptor. Ricin A2 was four times more toxic to macrophages than A1, in agreement with the higher affinity of A2 compared to the A1. These experiments suggest that the high mannose chains on the A chain promote mannose-receptor-mediated endocytosis by providing the initial binding to the cell surface. Once the toxin is accumulated inside the cell however, the carbohydrates do not seem to influence intracellular transport and/or translocation of the ricin A chain into the cytoplasm.

Receptor mediated glycotargeting

Glycotargeting relies on carrier molecules possessing carbohydrates that are recognized and internalized by cell surface mammalian lectins. Numerous types of glycotargeting vehicles have been designed based on the covalent attachment of saccharides to proteins, polymers and other aglycones. These carriers have found their major applications in antiviral therapy, immunoactivation, enzyme replacement therapy and gene therapy. This review compared different types of glycotargeting agents and the lectins which have been successfully targeted to treat both model and human diseases. It may be concluded that the discovery of new mammalian lectins which endocytose their ligands will lead to the rapid development of new glycotargeting agents founded on the principles of carbohydrate-protein interactions.

Glycopeptide-albumin derivative: it preparation and histochemical ligand properties

Carrier-immobilized mono- or disaccharides and other carbohydrate structures, derived by custom-made chemical synthesis, have already proven to be valuable ligands for localizing carbohydrate-binding proteins in tissue sections. Defined purified glycopeptides, as components of neoglycoproteins, offer the possibility of increasing their structural complexity and, thereby, their receptor selectivity. To test the feasibility of this approach, the glycopeptide man6-glcNAc2-asparagine derived from ovalbumin was purified after pronase digestion. It was coupled to bovine serum albumin as carrier protein with the homobifunctional linking agent bis-(sulphosuccinimidyl)suberate to yield the diglycosylated concanavalin A-reactive product. Following biotinylation, it was used to detect mannose-specific binding sites in fixed cells of seven human leukemia or lymphoma lines and in fixed, paraffin-embedded sections of human breast cancer. In comparison to chemically mannosylated bovine serum albumin with ten sites of glycosylation or to ovalbumin, this derivative produced a similar pattern of reaction with a quantitatively lower extent of staining in most cases. Remarkably, the presence of potential endogenous ligands for the detected receptor sites was ascertained using the plant lectin concanavalin A. Thus, the conjugation of a purified, deliberately selected glycopeptide to a suitable carrier produces a histochemical tool for detecting glycopeptide-specific binding sites.

Phagocytosis in Acanthamoeba: I. A mannose receptor is responsible for the binding and phagocytosis of yeast

We have examined the initial events in phagocytosis by Acanthamoeba castellanii in order to understand this process at the molecular level and have determined that phagocytosis in this organism is mediated by a receptor which recognizes mannose-rich elements in the particle to be phagocytosed. We demonstrate that the binding and internalization of yeast particles can be inhibited by the sugars (D(+)-mannose and D(-)-fructose in a stereospecific, concentration-dependent manner. This inhibition is specific; these sugars did not inhibit the uptake of latex beads by this organism. Using mannosylated neoglycoproteins, which are much more potent inhibitors of particle binding as compared with the free sugar, we demonstrate the presence of a receptor on the amoeba cell surface which is necessary for the binding of yeast as the initial event of phagocytosis. The Acanthamoeba mannose receptor also appears to be able to mediate the delivery of soluble mannose-rich molecules to a degradative compartment such as the lysosome. Knowledge of this receptor will allow a better understanding of the molecular events of phagocytosis.

Neoglycoproteins as carriers for receptor-mediated drug targeting in the treatment of experimental visceral leishmaniasis

Methotrexate (MTX) coupled to mannosyl bovine serum albumin (BSA) was taken up efficiently through the mannosyl receptors present on macrophages. Binding experiments indicate that conjugation does not decrease the affinity of the neoglycoprotein for its cell surface receptor. The drug conjugate eliminated intracellular amastigotes of Leishmania donovani in mouse peritoneal macrophages about 100 times more efficiently than free drug on the basis of 50% inhibitory dose. Inhibitory effect of the conjugate was directly proportional to the density of sugar on the neoglycoprotein carrier. Colchicine and monensin, inhibitors of receptor-mediated endocytosis, can prevent the leishmanicidal effect of the conjugate. Antileishmanial effect of the conjugate can be competitively inhibited by mannose-BSA and mannan. In a murine model of experimental visceral leishmaniasis the drug conjugate reduced the spleen parasite burden by more than 85% in a 30-day model whereas the same concentration of free drug caused little effect. These results indicate that MTX-neoglycoprotein conjugate binds specifically to macrophages, and is internalized and degraded in lysosomes releasing the active drug to act on Leishmania parasites. These results also represent the potential for a general approach to intracellular targeting of clinical agents for macrophage-associated disorders.

Uptake and processing of glycoproteins by isolated rat hepatic endothelial and Kupffer cells

Mannose-(Man) and N-acetylglucosamine- (GlcNAc)-terminated glycoproteins are cleared from blood by carbohydrate-specific receptors present on both hepatic endothelial and Kupffer cells. It is not known whether the same receptors are present on each cell type or the relative contributions to glycoprotein metabolism made by Kupffer and endothelial cells. Here we report experiments where data from glycoprotein metabolism by purified populations of isolated rat hepatic endothelial and Kupffer cells have been analyzed by mathematical modelling and parameter estimation. Kupffer cells had significantly higher binding rate constants (k'21) than endothelial cells for agalactoorosomucoid (AGOR) and hyaluronidase, but lower k12 ('off-rate') indicating that Kupffer cells had higher affinities for Man/GlcNAc-terminated glycoproteins than endothelial receptors. Furthermore, although endothelial cells had similar affinities (k'21 and k12) for AGOR and hyaluronidase, the 'off-rate' of Kupffer cells was significantly greater for AGOR than for hyaluronidase, indicating that Kupffer cell receptors have lower affinity for AGOR. Internalization and ligand catabolic rates also differed between the two cell types. The data indicate that Kupffer and endothelial cells appear to have different Man/GlcNAc receptors and that the destination of a glycoprotein and its subsequent processing is determined by the structure of a glycoprotein's oligosaccharide.

Endocytosis of alpha 1-acid glycoprotein variants and of neoglycoproteins containing mannose derivatives by a mouse hybridoma cell line (2C11-12). Comparison with mouse peritoneal macrophages

Macrophages from various origins are known to express membrane lectins that mediate the endocytosis of mannose-bearing glycoconjugates. Most macrophage tumor cell-lines lack such receptors. In this paper we show by flow cytometry analysis that a newly generated macrophage hybridoma (2C11-12), which displays several macrophage characteristics, also expresses mannose membrane lectins, resulting in the internalization of fluoresceinylated neoglycoproteins into acidic compartments. Thioglycolate elicited mouse peritoneal macrophages and the 2C11-12 hybridomas were compared by flow cytometry with regard to the binding and endocytosis of alpha 1-acid glycoprotein (AGP) variants separated by affinity chromatography on immobilized concanavalin A. AGP C eluted specifically with methyl alpha-mannopyranoside, which contains two bi-antennary oligosaccharides, was endocytosed as mannosylated serum albumin (Man-BSA). In both types of macrophages, the fluoresceinylated ligands were internalized in acidic compartments as demonstrated by the fluorescence intensity increase upon monensin post-incubation. However the behaviour of the internalized ligands was found to be quite different. AGP C and Man-BSA were rapidly degraded by thioglycolate elicited peritoneal macrophages and excreted in the medium as small peptide fragments; conversely they remained a longer time in the 2C11-12 hybridoma.

Neo-mannosylated liposomes: synthesis and interaction with mouse Kupffer cells and resident peritoneal macrophages

In order to target liposomes to cells expressing at their surface mannose receptors, e.g. mouse Kupffer cells and peritoneal macrophages, we have developed a new synthetic strategy which allows a chemically well defined preparation of neo-mannosylated vesicles. alpha-D-Thiomannopyranoside residues, substituted with a hydrophilic spacer arm and functionalized with a sulfhydryl group, were covalently coupled to preformed large unilamellar vesicles containing 4-(p-maleimidophenyl)butyryl phosphatidylethanolamine. Liposomes, containing 15 mol% of mannosyl residues, were specifically aggregated with concanavalin A; this aggregation could be reversed by an excess of free methyl alpha-D-mannopyranoside indicating that the surface ligands were freely accessible to the lectin. The neo-mannosylated liposomes presented in vitro an increased binding to cells possessing alpha-D-mannose specific binding sites. At 37 degrees C a specific binding, up to 9-fold compared to control vesicles, was observed. These neo-mannosylated vesicles represent attractive tools for targeting bio-active molecules to macrophage-associated diseases.

Techniques for using antisense oligodeoxyribonucleotides to study gene expression

Molecular biology is providing powerful tools for cloning and sequencing genes. The more difficult task is that of ascribing functions to the specific DNA sequences that appear to code for proteins, the "open reading frames," or of regulating the expression of known genes in biological systems in order to determine their contributions to cellular functions. The classical genetic approach of making mutants is difficult in eukaryotic systems, with the exception of yeasts and viruses, and has proved of limited utility. A promising approach to this problem has been to introduce into either the in vitro assay or tissue culture system oligodeoxyribonucleotides with nucleotide sequences complementary to the protein coding or "sense" sequence, usually referred to as "antisense" oligonucleotides. The term MATAGEN (MAsking TApe for Gene ExpressioN) has also been used for these compounds, which appear to inhibit gene expression predominantly by hybridization arrest of translation. Interest in the use of antisense molecules for the study of gene expression and regulation has increased dramatically in the past few years. The demonstrated utility of the antisense oligomer in both in vitro and tissue culture assays, the increased availability of nucleotide sequence data as well as improvements in nucleic acid sequencing techniques, and the automation of synthetic procedures for their preparation have made studies using these molecules more practical. This review focuses on short oligodeoxyribonucleotides, which offer important stability and synthetic advantages over the use of antisense RNA transcripts, and is intended as an introduction to practical approaches in the use of antisense oligodeoxyribonucleotides in biological systems. For synthetic techniques, the reader is referred to the individual references cited.

Enhancement of macromolecular ligand binding by rabbit alveolar macrophages by mannose oligosaccharides and related compounds

When rabbit alveolar macrophages were incubated with 10 mM D-mannose, binding of macromolecular ligands containing D-mannose, such as bovine serum albumin modified with mannose (Man-BSA), was enhanced more than 100%, but was inhibited at higher concentrations [C.A. Hoppe and Y. C. Lee (1982) J. Biol. Chem. 257, 12831-12834]. This phenomenon was further investigated with ovalbumin-derived glycopeptide, Asn(GlcNA2,Man5), and with a wide variety of synthetic mannose oligosaccharides. The extent of enhancement is related to the fine structure of the oligosaccharide groups, but the results are complicated by concurrent inhibition exerted by these compounds. It appears that the more inhibitory a compound is, the less capable it is of exerting the enhancement effect. Thus, small mannose derivatives such as glycosides, including clustered mannosides based on tris(hydroxymethyl)aminomethane [Y. C. Lee (1978) Carbohydr. Res. 67, 509-514], and most of the biantennary mannose oligosaccharides were found to be effective in enhancing the binding of radiolabeled Man-BSA. Triantennary oligosaccharides, on the other hand, showed only a slight enhancement effect and a much stronger inhibitory effect. The effects of ligand size, valency, as well as the fine structure on enhancement are discussed.

Rat liver endothelial cells have a greater capacity than Kupffer cells to endocytose N-acetylglucosamine- and mannose-terminated glycoproteins

The capacity of rat liver Kupffer and endothelial cells to endocytose glycoproteins with N-acetylglucosamine- or mannose-terminated oligosaccharide chains was studied. For this purpose, agalactoorosomucoid, ahexosaminoorosomucoid and horseradish peroxidase were used as ligands. A reliable determination of the amount of ligand endocytosed in vivo or in vitro was made possible by using the recently developed cold pronase method for the isolation and purification of Kupffer and endothelial cells. Both cell types participated in the uptake of the ligands in vivo as well as in vitro, but their endocytic capacity was several times greater in vivo than in vitro. Under both conditions, endothelial cells possessed a greater capacity to endocytose the ligands than did Kupffer cells. Since the total number of endothelial cells in the liver is at least twice the number of Kupffer cells, the contribution of endothelial cells to the liver uptake of N-acetylglucosamine-terminated glycoproteins in vivo was estimated to be 3 to 7 times higher than that of the Kupffer cells. In vitro experiments showed that the uptake of the glycoproteins followed saturation kinetics and was strongly inhibited at 4 degrees C and in the presence of mannan. Ultrastructural investigations revealed that horseradish peroxidase was taken up by all Kupffer and endothelial cells. These results emphasize the important role liver endothelial cells play in the clearance of specific glycoproteins from the circulation.

A human IgM M-protein in a patient with unknown bleeding disorder binds to beta-galactosyl and beta-glucosyl residues

In a patient with an unknown bleeding disorder and an IgM lambda paraproteinemia, we demonstrated by thin-layer chromatography immunostaining and enzyme-linked immunosorbent assay that this protein specifically bound to a number of glycolipids and glycoproteins which have terminal beta-galactosyl or beta-glucosyl residues. Binding to galactosylceramide or glucosylceramide was inhibited by both galactosylceramide and glucosylceramide. From these studies, it is apparent that the M-protein recognized both beta-galactosyl and beta-glucosyl residues. This M-protein was also shown to prolong the partial thromboplastin time of normal plasma. Thus, this case represents an example of anti-carbohydrate specificity of an IgM M-protein in association with a spontaneous bleeding disorder.

Preparation of a high-affinity photolabeling reagent for the Gal/GalNAc lectin of mammalian liver: demonstration of galactose-combining sites on each subunit of rabbit hepatic lectin

On the basis of the knowledge that the D-galactose/N-acetyl-D-galactosamine-specific lectin of rabbit liver can tolerate a large group on the C-6 hydroxyl group of a galactoside [Lee, R. T. (1982) Biochemistry 21, 1045-1050], we prepared a high-affinity photolabeling reagent for this lectin from a triantennary glycopeptide fraction of asialofetuin. The C-6 hydroxyl group of a D-galactopyranoside was converted, under mild conditions, into a primary amino group. The procedure involves conversion of the hydroxyl group to an oxo group with galactose oxidase, followed by reductive amination using benzylamine and sodium cyanoborohydride. Catalytic hydrogenolysis of the benzylamino derivative yielded the desired 6-amino-6-deoxy-D-galactoside. A 4-azidobenzoyl group was attached to the newly produced amino group to yield a photoactivatable affinity-labeling reagent. The reagent labeled the Triton-solubilized, purified hepatic lectins of rabbit and rat in a photo- and affinity-dependent manner. All the polypeptide subunits of the lectins were labeled, indicating that each subunit contains at least one D-galactose-combining site. In the case of the rabbit hepatic lectin, the minor subunit (46 kDa) was labeled more efficiently than the major one (40 kDa).

Ultracryotomy for the study of unfixed membranes

Plasma membranes from chromaffin cells of bovine adrenal medullae and from chicken macrophages were isolated on a urografin density gradient, frozen and sectioned without previous chemical fixation. Their receptor binding sites were localized by specific labelling. The sections were then post-fixed in the presence of K2Cr2O7 to produce positive staining of the membrane proteins. Chromaffin cell membranes formed single vesicles. The nicotinic acetylcholine receptor (localized using a monoclonal antibody against its cholinergic binding site) was always found in patches on the surface of vesicles, whose profiles corresponded to thickened bilayers. Macrophage membrane vesicles were agglutinated. The mannose receptor (localized using the ligand, mannosylferritin) was randomly distributed within the electron-dense coat of the agglutinated vesicles or on electron-dense caps involved in agglutination. The binding sites of both receptors were intact, as revealed by their being recognized by a monoclonal antibody against their cholinergic binding sites and by the active binding of the mannosylated ligand which was inhibited by mannan. The distribution of the receptors on the vesicles reflected their distribution on the cell surface.

High-mannose structure of apolipoprotein-B from low-density lipoproteins of human plasma

Human plasma low-density lipoproteins were purified by flotation followed by gel filtration. The protein moiety of the lipoproteins, apolipoprotein-B, which was detected by polyacrylamide gel electrophoresis as the only protein component, contained 4.4% (by weight) carbohydrate. Glycopeptides liberated from apolipoprotein-B by pronase were fractionated by affinity chromatography on concanavalin-A--Sepharose. The results indicated that high-mannose glycopeptides interacting strongly with the lectin comprise about 37% of the total monosaccharides of apolipoprotein-B. Thus, as compared to the total serum glycoproteins having about 5% of their monosaccharides in high-mannose glycopeptides, low-density lipoproteins are relatively enriched in these structures amounting up to about 10% of the total high-mannose oligosaccharides in serum. The rest of the carbohydrates in low-density lipoproteins are suggested to be mainly biantennary acidic oligosaccharides interacting weakly with concanavalin A. The oligomannosidic chains from native low-density lipoproteins and isolated glycopeptides were released by digestion with endo-beta-N-acetylglucosaminidase H. Thin-layer chromatography of the released oligosaccharides indicated that apolipoprotein-B contains five different oligomannosidic structures varying in the number of the mannose residues from Man5GlcNAc to Man9GlcNAc. Separation of the per-O-benzoylated high-mannose oligosaccharides by high-pressure liquid chromatography revealed the same polymeric structures in a molar ratio (from Man5 to Man9) of 10:2:3:2:3. Apolipoprotein-B in low-density lipoproteins was calculated to contain five high-mannose chains in total. The different high-mannose oligosaccharides liberated by endo-beta-N-acetylglucosaminidase H were isolated with high-pressure liquid chromatography after reduction with NaBH4, and subjected to methylation analysis with gas-liquid chromatography--mass spectrometry. The data of these studies and the results of exoglycosidase treatment suggest the following structure for the main high-mannose oligosaccharide: (formula: see text) The higher polymeric structures are composed of chains in which the Man5GlcNAc structure is continued by one to four Man(alpha 1-2) residues.

Different modes of ligand binding to the hepatic galactose/N-acetylgalactosamine lectin on the surface of rabbit hepatocytes

A study of the binding of three different 125I-labeled, galactose-terminated ligands to the hepatic galactose/N-acetylgalactosamine-specific lectin found on the surface of rabbit hepatocytes revealed that the different ligands manifest different physical parameters of binding. Asialoorosomucoid (125I-ASOR) binding was best described as involving two independent classes of binding sites on rabbit hepatocytes, with 161 000 sites/cell with a dissociation constant of 0.44 nM and 292 000 sites/cell with a Kd of 9.7 nM. Asialotriantennary glycopeptide purified from human alpha-1 protease inhibitor and modified with tyrosine at the N-terminus to permit radioiodination (TRI) [Lee, Y. C., Townsend, R. R., Hardy, M. R., Lönngren, J., Arnarp, J., Haraldsson, M., & Lönn, H. (1983) J. Biol. Chem. 258, 199-202] was also found to bind to two apparent classes of binding sites but with different binding parameters: 292 000 sites/cell of Kd = 1.47 nM and 982 000 sites/cell of Kd = 25.3 nM. A synthetic ligand, alpha,beta-diaspartamide of tris[(beta-lactosyloxy)methyl](6-aminohexanamido)methane (di-tris-lac) containing six nonreducing galactose residues [Lee, R. T., Lin, P., & Lee, Y. C. (1984) Biochemistry 23, 4255-4261], was found to bind to 817 000 sites/cell of Kd = 0.63 nM and 1.23 X 10(6) sites/cell of Kd = 25.3 nM. Thus, there were many more total binding sites for TRI or di-tris-lac on the surface of rabbit hepatocytes than there were for asialoorosomucoid, although the dissociation constants were similar for all three ligands.(ABSTRACT TRUNCATED AT 250 WORDS)