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

Preparation and characterization of the Adriamycin-loaded amphiphilic chitosan nanoparticles and their application in the treatment of liver cancer

In the present study, two nanoparticles including lactose myristoyl carboxymethyl chitosan (LMCC) and algal polysaccharide myristoyl carboxymethyl chitosan (AMCC), were obtained for hepatic-targeted Adriamycin (ADM) drug delivery systems. ADM was successfully loaded into the LMCC or AMCC nanoparticle by dialysis. The release function and liver targeting of the nanoparticles was explored, and it was revealed that ADM release from the nanoparticles was greatest at acidic pH 5.5. ADM-conjugated nanoparticles were readily taken up by HU7 human hepatocellular carcinoma cells, relative to HT22 mouse hippocampal neuron cells in vitro. In vivo, ADM-loaded nanoparticles had significant antitumor efficacy with a 62.7% inhibition rate, followed by ADM and ADM-AMCC (51.2 and 42.5%, respectively). The tissue distribution study confirmed that ADM-LMCC had an improved liver delivery efficacy, by comparison with ADM. Furthermore, a series of safety studies, including hemolysis, acute toxicity and organ toxicity, revealed that the ADM-loaded LMCC and AMCC nanoparticles had advantages over the commercially available injectable preparation of Adriamycin hydrochloride, in terms of low toxicity levels and increased tolerated dose. These results indicated that LMCC is a promising carrier for injectable ADM nanoparticle and ADM-conjugated nanoparticles may improve the efficacy of ADM by hepatic targeting.

M2-like macrophages are responsible for collagen degradation through a mannose receptor-mediated pathway

Tissue remodeling processes critically depend on the timely removal and remodeling of preexisting collagen scaffolds. Nevertheless, many aspects related to the turnover of this abundant extracellular matrix component in vivo are still incompletely understood. We therefore took advantage of recent advances in optical imaging to develop an assay to visualize collagen turnover in situ and identify cell types and molecules involved in this process. Collagen introduced into the dermis of mice underwent cellular endocytosis in a partially matrix metalloproteinase-dependent manner and was subsequently routed to lysosomes for complete degradation. Collagen uptake was predominantly executed by a quantitatively minor population of M2-like macrophages, whereas more abundant Col1a1-expressing fibroblasts and Cx3cr1-expressing macrophages internalized collagen at lower levels. Genetic ablation of the collagen receptors mannose receptor (Mrc1) and urokinase plasminogen activator receptor-associated protein (Endo180 and Mrc2) impaired this intracellular collagen degradation pathway. This study demonstrates the importance of receptor-mediated cellular uptake to collagen turnover in vivo and identifies a key role of M2-like macrophages in this process.

Induction of hepatic tissue-type plasminogen activator and type 1 plasminogen activator-inhibitor gene expressions and appearance of their translation products in the bile following acute liver injury in rats

BACKGROUND/AIMS

The plasminogen activator (PA)-plasmin system is primarily involved in fibrinolysis, but is also in the patho/physiological events in which breakdown of extracellular matrices is evoked topically. In this present study, we examined the expression of fibrinolytic factors, tissue-type PA (t-PA) and Type 1 PA inhibitor (PAI-1), in acute liver injury.

METHODS

Acute liver injury was produced in rats by the intraperitoneal administration of carbon tetrachloride (CCl(4)). Plasma aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities were measured to verify the hepatocellular damage. t-PA and PAI-1 gene expressions were measured by Northern blotting, and the cell type(s) expressing these genes was identified by in situ hybridization. t-PA and PAI-1 levels were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

A single intraperitoneal administration of CCl(4) caused severe acute parenchymatous liver injury. Both t-PA and PAI-1 gene expressions were induced by the acute liver injury, and plasma t-PA and PAI-1 concentrations were also increased. In situ hybridization studies demonstrated that the hepatocytes were the cells expressing t-PA and PAI-1 genes during the acute liver injury. t-PA was also augmented in the bile, whereas PAI-1 was decreased there.

CONCLUSIONS

t-PA and PAI-1 gene expressions are induced in the hepatocytes of rats with acute liver injury. These fibrinolytic factors induced by liver injury may play important roles in liver regeneration.

Chemical modification of hyaluronidase regulates its inhibition by heparin

Chemical modification of surface amino groups of bovine testicular hyaluronidase with aldehyde dextran was conducted. It was found that with the increase of modification degree of hyaluronidase amino groups the value of residual enzymatic catalytic activity is decreased rather monotonously. It turned out that the value of inhibition of enzyme activity by heparin considerably depends on modification degree of enzyme. This dependence is of a threshold character. Sharp conformational changes in the enzyme occurring at 70-90% degree of its modification considerably lowers heparin inhibition. The higher the degree of hyaluronidase modification, the weaker its inhibition by heparin. More completely/deeply modified derivatives of hyaluronidase (modification degree 96-100%) are practically not inhibited by heparin. Thus, chemical conjugation of hyaluronidase with aldehyde dextran regulates the value of enzyme inhibition by heparin. Hyaluronidase modification becomes an informative tool to study the mechanism of inhibition of its enzyme activity and an efficient means for the development of new therapeutic preparations improving tissue permeability during cardiovascular injuries.

The hepatic clearance of recombinant tissue-type plasminogen activator decreases after an inflammatory stimulus

We have shown that tissue-type plasminogen activator (tPA) and plasma kallikrein share a common pathway for liver clearance and that the hepatic clearance rate of plasma kallikrein increases during the acute-phase (AP) response. We now report the clearance of tPA from the circulation and by the isolated, exsanguinated and in situ perfused rat liver during the AP response (48-h ex-turpentine treatment). For the sake of comparison, the hepatic clearance of a tissue kallikrein and thrombin was also studied. We verified that, in vivo, the clearance of 125I-tPA from the circulation of turpentine-treated rats (2.2 +/- 0.2 ml/min, N = 7) decreases significantly (P = 0.016) when compared to normal rats (3.2 +/- 0.3 ml/min, N = 6). The AP response does not modify the tissue distribution of administered 125I-tPA and the liver accounts for most of the 125I-tPA (>80%) cleared from the circulation. The clearance rate of tPA by the isolated and perfused liver of turpentine-treated rats (15.5 +/- 1.3 microg/min, N = 4) was slower (P = 0.003) than the clearance rate by the liver of normal rats (22. 5 +/- 0.7 microg/min, N = 10). After the inflammatory stimulus and additional Kupffer cell ablation (GdCl3 treatment), tPA was cleared by the perfused liver at 16.2 +/- 2.4 microg/min (N = 5), suggesting that Kupffer cells have a minor influence on the hepatic tPA clearance during the AP response. In contrast, hepatic clearance rates of thrombin and pancreatic kallikrein were not altered during the AP response. These results contribute to explaining why the thrombolytic efficacy of tPA does not correlate with the dose administered.

Mannose receptor and its putative ligands in normal murine lymphoid and nonlymphoid organs: In situ expression of mannose receptor by selected macrophages, endothelial cells, perivascular microglia, and mesangial cells, but not dendritic cells

The mannose receptor (MR) has established roles in macrophage (Mphi) phagocytosis of microorganisms and endocytic clearance of host-derived glycoproteins, and has recently been implicated in antigen capture by dendritic cells (DCs) in vitro. MR is the founder member of a family of homologous proteins, and its recognition properties differ according to its tissue of origin. Given this heterogeneity and our recent discovery of a soluble form of MR in mouse serum, we studied the sites of synthesis of MR mRNA and expression of MR protein in normal mouse tissues. We demonstrate that synthesis and expression occur at identical sites, and that mature Mphi and endothelium are heterogeneous with respect to MR expression, additionally describing MR on perivascular microglia and glomerular mesangial cells. However, MR was not detected on DCs in situ, or on marginal zone or subcapsular sinus Mphi, both of which have MR-like binding activities. We also compared expression of MR to the binding of a recombinant probe containing the cysteine-rich domain of MR. We show that MR and its putative ligand(s) are expressed at nonoverlapping sites within lymphoid organs, consistent with a transfer function for soluble MR. Therefore, in addition to endocytic and phagocytic roles, MR may play an important role in antigen recognition and transport within lymphoid organs.

Human epidermal Langerhans cells express the mannose-fucose binding receptor

Sugar receptors are being increasingly implicated in host-pathogen interactions because of their specific recognition of carbohydrates of microorganisms. The aim of this study was to identify sugar receptors expressed on the surface of human epidermal Langerhans cells (LC). To this end, binding of a panel of fluorescent neoglycoproteins to human epidermal LC was analyzed by quantitative flow cytofluorometry after standardization with calibrated beads. We demonstrate that fresh human LC are the only cells isolated from healthy epidermis which express a membrane receptor specific for fucose-bovine serum albumin (BSA) and mannose-BSA. Quantitative analysis of mannose-BSA or fucose-BSA binding showed non-linear Scatchard plots, denoting the presence of high and moderate affinity binding on the LC surface. The binding parameters of these two ligands were not significantly different. Mannan, the yeast mannose-rich polysaccharide, fucose-BSA, mannose-BSA and free fucose are strong competitors of the three known ligands of the mannose receptor, i.e. fucose-BSA, mannose-BSA and fluorescein isothiocyanate dextran. The amount of mannose-BSA and fucose-BSA bound to LC was 1.5-fold higher at 37 degrees C than at 4 degrees C, suggesting an internalization process. Antibodies raised against the human macrophage mannose receptor strongly stained CD1a-positive LC but not CD1a-negative population. Taken together, our data demonstrate that fresh human LC are the only cells in the epidermis to express a fucose-mannose receptor on their surface.

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.

Receptors for plasminogen and t-PA: an update

Over the past decade, the existence of cell-surface receptors for components of the plasminogen system, t-PA, u-PA, plasminogen and plasmin, has been demonstrated. Plasminogen receptors have been detected on virtually all cell types tested, and occupancy has also been demonstrated in biological settings. Characteristic features of plasminogen receptors include their relatively low affinity and their extraordinarily high density on many cells. These receptors recognize the lysine binding sites associated with the kringles of plasminogen. Plasminogen receptors include proteins with carboxyl-terminal lysine residues (enolase and annexin II are representatives) and nonproteins, such as gangliosides. Plasminogen binding to cells enhances plasmin activity by augmenting plasminogen activation, increasing the enzymatic activity of plasmin, and protecting plasmin for inactivation by inhibitors. t-PA receptors serve two major functions, clearance and cell-surface localization. The liver is the main organ for t-PA clearance; parenchymal, endothelial and Kupffer cells are all capable of t-PA uptake. Clearance receptors on these cells are heterogeneous and include ones which recognize the carbohydrate side chains of t-PA and ones which take up t-PA: PAI-1 complexes. Receptors which recognize free t-PA also mediate liver clearance, and alpha 2-MR/LRP is a representative of this latter category. Receptors that localize t-PA on cell surfaces serve a profibrinolytic function. Vascular endothelial cells are rich in such receptors, and annexin II is a representative of these t-PA binding sites. Circulating blood cells also bind t-PA, and some of the sites on these cells are shared with plasminogen. Cells of neuronal origin are capable of binding t-PA with high affinity; and amphoterin, a protein involved in neurite outgrowth, may be a neuronal t-PA receptor. Overall, the plasminogen system is one of the most widely distributed and versatile of the cell surface-proteinase systems. By activating bound plasminogen by cell-bound plasminogen activators, the cell harnesses the broad proteolytic activity of plasmin. Cells can then utilize this activity to perform functions such as assisting in cell migration.

A mannose receptor mediates mannosyl-rich glycoprotein-induced mitogenesis in bovine airway smooth muscle cells

The putative mannose receptor (MR), previously implicated in mannosyl-rich glycoprotein-induced mitogenesis in bovine airway smooth muscle (ASM) cells, was studied to determine its properties. Specific binding of the mitogenic neoglycoprotein, mannosylated bovine serum albumin (Man-BSA) to ASM cells was saturable, with an apparent Kd = 5.0 x 10(-8) M. Cell-bound ManBSA-colloidal gold conjugate was localized by electron microscopy to clathrin-coated pits on the cell surface, and was found to undergo internalization to endosomes; this was inhibitable by weak bases and swainsonine, that also inhibited ligand-induced mitogenesis. The ASM-MR, isolated by mannose-affinity chromatography, had the same apparent molecular mass as the macrophage (Mø) MR (M(r) = 175 kD), and was immunoprecipitated by an anti-MøMR immune serum. This antiserum blocked 125I-labeled-ManBSA binding to intact ASM cells, stimulated mitogenesis, and immunolocalized the ASM-MR in cytoplasmic vesicles compatible with endosomes. A monoclonal antibody directed against the MøMR also reacted with the ASM-MR; like the polyclonal antibodies, it stimulated mitogenesis as effectively as beta-hexosaminidases. These data indicate that the ASM-MR shares a number of functional and structural properties with the MøMR and suggest that similar receptors may have different main functions in different cells.

Receptor-mediated endocytosis of plasminogen activators and activator/inhibitor complexes

Recent findings have elucidated the mechanism for clearance from the extracellular space of the two types of plasminogen activators, urokinase-type plasminogen activator (u-PA) and tissue-type plasminogen activator (t-PA), and their type-1 inhibitor (PAI-1). Activator/PAI-1 complexes and uncomplexed t-PA bind to the multi-ligand receptors alpha 2-macroglobulin receptor/low density lipoprotein receptor-related protein (alpha 2MR) and epithelial glycoprotein 330 (gp330). These receptors mediate endocytosis and degradation of u-PA/PAI-1 complex bound to the glycosyl phosphatidyl inositol-anchored urokinase receptor (u-PAR) on cell surfaces, and participate, in cooperation with other receptors, in hepatic clearance of activator/PAI-1 complexes and uncomplexed t-PA from blood plasma. The alpha 2MR- and gp330-mediated endocytosis of a ligand (u-PA/PAI-1 complex) initially bound to another receptor (u-PAR) is a novel kind of interaction between membrane receptors. Binding to alpha 2MR and gp330 is a novel kind of molecular recognition of serine proteinases and serpins.