Effect of substituted dextran derivative on complement activation in vivo

Synthesis and characterization of a new polysaccharide-graft-polymethacrylate copolymer for three-dimensional hybrid hydrogels

Hybrid materials constituted by hydrophobic and hydrophilic biocompatible macromolecules are useful for biomedical applications. In this context, a well-known acrylic monomer (methyl methacrylate) was polymerized and grafted onto the polysaccharide dextran by the use of ceric ammonium nitrate as a redox initiator in aqueous nitric acid medium. The effects of concentrations of dextran, acrylic monomer, and ceric ions on the copolymerization yields were investigated in detail. The obtained polymers were studied by solubility measurements, Fourier transform infrared spectrometry, (13)C nuclear magnetic resonance spectroscopy, and viscosimetric analysis. Interestingly, we found conditions to form transparent and homogeneous thin films or 3D structures with hybrid properties. Indeed, the copolymer, but not dextran or PMMA, could be dissolved in water/THF (20/80 v/v). The thermomechanical properties of the resulting copolymer analyzed by differential scanning calorimetry and dynamic mechanical analysis showed the occurrence of a single glass-transition temperature and a marked difference with the two homopolymers. The cytocompatibility of the copolymer with human endothelial cells was evidenced by the normal cell adhesion, proliferation, and morphology after 5 days in culture on these gels. In conclusion, this type of copolymer with hybrid properties of two biocompatible macromolecules could be of great interest as a 3D scaffold or for coating in biomedical applications.

A glycopolymer chaperone for fibroblast growth factor-2

Mono- and disaccharide-containing glycopolymers were synthesized by cyanoxyl-mediated polymerization of acrylamide with acrylate-derivatized mono- and disaccharides. We demonstrate that a glycopolymer bearing pendant, fully sulfated lactose units effectively replaces heparin and heparan sulfate as a molecular chaperone for fibroblast growth factor-2 (FGF-2). Specifically, a compound was identified that protects FGF-2 from proteolytic, acid, and heat-induced degradation, while selectively promoting growth factor and receptor dimerization. Significantly, the capacity of this heparin-mimic to promote an FGF-2 specific proliferative cell response was confirmed and suggests potential applications for this compound and related derivatives in areas related to therapeutic angiogenesis.

Heparin-like polymers modulate proinflammatory cytokine production by lipopolysaccharide-stimulated human monocytes

The search for heparin-like materials remains an intensive field of research. In this context, we studied the immunomodulatory properties of semisynthetic dextran derivatives and naturally occurring sulfated polysaccharides present in brown seaweed (fucans). In this study, we investigated the functional potencies of fucan and dextran derivatives by analyzing their effects on the release of proinflammatory cytokines by resting or lipopolysaccharide (LPS)-stimulated human monocytes and their interactions on monocyte surfaces. The results showed that fucan, dextran derivatives, and heparin differentially (1) triggered interleukin-1alpha, tumor necrosis factor alpha, interleukin-6, and interleukin-8 production by monocytes in a dose-dependent manner, (2) modulated cytokine production by LPS-stimulated monocytes, and (3) specifically inhibited the binding of biotinylated LPS to monocyte membranes. Taken together, these data indicated that fucan and dextran derivatives displayed interesting immunomodulatory effects on human blood cells that could be relevant as new drugs or biomaterial coatings. Indeed, such polysaccharides, by regulating monocyte activation, could contribute to the improved biocompatibility of implants.

Toward new biomaterials

Polymers are widely used for a large range of medical devices used as biomaterials on a temporary, intermittent, and long-term basis. It is now well accepted that the initial rapid adsorption of proteins to polymeric surfaces affects the performance of these biomaterials. However, protein adsorption to a polymer surface can be modulated by an appropriate design of the interface. Extensive study has shown that these interactions can be minimized by coating with a highly hydrated layer (hydrogel), by grafting on the surface different biomolecules, or by creating domains with chemical functions (charges, hydrophilic groups). Our laboratory has investigated the latter approach over the past 2 decades, in particular the synthesis and the biological activities of polymers to improve the biocompatibility of blood-contacting devices. These soluble and insoluble polymers were obtained by chemical substitution of macromolecular chains with suitable groups able to develop specific interactions with biological components. Applied to compatibility with the blood and the immune systems, this concept has been extended to interactions of polymeric biomaterials with eukaryotic and prokaryotic cells. The design of new biomaterials with low bacterial attachment is thus under intensive study. After a brief overview of current trends in the surface modifications of biocompatible materials, we will describe how biospecific polymers can be obtained and review our recent results on the inhibition of bacterial adhesion using one type of functionalized polymer obtained by random substitution. This strategy, applied to existing or new materials, seems promising for the limitation of biomaterial-associated infections.

Inhibition by heparin and derivatized dextrans of Staphylococcus epidermidis adhesion to in vitro fibronectin-coated or explanted polymer surfaces

The ability of Staphylococcus aureus to recognize several extracellular matrix or plasma proteins (e.g., fibrinogen, fibronectin, and collagen) promotes bacterial attachment to artificial surfaces. Whereas most S. aureus clinical isolates elaborate a wide repertoire of bacterial surface receptors' called adhesins, exhibiting specific binding of individual host proteins, S. epidermidis is lacking most of such protein adhesins. To document the interactions between S. epidermidis and various surface-adsorbed proteins, we first compared promotion of bacterial attachment by seven purified human proteins immobilized onto poly(methyl methacrylate) (PMMA) coverslips. Only two of them, namely fibronectin and fibrinogen, exhibited adhesion-promoting activities. In the presence of native heparin or two functionalized dextrans (CMDBS for Carboxy Methyl, Benzylamide sulfonate/sulfate), a dose-dependent inhibition of S. epidermidis adhesion to fibronectin-coated, but not to fibrinogen-coated surfaces was observed. The inhibitory effects of each CMDBS were much stronger than that of native heparin. In contrast, a control highly negatively charged, dextran exclusively substituted with carboxy methyl groups exerted no inhibition on S. epidermidis adhesion. To evaluate how CMDBS could interfere with S. epidermidis attachment to coverslips coated in vivo with extracellular matrix components, we also tested PMMA surfaces retrieved from tissue cages subcutaneously implanted in guinea pigs. Each CMDBS, but not heparin, strongly inhibited S. epidermidis adhesion to explanted coverslips, even in the presence of tissue cage fluid. In conclusion, fibronectin plays an important role in promoting S. epidermidis attachment to implanted biomaterials. Furthermore, S. epidermidis adhesion to fibronectin-coated or implanted biomaterials can be efficiently blocked in vitro by CMDBS.

Interactions of functionalized dextran-coated liposomes with vascular smooth muscle cells

Synthetic polymers are commonly used in the medical field as implants, polymeric drugs, or drug delivery systems. Among them, bioactive sulfated polysaccharides such as chemically modified dextrans are described to exhibit various properties including the inhibition of smooth muscle cell (SMC) growth. SMCs are key cellular components involved in the physiopathology of the vascular walls especially in atherosclerosis or after vascular surgeries. Interestingly, binding sites on vascular SMCs were already observed for an antiproliferative functionalized dextran (FDx). In this context, we hypothesized that this bioactive polymer could be used as a targeting moiety on the surface of drug delivery systems. In this work, liposomes constituted of phosphatidylcholine, phosphatidylethanolamine and cholesterol (70/10/20 mol.%) were prepared and coated with FDx hydrophobized by a cholesterol anchor (CholFDx) which penetrates the lipid bilayer during the liposome formation. The liposome interactions with SMCs were then followed using radiolabeled liposomes and fluorolabeled liposomes. Results of radioactivity on SMCs indicated higher interactions with CholFDx-coated liposomes as compared to uncoated liposomes. The fluorescence of cells incubated with fluorolabeled CholFDx-coated liposomes also evidenced the liposome binding on SMC membranes. These data demonstrated that liposomes coated with FDx interacted with vascular SMCs. Consequently, the coating with such bioactive polymers appears promising for the design of new drug delivery systems for the targeting of vascular cells.

Carboxymethyl benzylamide sulfonate dextrans (CMDBS), a family of biospecific polymers endowed with numerous biological properties: a review

The functionalized dextrans termed carboxymethyl benzylamide sulfonate dextran (CMDBS) represent a family encompassing a wide range of polymers. These soluble macromolecular compounds, which are substituted with specific chemical functional groups, are designed to interact with living systems. By analogy with glycosaminoglycan heparin, a natural highly charged anionic polysaccharide that exerts a variety of biological effects, we postulated that CMDBS compounds also possess binding sites capable of specific interactions with biological constituents, depending on the overall composition of the polymer. The synthesis and heparin-like properties of these CMDBS have been extensively investigated. Thus, it appears that dextran derivatives can mimic the action of heparin in regard to its interactions with antithrombin and serine proteases involved in blood coagulation. Other derivatives interact with various components of the immune system or with adhesive proteins such as fibronectin in modulating the proliferation of Staphylococcus aureus. Because they are able to stimulate wound healing in various in vivo models, these polysaccharides may also constitute a family of tissue repair agents because of their protecting and potentiating effects with heparin binding growth factors. Moreover, dextran derivatives in contact with cells such as endothelial cells, smooth muscle cells, or tumoral cells can affect both cell proliferation and metabolism. It appears that these bioactive polymers are also efficient tools to investigate the precise mechanism of action of individual biological activities by contrasting their mode of action to that of heparin. In addition to their numerous biological properties and biospecificity, functionalized dextrans are relatively simple to manufacture and exempt of donor contaminant, which make them attractive in a variety of clinical applications.

Liposomes coated with chemically modified dextran interact with human endothelial cells

Some liposomal formulations are now in clinical use. New applications in biology and medicine using targeted liposomes remain an intensive research area. In this context, liposomes constituted of phosphatidylcholine (PC), phosphatidylethanolamine (PE), and cholesterol (70/10/20 mol %) were prepared by detergent dialysis and coated with dextran (Dx) or functionalized dextran (FDx), both hydrophobized by a cholesterol anchor which penetrates the lipid bilayer during the vesicle formation. The coating of liposomes with these polysaccharides was performed because chemically modified dextran but not native Dx interacted with vascular cells. The liposome uptake by human endothelial cells was followed using uncoated and coated liposomes radiolabeled with a neutral lipid (3H-cholesterol) and a polar phospholipid (14C-PC). The results indicated for both radiolabels a preferential uptake by endothelial cells of FDx-coated liposomes compared to uncoated or Dx-coated liposomes. Addition to the culture medium of calcium up to 10 mM further enhanced the level and rate of incorporation of FDx-coated liposomes, whereas interaction of endothelial cells with uncoated liposomes or liposomes coated with Dx was poorly affected. Liposome membranes were then labeled with N-(lissamine rhodamine B sulfonyl)diacyl-PE and liposome uptake by endothelial cells was observed by fluorescence microscopy. The punctate intracellular fluorescence of cells incubated at 37 degrees C with fluorolabeled liposomes is indicative of the liposome localization within the endocytotic pathway of the cells. Altogether, these data demonstrate that coating of liposomes with FDx enable specific interactions with human endothelial cells in culture. Consequently, these liposomes coated with bioactive polymers represent an attractive approach as materials for use as drug delivery vehicles targeting vascular cells.

Fluorescent and radiolabeling of polysaccharides: binding and internalization experiments on vascular cells

Glycosaminoglycans (GAGs) such as heparan sulfates are complex carbohydrate polymers. These structural components of the extracellular matrix are essential for the adhesion, migration, and regulation of cellular growth. To understand the physiological role of GAGs and GAG analogues, a practical approach consists of labeling and detecting them in cell extracts, or analyzing binding domains and their distributions into the cells. We propose a convenient and reliable method for preparing and labeling amino-enriched, polysaccharides with the fluorescent derivative 5-[(4,6-dichlorotriazine-2-yl)amino]-fluorescein (DTAF). Radioiodination is then performed on the DTAF moiety. This method was applied to polysaccharides known to inhibit vascular smooth-muscle cell (SMC) proliferation such as functionalized dextrans derived from poly(alpha 1-6 glucose) and fucan, poly(L-fucose 4-sulfate) extracted from brown seaweed. Using autoradiography and confocal microscopy, we observed the fixation and internalization of labeled antiproliferative products in SMCs from rat aorta. These probes can be useful for the understanding of polysaccharide-cell interactions. In addition, the method presented here can be applied to various synthetic or natural biomedical materials.

Antiproliferative polysaccharides modulate distribution and phenotypic expression of collagens by gingival fibroblasts

Gingival fibroblasts are particularly involved in the physiologic maintenance and repair of periodontium. During these processes, cell proliferation and synthesis of a collagen-rich gingival matrix should be controlled. A dextran derivative, namely, carboxy methyl dextran benzylamide sulfonate (CMDBS), considered to be a functional analog of heparin, was previously described to regulate proliferation of different types of cells and independently to modulate the expression of collagen biosynthesis. In this report, we demonstrate that CMDBS and heparin inhibited gingival fibroblast proliferation. We then analyzed collagen biosynthesis by measuring the incorporation of the radiolabeled [3H]proline precursor into collagen by postconfluent gingival fibroblasts. Our results showed CMDBS did not alter total collagen synthesis; it induced the preferential accumulation of newly synthesized collagen into the pericellular matrix; and it decreased the expression of type III collagen, particularly in the cell layer. Taken together, our results suggest that by inhibiting cell proliferation, CMDBS could induce the synthesis of an extracellular collagenous matrix which forms a network between gingival fibroblasts.

Controlling the complement system in inflammation

Inappropriate or excessive activation of the complement system can lead to harmful, potentially life-threatening consequences due to severe inflammatory tissue destruction. These consequences are clinically manifested in various disorders, including septic shock, multiple organ failure and hyperacute graft rejection. Genetic complement deficiencies or complement depletion have been proven to be beneficial in reducing tissue injury in a number of animal models of severe complement-dependent inflammation. It is therefore believed that therapeutic inhibition of complement is likely to arrest the process of certain diseases. Attempts to efficiently inhibit complement include the application of endogenous soluble complement inhibitors (C1-inhibitor, recombinant soluble complement receptor 1- rsCR1), the administration of antibodies, either blocking key proteins of the cascade reaction (e.g. C3, C5), neutralizing the action of the complement-derived anaphylatoxin C5a, or interfering with complement receptor 3 (CR3, CD18/11b)-mediated adhesion of inflammatory cells to the vascular endothelium. In addition, incorporation of membrane-bound complement regulators (DAF-CD55, MCP-CD46, CD59) has become possible by transfection of the correspondent cDNA into xenogeneic cells. Thereby, protection against complement-mediated inflammatory tissue damage could be achieved in various animal models of sepsis, myocardial as well as intestinal ischemia/reperfusion injury, adult respiratory distress syndrome, nephritis and graft rejection. Supported by results from first clinical trials, complement inhibition appears to be a suitable therapeutic approach to control inflammation. Current strategies to specifically inhibit complement in inflammation have been discussed at a recent meeting on the 'Immune Consequences of Trauma, Shock and Sepsis', held from March 4-8, 1997, in Munich, Germany. The Congress (chairman: E. Faist, Munich, Germany), which was held in close cooperation with various national and international shock and trauma societies, was attended by about 2000 delegates from 40 countries. The major objective of the meeting was to provide an overview on the most state-of-the-art methods to prevent multiple organ dysfunction syndrome (MODS)/multiple organ failure (MOF) following the systemic inflammatory response (SIRS) to severe trauma. One of the largest symposia held within the Congress was devoted to current aspects of controlling complement in inflammation (for abstracts see: Shock 1997, 7 Suppl., 71-75). After providing the audience with information on the scientific background by addressing the clinical relevance of complement activation (G.O. Till, Ann Arbor, MI, USA) and discussing recent developments in modern complement diagnosis (J. Köhl, Hannover, Germany), B.P. Morgan (Cardiff, UK) introduced the symposium's special issue by giving an overview on complement regulatory molecules. Selected topics included overviews on the application of C1 inhibitor (C.E. Hack, Amsterdam, NL), sCR1 (U.S. Ryan, Needham, MA, USA), antibodies to C5 (Y. Wang, New Haven CT, USA) and to the anaphylatoxin C5a (M. Oppermann, Göttingen, Germany), and a report on complement inhibition in cardiopulmonary bypass (T.E. Mollnes, Bodø, Norway). The growing interest of clinicians in complement-directed anti-inflammatory therapy, and the fact that only some of the various aspects of therapeutic complement inhibition could be addressed on the meeting, has motivated the author to expand a Congress report into a short comprehensive review on recent strategies to control complement in inflammation.

Randomness and biospecificity: random copolymers are capable of biospecific molecular recognition in living systems

Biospecific molecular recognition in living systems is known to be based on the lock and key principle as proposed by Emil Fischer. Based on this concept, biospecific polymers have been produced synthetically by attaching biospecific 'keys' to the polymer chain. We postulate that biospecificity can be achieved by alternative means, namely random substitution of a preformed polymer with suitable chemical groups or random copolymerization of suitable functional monomers. Such polymers, we suggest, will contain arrangements of the chemical functions which mimic natural biospecific sites and the probability of occurrence of such arrangements will depend on the average composition of the polymer. In support of this principle, we have developed several functional random copolymer systems which possess a variety of biological properties depending on the type of chemical function. Examples are: polymers possessing anticoagulant properties similar to those of heparin; polymers which interact specifically with components of the immune system; and polymers which, in contact with cells, affect their growth and metabolism. In the case of statistical copolymers possessing 'DNA-like' properties obtained by phosphorylation of hydroxylated polystyrene derivatives, Monte Carlo simulations were used to determine the distribution of phosphodiester (PDE) groups along the chains and to compute the probabilities of occurrence of particular arrangements of PDE found in the 'DNA-like' sites. The results showed that these sites are made up of PDE groups separated by distances that closely match those between the same groups along a generatrix of the DNA double-helix cylinder. These findings offer the prospect of manufacturing polymeric biomaterials endowed with biomimetic character. Moreover, they provide the basis for a hypothesis regarding the appearance of biospecificity at the origin of life, suggesting that biospecific structures may have evolved by natural selection from purely random copolymers. It is likely therefore that biospecificity is a continuous function of randomness, arising from purely statistical distributions of reactivity and evolving into precisely defined structures such as those involved in ligand-receptor interactions.

Antiviral activity of derivatized dextrans on HIV-1 infection of primary macrophages and blood lymphocytes

The present study demonstrates at the molecular level that dextran derivatives carboxymethyl dextran benzylamine (CMDB) and carboxymethyl dextran benzylamine sulfonate (CMDBS), characterized by a statistical distribution of anionic carboxylic groups, hydrophobic benzylamide units, and/or sulfonate moieties, interact with HIV-1 LAI gp120 and V3 consensus clades B domain. Only limited interaction was observed with carboxy-methyl dextran (CMD) or dextran (D) under the same conditions. CMDBS and CMDB (1 microM) strongly inhibited HIV-1 infection of primary macrophages and primary CD4+ lymphocytes by macrophage-tropic and T lymphocyte-tropic strains, respectively, while D or CMD had more limited effects on M-tropic infection of primary macrophages and exert no inhibitory effect on M- or T-tropic infection of primary lymphocytes. CMDBS and CMDB (1 microM) had limited but significant effect on oligomerized soluble recombinant gp120 binding to primary macrophages while they clearly inhibit (> 50%) such binding to primary lymphocytes. In conclusion, the inhibitory effect of CMDB and the CMDBS, is observed for HIV M- and T-tropic strain infections of primary lymphocytes and macrophages which indicates that these compounds interfere with steps of HIV replicative cycle which neither depend on the virus nor on the cell.

Affinity chromatography of human anti-dextran antibodies. Isolation of two distinct populations

Affinity chromatography is a very efficient method for antibody purification. Two affinity chromatography supports were prepared to analyze the specificity of anti-dextran antibodies. Silica beads were grafted with native dextran or with functionalized dextran. The anti-dextran antibodies present in some human sera were analyzed by enzyme-linked immunosorbent assay method. These antibodies play an important role in severe dextran-induced anaphylactic reactions in humans by forming immune complexes with clinical dextran. The results indicated that two distinct populations of anti-dextran antibodies were purified from human serum, using dextran-coated silica beads. Elution from this support with an oligo-dextran of 4000 g/mol allowed the isolation of one population that only recognized native dextran as antigen. Functionalized dextran coated on dextran silica beads led to the purification, with a glycine-HCl buffer, of another subclass of antibodies that recognized substituted dextran derivatives. Furthermore, these antibodies could be useful tools for in vitro and in vivo investigations using dextran derivatives as bio-active polysaccharides.

Sulfonated dextran inhibits complement activation and complement-dependent cytotoxicity in an in vitro model of hyperacute xenograft rejection

In the present study, we demonstrate that a substituted soluble dextran derivative bearing 73% carboxylic groups and 15% benzylamide sulfonate groups, termed CMDBS25, inhibits complement activation and complement-mediated damage in an in vitro model of xenogeneic rejection. Incubation of porcine aortic endothelial cells with normal human serum resulted in time-dependent complement consumption as assessed by C3a generation in the fluid phase and deposition of activated complement fragments C3, C5 and of C5b-9 on target cells. The presence of C5b-9 membrane attack complex was associated with 51Cr release from prelabelled endothelial cells. The addition of 5-25 mg of CMDBS25/ml under the experimental conditions used, inhibited complement activation and C3a generation in a dose-dependent fashion. CMDBS25 (25 mg/ml) totally suppressed iC3b, C5 and C5b-9 cytolytic complex deposition on cells and inhibits by 42% lysis of target endothelial cells. Native dextran had no effect. Our observations document the anti-complementary properties of sulfonated dextran derivatives and their potential as therapeutic agents for the prevention of complement-dependent hyperacute xenograft rejection.