New heparin-like insoluble materials: part I

Heparin mimetics with anticoagulant activity

Heparin, a sulfated polysaccharide belonging to the glycosaminoglycan family, has been widely used as an anticoagulant drug for decades and remains the most commonly used parenteral anticoagulant in adults and children. However, heparin has important clinical limitations and is derived from animal sources which pose significant safety and supply problems. The ever growing shortage of the raw material for heparin manufacturing may become a very significant issue in the future. These global limitations have prompted much research, especially following the recent well-publicized contamination scandal, into the development of alternative anticoagulants derived from non-animal and/or totally synthetic sources that mimic the structural features and properties of heparin. Such compounds, termed heparin mimetics, are also needed as anticoagulant materials for use in biomedical applications (e.g., stents, grafts, implants etc.). This review encompasses the development of heparin mimetics of various structural classes, including synthetic polymers and non-carbohydrate small molecules as well as sulfated oligo- and polysaccharides, and fondaparinux derivatives and conjugates, with a focus on developments in the past 10 years.

Sulfation of silk sericin and anticoagulant activity of sulfated sericin

Silk sericin extracted from a cocoon was sulfated by chlorosulfonic acid. Sulfation of sericin was confirmed by FT-IR and the reaction efficiency was calculated as 44.9%. 1H-NMR suggested that sulfation mainly occurred at serine residues in the sericin molecule. The sulfated sericin was separated in three fractions by gel-filtration chromatography using Sephacryl S-200. The sulfate group content and amino-acid composition of each fraction were almost identical, while the anticoagulant activity differed for each fraction of sulfated sericin. Higher anticoagulant activity was observed for the higher-molecular-mass fraction. The anticoagulant activity of sulfated sericin was estimated at 1/10 to 1/20 of heparin.

Sulfation of silk fibroin by chlorosulfonic acid and the anticoagulant activity

Silk fibroin (Bombyx mori) was sulfated using chlorosulfonic acid in pyridine. FT-IR spectra showed introduction of sulfate group by this reaction; NMR spectra indicated that sulfation occurred mainly at tyrosine and serine residues. Molecular size decreased and dispersed with sulfation. The molecular weight was estimated in around 20,000 by GPC using protein standards. Amino acid composition suggested that sulfated fibroin came from H-chain of fibroin; the crystal region of fibroin molecule remained in sulfated fibroin. The amount of sulfate groups increased with overall reaction time. The maximum amount was estimated in 1.0 mmol/g by acidimetric titration. Sulfation efficiency was calculated as 66.7%. Blood coagulation was prevented by 0.5 mg of sulfated fibroin in 1 ml of blood, while original fibroin did not show any effect. Anticoagulant activity of sulfated fibroin strongly depends on the amount of sulfate groups introduced. These results indicate that sulfate group introduction results in addition of anticoagulant function to silk fibroin. Sulfated fibroin is a new type of anticoagulant material having a protein backbone.

Polystyrene derivatives substituted with arginine interact with Babanki (Togaviridae) and Kedougou (Flaviviridae) viruses

Outbreaks of new or old diseases appear primarily in tropical zones such as Africa, south and central America, or Asia. Among these diseases, those induced by Arboviruses (the best known of which are being yellow fever, dengue, Ebola, and Sindbis) are under intensive observation by the World Health Organization. Rapid isolation and identification of the viral species is the first step in the diagnosis, study, and control of epidemics. One major problem with the isolation of viruses is capturing sufficient numbers of viral particles to test. The work presented in this report addresses this question. We have tested the interaction between Babanki (Togaviridae), Kedougou (Flaviviridae) viruses, and a range of insoluble polystyrene derivatives substituted with arginine groups. Insoluble functionalized copolymers were found to develop specific interactions with viruses through chemical groups present on their surfaces. The adsorption of viruses varied according to the percentage of arginine substituted onto the polymer, with a maximum value for both viruses of about 20% of grafting rate. It was also found that the Kedougou virus displayed the highest affinity for this polymer.

Anticoagulant mechanism of sulfonated polyisoprenes

The influence of sulfonated polyisoprene (SPIP) on coagulation factors and human blood cells was investigated to elucidate and compare its anticoagulant mechanism with that of heparin. While the number of red cells was unaffected, the number of platelets decreased dramatically in the presence of SPIP due to aggregation. Using a synthetic peptide substrate to assay thrombin activity in the presence of its natural inhibitor, antithrombin (AT), we observed no stimulation by SPIP of AT-mediated inhibition. Nevertheless, thrombin cleavage of its natural substrate fibrinogen to fibrin peptide A was slightly inhibited. SPIP altered the electrophoretic mobility of fibrinogen and completely inhibited fibrinogen from clotting. We detected no significant influence of SPIP on factors II, VII, IX, and X, while factor XI and factors V and VIII were only slightly affected. Therefore, the main mechanism of SPIP's anticoagulant activity appears to be a strong interaction with fibrinogen and fibrin monomer, first, to prevent proteolytic conversion of the former to the latter and second, to inhibit polymerization of the fibrin monomer, once formed.

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.

Biospecific polymers: recognition of phosphorylated polystyrene derivatives by anti-DNA antibodies

The recognition of DNA-like phosphorylated polymers by anti-DNA antibodies from the plasma of systemic lupus erythematosus patients was evidenced a few years ago by our research group. However, the radioimmunological Farr assay used for the assessment of anti-DNA antibodies adsorption was not sensitive enough to give accurate results, particularly in the case of weak levels of antibodies. An alternative method based on the use of radiolabelled species was set up in order to check the validity of previous results. Polystyrene resins with different levels in phosphate groups substitution were assessed with regard to their interactions with anti-DNA antibodies. Results show that the anti-DNA antibodies affinity is dependent on the composition of the polymers and reaches a maximum for a composition of 17.5-22.5 mol of phosphorus per 100 mol of monomeric units. This composition corresponds to the DNA-like polymer previously described. A computer-assisted method was used in order to have an insight into the structure of the active sites responsible for the DNA-like behaviour of this polymer. Numerical simulations of the phosphorylation reaction were performed using a Monte Carlo method, taking the structure predictions and the environment of the phosphorylated units into account. A number of thus generated virtual polymers correlated with the experimental results of the adsorption of anti-DNA antibodies. The chemical structure of the active site was determined by computations introducing selected hypotheses on the structure of the phosphorylated units. Moreover, since the number of active sites is directly related to the number of adsorbed anti-DNA antibodies in the experimental results, the most probable structure of the active sites is proposed and compared to a fragment of DNA. Conclusions are that the distances between the phosphate groups in the active sites of the DNA-like polymer and in the DNA fragment are similar. Optimal conditions for the purification of SLE sera by highly specific liquid chromatography using phosphorylated polystyrene resins of precise compositions as stationary phases can thus be envisaged, as well as a new method for the detection of anti-DNA antibodies.

The engineering of biomaterials exhibiting recognition and specificity

Although synthetic materials are now widely used in implanted medical devices, they are not engineered for recognition and specificity. This article considers the design of polymer surfaces that might be specifically recognized and trigger normal healing pathways. The technological advances that will contribute to biorecognition biomaterials include surfaces to inhibit non-specific interactions, self-assembly to create ordered surface structures and strategies to place recognition sites on surfaces by random arrays of groups and by templates.

Heparin-like functionalized polymer surfaces: discrimination between catalytic and adsorption processes during the course of thrombin inhibition

Thrombus formation on blood-contacting artificial surfaces is a major problem. Antithrombogenic polymer surfaces have been obtained either by heparin binding, or by grafting sulphonate and/or amino acid sulphonamide groups on insoluble polystyrene. In addition to their capacity to adsorb thrombin, such surfaces were shown to be able to catalyse its inhibition by antithrombin III (AT), i.e. they are endowed with heparin-like activity. The results were mainly obtained by using clotting assays. In many cases, delineating adsorption and catalytic processes by such assays is not possible when evaluating anticoagulant polymer surfaces. To overcome this problem, the kinetics of thrombin adsorption and inhibitions by AT and heparin cofactor II (HC) in the presence of such surfaces have been measured by using an assay performed with a thrombin-specific chromogenic substrate. A simple kinetic model of thrombin consumption is proposed. The relevant calculations, carried out with the help of a computer program, lead to determination of relative second order rate constants of thrombin adsorption and inhibitions by AT and HC in the presence of the polymers. In addition to thrombin adsorption, polystyrene surfaces bearing only sulphonate groups catalyse inhibition by AT, whereas polystyrene surfaces bearing either aspartate, glycinate or isophthalate sulphonamide groups catalyse both inhibitions by AT and HC.

Heparin-like anticoagulant activity of sulphonated poly(ethylene oxide) and sulphonated poly(ethylene oxide)-grafted polyurethane

Sulphonated poly(ethylene oxide) (PEO-SO3) and PEO-SO3-grafted polyurethane (PU-PEO-SO3) were prepared by bulk modification and their anticoagulant and heparin-like activities were investigated. Anticoagulant activity measured by activated partial thromboplastin time of PU-PEO-SO3 displayed 2%, whereas that of PEO-SO3 itself reached 14% as compared to free heparin. In addition, the anticoagulant effects of these sulphonated polymers were not due to factor Xa inhibition but mainly thrombin inhibition. From the clotting time measurements using reptilase instead of thrombin and antithrombin III (AT III), PEO-SO3 and PU-PEO-SO3 indicated heparin-like activity which represents both prolonged thrombin time (TT) and normal reptilase time and increased TT in the presence of AT III. Thrombin was also neutralized by sulphonated polymers to a great extent. Therefore, the anticoagulant and heparin-like activities of PEO-SO3 and PU-PEO-SO3 seem to contribute to their improved blood compatibility.

Tyrosyl sulfamide derivatives as ligands for affinity adsorption of anti FVIII antibodies

Human anti factor VIII (anti FVIII) antibodies neutralize factor VIII procoagulant activity. These antibodies appear in about 5-10% of severely affected haemophiliac A patients treated with FVIII concentrates. In order to obtain non-thrombogenic materials able to interact specifically with anti FVIII, we have grafted amino acid residues which mimic part of the epitope of the FVIII molecule recognized by the anti FVIII. For this purpose, crosslinked polystyrenes functionalized with sulfonate and tyrosyl or methyl ester tyrosyl sulfamide groups have been synthesized and characterized. The in vitro removal of anti FVIII from haemophiliac patient plasma with antibodies, was performed on these different active supports. These polymers exhibit strong and selective affinity for the anti FVIII. The adsorption of the antibodies vary with the percentage of units bearing methyl ester tyrosyl sulfamide groups and present a maximum at 25% grafting rate. For the more efficient resin, the affinity constant, determined for the adsorption isotherm for the anti FVIII is about 10(9) M-1, whereas the affinity constant for the IgG in the same experimental conditions, is low (10(5) M-1). The influence of different chemical groups on the polymeric phase, on their affinity for the inhibitors was also studied. The most active resins can be selected and used in an extracorporeal circulation to reduce the concentration of anti FVIII in a blood epuration process.

Interactions of plasminogen and fibrinogen with model silica glass surfaces: adsorption from plasma and enzymatic activity studies

The adsorption of fibrinogen and plasminogen from plasma to silica glass, sulfonated silica glass, and lysine-derivatized silica glass has been investigated. The data indicate that the sulfonated material has a high affinity for both fibrinogen and plasminogen, but that the ratio of plasminogen to fibrinogen is greater on the lysine-derivatized surface. The adsorption data also suggest plasminogen as a possible contributor to the fibrinogen Vroman effect, whereby initially absorbed fibrinogen is displaced from the surface. The plasmin activity of plasminogen adsorbed to the lysine-derivatized silica glass and its sulfonated precursor was assessed by both a chromogenic substrate assay and a radioimmunoassay for the plasmin cleavage product of fibrinogen, the B beta 1-42 peptide. The data indicate that 1) the adsorbed plasminogen is not inherently plasmin-like; 2) the enzymatic activity associated with the bound plasminogen is significantly enhanced on both surfaces in the presence of activator; and 3) in the presence of activator, the plasmin activity per mole of bound plasminogen on the lysinized material is approximately a factor of two greater than on the sulfonated material based on the chromogenic substrate assay, and a factor of four greater based on the B beta 1-42 radioimmunoassay. The lysinized material thus exhibits several properties that are different from its sulfonated precursor. It adsorbs more plasminogen relative to fibrinogen after the Vroman peak, and this adsorbed plasminogen appears to be in a conformation that is more readily activated to plasmin. Once activated, the surface bound plasmin shows enhanced ability to cleave either a low molecular weight chromogenic substrate or a macromolecular substrate.(ABSTRACT TRUNCATED AT 250 WORDS)

Conformational changes of fibronectin induced by polystyrene derivatives with a heparin-like function

It was previously reported that polystyrene substituted with the sulfonate group, PSSO3, which has anticoagulant heparin-like properties, and then coated with fibronectin supports the growth of human umbilical vein endothelial cells. On the other hand, polystyrene substituted with the amino acid sulfamide group, PSSO2-Asp, which has a higher anticoagulant activity, and then coated with fibronectin no longer supported the growth of endothelial cells. We report here that, while the affinity of fibronectin to either polymer is of the same order of magnitude, fibronectin is adsorbed onto the PSSO2-Asp polymer in a different conformation compared to the PSSO3 polymer. This was shown by a higher binding of polyclonal antifibronectin antibodies to fibronectin-coated PSSO2-Asp polymer, and by a decreased susceptibility of the coated fibronectin to proteolysis by thermolysin. This study provides evidence that a solid phase substrate with a strong heparin-like function may influence the conformation and biological properties of fibronectin.

Effect of sulfonation of segmented polyurethanes on the transient adsorption of fibrinogen from plasma: possible correlation with anticoagulant behavior

The influence of polyurethane sulfonation on fibrinogen adsorption from plasma and on plasma coagulation has been investigated. Sulfonated polyurethanes were synthesized using a two-step solution polymerization in which a diamino disulfonic acid was used as chain extender, thus incorporating sulfonate groups into the hard segments. Polymer molecular weights were determined by size exclusion chromatography and weight average values were in the range of 50,000 to 200,000. Equilibrium water uptake of solid polymer specimens was substantial and was found to increase with increasing sulfonate content. Titration of sulfonate groups allowed an estimate of the retention of free sulfonate in the polymers which ranged from 50 to 85%. Loss of free sulfonate is attributed to reaction of isocyanate with sulfonate groups during chain extension. Both surface chemistry and hydrophilicity were assessed using a combination of ESCA and water contact angle measurements. The ESCA data indicate enrichment of soft segment in the surface. Contact angles show increasing hydrophilicity with increasing sulfur content. Fibrinogen adsorption from plasma to the sulfonated polyurethane surfaces was studied using radioiodine labeling. Fibrinogen surface concentration was found to increase strongly as sulfonate content increased. Fibrinogen adsorption behavior is quite different from that of conventional unsulfonated polyurethanes in the sense that the adsorption levels are much higher and there is little displacement of initially adsorbed fibrinogen (Vroman effect). The data are interpreted in terms of two mechanisms: fibrinogen uptake (i.e., absorption) into a polymer-plasma "gel" hypothesized to exist at the surface of these materials, and adsorption in the usual sense. Thrombin times of human plasma in which polymer particles were suspended were prolonged and were found to increase with increasing sulfonate content of the polymers, suggesting that sulfonate groups confer a measure of anticoagulant activity on these materials.

Anticoagulant effects of sulphonated polyurethanes

Sulphonated polyurethanes have been shown to have excellent blood contacting properties. In this paper, similar polyurethanes which are water soluble have been investigated to determine their influence on thrombus formation. These polymers were shown to delay clotting times in the following ways: by direct complex formation between the polymer and thrombin; by interference with fibrin polymerization; and by complex interactions between polymer, thrombin, plasma antiproteases and fibrinogen in plasma.

Effect of carboxylate and/or sulphonate ion incorporation on the physical and blood-contacting properties of a polyetherurethane

Propyl sulphonate and ethyl carboxylate groups were grafted on to the backbone of a polytetramethylene oxide-based polyurethane (PEU). The effects of ion type and ion content on the polymer's bulk, surface, and blood-contacting properties were evaluated. Ion incorporation disrupted the packing of the hard segment but had little effect on the overall microphase separation of the polymers. The mechanical properties of the ionomers were improved relative to the base PEU, although the carboxylate-containing ionomers were weaker than the sulphonate-containing polymers. As expected, the polymer's water absorption and surface polarity increased with increasing ion content. Dynamic and static contact angle analysis indicated that the propyl sulphonate-containing polymers were more polar than the ethyl carboxylate-containing polymers at the same ion content which is attributed to the higher ionic strength of the sulphonate ion. The carboxylate-containing polymers had no statistically significant effect on the polymer's canine ex vivo blood-contacting response. At the same ion content, propyl sulphonate incorporation significantly reduced platelet deposition for very short blood-contacting times. When both ion types were present in the polymer, the propyl sulphonate group appeared to be the primary factor determining the polymer's blood-contacting response. The polymer containing 20 mol% propyl sulphonate groups significantly reduced platelet deposition and activation while also exhibiting enhanced fibrinogen deposition.

Plasmatic antiproteinase activity enhancement by insoluble functionalized polystyrene surfaces

Antithrombogenic functional polymer surfaces have been obtained by grafting heparin or by substituting insoluble polystyrene with sulphonate and/or amino acid sulphamide groups. Their heparin-like properties have been related to their catalytic effects on the antithrombin III - thrombin complex formation. Amongst these antithrombogenic surfaces, this study demonstrates that some insoluble amino acid sulphamide derivatives of polystyrene strongly potentiate heparin cofactor II, in addition to antithrombin III. In contrast, an insoluble polystyrene sulphonate and, to a lesser extent, an insoluble heparin copolymer, are better catalysts of antithrombin III. It is hypothesized that such different behaviours result from different conformations of the species adsorbed onto the surfaces. The conclusions support the possible use of such amino acid sulphamide groups to prepare antithrombogenic surfaces in contact with blood.

Selective binding of plasmin in the presence of excess plasminogen by certain anionic polystyrene resins

Contact of plasminogen with sulfonate or sulfonyl-glutamate derivatized polystyrene resins has previously been reported to lead to the formation of an active single-chain form of the plasminogen (Kichenin-Martin et al., Thrombosis Research, 52, 469-478, 1988). Attempts to duplicate this finding revealed instead that these polymers selectively adsorb active plasmin and thus remove it even in the presence of a great excess of plasminogen. Under optimum conditions 4.0 mg/mL plasminogen containing 3% plasmin was freed of one half of this contaminant by exposure to 6-9 mg of dry resin per mL in a batch mode. Neither ordinary polystyrene nor Dowex nor Sephadex cation exchange resins displayed these properties. The separation is based on the more rapid binding of plasmin to the active resins and is thus kinetically controlled.

Affinity chromatography of fibroblast growth factors on substituted polystyrene

The heparin-binding growth factors aFGF and bFGF (acidic and basic fibroblast growth factor) from crude bovine brain extract were co-eluted with purified [125I]aFGF and/or [125I]bFGF as tracers from heparin-Sepharose and from several insoluble substituted polystyrenes used as stationary phases in low-pressure affinity chromatography. The ability of the resins to isolate FGFs was determined by measuring the eluted radioactivity. It was demonstrated that the various substituted polystyrene resins retain [125I]aFGF and [125I]bFGF with different specificities according to the chemical nature of the substituted groups bound to the polystyrene support. Bifunctional resins substituted with sulphonate and phenylalanine sulphamide groups adsorbed both [125I]aFGF and [125I]bFGF whereas bifunctional resins substituted with sulphonate and sulphamide serine adsorbed only [125I]bFGF. These stationary phases could be adapted to high-performance affinity chromatography and used to isolate growth factors of the FGF family.

Interactions of biospecific functional polymers with blood proteins and cells

Biospecific functional polymers, i.e. synthetic or artificial polymers substituted with specific chemical functional groups carried by the macromolecular chain are designed to interact with living systems. These polymers are either insoluble or soluble, derived from polystyrene and dextran. Polymers substituted with aryl sulfonate and carboxyl groups specifically interact with antithrombin III and serine-proteases involved in the coagulation of blood. As a consequence, these polymers possess heparin-like activity and are therefore of low thrombogenicity when exposed to flowing blood. Other functional polymers have been prepared in order to interact with various components of the immune system. Soluble and insoluble functional polymers in contact with cells can affect both cell proliferation and metabolism. Some functional polymers have the ability to inhibit or to stimulate cell growth while others can alter cell function without a change in growth characteristics. The functional polymers described have possible applications as plasma expanders, non-thrombogenic catheters, non-complement activating surfaces and other applications in oncology, biotechnology and immunochemistry.

Adsorption of plasma proteins onto anticoagulant polystyrene derivatives: a fluorescence study

Quenching of fluorescence was used to monitor adsorption of thrombin (T), antithrombin (AT) and their inactive complex (T-AT) onto three anticoagulant biomaterials made of polystyrene beads bearing the functional groups of heparin. An adsorption capacity of 0.12 mumol of T per mg of polymer allowed the formation of a monolayer of protein at the polymer surface. An affinity constant of 3 x 10(7) l.mol-1 between thrombin and polymer was estimated, whatever the polymer used. The affinity of T-AT was similar although weaker. Desorption of proteins from the polymeric interface by means of polycations (polybrene and polylysine) showed that the inactive complex T-AT is more quantitatively and easily released than thrombin.

Heparin-like tubings. III. Kinetics and mechanism of thrombin, antithrombin III and thrombin-antithrombin complex adsorption under controlled-flow conditions

In previous papers, we described treated tubular materials which exhibit an heparin-like antithrombic activity under dynamic conditions. In order to ascertain the heparin-like mechanism of this activity, we have studied the interactions of thrombin, antithrombin III and thrombin-antithrombin III complex with the inner face of these treated tubings under controlled-flow conditions. Moreover, the kinetics of the adsorption of thrombin were studied at different flow rates to establish the rate-determining step.

Heparin-like tubings. I. Preparation, characterization and biological in vitro activity assessment

In order to prepare tubular materials which could be used in blood-circulating medical devices, polystyrene was grafted by irradiation on to polyethylene tubings. A chemical surface treatment was used which resulted in the functionalization of the inner face of the tubing. This procedure is described and the chemical assessment of the constitution of the functionalized polymer has been completed. Tubing, the inner face of which is made of polyethylene-polystyrene copolymer in which polystyrene moieties were substituted with sulphonate and aspartic acid sulphamid groups, was tested for antithrombic properties in a circulating device under controlled transport conditions and by use of purified proteins.

Control and isotopic quantification of affinity of antithrombin III for heparin-like surfaces

Heparin-like materials, characterized by a defined superficial density of functional groups which activate antithrombin III (AT III), when in contact with blood specifically inhibit thrombin as soon as it appears. This paper describes an isotopic method to estimate this density and to visualize the distribution of the affinity sites concerned, both directly with AT III labelled with 125Iodine and indirectly with an anti AT III monoclonal antibody labelled with 111Indium.

Matrix-driven translocation: dependence on interaction of amino-terminal domain of fibronectin with heparin-like surface components of cells or particles

During the process of matrix-driven translocation, certain types of cells or polystyrene latex beads are transported between compositionally different regions of a collagen matrix. Under appropriate conditions this translocation depends on an interaction between the cell or particle surface and fibronectin. We now show that this interaction takes place at a site located within the first 31 kDa of the amino-terminal end of the fibronectin molecule. Using defined fibronectin fragments and monoclonal antibodies directed against specific fibronectin domains, this site is established as both necessary and sufficient for the promotion of matrix-driven translocation. Competition experiments using heparin, heparan sulfate, and other sulfated polysaccharides show that this fibronectin site interacts with heparin-like cell or particle surface components in promoting matrix-driven translocation. Treatment of cells with heparinase renders them unresponsive to the translocational effect. An antibody directed against the amino-terminal domain of fibronectin completely inhibits matrix-driven translocation without interfering with heparin binding, suggesting that a post-binding conformational change in fibronectin may be required for promotion of the effect.

Heparin-like activity of insoluble sulphonated polystyrene resins. Part III: Binding of dicarboxylic amino acids

It has been demonstrated previously that polystyrene sulphonate possesses anticoagulant properties and that the binding of some amino acids could enhance the heparin-like properties of such resins. These properties depend on the surface density of the active groups, the nature and binding of the group and on the net change borne by the polymer. In this paper, we describe the preparation of copolystyrene (sulphonate-dicarboxylic amino acid sulphamide) resins. By measuring their antithrombotic-surface-activity, we demonstrate that the activity developed by each carboxyl group is at least roughly the same as the activity of one sulphonate group, except in the case of aspartic acid sulphamide resin for which a cooperative effect is shown. The anticoagulant properties of resins bearing phosphonate or monocarboxylic amino acid sulphamides are also examined.

Heparin-like activity of insoluble sulphonated polystyrene resins. Part I: Influence of the surface density, nature and binding of substituted anionic groups

It was previously demonstrated that copolystyrene (sulphonate-amino acid sulphamide) resins possessed an anticoagulant heparin-like activity in the presence of blood plasma. Taking into account the variable surfaces of swollen resins developed by these dry resins, it is now shown that the antithrombic activity of crosslinked sulphonated polystyrene is linearly dependent on the surface density of the sulphonate groups. This fact implies that the presence of such isolated groups is sufficient to obtain a catalytic site for increasing the rate of inactivation of thrombin by plasmatic proteins. It is also shown that replacing sulphonate groups either by directly backbone-bonded carboxylate groups or by methionine linked by amide bonds to polystyrene backbone is not sufficient to endow the resulting resins with a significant anticoagulant activity.

Heparinizable graft copolymers from chlorosulphonated polyethylene with poly(amido-amine) segments

The synthesis and the physical characterization of three graft copolymers (PES/PAA) obtained from chlorosulphonated polyethylene (PECS) and three different secondary amino end-capped poly(amido-amine)s are reported. The properties of these heparinizable materials appear to be suitable for constructing prosthetic devices for biomedical use. The heparin adsorbing ability and the stability of the complex with heparin of the three copolymers have been evaluated, by means of biological tests, as activated Partial Thromboplastin Time (PTT) and Thrombin Time (TT).

Anticoagulant activity of dextran derivatives. Part I: Synthesis and characterization

Substituted dextrans bearing carboxymethyl and benzylsulphonate groups have been prepared. These materials exhibit an antithrombic activity correlated with the ratio of each substituent. The highest activity is obtained when the dextran derivative contains more than 50% of carboxylic acid groups and simultaneously about 15% of benzylsulphonate functions.

Interactions of human platelets with insoluble anticoagulant modified polystyrene resins

The interactions of two insoluble anticoagulant polystyrene derivatives with human platelets were studied in an in vitro system similar to a chromatography column. Blood was pumped through the column and platelets were counted before and after passage through the column. Interaction of platelets with the beads led to retention of platelets in the column. The same experiment was performed with several donors. Different pretreatments were assayed and compared for both materials: platelet poor plasma, antithrombin III-depleted platelet poor plasma and an antithrombin III solution. Platelet retention depends on the polymer composition: the material containing glutamic acid sulphamide groups, which has a larger anticoagulant activity in plasma than the materials only substituted by sulphonate groups, is always less reactive towards platelets. The differences in the effects of pretreatment on both materials can be correlated with the variations of antithrombin adsorption on the synthetic surfaces.

Preparation of an asymmetric semipermeable membrane with anticoagulant activity

In this paper we report the preparation of a new asymmetric semipermeable styrene-isoprene-styrene block-copolymer membrane. Its modification by addition of gaseous N-chlorosulphonylisocyanate alters neither its permselectivity nor its water permeability rate. This modified membrane possesses an antithrombic activity which depends on antithrombin III. The actual active surface in contact with proteins is very large because the whole macroporous underlayer is modified and accessible to the proteins.

Adsorption of purified thrombin or antithrombin III for two insoluble anticoagulant polystyrene derivatives: II. Competition with the other plasma proteins

In the preceding paper, we described results concerning the adsorption of purified thrombin and antithrombin III on two insoluble anticoagulant polystyrene derivatives. We now report similar results obtained in a plasma system. In each case, the purified protein was mixed with fresh platelet poor plasma in order to maintain the same concentrations of all the other plasma proteins. The thrombin molecule was modified by alkyl phosphorylation of the active serine site prior to mixing with plasma. The adsorption of antithrombin was found to be reduced 8 to 9 times when the protein solution was substituted by diluted plasma. In contrast, the thrombin adsorption only depends on the substituents bound on the polymeric chain. These results are supported by those of the study of the competition between purified antithrombin and albumin.