Interactions between Human Plasma Proteins and Heparin-Poly(Methyl Methacrylate) Copolymer

A solid Heparin-PMMA copolymer has been synthetized by a radical polymerization of methyl methacrylate from oxidative reaction initiated by Ce4+ ions in the presence of heparin. Covalently linked heparin was 10% of copolymer weight. The antithrombin activity of the copolymer corresponded to 1% of grafted heparin. PMMA sequence of the copolymer played the leading role in fibrinogen, immunoglobulins, transferrin and albumin adsorption. These proteins adsorbed on the copolymer, showed different competitive desorption pattern in the presence of whole plasma: fibrinogen presented the highest degree of affinity for the copolymer. The heparin part of the copolymer was responsible for antithrombin III adsorption and for decrease of factor V activity. Active antithrombin III was eluted. An inactivation of factor V in plasma was observed using high concentrations of soluble heparin. This result suggested that copolymer heparin chains, even devoid of antithrombin activity, were involved in this inactivation. With Heparin-PMMA copolymer, plasma clotting pro-enzymes behaved differently than on heparin-sepharose copolymer: disappearance of factor XI activity, decrease in prekallikrein activity and activation of factor IX were observed. PMMA sequences were responsible for factor IX activation.

Mechanism of factor IXa inhibition by antithrombin in the presence of unfractionated and low molecular weight heparins and fucoidan

Heparin exerts its anticoagulant activity by catalysing the inhibition of coagulation proteases by antithrombin (AT). Its main target is thrombin but it also catalyses the inhibition of the other serine-proteases of the coagulation cascade, such as factor IXa (fIXa). The aim of this study was to compare the catalysis of inhibition of blood fIXa by antithrombin in the presence of several sulfated polysaccharides with anticoagulant activity, i.e. heparin, three widely used in therapeutics low molecular weight heparins (LMWH) and fucoidan. Plots of the second-order rate constants of the fIXa-antithrombin reaction vs. the concentration of added heparin and LMWH are bell-shaped and fit the kinetic model established for thrombin-antithrombin reaction by Jordan R., Beeler D., Rosenberg R. (1979) J. Biol. Chem., 254, 2902-2913. In the ascending branch, the catalyst (C) binds quickly to the inhibitor (I) to form a catalyst-inhibitor (CI) complex which is more reactive towards the enzyme (E) than the free inhibitor, leading to the formation of an inactive enzyme-inhibitor complex (EI) and the release of free catalyst, in a rate-limiting second step. After a maximum corresponding to an optimal catalyst concentration, the decrease in the reaction rate was in keeping with the formation of a catalyst-enzyme (CE) complex, whose inactivation by the CI complex was slower than that of the free enzyme. Maximum second-order rate constants for the inhibition of fIXa by AT were 105, 6.8, 12.24 and 22 microM-1 min-1 with heparin, Enoxaparin, Fraxiparin and Fragmin, respectively, leading to 3500-, 225-, 405- and 728-fold increases in the inhibition rate in the absence of polysaccharide, respectively. Fucoidan yielded 23-fold increase in the fIXa-antithrombin interaction rate. The kinetic profiles obtained with this polysaccharide exhibited ascending branch which correlated well with the kinetic model based on the formation of binary complexes (CI or CE). Fucoidan was covalently conjugated with a fluorescent probe (DTAF) and used in conjunction with fluorescence anisotropy to follow its binding to antithrombin, heparin cofactor II (HCII), thrombin and fIXa. The binding of fucoidan to these proteins occurred with low affinities when compared to heparin and LMWH. Fucoidan had higher affinity for the inhibitor HCII compared to antithrombin and enzymes. These data suggest that binding of heparins and fucoidan to the inhibitor (CI) is required for the polysaccharide-dependent enhancement in the rate of neutralization of the enzyme by the inhibitor.

Anticoagulant activity of dextran derivatives

Carboxymethyl dextran benzylamide sulfonate/sulfates (CMDBS) are synthetic polysaccharides with anticoagulant activity. We synthesized eight different highly substituted CMDBS and one CMDSu. We studied both their anticoagulant activity and the catalysis of thrombin (T) inhibition by heparin cofactor II (HCII) and antithrombin (AT) in the presence of these dextran derivatives relative to heparin and dextran sulfate (DXSu). The anticoagulant activity of CMDBS was due both to direct thrombin inhibition and to catalysis of thrombin inhibition by HCII. The anticoagulant and catalytic activities of CMDBS were related mainly to their molecular weight and sulfate content. The interaction of the dextran derivatives with thrombin does not involve the active site of the enzyme. A kinetic study showed that all the CMDBS exhibited higher affinity for thrombin than heparin did but lower affinity than DXSu did, suggesting that the benzylamide and sulfate groups potentiate the interaction between the dextran derivatives and thrombin. This study shows that the mechanism by which the dextran derivatives inhibit thrombin is original and is related to preferential interaction with thrombin; this both inhibits the clotting activity of the enzyme and increases the reaction rate of thrombin inhibition by HCII.

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.

Fractionation of RNA polymerase II transcription factors from HeLa cell nuclear extracts by affinity chromatography on "DNA-like" phosphorylated polystyrene

It was previously shown that phosphorylated cross-linked polystyrene derivatives specifically interacted with anti-DNA antibodies and anti-phospholipid antibodies present in the sera of systemic lupus erythematosus patients. These resins are potential candidates as stationary phases in affinity chromatography. We wondered whether these biospecific resins might allow the fractionation of DNA binding proteins such as RNA polymerase II transcription factors from HeLa cell nuclear extracts. Indeed, these proteins play a major role in gene regulation in mammalian cells and their purification still requires numerous steps. To study the biospecificity of DNA-like phosphorylated polystyrene derivatives, ethanolamine sulfamide crosslinked polystyrene derivatives were phosphorylated at various rates and HeLa cell nuclear extracts were adsorbed on these resins. Adsorbed proteins were eluted with increasing concentrations of aqueous potassium chloride. Collected fractions were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and the biological activities of the eluted transcription factors were tested by in vitro transcription assay. Results showed that the elution of transcription factors depended on the substitution rate in phosphoester groups of the resins. It appears that specific interactions were developed between the polymers and the transcription factors. Moreover, the eluted transcription factors kept their biological activity. These results lead us to propose the purification of RNA polymerase II transcription factors using the phosphorylated polystyrene resins as stationary phases.

Biospecific interactions of vitamin K-dependent factors with phospholipid-like polystyrene derivatives. Part II: factor IX

We previously demonstrated that phosphorylated polystyrene derivatives exhibit phospholipid-like behaviour and therefore are able to interact with factor II, one of the vitamin K-dependent coagulation factors. Under the same conditions as for factor II, we examined the interactions of factor IX with phosphorylated resins of various compositions in phosphate groups: these studies were carried out with or without albumin precoating of the polymers and either in the presence or absence of calcium ions. Adsorption experiments show that, in the absence of calcium ions, only one class of adsorption sites of factor IX can be evidenced with the interactions taking place through the formation of binary complexes, whereas in the presence of calcium ions, the affinity of factor IX for phosphorylated resins becomes very high and two types of adsorption sites have been evidenced with biospecific ternary complexes being formed. The domains of predominance of these complexes were determined. Moreover, the only functional groups borne by the phosphorylated polystyrene resins involved in factor IX-polymer interactions are phosphodiester groups. Comparison between factor II and factor IX adsorption onto the same polymers leads to the conclusion that the observed differences probably reflect the differences in the Gla domains of the vitamin K-dependent factors. Finally, this study demonstrates that phosphorylated polystyrene derivatives can be used as stationary phases for purification of factor IX by highly specific liquid biochromatography.

Randomly phosphorylated polystyrene derivatives interact with RNA polymerase II transcription factors: part I

Insoluble functional synthetic random copolymers are able to develop at their surfaces specific interactions with biologic components. Crosslinked phosphorylated polystyrene derivatives were previously shown to mimic DNA antigen because they interacted with anti-DNA antibodies found in the sera of systemic lupus erythematosus patients. These biospecific surfaces were postulated to be able to bind other DNA-binding proteins such as RNA polymerase II transcription factors. Indeed, these proteins play a major role in gene regulation in mammalian cells. This hypothesis was checked by adsorption and elution of HeLa cell nuclear extracts on a 72% phosphorylated resin. The composition of the eluted fractions were analyzed by electrophoresis, and the biologic activity of the transcription factors was tested using an in vitro transcription assay. The results showed that USF, TATA-binding protein (TBP), and TFIIB were specifically adsorbed on the polymer and that all eluted factors kept their biologic activity. Therefore, randomly phosphorylated polystyrene derivatives may be useful for the fractionation of RNA polymerase II transcription factors.

Mechanism of thrombin inhibition by heparin cofactor II in the presence of dermatan sulphates, native or oversulphated, and a heparin-like dextran derivative

The kinetics of thrombin inhibition by heparin cofactor II (HC II) in the presence of dermatan sulphates, native (DS), or oversulphated (DSS 1 and DSS 2) and a biospecific dextran derivative substituted with carboxymethyl, carboxymethyl-benzylamide and carboxymethyl benzylamide-sulphonate functional groups (CMDBS), has been studied as a function of the sulphated polysaccharide concentration. The initial HC II and thrombin concentrations were set at equimolar levels. Analysis of the experimental data obtained for DS, DSS1 and DSS2 was performed using a previously described model which allows computation of the dissociation constant (KPS,HC) of the polysaccharide-HC II complex and the rate constant of thrombin inhibition by the polysaccharide-HC II complex (k). A KPS.HC of 9.6 x'10(-7) M and a k of 4.5 x 10(9) M-1 min-1 were found for DS, whereas KPS,HC 2.1 x 10(-6) M, k 1.1 x 10(10) M-1 min-1 and KPS,HC 4.3 x 10(-7) M, k 1.4 x 10(10) M-1 min-1 were found for DSS1 and DSS2, respectively. Knowing that DSS1 has a sulphur content per disaccharide of 7.8%, compared with 11.5% for DSS2, these results indicate that the polysaccharide affinity for HC II is increased only in the case of DSS 2, whereas the oversulphation increases the reactivities towards thrombin of both complexes DSS1-HC II and DSS2-HC II. A better conformation of these complexes may favour a faster interaction with the protease. Unlike heparin, DS at concentrations higher than 10(-5) M does not modify the reaction rate of thrombin inhibition, a fact which can be explained by the absence of complex formation between DS and thrombin. The experimental data obtained for CMDBS fit a kinetic model in which the biospecific dextran derivative rapidly forms a complex with thrombin which is more reactive towards HC II than the free protease. The reaction rate remained unchanged for CMDBS concentrations equal to or higher than 10(-5) M, whereas CMDBS was found to interfere strongly with the fibrinogen-thrombin interaction. These data suggest that CMDBS has a strong affinity for the protease and no affinity for HC II. The computed dissociation constant of the CMDBS-thrombin complex (KPS,E) was 2.4 x 10(-7) M and the rate constant of the reaction of this complex with HC II (k) was 1.7 x 10(8) M-1 min-1. These findings indicate that CMDBS exerts its catalytic effect through a unique mechanism of action and may constitute a new class of anticoagulant drugs.

Mechanism of thrombin inhibition by antithrombin and heparin cofactor II in the presence of heparin

The kinetics of thrombin inhibition by antithrombin (AT) and heparin cofactor II (HC II) were analysed as a function of the heparin concentration, from 10(-9) to 10(-4) M. The initial concentrations of inhibitor (l) and thrombin (E) were set at equimolar levels (CI = CE = 10(-8) M). The experimental data indicate that the reaction of thrombin inhibition was second-order both in the absence and in the presence of heparin, and that the apparent rate constant increased at heparin concentrations ranging from 10(-9) to 10(-6) M and decreased at higher concentrations. The data fit with the kinetic model established by Jordan et al. [J. Biol. Chem. 1979, 254, 2902-2913] for the catalysis of the thrombin-AT reaction by a low-molecular-weight heparin fraction. In this model, heparin (H) binds quickly to the inhibitor (I) and forms a heparin-inhibitor complex (HI), which is more reactive than the free inhibitor towards thrombin, leading to the formation of an inactive inhibitor-thrombin complex (I*E) and the release of free heparin, in a second step which is rate limiting. KH,I, the dissociation constant of HI, and k, the second-order rate constant of free thrombin inhibition by HI, were found to be 3.7 x 10(-7) M and 1.3 x 10(9) M-1 min-1, respectively, for AT, compared to a KH,I of 2.0 x 10(-6) M and k of 6.4 x 10(9) M-1 min-1 for HC II. These data indicate that heparin-HC II complex reactivity is greater than that of the heparin-AT complex towards thrombin, whereas heparin affinity is stronger for AT. At heparin concentrations higher than 10(-6) M, the decrease in the reaction rate was in keeping with the formation of a heparin-thrombin complex (HE), whose inactivation by the heparin-inhibitor complex (HI) is slower than that of the free protease.

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.

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.

Silicone derivatives for contact lenses: functionalization, chemical characterization, and cell compatibility assessment

Epoxy ring-opening functionalization of polymers at random sites along chains with various chemical groups has been demonstrated. The reaction is performed in an aqueous solution under mild conditions in order to minimize degradation of the macromolecular chains. Silicone lenses made of copolymers with epoxy side chains were functionalized with 4-hydroxybutyric acid, sodium salt. The carboxylated silicone derivatives were characterized by ESCA and radiotracers. A mean value of 30% reaction yield was concluded, based upon data from both methods; nevertheless, the latter can be improved up to 50% or more if the conditions of preparation of the epoxydized silicone lenses are optimized. Derivatized silicones were coated in the wells of culture plates to evaluate the cell compatibility of these new polymers with a fibroblast cell line (McCoy's). No cellular toxicity was observed.

Activation of the complement system by polysaccharidic surfaces bearing carboxymethyl, carboxymethylbenzylamide and carboxymethylbenzylamide sulphonate groups

Substituted Sephadex derivatives bearing carboxymethyl (CM), CM-benzylamide (CMB), CM-propylamide (CMP) and CMB-sulphonate (CMBS) groups are used as models of polysaccharidic surfaces to measure the effects of substituting OH groups on the complement activating capacity (CAC) of the modified surfaces in normal human serum. CM substitution decreases and can suppress the CAC of Sephadex. Low CMB substitution also decreases the CAC, whereas high CMB or CMP substitutions increase it again after a minimum. In addition to C3 cleavage occurring at high substitution with CMB or CMP groups, the presence of CMB induces consumption of a protein, limiting CH50 measurements. The CAC variations could be due to rearrangements of the polymer surfaces at the aqueous interface with proteins. Highly substituted CMB-bearing surfaces could activate complement-like polystyrene surfaces. The presence of CMBS groups does not reduce the CAC of the surface. Such polymer surfaces, which are heparin-like concerning coagulation, are not heparin-like concerning complement inhibition.

RINm5F cell culture on Sephadex derivatives

Interactions between polystyrene sodium sulfonate and insulin-secreting RINm5F cells have been previously described. When cultured on these microcarriers, cells exhibited normal growth, altered morphology, and inhibition of the insulin secretion was observed. For the sake of comparison, interactions of RINm5F cells with Sephadex derivatives, namely, carboxymethyl Sephadex (CM Seph), benzylaminated CM Seph (CMB Seph), and sulfonated CMB Seph (CMBS Seph), as well Sephadex, were studied. Cells attached poorly and did not spread onto Sephadex and CM Seph microcarriers, but all other characteristics were normal. In contrast, with cells cultured on CMB Seph and CMBS Seph microcarriers cell attachment, morphology, and growth rate were comparable to those of cells grown on classic plastic wells. But, in the latter case, surprisingly, insulin secretion was enhanced. This effect is composition of the microcarriers dependent. The insulin secretion per cell-microcarriers composition relationship suggests a specific interaction between an unknown membrane receptor of RINm5F cells and a composite ligand site made of a combination of different chemical functional groups present at the microcarriers surface.

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.

Human umbilical vein endothelial cell culture on heparin-like microcarriers

Biospecific functional polymers, i.e., polymers randomly substituted with specific chemical functional groups, were designed to interact with living systems. Interactions between polystyrene sodium sulfonate (PSSO3Na) and insulin secreting RINm5F cells have been previously described. For the sake of comparison, interactions of PSSO3Na with human umbilical vein endothelial cells (HUVEC) were studied. In this case, the interaction is indirect, i.e., mediated by a binding protein, fibronectin (Fn). This was evidenced by HUVEC culture on Fn precoated PSSO3Na microcarriers. The interactions between PSSO3Na and HUVEC result in a biologically normal proliferation of cells and synthesis and secretion of Von Willebrand Factor (VWF). These results show that different biospecific interactions may occur between cells in culture, binding proteins and polymers randomly substituted with suitable functional groups. HUVEC, when cultured on heparin-like microcarriers, behave differently from other cells like RINm5F, whose interaction with the same polymers is not mediated by binding proteins.

Regulation by sulphonate groups of complement activation induced by hydroxymethyl groups on polystyrene surfaces

Reducing the complement-activating capacity of a polymer surface is important in improving its blood compatibility. Polystyrene surfaces bearing hydroxymethyl (CH2OH) groups activate the alternative pathway of complement. This activation depends strongly on the density of the groups. Polystyrene surfaces bearing sulphonate (SO3-) groups adsorb proteins, resulting in an apparent activation. Polystyrene surfaces bearing both types of groups in close proportions are not activators in human serum, due to the adsorption of a protein of the alternative pathway, which has a protecting effect, not found when a polymer surface bearing hydroxyl groups is mixed in serum with another polymer surface bearing SO3- groups. In the presence of purified proteins of alternative pathway, C3 convertase activity can be created on each of these surfaces by deposition of C3b, but their susceptibility to inactivation by regulatory proteins H and I depends on the types of chemical groups present on the surface and whether the surfaces were passivated or not before C3b deposition.

Complement activation and adsorption of protein fragments by functionalized polymer surfaces in human serum

The interactions between blood and polymer surfaces used in extracorporeal circulations result in variable activations of the immune system of complement. Measuring concentrations of C3a or C5a in supernatant blood or serum after contact with the surface has been the most usual way of assessing this activation. Most polymer surfaces bearing various chemical groups were found to adsorb C3a and sometimes C5a. After taking into account adsorption, a good correlation was found between total C3a generated and CH50 units consumed by most of the polymer samples tested. Measuring only C3a remaining in the fluid phase should not be considered sufficient to conclude that a material surface is not an activator of complement.

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.

Insoluble DNA-like phosphorylated polystyrene: specific interactions with anti-DNA antibodies from systemic lupus erythematosus patients

Systemic lupus erythematosus (SLE) is an autoimmune disease. Antibodies directed mainly against DNA and/or phospholipids are present in the serum of SLE patients. Therefore phosphorylated polystyrene derivatives acting as DNA-like polymers should be able to interact with the SLE anti-DNA antibodies. Such functional polymers were synthesized and subsequently their interactions with the anti-DNA antibodies studied. Adsorption experiments performed with both anti-DNA antibodies and normal immunoglobulins showed high affinity constants of the phosphorylated polymer for anti-DNA antibodies (4 x 10(9) M-1) whereas for normal IgG the affinity was low (2 x 10(5) M-1). Moreover, the interaction was specific involving the idiotypic moiety of the anti-DNA antibodies and an array of phosphoester groups at the surface of this biomaterial.

Interactions of functionalized polystyrene derivatives with the complement system in human serum

The interactions between blood and insoluble polysaccharidic surfaces result in activation of the immune system of complement. When substituted with carboxymethyl groups, Sephadex loses its capacity to activate complement, whereas Sephadex sulphate has been described as an activator. In order to elucidate the molecular mechanisms of complement activation and inhibition, a simpler polymer model has been chosen: it consists of an insoluble polystyrene backbone on which either isolated hydroxymethyl or sulphonate groups or both are present. The surfaces bearing the isolated groups consume complement but the mechanisms involved are quite different. In contrast, a surface bearing equal proportions of both types of groups is a non-activator. Such model surfaces can be very useful for designing artificial surfaces able to control in situ complement activation.

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.

Regulation of the human alternative complement pathway: formation of a ternary complex between factor H, surface-bound C3b and chemical groups on nonactivating surfaces

Sephadex [alpha(1----6) cross-linked dextran] activates the human alternative pathway of complement. Substitution of hydroxyl groups of Sephadex with carboxymethyl groups (CM) results in a dose-dependent decrease of the activating capacity of the polymer in normal human serum. Sephadex bearing one CM group/glycosyl unit (CM-Seph 0.95) exhibited no activating capacity. CM groups did not interfere with the ability of the polymer to covalently bind C3b in the presence of purified alternative pathway proteins nor with the capacity of bound-C3b to form a C3 convertase in the absence of regulatory proteins. C3b that was bound to CM-Seph 0.95 was more susceptible to inactivation by factors H and I in serum than C3b bound to Sephadex. Binding studies using 125I-labeled H demonstrated that H bound with a similar affinity to the activating particle Sephadex, to Sephadex bearing C3b and to the nonactivating particle CM-Seph 0.95. However, factor H bound with a 5- to 7-fold higher affinity to CM-Seph 0.95 bearing C3b. These results demonstrate a requirement for both CM groups and C3b molecules in order for H to bind with high affinity to C3b on the non-activating surface, and indicate that H formed a ternary complex with surface-bound C3b and CM groups on CM-Seph 0.95. Using a chemically defined model system, the present study provides a molecular basis for the enhanced interaction between surface-bound C3b and factor H on nonactivators of the human alternative pathway.

Contributions of negatively charged chemical groups to the surface-dependent activation of human plasma by soluble dextran derivatives

Negatively charged surfaces are known to promote contact activation. The mechanism responsible for increasing affinity for surfaces is not yet quite understood, although the presence of negative charge densities is thought to be a prerequisite. With the availability of soluble dextran derivatives, varyingly substituted with charged methylcarboxylate, methylbenzylamide sulphonate and uncharged methylbenzylamide residues, we were able to discriminate between the contributions of these chemical moieties to contact activation, thus suggesting that the stimulating properties of synthetic negatively charged surfaces should also be described in terms of specific interactions instead of global negative charge density. This could be effected by quantifying the activating capacities as a function of the chemical group composition. A direct correlation linking activating capacities to anticoagulant properties has been observed.

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.

Specific antibodies enhance Sephadex-induced activation of the alternative complement pathway in human serum

Sephadex beads, which resemble cellulose in their basic chemical structure, were used to study the molecular mechanisms by which cellulosic dialysis membranes activate the alternative complement pathway in normal human serum. Sera from different individuals were found to vary in the extent of activation which occurred following incubation with a fixed amount (surface area) of polymer. Preadsorption of serum with an excess of Sephadex at 2 degrees C resulted in loss of activation when the absorbed serum was interacted with fresh Sephadex beads. Acid eluted proteins from absorbed Sephadex restored the capacity of preadsorbed serum to activate complement in the presence of fresh Sephadex. Adsorption of the immunoglobulin G (IgG) fraction and of F(ab')2 fragments from IgG prepared from the plasma of a normal individual with Sephadex, resulted in the specific binding of some IgG and F(ab'2) molecules to the particles. IgG and F(ab')2 coated beads activated complement in Sephadex-adsorbed serum. Thus, specific anti-dextran IgG antibodies trigger activation of the alternative complement pathway by Sephadex in human serum. The effect is independent of the Fc region of IgG. These results suggest that specific antibodies could be important in determining complement activation in vivo in patients undergoing haemodialysis with cellulosic membranes.

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. II. Mechanism of the thrombin-antithrombin III reaction at the surface

In a previous paper we described the surface treatment of tubings made of polystyrene grafted by irradiation onto polyethylene tubular materials. As a result, polystyrene moieties of their inner face were substituted by sulphonate and aspartic acid sulphamide groups. In order to study the mechanism of the thrombin-antithrombin III reaction occurring at the modified surface and to determine the kinetics of the reaction, step by step experiments were set up involving either the protease adsorbed at the surface reacting with the antiprotease circulating in the solution or the opposite. These procedures allowed us to demonstrate the heparin-like catalytic activity of the tubings.

Absence of effect of heparin on insulin secretion

Bioartificial pancreatic devices containing isolated islets of Langerhans have been designed, in which the blood of the recipient circulates in contact with an artificial membrane, protecting the islets against immune rejection. This system assumes that heparin, required to prevent blood clotting, does not alter insulin secretion. However, heparin has been reported to inhibit in vitro insulin secretion by rat islets and to suppress in vivo insulin secretion in dogs. Therefore, the following evaluation was made on the effect of different heparin preparations on insulin secretion. (a) Isolated rat islets of Langerhans were perfused or incubated in the absence or presence of 20 micrograms/ml heparin; insulin secretion in response to a stimulation by glucose 20 mM was not altered by the presence of heparin. (b) Insulin secretion by an insulin-secreting cell line (RINm5F) in response to leucine and theophylline was not suppressed by heparin up to 100 micrograms/ml concentration. However, an inhibitory effect was observed at 200 micrograms/ml, which is 100 times higher than the heparin concentration commonly used for therapeutic use. (c) Neither in normal rats nor in dogs did heparin alter portal plasma insulin levels and the increase in plasma insulin following an intravenous injection of glucose. In conclusion, these data do not confirm the formerly observed inhibitory effect of heparin, which can therefore be used for the in vivo evaluation of a bioartificial pancreas.

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.

The ability of Sephadex to activate human complement is suppressed in specifically substituted functional Sephadex derivatives

The capacity of Sephadex and of chemically substituted Sephadex derivatives to activate human complement was examined by incubating polymer particles in normal human serum (NHS) under conditions that allow classical and/or alternative pathway activation, and by determining complement consumption or generation of C3a antigen in serum. Sephadex was found to activate complement in NHS, mainly through the alternative pathway. The complement-activating capacity of Sephadex was directly related to the surface area of polymer that could interact with serum. Substitution of hydroxyl groups of Sephadex with carboxymethyl (CM) groups suppressed the complement-activating capacity of the polymer in a dose-dependent fashion so that Sephadex bearing an average of one or more CM groups per saccharidic unit exhibited no complement-activating ability. Blocking of CM groups on CM sephadex with amide bonds did not restore a complement-activating capacity to the polymer, indicating that intact hydroxyl groups of the sugar units are required for complement activation by Sephadex. CM Sephadex was also found to adsorb C3adesArg which bound to the polymer with a calculated affinity of 1 x 10(6) l x M-1. Substitution of Sephadex with carboxymethyl and benzylamide sulphonate groups which confers to the polymer the capacity to catalyse thrombin inactivation on its surface also suppressed the complement-activating capacity of Sephadex. Sephadex derivatives that lack complement-activating properties and adsorb anaphylatoxins may provide useful models for the design of cellulosic membranes and biomaterials with blood compatible properties.

Reversible morphological and functional abnormalities of RINm5F cells cultured on polystyrene sulfonate beads

RINm5F cells (an insulin-secreting cell line) were cultured on PSSO3Na microbeads under static conditions. The cell growth rate was either identical to that of cells grown on plastic wells or slower, depending on the initial cell concentration. With both supports, it was similarly influenced by the fetal calf serum concentration in the culture medium, and protein content per cell was identical. However, no spreading was observed when cells were cultured on microbeads. RINm5F cells cultured on plastic wells responded to arginine + theophylline and to leucine + theophylline by a significant increase in insulin secretion. By contrast, in cells cultured on PSSO3Na microbeads, the increase in this secretion was only slight or nil. All these abnormalities were reversible. Thus, when cells cultured on microbeads were detached and seeded on plastic wells, normal spreading and insulin secretion were observed. Lastly, PSSO3Na beads had an acute suppressive effect on insulin secretion by cells cultured on plastic wells. This study provides an example of cell-biomaterial interaction in which cell growth is possible, but with altered cell function.

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.

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.