Quantum-chemical calculations of the electronic structure of 2-amino-1,3-dicyano-5,6,7,8-tetrahydronaphthalene derivatives.

The UV-Visible absorption spectra of six, newly synthesized donor-substituted 2-amino-1,3-dicyano-5,6,7,8-tetrahydronaphthalene have been measured in methylcyclohexane (MCH) and assigned with the help of quantum-chemical calculations. Our calculations have been performed to assess information regarding the electronic state energy values, corresponding oscillator strengths, x-, y-, z-components of the transition dipole moments and molecular orbitals involved in the main electronic transitions of the studied compounds. Additionally, the experimental absorption transition dipole moments were calculated, on the basis of spectroscopic data, and compared with results of our quantum-chemical calculations. On the basis of the experimental results and quantum-chemical calculations, it was shown that the long-wavelength absorption band involves an overlap of three electronic transitions of different character. For all studied donor-acceptor (D-A) compounds in vapour-phase, the long-wavelength transition (S0→S1) does not possess charge transfer character, whereas the S0→S2 transition possesses electron transfer character e.g., π-electrons of the acceptor moiety are moved to the donor part. Moreover, it is found that the electronic structure of the studied biphenyl derivatives can be approximately described within composite-model of decoupled moieties: donor and acceptor.

Excited-state dynamics of ethyl 5-(4-aminophenyl)-3-amino-2,4-dicyanobenzoate.

The photophysics and excited-state dynamics of ethyl 5-(4-aminophenyl)-3-amino-2,4-dicyanobenzoate (EAADCy) in solvents of varying polarity and viscosity have been studied using femtosecond transient absorption spectroscopy. Global analysis of the time-resolved spectra revealed three processes occurring in an optically excited molecule. The sequence of reactions begins with a transition from an initially excited Franck-Condon state to the nonrelaxed intramolecular charge transfer (ICT(NR)) state which is associated with a partial electron transfer. This process is followed by an additional relaxation to a more relaxed intramolecular charge transfer (ICT(R)) state with stronger charge transfer character and flattened geometry. The lifetime of the flattened charge transfer form (ICT(R)) shortens from 200 to 300 ps in medium polar solvents down to 10 ps in strongly polar solvents. On the other hand, increase of viscosity by 1 order of magnitude leads to deceleration of processes involving twist of the donor and acceptor moieties by a factor of approximately 2.5. Observation of long-lived fluorescence of EAADCy in medium polar solvent suggests that charge transfer is possible only from a hot Franck-Condon state, but not from a relaxed locally excited state which exhibits short-wavelength fluorescence on a nanosecond time scale.

Influence of prototropic reactions on the absorption and fluorescence spectra of methyl p-dimethylaminobenzoate and its two ortho derivatives.

The influence of prototropic reactions on the spectral characteristics of methyl p-dimethylaminobenzoate (I) and its o-methoxy (II) and o-hydroxy (III) derivatives has been studied using steady-state spectroscopic technique and quantum-chemical calculations. This study concerns the solvent-induced shift of the absorption, locally excited (LE) and intramolecular charge transfer (ICT) fluorescence bands in the neat tetrahydrofuran (THF) and its hydrochloric acid solutions at different HCl concentrations. On the basis of the experimental results and quantum-chemical calculations, it was shown that in a hydrochloric acid solution the studied molecules exist as a mixture of neutral, mono-, and dicationic forms. Additionally, the results of spectroscopic measurements were used to calculate, according to the Benesi-Hildebrand method, the equilibrium constants of protopropic reactions in the ground, S(0), and excited, S(1), states. Our findings predestine molecules I and II to be used as acid fluorescence probes in a region of 0-2.5 M of [H(+)] concentrations.

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.

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.

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.

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.

Biospecific interactions of Vitamin K-dependent factors with phospholipid-like polystyrene derivatives. Part I: Factor II.

Phosphorylated polystyrene derivatives with different compositions in phosphate groups were shown to be either recognized as phospholipidic or as DNA-like surfaces by antibodies from Systemic Lupus Erythematosus patients. In order to check whether these polymers were able to interact with Vitamin K-dependent coagulation factors, phosphorylated resins of various compositions in phosphate groups were assessed with regard to their interactions with Factor II, one of the Vitamin K-dependent factors. These studies were performed either in the presence or the absence of calcium ions, and with or without albumin precoating of the polymers. The results show that the affinity of the protein for the polymer is increased in the presence of calcium ions and depends on the composition of the polymer. The protein-polymer interactions involve the formation of binary or ternary complexes and the domains of predominance of these complexes were determined as a function of the calcium ion concentration in the assay. This allowed us to propose optimal conditions for Factor II purification by highly specific liquid chromatography using phosphorylated polystyrene resins of given compositions as stationary phases.

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.

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.

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.