Anticoagulant effects of sulphonated polyisoprenes

Molecular and Structure-Properties Comparison of an Anionically Synthesized Diblock Copolymer of the PS-b-PI Sequence and Its Hydrogenated or Sulfonated Derivatives

An approach to obtaining various nanostructures utilizing a well-studied polystyrene-b-poly(isoprene) or PS-b-PI diblock copolymer system through chemical modification reactions is reported. The complete hydrogenation and partial sulfonation to the susceptible carbon double bonds of the PI segment led to the preparation of [polystyrene-b-poly(ethylene-alt-propylene)] as well as [polystyrene-b-poly(sulfonated isoprene-co-isoprene)], respectively. The hydrogenation of the polyisoprene block results in enhanced segmental immiscibility, whereas the relative sulfonation induces an amphiphilic character in the final modified material. The successful synthesis of the pristine diblock copolymer through anionic polymerization and the relative chemical modification reactions were verified using several molecular and structural characterization techniques. The thin film structure–properties relationship was investigated using atomic force microscopy under various conditions such as different solvents and annealing temperatures. Small-angle X-ray scattering was employed to identify the different observed nanostructures and their evolution upon thermal annealing.

Surface-Modifying Polymers for Blood-Contacting Polymeric Biomaterials

Bulk blending is considered as one of the most effective and straightforward ways to improve the hemo-compatibility of blood-contacting polymeric biomaterials among many surface modification methods. Zwitterionic structure-, glycocalyx-like structure-, and heparin-like structure-based oligomers have been synthesized as additives and blended with base polymers to improve the blood compatibility of base polymers. Fluorinated end- and side-functionalized oligomers could promote the migration of functionalized groups to the surface of biomedical polymers without changing their bulk properties, and it highly depends on the number and concentration of functional groups. Moreover, oligomers having both zwitterion and fluorine are receiving considerable attention due to their desirable phase separation, which can avoid undesired protein adsorption and platelet adhesion. The surface analysis of the surface-modified materials is usually investigated by analytical tools such as contact angle measurement, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). Blood compatibility is mainly evaluated via platelet adhesion and protein adsorption test, and the result showed a significant decrease in the amount of undesirable adsorption. These analyses indicated that surface modification using bulk blending technique effectively improves blood compatibility of polymeric biomaterials.

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.

Surface modification of poly(ether sulfone) membrane with a synthesized negatively charged copolymer

In this study, we provide a new method to modify poly(ether sulfone) (PES) membrane with good biocompatibility, for which diazotized PES (PES-N2(+)) membrane is covalently coated by a negatively charged copolymer of sodium sulfonated poly(styrene-alt-maleic anhydride) (NaSPS-MA). First, aminated PES (PES-NH2) is synthesized by nitro reduction reaction of nitro-PES (PES-NO2), and then blends with pristine PES to prepare PES/PES-NH2 membrane; then the membrane is treated with NaNO2 aqueous solution at acid condition; after surface diazo reaction, surface positively charged PES/PES-N2(+) membrane is prepared. Second, poly(styrene-alt-maleic anhydride) (PS-alt-MA) is synthesized, then sulfonated and treated by sodium hydroxide solution to obtain sodium sulfonated (PS-alt-MA) (NaSPS-MA). Finally, the negatively charged NaSPS-MA copolymer is coated onto the surface positively charged PES/PES-N2(+) membrane via electrostatic interaction; after UV-cross-linking, the linkage between the PES-N2(+) and NaSPS-MA changes to a covalent bond. The surface-modified PES membrane is characterized by FT-IR spectroscopy, X-ray photoelectron spectroscopy (XPS) analyses, and surface zeta potential analyses. The modified membrane exhibits good hemocompatibility and cytocompatibility, and the improved biocompatibility might have resulted from the existence of the hydrophilic groups (sodium carboxylate (-COONa) and sodium sulfonate (-SO3Na)). Moreover, the stability of the modified membrane is also investigated. The results indicated that the modified PES membrane using negatively charged copolymers had a lot of potential in blood purification fields and bioartificial liver supports for a long time.

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.

Anticoagulant activity of enzymatically synthesized amylose derivatives containing carboxy or sulfonate groups

Heparin is an extracellular matrix polysaccharide. It is widely employed as an anticoagulant and can be used to form an anticoagulant surface on various medical devices such as renal dialysis devices to prevent thrombosis. However, heparin may cause hemorrhage and thrombocytopenia. Moreover, commercially available heparin may be contaminated with viruses and allergens of animal origin, as it is derived mainly from porcine or bovine tissue. To avoid these problems, we prepared succinated and sulfonated enzymatically synthesized amylose (SucESA and SulfESA, respectively) and assessed their anticoagulant activity. SucESA and SulfESA inhibited factor Xa activity in normal human plasma to an equal extent. However, SucESA strongly inhibited thrombin activity, whereas SulfESA only inhibited it slightly. These results suggest that SucESA inhibits the activities of both factor Xa (or its upstream coagulation factors) and thrombin and that SulfESA inhibits only factor Xa activity (or that of its upstream coagulation factors). SucESA and SulfESA with a high degree of substitution strongly inhibited factor Xa and thrombin activity compared with those of the derivatives with a low degree of substitution, even when present in high concentrations. This suggests that the density of the anion group determines the degree of inhibition of factor Xa and thrombin activity. SucESA, which has a high molecular weight, inhibited thrombin activity to a greater degree than low molecular weight SucESA. Because SucESA and SulfESA inhibited both purified factor Xa and thrombin irrespective of the presence of antithrombin, it is suggested that SucESA and SulfESA inhibit via direct action with both enzymes.

Fabrication of permeable tubular constructs from chemically modified chitosan with enhanced antithrombogenic property

The failure of artificial vascular grafts in small diameter vessel replacement is mainly due to the early formation of thrombosis. To prevent the occurrence of thrombosis, much effort has been focused on developing an anti-thrombogenic coating of synthetic vascular prostheses or artificial conduits with improved anti-thrombogenic properties. Because surface coatings may be unstable for long-term applications, a bulk material with anti-thrombogenic property is desirable for the fabrication of vascular grafts or conduits. To this end, we have chemically modified chitosan by phthalization to derive an anti-thrombogenic material for the fabrication of vascular grafts. The chemical structure of phthalized chitosan was characterized with infrared spectroscopy. The hydrophilicity was examined with contact angle measurement, and the molecular weight distribution was measured using gel permeation chromatography (GPC). Protein adsorption, hemolysis, and platelet adhesion assays were used to confirm the enhanced anti-thrombogenic properties of this phthalized chitosan. Cytotoxicity and proliferation assays were performed to test its high biocompatibility. With its improved solubility and processibility, this phthalized chitosan was fabricated into selective permeable tubular constructs of varying sizes and morphology through a wet phase-inversion process. With improved anti-thrombogenic property, biocompatibility, and great processibility, phthalized chitosan has great potential as the material for the fabrication of small diameter vascular grafts.

Sulfated sericin is a novel anticoagulant influencing the blood coagulation cascade

Sulfated sericin's influence on factors in the blood coagulation cascade was investigated to elucidate its anticoagulant mechanism. Prolongation of the prothrombin time (PT) and activated partial thromboplastin time (APTT) were observed in the presence of sulfated sericin. Fluorogenic peptide substrates on thrombin (factor IIa) and factor Xa were used to study the influence of sulfate sericin on their respective activities. Sulfated sericin inhibited neither thrombin nor factor Xa in the presence of antithrombin III (AT III). Gel electrophoresis was used to examine fibrinogen-fibrin conversion by thrombin in the presence of sulfated sericin. FPA and FPB release from fibrinogen by thrombin proceeded in the presence of sulfated sericin. The behavior of polymerization of fibrin monomer (FM) was affected by the presence of sulfated sericin. No initial lag time in the polymerization process was observed by addition of sulfated sericin to FM. This result means that sulfated sericin will interfere in the build-up of normal double-strand fibrils of FM during formation of fibrin fiber. Scanning electron microscopy (SEM) observations supported this inference. The anticoagulant mechanism of sulfated sericin is inferred to interfere with the initial polymerization process of FM.

Synthesis and evaluation of a small library of graftable thrombin inhibitors derived from (l)-arginine

Novel piperazinyl-amide derivatives of N-alpha-(aryl-sulfonyl)-L-arginine were synthesized as graftable thrombin inhibitors, in the context of biomaterials' design. The possible disturbance of biological activity due to a variable spacer-arm fixed on the N-4 piperazinyl position and the introduction of a trifluoromethyl group as XPS (X-ray Photoelectron Spectroscopy) tag on the sulfonamide moiety were evaluated in vitro against human alpha-thrombin. All the compounds of the library were found to be active at the micromolar level, as the reference TAME (N-tosyl-L-arginine methyl ester). The blood compatibilization improvement of poly(ethylene terephthalate) (PET) membrane, coated or grafted by wet chemistry treatment with one representative inhibitor of the library, was also evaluated, showing interesting decrease in blood clot formation.

Gastrodin Interaction with Human Fibrinogen: Anticoagulant Effects and Binding Studies

In an effort to identify the anticoagulant activity of gastrodin (GAS) and to investigate the possibility of its use as a novel anticoagulant drug, the binding characteristics of GAS to human fibrinogen (Fg) were studied by using a quartz crystal microbalance (QCM) biosensor, anticoagulant animal experiments, and a molecular docking simulation. Real-time kinetic analysis with the QCM biosensor revealed that the in vitro binding of GAS to Fg was strong under physiological ionic conditions as the determined equilibrium dissociation constant (KD) was 1.94 x 10(-6) M. To check whether this strong binding may influence the natural coagulation function of Fg, the in vivo effect of GAS on the coagulation system of rats was examined. The results showed that GAS can significantly prolong the coagulation time (CT) and decrease the Fg content, while it had no effect on the activated kaolin partial thromboplastin time (KPTT) or prothrombin time (PT) in rats. To clarify the mechanism of the specific interaction, a molecular docking simulation was also performed to provide reasonable binding models for the interaction of GAS with Fg at the atomic level. GAS binds strongly to the inherent polymerization sites "a" and "b" (holes) on the Fg molecule with similar binding free energies of about -34 kJ mol(-1). Altogether, these findings confirmed first that GAS possesses anticoagulant activity and that the possible anticoagulation mechanism of GAS mainly involves its interference with the knob-to-hole interactions between fibrin molecules, thereby effectively inhibiting the formation of clots and decreasing the risk of thrombosis. The study has also shown the potential usefulness of QCM biosensor technology for the rapid screening of drug-protein interactions.

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.

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.

Tissue factor pathway inhibitor as a universal anticoagulant for use in clinical laboratory tests

Tissue factor pathway inhibitor (TFPI) is a protease inhibitor of extrinsic coagulation. The present study investigates the possibility of utilizing TFPI as a universal anticoagulant in clinical laboratory tests. The optimal concentration of TFPI for use in clinical laboratory tests was found to be 1 microl TFPI/ml blood (100 mmol TFPI/ml blood); the subsequent analyses were conducted at this concentration. In hematological tests, complete blood cell count and differential white blood cell count were done with an automatic blood analyzer. The results except for platelet and white blood cell counts were similar for ethylenediaminetetraacetic acid (EDTA)-treated and TFPI-treated samples. The effects of TFPI on platelet count were more pronounced when blood samples were stored at 4 degrees C than at room temperature. The effects of TFPI on cell morphology were evaluated by spreading blood samples into thin films and applying a Giemsa stain. The results showed that TFPI did not alter the morphology of blood cells. An automatic biochemical analyzer performed seventeen basic biochemical tests on serum samples and TFPI-treated plasma samples. The results of seventeen tests were comparable between TFPI-treated samples and EDTA-treated samples. The prothrombin time for TFPI-treated plasma samples was longer than that for citrated plasma samples. Nonetheless, in activated partial thromboplastin time tests, the addition of the reagent caused turbidity and partial coagulation, thus demonstrating that TFPI is not suitable for this assay. These findings suggest that although some tests cannot be performed with TFPI, this compound may be useful as a universal anticoagulant in the future.

Synthetic polymer sulphonated polyisoprene as a universal anticoagulant for laboratory testing

To evaluate the feasibility of a synthetic polymer, sulphonated polyisoprene (SPIP), to be used as a new laboratory anticoagulant, hematological items were compared between blood samples anticoagulated with EDTA and SPIP, as were biochemical and electrolyte items between serum samples and SPIP-anticoagulated blood. Among hematological items, the average platelet count of the SPIP group was significantly lower than that of the EDTA group, due to platelet aggregation in the SPIP group. Addition of kanamycin to SPIP, but not of aspirin or prostaglandin E1, restored platelet count to about 80% of that in the EDTA group, and increased coefficients of correlation with the EDTA group for most hematological items examined. For biochemical and electrolyte items, high (> 0.95) correlation coefficients were obtained for 15 of 18 items between the serum and SPIP-anticoagulated samples. However, for some of these items, the addition of kanamycin decreased coefficients of correlation. Thus, SPIPs are excellent candidates for new anticoagulants that can be used for evaluation of hematological, biochemical, and electrolyte items with a single test tube in routine laboratory work. However, some improvements are required for use of kanamycin as an additive to inhibit platelet aggregation induced by SPIP, and in maintaining reliability of biochemical and electrolyte measurements.