Effect of a pentosan polysulphate upon thrombin and factor Xa inactivation by antithrombin III

Pentosan Polysulfate Affords Pleotropic Protection to Multiple Cells and Tissues

Pentosan polysulfate (PPS), a small semi-synthetic highly sulfated heparan sulfate (HS)-like molecule, shares many of the interactive properties of HS. The aim of this review was to outline the potential of PPS as an interventional therapeutic protective agent in physiological processes affecting pathological tissues. PPS is a multifunctional molecule with diverse therapeutic actions against many disease processes. PPS has been used for decades in the treatment of interstitial cystitis and painful bowel disease, it has tissue-protective properties as a protease inhibitor in cartilage, tendon and IVD, and it has been used as a cell-directive component in bioscaffolds in tissue engineering applications. PPS regulates complement activation, coagulation, fibrinolysis and thrombocytopenia, and it promotes the synthesis of hyaluronan. Nerve growth factor production in osteocytes is inhibited by PPS, reducing bone pain in osteoarthritis and rheumatoid arthritis (OA/RA). PPS also removes fatty compounds from lipid-engorged subchondral blood vessels in OA/RA cartilage, reducing joint pain. PPS regulates cytokine and inflammatory mediator production and is also an anti-tumor agent that promotes the proliferation and differentiation of mesenchymal stem cells and the development of progenitor cell lineages that have proven to be useful in strategies designed to effect repair of the degenerate intervertebral disc (IVD) and OA cartilage. PPS stimulates proteoglycan synthesis by chondrocytes in the presence or absence of interleukin (IL)-1, and stimulates hyaluronan production by synoviocytes. PPS is thus a multifunctional tissue-protective molecule of potential therapeutic application for a diverse range of disease processes.

Structure and anticoagulant activity of a fucosylated chondroitin sulfate from echinoderm. Sulfated fucose branches on the polysaccharide account for its high anticoagulant action

A polysaccharide isolated from the body wall of the sea cucumber Ludwigothurea grisea has a backbone like that of mammalian chondroitin sulfate: [4-beta-D-GlcA-1-->3-beta-D-GalNAc-1]n but substituted at the 3-position of the beta--glucuronic acid residues with sulfated alpha--fucopyranosyl branches (Vieira, R. P., Mulloy, B., and Mourão, P. A. S. (1991) J. Biol. Chem. 266, 13530-13536). Mild acid hydrolysis removes the sulfated alpha--fucose branches, and cleaved residues have been characterized by 1H NMR spectroscopy; the most abundant species is fucose 4-O-monosulfate, but 2,4- and 3, 4-di-O-sulfated residues are also present. Degradation of the remaining polysaccharide with chondroitin ABC lyase shows that the sulfated alpha-L-fucose residues released by mild acid hydrolysis are concentrated toward the non-reducing end of the polysaccharide chains; enzyme-resistant polysaccharide material includes the reducing terminal and carries acid-resistant -fucose substitution. The sulfated alpha-L-fucose branches confer anticoagulant activity on the polysaccharide. The specific activity of fucosylated chondroitin sulfate in the activated partial thromboplastin time assay is greater than that of a linear homopolymeric alpha-L-fucan with about the same level of sulfation; this activity is lost on defucosylation or desulfation but not on carboxyl-reduction of the polymer. Assays with purified reagents show that the fucosylated chondroitin sulfate can potentiate the thrombin inhibition activity of both antithrombin and heparin cofactor II.

Heparin enhances the catalytic activity of des-ETW-thrombin

The thrombin mutant, des-ETW-thrombin, lacking Glu(146), Thr(147), and Trp(148) within a unique insertion loop located at the extreme end of the primary specificity pocket, has been shown previously to exhibit reduced catalytic activity with respect to macromolecular and synthetic thrombin substrates and reduced or enhanced susceptibility to inhibition. Investigation of the hydrolysis of peptidyl p-nitroanilide substrates by des-ETW-thrombin showed increased activity in the presence of heparin and other sulphated glycosaminoglycans. No effect was observed upon the activity of wild-type thrombin. Heparin was found to decrease the K(m) for cleavage of four thrombin-specific substrates by des-ETW-thrombin by 3-4-fold. Similarly, pentosan polysulphate (PPS) decreased the K(m) with these substrates by 8-10-fold. Heparin also increased the rate of inhibition of des-ETW-thrombin by antithrombin III and D-phenylalanyl-prolyl-arginylchloromethane (PPACK). The inhibition of des-ETW-thrombin by a number of thrombin-specific peptide boronic acids also showed significant reduction in the final K(i) in the presence of heparin, due to reduction in the off-rate. A peptide analogue of a sequence of hirudin which binds thrombin tightly to exosite I (fibrinogen recognition site) potentiated the activity of des-ETW-thrombin against peptide p-nitroanilide substrates in a manner similar to heparin. The K(i) for the inhibition of des-ETW-thrombin by p-aminobenzamidine was decreased by these ligands from 9.7 mM to 7.5 mM, 5.1 mM, and 2.5 mM in the presence of heparin, hirudin peptide and PPS respectively, suggesting the increased catalytic activity is due to enhanced access to the primary specificity pocket. The positive influence of these ligands on des-ETW-thrombin was reversed in the presence of ATP or ADP; the latter has previously been shown to inhibit thrombin activity by blocking initial interaction with fibrinogen at exosite 1. Because the effect of heparin and PPS is similar to that of hirudin peptide, it is proposed that the most likely mechanism is that binding at the heparin-binding site (thrombin exosite 2) facilitates interaction at exosite 1 causing a conformational change which partially corrects the defective ground-state binding of the mutant thrombin. Although no effect was observed upon the activity of wild-type thrombin, our findings do provide further evidence of an allosteric property of thrombin which may control the geometry of, and access to, the primary specificity pocket.

Location of tumour cells in colon tissue by Texas red labelled pentosan polysulphate, an inhibitor of a cell surface protease

Pentosan polysulphate (PPS), a highly negatively charged polysaccharide, is a significant inhibitor of an isoenzymic form of a cell surface protease referred to as guanidinobenzoatase GB, associated with colonic carcinoma tissues in frozen sections and free GB in solution, in a concentration-dependent manner. However PPS failed to recognise and bind to the isoenzymic form of GB associated with normal colon epithelial cell surfaces. Texas red labelled PPS (TR-PPS) binds to the tumour cell surfaces of colonic carcinoma and colonic polyps and these cells fluoresce red, whilst the normal colon cell surfaces failed to bind the TR-PPS, and hence lacked red fluorescence. Polysulphonated suramin also selectively recognised and inhibited the colonic carcinoma GB isoenzyme. The kinetic data indicated that this inhibition was not caused by a mere polyanionic effect, since highly sulphated heparin failed to show a significant inhibition of colonic carcinoma GB, however trypan blue did show 50% inhibition. Kinetic studies have also shown that PPS is a non-competitive, reversible inhibitor of colonic carcinoma GB, with an apparent Km 6.8 x 10(-7) M. Gel analysis has shown that PPS binds to another site, distinct from the active centre, and after binding PPS changed the conformation of GB. These studies suggest that TR-PPS is a potent inhibitor of colonic carcinoma GB, and can be used as a novel fluorescent probe for the location of tumour cells in frozen sections of human colon tissues. PSS could also have potential as a vehicle for the transport of cytotoxic compounds to carcinoma cells of the colon.

Fluorescence and circular dichroism studies during the interactions of sulfated polysaccharides with antithrombin III

The changes in relative fluorescence of antithrombin III (AT-III) during its interaction with sulfated xylans were compared with that of sulfated glycosaminoglycans by measuring the ratio of the increase in fluorescence of AT-III in the presence of sulfated polysaccharide to the fluorescence of AT-III alone for various mass ratios. Interactions of corn cob xylan sulfate (CCXS) and sodium pentosan polysulfate (SP-54) with AT-III resulted in enhancements of relative fluorescence which were lower than commercial heparin. At mass ratios below 1, heparan sulfate and low molecular weight heparin (LMWH) gave increases in the relative fluorescence higher than that of commercial heparin, while highly sulfated semisynthetic chondroitin sulfates A and C gave much smaller increases. The relative fluorescence enhancements of AT-III by heparan sulfate, commercial heparin, LMWH and heparin derived pentasaccharide (HDP) increased with increasing mass ratios while the enhancements by CCXS, SP-54 and the highly sulfated chondroitin sulfates A and C were reversed at higher mass ratios. The estimated dissociation constants (kd) for the interaction of AT-III and the heparin-related compounds showed that heparin sulfate and LMWH gave the lowest kd values indicating a higher affinity for AT-III while commercial heparin and HDP gave higher kd values, indicating a lower affinity for AT-III. SP-54 gave a kd value lower than CCXS, indicating a greater affinity for AT-III. A comparison of the near ultraviolet (UV) circular dichroism (CD) spectrum of AT-III alone and during its interaction with oat spelts xylan sulfate (OSXS) showed enhancements of the two aromatic amino acid regions corresponding to phenylalanine and tryptophan.

Altering the course of proliferative nephritides: the challenge of the 1990s

There is considerable evidence based on experimental pathology that heparin/heparinoids will benefit the course of the various forms of human proliferative nephritis. An alternative to heparin may be pentosan polysulphate. Another possibility is the infusion of prostaglandin E1 because of its anti-inflammatory and potentially antiproliferative actions. Both these approaches mimic natural pathophysiological control mechanisms.

Anticoagulant properties of semisynthetic polysaccharide sulfates

Several naturally occurring polysaccharides were purified and subsequently sulfated by chlorosulfonic acid-pyridine complex. These were isolated as the sodium salt and further purified by ECTEOLA cellulose chromatography. Anticoagulant properties of the sulfated polysaccharides were compared with commercial heparin by measuring their in vitro effects on activated partial thromboplastin time (APTT), prothrombin time (PT) and thrombin time (TT) using pooled normal human plasma. In general, all the compounds exhibited antithrombic (anti-TT) properties similar to heparin but were less effective than heparin in inhibiting APTT or PT. The in vivo anticoagulant properties were also compared with commercial heparin by injecting rats a single intraperitoneal dose and measuring plasma APTT at 2, 4 and 6 hour intervals. All of the compounds including heparin increased APTT significantly at 2 hours and then gradually returned to near normal value after 6 hours. Larchwood xylan sulfate was almost as active as heparin in inhibiting APTT while the rest of the compounds were less active. Toxicological studies using rats showed wide variations in the LD50 of various compounds. Sulfated xylan and heparin were least toxic while sulfated polysaccharide of locust bean was most toxic. For most of the compounds the LD50 was 5-100 fold higher than the effective dosage.

Clinical and biochemical characterization of antithrombin III Franconville, a variant with Pro 41 Leu mutation

We describe a familial study of AT III, a type III antithrombin III variant which was identified in the propositus by gene analysis as Pro 41 Leu heterozygous mutation. None of the four members of the family who presented with defective heparin cofactor (hep-cofactor) activity, and therefore probably carried the mutation, had experienced deep venous thrombosis. The abnormal AT III was purified from the propositus' plasma, taking advantage of the difference in NaCl concentrations required to elute variant and normal AT III from heparin-Sepharose. The antithrombin and anti-Xa activities of the purified variant AT III were comparable to those observed for normal AT III, but hep-cofactor activity was strikingly reduced. The enhancement by heparin of thrombin and F Xa inhibition by normal and variant AT III was compared in the absence of NaCl and in the presence of normal NaCl concentrations. The difference between the degrees of inhibition by normal and variant AT III was maximal at physiological ionic strength (i.e. at a concentration of 0.15 M). The quantification of heparin AT III interaction with both normal and variant purified proteins in a double reciprocal plot yielded similar dissociation constants but a 9-fold decrease in the maximal pseudo-first order constant. This suggests that Pro 41 is more involved in the molecular changes induced by heparin than in the primary binding of the activator.

Influence of chemical modification of tryptophan residues on the properties of human antithrombin III

According to the reaction conditions selected, chemical modification of tryptophan residues in antithrombin III by dimethyl (2-hydroxy-5 nitrobenzyl) sulfonium bromide (HNBSB) generated products with similar levels of modification (equivalent to 0.9 mole 2-hydroxy-5-nitrobenzyl (HNB) incorporated/mole of antithrombin III) but with high or low affinity for heparin. These products were subjected to digestion by cyanogen bromide and shown to be modified equivalently in fragment II containing Trp 189 and Trp 225 and fragment III containing Trp 49. The molar level of incorporation of HNB into these fragments was similar in the high and low affinity forms. Both high and low affinity forms showed loss of heparin cofactor activity. A recovery of heparin cofactor activity towards coagulation factor Xa was observed upon prolonged storage of low affinity forms at -70 degrees C. It is considered that the loss of high affinity for heparin upon modification of antithrombin III arises from change or stabilization of conformation associated with tryptophan modification and is not a singular property of modification of Trp 49.

Effect of a heparan sulphate with high affinity for antithrombin III upon inactivation of thrombin and coagulation factor Xa

The kinetics of inhibition of human alpha-thrombin and coagulation Factor Xa by antithrombin III were examined under pseudo-first-order reaction conditions as a function of the concentration of heparan sulphate with high affinity for antithrombin III. The maximum observed second-order rate constant was, for the antithrombin III-thrombin reaction, 1.2 x 10(9) M-1.min-1 compared with 2.4 x 10(9) M-1.min-1 in the presence of high-affinity heparin. However, the maximum rate was catalysed by much higher concentrations of heparan sulphate (1.3 microM) than of heparin (0.025 microM). Differences were also observed in the maximal acceleration of the antithrombin III-Factor Xa interaction: 1.2 x 10(9) M-1.min-1 at 0.2 microM-heparin sulphate compared with 2.2 x 10(9) M-1.min-1 at 0.04 microM-heparin. The differences in properties of heparan sulphate and heparin were analysed by using the random bi-reactant model of heparin action [Griffith (1983) Proc. Natl. Acad. Sci. U.S.A. 80, 5460-5464]. It was observed that the apparent binding affinity for thrombin was higher for heparan sulphate (180 nM) than for heparin (14 nM). The rate constant for transformation of the antithrombin III-Factor Xa complex into irreversible product differed between heparan sulphate (96 min-1) and heparin (429 min-1). These properties of the high-affinity heparan sulphate may be of importance in consideration of a putative role in the control of intravascular haemostasis.

Effect of oversulphated chondroitin and dermatan sulphate upon thrombin and factor Xa inactivation by antithrombin III or heparin cofactor II

The kinetics of inhibition of human thrombin and Factor Xa by antithrombin III or heparin cofactor II were examined under pseudo-first-order conditions as a function of the concentration of naturally occurring oversulphated chondroitin and dermatan sulphates. The sulphated glycosaminoglycans (GAGs) studied were chondroitin sulphate D (CSD) (GlcA-2-SO4-GalNAc-6-SO4), chondroitin sulphate K (CSK) (GlcA-3-SO4-GalNAc-4-SO4), chondroitin sulphate H (CSH) (IdA-GalNAc-4,6-diSO4) and polysulphated dermatan sulphate (DPS) (IdA-2-SO4 or -3-SO4-GalNAc-4,6-diSO4). The data for the antithrombin III inhibition of thrombin showed a low degree of maximal potentiation of this interaction (congruent to 10-fold), which would appear to be characteristic of GAGs devoid of the high-affinity antithrombin III binding site. In contrast there was a greater potentiation of the inhibition of thrombin by heparin cofactor II with DPS showing an activity comparable to heparin in this interaction at a concentration two orders of magnitude lower than dermatan sulphate. DPS potentiated antithrombin III-Factor Xa interaction by 1200-fold, similar to that shown by high-affinity heparin of 6 kDa. The antithrombin III-Factor Xa interaction was potentiated by all other GAGs studied to a degree similar to that of heparin pentasaccharide with high affinity for antithrombin III. The findings suggest more stringent structural requirements for GAG stimulation of antithrombin-thrombin interaction than for antithrombin-Factor Xa or heparin cofactor-thrombin interaction, which may also be of significance in physiological control of haemostasis.

Comparison of the molecular mass dependency of heparin stimulation of heparin cofactor II:thrombin interaction to antithrombin III:thrombin interaction

The influence of increasing concentrations of heparin of different molecular mass (Mr) has been compared in potentiation of the rate of heparin cofactor II:thrombin interaction and of antithrombin III:thrombin interaction. Unfractionated and fractionated heparin showed a concentration dependent ascending and descending limb of stimulation of the rate for both inhibitors. Unfractionated heparin and fractions of 16.5 KDa or less showed a peak acceleration of the rate of interaction of thrombin with both inhibitors at 0.3 X 10(-6) M heparin although the observed maximum rate at this peak decreased with fall in Mr. For both inhibitors two high Mr fractions showed peak stimulation at a lower heparin concentration (0.3 X 10(-7) M) and approximately two-fold greater increase in rate than that observed with unfractionated heparin. Potentiation of heparin cofactor II inhibitory activity differed from that of antithrombin III in that it was reversed by lower ionic strength and was not reversed by a heparin pentasaccharide with high affinity for antithrombin III. It is proposed that differences in the profiles of stimulation by high Mr fractions to those of lower Mr are related to higher binding affinities for the inhibitor permitting maximal binding of heparin before the descending part of the slope due to saturation of thrombin (according to the template hypothesis).

Thrombin inhibitory activity of heparin cofactor II depends on the molecular weight and sulfate amount of dextran sulfate

The effect of molecular weight and sulfate amount of sulfated polysaccharide on the thrombin inhibitory activity of heparin cofactor II was investigated by using various dextran sulfate fractions with different molecular weight and sulfur content. The activity of dextran sulfate fractions of each size increased as the sulfur content was increased from 9 to 18%, and the activity decreased in molecules below 10 kDa. The maximum second order rate constant of heparin cofactor II-thrombin reaction in the presence of the fractions of over-10 kDa and 18% sulfur was 2.7 X 10(8) M-1 min-1 that was almost same as in the presence of heparin or dermatan sulfate. On the other hand, dextran sulfate accelerated antithrombin III-thrombin reaction only about 40-fold less than heparin. These results indicate that a large molecular size and significant amount of sulfate groups are only essential in the acceleration of the thrombin inhibitory activity of heparin cofactor II, whereas a specific sequence of heparin is required to that of antithrombin III.

The relative molecular mass dependence of the anti-factor Xa properties of heparin

The effect of heparin fractions of various Mr, with high affinity for antithrombin III, on the kinetics of the reaction between factor Xa and antithrombin III have been studied using purified human proteins. Each of the heparin fractions, which varied between pentasaccharide and Mr 32,000, accelerated the inhibition of factor Xa although an increasing rate of inhibition was observed with increasing Mr. The chemically synthesized pentasaccharide preparation (Mr 1714) gave a maximum inhibition rate constant of 1.2 X 10(7) M-1 X min-1, compared with 6.3 X 10(4) M-1 X min-1 in the absence of heparin, and this rose progressively to 4.2 X 10(8) M-1 X min-1 with the two fractions of highest Mr (22,500 and 32,000). The 35-fold difference in inhibition rates observed with the high-affinity fractions was virtually abolished by the presence of 0.3 M-NaCl. The disparity in these rates of inhibition was shown to be due to a change in the Km for factor Xa when a two-substrate model of heparin catalysis was used. The Km for factor Xa rose from 28 nM for the fraction of Mr 32,000 to 770 nM for the pentasaccharide, whilst 0.3 M-NaCl also caused an increase in Km with the high-Mr fraction. These data suggest that the increased rates of inhibition observed with heparins of higher Mr may be due to an involvement of heparin binding to factor Xa as well as to antithrombin III.

The anticoagulant properties of mast cell product, chondroitin sulphate E

The anticoagulant potency in vitro of chondroitin sulphate E has been found to be similar to that of the heparinoids. In purified systems chondroitin sulphate E was shown to be principally an activator of heparin cofactor II. Maximum acceleration of heparin cofactor II:thrombin interaction was 185-fold (9.3 X 10(7) M-1 min-1), antithrombin III:thrombin interaction was 11-fold (4.16 X 10(6) M-1 min-1) and antithrombin III:factor Xa was 146-fold (3.86 X 10(6) M-1 min-1). Chondroitin sulphate E was observed to prolong the thrombin clotting time of fibrinogen in the absence of antithrombin III and heparin cofactor II. The effect appeared to be related to interference in thrombin:fibrinogen interaction rather than in fibrin monomer polymerization.

Pentosan polysulphate: activation of heparin cofactor II or antithrombin III according to molecular weight fractionation

The relative potency of pentosan polysulphate in activation of heparin cofactor II/thrombin interaction has been compared to heparin and dermatan sulphate and found to be within the same order. A skewed distribution of molecular weight forms was observed upon gel filtration of pentosan polysulphate with an average molecular weight of 4500 daltons. Two peaks of activity were observed in activation of heparin cofactor II. The greatest activity was observed in high molecular weight fractions (5-fold greater than that of average molecular weight) and a concentration-dependent profile indicated a template mechanism of action. A lower peak of activity was observed at average molecular weight and the effect of increasing concentrations of this material on activity indicated a mechanism involving binding to proteinase inhibitor or proteinase alone. Potentiation of antithrombin III/thrombin interaction was observed only in fractions greater than the average molecular weight. Concentration-dependent profiles indicated binding to antithrombin III and thrombin was a requisite of activation. A fraction of low molecular weight showed no property of activation of antithrombin III or heparin cofactor II/thrombin interaction. Three fractions of high, average and low molecular weights tested in clotting assays showed relative potencies corresponding to those observed in the purified systems.

The acceleration of the inhibition of platelet prothrombinase complex by heparin

The influence of heparin on the inhibition of factor Xa has been studied under conditions where factor Xa is bound to collagen-thrombin-stimulated platelets to form the prothrombinase complex. Unfractionated heparin was found to cause a concentration-dependent acceleration of the inhibition of the platelet prothrombinase complex up to a maximum rate constant of 4.1 X 10(7) M-1 X min-1 at heparin concentrations of 0.2 microM and above. This is equivalent to a 4800-fold acceleration over the rate constant for the inhibition in the absence of heparin, and is 6.8-fold lower than the rate constant for the inhibition of uncomplexed factor Xa in the presence of saturating concentrations of heparin which was determined as 2.8 X 10(8) M-1 X min-1. The effects of three Mr fractions of heparin were also studied. These were a gel-filtered heparin of Mr 15000, a gel-filtered heparin of Mr 6000 and a heparin oligosaccharide (primarily 8-10 monosaccharide units) prepared by nitrous acid depolymerization, each with high affinity for antithrombin III. These fractions all accelerated the rate of the antithrombin III inhibition of the platelet prothrombinase complex, with maximum rate constants of 6.8 X 10(7), 1.4 X 10(7) and 9.8 X 10(6) M-1 X min-1, respectively. On comparison with the effect of these heparin fractions on the rate of inhibition of uncomplexed factor Xa a progressively increasing disparity between the rate of inhibition of uncomplexed and complexed factor Xa was observed, rising from 1.7-fold with the oligosaccharide to 6.8-fold with the unfractionated heparin. A possible mechanism for this differential activity between uncomplexed and complexed factor Xa with the various heparin fractions is discussed in terms of an involvement of heparin binding to factor Xa.