Correlation of sulfate content and degree of carboxylation of heparin and related glycosaminoglycans with anticomplement activity. Relationships to the anticoagulant and platelet-aggregating activities

Polysaccharides from Sargassum thunbergii: Monthly variations and anti-complement and anti-tumour activities

Monthly variations of polysaccharides from Sargassum thunbergii and their anti-complement and anti-tumour activities were investigated. It was observed that an increase in fucose and total sugar contents occurred during the growth period (from early April to mid-June), accompanied by a decrease in molar ratios of other monosaccharides to fucose. The highest yields were obtained from early July to early September, which was in accordance with the significant increase in molar ratio of glucose to fucose and decrease in molar ratio of other monosaccharides to fucose. And the above results suggested that S. Thunbergii synthesized large amount of laminaran, the storage substance of brown algae, during the senescence period. However, sulfate contents were relatively stable in the life cycle of S. thunbergii. These results suggested that S. thunbergii synthesized complex sulfated heteropolysacchairdes during inactive period, while during other periods, it synthesized more sulfated galactofucan. All polysaccharides showed anti-complement activity, suggesting that the harvesting time did not influence the anti-complement activities. In the anti-tumour assay in vitro, the polysaccharides taken during the senescence period had much lower anti-tumour activity, suggesting that fucoidan, but not laminaran, determined the anti-tumour activities. Therefore, polysaccharides from S. thunbergii might have great potential in anti-complement and anti-tumour application.

Old and new applications of non-anticoagulant heparin

The aim of this chapter is to provide an overview of non-anticoagulant effects of heparins and their potential use in new therapeutic applications. Heparin and heparin derivatives have been tested in inflammatory, pulmonary and reproductive diseases, in cardiovascular, nephro- and neuro-tissue protection and repair, but also as agents against angiogenesis, atheroschlerosis, metastasis, protozoa and viruses. Targeting and inhibition of specific mediators involved in the inflammatory process, promoting some of the above mentioned pathologies, are reported along with recent studies of heparin conjugates and oral delivery systems. Some reports from the institute of the authors, such as those devoted to glycol-split heparins are also included. Among the members and derivatives of this class, several are undergoing clinical trials as antimetastatic and antimalarial agents and for the treatment of labour pain and severe hereditary anaemia. Other heparins, whose therapeutic targets are non-anticoagulant such as nephropathies, retinopathies and cystic fibrosis are also under investigation.

Structural analysis and anti-complement activity of polysaccharides from Kjellmaniella crsaaifolia

Two polysaccharides, named KCA and KCW, were extracted from Kjellmaniella crassifolia using dilute hydrochloric acid and water, respectively. Composition analysis showed that these polysaccharides predominantly consisted of fucose, with galactose, mannose and glucuronic acid as minor components. After degradation and partial desulfation, electrospray ionization mass spectrometry (ESI-MS) was performed, which showed that the polysaccharides consisted of sulfated fucooligosaccharides, sulfated galactofucooligosaccharides and methyl glycosides of mono-sulfated/multi-sulfated fucooligosaccharides. The structures of the oligomeric fragments were further characterized by electrospray ionization collision-induced dissociation tandem mass spectrometry (ESI-CID-MS2 and ESI-CID-MS3). Moreover, the activity of KCA and KCW against the hemolytic activity of both the classical and alternative complement pathways was determined. The activity of KCA was found to be similar to KCW, suggesting that the method of extraction did not influence the activity. In addition, the degraded polysaccharides (DKCA and DKCW) displayed lower activity levels than the crude polysaccharides (KCA and KCW), indicating that molecular weight had an effect on activity. Moreover, the desulfated fractions (ds-DKCA and ds-DKCW) showed less or no activity, which confirmed that sulfate was important for activity. In conclusion, polysaccharides from K. crassifolia may be good candidates for the treatment of diseases involving the complement pathway.

Isolation and characterization of an anti-complementary polysaccharide D3-S1 from the roots of Bupleurum smithii

The preliminary data from hemolytic assays indicated that the hot-water extract of the roots of Bupleurum smithii had anti-complementary activity. Further bioactivity-guided fractionation led to the isolation of D3-S1, a homogeneous form of acidic polysaccharide. D3-S1 was a branched polysaccharide with average molecular weight about 2,000,000 Da, composed of Ara, Gal and GalA in the ratio of 2.6:1.0:1.2, along with trace of Rha, Glc, Xyl and Man. Methylation analysis and NMR identified the linkages of the residues of D3-S1. Functional analysis showed that D3-S1 inhibited complement activation on both the classic and alternative pathways with CH(50) value of 0.34+/-0.02 mg/ml and AP(50) value of 0.081+/-0.003 mg/ml, respectively. Preliminary mechanism studies by using complement component depleted-sera indicated that D3-S1 selectively interacts with C1s, C3 and C4, but not C1q, C1r, C2, C5 and C9. The results suggested that D3-S1 could be of potential benefits in treatment of the complement-associated diseases.

Effect of low-molecular weight dextran sulfate on coagulation and platelet function tests

Low-molecular weight dextran sulfate (DXS 5000, M(r) 5 kDa) was found to control selectively complement activation without affecting contact activation. However, DXS 5000 being a glycosaminoglycan (GAG) may inhibit coagulation, which might bear the risk of bleeding complications and limit its clinical use. We investigated the influence of DXS 5000 on the prothrombin time (PT), the activated partial thromboplastin time (aPTT), the thrombin time (TT), the inhibitory capacity of human plasma against activated factor X (FXa), and on platelet function as assessed by the platelet function analyzer (PFA-100) and by platelet aggregation studies. The PT steadily increased with increasing DXS 5000 concentration, whereas the aPTT was already prolonged (>300 s) at low DXS 5000 concentrations (100 microg/ml). The TT was >120 s at DXS 5000 concentrations of 1000 microg/ml. The inhibitory capacity of human plasma against FXa was dose-dependently increased by DXS 5000. With increasing DXS 5000 concentrations, a prolonged PFA-100 closure time (CT) was observed. Detailed aggregation studies revealed a dose-dependent inhibition of platelet aggregation with ristocetin by DXS 5000, whereas aggregation with ADP, collagen, and arachidonate was unaffected. DXS 5000 induces a disturbance of primary and secondary hemostasis.

Heparin in inflammation: potential therapeutic applications beyond anticoagulation

In this chapter we have described anti-inflammatory functions of heparin distinct from its traditional anticoagulant activity. We have presented in vivo data showing heparin's beneficial effects in various preclinical models of inflammatory disease as well as discussed some clinical studies showing that the anti-inflammatory activities of heparin may translate into therapeutic uses. In vivo models that use low-anticoagulant heparins indicate that the anticoagulant activity can be distinguished from heparin's anti-inflammatory properties. In certain cases such as hypovolemic shock, the efficacy of a low-anticoagulant heparin derivative (GM1892) exceeds heparin. Data also suggest that nonconventional delivery of heparin, specifically via inhalation, has therapeutic potential in improving drug pharmacokinetics (as determined by measuring blood coagulation parameters) and in reducing the persistent concerns of systemic hemorrhagic complications. Results from larger clinical trials with heparin and LMW heparins are eagerly anticipated and will allow us to assess our predictions on the effectiveness of this drug class to treat a variety of human inflammatory diseases.

Relationships between chemical characteristics and anticomplementary activity of fucans

We have shown previously that a low-molecular-weight fucan extracted from the brown seaweed Ascophylum nodosum strongly inhibited human complement activation in vitro and its mechanism of action was largely elucidated. We further investigated the influence of molecular weight and chemical composition of fucan on its anticomplementary activity. The capacity of 12 fragments of fucan (ranging from a molecular weight of 4100 to 214,000) to prevent complement-mediated haemolysis of sheep erythrocytes (classical pathway) and of rabbit erythrocytes (alternative pathway) increased with increasing molecular weight, and reached a plateau for 40,000 and 13,500, respectively. The most potent fucan fractions were 40-fold more active than heparin in inhibiting the classical pathway. They were, however, as active as heparin in inhibiting the alternative pathway. In addition, we have developed a haemolytic test based on the CH50 protocol, which allows discrimination between activators and inhibitors of complement proteins. Although the mannose content within the different fucan fragments did not vary, the galactose and glucuronic acid contents increased with increasing activity, suggesting that these residues should be essential for full anticomplementary activity. Meanwhile, sulphate groups appeared to be necessary, but were clearly not a sufficient requirement for anticomplementary activity of fucans. Taken together, these data illustrate the prospects for the use of fucans as potential anti-inflammatory agents.

Effects of heparin and N-acetyl heparin on ischemia/reperfusion-induced alterations in myocardial function in the rabbit isolated heart

Evidence is presented that heparin pretreatment produces protective effects on myocardial tissue distinct from its anticoagulant activity. The present study examines the ability of heparin sulfate and N-acetyl heparin (a derivative of heparin devoid of anticoagulant effects) to protect the heart from injury associated with global ischemia and reperfusion. Male New Zealand White rabbits were administered either heparin sulfate (n = 7, 300 U/kg i.v.), N-acetyl heparin (n = 6, 1.73 mg/kg i.v.), or vehicle (n = 6). Two hours after treatment, the hearts were removed, perfused on a Langendorff apparatus, and subjected to 30 minutes of global ischemia, followed by 45 minutes of reperfusion. During reperfusion, creatine kinase concentrations in the coronary sinus effluent were greater in hearts from vehicle-treated rabbits compared with hearts from N-acetyl heparin-treated and heparin-treated rabbits. Left ventricular end-diastolic pressure after 45 minutes of reperfusion in the vehicle-treated group was 64 +/- 15 mm Hg compared with 17 +/- 4 and 10 +/- 3 mm Hg in the heparin-pretreated and N-acetyl heparin-pretreated groups, respectively. Heparin, but not N-acetyl heparin, increased the activated partial thromboplastin time, consistent with its known anticoagulant action. Heparin and N-acetyl heparin inhibited complement-mediated erythrocyte lysis in a concentration-dependent manner. The glycosaminoglycans, in contrast to r-hirudin, reduced complement activation-induced injury in the rabbit isolated heart. The results demonstrate that heparin or N-acetyl heparin, administered to the intact rabbit, protects the isolated heart from subsequent myocardial dysfunction secondary to ischemia/reperfusion. The cardioprotective effects of heparin and N-acetyl heparin are independent of an antithrombin mechanism.

Structure-function relationships in the inhibitory effect of heparin on complement activation: independency of the anti-coagulant and anti-complementary sites on the heparin molecule

Fluid phase heparin inhibits formation of the classical and alternative pathway C3 convertase of complement in assays performed either with purified complement proteins or in whole serum. Experiments using oligosaccharides of homogeneous mol. wt obtained by mild nitrous hydrolysis of heparin, demonstrated that the inhibitory activity of heparin increased exponentially with mol. wt for fragments containing between 4 and 14 saccharidic units and that fragments of mol. wt above 4700 (greater than 14 saccharidic units) had a similar anti-complementary activity to that of native heparin. Fragments of homogeneous mol. wt (octasaccharides) separated by ion exchange chromatography on the basis of negative charges, exhibited increasing inhibitory activity with increasing sulfate content. Over-sulfation of fragments of defined mol. wt resulted in a constant enhancement of the relative capacity of each fragment species to inhibit formation of the classical and alternative pathway C3 convertases. A synthetic pentasaccharide representing the minimal critical sequence responsible for the binding of heparin to anti-thrombin III exhibited a similar inhibitory capacity on formation of the C3 convertases as another synthetic pentasaccharide that was devoid of anti-Xa activity. These studies contribute to define a minimal structure of the heparin molecule with C3b- and C4b-binding capacity and definitively establish the independency of the anti-coagulant and anti-complementary sites on the heparin molecule.

Molecular weight dependency of the acquired anticomplementary and anticoagulant activities of specifically substituted dextrans

Dextran that had been substituted with carboxylic and benzylamine sulphonated groups was fractionated by gel chromatography into fractions, of narrow molecular weight distribution from 6000 to 190,000 daltons and of similar chemical composition. The fractions exhibited anticomplementary and anticoagulant activities that rapidly increased with molecular weight and tended to plateau above approximately 20,000 and 40,000 daltons respectively. Anticoagulant activity was lower than that of heparin, whereas the capacity of the fractions to inhibit formation of the classical and alternative C3 convertases in a purified system was similar to that of heparin and their ability to inhibit CH50 in whole serum was higher than that of heparin. The data argue for a random distribution of structurally independent anticoagulant and anticomplementary sites along the macromolecular chains of substituted dextrans.

Small heparin fragments regulate the amplification pathway of complement

Heparin is a highly sulfated, polydisperse and heterogeneous glycosaminoglycan which has been well characterized for its ability to regulate multiple sites in the complement cascade. Although previous studies demonstrated the relationship between degree of sulfation, particularly O-sulfation, and complement inhibiting capacity, they left unclear the relationship between the size of the heparin molecule and its ability to inhibit complement. Therefore, although the structure-activity relationship for heparin is well understood for anticoagulant activity, it is ill defined for the complement system. The present studies were designed to examine depolymerized heparin to determine which fragments were capable of inhibiting amplification pathway activation. We found that as the size of the molecule increases the ability to regulate complement increases; below 1000 Da the fragments were essentially inactive and above 3500 Da they had the same activity as does commercial heparin. Furthermore, we examined the five major tetrasaccharides of heparin and found that the degree of sulfation did correlate with the ability to inhibit complement. These studies have for the first time begun to examine the minimal structural requirements for heparin to regulate complement.

The anticoagulant activity of dermatan sulphates: evidence against the involvement of antithrombin III

Anticoagulant activity of dermatan sulphates is unaffected by antiserum specific for antithrombin III (AT III) unless the glycosaminoglycan preparation contains demonstrable heparin. 2 Only dermatan sulphate preparations of considerable heparin content potentiate AT III inhibition of thrombin, factor Xa and plasmin. 3 These data suggest that dermatan sulphates exert anticoagulant activity which, unlike that of heparin, is largely or totally independent of AT III.