Molecular basis for the susceptibility of fibrin-bound thrombin to inactivation by heparin cofactor ii in the presence of dermatan sulfate but not heparin

Sulfated Polysaccharides with Anticoagulant Potential: A Review Focusing on Structure-Activity Relationship and Action Mechanism

Thromboembolism is the culprit of cardiovascular diseases, leading to the highest global mortality rate. Anticoagulation emerges as the primary approach for managing thrombotic conditions. Notably, sulfated polysaccharides exhibit favorable anticoagulant efficacy with reduced side effects. This review focuses on the structure-anticoagulant activity relationship of sulfated polysaccharides and the underlying action mechanisms. It is concluded that chlorosulfonicacid-pyridine method serves as the preferred technique to synthesize sulfated polysaccharides. The anticoagulant activity of sulfated polysaccharides is linked to the substitution site of sulfate groups, degree of substitution, molecular weight, main side chain structure, and glycosidic bond conformation. Moreover, sulfated polysaccharides exert anticoagulant activity via various pathways, including the inhibition of blood coagulation factors, activation of antithrombin III and heparin cofactor II, antiplatelet aggregation, and promotion of the fibrinolytic system.

Mannose 2, 3, 4, 5, 6-O-pentasulfate (MPS): a partial activator of human heparin cofactor II with anticoagulation potential

Thromboembolic diseases are a major cause of mortality in human and the currently available anticoagulants are associated with various drawbacks, therefore the search for anticoagulants that have better safety profile is highly desirable. Compounds that are part of the dietary routine can be modified to possibly increase their anticoagulant potential. We show mannose 2,3,4,5,6-O-pentasulfate (MPS) as a synthetically modified form of mannose that has appreciable anticoagulation properties. An in silico study identified that mannose in sulfated form can bind effectively to the heparin-binding site of antithrombin (ATIII) and heparin cofactor II (HCII). Mannose was sulfated using a simple sulfation strategy-involving triethylamine-sulfur trioxide adduct. HCII and ATIII were purified from human plasma and the binding analysis using fluorometer and isothermal calorimetry showed that MPS binds at a unique site. A thrombin inhibition analysis using the chromogenic substrate showed that MPS partially enhances the activity of HCII. Further an assessment of in vitro blood coagulation assays using human plasma showed that the activated partial thromboplastin time (APTT) and prothrombin time (PT) were prolonged in the presence of MPS. A molecular dynamics simulation analysis of the HCII-MPS complex showed fluctuations in a N-terminal loop and the cofactor binding site of HCII. The results indicate that MPS is a promising lead due to its effect on the in vitro coagulation rate.Communicated by Ramaswamy H. Sarma.

Heterologous production of chondroitin

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Chondroitin sulfate (CS) is a glycosaminoglycan with a growing variety of applications.

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CS can be produced from microbial fermentation of native or engineered strains.

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Synthetic biology tools are being used to improve CS yields in different hosts.

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Integrated polymerization and sulfation can generate cost-effective CS.

Chondroitin sulfate (CS) is a glycosaminoglycan with a broad range of applications being a popular dietary supplement for osteoarthritis. Usually, CS is extracted from animal sources. However, the known risks of animal products use have been driving the search for alternative methods and sources to obtain this compound. Several pathogenic bacteria naturally produce chondroitin-like polysaccharides through well-known pathways and, therefore, have been the basis for numerous studies that aim to produce chondroitin using non-pathogenic hosts. However, the yields obtained are not enough to meet the high demand for this glycosaminoglycan. Metabolic engineering strategies have been used to construct improved heterologous hosts. The identification of metabolic bottlenecks and regulation points, and the screening for efficient enzymes are key points for constructing microbial cell factories with improved chondroitin yields to achieve industrial CS production. The recent advances on enzymatic and microbial strategies to produce non-animal chondroitin are herein reviewed. Challenges and prospects for future research are also discussed.

Mechanisms of Immunothrombosis by SARS-CoV-2

SARS-CoV-2 contains certain molecules that are related to the presence of immunothrombosis. Here, we review the pathogen and damage-associated molecular patterns. We also study the imbalance of different molecules participating in immunothrombosis, such as tissue factor, factors of the contact system, histones, and the role of cells, such as endothelial cells, platelets, and neutrophil extracellular traps. Regarding the pathogenetic mechanism, we discuss clinical trials, case-control studies, comparative and translational studies, and observational studies of regulatory or inhibitory molecules, more specifically, extracellular DNA and RNA, histones, sensors for RNA and DNA, as well as heparin and heparinoids. Overall, it appears that a network of cells and molecules identified in this axis is simultaneously but differentially affecting patients at different stages of COVID-19, and this is characterized by endothelial damage, microthrombosis, and inflammation.

Anticoagulant and Antithrombotic Properties in Vitro and in Vivo of a Novel Sulfated Polysaccharide from Marine Green Alga Monostroma nitidum

Sulfated polysaccharides from marine algae have high potential as promising candidates for marine drug development. In this study, a homogeneous sulfated polysaccharide from the marine green alga Monostroma nitidum, designated MS-1, was isolated using water extraction and anion-exchange and size-exclusion chromatography. Results of chemical and spectroscopic analyses showed that MS-1 mainly consisted of →3)-α-l-Rhap-(1→ and →2)-α-l-Rhap-(1→ residues, with additional branches consisting of 4-linked β-d-xylose, 4-/6-linked d-glucose, terminal β-d-glucuronic acid, and 3-/2-linked α-l-rhamnose. Sulfate ester groups substituted mainly at C-2/C-4 of →3)-α-l-Rhap-(1→ and C-4 of →2)-α-l-Rhap-(1→ residues, slightly at C-2 of terminal β-d-glucuronic residues. MS-1 exhibited strong anticoagulant activity in vitro and in vivo as evaluated by the activated partial thromboplastin time and thrombin time assays, and significantly decreased platelet aggregation. The anticoagulant activity mechanism of MS-1 was mainly attributed to strong potentiation thrombin by heparin cofactor-II, and it also hastened thrombin and coagulation factor Xa inhibitions by potentiating antithrombin-III. MS-1 possessed markedly thrombolytic activity evaluated by plasminogen activator inhibitior-1, fibrin degradation products, and D-dimer levels using rats plasma, and recanalization rate by FeCl₃-induced carotid artery thrombosis in mice. MS-1 exhibited strong antithrombotic activity in vitro and in vivo evaluated by the wet weighs and lengths of thrombus, and thrombus occlusion time by electrically-induced carotid artery thrombosis in rats. These results suggested that MS-1 could be a promising marine drug for prevention and therapy of thromboembolic disease.

Structural Characteristics and Anticoagulant Property In Vitro and In Vivo of a Seaweed Sulfated Rhamnan

Great diversity and metabolite complexity of seaweeds offer a unique and exclusive source of renewable drug molecules. Polysaccharide from seaweed has potential as a promising candidate for marine drug development. In the present study, seaweed polysaccharide (SPm) was isolated from Monostroma angicava, the polymeric repeat units and anticoagulant property in vitro and in vivo of SPm were investigated. SPm was a sulfated polysaccharide which was mainly constituted by 3-linked, 2-linked-α-l-rhamnose residues with partially sulfate groups at C-2 of 3-linked α-l-rhamnose residues and C-3 of 2-linked α-l-rhamnose residues. Small amounts of xylose and glucuronic acid exist in the forms of β-d-Xylp(4SO₄)-(1→ and β-d-GlcA-(1→. SPm effectively prolonged clotting time as evaluated by the activated partial thromboplastin time and thrombin time assays, and exhibited strong anticoagulant activity in vitro and in vivo. The fibrin(ogen)olytic and thrombolytic properties of SPm were evaluated by plasminogen activator inhibitior-1, fibrin degradation products, D-dimer and clot lytic rate assays using rats plasma, and the results showed that SPm possessed high fibrin(ogen)olytic and thrombolytic properties. These results suggested that SPm has potential as a novel anticoagulant agent.

Sulodexide Monotherapy in Chronic Idiopathic Subjective Tinnitus: A Randomized Controlled Trial

Objective To report the therapeutic value of sulodexide monotherapy in the management of patients with chronic subjective idiopathic tinnitus. Study Design Randomized double-blinded controlled trial. Setting Single tertiary care institution. Subjects and Methods Observations from 124 patients who received either sulodexide or placebo were collected from the patients' medical records. Computer-generated tables were used to allocate treatments. Patients took 1 tablet of the drug or placebo each morning and evening for 40 consecutive days. The response was assessed by the Tinnitus Handicap Inventory and the Mini-Tinnitus Questionnaire. Results Between 2014 and 2017, 124 patients were divided into 2 treatment arms. The sulodexide group encompassed 63 patients, whereas the placebo arm contained 61 patients. Tinnitus Handicap Inventory and Mini-Tinnitus Questionnaire scores were more decreased in the sulodexide arm compared to the placebo group ( P = .03 and P < .01, respectively). Conclusions Sulodexide monotherapy decreases chronic subjective idiopathic tinnitus.

New Anticoagulants for the Prevention and Treatment of Venous Thromboembolism

Anticoagulant drugs, like vitamin K antagonists and heparin, have been the mainstay for the treatment and prevention of venous thromboembolic disease for many years. Although effective if appropriately used, traditional anticoagulants have several limitations such as unpredictable pharmacologic and pharmacokinetic responses and various adverse effects including serious bleeding complications. New oral anticoagulants have recently emerged as an alternative because of their rapid onset/offset of action, predictable linear dose-response relationships and fewer drug interactions. However, they are still associated with problems such as bleeding, lack of reversal agents and standard laboratory monitoring. In an attempt to overcome these drawbacks, key steps of the hemostatic pathway are investigated as targets for anticoagulation. Here we reviewed the traditional and new anticoagulants with respect to their targets in the coagulation cascade, along with their therapeutic advantages and disadvantages. In addition, investigational anticoagulant drugs currently in the development stages were introduced.

The detection of thrombin using a mixture of a fluorescent conjugated polyelectrolyte and fibrinogen and implementation of a logic gate

A highly sensitive and selective detection of thrombin is accomplished using an emission color-tunable conjugated polyelectrolyte. An implementation of a combined logic gate was realized upon emission modulation of the system including the polymer, fibrinogen, thrombin, and heparin.

Alterations of fibrin network structure mediated by dermatan sulfate

Dermatan sulfate (DS) is well-known for its anticoagulant activity through binding to heparin cofactor II (HCII) to enhance thrombin inhibition. It has also been reported that DS has a profibrinolytic effect. We have evaluated the effects of DS solutions (4-20 μg/mL) on the formation (by kinetic studies), structure (by electron microscopy and compaction assays) and lysis (with urokinase-type plasminogen activator) of plasma fibrin networks. The results showed that DS significantly prolonged the lag phase and decreased the fibrin formation rate and the optical density of the final networks versus control, in a concentration dependent way. DS-associated networks presented a minor network percentage compared with control, composed of lower number of fibers per field, which resulted significantly thinner and longer. Moreover, DS rendered gels more sensible to rupture by centrifugal force and more susceptible to lysis. When fibrin formation kinetic assays were performed with purified fibrinogen instead of plasma, in the absence of HCII, the optical density of final DS-associated networks was statistically lower than control. Therefore, a direct effect of DS on the thickness of fibers was observed. Since in all in vitro assays low DS concentrations were used, it could be postulated that the fibrin features described above are plausible to be found in in vivo thrombi and therefore, DS would contribute to the formation of less thrombogenic clots.

Lytic and mechanical stability of clots composed of fibrin and blood vessel wall components

BACKGROUND

Proteases expressed in atherosclerotic plaque lesions generate collagen fragments, release glycosaminoglycans (chondroitin sulfate [CS] and dermatan sulfate [DS]) and expose extracellular matrix (ECM) proteins (e.g. decorin) at sites of fibrin formation.

OBJECTIVE

Here we address the effect of these vessel wall components on the lysis of fibrin by the tissue plasminogen activator (tPA)/plasminogen system and on the mechanical stability of clots.

METHODS AND RESULTS

MMP-8-digested collagen fragments, isolated CS, DS, glycosylated decorin and its core protein were used to prepare mixed matrices with fibrin (additives present at a 50-fold lower mass concentration than fibrinogen). Scanning electron microscopy (SEM) showed that the presence of ECM components resulted in a coarse fibrin structure, most pronounced for glycosylated decorin causing an increase in the median fiber diameter from 85 to 187 nm. Rheological measurements indicated that these structural alterations were coupled to decreased shear resistance (1.8-fold lower shear stress needed for gel/fluid transition of the clots containing glycosylated decorin) and rigidity (reduction of the storage modulus from 54.3 to 33.2 Pa). The lytic susceptibility of the modified fibrin structures was increased. The time to 50% lysis by plasmin was reduced approximately 2-fold for all investigated ECM components (apart from the core protein of decorin which produced a moderate reduction of the lysis time by 25%), whereas fibrin-dependent plasminogen activation by tPA was inhibited by up to 30%.

CONCLUSION

ECM components compromise the chemical and mechanical stability of fibrin as a result of changes in its ultrastructure.

Thrombin inhibitors: surgical considerations and pharmacology

The new thrombin inhibitors have provided an exciting opportunity for effective thromboprophylaxis without some of the disadvantages of the current anticoagulants. These drugs are orally administered, have predictable pharmacokinetics and dose-response, do not require monitoring and have an acceptable safety profile when used appropriately. However, inappropriate prescribing of these drugs may lead to catastrophic consequences. Clinicians need to be aware of some of the drawbacks associated with the use of dabigatran and, in particular, its reduced clearance in the setting of renal failure and the lack of an effective reversing agent when bleeding does occur. In this review, the evidence for efficacy and safety of dabigatran is discussed. We also aim to provide practical clinical advice on the pre- and post-operative management of the elective and emergency surgical patient on dabigatran and provide guidelines for the management of acute haemorrhage in the context of dabigatran therapy.

Chemical characteristic of an anticoagulant-active sulfated polysaccharide from Enteromorpha clathrata

A sulfated polysaccharide FEP from marine green alga Enteromorpha clathrata was extracted with hot water and further purified by ion-exchange and size-exclusion chromatography. Results of chemical and spectroscopic analyses showed that FEP was a high arabinose-containing sulfated polysaccharide with sulfate ester of 31.0%, and its average molecular weight was about 511kDa. The backbone of FEP was mainly composed of (1→4)-linked β-L-arabinopyranose residues with partially sulfate groups at the C-3 position. In vitro anticoagulant assay indicated that FEP effectively prolonged the activated partial thromboplastin time and thrombin time. The investigation demonstrated that FEP was a novel sulfated polysaccharide with different chemical characteristics from other sulfated polysaccharides from marine algae, and could be a potential source of anticoagulant.

Dabigatran: review of pharmacology and management of bleeding complications of this novel oral anticoagulant

Dabigatran (Pradaxa) is a competitive direct thrombin inhibitor approved by the US FDA for prevention of embolic stroke in patients with nonvalvular atrial fibrillation. Dabigatran has a pharmacokinetic profile that produces predictable anticoagulation responses, does not undergo CYP 450 metabolism, has few drug-drug and drug-food interactions, and does not require frequent laboratory monitoring of clotting parameters. Clinicians are rapidly prescribing this agent as a replacement for warfarin therapy. However, no therapeutic agent has been accepted to reliably reverse the hemorrhagic complications of dabigatran. As of yet, there is no solid evidence to guide management of bleeding complications; management should start with local control of bleeding when possible and transfusion of pRBCs if needed. Transfusion of FFP would not be expected to help control bleeding. Limited and mixed data exist for transfusion of factor VIIa and prothrombin complex concentrates; these therapies should be considered as well as dialysis, which will increase elimination in patients with life-threatening or closed-space bleeding due to dabigatran. We present an article that reviews the pharmacokinetics, clinical trial literature, and consensus guidelines regarding this novel oral anticoagulant.

A biologically active surface enzyme assembly that attenuates thrombus formation

Activation of hemostatic pathways by blood-contacting materials remains a major hurdle in the development of clinically durable artificial organs and implantable devices. We postulate that surface-induced thrombosis may be attenuated by the reconstitution onto blood contacting surfaces of bioactive enzymes that regulate the production of thrombin, a central mediator of both clotting and platelet activation cascades. Thrombomodulin (TM), a transmembrane protein expressed by endothelial cells, is an established negative regulator of thrombin generation in the circulatory system. Traditional techniques to covalently immobilize enzymes on solid supports may modify residues contained within or near the catalytic site, thus reducing the bioactivity of surface enzyme assemblies. In this report, we present a molecular engineering and bioorthogonal chemistry approach to site-specifically immobilize a biologically active recombinant human TM fragment onto the luminal surface of small diameter prosthetic vascular grafts. Bioactivity and biostability of TM modified grafts is confirmed in vitro and the capacity of modified grafts to reduce platelet activation is demonstrated using a non-human primate model. These studies indicate that molecularly engineered interfaces that display TM actively limit surface-induced thrombus formation.

Gold nanoparticle-based colorimetric assays for coagulation-related proteins and their inhibition reactions

In this paper, we describe two simple, label-free, homogenous assays using gold nanoparticles (Au NPs)-one to detect coagulation-related proteins and the other to screen inhibition reactions. The first nanosensor functions on the basis of the fact that thrombin catalyzes fibrinogen to form long-chain fibrins, which then induce aggregation of Au NPs. We applied this sensor to study the interactions of thrombin, inhibitors, cofactors, and antidotes. We further used thrombin-conjugated Au NPs (Thr-Au NPs) to analyze the levels of fibrinogen in plasma samples via fibrinogen-induced aggregation of Thr-Au NPs. The limit of detection (LOD; S/N=3) of this sensor for fibrinogen in plasma was 10nM. The Thr-Au NP probe provided quantitative results for fibrinogen in plasma samples that correlated (R(2)=0.97) with those obtained using a clinical von Clauss clotting rate assay. In addition, the Thr-Au NP-based sensor could be used to monitor thrombin concentrations in plasma samples under physiological conditions. Compared with conventional assays, these label-free assays offer several advantages, such as rapid and simple readout by the naked eye or by UV-vis absorption spectroscopy.

Tissue factor pathway inhibitor release and depletion by sulodexide in humans

PURPOSE

Anticoagulant tissue factor pathway inhibitor (TFPI) is released from its endothelial stores by heparin, which may lead to its untoward depletion. We investigated the effects of sulodexide--a commercially available mixture of heparan and dermatan sulfate, on plasma TFPI release and depletion.

MATERIAL AND METHODS

An open-label pilot trial of intravenous and/or oral sulodexide effects on plasma immunoreactive total TFPI antigen level was performed in 11 healthy men. The drug was initially administered i.v. at a single dose of 120 mg, thenorally for 12 days (50 mg b.i.d), and again by i.v route after 2 weeks.

RESULTS

Sulodexide injections induced marked increases in plasma TFPI; they were more pronounced on day 14 than on study initiation (3-fold vs. 2-fold after 10 min) and still evident after 120 min. TFPI levels did not change when measured at 120 min after oral sulodexide administration. The percentage increment in plasma TFPI after 10 min from initial sulodexide injection inversely correlated with baseline TFPI levels (r = - 0.664, P = 0.026). On day 14, the association became strong (r = - 0.970, P < 0.0001) and evident also after 120 min (r = - 0.810, P < 0.002). Baseline TFPI levels decreased over the trial; on day 14 they were lower by 34% than on study initiation (P = 0.001).

CONCLUSIONS

TFPI release by i.v. sulodexide and its depletion during oral administration of this heparinoid compound constitute novel and likely important hemostatic effects of the drug.

Vascular dermatan sulfate and heparin cofactor II

Heparin cofactor II (HCII) is a plasma protease inhibitor of the serpin family that inactivates thrombin by forming a covalent 1:1 complex. The rate of complex formation increases more than 1000-fold in the presence of dermatan sulfate (DS). Endothelial injury allows circulating HCII to enter the vessel wall, where it binds to DS and presumably becomes activated. Mice that lack HCII develop carotid artery thrombosis more rapidly than wild-type mice after oxidative damage to the endothelium. These mice also have increased arterial neointima formation following mechanical injury and develop more extensive atherosclerotic lesions when made hypercholesterolemic. Similarly, low plasma HCII levels appear to be a risk factor for atherosclerosis and in-stent restenosis in human subjects. These observations suggest that a major function of the HCII-DS system is to regulate the physiologic response to arterial injury.

Recent advances in the structural study of functional chondroitin sulfate and dermatan sulfate in health and disease

Chondroitin sulfate (CS) dermatan sulfate (DS), and CS/DS hybrid chains are biologically active like heparan sulfate, and structurally the most complex species of the glycosaminoglycan family along with heparan sulfate. They exist at the cell surface and extracellular matrix in the form of proteoglycans. They function as regulators of functional proteins such as growth factors, cytokines, chemokines, adhesion molecules, and lipoproteins through interactions with the ligands of these proteins via specific saccharide domains. Structural alterations have been often implicated in pathological conditions, such as cancer and atherosclerosis. Recent microsequencing of CS/DS oligosaccharides that bind growth factors, such as pleiotrophin, and various monoclonal antibodies against CS/DS, have revealed a considerable number of unique oligosaccharide sequences. This review focuses on recent advances in the study of the structure-function relation of CS, DS and their hybrid chains in physiological and pathological conditions.

Bivalent binding to gammaA/gamma'-fibrin engages both exosites of thrombin and protects it from inhibition by the antithrombin-heparin complex

Thrombin exosite 1 binds the predominant gamma(A)/gamma(A)-fibrin form with low affinity. A subpopulation of fibrin molecules, gamma(A)/gamma'-fibrin, has an extended COOH terminus gamma'-chain that binds exosite 2 of thrombin. Bivalent binding to gamma(A)/gamma'-fibrin increases the affinity of thrombin 10-fold, as determined by surface plasmon resonance. Because of its higher affinity, thrombin dissociates 7-fold more slowly from gamma(A)/gamma'-fibrin clots than from gamma(A)/gamma(A)-fibrin clots. After 24 h of washing, however, both gamma(A)/gamma'- and gamma(A)/gamma(A)-fibrin clots generate fibrinopeptide A when incubated with fibrinogen, indicating the retention of active thrombin. Previous studies demonstrated that heparin heightens the affinity of thrombin for fibrin by simultaneously binding to fibrin and exosite 2 on thrombin to generate a ternary heparin-thrombin-fibrin complex that protects thrombin from inhibition by antithrombin and heparin cofactor II. In contrast, dermatan sulfate does not promote ternary complex formation because it does not bind to fibrin. Heparin-catalyzed rates of thrombin inhibition by antithrombin were 5-fold slower in gamma(A)/gamma'-fibrin clots than they were in gamma(A)/gamma(A)-fibrin clots. This difference reflects bivalent binding of thrombin to gamma(A)/gamma'-fibrin because (a) it is abolished by addition of a gamma'-chain-directed antibody that blocks exosite 2-mediated binding of thrombin to the gamma'-chain and (b) the dermatan sulfate-catalyzed rate of thrombin inhibition by heparin cofactor II also is lower with gamma(A)/gamma'-fibrin than with gamma(A)/gamma(A)-fibrin clots. Thus, bivalent binding of thrombin to gamma(A)/gamma'-fibrin protects thrombin from inhibition, raising the possibility that gamma(A)/gamma'-fibrin serves as a reservoir of active thrombin that renders thrombi thrombogenic.

Accelerated atherogenesis and neointima formation in heparin cofactor II deficient mice

Heparin cofactor II (HCII) is a plasma protein that inhibits thrombin when bound to dermatan sulfate or heparin. HCII-deficient mice are viable and fertile but rapidly develop thrombosis of the carotid artery after endothelial injury. We now report the effects of HCII deficiency on atherogenesis and neointima formation. HCII-null or wild-type mice, both on an apolipoprotein E-null background, were fed an atherogenic diet for 12 weeks. HCII-null mice developed plaque areas in the aortic arch approximately 64% larger than wild-type mice despite having similar plasma lipid and glucose levels. Neointima formation was induced by mechanical dilation of the common carotid artery. Thrombin activity, determined by hirudin binding or chromogenic substrate hydrolysis within 1 hour after injury, was higher in the arterial walls of HCII-null mice than in wild-type mice. After 3 weeks, the median neointimal area was 2- to 3-fold greater in HCII-null than in wild-type mice. Dermatan sulfate administered intravenously within 48 hours after injury inhibited neointima formation in wild-type mice but had no effect in HCII-null mice. Heparin did not inhibit neointima formation. We conclude that HCII deficiency promotes atherogenesis and neointima formation and that treatment with dermatan sulfate reduces neointima formation in an HCII-dependent manner.

Functions of Chondroitin Sulfate/Dermatan Sulfate Chains in Brain Development

Chondroitin sulfate (CS) and dermatan sulfate (DS) have been implicated in the processes of neural development in the brain. In this study, we characterized developmentally regulated brain CS/DS chains using a single chain antibody, GD3G7, produced by the phage display technique. Evaluation of the specificity of GD3G7 toward various glycosaminoglycan preparations showed that this antibody specifically reacted with squid CS-E (rich in the GlcUAbeta1-3GalNAc(4,6-O-sulfate) disaccharide unit E), hagfish CS-H (rich in the IdoUAalpha1-3GalNAc(4,6-O-sulfate) unit iE), and shark skin DS (rich in both E and iE units). In situ hybridization for the expression of N-acetylgalac-tosamine-4-sulfate 6-O-sulfotransferase in the postnatal mouse brain, which is involved in the biosynthesis of CS/DS-E, showed a widespread expression of the transcript in the developing brain except at postnatal day 7, where strong expression was observed in the external granule cell layer in the cerebellum. The expression switched from the external to internal granule cell layer with development. Immunohistochemical localization of GD3G7 in the mouse brain showed that the epitope was relatively abundant in the cerebellum, hippocampus, and olfactory bulb. GD3G7 suppressed the growth of neurites in embryonic hippocampal neurons mediated by CS-E, suggesting that the epitope is embedded in the neurite outgrowth-promoting motif of CS-E. In addition, a CS-E decasaccharide fraction was found to be the critical minimal structure needed for recognition by GD3G7. Four discrete decasaccharide epitopic sequences were identified. The antibody GD3G7 has broad applications in investigations of CS/DS chains during the central nervous system's development and under various pathological conditions.

Sulodexide: a renewed interest in this glycosaminoglycan

Glycosaminoglycans (GAGs) are the most abundant group of heteropolysaccharides found in the body. These long unbranched molecules contain a repeating disaccharide unit. GAGs are located primarily in the extracellular matrix or on the surface of cells. These molecules serve as lubricants in the joints while at the same time providing structural rigidity to cells. Sulodexide is a highly purified glycosaminoglycan composed of a fast mobility heparin fraction as well as dermatan sulfate. Sulodexide differs from other glycosaminoglycans, like heparin, by having a longer half-life and a reduced effect on systemic clotting and bleeding. In addition, sulodexide demonstrates a lipolytic activity that is increased in comparison to heparin. Oral administration of sulodexide results in the release of tissue plasminogen activator and an increase in fibrinolytic activities. An increasing body of research has demonstrated the safety and efficacy of sulodexide in a wide range of vascular pathologies.

Effect of oversulfated dermatan sulfate derivatives on platelet aggregation

We have investigated the effect on human platelet aggregation of native dermatan sulfate (DS) and three oversulfated DS derivatives with different sulfur contents, and compared it with that of unfractionated heparin. An inhibitory effect on collagen-induced platelet aggregation was observed only with unfractionated heparin at high concentrations, whereas no inhibitory effect was observed when arachidonic acid was used. Heparin was the most potent inhibitor of the thrombin-induced platelet aggregation in platelet-rich plasma (PRP), whereas the oversulfated DS had a higher potency than the native DS. All these glycosaminoglycans (GAGs) also inhibited thrombin-induced aggregation of washed platelets in the presence of antithrombin (AT) or heparin cofactor II (HCII) but not in their absence. Heparin was by far the most potent inhibitor of washed platelet aggregation in the presence of AT, whereas the inhibitory effects of the DS (native or oversulfated) were lower but dependent on the sulfur content. In the presence of HCII, DSb, a slightly oversulfated DS, had the highest inhibitory effect, whereas heparin and DSd, the most oversulfated derivative, had lower potencies in this case. These data suggest that the inhibition of thrombin-induced platelet aggregation by the oversulfated DS derivatives is related to their ability to potentiate thrombin inactivation by AT or HCII. Hence, the oversulfated DS derivatives may not have an effect per se on the inhibition of platelet aggregation. They may constitute a new class of anticoagulants with enhanced anticoagulant effects in comparison with the native DS, but with only minor side-effects of bleeding in comparison with heparin.

Heparin cofactor II modulates the response to vascular injury

Heparin cofactor II (HCII) has several biochemical properties that distinguish it from other serpins: (1) it specifically inhibits thrombin; (2) the mechanism of inhibition involves binding of an acidic domain in HCII to thrombin exosite I; and (3) the rate of inhibition increases dramatically in the presence of dermatan sulfate molecules having specific structures. Human studies suggest that high plasma HCII levels are protective against in-stent restenosis and atherosclerosis. Studies with HCII knockout mice directly support the hypothesis that HCII interacts with dermatan sulfate in the arterial wall after endothelial injury and thereby exerts an antithrombotic effect. In addition, HCII deficiency appears to promote neointima formation and atherogenesis in mice. These results suggest that HCII plays a unique and important role in vascular homeostasis.

Detection of oligosaccharide ligands for Hepatocyte growth factor/Scatter factor (HGF/SF), Keratinocyte growth factor (KGF/FGF-7), RANTES and Heparin cofactor II by neoglycolipid microarrays of glycosaminoglycan-derived oligosaccharide fragments

Neoglycolipid technology is eminently adaptable for microarray design for high-throughput detection and specificity assignments of carbohydrate-protein interactions. Dermatan sulfate (DS) is known to play an important role because of its ability to bind growth factors as well as chemokines and to modulate their biological activities during inflammation and response to injury. We prepared various iduronic acid-rich fragments from DS by complete digestion with chondroitinase ACI, and investigated whether the DS-binding proteins, such as HGF/SF, RANTES, KGF/FGF-7 and HCII, can detect their oligosaccharide ligands in a neoglycolipid microarray. First, a comparison of the intensity of binding signals obtained from chondroitin oligosaccharides with those of heparin oligosaccharides showed that our microarray system is feasible not only to single-out the oligosaccharide ligands, but also to detect the difference between an intrinsic interaction unrelated only to electrostatic interaction and non-specific electrostatic interaction. Second, HGF/SF, KGF/FGF-7 and HCII showed preferential binding to iduronic acid-rich fragments of DS oligosaccharides that are greater than 8-mers in lengths. In contrast, RANTES binding seemed to depend only on the negative charges; their binding intensity towards the DS oligosaccharides was somewhat stronger than the binding of HGF/SF, KGF/FGF-7 and HCII. Third, the use of polyvinylpyrrolidone-40 (PVP-40), ovalbumin (OV) and Tween 20 in place of BSA as a blotting agent was useful in these glycosaminoglycan dependent reactions to minimize background due to non-specific interactions.

Clinical development of bivalirudin (Angiox): rationale for thrombin-specific anticoagulation in percutaneous coronary intervention and acute coronary syndromes

As the pathophysiology of acute coronary syndromes (ACS) has been clarified in recent years, major advances have been made in the management of the disease. The magnitude of the thrombotic process triggered upon plaque disruption is modulated by different elements that determine plaque and blood thrombogenicity. Thrombin plays a pivotal role in ACS because of its extensive procoagulant and prothrombotic actions. Antithrombotic therapy and powerful antiplatelet therapies, in addition to early percutaneous coronary intervention (PCI), have become central in the management of ACS. A number of options for anticoagulation regimens are available. However, many agents currently used have significant limitations, recognition of which has led to the development, evaluation and clinical introduction of the class of thrombin-specific anticoagulant agents. This paper will discuss the clinical development of the direct thrombin inhibitor bivalirudin as the core anticoagulant in the contemporary PCI setting and the implications for its use in ACS.

A tandem mass spectrometric approach to determination of chondroitin/dermatan sulfate oligosaccharide glycoforms

Dermatan sulfate (DS) chains are variants of chondroitin sulfate (CS) that are expressed in mammalian extracellular matrices and are particularly prevalent in skin. DS has been implicated in varied biological processes including wound repair, infection, cardiovascular disease, tumorigenesis, and fibrosis. The biological activities of DS have been attributed to its high content of IdoA(alpha1-3)GalNAc4S(beta1-4) disaccharide units. Mature CS/DS chains consist of blocks with high and low GlcA/IdoA ratios, and sulfation may occur at the 4- and/or 6-position of GalNAc and 2-position of IdoA. Traditional methods for the analysis of CS/DS chains involve differential digestion with specific chondroitinases followed by steps of chromatographic isolation of the products and di-saccharide analysis on the individual fraction. This work reports the use of tandem mass spectrometry to determine the patterns of sulfation and epimerization of CS/DS oligosaccharides in a single step. The approach is first validated and then applied to a series of skin DS samples and to decorins from three different tissues. DS samples ranged from 74 to 99% of CSB-like repeats, using this approach. Decorin samples ranged from 30% CSB-like repeats for those samples from articular cartilage to 75% for those from sclera. These values agree with known levels of glucuronyl C5-epimerase in these tissues.

Intimatan (dermatan 4,6-O-disulfate) prevents rethrombosis after successful thrombolysis in the canine model of deep vessel wall injury

INTRODUCTION

Intimatan (dermatan 4,6-O-disulfate), a heparin cofactor II (HCII) agonist, inhibits both the fluid phase and thrombus bound thrombin. The efficacy of Intimatan as an adjunctive anticoagulant during thrombolysis was evaluated in the canine model of arterial injury.

MATERIALS AND METHODS

After forming an occlusive thrombus in the right carotid artery (RCA), twenty-one dogs were administered recombinant tissue plasminogen activator (rt-PA) intra-arterially to achieve thrombolysis in the presence of either 0.9% NaCl or Intimatan (9 mg/kg bolus+300 mug/kg/min i.v. infusion). Next, the left carotid arteries (LCA) of the same animals were injured in the presence of either Intimatan or 0.9% NaCl.

RESULTS

The incidence of RCA rethrombosis between the Intimatan and control groups was 2/9 and 8/12, respectively. The quality of RCA blood flow, i.e., patency score (Scale of 0-3, i.e., no flow to high flow, respectively), was 2.3+/-0.4 (Intimatan) versus 0.9+/-0.4 (0.9% NaCl). The incidence of primary thrombosis was determined among the groups as 0/9 (Intimatan) versus 7/12 (0.9% NaCl); the patency score was 2.8+/-0.1 (Intimatan) versus 0.9+/-0.4 (0.9% NaCl). Intimatan resulted in a >90% ex vivo inhibition of gamma-thrombin-induced platelet aggregation whereas 0.9% NaCl had no inhibitory effect. Clot-bound thrombin activity was reduced significantly by Intimatan. Intimatan induced <2-fold change in aPTT and bleeding time (BT) when corrected for the 0.9% NaCl group.

CONCLUSIONS

Intimatan significantly reduces the incidence of both primary and secondary arterial thrombosis while maintaining a high-grade vessel patency score with only moderate increases in BT and aPTT.

Structural insights into biological roles of protein-glycosaminoglycan interactions

The extracellular environment is largely comprised of complex polysaccharides, which were historically considered inert materials that hydrated the cells and contributed to the structural scaffolds. Recent advances in development of sophisticated analytical techniques have brought about a dramatic transformation in understanding the numerous biological roles of these complex polysaccharides. Glycosaminoglycans (GAGs) are a class of these polysaccharides, which bind to a wide variety of proteins and signaling molecules in the cellular environment and modulate their activity, thus impinging on fundamental biological processes. Despite the importance of GAGs modulating biological functions, there are relatively few examples that demonstrate specificity of GAG-protein interactions, which in turn define the structure-function relationships of these polysaccharides. Focusing on heparin/heparan (HSGAGs) and chondroitin/dermatan sulfate (CSGAGs), this review provides structural insights into the oligosaccharide-protein interactions and discusses some key and challenging aspects of understanding GAG structure-function relationships.