Therapeutic Effect of a Low Molecular Weight Dermatan Sulphate (Desmin 370) in Rat Venous Thrombosis - Evidence for an Anticoagulant-Independent Mechanism

Insight into the profibrinolytic activity of dermatan sulfate: effects on the activation of plasminogen mediated by tissue and urinary plasminogen activators

INTRODUCTION

Dermatan sulfate (DS) is well-known for its anticoagulant activity through binding to heparin cofactor II to enhance antithrombin action. It has also been suggested that DS has a profibrinolytic effect, although the exact molecular mechanism is as yet unknown.

MATERIALS AND METHODS

An in vitro amidolytic method was used to study the effect of high and low molecular weight-DS on the activation of Glu and Lys-plasminogen by tissue and urinary plasminogen activators (t-PA and u-PA).

RESULTS

Both high and low molecular weight-DS exhibited a stimulating effect on the activation of plasminogen by PAs. Interestingly, high molecular weight-DS stimulated Glu and Lys-plasminogen activation by t-PA and u-PA in a way and to an extent similar to that in which fibrin(ogen) degradation products (PDF) increased the t-PA assay. Meanwhile low molecular weight-DS had a lower effect. No DS had any effect on plasmin or u-PA amidolytic activity. The facilitation of the conversion of Glu-plasminogen to plasmin in the presence of DS was confirmed by SDS-PAGE; high molecular weight-DS effect was greater than low molecular weight-DS in accordance with the chromogenic assays. Moreover, the combination of PDF and high and low molecular weight-DS, respectively, did not further stimulate t-PA activation of either Glu or Lys-plasminogen suggesting that both substances may compete for the same binding sites.

CONCLUSIONS

Through in vitro assays we demonstrated that high and low molecular weight-DS enhance plasminogen activation by u-PA and t-PA, suggesting that the profibrinolytic activity of DS might be via potentiation of plasminogen conversion to plasmin.

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.

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.

The therapeutic potential of novel anticoagulants

Conventional anticoagulant therapy has been based on indirect inhibition of coagulation factors with heparin and warfarin. These agents display liabilities prompting the development of new anticoagulants over the last two decades. The first to be developed was a series of low molecular weight heparins(LMWHs). Their favourable pharmacokinetic profiles and risk/benefit ratios led to widespread use in Europe and, more recently, approval for their use in the USA. Paralleling the development of LMWHs has been the pursuit of a different strategy focused on direct rather than indirect inhibition of enzymes in the coagulation cascade. In contrast to heparin, LMWHs, or other glycosaminoglycans, direct inhibitors exert their effects independent of either antithrombin III (ATIII) or heparin cofactor II (HCII) and more effectively inhibit clot-bound thrombin or FXa. Highly potent, selective (versus other serine proteases)direct thrombin and FXa inhibitors have been identified and isolated from natural sources, such as leeches, ticks and hookworms. The recombinant forms and analogues of the senatural proteins have been produced using molecular biology techniques, i.e., rHirudin, Hirulogs, recombinant tick anticoagulant peptide (rTAP), recombinant antistasin (rATS) and recombinant nematode anticoagulant peptide-5 (rNAP-5). The design of novel structures or the modification of existing chemicals has led to the synthesis of many non-peptide, low molecular weight inhibitors of thrombin and FXa. Some of them are orally active and may be suitable for long-term clinical use. In addition, considerable progress has been made in developing specific TF/VIIa complex inhibitors. The anticoagulation properties of the new agents are being characterised in experimental studies. Some of them have been advanced to large scale clinical trials and their effectiveness, and sometimes relative ineffectiveness,in arterial and venous thromboembolic disorders has been demonstrated. They are being tested for their potential as new antithrombotic agents that act via direct enzyme inhibition. Thus,the clinician should in future be able to target different thrombotic conditions with proven, specific anticoagulant interventions.

Targeting thrombin – rational drug design from natural mechanisms

It is difficult to overstate the medical importance of the serine protease thrombin. Thrombin is involved in many diverse processes, such as cell signaling and memory, but it is the crucial role that it plays in blood coagulation that commands the interest of the medical community. Thrombosis is the most common cause of death in the industrialized world and, whether through venous thromboembolism, myocardial infarction or stroke, ultimately involves the inappropriate activity of thrombin. The number and type of intrinsic and extrinsic natural mechanisms of targeting thrombin that have evolved validate thrombin as an important physiological target, and provide strategies to knock it out. The more we learn about the natural mechanisms that determine thrombin specificity the more likely we are to develop compounds that selectively alter thrombin activity. In this article, we review the natural mechanisms that regulate thrombin activity and novel approaches to inhibit thrombin based on these mechanisms.

Bioavailability of Desmin, a low molecular weight dermatan sulfate, after subcutaneous administration to healthy volunteers

The bioavailability of two different s.c. doses of Desmin (a new low molecular weight dermatan sulfate) was evaluated in 12 healthy volunteers (6 men, 6 women aged 22-45 years) who were injected, on 3 separate days and with a wash-out period of at least 21 days between each administration, with 200 and 300 mg of Desmin by the s.c. route and 200 mg by the i.v. route. Immediately before injection and at various times thereafter (after 15 min and 30 min for i.v. only and after 1, 2, 3, 4, 6, 8, 12, and 24 h for both s.c. and i.v. dosing), blood samples were drawn to investigate bioavailability by measuring several coagulation parameters: activated partial thromboplastin time, thrombin time, inhibition of factor Xa, Heptest, and heparin cofactor II. Furthermore the local tolerance of the s.c. and i.v. injections were investigated. The s.c. administration of the two Desmin doses had a negligible effect on the activated partial thromboplastin time and a very small effect on the thrombin time, measured with human thrombin; in contrast, Heptest, heparin cofactor II, and anti-Xa activities increased, with a good drug bioavailability (more than 100%). The plasma effects of Desmin were dose dependent only when measured by Heptest, which also gave a greater response after the s.c. administrations. There were no symptoms of intolerance or pain at the injection site after single i.v. and s.c. Desmin administration.

Thrombolysis enhancing activity of a low molecular weight dermatan sulfate (Desmin 370) in experimental pulmonary embolism in rats

The effect of Desmin 370 (D370), a low molecular weight dermatan sulfate, on the extent of lysis of radiolabelled pulmonary emboli in rats was evaluated. 125I-fibrin labelled blood clots were embolized into the lungs via a jugular vein, and the degree of lysis was calculated, at predetermined intervals, by the residual radioactivity in the lungs. A single i.v. injection of D370 (50 mg/kg) caused a significant increase in the rate of lysis, which was visible at 30 min and persisted for the whole experimental period (2 h). This effect was prevented by epsilon-aminocaproic acid (1 g/kg). At comparable antithrombotic dosages, heparin (2 mg/kg) also produced a significant enhancement of thrombolysis while hirudin (2 mg/kg) was totally ineffective. Heparin, however, produced a much more pronounced anticoagulant effect than D370. No changes in the plasma levels of plasminogen activator and plasminogen activator inhibitor activities were observed after treatment with D370. Moreover, the dermatan sulfate failed to enhance the blood fibrinolytic activity measured by a solid phase 125I-fibrin assay. These results extend previous data indicating that D370 may be efficient also in the therapy of thrombosis and provide direct evidence that this effect occurs, at least in part, via degradation of thrombus associated fibrin.

The treatment of deep vein thrombosis with continuous intravenous low-molecular-weight dermatan sulphate (Desmin). A pilot study

Eight patients with femoro-popliteal or sural DVT, confirmed by phlebography, were treated with intravenous Desmin (LMW-dermatan sulphate): on the first day, after an initial i.v. injection of 400 mg, all patients received an infusion of 800 mg in 500 ml of saline, during 24 hours; this infusion was repeated in each of the subsequent 9 days (global treatment period: 10 days). To monitor efficacy of the antithrombotic treatment a phlebography, with calculation of Marder score, was repeated at the end of treatment. Laboratory tests monitoring blood coagulation were carried out: aPTT, TT, PT. Factor Xa inhibition (by chronometric and chromogenic method), Stachrom DS, fibrinogen, prothrombin fragments F1 + 2 and TAT. Seven patients completed the ten-day treatment: 6 patients evidenced good improvement of the phlebographic patterns, 1 remained stationary and 1 patient was withdrawn due to adverse events. During the ten days treatment we did not observe any variation of blood coagulation tests. Desmin tolerability was good and no haemorrhagic episodes were registered. The collected results point to a good antithrombotic activity of the new LMW-dermatan sulphate, that deserves to be further evaluated with controlled investigations on larger number of patients.

DHG, a new depolymerized holothurian glycosaminoglycan, exerts an antithrombotic effect with less bleeding than unfractionated or low molecular weight heparin, in rats

We characterized the antithrombotic, haemorrhagic, and ex vivo anticoagulant effects of a recently identified depolymerized holothurian glycosaminoglycan (DHG), and compared these effects with those of unfractionated heparin (UFH), low molecular weight heparin (LMWH), and dermatan sulfate (DS). In thrombin-induced venous thrombus formation in rats, DHG had a significant preventive effect at 0.3 mg/kg or more at 5 min after i.v., administration. UFH, LMWH, and DS also showed a significant antithrombotic effect at 0.3, 0.3, and 1 mg/kg, respectively, under the same experimental conditions. After rat tail transection, DHG, UFH, LMWH, and DS prolonged the bleeding time significantly at 10, 1, 1, and 10 mg/kg, respectively, at 5 min after i.v., injection. Therefore, DHG exerts its antithrombotic effect with less bleeding than UFH and LMWH in experimental animals. DHG prolonged the activated partial thromboplastin time in a dose-dependent manner at 0.3-3 mg/kg, at which dose an antithrombotic effect was exhibited without any significant haemorrhagic effect. All of these glycosaminoglycans prolonged thrombin clotting time markedly at their haemorrhagic doses.

Active site for heparin cofactor II in low molecular mass dermatan sulfate. Contribution to the antithrombotic activity of fractions with high affinity for heparin cofactor II

Dermatan sulfate (DS) is currently under clinical investigation as new antithrombotic agent. Unlike heparin, DS does not act through Antithrombin III (ATIII) but primarily through thrombin on Heparin Cofactor II (HCII). HCII is activated by the oversulfated sequence (IdoA2SO3-GalNAc4SO3)4 or by both the sequences (IdoA2SO3-GalNAc4SO3)n and (IdoA-GalNAc-4,6SO3)n, [n > or = 2]. A Low Molecular Mass Dermatan Sulfate (LMM-DS), endowed with a bioavailability three-four times higher than DS, by subcutaneous route, was obtained by chemical depolymerization of DS. The LMM-DS was fractionated by anion exchange and size exclusion chromatography. Fractions with high and low charge densities, high and low molecular masses, and high (2.66) and low (0.07) potencies on HCII were isolated. A relationship between the in vitro HCII-mediated inhibition of thrombin and the chain length of DS fractions containing oversulfated sequences was found [by a multiple regression test]. The in vivo activity increased until it reached a plateau. The important influence on the HCII activity of natural IdoA-GalNAc-4,6SO3 disaccharide was confirmed by investigation on oversulfated DS obtained by a limited and selective chemical 6-O-sulfation in GalNAc4SO3 units of DS.

Postphlebitic syndrome: clinical activity and tolerability of desmin, new LMW dermatan sulfate

One hundred patients suffering from postphlebitic syndrome of the lower limbs were enrolled in an open, randomized, and multicenter (six centers) trial for a period of eighteen months. Patients were randomly assigned to three treatment groups to receive (for ninety consecutive days) Desmin, a new low-molecular-weight dermatan sulfate, at the dose, respectively, of 100 mg once daily by subcutaneous (SC) route (36 patients), 100 mg twice a day by SC route (33 patients), and 200 mg once daily by intramuscular (IM) route (31 patients). The general and local tolerability and the clinical efficacy of the drug were evaluated by means of clinical, instrumental, and laboratory parameters. Desmin is effective in the decompensation stage of postphlebitic syndrome; this was demonstrated by a significant reduction in the severity of a number of typical symptoms as well as by the drug's positive effect on venous tone as confirmed by phlebotensiometric examination. The daily dose of 200 mg (either SC or IM) was more effective than the 100 mg dose. The results obtained at the end of the trial (ninety days) were statistically better than those obtained after thirty days of treatment. This trial demonstrated that both the systemic and the local (at the site of injection) tolerability of the drug, administered for three months, were good and without significant variations in the laboratory parameters monitored.

Tolerability and clinical efficacy of desmin in the treatment of superficial thrombovaricophlebitis

Fifty-six patients with superficial thrombovaricophlebitis of the lower limbs were enrolled in an open and multicenter (4 centers) trial for a period of thirty days. Patients were randomly allocated to three treatment groups to receive a new low-molecular-weight dermatan sulfate (Desmin) at the dose, respectively, of 100 mg once daily by subcutaneous (SC) route, 100 mg twice a day SC, and 200 mg once daily by intramuscular (IM) route. The general and local tolerability and the clinical efficacy of the drug were evaluated by means of clinical, instrumental, and laboratory parameters. Desmin proved capable of effectively improving the symptoms of patients affected by thrombovaricophlebitis, inducing rapid regression by the tenth day of treatment. The daily dose of 200 mg (either SC or IM) was more effective than the 100 mg dose. The systemic tolerability of the drug, administered for the first time for one month, was extremely good, without significant variations in the relevant laboratory tests. Local tolerance (at the site of injection) of the drug was also good.

Capillary electrophoresis of heparin and dermatan sulfate unsaturated disaccharides with triethylamine and acetonitrile as electrolyte additives

Capillary electrophoresis at constant voltage with the addition of triethylamine as electrolyte to a running buffer containing borate using fused-silica capillaries permits the complete resolution in less than 30 min of 11 standard heparin and 8 standard dermatan sulfate disaccharides, which represent degradation products of heparin and dermatan sulfate by specific lyases. Triethylamine influences the migration time of disaccharides by reducing both their electrophoretic mobility towards the anode and the electroosmotic flow towards the cathode. A modulated combination of these effects together with borate-disaccharide complex formation is responsible for separation, especially in the case of isomers which differ in the position of the sulfate groups. The addition of acetonitrile did not introduce any favourable effect in the separation of disaccharide mixtures. Under these conditions different dermatan sulfates were analysed to assess the source of the preparations.

Pharmacology of desmin (low molecular weight dermatan sulphate) in healthy volunteers following intravenous bolus administration of different dosages (200, 400, 800 mg)

Eight healthy volunteers (6 males, 2 females, mean age 31.6 yrs), were administered--on three separate days--200, 400 and 800 mg of a new low molecular weight Dermatan sulphate (Desmin), given as a single i.v. bolus (2 min.) injection. Before each administration and 10, 20, 30 min., 1, 2, 4, 8, 12, 24 hours after, blood samples were drawn and the following coagulative assays performed: aPTT (activated Partial Thromboplastin Time), TT (Thrombin Time), anti Xa (Xa Factor inhibition), Heptest, Stachrom D.S.. Furthermore, a kinetic analysis was performed on the activity curves calculated on the Heptest and Stachrom data. Plasma peak values and half lives of the parameters checked showed a clear dose-effect relationship. aPTT and TT showed very short-lasting variations and the inhibition of Factor Xa was moderate, but significant. The most evident and specific effects of Desmin were those on Heptest and Stachrom D.S.: both tests were influenced in a clear-cut and dose-dependent way, mainly as a consequence of the action of Desmin on HCII, with partially different kinetic patterns. A series of in vitro experiments proved an anti Xa effect of Desmin, mediated by antithrombin III, well above the possible interference of the small (< 1%) heparin contaminants in Desmin. An even more marked anti Xa activity was seen in the in vivo study, an observation so far unrecognized for this type of drug: some possible interpretations of this fact are discussed.

Pharmacodynamic characteristics of low-molecular-weight dermatan sulphate after subcutaneous administration in acute myocardial infarction

Sixteen patients (5 female and 11 male, mean age 59.1 years) who had had an acute myocardial infarction within the previous 7 days, were enrolled in an open pharmacodynamic study. Patients were randomly allocated to two treatment groups and given a single subcutaneous dose of 100 or 200 mg of a new low-molecular-weight dermatan sulphate. The drug pharmacodynamic profile was determined 1, 2, 4, 6, 8, 12 and 24 h after administration. The following coagulation and fibrinolysis tests were performed: activated partial thromboplastin time, thrombin time, activated factor X inhibition, Heptest (global clotting time), heparin cofactor II affinity, functional and antigenic plasminogen activator inhibitor and fibrin plate assay. Both Heptest and heparin cofactor II affinity were significantly increased (P < 0.001) in a dose-dependent manner. The XaI was enhanced, though to a lesser extent. None of the other coagulation or fibrinolysis tests showed significant changes at either dose. Systemic and local tolerance were always very good.

Acute and chronic effects of a new low molecular weight dermatan sulphate (Desmin 370) on blood coagulation and fibrinolysis in healthy subjects

The acute and chronic effects on blood coagulation and fibrinolysis of a new molecular weight dermatan sulphate (Desmin 370) have been investigated in a double blind, placebo-controlled cross over study in 12 healthy volunteers. The compound (100 and 200 mg) was injected IM and the expected heparin cofactor II potentiating effect, reflecting dermatan sulphate activity, peaked after 2 h and was still detectable after 9 h. Surprisingly for this type of compound, a substantial increase in anti-Xa activity also appeared and lasted up to 12 h in the absence of a significant change in aPTT. The bovine-thrombin time was not changed, while human-thrombin times were slightly, albeit non-significantly, prolonged. The activity of t-PA was increased 6h after the higher dose, but the overall pattern of fibrinolytic activities did not suggest any important change after drug treatment in comparison to placebo. No residual or cumulative effect on any of the investigated parameters was detectable 24 h after the injection on the 4th and 8th days during repeated daily administration. Parallel in vitro and in vivo investigations showed that the unexpected anti-Xa effect was not attributable to contamination by traces of low molecular weight heparin. Desmin 370, a low molecular weight dermatan sulphate that potentiates heparin cofactor II and also inhibits Factor Xa, deserves clinical evaluation as an antithrombotic agent.

Effects of glycosaminoglycans on platelet and leucocyte function: role of N-sulfation

The effect of glycosaminoglycans (GAGs) such as sulodexide, low molecular mass dermatan sulfate, heparin and some derivatives with different degrees and types of sulfation was studied on cathepsin G- or thrombin-stimulated platelets and n-formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated polymorphonuclear leucocytes (PMNs). All GAGs (0.01-20 micrograms/mL) inhibited both platelet aggregation induced by cathepsin G and its catalytic activity. Thrombin-induced platelet aggregation in contrast was only prevented by heparin, sulodexide and dermatan (2-100 micrograms/mL). All GAGs, except 2-O,N-desulfated heparin, inhibited beta-glucuronidase and lysozyme release, as well as beta-glucuronidase activity and PMN superoxide production by the peptide fMLP. The efficacy of GAGs was clearly dependent on the degree and type of sulfation since dermatan and N-desulfated heparins were comparatively less effective. The observation that heparin and other GAGs inhibit platelet activation induced by the PMN protease cathepsin G may help determine whether mechanisms of action other than anticoagulation are critical in the antithrombotic activity of heparin and related compounds.