Sulodexidearenewedinterestinthisglycosaminoglycan.pdf

Sulodexide: A Renewed Interest in This Glycosaminoglycan

D. Adam Lauver and Benedict R. Lucchesi

Department ofPharmacology, University ofMichigan Medical School, Ann Arbor, Michigan, USA

Keywords: Anticoagulants — Diabetic nephropathy — Glycosaminoglycans — Reperfusion injury — Sulodexide — Vessel™.

ABSTRACT

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.

INTRODUCTION

Glycosaminoglycans (GAGs) are a naturally occurring group of compounds that have found clinical use in the prevention of thrombotic events. This group of molecules makes up the most abundant group of heteropolysaccharides in the body. GAGs are negatively charged molecules characterized by long, unbranched polysaccharide chains that contain a repeating disaccharide unit. The disaccharide units contain either of two modified sugars, N-acetylgalactosamine or N-acetylglucosamine, and a uronic acid such as glucuronate or iduronate (26,43,56).

Cardiovascular Drug Reviews Vol. 24, No. 3–4, pp. 214–226 © 2006 The Authors Journal compilation © 2006 Blackwell Publishing, Inc.

Address correspondence and reprint requests to: Dr. Benedict R. Lucchesi, Department of Pharmacology, University of Michigan Medical School, 1301C MSRB III, 1150 West Medical Center Drive, Ann Arbor, MI 48109-0632, USA. Tel.: +1 (734) 647-3134; Fax: +1 (734) 647-4782; E-mail: benluc@umich.edu

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Clinical usage of GAGs for the treatment of thrombotic diseases is not without risks however. For example, heparin has been shown to have various side effects including heparin-induced thrombocytopenia. Therefore, efforts to develop alternative therapies have resulted in the introduction of low molecular weight heparins and small molecules targeted to selective sites in the coagulation cascade.

One of these alternatives, sulodexide, is a highly purified GAG that is composed of two distinct fractions. The mixture of GAGs is obtained from the porcine intestinal mucosa by a patented process (37). The chemical composition of sulodexide is defined as 80% fast mobility heparin (FMH) and 20% dermatan sulfate (DS). FMH fraction is described based on its electrophoretic mobility. The FMH component is present in commercial unfractionated heparin together with a slower electrophoretic mobility fraction. FMH and DS are further characterized by having a lower degree of sulfation and lower anticoagulant activity than unfractionated heparin.

The low molecular weight of both sulodexide fractions allows for extensive oral absorption compared to heparin. In rats, pharmacodynamic effects were observed within three hours of oral administration and a cellular distribution of fluorescent material was observed in the kidney, liver and endothelium of veins and arteries (21,67). The pharmacokinetics in man has been evaluated using deuterium-labeled sulodexide (12). A single 100 mg dose of deuterated sulodexide was administered to healthy volunteers intravenously or orally. After intravenous dosage the elimination half-life of the FMH was 1.0 h and DS was 1.6 h. Peak plasma levels were 20 mgL and 8 mgL, respectively. Oral administration of sulodexide resulted in peak plasma levels of both compounds ranging from 0.2–1.0 mgL approximately 1–10 h after dosing.

Sulodexide (Vessel™), a product developed by Alfa Wassermann, has been marketed for more than twenty years in Italy, Spain, Eastern Europe, South America, and Asia for the treatment of various cardiovascular conditions. Currently, Keryx Biopharmaceuticals is developing sulodexide (Sulonex™) as a treatment for diabetic nephropathy in North America. Sulonex™ is currently in Phase III and Phase IV clinical trials under a Special Protocol Assessment with the United States Food and Drug Administration.

PHARMACOLOGY AND CLINICAL STUDIES

Anticoagulant and Antithrombotic Activity

Survivors of acute myocardial infarction are at high risk for the recurrence of thrombosis and sudden cardiac arrest is a major health problem, causing about 330,000 deaths each year among U.S. adults either before reaching a hospital or in an emergency room. Major research efforts in academic settings and pharmaceutical companies have focused on investigating various antithrombotic agents for the secondary prevention of acute coronary syndrome. The goal is to develop agents that can be administered by the oral route with minimal potential for inducing marked alterations in hemostasis.

GAGs exert an antithrombotic action by interacting with naturally occurring serine protease inhibitors such as antithrombin III (ATIII) and heparin cofactor II (HCII) (3,17). As a result of these interactions, the inhibition of activated serine proteases in the coagulation cascade by ATIII and HCII is accelerated more than 1000 fold (38,42,69). Thrombin is the central serine protease of the coagulation system as it promotes cleavage of fibrinogen into fibrin, which then polymerizes leading to the formation of occlusive arterial or venous thrombi (58,59) or thromboemboli originating from the left atrium in patients with atrial fibrillation. Thrombin can also exert positive feedback on itself by activating factor VIII and factor V (30). The inhibition of thrombin formation and its proteolytic action are the primary mechanisms by which GAGs exert their anticoagulant and antithrombotic effects (57,71).

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Thrombin is the essential serine protease of the coagulation cascade that promotes the deposition of thrombi by cleaving fibrinogen to fibrin, which then polymerizes, under the influence of thrombin-induced activation of FXIII thereby forming a stable occlusive intravascular thrombus. Thrombin also exerts a positive feedback on its own generation by activating FVIII and FV.

The FMH and DS fractions of sulodexide accelerate the inhibition of thrombin by their simultaneous interactions with ATIII and HCII, respectively (10,52). As a result, they directly inhibit thrombin and also thrombin generation by inhibiting the feedback activation of prothrombin (30). Sulodexide prolongs the thrombin clotting time and the activated partial thromboplastin time (aPTT).

The heparin-induced activation of ATIII retards thrombus growth and thrombus formation along with the induction of a hypocoagulable state. A major limitation to the efficacy of heparin is its inability to inhibit the proteolytic activity of thrombin that is bound to fibrin or incorporated into the thrombus. In contrast, the inhibition of fibrinbound thrombin by the HCIIDS complex is not impaired (50). In an in vivo study (8), it was determined that pretreatment with heparin, 10 antithrombin units per 1 kg (10 Ukg), inhibited clot formation to the same extent as 5 Ukg of sulodexide. Thus, sulodexide administered in half the antithrombin dose of heparin was equally as effective in preventing thrombus formation. The results are consistent with the hypothesis that thrombin inhibition by the simultaneous activation of ATIII and HCII has a greater efficacy than heparin. The synergistic effect is evident by the observation that a lower dose of sulodexide achieved an equivalent antithrombotic effect as a higher dose of heparin in preventing thrombosis (7,8,18). The greater efficacy of sulodexide derives from its dual action of catalyzing the inhibition of thrombin by ATIII and by HCII with the added advantage of a limited potential for inducing increased bleeding. The latter may be related to the absence of an influence on aPTT as indicated by the lack of interference of sulodexide on the intrinsic coagulation pathway (53). The different sites in the coagulation cascade where sulodexide exerts anticoagulant effects are illustrated in a review by Davie and Kulman (22).

In an acute experimental model where the thrombus formation was induced in the carotid arteries of rats by electrical stimulation, sulodexide significantly prolonged the time to vessel occlusion (maximum fall in temperature) in a dose-dependent manner after intravenous bolus administration, with an efficacy similar to that of heparin or aspirin (2). The study results also demonstrated the ability of sulodexide to prevent ex vivo platelet aggregation in response to thrombin, but not to arachidonic acid. The ability to preserve partial platelet reactivity might account for the fact that sulodexide exhibits a limited potential to induce uncontrolled bleeding.

Using a chronic rat model of arterial thrombosis, sulodexide was compared to heparin to analyze the ratios of the antithromboticbleeding effects of the respective anticoagulants (40). At doses that were equally as effective at preventing arterial thrombosis, heparin-bleeding time was 2 times longer than baseline, while sulodexide produced a 25% prolongation in bleeding time.

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Clinical trials have demonstrated the beneficial effects of sulodexide in the treatment of deep vein thrombosis. Errichi et al. reported that after 6, 12, and 24 months of oral sulodexide treatment (50 mg daily) the recurrence of deep vein thrombosis was significantly attenuated $( p < 0 . 0 5 )$ in high-risk subjects (27). A more recent trial compared sulodexide with acenocoumarol in the secondary prophylaxis of patients with deep vein thrombosis (14). In this study a fixed dose of sulodexide (30 mg, four doses per day) was compared with adjusted doses (international normalized ratio) of acenocoumarol. There were no differences in either clinical evolution of the disease or the number of venous recurrences over the course of the treatment period between groups. In the group treated with sulodexide there were no hemorrhagic complications. In the acenocoumarol group, however, one major hemorrhage (requiring discontinuation of the anticoagulant) and nine minor hemorrhages (not requiring discontinuation of the anticoagulant) were recorded. The difference in adverse events was statistically significant $( p = 0 . 0 1 4 )$ . These results coupled with the high cost of acenocoumarol monitoring reinforce the benefits of sulodexide in the management of certain thrombotic diseases.

Sulodexide has also been found effective in the treatment of venous leg ulcers (15). Chronic venous stasis of the lower extremities results in endothelial damage causing the formation of thrombi. Impairment of the microcirculation of the skin induces chronic inflammation and ulceration. In this study 235 patients undergoing local treatment of leg ulcers were randomized to either sulodexide (60 mg daily i.m. for 20 days, followed by 100 mgday p.o. for 70 days) or placebo treatment groups. The proportion of patients with complete ulcer healing was higher in the sulodexide group at 2 months $( p = 0 . 0 1 8 )$ and 3 months. Additionally, ulcer surface area and fibrinogen levels were significantly reduced in the sulodexide group compared to placebo $( p = 0 . 0 0 4 $ and 0.006, respectively).

Similarly, the beneficial effects of sulodexide have been seen in the treatment of intermittent claudication. Intermittent claudication is defined as painful cramping in the legs that is present during exercise or walking and occurs as a result of decreased blood flow to the legs. This phenomenon occurs in individuals with peripheral arterial obstructive disease. In a randomized, double-blind, placebo controlled trial (16), sulodexide (60 mg daily i.m. for 20 days, followed by 100 mgday p.o. for 6 months) successfully doubled the pain free walking distance in 23.8% of patients while only 9.1% achieved a doubling in the placebo group $( p = 0 . 0 0 1 )$ . The pain-free walking distance increased by $8 3 . 2 \pm 8 . 6$ m (mean ± standard error) with sulodexide and $3 6 . 7 \pm 6 . 2$ m with placebo.

In addition to the antithrombotic effects of sulodexide, administration of the compound to animals with preexisting thrombi demonstrates a dose dependent reduction in thrombus size (4). It was suggested that this effect could be attributed to the activation of tissue plasminogenic activator andor the inhibition of plasminogenic activator 1 (12,20).

Prevention of Reperfusion Injury

The restoration of myocardial blood flow to a previously ischemic region is associated with a complex series of events leading to tissue injury greater than that which is attributed to the original period of flow deprivation, an event referred to as “reperfusion injury.”

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The complement system is a component of the innate immune system consisting of a group of proteins circulating in the blood. The components of the complement system act together to recognize and destroy foreign pathogens. Activation of the complement system, however, can also have adverse effects on host tissues. In the setting of myocardial reperfusion injury, the complement system represents an integral mechanism through which the ischemic tissue undergoes injury leading to irreversible tissue injury and cell death (45,61). Previous studies provided evidence for the role of complement by demonstrating the deposition of the terminal complement complex, or the membrane attack complex (MAC), in irreversibly injured myocardial tissue (68). The authors offered the suggestion that the initial period of ischemia may cause loss of the ability of the heart muscle cells to regulate complement turnover at the membrane level. The resulting deposition of C5b-9 (membrane attack complex) on the cell membranes may contribute to functional disturbance and irreversible damage of myocardial cells during the infarction process. It is hypothesized that pharmacological inhibition of complement activation would be beneficial in reducing tissue injury associated with ischemia and reperfusion.

Various GAGs have been reported by our laboratory to be of benefit to the ischemic myocardium by preserving contractile function and reducing tissue injury (6,29,35,46,70). In addition, selective GAGs are known to possess anti-complement activity in addition to their classical roles as anticoagulants. Recently we reported that sulodexide effectively reduced myocardial infarct size after ischemia and reperfusion in the rabbit heart when administered periodically throughout the four hour reperfusion period (48) (Fig. 1). Sulodexide was demonstrated to inhibit complement activation, possibly through the inhibition of C-reactive protein (CRP), resulting in a reduction in the extent of myocardial injury associated with ischemiareperfusion (Fig. 2). The data indicate that there is a separation between the anticoagulant and anti-complement effects of sulodexide by utilizing a dose of the compound that was found previously to have little or no effect on coagulation (37) while retaining the ability to protect the ischemic myocardium.

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Heparin and related non-anticoagulant glycosaminoglycans are reported to reduce the extent of myocardial injury. This effect has been attributed to an anti-inflammatory action mediated in part through complement inhibition (50,60). However, heparin possesses other pharmacodynamic properties that could explain its cytoprotective actions. A comparison between heparin and an o-desulfated non-anticoagulant heparin with greatly reduced anti-complement activity administered at the time of coronary artery reperfusion in a canine model of myocardial infarction, equally reduced neutrophil adherence to ischemic-reperfused coronary artery endothelium, influx of neutrophils into ischemic-reperfused myocardium, myocardial necrosis, and release of creatine kinase into plasma (72). The authors report that heparin or o-desulfated heparin also prevented dysfunction of endothelial-dependent coronary relaxation following ischemic injury. In addition, heparin and o-desulfated heparin inhibited translocation of the transcription nuclear factor-kappaB (NF-êB) from the cytoplasm to the nucleus in human endothelial cells and decreased NF-êB DNA binding in human endothelium and ischemic-reperfused rat myocardium. Thus, it was observed that heparin and non-anticoagulant heparin decrease ischemia-reperfusion injury by disrupting multiple levels of the inflammatory cascade, including the novel observation that heparins inhibit activation of the proinflammatory transcription factor NF-êB. That a similar mechanism(s) might apply to sulodexide is suggested by the many studies involving the anti-inflammatory actions attributable to a wide range of glycosaminoglycans (39,63).

It is understood that heparin and other GAGs have therapeutic uses beyond their traditional role as anticoagulants (63). The parenteral administration of sulodexide results in a decrease in myocardial infarct size in a model of in vivo regional ischemiareperfusion (48). The results are in accordance with previous studies in which it was found that other glycosaminoglycans have the ability to reduce infarct size in vivo (6,29,34,47,70). The chemical composition of sulodexide is defined as 80% low molecular mass (7000 Da) heparin fraction and 20% DS. Low-molecular mass heparin contains the same dimeric components as unfractionated heparin, but has a lower degree of sulfation and shorter polysaccharide chain length. DS is a polysaccharide made up of many various disaccharide units with a mean molecular mass of 25,000 Da. As a result of the presence of both fractions, sulodexide potentiates the antiprotease activities of both antithrombin III and heparin cofactor II simultaneously. Although structurally similar, sulodexide has major differences from unfractionated heparin including prolonged half-life, reduced effect on global coagulation, and oral bioavailability (8,9). Low-molecular mass heparin has previously been shown to reduce infarct size following ischemia and reperfusion (34,51); however, DS has yet to be individually investigated. Due to their ability to inhibit the complement cascade, it is hypothesized that GAGs may prevent the adverse events associated with complement activation associated with ischemia reperfusion. Activation of the complement cascade leads to the assembly of the MAC on cell membranes. Deposition of a sufficient number of the lytic membrane attack complexes on a nucleated target cell results in disruption of the cell membrane and ultimately cell lysis. Intravenous administration of 0.5 mgkg sulodexide, commencing immediately upon reperfusion and at hourly intervals during reperfusion was associated with a significant decrease in myo-

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