Further Studies on the Mechanisms for the Antithrombotic Effects of Sulfated Polysaccharides in Rabbits

The pathobiology of osteoarthritis and the rationale for the use of pentosan polysulfate for its treatment

OBJECTIVES

Structure-modifying osteoarthritis (OA) drugs (SMOADs) may be defined as agents that reverse, retard, or stabilize the underlying pathology of OA, thereby providing symptomatic relief in the long-term. The objective of this review was to evaluate the literature on sodium pentosan polysulfate (NaPPS) and calcium pentosan polysulfate (CaPPS), with respect to the pathobiology of OA to ascertain whether these agents should be classified as SMOADs.

METHODS

Published studies on NaPPS and CaPPS were selected on the basis of their relevance to the known pathobiology of OA, which also was reviewed.

RESULTS

Both NaPPS and CaPPS exhibit a wide range of pharmacological activities. Of significance was the ability of these agents to support chondrocyte anabolic activities and attenuate catabolic events responsible for loss of components of the cartilage extracellular matrix in OA joints. Although some of the anti-catabolic activities may be mediated through direct enzyme inhibition, NaPPS and CaPPS also have been shown to enter chondrocytes and bind to promoter proteins and alter gene expression of matrix metalloproteinases and possibly other mediators. In rat models of arthritis, NaPPS and CaPPS reduced joint swelling and inflammatory mediator levels in pouch fluids. Moreover, synoviocyte biosynthesis of high-molecular-weight hyaluronan, which is diminished in OA, was normalized when these cells were incubated with NaPPS and CaPPS or after intraarticular injection of NaPPS into arthritic joints. In rabbit, canine, and ovine models of OA, NaPPS and CaPPS preserved cartilage integrity, proteoglycan synthesis, and reduced matrix metalloproteinase activity. NaPPS and CaPPS stimulated the release of tissue plasminogen activator (t-PA), superoxide dismutase, and lipases from vascular endothelium while concomitantly decreasing plasma levels of the endogenous plasminogen activator inhibitor PAI-1. The net thrombolytic and lipolytic effects exhibited by NaPPS and CaPPS may serve to improve blood flow through subchondral capillaries of OA joints and improve bone cell nutrition. In geriatric OA dogs, NaPPS and CaPPS reduced symptoms, as well as normalized their thrombolytic status, threshold for platelet activation, and plasma triglyceride levels. These hematologic parameters were shown to be abnormal in OA animals before drug treatment. Similar outcomes were observed in OA patients when CaPPS or NaPPS were given orally or parenterally in both open and double-blind trials.

CONCLUSIONS

The data presented in this review support the contention that NaPPS and CaPPS should be classified as SMOADs. However, additional long-term clinical studies employing methods of assessing joint structural changes will be needed to confirm this view.

A phase I study of pentosan polysulfate sodium in patients with advanced malignancies

BACKGROUND

Pentosan polysulfate (xylanopolyhydrogensulfate) is a semi-synthetic sulfated heparinoid polysaccharide which has been used as an anticoagulant for nearly thirty years in Europe. It antagonizes the binding of bFGF to cell surface receptors and has thus been evaluated for antitumor activity in several animal models and human tumor cell lines. In two angiogenic models pentosan has been shown to inhibit bFGF stimulation of angiogenesis. Previous clinical studies have determined the coagulation effects of pentosan to be the dose-limiting toxicity.

PATIENTS AND METHODS

We conducted a phase I study designed to define the duration-limiting toxicity associated with progressive prolongation of a continuous intravenous infusion (three, five, and eight weeks). This study was not designed to escalate the dose of pentosan beyond that required to maintain the activated partial thromboplastin time (aPTT) between 1.8 and 2.2 times the baseline value.

RESULTS

Thirteen patients with advanced stage metastatic cancer were enrolled (median age 50 years, range 34 to 61 years). Four patients were treated in cohort #1 (three weeks of infusional therapy), five patients were treated in cohort #2 (five weeks of therapy), and four patients in cohort #3 (eight weeks of therapy). All patients experienced a progressive prolongation of their aPTT and PT. Furthermore, all patients experienced at least grade I thrombocytopenia. Other complications were, in general, mild. One patient developed grade III liver abnormalities while receiving the eight-week infusion and another patient developed grade IV thrombocytopenia while receiving the same regimen. One patient with colon cancer had stable disease for 24 weeks, while the remaining 12 patients had no objective evidence of response.

CONCLUSION

Pentosan was well tolerated when doses were adjusted for aPTT prolongations and a five-week cycle appeared to be the maximum tolerated duration of infusion (initially 4 mg/kg/day). One patient had stable disease, but there was no objective tumor response noted in the remaining 12 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.

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.

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.

The effect of the beta-D-xyloside naroparcil on circulating plasma glycosaminoglycans. An explanation for its known antithrombotic activity in the rabbit

Beta-D-Xylosides are known to initiate or prime free glycosaminoglycan (GAG) chain synthesis in cell and tissue culture. As such, the effect of the venous antithrombotic beta-D-xyloside, naroparcil, was investigated on the plasma GAG profile in the rabbit after oral administration. Using dose-response experiments, we showed that antithrombin activity via antithrombin III and heparin cofactor II was increased in parallel with GAG plasma levels compared to control. A more detailed qualitative examination of plasma GAGs by cellulose acetate electrophoresis and ion-exchange chromatography, following oral administration of naroparcil at 400 mg/kg, revealed the presence of higher density charged molecules compared to control. The extracted GAGs were found to activate inhibition of thrombin by heparin cofactor II and contained approximately 25% of a dermatan sulfate-like compound (undetectable in control), which could be responsible for the antithrombotic effect. Using radiolabeled naroparcil, we found radiolabeled GAG fractions and the fact that naroparcil was a substrate for galactosyltransferase I, the second enzyme responsible for GAG chain polymerization, suggested that the compound could initiate in vivo the biosynthesis of antithrombotic free GAG chains. This is, to our knowledge, the first description of the in vivo effect of a beta-D-xyloside on GAG biosynthesis; furthermore, this is correlated with an antithrombotic action.

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.

Growth factor targeted and conventional therapy of breast cancer

Sustained breast cancer growth and metastasis requires paracrine signals between the tumor cells and the normal surrounding host tissue. One crucial function of these signals is to recruit endothelial cells and thus new blood vessels for the nourishment of the expanding tumor mass. This proliferation and migration of endothelial cells in the vicinity of progressing tumors contrasts with the extremely low turn-over rate of endothelial cells in the healthy adult. A blockade of tumor-induced endothelial cell proliferation should inhibit tumor growth and potentially metastasis with only few adverse effects. Different therapeutic approaches that take advantage of this situation are discussed with respect to their interaction with conventional therapies of breast cancer.

Effects of subcutaneously administered dermatan sulfate (MF 701) on the coagulation and fibrinolytic parameters of healthy volunteers

Eight healthy volunteers were given single subcutaneous doses of dermatan sulfate (DS, 100, 200 and 400 mg), heparin (5,000 IU) and placebo in random order. Wash-out between treatments was greater than or equal to 10 days. Serial blood samples were taken before and up to 24 hours after treatment to measure coagulation and fibrinolytic parameters. Thrombin generation was significantly inhibited by DS and heparin as compared to placebo. The effect of DS was dose-dependent. Peak inhibition after 200 mg DS was comparable to that of 5,000 IU heparin, but lasted longer. A small, bordeline significant prolongation of APTT was observed after 400 mg DS and heparin. The changes in PAI and fibrinolytic activities were those of the circadian variation. No changes were seen in the other parameters tested. In conclusion, single s.c. doses of DS (200, or 400 mg) inhibit ex vivo thrombin generation equally or more than 5,000 IU heparin and for a longer time. The effect of both treatments on fibrinolysis is negligible.

Antithrombotic potencies of heparins in relation to their antifactor Xa and antithrombin activities: an experimental study in two models of thrombosis in the rabbit

Our purpose was to determine the relative contribution of the antifactor Xa and antithrombin activities of heparin to its antithrombotic potency. The antithrombotic activities of unfractionated heparin (UH), two low molecular weight heparins (LMWH, CY 216 and CY 222) with increasing anti-factor Xa/antithrombin ratio and a synthetic pentasaccharide (PS) with high affinity to antithrombin III and no antithrombin activity were evaluated. In the Wessler-thromboplastin model, the most potent antithrombotic agent, on a weight basis, was UH followed by CY 216, CY 222 and the PS which was 40 times less potent than UH. On an antithrombin unit basis, the antithrombotic potencies of UH, CY 216 and of CY 222 were equivalent. Thus, in this model, the antithrombotic effect results from the catalytic action of UH or LMWH on thrombin inhibition. In the Wessler-serum model, on a weight basis, the antithrombotic effectiveness of UH was unchanged, those of CY 216 and CY 222 were doubled, and that of the PS was increased 10 times. On an anti-factor Xa unit basis, CY 216 was as effective as UH, and PS as effective as CY 222. On an antithrombin unit basis, CY 216 and CY 222 were equivalent and more potent than UH. Thus, in this model, the antifactor Xa activity of heparin becomes important for its antithrombotic property. After a single subcutaneous injection of 1000 antifactor Xa U/kg, the antithrombotic effects of UH were maintained for more than 14 h in the two models. After injection of the same dose of CY 216 significant antithrombotic effects were observed only for 9 h, in the Wessler-thromboplastin model but for 18 h in the Wessler-serum model. At that time, no detectable antithrombin activity was measurable in the plasma while 0.11 units of antifactor Xa activity/ml was detected. Thus, the relative contribution of the anti-factor Xa and antithrombin activities to the antithrombotic effect of a LMWH differs according to the nature of the thrombogenic stimulus.