Anticoagulant Activity and Mechanism of Non-Anticoagulant Sulfated Polysaccharides

Abstract 1208

Fucoidans are sulfated polysaccharides which are extracted from brown seaweeds and echinoderms and have a wide variety of biological activities. Described as non-anticoagulant polysaccharides (NASPs), they have been demonstrated to improve clotting in FVIII- and FIX-deficient plasma (Liu et al., 2006), making them good candidates for hemophilia treatment. However, fucoidans have also been extensively studied for their anticoagulant effects (Pereira et al., 1999), which usually occur at much higher concentrations than the procoagulant activity. This opens a large procoagulant window where procoagulant activities exceed anticoagulant effects. When analyzed by a global hemostatic thrombin generation assay in hemophilia plasma the onset of procoagulant activity is observed at concentrations as low as 0.01 μg/mL with optimal activity at about 1 μg/mL. Reversal of procoagulant activity is seen at concentrations higher than 10 μg/mL. Fucoidans and other sulfated polysaccharides activate different anticoagulant mechanisms depending on their structural properties. Branched fucoidans extracted from brown algae have been shown to directly inhibit thrombin, while linear fucoidan from echinoderms activates antithrombin III (ATIII) or heparin cofactor II (HCII)-mediated thrombin inhibition (Pereira et al., 1999). Sulfated galactans also have serpin-dependent and -independent anticoagulant activities (Glauser et al., 2009). In this study we analyzed fucoidans from several brown algae species for their anticoagulant properties and mode of action to identify the candidate with the best procoagulant and lowest anticoagulant activity.

NASPs from several brown algae species including L. japonica (L.j.), F. vesiculosus (F.v.), and U. pinnatifida (U.p.) showed different anticoagulant activities in an activated partial thromboplastin time (aPTT) assay. U.p. fucoidan was about twice as anticoagulant as the other fucoidan preparations, increasing clotting time by 50% at a concentration of 4 μg/mL. In addition, NASPs were analyzed in ATIII- and HCII-thrombin model assays. L.j. fucoidan activated ATIII-mediated thrombin inhibition, whereas the other fucoidans showed no effect on ATIII. Fucoidans from L.j. and F.v. had a direct effect on thrombin, starting at about 10 μg/mL. By contrast, U.p. fucoidan did not directly affect thrombin. However, all preparations increased HCII-mediated thrombin inhibition at concentrations below 1 μg/mL. This suggests that HCII is the main target for the anticoagulant activity of fucoidans. Nevertheless, we observed substantial differences between the fucoidan candidates which will be correlated to structural properties.

Our work describes the assessment of anticoagulant activities of a variety of fucoidan species to better understand their intertwined pro- and anticoagulant effects. This provides important mechanistic insights for the development of hemophilia therapies.