To cite this article: Quinder e A-LG, Santos GRC, Oliveira S-NMCG, Glauser BF, Fontes BP, Queiroz INL, Benevides NMB, Pomin VH, Mourão PAS. Is the antithrombotic effect of sulfated galactans independent of serpin? J Thromb Haemost 2014; 12: 43-53.Summary. Background: Sulfated galactans are polysaccharides with heterogeneous structures that frequently show anticoagulant activity. Their anticoagulant mechanisms are complex and distinct from those observed for heparin. Sulfated galactans act through a combination of effects involving serpin-dependent and serpin-independent mechanisms. Interestingly, these polymers can also induce blood coagulation due to activation of factor XII (FXII). Objectives: The structure of a complex sulfated galactan from the red alga Acanthophora muscoides was characterized by solution nuclear magnetic resonance. This polysaccharide and another previously characterized algal sulfated galactan from Botryocladia occidentalis were each used in in vitro and in vivo anticoagulant and antithrombotic assays to understand the possible structural determinants of their functional effects. Results and Conclusions: The serpin-dependent anticoagulant effects and FXIIrelated procoagulant effects of the sulfated galactans decreased in parallel with the molecular size. The serpinindependent anticoagulation also correlated with the chemical structure of the sulfated galactans. The sulfated galactan from A. muscoides, which showed mostly serpinindependent anticoagulant activity and reduced activation of FXII, drastically reduced arterial thrombus formation. However, the sulfated galactans produced opposite effects on venous thrombosis; this difference appears to result from the tenuous balance between the various effects on coagulation, including serpin-dependent and serpin-independent anticoagulation and FXIIa-dependent procoagulation. This study of novel sulfated polysaccharides with distinct effects on coagulation and thrombosis helps to establish the minimal structural-function relationship required for the development of antithrombotic drugs.

Fucosylated chondroitin sulfate (FucCS) is a potent anticoagulant polysaccharide extracted from sea cucumber. Its anticoagulant activity is attributed to the presence of unique branches of sulfated fucose. Although this glycosaminoglycan exerts an antithrombotic effect following oral administration, high doses are necessary to achieve the maximum effect. The diminished activity of FucCS following oral administration is likely due to its degradation in the gastrointestinal tract and its limited ability to cross the intestinal cell membranes. The latter aspect is particularly difficult to overcome. However, gastro-resistant tablet formulation may help limit the degradation of FucCS in the gastrointestinal tract. In the present work, we found that the oral administration of FucCS as gastro-resistant tablets produces a more potent and prolonged anticoagulant effect compared with its administration as an aqueous solution, with no significant changes in the bleeding tendency or arterial blood pressure. Experiments using animal models of arterial thrombosis initiated by endothelial injury demonstrated that FucCS delivered as gastro-protective tablets produced a potent antithrombotic effect, whereas its aqueous solution was ineffective. However, there was no significant difference between the effects of FucCS delivered as gastro-resistant tablets or as aqueous solution in a venous thrombosis model, likely due to the high dose of thromboplastin used. New oral anticoagulants tested in these experimental models for comparison showed significantly increased bleeding tendencies. Our study provides a framework for developing effective oral anticoagulants based on sulfated polysaccharides from marine organisms. The present results suggest that FucCS is a promising oral anticoagulant.

Heparin is a centennial anticoagulant drug broadly employed for treatment and prophylaxis of thromboembolic conditions. Although unfractionated heparin (UFH) has already been shown to have remarkable pharmacological potential for treating a variety of diseases unrelated with thromboembolism, including cancer, atherosclerosis, inflammation, and virus infections, its high anticoagulant potency makes the doses necessary to exert non-hemostatic effects unsafe due to an elevated bleeding risk. Our group recently developed a new low-anticoagulant bovine heparin (LABH) bearing the same disaccharide building blocks of the UFH gold standard sourced from porcine mucosa (HPI) but with anticoagulant potency approximately 85% lower (approximately 25 and 180 Heparin International Units [IU]/mg). In the present work, we investigated the pharmacokinetics profile, bleeding potential, and anticancer properties of LABH administered subcutaneous into mice. LABH showed pharmacokinetics profile similar to HPI but different from the low-molecular weight heparin (LMWH) enoxaparin and diminished bleeding potential, even at high doses. Subcutaneous treatment with LABH delays the early progression of Lewis lung carcinoma, improves survival, and brings beneficial health outcomes to the mice, without the advent of adverse effects (hemorrhage/mortality) seen in the animals treated with HPI. These results demonstrate that LABH is a promising candidate for prospecting new therapeutic uses for UFH.