Insights on chemical-biological correlations learned from investigations on the sulfated galactan from the marine alga Bothryocladia occidentalis.

Marine organisms have been proven to be a valuable source of bioactive compounds. Among them, we highlight the sulfated galactans (SGs) from seaweeds, which besides being massively exploited as industrial thickening and gelling agents (agarans and carrageenans), have also shown promising pharmacological properties. Investigations on the non-agaran/-carrageenan SG from the red algae Bothryocladia occidentalis (SGBo) have demonstrated clear correlations between physical-chemical features and biological activities. SGBo is composed of 2,3-disulfated (~33%) or 2-sulfated (33%) α-D-galactose linked to non- or 2-sulfated β-D-galactose repetitive disaccharide units. The notable serpin-dependent/-independent anticoagulant activity of SGBo (~130 international units [IU]/mg) is higher than those of other SGs containing less 2,3-disulfated α-D-galactose units and their low-molecular-weight derivatives, and thus is directly correlated to its high molecular mass (>200 kDa) and sulfation pattern. Although SGBo has antithrombotic efficacy equivalent to heparin and decreased bleeding potential at low-doses, high-doses substantially increase thrombus formation in animal models. Such an odd dose-dependent dual antithrombotic/prothrombotic activity has been attributed to the ability of SGBo to activate factor XII. In addition to anticoagulant properties, SGBo also exerts antimalarial, antileishmanial and antiophidic activities, and, therefore, has a remarkable potential for the research and development of novel drugs.