Structural and Functional Characterization of Fucoidan and Its Procoagulant Effect in An Ex Vivo Model of Factor VIII-Inhibited Guinea Pigs

Abstract 2262

Fucoidans are sulfated polysaccharides extracted and purified from brown seaweeds. Described as non-anticoagulant polysaccharides (NASPs), they have been shown to improve clotting in FVIII- and FIX-deficient plasma (Liu et al. Thromb Haemost 2006;95:68), making them good candidates for hemophilia treatment. NASP orally administered to hemophilia A dogs over several weeks resulted in correction to normal ranges in thromboelastography (TEG) parameters and improvement of the cuticle bleeding time (Prasad et al. Blood 2008;111:672). We screened extracts of eleven brown algae species to select the most active, high-quality, homogeneous fucoidan. In-depth structural analysis and assessment of the pro-/anticoagulant and TFPI-inhibiting activities of a selected set of fucoidan preparations was performed. The effect of the best fucoidan candidate was studied in a novel guinea pig model by whole blood TEG monitoring supported by calibrated automated thrombographic (CAT) analysis.

Comparative structural studies of fucoidans included monosaccharide composition and elemental analysis, molecular weight and overall structural determination by NMR. ¹³C-NMR spectroscopy gave a comprehensive picture of fucoidan structure including fucose and alginate content and the relative heterogeneity of the preparation distinguishing between fucoidans of different algae species. Heterogeneity of the materials was highest in U. pinnatifida and L. japonica and lowest in F. vesiculosus (F.v.) samples. Procoagualant activity was shown by CAT and rotation thromboelastometry. Clotting parameters of FVIII-inhibited human blood or plasma were corrected to normal levels at 1 and 3 μg/mL depending on the fucoidan. In addition, the fucoidans were analyzed by BiaCore and a modified dilute prothrombin time assay to show binding to TFPI and inhibition of full-length TFPI activity. The screening process supported the identification and optimization of new fucoidan-specific analytical methods.

Furthermore, a CAT protocol optimized for guinea pig plasma was used to show the procoagulant effect of the overall best fucoidan candidate. We spiked F.v. fucoidan into FVIII-inhibited guinea pig plasma between 1 and 100μg/mL and triggered thrombin generation with low amounts of tissue factor. The FVIII-inhibited guinea pig plasma was corrected to normal CAT parameters at ∼30μg/mL NASP. Based on our findings in the CAT assay, we designed a dosage pattern for studying the procoagulant effect using TEG in FVIII-inhibited Dunkin Hartley guinea pigs (n=10) after intravenous administration of 0.1 to 1.6mg/kg NASP. The primary endpoint assessed was R-time (time to clotting). FVIII-inhibited guinea pigs showed a median R-time of ≥120min (no clotting), while R-time was reduced in a non-linear dose-dependent manner after administration of NASP down to 69min (0.4mg/kg NASP). Thus, the results generated in in vitro tests, were confirmed in vivo. This new animal model of induced hemophilia will support the development of alternative hemophilia therapeutics.