ACTIVE SITE FOR HEPARIN COFACTOR II IN LOW MOLECULAR MASS DERMATAN SULFATE. CONTRIBUTION TO THE ANTITHROMBOTIC ACTIVITY OF FRACTIONS WITH HIGH AFFINITY FOR HEPARIN COFACTOR II

Abstract Dermatan sulfate (DS) is currently under clinical investigation as new antithrombotic agent. Unlike heparin, DS does not act through Antithrombin III (ATIII) but primarily through thrombin on Heparin Cofactor II (HCII). HCII is activated by the oversulfated sequence (IdoA2SO 3 -GalNAc4SO 3 ) 4 or by both the sequences (IdoA2SO 3 -GalNAc4SO 3 )n and (IdoA-GalNAc-4,6SO 3 )n, [n ≥ 2]. A Low Molecular Mass Dermatan Sulfate (LMM-DS), endowed with a bioavailability three-four times higher than DS, by subcutaneous route, was obtained by chemical depolymerization of DS. The LMM-DS was fractionated by anion exchange and size exclusion chromatography. Fractions with high and low charge densities, high and low molecular masses, and high (2.66) and low (0.07) potencies on HCII were isolated. A relationship between the in vitro HCII-mediated inhibition of thrombin and the chain length of DS fractions containing oversulfated sequences was found [by a multiple regression test]. The in vivo activity increased until it reached a plateau. The important influence on the HCII activity of natural IdoA-GalNAc-4,6SO 3 disaccharide was confirmed by investigation on oversulfated DS obtained by a limited and selective chemical 6-O-sulfation in GalNAc4SO 3 units of DS.