Additive thrombin inhibition by fast moving heparin and dermatan sulfate explains the anticoagulant effect of sulodexide,a natural mixture of glycosaminoglycans

Introduction: The aim of the study was to evaluate the mechanism of the anticoagulant action of sulodexide, a mixture of glycosaminoglycans (GAGs) composed of dermatan sulfate (DS) and fast moving heparin (FMH), in vitro. Materials and methods: Thrombin clotting time (TCT) was measured in human platelet poor plasma (PPP). A chromogenic substrate assay was used to determine the pseudo-first order constant kinetic of thrombin inhibition (k′=k_obs/min) either in defibrinated PPP or antithrombin (AT) or heparin cofactor II (HCII) depleted defibrinated PPP in the absence and presence of sulodexide or its components, alone and in combination. The interaction between DS and FMH was analysed by both the algebraic fractional and isobole graphical methods. Results: Sulodexide, DS and FMH produced a dose-dependent prolongation of TCT with unclottable TCT at sulodexide above 4 μg/ml and at DS or FMH above 5 μg/ml. Sulodexide and its components alone and in combination produced a dose-dependent linear increase in the rate of thrombin inhibition in defibrinated PPP. The algebraic fractional and the isobole graphical methods indicated an additive effect between DS and FMH. In AT depleted PPP, the dose-dependent increase in k′ produced by sulodexide was significantly lower than in PPP, while the dose-dependent increase in k′ produced by DS was similar to the increase produced in PPP. In HCII depleted PPP, the dose-dependent increase in k′ produced by sulodexide was significantly lower than in PPP, while the dose-dependent increase in k′ produced by FMH was similar to the increase produced in PPP. Conclusions: Thrombin inhibition produced by sulodexide is due to the additive effect of its components, namely, HCII catalysis by DS and AT catalysis by FMH.