Comparative antithrombotic and hemorrhagic effects of dermatan sulfate, heparan sulfate and heparin

Dermatan sulfate and heparan sulfate are currently under development as potential antithrombotic drugs. In our studies we have evaluated the relative antithrombotic and bleeding effects of these two agents in comparison to heparin, the commonly used anticoagulant. In a rabbit model of stasis thrombosis, a 500 micrograms/kg IV dose of dermatan or heparan produced 50-60% inhibition of induced in vivo thrombosis. At 750 micrograms/kg, both agents produced greater than 75% inhibition of thrombosis. Ex vivo measurement of plasma samples obtained from these animals demonstrated variable clotting effects at the lower dose and a proportional increase in the clotting activity at the higher dose. No anti-Xa or anti-IIa activity was observed in any sample. In contrast, animals treated with only 100 micrograms/kg heparin showed complete inhibition of induced thrombosis with significant anti-Xa and anti-IIa activities as well as prolongation of the clotting assays (APTT, TT and HeptestR). In the hemorrhagic studies utilizing a rabbit ear blood loss model, a 5.0 mg/kg IV dose of dermatan or heparan produced much less blood loss than heparin. On a gravimetric basis, dermatan and heparan were 10 fold less hemorrhagic than heparin. These results indicate that the relative contribution of plasmatic and cellular sites to the mediation of the antithrombotic action of heparin, dermatan and heparan differ. Although the antithrombotic dosages of dermatan and heparan are higher than heparin, due to the different mechanisms of action of each agent, a better safety index may be provided by dermatan and heparan than heparin.