The importance of thrombin inhibition for the expression of the anticoagulant activities of heparin, dermatan sulphate, low molecular weight heparin and pentosan polysulphate.

The effects of standard heparin, three low molecular weight derivatives of heparin, dermatan sulphate and pentosan polysulphate on the intrinsic coagulation pathway were compared in order to evaluate the contributions of the anti-factor Xa and anti-thrombin activities to their anticoagulant activities. The anticoagulant potency was measured by the ability of each sulphated polysaccharide to inhibit the generation of thrombin activity in plasma. Similarly, the ability of the six sulphated polysaccharides to enhance the rates of inactivation either factor Xa or thrombin in defibrinated plasma containing calcium chloride and cephalin were also determined. Standard heparin was the only sulphated polysaccharide that could equally inhibit thrombin generation and enhance the inactivation of factor Xa and thrombin by plasma. Dermatan sulphate and pentosan polysulphate were more effective as inhibitors of thrombin generation than potentiators of factor Xa inactivation. The two smallest derivatives of heparin, which had high anti-factor Xa (but low antithrombin) activity, were the poorest inhibitors of thrombin generation. Our results therefore suggest that only sulphated polysaccharides that enhance the inactivation of thrombin by plasma and/or inhibit the generation of thrombin activity in plasma are good anticoagulants. These two activities of sulphated polysaccharides appear to be good predictors of the relative antithrombotic potency in vivo.