Anticoagulant properties in vitro of heparan sulphates

The anticoagulant properties in vitro of eight heparan sulphate preparations were studied using clotting (APTT, anti-Xa) and amidolytic (anti-Xa, anti-thrombin) assays. Activities ranged from very low levels (less than 5 iu/mg) up to values similar to those of heparin. Activities measured by APTT assay showed the best correlation with the sulphate to carboxylate ratio of the heparan sulphates. Highest activities were obtained in the anti-Xa clotting assay, these being approximately two-fold greater than activities in the anti-Xa amidolytic assay. Five of the heparan sulphate preparations were readily neutralised by protamine sulphate, whereas the three heparans with the lowest sulphate to carboxylate ratio were much more resistant to neutralisation. After fractionating each heparan sulphate into At III-binding and non-binding material, it was found that the anti-coagulant properties were associated only with the former. It is concluded that these properties are dependent on the activation of At III.