Effect of New Synthetic Heparin Mimetics on Whole Blood Thrombin Generation In Vivo and In Vitro in Rats

Abstract

SummaryThe effect of new heparin mimetics (synthetic oligosaccharides) was studied in vitro with regard to thrombin generation (TG) in rat platelet rich plasma (PRP) and whole blood (WB) and in vivo on stasis-induced venous thrombosis in the rat.TG in PRP and in WB was highly dependent on platelet count and strongly influenced by the haematocrit. The peak of TG appeared to be significantly higher in WB than in PRP whereas the endogenous thrombin potential (ETP) was not significantly different under either condition.The effect of hirudin, the synthetic pentasaccharide SR90107/ Org31540 (SP) and heparin were measured on TG in PRP and WB. We then compared the effect of two new synthetic heparin mimetics (SR121903A and SanOrg123781) with potent and comparable antithrombin (AT) mediated activity against factor Xa and thrombin. These two compounds were made of a pentasaccharide with a high affinity to AT, prolonged at the non-reducing end by an oligosaccharide chain recognised by thrombin. In SR121903A, the charge density and charge distribution was analogous to that of heparin whereas in SanOrg123781 the charges were only located on the last 5 saccharides of the non-reducing end of the molecule. In PRP and in WB, SR121903A acted on the lag time and on the AUC whereas SanOrg123781 inhibited thrombin formation with no effect on the lag time. SanOrg123781 was more potent in inhibiting TG than SR121903A. This difference was due to the structures of the compounds that differed in their ability to be neutralised by platelet factor 4. The antithrombotic effect of the two compounds was examined in a venous thrombosis model in rats. We observed that SanOrg123781 was more active than SR121903A and heparin.Taken together, these results indicate that the activity of oligosaccharides is greatly influenced by the global charge density of the molecule and show that SanOrg123781 is a potent and promising antithrombotic drug candidate.