IN-VITRO EFFECTS OF APROSULATE SODIUM, A NOVEL ANTICOAGULANT, ON PLATELET ACTIVATION - POSSIBLE MECHANISM FOR ANTIPLATELET ACTION

Aprosulate sodium, a bis-lactobionic acid amide derivative, is a novel synthetic polyanion with potent anticoagulant activities. In the pres ent study, the effects of aprosulate on platelet aggregation were inve stigated in a plasma-free system. Aprosulate inhibited thrombin (0.03- 0.3 U/ml)-induced aggregation in rat washed platelets in a concentrati on-dependent manner, with an IC50 value of 0.38 mu g/ml. In contrast, aprosulate, at up to 10 mu g/ml, did not affect collagen (1 mu g/ml) - or ADP (3 mu M)-induced aggregation. In fura 2-loaded platelets, lets , aprosulate (1-10 mu g/ml) inhibited intracellular Ca2+ mobilization induced by thrombin, but not that by ADP. Protamine, a highly basic pr otein, abolished aprosulate-mediated inhibition of thrombin-induced pl atelet aggregation, suggesting that the observed inhibition is primari ly due to the negative charge contained on the aprosulate molecule. In human platelets, aprosulate inhibited thrombin-induced aggregation, b ut failed to inhibit platelet aggregation induced by SFLLRN, a synthet ic tethered ligand of a thrombin receptor. Antiplatelet profiles of ap rosulate were largely similar to those of heparin, although heparin in hibited both thrombin- and collagen-induced aggregation. These in vitr o studies indicate that aprosulate is capable of inhibiting thrombin-i nduced platelet activation and that this effect is independent of its anticoagulant activity. These results suggest that the polyanionic fea ture of aprosulate plays an essential role in promoting its antiplatel et activities, and that a plausible mechanism to explain the observed inhibition conferred by this agent, would be one which involves blocki ng the plateIet-thrombin interaction.