The In Vitro Effect of Ticlopidine on Fibrinogen and Factor VIII Binding to Human Platelets

Summary

The mode of action of the antiplatelet agent ticlopidine is not yet fully understood. Its multiple effects on platelet function include prolongation of the bleeding time, reduction in primary and secondary Waves of ADP-induced aggregation and inhibition of collagen and thrombin-induced aggregation. We have studied the in vitro effects of ticlopidine on fibrinogen binding induced by ADP and adrenaline as well as factor VIII/vWF binding induced by ristocetin.

¹²⁵I-fibrinogen binding was measured in suspensions of freshly washed normal platelets stimulated by 10 μM ADP or 10 μM adrenaline. The binding of ¹²⁵I-factor VIII/vWF in the presence of 1 mg/ml ristocetin was measured in both washed and paraformaldehyde-fixed platelets. Ticlopidine at final concentrations of 200, 100, 50 and 25 μM inhibited both ADP and adrenaline-induced fibrinogen binding in a dose-dependent manner. The mean % inhibition of ADP-induced fibrinogen binding was 82, 73, 42 and 32 respectively. The mean % inhibition of adrenaline induced fibrinogen binding was 86, 82, 60 and 35 respectively. In contrast, the factor VIII/vWF binding was unaffected by ticlopidine at all concentrations except at 200 μM using fresh platelets where a slight inhibition (19%) was observed.

These results suggest that ticlopidine either inhibits platelet activation and consequently fibrinogen binding, or inhibits the binding directly, presumably by having an effect on the specific configuration of the platelet membrane required for normal fibrinogen binding.

Keywords

Ticlopidine - Fibrinogen binding - Factor VIII/vWF binding - Platelets

• References

• 1 Lecrubier C, Conard J, Samama M, Bousser MG. Essai d’un nouvel agent anti-agrégant: La ticlopidine. Thérapie 1977; 32: 189-194
• 2 O’Brien JR, Etherington MD, Shuttleworth RD. Ticlopidine - an antiplatelet drug: effects in human volunteers. Thromb Res 1978; 13: 245-254
• 3 David JL, Monfort F, Herion F, Raskinet R. Compared effects of three dose levels of ticlopidine on platelet function in normal subjects. Thromb Res 1979; 14: 35-49
• 4 Nunn B, Lindsay R. Effect of ticlopidine on human platelet responsiveness ex vivo: comparison with aspirin. Thromb Res 1980; 18: 807-813
• 5 Conard J, Lecrubier C, Scarabin PY, Horellon MH, Samama M, Bousser MG. Effects of long term administration of ticlopidine on platelet function and hemostatic variables. Thromb Res 1980; 20: 143-148
• 6 Lips JP M, Sixma JJ, Schiphorst ME. The effect of ticlopidine administration to humans on the binding of adenosine diphosphate to blood platelets. Thromb Res 1980; 17: 19-27
• 7 Lee H, Nurden AT, Thomaidis A, Caen JP. Relationship between fibrinogen binding and the platelet glycoprotein deficiencies in Glanzmann’s thrombasthenia type I and type II. Br J Haematol (accepted for publication).
• 8 Nurden AT, Caen JP. The different glycoprotein abnormalities in thrombasthenic and Bernard-Soulier platelets. Semin Hematol 1979; 16: 234-250
• 9 Kao KJ, Pizzo SV, McKee PA. Demonstration and characterization of specific binding sites for Factor VIII/von Willebrand Factor on human platelets. Clin Invest 1979; 63: 656-664
• 10 Patscheke H, Worner P. Platelet activation detected by turbidimetric shape-change analysis. Thromb Res 1978; 12: 485-496
• 11 Allain JP, Cooper HA, Wagner RH, Brinkhous KM. Platelets fixed with paraformaldehyde: a new reagent for assay of von Willebrand Factor and platelet aggregating factor. J Lab Clin Med 1975; 85: 318-328
• 12 Over J, Sixma JJ, Doucet-de Bruine MH M, Trieschnigg AM C, Vlooswijk RA A, Beeser-Visser NH, Bouma BN. Survival of ¹²⁵iodine-labeled factor VIII in normals and patients with classic hemophilia. Observations on the heterogeneity of human factor VIII J Clin Invest 1978; 62: 223-234
• 13 Lagarde M, Ghazi IDechavanne. Effects of ticlopidine on platelet prostaglandin metabolism. Possible consequences for prostacyclin production Prostaglandins and Med 1979; 2: 433-439
• 14 Hawiger J, Parkinson S, Timmons S. Prostacyclin inhibits mobilisation of fibrinogen-binding sites on human ADP- and thrombin-treated platelets. Nature 1980; 283: 195-197
• 15 Ashida SI, Abiko Y. Mode of action of ticlopidine in inhibition of platelet aggregation in the rat. Thromb Haemostas 1979; 42: 436-449
• 16 Bennett JS, Vilaire G. Exposure of platelet fibrinogen receptors by ADP and epinephrine. J Clin Invest 1979; 64: 1393-1401
• 17 Plow EF, Marguerie G. Induction of the fibrinogen receptor on human platelets by epinephrine and the combination of epinephrine and ADP. J Biol Chem 1980; 255: 10971-10977
• 18 Johnson M, Walton PL, Cotton RC, Strachan CJ L. Pharmacological evaluation of ticlopidine a novel inhibitor of platelet function. Thromb Haemostas 1977; 38: 64-65