title: A critical role for thrombin in platelet aggregation under high shear stress.
abstract: The serine protease, thrombin, plays a crucial role in both coagulation and platelet activation. Anhydrothrombin (AhT) is a catalytically inactive derivative of thrombin in which dehydroalanine replaces the active-site serine. AhT retains affinity for natural substrates of thrombin and may be a competitive inhibitor of thrombin-mediated coagulation and platelet reactions. In the present study, thrombelastography showed that AhT not only delayed the onset and the progress of the coagulation process but impaired clot strength, indicating that AhT may have both anticoagulant and antiplatelet activity. In addition, AhT prolonged the activated partial thromboplastin time dose-dependently, but had little effect on the prothrombin time, suggesting that its principal activity was mediated in the intrinsic coagulation pathway. AhT inhibited thrombin-induced aggregation of platelet-rich plasma. Complete inhibition of aggregation was evident at a concentration of 1.85 microM AhT. Furthermore, 3.7 microM of AhT almost completely abolished shear-induced platelet aggregation in PRP. Interpretation of this in vitro study requires confirmation in vivo, but the findings suggest that thrombin plays a critical role in shear related platelet mechanisms. AhT may be a useful tool for investigating platelet-based coagulation reactions and may provide the basis for a novel class of antithrombotic agents.
authors.affiliation: Department of Pediatrics, Nara Medical University, 840 Shijo-cho, Kashihara, Nara 634-8522, Japan. ysakurai@naramed-u.ac.jp
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Sakurai
authors.forename: Midori
authors.initials: M
authors.lastname: Shima
authors.forename: John
authors.initials: J
authors.lastname: Giddings
authors.forename: Masahiro
authors.initials: M
authors.lastname: Takeyama
authors.forename: Shogo
authors.initials: S
authors.lastname: Kasuda
authors.forename: Keiji
authors.initials: K
authors.lastname: Nogami
authors.forename: Katsumi
authors.initials: K
authors.lastname: Nishiya
authors.forename: Akira
authors.initials: A
authors.lastname: Yoshioka
mesh_terms: D000925:Anticoagulants / Q000494:pharmacology; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000008:administration & dosage; D066298:In Vitro Techniques; D010314:Partial Thromboplastin Time; D010974:Platelet Aggregation / Q000187:drug effects / Q000502:physiology*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000378:metabolism; D011517:Prothrombin Time; D013314:Stress, Mechanical; D013916:Thrombelastography; D013917:Thrombin / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000494:pharmacology / Q000502:physiology*; D014841:von Willebrand Factor / Q000378:metabolism
chemical_list: D000925:Anticoagulants; D007140:Immunoglobulin Fab Fragments; D010975:Platelet Aggregation Inhibitors; D019038:Platelet Glycoprotein GPIb-IX Complex; D014841:von Willebrand Factor; D013917:Thrombin