Effects of the selective inhibition of platelet thromboxane synthesis on the platelet‐subendothelium interaction

Abstract

1 Drugs that inhibit TxA 2 synthesis are used to reduce platelet aggregation. The aim of this study was to compare the eects of a cyclo-oxygenase (COX) inhibitor (acetylsalicylic acid, ASA), a thromboxane synthetase (TxS) inhibitor (dazoxiben) and a dual TxS inhibitor and TxA 2 receptor blocker (DT-TX 30) on platelet aggregation and the platelet-subendothelium interaction in¯ow conditions. 2 The techniques used in this in vitro study were platelet aggregometry in whole blood, and measurement of platelet thromboxane B 2 and prostaglandin E 2 production and leucocyte production of 6-keto-PGF 1a . The platelet-subendothelium interaction was evaluated in rabbit aorta subendothelium preparations exposed to¯owing blood at a shear stress of 800 s 71. Morphometric methods were used to calculate the percentage of subendothelium occupied by platelets. 3 The 50% inhibitory concentration (IC 50 ) of DT-TX 30 in whole blood was in the range of 10 77 mM (induced with collagen or arachidonic acid) to 10 75 mM (induced with thrombin) or 10 74(induced with ADP). IC 50 values under all experimental conditions were lower with DT ± TX 30 than with ASA. For thromboxane B 2 the IC 50 were: ASA 0.84+0.05 mM, dazoxiben 765+54 mM, DT ± TX 30 8.54+0.60 mM. Prostaglandin E 2 was inhibited only by ASA (IC 50 1.21+0.08 mM). Leucocyte 6-keto-PGF 1a was inhibited by ASA (IC 50 6.58+0.76 mM) and increased by dazoxiben and DT ± TX 30. The greatest reduction in percentage subendothelial surface occupied by platelets after blood perfusion was seen after treatment with DT ± TX 30 in the range of concentrations that inhibited collagen-induced platelet aggregation (control group: 31.20+3.8%, DT-TX 30 at 0.1 mM: 10.71+0.55%, at 1.0 mM: 6.53+0.44%, at 5.0 mM; 1.48+0.07%). All three drugs reduced thrombus formation, although ASA (unlike dazoxiben or DT ± TX 30) increased the percentage surface occupied by adhesions. 4 In conclusion, the eect of speci®c blockage of TxS together with blockage of membrane receptors for TxA 2 can surpass the eect of ASA in inhibiting the platelet-subendothelium interaction in¯ow conditions.

Increased platelet deposition on extracellular matrix under flow conditions in patients with antiphospholipid syndrome who experience thrombotic events

“…However, controversial data regarding the effect of aspirin on platelet adhesion under flow conditions have been published. Several studies in which venous or arterial shear stress was evaluated showed no such effect (40, 41) or even increasing effects on platelet adhesion (42, 43), while others showed a moderate inhibitory effect of aspirin on platelet adhesion and thrombus formation (44–46). However, the models and shear rates used were different in the different studies.…”

Serotonin Potentiates High-Glucose^|^ndash;Induced Endothelial Injury: the Role of Serotonin and 5-HT2A Receptors in Promoting Thrombosis in Diabetes

“…Sarpogrelate was used at concentrations that inhibit aggregation of human and rat platelets (22), and aspirin was used at a concentration that inhibits aggregation of human platelets (23).…”

15,16-Dihydrotanshinone I, a major component from Salvia miltiorrhiza Bunge (Dansham), inhibits rabbit platelet aggregation by suppressing intracellular calcium mobilization

“…However, 15,16-dihydrotanshinone had no effect in thrombin-activated platelets. This inhibitory effect of 15,16-dihydrotanshinone on TxA 2 was greater than that for aspirin (acetylsalicylic acid, 500 M), a well-known COX-1 inhibitor that leads to inhibition of synthesis of TxA 2 , PGE 2 and prostacyclin in human (De La Cruz et al, 2002). However, the discrepancy in the potencies for the inhibitory effects on platelet aggregation and thromboxane B 2 production appear to indicate that the antiplatelet activity of 15,16-dihydrotanshinone is ascribed only in part to the inhibition of TxA 2 production with the possible involvement of inhibition of thromboxaneindependent pathways for its antiplatelet activity.…”

“…Thus, it seems likely that the inhibitory effect of 15,16-dihydrotanshinone I on phosphoinositide breakdown and the resulting decrease in [Ca 2+ ] i mobilization could in turn lead to a significant blockade of arachidonic acid liberation by PLC and cPLA 2 , which are the two main types of [Ca 2+ ] isensitive enzymes responsible for liberating arachidonic acid (Balsinde et al, 2002;Drayer et al, 1995). Arachidonic acid (AA), mainly released from the cell membrane phospholipid by phospholipase A 2 (PLA 2 ), is converted to various eicosanoids by cyclooxygenase (COX) and lipoxygenase (LO) (Kim et al, 2002), the COX-produced metabolites playing an fundamental role in the process of arterial thrombus formation (De La Cruz et al, 2002). 15,16-Dihydrotanshinone I inhibited collagen-induced arachidonic Fig.…”

“…Thromboxane A 2 (TxA 2 ) is a potent stimulator of both platelet and smooth muscle leading to platelet aggregation and vasoconstriction, respectively, with implication of its production in the pathogenesis of atherosclerosis and myocardial infarction (Bos et al, 2004;De La Cruz et al, 2002). Thus, we further investigated if 15,16-dihydrotanshinone could inhibit TxA 2 production through arachidonic acid metabolic cascade.…”