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Unusual effects of aspirin on ticlopidine induced thrombolysis
  1. R J Gryglewski,
  2. W Uracz,
  3. J Święs
  1. Chair of Pharmacology, Jagiellonian University Medical College, Grzegórzecka 16, 31-531 Cracow, Poland
  1. Professor R J Gryglewski

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For hundreds of years salicylates have been used to treat fever and pain. Following the discovery that aspirin inhibits the biosynthesis of prostanoids,1 particularly thromboxane A2 (TXA2) in blood platelets, aspirin gained a new clinical indication as an antiplatelet and antithrombotic drug. Aspirin acetylates the serine 529 residue of cyclo-oxygenase 1 (COX-1) in platelets and megakaryocytes2; however, tyrosyl residues in inducible COX-2 are also acetylated.3 The anti-inflammatory action of aspirin depends on its interaction with COX-2 and subsequent removal of proinflammatory prostanoids or, possibly, on the appearance of cytoprotective 15-epi-lipoxins.4 Only diclofenac induced COX-2 remains insensitive to aspirin.5 Inhibition of nuclear factor kappa B (NFκB) activation is another mechanism of anti-inflammatory action of salicylates.6 Many unusual actions of aspirin are associated with its acetylating power that extends beyond serine residues in COX-1 or tyrosine residues in COX-2. For instance, the anti-cataract effect of aspirin seems to be associated with acetylation of cysteinyl residues of lens γ-crystallins which prevents the formation of opaque disulphide bonding.7 Aspirin affects the rheological properties of erythrocytes,8 decreases erythrocyte mediated activation of platelets,9 and modifies the functioning of haemoglobin by acetylation of its lysyl residues.10 Even platelet membranes possess protein sites available for acetylation by aspirin.11 In humans thrombinogenesis is inhibited by aspirin, possibly as a consequence of acetylation of either platelet membranes or active sites of prothrombin.12 The relation between sodium salicylate and aspirin is complex. Protective effects of sodium salicylate against inhibition of COX by aspirin have been reported in many systems including patients with aspirin induced asthma.13 On the other hand, both drugs enhance the generation of nitric oxide by activated murine macrophages14 or by cultured rat smooth muscle cells.15

The antithrombotic activity of …

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