title: In the presence of strong P2Y12 receptor blockade, aspirin provides little additional inhibition of platelet aggregation.
abstract: BACKGROUND
  Aspirin and antagonists of platelet ADP P2Y(12) receptors are often coprescribed for protection against thrombotic events. However, blockade of platelet P2Y(12) receptors can inhibit thromboxane A(2) (TXA(2))-dependent pathways of platelet activation independently of aspirin.
  
  
  OBJECTIVE
  To assess in vitro whether aspirin adds additional antiaggregatory effects to strong P2Y(12) receptor blockade.
  
  
  METHODS
  With the use of platelet-rich plasma from healthy volunteers, determinations were made in 96-well plates of platelet aggregation, TXA(2) production and ADP/ATP release caused by ADP, arachidonic acid, collagen, epinephrine, TRAP-6 amide and U46619 (six concentrations of each) in the presence of prasugrel active metabolite (PAM; 0.1-10 μmol L(-1)), aspirin (30 μmol L(-1)), PAM + aspirin or vehicle. results: PAM concentration-dependently inhibited aggregation; for example, aggregation in response to all concentrations of ADP and U46619 was inhibited by ≥ 95% by PAM at > 3 μmol L(-1) . In further tests of PAM (3 μmol L(-1)), aspirin (30 μmol L(-1)) and PAM + aspirin, aspirin generally failed to produce more inhibition than PAM or additional inhibition to that caused by PAM. The antiaggregatory effects of PAM were associated with reductions in the platelet release of both TXA(2) and ATP + ADP. Similar effects were found when either citrate or lepirudin were used as anticoagulants, and when traditional light transmission aggregometry was conducted at low stirring speeds.
  
  
  CONCLUSIONS
  P2Y(12) receptors are critical to the generation of irreversible aggregation through the TXA(2) -dependent pathway. As a result, strong P2Y(12) receptor blockade alone causes inhibition of platelet aggregation that is little enhanced by aspirin. The clinical relevance of these observations remains to be determined.
authors.affiliation: The William Harvey Research Institute, Barts & the London School of Medicine & Dentistry, Queen Mary University of London, London, UK.
authors.forename: P C J
authors.initials: PC
authors.lastname: Armstrong
authors.forename: P D
authors.initials: PD
authors.lastname: Leadbeater
authors.forename: M V
authors.initials: MV
authors.lastname: Chan
authors.forename: N S
authors.initials: NS
authors.lastname: Kirkby
authors.forename: J A
authors.initials: JA
authors.lastname: Jakubowski
authors.forename: J A
authors.initials: JA
authors.lastname: Mitchell
authors.forename: T D
authors.initials: TD
authors.lastname: Warner
mesh_terms: D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology; D000244:Adenosine Diphosphate / Q000097:blood; D000255:Adenosine Triphosphate / Q000097:blood / Q000494:pharmacology; D016718:Arachidonic Acid / Q000494:pharmacology; D001241:Aspirin / Q000008:administration & dosage*; D003094:Collagen / Q000494:pharmacology; D004357:Drug Synergism; D004837:Epinephrine / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D010446:Peptide Fragments / Q000494:pharmacology; D010879:Piperazines / Q000008:administration & dosage; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000008:administration & dosage; D058921:Purinergic P2Y Receptor Antagonists / Q000008:administration & dosage*; D058925:Receptors, Purinergic P2Y12 / Q000097:blood*; D013928:Thromboxane A2 / Q000097:blood
chemical_list: C548576:P2RY12 protein, human; D010446:Peptide Fragments; D010879:Piperazines; D010975:Platelet Aggregation Inhibitors; D058921:Purinergic P2Y Receptor Antagonists; C510685:R-138727; D058925:Receptors, Purinergic P2Y12; C082835:thrombin receptor peptide (42-47); D016718:Arachidonic Acid; D013928:Thromboxane A2; D000244:Adenosine Diphosphate; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D000255:Adenosine Triphosphate; D003094:Collagen; D001241:Aspirin; D004837:Epinephrine