title: Flavonoids inhibit the platelet TxA(2) signalling pathway and antagonize TxA(2) receptors (TP) in platelets and smooth muscle cells.
abstract: OBJECTIVE
  Flavonoids may affect platelet function by several mechanisms, including antagonism of TxA(2) receptors (TP). These TP are present in many tissues and modulate different signalling cascades. We explored whether flavonoids affect platelet TP signalling, and if they bind to TP expressed in other cell types.
  
  
  METHODS
  Platelets were treated with flavonoids, or other selected inhibitors, and then stimulated with U46619. Similar assays were performed in aspirinized platelets activated with thrombin. Effects on calcium release were analysed by fluorometry and changes in whole protein tyrosine phosphorylation and activation of ERK 1/2 by Western blot analysis. The binding of flavonoids to TP in platelets, human myometrium and TPalpha- and TPbeta-transfected HEK 293T cells was explored using binding assays and the TP antagonist (3)H-SQ29548.
  
  
  RESULTS
  Apigenin, genistein, luteolin and quercetin impaired U46619-induced calcium mobilization in a concentration-dependent manner (IC(50) 10-30 microm). These flavonoids caused a significant impairment of U46619-induced platelet tyrosine phosphorylation and of ERK 1/2 activation. By contrast, in aspirin-treated platelets all these flavonoids, except quercetin, displayed minor effects on thrombin-induced calcium mobilization, ERK 1/2 and total tyrosine phosphorylation. Finally, apigenin, genistein and luteolin inhibited by >50% (3)H-SQ29548 binding to different cell types.
  
  
  CONCLUSIONS
  These data further suggest that flavonoids may inhibit platelet function by binding to TP and by subsequent abrogation of downstream signalling. Binding of these compounds to TP occurs in human myometrium and in TP-transfected HEK 293T cells and suggests that antagonism of TP might mediate the effects of flavonoids in different tissues.
authors.affiliation: Unit of Haematology and Clinical Oncology, Centro Regional de Hemodonación, University of Murcia, Murcia, Spain.
authors.forename: José A
authors.initials: JA
authors.lastname: Guerrero
authors.forename: Leyre
authors.initials: L
authors.lastname: Navarro-Nuñez
authors.forename: María L
authors.initials: ML
authors.lastname: Lozano
authors.forename: Constantino
authors.initials: C
authors.lastname: Martínez
authors.forename: Vicente
authors.initials: V
authors.lastname: Vicente
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Gibbins
authors.forename: José
authors.initials: J
authors.lastname: Rivera
mesh_terms: D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D002450:Cell Communication / Q000187:drug effects; D005260:Female; D005419:Flavonoids / Q000494:pharmacology*; D006801:Humans; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects; D009215:Myometrium / Q000378:metabolism; D044244:Receptors, Thromboxane A2, Prostaglandin H2 / Q000037:antagonists & inhibitors*
chemical_list: D005419:Flavonoids; D044244:Receptors, Thromboxane A2, Prostaglandin H2