title: Effects of platelet inhibitors on propyl gallate-induced platelet aggregation, protein tyrosine phosphorylation, and platelet factor 3 activation.
abstract: Propyl gallate (PG) is a platelet agonist characterized by inducing platelet aggregation, protein tyrosine phosphorylation, and platelet factor 3 activity. The mechanisms of platelet activation following PG stimulation were examined by pre-incubating platelets with well-defined platelet inhibitors using platelet aggregation, protein tyrosine phosphorylation, activated plasma clotting time, and annexin V binding by flow cytometry. PG-induced platelet aggregation and tyrosine phosphorylation of multiple proteins were substantially abolished by aspirin, apyrase, and abciximab (c7E3), suggesting that PG is associated with activation of platelet cyclooxygenase 1, adenosine phosphate receptors, and glycoprotein IIb/IIIa, respectively. The phosphorylation of the cytoskeletal enzyme pp60(c-src) increased following PG stimulation, but was blunted by pre-incubation of platelets with aspirin, apyrase, and c7E3, suggesting that tyrosine kinase is important for the signal transduction of platelet aggregation. Propyl gallate also activates platelet factor 3 by decreasing the platelet coagulation time and increasing platelet annexin V binding. Platelet incubation with aspirin, apyrase, and c7E3 did not alter PG-induced platelet coagulation and annexin V binding. The results suggest that platelet factor 3 activation and membrane phosphotidylserine expression were not involved with activation of platelet cyclooxygenase, adenosine phosphate receptors, and glycoprotein IIb/IIIa. PG is unique in its ability to stimulate platelet aggregation and coagulation simultaneously, and platelet inhibitors in this study affect only platelet aggregation but not platelet coagulation.
authors.affiliation: Department of Pathology, University of Michigan Medical School, Ann Arbor, Michigan 48109-0602, USA. hxiao@umich.edu
authors.forename: Hongyan
authors.initials: H
authors.lastname: Xiao
authors.forename: Richard
authors.initials: R
authors.lastname: Kovics
authors.forename: Van
authors.initials: V
authors.lastname: Jackson
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Remick
mesh_terms: D017304:Annexin A5 / Q000378:metabolism; D000975:Antioxidants / Q000494:pharmacology; D001081:Apyrase / Q000494:pharmacology; D001241:Aspirin / Q000494:pharmacology; D006801:Humans; D010766:Phosphorylation / Q000187:drug effects; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D010977:Platelet Factor 3 / Q000187:drug effects / Q000378:metabolism*; D011435:Propyl Gallate / Q000494:pharmacology*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism
chemical_list: D017304:Annexin A5; D000975:Antioxidants; D010975:Platelet Aggregation Inhibitors; D010977:Platelet Factor 3; D011435:Propyl Gallate; D011505:Protein-Tyrosine Kinases; D016392:Proto-Oncogene Proteins pp60(c-src); D001081:Apyrase; D001241:Aspirin