title: M(r) 6,400 aurin tricarboxylic acid directly activates platelets.
abstract: ATA is a novel anticoagulant polymeric anionic aromatic compound that inhibits von Willebrand factor binding to platelet glycoprotein Ib and thereby prevents ristocetin- and shear stress-induced platelet aggregation. To investigate its mechanism of action, ATA fractions of homogeneous M(r) have been prepared by size exclusion chromatography. ATA fractions of M(r) > or = 2,500 are most effective at inhibiting vWF-mediated platelet aggregation, and ATA of M(r) = 2,500 also inhibits thrombin-induced platelet activation. Paradoxical results were observed in studies of ATA with M(r) = 6,400. This fraction of ATA stimulates aggregation of washed platelets or platelet-rich-plasma. The dose/response of aggregation shows a bell-shaped curve with maximal aggregation at approximately 2 micrograms/ml. Platelet aggregation is associated with phosphoinositide turnover and protein kinase C- and calcium-dependent protein phosphorylation. Platelet signalling responses to ATA are inhibited by platelet pretreatment with PGI2 or dibutyryl-cyclic AMP, but are unaffected by inhibiting platelet cyclooxygenase with aspirin. These results suggest that M(r) 6,400 ATA directly activates platelet phospholipase C to initiate platelet aggregation. This effect, unique to M(r) 6,400 ATA, could potentially mitigate ATA's beneficial anti-thrombotic effect on vWF-mediated platelet responses, and should be considered when analyzing results of experiments that utilize unfractionated ATA.
authors.affiliation: Baylor College of Medicine, VA Medical Center, Houston, TX 77030.
authors.forename: Z
authors.initials: Z
authors.lastname: Guo
authors.forename: M J
authors.initials: MJ
authors.lastname: Weinstein
authors.forename: M D
authors.initials: MD
authors.lastname: Phillips
authors.forename: M H
authors.initials: MH
authors.lastname: Kroll
mesh_terms: D001312:Aurintricarboxylic Acid / Q000494:pharmacology*; D006801:Humans; D008970:Molecular Weight; D015539:Platelet Activation / Q000187:drug effects*; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D011493:Protein Kinase C / Q000097:blood
chemical_list: D010975:Platelet Aggregation Inhibitors; D001312:Aurintricarboxylic Acid; D011493:Protein Kinase C