title: The in-vitro effect of tirofiban, glycoprotein IIb/IIIa antagonist, on various responses of porcine blood platelets.
abstract: The present study systematically evaluates the in-vitro effect of tirofiban, glycoprotein IIb/IIIa (integrins alphaIIbbetaIII) antagonist, on porcine blood platelets. It was found that tirofiban at concentrations up to 5,000 ng/ml did not affect the calcium signal produced by thrombin. Tirofiban, in a concentration-dependent manner reduced platelet aggregation evoked by ADP (IC50 approximately 70 ng/ml), collagen (IC50 approximately 200 ng/ml), and thrombin (IC50 approximately 5,000 ng/ml). Substantial thrombin-evoked platelet aggregation still occurred at high (5,000 ng/ml) tirofiban concentrations. The concentrations of tirofiban completely blocking the optical aggregation evoked by ADP or collagen failed to eliminate microaggregate formation totally. Tirofiban strongly inhibited the dense-granule and lysosome secretion induced by ADP (IC50 approximately 70-170 ng/ml), moderately inhibited that induced by collagen (IC50 approximately 420-500 ng/ml) and very poorly inhibited that elicited by thrombin (IC50 approximately 1,500-5,000 ng/ml). The extent of the inhibition of aggregation and secretion rose as concentrations of the stimulus lowered. Tirofiban was a moderate inhibitor (IC50 approximately 200 ng/ml) of adhesion and a poor inhibitor of platelet procoagulant response induced by collagen. Thromboelastography measurements indicate that, in whole blood, tirofiban, up to concentrations of 2,000 ng/ml, did not affect the kinetics of tissue factor induced clot formation. The obtained results reveal that in porcine platelets, the maximal concentrations of tirofiban used in human medicine (250 ng/ml), effectively block platelet responses triggered by ADP, partly block those induced by collagen and very poorly block those evoked by thrombin. The reason for this phenomenon seems to be the inability of tirofiban to reduce platelet secretion completely.
authors.affiliation: Department of Physical Chemistry, Medical University of Bialystok, Kilinskiego 1, 15-089 Bialystok, Poland.
authors.forename: Michał
authors.initials: M
authors.lastname: Ciborowski
authors.forename: Marian
authors.initials: M
authors.lastname: Tomasiak
authors.forename: Tomasz
authors.initials: T
authors.lastname: Rusak
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Winnicka
authors.forename: Sławomir
authors.initials: S
authors.lastname: Dobrzycki
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001779:Blood Coagulation Factors / Q000032:analysis; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects; D003094:Collagen / Q000494:pharmacology; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005260:Female; D066298:In Vitro Techniques; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism; D008297:Male; D015539:Platelet Activation / Q000187:drug effects*; D010973:Platelet Adhesiveness / Q000187:drug effects; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000008:administration & dosage / Q000494:pharmacology*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000037:antagonists & inhibitors*; D034421:Sus scrofa; D013916:Thrombelastography; D013917:Thrombin / Q000494:pharmacology; D000077466:Tirofiban; D014443:Tyrosine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D001779:Blood Coagulation Factors; D010975:Platelet Aggregation Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; C049426:platelet procoagulant factor; D014443:Tyrosine; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D003094:Collagen; D013917:Thrombin; D000077466:Tirofiban