title: Is TRAP-6 suitable as a positive control for platelet reactivity when assessing response to clopidogrel?
abstract: Adenosine 5′-diphosphate (ADP) inducible aggregation is used to assess platelet response to thienopyridines. Thrombin receptor-activating peptide-6 (TRAP-6) inducible aggregation may serve as a positive control because it acts via the thrombin receptor protease-activating receptor-1, which is not blocked by thienopyridines. We therefore investigated if TRAP-6 is suitable as a positive control when assessing residual platelet reactivity to ADP. Platelet response to clopidogrel was assessed in 200 patients on dual antiplatelet therapy using ADP inducible platelet aggregation by light transmission aggregometry (LTA), multiple electrode aggregometry (MEA), and the shear-dependent Impact-R. Test specificities were monitored by TRAP-6 inducible platelet aggregation. The aggregation-independent vasodilator-stimulated phosphoprotein (VASP) phosphorylation assay served for comparisons. ADP inducible aggregation was correlated to that by TRAP-6 (r = 0.33 to 0.72; p < 0.001 for all assays). A linear correlation was seen within MEA (r = 0.72). LTA TRAP-6 correlated weakly with the VASP assay (r = 0.19; p = 0.01), while there were no correlations of TRAP-6 responses by MEA or the Impact-R with the VASP assay (r = 0.03 and &#x2212;0.09; p > 0.05). In all three assays, differences between ADP and TRAP-6 inducible aggregation varied considerably. Within MEA, TRAP-6 inducible aggregation was almost always stronger than ADP inducible aggregation, while within LTA and the Impact-R, weak responses to ADP were associated with both, weak and strong responses to TRAP-6. In conclusion, the application of TRAP-6 as a positive control for platelet reactivity has major limitations and results need to be cautiously interpreted on an individual basis.
authors.affiliation: Division of Angiology, Department of Internal Medicine II, Medical University of Vienna, Vienna, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Gremmel
authors.forename: Andreas
authors.initials: A
authors.lastname: Calatzis
authors.forename: Sabine
authors.initials: S
authors.lastname: Steiner
authors.forename: Alexandra
authors.initials: A
authors.lastname: Kaider
authors.forename: Daniela
authors.initials: D
authors.lastname: Seidinger
authors.forename: Renate
authors.initials: R
authors.lastname: Koppensteiner
authors.forename: Christoph W
authors.initials: CW
authors.lastname: Kopp
authors.forename: Simon
authors.initials: S
authors.lastname: Panzer
mesh_terms: D000244:Adenosine Diphosphate / Q000097:blood / Q000494:pharmacology; D000368:Aged; D001792:Blood Platelets / Q000166:cytology / Q000187:drug effects*; D015815:Cell Adhesion Molecules / Q000097:blood; D000077144:Clopidogrel; D005260:Female; D006801:Humans; D008297:Male; D008840:Microfilament Proteins / Q000097:blood; D010446:Peptide Fragments / Q000494:pharmacology*; D010750:Phosphoproteins / Q000097:blood; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D010979:Platelet Function Tests / Q000379:methods; D013988:Ticlopidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000098662:Vasodilator-Stimulated Phosphoprotein
chemical_list: D015815:Cell Adhesion Molecules; D008840:Microfilament Proteins; D010446:Peptide Fragments; D010750:Phosphoproteins; D010975:Platelet Aggregation Inhibitors; C082835:thrombin receptor peptide (42-47); D000098662:Vasodilator-Stimulated Phosphoprotein; D000244:Adenosine Diphosphate; D000077144:Clopidogrel; D013988:Ticlopidine