Summary
We searched for additional anti-platelet effects of clopidogrel in coronary artery
disease (CAD) patients treated with aspirin. Response to clopidogrel was also stratified
according to aspirin resistance. Out of 76 screened aspirin-treated CAD male patients,
five were aspirin-resistant based on arachidonic acid (AA) and ADP aggregometry.These
five patients and 15 aspirin-sensitive patients entered the proper study. Platelet
function was assessed at baseline and after one week of additional clopidogrel treatment
using aggregometry, flow cytometry (ADP, TRAP-6) and platelet reactivity index (PRI)
based on VASP (vasodilatorstimulated phosphoprotein) expression.We evaluated the same
markers in 15 healthy men after aspirin treatment. In healthy subjects aspirin did
not affect resting or ADP-induced activated GPIIb/IIIa and P-selectin expression.
The P-selectin expression on ADP-activated platelets was increased (p<0.01) in aspirin
treated ASA-resistant CAD patients as compared to ASA-sensitive group or aspirin-treated
healthy subjects. Clopidogrel significantly decreased ADP and AA-induced platelet
aggregation and overcame aspirin resistance in four of five patients. Expression of
ADP-induced activation markers was significantly lowered after clopidogrel in all
patients.Out of 20 patients,five did not respond to clopidogrel (<10% inhibition of
ADP aggregation), and this group showed no change in expression of ADPinduced activation
markers after clopidogrel. Clopidogrel treatment significantly reduced PRI only in
the clopidogrel-sensitive group. In conclusion, the addition of clopidogrel to aspirin
provides greater inhibition of platelets and can overcome aspirin resistance. Flow
cytometric analysis of platelets is useful for monitoring of clopidogrel therapy.
Keywords
Aggregation - aspirin - clopidogrel - flow cytometry - platelets