Heterogeneity in platelet cyclooxygenase inhibition by aspirin in coronary artery disease.
BACKGROUND
Platelets, long believed to be incapable of de novo protein synthesis, may retain their ability to form the cyclooxygenase (COX) enzyme once it has been inactivated by aspirin. This may explain the inefficacy of the drug to induce sustained platelet inhibition in certain patients. We evaluated the stability of platelet inhibition following once-daily enteric-coated aspirin administration.


METHODS
Platelet responsiveness to aspirin was evaluated in 11 stable coronary artery disease patients on chronic aspirin therapy before and 1, 3, 8, and 24h after observed ingestion of 80-mg enteric-coated aspirin. Inhibition of the COX pathway was measured pharmacologically through plasma thromboxane (Tx) B(2) levels, and functionally by light transmission aggregometry in response to arachidonic acid. COX-independent platelet activity was measured in response to adenosine diphosphate, epinephrine and collagen.


RESULTS
Plasma TxB(2) levels showed profound inhibition of TxA(2) formation, which was stable throughout 24h, in all but 1 subject. This subject had optimal response to aspirin (inhibition of platelet TxA(2) production within 1h), but recovered the ability to synthesize TxA(2) within 24h of aspirin ingestion. Arachidonic acid-induced platelet aggregation closely mirrored TxB(2) formation in this patient, portraying a functional ability of the platelet to aggregate within 24h of aspirin ingestion. COX-independent platelet aggregation triggered TxA(2) production to a similar extent in all patients, likely through signal-dependent protein synthesis.


CONCLUSIONS
COX-dependent platelet activity is recovered in certain individuals within 24h of aspirin administration. Further research should consider increasing aspirin dosing frequency to twice daily, to allow sustained inhibition in such subjects.
Lordkipanidzé
Marie
M
Faculty of Pharmacy, Hôpital du Sacré-Cœur de Montréal, Montréal, Canada.
Pharand
Chantal
C
Schampaert
Erick
E
Palisaitis
Donald A
DA
Diodati
Jean G
JG
D000328:Adult; D001241:Aspirin / Q000494:pharmacology / Q000627:therapeutic use*; D003324:Coronary Artery Disease / Q000188:drug therapy* / Q000201:enzymology*; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology / Q000627:therapeutic use*; D005260:Female; D018740:Genetic Heterogeneity / Q000187:drug effects; D006801:Humans; D008297:Male; D008875:Middle Aged; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology / Q000627:therapeutic use*; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism; D013928:Thromboxane A2 / Q000037:antagonists & inhibitors / Q000378:metabolism; D013929:Thromboxane B2 / Q000037:antagonists & inhibitors / Q000378:metabolism
D016861:Cyclooxygenase Inhibitors; D010975:Platelet Aggregation Inhibitors; D013929:Thromboxane B2; D013928:Thromboxane A2; D011451:Prostaglandin-Endoperoxide Synthases; D001241:Aspirin