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J Thromb Haemost. 2007 Mar;5(3):490-6.

Reticulated platelets and uninhibited COX-1 and COX-2 decrease the antiplatelet effects of aspirin.

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  • 1Department of Cardiology, Emory University, Atlanta, GA 77030, USA. nkleiman@tmh.tmc.edu

Abstract

BACKGROUND:

The mechanisms for the variability in antiplatelet effects of aspirin are unclear. Immature (reticulated) platelets may modulate the antiplatelet effects of aspirin through uninhibited cyclooxygenase (COX)-1 and COX-2.

OBJECTIVES:

To evaluate the role of reticulated platelets in the antiplatelet effects of aspirin.

METHODS:

Sixty healthy volunteers had platelet studies performed before and 24 h after a single 325-mg dose of aspirin. Platelet studies included light transmission aggregometry; P-selectin and integrin alpha(IIb)beta(3) expression, and serum thromboxane B(2) (TxB(2)) levels. Reticulated platelets and platelet COX-2 expression were measured using flow cytometry.

RESULTS:

Subjects were divided into tertiles based on the percentage of reticulated platelets in whole blood. Baseline platelet aggregation to 1 microg mL(-1) collagen, and postaspirin aggregations to 5 microm and 20 microm ADP and collagen, were greater in the upper than in the lower tertile of reticulated platelets. Stimulated P-selectin and integrin alpha(IIb)beta(3) expression were also higher in the upper tertile both before and after aspirin. Platelet COX-2 expression was detected in 12 +/- 7% (n = 10) of platelets in the upper tertile, and in 7 +/- 3% (n = 12) of platelets in the lower two tertiles (P = 0.03). Postaspirin serum TxB(2) levels were higher in the upper (5.5 +/- 4 ng mL(-1)) than in the lower tertile (3.2 +/- 2.5 ng mL(-1), P = 0.03), and decreased even further with ex vivo additional COX-1 and COX-2 inhibition. The incidence of aspirin resistance (>or= 70% platelet aggregation to 5 microm ADP) was significantly higher in the upper tertile (45%) than in the lower tertile (5%, P < 0.0001).

CONCLUSIONS:

Reticulated platelets are associated with diminished antiplatelet effects of aspirin and increased aspirin resistance, possibly because of increased reactivity, and uninhibited COX-1 and COX-2 activity.

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