Differences in the influence of the interaction between acetylsalicylic acid and salicylic acid on platelet function in whole blood and isolated platelets: Influence of neutrophils

The aim of this study was to characterize the influence of the interaction between acetylsalicylic acid (ASA) and salicylic acid (SA) on the inhibition by ASA of platelet aggregation in platelets isolated from whole blood, and to determine whether leukocytes influence this pharmacological interaction. This in vitro study was done in human blood from which we prepared samples of whole blood, platelet-rich plasma (PRP), PRP plus mononuclear leukocytes, and PRP plus neutrophils. The variables recorded were maximum platelet aggregation intensity, thromboxane B2 (TxB2) production, and nitric oxide (NO) production (N = 10 different samples in each type of experiment). Different concentrations of ASA and SA were incubated with all samples. In PRP, the concentration of ASA that inhibited maximum aggregation by 50% (IC50) (281 ± 16 μM) increased with increasing SA concentration to a maximum of more than 2 mM when 500 μM SA was used. In whole blood, the IC50 for ASA (24.9 ± 1.2 μM) decreased with decreasing SA concentrations to 7.9 ± 0.8 μM with 50 μM SA and 15.6 ± 0.9 μM with 125 μM SA, and increased to 46.2 ± 2.6 μM with 250 μM SA and 96.3 ± 7.2 μM with 500 μM SA. In experiments with PRP + neutrophils the IC50 of ASA increased in the presence of all concentrations of SA. The antagonistic interactions were also reflected in the changes in TxB2 production in all samples. In samples of neutrophils incubated with ASA, the curve for NO production was shifted to the right, a finding that paralleled the changes in platelet aggregation. In conclusion, the influence of the interaction between ASA and its metabolite SA on platelet aggregation difference depending on the type of sample, and was antagonistic in PRP but partially agonistic in whole blood. Nitric oxide synthesis showed an additive effect of the two compounds.