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Abstract-F 2 -isoprostanes are prostaglandin (PG) isomers produced in vivo through free radical-catalyzed peroxidation of arachidonic acid, which may affect platelet function. The current study investigated the effects of 8-epiprostaglandin F 2␣

SummaryWe studied in vitro the antiplatelet activity of a new nitroderivative chemically related to acetylsalicylic acid: 2 acetoxybenzoate 2-[l-nitroxy-methyl]-phenyl ester (NCX 4016), in order to identify any effects due to the release of nitric oxide and the blockade of cyclooxygenaseThe effects of scalar doses of NCX 4016 on the early phase of platelet activation, platelet aggregation and thromboxane A2 production were investigated. We observed inhibitory effects of NCX 4016 on platelet adhesion (IC50 = 7.3 × 10−5 M), platelet cytosolic calcium concentration, assayed by fluorescent probe Fura 2, and the expression of glycoprotein IMIIa (CD41 / αIIbβ3) (IC50 = 3.4 × 10−5 M) and P-selec-tin (CD62 / GMP-140) (IC50 = 4.9 × 10−5 M) measured by flow cytometry. NCX 4016 also prevented thrombin-induced platelet aggregation (IC50 = 3.9 × 10−5 M). None of these parameters were affected by acetylsalicylic acid. These inhibitory activities of NCX 4016 were abolished by oxyhaemoglobin and methylene blue. Intracellular cyclic GMP observed during thrombin-induced aggregation was increased by incubation with NCX 4016. These results appear to be attributable to the release of nitric oxide, which activates soluble platelet guanylyl-cyclase and promotes intracellular cyclic GMP increase. NCX 4016 almost completely inhibited platelet thromboxane A2 production and arachidonic acid-induced platelet aggregation. This also occurred in the presence of oxyhaemoglobin and methylene blue, indicating that its antiplatelet activity can be attributed not only to nitric oxide release but also to cyclo-oxygenase inhibition.

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Summary. The membrane complex a IIb b 3 is the major receptor for fibrinogen and is involved in platelet adhesion and aggregation. Evidence has been presented that the Pl A2 allele of the b 3 Pl A1/A2 gene polymorphism might be an independent risk factor for coronary thrombosis, but the matter is still controversial. We investigated the relationship between this polymorphism and possible alterations of platelet functions in vitro. The platelet adhesion to fibrinogen-coated microplate wells and the aggregation induced by several different agonists were tested in 63 healthy volunteers, among them, 49 subjects with Pl A1/A1 polymorphism, 12 subjects with Pl A1/A2 polymorphism and two subjects with Pl A2/A2 polymorphism. Subjects with Pl A1/A2polymorphism or with Pl A2/A2 polymorphism showed significantly lower platelet responses as compared with Pl A1/A1 subjects when either arachidonic acid or the thromboxane A 2 analogue, U46619, were used as agonists.In resting condition and after thrombin or ADP stimulation, platelet function was normal in all the subjects. An increased sensitivity to the anti-aggregatory effect of acetylsalicylic acid was observed in platelets from subjects with the Pl A2 allele. Finally, using a flow-cytometric evaluation and determining the b-thromboglobulin plasma levels, we did not find any evidence of a Pl A2 platelet hyperreactivity ex vivo. Our findings are not consistent with the hypothesis that the purported increase of cardiovascular risk in these subjects may be as a result of platelet hyperactivation. On the contrary, the Pl A2 allele is associated with a platelet functional deficiency, specifically linked to the activation of the fibrinogen receptor by thromboxane A 2 .