BACKGROUND: One reason for the lower incidence of cardiovascular diseases in Asian countries may be the high intake of isoflavonoids and their antiplatelet effects may be an important factor. To date, there is limited comparison of a range of isoflavonoids and knowledge of their effects at different levels of platelet aggregation. PURPOSE: To screen the antiplatelet effects of a number of isoflavonoids on the arachidonic acid based aggregation pathway and investigate how the antiplatelet activity might occur. METHODS: The antiplatelet effects were first screened in whole human blood where platelet aggregation was induced by arachidonic acid. Further analysis was targeted at search of the mechanism of action. RESULTS: Thirteen of the eighteen tested isoflavonoids had significant inhibitory effect on platelet aggregation in whole human blood. Genistein had the same potency as clinically used acetylsalicylic acid (ASA) while tectorigenin was clearly stronger than ASA. Further analyses showed that the effect of tectorigenin was not based on inhibition of cyclooxygenase-1 in contrast to ASA or thromboxane synthase but by competitive antagonism at thromboxane receptors. CONCLUSION: Tectorigenin is a more potent antiplatelet compound than ASA and thus an interesting substance for further testing.

Department of Pharmaceutical Botany and Ecology Faculty of Pharmacy in Hradec Králové Charles University Akademika Heyrovského 1203 500 05 Hradec Králové Czech Republic

Department of Pharmacognosy Faculty of Pharmacy in Hradec Králové Charles University Akademika Heyrovského 1203 500 05 Hradec Králové Czech Republic

Department of Pharmacology and Toxicology Faculty of Pharmacy in Hradec Králové Charles University Akademika Heyrovského 1203 500 05 Hradec Králové Czech Republic

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The Effect of Silymarin Flavonolignans and Their Sulfated Conjugates on Platelet Aggregation and Blood Vessels Ex Vivo