Calcium mobilization by the plant estrogen ferutinin does not induce blood platelet aggregation

Abstract

Platelet activation is closely associated with an increase in intracellular Ca2+ concentration. Various compounds including Ca2+ ionophores are able to trigger platelet aggregation by increasing intracellular Ca2+ concentration in platelets. In the present study, we monitored the effect of the phytoestrogen ferutinin, which acts as a Ca2+ ionophore in human blood platelets; its ionophore-like properties include upregulation of [Ca2+]in, activation of fibrinogen receptors and increased fibrinogen binding. Using spectrofluorometry and triple-color flow cytometry, we demonstrate that ferutinin increases [Ca ] in both isolated platelets and platelets in whole blood from humans. This effect was almost completely blocked by the Ca2+ chelator EGTA and was not sensitive to either Gd3+ or econazole, which inhibit VOC and SOC channels, respectively. Nor was the effect sensitive to thapsigargin, an inhibitor of endoplasmic reticulum Ca2+ ATPases. Ferutinin stimulated the expression of the active form of the GPIIb-IIIa complex and whole blood platelet aggregation only weakly and had no statistically significant effect on the binding of fibrinogen. These results demonstrate apparently inconsistent effects of ferutinin, which raises intraplatelet Ca2+ concentration but fails to have an effect on spontaneous blood platelet aggregation. This pattern of responses may be caused by the combination of ferutinin’s Ca2+ ionophoric and estrogenic properties.