The phytoestrogen 8-prenylnaringenin inhibits agonist-dependent activation of human platelets.

BACKGROUND: Phytoestrogens are plant-derived polyphenolic compounds that exert beneficial effects on human health, mostly related to their estrogen mimetic activity. In particular a strong correlation between phytoestrogens intake and a lower risk of cardiovascular diseases has been reported. The flavanone 8-prenylnaringenin, extracted from hop flowers, has been identified as a novel phytoestrogen, unique with respect to estrogen receptors specificity and potency. However, to date no investigations on the 8-prenylnaringenin role in modulating platelet function have been undertaken. METHODS: We evaluated the effect of 8-prenylnaringenin on platelet aggregation, intracellular calcium mobilization and protein phosphorylation triggered by thrombin and collagen, and platelet adhesion and dense granule secretion triggered by collagen. RESULTS: 8-Prenylnaringenin inhibited platelet aggregation induced by different agonists and platelet adhesion to collagen matrix. 8-Prenylnaringenin directly increased intracellular cAMP and cGMP levels and thus promoted VASP phosphorylation. However, these molecular events were not responsible for the inhibitory action of 8-prenylnaringenin on platelets. Moreover, 8-prenylnaringenin inhibited the phosphorylation of Pyk2, Akt, and ERK1/2. Finally, 8-prenylnaringenin suppressed the mobilization of calcium and the secretion of dense granules. All these effects were independent of estrogen receptors recruitment. CONCLUSIONS: 8-Prenylnaringenin exerted anti-aggregatory and anti-adhesive effects on human platelets, independently of estrogen receptors, acting as an inhibitor of multiple proteins essential for the morphological and biochemical transformations that occur during platelet activation and aggregation. GENERAL SIGNIFICANCE: 8-Prenylnaringenin may represent a useful tool in the therapy and prevention of vascular diseases associated with platelet aggregation, such as atherosclerosis, myocardial infarction, coronary artery disease, and thrombosis.

Membrane lipid rafts coordinate estrogen-dependent signaling in human platelets.

The impact of estrogens on the viability of cardiovascular system and their ability to regulate platelet function is still an open and debated question. We have previously shown that estrogen is able to significantly potentiate the aggregation induced by low doses of thrombin and to initiate a rapid and reversible signaling pathway mediated by ERbeta-directed activation of the tyrosine kinases Src and Pyk2 at the level of the plasma membrane. Lipid rafts are critical, cholesterol-enriched membrane domains, which play a major role in blood platelet activation processes. In this work, we investigated the role of lipid rafts in 17beta-estradiol signaling in human platelets. We observed that membrane rafts were essential for both 17beta-estradiol-dependent potentiation of platelet aggregation induced by subthreshold concentrations of thrombin and 17beta-estradiol-induced phosphorylation of Src. 17beta-estradiol caused the reversible translocation of ERbeta to the raft fractions and promoted the rapid and transient recruitment to, and activation within the membrane raft domains of the tyrosine kinases Src and Pyk2. The raft integrity was essential with this respect, as these effects of 17beta-estradiol were completely inhibited by cholesterol depletion. This paper provides evidence for the first time that membrane lipid rafts coordinate estrogen signaling in human platelets.