Antiplatelet effects of flavonoid aglycones on platelet activation are mediated by inhibition of phosphodiesterases

Flavonoids are a group of polyphenolic compounds found in different plants. Considered safe with favorable pharmacological effects and a wide therapeutic window, flavonoids emerge as promising candidates for medical application, including treatment and prevention of cardiovascular events. Antiplatelet activity for these compounds has been established, however the molecular mechanisms responsible for platelet inhibition and whether it is mediated by cyclic nucleotides dependent pathways are not known. In this study, we defined the molecular mechanisms of platelet inhibitory effects of six aglycones: luteolin, myricetin, eriodictyol, quercetin, kaempferol, and apigenin. All compounds significantly inhibited thrombin-induced platelet activation and decreased the level of reactive oxygen species (ROS) formation in activated platelets without affecting platelet viability, apoptosis induction, or formation of procoagulant platelets. Aglycones increased cyclic nucleotide concentrations and induced VASP phosphorylation. cAMP concentration was increased by luteolin, myricetin, quercetin, and apigenin, and all tested compounds increased cGMP concentration, which was not mediated by adenylyl or guanylyl cyclase activation. To test whether some of the compounds can dampen phosphodiesterase (PDE) activity, we used a Förster resonance energy transfer (FRET) based assay on HEK293 cells. The tested aglycones strongly inhibited PDE2 activity, whereas PDE5 was inhibited only moderately. In summary, we showed that all tested aglycones inhibit platelets by elevation of cAMP/cGMP levels, PKA/PKG activation, and inhibition of PDE2 and PDE5.

This work was supported by Russian Science Foundation (the RSF grant 23-15-00142).