Isolation and Characterization of a New Flavone C-glycoside Isoembinin from Iris Lacteal along with Its Effects on Platelet Activation

One new compound isoembinin 1 along with ten known compounds 2-11 were isolated from the terrestrial parts of Iris lactea Pall. All of the compound structures were determined through extensive 1D and 2D NMR experiments along with HR-ESIMS analysis and comparison with literature data. Because many flavonoids exert antiplatelet and antioxidant activity we tested the effects of the isolated flavone C-glycosides 1-9 on platelet activation and reactive oxygen species (ROS) production. Platelet reactivity was assessed by activation of αIIbβ3 integrins activation and ROS production by DCF-DA fluorescence. For the analysis of whether protein kinase A or G are involved in the platelet inhibition, the activity of these kinases was analyzed by phosphorylation of their common substrate in platelets. In all experiments apigenin, which inhibit platelet activation was used as a positive control. All isolated flavone C-glycosides inhibited platelet αIIbβ3 integrins activation with IC50 in the µM range, however this inhibitory effect was found to not be mediated through the prevention of ROS formation or by the activation of cyclic nucleotide pathways. Structure-activity comparison between apigenin and compounds 1-9 shows that the presence of C-glycoside and O-glycoside residues on the aglycone apigenin diminish the degree of platelet inhibition.