Inhibition of platelet activation and endothelial cell injury by flavan-3-ol and saikosaponin compounds

The effects of flavan-3-ol and saikosaponin compounds on platelet aggregation, platelet thromboxane biosynthesis and H₂O₂-induced endothelial cell injury were studied. Seven flavan-3-ol compounds isolated from Camellia sinensis L. var sinensis O. Kuntze (Theaceae) and three saikosaponin compounds isolated from Bupleurum falcatum L. (Umbelliferae) were used. Among the 10 compounds tested, only epigallocatechin and saikosaponin a significantly inhibited human platelet aggregation induced by ADP, and the potency of inhibition was comparable with aspirin. Both of epigallocatechin and saikosaponin a dose-dependently inhibited the platelet thromboxane formation from exogenous and endogenous arachidonic acid. In the prevention of H₂O₂-induced endothelial cell injury in culture, only gallocatechin-3-0-gallate and epicatechin-3-0-gallate were effective. The inhibitory effect of epigallocatechin and saikosaponin a on platelet activation and the cytoprotective effect of gallocatechin-3-0-gallate and epicatechin-3-0-gallate on H₂O₂-induced endothelial cell injury could give evidence of explaining the possible role of flavan-3-ol and saikosaponin compounds in maintaining vascular homeostasis.