Inhibitory effects of total saponin from Korean Red Ginseng on [Ca2+]i mobilization through phosphorylation of cyclic adenosine monophosphate-dependent protein kinase catalytic subunit and inositol 1,4,5-trisphosphate receptor type I in human platelets

BackgroundIntracellular Ca2+([Ca2+]i) is a platelet aggregation-inducing molecule. Therefore, understanding the inhibitory mechanism of [Ca2+]i mobilization is very important to evaluate the antiplatelet effect of a substance. This study was carried out to understand the Ca2+-antagonistic effect of total saponin from Korean Red Ginseng (KRG-TS).MethodsWe investigated the Ca2+-antagonistic effect of KRG-TS on cyclic nucleotides-associated phosphorylation of inositol 1,4,5-trisphosphate receptor type I (IP3RI) and cyclic adenosine monophosphate (cAMP)-dependent protein kinase (PKA) in thrombin (0.05 U/mL)-stimulated human platelet aggregation.ResultsThe inhibition of [Ca2+]i mobilization by KRG-TS was increased by a PKA inhibitor (Rp-8-Br-cAMPS), which was more stronger than the inhibition by a cyclic guanosine monophosphate (cGMP)-dependent protein kinase (PKG) inhibitor (Rp-8-Br-cGMPS). In addition, Rp-8-Br-cAMPS inhibited phosphorylation of PKA catalytic subunit (PKAc) (Thr197) by KRG-TS. The phosphorylation of IP3RI (Ser1756) by KRG-TS was very strongly inhibited by Rp-8-Br-cAMPS compared with that by Rp-8-Br-cGMPS. These results suggest that the inhibitory effect of [Ca2+]i mobilization by KRG-TS is more strongly dependent on a cAMP/PKA pathway than a cGMP/PKG pathway. KRG-TS also inhibited the release of adenosine triphosphate and serotonin. In addition, only G-Rg3 of protopanaxadiol in KRG-TS inhibited thrombin-induced platelet aggregation.ConclusionThese results strongly indicate that KRG-TS is a potent beneficial compound that inhibits [Ca2+]i mobilization in thrombin–platelet interactions, which may result in the prevention of platelet aggregation-mediated thrombotic disease.