Cordycepin-Enriched WIB801C from Cordyceps militaris Inhibits Collagen-Induced [Ca(2+)](i) Mobilization via cAMP-Dependent Phosphorylation of Inositol 1, 4, 5-Trisphosphate Receptor in Human Platelets

In this study, we prepared cordycepin-enriched (CE)-WIB801C, a n-butanol extract of Cordyceps militaris-hypha, and investigated the effect of CE-WIB801C on collagen-induced human platelet aggregation. CE-WIB801C dose-dependently inhibited collagen-induced platelet aggregation, and its IC(50) value was 175 μg/ml. CE-WIB801C increased cAMP level more than cGMP level, but inhibited collagen-elevated [Ca(2+)](i) mobilization and thromboxane A(2) (TXA(2)) production. cAMP-dependent protein kinase (A-kinase) inhibitor Rp-8-Br-cAMPS increased the CE-WIB801C-downregulated [Ca(2+)](i) level in a dose dependent manner, and strongly inhibited CE-WIB801C-induced inositol 1, 4, 5-trisphosphate receptor (IP(3)R) phosphorylation. These results suggest that the inhibition of [Ca(2+)](i) mobilization by CE-WIB801C is resulted from the cAMP/A-kinase-dependent phosphorylation of IP(3)R. CE-WIB801C suppressed TXA(2) production, but did not inhibit the activities of cyclooxygenase-1 (COX-1) and TXA(2) synthase (TXAS). These results suggest that the inhibition of TXA(2) production by WIB801C is not resulted from the direct inhibition of COX-1 and TXAS. In this study, we demonstrate that CE-WIB801C with cAMP-dependent Ca(2+)-antagonistic antiplatelet effects may have preventive or therapeutic potential for platelet aggregation-mediated diseases, such as thrombosis, myocardial infarction, atherosclerosis, and ischemic cerebrovascular disease.