title: Daphnoretin, a new protein kinase C activator isolated from Wikstroemia indica C.A. Mey.
abstract: Daphnoretin, a biologically active principle isolated from Wikstroemia indica C.A. Mey., caused platelet aggregation in washed rabbit platelets, platelet-rich plasma and whole blood. The aggregation of and ATP release from platelets induced by daphnoretin were similar to phorbol ester- and diacylglycerol-induced aggregation and release. The EC50 values of daphnoretin-, phorbol 12,13-dibutyrate (PDBu)- and 1-oleoyl-2-acetylglycerol (OAG)-induced platelet aggregation in washed rabbit platelets were 17.2 +/- 2.8 microM, 20.6 +/- 2.1 nM and 38.6 +/- 1.7 microM respectively. Platelet aggregation induced by daphnoretin and PDBu was not inhibited by indomethacin, BN52021 or sodium nitroprusside. ADP-scavenging systems, apyrase and phosphocreatine/creatine kinase, showed weak inhibition of the aggregation, and EGTA, triflavin, verapamil and prostaglandin E1 markedly inhibited the aggregation. Staurosporine, a potent protein kinase C inhibitor, suppressed daphnoretin-, PDBu- and OAG-induced aggregation and ATP release in a concentration-dependent manner. The IC50 values of staurosporine on daphnoretin (50 microM)-, PDBu (100 nM)- and OAG (50 microM)-induced aggregation were 37.7 +/- 8.3, 52.2 +/- 6.3 and 42.8 +/- 8.9 nM respectively. Daphnoretin did not cause significant thromboxane B2 formation in rabbit platelets. Neither daphnoretin nor PDBu caused [3H]inositol monophosphate formation or an increase in intracellular Ca2+ concentration in myo-[3H]inositol-labelled and Fura-2-loaded platelets. Platelet cytosolic protein kinase C was activated by daphnoretin and PDBu in a concentration-dependent manner with an EC50 of 12.4 +/- 1.2 microM and 18.7 +/- 1.4 nM respectively. Membrane-associated protein kinase C activity was increased by either daphnoretin or PDBu. [3H]PDBu binding to washed rabbit platelets was inhibited by daphnoretin in a concentration-dependent manner with an IC50 value of 45.2 +/- 5.2 microM. These results indicate that daphnoretin is a protein kinase C activator in rabbit platelets.
authors.affiliation: Pharmacological Institute, College of Medicine, National Taiwan University, Taipei.
authors.forename: F N
authors.initials: FN
authors.lastname: Ko
authors.forename: Y L
authors.initials: YL
authors.lastname: Chang
authors.forename: Y H
authors.initials: YH
authors.lastname: Kuo
authors.forename: Y L
authors.initials: YL
authors.lastname: Lin
authors.forename: C M
authors.initials: CM
authors.lastname: Teng
mesh_terms: D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D001692:Biological Transport; D002118:Calcium / Q000032:analysis; D003374:Coumarins / Q000494:pharmacology*; D004075:Diglycerides / Q000494:pharmacology; D004789:Enzyme Activation; D007295:Inositol Phosphates / Q000096:biosynthesis; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010946:Plants, Medicinal / Q000737:chemistry*; D010974:Platelet Aggregation / Q000187:drug effects*; D011493:Protein Kinase C / Q000187:drug effects* / Q000378:metabolism; D011817:Rabbits; D013929:Thromboxane B2 / Q000096:biosynthesis
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D003374:Coumarins; D004075:Diglycerides; D007295:Inositol Phosphates; C035316:daphnoretin; D015240:Phorbol 12,13-Dibutyrate; D013929:Thromboxane B2; C038237:1-oleoyl-2-acetylglycerol; D011493:Protein Kinase C; D002118:Calcium