title: alpha-Naphthoflavone, a potent antiplatelet flavonoid, is mediated through inhibition of phospholipase C activity and stimulation of cyclic GMP formation.
abstract: The aim of this study was to systematically examine the inhibitory mechanisms of the flavonoid alpha-naphthoflavone (alpha-NF) in platelet activation. In this study, alpha-NF concentration dependently (5-20 microM) inhibited platelet aggregation stimulated by agonists. alpha-NF (5 and 10 microM) inhibited intracellular Ca(2+) mobilization, phosphoinositide breakdown, and thromboxane A(2) formation stimulated by collagen (1 microg/mL) in human platelets. In addition, alpha-NF (5 and 10 microM) markedly increased levels of cyclic GMP and cyclic GMP-induced vasodilator-stimulated phosphoprotein (VASP) Ser(157) phosphorylation. Rapid phosphorylation of a platelet protein of Mr 47,000 (P47), a marker of protein kinase C activation, was triggered by phorbol-12,13-dibutyrate (60 nM). This phosphorylation was markedly inhibited by alpha-NF (5 and 10 microM). However, alpha-NF (5 and 10 microM) did not reduce the electron spin resonance (ESR) signal intensity of hydroxyl radicals in collagen (1 microg/mL)-activated platelets. These results indicate that the antiplatelet activity of alpha-NF may be involved in the following pathways. (1) alpha-NF may inhibit the activation of phospholipase C, followed by inhibition of phosphoinositide breakdown, protein kinase C activation, and thromboxane A(2) formation, thereby leading to inhibition of intracellular Ca(2+) mobilization. (2) alpha-NF also activated the formation of cyclic GMP, resulting in inhibition of platelet aggregation. These results strongly indicate that alpha-NF appears to represent a novel and potent antiplatelet agent for treatment of arterial thromboembolism.
authors.affiliation: Graduate Institute of Pharmacology and Graduate Institute of Medical Sciences, Taipei Medical University, Taiwan.
authors.forename: George
authors.initials: G
authors.lastname: Hsiao
authors.forename: Ching-Yi
authors.initials: CY
authors.lastname: Chang
authors.forename: Ming-Yi
authors.initials: MY
authors.lastname: Shen
authors.forename: Duen-Suey
authors.initials: DS
authors.lastname: Chou
authors.forename: Shu-Hw
authors.initials: SH
authors.lastname: Tzeng
authors.forename: Tzeng-Fu
authors.initials: TF
authors.lastname: Chen
authors.forename: Joen-Rong
authors.initials: JR
authors.lastname: Sheu
mesh_terms: D001571:Benzoflavones / Q000494:pharmacology*; D001792:Blood Platelets / Q000737:chemistry; D002118:Calcium / Q000097:blood; D015815:Cell Adhesion Molecules / Q000097:blood; D003094:Collagen / Q000494:pharmacology; D006152:Cyclic GMP / Q000096:biosynthesis*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005434:Flow Cytometry; D006801:Humans; D008840:Microfilament Proteins; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000097:blood; D010750:Phosphoproteins / Q000097:blood; D010766:Phosphorylation; D015539:Platelet Activation / Q000187:drug effects*; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000032:analysis / Q000737:chemistry; D011487:Protein Conformation / Q000187:drug effects; D013929:Thromboxane B2 / Q000097:blood; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors*; D000098662:Vasodilator-Stimulated Phosphoprotein
chemical_list: D001571:Benzoflavones; D015815:Cell Adhesion Molecules; D004791:Enzyme Inhibitors; D008840:Microfilament Proteins; D010716:Phosphatidylinositols; D010750:Phosphoproteins; D010975:Platelet Aggregation Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D000098662:Vasodilator-Stimulated Phosphoprotein; D015240:Phorbol 12,13-Dibutyrate; D013929:Thromboxane B2; C011512:alpha-naphthoflavone; D003094:Collagen; D010738:Type C Phospholipases; D006152:Cyclic GMP; D002118:Calcium