title: Thromboxane A2 synthase inhibition and thromboxane A2 receptor blockade by 2-[(4-cyanophenyl)amino]-3-chloro-1,4-naphthalenedione (NQ-Y15) in rat platelets.
abstract: The effects of 2-[(4-acetylphenyl)amino]-3-chloro-1,4-naphthalenedione (NQ-Y15), a synthetic 1,4-naphthoquinone derivative, on platelet activity and its mechanism of action were investigated. NQ-Y15 caused a concentration-dependent inhibition of the aggregation induced by thrombin, collagen, arachidonic acid (AA), and A23187. The IC50 values of NQ-Y15 on thrombin (0.1 U/mL)-, collagen (10 microg/mL)-, AA (50 microM)-, and A23187 (2 microM)-induced aggregation were 36.2 +/- 1.5, 6.7 +/- 0.7, 35.4 +/- 1.7, and 93.1 +/- 1.4 microM, respectively. NQ-Y15 also inhibited thrombin-, collagen-, AA-, and A23187-stimulated serotonin secretion in a concentration-dependent manner. However, a high concentration (100 microM) of NQ-Y15 showed no significant inhibitory effect on ADP-induced primary aggregation, which is independent of thromboxane A2 (TXA2) production in rat platelets. In fura-2-loaded platelets, the elevation of intracellular free calcium concentration stimulated by AA, thrombin, and 4-bromo-A23187 was inhibited by NQ-Y15 in a concentration-dependent manner. The formation of TXA2 caused by AA, thrombin, and collagen was inhibited significantly by NQ-Y15. NQ-Y15 inhibited TXA2 synthase in intact rat platelets, since this agent reduced the conversion of prostaglandin (PG) H2 to TXA2. Similarly, NQ-Y15 selectively inhibited the TXA2 synthase activity in human platelet microsomes, whereas it had no effect on activity of phospholipase A2, cyclooxygenase, and PGI2 synthase in vitro. NQ-Y15 inhibited platelet aggregation induced by the endoperoxide analogue U46619 in human platelets, indicating TXA2 receptor antagonism, possibly of a competitive nature. These results suggest that the antiplatelet effect of NQ-Y15 is due to a combination of TXA2 synthase inhibition with TXA2 receptor blockade, and that it may be useful as an antithrombotic agent.
authors.affiliation: College of Pharmacy, Seoul National University, Korea.
authors.forename: T S
authors.initials: TS
authors.lastname: Chang
authors.forename: H M
authors.initials: HM
authors.lastname: Kim
authors.forename: K S
authors.initials: KS
authors.lastname: Lee
authors.forename: L Y
authors.initials: LY
authors.lastname: Khil
authors.forename: W C
authors.initials: WC
authors.lastname: Mar
authors.forename: C K
authors.initials: CK
authors.lastname: Ryu
authors.forename: C K
authors.initials: CK
authors.lastname: Moon
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D005260:Female; D009285:Naphthoquinones / Q000494:pharmacology*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017482:Receptors, Thromboxane / Q000037:antagonists & inhibitors*; D012701:Serotonin / Q000378:metabolism; D013928:Thromboxane A2 / Q000037:antagonists & inhibitors; D013929:Thromboxane B2 / Q000378:metabolism; D013930:Thromboxane-A Synthase / Q000037:antagonists & inhibitors*
chemical_list: C107675:NQ Y15; D009285:Naphthoquinones; D010975:Platelet Aggregation Inhibitors; D017482:Receptors, Thromboxane; D012701:Serotonin; D013929:Thromboxane B2; D013928:Thromboxane A2; D011451:Prostaglandin-Endoperoxide Synthases; D013930:Thromboxane-A Synthase; D002118:Calcium