title: An antithrombotic agent, NQ301, inhibits thromboxane A2 receptor and synthase activity in rabbit platelets.
abstract: In previous studies we have reported that NQ301, a synthetic 1,4-naphthoquinone derivative, displays a potent antithrombotic activity, and that this might be due to antiplatelet effect, which was mediated by the inhibition of cytosolic Ca(2+) mobilization in activated platelets. In the present study, the effect of NQ301 on arachidonic acid cascade in activated platelets has been examined. NQ301 concentration-dependently inhibited washed rabbit platelet aggregation induced by collagen (10 microg/ml), arachidonic acid (100 microM) and U46619 (1 microM), a thromboxane A2 receptor agonist, with IC50 values of 0.60+/-0.02, 0.78+/-0.04 and 0.58+/-0.04 microM, respectively. NQ301 also produced a shift to the right of the concentration-effect curve of U46619, indicating a competitive type of antagonism on thromboxane A2/prostaglandin H2 receptor. NQ301 slightly inhibited collagen-induced arachidonic acid liberation. In addition, NQ301 potently suppressed thromboxane B2 formation by platelets that were exposed to arachidonic acid in a concentration-dependent manner, but had no effect on the production of prostaglandin D2, indicating an inhibitory effect on thromboxane A2 synthase. This was supported by thromboxane A2 synthase activity assay that NQ301 concentration-dependently inhibited thromboxane B2 formation converted from prostaglandin H2. Moreover, NQ301 concentration-dependently inhibited 12-hydroxy-5,8,10,14-eicosatetraenoic acid formation by platelets that were exposed to arachidonic acid. Taken together, these results suggest that NQ301 has a potential to inhibit thromboxane A2 synthase activity with thromboxane A2/prostaglandin H2 receptor blockade, and modulate arachidonic acid liberation as well as 12-hydroxy-5,8,10,14-eicosatetraenoic acid formation in platelets. This may also be a convincing mechanism for the antithrombotic action of NQ301.
authors.affiliation: College of Pharmacy, Chungbuk National University, Cheongju, 361-763, Korea.
authors.forename: Yong-Ri
authors.initials: YR
authors.lastname: Jin
authors.forename: Mi-Ra
authors.initials: MR
authors.lastname: Cho
authors.forename: Kyung-Sup
authors.initials: KS
authors.lastname: Lee
authors.forename: Jung-Jin
authors.initials: JJ
authors.lastname: Lee
authors.forename: Yong
authors.initials: Y
authors.lastname: Lim
authors.forename: Xiang-Hua
authors.initials: XH
authors.lastname: Han
authors.forename: Ki-Wan
authors.initials: KW
authors.lastname: Oh
authors.forename: Jin-Tae
authors.initials: JT
authors.lastname: Hong
authors.forename: Hwan-Soo
authors.initials: HS
authors.lastname: Yoo
authors.forename: Yeo-Pyo
authors.initials: YP
authors.lastname: Yun
mesh_terms: D019377:12-Hydroxy-5,8,10,14-eicosatetraenoic Acid / Q000378:metabolism; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D001792:Blood Platelets / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D003094:Collagen; D004305:Dose-Response Relationship, Drug; D005343:Fibrinolytic Agents / Q000494:pharmacology*; D066298:In Vitro Techniques; D020128:Inhibitory Concentration 50; D009285:Naphthoquinones / Q000494:pharmacology*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D015230:Prostaglandin D2 / Q000378:metabolism; D011817:Rabbits; D044244:Receptors, Thromboxane A2, Prostaglandin H2 / Q000037:antagonists & inhibitors*; D013929:Thromboxane B2 / Q000378:metabolism; D013930:Thromboxane-A Synthase / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D005343:Fibrinolytic Agents; C407684:NQ301; D009285:Naphthoquinones; D010975:Platelet Aggregation Inhibitors; D044244:Receptors, Thromboxane A2, Prostaglandin H2; D016718:Arachidonic Acid; D013929:Thromboxane B2; D019377:12-Hydroxy-5,8,10,14-eicosatetraenoic Acid; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D003094:Collagen; D013930:Thromboxane-A Synthase; D015230:Prostaglandin D2