13-Azaprostanoic acid: a specific antagonist of the human blood platelet thromboxane/endoperoxide receptor.

Abstract

A newly synthesized 13-aza derivative of prostanoic acid (13-APA) specifically inhibited human platelet aggregation induced by arachidonic acid, prostaglandin H2, or the stable endoperoxide analog (15S)hyhroxy-9a,11a-epoxymethano)prosta-5Z,13E-dienoic acid. 13-APA also inhibited [14C]serotonin release in response to arachidonic acid, ADP, or thrombin but did not inhibit primar aregation induced by ADP or tirombin. 13-APA completely blocked prostaglandin H2-induced aggregation in indomethacin-treated resuspended platelets but did not inhibit thromboxane synthesis. We therefore conclude that 13APA acts as a direct antagonist of the platelet thromboxane/endoperoxide receptor. The aggregation of human blood platelets by arachidonic acid is mediated through the production of highly reactive intermediates, thromboxane A2 (TXA2) and prostaglandin H2 (PGH2) (1-7). Considerable attention has focused on a pharmacological means of decreasing the in vivo platelet reactivity through inhibition of arachidonic acid metabolism. Thus, the nonsteroidal antiinflammatory agents (e.g., aspirin) which block the synthesis of PGH2 (8-11) (and hence TXA2) are currently being evaluated for their effectiveness in the treatment of thromboembolic disorders (12)(13)(14)(15)(16)(17). An alternative and potentially more specific means of inhibiting arachidonic acid-induced platelet aggregation would involve the development of compounds that selectively block the interaction of TXA2 and PGH2 with the platelet receptor(s). Recently, Fitzpatrick et al. (18) reported that 9,11-epoxyiminoprosta-5,13-dienoic acid antagonizes TXA2 stimulation of platelet aggregation. However, it was also demonstrated that 9,11-iminoprostadienoic acid exhibited activity inconsistent with selective TXA2 receptor antagonism-e.g., 9,11-iminoprostadienoic acid inhibited prostacyclin (PGI2) synthesis in rabbit lung microsomes and BALB 3T3 cells and stimulated coronary smooth muscle. To date then, no specific antagonist of the TXA2 or PGH2 receptor has been reported.We have previously demonstrated that nitrogen-substituted derivatives of prostanoic acid are potent and specific inhibitors of arachidonic acid-induced aggregation (ref. 19, §). The inhibitory activity of the 13-azaprostanoate series was found to be highly sensitive to the stereochemistry of the 5-membered ring and the length of the amino side chain. Any deviation from the natural prostaglandin carbon skeletal arrangement resulted in decreased potency. In the present report, we provide evidence that 13-azaprostanoic acid (13-APA) inhibits arachadonic acid-induced aggregation by directly antagonizing the action of TXA2 or PGH2 at the receptor level.MATERIALS AND METHODS 13-APA was synthesized as described (19). Human blood, collected into sodium citrate (0.38% final concentration), was obtained from apparently healthy donors who had not received medication for 4 days prior to the study. Platelet-rich plasma (PRP) was prepared by centrifugation of the whole blood at 167 X g for 15 min, and the pla...

Enhancement of collagen‐induced phosphoinositide turnover by thromboxane A2 analogue through Ca2+ mobilization in human platelets

“…The basal levels of 32P incorporation into PA and MLC phosphorylation were 320 cpm and 0. These effects of STA2 were blocked by 13-azaprostanoic acid, which is an antagonist for a TXAz receptor [16] (not shown).…”

Protective Effects of KW-3635, a Thromboxane A2 Antagonist, on Arachidonic Acid-Induced Transient Cerebral Ischemia in Dogs.

“…The AA-induced contraction is assumed to be mediated by the formation of TXA2 (27) and prostaglandin H2, both of which are released from the ag gregated platelets (28,29) or vasculature (27). In fact, the TXA2 receptor has been regarded to be the same as the PGH2 receptor (30). Considering these observations, there is a possibility that the AA-induced cerebral injury is produced not only by platelet microemboli but also by contraction of the cerebral vasculature.…”

Repurposing an old drug for a new use: glybenclamide exerts antiplatelet activity by interacting with the thromboxane A2 receptor

“…Of note, due to a host of reasons, the use of antagonists developed (which were not rationally designed) [18][19][20][21]41] . Nonetheless, it is anticipated that recent literature regarding the ligand-binding domain of TPR will aid the discovery of TPR antagonists [42,43] .…”

“…While, the former has been successfully targeted by the platelet COX-1 inhibitor aspirin, this therapeutic agent is associated with undesirable adverse effects (such as gastric ulcers) [15,16] , and resistance [17] . Regarding TPR antagonists; while many were developed [18][19][20][21] , none of them is currently available for clinical use. Thus, there is still considerable interest in developing TPR antagonists.…”