Prostaglandin E2Differentially Modulates Human Platelet Function through the Prostanoid EP2 and EP3 Receptors (original) (raw)
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PGE2 decreases reactivity of human platelets by activating EP2 and EP4
Thrombosis Research, 2010
Introduction: Platelet hyperreactivity associates with cardiovascular events in humans. Studies in mice and humans suggest that prostaglandin E 2 (PGE 2 ) regulates platelet activation. In mice, activation of the PGE 2 receptor subtype 3 (EP3) promotes thrombosis, but the significance of EP3 in humans is less well understood.
British Journal of Pharmacology, 1993
The 16‐phenoxy prostaglandin E analogue sulprostone consistently potentiates primary aggregation waves induced by adenosine 5′‐diphosphate (ADP), PAF and 11,9‐epoxymethano PGH2 (U‐46619) in platelet‐rich plasma from human donors. The effect is not blocked by the TP‐receptor antagonists, EP 092 and GR 32191. The high potency of sulprostone (threshold concentration = 4–10 nm) and the weak block of sulprostone potentiation by the EP1‐receptor antagonist, AH 6809 (pA2 = 4.3) suggest the involvement of EP3‐receptors as opposed to EP1‐ or EP2‐subtypes. Eight prostaglandin E (PGE) analogues were compared against sulprostone for their effects on PAF‐induced aggregation in human platelet‐rich plasma (PRP) in the presence of GR 32191 and the DP‐receptor antagonist, BW A868C. PGE2 and 11‐deoxy PGE2‐1‐alcohol showed evidence of both potentiating and inhibitory actions and butaprost showed only inhibitory activity at high concentrations. The remaining analogues always elicited potentiation, with...
Mechanisms of action of proteinase-activated receptor agonists on human platelets
British Journal of Pharmacology, 2002
We studied the activation of human platelets by thrombin and proteinase activated receptor (PAR)-activating peptides (PAR-APs) [SFLLRNPNDKYEPF-amide (TRAP), TFLLR-amide (PAR1AP) and AYPGKF-amide (PAR4AP)]. 2 PAR agonist-induced platelet aggregation, glycoprotein (GP) Ib and GPIIb/IIIa surface expression and ADP release were measured by light aggregometry,¯ow cytometry and chemiluminescence. 3 Aggregation inhibitors, including prostacyclin (PGI 2), nitric oxide-releasing agent (S-nitrosoglutathione, GSNO), aspirin, apyrase, and phenanthroline were used to study the susceptibility of PAR agonist-induced aggregation to pharmacological inhibition. 4 Thrombin was the most potent platelet agonist, followed by PAR1AP, TRAP and PAR4AP. 5 The aggregatory potencies of PAR-APs were not modi®ed by the aminopeptidase inhibitor, amastatin. 6 Subthreshold concentrations of PAR1AP potentiated the eects of PAR4AP to stimulate maximal aggregation. 7 Both PGI 2 and GSNO reduced PAR agonist-induced aggregation and diminished GPIIb/IIIa upregulation. 8 PAR agonist-induced aggregation was aspirin-insensitive indicating a minor role for TXA 2. 9 In contrast, phenanthroline and apyrase signi®cantly enhanced the anti-aggregatory eects of aspirin against thrombin-, PAR1AP-and TRAP-induced aggregation suggesting the involvement of ADP-and MMP-2-dependent pathways. 10 PAR4AP-induced aggregation (but not PAR1AP-induced aggregation) was entirely ADPdependent (abolished by apyrase) and resistant to phenanthroline (MMP-2-independent). 11 Thus, the mechanisms of PAR1 and 4-induced platelet aggregation are distinct and depend dierentially on their ability to interact with pathways of aggregation, along with the subsequent activation of GPIIb/IIIa receptors.
Cell Calcium, 2004
P2Y 12 antagonists such as clopidogrel and AR-C69931MX inhibit aggregation by antagonizing the effects of ADP at P2Y 12 receptors on platelets. Agents such as PGE 1 also inhibit aggregation by stimulating adenylate cyclase to produce cAMP, which interferes with Ca 2+ mobilization within the cell. Since one facet of P2Y 12 receptors is that they mediate inhibition of adenylate cyclase by ADP, it might be expected that P2Y 12 antagonists would interact with PGE 1 . We have explored the effects of PGE 1 and AR-C69931MX singly and in combination on ADP-induced intracellular Ca 2+ ([Ca 2+ ] i ) responses and aggregation. PGE 1 alone caused parallel dose-dependent inhibition of [Ca 2+ ] i and aggregation responses. AR-C66931MX alone caused only partial inhibition of [Ca 2+ ] i despite a marked inhibitory effect on aggregation. Combinations of PGE 1 with AR-C66931MX were found to act in synergy to reduce both [Ca 2+ ] i and aggregation. This effect was confirmed in patients with acute coronary syndromes by studying the inhibitory effects of PGE 1 on [Ca 2+ ] i and aggregation before and after clopidogrel. In summary, we have shown that P2Y 12 antagonists interact with natural agents such as PGE 1 to provide more effective inhibition of [Ca 2+ ] i and platelet aggregation. This would contribute to the effectiveness of P2Y 12 antagonists as antithrombotic agents in man.
Platelets, 2008
Receptors for prostanoids on platelets include the EP3 receptor for which the natural agonist is the inflammatory mediator prostaglandin E 2 (PGE 2 ) produced in atherosclerotic plaques. EP3 is implicated in atherothrombosis and an EP3 antagonist might provide atherosclerotic lesion-specific antithrombotic therapy. DG-041 (2,3-dichlorothiophene-5-sulfonic acid, 3-[1-(2,4-dichlorobenzyl)-5-fluoro-3-methyl-1H-indol-7-yl]acryloylamide) is a direct-acting EP3 antagonist currently being evaluated in Phase 2 clinical trials. We have examined the contributions of EP3 to platelet function using the selective EP3 agonist sulprostone and also PGE 2 , and determined the effects of DG-041 on these. Studies were in human platelet-rich plasma or whole blood and included aggregometry and flow cytometry. Sulprostone enhanced aggregation induced by primary agonists including collagen, TRAP, platelet activating factor, U46619, serotonin and adenosine diphosphate, and enhanced P-selectin expression and platelet-leukocyte conjugate formation. It inhibited adenylate cyclase (measured by vasodilator-stimulated phosphoprotein phosphorylation) and enhanced Ca 2þ mobilization. It potentiated platelet function even in the presence of aspirin and/or AR-C69931 (a P2Y 12 antagonist). DG-041 antagonized the effects of sulprostone on platelet function. The effect of PGE 2 on platelet aggregation depended on the nature of the agonist and the concentration of PGE 2 used as a consequence of both pro-aggregatory effects via EP3 and anti-aggregatory effects via other receptors. DG-041 potentiated the protective effects of PGE 2 on platelet aggregation by inhibiting the pro-aggregatory effect via EP3 stimulation. DG-041 remained effective in the presence of a P2Y 12 antagonist and aspirin. DG-041 warrants continued investigation as a potential agent for the treatment of atherothrombosis without inducing unwanted bleeding risk.
Acs Chemical Biology, 2009
Myocardial infarction and stroke are caused by blood clots forming over a ruptured or denuded atherosclerotic plaque (atherothrombosis). Production of prostaglandin E 2 (PGE 2 ) by an inflamed plaque exacerbates atherothrombosis and may limit the effectiveness of current therapeutics. Platelets express multiple G-protein coupled receptors, including receptors for ADP and PGE 2 . ADP can mobilize Ca 2ϩ and through the P 2 Y 12 receptor can inhibit cAMP production, causing platelet activation and aggregation. Clopidogrel (Plavix), a selective P 2 Y 12 antagonist, prevents platelets from clotting but thereby increases the risk of severe or fatal bleeding. The platelet EP 3 receptor for PGE 2 , like the P 2 Y 12 receptor, also inhibits cAMP synthesis. However, unlike ADP, facilitation of platelet aggregation via the PGE 2 /EP 3 pathway is dependent on co-agonists that can mobilize Ca 2ϩ . We used a ligand-based design strategy to develop peri-substituted bicylic acylsulfonamides as potent and selective EP 3 antagonists. We show that DG-041, a selective EP 3 antagonist, inhibits PGE 2 facilitation of platelet aggregation in vitro and ex vivo. PGE 2 can resensitize platelets to agonist even when the P 2 Y 12 receptor has been blocked by clopidogrel, and this can be inhibited by DG-041. Unlike clopidogrel, DG-041 does not affect bleeding time in rats, nor is bleeding time further increased when DG-041 is co-administered with clopidogrel. This indicates that EP 3 antagonists potentially have a superior safety profile compared to P 2 Y 12 antagonists and represent a novel class of antiplatelet agents.
Journal of Thrombosis and Haemostasis, 2007
Background: Activation of two receptors for adenosine diphosphate (ADP), P2Y 1 and P2Y 12 , is necessary for ADP-induced platelet aggregation (PA). It is generally believed that the antithrombotic effects of drugs inhibiting P2Y 12 , such as clopidogrel, are uniquely mediated by inhibition of P2Y 12-dependent PA. However, as P2Y 12 is negatively coupled to adenylyl cyclase (AC), its inhibition may also exert antithrombotic effects through the potentiation of prostacyclin (PGI 2), which inhibit PA by stimulating AC. Objectives: To test whether inhibition of P2Y 12 potentiates the antiplatelet effects of PGI 2. Methods: We measured the effects of PGI 2 (0.01-10 lM) on PA of washed human platelets induced by thrombin (0.5 U mL)1) in the presence or absence of ARC69931MX (anti-P2Y 12) or MRS2500 (anti-P2Y 1). Results: PGI 2 inhibited PA in the presence of anti-P2Y 12 , but not in the presence of anti-P2Y 1 or in the absence of inhibitors. In contrast, dibutyryl-cyclicAMP inhibited PA both in the presence and absence of anti-P2Y 1 or anti-P2Y 12. PGI 2 increased platelet cyclicAMP levels only in the absence of thrombin or in the presence of thrombin plus anti-P2Y 12. Conclusions: PGI 2 did not inhibit PA induced by thrombin, because its effect on AC was prevented by released ADP interacting with P2Y 12. Anti-P2Y 12 drugs, by rescuing AC activity, potentiate the antiplatelet effect of PGI 2 , which may contribute to their antithrombotic effect.
Acta Anaesthesiologica Scandinavica, 2002
Background: The inhibitory effect of prostaglandin E 1 (PGE 1) on platelet aggregation is considered an important characteristic of this agent. However, the concentration of PGE 1 to inhibit aggregation in vitro is higher than those of clinical use (1 ng/ml). To clarify whether PGE 1 at clinically relevant concentrations inhibits aggregation under synergic action with endothelial cellderived factors (nitric oxide and prostacyclin), we evaluated the minimum effective concentration of PGE 1 to enhance the antiaggregating activity of endothelial cells. Methods: Inhibitory effects of PGE 1 and/or the incubation buffer from cultured porcine aortic endothelial (PAE) cells on human platelet aggregation induced by 2 mg/ml collagen were examined by turbidimetry. Results: PGE 1 concentration-dependently (Ͼ3 ng/ml) inhibited aggregation: the incubation buffer from PAE cells stimulated by bradykinin also inhibited aggregation. Bradykinin concentration-dependently increased the anti-aggregating activity of the PAE incubation buffer. The half-maximum effective concentration of bradykinin to inhibit aggregation (95.4∫22.3 nM) was significantly decreased to 10.3∫2.5 nM by 0.1 ng/ml PGE 1 Prostaglandin E 1 (PGE 1) has been clinically administrated for the treatment of peripheral arterial occlusive disease (1-3) and Raynaud's disease (4) because of its potent vasodilatory effect. Perioperative use of this agent to improve the survival of pedicle musculocutaneous flaps (5) has also been reported. As the aggregation of platelets is implicated in the pathogenesis of these clinical situations, the anti-aggregating in vitro effect of PGE 1 is considered an important characteristic of this agent. However, the effective concentration of PGE 1 for anti-aggregation (6-8) was higher than concentrations for clinical use (Յ1 ng/ml, 2.8 nM) (9-12), suggesting that a certain mechanism(s) is involved in the action of PGE 1 in vivo. We and other investigators have reported that endothelial cell-derived prostacyclin (EDPGI 2) shows a potent synergic, anti-aggregatory action with nitric