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P Savi

Publications and source records attributed to P Savi.

At least 19 recordsLinked to original sources
PubMed2004

Gi-dependent and -independent mechanisms downstream of the P2Y12 ADP-receptor.

The P2Y12 ADP receptor is one of the major regulators of platelet activation and the target of antithrombotic thienopyridines (ticlopidine and clopidogrel). It has been recently cloned but the signaling pathways triggered by this receptor are still poorly documented. Here, we show that stimulation of the human P2Y12 receptor stably expressed in Chinese hamster ovary cells activates two major intracellular signaling mechanisms leading either to cell proliferation or to actin cytoskeleton reorganization. Both effects were blocked by the active metabolite of clopidogrel, a specific antagonist of P2Y12. The P2Y12-mediated stimulation of proliferation required the pertussis toxin-sensitive activation of PI3-kinase/Akt upstream of MAP-kinases. A partial contribution of a transactivation mechanism, through the tyrosine kinase receptor platelet-derived growth factor (PDGF)-R-beta, was also observed. Conversely, the P2Y12-mediated reorganization of the actin cytoskeleton was Gi-independent, requiring activation of RhoA and Rho-kinase. Our results provide new insights into the molecular basis of P2Y12-mediated intracellular signaling. These data may prove to be useful for a better understanding of the physiological role of P2Y12, particularly in platelets and glial cells which express this important therapeutic target.

Actins↗
PubMed2003

Comparative effects of two synthetic oligosaccharides on platelet activation induced by plasma from HIT patients.

Heparin-induced thrombocytopenia (HIT) is a serious secondary event encountered in the clinical use of heparin. HIT results from the consumption of platelets that are immunologically activated by antibodies directed against complexes formed by platelet factor 4 (PF4) and sulfated polysaccharides that activate platelet aggregation, leading to paradoxical, life-threatening thrombosis. There is strong evidence that the ability of heparin and related compounds to induce HIT is closely linked to the structure of the polysaccharide, and particularly to its negative charge and to the length of the molecule. To test this hypothesis, we synthesized two sulfated oligosaccharides: SanOrg123781, a 16-mer, presenting two terminal charged domains separated by a 7-mer neutral linker, and SR121903, a highly sulfated 17-mer. Both of them displayed strong anti-factor (F) Xa and anti-FIIa activities but their affinities for PF4 were markedly different. SR121903 displaced PF4-bound heparin, whereas SanOrg123781 did not, underlining the importance of the charge of the molecule for the interaction with PF4. Platelet studies, in the presence of HIT serum, showed that SR121903 induced the secretion of platelet-dense granules (measured by the release of serotonin) whereas SanOrg123781 did not, a result in accordance with an absence of affinity of this molecule for PF4. These results were confirmed by measurements of platelet activation by flow cytometry (measured by annexin V binding, CD62 detection and activation of the GpIIb-IIIa complexes). In conclusion, we have demonstrated the importance of the charge of the polysaccharides in the HIT-induced platelet reactions measured by diverse methods, of which some are described for this purpose for the first time.

Cell Degranulation↗
PubMed2001

P2y(12), a new platelet ADP receptor, target of clopidogrel.

The binding characteristics of (33)P-2MeS-ADP, a stable analogue of ADP, were determined on CHO cells transfected with the human P2Y(12) receptor, a novel purinergic receptor. These transfected CHO cells displayed a strong affinity for (33)P-2MeS-ADP, the binding characteristics of which corresponded in all points to those observed on platelets. In particular, this receptor recognised purines with the following order of potency: 2MeS-ADP = 2MeS-ATP > ADP = ATPgammaS = ATP >> UTP, a binding profile which is similar to that obtained in platelets. The binding of (33)P-2MeS-ADP was antagonised by pCMPS but not by MRS2179 and FSBA, antagonists of P2Y(1) and aggregin, respectively. Moreover, the binding of (33)P-2MeS-ADP to these cells was strongly and irreversibly inhibited by the active metabolite of clopidogrel with a potency which was consistent with that observed for this compound on platelets. Like in platelets, 2MeS-ADP induced adenylyl cyclase down-regulation in these P2Y(12) transfected CHO cells, an effect which was absent in the corresponding non-transfected cells. As already shown in platelets, the active metabolite of clopidogrel antagonised 2MeS-ADP-induced inhibition of adenylyl cyclase on transfected cells. Our results confirm that P2Y(12) is the previously called "platelet P2t(AC)" receptor and show that this receptor is antagonised by the active metabolite of clopidogrel.

Adenosine Diphosphate↗
PubMed2001

Cotranscription and intergenic splicing of human P2Y11 and SSF1 genes.

The P2Y(11) receptor is an ATP receptor positively coupled to the cAMP and phosphoinositide pathways. Ssf1 is a Saccharomyces cerevisiae nuclear protein, which plays an important role in mating. The gene encoding the human orthologue of SSF1 is adjacent to the P2Y(11) gene on chromosome 19. During the screening of placenta cDNA libraries, we isolated a chimeric clone resulting from the intergenic splicing between the P2Y(11) and SSF1 genes. The fusion protein was stably expressed in CHO-K1 cells where it generated a cAMP response to ATP qualitatively indistinguishable from that of the P2Y(11) receptor. According to both Western blotting and cAMP response, the expression of the fusion protein in the transfected cells was clearly lower than that of the P2Y(11) receptor. Both P2Y(11) and SSF1 probes detected a 5.6-kb messenger RNA with a similar pattern of intensity in each of 11 human tissues. The ubiquitous presence of chimeric transcripts and their up-regulation during granulocytic differentiation indicate that the transgenic splicing between the P2Y(11) and the SSF1 genes is a common and regulated phenomenon. There are very few examples of intergenic splicing in mammalian cells, and this is the first case involving a G-protein-coupled receptor.

Adenine Nucleotides↗
PubMed2001

Detection of bradykinin B1 receptors in rat aortic smooth muscle cells.

The tritiated bradykinin B1 receptor agonist [3H]des-Arg(10)-kallidin bound to a single class of high-affinity binding sites (K(d) = 0.5 +/- 0.16 nM; B(max) = 15,000 +/- 8,000 sites/cell) on cultured rat aortic smooth muscle cells. [3H]Des-Arg(10)-kallidin association and dissociation kinetics were monoexponential, making it possible to determine the association and dissociation rate constants (k(+1) = 1.5 10(5) M(-1) sec(-1); k(-1) = 4.2 10(-5) sec(-1)). [3H]Des-Arg(10)-kallidin binding was inhibited by specific ligands of bradykinin B1 and B2 receptors with a rank order of potency consistent with that known for bradykinin B1 receptors in other species (des-Arg(9)-[Leu(8)]bradykinin = des-Arg(10)-kallidin = des-Arg(9)-bradykinin = des-Arg(10)-[Leu(9)]kallidin > des-Arg(10)-HOE-140 >> bradykinin >> HOE-140). Bradykinin B1 receptor mRNA was also detected in these cells. Des-Arg(10)-kallidin increased cytosolic free Ca2+ levels, phosphoinositide turnover, and arachidonic acid release at nanomolar concentrations (respective EC(50) values: 16 +/- 2, 4 +/- 2.7, 6 +/- 2 nM). These functional effects of des-Arg(10)-kallidin could be blocked by the bradykinin B1 receptor antagonist des-Arg(9)-[Leu(8)]bradykinin, but were not sensitive to bradykinin B2 receptor antagonists. These results therefore show that rat aortic smooth muscle cells in culture express functional bradykinin B1 receptors.

Animals↗
PubMed2001

Deficiency or inhibition of Gas6 causes platelet dysfunction and protects mice against thrombosis.

The growth arrest-specific gene 6 product (Gas6) is a secreted protein related to the anticoagulant protein S but its role in hemostasis is unknown. Here we show that inactivation of the Gas6 gene prevented venous and arterial thrombosis in mice, and protected against fatal collagen/epinephrine-induced thrombo embolism. Gas6-/- mice did not, however, suffer spontaneous bleeding and had normal bleeding after tail clipping. In addition, we found that Gas6 antibodies inhibited platelet aggregation in vitro and protected mice against fatal thrombo embolism without causing bleeding in vivo. Gas6 amplified platelet aggregation and secretion in response to known agonists. Platelet dysfunction in Gas6-/- mice resembled that of patients with platelet signaling transduction defects. Thus, Gas6 is a platelet-response amplifier that plays a significant role in thrombosis. These findings warrant further evaluation of the possible therapeutic use of Gas6 inhibition for prevention of thrombosis.

Animals↗
PubMed2001

Antiplatelet and antithrombotic activity of SL65.0472, a mixed 5-HT1B/5-HT2A receptor antagonist.

The antiplatelet and antithrombotic activity of SL65.0472 (7-fluoro-2-oxo-4-[2-[4-(thieno [3,2-c]pyrin-4-yl) piperazin-1-yl]ethyl]-1,2-di-hydroquinoline-acetamide), a mixed 5-HT1B/5-HT2A receptor antagonist was investigated on 5HT-induced human platelet activation in vitro, and in rat, rabbit and canine platelet dependent thrombosis models. SL65.0472 inhibited 5-HT-induced platelet shape change in the presence of EDTA (IC50 values = 35, 69 and 225 nM in rabbit, rat and human platelet rich plasma (PRP)), and also inhibited aggregation induced in human PRP by 3-5 microM 5-HT + threshold concentrations of ADP (0.5-1 microM) or collagen (0.3 microg/ml) with mean IC50 values of 49 +/- 13 and 48 +/- 6 nM respectively. SL65.0472 inhibited thrombus formation when given both intravenously 5 min and orally 2 h prior to assembly of an arterio-venous (A-V) shunt in rats as from 0.1 and 0.3 mg/kg respectively. It was active in a rabbit A-V shunt model with significant decreases in thrombus weight as from 0.1 mg/kg i. v. and at 10 mg/kg p.o. The delay to occlusion in an electric current-induced rabbit femoral artery thrombosis model was increased by 251% (p <0.05) after 20 mg/kg p.o. SL65.0472 (30 microg/kg i.v.) virtually abolished coronary cyclic flow variations (7.2 +/- 1.0/h to 0.6 +/- 0.6/h, p <0.05) and increased minimum coronary blood flow (1.2 +/- 0.8 ml/min to 31.8 +/- 8.4 ml/min, p <0.05) in a coronary artery thrombosis model in the anaesthetised dog. Finally, SL65.0472 significantly increased the amount of blood lost after rat tail transection at 3 mg/kg p.o. Thus the anti-5-HT2A component of SL65.0472 is reflected by its ability to inhibit 5-HT-induced platelet activation, and platelet-rich thrombus formation.

Animals↗
PubMed2001

Studies on the binding of 3H-SR121566, an inhibitor of Gp IIb-IIIa activation.

SR121566 is a new synthetic agent which inhibits the binding of fibrinogen to activated platelets, and platelet aggregation. 3H-SR121566 bound with nanomolar affinity (KD ranging from 45 to 72 nM) to Gp IIb-IIIa expressing cells only. On activated human platelets, this ligand allowed the detection of a maximal number of 100-140,000 binding sites. The binding of SR121566 to platelets, was displaced by several agents including RGD-containing peptides and synthetic RGD mimetics, but not by ReoPro, a humanised monoclonal antibody which inhibits the binding of fibrinogen to the Gp IIb-IIIa complex. Neither the fibrinogen dodecapeptide nor fibrinogen itself were able to compete with SR121566 whether platelets were activated or not. Flow cytometry studies indicated that SR121566 which did not activate Gp IIb-IIIa by itself, dose-dependently prevented the detection of activation-induced binding sites on TRAP-stimulated platelets in the presence or absence of exogenous fibrinogen, indicating a direct effect on the activation state of the Gp IIb-IIIa complex. Moreover, SR121566 was able to reverse the activation of Gp IIb-IIIa and to displace the binding of fibrinogen when added up to 5 min after TRAP stimulation of platelets. When added at later times (15 to 30 min), SR121566 failed to displace fibrinogen binding, even if SR121566 binding sites were still accessible and the Gp IIb-IIIa complex not activated. In conclusion, our study is in accordance with the finding that fibrinogen is recognised by the activated Gp IIb-IIIa complex through the dodecapeptide sequence present on its gamma chain, and that this interaction is inhibited by SR121566 by preventing and reversing the activated conformation of Gp IIb-IIIa and not by direct competition with fibrinogen.

Abciximab↗
PubMed2001

SR123781A, a synthetic heparin mimetic.

SR123781A, a synthetic hexadecasaccharide comprising an antithrombin (AT) binding domain, a thrombin binding domain, and a neutral methylated hexasaccharide sequence, was obtained from glucose through a convergent synthesis. SR123781A showed high affinity for human AT (Kd = 58 +/- 22 nM) and was a potent catalyst of its inhibitory effect with regard to factor Xa (IC50) = 77 +/- 5 ng/ml - 297 +/- 13 U/mg) and thrombin (IC50 = 4.0 +/- 0.5 ng/ml - 150 +/- 30 U/mg). SR123781A which acted exclusively via AT (no effect via heparin cofactor II at a concentration of 6 microg/ml) inhibited thrombin generation occurring via both the extrinsic and intrinsic pathways in vitro in human plasma. SR123781A did not compete for 3H-heparin binding to PF4 and did not activate platelets in the presence of plasma from patients with heparin-induced thrombocytopenia. After intravenous or subcutaneous administration to rats, rabbits or baboons, SR123781A displayed prolonged anti-factor Xa and anti-factor IIa activity ex vivo. After intravenous injection to baboons, decreases of the anti-factor Xa and anti-thrombin activities were parallel and disappeared with the same pharmacodynamics. Intravenous administrations of SR123781A strongly inhibited thrombus formation in an experimental model of thromboplastin-induced venous thrombosis in rats with an ED50 value of 18 +/- 0.1 microg/kg (vs 77 +/- 3 microg/kg for heparin). SR123781A inhibited arterial thrombus formation induced on a silk thread in an arterio-venous shunt and in the vena cava (ED50 values of 225 +/- 10 and 27 +/- 8 microg/kg, respectively). Compared to standard and low molecular weight heparin and to presently used drugs, SR123781A exhibited a highly favourable antithrombotic/bleeding ratio therefore showing that it might be considered as a promising compound in the treatment and prevention of various thrombotic diseases.

Animals↗
PubMed2000

FcgammaRIIA requires a Gi-dependent pathway for an efficient stimulation of phosphoinositide 3-kinase, calcium mobilization, and platelet aggregation.

FcgammaRIIA, the only Fcgamma receptor present in platelets, is involved in heparin-associated thrombocytopenia (HIT). Recently, adenosine diphosphate (ADP) has been shown to play a major role in platelet activation and aggregation induced by FcgammaRIIA cross-linking or by sera from HIT patients. Herein, we investigated the mechanism of action of ADP as a cofactor in FcgammaRIIA-dependent platelet activation, which is classically known to involve tyrosine kinases. We first got pharmacologic evidence that the ADP receptor coupled to Gi was required for HIT sera or FcgammaRIIA clustering-induced platelet secretion and aggregation. Interestingly, the signaling from this ADP receptor could be replaced by triggering another Gi-coupled receptor, the alpha(2A)-adrenergic receptor. ADP scavengers did not significantly affect the tyrosine phosphorylation cascade initiated by FcgammaRIIA cross-linking. Conversely, the Gi-dependent signaling pathway, initiated either by ADP or epinephrine, was required for FcgammaRIIA-mediated phospholipase C activation and calcium mobilization. Indeed, concomitant signaling from Gi and FcgammaRIIA itself was necessary for an efficient synthesis of phosphatidylinositol 3,4,5-trisphosphate, a second messenger playing a critical role in the process of phospholipase Cgamma2 activation. Altogether, our data demonstrate that converging signaling pathways from Gi and tyrosine kinases are required for platelet secretion and aggregation induced by FcgammaRIIA.

Adenosine Diphosphate↗
PubMed2000

Effect of aspirin on platelet desaggregation induced by SR121566, a potent GP-IIb/IIIa antagonist.

Since results of recent clinical trial, performed in patients suffering from acute coronary syndromes, suggested that aspirin improved the efficacy of an anti-GP-IIb/IIIa therapy, this work was set to study the mechanism underlying such a mechanism of aspirin. SR121566 (3 mg/kg, i.v.), a new selective antagonist of the GP-IIb/IIIa complex inhibited thrombus formation which occurred following electrical stimulation of the carotid artery of rabbits. On rabbits pre-treated with aspirin (10 mg/kg, i.v.), a bolus injection of SR121566 produced a strong reversal of thrombosis compared with the effect obtained on rabbits treated with SR121566 alone. In vitro, the addition of SR121566 to human platelets during the ADP-induced aggregation process resulted in a reversal of the aggregation which was nearly complete when it was added 30 s after the induction of aggregation, but progressively decreased when SR121566 was added at later times. ADP-induced platelet aggregation in the presence of aspirin (1 mM) was comparable to that obtained in control platelet-rich plasma, but the addition of SR121566 at all time points of the aggregation process was followed by a complete reversal of the aggregation even at later time points (> 120 s). Histological examination of the platelet aggregates showed a clear-cut difference in the platelet content between control and aspirin-treated platelets which contained much more dense granules. Inhibition of the release of thrombospondin by aspirin may account for a significant part of its pro-desaggregating activity as demonstrated by the effect of the tetrapeptide VTCG, an inhibitor of the binding of thrombospondin to its receptor, which strongly potentiated the activity of SR121566 as a desaggregating agent. Therefore, our study shows that aspirin pretreatment promotes a 'thrombolytic' activity of GP-IIb/IIIa inhibitors and, in particular, of SR121566, a potent and selective member of this new class of compounds. This effect is mainly due to an inhibition of the release of the platelet granule content and in particular to thrombospondin. This observation may contribute to a greater efficacy of GP-IIb/IIIa inhibitors for the treatment of thrombosis in atherosclerotic patients.

Adenosine Diphosphate↗
PubMed2000

Identification and biological activity of the active metabolite of clopidogrel.

Like ticlopidine, the ADP receptor antagonist clopidogrel is inactive in vitro and must be administered i.v. or orally to exhibit antiaggregatory and antithrombotic activities. We have previously shown that hepatic metabolism is necessary for activity. This study demonstrates that an active metabolite can be generated from human liver microsomes incubated with clopidogrel. Using several analytical methodologies (LC/MS, NMR, chiral supercritical fluid chromatography), we have identified its structure. In vitro, this highly unstable compound, different from that formed from ticlopidine, exhibited all the biological activities of clopidogrel observed ex vivo: Irreversible inhibition of the binding of 33P-2MeS-ADP to washed human platelets (IC50) = 0.53 microM), selective inhibition of ADP-induced platelet aggregation (IC)50 = 1.8 microM) and ADP-induced adenylyl cyclase down-regulation. The irreversible modification of the ADP-receptor site which is responsible for the biological activity could be explained by the formation of a disulfide bridge between the reactive thiol group of the active metabolite and a cysteine residue of the platelet ADP receptor.

Blood Platelets↗
PubMed1999

Nerve growth factor (NGF) exerts its pro-apoptotic effect via the P75NTR receptor in a cell cycle-dependent manner.

Nerve growth factor (NGF), the prototypic member of the neurotrophin family of growth factors, exerts its action via two receptors, P75NTR and TrkA, the expression of which varies at the cell surface of neuroblastoma cells (SH-SY5Y cells) in a cycle phase-specific manner. NGF was pro-apoptotic on growing cells expressing preferentially P75NTR and exhibited a potent anti-apoptotic effect on quiescent cells, when TrkA was prevalent at the cell surface, showing that NGF can have a dual action on SH-SY5Y cells depending on the relative cell surface expression of TrkA and P75NTR. The pro-apoptotic activity of NGF but not its anti-apoptotic activity was abrogated by an antibody against the extracellular domain of P75NTR and in cell isolated from P75NTR knock-out mice indicating that NGF exhibits a proapoptotic activity via P75NTR exclusively. On the other hand, we showed that the anti-apoptotic activity of NGF was specifically mediated by an interaction with TrkA with no contribution of P75NTR, as demonstrated on SK-N-BE cells transfected with TrkA in which NGF was a potent anti-apoptotic compound but did not exhibit any pro-apoptotic activity. These results support the hypothesis that the survival response to NGF depends on its binding to TrkA without any involvement of P75NTR which in turn selectively mediates the pro-apoptotic activity of NGF with no contribution of TrkA and show that, depending on the growth state of the cells, NGF exhibits dual pro- or anti-apoptotic properties via P75NTR and TrkA, respectively.

Animals↗
PubMed1999

Relaxant effect of 2-methyl-thio-adenosine diphosphate on rat thoracic aorta: effect of clopidogrel.

The main aim of this study was to determine the functional effect of 2-methyl-thio-adenosine diphosphate (2MeS-ADP) on vascular purinoceptors, in comparison with that of a characterised agonist of the P2Y1 receptor, 2-methyl-thio-adenosine triphosphate (2MeS-ATP), and of the P2Y2 receptor, uridine triphosphate (UTP). On phenylephrine-precontracted rat aortic rings, mounted isometrically in organ baths, we found that 2MeS-ADP (10(-9) to 10(-6) M) induced concentration-dependent relaxation of rings with a functional endothelium. Mechanical removal of the endothelium abolished the relaxant effect of 2MeS-ADP. The 2MeS-ADP-induced relaxation of phenylephrine-precontracted rings was inhibited by Nomega-nitro-L-arginine methyl ester (L-NAME) (100 microM) but not by indomethacin (100 microM) or aspirin (1 mM), indicating that the 2MeS-ADP-induced relaxation was nitric oxide (NO) synthase-mediated but not cyclooxygenase-dependent. Repeated stimulation with 2MeS-ADP resulted in desensitisation of the receptor. Under these conditions, the relaxant effect of 2MeS-ATP was abolished. On the contrary, UTP-induced relaxation was not affected, showing that 2MeS-ADP and 2MeS-ATP but not UTP shared the same receptor. Suramin (100 microM), a non-specific P2 inhibitor, abolished the effect of 2MeS-ADP, 2MeS-ATP and UTP. In contrast, pyridoxal-phosphate-6-azophenyl-2'-4'-disulphonic acid (PPADS) and adenosine-3'-phosphate-5'-phosphosulphate (A3P5PS) abolished only the vasodilator responses to 2MeS-ADP and 2MeS-ATP and did not affect the relaxant effect of UTP, showing that 2MeS-ADP acted through the P2Y1 receptor. Clopidogrel, a potent platelet ADP receptor antagonist, at a dose that strongly inhibited ADP-induced platelet aggregation ex vivo, did not modify the relaxant responses to 2MeS-ADP or 2MeS-ATP. In conclusion, these results showed that 2MeS-ADP induces endothelium-dependent, NO-mediated relaxation of rat aortic rings. This effect, resistant to clopidogrel treatment, occurred through activation of the P2Y1 receptor.

Adenosine Diphosphate↗
PubMed1999

The antithrombotic efficacy of the GP IIb/IIIa antagonist SR121787 is potentiated by antithrombin-dependent factor Xa inhibition without an increase in the bleeding risk in the rabbit.

Current antithrombotic therapy in acute coronary symptoms is only partially effective and exhibits bleeding complications. These experiments were designed to address the antithrombotic and hemorrhagic interactions of the novel glycoprotein (GP) IIb/IIIa antagonist SR121787 in combination with the indirect inhibitor of factor Xa, SR90107/ORG31540. Thrombogenesis was initiated by electrolytic injury of the intimal surface of the carotid artery, and thrombus formation was assessed by recording carotid blood flow and by measuring thrombus weight 45 min after electrical stimulation. SR121787 was an efficacious antithrombotic agent in this model (ED50 = 16.3+/-0.3 mg/kg, p.o.), whereas heparin (4.5 mg/kg, i.v.) and SR90107/ORG31540 [1 mg/kg (850 aXa anti-units/kg), i.v.] were only marginally effective (17 and 27% inhibition of carotid blood flow reduction, respectively). Coadministrations of heparin (4.5 mg/kg, i.v.) or SR90107/ORG31540 (0.5 mg/kg, i.v.) were found to potentiate the antithrombotic efficacy of threshold doses of SR121787 (5 or 10 mg/kg, p.o.). The enhancement of the antithrombotic efficacy of SR121787 by SR90107/ORG31540 was--contrary to the association of SR121787 with heparin--not accompanied by an increased blood loss from the incised rabbit ear. Coadministrations of heparin or SR90107/ORG31540 did not influence the ex vivo antiaggregatory activity of SR121787. SR121787 coadministration did not alter the systemic anticoagulant activities in heparin or SR90107/ORG31540-treated animals. These data suggest the potential for optimized antithrombotic treatment in acute coronary syndromes when a GP IIb/IIIa antagonist (SR121787) is combined with an antithrombin-dependent factor Xa inhibitor (SR90107/ORG31540).

Animals↗
PubMed1999

Interspecies comparison of the antiplatelet, antithrombotic, and hemorrhagic effects of SR 121566A, a novel nonpeptide GP IIb/IIIa antagonist.

We report the results from an interspecies comparison of the antiplatelet, antithrombotic, and hemorrhagic actions of SR 121566A, a novel nonpeptide antiplatelet agent with high affinity and specificity for the GP IIb/IIIa complex. SR 121566A exhibited in vitro antiplatelet activity against adenosine diphosphate (ADP)-induced aggregation with a rank order of potency [humans = baboons = dogs] > marmosets > guinea pigs > rabbits. These in vitro findings were predictive for the ex vivo antiplatelet potency after i.v. administration of SR 121566A to dogs, guinea pigs, and rabbits [median effective dose (ED50) values, 0.02, 0.05, and 0.15 mg/kg]. The antiplatelet actions of SR 121566A translated into an acute antithrombotic effect in an arteriovenous shunt model after i.v. administration in dogs, guinea pigs, rabbits, and marmosets (ED50, 0.08, 0.10, 0.50, and 0.007 mg/kg). Hemorrhagic effects of SR 121566A were observed in guinea pigs and rabbits at doses that represented 2-3 times the antithrombotic ED50, whereas in marmosets, no bleeding was observed at the antithrombotic ED90. These results demonstrate that SR 121566A exhibits favorable actions in terms of antithrombotic potency and hemostatic safety in different animal species, suggesting that, in humans, SR 121566A will be a good candidate as an antithrombotic compound.

Adenosine Diphosphate↗