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

Effects of SanOrg123781A, a Synthetic Hexadecasaccharide, in a Mouse Model of Electrically Induced Carotid Artery Injury: Synergism with the Antiplatelet Agent Clopidogrel

SanOrg123781A is a synthetic hexadecasaccharide that displays antithrombin-dependent inhibition of factor Xa and thrombin and potent antithrombotic effects. The antithrombotic activity of SanOrg123781A has been studied in a new mouse model of arterial thrombosis, where thrombus formation was induced by the application of an electrical current to the adventitial surface of a carotid artery. In this model, antiplatelet agents such as the ADP-receptor antagonist clopidogrel (30 mg/kg, p.o. 2 h before stimulation) and the GpIIb/IIIa antagonist SR121566A [3-(N-[4-(4-[amino(imino)methyl]phenyl)-1,3-thiazol-2-yl]-N-[1-(carboxymethyl)piperidin-4-yl]amino)propionic acid, trihydrochloride] (0.3 mg/kg, i.v. 5 min before stimulation) strongly prolonged the time to occlusion (TTO) (761 and 473% increases, respectively), whereas aspirin was devoid of antithrombotic activity. Standard heparin (2 mg/kg, i.v.), the low molecular weight heparin enoxaparin (20 mg/kg, i.v.), and the synthetic, antithrombin-dependent inhibitor of factor Xa fondaparinux (10 mg/kg, i.v.) were also active in this model (742, 707, and 602% TTO increases, respectively). Interestingly, SanOrg123781A was active at much lower doses than the other oligosaccharides (554% increase in TTO at 0.3 mg/kg, i.v. 5 min before stimulation). Low doses of SanOrg123781A administered in combination with low doses of clopidogrel led to a marked increase in TTO, which was statistically more important than the additive effects of the two compounds given alone. These results indicate that SanOrg123781A exerts a potent antithrombotic activity in a mouse model of arterial thrombosis when compared with reference compounds and show that the combination of SanOrg123781A with clopidogrel leads to a marked synergistic antithrombotic effect.

Simultaneous isolation of platelet factor 4 and glycoprotein IIb–IIIa complex from rabbit platelets, and characterization of specific chicken antibodies to assay them

Rabbits are frequently used as models for studying coagulation and platelet disorders. However, few reports on literature have dealt with the purification and characterization of rabbit platelet proteins. Herein a protocol for the simultaneous purification of rabbit platelet factor 4 (PF4) and platelet glycoprotein IIb-IIIa (GPIIb-IIIa, integrin alpha(IIb)beta(3)) is described. Specific antibodies were raised in laying chicken, which were used for assaying PF4 by ELISA, and GPIIb-IIIa by direct immunofluorescence and flow cytometry. Furthermore, the binding of monoclonal antibodies specific for GPIIb-IIIa complex (P2), ligand-induced binding site of GPIIIa (LIBS1) and rabbit P-selectin (12A7), as well as of polyclonal IgY specific for rabbit GPIIb-IIIa, was compared in quiescent and thrombin-activated platelets. Polyclonal anti-rabbit PF4 IgY was a specific and sensitive probe that could be used for assaying PF4 in plasma samples. GPIIb-IIIa expression was increased in thrombin-activated platelets, as evaluated by flow cytometric analysis using P2 and polyclonal antibodies raised in chickens. Rabbit GPIIb-IIIa also exhibited a conformational modification that caused the appearance of ligand-induced binding sites. Increased P-selectin expression, used as a positive control, was also noticeable in thrombin-activated platelets. These data evidence that antibodies raised in laying chickens specific to rabbit PF4 and GPIIb-IIIa, as well as certain monoclonal antibodies specific for human GPIIb-IIIa, may be used for investigating rabbit platelet physiology.

Pharmacological properties of YM-57029, a novel platelet glycoprotein IIb/IIIa antagonist

The pharmacological properties of YM-57029 [4-[4-(4-carbamimidoylphenyl)-3-oxopiperazin-1-yl]piperidino]acetic acid monohydrochloride trihydrate), a novel glycoprotein IIb/IIIa antagonist were examined in this study. YM-57029 inhibited fibrinogen binding to purified glycoprotein IIb/IIIa, 1000-fold more potently than the tetrapeptide arginine-glycine-aspartic acid-serine (RGDS). YM-57029 concentration-dependently inhibited ADP-, collagen- and high shear stress-induced platelet aggregation, strongly inhibited ATP release from platelets activated by ADP, and enhanced deaggregation of ADP-induced platelet aggregates. In a pro-aggregatory activity study, RGDS or SC-54701A ((S)-3-[3-[(4-amidinophenyl)carbamoyl]propionamido]-4-pentynoic acid monohydrochloride) caused prominent small aggregate formation. At a higher concentration, RGDS induced medium and large size aggregates, and SC-54701A induced medium aggregates. In contrast, YM-57029 produced only a few small and no larger size aggregates. Ex vivo ADP-induced platelet aggregation and platelet retention to collagen-coated plastic beads were dose-dependently inhibited by YM-57029 after intravenous bolus injection in guinea pigs. YM-57029 produced dose-dependent antithrombotic effects in carotid artery thrombosis and arterio-venous shunt thrombosis models in guinea pigs at 10 and 30 microg/kg, respectively. At these doses, YM-57029 prolonged template bleeding time. These results suggest that YM-57029 is a potent glycoprotein IIb/IIIa antagonist which has less pro-aggregatory effect. It may be a promising antiplatelet agent for thromboembolic diseases, and a good prototype for developing an orally active compound.

Comparative effects of ionic and nonionic iodinated low-osmolar contrast media on platelet function with the PFA-100 (platelet function analyzer)

RATIONALE AND OBJECTIVES

This study was designed to (1) compare the effects of ionic (ioxaglate) and nonionic (iodixanol and iohexol) iodinated low-osmolar contrast media (CM) on platelet function in human whole blood by using the new PFA-100trade mark, a "platelet function analyzer"; (2) determine the animal species closest to human with regard to platelet reactivity to CM; and (3) evaluate which element of the ioxaglate solution supports this activity.

METHODS

For all studies, platelet adhesion and aggregation were measured using the PFA-100trade mark system with adenosine diphosphate-primed collagen membrane cartridges. Results are shown as the membrane closure time (MCT; the longer the MCT, the greater the antiaggregatory effect) and given as medians. Citrated whole-blood samples from six healthy volunteers were mixed for 1 minute with a 10% (vol/vol) solution of ioxaglate, iodixanol, or iohexol or their respective ionic and nonionic controls (isotonic saline and mannitol). The test solution/control solution ratio for the MCT was calculated for the blood of humans, guinea pigs, rabbits, dogs, and rats. Isotonic saline and iso-osmolar (280 mOsm/kg) and hyperosmolar (560 mOsm/kg) solutions of meglumine hydrochloride, meglumine ioxaglate (560 mOsm/kg), and sodium ioxaglate (600 mOsm/kg) were tested under similar conditions.

RESULTS

All three CM caused significant prolongation of MCT when compared with their respective controls (ioxaglate: 300 seconds, ie, "no closure" on the PFA-100trade mark system; iodixanol: 179 seconds; iohexol: 171 seconds; saline: 115 seconds; mannitol: 118 seconds). The antiplatelet effect of ioxaglate was higher than that of iodixanol and iohexol (P < 0.05). The animal species tested did not differ significantly from the human species with regard to an effect of their blood on MCT. Both ioxaglic acid salts caused a higher prolongation of MCT when compared with saline (sodium salt: 259 seconds; meglumine salt: 212 seconds; P < 0.05 vs. saline) but not versus the ioxaglate commercial solution. Conversely, both iso- and hyperosmolar solutions of meglumine hydrochloride (108 and 128 seconds, respectively) did not lengthen MCT versus saline, but their MCTs were shorter than that of the commercial solution of ioxaglate (P < 0.05).

CONCLUSIONS

The ionic CM ioxaglate displayed a greater antiaggregatory effect on human platelets than did both iso-osmolar (iodixanol) and hyperosmolar (iohexol) nonionic CM. This effect seems to be linked to the ioxaglic moiety, because neither osmolality nor sodium or meglumine appeared to play a significant role.