Biomedical subjects

A Bernat

Publications and source records attributed to A Bernat.

At least 37 records · Page 2Linked to original sources

PubMed1998

Prevention of thrombosis and enhancement of thrombolysis in rabbits by SR 121787, a glycoprotein II/III antagonist.

SR 121566, a novel nonpeptide antiplatelet agent with high affinity and specificity for the GP IIb/IIIa complex, exhibits potent in vitro antiaggregating activity in rabbit platelets. This paper reports results from a study in rabbits about the efficacy and tolerability of SR 121787, the prodrug of SR 121566. After p.o. pretreatment with SR 121787, ADP-, arachidonic acid- and collagen-induced rabbit platelet aggregation was inhibited ex vivo in a dose-dependent manner (ED50 between 2.3 and 6.1 mg/kg). Collagen-induced thrombocytopenia was totally abolished by SR 121787 at 20 mg/kg p.o. In a carotid artery lesion model of arterial thrombosis, p.o. administration of SR 121787 resulted in a dose-dependent inhibition of thrombosis with a maximum effect of 68% (ED50 = 16.0 +/- 0.3 mg/kg). Recombinant tissue plasminogen activator-induced thrombolysis of a preformed thrombus in the jugular vein was potentiated by SR 121787 at doses between 1 and 6 mg/kg i.v. In an ear incision bleeding model, SR 121787 at doses up to 15 mg/kg p.o. did not cause an increase in blood loss. These results demonstrate that SR 121787 exerts oral antiplatelet, antithrombotic and thrombolysis-enhancing efficacy in rabbits. SR 121787 appears to be a promising compound for evaluation under clinical conditions in the therapy of acute coronary syndromes.

Animals↗

PubMed1998

SR 121787, a new orally active fibrinogen receptor antagonist.

The aim of this study was to describe the pharmacological properties of SR 121787, a new antiaggregating drug which is metabolized in vivo into SR 121566, a potent non-peptide antagonist of Gp IIb/IIIa. In vitro, SR 121566 antagonized the binding of [125I]-fibrinogen (IC50 = 19.8+/-6.3 nM) and of [125I]-L-692,884, an RGD-containing peptide (IC50 = 291+/-96 nM) to activated human platelets. SR 121566 inhibited the aggregation of human platelets induced by ADP, collagen, thrombin, arachidonic acid and PAF at concentrations lower than 0.1 microM. Adhesion of human platelets to adhesive proteins was inhibited by SR 121566 (IC50 = 40.3+/-2.5 nM) only when Gp IIb/IIIa and fibrinogen were involved. No effect was found with regard to other adhesive proteins and/or other integrins. SR 121787 demonstrated a potent and sustained antiaggregating effect when administered intravenously to baboons at a dose 50 microg/kg, and eight hours after the administration of 100 microg/kg, ADP-induced aggregation was still strongly inhibited (more than 80%). A single oral administration of 2 mg/kg of SR 121787 produced a nearly complete inhibition of platelet aggregation for up to 8 h (ED50 at 8 h = 193+/-20 microg/kg), a significant residual antiaggregating activity being still observed 24h after the administration. When administered orally to rabbits, SR 121787 exhibited a potent antiaggregating (ED50 = 2.3+/-0.3 mg/kg) and antithrombotic activity in an arterio-venous shunt thrombosis model (ED50 = 10.4+/-0.8 mg/kg). After oral and IV administration, SR 121787 was well tolerated suggesting that SR 121787, the most potent and long lasting orally active Gp IIb/IIIa antagonist described to date, is a promising antithrombotic compound.

Administration, Oral↗

PubMed1998

The antiaggregating and antithrombotic activity of clopidogrel is potentiated by aspirin in several experimental models in the rabbit.

It is unknown whether the addition of aspirin might increase both the efficacy and the potency of clopidogrel, a potent and selective ADP blocker. For that purpose, the efficacy of clopidogrel (1-20 mg/kg, p.o.) administered orally to rabbits alone or in combination with aspirin (0.1-10 mg/kg, p.o.) was determined in several experimental models. A potent synergistic effect of the clopidogrel/aspirin association was demonstrated with regard to collagen-induced platelet aggregation measured ex vivo. Similarly, aspirin potentiated the antithrombotic activity of clopidogrel measured with regard to experimental thrombosis induced by a silk thread or on stents placed in an arteriovenous shunt, thrombus formation following electrical stimulation of the rabbit carotid artery and with regard to 111In-labeled platelet deposition on a stent implanted in an arteriovenous shunt or on the subendothelium following air drying injury of the rabbit carotid artery. A similar potentiating effect of aspirin was obtained with regard to myointimal proliferation (restenosis) in the femoral arteries of atherosclerotic rabbits which occurred as a consequence of stent placement. The clopidogrel/aspirin combination showed only additive-type effects on bleeding time prolongation induced by ear transection in the rabbit, therefore showing that combined inhibition of cyclooxygenase and ADP's effects provide a marked enhanced antithrombotic efficacy. Such a combination may provide substantial protection against platelet aggregation leading to thrombotic occlusion at sites of endothelial injuries and coronary artery stenosis in humans.

Animals↗

PubMed1997

New orally active non-peptide fibrinogen receptor (GpIIb-IIIa) antagonists: identification of ethyl 3-[N-[4-[4-[amino[(ethoxycarbonyl) imino]methyl]phenyl]-1,3-thiazol-2-yl]-N-[1-[(ethoxycarbonyl)methyl]pip erid -4-yl]amino]propionate (SR 121787) as a potent and long-acting antithrombotic agent.

The platelet fibrinogen receptor GpIIb-IIIa is currently considered a target of choice for drugs used in the prevention and treatment of thrombosis. Ethyl 3-[N-[4-[4-[amino[(ethoxycarbonyl)-imino] methyl]phenyl]-1,3-thiazol-2-yl]-N-[1-[(ethoxycarbonyl)methyl] piperid-4-yl] amino]propionate (6, SR 121787) is a new antiaggregating agent which generates in vivo the corresponding diacid 19d (SR 121566), non-peptide GpIIb-IIIa antagonist. In vitro, 19d inhibited ADP-induced aggregation of human and baboon platelets (IC50 = 46 +/- 11 and 54 +/- 6 nM, respectively), and on human platelets, 19d antagonized the binding of 125I-labeled fibrinogen (IC50 = 19.2 +/- 6.2 nM). Ex vivo, 8 h after an i.v. administration of 19d (100 micrograms/kg, i.v.) to baboons, ADP-induced aggregation was strongly inhibited (more than 90%). At 8 h, the ED50 value was 24 +/- 3.3 micrograms/kg), and even 24 h after the administration of a single dose of 100 micrograms/kg of 19d, platelet aggregation was still significantly inhibited (50 +/- 6% inhibition, P < 0.05). In the same species, the oral administration of 500 micrograms/kg of 6 produced a nearly complete inhibition of aggregation for up to 8 h (ED50 at 8 h was 193 +/- 20 micrograms/kg). After an oral dose of 2 mg/kg of 6, an antiaggregating effect was still observed at 24 h (44 +/- 12% inhibition, P < 0.05). 6 was well tolerated in animals, showing that, on the basis of these studies, it is a suitable candidate for development as an orally active antithrombotic agent.

Adenosine Diphosphate↗

PubMed1997

Synthesis and pharmacological properties of a close analogue of an antithrombotic pentasaccharide (SR 90107A/ORG 31540).

The synthetic pentasaccharide (1) corresponding to the heparin sequence which binds to, and activates, antithrombin III (AT III) is a potent antithrombotic compound in several animal models of venous thrombosis. We describe here the preparation and the pharmacological properties of 34, an analogue of oligosaccharide 1 with the latter's N-sulfates being replaced by sulfate esters and hydroxyl groups being methylated. These structural modifications allow a simpler and more efficient synthesis of such anionic oligosaccharides. Affinity for human AT III, anti-factor Xa activity, ability to inhibit thrombin generation, antithrombotic activity in a rat model of venous thrombosis, and elimination half-life in the rat have been determined for 1 and 34. Surprisingly, introduction of O-sulfates in place of N-sulfates, and methylation of hydroxyl groups, contributes to reinforce the binding to AT III, resulting in an improved pharmacological profile.

Animals↗

PubMed1997

The synthetic pentasaccharide SR 90107A/Org 31540 does not release lipase activity into the plasma.

The present study was designed to find out whether the synthetic pentasaccharide SR 90107A/Org 31540, which is presently being evaluated in clinical trials as an antithrombotic agent, influences lipoprotein metabolism in rats as determined by plasma triglyceride (TG) lipase activity. A comparison with three clinically used sulphated polysaccharides-unfractionated heparin (UFH), low molecular weight heparin (LMWH) and pentosan polysulphate (PPS)- was performed. UFH evoked a dose-dependent increase in plasma TG lipase activity which plateaued at doses > or = 1 mg/kg i.v.. PPS and LMWH demonstrated a lower efficacy than heparin at 0.3 and 1 mg/kg i.v., but the maximum lipase releasing effect at 3 mg/kg i.v. was identical for UFH, PPS and LMWH. SR 90107A/Org 31540 did not release TG lipase activity at single i.v. doses up to 3 mg/kg. Repeated-dose experiments with SR 90107A/Org 31540 (1 mg/kg s.c. for 9 days) revealed no influence on the lipase releasing effect of UFH (1 mg/kg i.v. on day 10). These results demonstrate that SR 90107A/Org 31540 does not influence lipid metabolism in rats through lipase release, suggesting that SR 90107A/Org 31540 may offer an advantage over UFH and LMWH in clinical situations where an anticoagulant/antithrombotic effect is desired, but both an increase in plasma free fatty acids and atherogenic alterations of lipoprotein metabolism are considered harmful.

Animals↗

PubMed1997

Neurotensin induces the release of prostacyclin from human umbilical vein endothelial cells in vitro and increases plasma prostacyclin levels in the rat.

Human umbilical vein endothelial cells express high affinity neurotensin receptors which are coupled to phosphoinositide turnover and 45Ca2+ efflux (Schaeffer et al., 1995. J. Biol. Chem. 270, 3409-3413). In order to assess the physiological significance of neurotensin receptor activation in endothelial cells, we have compared the in vitro effect of neurotensin on prostacyclin release and cytosolic free calcium increase ([Ca2+]i) as determined by fura-2 fluorescence experiments to the in vivo effect of neurotensin on blood pressure and haematocrit. Neurotensin increased [Ca2+]i levels at low concentrations (EC50 = 4.2 +/- 0.2 nM, n = 3). At similar concentrations, neurotensin was also able to induce prostacyclin release from human umbilical vein endothelial cells (EC50 = 14 +/- 1 nM, n = 3) as determined by a 6-keto-prostaglandin F1 alpha enzyme immunoassay. The neurotensin (100 nM)-induced [Ca2+]i increase and prostacyclin release were inhibited by the specific non-peptide neurotensin receptor antagonist SR 48692 at similar concentrations (IC50 = 41 +/- 16 nM and 86 +/- 17 nM, respectively, n = 3), confirming that these responses were mediated by high affinity neurotensin receptors. Intravenous injection of neurotensin (1-4 nmol/kg i.v.) in the rat resulted in a drop of blood pressure and increased haematocrit, and nearly doubled the plasma levels of 6-keto-prostaglandin F1 alpha, the stable metabolite of prostacyclin. Whereas indomethacin (10 mg/kg i.v.) pretreatment significantly reduced the effect of neurotensin on blood pressure, it did not alter its effect on haematocrit. These results suggest that prostacyclin release plays a role in the hypotensive effects of neurotensin, but is not involved in its effects on haematocrit.

6-Ketoprostaglandin F1 alpha↗

PubMed1997

Effect of SR 27417, a novel PAF antagonist on antigen-induced hypotension in the rat.

SR 27417, a potent PAF receptor antagonist, inhibited in a dose-dependent manner the hypotensive effect of PAF in rats. It protected rats with an ED50 value of 6 +/- 2 micrograms/kg (n = 6), when given i.v., 1 min before PAF administration. After i.v. administration, SR 27417 exhibited extended duration of action, a significant protective effect was observed up to 48 h after the administration. After i.v. injection, SR 27417 (0.3, 1 and 3 mg/kg) afforded dose-dependent protection of actively sensitized rats against ovalbumin-induced hypotension but also totally reversed established antigen-induced hypotension. These results therefore confirm that PAF plays a major role in anaphylactic shock and suggest that SR 27417 may be an effective prophylactic as well as a potent curative drug in this pathology.

Animals↗

PubMed1997

Pharmacokinetic study of three synthetic AT-binding pentasaccharides in various animal species-extrapolation to humans.

The 'synthetic pentasaccharide', SR 90107A/Org 31540 (SP) representing the minimal AT-binding sequence of heparin is a catalyst of factor Xa inhibition. Affinity of SP, Sanorg 32701 (32701) and SR 80027 (80027), two close analogues of SP for rat, rabbit, baboon and human AT has been evaluated. The dissociation constants (Kd) for AT of the three species were in the range of 41-132, 1.4-6.2 and 2.8-4.6 nM for SP, 80027 and 32701, respectively. Comparative pharmacokinetics (PK) of their anti-factor Xa activities were determined in rats, rabbits and baboons. An apparent correlation could be demonstrated between half-lives of elimination and the corresponding Kd for AT in rats and rabbits whereas in baboons, such a correlation was not found. These results showed that despite Kd values ten times lower for 32701 than for SP, both compounds showed close PK parameters in baboons whereas the very low Kd value for 80027 was associated with an extended terminal half-life in this species. The predicted human PK parameters were determined using an allometric model: an empirical approach based on the integration of data obtained in various animal species which allows the extrapolation to humans. The values obtained for the terminal half-lives of SP, 80027 and 32701 were 14.1, 88 and 6.5 h, respectively. For SP, calculation by allometry correlated well with the values observed in man. Since knowledge of duration of activity is pivotal for appropriate design of phase I clinical studies of anti-Xa oligosaccharides, allometry appears to be an interesting tool to predict the duration of action of such compounds in man.

Animals↗

PubMed1997

Antiplatelet and antithrombotic efficacy of SR 121787, a nonpeptide orally active GP IIb/IIIa antagonist, in rabbits: comparison with clopidogrel and aspirin.

Previous reports indicate that rabbits are not an appropriate species for testing glycoprotein (GP) IIb/IIIa antagonists because tested compounds caused only a weak inhibitory action on aggregation of rabbit platelets. SR 121566 is a novel low-molecular-weight antiplatelet agent with high affinity and specificity for the GP IIb/IIIa complex. In this study, SR 121566 exhibited a potent dose-dependent inhibition of adenosine diphosphate (ADP)-induced aggregation of rabbit platelets in vitro [median inhibitory concentration (IC50), 0.8 +/- 0.04 microM], whereas the GP IIb/IIIa antagonists SC 52012A and GR 144053F were devoid of antiplatelet activity. After oral administration of SR 121787, the prodrug of SR 121566, rabbit platelet aggregation ex vivo was inhibited in a dose-dependent manner [median effective dose (ED50) for ADP- arachidonic acid (AA)- and collagen-induced aggregation 2 h after gavage, 2.3 +/- 0.3, 6.1 +/- 0.9, and 2.5 +/- 0.4 mg/kg], a 58% inhibition of ADP-induced platelet aggregation being still observed 6 h after single oral treatment with 20 mg/kg. In an arteriovenous-shunt model, oral administration of SR 121787 resulted in a dose-dependent inhibition of thrombus growth (ED50, 10.4 +/- 0.8 mg/kg). Clopidogrel revealed a maximal inhibitory efficacy of 40% at 20 mg/kg p.o., and aspirin, at 100 mg/kg p.o., was without effect in this model. SR 121787 at oral doses < or = 10 mg/kg, did not cause an increase in blood loss after incision of the rabbit ear. In conclusion, SR 121787 is the first GP IIb/IIIa antagonist with oral antiplatelet and antithrombotic activity in rabbits.

Animals↗

PubMed1997

V2 receptor antagonism of DDAVP-induced release of hemostasis factors in conscious dogs.

The synthetic arginine vasopressin (AVP) analog 1-desamino-8-D-arginine vasopressin (DDAVP) is used in a variety of hemorrhagic disorders. The present experiments were designed to further characterize the mechanism of DDAVP-induced release of hemostasis factors. The [3H]AVP-labeled AVP receptor in canine renomedullary membranes exhibited an AVP V2 profile because the V2 receptor agonist DDAVP displayed similar subnanomolar affinities as the natural hormone AVP, whereas the two selective V1a compounds SR 49059 and d(CH2)5Tyr(Me)AVP as well as the selective V1b agonist D-Pal and oxytocin were much less potent. The rank order of the binding affinities of three V2 receptor antagonists was SR 121463 (a newly described selective V2 receptor antagonist) > OPC 31260 >> d(CH2)5D-Ile2,Ile4AVP. In conscious dogs, DDAVP (0.1-1 microg/kg I.V.) caused a dose-related increase (maximum, 43-52% at 30 min) in plasma levels of factor VIII (FVIII), von Willebrand factor (vWF) and tissue-type plasminogen activator (t-PA), but not in levels of plasminogen activator inhibitor-1. A DDAVP-induced hemostasis factor release was also observed in bilaterally nephrectomized dogs. Pretreatment with SR 121463 inhibited DDAVP-induced (1 microg/kg I.V.) increases in FVIII, vWF and t-PA plasma levels in a dose-dependent manner (ID50 = 14.0 +/- 4.0, 12.4 +/- 3.0 and 16.7 +/- 1.0 microg/kg I.V., respectively). OPC 31260 (300 microg/kg I.V.) revealed a lower activity than SR 121463, and d(CH2)5[D-Ile2,Ile4]AVP (30 microg/kg I.V.) was without effect on the DDAVP response. Pretreatment with SR 49059 (1 mg/kg I.V.) and SR 27417 (a platelet-activating factor receptor antagonist) (1 mg/kg I.V.) had no effect on the DDAVP-induced (1 microg/kg I.V.) increases in FVIII, vWF and t-PA plasma levels. The present results, therefore, strongly suggest that the effect of DDAVP on hemostasis factors occurs via a specific interaction with extrarenal V2 receptors.

Animals↗

PubMed1997

Comparative effects of two direct and indirect factor Xa inhibitors on free and clot-bound prothrombinase.

Factor Xa, as with thrombin, binds to the clot and contributes to the propensity of thrombi to activate the coagulation system. The aim of this work was to compare the extent of prothrombinase inhibition produced by two factor Xa inhibitors: the antithrombin III-dependent synthetic pentasaccharide (SR 90107/Org 31540) and DX-9065A, a direct factor Xa inhibitor. When incubated together with prothrombin, factor Xa, phospholipids, antithrombin III and calcium, clots formed from human plasma exhibited a prothrombinase activity as measured through fragment 1-2 (F1+2) generation. Ten washes of the clot were required to achieve complete removal of unbound factor Xa. The absence of F1+2 generation brought about by washed clots in buffer when factor V was omitted, or in the presence of annexin V, indicated that they contained bound factor Xa and phospholipids but no factor V/Va. In all tested experimental conditions, clot-bound-factor Xa-induced F1+2 generation was inhibited by SR 90107/AT and DX-9065A with IC50 in the same range of concentrations (0.5 microM). In contrast, the inhibition of prothrombinase formed with factor Xa, factor Va phospholipids and calcium in buffer was observed at significantly lower concentrations of DX-9065A than of SR 90107/AT (respective IC50 concentrations: 0.1 and 70 microM). In vivo, fibrin accretion onto a preformed thrombus as well as venous thrombosis induced in the jugular vein of rabbits was inhibited by SR 90107 and DX-9065A in the same range of concentrations therefore showing that inhibition of clot-bound factor Xa is a predominant factor for the antithrombotic activity of both direct and indirect inhibitors for factor Xa.

Animals↗

PubMed1996

Hypoxia primes endotoxin-induced tissue factor expression in human monocytes and endothelial cells by a PAF-dependent mechanism.

Tissue factor (TF) is a glycoprotein which acts as a trigger of the coagulation cascade. TF expression may be induced at the surface of monocytes and endothelial cells by several stimuli including bacterial endotoxin (LPS) and cytokines (IL 1 beta, TNF alpha) and there is a large body of evidence for the involvement of hypoxia as a primaring factor in the process leading to thrombosis. To define the molecular basis underlying this phenomenon, we evaluated the relative role of platelet activating factor (PAF). PAF primed human monocytes and human umbilical vein endothelial cells (HUVEC) for TF expression following exposure to E coli LPS but was unable to enhance the induction of TF expression by IL 1 beta. The priming effect of PAF with regard to LPS occurred in a time- and dose-dependent manner and was inhibited by the PAF receptor antagonist SR 27417. When HUVEC or monocytes were exposed to an hypoxic environment, a significant rise in LPS-induced TF expression was observed. Hypoxia had no effect on IL 1-induced TF expression. The enhanced LPS-induced TF expression in both cell types was mediated by PAF as indicated by the inhibition obtained with SR 27417, added during hypoxia. Although the importance of hypoxia in the etiology of venous thrombosis has been acknowledged for a long time, evaluation of the relative importance of PAF in the process leading to thrombus formation is still lacking. Stasis-induced thrombosis performed in the rabbit jugular vein was enhanced in a dose-dependent manner by the prior i.v. administration of LPS (0.05 to 100 micrograms/ kg, i.v.). SR 27417 administered simultaneously with LPS prevented thrombus formation with an ED50 value of 0.1 +/- 0.04 mg/kg. These results therefore show that hypoxia promotes LPS-induced TF expression in HUVEC and human monocytes through a PAF-dependent mechanism in vitro and in vivo.

Animals↗

PubMed1996

Effect of SR 140333, a selective NK1 antagonist, on antigen-induced oedema formation in rat skin.

SR 140333, the first member of a newly developed neurokinin-1 (NK1) receptor antagonist series, inhibited in a dose-dependent manner oedema formation in rat skin when administered i.d. premixed with [Arg6,Sar9,Met(O2)11]substance P(6-11) (NK1 ago), a selective agonist of the NK1 receptor or substance P (SP) (ED50 values = 0.9 +/- 0.3 and 0.8 +/- 0.2 nmol/site, respectively) (n = 9). SR 140333 protected rats from NK1 ago- or SP-induced plasma extravasation with ED50 values of 35 +/- 7 and 43 +/- 6 micrograms/kg, respectively, when given i.v. 15 min before the challenge. In ovalbumin-presensitized rats, SR 140333, premixed with the allergen, inhibited in a dose-dependent manner plasma exudation (ED50 = 0.18 +/- 0.04 nmol/site, i.d.) (n = 15). Intravenous injection of SR 140333 inhibited allergen-induced vascular permeability (ED50 = 87 +/- 14 micrograms/kg). These results therefore show that NK1 plays a major role in the development of cutaneous anaphylaxis and that SR 140333 may be an effective prophylactic drug.

Allergens↗

PubMed1996

Biochemical and pharmacological properties of SANORG 32701. Comparison with the "synthetic pentasaccharide' (SR 90107/ORG 31540) and standard heparin.

SANORG 32701 is a new sulfated pentasaccharide obtained by total chemical synthesis. It is analogue of the "synthetic pentasaccharide" (SR 90107/ORG 31540), which represents the antithrombin III (AT-III) binding site of heparin. Like SR 90107, it shows high affinity for human AT-III (Kd = 3.7 +/- 0.7 nmol/L) and is a potent catalyst of its inhibitory effect with regard to factor Xa (1100 +/- 31 versus 850 +/- 27 anti-Xa U/mg for SR 90107). SANORG 32701 inhibited thrombin generation occurring via both the extrinsic and intrinsic pathways in vitro. After intravenous or subcutaneous administration to rabbits or rats, SANORG 32701 displayed prolonged anti-factor Xa activity and inhibition of thrombin generation ex vivo. SANORG 32701 was slowly eliminated, showing elimination half-lives between 2.8 and 4.9 hours with different doses. SANORG 32701 displayed antithrombotic activity by virtue of its potentiation of the anti-factor Xa activity of AT-III. It strongly inhibited thrombus formation in an experimental model of thromboplastin-induced venous thrombosis in rats (intravenously) and rabbits (subcutaneously) (ED50 values were 25.5 +/- 4.1 and 91 +/- 12.7 nmol/kg, respectively). SANORG 32701 inhibited the accretion of fibrinogen I 125 to a preformed thrombus in the rabbit jugular vein and significantly reduced thrombus growth occurring after electrical stimulation of the rabbit carotid artery. In the rabbit, intravenous injection of SANORG 32701 enhanced tissue plasminogen activator (TPA)-induced thrombolysis, suggesting that concomitant use of SANORG 32701 during TPA therapy may be helpful in preventing thrombus accretion, thus facilitating clot lysis. In the rat, SANORG 32701 potently inhibited thrombus formation induced on a silk thread in an arteriovenous shunt and in the vena cava. Compared with standard heparin, SANORG 32701 (1000 nmol/kg IV) caused only minimal bleeding enhancement and exhibited a favorable antithrombotic activity/ bleeding risk ratio, therefore showing that it might be considered as a promising compound in the treatment and prevention of various thrombotic diseases.

Animals↗

PubMed1996

DX 9065A a novel, synthetic, selective and orally active inhibitor of factor Xa: in vitro and in vivo studies.

DX 9065A is the first member of a newly developed series of synthetic and selective inhibitors of factor Xa. DX 9065A inhibited in a dose-dependent manner human factor Xa with K iota value of 3.1 +/- 0.5 nM. Steady-state studies revealed that DX 9065A was a competitive inhibitor of factor Xa. DX 9065A inhibited thrombin generation occurring via both the extrinsic and intrinsic pathway in vitro and in vivo. After i.v. injection to rabbits, DX 9065A displayed prolonged anti-factor Xa activity and inhibition of thrombin generation. Pretreatment of mice with DX 9065A dose-dependently improved the survival rate of mice injected with a lethal dose of tissue factor (ED50 = 1.1 +/- 0.2 mg/kg). After p.o. administration, DX 9065A caused a reduction in tissue factor-induced mortality of mice with ED50 value of 56 +/- 7 mg/kg. When given i.v. to rats, DX 9065A exhibited a dose-dependent antithrombotic effect against factor Xa + stasis-induced venous thrombosis (ED50 = 1.2 +/- 0.7 mg/kg i.v.), but also in an arteriovenous shunt thrombosis model (ED50 = 8.1 +/- 3.5 mg/kg i.v.) without affecting bleeding time significantly. Similar effects were obtained after s.c. or p.o. administration. In rabbits, after i.v., s.c. or p.o. administration, DX 9065A inhibited stasis-induced thrombosis after injection of tissue factor with ED50 values of 0.03 +/- 0.01, 0.3 +/- 0.07 and 50.5 +/- 19 mg/kg, respectively (n = 10). DX 9065A inhibited in a dose-dependent manner endotoxin-induced venous thrombosis in the rabbit (ED50 = 0.25 +/- 0.1 mg/kg i.v.) (n = 5) and reduced the decrease in platelet number and circulating fibrinogen levels in an experimental model of tissue factor-induced disseminated intravascular coagulation. Compared to standard heparin, DX 9065A exhibited a favorable antithrombotic/bleeding ratio, therefore showing that it might be considered as a promising compound in the treatment and prevention of various thrombotic diseases.

Animals↗

PubMed1996

The antiaggregating and antithrombotic activity of ticlopidine is potentiated by aspirin in the rat.

Since ticlopidine specifically inhibits ADP-induced platelet aggregation without affecting prostaglandin metabolism, it seemed interesting to evaluate the effect of aspirin with regard to the antithrombotic efficacy of ticlopidine. Ticlopidine was administered orally to rats alone or in combination with aspirin and the efficacy of the association was determined in several experimental models. A synergistic effect of the ticlopidine/aspirin association was demonstrated with regard to ADP-and collagen-induced platelet aggregation measured ex vivo but also in several experimental thrombosis models including silk thread-induced thrombosis in an arteriovenous shunt, wire coil-induced thrombosis and 111In-labelled platelet deposition on the subendothelium following air drying injury of the rat carotid artery. Similar results were obtained with regard to myointimal proliferation following air-induced injury of the rat carotid artery which occurred as a consequence of vascular injury. The ticlopidine/aspirin combination showed only additive-type effects on bleeding time prolongation induced by tail transection in the rat.

Animals↗

PubMed1996

Antagonism of SR 90107A/Org 31540-induced bleeding by protamine sulfate in rats and mice.

The neutralization by protamine sulfate of bleeding enhancement induced by the potent anti-factor Xa pentasaccharide SR 90107A/Org 31540 and by heparin has been studied in rats and mice. Bleeding, as measured by transection of the tail of anaesthetised rats or mice, was increased following the administration of heparin and very high doses of SR 90107A/Org 31540. In rats, i.v. doses of 0.6 mg/kg heparin or 15 mg/kg SR 90107A/Org 31540 were required to enhance bleeding time to approximately the same extent (5- or 7-fold increase), whereas in mice a 13-fold increase in blood loss was observed with i.v. doses of 3 mg/kg heparin or 10 mg/kg SR 90107A/Org 31540. Protamine sulfate (10 mg/kg i.v.) reduced bleeding in rats and mice induced by both compounds. It also neutralized the anti-factor Xa activity as well as the antithrombotic activity of heparin as observed in venous thrombosis models in both species. However, protamine sulfate neither affected the anti-factor Xa activity nor the antithrombotic activity of SR 90107A/Org 31540 in rats and mice. The present results suggest that protamine sulfate may be regarded as a potential antidote to neutralize bleeding side-effects in cases of SR 90107A/Org 31540 overdosing.

Animals↗