A comparison of the beta-D-xyloside, odiparcil, to warfarin in a rat model of venous thrombosis.

BACKGROUND: A significant need exists for new chronic oral anticoagulation therapies to replace warfarin. Previous studies have shown that beta-D-xylosides, which prime glycosaminoglycan (GAG) synthesis, have antithrombin and antithrombotic activity. In the following report, a new orally active beta-D-xyloside (odiparcil) has been characterized in a rat model of venous thrombosis and its efficacy and bleeding liability compared to warfarin. Additionally, studies were conducted to investigate odiparcil's ex vivo antithrombin and antiplatelet activity, and also to explore the potential utility of protamine sulfate as a neutralizing agent. METHODS AND RESULTS: In vivo thrombosis studies were conducted in a rat inferior vena cava model, and bleeding studies in a rat tail transection model. Following oral dosing, warfarin and odiparcil produced dose-related suppression of thrombus formation. A therapeutically relevant dose of warfarin in this model (international normalized ratio; INR 3.0) achieved approximately 65% inhibition of thrombus formation. Warfarin caused dose-related significant increases in bleeding indices. Odiparcil antithrombotic activity was limited by its mechanism to a maximum suppression of thrombus formation of 65-70%, and did not prolong bleeding indices. Additionally, odiparcil-induced heparin cofactor II (HCII)-dependent antithrombin activity was shown to be a function of dermatan sulfate-like GAG production. Other than thrombin-related effects, no odiparcil effects on platelet function were observed. In antidote studies, it was demonstrated that odiparcil-induced antithrombotic activity could be partially neutralized by protamine sulfate. CONCLUSIONS: These experiments suggest that an antithrombotic approach based upon xyloside induction of circulating GAGs may have the potential to approximate the efficacy of warfarin and yet with a reduced risk to hemostasis.

Comparing the antithrombotic efficacy of a humanized anti-factor IX(a) monoclonal antibody (SB 249417) to the low molecular weight heparin enoxaparin in a rat model of arterial thrombosis.

A humanized inhibitory anti-factor IX(a) antibody (SB 249417) has been compared to enoxaparin (Lovenox) in a rat model of arterial thrombosis. Pretreatment of rats with either SB 249417 (3.0 mg/kg, i. v.) or enoxaparin (30.0 mg/kg, i.v. or s.c.) resulted in comparable and significant reductions in thrombus formation. However, the efficacious dose of enoxaparin resulted in >30-fold increase in the aPTT over baseline, while the efficacious dose of SB 249417 prolonged the aPTT by only approximately 3-fold. Additionally, pretreatment with SB 249417 resulted in sustained blood flow and arterial patency throughout the experiment in >80% of rats treated. In contrast, <30% of rats pretreated with enoxaparin remained patent throughout the experiment. The data in this report indicate that the selective inhibition of factor IX(a) with the monoclonal antibody SB 249417 produces a superior antithrombotic profile to that of the low molecular weight heparin enoxaparin.

The in vivo pharmacological profile of the novel glycoprotein IIb/IIIa antagonist, SK&F 106760.

The in vivo pharmacological profile of SK&F 106760 [N alpha-acetyl-cyclo(S,S)-cysteinyl-N alpha-methylarginyl-glycyl-aspartyl-penicillamine-amide], a novel, potent glycoprotein IIb/IIIa (GPIIb/IIIa) antagonist has been investigated. In conscious dogs, SK&F 106760 (0.3-3 mg/kg i.v.) produced a dose-related inhibition of ex vivo whole blood platelet aggregation induced by collagen (5 micrograms/ml) with complete inhibition being produced for 5, 90 and 165 min after administration of 0.3, 1 and 3 mg/kg i.v., respectively. Plasma levels of SK&F 106760 were measured by high-performance liquid chromatography after i.v. bolus administration of 1 mg/kg. An initial alpha-disposition phase with a T1/2 of 11 +/- 6 min was followed by a longer terminal beta-elimination phase with a T1/2 of 66 +/- 12 min, which accounted for 79 +/- 9% of the total area under the plasma concentration-time curve. The apparent steady-state volume of distribution was 259 +/- 26 ml/kg and the plasma clearance was 3.4 +/- 0.8 ml/min/kg. The plasma concentration of SK&F 106760 at which collagen-induced ex vivo whole blood aggregation was inhibited by 50% was estimated to be 593 +/- 52 nM. After intraduodenal and intrajejunal administration of 3 mg/kg, SK&F 106760 had a bioavailability of 3 to 6% and produced a peak inhibition of ex vivo platelet aggregation of 40 to 50%. In anesthetized dogs, SK&F 106760 (0.3-3.0 mg/kg i.v.) produced a complete inhibition of platelet-dependent coronary artery thrombosis, with a dose-related duration of action.(ABSTRACT TRUNCATED AT 250 WORDS)

Investigation of conformational specificity at GPIIb/IIIa: evaluation of conformationally constrained RGD peptides.

RGD-containing proteins and peptides are known to bind to the platelet GPIIb/IIIa receptor and inhibit platelet aggregation. That a conformational component to the specificity exists is suggested by significantly lower activity of linear RGD analogs relative to closely related cyclic peptides and small proteins containing the RGD sequence. Recently, conformations for a suite of RGD containing cyclic peptides have been defined by NMR-based methods and, for one molecule, by X-ray diffraction. We report here the NMR-based conformational analysis of an additional cyclic peptide, cyclo(Pro-Arg-Gly-Asp-D-Pro-Gly), and compare the conformational variations in the suite of peptides and related analogs. Biological activity data for these peptides shows a preference of the platelet GPIIb/IIIa receptor for one conformation of the RGD sequence, but suggests its ability to bind a second, distinct conformation.

Effect of fenoldopam on the acute and subacute nephrotoxicity produced by amphotericin B in the dog.

The effect of the selective dopamine DA1 receptor agonist fenoldopam (1 microgram/kg/min i.v.) on the acute nephrotoxic response to amphotericin B (2 mg/kg i.v.) has been studied in the anesthetized dog. Animals were prepared for the measurement of blood pressure, renal blood flow, urine flow, glomerular filtration rate and sodium and potassium excretion. Amphotericin B was given over 20 min and the animals were followed for an additional 160 min. The fenoldopam infusion was started 20 min before amphotericin B and was continued for the duration of the experiment. In control animals, amphotericin B markedly increased renal vascular resistance without affecting blood pressure and thus produced a significant reduction in renal blood flow. The renal vasoconstrictor response to amphotericin B was not attenuated by fenoldopam. Concomitant with the renal vasoconstriction produced by amphotericin B was a marked reduction in glomerular filtration rate, sodium excretion and urine flow rate, which lasted for at least 160 min after amphotericin B treatment. Fenoldopam did not have any effect on the initial reductions in glomerular filtration rate, sodium excretion and urine flow rate but did produce a significant return of these parameters toward control levels by 160 min, despite the continued renal vasoconstriction. The effect of fenoldopam (0.5 microgram/kg/min) given continuously by i.v. infusion on the subacute nephrotoxic response produced by amphotericin B given every other day for 8 days was also investigated. One day after the start of the fenoldopam infusion, venous samples were drawn for the analysis of serum creatinine and blood urea nitrogen.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of the dopamine beta-hydroxylase inhibitor, SK&F 102698, on blood pressure in the 1-kidney, 1-clip hypertensive dog.

The acute and chronic effects of a potent selective dopamine beta-hydroxylase inhibitor, SK&F 102698, were assessed in chronically instrumented 1-kidney, 1-clip Goldblatt hypertensive dogs. Blood pressure measured directly from either a carotid loop or from a vascular access port and cardiac output measured by impedence cardiography were monitored following acute (30 and 100 mg/kg, p.o.) and chronic (30 mg/kg/day for 4 days) administration of SK&F 102698. The data indicate that SK&F 102698 failed to alter blood pressure, cardiac output or total peripheral resistance after either acute or chronic administration. It is concluded that dopamine beta-hydroxylase inhibition with SK&F 102698 is not an effective antihypertensive agent in the 1-kidney, 1-clip Goldblatt hypertensive dog model.

Effect of fenoldopam in dogs with spontaneous renal insufficiency.

Fenoldopam administration orally or i.v. resulted in significant increases in paraaminohippuric acid (PAH) clearance in both four control dogs and four dogs with chronic renal failure. Oral fenoldopam resulted in significant plasma levels of fenoldopam sulfate metabolites. One metabolite, fenoldopam-8-sulfate, a potential inhibitor of organic anion transport, did not depress renal cortical slice accumulation of PAH. The data therefore indicate that in dogs with chronic renal failure, PAH clearance after fenoldopam administration is a reliable measure of renal plasma flow, and fenoldopam can result in an increase in renal plasma flow.

Effect of cyclo-oxygenase blockade on the renal actions of vasopressin and SK&F 105494 in the rhesus monkey.

1. Vasopressin administration to pentobarbitone-anaesthetized, hydrated female rhesus monkeys resulted in dose-dependent increases in urine osmolality and decreases in urine flow. Treatment with indomethacin at a dose (5 mg kg-1, i.v.) that reduced urinary prostaglandin E2 (PGE2) excretion by at least 70% did not alter these responses. 2. The vasopressin antagonist, SK&F 105494 (Pas1,6D-Tyr(Et)2Val4Arg7D-Arg8desGly9 arginine vasopressin; 10 micrograms kg-1), caused significant rightward shifts (P less than 0.05) of both the vasopressin-urine osmolality and the vasopressin-urine flow dose-response curves. Treatment with indomethacin did not alter these responses. 3. SK&F 105494 alone or after indomethacin treatment had minimal effects on urine osmolality and urine flow. 4. The data indicate that indomethacin does not alter the antidiuretic activity of vasopressin in the rhesus monkey and that SK&F 105494 is a potent antagonist of exogenous vasopressin with minimal agonist activity.

The effect of diltiazem on the coronary haemodynamic and cardiac functional effects produced by intracoronary administration of endothelin-1 in the anaesthetized dog.

1. We have studied the effect of the calcium channel antagonist, diltiazem, on the coronary haemodynamic and cardiac functional responses produced by intracoronary (i.c.) administration of endothelin-1 (ET-1) in anaesthetized dogs. 2. ET-1, 1, 3 and 10 ng kg-1 i.c., produced dose-related increases in coronary blood flow with no cardiac functional or systemic haemodynamic changes. ET-1, 30, 100 and 300 ng kg-1 i.c., produced dose-related reductions in coronary artery blood flow. The reduction in coronary blood flow was accompanied by dose-related falls in cardiac output, mean arterial pressure, +dP/dt and -dP/dt and increases in left ventricular end-diastolic pressure. However, there was no reflex tachycardia in response to the fall in blood pressure and at 300 ng kg-1, ET-1 produced a 22% reduction in heart rate. 3. Following a series of abnormal ECG changes, four out of five dogs died of ventricular fibrillation at 13 +/- 2 min after 300 ng kg-1 ET-1. 4. The administration of diltiazem (15 micrograms kg-1 min-1, i.v.) reduced mean arterial pressure by 10% and heart rate by 15%, and increased coronary blood flow by 39%. Diltiazem did not have any significant effect on the coronary dilator response to low doses of ET-1. Although there was a general trend for diltiazem to inhibit the coronary vasoconstrictor responses to ET-1, diltiazem significantly attenuated only the reduction in coronary blood flow produced by 100 ng kg-1 ET-1 by 60% but not the response to 30 or 300 ng kg-1 ET-1. Two out of five diltiazem-treated dogs died of ventricular fibrillation with a mean time to death of 20 min following treatment with ET-1 (300 kg- 1). 5. ET-1 is a very potent coronary vasodilator. At slightly higher doses ET-1 is also a coronary vasoconstrictor. ET-1 also appears to have direct cardiotoxicity independent of myocardial ischaemia. The vasoconstrictor activity and direct cardiotoxicity are only weakly inhibited by diltiazem.

Vasopressin receptor antagonism in rhesus monkey and man: stereochemical requirements.

The vasopressin antidiuretic (V2) antagonist activity of the position 6 stereoisomers of four vasopressin analogs were tested for water diuretic activity in the rhesus monkey and for activity to inhibit vasopressin-stimulated adenylate cyclase activity in rhesus monkey and human renomedullary tissue in vitro. Replacement of the mercapto groups of the cysteine residues with methylene groups resulted in compounds having similar in vitro potencies to their disulfide analogs; however, these 'dicarba' compounds demonstrated more potent aquaretic activity. Position 6 D enantiomers were associated with less vasopressin antagonist activity in vitro in both species. Based upon these studies, the most potent aquaretic structure identified was the dicarba analog SK & F 105494.

Flushing and haemodynamic responses to vasopressin peptides in the rhesus monkey.

1. The mechanism of the flushing, hypotension and tachycardia associated with i.v. administration of desGlyd(CH2)5D-Tyr(Et)VAVP (SK&F 101926; 25 micrograms kg-1) and the selective V2 antidiuretic agonist, desamino-8-D-arginine vasopressin (dDAVP; 3 micrograms kg-1) was studied in ketamine-anaesthetized rhesus monkeys. 2. The flushing associated with SK&F 101926 was reduced by pretreatment with a mast cell stabilizer and by repeated administration of peptide (within 2-4 weeks). A similar desensitization to dDAVP-associated flushing was observed on repeated administration. 3. Treatment with dDAVP also resulted in reduced SK&F 101926-associated flushing. 4. The hypotension associated with SK&F 101926 was not affected by pretreatment with a mast cell stabilizer. A similar degree of hypotension was observed with repeated administration of either SK&F 101926 or dDAVP. 5. The tachycardia associated with SK&F 101926 was reduced by pretreatment with a mast cell stabilizer or repeated administration of SK&F 101926. Repeated administration of dDAVP, however, resulted in an enhanced tachycardia. 6. Indomethacin (5 mg kg-1 i.v.) did not alter the flushing or the hypotension associated with the administration of either SK&F 101926 or dDAVP, but resulted in an enhanced tachycardia to SK&F 101926. 7. Administration of a selective V1 vasopressor antagonist did not result in flushing, hypotension or tachycardia. 8. It was concluded that the flushing response to vasopressin-like peptides in rhesus monkeys may be due to an action on mast cells, whereas the haemodynamic responses are not, but probably involve direct vasodilator actions.

SK&F 105494 is a potent antidiuretic hormone antagonist in the rhesus monkey (Macaca mulatta).

The vasopressin analog desGly(CH2)5D-Tyr(Et)VAVP (SK&F 101926) is a potent antagonist of the antidiuretic action of vasopressin in rats, dogs, and squirrel monkeys, demonstrating minimal agonist activity in these species. In humans, however, SK&F 101926 was a potent full antidiuretic agonist. This agonist response was not predicted by in vitro studies with human tissue. The purpose of the present study was to determine if the agonist activity of SK&F 101926 could be modeled in an old-world primate, the rhesus monkey, and, if agonist activity was demonstrated, to determine how SK&F 101926 could be modified to reduce agonist activity and permit the elaboration of antagonist activity in that species. We observed that i.v. administration of SK&F 101926 to the hydrated rhesus monkey resulted in a full antidiuretic agonist response, as observed in humans, and did not reduce urine osmolality or increase urine flow when administered to hydropenic rhesus monkeys. Changing the terminal amino acids from Pro7, Arg8 to Arg7, D-Arg8 produced a compound (SK&F 104146) that was also an agonist, although less potent than SK&F 101926. Further substitution in SK&F 104146 of the sulfide groups of cysteine residues with methyl groups in the peptide ring to produce a "dicarba bridge" resulted in a compound (SK&F 105494) that was associated with minimal agonist activity in hydrated monkeys. Administration of SK&F 105494 (30 micrograms/kg i.v.) reduced urine osmolality from 629 +/- 20 to 91 +/- 7 mosmol/kg H2O (P less than .01) and increased free water clearance to positive levels (from -0.16 +/- 0.03 to 0.73 +/- 0.18 ml/min; P less than .05) in anesthetized hydropenic monkeys.